U.S. patent application number 15/915464 was filed with the patent office on 2018-07-12 for lubricant-impregnated surfaces for electrochemical applications, and devices and systems using the same.
The applicant listed for this patent is Massachusetts Institute of Technology. Invention is credited to Xinwei Chen, Yet-Ming Chiang, Brian Richmond Solomon, Kripa Kiran Varanasi.
Application Number | 20180197686 15/915464 |
Document ID | / |
Family ID | 53514402 |
Filed Date | 2018-07-12 |
United States Patent
Application |
20180197686 |
Kind Code |
A1 |
Solomon; Brian Richmond ; et
al. |
July 12, 2018 |
LUBRICANT-IMPREGNATED SURFACES FOR ELECTROCHEMICAL APPLICATIONS,
AND DEVICES AND SYSTEMS USING THE SAME
Abstract
In certain embodiments, the invention relates to an
electrochemical device having a liquid lubricant impregnated
surface. At least a portion of the interior surface of the
electrochemical device includes a portion that includes a plurality
of solid features disposed therein. The plurality of solid features
define a plurality of regions therebetween. A lubricant is disposed
in the plurality of regions which retain the liquid lubricant in
the plurality of regions during operation of the device. An
electroactive phase comes in contact with at least the portion of
the interior surface. The liquid lubricant impregnated surface
introduces a slip at the surface when the electroactive phase flows
along the surface. The electroactive phase may be a yield stress
fluid.
Inventors: |
Solomon; Brian Richmond;
(Gaithersburg, MD) ; Chen; Xinwei; (Cambridge,
MA) ; Chiang; Yet-Ming; (Weston, MA) ;
Varanasi; Kripa Kiran; (Lexington, MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Massachusetts Institute of Technology |
Cambridge |
MA |
US |
|
|
Family ID: |
53514402 |
Appl. No.: |
15/915464 |
Filed: |
March 8, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14744792 |
Jun 19, 2015 |
9947481 |
|
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15915464 |
|
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62014207 |
Jun 19, 2014 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01M 10/052 20130101;
H01M 8/12 20130101; H01G 11/38 20130101; H01G 9/145 20130101; H01M
10/02 20130101; Y02E 60/10 20130101; H01G 9/035 20130101; H01M
12/06 20130101; Y02E 60/13 20130101; H01G 11/64 20130101; Y02E
60/50 20130101; H01G 9/048 20130101; H01M 10/36 20130101; C09D
5/037 20130101; H01G 11/06 20130101; H01M 8/02 20130101; H01M 8/188
20130101; H01G 11/26 20130101 |
International
Class: |
H01G 9/145 20060101
H01G009/145; H01M 12/06 20060101 H01M012/06; H01M 10/36 20060101
H01M010/36; H01M 10/052 20060101 H01M010/052; H01M 8/18 20060101
H01M008/18; H01M 8/12 20060101 H01M008/12; H01M 8/02 20060101
H01M008/02; H01G 9/035 20060101 H01G009/035; H01G 9/048 20060101
H01G009/048; H01M 10/02 20060101 H01M010/02; C09D 5/03 20060101
C09D005/03 |
Goverment Interests
GOVERNMENT LICENSE RIGHTS
[0002] This invention was made with government support under U.S.
Department of Energy Grant No. DOE-FOA-0000559, Energy Innovation
Hub--Batteries and Energy Storage, and Subcontract No. 3F-31144,
issued under DOE Prime Contract No. DE-AC02-06CH11357 between the
United States Government and UChicago Argonne, LLC representing
Argonne National Laboratory. The government has certain rights in
the invention.
Claims
1. An electrochemical device comprising: an interior surface, at
least a first portion of which comprises a plurality of solid
features disposed thereon, the plurality of solid features defining
a plurality of regions therebetween, and a liquid lubricant
disposed in the plurality of regions, the plurality of solid
features retaining the liquid lubricant in the plurality of regions
during operation of the device, thereby providing a liquid
lubricant impregnated surface; and an electroactive phase in
contact with at least the first portion of the interior surface,
wherein the liquid lubricant impregnated surface introduces a slip
at the surface (e.g., where a ratio of slip velocity against mean
velocity (u.sub.w/ ) is greater than 0.9) when the electroactive
phase flows along the surface (e.g., thereby providing low shear
rate and high slip ratio (u.sub.w/ ) at the surface and promoting
plug flow of the electroactive phase within the device).
2. The electrochemical device of claim 1, wherein the electroactive
phase is a non-Newtonian fluid.
3. The electrochemical device of claim 2, wherein the electroactive
phase is a yield-stress fluid.
4. The electrochemical device of claim 3, wherein the electroactive
phase has a yield-stress between 1 Pa to 2 kPa.
5. The electrochemical device of any one of the preceding claims,
wherein the electroactive phase flows along the first portion of
the interior surface such that the first portion is substantially
free from residue left by the electroactive phase along its path of
flow (e.g., less than 10%, less than 5%, less than 1%, less than
0.5%, less than 0.1% of residue of electroactive phase
remaining).
6. The electrochemical device of any one of the preceding claims,
wherein the first portion enables flowing of the electroactive
phase solely due to gravity.
7. The electrochemical device of any one of the preceding claims,
wherein the electroactive phase comprises at least one solvent and
at least one electrolyte.
8. The electrochemical device of claim 7, wherein the electrolyte
is a lithium-containing salt (e.g., LiPF.sub.6, LiBF.sub.4, LiTFSI,
LiFSI, LiClO.sub.4, LiAlCl.sub.4, LiGaCl.sub.4) in an organic
solvent or combination of solvents or in an aqueous-based solvent
or combination of solvents; or wherein the electrolyte is selected
from the group consisting of iron/chromium, bromine/polysulfide,
vanadium, zinc/bromine, lithium polysulfide, vanadium,
tris(bipyridine)nickel(II)tetrafluoroborate/tris(bipyridine)iron(II)tetra-
fluoroborate
(Ni(Bpy).sub.3(BF.sub.4).sub.2/Fe(BPy).sub.3(BF.sub.4).sub.2),
tris(bipyridine)ruthenium(II) ((Ru(bpy).sub.3].sup.2+), and
zinc/cerium.
9. The electrochemical device of claim 7, wherein the solvent is
selected from the list consisting of water, alkyl carbonates (e.g.,
ethylene carbonate, diethyl carbonate, dimethyl carbonate,
propylene carbonate), alkyl phosphonates, phosphites, acetonitrile,
propylene carbonate, glyme, diglyme, triglyme, tetraglyme,
polyglyme, dioxolane (1,3-dioxolane), dimethyl sulfoxide (DMSO),
dichloromethane, ethylene carbonate, tetrahydrafuran (THF), methane
sulfonic acid, dimethyl ether (DEM), tetraethylene glycol dimethyl
ether (TEG-DME) and dimethoxyethane, and any combination or
derivative thereof.
10. The electrochemical device of any one of the preceding claims,
wherein the electroactive phase further comprises at least one
flame-retardant additives (e.g., trimethlyphosphate (TMP)) and/or
at least one ion transport enhancer.
11. The electrochemical device of any one of the preceding claims,
wherein the electroactive phase includes at least one conductive
additive selected from the group consisting of: metal carbides,
metal nitrides, carbon black, graphitic carbon powder, carbon
fibers, carbon microfibers, vapor-grown carbon fibers (VGCF),
fullerenes, carbon nanotubes (CNTs), multiwall carbon nanotubes
(MWNTs), single wall carbon nanotubes (SWNTs), graphene sheets, and
materials comprising fullerenic fragments that are not
predominantly a closed shell or tube of the graphene sheet, and any
combination or mixture thereof.
12. The electrochemical device claim 11, wherein the conductive
additive is carbon black.
13. The electrochemical device of claim 12, wherein the carbon
black is present in the electroactive phase in an amount from
between 0.25 vol % to 3 vol %.
14. The electrochemical device of any one of the preceding claims,
wherein the liquid lubricant impregnated surface promotes plug
flow, wherein a ratio of slip velocity against mean velocity
(u.sub.w/ ) is greater than 0.9.
15. The electrochemical device of any one of the preceding claims,
wherein at least one of the conditions or any combination of
conditions (a) through (e) is satisfied: (a) wherein the solid
features have an average dimension in a range of up to 200 microns;
(b) wherein the solid features comprise particles; (c) wherein a
ratio of an exposed surface area of the plurality of solid features
to an exposed surface area of the liquid lubricant contained in the
plurality of regions is less than 0.5; (d) wherein the solid
features comprise particles and wherein an average spacing between
adjacent particles or clusters of particles is in a range of up to
200 microns; and (e) wherein the interior surface (without the
plurality of solid features and the liquid lubricant) has a first
roll-off angle and wherein the plurality of solid features and the
liquid lubricant collectively define a liquid-impregnated surface,
the liquid-impregnated surface having a second roll-off angle, the
second roll-off angle being less than the first roll-off angle;
16. The electrochemical device of claim 15, wherein the ratio of
the exposed surface area of the plurality of solid features to the
exposed surface area of the liquid contained in the plurality of
regions is less than 0.3.
17. The electrochemical device of claim 15, wherein the ratio of
the exposed surface area of the plurality of solid features to the
exposed surface area of the liquid contained in the plurality of
regions greater than 0 and less than 0.2.
18. The electrochemical device of claim 15, wherein the second
roll-off angle is less than 2.degree..
19. The electrochemical device of any one of the preceding claims,
wherein the electrochemical device is a member selected from the
group consisting of: a battery (e.g., flow battery, aqueous
battery, non-aqueous battery, metal-air battery), a fuel cell
(e.g., gravity-induced flow cell), and a capacitor (e.g.,
electrolytic capacitor, flow capacitor).
20. The electrochemical device of any one of claims 1-19, wherein
the first portion passively promotes at least one effect selected
from the list consisting of: (i) increases nucleation of insoluble
materials (e.g., of reacting material, e.g., insoluble lithium
sulfide species) formed during operation of the electrochemical
device, (ii) increases growth of insoluble materials (e.g., of
reacting material, e.g., insoluble lithium sulfide species) formed
during operation of the electrochemical device, (iii) increases
precipitation of insoluble materials (e.g., of reacting material,
e.g., insoluble lithium sulfide species) formed during operation of
the electrochemical device, (iv) increases segregation of insoluble
materials (e.g., of reacting material, e.g., insoluble lithium
sulfide species) formed during operation of the electrochemical
device at desired locations on the internal surface of the
electrochemical device.
21. The electrochemical device of any one of claims 1-19, wherein
the first portion passively promotes at least one effect selected
from the list consisting of: (i) inhibits nucleation (e.g., of
scale or of reacting material, e.g., insoluble lithium sulfide
species), (ii) decreases growth (e.g., of scale or reacting
material, e.g., insoluble lithium sulfide species), (iii) inhibits
precipitation (e.g., of reacting material, e.g., insoluble lithium
sulfide species), (iv) decreases segregation (e.g., of scale or of
reacting material, e.g., insoluble lithium sulfide species) at
undesired locations (e.g., surfaces that are not electrically
connected to the terminals of the battery or are otherwise
electrochemically inactive) on the internal surface of the
electrochemical device of insoluble materials formed during
operation of the electrochemical device.
22. The electrochemical device of any one of the preceding claims,
wherein the first portion passively extends an operating
temperature range of the electrochemical device (e.g., the
electrochemical device may be operated at lower temperatures, e.g.,
wherein the liquid-lubricant impregnated surface inhibits
crystallization of electroactive phase components).
23. The electrochemical device of any one of the preceding claims,
wherein a second portion (e.g., other than the first portion) of
the internal surface does not comprise the plurality of solid
features disposed thereon.
24. The electrochemical device of claim 23, wherein the internal
surface includes one or more first portions comprising the
plurality of solid features disposed thereon and one or more second
portions not comprising the plurality of solid features disposed
thereon.
25. The electrochemical device of any one of the preceding claims,
wherein the first portion is electronically conductive.
26. The electrochemical device of any one of the preceding claims,
wherein the plurality of solid features comprise an electronically
conductive material (e.g., nanoparticles suspended in a percolating
network of carbon black in TEG-DME) and/or wherein the liquid
lubricant comprises an electronically conductive suspension or
polymer solution (e.g., a percolating network of carbon black in a
vacuum pump oil (e.g., KRYTOX.RTM. 1506)).
27. The electrochemical device of any one of claims 1-24, wherein
the first portion is ionically conductive.
28. The electrochemical device of claim 27, wherein the plurality
of solid features comprise an ion-conducting glass or polymer and
wherein the liquid lubricant comprises an ionically conductive
liquid (e.g., an electrolyte).
29. The electrochemical device of any one of the preceding claims,
wherein the liquid lubricant is electrochemically stable (e.g.,
where an amount of side reactions due to the liquid lubricant is
less than 5%, less than 3%, or less than 1% of total
electrochemical reactions).
30. The electrochemical device of any one of the preceding claims,
wherein the liquid lubricant is thermodynamically stable (e.g.,
wherein when surface tension of the liquid lubricant is subtracted
from surface tension of an electrolyte solvent, the resulting value
is greater than zero).
31. The electrochemical device of any one of the preceding claims,
wherein the liquid lubricant is immiscible or partially miscible
(e.g., less than 5%, less than 3%, less than 1% miscibility) with
the electroactive phase.
32. The electrochemical device of any one of the preceding claims,
wherein the plurality of solid features comprise at least one
material selected from the group consisting of: hydrocarbons,
(e.g., alkanes, and fluoropolymers (e.g., polytetrafluoroethylene,
trichloro(1H,1H,2H,2H-perfluorooctyl)silane (TCS),
octadecyltrichlorosilane (OTS),
heptadecafluoro-1,1,2,2-tetrahydrodecyltrichlorosilane,
fluoroPOSS)), ceramics (e.g., titanium carbide, titanium nitride,
chromium nitride, boron nitride, chromium carbide, molybdenum
carbide, titanium carbonitride, electroless nickel, zirconium
nitride, fluorinated silicon dioxide, titanium dioxide, tantalum
oxide, tantalum nitride, diamond-like carbon, fluorinated
diamond-like carbon, and/or combinations thereof. Intermetallic
compounds may include, for example, nickel aluminide, titanium
aluminide, and/or combinations thereof), polymeric materials (e.g.,
polytetrafluoroethylene, fluoroacrylate, fluorourethane,
fluorosilicone, fluorosilane, modified carbonate, chlorosilanes,
silicone, polydimethylsiloxane (PDMS), and/or combinations
thereof), fluorinated materials, intermetallic compounds, composite
materials.
33. The electrochemical device of any one of the preceding claims,
wherein the liquid lubricant is selected from the list consisting
of oil-based lubricants (e.g., silicone oils, e.g., 10 cSt silicone
oil, 1000 cSt silicone oil); ionic liquids (e.g., BMI-IM, e.g.,
having ionic conductivity between 1 mS/cm to 10 mS/cm); hexadecane,
vacuum pump oils (e.g., perfluorinated vacuum oils), fluorocarbons
(e.g., perfluoro-tripentylamine), shear-thinning fluids,
shear-thickening fluids, liquid polymers, dissolved polymers,
viscoelastic fluids, liquid fluoroPOSS, hydrocarbon liquids,
fluorocarbon liquids, and/or electronically conducting liquids
(e.g., lubricant suspended with electronically-conducting
particles).
34. The electroactive device of any one of the preceding claims,
comprising: a first volume comprising the electroactive phase
(e.g., flow electrode, e.g., lithium polysulfide suspension); a
second volume separated from the first volume by a separator (e.g.,
membrane, e.g. ion-permeable membrane), wherein the separator
spatially separates a positive current collector and a negative
current collector, wherein the electroactive phase flows from the
first volume to the second volume during operation of the
electroactive device.
35. The electroactive device of claim 34, wherein the separator is
coated with or comprises a liquid-lubricant impregnated
surface.
36. The electroactive phase of claim 34 or 35, wherein the first
portion is disposed at an interior surface of the first volume
(e.g., the liquid lubricant impregnated surface is disposed at the
interior surface of the first volume).
37. An electroactive device, comprising: a positive electrode
current collector; a negative electrode current collector; and an
ion-permeable membrane separating the positive current collector
and the negative current collector; a positive electrode disposed
between the positive electrode current collector and the
ion-permeable membrane, the positive electrode current collector
and the ion-permeable membrane defining a positive electroactive
zone accommodating the positive electrode; and a negative electrode
disposed between the negative electrode current collector and the
ion-permeable membrane; the negative electrode current collector
and the ion-permeable membrane defining a negative electroactive
zone accommodating the negative electrode, wherein at least a
portion of the positive electrode current collector surface that
comes into contact with the positive electrode and/or at least a
portion of the negative electrode current collector surface that
comes into contact with the negative electrode comprises a
plurality of solid features disposed thereon, the plurality of
solid features defining a plurality of regions therebetween, and a
liquid lubricant disposed in the plurality of regions, the
plurality of solid features retaining the liquid lubricant in the
plurality of regions during operation of the device, thereby
providing a liquid lubricant impregnated surface, wherein the
liquid lubricant impregnated surface introduces a slip at the
surface (e.g., where a ratio of slip velocity against mean velocity
(u.sub.w/ ) is greater than 0.9) when the positive electrode or the
negative electrode flows along the surface and promotes plug flow
of the positive electrode or the negative electrode along the
surface.
38. The electroactive device of claim 37, further comprising a
positive electrode storage tank and a negative electrode storage
tank, wherein at least a portion of an internal surface of the
positive electrode storage tank and/or the negative electrode
storage tank comprises or is coated with a liquid lubricant
impregnated surface.
39. The electroactive device of claim 37, further comprising a
positive electrode storage tank and a negative electrode storage
tank, wherein the positive electrode storage tank and the negative
electrode storage tank are connected to the electroactive zone via
piping, wherein at least a portion of an internal surface of the
piping comprises or is coated with a liquid lubricant impregnated
surface.
40. The electroactive device of any one of claims 37-39, wherein
the ion-permeable membrane comprises or is coated with a
liquid-lubricant impregnated surface.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to and the benefit of, and
incorporates herein by reference in its entirety, U.S. Provisional
Patent Application No. 62/014,207, filed Jun. 19, 2014.
FIELD OF INVENTION
[0003] This invention relates generally to electrochemical
applications, devices, and systems. More particularly, in some
embodiments, the invention relates to articles and methods that
promote flow (e.g., of an electroactive phase) in electrochemical
systems (e.g., batteries, fuel cells, capacitors) by encapsulating
or impregnating a secondary liquid in surface textures of the
electrochemical systems.
BACKGROUND
[0004] Electrochemical energy storage devices include primary
(disposable) and secondary (rechargeable) batteries of almost any
type, including but not limited to alkali ion and alkaline earth
ion batteries and flow batteries as described in U.S. Provisional
Patent Application Ser. Nos. 61/912,215, filed on Dec. 5, 2013,
61/911,101, filed on Dec. 3, 2013, 61/903,574 filed on Nov. 13,
2013, 61/903,739 filed on Nov. 13, 2013, 61/892,588, filed on Oct.
18, 2013, 61/831,321, U.S. patent application Ser. No. 14/172,648,
filed on Dec. 4, 2014, Ser. No. 13/083,167, filed on Apr. 8, 2011,
Ser. No. 12/970,753, filed on Dec. 16, 2010, Ser. No. 13/404,735
(now U.S. Pat. No. 8,582,807), filed on Feb. 24, 2012, and U.S.
Pat. No. 7,338,734, filed on Dec. 23, 2002, U.S. Pat. No.
8,722,227, filed on Aug. 26, 2013, U.S. Pat. No. 8,148,013, filed
on Sep. 17, 2007, each of which is hereby incorporated by reference
in its entirety.
[0005] Fuel cells include any fuel cell type in which at least one
of the fuels or reactants is a condensed phase, including instances
where the fuel is liquid or semi-solid, and where the fuel cell
uses a physical membrane or is "membraneless" with electronic
isolation of the electroactive reactants being achieved through
controlled flow of one or more fluid phases.
