U.S. patent application number 17/705758 was filed with the patent office on 2022-07-14 for high voltage electrolyte additives.
The applicant listed for this patent is Wildcat Discovery Technologies, Inc.. Invention is credited to Gang Cheng, Jinhua Huang, Ye Zhu.
Application Number | 20220223913 17/705758 |
Document ID | / |
Family ID | 1000006239048 |
Filed Date | 2022-07-14 |
United States Patent
Application |
20220223913 |
Kind Code |
A1 |
Cheng; Gang ; et
al. |
July 14, 2022 |
HIGH VOLTAGE ELECTROLYTE ADDITIVES
Abstract
Described herein are additives for use in electrolytes that
provide a number of desirable characteristics when implemented
within batteries, such as high capacity retention during battery
cycling at high temperatures. In some embodiments, a high voltage
electrolyte includes a base electrolyte and one or more vinylsilane
or fluorosilane additives, which impart these desirable performance
characteristics.
Inventors: |
Cheng; Gang; (San Diego,
CA) ; Huang; Jinhua; (San Diego, CA) ; Zhu;
Ye; (San Diego, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Wildcat Discovery Technologies, Inc. |
San Diego |
CA |
US |
|
|
Family ID: |
1000006239048 |
Appl. No.: |
17/705758 |
Filed: |
March 28, 2022 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15991899 |
May 29, 2018 |
11322778 |
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17705758 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01M 2300/0025 20130101;
H01M 10/0525 20130101; H01M 10/0567 20130101; H01M 4/525 20130101;
H01M 10/4235 20130101 |
International
Class: |
H01M 10/0567 20060101
H01M010/0567; H01M 10/0525 20060101 H01M010/0525; H01M 10/42
20060101 H01M010/42; H01M 4/525 20060101 H01M004/525 |
Claims
1. A lithium ion battery, comprising: an anode; a cathode; and a
liquid electrolyte comprising a lithium salt; a solvent, and an
additive wherein the additive is selected from the group consisting
of tetravinylsilane, trivinylmethylsilane, trinvinylphenylsilane
and combination thereof.
2. The lithium ion battery of claim 1, wherein the cathode is an
oxide comprised of nickel and cobalt.
3. The lithium ion battery of claim 2, wherein the oxide is a
nickel manganese cobalt oxide or nickel cobalt aluminum oxide.
4. The lithium ion battery of 1, wherein the additive is present in
a concentration of 0.2% to 10% by weight of the liquid
electrolyte.
5. The lithium ion battery of claim 4, wherein the concentration is
0.2% to 2%.
6. The lithium ion battery of claim 5, wherein the concentration is
0.2% to 1%.
7. The lithium ion battery of claim 1, wherein the concentration is
1%.
8. The lithium ion battery of claim 4, wherein the additive is the
only additive present in the liquid electrolyte.
9. The lithium ion battery of claim 5, wherein the only additive
present in the liquid electrolyte.
10. The lithium ion battery of claim 6, wherein the additive is the
only additive present in the liquid electrolyte.
11. The lithium ion battery of claim 7, wherein the additive is the
only additive present in the liquid electrolyte.
12. The lithium ion battery of claim 1, wherein the additive is
tetravinylsilane.
13. The lithium ion battery of claim 1, wherein the additive is
trinvinylphenylsilane.
14. The lithium ion battery of claim 1, wherein the additive is
trivinylmethylsilane.
15-18. (canceled)
Description
BACKGROUND OF THE INVENTION
[0001] The present invention is in the field of battery technology
and, more particularly, in the area of additive compounds for use
with high-energy electrodes in electrochemical cells.
[0002] A liquid electrolyte serves to transport ions between
electrodes in a battery. Organic carbonate-based electrolytes are
most commonly used in lithium-ion ("Li-ion") batteries and, more
recently, efforts have been made to develop new classes of
electrolytes based on sulfones, silanes, and nitriles.
Unfortunately, these conventional electrolytes typically cannot be
operated at high voltages, since they are unstable above 4.3 V or
other high voltages. At high voltages, conventional electrolytes
can decompose, for example, by catalytic oxidation in the presence
of cathode materials, to produce undesirable products that affect
both the performance and safety of a battery. Conventional
electrolytes may also be degraded by reduction by the anodes when
the cells are charged to high voltages, such as 4.3 V or above.
[0003] As described in more detail below, solvents, salts, or
additives have been incorporated into the electrolyte to decompose
on the electrode to form a protective film called a solid
electrolyte interphase (SEI). Depending on the exact chemical
system, this film can be composed of organic or inorganic lithium
salts, organic molecules, oligomers, or polymers. Often, several
components of the electrolyte are involved in the formation of the
SEI (e.g., lithium salt, solvent, and additives). As a result,
depending on the rate of decomposition of the different components,
the SEI can be more or less homogenous.
[0004] In past research, organic compounds containing polymerizable
functional groups such as alkenes, furan, thiophene, and pyrrole
had been reported to form an SEI on the cathode of lithium ion
batteries. See, e.g., Y.-S. Lee et al., Journal of Power Sources
196 (2011) 6997-7001. These additives likely undergo polymerization
during cell charging to form passivation films on the electrodes.
SEIs are known to contain high molecular weight species. However,
in situ polymerization during the initial charge often cannot be
controlled in a precise enough manner to prevent non-uniform SEIs
comprised of polymer or oligomer mixtures with either heterogeneous
molecular weight, heterogeneous composition, or even undesired
adducts. The non-uniformity of the SEI often results in poor
mechanical and electrochemical stability, which is believed to be a
main cause of cycle life degradation in lithium ion batteries.
Thus, the improvement in cell performance using these materials is
limited.
[0005] Further, certain organic polymers have also been used as
solid electrolytes for lithium ion batteries due to the generally
low volatility and safety of polymeric molecules as compared to
smaller organic molecules, such as organic carbonates. However,
practical application of such systems has been limited due to poor
ionic conductivity.
[0006] For high-energy cathode materials, electrolyte stability
remains a challenge. Recently, the need for better performance and
higher capacity lithium ion secondary batteries used for power
sources is dramatically increasing. Lithium transition metal oxides
such as LiCoO.sub.2 ("LCO") and
LiNi.sub.0.33Mn.sub.0.33Co.sub.0.33O.sub.2 ("NMC") are
state-of-the-art high-energy cathode materials used in commercial
batteries. Yet only about 50% of the theoretical capacity of LCO or
NMC cathodes can be used with stable cycle life. To obtain the
higher capacity, batteries containing these high-energy materials
need to be operated at higher voltages, such as voltages up to
about 4.7V. However, above about 4.3V, conventional electrolytes
degrade and this leads to a significant deterioration of the cycle
life. Further, the decomposition of the electrolyte at higher
voltages can generate gas (such as CO.sub.2, O.sub.2, ethylene,
H.sub.2) and acidic products, both of which can damage a battery.
These effects are further enhanced in "high nickel" NMC
compositions such as LiNi.sub.0.6Mn.sub.0.2Co.sub.0.2O.sub.2 or
LiNi.sub.0.8Mn.sub.0.1Co.sub.0.1O.sub.2 or others, which can
provide higher capacities due to the electrochemistry of the
nickel.
