U.S. patent application number 17/511522 was filed with the patent office on 2022-04-21 for regenerable battery electrode.
The applicant listed for this patent is Brookhaven Science Associates, LLC, The Research Foundation For The State University of New York. Invention is credited to Amy Catherine Marschilok, Altug S. Poyraz, Esther Sans Takeuchi, Kenneth James Takeuchi.
Application Number | 20220123293 17/511522 |
Document ID | / |
Family ID | 1000006062441 |
Filed Date | 2022-04-21 |
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United States Patent
Application |
20220123293 |
Kind Code |
A1 |
Takeuchi; Esther Sans ; et
al. |
April 21, 2022 |
REGENERABLE BATTERY ELECTRODE
Abstract
A binder-free, self-supporting electrode including an
electrochemically active material in the absence of a binder and a
current collector is claimed. The electrochemically active material
is a self-supporting transition metal oxide. A method of
regenerating the electrode to restore capacity of the electrode is
also claimed.
Inventors: |
Takeuchi; Esther Sans;
(South Setauket, NY) ; Poyraz; Altug S.; (Port
Jefferson, NY) ; Takeuchi; Kenneth James; (South
Setauket, NY) ; Marschilok; Amy Catherine; (Stony
Brook, NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Brookhaven Science Associates, LLC
The Research Foundation For The State University of New
York |
Upton
Albany |
NY
NY |
US
US |
|
|
Family ID: |
1000006062441 |
Appl. No.: |
17/511522 |
Filed: |
October 26, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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15772564 |
May 1, 2018 |
11201325 |
|
|
PCT/US2016/063814 |
Nov 28, 2016 |
|
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17511522 |
|
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62261562 |
Dec 1, 2015 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01M 10/54 20130101;
H01M 4/625 20130101; H01M 2220/30 20130101; Y02T 10/70 20130101;
C01P 2006/40 20130101; C01G 45/1228 20130101; H01M 4/505 20130101;
H01M 4/48 20130101; H01M 4/624 20130101; H01M 4/131 20130101; Y02W
30/84 20150501; H01M 10/052 20130101 |
International
Class: |
H01M 4/505 20060101
H01M004/505; H01M 4/131 20060101 H01M004/131; H01M 10/052 20060101
H01M010/052; H01M 10/54 20060101 H01M010/54; H01M 4/48 20060101
H01M004/48; H01M 4/62 20060101 H01M004/62; C01G 45/12 20060101
C01G045/12 |
Goverment Interests
STATEMENT OF GOVERNMENT LICENSE RIGHTS
[0002] This invention was made with Government support under
contract number DE-SC0012704, awarded by the U.S. Department of
Energy. The United States Government has certain rights in this
invention.
Claims
1. A method of regenerating a cycled electrode comprising: removing
the cycled electrode from a battery with capacity fade, where the
cycled electrode comprises an electrochemically active material in
the absence of a binder and a current collector; regenerating the
electrode by a thermal treatment under air; and placing the
regenerated electrode in the battery to restore capacity.
2. The method of claim 1, wherein the battery has undergone at
least 50 cycles prior to electrode regeneration.
3. The method of claim 1, wherein the electrochemically active
material is selected from the group consisting of Zn.sub.xO.sub.y,
Mn.sub.xO.sub.y, V.sub.xO.sub.y, Fe.sub.xO.sub.y, Sn.sub.xO.sub.y,
La.sub.xMn.sub.yO.sub.z, Ni.sub.xCo.sub.yO.sub.z, and
Mo.sub.xO.sub.y, wherein x, y, and z are numbers greater than
0.
4. The method of claim 1, wherein electrochemically active material
is a self-supporting transition metal oxide comprising
nanofibers.
5. The method of claim 1, further comprising no more than about 20%
based upon the total weight of the electrode of a conductive
additive selected from the group consisting of nanostructured
carbon, graphitic carbon, conductive metal nanoparticles, and metal
wire mesh.
6. The method of claim 1, wherein the thermal treatment includes
heating the electrode to a temperature greater than 200.degree. C.
and less than a thermal decomposition temperature of the
electrode.
7. A method of regenerating an electrode comprising: providing the
electrode from a battery having a delivered capacity below 60
mAh/g, where the electrode has an electrochemically active material
in the absence of a binder and a current collector, and where the
electrochemically active material is a self-supporting transition
metal oxide, and regenerating the electrode by a thermal treatment
under air, wherein the regenerated electrode in a battery has a
capacity above 100 mAh/g.
8. The method of claim 7 , wherein the electrochemically active
material is selected from the group consisting of Zn.sub.xO.sub.y,
Mn.sub.xO.sub.y, V.sub.xO.sub.y, Fe.sub.xO.sub.y, Sn.sub.xO.sub.y,
La.sub.xMn.sub.yO.sub.z, Ni.sub.xCo.sub.yO.sub.z, and
Mo.sub.xO.sub.y, wherein x, y, and z are numbers greater than
0.
9. The method of claim 7, wherein the self-supporting transition
metal oxide comprises nanofibers.
10. The electrode of claim 7, further comprising no more than about
20% based upon the total weight of the electrode of a conductive
additive selected from the group consisting of nanostructured
carbon, graphitic carbon, conductive metal nanoparticles, and metal
wire mesh.
11. The method of claim 7, wherein the thermal treatment includes
heating the electrode to a temperature greater than 200.degree. C.
and less than a thermal decomposition temperature of the
electrode.
12. A method of regenerating a self-supporting, binder-free
electrode comprising: providing a battery with a self-supporting,
binder-free electrode having an electrochemically active material
in the absence of a binder and a current collector, wherein the
electrochemically active material is a self-supporting transition
metal oxide; obtaining the electrode from the battery after
capacity fade; regenerating the electrode by a thermal treatment
under air; and placing the regenerated electrode in the battery or
in a new battery, wherein the battery or the new battery has a
capacity above 100 mAh/g.
13. The method of claim 12, wherein the battery has undergone at
least 50 cycles prior to electrode regeneration.
14. The method of claim 12, wherein the battery has undergone at
least 250 cycles prior to electrode regeneration.
15. The method of claim 12, wherein the electrochemically active
material is selected from the group consisting of Zn.sub.xO.sub.y,
Mn.sub.xO.sub.y, V.sub.xO.sub.y, Fe.sub.xO.sub.y, Sn.sub.xO.sub.y,
La.sub.xMn.sub.yO.sub.z, Ni.sub.xCo.sub.yO.sub.z, and
Mo.sub.xO.sub.y, wherein x, y, and z are numbers greater than
0.
16. The method of claim 12, wherein the self-supporting transition
metal oxide comprises nanofibers.
17. The electrode of claim 12, further comprising no more than
about 20% based upon the total weight of the electrode of a
conductive additive selected from the group consisting of
nanostructured carbon, graphitic carbon, conductive metal
nanoparticles, and metal wire mesh.
18. The method of claim 17, wherein the conductive additive is
nanostructured carbon and the nanostructure carbon is multi-walled
carbon nanotubes, fullerene, or graphene.
19. The method of claim 12, wherein the thermal treatment includes
heating the electrode to a temperature of between 200.degree. C.
and 400.degree. C.
20. The method of claim 12, wherein the thermal treatment includes
heating the electrode to a temperature greater than 200.degree. C.
and less than a thermal decomposition temperature of the electrode.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation application of U.S.
application Ser. No. 15/772,564, filed on May 1, 2018 which claims
priority to International Application No. PCT/US2016/063814 filed
on Nov. 28, 2016 which claims priority to U.S. Provisional
Application No. 62/261,562 filed on Dec. 1, 2015, the contents of
each of which are herein incorporated by reference in their
entirety.
