U.S. patent application number 16/898692 was filed with the patent office on 2022-03-10 for electrolyte additives for an electrochemical cell.
This patent application is currently assigned to Natron Energy, Inc.. The applicant listed for this patent is Natron Energy, Inc.. Invention is credited to Daniel Friebel, Peter Benjamin Herman, Majid Keshavarz, Alex J. Klevay, Grace Marjorie Yee.
Application Number | 20220077497 16/898692 |
Document ID | / |
Family ID | 1000004903802 |
Filed Date | 2022-03-10 |
United States Patent
Application |
20220077497 |
Kind Code |
A1 |
Keshavarz; Majid ; et
al. |
March 10, 2022 |
ELECTROLYTE ADDITIVES FOR AN ELECTROCHEMICAL CELL
Abstract
A system and method for a liquid electrolyte used in secondary
electrochemical cells having at least one electrode including a
TMCCC material, the liquid electrolyte enabling an increased
lifetime while allowing for fast discharge to extremely high depth
of discharge. The addition of dinitriles to liquid electrolytes in
electrochemical cells in which energy storage is achieved by ion
intercalation in transition metal cyanide coordination compounds
(TMCCC) has the advantage of increasing device lifetime by
inhibiting common chemical and electrochemical degradation
mechanisms.
Inventors: |
Keshavarz; Majid;
(Pleasanton, CA) ; Friebel; Daniel; (San Carlos,
CA) ; Herman; Peter Benjamin; (San Jose, CA) ;
Yee; Grace Marjorie; (San Francisco, CA) ; Klevay;
Alex J.; (San Jose, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Natron Energy, Inc. |
Santa Clara |
CA |
US |
|
|
Assignee: |
Natron Energy, Inc.
Santa Clara
CA
|
Family ID: |
1000004903802 |
Appl. No.: |
16/898692 |
Filed: |
June 11, 2020 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01M 10/0569 20130101;
H01M 10/0567 20130101; H01M 2300/0028 20130101 |
International
Class: |
H01M 10/0567 20060101
H01M010/0567; H01M 10/0569 20060101 H01M010/0569 |
Claims
1. An electrochemical cell, comprising: an electrolyte; an anode
electrode in electrical communication with said electrolyte; and a
cathode electrode in electrical communication with said
electrolyte; wherein said anode electrode includes a first
transition metal cyanide coordination compound material and said
cathode electrode includes a second transition metal cyanide
coordination compound different from said first transition metal
cyanide coordination compound material; and wherein said
electrolyte includes a mononitrile solvent, one or more alkali
metal salts in solution with said solvent, and an additive disposed
within said solvent; wherein said mononitrile solvent includes
acetonitrile; and wherein said additive includes a dinitrile
material.
2. The electrochemical cell of claim 1 wherein each said transition
metal cyanide coordination compound material includes a composition
A.sub.xP.sub.y[R(CN).sub.(6)].sub.z n(H.sub.2O), wherein A includes
an alkali metal cation, wherein a P includes a transition metal
cation, wherein R includes a transition metal cation, and wherein
0.ltoreq.x.ltoreq.2, y=1, 0.75.ltoreq.z.ltoreq.1, and
0.ltoreq.n.ltoreq.6.
3. The electrochemical cell of claim 2 wherein P of said cathode
electrode includes at least one of manganese and iron; and wherein
R of said cathode electrode includes iron.
4. The electrochemical cell of claim 1 in which said dinitrile
material includes a linear dinitrile material.
5. The electrochemical cell of claim 4 in which said linear
dinitrile material includes succinonitrile.
6. (canceled)
7. The electrochemical cell of claim 1 having a weight ratio N of
said solvent to said additive wherein 70:30<N<99:1.
8. (canceled)
9. The electrochemical cell of claim 2 wherein P of said anode
electrode includes at least one of manganese and iron; and wherein
R of said anode electrode includes manganese.
10. The electrochemical cell of claim 3 wherein R for said anode
electrode includes manganese.
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to improvement in
secondary electrochemical cells, and more specifically, but not
exclusively, to increasing device lifetime through inhibition of
one or more degradation mechanisms in a rechargeable
electrochemical device having at least one electrode including a
transition metal cyanide coordination compound (TMCCC)
material.
BACKGROUND OF THE INVENTION
[0002] The subject matter discussed in the background section
should not be assumed to be prior art merely as a result of its
mention in the background section. Similarly, a problem mentioned
in the background section or associated with the subject matter of
the background section should not be assumed to have been
previously recognized in the prior art. The subject matter in the
background section merely represents different approaches, which in
and of themselves may also be inventions.
[0003] It is recognized in electrochemistry that it is unlikely
that there will be a single battery that works optimally for every
application. Selecting the right battery for an application is
about identifying the most important battery metrics and trading
these off against others. For instance, when one desires a lot of
power for an application, cell internal resistance is often
minimized, and this may be done by increasing electrode surface
area. But this also increases inactive components such as current
collectors and conductive aid, so energy density could be traded
off to gain power.
[0004] Important considerations may include metrics such as
flexibility, safety, energy density, power density, voltage, cost,
shelf life, operational life, form factor (e.g., thickness),
commercial availability, temperature range, and cycle life.
[0005] Research, development, and manufacture of various battery
configurations focus on increasing selected subsets of these
metrics which may include particular tuning for specific
applications. Specialization of batteries have allowed for improved
batteries for a wide range of applications.
[0006] As a consequence, the components of any particular battery
are tailored for the desired solution which often means that one
component in one battery solution may not perform similarly in
another battery solution.
[0007] Discussed herein is a class of secondary electrochemical
cells that include a transition metal cyanide coordination compound
(TMCCC) material. More specifically, this class of electrochemical
cell includes liquid electrolytes in which energy storage is
achieved by ion intercalation in one or more electrodes including
the TMCCC material.