[0007] Many of these same challenges occur when a battery is
operated at high temperature. That is, conventional electrolytes
can decompose by oxidation or may be degraded by reduction at high
temperature analogous to the way these mechanisms affect the
electrolytes at high voltage. Other parasitic reactions can also
occur at elevated temperature.
[0008] As disclosed herein, these challenges and others are
addressed in high energy lithium ion secondary batteries including
cathode active materials that are capable of operation at high
voltage.
BRIEF SUMMARY OF THE INVENTION
[0009] Certain embodiments of the invention include a lithium ion
battery having an anode, a cathode, and a liquid electrolyte. The
liquid electrolyte is formulated from a lithium salt, a solvent,
and an additive. The additive is represented by the formula
(M-R.sub.x).sub.y where x is an integer from 1 to 5, y is an
integer from 1 to 6, M comprises a metalloid moiety, and at least
one R.sub.x comprises a vinyl moiety or a fluorine moiety. In some
preferred embodiments, y=1. In certain embodiments, x=3 or x=4. In
certain embodiments, more than one R.sub.x includes a vinyl moiety.
In certain embodiments, at least three of R.sub.x include the same
vinyl moiety. In certain embodiments, at least four of R.sub.x
include the same vinyl moiety. In certain embodiments, each R.sub.x
includes the same vinyl moiety. In certain embodiments, one R.sub.x
includes a fluorine moiety. In certain embodiments, more than one
R.sub.x includes a fluorine moiety. In certain embodiments, more
than one R.sub.x includes the same fluorine moiety.
[0010] Certain preferred additives are represented by Formula
(A):
##STR00001##
[0011] Embodiments of the invention include liquid electrolytes
formulated from a mixture or solution that includes a lithium salt,
a solvent, and an additive as disclosed herein. Embodiments of the
invention include the liquid electrolyte as formulated and such
liquid electrolytes that have undergone multiple charge/discharge
cycles. Embodiments of the invention include the methods of making
the liquid electrolytes disclosed herein, in the formulations
disclosed herein, and the methods of making lithium ion batteries
having the liquid electrolytes disclosed herein as
constituents.
[0012] Other aspects and embodiments of the invention are also
contemplated. The foregoing summary and the following detailed
description are not meant to restrict the invention to any
particular embodiment but are merely meant to describe some
embodiments of the invention.
BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS
[0013] FIG. 1 illustrates a lithium ion battery implemented in
accordance with an embodiment of the invention.
[0014] FIG. 2 illustrates the operation of a lithium ion battery
and a graphical representation of an illustrative non-limiting
mechanism of action of an electrolyte including an additive
compound, according to an embodiment of the invention.
[0015] FIG. 3 illustrates electrochemical characterization of
capacity retention versus cycle number for batteries containing
liquid electrolytes having additives according to certain
embodiments of the invention.
[0016] FIG. 4 illustrates electrochemical characterization of
capacity retention versus cycle number for batteries containing
liquid electrolytes having additives according to certain
embodiments of the invention.
[0017] FIG. 5 illustrates electrochemical characterization of
capacity retention versus cycle number for batteries containing
liquid electrolytes having additives according to certain
embodiments of the invention.
[0018] FIG. 6 illustrates electrochemical characterization of
capacity retention versus cycle number for batteries containing
liquid electrolytes having additives according to certain
embodiments of the invention.
[0019] FIG. 7 illustrates electrochemical characterization of
capacity retention versus cycle number for batteries containing
liquid electrolytes having additives according to certain
embodiments of the invention.
[0020] FIG. 8 illustrates electrochemical characterization of
capacity retention versus cycle number for batteries containing
liquid electrolytes having additives according to certain
embodiments of the invention.
[0021] FIG. 9 illustrates electrochemical characterization of
capacity retention versus cycle number for batteries containing
liquid electrolytes having additives according to certain
embodiments of the invention.
[0022] FIG. 10 illustrates electrochemical characterization of
capacity retention versus cycle number for batteries containing
liquid electrolytes having additives according to certain
embodiments of the invention.
[0023] FIG. 11 illustrates electrochemical characterization of
capacity retention versus cycle number for batteries containing
liquid electrolytes having additives according to certain
embodiments of the invention.
[0024] FIG. 12 illustrates electrochemical characterization of
capacity retention versus cycle number for batteries containing
liquid electrolytes having additives according to certain
embodiments of the invention.
[0025] FIG. 13 illustrates electrochemical characterization of
capacity retention versus cycle number for batteries containing
liquid electrolytes having additives according to certain
embodiments of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0026] 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. Each term is
further explained and exemplified throughout the description,
figures, and examples. Any interpretation of the terms in this
description should take into account the full description, figures,
and examples presented herein.
[0027] The singular terms "a," "an," and "the" include the plural
unless the context clearly dictates otherwise. Thus, for example,
reference to an object can include multiple objects unless the
context clearly dictates otherwise.
[0028] 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.
[0029] The term "about" refers to the range of values approximately
near the given value in order to account for typical tolerance
levels, measurement precision, or other variability of the
embodiments described herein.
[0030] The term "capacity" refers to the amount (e.g., total or
maximum amount) of electrons or lithium ions a material is able to
hold (or discharge) per unit mass and can be expressed in units of
mAh/g. In certain aspects and embodiments, specific capacity can be
measured in a constant current discharge (or charge) analysis,
which includes discharge (or charge) at a defined rate over a
defined voltage range against a defined counter electrode. For
example, specific capacity can be measured upon discharge at a rate
of about 0.05 C (e.g., about 8.75 mA/g) from 4.45 V to 3.0 V versus
a Li/Li.sup.+ counter electrode. Other discharge rates and other
voltage ranges also can be used, such as a rate of about 0.1 C
(e.g., about 17.5 mA/g), or about 0.5 C (e.g., about 87.5 mA/g), or
about 1.0 C (e.g., about 175 mA/g).
[0031] A rate "C" refers to either (depending on context) the
discharge current as a fraction or multiple relative to a "1 C"
current value under which a battery (in a substantially fully
charged state) would substantially fully discharge in one hour, or
the charge current as a fraction or multiple relative to a "1 C"
current value under which the battery (in a substantially fully
discharged state) would substantially fully charge in one hour.
[0032] The term "coulombic efficiency" is sometimes abbreviated
herein as CE and refers the efficiency with which charge is
transferred in a given cycle.
[0033] The term "rated charge voltage" refers to an upper end of a
voltage range during operation of a battery, such as a maximum
voltage during charging, discharging, and/or cycling of the
battery. In some aspects and some embodiments, a rated charge
voltage refers to a maximum voltage upon charging a battery from a
substantially fully discharged state through its (maximum) specific
capacity at an initial cycle, such as the 1st cycle, the 2nd cycle,
or the 3rd cycle. In some aspects and some embodiments, a rated
charge voltage refers to a maximum voltage during operation of a
battery to substantially maintain one or more of its performance
characteristics, such as one or more of coulombic efficiency,
retention of specific capacity, retention of energy density, and
rate capability.