BACKGROUND OF THE INVENTION
[0003] Portable electric energy storage issues associated with
devices such as consumer electronics and electric vehicles, along
with stationary electric energy storage concerns associated with
renewable energy generation and the grid, continue to stimulate
research in electric energy storage, including batteries. Thus,
rechargeable lithium ion batteries (LIBs) occupy a prominent
consumer presence due to their high cell potential and gravimetric
energy density. However, long electrode cycle lifetimes of LIBs
remain a challenge. While a number of factors can contribute to
limited LIB usable cycle lifetimes, cathode degradation is a
significant factor. Thus, a variety of LIB cathode materials have
been studied, including oxides of a variety of first row transition
metals (i.e. Mn, Fe, V, Co, and Ni). Under extended
lithiation/delithiation cycling, issues including structural
strain, amorphization, and irreversible phase changes typically
occur at the LIB cathode, resulting in an irreversible capacity
loss. Thus environmental concerns, such as disposal and recycling
issues, and economic concerns remain.
[0004] Currently used or proposed cathode recycling processes are
multistep procedures which involve sequences of mechanical,
thermal, and chemical leaching steps. During the mechanical
recycling processes, the used cathodes are mechanically crushed and
sieved multiple times and the components of the cathode are
separated magnetically, gravimetrically (by density), and/or by
size (sieving). However, separation is not always efficient;
therefore further chemical leaching processes are frequently
required for total recovery. Acid digestion is the most common
chemical leaching process, and uses highly corrosive concentrated
acids or bases. In addition, chemical leaching also requires a
neutralizing chemical treatment to recover digested metals. A
significant advance in this field was described recently (Chen, et
al., "Environmentally friendly recycling and effective repairing of
cathode powders from spent LiFePO.sub.4 batteries" Green Chem.,
2016,18, 2500-2506, DOI: 10.1039/C5GC02650D) whereby cathode
powders from spent LiFePO.sub.4 batteries could be recycled for the
first time, using a heat-treatment process. However, the recycled
electroactive material required significant reprocessing to
generate a new cathode structure.
[0005] Accordingly, there is a need for new electrodes which may be
regenerated easily and effectively by recreation of only the
cathode and provide restored capacity without cell
reconstruction.
SUMMARY OF THE INVENTION
[0006] An electrode structure with active material and no binder is
disclosed herein which may enable the regeneration of an electrode
to regain its activity after cycle testing. After cycling of a
battery with accompanying capacity fade, the electrode could be
regenerated by a heat treatment process. The regeneration process
may be able to restore capacity to the electrode. The capacity
increase as a result of regeneration may be retained during
cycling. The regenerated cathodes may deliver .about.200% higher
capacity than that of a control cell.
[0007] The invention relates to a binder-free, self-supporting
electrode including an electrochemically active material in the
absence of a binder and a current collector, wherein the
electrochemically active material is a self-supporting transition
metal oxide. The self-supporting transition metal oxide is selected
from the group consisting of Zn.sub.xO.sub.y, Mn.sub.xO.sub.y,
V.sub.xO.sub.y, Fe.sub.xO.sub.y, Sn.sub.xO.sub.y,
La.sub.xMn.sub.yO.sub.z, Ni.sub.xCo.sub.yO.sub.z, Mo.sub.xO.sub.y,
and Mn.sub.wNi.sub.xCo.sub.yO.sub.z, wherein x, y, and z are
numbers greater than 0. Preferably, the self-supporting transition
metal oxide is cryptomelane type manganese dioxide OMS-2.
Furthermore, the self-supporting transition metal oxide preferably
includes nanofibers. The electrode includes no more than about 20%
based upon the total weight of the electrode of a conductive
additive selected from the group consisting of nanostructured
carbon, graphitic carbon, conductive metal nanoparticles, and metal
wire mesh. Preferably, the conductive additive is nanostructured
carbon and the nanostructure carbon is multi-walled carbon
nanotubes, fullerene, or graphene. The preferred nanostructured
carbon is multi-walled carbon nanotubes. The weight ratio of active
material to conductive additive is about 5:0 or higher.
[0008] Another aspect of the invention relates to a method of
regenerating a self-supporting, binder-free electrode including
providing a battery with a self-supporting, binder-free electrode
described above; removing the electrode from a battery with
capacity fade; and regenerating the electrode by a thermal
treatment under air, and placing the regenerated electrode in the
battery or a new battery.
[0009] In a preferred embodiment, the battery has undergone at
least 50 cycles prior to electrode regeneration. In another
preferred embodiment, the battery has undergone at least 250 cycles
prior to electrode regeneration.
[0010] Another aspect of the invention relates to a binder-free,
self-supporting electrode consisting essentially of an
electrochemically active material in the absence of a binder and a
current collector, wherein the electrochemically active material is
a self-supporting transition metal oxide.
DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1A shows a comparison of the powder X-ray diffraction
(PXRD) patterns of BFSSC with 0 and 20% w.t CNT and pwdr-OMS-2.
[0012] FIG. 1B shows 20% CNT containing BFSSC-20.
[0013] FIG. 1C shows four-probe resistivity measurements of BFSSCs
with varying CNT content (0%, 5%, 10%, 15%, and 20%).
[0014] FIG. 2 Thermal Gravimetric Analysis (TGA) profiles of powder
OMS-2 (Pwdr OMS-2), 0&20% CNT containing binder free
self-supporting cathode materials, BFSSC-0 and BFSSC-20,
respectively. The weight % of CNT in BFSSC-20 was calculated as
18%.
[0015] FIGS. 3A, 3B, and 3C and Table 1 show Mn 2p, Mn 3s, and O1s
spectral ranges and peak positions. Binding energies (BEs) of
Mn2p.sub.1/2 and Mn2p.sub.3/2 doublets are in the ranges of
654.1-654.3 and 642.7-642.9, respectively (FIG. 3A and Table
1).
[0016] X-ray Photoelectron spectra (XPS) of powder (Pwdr-OMS-2),
20% (BFSSC-20) and 0% (BFSSC-0) CNT containing binder free
self-supporting cathode materials. FIG. 3A) Mn 2p, FIG. 3B) Mn
3s,
[0017] FIG. 3C shows the O1s spectral region of OMS-2 materials.
O1s peaks were deconvoluted into three different oxygen species
(Mn--O--Mn, Mn--OH, and H--O--H (physisorbed water)) and the peak
areas of these different oxygen species are presented in Table
1.
[0018] FIGS. 4A-4F SEM images shows as made wirelike OMS-2
materials are consist of nano-fiber bundles, FIGS. 4A and 4B. Upon
dispersion and sonication in NMP, the bundles were opened and
restacked as individual fibers as seen in the SEM images of the
BFSSC surfaces (FIG. 4E). NMP (1-Methyl-2-pyrrolidone) was chosen
as dispersing solvent in our studies since it can disperse both CNT
and OMS-2 fibers effectively to form homogeneous and stable
suspensions (41). The cross sectional SEM image of BFSSC-20 shows
that the surface has a flat and smooth surface morphology along
with a consistent thickness of 180 .mu.m (FIG. 4D).
[0019] FIG. 4C Schematic diagram of broken BFSSC-20 paper material
to observe side and face views, FIG. 4D is the view from side
(thickness .about.180 nm), FIGS. 4E and 4F are the images of the
surface of BFSSC material with 5 k and 15 k magnifications,
respectively.
[0020] FIG. 5A shows the cycling performance of pwdr-OMS-2,
BFSSC-0, and BFSSC-20 over 100 cycles. In the figure, the capacity
of pwdr-OMS-2 was calculated both per gram of cathode (solid
triangle) and per gram of active material (open triangle) and
capacities of BFSSCs were calculated per gram of cathode. FIGS. 5B
and 5C show the representative charge and discharge curves at
1.sup.st, 10, 50.sup.th, and 100.sup.th cycles of BFSSC-20 and
pwder-OMS-2, respectively.
[0021] FIG. 5A) Evolution of discharge capacity over 100 cycles for
BFSSC-20 (solid square), BFSSC-0 (solid circle), and powder OMS-2
coating (solid triangle). The capacities were calculated based on
the total cathode weight. Open triangle shows the discharge
capacity of powder OMS-2 coating where the capacity was calculated
per gram of active material. The cells were discharged-charged at a
rate of 0.09 mA/cm2. Representative discharge profiles at cycles 1,
10, 50, and 100 were shown at FIG. 5B) for BFSSC-20 and FIG. 5C)
for Powder OMS-2 coating.