[0006] A battery stores electrochemical energy by separating two
half cells (e.g., a conductive electrode and surrounding conductive
electrolytes) with different electro-chemical potential. Each
half-cell has an electromotive force, determined by its ability to
drive electric current from the interior to the exterior of the
cell. A difference in electrochemical potentials and/or
electromotive forces generates an electric current when a
conductive material connects the electrodes.
[0007] Rechargeable batteries can be constructed using static
negative electrode/electrolyte and positive electrode/electrolyte
media. Rechargeable batteries can be restored (e.g., recharged) by
applying reverse current and/or voltage. Lead-acid batteries used
in vehicles and lithium ion batteries for portable electronics are
some examples of rechargeable batteries. In rechargeable batteries,
the electrode active materials generally need to be able to accept
(e.g., to be charged) and provide (e.g., to discharge) ions.
[0008] A flow battery is a rechargeable battery that has soluble
metal ions in liquid solutions. The ability of a flow battery to be
recharged is generally provided by oxidation and reduction of two
flowing electrolyte liquids separated by a membrane. A flow battery
typically includes reservoirs for storing electrolytes, a membrane
for ion exchange, and pumps for controlling flow of the
electrolytes.
[0009] Redox flow batteries, also referred to as flow cells, redox
batteries, or reversible fuel cells are energy storage devices in
which the positive and negative electrode reactants are soluble
metal ions in liquid solution that are oxidized or reduced during
the operation of the cell. Using two reversible redox couples,
liquid state redox reactions are carried out at the positive and
negative electrodes. A redox flow cell typically has a
power-generating assembly comprising at least an ionically
transporting membrane separating the positive and negative
electrode reactants (also called catholyte and anolyte
respectively), and positive and negative current collectors (also
called electrodes) which facilitate the transfer of electrons to
the external circuit but do not participate in the redox reaction
(i.e., the current collector materials themselves do not undergo
Faradaic activity). Redox flow batteries have been discussed, for
example, by C. Ponce de Leon, A. Frias-Ferrer, J. Gonzalez-Garcia,
D. A. Szantos and F. C. Walsh, "Redox Flow Batteries for Energy
Conversion," J. Power Sources, 160, 716 (2006), M. Bartolozzi,
"Development of Redox Flow Batteries: A Historical Bibliography,"
J. Power Sources, 27, 219 (1989), and by M. Skyllas-Kazacos and F.
Grossmith, "Efficient Vanadium Redox Flow Cell," Journal of the
Electrochemical Society, 134, 2950 (1987).
[0010] Some batteries (e.g., flow batteries) have significant
pumping losses due to a variety of factors, including a combination
of high flow electrode viscosity, high flow velocity during
operation, and/or narrow channel cross-sectional dimensions and/or
long channel length. Some flow batteries utilize flow electrodes
with non-Newtonian rheology (e.g., yield-stress fluids), for
example, the high energy density flow electrodes described in U.S.
Provisional Patent Application Ser. Nos. 61/892,588, filed on Oct.
18, 2013, 61/903,574, filed on Nov. 13, 2013, 61/903,739, filed on
Nov. 13, 2013, U.S. patent application Ser. No. 12/970,753, filed
on Dec. 16, 2010, U.S. Pat. No. 8,722,227, filed on Aug. 26, 2013,
each of which is incorporated herein by reference in its entirety
and publications M. Duduta, B. Y. Ho, V. C. Wood, P. Limthongkul,
V. E. Brunini, W. C. Carter, Y.-M. Chiang, "Semi-Solid Lithium
Rechargeable Flow Battery," Adv. Energy Mater., 1[4] 511-516 (2011)
(DOI: 10.1002/aenm.201100152) and F. Y. Fan, W. H. Woodford, Z. Li,
N. Baram. K. C. Smith, A. Helal, G. H. McKinley, W. C. Carter,
Y.-M. Chiang, "Polysulfide Flow Batteries Enabled by Percolating
Nanoscale Conductor Networks," Nano Letters, 5 Mar. 2014, DOI:
10.1021/n1500740t, the disclosure of each of these publications
being incorporated herein by reference in its entirety.
[0011] In some instances, the flow electrodes have a continuous
percolating network of an electronic conductor phase that imparts
electronic conductivity to the flow electrodes. The rheology of the
flow electrodes may be non-Newtonian by possessing, for example,
shear-thinning behavior, or Bingham plastic or Hershel-Bulkley
rheology wherein there is a measurable yield stress to the fluid
followed by Newtonian or non-Newtonian viscosity after the yields
stress is overcome. High energy density fluid electrodes for high
energy density flow batteries typically have non-Newtonian
rheology, especially when formulated as suspensions which increase
electrical conductivity, energy density, or both. The rheology of
the flow electrodes can result in significant pumping energy losses
and/or decreases in electrochemical energy efficiency (e.g., in a
flow battery).
[0012] Thus, there is a need for improved articles and methods for
promoting flow of electroactive phases of electrochemical devices.
For example, there is a need for robust surfaces that promote
electrode flow in batteries.
SUMMARY OF INVENTION
[0013] Presented herein are systems and methods for promoting,
manipulating, and controlling the flow of electroactive phases of
electrochemical devices by providing at least one surface (or a
portion thereof) that includes a liquid lubricant impregnated
within its surface features. For example, the at least one surface
is a non-wetting surface that includes a liquid impregnated within
a matrix of micro and/or nano-engineered features on the surface,
or a liquid filling pores or other wells on the surface. In some
embodiments, the liquid fills the spaces between/within the surface
features, and the liquid is held between/within the surface
features. In some implementations, the liquid stably is held
between/within the surface feature regardless of orientation of the
electrochemical device. The at least one liquid-lubricant
impregnated surface may be resistant to impalement (e.g., by the
flowing phase, e.g., electroactive phase). The surface may be
configured to reduce viscous drag on the surface. The surface may
also serve to minimize accumulation of impinging/flowing phases
(e.g., electroactive phase) in some implementations.
[0014] Through proper selection of the impregnating liquid, the
liquid-impregnated surfaces described herein are easily
customizable to suit a desired application. In some embodiments, an
existing article is retrofitted to include the at least one surface
described herein.
[0015] One aspect of the invention relates to an electrochemical
device that includes an interior surface, at least a first portion
of which includes a plurality of solid features disposed thereon,
the plurality of solid features defining a plurality of regions
therebetween, and a liquid lubricant disposed in the plurality of
regions, the plurality of solid features retaining the liquid
lubricant in the plurality of regions during operation of the
device, thereby providing a liquid lubricant impregnated surface.
The electrochemical device also includes an electroactive phase in
contact with at least the first portion of the interior surface,
wherein the liquid lubricant impregnated surface introduces a slip
at the surface (e.g., where a ratio of slip velocity against mean
velocity (u.sub.w/ ) is greater than 0.9) when the electroactive
phase flows along the surface (e.g., thereby providing low shear
rate and high slip ratio at the surface and promoting plug flow of
the electroactive phase within the device). In some embodiments, a
ratio of slip velocity against mean velocity (u.sub.w/ ) is greater
than 0.9. In some embodiments, a ratio of slip velocity against
mean velocity (u.sub.w/ ) is greater than 0.85. In some
embodiments, a ratio of slip velocity against mean velocity
(u.sub.w/ ) is greater than 0.8. In some embodiments, a ratio of
slip velocity against mean velocity (u.sub.w/ ) is greater than
0.75.
[0016] In some embodiments, the electroactive phase is a
non-Newtonian fluid. In some embodiments, the electroactive phase
is a yield-stress fluid. The electrochemical device of claim 3,
wherein the electroactive phase has a yield-stress between 1 Pa and
2 kPa (e.g., between 1 Pa and 5 Pa, between 1 Pa and 20 Pa, between
5 Pa and 40 Pa, between 25 Pa and 100 Pa, between 50 Pa and 250 Pa,
between 150 Pa and 350 Pa, between 250 Pa and 500 Pa, between 400
Pa and 600 Pa, between 500 Pa and 800 Pa, between 750 Pa and 1 kPa,
between 900 Pa and 1.25 kPa, between 1 kPa and 1.5 kPa, between
1.25 kPa and 1.75 kPa, between 1.5 kPa and 2 kPa).
[0017] In some embodiments, the electroactive phase flows along the
first portion of the interior surface such that the first portion
is substantially free from residue left by the electroactive phase
along its path of flow (e.g., the electroactive phase does not
smudge or smear on the surface, e.g., less than 10%, less than 5%,
or less than 1% of the electroactive surface is left on the
surface).
[0018] In some embodiments, the first portion enables flowing of
the electroactive phase solely due to gravity (e.g., such that no
other force is required for the electroactive phase to flow along
the surface; e.g., where tilting the electroactive device at an
angle enables the electroactive phase to flow along the surface,
without requiring application of any other force).
[0019] In some embodiments, the electroactive phase includes at
least one solvent and at least one electrolyte. In some
embodiments, the electrolyte is a Lithium-containing salt (e.g., in
organic solvent or combination of organic solvents or in
aqueous-based solvent or combination of solvents). In some
embodiments, the Lithium-containing salt is selected from the group
consisting of LiPF.sub.6, LiBF.sub.4, LiTFSI, LiFSI, LiClO.sub.4,
LiAlCl.sub.4, and LiGaCl.sub.4 in organic solvent or combination of
solvents or in aqueous-based solvent or combination of solvents. In
some embodiments, the electrolyte is selected from the group
consisting of iron/chromium, bromine/polysulfide, vanadium,
zinc/bromine, lithium polysulfide, vanadium,
tris(bipyridine)nickel(II)tetrafluoroborate/tris(bipyridine)iron(II)tetra-
fluoroborate
(Ni(Bpy).sub.3(BF.sub.4).sub.2/Fe(BPy).sub.3(BF.sub.4).sub.2),
tris(bipyridine)ruthenium(II) ((Ru(bpy).sub.3].sup.2+), and
zinc/cerium.
[0020] In some embodiments, the solvent is selected from the list
consisting of water, alkyl carbonates (e.g., ethylene carbonate,
diethyl carbonate, dimethyl carbonate, propylene carbonate), alkyl
phosphonates, phosphites, acetonitrile, propylene carbonate, glyme,
diglyme, triglyme, tetraglyme, polyglyme, dioxolane
(1,3-dioxolane), dimethyl sulfoxide (DMSO), dichloromethane,
ethylene carbonate, tetrahydrafuran (THF), methane sulfonic acid,
dimethyl ether (DEM), tetraethylene glycol dimethyl ether (TEG-DME)
and dimethoxyethane, and any combination or derivative thereof.
[0021] In some embodiments, the electroactive phase also includes
flame-retardant additives (e.g., trimethlyphosphate (TMP)) and/or
ion transport enhancer(s). In some embodiments, the electroactive
phase includes a flame retardant additive or a combination of flame
retardant additives. In some embodiments, the electroactive phase
includes an ion transport enhancer or a combination of ion
transport enhancers.
[0022] In some embodiments, the electroactive phase includes at
least one conductive additive selected from the group consisting
of: metal carbides, metal nitrides, carbon black, graphitic carbon
powder, carbon fibers, carbon microfibers, vapor-grown carbon
fibers (VGCF), fullerenes, carbon nanotubes (CNTs), multiwall
carbon nanotubes (MWNTs), single wall carbon nanotubes (SWNTs),
graphene sheets, and materials comprising fullerenic fragments that
are not predominantly a closed shell or tube of the graphene sheet,
and any combination or mixture thereof. In some embodiments, the
conductive additive is carbon black. In some embodiments, the
carbon black is present in the electroactive phase in an amount of
from between 0.25 vol % to 3 vol % (e.g., between 0.25 vol % to 0.5
vol %, 0.3 vol % to 0.6 vol %, 0.5 vol % to 0.8 vol %, 0.75 vol %
to 1 vol %, 0.85 vol % to 1.25 vol %, 1 vol % to 1.5 vol %; 1.25
vol % to 1.75 vol %, 1.5 vol % to 2 vol %; 1.75 vol % to 2.25 vol
%, 2 vol % to 2.5 vol %, 2.25 vol % to 2.75 vol %, 2.5 vol % to 3
vol %). In some embodiments, the electroactive phase flows solely
due to gravity when the carbon black is present in the
electroactive phase in an amount greater than 0.25 vol % (e.g.,
greater than 0.5 vol %, greater than 1 vol %, greater than 2 vol %,
greater than 2.5 vol %, between 0.25 vol % to 3 vol %).
[0023] In some embodiments, the liquid lubricant impregnated
surface promotes plug flow, wherein a ratio of slip velocity
against mean velocity (u.sub.w/ ) is greater than 0.9.
[0024] In some embodiments, the electrochemical device is designed
such that at least one of the conditions or any combination of
conditions (a) through (e) is satisfied: (a) wherein the solid
features have an average dimension in a range of up to 200 microns
(e.g., 1-200 microns, 1-10 microns, 5-15 microns, 10-50 microns,
25-75 microns, 50-100 microns, 75-125 microns, 100-150 microns,
125-175 microns, 150-200 microns, 1 nm-1 micron, 1-10 nm, 5-20 nm,
15-50 nm, 25-75 nm, 50-100 nm, 75-150 nm, 100-300 nm, 250-500 nm,
350-700 nm, 650-800 nm, 750-950 nm); (b) wherein the solid features
comprise particles; (c) wherein a ratio of an exposed surface area
of the plurality of solid features to an exposed surface area of
the liquid lubricant contained in the plurality of regions is less
than 0.5 (e.g., less than 0.4, less than 0.3, less than 0.2, less
than 0.1); (d) wherein the solid features comprise particles and
wherein an average spacing between adjacent particles or clusters
of particles is in a range of up to 200 microns (e.g., 1-200
microns, 1-10 microns, 5-15 microns, 10-50 microns, 25-75 microns,
50-100 microns, 75-125 microns, 100-150 microns, 125-175 microns,
150-200 microns, 1 nm-1 micron, 1-10 nm, 5-20 nm, 15-50 nm, 25-75
nm, 50-100 nm, 75-150 nm, 100-300 nm, 250-500 nm, 350-700 nm,
650-800 nm, 750-950 nm); (e) wherein the interior surface (without
the plurality of solid features and the liquid lubricant) has a
first roll-off angle and wherein the plurality of solid features
and the liquid lubricant collectively define a liquid-impregnated
surface, the liquid-impregnated surface having a second roll-off
angle, the second roll-off angle being less than the first roll-off
angle.
[0025] In some embodiments, a ratio of an exposed surface area of
the plurality of solid features to an exposed surface area of the
liquid contained in the plurality of regions is less than 0.3. In
some embodiments, a ratio of an exposed surface area of the
plurality of solid features to an exposed surface area of the
liquid contained in the plurality of regions greater than 0 and
less than 0.2. In some embodiments, the second roll-off angle is
less than 2.degree..
[0026] In some embodiments, the electrochemical device is a member
selected from the group consisting of: a battery (e.g., flow
battery, aqueous battery, non-aqueous battery, metal-air battery),
a fuel cell (e.g., gravity-induced flow cell), and a capacitor
(e.g., electrolytic capacitor, flow capacitor).
[0027] In some embodiments, the first portion passively (e.g., the
effect is a property of the surface and does not require, e.g.,
application of additional forces to be achieved) promotes at least
one effect selected from the list consisting of: (i) increases
nucleation of insoluble materials (e.g., of reacting material,
e.g., insoluble lithium sulfide species) formed during operation of
the electrochemical device, (ii) increases growth of insoluble
materials (e.g., of reacting material, e.g., insoluble lithium
sulfide species) formed during operation of the electrochemical
device, (iii) increases precipitation of insoluble materials (e.g.,
of reacting material, e.g., insoluble lithium sulfide species)
formed during operation of the electrochemical device, (iv)
increases segregation of insoluble materials (e.g., of reacting
material, e.g., insoluble lithium sulfide species) formed during
operation of the electrochemical device at desired locations (e.g.,
at the electroactive region) on the internal surface of the
electrochemical device.
[0028] In some embodiments, the first portion passively promotes at
least one effect selected from the list consisting of: (i) inhibits
nucleation (e.g., of scale or of reacting material, e.g., insoluble
lithium sulfide species as discussed herein), (ii) decreases growth
(e.g., of scale or reacting material, e.g., insoluble lithium
sulfide species as discussed herein), (iii) inhibits precipitation
(e.g., of reacting material, e.g., insoluble lithium sulfide
species as discussed herein), (iv) decreases segregation (e.g., of
scale or of reacting material, e.g., insoluble lithium sulfide
species as discussed herein) at undesired locations (e.g., away
from the electroactive region (because, e.g., if undesired
nucleation takes place away from the electroactive region, battery
capacity may be lost)) on the internal surface of the
electrochemical device of insoluble materials formed during
operation of the electrochemical device.
[0029] In some embodiments, the first portion passively extends an
operating temperature range of the electrochemical device (e.g.,
the electrochemical device may be operated at lower temperatures,
e.g., wherein the liquid-lubricant impregnated surface inhibits
crystallization of electroactive phase components). In some
embodiments, the electroactive device may be successfully operated
at temperatures lower than the crystallization temperature of the
electroactive phase components. In some embodiments, the
electroactive phase flows along the liquid lubricant impregnated
surface at temperatures below the crystallization temperature of
the electroactive phase components. In some embodiments, the
electroactive phase flows along the liquid lubricant impregnated
surface at temperatures below the crystallization temperature of
the electroactive phase components without leaving a residue along
its path of flow (or, e.g., where the path of flow is essentially
free from electroactive phase residue).
[0030] In some embodiments, a second portion (e.g., other than the
first portion) of the internal surface does not comprise the
plurality of solid features disposed thereon (for example, where a
portion of the internal surface includes a liquid lubricant
impregnated surface and a portion of the internal surface does not
include a liquid lubricant impregnated surface). The first and
second portions may be designed or patterned in any desired
patterns depending on desired electrochemical device performance
specifications. For example, in some embodiments, the path of flow
of the electroactive phase includes regions that include liquid
lubricant impregnated surfaces and regions that do not include
liquid lubricant impregnated surface.
[0031] In some embodiments, the internal surface includes one or
more first portions comprising the plurality of solid features
disposed thereon and one or more second portions not comprising the
plurality of solid features disposed thereon.
[0032] In some embodiments, the first portion is electronically
conductive. In some embodiments, the first portion is not
electronically conductive. In some embodiments, the second portion
is electronically conductive. In some embodiments, the second
portion is not electronically conductive.
[0033] In some embodiments, the plurality of solid features include
an electronically conductive material (e.g., nanoparticles (or
microparticles or combination of nanoparticles and microparticles)
suspended in a percolating network of carbon black (or other
conductive additive) in TEG-DME (or another suitable solvent))
and/or wherein the liquid lubricant comprises an electronically
conductive suspension or polymer solution (e.g., a percolating
network of carbon black (or another conductive additive) in a
vacuum pump oil (e.g., KRYTOX.RTM. 1506)).
[0034] In some embodiments, the first portion is ionically
conductive. In some embodiments, the plurality of solid features
include an ion-conducting glass or polymer. In some embodiments,
the plurality of solid features include an ion-conducting glass or
polymer and the liquid lubricant includes an ionically conductive
liquid (e.g., an electrolyte).
[0035] In some embodiments, the liquid lubricant is selected such
that it is electrochemically stable (e.g., where an amount of side
reactions due to the liquid lubricant is less than 5%, less than
4%, less than 3%, less than 2%, less than 1%, less than 0.5%, less
than 0.1% of total electrochemical reactions). Some embodiments
discussed herein relate to methods of selecting appropriate liquid
lubricants to be used in electrochemical devices discussed herein,
wherein one of the criteria for selecting the liquid lubricant is
its electrochemical stability (e.g., such that an amount of side
reactions due to the liquid lubricant is less than 5%, less than
4%, less than 3%, less than 2%, less than 1%, less than 0.5%, less
than 0.1% of the total electrochemical reactions).
[0036] In some embodiments, the liquid lubricant is
thermodynamically stable (e.g., wherein when surface tension of the
liquid lubricant is subtracted from surface tension of an
electrolyte solvent, the resulting value is greater than zero).
[0037] In some embodiments, the liquid lubricant is immiscible or
partially miscible (e.g., less than 5%, less than 4%, less than 3%,
less than 2%, less than 1%, less than 0.5%, less than 0.1%
miscibility) with the electroactive phase.