[0008] Performance of this class of electrochemical cell may
implicate a rate of parasitic reactions during operation of the
cell. Some solutions may include operation within a narrower
voltage window in order to diminish the rate of parasitic reactions
that result in cell degradation. However, this alternative results
in a low utilization of the energy stored by the cell. Operating
electrochemical devices within a narrower voltage window may result
in significantly diminished energy.
[0009] Performance of this class of electrochemical cell is related
to the composition of the liquid electrolytes. When one liquid
electrolyte includes an undesirable rate of parasitic reactions,
one solution may be to substitute a different liquid electrolyte
that reduces the rate of parasitic reactions. However, that
substituted liquid electrolyte may alter performance, such as
decreasing electrolyte conductivity which may lower maximum charge
and discharge power. Electrolytes with an entirely different
solvent system, including most polar-aprotic solvents other than
acetonitrile as the primary solvent, are disadvantageous because
their ionic conductivity is significantly lower than that of
electrolytes containing acetonitrile, and therefore precludes their
application when high rate capability is desired.
[0010] It may be advantageous to implement a new class of liquid
electrolyte for secondary electrochemical cells having at least one
electrode including a TMCCC material.
BRIEF SUMMARY OF THE INVENTION
[0011] Disclosed is a system and method for a liquid electrolyte
used in secondary electrochemical cells having at least one
electrode including a TMCCC material, the liquid electrolyte
enabling an increased lifetime while allowing for fast discharge to
extremely high depth of discharge. The following summary of the
invention is provided to facilitate an understanding of some of the
technical features related to secondary electrochemical cells
including at least one TMCCC electrode and is not intended to be a
full description of the present invention. A full appreciation of
the various aspects of the invention can be gained by taking the
entire specification, claims, drawings, and abstract as a whole.
The present invention is applicable to other configurations of
electrochemical cells and components in addition to the examples
discussed and disclosed herein. For example, other electrode
materials of an electrochemical cell that may be considered "wet"
that may contribute significant quantities of water, in the context
of that cell chemistry, to the cell during operation.
[0012] A class of additives for liquid electrolytes in
electrochemical cells having an anode electrode and a cathode
electrode, in which the electrolyte salt is an alkali metal salt
and at least one of the two electrodes contains a TMCCC material
capable of intercalation and deintercalation reactions with alkali
metal cations.
[0013] Some liquid electrolytes may include solutions of an alkali
metal salt, or a mixture of several different alkali metal salts,
and a dinitrile additive, in a mononitrile solvent.
[0014] An electrochemical cell including an electrolyte; an anode
electrode in electrical communication with the electrolyte; and a
cathode electrode in electrical communication with the electrolyte;
wherein at least one the electrode includes a transition metal
cyanide coordination compound material; and wherein the electrolyte
includes a mononitrile solvent, one or more alkali metal salts in
solution with the solvent, and an additive disposed within the
solvent; and wherein the additive includes a dinitrile
material.
[0015] A liquid electrolyte for a secondary electrochemical cell
having at least one electrode including a transition metal cyanide
coordination material, including a mononitrile solvent; and a
dinitrile additive disposed within the mononitrile solvent.
[0016] Any of the embodiments described herein may be used alone or
together with one another in any combination. Inventions
encompassed within this specification may also include embodiments
that are only partially mentioned or alluded to or are not
mentioned or alluded to at all in this brief summary or in the
abstract. Although various embodiments of the invention may have
been motivated by various deficiencies with the prior art, which
may be discussed or alluded to in one or more places in the
specification, the embodiments of the invention do not necessarily
address any of these deficiencies. In other words, different
embodiments of the invention may address different deficiencies
that may be discussed in the specification. Some embodiments may
only partially address some deficiencies or just one deficiency
that may be discussed in the specification, and some embodiments
may not address any of these deficiencies.
[0017] Other features, benefits, and advantages of the present
invention will be apparent upon a review of the present disclosure,
including the specification, drawings, and claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] The accompanying figures, in which like reference numerals
refer to identical or functionally-similar elements throughout the
separate views and which are incorporated in and form a part of the
specification, further illustrate the present invention and,
together with the detailed description of the invention, serve to
explain the principles of the present invention.
[0019] FIG. 1 illustrates cell energy versus time during float
testing;
[0020] FIG. 2 illustrates cell capacity versus time during float
testing;
[0021] FIG. 3 illustrates coulombic efficiency versus time during
float testing;
[0022] FIG. 4 illustrates steady state float current versus time
during float testing;
[0023] FIG. 5 illustrates 1C constant-current charge-discharge
voltage profiles;
[0024] FIG. 6 illustrates cell energy versus time during float
testing;
[0025] FIG. 7 illustrates cell capacity versus time during float
testing;
[0026] FIG. 8 illustrates coulombic efficiency versus time during
float testing;
[0027] FIG. 9 illustrates steady state float current versus time
during float testing;
[0028] FIG. 10 illustrates a post-mortem SEM image;
[0029] FIG. 11 illustrates an EDX spectrum of Selected Area 1 in
FIG. 10;
[0030] FIG. 12 illustrates an EDX spectrum of Selected Area 2 in
FIG. 10;
[0031] FIG. 13 illustrates an FTIR of electrolyte extracted from
aged cells;
[0032] FIG. 14 illustrates a magnified region of the FTIR spectra
in FIG. 13; and
[0033] FIG. 15 illustrates a magnified region of the FTIR spectra
in FIG. 13.
DETAILED DESCRIPTION OF THE INVENTION
[0034] Embodiments of the present invention provide a system and
method for a liquid electrolyte used in secondary electrochemical
cells having at least one electrode including a TMCCC material, the
liquid electrolyte enabling an increased lifetime while allowing
for fast discharge to extremely high depth of discharge. The
following description is presented to enable one of ordinary skill
in the art to make and use the invention and is provided in the
context of a patent application and its requirements.
[0035] Various modifications to the preferred embodiment and the
generic principles and features described herein will be readily
apparent to those skilled in the art. Thus, the present invention
is not intended to be limited to the embodiment shown but is to be
accorded the widest scope consistent with the principles and
features described herein.