[0022] FIGS. 6A-6D. shows galvanostatic intermittent titration
technique (GITT) conducted on cells with BFSSC cathodes.
Galvanostatic Intermittent Titration Technique (GITT) plots of FIG.
6A) BFSSC-20 (20% CNT) and FIG. 6B) Powder OMS-2. 40 mA/g pulses
for 10 min and 20 h rest in between the pulses. Diffusion
coefficient plots of FIG. 6C) BFSSC-20 (20% CNT) and FIG. 6D)
Powder OMS-2.
[0023] FIGS. 7A-7C Electrochemical impedance spectroscopy (EIS)
measurements of coin cells with FIG. 7A) BFSSC-20 (20% CNT) and
BFSSC-0 (0% CNT). The inset is the low-resistance part of BFSSC-20.
FIG. 7B) The impedence measurements of powder OMS-2 coatings with
varying coating thicknesses. FIG. 7C) The equivalent electrical
circuit used to fit the impedance spectra.
[0024] FIG. 8. Capacity versus cycle number for lithium anode/BFSSC
cells under galvanostatic control. The first 50 cycles were for a
group of cells using as prepared electrodes. After 50 cycles, three
of the cells were selected for regeneration (noted as pink, blue
and red). Cycles 50 to 100 for the control cell (black) were
continued as for cycles 1-50. The regenerated electrodes were
reinserted into cells and the testing was continued.
[0025] FIGS. 9A-9D Morphology of OMS-2. SEM images of a OMS-2
material with different magnifications: FIG. 9A) 2kx, scale bar 10
.mu.m. FIG. 9B) 5kx, scale bar 5 .mu.m. FIG. 9C) 10kx, scale bar 1
.mu.m. FIG. 9D) 20kx, scale bar 1 .mu.m.
[0026] FIGS. 10A and 10B Electrochemical Performance of BFSSCs.
FIG. 10A) Galvanostatic cycling performances and FIG. 10B)
Coulombic efficiencies of the binder free self-supporting cathode
(BFSSC) cycled for 250 cycles (Control cell) and Regenerated BFSSC.
BFSSC was regenerated four (4) times after 50 cycles by rinsing
with 5 DMC first and then heating under air for 2 h at 300.degree.
C. Current density was 50 mA/g (2.0 and 3.9 V vs. Li/Li+).
[0027] FIG. 11 Representative charge/discharge profiles of BFSSC.
Initial Galvanostatic Charge/discharge profiles of regenerated
BFSSC after the regeneration steps. Cycle numbers are 1, 51, 101,
151, and 201. Current density was 50 mA/g (2.0 and 3.9 V vs.
Li/Li+).
[0028] FIGS. 12A-12D Effect of Battery cycling and Regeneration on
the BFSSC. FIG. 12A) X-ray Diffraction (XRD) patterns of as-made
BFSSC and BFSSCs galvanostatically cycled for 100 and 300 times
with 50 mA/g rate. FIG. 12B) Scherrer crystallite sizes of (200)
and (310) planes of as-made, 100 times and 300 times cycled BFSSCs,
and regenerated BFSSC after 100 cycles. FIG. 12C) XRD patterns of
as-made and regenerated BFSSCs. FIG. 12D) Image of BFSSC.
[0029] FIG. 13 Visual and physicochemical properties of BFSSC.
Image of a BFSSC material along with the average weight, thickness,
and BET surface area. In BFSSC, OMS-2/CNT weight ratio is 5/1,
corresponding to 83 wt. % of OMS-2.
[0030] FIGS. 14A-14D High-resolution STEM images showing
crystallinity and amorphization of the pristine, 100 cycled, 300
cycled and regenerated BFSSC. FIG. 14A) The pristine sample viewed
along the [012] direction, revealing high crystallinity throughout
the entire nanorod with a clean crystalline surface. The inset is a
magnified area form the boxed region from the edge embedded with
the structural model. FIG. 14B) The 100-cycled sample viewed along
the [015] zone axis. Although overall the nanorod remains
crystalline, the fuzzy contrast and spackle intensity suggest
significant amorphization on the sample. The amorphous patches
appear at the edge of the image (see the inset) indicate they cover
the entire surface of the nanorod. Lattice distortion related
defects were also observed. FIG. 14C) The 300-cycled sample. Very
thick amorphous layer on surface make the atomic structure in the
interior of the nanorod barely visible. FIG. 14D) The regenerated
sample after 150 cycles viewed along the [1-21] direction. The
amorphous patches on the surface (see the enlarge image in inset
from the same boxed area at the edge) has clearly transformed into
a single crystal, being consistent with the x-ray and
electrochemistry data.
[0031] FIG. 15 Diffraction pattern comparison. X-ray Diffraction
(XRD) patterns of as-made grounded OMS-2 and binder free
self-supporting cathode BFSSC (83wt. % OMS-2) materials.
(K.sub.xMn.sub.8O.sub.16, JCPDS 029-1020).
[0032] FIG. 16: Thermal stability and water content of OMS-2.
Thermal Gravimetric Analysis (TGA) profile of OMS-2
(.alpha.-MnO.sub.2). The TGA graph is split into three parts,
separated by dashed lines, physisorbed water (RT-250.degree. C.),
Structural (Tunnel) Water (250-.about.450.degree. C.), and O.sub.2
evolution (thermal decomposition) (>450.degree. C.).
[0033] FIG. 17 Schematic representation of cathode regeneration
process: A coin-cell assembled with as-made BFSSC. Used battery was
disassembled and BFFSC was removed. BFSSC was regenerated by
rinsing with DMC first and then heating under air for 2 h at
300.degree. C. A new battery was assembled with the regenerated
BFSSC.
[0034] FIG. 18 Regeneration Control experiment. Galvanostatic
cycling performance of BFSSC regenerated by only rinsing with DMC
and dried at RT in a vacuum oven (No heating). Current density was
50 mA/g (2.0 and 3.9 V vs. Li/Li.sup.+).
[0035] FIGS. 19A-19D Low-magnification STEM images showing size
difference of the pristine, 100 cycled, 300 cycled and regenerated
BFSSC. FIG. 19A) The pristine sample; FIG. 19B) The 100 cycled
sample; FIG. 19C) the 300 cycled sample; and FIG. 19D) the
regenerated sample. Insets are enlarged image of the corresponding
nanorods.
DETAILED DESCRIPTION
[0036] The present invention relates to a binder-free,
self-supporting electrode including an electrochemically active
material. The electrochemically active material is a
self-supporting transition metal oxide. The transition metal oxide
is self-supporting because of its fibrous morphology. For example,
these transition metal oxides can be formulated as long,
nanofibers. The long, nanofibers need no further means of support
unlike conventional electrodes which are commonly deposited on
carbon. In other words, the transition metal oxides of the
invention differ from conventional electrodes because they do not
need to be anchored, deposited, or placed on a support.
[0037] Examples of transition metals with fibrous morphologies
include, but are not limited to, Zn.sub.xO.sub.y, Mn.sub.xO.sub.y,
V.sub.xO.sub.y, Fe.sub.xO.sub.y, Sn.sub.xO.sub.y,
La.sub.xMn.sub.yO.sub.z, Ni.sub.xCo.sub.yO.sub.z, Mo.sub.xO.sub.y,
and Mn.sub.wNi.sub.xCo.sub.yO.sub.z, wherein x, y, and z are
numbers greater than 0. For example, preferred transition metal
oxides include ZnO, MnO.sub.2, V.sub.2O.sub.5, Fe.sub.2O.sub.3,
SnO.sub.2, VO.sub.2, LaMnO.sub.3, and NiCo.sub.2O.sub.4. Most
preferably, the electrochemically active material is cryptomelane
type manganese oxide (OMS-2, a group of octahedral molecular
sieves, K.sub.x1Mn.sub.8O.sub.16, wherein
0.6.gtoreq.x1.gtoreq.1.2).