[0034] The term "rated cut-off voltage" refers to a lower end of a
voltage range during operation of a battery, such as a minimum
voltage during charging, discharging, and/or cycling of the
battery. In some aspects and some embodiments, a rated cut-off
voltage refers to a minimum voltage upon discharging a battery from
a substantially fully charged state through its (maximum) specific
capacity at an initial cycle, such as the 1st cycle, the 2nd cycle,
or the 3rd cycle, and, in such aspects and embodiments, a rated
cut-off voltage also can be referred to as a rated discharge
voltage. In some aspects and some embodiments, a rated cut-off
voltage refers to a minimum voltage during operation of a battery
to substantially maintain one or more of its performance
characteristics, such as one or more of coulombic efficiency,
retention of specific capacity, retention of energy density, and
rate capability.
[0035] The "maximum voltage" refers to the voltage at which both
the anode and the cathode are fully charged. In an electrochemical
cell, each electrode may have a given specific capacity and one of
the electrodes will be the limiting electrode such that one
electrode will be fully charged and the other will be as fully
charged as it can be for that specific pairing of electrodes. The
process of matching the specific capacities of the electrodes to
achieve the desired capacity of the electrochemical cell is
"capacity matching."
[0036] The term "NMC" refers generally to electrically active
materials containing LiNi.sub.xMn.sub.yCo.sub.zO.sub.w, where
0<x<1, 0<y<1, 0<z<1, x+y+z=1, and
0<w.ltoreq.2. NMC cathode materials include, but are not limited
to, electrically active materials containing
LiNi.sub.0.33Mn.sub.0.33Co.sub.0.33O.sub.2,
LiNi.sub.0.6Mn.sub.0.2Co.sub.0.2O.sub.2,
LiNi.sub.0.8Mn.sub.0.1Co.sub.0.1O.sub.2, and
LiNi.sub.0.5Mn.sub.0.3Co.sub.0.2O.sub.2.
[0037] The term "NCA" refers generally to cathode materials
containing nickel, cobalt, and aluminum, such as
LiNi.sub.0.8Co.sub.0.5Al.sub.0.5O.sub.2.
[0038] The term "moiety" refers generally to a distinct,
structurally identifiable, structurally isolated, or structurally
named portion of a molecule.
[0039] The term "vinyl" refers generally to a chemical group
represented by the general molecular formula RCH.dbd.CH.sub.2,
where R is preferably an organic moiety.
[0040] The term "allyl" refers generally to a chemical group
represented by the general molecular formula
RCH.sub.2CH.dbd.CH.sub.2, where R is preferably an organic
moiety.
[0041] The term "polymer" refers generally to a molecule whose
structure is composed of multiple repeating units whose Jus t
structure can be linear or branched.
[0042] The term "metalloid" refers generally to a chemical element
with properties that are in-between or a mixture of those of metals
and nonmetals, including boron (B), silicon (Si), germanium (Ge),
arsenic (As), antimony (Sb), tellurium (Te), carbon (C), aluminum
(Al), selenium (Se), polonium (Po), and astatine (At).
[0043] The term "post-transition metal" refers generally to a
chemical element selected from the group consisting of gallium
(Ga), indium (In), thallium (Th), tin (Sn), lead (Pb), bismuth
(Bi), aluminum (Al), germanium (Ge), antimony (Sb), and polonium
(Po).
[0044] To the extent certain battery characteristics can vary with
temperature, such characteristics are specified at room temperature
(about 30 degrees C.), unless the context clearly dictates
otherwise.
[0045] Ranges presented herein are inclusive of their endpoints.
Thus, for example, the range 1 to 3 includes the values 1 and 3 as
well as intermediate values.
[0046] FIG. 1 illustrates a lithium ion battery 100 implemented in
accordance with an embodiment of the invention. The battery 100
includes an anode 102, a cathode 106, and a separator 108 that is
disposed between the anode 102 and the cathode 106. In the
illustrated embodiment, the battery 100 also includes an
electrolyte 104, which is disposed within and between the anode 102
and the cathode 106 and remains stable during high voltage battery
cycling. The electrolyte 104 can be a liquid, a gel, or a solid
electrolyte.
[0047] The operation of the battery 100 is based upon reversible
intercalation and de-intercalation of lithium ions into and from
host materials of the anode 102 and the cathode 106. Other
implementations of the battery 100 are contemplated, such as those
based on conversion chemistry. Referring to FIG. 1, the voltage of
the battery 100 is based on redox potentials of the anode 102 and
the cathode 106, where lithium ions are accommodated or released at
a lower potential in the former and a higher potential in the
latter. To allow both a higher energy density and a higher voltage
platform to deliver that energy, the cathode 106 includes an active
cathode material for high voltage operations at or above 4.3V.
[0048] Examples of suitable high voltage cathode materials include
phosphates, fluorophosphates, fluorosulfates, fluorosilicates,
spinels, lithium-rich layered oxides, and composite layered oxides.
Further examples of suitable cathode materials include: spinel
structure lithium metal oxides, layered structure lithium metal
oxides, lithium-rich layered structured lithium metal oxides,
lithium metal silicates, lithium metal phosphates, metal fluorides,
metal oxides, sulfur, and metal sulfides. Examples of suitable
anode materials include conventional anode materials used in
lithium ion batteries, such as lithium, graphite
("Li.sub.xC.sub.6"), and other carbon, silicate, or oxide-based
anode materials.
[0049] FIG. 2 illustrates operation of a lithium ion battery and an
illustrative, non-limiting mechanism of action of an improved
electrolyte, according to an embodiment of the invention. Without
being bound by a particular theory not recited in the claims, the
inclusion of one or more stabilizing additive compounds in an
electrolyte solution can, upon operation of the battery (e.g.,
during conditioning thereof), passivate a high voltage cathode
material, thereby reducing or preventing reactions between bulk
electrolyte components and the cathode material that can degrade
battery performance.
[0050] Referring to FIG. 2, a liquid electrolyte 202 includes a
base electrolyte, and, during initial battery cycling, components
within the base electrolyte can assist in the in-situ formation of
a protective film (in the form of a solid electrolyte interface
("SEI") 206) on or next to an anode 204. The anode SEI 206 can
inhibit reductive decomposition of the high voltage electrolyte
202. Preferably, and without being bound by theory not recited in
the claims, for operation at voltages at or above 4.2 V, the liquid
electrolyte 202 can also include additives that can assist in the
in-situ formation of a protective film (in the form of a SEI 208 or
another derivative) on or next to a cathode 200. The cathode SEI
208 can inhibit oxidative decomposition of the high voltage
electrolyte 202 that can otherwise occur during high voltage
operations. As such, the cathode SEI 208 can inhibit oxidative
reactions in a counterpart manner to the inhibition of reductive
reactions by the anode SEI 206. In the illustrated embodiment, the
cathode SEI 208 can have a thickness in the sub-micron range, and
can include one or more chemical elements corresponding to, or
derived from, those present in one or more additives, such as
silicon or other heteroatom included in one or more additives.