Definitions
[0036] Unless otherwise defined, all terms (including technical and
scientific terms) used herein have the same meaning as commonly
understood by one of ordinary skill in the art to which this
general inventive concept belongs. It will be further understood
that terms, such as those defined in commonly used dictionaries,
should be interpreted as having a meaning that is consistent with
their meaning in the context of the relevant art and the present
disclosure, and will not be interpreted in an idealized or overly
formal sense unless expressly so defined herein.
[0037] The following definitions apply to some of the aspects
described with respect to some embodiments of the invention. These
definitions may likewise be expanded upon herein.
[0038] As used herein, the term "or" includes "and/or" and the term
"and/or" includes any and all combinations of one or more of the
associated listed items. Expressions such as "at least one of,"
when preceding a list of elements, modify the entire list of
elements and do not modify the individual elements of the list.
[0039] As used herein, the singular terms "a," "an," and "the"
include plural referents unless the context clearly dictates
otherwise. Thus, for example, reference to an object can include
multiple objects unless the context clearly dictates otherwise.
[0040] Also, as used in the description herein and throughout the
claims that follow, the meaning of "in" includes "in" and "on"
unless the context clearly dictates otherwise. It will be
understood that when an element is referred to as being "on"
another element, it can be directly on the other element or
intervening elements may be present therebetween. In contrast, when
an element is referred to as being "directly on" another element,
there are no intervening elements present.
[0041] As used herein, the term "set" refers to a collection of one
or more objects. Thus, for example, a set of objects can include a
single object or multiple objects. Objects of a set also can be
referred to as members of the set. Objects of a set can be the same
or different. In some instances, objects of a set can share one or
more common properties.
[0042] As used herein, the term "adjacent" refers to being near or
adjoining. Adjacent objects can be spaced apart from one another or
can be in actual or direct contact with one another. In some
instances, adjacent objects can be coupled to one another or can be
formed integrally with one another.
[0043] As used herein, the terms "connect," "connected," and
"connecting" refer to a direct attachment or link. Connected
objects have no or no substantial intermediary object or set of
objects, as the context indicates.
[0044] As used herein, the terms "couple," "coupled," and
"coupling" refer to an operational connection or linking. Coupled
objects can be directly connected to one another or can be
indirectly connected to one another, such as via an intermediary
set of objects.
[0045] The use of the term "about" applies to all numeric values,
whether or not explicitly indicated. This term generally refers to
a range of numbers that one of ordinary skill in the art would
consider as a reasonable amount of deviation to the recited numeric
values (i.e., having the equivalent function or result). For
example, this term can be construed as including a deviation of
.+-.10 percent of the given numeric value provided such a deviation
does not alter the end function or result of the value. Therefore,
a value of about 1% can be construed to be a range from 0.9% to
1.1%.
[0046] As used herein, the terms "substantially" and "substantial"
refer to a considerable degree or extent. When used in conjunction
with an event or circumstance, the terms can refer to instances in
which the event or circumstance occurs precisely as well as
instances in which the event or circumstance occurs to a close
approximation, such as accounting for typical tolerance levels or
variability of the embodiments described herein.
[0047] As used herein, the terms "optional" and "optionally" mean
that the subsequently described event or circumstance may or may
not occur and that the description includes instances where the
event or circumstance occurs and instances in which it does
not.
[0048] As used herein, the term "size" refers to a characteristic
dimension of an object. Thus, for example, a size of an object that
is spherical can refer to a diameter of the object. In the case of
an object that is non-spherical, a size of the non-spherical object
can refer to a diameter of a corresponding spherical object, where
the corresponding spherical object exhibits or has a particular set
of derivable or measurable properties that are substantially the
same as those of the non-spherical object. Thus, for example, a
size of a non-spherical object can refer to a diameter of a
corresponding spherical object that exhibits light scattering or
other properties that are substantially the same as those of the
non-spherical object. Alternatively, or in conjunction, a size of a
non-spherical object can refer to an average of various orthogonal
dimensions of the object. Thus, for example, a size of an object
that is a spheroidal can refer to an average of a major axis and a
minor axis of the object. When referring to a set of objects as
having a particular size, it is contemplated that the objects can
have a distribution of sizes around the particular size. Thus, as
used herein, a size of a set of objects can refer to a typical size
of a distribution of sizes, such as an average size, a median size,
or a peak size.
[0049] As used herein, the term "dinitrile" means an organic
chemical compound containing two, but not more than two, nitrile
groups. A nitrile is any organic compound that include a
--C.ident.N functional group (for purposes of this disclosure, the
prefix cyano--may be used interchangeably with the term nitrile).
For purposes of this application, a term "polynitrile" may be used
to identify materials including two or more nitrile groups, with
polynitrile materials including dinitrile materials while excluding
mononitrile (a single nitrile group) materials. As further
described herein, the mononitrile solvent and the dinitrile
additives are desirable, purposeful, and functional and are present
in sufficient quantities designed to meet design goals for the
reduction of a rate of parasitic reactions resulting from water
leaving an electrode during operation. This is distinguished from
any situation in which the nitrile groups are viewed as
undesirable, unpurposeful, and degrading such as a trace or
impurity that decreases desired performance or other cell
metric.