[0038] In some embodiments, the plurality of solid features include
at least one material selected from the group consisting of:
hydrocarbons, (e.g., alkanes, and fluoropolymers (e.g.,
polytetrafluoroethylene,
trichloro(1H,1H,2H,2H-perfluorooctyl)silane (TCS),
octadecyltrichlorosilane (OTS),
heptadecafluoro-1,1,2,2-tetrahydrodecyltrichlorosilane,
fluoroPOSS)), ceramics (e.g., titanium carbide, titanium nitride,
chromium nitride, boron nitride, chromium carbide, molybdenum
carbide, titanium carbonitride, electroless nickel, zirconium
nitride, fluorinated silicon dioxide, titanium dioxide, tantalum
oxide, tantalum nitride, diamond-like carbon, fluorinated
diamond-like carbon, and/or combinations thereof. Intermetallic
compounds may include, for example, nickel aluminide, titanium
aluminide, and/or combinations thereof), polymeric materials (e.g.,
polytetrafluoroethylene, fluoroacrylate, fluorourethane,
fluorosilicone, fluorosilane, modified carbonate, chlorosilanes,
silicone, polydimethylsiloxane (PDMS), and/or combination thereof),
fluorinated materials, intermetallic compounds, composite
materials, and any combination thereof.
[0039] In some embodiments, the liquid lubricant is selected from
the list consisting of oil-based lubricants (e.g., silicone oils,
e.g., 10 cSt silicone oil, 1000 cSt silicone oil); ionic liquids
(e.g., BMI-IM, e.g., having ionic conductivity between 1 mS/cm to
10 mS/cm); hexadecane, vacuum pump oils (e.g., perfluorinated
vacuum oils), fluorocarbons (e.g., perfluoro-tripentylamine),
shear-thinning fluids, shear-thickening fluids, liquid polymers,
dissolved polymers, viscoelastic fluids, liquid fluoroPOSS,
hydrocarbon liquids, fluorocarbon liquids, and/or electronically
conducting liquids.
[0040] In some embodiments, the electroactive device includes a
first volume including the electroactive phase (e.g., flow
electrode, e.g., lithium polysulfide suspension); a second volume
separated from the first volume by a separator (e.g., membrane,
e.g. ion-permeable membrane), wherein the separator spatially
separates a positive current collector and a negative current
collector. In some embodiments, the separator is coated with or
includes a liquid-lubricant impregnated surface.
[0041] Another aspect of the present invention relates to an
electrochemical device including a positive electrode current
collector; a negative electrode current collector; and an
ion-permeable membrane separating the positive current collector
and the negative current collector; a positive electrode disposed
between the positive electrode current collector and the
ion-permeable membrane; the positive electrode current collector
and the ion-permeable membrane defining a positive electroactive
zone accommodating the positive electrode; and a negative electrode
disposed between the negative electrode current collector and the
ion-permeable membrane; the negative electrode current collector
and the ion-permeable membrane defining a negative electroactive
zone accommodating the negative electrode, wherein at least a
portion of the positive electrode current collector surface that
comes into contact with the positive electrode and/or at least a
portion of the negative electrode current collector surface that
comes into contact with the negative electrode comprises a
plurality of solid features disposed thereon, the plurality of
solid features defining a plurality of regions therebetween, and a
liquid lubricant disposed in the plurality of regions, the
plurality of solid features retaining the liquid lubricant in the
plurality of regions during operation of the device, thereby
providing a liquid lubricant impregnated surface, wherein the
liquid lubricant impregnated surface introduces a slip at the
surface (e.g., where a ratio of slip velocity against mean velocity
(u.sub.w/ ) is greater than 0.9) when the positive electrode or the
negative electrode flows along the surface and promoting plug flow
of the positive electrode or the negative electrode along the
surface.
[0042] In some embodiments, the electroactive device includes a
positive electrode storage tank and a negative electrode storage
tank, wherein at least a portion of an internal surface of the
positive electrode storage tank and/or the negative electrode
storage tank includes or is coated with a liquid lubricant
impregnated surface. In some embodiments, the electroactive device
includes a positive electrode storage tank and a negative electrode
storage tank, wherein the positive electrode storage tank and the
negative electrode storage tank are connected to the electroactive
zone via piping, wherein at least a portion of an internal surface
of the piping includes or is coated with a liquid lubricant
impregnated surface.
[0043] In some embodiments, the ion-permeable membrane includes or
is coated with a liquid-lubricant impregnated surface.
[0044] Some embodiments described herein relate to methods of
manufacturing electrochemical devices discussed herein. Some
embodiments described herein relate to methods of retrofitting
electrochemical devices with liquid lubricant impregnated surfaces
discussed herein. Some embodiments described herein relate to
improving slip of electroactive phase materials in electroactive
devices by introducing a lubricant impregnated surface on surfaces
of the electroactive devices that come into contact with
electroactive phase materials.
[0045] Elements of embodiments discussed with respect to a given
aspect of the invention may be used in various embodiments of
another aspect of the invention. For example, it is contemplated
that features of dependent claims depending from one independent
claim can be used in apparatus and/or methods of any of the other
independent claims.
BRIEF DESCRIPTION OF THE DRAWING
[0046] The foregoing and other objects, aspects, features, and
advantages of the present disclosure will become more apparent and
better understood by referring to the following description taken
in conjunction with the accompanying drawings, in which:
[0047] FIG. 1A is a schematic cross-sectional view of a liquid in
contact with a liquid-impregnated surface, in accordance with
certain embodiments of the invention.
[0048] FIG. 1B is a schematic cross-sectional view of a droplet
resting on a liquid-impregnated surface, in accordance with certain
embodiments of the invention.
[0049] FIG. 1C illustrates schematics of wetting configurations
outside and underneath a drop. The total interface energies per
unit area are calculated for each configuration by summing the
individual interfacial energy contributions. Equivalent
requirements for stability of each configuration are also shown in
FIG. 1C.
[0050] FIGS. 1D-1F illustrate schematics of electrolyte flow
between flow cell walls, in accordance with certain embodiments of
the present invention.
[0051] FIG. 1D depicts macroscopic motion of an electrolyte between
walls of a flow battery, in accordance with certain embodiments of
the present invention.
[0052] FIG. 1E depicts an electrolyte moving on a regular (non-LIS)
surface. As shown in FIG. 1E, the advancing contact line pins on
asperities and results in a stick-slip motion of the electrolyte on
the non-LIS surface.
[0053] FIG. 1F depicts an electrolyte moving on a LIS surface. As
shown in FIG. 1F, the advancing contact line moves freely along the
LIS surface with no stick-slip motion, in accordance with certain
embodiments of the present invention.
[0054] FIG. 2 is a plot showing exemplary electrochemical impedance
spectroscopy as a function of carbon black (Ketjenblack, KB)
loading, in accordance with certain embodiments of the present
invention.
[0055] FIGS. 3A and 3B illustrate a concept of a gravity-induced
flow battery, in accordance with certain embodiments of the present
invention. In this example, the lithium polysulfide suspension
(cathode) 302 can be loaded into half of the flow channel of the
battery 300. By tilting the device (battery) 300 at a sufficient
angle .alpha., as shown in FIG. 3B, the Lithium polysulfide
suspension 302 flows along the interior surface of the battery 300
due to gravitational force. Discharging and charging can be carried
out in the electro-active region, e.g., between the current
collectors 304.
[0056] FIG. 4 illustrates the behavior of droplets of an exemplary
flow electrode (cathode) on different surfaces, at different
tilting angles a, at different time periods (.alpha.=40.degree. on
a TEFLON.RTM. (a polytetrafluoroethylene) surface in the left
portion of FIG. 4; .alpha.=70.degree. on TEFLON.RTM. surface in the
middle portion of FIG. 4; and .alpha.=40.degree. on a LIS in the
right portion of FIG. 4), in accordance with certain embodiments of
the present invention.
[0057] FIG. 5 illustrates schematics of velocity profiles without
boundary slip (left side) and with slip (right side), in accordance
with certain embodiments of the present invention. As shown, for
example, in FIG. 5, a LIS introduces slip boundary conditions,
which results in significant changes in the velocity profile.
[0058] FIGS. 6A-6F show cyclic voltogramms (current density at the
working electrode (y-axis) versus applied voltage (x-axis)) for
various surfaces, in accordance with certain embodiments of the
present invention. FIG. 6A is a cyclic voltogramm for a surface
that is not impregnated with any lubricant, and FIGS. 6B-6F are
cyclic voltogramms for surfaces impregnated with various different
lubricants, as designated in FIGS. 6B-6F. FIGS. 6B-6F illustrate
cyclic voltammetry (CV) of lubricants and electroactive phases
(TEG-DME (tetraethylene glycol dimethyl ether), 0.5M LiTFSi
(Lithium bis(trifluoromethane sulfonyl) imide), 1 wt % LiNO.sub.3
(Lithium Nitrate)) to probe the electrochemistry of the mixture.
The tests were performed with a Swagelok cell configuration in a
horizontal manner. Arrows in FIGS. 6D-6F indicate that reactions
occurred during the CV test on the stability of lubrications,
showing the lubricant is not electrochemically stable at the tested
voltages.
[0059] FIG. 7 shows CV of lubricants, TEG-DME (solvent) and
electrolyte (TEG-DME, 0.5M LiTFSi, 1 wt % LiNO.sub.3) to probe
electrochemical properties of the mixture, in accordance with
certain embodiments of the present invention. The tests were
performed based on a Swagelok cell configuration in a horizontal
manner. No carbon felt was included unless otherwise stated. As
shown in FIG. 7, 10 cSt silicone oil was experimentally found to be
the least electrochemically active lubricant.
[0060] FIG. 8 depicts CV of lubricants, TEG-DME (solvent) and
electrolyte (TEG-DME, 0.5M LiTFSi, 1 wt % LiNO.sub.3) to probe
electrochemical properties of the pure lubricant, in accordance
with certain embodiments of the present invention. The tests were
performed based on a Swagelok cell configuration in a horizontal
manner. No carbon felt was used unless otherwise stated.
[0061] FIGS. 9A-9E show images of silicone oil droplets on certain
surfaces, in accordance with certain embodiments of the present
invention. The surfaces in FIGS. 9A-9C were exposed to air while
the surfaces in FIGS. 9D-9F were immersed in TEG-DME. Surfaces in
FIGS. 9A and 9D are made from polydimethylsiloxane (PDMS)
functionalized with n-octadecyltrichlorosilane (OTS). Surfaces in
FIGS. 9B and 9E are made from un-modified PDMS. Surface in FIG. 9C
is PDMS functionalized with
trichloro(1H,1H,2H,2H-perfluorooctyl)silane (FOTS). All surfaces
except the one shown in FIG. 9A are non-wetting and prevent
silicone oil from spreading.
[0062] FIG. 10 is a cross-sectional illustration of a redox flow
battery, in accordance with certain embodiments of the present
invention.
[0063] FIG. 11 is a schematic illustration of an exemplary redox
flow cell for a lithium battery system, in accordance with certain
embodiments of the present invention.
[0064] FIG. 12 is a critical displacement profile map for the flow
of a Bingham-plastic with wall slip, in accordance with certain
embodiments of the present invention.
[0065] FIG. 13 is a schematic illustration of an exemplary aqueous
or non-aqueous battery, in accordance with certain embodiments of
the present invention.
[0066] FIG. 14 is a schematic illustration of an exemplary
metal-air battery, in accordance with certain embodiments of the
present invention.
[0067] FIG. 15 is a schematic illustration of an exemplary fuel
cell, in accordance with certain embodiments of the present
invention.
[0068] FIG. 16 is a schematic illustration of an exemplary
electrolytic capacitor, in accordance with certain embodiments of
the present invention.
[0069] FIG. 17 is a schematic illustration of an exemplary flow
capacitor, in accordance with certain embodiments of the present
invention.
DETAILED DESCRIPTION
[0070] In order for the present disclosure to be more readily
understood, certain terms are first defined below. Additional
definitions for the following terms and other terms are set forth
throughout the specification.
[0071] In this application, the use of "or" means "and/or" unless
stated otherwise. As used in this application, the term "comprise"
and variations of the term, such as "comprising" and "comprises,"
are not intended to exclude other additives, components, integers
or steps. As used in this application, the terms "about" and
"approximately" are used as equivalents. Any numerals used in this
application with or without about/approximately are meant to cover
any normal fluctuations appreciated by one of ordinary skill in the
relevant art.
[0072] As used herein, the term "approximately" or "about," as
applied to one or more values of interest, refers to a value that
is similar to a stated reference value. In certain embodiments, the
term "approximately" or "about" refers to a range of values that
fall within 25%, 20%, 19%, 18%, 17%, 16%, 15%, 14%, 13%, 12%, 11%,
10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, or less in either
direction (greater than or less than) of the stated reference value
unless otherwise stated or otherwise evident from the context
(except where such number would exceed 100% of a possible
value).
[0073] Many methodologies described herein include a step of
"determining". Those of ordinary skill in the art, reading the
present specification, will appreciate that such "determining" can
utilize or be accomplished through use of any of a variety of
techniques available to those skilled in the art, including for
example specific techniques explicitly referred to herein. In some
embodiments, determining involves manipulation of a physical
sample. In some embodiments, determining involves consideration
and/or manipulation of data or information, for example utilizing a
computer or other processing unit adapted to perform a relevant
analysis. In some embodiments, determining involves receiving
relevant information and/or materials from a source. In some
embodiments, determining involves comparing one or more features of
a sample or entity to a comparable reference.
[0074] As used herein, the term "substantially" refers to the
qualitative condition of exhibiting total or near-total extent or
degree of a characteristic or property of interest. One of ordinary
skill in the biological arts will understand that biological and
chemical phenomena rarely, if ever, go to completion and/or proceed
to completeness or achieve or avoid an absolute result. The term
"substantially" is therefore used herein to capture the potential
lack of completeness inherent in many biological and chemical
phenomena.
[0075] In certain embodiments, a static contact angle .theta.
between a liquid and a solid is defined as the angle formed by a
liquid drop on a solid surface as measured between a tangent at the
contact line, where the three phases--solid, liquid, and
vapor--meet, and the horizontal. The term "contact angle" usually
implies the static contact angle .theta. since the liquid is merely
resting on the solid without any movement.
[0076] As used herein, dynamic contact angle, .theta..sub.d, is a
contact angle made by a moving liquid on a solid surface. In the
context of droplet impingement, .theta..sub.d may exist during
either advancing or receding movement.
[0077] As used herein, a surface is "non-wetting" if it has a
dynamic contact angle with a liquid of at least 90 degrees.
Examples of non-wetting surfaces include, for example,
superhydrophobic surfaces, superoleophobic surfaces, and
supermetallophobic surfaces.
[0078] As used herein, contact angle hysteresis (CAH) is
CAH=.theta..sub.a-.theta..sub.r, where .theta..sub.a and
.theta..sub.r are advancing and receding contact angles,
respectively, formed by a liquid on a solid surface. The advancing
contact angle .theta..sub.a is the contact angle formed at the
instant when a contact line is about to advance, whereas the
receding contact angle .theta..sub.r is the contact angle formed
when a contact line is about to recede.
[0079] It is contemplated that compositions, mixtures, systems,
devices, methods, and processes of the claimed invention encompass
variations and adaptations developed using information from the
embodiments described herein. Adaptation and/or modification of the
compositions, mixtures, systems, devices, methods, and processes
described herein may be performed by those of ordinary skill in the
relevant art.
[0080] Throughout the description, where compositions, articles,
and devices are described as having, including, or comprising
specific components, or where processes and methods are described
as having, including, or comprising specific steps, it is
contemplated that, additionally, there are compositions, articles,
and devices of the present invention that consist essentially of,
or consist of, the recited components, and that there are processes
and methods according to the present invention that consist
essentially of, or consist of, the recited processing steps.
[0081] Similarly, where compositions, articles, and devices are
described as having, including, or comprising specific compounds
and/or materials, it is contemplated that, additionally, there are
compositions, articles, and devices of the present invention that
consist essentially of, or consist of, the recited compounds and/or
materials.
[0082] It should be understood that the order of steps or order for
performing certain action is immaterial so long as the invention
remains operable. Moreover, two or more steps or actions may be
conducted simultaneously.
[0083] The mention herein of any publication is not an admission
that the publication serves as prior art with respect to any of the
claims presented herein. Headers are provided for organizational
purposes and are not meant to be limiting.
[0084] Described herein are technologies that may be applied to
portions (e.g., interior surfaces or parts thereof) of various
electrochemical devices (e.g., batteries (e.g., flow batteries,
aqueous batteries, non-aqueous batteries, metal air batteries) fuel
cells, capacitors (e.g., electrolytic capacitors, flow
capacitors)). In some embodiments, the electrochemical device is a
battery. In some embodiments, the battery is a flow battery, an
aqueous battery, a non-aqueous battery, or a metal-air battery. In
some embodiments, the electrochemical device is a fuel cell. In
some embodiments, the electrochemical device is a capacitor. In
some embodiments, the capacitor is an electrolytic capacitor or a
flow capacitor.
[0085] The advent of micro/nano-engineered surfaces in the last
decade has opened up new techniques for enhancing a wide variety of
physical phenomena in thermofluids sciences. For example, the use
of micro/nano surface textures has provided non-wetting surfaces
capable of achieving less viscous drag, reduced adhesion to ice and
other materials, self-cleaning, and water repellency. These
improvements result generally from diminished contact (i.e., less
wetting) between the solid surfaces and adjacent liquids.
[0086] One type of non-wetting surface of interest is a
superhydrophobic surface. In general, a superhydrophobic surface
includes micro/nano-scale roughness on an intrinsically hydrophobic
surface, such as a hydrophobic coating. Superhydrophobic surfaces
resist contact with water by virtue of an air-water interface
within the micro/nano surface textures.
[0087] Some embodiments described herein relate to flow batteries
that have one or more internal surfaces coated (e.g., at time of
manufacture or via retrofitting) with a liquid-impregnated surface
(LIS) to lower pumping energy losses and/or to improve
electrochemical efficiency of the flow battery. In some
embodiments, the flow battery uses aqueous electrochemistry. In
some embodiments, the flow battery uses non-aqueous
electrochemistry. As shown, for example, in publication titled,
"Maximizing Energetic Efficiency in Flow Batteries Utilizing
Non-Newtonian Fluids," by Kyle C. Smith, W. Craig Carter and Y.-M.
Chiang, J. Electrochem. Soc., 161 (4) pp. A486-A496 (2014), which
is incorporated herein by reference in its entirety, introducing
slip at the interface between a flow battery electrode (also
referred to as electrolytes, catholytes, and anolytes) and the
internal wall of a flow channel lowers the energy consumed in
pumping the flow electrode, and also increases the electrochemical
efficiency of the electrochemical device (e.g., flow battery, flow
cell).
[0088] The effects of slip and viscoplastic flow do not occur
independently--they are fluid-mechanically coupled through
rheological constitutive and momentum balance equations.
Consideration of this coupling is necessary to quantify the
efficiency trade-offs between the rheological and transport
properties of semi-solid suspensions. Slip can be modeled by a
linear velocity/shear-stress relationship
u.sub.w=.beta..tau..sub.w, where u.sub.w and .tau..sub.w are
velocity and shear stress, respectively, at the channel wall and
.beta. is the Navier slip coefficient. Various means can be
employed to control the degree of wall slip, including surface
roughness and the volume fraction of suspended particles. A
viscoplastic case, a Bingham plastic, for which viscosity .mu.
varies with shear rate {dot over (.gamma.)} as
.mu.=.mu..sub..rho.+.tau..sub.0/|{dot over (.gamma.)}|, and the
flow is rigid (i.e., |{dot over (.gamma.)}=0) for shear stresses
less than the yield stress .tau..sub.0 can be modeled. This
rheology exhibits shear-thinning behavior (in other words,
viscosity .mu. decreases monotonically with increasing shear-rate
magnitude |{dot over (.gamma.)}|), with viscosity converging to the
material-dependent plastic viscosity .mu..sub..rho. at high shear
rates (for example, .mu.(|{dot over (.gamma.)}|,
.fwdarw..infin.)=.mu..sub..rho.). The pressure-driven (for example,
Poiseuille) velocity profiles of these fluids are governed by
momentum balance, and their shape is uniform where rigid, and
quadratic in space where flowing. The critical aliquot factor for a
given velocity profile depends on two dimensionless numbers: the
Bingham number [B.sub.n=.tau..sub.0w/(2.mu..sub..rho. )], and the
slip number (Sl=2.mu..sub..rho./w). B.sub.n is a characteristic
scale of elastic shear stresses (given by yield stress .tau..sub.0)
relative to the characteristic contribution from viscoplastic
stress (given by 2.mu..sub..rho. /w). Sl is a measure of the flow's
slipperiness and is the ratio of the slip extrapolation length to
the channel's half-width in the high-velocity limit
(B.sub.n.fwdarw.0).