[0038] Binders and current collectors are also not necessary for
the functioning of the electrode. Binders and current collectors
for electrodes are well-known in the art. Examples of binders not
necessary for the invention include, but are not limited to,
polymer binders, water-based binders, and conductive binders.
Examples of binders include polyvinylidene difluoride (PVDF),
styrene butadiene rubber (SBR), polytetrafluoroethylene (PTFE),
sodium-carboxyl-methyl-cellulose (CMC), poly
(acrylaminde-co-diallyldimethylammonium) (AMAC), poly (acrylic
acid) (PAA), polyaniline (PANI), polypyrrole (PPY), conducting
polymer hydrogels (CPHs), Nafion, lignin, and combinations thereof.
Examples of current collectors not necessary for the invention
include, but are not limited to, Al and Cu foils.
[0039] The invention may optionally include conductive additives
that are present for the purpose of increased conductivity, and not
for structural purposes to support the electrode. In other words,
the electrode is self-supporting without the required presence of a
conductive additive. Additionally, the presence of a conductive
additive in the electrode is minimal enough such that the
conductive additive will not function as a support for the
electrode. Accordingly, the quantity of conductive additives is
limited to no more than about 20% based upon the total weight of
the electrode in order to distinguish the additives from structural
supports.
[0040] Additives to increase conductivity in an electrode are well
known in the art. Some conductive additives include, but are not
limited to, any graphitic carbon, nanostructured carbon, metal wire
mesh, and metal nanoparticles such as Ag, Zn, Ni, and Cu. Examples
of graphitic carbon include carbon black, graphite, Super P, and
Kagen Black.
[0041] Nanostructured carbon includes, but is not limited to,
fullerenic carbon (e.g., fullerenes and carbon nanotubes),
graphenes, and polyacetylenes. Carbon nanotubes include, e.g.,
single-walled carbon nanotubes (SWNTs), few-walled carbon nanotubes
(FWNTs), and multi-walled carbon nanotubes (MWNTs).
[0042] The term "nanostructured carbon" may exclude functionalized
carbon materials, i.e., nanostructured carbon containing various
functional groups incorporated in or attached to the carbon
framework. The functional groups may include or exclude, for
example, oxygen functional groups such as --OH and --COOH. Thus,
the term "nanostructured carbon" excludes oxygen-functionalized
nanostructured carbon. Types of excluded oxygen-functionalized
nanostructured carbon includes materials such as, for example,
oxidized FWNTs, oxidized MWNTs (including MWNT-COOH), graphene
oxide (GO), reduced graphene oxide (rGO), and rGO--COOH.
[0043] Additionally, the carbon nanotubes may or may not include
composites, i.e., when another element or compound is nucleated on
the carbon nanotubes. For example, sulfur is not nucleated upon the
carbon nanotubes, and the carbon nanotubes are not sulfur-carbon
nanotube composites. Furthermore, the carbon nanostructures are not
synthesized on carbon felt.
[0044] The term "nanostructured" refers to articles having at least
one cross-sectional dimension on the nanometer scale, e.g., less
than about I .mu.m, less than about 500 nm, less than about 250 nm,
less than about 100 nm, less than about 75 nm, less than about 50
nm, less than about 25 nm, less than about 10 nm, or, in some
cases, less than about I nm. Nanostructured carbon includes
materials that have features on the nanometer scale in at least
one, at least two, or in all three dimensions.
[0045] The conductive additive may not be present in the invention.
However, the conductive element may be present in the invention in
quantities whereby it is not a structural element of the electrode,
and it is present in the invention solely to increase conductivity
of the electrode and electrochemical performance of the electrode
in general by decreasing the charge polarization.
[0046] For example, the conductive additive may be present in the
invention in minimum amount of about 0%, 0.1%, 0.5%, I %, 2%, 3%,
4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%,
18%, or 19% based upon the total weight of the electrode.
[0047] Likewise, the conductive additive may be present in the
invention in a maximum amount of about 20%, 19%, 18%, 17%, 16%,
15%, 14%, 13%, 12%, 11%, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, or I
% based upon the total weight of the electrode. Each of the
above-listed minima and maxima may be combined to create a range.
For example, the conductive additive may be a carbon nanotube
present in a minimum amount of about 9% and a maximum amount of
about 20%.
[0048] In a preferred aspect of the invention, the transition metal
oxide is OMS-2 and a conductive additive such as multi-walled
carbon nanotube is present in a preferred ratio of about 5:0 or
higher, OMS-2 to multi-walled carbon nanotube.
[0049] In another preferred aspect of the invention, no conductive
additive is present.
[0050] Another embodiment of the invention relates to a
binder-free, self-supporting electrode consisting essentially of an
electrochemically active material in the absence of a binder and a
current collector, wherein the electrochemically active material is
a self-supporting transition metal oxide. The term "consisting
essentially of" would exclude the presence any additive included in
the electrode in quantities such that the additive would function
as a structural element. The electrode is self-supporting
exclusively because of the fibrous morphology of the translation
metal oxide. Conductive additives such as any carbon form may be
present in this embodiment of the invention, but they are not
present in quantities to be considered structural elements. In
other words, "consisting essentially of" would include the presence
of up to about 20% by total weight of the electrode of a conductive
additive according to the invention.
[0051] In another embodiment, the invention relates to a
binder-free, self-supporting electrode consisting of cryptomelane
type manganese dioxide OMS-2 nanofibers and a nanostructured
carbon. The nanostructured carbon may be present in a maximum
amount of about 20% of the total composition and a minimum amount
of 0% of the total composition.
[0052] The invention also relates to a method of recycling the
electrodes described above. The electrode of the invention may be
regenerated by thermal treatment so it can be placed in a new
battery and re-used. Regenerated electrodes display restored
crystallinity and oxidation state of the transition metal centers
with resulting electrochemistry (capacity and coulombic efficiency)
similar to that of freshly prepared electrodes.
[0053] After a battery containing the electrode of the invention
had undergone a significant number of cycles and the capacity had
faded, the electrode may be regenerated by removing it from the old
battery and rinsing, if necessary, to remove, for example, lithium
salt from the electrode surface. Any organic solvent can be used to
rinse the battery that can dissolve lithium salt, e.g., DMC
(dimethyl carbonate), DEC (diethyl carbonate), EMC (ethyl methyl
carbonate), EA (ethyl acetate), MB (methyl butyrate), EB (ethyl
butyrate), DMM (dimethoxymethane), DME (dimethoxyethane), and THF
(tetrahydrofuran), etc. The electrode is then placed in an oven
heated to a temperature high enough so that the transition metal
oxide is fully oxidized and low enough so that the electrode is not
subject to thermal decomposition. The temperature and duration of
the regeneration with respect to a given electrode can be
determined by a person having ordinary skill. For example, for an
OMS-2/MWNT electrode, regeneration may take place in a 300.degree.
C. oven for approximately 2 hours.
[0054] After the electrode is thermally regenerated, the
regenerated electrode may be placed in the same battery or in a new
battery. The number of discharge-charge cycles before regeneration
may be determined by monitoring the performance of the battery to
determine capacity fade. The number of cycles may be anywhere
between from about 50 to a number of cycles even greater than about
250.
[0055] The invention may be practiced in the absence of any element
which is not specifically disclosed herein.
[0056] Examples have been set forth below for the purpose of
illustration and to describe the best mode of the invention at the
present time. The scope of the invention is not to be in any way
limited by the examples set forth herein.
EXAMPLES
Example 1. Materials Characterization
[0057] Potassium containing cryptomelane type OMS (OMS-2) fibers
were synthesized by the redox reaction between Mn.sup.2+ and
S.sub.2O.sub.8.sup.2- under hydrothermal conditions. Binder-free
self-supporting cathode (BFSSC) materials were prepared by
dispersing the fibers with varying amounts of multiwall carbon
nanotube (CNT) in NMP and filtering through a glass membrane. For
comparison, as made OMS-2 fibers were grounded to fine powder and
labeled as Pwdr-OMS-2. FIG. 1A shows the X-ray diffraction (XRD)
patterns of BFSSC with 0 and 20% w.t CNT and pwdr-OMS-2.