Advantageously, one or more additives can preferentially passivate
the cathode 200 and can selectively contribute towards film
formation on the cathode 200, rather than the anode 204. Such
preferential or selective film formation on the cathode 200 can
impart stability against oxidative decomposition, with little or no
additional film formation on the anode 204 (beyond the anode SEI
206) that can otherwise degrade battery performance through
resistive losses. More generally, one or more additives can
decompose below a redox potential of the cathode material and above
a redox potential of SEI formation on the anode 204.
[0051] Without being bound by a particular theory not recited in
the claims, the formation of the cathode SEI 208 can occur through
one or more of the following mechanisms: (1) the additive
compound(s) can react to form the cathode SEI 208, which inhibits
further oxidative decomposition of electrolyte components; (2) the
additive compound(s) or its reaction product(s) form or improve the
quality of a passivation film on the cathode or anode; (3) the
additive compounds can form an intermediate product, such as a
complex with LiPF.sub.6 or a cathode material, which intermediate
product then forms the cathode SEI 208 that inhibits further
oxidative decomposition of electrolyte components; (4) the additive
compounds can form an intermediate product, such as a complex with
LiPF.sub.6, which then reacts during initial charging. The
resulting product can then further react during initial charging to
form the cathode SEI 208, which inhibits further oxidative
decomposition of electrolyte components; (5) the additive compounds
can stabilize the cathode material by preventing metal ion
dissolution.
[0052] Other mechanisms of action of the electrolyte 202 are
contemplated, according to an embodiment of the invention. For
example, and in place of, or in combination with, forming or
improving the quality of the cathode SEI 208, one or more additives
or a derivative thereof (e.g., their reaction product) can form or
improve the quality of the anode SEI 206, such as to reduce the
resistance for lithium ion diffusion through the anode SEI 206. As
another example, one or more additives or a derivative thereof
(e.g., their reaction product) can improve the stability of the
electrolyte 202 by chemically reacting or forming a complex with
other electrolyte components. As a further example, one or more
additives or a derivative thereof (e.g., their reaction product)
can scavenge decomposition products of other electrolyte components
or dissolved electrode materials in the electrolyte 202 by chemical
reaction or complex formation. Any one or more of the cathode SEI
208, the anode SEI 206, and the other reaction products or
complexes can be viewed as derivatives, which can include one or
more chemical elements corresponding to, or derived from, those
present in one or more additives, such as a heteroatom included in
the additives.
[0053] Liquid electrolytes according to some embodiments of the
invention can be formed by starting with a conventional, or base,
electrolyte and mixing in additives according the embodiments
disclosed herein. The resulting liquid electrolyte can have
properties particularly suited for operation at high voltage, high
temperature, or both. The base electrolyte can include one or more
solvents and one or more salts, such as lithium-containing salts in
the case of lithium ion batteries. Examples of suitable solvents
include non-aqueous electrolyte solvents for use in lithium ion
batteries, including carbonates, such as ethylene carbonate,
dimethyl carbonate, ethyl methyl carbonate, propylene carbonate,
methyl propyl carbonate, and diethyl carbonate; sulfones; silanes;
nitriles; esters; ethers; and combinations thereof. The base
electrolyte can also include additional small molecule
additives.
[0054] An amount of an additive also can be expressed in terms of a
ratio of the number of moles of the additive per unit surface area
of either, or both, electrode materials. For example, an amount of
a compound can be in the range of about 10.sup.-7 mol/m.sup.2 to
about 10.sup.-2 mol/m.sup.2, such as from about 10.sup.-7
mol/m.sup.2 to about 10.sup.-5 mol/m.sup.2, from about 10.sup.-5
mol/m.sup.2 to about 10-3 mol/m.sup.2, from about 10.sup.-6
mol/m.sup.2 to about 10.sup.-4 mol/m.sup.2, or from about 10-4
mol/m.sup.2 to about 10.sup.-2 mol/m.sup.2. As further described
below, a additive can be consumed or can react, decompose, or
undergo other modifications during initial battery cycling. As
such, an amount of a compound can refer to an initial amount of the
compound used during the formation of the liquid electrolyte
solutions, or can refer to an initial amount of the additive within
the electrolyte solution prior to battery cycling (or prior to any
significant amount of battery cycling).
[0055] Resulting performance characteristics of a battery can
depend upon the identity of a particular additive used to form the
liquid electrolyte solution, an amount of the additive used, and,
in the case of a combination of multiple additives, a relative
amount of each additive within the combination. Accordingly, the
resulting performance characteristics can be fine-tuned or
optimized by proper selection of the additive(s) and adjusting
amounts of the additive(s) in the electrolyte formulas.
[0056] Preparing the liquid electrolyte solution can be carried out
using a variety of techniques, such as by mixing the base
electrolyte and the additives, dispersing the additives within the
base electrolyte, dissolving the additives within the base
electrolyte, or otherwise placing these components in contact with
one another. The additives can be provided in a liquid form, a
powdered form (or another solid form), or a combination thereof.
The additives can be incorporated in the electrolyte solutions
prior to, during, or subsequent to battery assembly.
[0057] The electrolyte solutions described herein can be used for a
variety of batteries containing a high voltage cathode or a low
voltage cathode, and in batteries operated at high temperatures.
For example, the electrolyte solutions can be substituted in place
of, or used in conjunction with, conventional electrolytes for
lithium ion batteries for operations at or above 4.3 V. In
particular, these additives are useful for lithium ion batteries
containing NMC and NCA active materials.
[0058] Batteries having the liquid electrolyte solutions can be
conditioned by cycling prior to commercial sale or use in commerce.
Such conditioning can include, for example, providing a battery,
and cycling such battery through at least 1, at least 2, at least
3, at least 4, or at least 5 cycles, each cycle including charging
the battery and discharging the battery at a rate of 0.05 C (e.g.,
a current of 8.75 mA/g) between 4.45V and 3.0 V (or another voltage
range) versus a reference counter electrode, such as a graphite
anode. Charging and discharging can be carried out at a higher or
lower rate, such as at a rate of 0.1 C (e.g., a current of 17.5
mA/g), at a rate of 0.5 C (e.g., a current of 87.5 mA/g), or at a
rate of 1 C (e.g., a current of 175 mA/g). Typically a battery is
conditioned with 1 cycle by charging at 0.05 C rate to 4.45V
followed by applying constant voltage until the current reaches
0.02 C, and then discharging at 0.05 C rate to 3V.
[0059] The an amount of a particular additive can be expressed in
terms of a weight percent of the additive relative to a total
weight of the liquid electrolyte solution (or wt. %). For example,
an amount of an additive can be in the range of about 0.01 wt. % to
about 30 wt. %, such as from about 0.05 wt. % to about 30 wt. %,
from about 0.01 wt. % to about 20 wt. %, from about 0.2 wt. % to
about 15 wt. %, from about 0.2 wt. % to about 10 wt. %, from about
0.2 wt. % to about 5 wt. %, or from about 0.2 wt. % to about 1 wt.