[0089] Referring now to FIG. 12, a critical displacement profile
map for the flow of a Bingham-plastic with wall slip is shown.
Displacement profiles are depicted at the points specified by
circles. The variations of slip ratios s with yield radius R.sub.y
for suspensions with constant slip number Sl (0, 10.sup.-2,
10.sup.-1, and 10.sup.0) are represented by dark dashed lines, upon
which triangular symbols indicate the product of Bingham and slip
numbers, BnSl, for particular flow conditions (as shown in legend
of FIG. 12). The dotted contours of constant critical aliquot
factor ({tilde over (m)}=0.70, 0.75, 0.80, 0.85, 0.90, 0.95, and
1.00) are superimposed on the map.
[0090] FIG. 12 shows the space of suspension displacement profiles
(i.e., path of suspension parcels during an intermittent flow
pulse) for a Bingham plastic with slip, when displaced at a
critical aliquot factor corresponding to the particular velocity
profile. Each displacement profile is described geometrically by
the flow's yield radius Ry (half the width of the flow's rigid
core) and the slip ratio s (ratio of the slip velocity u.sub.w to
the mean velocity ( ). For a fixed yield radius Ry the displacement
profile becomes more plug-like as the slip ratio s increases (i.e.,
along a vertically ascending line on FIG. 12). For a fixed slip
ratio s the displacement profile becomes plug-like as the yield
radius Ry increases (i.e., along a horizontal line moving rightward
on FIG. 12). The slip ratio s and yield radius Ry depend on the
Bingham number Bn and slip number Sl. In other words, for each
point defined by (Ry,s) on the displacement profile map (FIG. 12),
there corresponds a pair (Bn,Sl). For a particular slip number Sl,
the yield radius Ry and slip ratio s evolve as Bingham number Bn is
varied (FIG. 12, dark-dashed lines). FIG. 12 shows such curves for
several slip numbers (0, 10.sup.-2, 10.sup.-1, and 10.sup.0).
Points are marked along each constant-Sl curve by triangular
symbols that indicate the corresponding Bingham number Bn (see FIG.
12, legend). These curves can be thought of as "flowcurves" along
which volumetric flow-rate is adjusted continuously, because an
increase in Bingham number Bn is equivalent to a decrease in mean
flow velocity when material properties and channel width are fixed.
For a given constant-Sl curve, both yield radius Ry and slip ratio
s increase with increasing Bingham number Bn, in other words, flow
uniformity increases with increasing Bn.
[0091] The set of possible velocity profiles for Bingham-plastic
flow with slip comprise a two-dimensional space as shown in FIG.
12. Superimposed on this map are light dotted curves along which
critical aliquot factor {tilde over (m)} is constant; the
particular curves shown in FIG. 12 are for {tilde over (m)} equal
to 0.70, 0.75, 0.80, 0.85, 0.90, 0.95, and 1.00. Accordingly, given
a specific velocity profile (determined by Bingham number Bn and
slip number Sl) a critical aliquot factor that maximizes discharge
capacity and energetic efficiency may be determined.
[0092] In some embodiments, slip ratio s (calculated as ratio of
the slip velocity to the mean velocity, u.sub.w/ ) is equal to or
greater than 0.9. In some embodiments, the use of LIS on various
surface(s) of electrochemical devices enables plug-like flow of the
electroactive phase with a slip ratio s that is equal to or greater
than 0.9.
[0093] In some instances, as discussed above, flow electrodes have
a continuous percolating network of an electronic conductor phase
that imparts electronic conductivity to the flow electrodes. As
also discussed above, the rheology of the flow electrodes may be
non-Newtonian by possessing, for example, shear-thinning behavior,
or Bingham plastic or Hershel-Bulkley rheology, wherein there is a
measureable yield stress to the fluid followed by Newtonian or
non-Newtonian viscosity after the yield stress is overcome. For
example, in some embodiments, flow electrodes may be composed of
non-Newtonian fluids (e.g., with shear-thinning behavior, or
Bingham plastic or Hershel-Bulkley rheology), where there is a
measurable yield stress to the fluid. Bingham plastics (e.g., yield
stress fluids) are fluids that require a finite yield stress before
beginning to flow. Typically, Bingham plastics will not flow solely
via gravitational forces; in other words, an additional force
(e.g., in addition to gravity) needs to be applied to Bingham
plastics in order for Bingham plastics to flow. Shear-thinning
fluids (also known as thixotropic fluids) are fluids with
viscosities that depend on the time history of shear (and whose
viscosities decrease as shear is continually applied).
Shear-thinning fluids need to be agitated over time to begin to
thin (and flow). Shear-thinning fluids typically will not flow
solely via gravitational forces; in other words, an additional
force (e.g., in addition to gravity) needs to be applied to
shear-thinning fluids in order for shear-thinning fluids to
flow.
[0094] Lubricant-impregnated surfaces (LISs) have been explored for
their slippery properties in some applications. Whereas a
superhydrophobic surface is a surface composed of solid and air, a
LIS is a surface composed of, for example, a solid and a liquid
lubricant. Compared to superhydrophobic surfaces, LISs are more
robust to pressure and are self-healing. The slippery properties of
LISs led to incorporation of these surfaces for heat transfer,
anti-icing, and biological systems. LISs typically have low contact
angle hysteresis (<1.degree.) with high droplet mobility.
Surfaces of this type give rise to advantages in electrochemical
systems that have previously not been conceived or explored. Some
exemplary LISs are described, for example, in U.S. Pat. No.
8,574,704, filed on Aug. 16, 2012 and U.S. Pat. No. 8,535,779,
filed on Jul. 17, 2012, the disclosure of each of which is
incorporated herein by reference in its entirety.
[0095] Referring to FIG. 1A, in certain embodiments, a non-wetting,
liquid-impregnated surface 120 is provided that includes a solid
122 in the form of textures (e.g., posts 124) that are impregnated
with an impregnating liquid 126, rather than a gas. The solid can
be a coating on a substrate or the solid can be the substrate
itself (e.g., internal surface of a battery or flow cell). In the
depicted embodiment, a contacting liquid 128 (e.g., electrochemical
phase) in contact with the surface, rests on the posts 124 (or
other suitable surface texture) of the surface 120. In the regions
between the posts 124, the contacting liquid 128 is supported by
the impregnating liquid 126. In certain embodiments, the contacting
liquid 128 is immiscible with the impregnating liquid 126
(immiscibility is discussed in further detail below). In some
embodiments, the impregnating liquid 126 forms a thin (e.g.,
several nanometers, e.g., 1-10 nm, 5-15 nm, 10-30 nm, 25-50 nm,
40-75 nm, 50-100 nm) layer on top of the posts 124 (or other solid
surface features); in such embodiments, the contacting liquid 128
is in contact with the impregnating liquid 126.
[0096] The solid 122 may include any intrinsically hydrophobic,
oleophobic, and/or metallophobic material or coating. For example,
the solid 122 may include: hydrocarbons, such as alkanes, and
fluoropolymers, such as TEFLON.RTM.,
trichloro(1H,1H,2H,2H-perfluorooctyl)silane (TCS),
octadecyltrichlorosilane (OTS),
heptadecafluoro-1,1,2,2-tetrahydrodecyltrichlorosilane, fluoroPOSS,
and/or other fluoropolymers. Additional possible materials or
coatings for the solid 122 include: ceramics, polymeric materials,
fluorinated materials, intermetallic compounds, and composite
materials. Polymeric materials may include, for example,
polytetrafluoroethylene, fluoroacrylate, fluorourethane,
fluorosilicone, fluorosilane, modified carbonate, chlorosilanes,
silicone, polydimethylsiloxane (PDMS), and/or combinations thereof.
Ceramics may include, for example, titanium carbide, titanium
nitride, chromium nitride, boron nitride, chromium carbide,
molybdenum carbide, titanium carbonitride, electroless nickel,
zirconium nitride, fluorinated silicon dioxide, titanium dioxide,
tantalum oxide, tantalum nitride, diamond-like carbon, fluorinated
diamond-like carbon, and/or combinations thereof. Intermetallic
compounds may include, for example, nickel aluminide, titanium
aluminide, and/or combinations thereof.
[0097] In some embodiments, the solid 122 is a coating of an
underlying substrate, where the substrate and/or the solid 122
comprises any suitable material for use in an electrochemical
device. In some embodiments, the substrate or the coating includes
(or is made of) a material such as, for example, PTFE
(TEFLON.RTM.), rare earth elements (e.g., rare earth oxides, e.g.,
ceria), and silicons. In some embodiments, the underlying substrate
is a commercial TEFLON.RTM. membrane, for example, a commercial
PTFE membrane available from Stelitech Corporation (e.g., laminated
PTFE membranes that are chemically and biologically inert, stable
up to, e.g., 260.degree. C. (500.degree. F.) or higher, and
naturally hydrophobic). In some embodiments, PTFE membranes
composed of fibers provide a desired level of roughness for
electrochemical devices used herein. In some embodiments, the
underlying substrate is an electronically conductive surface. In
some embodiments, the electronically conductive surface includes
metals. In some embodiments, the electronically conductive surface
includes a material selected from the group consisting of Carbon
(graphene), Silver, Copper, Gold, Aluminum, Calcium, Tungsten,
Zinc, Nickel, Lithium, Iron, Platinum, Tin, Carbon steel, Lead,
Titanium, Grain oriented electrical steel, Manganin, Constantan,
Stainless steel, Mercury, Nichrome, Carbon (graphite), and any
combination thereof. In some embodiments, the substrate includes an
electrically conductive plastic (e.g., radical polymers, e.g.,
Poly(2,2,6,6-tetramethylpiperidinyloxy methacrylate) (PTMA)).
[0098] The use of rare earth elements in non-wetting surfaces is
discussed, for example, in U.S. Application Publication No.
2013/0251946, filed on Jan. 15, 2013, the disclosure of which is
incorporated herein by reference in its entirety. In certain
embodiments, the rare earth element material comprises a rare earth
oxide, a rare earth carbide, a rare earth nitride, a rare earth
fluoride, and/or a rare earth boride. In certain embodiments, the
rare earth element material comprises scandium oxide
(Sc.sub.2O.sub.3), yttrium oxide (Y.sub.2O.sub.3), lanthanum oxide
(La.sub.2O.sub.3), cerium oxide (CeO.sub.2), praseodymium oxide
(Pr.sub.6O.sub.ii), neodymium oxide (Nd.sub.2O.sub.3), samarium
oxide (Sm.sub.2O.sub.3), europium oxide (Eu.sub.2O.sub.3),
gadolinium oxide (Gd.sub.2O.sub.3), terbium oxide
(Tb.sub.4O.sub.7), dysprosium oxide (Dy.sub.2O.sub.3), holmium
oxide (Ho.sub.2O.sub.3), erbium oxide (Er.sub.2O.sub.3), thulium
oxide (Tm.sub.2O.sub.3), ytterbium oxide (Yb.sub.2O.sub.3),
lutetium oxide (Lu.sub.2O.sub.3), cerium carbide (CeC.sub.2),
praseodymium carbide (PrC.sub.2), neodymium carbide (NdC.sub.2),
samarium carbide (SmC.sub.2), europium carbide (EuC.sub.2),
gadolinium carbide (GdC.sub.2), terbium carbide (TbC.sub.2),
dysprosium carbide (DyC.sub.2), holmium carbide (HoC.sub.2), erbium
carbide (ErC.sub.2), thulium carbide (TmC.sub.2), ytterbium carbide
(YbC.sub.2), lutetium carbide (LuC.sub.2), cerium nitride (CeN),
praseodymium nitride (PrN), neodymium nitride (NdN), samarium
nitride (SmN), europium nitride (EuN), gadolinium nitride (GdN),
terbium nitride (TbN), dysprosium nitride (DyN), holmium nitride
(HoN), erbium nitride (ErN), thulium nitride (TmN), ytterbium
nitride (YbN), lutetium nitride (LuN), cerium fluoride (CeF.sub.3),
praseodymium fluoride (PrF.sub.3), neodymium fluoride (NdF.sub.3),
samarium fluoride (SmF.sub.3), europium fluoride (EuF.sub.3),
gadolinium fluoride (GdF.sub.3), terbium fluoride (TbF.sub.3),
dysprosium fluoride (DyF.sub.3), holmium fluoride (HoF.sub.3),
erbium fluoride (ErF.sub.3), thulium fluoride (TmF.sub.3),
ytterbium fluoride (YbF.sub.3), and/or lutetium fluoride
(LuF.sub.3).
[0099] A variety of methods may be used to produce the surface
texture in a LIS, as discussed above. In some embodiments,
photolithography may be used, especially for relatively small size
scale and flat surfaces. In some embodiments, chemical etching
processes may be used, especially for metal oxides and plastics.
Certain materials have intrinsically low surface energies (e.g.,
lower than about 50 mN/m, lower than 40 mN/m, lower than 30 mN/m,
lower than 25 mN/m, between 25 and 50 mN/m, etc.) that meet the
thermodynamic requirements (e.g., polycarbonate and other polymers,
certain metals, certain ceramics (e.g., oxides of the
lanthanides)), and are used without substantial additional
processing (e.g., used without requiring, e.g., chemical vapor
deposition or solution based deposition of low surface energy
material (e.g., non-fluorinated (carbon chain) silanes and
thiols)). In some embodiments, chemical vapor deposition of a
hydrophobic monomer or grafting of a hydrophobic thiol may be used
to produce surfaces with the thermodynamic requirements for
LISs.
[0100] In some embodiments, a metal surface (e.g., an
electronically conductive metal surface) is etched to provide a
rough surface texture. In some embodiments, a thin (e.g., several
nano-scale or micro-scale) layer of material with a low surface
energy (e.g., below 50 mN/m) is applied to the roughened metal
surface. In some embodiments, the thin layer is a monolayer (e.g.,
molecularly thin) or the thin layer may be thicker so long at the
thin layer does not cover up the rough texture (e.g., such that
sufficient surface roughness remains on the surface after
application of the thin layer). In some embodiments, the thin layer
can be deposited by a number of suitable processes, including vapor
deposition and solution-based deposition. In some embodiments, a
number of common chemicals can be used to form the thin monolayer,
including fluorinated and non-fluorinated (carbon chain) silanes
and thiols. In some embodiments, the low surface energy material is
PTFE. In some embodiments, the low surface energy material is a
rare earth oxide. In some embodiments, the low surface energy
material is at least one material listed above as a component
making up the solid 122.
[0101] The textures within the liquid-impregnated surface 120 are
physical textures or surface roughness. The textures may be random,
including fractal, or patterned. In certain embodiments, the
textures are micro-scale and/or nano-scale features. For example,
the textures may have a length scale L (e.g., an average pore
diameter, or an average protrusion height) that is less than about
100 microns, less than about 10 microns, less than about 1 micron,
less than about 0.1 microns, or less than about 0.01 microns. In
certain embodiments, the texture includes posts 124 or other
protrusions, such as spherical or hemispherical protrusions.
Rounded protrusions may be preferable in some embodiments to avoid
sharp solid edges and minimize pinning of liquid edges. The texture
may be introduced to the surface using any conventional method,
including mechanical and/or chemical methods such as lithography,
self-assembly, and deposition, for example. In some embodiments,
the surface features (e.g., particles) are spray-deposited (e.g.,
deposited by aerosol or other spray mechanism).
[0102] In some embodiments, the solid features have a height no
greater than about 100 micrometers. In certain embodiments, the
features are posts (e.g., posts 124). In certain embodiments, the
features include one or more spherical particles, nanoneedles,
nanograss, and/or random geometry features that provides surface
roughness. In certain embodiments, the feature comprises one or
more pores, cavities, interconnected pores, and/or interconnected
cavities. In certain embodiments, the surface comprises porous
media with a plurality of pores having different sizes.
[0103] The impregnating liquid 126 may be any type of liquid that
is capable of providing the desired non-wetting properties for
desired applications. For example, the impregnating liquid 126 may
be oil-based (e.g., silicone oil). In certain embodiments, the
impregnating liquid 126 is an ionic liquid (e.g., BMI-IM). Other
examples of possible impregnating liquids include hexadecane,
vacuum pump oils (e.g., FOMBLIN.RTM. 06/6, KRYTOX.RTM. 1506)
silicone oils (e.g., 10 cSt or 1000 cSt), fluorocarbons (e.g.,
perfluoro-tripentylamine, FC-70), shear-thinning fluids,
shear-thickening fluids, liquid polymers, dissolved polymers,
viscoelastic fluids, and/or liquid fluoroPOSS. In certain
embodiments, the impregnating liquid is (or comprises) a
hydrocarbon liquid, and/or a fluorocarbon liquid. In some
embodiments, the impregnating liquid 126 is electronically or
ionically conducting. In some embodiments, the impregnating liquid
includes additional components that impart electric or ionic
conductivity.
[0104] In some embodiments, the impregnating liquid 126 includes
electronically-conducting particles (e.g., nanoparticles,
microparticles) suspended therein (e.g., any impregnating liquid
126 discussed herein with electronically conducting particles
suspended therein). In some embodiments, the
electronically-conducting particles suspended in the impregnating
liquid include nano-sized carbon particles or nano-sized metal
particles. In some embodiments, the electronically-conducting
particles form a percolating network of electronically-conducting
particles, which allows a layer (e.g., layer 128 in FIG. 1A) to be
electronically conducting. In some embodiments, the LIS (e.g., LIS
comprising an impregnating liquid 126 including
electronically-conducting particles suspended therein) is applied
to the current collector.
[0105] In some embodiments, a "percolating conductive network,"
refers to particles that are electronically connected, such that
electronic charge carriers can be transported throughout the
network. The particles themselves may be in actual physical contact
with each other and/or some of the particles may not necessarily be
in actual physical contact, but the particles may be positioned
near enough to each other (e.g., as in a suspension) such that the
particles are electronically connected and electronic charge
carriers can be transported between the particles. Without being
bound by a particular theory, a percolating conductive network may
be formed in some embodiments by electronically conductive
particles undergoing diffusion-limited aggregation (DLA).
Diffusion-limited aggregation refers to a process where particles
undergoing a random walk due to Brownian motion exhibit
"hit-and-stick" behavior; that is, they stick to other particles
they hit--and thereby aggregate to form fractal networks. Such
networks may have a self-similar structure when observed at varying
magnifications.
[0106] In some embodiments, the impregnating liquid 126 is made
shear thickening with the introduction of nano particles. A
shear-thickening impregnating liquid 126 may be desirable for
preventing impalement and resisting impact from impinging liquids,
for example.
[0107] In some embodiments, the impregnating liquids 126 with low
vapor pressures (e.g., less than 0.1 mmHg, less than 0.001 mmHg,
less than 0.00001 mmHg, or less than 0.000001 mmHg) are used. In
certain embodiments, the impregnating liquid 126 has a freezing
point of less than -20.degree. C., less than -40.degree. C., or
about -60.degree. C. In certain embodiments, the surface tension of
the impregnating liquid 126 is about 15 mN/m, about 20 mN/m, or
about 40 mN/m (e.g., ionic liquids). In certain embodiments, the
viscosity of the impregnating liquid 126 is from about 10 cSt to
about 1000 cSt).