[0050] Disclosed herein is a new class of liquid electrolytes that
enable increased lifetime of electrochemical energy storage
devices, while at the same time allowing for fast discharge to
extremely high depth of discharge. Electrolytes containing
dinitrile additives were found to have several advantages,
including: (i) in electrochemical devices that suffer degradation
due to leaching of transition metal ions from electrode materials,
the formation of transition metal oxide precipitates that degrade
cell performance is diminished; (ii) in electrochemical devices
that degrade due to the presence of water impurities, which are
difficult to remove from common electrode materials, electrolyte
solvents and electrolyte salts, unwanted reactions between
nitrile-containing electrolyte solvents and water are suppressed by
dinitrile additives. These effects are demonstrated herein with a
unique sodium-ion battery in which at least one electrode material
contains a significant concentration of water as part of its
crystal lattice, some of which is released while the device is
operated. With regards to dramatically enhancing the tolerance of
electrochemical cells to water impurities, some of the examples
provide a multitude of advantages, including significant cost
savings in cell manufacturing processes that often require
time-consuming and energy-intensive drying protocols and
construction of controlled processing environments such as dry
rooms and glove boxes around entire assembly lines, and
opportunities for novel electrode materials for which full
dehydration is highly disadvantageous or unfeasible.
[0051] Literature includes a discussion of certain uses of
acetonitrile-dinitrile solvent mixtures. For example, in
electrolytes for electric double layer capacitors (EDLC), see R1,
and in Li-ion batteries, see R2-R6. Therein, benefits such as high
ionic conductivity, stability of nitrile and dinitrile solvents
across wide electrochemical potential windows, and enhanced safety
against thermal runaway and fire due to the low vapor pressures of
dinitriles, appear to have been described. However, those
discussions appear to be limited to electrochemical structures
containing ceramic or carbonaceous electrodes that are designed to
be anhydrous (while water is an undesirable impurity, a certain
quantity of water may be tolerated as an impurity), and do not show
an improvement in cell stability performance as a result of the
addition of a dinitrile species to the electrolyte.
[0052] The examples provided below disclose electrochemical
structures and components that may afford significantly improved
calendar and cycle lifetime for an electrochemical device. The
examples describe novel and non-obvious elements that are unique in
design.
[0053] The examples include TMCCC electrode materials used in this
device that allow for fast ion transport and, during charge and
discharge, undergo either no phase transitions at all, or only
subtle structure changes. Therefore, these examples may offer much
higher rate capability and much longer cycle life, even when cycled
repeatedly to extremely high depth of discharge.
[0054] The degradation mechanism of the devices described in the
examples is different from typical degradation mechanisms in Li-ion
battery cells or in EDLCs, and the beneficial effect of dinitrile
additives in cells containing TMCCC electrode material cannot be
inferred from any of the benefits claimed in prior art disclosing
electrolytes containing dinitriles in Li-ion cells or EDLCs. In
particular, a new method of mitigating cell degradation mechanisms
is described in which solvent molecules are decomposed within their
nominal electrochemical stability window through reaction steps
such as hydrolysis that do not involve solvent reduction or
oxidation.
[0055] More generally, interactions between liquid nitrile-based
electrolytes and electrode materials that intercalate other ions
than Lit, such as the larger alkali metal ions Nat, Na.sup.+,
K.sup.+, Rb.sup.+, or Cs.sup.+ have not been addressed.
Intercalation mechanisms and ion-solvent interactions are
fundamentally different between Li.sup.+ and larger alkali metal
cations, due to the unique small ionic radius of Li.sup.+ (R7).
[0056] Some examples herein include a new class of additives for
liquid electrolytes in electrochemical cells having an electrolyte
including a solvent and an electrolyte salt, an anode electrode,
and a cathode electrode, in which the electrolyte salt includes an
alkali metal salt and at least one of the two electrodes includes a
TMCCC material capable of intercalation and deintercalation
reactions with alkali metal cations in the electrolyte.
[0057] The liquid electrolytes may include solutions of an alkali
metal salt, or a mixture of several different alkali metal salts,
and a dinitrile additive, in a mononitrile solvent. Preferred
examples of alkali metal salts include suitable salts containing an
alkali metal cation and an anion, wherein the alkali metal cation
is sodium, potassium, rubidium or cesium, and anions include, but
are not limited to, perchlorate, tetrafluoroborate,
hexafluorophosphate, difluoro-oxalatoborate, triflate,
bis(trifluoromethanesulfonyl)imide, dicyanamide, tricyanomethanide,
and mixtures thereof. Preferred examples of sodium salts include
sodium salts such as, but not limited to, sodium perchlorate,
sodium tetrafluoroborate, sodium hexafluorophosphate, sodium
difluoro-oxalatoborate, sodium triflate, sodium
bis(trifluoromethanesulfonyl)imide, sodium dicyanamide, and sodium
tricyanomethanide, and mixtures thereof. A preferred sodium salt
includes sodium bis(trifluoromethanesulfonyl)imide. Examples of
dinitrile additives include malonitrile, succinonitrile,
glutaronitrile, and adiponitrile. Additives of note include
succinonitrile and adiponitrile, with succinonitrile particularly
noteworthy in some cases. Examples of mononitrile solvents include
acetonitrile, propionitrile and butyronitrile. The mass ratios of
mononitrile solvent and dinitrile may range from approximately 99:1
to 70:30 with suitable salt concentrations that result in a liquid
solution at a desired operating temperature. The operating
temperature may be between -60.degree. C. and +80.degree. C., or a
narrower scope of temperatures within this range as needed or
desired.
[0058] Other organic electrolyte solvents that are
electrochemically inactive in the operating electrochemical
potential range of the TMCCC electrode and the counter electrode
may be used in a practical cell. These solvents include nitriles
such as succinonitrile or propionitrile, carbonates including
propylene carbonate or dimethyl carbonate, sulfones including
sulfolane and dimethyl sulfone, sulfoxides including dimethyl
sulfoxide, amides including dimethylformamide, ethers including
glymes including diglyme, triglyme, tetraglyme, 1,4-dioxane, or
1,3-dioxolane, lactones including gamma-valerolactone, glycol
ethers including methylene glycol monoethylether, or other
solvents, or a combination thereof. Other electrolyte salts that
are soluble in the electrolyte solvent and that are
electrochemically inactive in the operating electrochemical
potential range of the TMCCC electrode and the counter electrode
may be used in a practical cell. These salts may include sodium
hexafluorophosphate, sodium tetrafluoroborate, sodium perchlorate,
sodium (trifluoromethane)sulfonimide, sodium
4,5-dicyano-2-(trifluoromethyl)imidazolide, or other sodium salts,
or a combination thereof. Furthermore, as the TMCCC electrode or
its counterelectrode may undergo electrochemical reactions with
other cations such as lithium, potassium, or magnesium, these salts
may include lithium, potassium, or magnesium salts of
tetrafluoroborate, perchlorate, (fluoromethane)sulfonimide,
(trifluoromethane)sulfonimide,
4,5-dicyano-2-(trifluoromethyl)imidazolide, or a combination
thereof.