Diffractions lines of both BFSSC and pwdr-OMS-2 are in agreement
with the tetragonal cryptomelane phase (JCPDS file number 29-1020)
with substantially no detected impurities. One difference between
BFSSCs and pwdr-OMS-2 (and the standard pattern) may be the higher
relative intensities of (hk0) diffraction lines compared to (001)
lines. The (hk0) crystallographic planes may be parallel to the
2.times.2 tunnels. Therefore, higher intensities of (hk0) lines may
be related to preferential orientation of the nanofibers in a
certain crystal growth direction (c-axis). Yuan et al. also
reported particular orientations for paper-like OMS-2 fibers and
OMS-2 tetragonal prisms both prepared with similar hydrothermal
methods. Regardless of the CNT content BFSSCs show substantially
pure tetragonal cryptomelane phase with 14/m space group.
[0058] The structural purity of the BFSSC and pwdr-OMS-2 samples
was confirmed by Raman spectroscopy. Raman spectroscopy may be
sensitive for the detection of impurity phases (i .e. MnOOH,
Mn.sub.2O.sub.3, Mn.sub.3O.sub.4), phase evaluation, and tunnel
cation occupancy of OMS-2 materials. The Raman spectra of BFSSCs
feature four strong bands located at 185, 391, 582, and 640
cm.sup.-1 and a weak one at 332 cm-.sup.1. The detected bands were
assigned to substantially pure crystalline cryptomelane phase of
manganese dioxide. The strong bands at 582 and 640 cm.sup.-1 may be
due to symmetrical Mn-O stretching in a tetragonal structure with
an interstitial space consisting of 2.times.2 tunnels (21). The
low-frequency Raman band at 185cm.sup.-1 may be assigned to the
external vibration that derives from the translational motion of
the octahedral MnO.sub.6 units and the band at 391 cm.sup.-1 is
ascribed to the Mn--O bending vibrations.
[0059] BFSSC cathodes were prepared by punching out circular pieces
from OMS-2 membranes with a diameter of 1/2''. FIG. 1B shows 20%
CNT containing BFSSC-20. The average thickness and weight of
BFSSC-20 are 0.172.+-.0.012 mm and 12.1.+-.1.0 mg, respectively.
The measured thicknesses and weights are found to be very
consistent for all BFSSCs. Four-probe resistivity measurements of
BFSSCs with varying CNT content are presented in FIG. 1C. In the
lack of CNT (BFSSC-0), the resistivity was found to be 38.4.+-.1.1
.OMEGA.cm which is similar to the previously reported resistivity
values for OMS-2 materials. The resistivity values decreased
constantly with increasing CNT content and reached to
0.067.+-.0.003 .OMEGA.cm at a CNT content of 20% (BFSSC-20). BET
surface areas of pwdr-OMS-2 (58.0 m.sup.2/g) and BFSSC-20 (65.2
m.sup.2/g) are found to be close suggesting that there may be
no-change at the surface textural properties upon processing of
OMS-2 fibers to form OMS-2 membranes.
[0060] Thermal gravimetric analyses (TGA) of OMS-2 materials were
performed under air flow to determine the amounts of structural
(tunnel) water, thermal stabilities, and the CNT content (FIG. 2).
The weight loss profiles of OMS-2 materials can be separated in
three parts. (i) In the RT-250.degree. C. range, weight loss is
attributed to physisorbed water. The weight loss of BFSSCs and
pwdr-OMS-2 were around 1.8-2.0%. (ii) In the 250-450.degree. C.
range, the weight loss may be due to the loss of structural
(tunnel) water. The weight loss of pwdr-OMS-2 and BFSSC-0 were the
same (.about.I %) corresponding to .about.0.25 units of water per
molecular formula, KxMn.sub.8O.sub.16. In the same range, 20% CNT
containing BFSSC-20 showed larger weight loss, 6%. Notwithstanding
any particular theory it may be the thermal decomposition of CNT in
BFSSC-cathode in the range. The TGA profile of pure CNT shows an
offset temperature of 450.degree. C. The CNT decomposition may be
promoted to occur at slightly lower temperatures on the redox
active labile oxygen on the OMS-2 surface. (iii) At temperatures
higher than 450.degree. C., lattice oxygen evaluates from the
structure and manganese dioxide decomposes
(MnO.sub.2.fwdarw.Mn.sub.2O.sub.3.fwdarw.Mn.sub.3O.sub.4) (25, 29).
BFSSC-0 and pwdr-OMS-2 show two-step decomposition above
450.degree. C. The steps of pwdr-OMS-2 are at lower temperatures
(.about.500 & 700.degree. C.) compared to BFSSC-0 (.about.590
& 860.degree. C.). The actual CNT content of BFSSC-20 was found
to be 18% (21% w.r.t. weight of OMS-2) from the difference between
the percent weight changes of BFSSC-0 and BFSSC-20 at 750.degree.
C.
[0061] X-ray photoelectron spectroscopy (XPS) was employed in order
to investigate surface chemical composition and average manganese
oxidation state. Survey spectra of pwdr-OMS-2, BFSSC-0, and
BFSSC-20 were collected. The survey spectra show the characteristic
core level photoelectron peaks of Mn2p, Mn3s, Mn3p, K2s, K2p and
O1s and Auger signals of Mn and 0 with no surface impurities. FIG.
3 and Table 1 show Mn 2p, Mn 3s, and O1s spectral ranges and peak
positions. Binding energies (BEs) of Mn2p.sub.1/2 and Mn2p.sub.3/2
doublets are in the ranges of 654.1-654.3 and 642.7-642.9,
respectively (FIG. 3A and Table 1). [0062] These values are
consistent with the previously reported manganese dioxide Mn2p
values ruling out the presence of other lower valance manganese
oxide phases (i.e. MnO, Mn.sub.3O.sub.4, and Mn.sub.2O.sub.3).
TABLE-US-00001 [0062] TABLE 1 The summary of XPS data of OMS-2
powder and BFSSC Materials O1s Average Mn 2p {eV) Mn 3s {eV) Area
Oxidation Sample .sup.2P.sub.1/2 .sup.2P.sub.3/2 BE.sub.1.sup.a
BE.sub.2.sup.a dE.sup.b State.sup.c BE {eV) {%) State.sup.d Powder
OMS-2 654.2 642.7 89.17 84.55 4.62 Mn--O--Mn 529.87 86.9 3.75
Mn--O--H 531.66 11.1 H--O--H 533.17 2.0 BFSSC-20% CNT 654.3 642.9
89.16 84.62 4.54 Mn--O--Mn 530.08 78.3 3.84 Mn--O--H 531.80 16.9
H--O--H 533.45 4.8 BFSSC-0%CNT 654.1 642.7 89.06 84.51 4.55
Mn--O--Mn 529.76 73.2 3.83 Mn--O--H 531.69 25.8 H--O--H 533.24 1.0
.sup.aBinding energies of two chemical states were obtained for
Mn3s photoelectrons, .sup.b.DELTA.E = BE.sub.1 - BE.sub.2 of Mn3s
photoelectrons, .sup.cthree different chemical states of O as
indicated, were obtained from O1s spectral region, and
.sup.dAverage oxidation states (AOS) were calculated from the
.DELTA.E of Mn3s peaks (AOS = 8.956 - 1.126 .times.
.DELTA.E.sub.(3s)).