[0108] The impregnating liquid 126 may be introduced to the surface
120 using any conventional technique for applying a liquid to a
solid. In certain embodiments, a coating process, such as a dip
coating, blade coating, or roller coating, is used to apply the
impregnating liquid 126. In certain embodiments, the liquid
lubricant is mixed with a solvent and then sprayed, because the
solvent will reduce the liquid lubricant viscosity, allowing it to
spray more easily and more uniformly. Then, the solvent will dry
out of the coating. In certain embodiments, the method further
includes chemically modifying the substrate prior to applying the
texture to the substrate and/or chemically modifying the solid
features of the texture.
[0109] In some embodiments, after the impregnating liquid 126 has
been applied, capillary forces hold the liquid 126 in place between
the surface textures (e.g., between surface posts 124). Capillary
forces scale roughly with the inverse of feature-to-feature
distance or pore radius, and the features may be designed such that
the liquid is held in place in-between and/or within the features
despite movement of the surface and despite movement of fluids over
the surface. In some embodiments, the lubricant is stabilized by
the capillary forces arising from the microscopic texture, and
provided that the lubricant wets the solid preferentially, this
allows the electroactive phase to move (e.g., slide, roll, slip,
etc.) above the LIS surface with remarkable ease, as evidenced by
the extremely low contact angle hysteresis)(-1.degree. of the
electroactive phase. In some embodiments, in addition to low
hysteresis, these non-wetting surfaces can self-heal by capillary
wicking upon damage. Contact line morphology governs pinning of the
electroactive phase and hence its mobility on the surface.
[0110] In some embodiments, the impregnating liquid is held in
place between the features regardless of orientation of the article
(e.g., oriented at any angle). In some embodiments, the
impregnating liquid is not displaced (e.g., removed) from the
article (e.g., battery) during use, transport, and/or storage of
the article. In some embodiments, the impregnating liquid and the
article itself is shelf-stable, e.g., during storage and during the
useful life of the article.
[0111] In certain embodiments, nano-scale features (e.g., 1
nanometer to 1 micrometer) are used to facilitate stable
containment of the impregnating liquid in-between and/or within the
surface features, especially where high dynamic forces,
gravitational forces, and/or shearing could pose a threat to
removing the impregnating liquid from the surface. In some
embodiments, small (e.g., nano-scale) features may also be useful
to provide robustness.
[0112] In some embodiments, the LISs are useful for reducing
viscous drag between a solid surface (e.g., an interior surface of
an electroactive device) and a flowing liquid (e.g., electroactive
phase). In general, the viscous drag or shear stress exerted by a
liquid flowing over a solid surface is proportional to the
viscosity of the liquid and the shear rate adjacent to the surface.
A traditional assumption is that liquid molecules in contact with
the solid surface stick to the surface, in a so-called "no-slip"
boundary condition. While some slippage may occur between the
liquid and the surface, the no-slip boundary condition is a useful
assumption for most applications.
[0113] In certain embodiments, non-wetting surfaces, such as LISs,
are desirable as they induce a large amount of slip at the solid
surface. For example, referring again to FIG. 1A, when a contacting
liquid 128 (e.g., electroactive phase) is supported by an
impregnating liquid 126, the liquid-liquid interface is free to
flow or slip with respect to the underlying solid material. Drag
reductions of as much as 40% may be achieved due to this
slippage.
[0114] FIG. 1B is a schematic cross-sectional view of a liquid
droplet 202 (e.g., droplet of an electroactive phase) resting on a
liquid-impregnated surface 204, in accordance with certain
embodiments of the invention. In some embodiments, the morphology
of the droplet edge, which governs its mobility, is affected by the
properties of the impregnating liquid 126. For example, as
depicted, the droplet may "pick up" the impregnating liquid 126
locally near the droplet edges. The pooling of impregnating liquid
126 at the edges of the droplet gives rise to pinning forces. In
some embodiments, during droplet roll-off, the pinning forces, and
viscous forces resist droplet movement due to gravity
[0115] A thermodynamic framework that allows one to predict whether
a system will be stable for a given droplet, oil, and substrate
material will be discussed in further detail below. Droplets placed
on lubricant-impregnated surfaces exhibit fundamentally different
behavior compared to droplets placed on typical superhydrophobic
surfaces. In some embodiments, these four-phase systems can have up
to three different three-phase contact lines, giving up to twelve
different thermodynamic configurations. There are three possible
configurations to consider for the interface outside of the droplet
(in an air environment), and three possible configurations to
consider for the interface underneath the droplet (in a water
environment). These configurations are shown in FIG. 1C along with
the total interface energy of each configuration.
[0116] The configurations possible outside the droplet are A1 (not
impregnated, i.e., dry), A2 (impregnated with emergent features),
and A3 (impregnated with submerged features--i.e., encapsulated).
On the other hand, underneath the droplet, the possible
configurations are W1 (impaled), W2 (impregnated with emergent
features), and W3 (impregnated with submerged features--i.e.,
encapsulated). The stable configuration will be the one that has
the lowest total interface energy. Referring now to configurations
outside the droplet, the textured surface as it is slowly withdrawn
from a reservoir of oil could be in any of states A1, A2, and A3
depending on which has the lowest energy. For example, state A2
would be stable if it has the lowest total interface energy, i.e.
E.sub.A2<E.sub.A1, E.sub.A3. From FIG. 1C, this results in:
E.sub.A2<E.sub.A1(.gamma..sub.sa-.gamma..sub.os)/.gamma..sub.oa>(1-
-.PHI.)/(r-.PHI.) (1)
E.sub.A2<E.sub.A3.gamma..sub.sa-.gamma..sub.os-.gamma..sub.oa<0
(2)
where .gamma. is the interfacial tension between the two phases
designated by subscripts w, a, o, and s, where w is water, a is
air, and o is the impregnating liquid, s is solid surface, .PHI. is
the fraction of the projected area of the surface that is occupied
by the solid and r is the ratio of total surface area to the
projected area of the solid. In the case of square posts with width
"a", edge-to-edge spacing "b", and height "h",
.PHI.=a.sup.2/(a+b).sup.2 and r=1+4ah/(a+b).sup.2. Applying Young's
equation,
cos(.theta..sub.os(a))=(.gamma..sub.sa-.gamma..sub.os)/.gamma..sub.oa,
Eq. (1) reduces to the hemi-wicking criterion for the propagation
of oil through a textured surface:
cos(.theta..sub.os(a))>(1-.PHI.)/(r-.PHI.)=cos(.theta..sub.c).
This requirement can be conveniently expressed as
.theta..sub.os(a)<.theta..sub.r. In Eq. (2),
.gamma..sub.sa-.gamma..sub.os-.gamma..sub.oa, is simply the
spreading coefficient S.sub.os(a) of oil on the textured surface in
the presence of air. This may be reorganized as
(.gamma..sub.sa-.gamma..sub.os)/.gamma..sub.oa<1, and applying
Young's equation again, Eq. (2) can be written as
.theta..sub.os(a)>0. Expressing Eq. (1) in terms of the
spreading coefficient S.sub.os(a), yields:
-.gamma..sub.oa(r-1)/(r-.PHI.)<S.sub.os(a). The above
simplifications then lead to the following equivalent criteria for
the surface to be in state A2:
E.sub.A2<E.sub.A1,E.sub.A3.theta..sub.c>.theta..sub.os(a)>0-.ga-
mma..sub.oa(r-1)/(r-0)<S.sub.os(a)<0 (3)
[0117] Similarly, state A3 would be stable if E.sub.A3<E.sub.A2,
E.sub.A1. From FIG. 1C, this gives:
E.sub.A3<E.sub.A2.theta..sub.os(a)=0.gamma..sub.sa-.gamma..sub.os-.ga-
mma..sub.oa.ident.S.sub.os(a).gtoreq.0 (4)
E.sub.A3<E.sub.A1.theta..sub.os(a)<cos.sup.-1(1/r)S.sub.os(a)>--
.gamma..sub.oa(1/r) (5)
[0118] Note that Eq. (5) is automatically satisfied by Eq. (4),
thus the criterion for state A3 to be stable (i.e., encapsulation)
is given by Eq. (4). Following a similar procedure, the condition
for state A1 to be stable can be derived as
E.sub.A1<E.sub.A2,E.sub.A3.theta..sub.os(a)>.theta..sub.cS.sub.os(-
a)<-.gamma..sub.oa(r-1)/(r-.PHI.) (6)
[0119] The rightmost expression of Eq. (4) can be rewritten as
(.gamma..sub.sa-.gamma..sub.os)/.gamma..sub.oa.gtoreq.1. This
raises an important point: Young's equation would suggest that if
.theta..sub.os(a)=0, then (.gamma..sub.sa-.gamma..sub.os)
.gamma..sub.oa=1 (i.e., S.sub.os(a)=0). However,
.theta..sub.os(a)=0 is true also for the case that
(.gamma..sub.sa-.gamma..sub.os)/.gamma..sub.oa>1 (i.e.,
S.sub.os(a)>0). It is important to realize that Young's equation
predicts the contact angle based on balancing the surface tension
forces on a contact line--the equality only exists for a contact
line at static equilibrium. For a spreading film (S.sub.os(a)>0)
a static contact line does not exist, hence precluding the
applicability of Young's equation.
[0120] The configurations possible underneath the droplet are
discussed in the paragraphs below. Upon contact with water, the
interface beneath the droplet will attain one of the three
different states--W1, W2, or W3 (FIG. 1C)--depending on which has
the lowest energy. Applying the same method to determine the stable
configurations of the interface beneath the droplet, the stability
requirements take a form similar to Eqs. (3), (4), and (6), with
.gamma..sub.oa, .gamma..sub.sa, .theta..sub.os(a), S.sub.os(a),
replaced with .gamma..sub.ow, .gamma..sub.sw, .theta..sub.os(w),
S.sub.os(w) respectively. In addition, .theta..sub.c is not
affected by the surrounding environment as it is only a function of
the texture parameters, .PHI. and r. Thus, the texture will remain
impregnated with oil beneath the droplet with emergent post tops
(i.e., state W2) when:
E.sub.W2<E.sub.W1,E.sub.W3.theta..sub.c>.theta..sub.os(w)>0.gam-
ma..sub.ow(r-1)/(r-.PHI.)<S.sub.os(w)<0 (7)
State W3 will be stable (i.e., the oil will encapsulate the
texture) when:
E.sub.W3<E.sub.W1,E.sub.W2.theta..sub.os(w)=0.gamma..sub.sw-.gamma..s-
ub.os-.gamma..sub.ow.ident.S.sub.os(w).gtoreq.0 (8)
and the droplet will displace the oil and be impaled by the
textures (state W1) when:
E.sub.W1<E.sub.W2,E.sub.W3.theta..sub.os(w)>.theta..sub.cS.sub.os(-
w)<-.gamma..sub.ow(r-1)/(r-.PHI.) (9)
[0121] As depicted in FIG. 1F, in some embodiments, a LIS is
composed of textures that contain a lubricant (e.g., impregnating
liquid 126 of FIG. 1A). In some embodiments, as discussed above,
the lubricant is held between the surface features by capillary
forces. In some embodiments, the lubricant is stably held in place
between the surface features regardless of orientation of the
surface (e.g., the lubricant does not escape the surface features
via gravitational forces). The contact line of working fluid moves
across a LIS freely. An untreated surface (e.g., a surface without
a lubricant and/or impregnated liquid) on the other hand typically
has inherent roughness and the advancing contact line readily pins
on asperities, as depicted, for example, in FIG. 1E, resulting in
non-slip motion. On a LIS, the advancing contact line moves freely
with slip motion, as shown in FIG. 1F.
[0122] In some embodiments, LISs may be used to reduce friction
(e.g., viscous drag) between a solid surface and a flowing liquid,
e.g., where an electrochemically active component (e.g., charge
storing electrodes or electrochemical fuels) contacts the
surface(s) (or a portion of the surface(s)) of an electrochemical
device.
[0123] In some embodiments, charge storing electrodes may be
battery electrodes, flow battery electrodes (e.g., catholytes,
anolytes), capacitor electrodes, and flow capacitor electrodes.
[0124] In some embodiments, electrochemical fuels may include
condensed phase from which electrical energy is obtained through
the electrochemical reaction in a device. Condensed phase fuels may
be single phase or multiphase. Condensed phase fuels may include
organic or inorganic compound(s) (or any combination thereof). In
some embodiments, condensed phase fuels may include liquids, phase
separated liquids, solids, liquid-solid suspensions, semi-solids,
gels, micelles, and any combination thereof. In some embodiments,
the condensed phase includes water in a hydrogen fuel cell or water
in a methanol fuel cell.
[0125] In some embodiments, LISs are used to reduce friction during
operation of an electrochemical device where one or more
electroactive phases undergo flow through the device.
[0126] In some embodiments, LISs are used to reduce friction during
manufacture of an electrochemical device. In some embodiments, one
or more electroactive phases are flowed/transported along one or
more surface(s) (and/or portion(s) thereof) of the electrochemical
device during manufacture of the electrochemical device. In some
embodiments, any surface (or part or portion thereof) (e.g.,
pipeline for the manufacturing process) or any part of any
equipment that comes into contact with one or more electroactive
phases during manufacture of the electrochemical device includes or
is coated with a LIS. For example, devices that are coated with LIS
may lose less active material during pumping or transporting. In
manufacturing of conventional batteries, the components of the
battery are added to the cell and the cell is sealed (e.g., as in a
cylindrical battery cell). In some embodiments, the devices that
pump, transport, or otherwise come into contact with the
electrochemically active phases that are included in conventional
batteries (and other devices) are coated with LISs such that a
smaller fraction of the electrochemically active phase is lost
during the manufacturing processes.
[0127] In some embodiments, embodiments of the present invention
may be useful for flow batteries and similar devices, as the
surfaces described herein can lower pumping energy losses and/or
increase the electrochemical energy efficiency of flow batteries.
In some embodiments, LISs of the present invention enable the
electrode to flow where otherwise the yield stress of the electrode
cannot be overcome without the LIS (e.g., where the electrode would
not flow without the LIS or where the electrode would become pinned
to the surface, as shown, for example in FIG. 1E).
[0128] In some embodiments, LISs may influence or control flow
velocity, gradients in velocity, extent of slip, and/or direction
of flow of an electroactive phase or electrolyte in an
electrochemical device. In some embodiments, LISs allow for precise
control of the velocity and/or trajectory of movement of an
electroactive phase or electrolyte in an electrochemical
device.
[0129] In some embodiments, LISs may be used to facilitate and/or
control the flow of any viscous or yield-stress fluid(s) flowing
through a fluidic or microfluidic geometry for electrochemical
applications.
[0130] In some embodiments, a location of a reactant or product
phase on a LIS may be controlled by selecting lubricants and/or
surface coatings with desired properties (e.g., surface tension,
wettability, viscosity, melting/freezing point, and any combination
thereof). In some embodiments, LISs may increase or decrease an
amount of nucleation, growth, precipitation, or segregation of a
liquid or solid phase at the interface between LISs and
electroactive phases. For example, in a lithium-sulfur battery, the
sulfur undergoes a series of transformations, e.g., from S.sub.8 to
Li.sub.2S.sub.8, Li.sub.2S.sub.6, Li.sub.2S.sub.4, Li.sub.2S.sub.2,
and Li.sub.2S during cycling. Of these species, Li.sub.2S.sub.8,
Li.sub.2S.sub.6 are soluble in the electrolyte. Li.sub.2S.sub.4 is
insoluble in typical solvents (e.g., for example, Li.sub.2S.sub.4
is insoluble in TEG-DME) and, therefore, may deposit on surfaces.
If Li.sub.2S.sub.4 (or other insoluble species such as
Li.sub.2S.sub.2 or Li.sub.2S) deposit away from the electrode, that
material may not be recovered (e.g., such deposition would
typically result in loss of Li-bearing active material, and hence
loss of capacity of the battery). The use of a LIS may prevent
insoluble species, for example Li.sub.2S.sub.4 from depositing on
unwanted surfaces (e.g., from depositing on surfaces that are not
electrically connected to the terminals of the battery or are
otherwise electrochemically inactive). Similarly, Li.sub.2S.sub.2,
and Li.sub.2S are insoluble in typical solvents, and the use of a
LIS may prevent these species from depositing on unwanted surfaces
(e.g., from depositing on surfaces that are not electrochemically
active). In some embodiments, LISs may increase precipitation of a
phase (e.g., electroactive phase) at the interface by acting as a
heterogeneous nucleation surface, as discussed in further detail
below. In certain embodiments, LISs may serve to suppress
nucleation, growth, or precipitation of a phase (e.g.,
electroactive phase) at the interface by producing an interface
such that the precipitating phase has a high contact angle at the
interface.
[0131] In some embodiments, at least one surface (or any portion
thereof) in an electrochemical device may have (or be coated or
retrofitted with) a LIS. In some embodiments, a non-wetting
lubricant phase may be used to avoid infiltration into a porous
component or membrane of the device. In some embodiments, a current
collector of the device is selected to be non-wetting. In some
embodiments, a membrane covers the current collector. In some
embodiments, the membrane is filled with the working solvent (e.g.,
TEG-DME, which is not used as an impregnating liquid lubricant in
this embodiment). In some embodiments, the LIS, which comprises the
impregnating liquid lubricant, is provided before the current
collector. In some embodiments, the impregnating liquid lubricant
is selected such that it does not spread out of the LIS and cannot
and get into the membrane on the current collector, which would
prevent it from working properly, which is undesirable. In some
embodiments, the impregnating liquid lubricant is KRYTOX.RTM. 1506
(a fluorinated ether). In some embodiments, the impregnating liquid
lubricant (e.g., KRYTOX.RTM. 1506) is impregnated into a porous
TEFLON.RTM. membrane (e.g., having a pore size of about 0.2
.mu.m).
Flow Battery
[0132] In some embodiments, the electrochemical device is a flow
battery. In certain embodiment, a flow cathode is a solution and/or
suspension of lithium polysulfide Li.sub.xS.sub.y in aqueous or
non-aqueous electrolyte, and comprises a suspension of carbon black
that forms a percolating network providing electronic conductivity.
The non-aqueous electrolyte may, for example, be based on glymes
(e.g., tetraethylene glycol dimethyl ether (TEG-DME), diglyme,
dioxolane-dimethoxyethane (DOL-DME)), and may optionally include a
lithium salt (e.g., Bis(trifluoromethane)sulfonimide lithium salt
(LiTFSI)). A high carbon black content may be desired in some
embodiments to increase the electronic conductivity of the flow
cathode, but without compromising the ability of the electrode to
flow.
[0133] FIG. 2 is a plot showing exemplary electrochemical impedance
spectroscopy as a function of carbon black (Ketjenblack, KB)
loading, in accordance with certain embodiments of the present
invention. The suspension tested to construe the chart shown in
FIG. 2 included carbon black and an electrolyte (tetraethylene
glycol dimethyl ether (TEG-DME), 0.5M
bis(trifluoromethane)sulfonimide lithium salt (LiTFSI) and 1 wt %
LiNO.sub.3). The measurements were conducted with a Swagelok cell
with two parallel plates of 1.59 mm.
[0134] As seen, for example, in FIG. 2, the charge transfer
resistance of a lithium half-cell may decrease with increasing
amount of carbon black in the suspension. However, as the
concentration of carbon black increases, the viscosity of the
suspension also increases, and at sufficiently high concentrations
(e.g., carbon black loadings greater than or equal to (.gtoreq.)
about 0.15 vol %, 0.2 vol %, 0.3 vol %, 0.4 vol %, 0.45 vol %, 0.5
vol %), the flow cathode becomes a yield-stress fluid. In some
embodiments, a carbon network percolates at a carbon black volume
fraction of 0.15 vol %. Typically, any suspension with carbon black
loading of 0.15 vol % or greater may exhibit a yield-stress. For
example, TEG-DME exhibits a yield-stress of 0.2 Pa when loaded with
0.25 vol % carbon black. Yield-stress is typically not a linear
function with carbon black loading. For example, TEG-DME loaded
with 0.75 vol % carbon black has a yield-stress of 4 Pa, while
TEG-DME loaded with 1.5 vol % carbon black has a yield-stress of
about 42 Pa. Yield-stress fluids create difficulties in using such
flow electrodes in flow batteries. In some embodiments, use of LISs
enables overcoming these difficulties as these surfaces enable flow
of yield-stress fluids along the LISs. In some embodiments,
yield-stress fluids flow along the surfaces of the flow batteries
such that the interior surfaces of the flow batteries that are in
contact with the yield-stress fluids are substantially free from
residue left by the yield-stress fluids along the path of flow of
the yield-stress fluids. In some embodiments, no residue of the
yield-stress fluids is left along their path of flow. In some
embodiments, the yield-stress fluids flow along the surfaces of the
flow batteries solely due to gravity (e.g., without requiring an
application of an additional force, e.g., without requiring shaking
or otherwise agitating the yield-stress fluids).