[0059] Mass ratios with relatively high dinitrile content result in
a greater enhancement of cell lifetime than those with lower
dinitrile content as shown for adiponitrile and succinonitrile in
Examples 1 and 2, respectively, whereas initial electrolyte
conductivity increases with acetonitrile content, due to the low
viscosity of acetonitrile. Preferred mass ratios of acetonitrile
and dinitrile are in the range from 99:1 to 75:25. Particularly
preferred mass ratios are between 95:5 and 80:20 for some of the
applications described herein.
[0060] One mechanism by which dinitrile additives may enhance cell
life most is chelation of dissolved transition metal ions by the
individual dinitrile molecules. Side chemical reactions between the
electrodes and electrolyte that result in dissolved transition
metal ions are commonly observed with cathode materials in
lithium-ion and sodium-ion batteries, especially with cathode
materials containing manganese cations. In addition to cathode
materials that are made of mixed transition metal oxides, electrode
materials consisting of transition metal cyanide coordination
compound (TMCCC) materials are also subject to partial transition
metal dissolution reactions. Most commonly, TMCCC materials will
react with the electrolyte to release manganese or iron cations
into the electrolyte. The presence of a dinitrile electrolyte
additive may result in a formation of a chemically stable chelation
complex of one or more dinitrile molecules with the dissolved
transition metal ions, which may decrease a reactivity of these
ions towards other cell components.
[0061] Another possible advantage of electrolytes having
compositions that include one or more dinitrile additives may be an
enhanced tolerance of the electrochemical device towards water
impurities. Degradation mechanisms that involve unwanted reactions
with water can be exacerbated in battery cells that use TMCCC
electrodes, because TMCCC electrodes typically contain significant
amounts of intercalated and/or coordinated water molecules,
potentially a significant quantity of which may be released during
operation of the electrochemical cell including such electrodes.
The release of these water molecules from the TMCCC electrodes may
result in significant concentrations of water being present in the
electrolyte of thousands to tens of thousands of parts per million,
even in an event when the electrochemical cell is initially
constructed with anhydrous liquid electrolyte prior to
operation.
[0062] FIG. 1 illustrates cell energy versus time during float
testing at 1.86V with daily 1 hour discharge to 1.19V at an ambient
temperature of 40.degree. C., normalized to the discharge energy of
the first tested cycle, for cells containing a sodium manganese
iron hexacyanoferrate cathode, a sodium manganese
hexacyanomanganate anode, and acetonitrile-based electrolyte with
no additive (Control) and various concentrations of
adiponitrile.
[0063] FIG. 2 illustrates cell capacity versus time during float
testing at 1.86V with daily 1 hour discharge to 1.19V at an ambient
temperature of 40.degree. C., normalized to the discharge capacity
of the first tested cycle, for cells containing a sodium manganese
iron hexacyanoferrate cathode, a sodium manganese
hexacyanomanganate anode, and acetonitrile-based electrolyte with
no additive (Control) and various concentrations of
adiponitrile.
[0064] FIG. 3 illustrates coulombic efficiency versus time during
float testing at 1.86V with daily 1 hour discharge to 1.19V at an
ambient temperature of 40.degree. C., for cells containing a sodium
manganese iron hexacyanoferrate cathode, a sodium manganese
hexacyanomanganate anode, and acetonitrile-based electrolyte with
no additive (Control) and various concentrations of
adiponitrile.
[0065] FIG. 4 illustrates steady state float current versus time
during float testing at 1.86V with daily 1 hour discharge to 1.19V
at an ambient temperature of 40.degree. C., for cells containing a
sodium manganese iron hexacyanoferrate cathode, a sodium manganese
hexacyanomanganate anode, and acetonitrile-based electrolyte with
no additive (Control) and various concentrations of
adiponitrile.
[0066] FIG. 5 illustrates 1C constant-current charge-discharge
voltage profiles of cells containing a sodium manganese iron
hexacyanoferrate cathode, a sodium manganese hexacyanomanganate
anode, and acetonitrile-based electrolyte with or without (Control)
a 20% succinonitrile additive.
[0067] FIG. 6 illustrates cell energy versus time during float
testing at 1.81V with daily 1 hour discharge to 1.19V at an ambient
temperature of 55.degree. C., normalized to the discharge energy of
the first tested cycle, for cells containing a sodium manganese
iron hexacyanoferrate cathode, a sodium manganese
hexacyanomanganate anode, and acetonitrile-based electrolyte with
no additive (Control) and various concentrations of
succinonitrile.
[0068] FIG. 7 illustrates cell capacity versus time during float
testing at 1.81V with daily 1 hour discharge to 1.19V at an ambient
temperature of 55.degree. C., normalized to the discharge capacity
of the first tested cycle, for cells containing a sodium manganese
iron hexacyanoferrate cathode, a sodium manganese
hexacyanomanganate anode, and acetonitrile-based electrolyte with
no additive (Control) and various concentrations of
succinonitrile.
[0069] FIG. 8 illustrates coulombic efficiency versus time during
float testing at 1.81V with daily 1 hour discharge to 1.19V at an
ambient temperature of 55.degree. C., for cells containing a sodium
manganese iron hexacyanoferrate cathode, a sodium manganese
hexacyanomanganate anode, and acetonitrile-based electrolyte with
no additive (Control) and various concentrations of
succinonitrile.