[0063] XPS has been widely used for the determination of the
average oxidation state (AOS) of manganese oxide compounds (14, 31,
32, 34-37). Despite oxidation state calculations were reported
using Mn2p and O1s spectral regions, calculations using the
splitting between Mn3s main and satellite peaks
(.DELTA.E.sub.Mn.sub.3.sub.s) is the prominence and widely
confirmed method. The splitting originates from the exchange
coupling between 3s hole and 3d electrons and proportional to
(2S+1), where S is the spins of 3d ground state electron
configuration. In other words, lower oxidation states of high spin
manganese center causes a bigger splitting between M3s main and
satellite peaks. Galakhov et al. reported first time a linear
correlation between the .DELTA.EMn3s and AOS
(AOS=8.956-1.126.times..DELTA.E.sub.Mn.sub.3.sub.s), except the
3.0.sup.+-3.3.sup.+ manganese formal valance range (32, 35, 36).
FIG. 3B shows the Mn3s spectral region and Table 1 shows the
calculated AOSs. AOS of Pwdr-OMS-2 was calculated to be 3.75.
However, BFSSC-20 and BFSSC-0 demonstrated slightly higher
oxidation states 3.84 and 3.85, respectively. The calculated
oxidation states indicate mixed-valent nature of manganese in OMS-2
materials.
[0064] FIG. 3C shows the O1s spectral region of OMS-2 materials.
O1s peaks were deconvoluted into three different oxygen species and
the peak areas of these different oxygen species are presented in
Table 1. The oxygen species correspond to oxygen bounded to
manganese (Mn--O--Mn) at 529.87-580.08 eV, surface hydroxyls
(Mn--O--H) at 531.66-531.80 eV, and surface adsorbed water
(H--O--H) at 533.17-533.45 eV (14, 31, 39). Relative peak area
comparison suggests that the most of the oxygen is in the form of
lattice oxygen bounded to manganese (Mn--O--Mn). In addition,
pwdr-OMS sample has relatively lower hydroxyl content (11.1%)
suggesting a more defect-free structure or breakage of Mn--O--Mn to
form hydroxyl groups upon processing the nano-wires to obtain
BFSSCs (39, 40).
[0065] As made wire-like OMS-2 materials consist of nano-fiber
bundles, FIGS. 4A and 4B. Upon dispersion and sonication in NMP,
the bundles were opened and restacked as individual fibers as seen
in the SEM images of the BFSSC surfaces (FIG. 4E). NMP
(1-Methyl-2-pyrrolidone) was chosen as dispersing solvent in these
studies since it can disperse both CNT and OMS-2 fibers effectively
to form homogeneous and stable suspensions (41). The cross
sectional SEM image of BFSSC-20 shows that the surface has a flat
and smooth surface morphology along with a consistent thickness of
180 .mu.m (FIG. 4D). EDS mapping was also used to evaluate the
dispersion of CNT in the BFSSC-20. Carbon-mapping indicates
homogeneous carbon dispersion throughout the BFSSC surface.
However, SEM images of grounded pwdr-OMS-2 may be different than
the as-made OMS-2 wirelike material. Upon physical grounding, the
morphology may change to micron sized agglomerates formed by
shortened nano-fibers.
Example 2. Electrochemical Characterization of BFSSCs
[0066] Electrochemical performance of BFSSCs as cathodes in lithium
ion batteries was investigated via galvanostatic charge-discharge
tests. For the tests, experimental coin cells were assembled using
BFFSCs directly. For comparison, a prior art composite coating on
aluminum foil was prepared from pwdr-OMS-2 sample. The cells were
charged/discharged in a voltage range of 2.0-3.9 V and at two
different current densities; 0.09 mA/cm.sup.2 (FIG. 5) and 0.45
mA/cm.sup.2. FIG. 5A shows the cycling performance of pwdr-OMS-2,
BFSSC-0, and BFSSC-20 over 100 cycles. In the figure, the capacity
of pwdr-OMS-2 was calculated both 30 per gram of cathode (solid
triangle) and per gram of active material (open triangle) and
capacities of BFSSCs were calculated per gram of cathode. The
discharge capacities of BFSSC-20, BFSSC-0, and pwdr-OMS-2 are 107,
62, and 35 mAh/g at initial discharge and 53, 20, and 10 mAh/g at
100.sup.th cycle, respectively. BFSSC-20 showed the highest
gravimetric capacities throughout the test, maintaining >50mAh/g
after 100 cycles. Lower capacities of BFSSC-0 are attributed to the
high resistivity of the cathode due to the lack of conductive
additive (see FIG. 1C). Significantly lower capacities of
pwdr-OMS-2 can be explained by the electrochemically inactive
components of the composite coating (Aluminum, binder, and CNT).
The amount of active material (pwdr-OMS-2) in the coating is
.about.25% by weight which decreases the gravimetric capacity of
the cathode. In order to realize the real potential of BFSSCs the
capacity of the pwdr-OMS-2 coating was also calculated using the
amount of active material (FIG. 5A). The results are similar to the
one of BFSSC-20 except slightly higher discharge capacities in the
first .about.40 cycles. The discharge capacities of Pwdr-OMS-2 per
grams of active material were 139 mAh/g at 1.sup.st cycle, which
decreased to 55 mAh/g at 50.sup.th cycle and to 40 mAh/g at
100.sup.th cycle. Based on electrode weight, the present BFSSC
electrodes showed higher capacity relative to the prior art
Pwdr-OMS-2 electrodes.
[0067] One trend at the discharge capacity vs. cycle number plots
is the decreases at the capacities at initial cycle(s) (FIG. 5A).
Later, the capacity gradually continues to decrease but with a
smaller rate. For example, the initial discharge capacity of
BFSSC-20 decreased by 30% (107 to 76 mAh/g) in the first 10 cycles,
the decrease in the next 40 cycles was 22% (76 to 56 mAh/g), and in
the last 50 cycles the decrease was 3% (56 to 53 mAh/g). FIGS. 5B
and 5C show the representative charge and discharge curves at
1.sup.st, 10, 50.sup.th, and 100.sup.th cycles of BFSSC-20 and
pwdr-OMS-2, respectively. The discharge-charge profiles are found
to have similar characteristics except the gravimetric capacities.
The initial discharge curves show a step wise potential variation
with no-obvious plateau. The first shoulder (step) is around 2.7 V
and the second one is around 2.5 V vs. Li/Li+. Both shoulders
gradually fade after consecutive cycling and adopted a single slope
profile suggesting a single-phase insertion electrode (42). Similar
discharge profiles for OMS-2 (.alpha.-MnO.sub.2) materials were
observed previously for the materials synthesized by hydrothermal
methods (43-45). Surface area, crystallinity, tunnel occupation,
doping, and morphology are found to be other important factors
affecting the recyclability and discharge profiles of OMS-2
(.alpha.-MnO.sub.2) materials.
[0068] Galvanostatic intermittent titration technique (GITT) was
conducted on cells with BFSSC cathodes, FIG. 6. The diffusion
coefficients for the cathodes with and without CNTs were
determined, FIGS. 6C and 6D. Additionally, electrochemical
impedance spectroscopy was utilized to characterize the samples
with and without the added CNTs, FIG. 7. The impedance of the
sample with CNT is lower than that of pure OMS-2. Additionally, the
impedance is related to the thickness of the electrode where the
thicker electrode shows higher impedance, FIG. 7B.
Example 3. Regeneration of Electrode
[0069] The regeneration of electrodes was conducted in order to
restore the behavior of the cell. The electrodes were removed from
the cells after the capacity had decreased from the initial cell
capacity after cycling. The electrodes were heat treated at 200,
300 or 350.degree. C. under air. The same electrodes were
reinserted into active electrochemical cells and cell testing was
resumed, FIG. 8.
[0070] Prior to regeneration, the delivered capacities from the
cells were below 60 mAh/g. After heat treatment the cell capacities
were above 100 mAh/g. In particular, as the cells resumed cycle
testing under constant current, the capacity of the regenerated
electrodes remained at a high level. The control cell had a
delivered capacity of .about.30 mAh/g while the regenerated cells
had delivered capacities of .about.60-70 mAh/g, 2.times. that of
the control cell.
[0071] Thus, the regeneration process may be able to restore
capacity to the electrode. The capacity increase as a result of
regeneration may be retained during cycling. The regenerated
cathodes may delivered .about.200% higher capacity than that of the
control cell.