Gravity Induced Flow Cell ("GIF Cell")
[0135] In some embodiments, the electrode flows along a LIS surface
under the influence of gravity (e.g., a gravity-induced flow cell,
or GIF cell, as described in U.S. Patent Application 61/911,101,
filed on Dec. 3, 2013, which is incorporated herein by reference in
its entirety). In some embodiments, the electrode of a GIF cell
flows along a LIS surface solely due to gravitational forces (e.g.,
without requiring any agitation or other forces in order for the
electrode to move along the surface).
[0136] In some embodiments, the GIF cell includes first and second
reservoirs having a selected volume containing a flowable redox
electrode. In some embodiments, a membrane is provided separating
charged and discharged material. In some embodiments, the flow cell
includes an energy-extraction region including electronically
conductive current collectors through or adjacent to which the
flowable redox electrodes flow and to which charge transfer occurs.
In some embodiments, the current collector is a plate including
channels to direct flow and/or to increase surface area, a porous
electronically conductive material, or a percolating network of
conductor particles or fibers that flows with the electrode. In
some embodiments, structure is provided for altering orientation of
the flow cell with respect to gravity whereby gravity induces flow
of the redox electrodes between the first and second reservoirs. In
some embodiments, the GIF cell includes a motor for varying the
angle of the cell with respect to gravity. In some embodiments, the
energy extraction region has a volume and ratio of the volume of
the energy-extraction region to reservoir volume is selected to be
in the range of about 1 to about 1000.
[0137] In some embodiments, a stationary current collector includes
carbon. In some embodiments, the carbon is selected from the group
consisting of glassy carbon, disordered carbon, graphite, and
nanoparticulate carbon including fullerenes, carbon nanofibers, and
carbon nanotubes, graphene, and graphene oxide. In some
embodiments, the carbon may be in the form of a carbon plate, plate
with nonplanar surface features including channels, compacted
fibers, woven fibers, paper, or 3D reticulated foam. In some
embodiments, a stationary current collector may be a carbon coating
on a support or substrate comprising an insulating or conductive
material.
[0138] In some embodiments, the stationary current collector is a
metal or metal alloy such as aluminum, copper, nickel, and
stainless steel. In some embodiments, the metal or metal alloy may
be in the form of a metal plate, plate with nonplanar surface
features including channels, compacted metal fibers, woven metal
fibers, 3D reticulated metal foam. In some embodiments, a
stationary current collector may be a metal or metal alloy coating
on a support substrate comprising an insulating or conductive
material.
[0139] In some embodiments, the stationary current collector is a
metal oxide, including, for example, an electronically conductive
metal oxide such as indium-tin-oxide (ITO), titanium, oxide with an
oxygen/titanium atomic ratio less than 2, vanadium oxide with
oxygen/vanadium atomic ratio less than about 2.5, ruthenium oxide,
a transition metal oxide, a perovskite oxide, a spinel oxide
including but not limited to spinels containing the transition
metals Fe. Co, Mn and Ni, and mixtures and doped variants of such
oxides including those doped to impart n-type or p-type electronic
conductivity. The metal oxide may be in the form of a metal oxide
plate, plate with nonplanar surface features including channels,
metal fibers, or porous sintered metal oxide. In some embodiments,
a stationary current collector may be a metal oxide coating on a
support or substrate comprising an insulating or conductive
material.
[0140] In some embodiments, the electroactive phase of (e.g., of a
GIF cell) is a redox electrode. In some embodiments, the redox
electrode is a suspension. In some embodiments, the suspension
includes conductor particles and active material particles. In some
embodiments, due to the existence of a percolating electronically
conductive network in such suspensions, the percolating network
itself acts as an extended, mobile current collector allowing
electrochemical reaction to take place throughout the volume of the
flow electrode. In some embodiments, active materials suspensions
include those described in U.S. Pat. No. 8,722,227, which is
incorporated herein by reference in its entirety. In some
embodiments, the flowable redox electrode is a metal sulfide
composition described in PCT/US2014/014681, which is incorporated
herein by reference in its entirety. In some embodiments, the
flowable redox electrode working ion is an alkali ion selected from
the group consisting of Li.sup.+, Na.sup.+, K.sup.+, and Cs.sup.+.
In some embodiments, the working ion is a trivalent ion of aluminum
or yttrium. In some embodiments, the reservoirs and/or the
energy-extraction region includes a LIS surface, as discussed
herein.
[0141] In some embodiments, the electroactive phase includes water
as a solvent. In some embodiments, the electroactive phase is
non-aqueous. In some embodiments, the electroactive phase is a
suspension including conductor particles. In some embodiments, the
suspension includes an electronically percolating network, which
includes solids (e.g., carbons, metal oxides, metals, and metal
alloys). In some embodiments, the suspension is electronically
conductive. In some embodiments, the suspension is a mixed
electronic-ionic conductor.
[0142] FIGS. 3A and 3B show a schematic of a battery 300 (GIF
cell). A flow electrode 302 (e.g., the cathode when the counter
electrode is a stationary electrode (e.g., a Li metal electrode))
may be stored in a top compartment 312 of the battery 300. By
tilting the device 300 at an angle .alpha. (310), as shown in FIG.
3B, the flow electrode 302 may move from the top compartment 312 to
a lower compartment 314 due to gravity (e.g., solely due to
gravity, e.g., without requiring the application of additional
force(s) to enable flow of the flow electrode 302). Charging and
discharging of the flow electrode 302 may be carried out in the
electrochemical-active region (e.g., in between the current
collectors 304). As shown in FIGS. 3A and 3B, the battery includes
a current collector 304 that is in contact with a layer of lithium
306. The layer of lithium 306 is in contact with a separator 308.
In some embodiments, electronically conductive flow electrodes can
be used in this device (e.g., device 300). For example, carbon
black may be included in the electroactive phase (e.g., flow
electrode 302). In some embodiments, an increased content of carbon
black may increase electronic conductivity. However, in
conventional GIF cells, the maximum carbon black content (e.g.,
about 0.5 vol % or lower) is typically determined by flowability
(e.g., viscosity, yield stress of the flowing phase) with the given
gravitational force. In conventional systems, an amount of carbon
black higher than 0.5 vol % typically results in pinning of the
electroactive phase to the surface. A LIS may enable an
electroactive phase with higher carbon content (e.g., for example,
but not limited to, higher than 0.5 vol %, up to about 1 vol % or
higher than 1 vol %) to slip in GIF cells, since the yield stress
need not be overcome for flow to occur. This is particularly true
of flow battery designs where the cross-sectional dimensions of the
flow channels are substantially constant. In some embodiments, the
use of LIS surfaces allows electroactive phases (e.g., suspensions)
with any amount of carbon black loading to be used (e.g., there is
no upper limit of yield-stress).
[0143] In some embodiments, once a flow electrode overcomes a
required yield stress by gravitational force, it may pass through
the electroactive zone of the flow battery (i.e., the stack)
rapidly (e.g., flow quickly). Once the flow electrode overcomes the
required yield stress and starts moving, due to its high flow rate,
it may not have sufficient time at the electroactive zone to
produce desired current rates, which is undesirable in some
embodiments. In some embodiments, the use of LISs enables precise
control of flow rates of the flow electrode, resulting in high
electrochemical utilization of the flow electrodes and high
round-trip energy efficiency of the flow battery. In some
embodiments, the use of the LISs enables control of flow rates of
the flow electrode such that the flow electrode to be charged or
discharged has sufficient time at the electroactive zone to produce
desired current rates. For example, the speed at which the flow
electrode moves may be controlled by the viscosity of the
impregnating liquid. For example, in some embodiments, the use of
impregnating liquids with higher viscosity results in slowing down
the speed of the flow of the electroactive phase. In some
embodiments, the use of the LISs enables control of flow
trajectories of the flow electrode.
[0144] For example, in some embodiments, the flow electrode flows
from a first position (e.g., top compartment) to a second position
(e.g. bottom compartment), passing through an electroactive zone
(e.g., middle compartment located between the top compartment and
the bottom compartment) along its path of flow. In some
embodiments, the use of LISs allows for the flow electrode to flow
(or slip) at a first velocity from the first position to the
electroactive zone. In some embodiments, the use of LISs allows for
the flow electrode to flow (or slip) at a second velocity through
the electroactive zone, e.g., where the second velocity is slower
than the first velocity (so that, e.g., the flow electrode spends
sufficient time in the electroactive zone). In some embodiments,
the flow electrode stops (e.g., has no velocity) in at least a
portion of the electroactive zone. In some embodiments, the flow
electrode has a third velocity from the electroactive zone to the
second position (e.g., where the third velocity is the same as or
different than the first velocity).
[0145] FIG. 4 illustrates the behavior of droplets of an exemplary
flow electrode (cathode) on different surfaces, at different
tilting angles .alpha., at different time periods. In FIG. 4,
.alpha.=40.degree. on Teflon surface in the left portion of FIG. 4;
.alpha.=70.degree. on TEFLON.RTM. surface in the middle portion of
FIG. 4; and .alpha.=40.degree. on a LIS in the right portion of
FIG. 4. A non-stick surface (e.g., TEFLON.RTM.) is used in the
leftmost and middle experimental setups, and is found to increase
droplet slip compared to the underlying ABS-like plastic. The top
row of FIG. 4 (left, right, and middle) shows a droplet composed of
0.75 vol % carbon black (Ketjenblack EC-600JD, Akzo Nobel)
dispersed in 0.5 M LiTFSI, 1 wt % of LiNO.sub.3 and 2.5 M
Li.sub.2S.sub.8 (molarity with respect to sulfur) in TEG-DME. The
droplet is composed of fluid that is a yield-stress fluid, where
the yield stress is estimated to be 5 Pa (e.g., about the yield
stress of ordinary ketchup). The circles around the black droplets
in the top row of FIG. 4 indicate where the drops were initially
deposited (at t=0 seconds). The bottom row of FIG. 4 shows the
motion of the droplets after t=15 seconds. On a smooth TEFLON.RTM.
surface at a 40.degree. incline, the droplet did not move at all
(the droplet is stuck (pinned) to the surface), as shown in the
bottom left portion of FIG. 4. On the same surface inclined to
70.degree., the droplet also exhibits contact line pinning: while
the front of the droplet moved, the droplet left a trail of wetted
surface where the droplet was in contact with the TEFLON.RTM.
surface (e.g., after 15 seconds, a significant amount of the
droplet remained in the same position as it was at t=0), as shown
in the bottom middle portion of FIG. 4. On the LIS surface inclined
at 40.degree., the droplet of the flow electrode (cathode) moved in
the direction of the tilting angle .alpha. and left no fluid behind
(e.g., left no fluid along its path of flow), as shown in the
bottom right portion of FIG. 4. In FIG. 4 (right), the LIS was a
porous TEFLON.RTM. membrane (pore size of 0.2 .mu.m, Sterlitech)
impregnated with silicone oil.
[0146] As shown in FIG. 4 (rightmost), the LIS coated surface
allows the flow electrode droplet to move under gravitational force
without leaving any residue along the flow electrode path of flow
when the tilting angle .alpha.=40.degree.. The LIS exhibits
markedly improved slip as compared to the TEFLON.RTM. surface
without a LIS.
[0147] In some embodiments, when the flow electrode (cathode) moves
from a first location to a second location along its path of flow,
the first location from which the flow electrode (cathode) moves is
free of flow electrode (cathode) residue (e.g., the path of flow is
clean, the flow electrode (cathode) does not smear or smudge along
its path of flow as shown, for example, in the right portion of
FIG. 4). In some embodiments, when the flow electrode (cathode)
moves from a first location to a second location along its path of
flow, the first location from which the flow electrode (cathode)
moves is essentially free of flow electrode (cathode) (e.g., where
less than 10%, less than 7.5%, less than 5%, less than 2.5%, less
than 1%, less than 0.5%, less than 0.1%, less than 0.01%, less than
0.001% by weight of the flow electrode (cathode) remains in the
first location).
[0148] Thus, LISs allow flow electrodes with yield-stresses (e.g.,
yield stresses above 5 Pa, 5 Pa-20 Pa, 10 Pa-30 Pa, 20 Pa-40 Pa, 25
Pa-50 Pa, up to 50 Pa, 60 Pa, 50 Pa-100 Pa, 75 Pa-150 Pa, 100
Pa-250 Pa, 200 Pa-450 Pa, 400 Pa-650 Pa, 500 Pa-800 Pa, 750 Pa-900
Pa, 850 Pa-1.25 kPa, 1 kPa-1.5 kPa, 1.25 kPa-1.75 kPa, 1.5 kPa-2
kPa, 1.75 kPa-2 kPa, etc. (e.g., with appropriate geometry of the
cell design)) to be used and improves the performance of cells
using such electrodes, for example, by lowering the pressure
required to pump the fluid, or allowing controlled flow in a
passively driven flow battery, one example of which is a GIF
cell.
Advantages of Using LISs in Electrochemical Applications
[0149] In some embodiments, a LIS allows most of the flow electrode
(e.g., more than 75%, more than 80%, more than 90%, more than 95%,
more than 97%, more than 98%, more than 99%, more than 99.5%, more
than 99.9%) to pass through the electroactive region rather than
being left on the interior walls of the tank and/or the reservoir.
In other words, in some embodiments, a LIS allows the flow
electrode to flow without leaving a residue along its path of flow.
In some embodiments, the path of flow of the flow electrode is
substantially free from residue (e.g., less than 10%, less than 5%,
less than 3%, less than 2%, less than 1%, less than 0.5%, less than
0.1%, less than 0.01%, less than 0.001% of residue of the flow
electrode (calculated based on the total amount of the flow
electrode flowing along the path of flow) remains along the path of
flow of the flow electrode). In some embodiments, LISs help in
preventing flow instabilities (e.g., viscous fingering or
cavitation forming bubbles within the flow compartment) that can
block the flow. For example, in some embodiments, the use of LISs
reduces the occurrence of flow instabilities, e.g., that occur as a
result friction (shear stress), at the surface, and thus reduces
viscous fingering or cavitation forming bubbles.
[0150] In some embodiments, a LIS surface introduces slip when a
flowing fluid contacts the walls. As shown in FIG. 5, the slip
surface changes the shape of the velocity profile, closer to plug
flow (e.g., velocity at interface velocity at center of the flow)
than non-slip flow (e.g., velocity at interface <<velocity at
center of the flow). As shown by computational modeling in
"Maximizing Energetic Efficiency in Flow Batteries Utilizing
Non-Newtonian Fluids," by Kyle C. Smith, W. Craig Carter and Y.-M.
Chiang, J. Electrochem. Soc., 161 (4) pp. A486-A496 (2014), 8 plug
flow changes the dynamics of charge transfer during the
electrochemical reaction and leads to higher energy efficiency.
[0151] In some embodiments, slip may reduce shearing in the fluid.
The rate of shear in the fluid is related to the derivative of the
velocity. As shown in FIG. 5, a surface with slip has less shear in
the bulk fluid. For a battery, shearing can result in deteriorating
the electrolyte. For example, shearing in a lithium sulfide battery
using carbon black may destroy the conducting network of the carbon
black and make the suspension (flow cathode) less electronically
conductive. A LIS may introduce slip conditions, reducing this
effect.
Use of LIS Provides Benefits During Manufacturing of Non-Flow
Electrochemical Devices
[0152] The advantages of using LISs are not limited to flow-based
devices (e.g., flow batteries, flow capacitors, or fuel cells). In
some embodiments, electrode cavities in stationary or non-flow
electrochemical devices may be filled with a flowable electrode
during the manufacturing processes (e.g., as described in Y.-M.
Chiang, W. C. Carter, P. Limthongkul, R. Bazzarella, M. Duduta, J.
Disko, J. Cross, Semi-Solid Filled Battery and Method of
Manufacture, Int'l Patent Application WO2012088442A2, published
Jun. 28, 2012, which is incorporated herein by reference in its
entirety). As fluid flow is used primarily for the manufacturing
process, a LIS can enhance manufacturability by lowering the
required pressure to initiate flow (e.g., to overcome a yield
stress or to achieve steady state flow with a highly viscous
electrode suspension or paste), by improving the uniformity of
filling the electrode cavity, and/or by increasing the dimensions
or aspect ratio (e.g., length or width relative to thickness) of
the electrode that can be practically manufactured.
Controlling Phase Transitions/Deposition
[0153] Controlling Precipitate Formation
[0154] In some electrochemical systems, including, but not limited
to storage batteries and capacitors, the electrochemical reaction
involves a reacting material that is soluble at certain states of
charge of the device, but insoluble at other states of charge, or
under different operating conditions, such as, for example, at
different temperatures.
[0155] Lithium sulfur batteries are one example of such a device
where the reactive material undergoes solubility changes during
operation. Discharging a sulfur-based battery involves the chemical
transformation of S to Li.sub.2S. The sulfur positive electrode is
present as solid sulfur in some Li--S batteries, and as solubilized
polysulfide species in other types of Li--S batteries. Intermediate
polysulfides such as, for example, Li.sub.2S.sub.8,
Li.sub.2S.sub.6, Li.sub.2S.sub.4, Li.sub.2S.sub.2 are typically
formed during the electrochemical cycling process. In commonly used
solvents (for example, in TEG-DME), only Li.sub.2S.sub.8 and
Li.sub.2S.sub.6 species are soluble while Li.sub.2S is not soluble
and precipitates from the solution. If the non-soluble material
precipitates on the current collector during discharge, electron
transfer to and from the precipitate may subsequently occur,
allowing reversible precipitation and dissolution and providing
reversible storage capacity to the battery. However, the
precipitating material can also deposit on internal surfaces of the
electrochemical systems (e.g., batteries) that are not in contact
with the current collectors, especially as its solubility limit is
exceeded. Surfaces that act as heterogeneous nucleation sites for
the precipitating reaction product may be deposition sites where
the precipitate is electronically isolated from the current
collectors. In this instance, the precipitate cannot be
re-dissolved upon charge, and the charge storage capacity of the
isolated precipitate material becomes effectively lost, which is
undesirable. The stored capacity and energy of the battery may
thereby be degraded as the battery is cycled and increasing amounts
of precipitate (e.g., Li.sub.2S) are electrically isolated.
[0156] In some embodiments, LISs can be used to prevent undesirable
capacity loss due to precipitation of insoluble materials discussed
above. In some conventional systems, a loss of 5-80% (e.g., 5-15%,
10-25%, 20-35%, 30-45%, 40-60%, 45-65%, 50-70%, 65%-80%, 75%-80% of
capacity over 100 cycles as a result of precipitation of insoluble
materials is observed. In some embodiments, the use of LISs
provides a significant reduction in undesirable capacity loss due
to the precipitation of insoluble materials (e.g., Li.sub.2S). As
discussed above, a LIS provides a liquid interface between the
electroactive phase and the underlying surface of the
electrochemical device (e.g., battery). As such, the LIS interface
is extremely smooth (e.g., in some embodiments, the tops of the
solid features are coated with a thin layer of lubricant), and, in
addition, has a lower interfacial energy than most solid surfaces,
and therefore, is a less potent heterogeneous nucleation site than
typical solid-liquid interfaces within electrochemical devices. In
other words, the adhesion strength between the LIS and the
precipitate is lower than the adhesion strength between a solid
surface and precipitate. In some embodiments, the tops of the solid
features are not coated with a thin layer of lubricant. As such, in
some embodiments, LISs are used to inhibit nucleation of
precipitate formed in electrochemical systems, e.g., in some
embodiments, LISs are used to inhibit scale formation, acting as an
"antifouling coating." In some embodiments, LISs are used to
inhibit nucleation of precipitate formed in the electrochemical
active region (e.g., where the transformation from soluble
Li.sub.2S.sub.6 to Li.sub.2S results in insoluble species forming),
where the LIS prevents the insoluble species (e.g., Li.sub.2S) from
sticking to the current collector. In some embodiments, the
nucleation/precipitation may occur in the bulk fluid rather than on
the surface, which is typically not concerning because in such a
case, the precipitate is not lost by adhering to the surfaces away
from the current collector. In some embodiments, the desired
reactions for charging or discharging may be enhanced, as
nucleation/precipitation is less advantageous.