[0070] FIG. 9 illustrates steady state float current versus time
during float testing at 1.81V with daily 1 hour discharge to 1.19V
at an ambient temperature of 55.degree. C., for cells containing a
sodium manganese iron hexacyanoferrate cathode, a sodium manganese
hexacyanomanganate anode, and acetonitrile-based electrolyte with
no additive (Control) and various concentrations of
succinonitrile.
[0071] FIG. 10 illustrates post-mortem SEM image of a sodium
manganese iron hexacyanoferrate cathode taken from a cell
containing an acetonitrile-based electrolyte with no additives
after 340 days of float testing at 45.degree. C. at 1.86 V.
Selected Area 1 and Selected Area 2 mark the regions in which EDX
spectra in FIGS. 11 and 12 were recorded, respectively.
[0072] FIG. 11 illustrates EDX spectrum of Selected Area 1 in FIG.
10, showing the elemental composition characteristic of sodium
manganese iron hexacyanoferrate cathode active material with binder
and conductive carbon, and sodium
bis(trifluoromethanesulfonyl)imide.
[0073] FIG. 12 illustrates EDX spectrum of Selected Area 2 in FIG.
10, showing the elemental composition characteristic of a sodium
manganese iron hexacyanoferrate cathode covered with manganese
oxide precipitates, and sodium
bis(trifluoromethanesulfonyl)imide.
[0074] FIG. 13 illustrates FTIR of electrolyte extracted from aged
cells containing a sodium manganese iron hexacyanoferrate cathode
and a sodium manganese hexacyanomanganate anode. One cell was
filled with 0.88 M NaTFSI electrolyte made with 100% acetonitrile,
the other cell with electrolyte containing 0.88 M NaTFSI in
acetonitrile and 29.5% by weight succinonitrile. Both cells had
undergone constant-voltage float testing at 1.86 V with daily 1C
constant-current discharge to 1.19 V at an ambient temperature of
45.degree. C. for a duration of 340 days.
[0075] FIG. 14 illustrates magnified region of the FTIR spectra in
FIG. 13, and FIG. 15 illustrates magnified region of the FTIR
spectra in FIG. 13.
Example 1
[0076] Testing of sodium-ion battery cells containing a sodium
manganese iron hexacyanoferrate cathode, a sodium manganese
hexacyanomanganate anode, and mononitrile-based electrolyte
containing adiponitrile additive.
[0077] Electrolytes were prepared by mixing acetonitrile with
adiponitrile (ADN) to obtain two different adiponitrile
concentrations of 8.5% and 29.15% by weight. NaTFSI salt was
dissolved in the liquid mixtures to a concentration of 0.88 mol/L.
Two groups of otherwise identical pouch cells were filled with the
8.5% ADN and the 29.15% ADN electrolyte, respectively. A third
group was filled with a 0.88 mol/L NaTFSI/100% acetonitrile
solution to serve as a control group. Anodes and cathodes were
carefully selected to minimize differences in mass loadings between
cells, and to originate from the same respective material synthesis
and electrode coating runs. All cells were subjected to an
accelerated aging test, in which the cells were held at a constant
ambient temperature of 40.degree. C. and underwent a cycling
schedule consisting of constant-current charging at 1C to a cell
voltage of 1.86 V, followed by a 22 h constant-voltage period and
then a constant-current discharge at 1C to 1.19 V. All cells
exhibited approximately linear capacity fade over a test duration
of 20 days. The cell degradation was slowed down by the addition of
adiponitrile, and a monotonic decrease of fade rates with
increasing adiponitrile concentration was observed. (FIG. 1 and
FIG. 2). Significant improvements of the coulombic efficiency were
also achieved. The coulombic efficiency increased monotonically
with adiponitrile concentration, from 97% with no additive to 97.8%
and 98.5% with 8.5% and 29.15% adiponitrile, respectively (FIG. 3).
FIG. 4 illustrates a steady-state float current averaged over the
last 2 h of each float sequence, which can be seen as a measure of
the parasitic reaction rate. The adiponitrile additive at 8.5% and
29.15% reduces the steady-state float current by approximately 25%
and 50%, respectively.
Example 2
[0078] Testing of sodium-ion battery cells containing a sodium
manganese iron hexacyanoferrate cathode, a sodium manganese
hexacyanomanganate anode, and mononitrile-based electrolyte
containing succinonitrile additive.
[0079] Electrolytes were prepared by mixing acetonitrile with
succinonitrile (SN) to obtain two different succinonitrile contents
of 10%, 15%, and 20% by weight. NaTFSI salt was dissolved in the
liquid mixtures to give a salt concentration of 0.88 mol/L. Three
groups of otherwise identical pouch cells were filled with the 10%
SN, 15% SN, and 20% SN electrolyte, respectively. A fourth group
was filled with a 0.88 mol/L NaTFSI/100% acetonitrile solution to
serve as a control group. Anodes and cathodes were carefully
selected to minimize differences in mass loadings between cells,
and to originate from the same respective material synthesis and
electrode coating runs. The cells exhibited reversible voltage
profiles in 1C constant current charge-discharge cycling, and no
significant changes to the characteristic features of the voltage
profiles were found between cells with or without a dinitrile
additive (FIG. 5). All cells were subjected to an accelerated aging
test, in which the cells were held at an ambient temperature of
55.degree. C. and underwent a cycling schedule consisting of
constant-current charging at 1C to a cell voltage of 1.81 V,
followed by a 22 h constant-voltage period and then a
constant-current discharge at 1C to 1.19 V. The cell degradation
was significantly diminished by the addition of succinonitrile, as
indicated by the energy and capacity fade (FIG. 6 and FIG. 7), in
which cells with succinonitrile additive become clearly
distinguishable from the controls after 30 days. The addition of
succinonitrile was found to be highly effective at suppressing
parasitic reactions, as evident in increased coulombic efficiencies
and reduced float currents (FIG. 8 and FIG. 9). In the control
cells, low coulombic efficiencies, and high float currents during
the initial 20 days of testing indicate high parasitic reaction
rates. These parasitic reactions eventually diminish, presumably
because water released from at least one of the electrode materials
is consumed, but a second parasitic mechanism becomes apparent as
the steady-state float current increases again, which coincides
with accelerated capacity fade. The succinonitrile additive
improves the coulombic efficiency and diminishes the float current,
and a monotonic decrease of the float current and a monotonic
increase of the coulombic efficiency with succinonitrile
concentration are observed. Furthermore, the succinonitrile
additive prevents the second stage of cell degradation. After 30
days, the parasitic currents remain at a low level in cells with
succinonitrile. In contrast, the cells without additive suffer a
steady increase of parasitic current beginning at 25 days, and
after 60 days their parasitic currents are 2.times. as high as in
cells with succinonitrile.