Example 4
[0072] Preliminary results: i) M.sub.xMn.sub.8O.sub.16 (M=K.sup.+,
Ag.sup.+) material synthesis and characterization demonstrating
control of particle size, crystallite size, and covalent
character.
[0073] The inventors have been successful in the synthesis of
M.sub.xMn.sub.8O.sub.16 (M=K.sup.+, Ag.sup.+) materials by a
variety of methods allowing control of composition (M/Mn ratio),
physical properties (surface area, morphology) and crystallite
size. Specifically, Ag.sub.xMn.sub.8O.sub.16was prepared by an
ambient pressure reflux method and K.sub.xMn.sub.8O.sub.16
Cryptomelane type manganese dioxides (OMS-2) were synthesized using
three different methods, low-temperature hydrothermal (HT-OMS-2),
reflux (RF-OMS-2), and solvent-free (SF-OMS-2. (75-78)
[0074] For the synthesis of HT-OMS-2, manganese sulfate monohydrate
(Mn(SO.sub.4).H.sub.2O), potassium sulfate (K.sub.2SO.sub.4),
potassium persulfate (K.sub.2S.sub.2O.sub.8), and water were heated
in an autoclave. RF-OMS-2 was prepared by heating potassium
permanganate (KMnO.sub.4 ) and manganese sulfate monohydrate
(MnSO.sub.4.H.sub.2O) with nitric acid (HNO.sub.3) at reflux. For
the synthesis of SF-OMS-2, manganese acetate tetrahydrate
(Mn(Ac).sub.2.4H.sub.2O) and potassium permanganate (KMnO.sub.4 )
were heated at 120.degree. C. Structural formulas for OMS-2
materials were assigned from XRD, ICP-OES (K.sup.+ content), TGA
(water content), and XPS (AOS) results. Among all, RF-OMS-2,
K.sub.0.81Mn.sub.8O.sub.15.9, 1.06H.sub.2O, had the lowest amount
of oxygen defects and highest oxidation state.
[0075] In the case of Ag.sub.xMn.sub.8O.sub.16, the silver content
can be systematically modified through synthetic control leading to
a concomitant shift in crystallite size. A recent study of large
crystallite, high silver (H--Ag-MOS-2) content material versus
small crystallite, low silver content (L-Ag--OMS-2) material
demonstrated significant differences in structure, defects and size
impacting electrochemical performance.
[0076] The cations residing in tunnels of the manganese dioxides
balance the charge of manganese; therefore the average oxidation
state of manganese is lower for the materials with higher amounts
of cation (81-85). The high silver H--Ag--OMS-2 material shows less
angular distortion in the MnO.sub.6 octahedral structure but more
Mn-O bond-length variation. The L-Ag--OMS-2 sample shows a larger
value of 9.770 for the a and b dimension compared to 9.738 .ANG.
for the high silver sample, H--Ag--OMS-2. Prior studies on
hollandite manganese oxide tunnel structures have shown that Group
I metal cations (including K.sup.+) increase the dimensions of the
2.times.2 tunnels where higher occupancies of the tunnel ions
increase the lattice parameters. (86) In contrast, the results for
silver ions show that higher occupancy of silver decreases the a
and b lattice parameters as the silver content of x=1.8 has a
tunnel dimension of 4.873 .ANG. in the ab plane. (87) As the silver
content decreases to x=1.66 (H--Ag--OMS-2) and 1.22 (L-Ag--OMS-2),
the tunnel dimensions increase to 5.072 and 5.176 .ANG.,
respectively. Thus, the trend observed at all three silver levels
indicates decreased lattice parameters with increasing silver
content likely related to more covalent bonding character of the
silver ion compared to Group I metal ions.
[0077] Comparative electrochemical data in magnesium based
electrolyte was obtained for the M=Ag or K for
M.sub.xMn.sub.8O.sub.16 samples. The potassium based sample showed
improved capacity retention over the silver containing sample.
Example 5
[0078] Preliminary results: ii.) a robust, self-supporting,
regenerable positive electrode.
[0079] A novel cathode structure that is binder free
self-supporting (BFSSC) was developed where the active catalyst
(OMS-2) is the structural element of the electrodes. OMS-2
nanowires used for this study were prepared by a hydrothermal
method to form long nanowires (>10 .mu.m) grouped in bundles.
The chemical formula of K.sub.0.84Mn.sub.8O.sub.16.0.25H.sub.2O was
assigned based on analysis of the material. Multiwall carbon
nanotubes (MWNT) can be added in various ratios to enhance
electrical conductivity. Mixed valent (+3/+4) OMS-2
(.alpha.-MnO.sub.2) have been previously used as redox catalysts
for selective or total oxidation of organic compounds. As a
heterogeneous catalyst, the activity of OMS-2 decreases due to the
depletion of labile surface oxygens, surface adsorbed species
blocking the active sites, or/and reduction of manganese. OMS-2
catalysts can be regenerated by washing or/and heating under
oxidative atmospheres such as air (94, 100-104). Upon regeneration,
the oxidation state of manganese is restored and the surface of the
catalyst is repaired (94, 96, 100, 102). Manganese oxides, when
used as cathodes, experience similar irreversible manganese
reduction (Mn.sup.4+.fwdarw.Mn.sup.3+.fwdarw.Mn.sup.2+)
amorphization, crystal structure change, and cathode dissolution
(analogue of catalyst leaching).
[0080] In the cathode regeneration process, the cycled cathode was
removed from the battery, regenerated by a simple thermal treatment
under air and reused. The electrochemical performance of BFSSC
recovered after regeneration. The initial capacity for both cell
types was .about.115 mAh/g. After the first 50 cycles the capacity
degraded to 43 mAh/g. After regeneration, the capacity of the cell
was restored to 101 mAh/g. The process was repeated multiple (four)
times with recovery of performance each time. The delivered
capacities were almost totally restored after each of the
regeneration steps. The initial capacities after regeneration were
all higher than 95 mAh/g suggesting an almost full recovery of the
cathode performance. At the end of 250 cycles, the regenerated
BFSSC delivered 60 mAh/g capacity, almost five (5) times higher
than the BFSSC control cell (13 vs. 60 mAh/g). The effect of the
regeneration on the coulombic efficiencies was also
encouraging.
[0081] XPS--the relative amounts of lattice oxygen (O.sub.lat)
content on the surface increased from 45.5 to 67.9% after cathode
regeneration. It appears that high temperature regeneration (at
300.degree. C.) under an oxidative atmosphere (air) may promote
reoxidation and condensation of the manganese oxide structure in
the cycled BFSSC.
TABLE-US-00002 TABLE 2 XPS summary of as-made, cycled, and
regenerated BFSSCs O1s Average Mn 2p (eV) Mn 3s (eV) Area Oxidation
Sample 2p.sub.L/2 2p.sub.3/2 BE.sub.2.sup.d BE.sub.3.sup.d
.DELTA.E.sup.b State.sup.c BE (eV) {%) State.sup.d As-made 653.7
642.4 88.54 83.99 4..55 Olat 529.2 78.1 3.83 BFSSC Osurf 530.7 12.G
Oads 532.0 9.9 BFSSC@100.sup.th 653.1 64L6 88.95 83.83 5.12 Olat
529.1 45.5 3.20 cycle Osurf 530.5 51.9 Oads 533.7 2.6 BFSSC@
300.sup.th 653.1 64L5 39..14 33..35 5.79 Olat 529.3 12.4 2.43 cycle
Osurf 531.0 67.3 Oads 533.7 20.3 Regenerated 653.5 641.9 88.49
83.91 4.58 Olat 529.3 67.9 3.79 BFSSC Osurf 530.S 22.5 Oads 532.4
9.6 a Binding energies of two chemical states were obtained for
Mn3s photoelectrons, .sup.b.DELTA.E = BE.sub.1 - BE.sub.2 of Mn3s
photoelectrons, .sup.cthree different chemical states of O as
indicated, were obtained from O1s spectral region, and
.sup.dAverage oxidation states (AOS) were calculated from the
.DELTA.E of Mn3s peaks (AOS = 8.956 - 1.126 .times.