%, and, in the case of a combination of multiple additives, a total
amount of the additive can be in the range of about 0.01 wt. % to
about 30 wt. %, such as from about 0.05 wt. % to about 30 wt. %,
from about 0.01 wt. % to about 20 wt. %, from about 0.2 wt. % to
about 15 wt. %, from about 0.2 wt. % to about 10 wt. %, from about
0.2 wt. % to about 5 wt. %, or from about 0.2 wt. % to about 1 wt.
%.
[0060] In certain embodiments of the invention, the additive is
present at an amount that is significantly lower than the amount of
electrolyte salt present in the electrolyte formulation. The amount
of additive can be expressed as a weight percent of the total
weight of the electrolyte formulation. In certain embodiments of
the invention, the concentration of additive in the electronic
formulation is less than or equal to the concentration at which the
additive would be at the saturation point in the electrolyte
solvent. In certain embodiments of the invention, the concentration
of additive in the electronic formulation is less than or equal to
about 10 weight percent, more preferably less than or equal to
about 9 weight percent, more preferably less than or equal to about
8 weight percent, more preferably less than or equal to about 7
weight percent, more preferably less than or equal to about 6
weight percent, more preferably less than or equal to about 5
weight percent, more preferably less than or equal to about 4
weight percent, more preferably less than or equal to about 3
weight percent, and still more preferably less than or equal to
about 2 weight percent.
[0061] In certain embodiments of the invention, the concentration
of each additive in the electronic formulation is equal to about
10.0 wt %, 9.9 wt. %, 9.8 wt. %, 9.7 wt. %, 9.6 wt. %, 9.5 wt. %,
9.4 wt. %, 9.3 wt. %, 9.2 wt. %, 9.1 wt. %, 9.0 wt. %, 8.9 wt. %,
8.8 wt. %, 8.7 wt. %, 8.6 wt. %, 8.5 wt. %, 8.4 wt. %, 8.3 wt. %,
8.2 wt. %, 8.1 wt. %, 8.0 wt. %, 7.9 wt. %, 7.8 wt. %, 7.7 wt. %,
7.6 wt. %, 7.5 wt. %, 7.4 wt. %, 7.3 wt. %, 7.2 wt. %, 7.1 wt. %,
7.0 wt. %, 6.9 wt. %, 6.8 wt. %, 6.7 wt. %, 6.6 wt. %, 6.5 wt. %,
6.4 wt. %, 6.3 wt. %, 6.2 wt. %, 6.1 wt. %, 6.0 wt. %, 5.9 wt. %,
5.8 wt. %, 5.7 wt. %, 5.6 wt. %, 5.5 wt. %, 5.4 wt. %, 5.3 wt. %,
5.2 wt. %, 5.1 wt. %, 5.0 wt. %, 4.9 wt. %, 4.8 wt. %, 4.7 wt. %,
4.6 wt. %, 4.5 wt. %, 4.4 wt. %, 4.3 wt. %, 4.2 wt. %, 4.1 wt. %,
4.0 wt. %, 3.9 wt. %, 3.8 wt. %, 3.7 wt. %, 3.6 wt. %, 3.5 wt. %,
3.4 wt. %, 3.3 wt. %, 3.2 wt. %, 3.1 wt. %, 3.0 wt. %, 2.9 wt. %,
2.8 wt. %, 2.7 wt. %, 2.6 wt. %, 2.5 wt. %, 2.4 wt. %, 2.3 wt. %,
2.2 wt. %, 2.1 wt. %, 2.0 wt. %, 1.9 wt. %, 1.8 wt. %, 1.7 wt. %,
1.6 wt. %, 1.5 wt. %, 1.4 wt. %, 1.3 wt. %, 1.2 wt. %, 1.1 wt. %,
1.0 wt. %, 0.9 wt. %, 0.8 wt. %, 0.7 wt. %, 0.6 wt. %, 0.5 wt. %,
0.4 wt. %, 0.3 wt. %, 0.2 wt. %, or 0.1 wt. %. In certain
embodiments of the invention, the concentration of additive in the
electrolyte formulation is in the range of about 2.0 wt. % to about
0.5 wt. %.
[0062] According to certain embodiments of the invention, a stable
metalloid or post-transitional metal core combined with a
polymerizable organic moiety is used as an additive in electrolyte
formulations. The metalloid or post-transition metal core is
relatively chemically inert to impart electrochemical and
temperature stability. The polymerizable organic moiety can form a
network, such as a cross-linked polymeric network, at or near the
electrodes or the separator. The network can be formed under
electrochemical activation occurring during the formation cycles of
a rechargeable lithium ion battery and/or during the operation
cycles of a rechargeable lithium ion battery. The network can form
at the surface of an electrode and/or within the pores of an
electrode. The network can interact chemically with other compounds
and reaction products within the lithium-ion battery to form a
stable SEI. The compounds and reaction products include those that
originate from the electrode(s) and those that originate from the
electrolyte. Further, the network can protect the electrode(s) from
potentially harmful compounds and/or reaction products that may be
present in the battery or may be produced through the
electrochemistry occurring the battery. Certain potentially
reaction products may occur more readily when the battery is
operated or stored at elevated temperature. The network can protect
the electrode(s) from these harmful compounds as well.
[0063] Silicon is a preferred element among the metalloid elements
suitable for use in the core of the additives according to certain
embodiments of the invention. Silicon is relatively chemically
inert and is relatively stable at high temperatures. Similarly, tin
is a preferred element among the post-transition metal elements
suitable for use in the core of the additives according to certain
embodiments of the invention. Tin is relatively chemically inert
and is relatively stable at high temperatures.
[0064] Vinyl moieties and allyl moieties are among the simplest of
polymerizable organic moieties that can be included in the
additives according to certain embodiments of the invention. Vinyl
moieties and allyl moieties are sufficiently reactive to form the
protective networks disclosed herein. Further, certain vinyl
moieties and allyl moieties can be relatively structurally stable
under the conditions present during electrochemical activation.
That is, certain vinyl moieties and allyl moieties can maintain
their structure such that they react in predictable ways from the
intended reactive location. Vinyl moieties may be particularly
preferred for this reason.
[0065] According to certain embodiments of the invention, the
additive can be represented by the general formula M-R where M is a
moiety that includes a metalloid or post-transition metal and R is
an organic group that contains a polymerizable organic moiety such
as vinyl or allyl. Preferably, the additive can be represented by
the general formula M-R.sub.x where x is an integer from 1 to 5.
That is, the additive has a metalloid or post-transition metal core
and multiple organic groups that contain a polymerizable organic
moiety such as vinyl or allyl. In some cases, the additive is a
vinylsilane compound. That is, M includes silicon and R is an
organic group that contains a vinyl moiety. More preferably, the
vinylsilane compound has multiple organic groups that contain a
vinyl moiety. That is, M includes silicon, R.sub.x is an organic
group that contains a vinyl moiety, and x is an integer greater
than 1. Even more preferably, the vinylsilane compound has at least
three organic groups that contain a vinyl moiety. That is, M
includes silicon, R.sub.x is an organic group that contains a vinyl
moiety, and x is at least 3. In certain preferred embodiments, M
includes silicon, R.sub.x is an organic group that contains a vinyl
moiety, and x is 4.