Example 3
[0080] Post-mortem analysis of a sodium-ion battery cell containing
a sodium manganese iron hexacyanoferrate cathode and a sodium
manganese hexacyanomanganate anode using SEM-EDX.
[0081] A post-mortem analysis was performed on one cell made with
29.5% succinonitrile and one cell made without additives. Both
cells had undergone constant-voltage float testing at 1.86 V with
daily 1C constant-current discharge to 1.19 V for 340 days. The
cells were brought to a voltage of 1.56 V and disassembled under
dry nitrogen atmosphere.
[0082] This post-mortem analysis included use of scanning electron
microscopy imaging (SEM) and energy-dispersive x-ray spectroscopy
(EDX) on TMCCC electrodes after operation in electrochemical cells.
The composition of these TMCCC electrodes included manganese
cations. Characterization using the SEM and EDX techniques provide
evidence that manganese oxide precipitates had formed on a TMCCC
cathode that was operated in an electrolyte that did not contain
dinitrile additives. In another cell, which was made using the
identical design except for the electrolyte, which contained a
succinonitrile additive in a 70.54:29.46 mass ratio between
acetonitrile and succinonitrile (the dinitrile additive), no
manganese oxide precipitates were found with SEM-EDX. Thus, the
addition of the dinitrile electrolyte additive suppressed the
release of manganese cations from the TMCCC electrode and formation
of a manganese oxide impurity phase. This suppression is important
because the formation of that manganese oxide phase resulted in an
increase in the internal resistance of the cell and a decrease in
the cell's capacity and energy.
[0083] SEM images of the control cathode reveal regions with
brighter and darker contrast having otherwise similar surface
morphology (FIG. 10). EDX spectra were taken in regions with bright
and dark contrast, respectively. EDX found a difference in
elemental composition between the brighter and darker. An EDX
spectrum taken in a bright region (FIG. 11) shows nearly the same
composition as spectra of pristine cathode samples with relative
intensities of C, N, O, Na, Mn and Fe fluorescence lines reflecting
the composition of the cathode active material and additional
contributions from conductive carbon additive and binder to the C
fluorescence line. Sulfur and fluorine emission lines are also
present since some electrolyte salt remains within the electrodes
during sample preparation. A spectrum taken in a region that
appears darker in imaging is markedly different (FIG. 12); here,
the Fe fluorescence is strongly diminished and the intensities from
O and Mn are strongly enhanced. This indicates that in the darker
regions the cathode active material is covered with manganese oxide
precipitates.
[0084] In the SEM-EDX analysis of cathode samples from the cell
with 29.5% succinonitrile, no manganese oxide precipitates were
detected. This finding supports the hypothesis that dinitrile
additives such as succinonitrile suppress the release of manganese
cations from the TMCCC electrodes and the formation of metal oxide
precipitates.
Example 4
[0085] ATR-FTIR analysis of electrolyte extracted from a sodium-ion
battery cell containing a sodium manganese iron hexacyanoferrate
cathode and a sodium manganese hexacyanomanganate anode.
[0086] Electrolyte was extracted from each cell in Example 3 using
the following procedure: a 3 cm.times.2 cm section of each
electrode was enclosed in a centrifuge vial with an added amount of
0.1 mL acetonitrile. After allowing the added acetonitrile to soak
into the electrode, the vial was centrifuged at 6,500 rpm for 20
minutes. ATR-FTIR spectra of the thus obtained liquid extracts were
measured using a single-reflection diamond prism.
[0087] ATR-FTIR spectra of electrolyte extracted from the aged
cells with 0% and 29.5% succinonitrile are illustrated in FIG. 13.
All absorption bands in the pristine electrolyte can be assigned to
vibrational modes of acetonitrile and of the
bis(trifluoromethanesulfonyl)imide anion. Trace amounts of water
are also present, as indicated by broad absorption bands at
wavenumbers greater than 3400 cm-1 (FIG. 14).
[0088] The spectrum of the electrolyte extracted from the aged cell
in the control group shows additional bands characteristic of the
N--H stretch (3480 cm-1 and 3380 cm-1) (FIG. 13 and FIG. 14) and
C.dbd.O stretch modes (1680 cm-1) in acetamide (FIG. 13 and FIG.
15). In the spectrum of electrolyte extracted from the cell with
29.5% succinonitrile, the amide absorption bands are also present
but with strongly diminished intensity of approximately 30%
compared to the control sample. The C.dbd.O stretch mode appears at
slightly higher wavenumber (1690 cm-1), which could be explained by
the presence of succinonitrile.
[0089] The ATR-FTIR spectra reveal the presence of an acetamide
impurity in both cells, and that the concentration of acetamide is
strongly reduced in the presence of the succinonitrile additive. In
a cell containing electrolyte comprised of acetonitrile and
succinonitrile in a mass ratio of 70.54:29.46, characterization
using ATR-FTIR showed a concentration of acetamide three times
lower than in other cells containing an electrolyte containing
acetonitrile and no succinonitrile. All cells in this example were
otherwise identical, except for the addition of a dinitrile
electrolyte additive. No acetamide was initially present in either
of these cells. Acetamide is a common reaction product of
acetonitrile with water, indicating that water impurities in the
cell reacted with the electrolyte solvent during cell operation.