.DELTA.E.sub.(3s)).
Example 6. Materials Synthesis
[0082] Cryptomelane type manganese dioxide nanowire, octahedral
molecular sieve (OMS-2), was synthesized by a hydrothermal method,
previously reported by Yuan et al. (13). In a typical synthesis of
OMS-2, 3 mmol (0.51 g) of manganese sulfate monohydrate
(Mn(SO.sub.4).H.sub.2O), 3 mmol (0.52 g) of potassium sulfate
(K.sub.2SO.sub.4) 6 mmol (1.62 g) of potassium persulfate
(K.sub.2S.sub.2O.sub.8), and 10 ml of DDI water were added and
stirred in a Teflon vessel for 30 min at RT. The ratio of reactants
was 1:2:1:555.6. Later, the vessel was transferred to a stainless
steel autoclave and placed in an oven running at 200.degree. C. for
48 h. The resulting solid was washed several times with DDI water,
filtered, and dried in a vacuum oven running at 60.degree. C.
overnight. The dried solid material was grinded in a mortar to
obtain fine powder. The powder sample labeled as Powder-OMS-2.
Example 7. Electrode Fabrication--State of the Art Electrodes
[0083] As comparative controls to the present BFSSC materials,
composite cathodes were prepared on an aluminum foil (current
collector) by mixing conductive multiwall carbon nanotube (15 wt.
%), powder OMS-2 (70 wt. %), and Polyvinylidene fluoride (PVDF)
binder (15 wt. %). The thickness of the coating was adjusted using
doctor's blade. The circular composite cathodes were made at three
different thicknesses (0.008, 0.015, and 0.025 mm) and with the
area of 1.27 cm.sup.2. The composite cathodes were named as Pwdr
OMS-2-X, where X is the cathode thickness.
Example 8. Electrode Fabrication--Novel Binder Free Self-Supporting
Cathode (BFSSC)
[0084] Materials
[0085] As-made OMS-2 material (.about.270 mg) was dispersed in 300
mL of DDI water and stirred overnight. The suspension was allowed
to rest for a period of time and supernatant solution was decanted.
The process was repeated 6 more times (with 1 h stirring time) with
250 mL portions of water (2.times.), acetone (2.times.), and
1-Methyl-2-pyrrolidone (NMP) (2.times.), respectively. The
resulting suspension, OMS-2 nanowires dispersed in .about.50 mL of
NMP, was further sonicated for 1 h and then added to an another
suspension containing various amounts of multiwall carbon nanotube
(CNT) in 100 mL of NMP (total volume is .about.150 mL) and
sonicated together for an additional one hour. The amounts of CNT
in the final suspension were adjusted such a way that the weight
percent amounts of CNT (w.r.t. OMS-2) were 0, 5, 10, 15, and 20%.
Later, the suspensions were filtered through a glass frit Buchner
funnel and wash with NMP and ethanol and dried in a vacuum oven
over night. The formed OMS-2 membrane was peeled off and pressed
with a hydraulic hand press at 6 tons for 90 seconds to obtain a
good electrical contact. Circular pieces with 1/2'' diameter (1.27
cm.sup.2) were punched out to obtain binder free self-supporting
cathodes (BFSSC). The BFSSC cathodes were named as BFSSC-X where X
is the % CNT content, X=0, 5, 10, 15, or 20.
Example 9. Materials Characterization
[0086] X-ray diffraction (XRD) patterns of BFSSC and powder OMS-2
samples were collected with a Rigaku Ultima IV X-ray
diffractometer. Cu K.alpha. radiation (.lamda.=1.5406 A) was used
with Bragg-Brentano focusing geometry. N.sub.2 sorption
(adsorption-desorption) measurements were performed on a
Micrometrics Tristar II 3020 and multipoint BET (Brunauer, Emmett,
and Teller) method was used for calculating the surface area.
Thermogravimetric analysis (TGA) was performed with a TA
instruments SDT Q600 instrument under 10 cc/min air flow and in the
temperature range of 25-900.degree. C. Inductively coupled plasma
optical emission spectroscopy (ICP-OES) was done using with a
Thermo Scientific iCAP 6000 series spectrometer to determine the
elemental composition. The samples were digested in 50 wt. % nitric
acid and hydrogen peroxide H.sub.2O.sub.2 for ICP-OES measurements.
The conductivity of BFSSC samples were measured by a standard
linear four-point probe arrangement. Scanning electron microscopy
(SEM) images and energy dispersive spectra (EDS) of the OMS-2
samples were collected using JEOL JSM-6010PLUS instrument with the
accelerating voltage of 20 kV. X-ray photoelectron spectroscopy
(XPS) experiments were carried out in a UHV chamber equipped with
SPECS Phoibos 100 MCD analyzer and a non-monochromatized
Al--K.alpha. X-ray source (hv=1486.6 eV) operating with an
accelerating voltage of 10 kV and 30 mA current. The chamber
typically has a base pressure of 2.times.10-10 Torr. The powder
samples were pressed onto a conductive copper tape and mounted on a
sample holder. Charging effects were corrected by adjusting the
binding energy of C (1s) peak at 284.8 eV (14). Raman spectra were
collected using Horiba Scientific Xplora Raman Spectrometer with 1%
laser power (.lamda.=532 nm) to prevent thermal excitations and
50.times. optical lens.
Example 10. Electrochemical Characterization
[0087] Stainless steel experimental type coin cells with lithium
metal anodes were fabricated in an argon atmosphere glove box.
Cathodes (BFSSCs or coatings) of OMS-2 type manganese oxides, Tonen
E25 separator, lithium metal, and electrolyte consisting of 1 M
LiPF6 in ethylene carbonate-dimethylcarbonate (30:70 wt. ratio)
were employed in the cells. Electrochemical impedance spectroscopy
(EIS) was measured over the frequency range of 10 mHz-100 kHz at
30.degree. C. Analysis of the AC impedance measurements was
conducted using the ZView.RTM. software from Scribner Associates,
Version 3.4c to obtain the solution/ohmic and charge transfer
resistances. Warburg coefficients were calculated from the slope of
Z' vs. W -1/2 (angular) plot (15). Galvanostatic intermittent
titration technique (GITT) type testing was conducted with
intermittent discharge current of 40 mA/g for 10 min followed by
open circuit rest for 20 h. Cell discharge/charge tests were
performed at 37.degree. C. using a Maccor multichannel testing
system under the rates of 0.09 and 0.45 mA/cm.sup.2 and in the
voltage range of 2.0 to 3.9 V.
TABLE-US-00003 TABLE 3 The summary of EIS parameters and diffusion
coefficients R.sub.s.sup.a R.sub.CT.sup.b .sigma..sub.w .sup.c
D.sub.u+.sup.d Sample (.OMEGA.) (.OMEGA.) (.OMEGA.s.sup.-1)
(cm.sup.2/s) Pwdr OMS-2 .sup.e 2.3 127 0.17 NA (0.008 mm) Pwdr
OMS-2 .sup.e 2.3 198 0.78 NA (0.015 mm) Pwdr OMS-2 .sup.e 3.4 322
0.78 1.11*10.sup.-8-1.48*10.sup.-10 (0.025 mm) BFSSC-20 6.4 11 3.75
1.81*10.sup.-7-2.91*10.sup.-10 BFSSC-0 3.5 44 2.44
3.07*10.sup.-7-1.40*10.sup.-9
Example 11. Regeneration Method
[0088] The regeneration of the electrode is done by a simple
process. The binder free electrode self-supporting cathode (BFSSC)
is removed from the electrochemical cell once the delivered
capacity is lower than desired. The electrode is then rinsed with a
solvent or with water followed by heating in air. For the manganese
oxide material described here, temperatures ranging from 200 to
400.degree. C. were investigated with the most favorable results in
the 200-350.degree. C. range. After heating, the electrode is
simply reinserted to the cell.
* * * * *