[0066] In all of these general formulas in which R.sub.x is
present, the organic group that contains a vinyl moiety can be the
identical organic group for each "R.sub.x" or it can be a different
organic group for each "R.sub.x". For these vinylsilanes, the
distinguishing feature is that each of the "R.sub.x" organic groups
contains a vinyl moiety.
[0067] Preferred embodiments of the invention include electrolyte
formulations for lithium ion batteries in which the electrolyte
formulation includes a vinysilane additive. The vinylsilane
additives are particularly useful in liquid electrolyte
formulations, but may be useful in other electrolyte
formulations.
[0068] The structure-activity relationship of certain embodiments
of the inventive additives was investigated to determine: 1) the
effect on battery performance of the number of vinyl moiety
substitutions on a particular silane structure; 2) the effect on
battery performance of replacing the vinyl substitutions with other
unsaturated moieties, such as allyl; and 3) the importance of a
silicon-containing central core in the additives. The results
disclosed herein demonstrate that the combination of a vinyl moiety
and a silicon core is essential to improving capacity retention as
a function of cycle number in lithium ion batteries.
[0069] Without being bound by any hypothesis, mechanism, or mode of
action not recited in the claims, the vinylsilanes disclosed herein
likely improve capacity retention as a function of cycle number by
participating in the solid electrolyte interphase (SEI) formation
on the cathode, anode, or both. Further, the vinylsilanes disclosed
herein likely improve capacity retention as a function of cycle
number by scavenging for acidic reactive species and/or protonic
reactive species, which decreases chain reactions of solvent and
SEI decomposition caused by those reactive species.
[0070] Certain properties are preferred in the M-R.sub.x additives
for use in electrochemical cells. For example, the additives
preferably are: (i) either chemically resistant to oxidation and/or
reduction under the cell conditions or, if not chemically resistant
to oxidation and/or reduction, then the additives should react to
form intermediates or products that form a stable SEI film on the
anode, cathode, or both; (ii) sufficiently soluble and/or miscible
in the liquid electrolyte solution at room temperature; and (iii)
make the liquid electrolyte solution viscosity during battery
operation not worse than without the additive.
[0071] The following examples and methods describe specific aspects
of some embodiments of the invention to illustrate and provide a
description for those of ordinary skill in the art. The examples
and methods should not be construed as limiting the invention, as
the examples and methods merely provide specific methodology useful
in understanding and practicing some embodiments of the
invention.
[0072] One example of an additive represented by represented by the
general formula M-R.sub.x, where x is an integer from 1 to 5, is
tetravinylsilane, shown below in Formula (A):
##STR00002##
[0073] Another example of an additive represented by the general
formula M-R.sub.x, where x is an integer from 1 to 5, is
tetraallylsilane, shown below in Formula (B):
##STR00003##
[0074] Another example of an additive represented by the general
formula M-R.sub.x, where x is an integer from 1 to 5, is
trivinylmethylsilane, shown below in Formula (C):
##STR00004##
[0075] Another example of an additive represented by the general
formula M-R.sub.x, where x is an integer from 1 to 5, is
tetravinyltin, shown below in Formula (D):
##STR00005##
[0076] Another example of an additive represented by the general
formula M-R.sub.x, where x is an integer from 1 to 5, is
trivinylphenylsilane, shown below in Formula (E):
##STR00006##
[0077] Another example of an additive represented by the general
formula M-R.sub.x, where x is an integer from 1 to 5, is
2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane, shown
below in Formula (F):
##STR00007##
[0078] Another example of an additive represented by the general
formula M-R.sub.x, where x is an integer from 1 to 5, is
1,3-dimethyl tetravinyldisiloxane, shown below in Formula (G):
##STR00008##
[0079] The additives according to Formula (F) and Formula (G)
demonstrate that multiple M-R.sub.x moieties may be present in a
single additive. In other words, according to certain embodiments
of the invention, additives can be represented by the formula
(M-R.sub.x).sub.y where x is an integer from 1 to 5 and y is an
integer from 1 to 6. The organic group that contains a vinyl moiety
can be the identical organic group for each "R.sub.x" or it can be
a different organic group for each "R.sub.x". For these
vinylsilanes, the distinguishing feature is that each of the
"R.sub.x" organic groups contains a vinyl moiety. In the additive
(F), for example, one R.sub.x is a vinyl moiety, another R.sub.x is
a methyl, and another R.sub.x is an oxygen. The fourth available
bonding site of the silicon core is bonded to an oxygen that is an
R.sub.x of the neighboring M-R.sub.x moiety. Thus, the formula
(M-R.sub.x).sub.y is generic to both additive (F) and additive (G)
and multiple other possible vinylsilanes with repeating M-R.sub.x
moieties.
[0080] In another embodiment of additives useful for operating high
voltage and/or high temperature is an additive represented by the
general formula M-R.sub.x where M is silicon, at least one R.sub.x
is an organic group that contains a fluorine moiety, and x is an
integer from 1 to 5. One example of such an additive is
1,2-bis(methyldifluorosilyl) ethane, shown below in Formula
(H):
##STR00009##
[0081] The organic group that contains a fluorine moiety can be the
identical organic group for each "R.sub.x" or it can be a different
organic group for each "R.sub.x". For these fluorosilanes, the
distinguishing feature is that each of the "R.sub.x" organic groups
contains a fluorine moiety. In the additive (H), for example, two
of R.sub.x are a fluorine moiety, another R.sub.x is a methyl, and
another R.sub.x is an alkyl. The alkyl is bonded to an alkyl that
is an R.sub.x of the neighboring M-R.sub.x moiety.
[0082] Methods
[0083] Battery Cell Assembly. Battery cells were formed in a high
purity Argon filled glove box (M-Braun, O.sub.2 and humidity
content<0.1 ppm). In the case of the cathode, a commercial
LiNi.sub.0.5Mn.sub.0.3Co.sub.0.2O.sub.2 (referred to herein as NMC
532) or LiNi.sub.0.8Co.sub.0.5Al.sub.0.5O.sub.2 (referred to herein
as NCA) cathode material was mixed with dry poly(vinylidene
fluoride), carbon black powder, and liquid 1-methyl-2-pyrrolidinone
to form a slurry. The resulting slurry was deposited on an aluminum
current collector and dried to form a composite cathode film. In
the case of the anode, a graphitic carbon was mixed with dry
poly(vinylidene fluoride), carbon black powder, and liquid
1-methyl-2-pyrrolidinone to form a slurry. The resulting slurry was
deposited on a copper current collector and dried to form a
composite anode film. Each battery cell included the composite
cathode film, a polypropylene separator, and composite anode film.
A conventional liquid electrolyte formed from 1M of LiPF6 in
ethylene carbonate and ethyl methyl carbonate (EC:EMC=1:2) by
volume was mixed with the desired weight percentage of an
embodiment of the inventive additive and added to the battery cell.