This finding has important implications regarding the stability of
acetonitrile or other mononitrile electrolytes in electrochemical
energy storage devices. A common method of determining stability of
a new electrolyte relies on determining its electrochemical
stability window; this is typically done by measuring cyclic
voltammetry curves of the electrolyte in a three-electrode cell
with a chemically inert working electrode such as platinum metal or
glassy carbon. The stability window is then taken as the range of
electrochemical potentials within which the cyclic voltammetry plot
exhibits only small charge-discharge currents associated with the
electric double layer capacitance of the working electrode. Using
this method, mononitriles were reported to be among those solvents
that have the widest electrochemical stability windows. However,
this characterization fails to consider side reactions that do not
involve oxidation or reduction of nitriles. Our findings in Example
4 show that water, which is the most ubiquitous impurity in
anhydrous electrochemical devices, including Li-ion batteries and
EDLCs, is capable of decomposing acetonitrile in a reaction that is
independent of device voltage. Amides have significantly narrower
electrochemical stability windows than their parent nitriles.
Therefore, even when water is present only at trace levels, it can
set off a chain of parasitic reactions in which amide, or amide
oxidation and amide reduction products can continue to activate
nitrile solvent molecules. Dinitrile electrolyte additives break
this runaway reaction chain at an early stage by suppressing the
hydrolysis reaction. By preventing decomposition of the mononitrile
electrolyte solvent, the dinitrile additive extends the life of the
cell containing trace water impurities.
[0090] References: (The following references are discussed herein
and are hereby expressly incorporated their entireties by reference
thereto.) [0091] R1: U.S. Pat. No. 5,418,682. [0092] R2: U.S. Pat.
No. 9,666,906. [0093] R3: WO 2008/138132 A1; [0094] R4: Q. Zhang et
al., "Safety-Reinforced Succinonitrile-Based Electrolyte with
Interfacial Stability for High-Performance Lithium Batteries" Appl.
Mater. Interfaces 2017, 9 (35), 29820; [0095] R5: H. Duncan et al.,
"Electrolyte Formulations Based on Dinitrile Solvents for High
Voltage Li-Ion Batteries" J. Electrochem. Soc. 2013, 160 (6), A838;
[0096] R6: A. Abouimrane et al., "Investigation of Li salt doped
succinonitrile as potential solid electrolytes for lithium
batteries" J. Power Sources 2007, 174, 883; and [0097] R7: T. A.
Pham et al., "Solvation and Dynamics of Sodium and Potassium in
Ethylene Carbonate from Ab Initio Molecular Dynamics Simulations"
J. Phys. Chem. C 2017, 121 (40), 21913.
[0098] The systems and methods above have been described in general
terms as an aid to understanding details of preferred embodiments
of the present invention. In the description herein, numerous
specific details are provided, such as examples of components
and/or methods, to provide a thorough understanding of embodiments
of the present invention. Some features and benefits of the present
invention are realized in such modes and are not required in every
case. One skilled in the relevant art will recognize, however, that
an embodiment of the invention can be practiced without one or more
of the specific details, or with other apparatus, systems,
assemblies, methods, components, materials, parts, and/or the like.
In other instances, well-known structures, materials, or operations
are not specifically shown or described in detail to avoid
obscuring aspects of embodiments of the present invention.
[0099] Reference throughout this specification to "one embodiment",
"an embodiment", or "a specific embodiment" means that a particular
feature, structure, or characteristic described in connection with
the embodiment is included in at least one embodiment of the
present invention and not necessarily in all embodiments. Thus,
respective appearances of the phrases "in one embodiment", "in an
embodiment", or "in a specific embodiment" in various places
throughout this specification are not necessarily referring to the
same embodiment. Furthermore, the particular features, structures,
or characteristics of any specific embodiment of the present
invention may be combined in any suitable manner with one or more
other embodiments. It is to be understood that other variations and
modifications of the embodiments of the present invention described
and illustrated herein are possible in light of the teachings
herein and are to be considered as part of the spirit and scope of
the present invention.
[0100] It will also be appreciated that one or more of the elements
depicted in the drawings/figures can also be implemented in a more
separated or integrated manner, or even removed or rendered as
inoperable in certain cases, as is useful in accordance with a
particular application.
[0101] Additionally, any signal arrows in the drawings/Figures
should be considered only as exemplary, and not limiting, unless
otherwise specifically noted. Combinations of components or steps
will also be considered as being noted, where terminology is
foreseen as rendering the ability to separate or combine is
unclear.
[0102] The foregoing description of illustrated embodiments of the
present invention, including what is described in the Abstract, is
not intended to be exhaustive or to limit the invention to the
precise forms disclosed herein. While specific embodiments of, and
examples for, the invention are described herein for illustrative
purposes only, various equivalent modifications are possible within
the spirit and scope of the present invention, as those skilled in
the relevant art will recognize and appreciate. As indicated, these
modifications may be made to the present invention in light of the
foregoing description of illustrated embodiments of the present
invention and are to be included within the spirit and scope of the
present invention.
[0103] Thus, while the present invention has been described herein
with reference to particular embodiments thereof, a latitude of
modification, various changes and substitutions are intended in the
foregoing disclosures, and it will be appreciated that in some
instances some features of embodiments of the invention will be
employed without a corresponding use of other features without
departing from the scope and spirit of the invention as set forth.
Therefore, many modifications may be made to adapt a particular
situation or material to the essential scope and spirit of the
present invention. It is intended that the invention not be limited
to the particular terms used in following claims and/or to the
particular embodiment disclosed as the best mode contemplated for
carrying out this invention, but that the invention will include
any and all embodiments and equivalents falling within the scope of
the appended claims. Thus, the scope of the invention is to be
determined solely by the appended claims.
* * * * *