Inhibiting/preventing the precipitation and adherence of reacting
material (such as insoluble lithium sulfide species) to the
electroactive region surface(s) is beneficial to the reversibility
and energy density of a storage battery, and is an extension of the
antifouling function. Undesirable precipitation (and resulting
adherence of insoluble species to surface(s) of the
electrochemically active region) from solution can also occur in
other electrochemical systems such as capacitors and fuel cells. In
some embodiments, LISs are used to inhibit/prevent adherence of
insoluble lithium sulfide species to electroactive surfaces in
capacitors and fuel cells.
[0157] In some embodiments, the use of LISs mitigates the effects
of undesirable precipitation from solution in various
electrochemical systems. In some embodiments, the use of LISs
mitigates the effects of undesirable precipitation from solution in
various electrochemical systems by maintaining the reversibility of
the electrochemical device (e.g., battery) by, for example,
inhibiting/preventing adhesion of insoluble species to surface(s)
of electroactive region(s). In some embodiments, the use of LISs
mitigates the effects of undesirable precipitation from solution in
various electrochemical systems by maintaining the energy density
of the electrochemical device (e.g., battery, capacitor, flow cell,
etc.).
[0158] Delaying Freezing
[0159] In some embodiments, the use of LISs prevents the formation
of ice for similar reasons as discussed above in relation to
precipitation: the LIS is a less energetically favorable nucleation
site than other types of surfaces. In electrochemical systems that
use a liquid electrolyte, freezing of the electrolyte can cause
(and often does cause) its ionic conductivity to be greatly
decreased, amongst other possible detrimental effects such as
mechanical damage from crystallization. In some embodiments, the
use of a LIS extends the operating temperature range of an
electrochemical device to lower temperatures compared to the same
system without a LIS. With the use of a LIS, in some embodiments,
electrochemical systems can be undercooled further below the
freezing point of the liquid electrolyte before crystallization
occurs.
[0160] In some embodiments, the electrolyte includes a
lithium-containing salt. In some embodiments, a reduction in
temperature can result in crystallization of the lithium-containing
salt. In some conventional systems, the presence of a rough surface
increases the amount of nuclei sites that encourage the
crystallization of the salts. In some embodiments, LISs do not
allow these nuclei sites to form and thus prevents crystallization
of lithium-containing salts (and other similar electrolyte
components), which in turn extends the operating temperature range
of the battery.
Material Considerations for Designing and Selecting LIS
[0161] Various criteria affect the stability of LISs in
electrochemical systems. As discussed above, in some embodiments,
electrochemical systems (or portions or surfaces thereof) come into
contact with highly viscous and/or yield stress fluids, which
present particular challenges, as such fluids do not easily move
along surfaces. In some embodiments, at least one of the criteria
below, or a combination of different criteria below, or all the
criteria below are considered and/or optimized in selecting a
lubricant to be used in an electrochemical system.
[0162] Thermodynamic Stability.
[0163] In some embodiments, it is very important that the
electrolyte, electrode, or electrochemical fuel does not displace
the lubricant from the textured surface. In some embodiments, in
order to form a LIS, a lubricant may be impregnated within surface
textures and/or features spontaneously. The requirements for this
process are outlined in FIG. 1C (e.g., in some embodiments, the
system is designed such that either state W2 or W3 is achieved). In
the design of electrochemical systems discussed herein, when
referring to the table in FIG. 1C, the water phase (w) is the flow
electrode. The surface tension of the lubricant, the surface
tension of the textured surface, and the roughness of the textured
surface may determine the stability of the lubricant in the
textured surface. Various parameters affecting stability of the
lubricant are discussed, for example, in International Application
Publication No. WO 2014/078867, filed on Nov. 19, 2013. In some
embodiments, a combination of the following features may be
desired: a low surface tension lubricant (e.g., lower than about 50
mN/m), a low surface tension solid (e.g., lower than about 50
mN/m), and a high roughness solid may be desired. In some
embodiments, the solid features of the surface have a surface
roughness >50 nm, >100 nm, or <1 .mu.m. In some
embodiments, roughness of the surface provides or enables stable
impregnation of the lubricant therebetween or therewithin. In some
embodiments, roughness of the surface provides or enables stable
impregnation of the lubricant therebetween or therewithin, such
that .theta..sub.os(v), receding<.theta..sub.c where
.theta..sub.c is critical contact angle.
[0164] Immiscibility.
[0165] In some embodiments, the liquid phase(s) comprising the
electrolyte, electrode, or electrochemical fuel are immiscible or
substantially immiscible with the lubricant so that a well-defined
lubricant/electrolyte interface is produced. In some embodiments,
immiscibility also prevents the lubricant phase from contaminating
the electrochemically active phase(s). For example, in some
embodiments, lithium sulfide flow batteries may use polar, aprotic
solvents such as TEG-DME, diglyme, or dioxolane-dimethoxyethane
(DOL-DME); in such instances, the lubricant is chosen such that it
is immiscible with such solvents. In some embodiments, the
electrolyte or electrode or electrochemical fuel is aqueous in
nature; in such instances, the lubricant is chosen such that it is
immiscible with aqueous solutions or suspensions.
[0166] In some embodiments, the choice of the lubricant
(lubricating liquid) is contingent upon the material properties of
the electroactive phase. In some embodiments, desirable traits of
the lubricant with respect to the electroactive phase include
immiscibility or partial miscibility (<5% of its weight),
non-reactiveness, and/or a lower surface tension (than the
electroactive phase) (e.g., to form a stable system). In certain
embodiments, a higher surface tension (than the electroactive
phase) is preferred. In certain embodiments, the partial
miscibility of the lubricant with the electroactive phase results
in a change of surface tension of the electroactive phase such that
the spreading coefficient, S, of the lubricant on the electroactive
phase becomes negative and thereby the electroactive phase does not
spread over the primary phase, where S is defined according the
following Equation
(S=.gamma..sub.wa-.gamma..sub.oa-.gamma..sub.ow).
[0167] Some examples of such lubricants whose spreading coefficient
changes upon partial miscibility and which can be used as
lubricants with respect to an electroactive phase include
1,1-diphenyl-ethane, benzene, ionic liquid (e.g.,
1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide),
etc. In some embodiments, the lubricant is partially miscible with
the electroactive phase and the partial miscibility changes the
spreading coefficient of the lubricant on the electroactive phase,
such that the electroactive phase flows along the surface of the
LIS without getting cloaked by the lubricant.
[0168] Electrochemical Stability.
[0169] In some embodiments, the lubricant itself, as well as
mixtures of the lubricant and the working fluid of an
electrochemical device, are stable over the electrochemical window
of the device. Electrochemical devices are typically designed to
operate over a certain voltage on the basis of the activity and
stability of the components within. For example, in some
embodiments, a lithium sulfur battery may operate over a window of
about 1.6 V to 2.2 V with respect to Li/Li.sup.+. In some
embodiments, a lithium ion battery may operate over a window of
about 1.5V to 4.25V. In some embodiments, the lubricant phase of
the LIS, any mixtures produced upon combining the lubricant with
the working fluids of the electrochemical device, and any reaction
products produced between the lubricant or texture material and all
other components of the electrochemical device (e.g., flow cell)
are electrochemically stable over the operating voltage window. In
some embodiments, immiscible fluids may have some mutual
solubility. For example, although water and hexadecane are
considered insoluble, about 100 ppm of hexadecane dissolves in
water. In some embodiments, even trace levels, if electrochemically
active, can disrupt the functioning of the electrochemical system.
In some embodiments, "side reactions" that result in parasitic
current flow are such that they have negligible current over the
voltage window compared to the desired electrochemical reactions
(which is achieved by, e.g., proper selection of the lubricant). In
some embodiments, the lubricant is selected such that it does not
contribute a side reaction rate in excess of about 1% of the total
reaction rate, the two rates being measured on the basis of the
current produced, to be considered electrochemically active.
Tuning the Transport Properties of LISs
[0170] In some embodiments, a LIS structure comprising a substrate,
solid textures/features and a lubricant is applied to internal
surfaces (or part(s) or portion(s) thereof) of an electrochemical
device. For example, in some embodiments, a LIS is incorporated in
the walls of a flow battery or fuel cell tank, flow battery or fuel
cell stack, pipes, channels, cavities, manifolds, valves, seals,
pumps or any other internal surface(s).
[0171] In some embodiments, a LIS is designed and selected to
provide desired electronic or ionic or diffusional transport
properties (or any combination of these properties, as needed). In
some embodiments, a LIS is insulating, electronically conductive,
ionically conductive, mixed ionically and
electronically-conducting, semi-conducting, a diffusion barrier,
and/or a diffusion-enhancing medium (or a combination thereof). In
some embodiments, transport properties of the LIS are tuned
according to the needs of a particular component of an
electrochemical device.
[0172] In some embodiments, an electronically conductive LIS may be
used on the current collectors of a stationary battery, flow
battery, or fuel cell. In some embodiments, the electronically
conductive LIS is made by using an electronically conductive
material (e.g., conductive particles such as carbon black) as the
solid texture material, and/or by using an electronically
conductive suspension or polymer solution as the lubricant.
[0173] In some embodiments, an ionically conductive LIS is used on
a separator structure or other cell parts by incorporating a solid
ionic conductor (e.g., an ion-conducting glass, crystal, or
polymer) as a textured surface, or by using an ionically conductive
liquid (e.g., an electrolyte) as the lubricant phase.
[0174] In some embodiments, an insulating LIS is used to prevent
unwanted precipitation of electrochemical reaction products.
[0175] In some embodiments, a diffusion barrier LIS may be used to
prevent corrosion of system components. In some embodiments, the
electrochemical device is a flow battery. In some embodiments, the
flow battery includes organic solvent(s) in the flowable electrode.
In conventional systems, organic solvent(s) can corrode stainless
steel tanks or pipes (or other system components). Similarly, in
conventional systems, organic liquids (e.g., acids) in flow
batteries can also corrode the stainless steel tanks or pipes (or
other system components). In addition, in conventional systems such
as pouch cells, the organic solvent used in liquid electrolyte can
corrode the materials that are used to seal the cell. In some
embodiments, the use of a diffusion barrier LIS can be used to
inhibit/prevent corrosion of system components (e.g., caused by
organic solvents, acids, etc.).
Selectively Lubricated Surfaces
[0176] In some embodiments, an electrochemical device includes at
least one surface within the device that has slipperiness and at
least one surface that does not have slipperiness. Some embodiments
discussed herein relate to methods for producing selectively
lubricated surfaces (e.g., where at least a portion of the surface
has slipperiness and at least a portion of the surface does not
have slipperiness) on electrochemical devices (e.g., on internal
surfaces thereof). In some embodiments, it is desirable to have
surfaces that are lubricated on certain portions/surfaces of the
device and to avoid lubrication or to have a lesser degree of
lubrication on other surfaces within the same electrochemical
device.
[0177] In some embodiments, it is desirable to have selectively
lubricated surfaces for electrochemical cells. In some embodiments,
the electrochemical cells for which it is desirable to have
selectively lubricated surfaces include gravity-induced flow cell
(GIF cell) devices. In some embodiments, GIF cell devices are
designed such that the walls of the flow cell are slippery (e.g.,
include a LIS) but the current collectors are not slippery (e.g.,
do not include a LIS), in order to maintain a low resistance to
electronic charge transfer and/or a surface having a high exchange
current density.
[0178] In some embodiments, a silicone oil lubricant (10 cSt oil)
is designed such that it does not spread from a textured LIS
surface and does not infiltrate a porous polymer separator of a
battery (which could potentially prevent ion transport across the
membrane). In some embodiments, a lubricant is selected such that
it does not spread from a textured LIS surface and does not coat
the metal current collectors.
[0179] In some embodiments, when a liquid droplet is placed on a
smooth surface of a certain chemistry, the droplet makes a contact
angle .theta.. When the contact angle is zero, the liquid spreads
on the surface. In some embodiments, even if a contact angle of
liquid is greater than zero (e.g., non-spreading on the flat
surface), the liquid may spread over a surface that is not smooth.
This is referred to as hemi-wicking.
[0180] A liquid may hemi-wick across a surface when its contact
angle on a chemically identical smooth surface .theta. is less than
critical contact angle, .theta..sub.c=cos.sup.-1
[(1-.PHI.)/(r-.PHI.)]. Here, and as discussed above, .PHI. is the
fraction of the projected area of the textured surface that is
occupied by a solid (the solid fraction) and r is the ratio of
total surface area of the textured surface to its projected area.
For example, in some embodiments, surfaces non-wetting to
particular liquids have low surface energy and are sufficiently
flat. In some embodiments, surfaces in an electrochemical device
that are desirable to be maintained free of lubricant have a
contact angle greater than or equal to the critical contact angle
.theta..sub.c.
[0181] In some embodiments, the lubricant film encapsulating the
texture is stable only if it wets the texture completely
(.theta.=0), otherwise portions of the textures dewet and emerge
from the lubricant film. In some embodiments, complete
encapsulation of the texture is desirable in order to eliminate
pinning. In some embodiments, texture geometry and hierarchical
features can be exploited to reduce the emergent areas and achieve
roll-off angles close to those obtained with fully wetting
lubricants. In some embodiments, additional parameters, such as
droplet and texture size, as well as the substrate tilt angle, may
be modeled to achieve desired droplet (and/or other substance)
movement (e.g., rolling) properties and/or to deliver optimal
non-wetting properties.
Electrochemical Devices
[0182] In some embodiments, the electrochemical device is a flow
battery (or redox flow battery).
[0183] An exemplary redox flow energy storage device is illustrated
in FIG. 10. Redox flow energy storage device may include a positive
electrode current collector 1010 and a negative electrode current
collector 1020, separated by an ion permeable separator 1030.
Current collectors 1010, 1020 may be in the form of a thin sheet
and are spaced apart from separator 1030. In some embodiments, the
current collector 1010 (or a part or portion thereof) includes or
is coated with a LIS, as discussed above. In some embodiments, the
current collector 1020 (or a part or portion thereof) includes or
is coated with a LIS, as discussed above. Positive electrode
current collector 1010 and ion permeable separator 1030 define an
area, 1015, herein after referred to as the "positive electroactive
zone" that accommodates the positive flowable electrode active
material 1040. In some embodiments, the ion permeable separator
1030 includes or is coated with a LIS (e.g., on either side or on
both sides of the ion permeable separator 1030). In some
embodiments, a LIS is incorporated into the ion permeable separator
1030. In some embodiments, a LIS is incorporated into the ion
permeable separator 1030 (e.g., wherein the ion permeable separator
1030 is an ion selective membrane), wherein the lubricating liquid
is ionically conductive. Negative electrode current collector 1020
and ion permeable separator 1030 define an area, 1025, herein after
referred to as the "negative electroactive zone" that accommodates
the negative flowable electrode active material 1050. The
electrode-active materials can be flowable redox compositions and
can be transported to and from the electroactive zone at which the
electrochemical reaction occurs. The flowable redox composition can
include a semi-solid or a condensed liquid ion-storing
electroactive material, and optionally a fluid for supporting or
suspending the solid or condensed ion-storing liquid electrolyte.
As used herein, semi-solid refers to a mixture of liquid and solid
phases, such as a slurry, particle suspension, colloidal
suspension, emulsion, or micelle. In some embodiments, the emulsion
or micelle in a semi-solid includes a solid in at least one of the
liquid-containing phases. As used herein, condensed liquid or
condensed ion-storing liquid refers to a liquid that is not merely
a solvent as it is in the case of an aqueous flow cell catholyte or
anolyte, but rather that the liquid is itself redox-active. The
liquid form can also be diluted by or mixed with another,
non-redox-active liquid that is a diluent or solvent, including
mixing with such a diluents to form a lower-melting liquid phase,
emulsion or micelles including the ion-storing liquid.
[0184] The positive electrode flowable material 1040 can enter the
positive electroactive zone 1015 in the direction indicated by
arrow 1060. Positive electrode material 1040 can flow through the
electroactive zone and exit at the upper location of the
electroactive zone in the direction indicated by arrow 1065.
Similarly, the negative electrode flowable material 1050 can enter
the negative electroactive zone 1025 in the direction indicated by
arrow 1070. Negative electrode material 1050 can flow through the
electroactive zone and exits at the upper location of the
electroactive zone in the direction indicated by arrow 1075. The
direction of flow can be reversed, for example, when alternating
between charging and discharging operations. It is noted that the
illustration of the direction of flow is arbitrary in FIG. 10. Flow
can be continuous or intermittent. In some embodiments, the
positive and negative redox flow materials are stored in a storage
zone or tank (not shown) prior to use. In some embodiments, the
flowable redox electrode materials can be continuously renewed and
replaced from the storage zones, thus generating an energy storage
system with very high energy capacity. In some embodiments, a
transporting device is used to introduce positive and negative
ion-storing electroactive materials into the positive and negative
electroactive zones, respectively. In some embodiments, a
transporting device is used to transport depleted positive and
negative ion-storing electroactive materials out of the positive
and negative electroactive zones, respectively, and into storage
tanks for depleted electroactive materials for recharging. In some
embodiments, the transporting device can be a pump or any other
conventional device for fluid transport. In some specific
embodiments, the transporting device is a peristaltic pump.
[0185] During operation, the positive and negative electroactive
materials can undergo reduction and oxidation. Ions 1090 can move
across ion permeable membrane 1030 and electrons can flow through
an external circuit 1080 to generate current. In a typical flow
battery, the redox-active ions or ion complexes undergo oxidation
or reduction when they are in close proximity to or in contact with
a current collector that typically does not itself undergo redox
activity. Such a current collector may be made of carbon or
nonreactive metal, for example. Thus, the reaction rate of the
redox active species can be determined by the rate with which the
species are brought close enough to the current collector to be in
electrical communication, as well as the rate of the redox reaction
once it is in electrical communication with the current collector.
In some instances, the transport of ions across the ionically
conducting membrane may rate-limit the cell reaction. Thus the rate
of charge or discharge of the flow battery, or the power to energy
ratio, may be relatively low. The number of battery cells or total
area of the separators or electroactive zones and composition and
flow rates of the flowable redox compositions can be varied to
provide sufficient power for any given application.
[0186] An exemplary redox flow cell for a lithium battery (e.g.,
semi-solid lithium redox flow battery) is shown in FIG. 11. In this
example, the membrane 1110 can be a microporous membrane such as a
polymer separator film (e.g., Celgard.TM. 2400) that prevents
cathode particles 1120 and anode particles 1130 from crossing the
membrane, or can be a solid nonporous film of a lithium ion
conductor. The negative and positive electrode current collectors
1140, 1150 can be made of any suitable materials and can be made of
the same materials, or of different materials. In some embodiments,
the negative and positive electrode current collectors are made of
copper and aluminum, respectively. In some embodiments, the
negative electrode composition includes a graphite or hard carbon
suspension. In some embodiments, the positive electrode composition
includes LiCoO.sub.2 or LiFePO.sub.4 as the redox active component.
In some embodiments, carbon particulates are optionally added to
the cathode or anode suspensions to improve the electronic
conductivity of the suspensions. In some embodiments, the solvent
in which the positive and negative active material particles are
suspended is an alkyl carbonate mixture and includes a dissolved
lithium salt such as LiPF.sub.6.
[0187] In some embodiments, the current collector 1140 (or a part
or portion thereof) includes or is coated with a LIS, as discussed
above. In some embodiments, the current collector 1150 (or a part
or portion thereof) includes or is coated with a LIS, as discussed
above. In some embodiments, the membrane 1110 includes or is coated
with a LIS (e.g., on either side or on both sides of the membrane
1110). In some embodiments, a LIS is incorporated into the membrane
1110. In some embodiments, a LIS is incorporated into the membrane
1110 (e.g., wherein the membrane 1110 is an ion selective
membrane), wherein the lubricating liquid is ionically
conductive.