The battery cell was sealed and initially cycled at ambient
temperature using 0.1 C charge to upper cutoff voltage (up to 4.35
or 4.45 V for NMC532; up to 4.1V or 4.4V for NCA) followed by
constant voltage hold until the current dropped to 0.01 C and then
discharged to 3.0 V using 0.01 C constant current. The cycle was
repeated one more time prior to high temperature cycling.
[0084] High Temperature Testing. Test batteries were cycled up to
the desired voltage in an environment at a temperature of about 45
degrees Celsius using 0.5 C charge followed by constant voltage
hold until the current dropped to 0.025 C and then discharged to
3.0 V using 0.5 C constant current.
[0085] Table 1 summarizes certain data for the cycle life testing
of some embodiments of the additives disclosed herein as compared
to control and FIGS. 3 through 13 show the full cycle life
testing.
[0086] Results
TABLE-US-00001 TABLE 1 Summary of additive performance compared to
the control electrolyte 211th 1st Cycle Cycle 1st Capacity
Capacity, Cycle Retention, Cell Voltage and 30.degree. C. CE
45.degree. C. Additives Chemistry (mAh/g) (%) (%) None 4.35V 184.5
84.9 65.3 Control NMC532/Graphite 0.5 wt % A 4.35V 183.4 86.4 76.4
NMC532/Graphite 0.5 wt % B 4.35V 173.3 80.6 65.0 NMC532/Graphite
0.5 wt % C 4.35V 183.7 85.8 72.8 NMC532/Graphite 0.5 wt % D 4.35V
179.9 83.4 49.5 NMC532/Graphite None 4.45V 189.9 81.7 45.4 Control
NMC532/Graphite 0.5 wt % A 4.45V 195.0 86.5 70.7 NMC532/Graphite
2.0 wt % C 4.45V 192.4 8632 68.1 NMC532/Graphite 0.5 wt % E 4.45V
193.9 86.2 72.1 NMC532/Graphite 0.5 wt % F 4.45V 193.1 86.6 67.9
NMC532/Graphite 0.5 wt % G 4.45V 193.3 86.1 69.2 NMC532/Graphite
0.5 wt %H 4.45V 186.5 85.6 64.7 NMC532/Graphite None 4.1V 164.5
82.8 71.7 Control NCA/Graphite 0.5% wt % A 4.1V 161.1 83.6 76.7
NCA/Graphite None 4.4V 193.6 81.8 69.4 Control NCA/Graphite 0.5% wt
% A 4.4V 195.0 82.9 75.7 NCA/Graphite
[0087] FIG. 3 illustrates electrochemical characterization of
capacity retention versus cycle number for batteries containing
liquid electrolytes having additives according to certain
embodiments of the invention. In FIG. 3, the open circles represent
the data from the battery containing the control electrolyte, which
does not contain vinylsilane additives. The solid circles represent
the data from the battery containing a liquid electrolyte having
0.5 wt % of the additive according to Formula (A). The solid
triangles represent the data from the battery containing a liquid
electrolyte having 0.5 wt % of the additive according to Formula
(B). The crosses represent the data from the battery containing a
liquid electrolyte having 0.5 wt % of the additive according to
Formula (C). The charge/discharge cycling was conducted from 3V to
4.35V in an environment at 45 degrees Celsius. Each battery
included a NMC532 composite cathode and a graphite composite
anode.
[0088] FIG. 3 demonstrates performance differences related to
additive structural and chemical composition. For example, the
additive according to Formula (A) has four vinyl groups while the
additive according to Formula (B) has four allyl groups. The
capacity retention performance of the battery containing a liquid
electrolyte having 0.5 wt % of the additive according to Formula
(A) is significantly better than the capacity retention performance
of the battery containing the control. Surprisingly, when vinyl
groups were replaced by allyl groups (that is, the additive (A)
versus the additive (B)), the cycling performance of electrolyte
having additive (B) was significantly worse and showed little or no
benefit compared to the control electrolyte. These results indicate
that vinyl group may be essential to forming a stable SEI under
high voltage and high temperature conditions.
[0089] As another example of performance differences related to
additive structural and chemical composition, the additive (A),
which contains 4 vinyl moieties, demonstrated capacity retention
performance superior to that of the additive (C), which contains 3
vinyl moieties. Both of these additives demonstrated capacity
retention performance superior to that of additive (B) and control.
This data supports the hypothesis that multiple vinyl groups can
form a robust protective network on the electrode surface in high
voltage batteries undergoing cycling in a high temperature
environment.
[0090] FIG. 4 illustrates electrochemical characterization of
capacity retention versus cycle number for batteries containing
liquid electrolytes having additives according to certain
embodiments of the invention. In FIG. 4, the open circles represent
the data from the battery containing the control electrolyte, which
does not contain vinylsilane additives. The solid circles represent
the data from the battery containing a liquid electrolyte having
0.5 wt % of the additive according to Formula (A). The
charge/discharge cycling was conducted from 3V to 4.35V in an
environment at 45 degrees Celsius. Each battery included a NMC532
composite cathode and a graphite composite anode.
[0091] FIG. 5 illustrates electrochemical characterization of
capacity retention versus cycle number for batteries containing
liquid electrolytes having additives according to certain
embodiments of the invention. In FIG. 5, the open circles represent
the data from the battery containing the control electrolyte, which
does not contain vinylsilane additives. The solid circles represent
the data from the battery containing a liquid electrolyte having
0.5 wt % of the additive according to Formula (A) and the solid
stars represent the data from the battery containing a liquid
electrolyte having 0.5 wt % of the additive according to Formula
(D). The charge/discharge cycling was conducted from 3V to 4.35V in
an environment at 45 degrees Celsius. Each battery included a
NMC532 composite cathode and a graphite composite anode. FIG. 5
also demonstrates performance differences related to additive
structural and chemical composition. Formula (D) is identical to
Formula (A), except that the core of the molecule is the
post-transition metal tin rather than the metalloid silicon. There
is a substantial performance difference between the battery having
an electrolyte additive with a silicon core as compared to the
battery having an electrolyte additive with a tin core. This data
suggests that the silicon core is important in providing a robust
protective network on the electrode surface in high voltage
batteries undergoing cycling in a high temperature environment.
[0092] FIG. 6 illustrates electrochemical characterization of
capacity retention versus cycle number for batteries containing
liquid electrolytes having additives according to certain
embodiments of the invention. In FIG. 6, the open circles represent
the data from the battery containing the control electrolyte, which
does not contain vinylsilane additives. The solid circles represent
the data from the battery containing a liquid electrolyte having
0.5 wt % of the additive according to Formula (A). The
charge/discharge cycling was conducted from 3V to 4.45V in an
environment at 45 degrees Celsius. Each battery included a NMC532
composite cathode and a graphite composite anode. FIG. 6 tests the
same systems those in FIG. 4, and shows that the additive according
to Formula (A) performs in a similar fashion as compared to control
at the higher voltage (in this case 4.45V as compared to 4.35V in
FIG. 4). It is unexpected that an additive would be able to
maintain (or even improve) its superior performance over control at
an even higher voltage. It is further surprising that this superior
performance over control is maintained (or improved) in the
challenging high temperature environment.