[0188] In some embodiments, the positive electrode composition is
stored in positive electrode storage tank 1160, and is pumped into
the electroactive zone using pump 1165. In some embodiments, the
negative electrode composition is stored in negative electrode
storage tank 1170, and is pumped into the electroactive zone using
pump 1175. In some embodiments, at least a portion (or all) of the
interior surface of at least one storage tank 1160 and/or 1170 is
coated with or includes a LIS. In some embodiments, the interior
walls of at least one storage tank 1160 and/or 1170 are coated with
or include a LIS. In some embodiments, piping 1105, 1106, 1107, and
1108 connects the tanks 1160 and 1170 with the electroactive zones.
In some embodiments, at least a portion of interior surface of at
least one pipe 1105, 1106, 1107, and 1108 is coated with or
includes a LIS. In some embodiments, the interior surface of all
pipes 1105, 1106, 1107, and 1108 is coated with or includes a
LIS.
[0189] In some embodiments, at least one of the positive electrode
and the negative electrode includes a semi-solid or condensed
liquid ion-storing redox composition. In some embodiments, the
semi-solid or condensed liquid ion-storing redox composition
includes a conductive additive. In some embodiments, the conductive
additive is selected from the group consisting of metal carbides,
metal nitrides, carbon black, graphitic carbon powder, carbon
fibers, carbon microfibers, vapor-grown carbon fibers (VGCF),
fullerenes, carbon nanotubes (CNTs), multiwall carbon nanotubes
(MWNTs), single wall carbon nanotubes (SWNTs), graphene sheets, and
materials comprising fullerenic fragments that are not
predominantly a closed shell or tube of the graphene sheet, and any
combination or mixture thereof.
[0190] In some embodiments, the condensed liquid ion-storing redox
composition has the capability to take up or release ions. In some
embodiments, the condensed liquid ion-storing redox composition
remains substantially insoluble during operation of the energy
storage device. In some embodiments, the semi-solid or condensed
liquid ion-storing redox composition forms a continuously
electronically conductive network percolative pathway to the
negative current collector and/or the positive current collector.
In some embodiments, the positive electrode and the negative
electrode include a semi-solid or condensed liquid ion-storing
redox composition.
[0191] In some embodiments, the ion storage compound stores at
least one of lithium, sodium, or hydrogen (or a combination
thereof).
[0192] In some embodiments, the volume percentage of the
ion-storing solid phase is between 5% and 70%. In some embodiments,
the volume percentage of the total solids including the conductive
additive is between 10% and 75%. In some embodiments, the volume
percentage of the ion-storing solid phase is between 5% and 70% and
the volume percentage of the total solids including the conductive
additive is between 10% and 75%.
[0193] Aqueous Batteries:
[0194] In some embodiments, the electrochemical device is an
aqueous electrolyte battery, for example as shown in FIG. 13. In
some embodiments, the aqueous battery includes pouch cell material,
two current collectors, two electrodes, two aqueous electrolytes,
and a separator, arranged as shown in FIG. 13. In some embodiments,
the aqueous electrolyte battery is a stationary-electrode battery
or a flow battery. In some embodiments, aqueous batteries include
an electrolyte or electrode or electrochemical fuel that is
water-based; in such instances, the lubricant is chosen such that
it is immiscible with aqueous solutions or suspensions. In some
embodiments, one or more interior surfaces of said aqueous battery,
including the surfaces of components such as current collectors,
separators, flow channels, or the interior walls of the battery
housing, include an LIS in order to serve one or more of the
earlier described functions of the LIS. In some embodiments, a LIS
can be applied to the separator (e.g., on either or both sides of
the separator shown in FIG. 13). In some embodiments, a LIS can be
applied on the inside of the pouch cell material (e.g., pouch cell
material shown in FIG. 13) that is in contact with the cell
material. In some embodiments, the a LIS can be applied on any
surfaces of the current collector (e.g., surfaces of the current
collector in contact with the electrode as shown in FIG. 13).
[0195] Non-Aqueous Batteries:
[0196] In some embodiments, the electrochemical device is a
non-aqueous battery, for example, as shown in FIG. 13. In some
embodiments, the non-aqueous battery includes pouch cell material,
two current collectors, two electrodes, two aqueous electrolytes,
and a separator, arranged as shown in FIG. 13. In some embodiments,
the non-aqueous battery is a stationary-electrode battery or a flow
battery. In some embodiments, non-aqueous batteries include an
electrolyte or electrode or electrochemical fuel that is
non-aqueous in composition; in such instances, the lubricant is
chosen such that it is immiscible with non-aqueous solutions or
suspensions. In some embodiments, one or more interior surfaces of
said non-aqueous battery, including the surfaces of components such
as current collectors, separators, flow channels, or the interior
walls of the battery housing, include a LIS in order to serve one
or more of the earlier described functions of the LIS. In some
embodiments, a LIS can be applied to the separator (e.g., on either
or both sides of the separator shown in FIG. 13). In some
embodiments, a LIS can be applied on the inside of the pouch cell
material (e.g., pouch cell material shown in FIG. 13) that is in
contact with the cell material. In some embodiments, the a LIS can
be applied on any surfaces of the current collector (e.g., surfaces
of the current collector in contact with the electrode as shown in
FIG. 13.
[0197] Metal-Air Batteries:
[0198] In some embodiments, the electrochemical device is a
metal-air battery comprising a metal negative electrode and an air
positive electrode, as shown, for example, in FIG. 14. In some
embodiments, a metal-air battery includes pouch cell material, a
current collector, Li metal layer, an electrolyte (e.g., organic
electrolyte), a separator, an electrode, and a porous current
collector, arranged as shown, for example, in FIG. 14. In some
embodiments, said metal-air battery includes an aqueous or
non-aqueous electrolyte in contact with one or both electrodes. In
some embodiments, during discharge of said metal air battery, an
oxide, peroxide, hydroxide, or other salt of the metal is formed at
the positive electrode. In some embodiments, one or more interior
surfaces of said metal-air battery including the surfaces of
current collectors, separators, or interior walls of the battery
housing are coated with LIS in order to serve one or more of the
earlier described functions of the LIS. In some embodiments, a LIS
can be applied to any surface of the separator, e.g., either side
of the separator, as shown, for example in FIG. 14. In some
embodiments, a LIS is applied to the side of the separator that is
in contact with the electrolyte, as shown, for example, in FIG. 14.
In some embodiments, a LIS is applied to the side of the separator
that is in contact with the electrode, as shown, for example, in
FIG. 14. In some embodiments, a LIS is applied to the inside of the
pouch cell material that is in contact with the cell materials. In
some embodiments, a LIS is applied to the current collector. In
some embodiments, a LIS is applied to or is part of the porous
current collector.
[0199] Fuel Cells:
[0200] In some embodiments, the electrochemical device is a fuel
cell, in which the LIS may serve to control the behavior of a
liquid component, such as the phosphoric acid electrolyte layer in
a phosphoric acid fuel cell, or the condensation/nucleation of a
liquid phase from a vapor phase on one or more exposed component
surfaces, such as water on the exhaust side of a hydrogen fuel
cell. An exemplary fuel cell is shown in FIG. 15. In some
embodiments, a fuel cell includes a housing, an anode, a cathode,
and an electrolyte in contact with both the anode and the cathode,
as shown for example in FIG. 15. In some embodiments, a LIS can be
applied to the surface of the cathode material. In some
embodiments, a LIS is applied to the portion of the cathode
material that is in contact with the electrolyte, as shown in FIG.
15. In some embodiments, a LIS is applied in the inside of the
housing material that is in contact with water (e.g., as shown in
FIG. 15) or that is in contact with another liquid or fluid,
[0201] Electrolytic Capacitors:
[0202] An exemplary electrolytic capacitor is shown in FIG. 16. In
some embodiments, an electrolytic capacitor includes housing
material, an electrolyte (e.g., cathode), an oxide layer, and anode
(e.g., encapsulated by the oxide layer), arranged as shown, for
example in FIG. 16. In some embodiments, a LIS is used to coat one
or more internal surfaces of an electrolytic capacitor, including
the current collectors, separator, or internal surfaces of the
capacitor housing. In some embodiments, a LIS can be applied or
coated to the inside of the housing material that is in contact
with the electrolyte (e.g., cathode). Said electrolytic capacitor
may utilize an aqueous electrolyte, in which case the LIS may
contain a liquid that is immiscible with the aqueous electrolyte,
or the electrolytic capacitor may utilize a non-aqueous
electrolyte, in which case the LIS may contain a liquid immiscible
with the non-aqueous electrolyte.
[0203] Flow Capacitors:
[0204] In some embodiments, the flow capacitor is an
electrochemical flow capacitor disclosed, for example, in
PCT/US2012/024960, filed on Feb. 14, 2012, the disclosure of which
is incorporated by reference herein in its entirety. An exemplary
flow capacitor is shown in FIG. 17. In some embodiments, a flow
capacitor includes two current collectors a separator, one or more
pumps for pumping charged or discharged slurry (e.g., 4 pumps as
shown in FIG. 17), one or more tanks (e.g., 4 tanks housing charged
or discharged slurry as shown in FIG. 17), piping connecting the
tanks to the positive or negative half cells. In some embodiments,
at least one surface of at least one current collector (positive
current collector and/or negative current collector) is coated with
or includes a LIS. In some embodiments, uncharged slurry is stored
in uncharged slurry storage tanks. In some embodiments, charged
slurry is stored in charged slurry storage tanks. In some
embodiments, at least a part or portion of the interior surface of
at least one of the uncharged slurry and/or the charged slurry
storage tanks includes or is coated with a LIS. In some
embodiments, uncharged slurry is pumped from the tanks to the
positive and negative half cells via uncharged slurry pipes. In
some embodiments, charged slurry is pumped into the charged slurry
tanks via charged slurry pipes. In some embodiments, at least a
part or portion of the interior surface of the uncharged slurry
and/or the charged slurry pipes is coated with or includes a LIS.
In some embodiments, a separator includes or is coated with a LIS
(e.g., either or both sides (or any portion thereof) of the
separator shown in FIG. 17).
EXPERIMENTAL EXAMPLES
Example 1: LIS for a Lithium Polysulfide Flow Battery
[0205] This example demonstrates a lithium polysulfide flow battery
with a lubricant-impregnated surface (LIS).
[0206] Lithium polysulfide solutions comprising Li.sub.xS.sub.y
compounds dissolved in non-aqueous solvents form the basis for
flowable catholytes for use in stationary or flow batteries. A
representative electrolyte solution was prepared using TEG-DME
(.gtoreq.99%, Sigma-Aldrich), 0.5 M LiTFSI salt (.gtoreq.99.95%,
Sigma-Aldrich), and 1 wt % LiNO.sub.3 (ReagentPlus.RTM. grade,
Sigma-Aldrich). The solution did not include the lithium
polysulfide since in electrochemical tests of the lubricant and
solvent system, it is necessary to evaluate side reaction currents
without interference from the electrochemical couple. To design and
select materials for the LIS, several candidate lubricants of
various compositions were considered, as listed in Table 1
below.
[0207] Table 1 below illustrates compatibility of several candidate
lubricants with the electrolyte solvent TEG-DME. Immiscibility was
determined by vigorously shaking a 50 wt % lubricant, 50 wt %
TEG-DME mixtures and observing the respective phase volumes after
four hours. Thermodynamic stability (e.g., spreading coefficient)
is calculated from the lubricant surface tension and estimated
surface tension of the electrolyte solvent (TEG-DME). Positive
values are interpreted as thermodynamically stable and negative
values are interpreted as being thermodynamically unstable.
TABLE-US-00001 TABLE 1 Thermodynamic stability Surface tension
(Spreading Coefficient Lubricant Type (mN/m) Immiscibility
Estimation) perfluorodecalin fluorinated oil 19 immiscible 5 10 cSt
silicone silicone oil 20 slightly miscible 4 oil EMI-IM ionic
liquid 42 completely -18 miscible BMI-IM ionic liquid 34 completely
-10 miscible KRYTOX .RTM. fluorinated ether 17 immiscible 7 1506
FOMBLIN .RTM. fluorinated ether 20 immiscible 4 Ethyl Oleate fatty
acid ester 31 completely -7 miscible FC-70 fluorinated 18
immiscible 6 ether/alkane
[0208] FIG. 1C illustrates schematics of wetting configurations
outside and underneath an aqueous drop (column 2). The total
interface energies per unit area (column 3) are calculated for each
configuration by summing the individual interfacial energy
contributions. Equivalent requirements for stability of each
configuration are provided in column 4.
[0209] The thermodynamically stability of each lubricant was
calculated using the equations provided in FIG. 1C. A positive
numerical value (S.sub.ow(w)) predicts a lubricant to be
thermodynamically stable for the electrolyte solvent TEG-DME.
Values for the surface tension of TEG-DME are not readily
available, but are estimated to be close to that of
dimethoxyethane, which has similar chemical composition, and has a
surface tension of 24 mN/m. Surface roughness effects are excluded
from the calculation but can be incorporated for a more precise
prediction.
[0210] The miscibility of the candidate lubricants with TEG-DME was
evaluated. Immiscibility was determined by vigorously shaking a 50
wt % lubricant, 50 wt % TEG-DME mixtures and observing the
respective phase volumes after four hours. Only those lubricants
that were at most slightly miscible with TEG-DME, and in addition
were thermodynamically stable, were considered for further
evaluation. Accordingly, five of the eight candidate lubricants in
Table 1 were evaluated further: perfluorodecalin, 10 cSt silicone
oil, KRYTOX.RTM. 1506, FOMBLIN.RTM. (fluorinated lubricant,
perfluoropolyether vacuum oil), and FC-70.
[0211] Two types of electrochemical tests were carried out to
evaluate electrochemical stability in the voltage window of a
lithium-sulfur battery. In each test, cyclic voltammetry was
conducted in order to measure the current in a lithium half-cell
containing the fluid of interest. A Swagelok cell configuration was
used, in which the positive electrode (cathode) was composed of
carbon felt, the lubricant, and/or electrolyte solvent (TEG-DME).
The anode was lithium metal, and the separator was a Tonen
membrane. In one test, the lubricant alone was used as the sole
liquid phase in the cell. In the second test, mixtures of the
lubricant and the electrolyte solution in the volumetric ratio of
3:1 (lubricant: electrolyte) were tested. In each case, evidence
was sought for side reactions that produce current sufficiently
high as to interfere with the operation or long-term life of the
cell. Voltage was swept between 1.5V and 3.5V with respect to
Li/Li.sup.+, at a sweep rate of 10 mV/min.
[0212] FIGS. 6A-6F show the cyclic voltammetry test results for the
different lubricants. The electrolyte alone was used as a control,
and evidence for additional side reaction currents was sought. The
vertical scale, current density, is not the same between the
different plots in FIGS. 6A-6F. FIG. 7 plots all of the curves from
FIGS. 6A-6F together on the same scale.
[0213] FC-70, FOMBLIN.RTM. and perfluorodecalin all show
substantial current density exceeding -0.5 mA/cm.sup.2 in the
voltage window tested, and these lubricants were therefore
considered less desirable for some applications (although
potentially still usable) compared to the silicone oil and
KRYTOX.RTM. 1506.
[0214] The second test was then conducted in which the liquid phase
was a mixture of the lubricant and the electrolyte. As the cyclic
voltammogram in FIG. 8 illustrates, the currents for 10 cSt
silicone oil and for perfluorodecalin are much lower over the
measured voltage range than the other three evaluated lubricants.
The inset figure in FIG. 8 shows an expanded view of the data for
perfluorodecalin and silicone oil. Silicone oil was the most inert,
having immeasurably low current within the voltage window.
[0215] Based on these tests, the 10 cSt silicone oil was selected
for incorporation into a LIS.
[0216] To construct the LIS, a porous commercially available
TEFLON.RTM. membrane (pore size of 0.2 .mu.m, Sterlitech) was
immersed in a bath of 10 cSt silicone oil. To create a
thermodynamically stable film, the dip-coating withdrawal velocity
may be below a critical speed
V.sub.crit=0.121.mu..sub.0.gamma./(.delta./l.sub.c).sup.3/2 where,
.mu..sub.0 is the viscosity of the lubricant, .gamma. is the
surface tension, l.sub.c is the capillary length, and .delta. is
the depth of the pores of the membrane. Accordingly, the membrane
was withdrawn from the silicone oil bath at V=1 mm/s.
[0217] FIG. 4 illustrates the effectiveness of the LIS in producing
a super-slippery surface for a lithium polysulfide suspension (0.75
vol % carbon black suspended in TEG-DME solution that comprises of
0.5 M lithium LiTFSI, 1 wt % of LiNO.sub.3 and 2.5 M of sulfur in
the form of Li.sub.2S.sub.8). At an incline from the horizontal of
40.degree., a droplet of the suspension did not flow on an
untreated PTFE (TEFLON.RTM.) surface. At an incline of 70.degree.
from the horizontal, the droplet exhibited contact line pinning,
producing an elongated droplet. However, on the silicone oil
impregnated structure, the droplet slipped at 40.degree., and
exhibited no contact line pinning, as is seen by the undeformed
circular shape of the droplet.
Example 2: Surfaces Designed to be Selectively Wet by the
Lubricant
[0218] This example demonstrates exemplary LISs for GIF cells. In
GIF cells, lubricants should be prevented from spreading out from
the LIS and over a current collector, or infiltrating the porous
separator membrane.
[0219] In this example, surfaces designed to be selective to
wetting by the lubricant phase of a LIS, silicone oil (10 cSt),
were demonstrated. A droplet of silicone oil was placed on certain
surfaces to observe whether the silicone oil spreads.
[0220] FIGS. 9A-9E illustrate results showing that surface
functionalization can be used to produce surfaces that are wetting
and non-wetting to silicone oil. Several surface chemistries are
functionalized onto flat polydimethylsiloxane (PDMS) were examined.
Un-functionalized PDMS and PDMS functionalized with
trichloro(1H,1H,2H,2H-perfluorooctyl)silane were found to prevent
silicone oil from spreading (e.g., wetting) in air, as shown in
FIGS. 9B and 9C. On the other hand, PDMS functionalized with
n-octadecyltrichlorosilane allowed silicone oil to spread in air,
as shown in FIG. 9A.
[0221] In addition to experiments in air, the same surfaces were
examined for their wetting behavior in tetraethylene glycol
dimethyl ether (TEG-DME), a typical electrolyte solvent for Li
polysulfide flow batteries. The surfaces were immersed in TEG-DME
before a droplet of silicone oil was dropped onto each surface to
observe the wetting behavior. All the tested surfaces were not
wetted by the silicone oil, as shown in FIGS. 9D and 9E.
[0222] In some embodiments, the lubricant can be designed to either
wet or not wet a surface. In some embodiments, the lubricant can be
designed to either wet or not wet a surface when exposed to a
gaseous atmosphere. In some embodiments, the lubricant can be
designed to either wet or not wet a surface when the surface (and
lubricant) is covered by a fluid, such as an internal surface in a
liquid electrolyte filled device.
[0223] Most electrochemical devices are assembled in air or inert
gas environment before being filled with a liquid electrolyte, when
it is desirable to prevent the lubricant from wetting specific
surfaces, non-wetting behavior in both air and electrolyte is
desired to prevent the lubricant from spreading out from the LIS.
In this example, un-functionalized PDMS and PDMS functionalized
with trichloro(1H,1H,2H,2H-perfluorooctyl)silane are suitable
candidates for creating non-wetting surfaces in electrochemical
devices using TEG-DME as the electrolyte solvent. In one
configuration, a strip of non-wetting surface may be included on
either side of the metal current collector in the flow channel to
prevent the lubricant in the LIS regions from crossing over to the
current collector surfaces.
EQUIVALENTS
[0224] While the invention has been particularly shown and
described with reference to specific preferred embodiments, it
should be understood by those skilled in the art that various
changes in form and detail may be made therein without departing
from the spirit and scope of the invention as defined by the
appended claims.
* * * * *