[0093] FIG. 7 illustrates electrochemical characterization of
capacity retention versus cycle number for batteries containing
liquid electrolytes having additives according to certain
embodiments of the invention. In FIG. 7, the open circles represent
the data from the battery containing the control electrolyte, which
does not contain vinylsilane additives. The solid circles represent
the data from the battery containing a liquid electrolyte having 2
wt % of the additive according to Formula (C). The charge/discharge
cycling was conducted from 3V to 4.45V in an environment at 45
degrees Celsius. Each battery included a NMC532 composite cathode
and a graphite composite anode. Comparing FIG. 7 to FIG. 3, one can
see that a higher concentration of the additive C results in
improved performance compared to control under the higher voltage
conditions of FIG. 7. This result seems to confirm that increasing
the number of vinyl groups, either through the structure of the
additive or through the concentration of the additive, is
beneficial to the high voltage and high temperature performance of
lithium ion batteries.
[0094] FIG. 8 illustrates electrochemical characterization of
capacity retention versus cycle number for batteries containing
liquid electrolytes having additives according to certain
embodiments of the invention. In FIG. 8, the open circles represent
the data from the battery containing the control electrolyte, which
does not contain vinylsilane additives. The solid circles represent
the data from the battery containing a liquid electrolyte having
0.5 wt % of the additive according to Formula (E). The
charge/discharge cycling was conducted from 3V to 4.45V in an
environment at 45 degrees Celsius. Each battery included a NMC532
composite cathode and a graphite composite anode.
[0095] FIG. 9 illustrates electrochemical characterization of
capacity retention versus cycle number for batteries containing
liquid electrolytes having additives according to certain
embodiments of the invention. In FIG. 9, the open circles represent
the data from the battery containing the control electrolyte, which
does not contain vinylsilane additives. The solid circles represent
the data from the battery containing a liquid electrolyte having
0.5 wt % of the additive according to Formula (F). The
charge/discharge cycling was conducted from 3V to 4.45V in an
environment at 45 degrees Celsius. Each battery included a NMC532
composite cathode and a graphite composite anode.
[0096] FIG. 10 illustrates electrochemical characterization of
capacity retention versus cycle number for batteries containing
liquid electrolytes having additives according to certain
embodiments of the invention. In FIG. 10, the open circles
represent the data from the battery containing the control
electrolyte, which does not contain vinylsilane additives. The
solid circles represent the data from the battery containing a
liquid electrolyte having 0.5 wt % of the additive according to
Formula (G). The charge/discharge cycling was conducted from 3V to
4.45V in an environment at 45 degrees Celsius. Each battery
included a NMC532 composite cathode and a graphite composite
anode.
[0097] FIGS. 8, 9 and 10 demonstrate that multiple vinylsilanes are
capable of forming a robust protective network on the electrode
surface in high voltage batteries undergoing cycling in a high
temperature environment. The combination of the reactive vinyl
moieties around a metalloid core forms an effective protection
layer under electrochemical activation resulting in much improved
battery performance even at high voltage and high temperature.
[0098] FIG. 11 illustrates electrochemical characterization of
capacity retention versus cycle number for batteries containing
liquid electrolytes having additives according to certain
embodiments of the invention. In FIG. 11, the open circles
represent the data from the battery containing the control
electrolyte, which does not contain additives. The solid circles
represent the data from the battery containing a liquid electrolyte
having 0.5 wt % of the additive according to Formula (H). The
charge/discharge cycling was conducted from 3V to 4.45V in an
environment at 45 degrees Celsius. Each battery included a NMC532
composite cathode and a graphite composite anode.
[0099] The performance improvements of vinylsilanes are also
demonstrated in batteries having cathodes with NCA active
materials. FIG. 12 illustrates electrochemical characterization of
capacity retention versus cycle number for batteries containing
liquid electrolytes having additives according to certain
embodiments of the invention. In FIG. 12, the open circles
represent the data from the battery containing the control
electrolyte, which does not contain vinylsilane additives. The
solid circles represent the data from the battery containing a
liquid electrolyte having 0.5 wt % of the additive according to
Formula (A). The charge/discharge cycling was conducted from 3V to
4.1V in an environment at 45 degrees Celsius. Each battery included
a NCA composite cathode and a graphite composite anode. Similarly,
in FIG. 13, the open circles represent the data from the battery
containing the control electrolyte, which does not contain
vinylsilane additives. The solid circles represent the data from
the battery containing a liquid electrolyte having 0.5 wt % of the
additive according to Formula (A). The charge/discharge cycling was
conducted from 3V to 4.4V in an environment at 45 degrees Celsius.
Each battery included a NCA composite cathode and a graphite
composite anode.
[0100] The good performance of these electrolyte additives in
lithium ion battery cells having cathode active materials including
LiNi.sub.0.8Mn.sub.0.1Co.sub.0.1O.sub.2 or
LiNi.sub.0.8Co.sub.0.5Al.sub.0.5O.sub.2 is significant because high
nickel active materials (such as
LiNi.sub.0.8Mn.sub.0.1Co.sub.0.1O.sub.2 or
LiNi.sub.0.8Co.sub.0.5Al.sub.0.5O.sub.2) are desirable for many
battery applications. These materials are used to create
high-energy cathodes. Certain embodiments of the invention
disclosed herein demonstrate good performance in this challenging
high-energy environment. Prior to this disclosure, this type of
performance has not been demonstrated or predicted for the
additives disclosed herein.
[0101] The additives disclosed herein are particularly useful in
electrochemical cells in this the rated charge voltage and/or
maximum voltage of the cell is greater than 4.2V, greater than
4.3V, greater than 4.4V, greater than 4.5V, greater than 4.6V,
greater than 4.7V, greater than 4.8V, and/or greater than 4.9V.
These types of high voltage electrochemical cells include
electrodes that a designed to reliably operate through multiple
charge and discharge cycles at high voltages. The additives
disclosed herein enable such high voltage operation with
conventional electrolyte formulations, provided the additive is
also present in the liquid electrolyte. Further, the additives are
useful in such electrochemical cells when the cells are operated in
a high temperature environment, such as an environment at a
temperature of at least 45 degrees Celsius. Prior to this
disclosure, this type of performance has not been demonstrated for
the additives disclosed herein.
[0102] While the invention has been described with reference to the
specific embodiments thereof, it should be understood by those
skilled in the art that various changes may be made and equivalents
may be substituted without departing from the true spirit and scope
of the invention as defined by the appended claims. In addition,
many modifications may be made to adapt a particular situation,
material, composition, method, or process to the objective, spirit
and scope of the invention. All such modifications are intended to
be within the scope of the claims appended hereto. In particular,
while the methods disclosed herein have been described with
reference to particular operations performed in a particular order,
it will be understood that these operations may be combined,
sub-divided, or re-ordered to form an equivalent method without
departing from the teachings of the invention. Accordingly, unless
specifically indicated herein, the order and grouping of the
operations are not limitations of the invention.
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