U.S. patent application number 15/202406 was filed with the patent office on 2016-10-27 for cathode active material for overcharge protection in secondary lithium batteries.
The applicant listed for this patent is Johnson Controls Technology LLC. Invention is credited to Frederic C. Bonhomme, David R. Boone, Sung-Jin Cho, Peter B. Hallac, Alexandre Ndedi Ntepe, Qingfang Shi, Mohamed Taggougui.
Application Number | 20160315355 15/202406 |
Document ID | / |
Family ID | 47215777 |
Filed Date | 2016-10-27 |
United States Patent
Application |
20160315355 |
Kind Code |
A1 |
Hallac; Peter B. ; et
al. |
October 27, 2016 |
CATHODE ACTIVE MATERIAL FOR OVERCHARGE PROTECTION IN SECONDARY
LITHIUM BATTERIES
Abstract
A method of manufacturing a battery cathode includes forming a
mixture having a lithium metal oxide and an overcharge protection
additive, the overcharge protection additive having an operating
voltage higher than an operating voltage of the lithium metal
oxide. The lithium metal oxide is provided in an amount sufficient
to provide a desired operating capacity for a lithium ion battery
cell, and the overcharge protection additive has a higher operating
voltage than the lithium metal oxide such that the overcharge
protection additive can undergo reversible lithium removal during
overcharging of the lithium ion battery cell. The method also
includes contacting the mixture with a current collector.
Inventors: |
Hallac; Peter B.;
(Milwaukee, WI) ; Cho; Sung-Jin; (Whitefish Bay,
WI) ; Bonhomme; Frederic C.; (Thiensville, WI)
; Taggougui; Mohamed; (Bayside, WI) ; Boone; David
R.; (Waukesha, WI) ; Shi; Qingfang;
(Brookfield, WI) ; Ntepe; Alexandre Ndedi;
(Mequon, WI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Johnson Controls Technology LLC |
Wilmington |
DE |
US |
|
|
Family ID: |
47215777 |
Appl. No.: |
15/202406 |
Filed: |
July 5, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13664210 |
Oct 30, 2012 |
|
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15202406 |
|
|
|
|
61555261 |
Nov 3, 2011 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01M 2200/20 20130101;
H01M 10/44 20130101; H01M 2/345 20130101; H01M 10/4235 20130101;
H01M 4/364 20130101; H01M 4/628 20130101; H01M 10/0525 20130101;
H01M 4/5825 20130101; H02J 7/0029 20130101; H02J 7/00302 20200101;
H01M 4/525 20130101; H01M 4/131 20130101; H01M 4/0404 20130101;
H01M 4/485 20130101; Y02E 60/10 20130101; H01M 2004/028 20130101;
H01M 4/505 20130101; Y10T 29/49108 20150115 |
International
Class: |
H01M 10/42 20060101
H01M010/42; H01M 2/34 20060101 H01M002/34; H01M 4/505 20060101
H01M004/505; H01M 4/525 20060101 H01M004/525; H02J 7/00 20060101
H02J007/00; H01M 4/62 20060101 H01M004/62; H01M 4/36 20060101
H01M004/36; H01M 4/04 20060101 H01M004/04; H01M 10/44 20060101
H01M010/44; H01M 10/0525 20060101 H01M010/0525; H01M 4/131 20060101
H01M004/131 |
Claims
1. A method of employing an overcharge protection additive in a
lithium ion battery cell, the lithium ion battery cell having a
positive electrode comprising a mixture of a lithium metal oxide
and the overcharge protection additive, the overcharge protection
additive having an operating voltage higher than an operating
voltage of the lithium metal oxide, the method comprising:
operating the lithium ion battery cell at a voltage at which the
overcharge protection additive is inactive, and at an operating
capacity defined by the amount of the lithium metal oxide present
in the positive electrode, wherein a state of charge (SOC) of the
lithium ion battery cell is defined by the state of the lithium
metal oxide; and overcharging the lithium ion battery cell beyond
the operating voltage of the lithium metal oxide such that the
lithium ion battery cell is charged at least to 130% SOC and the
overcharge protection additive of the positive electrode becomes
active, the overcharging causing reversible lithium extraction from
the overcharge protection additive.
2. The method of claim 1, wherein during the overcharging the
overcharge protection additive accepts surplus current and prevents
sharp potential excursions in the potential of the positive
electrode resulting in a plateau-like voltage curve as the lithium
ion battery cell is charged beyond the capacity provided by the
lithium metal oxide.
3. The method of claim 1, comprising: releasing gas as a result of
oxidation of the overcharge protection additive during the
overcharging; and activating a current interrupt device (CID) in
the lithium ion battery cell using the released gas.
4. The method of claim 1, wherein the lithium metal oxide is
selected from the group consisting of lithium cobalt oxide, lithium
manganese oxide, lithium nickel manganese cobalt oxide, lithium
nickel cobalt aluminum oxide, lithium titanate, and mixtures
thereof.
5. The method of claim 4, wherein the overcharge protection
additive is selected from the group consisting of a Li-rich layered
oxide, a lithium oxide spinel, an olivine phosphate, and
combinations thereof.
6. The method of claim 1, wherein the overcharge protection
additive comprises a material of formula
xLi.sub.2M.sup.1O.sub.3(1-x)LiM.sup.2O.sub.2, wherein: M.sup.1 is
selected from the group consisting of Mn, Ti, and Zr; M.sup.2 is
selected from the group consisting of Mn, Ni, Co, Cr, and
combinations thereof; and x is greater than 0 and smaller than
1.
7. A method of manufacturing a lithium ion battery cell comprising:
producing a cathode active material by a process comprising mixing
a lithium metal oxide and an overcharge protection additive,
wherein the lithium metal oxide is in an amount sufficient to
provide a desired operating capacity for the lithium ion battery
cell, and wherein the overcharge protection additive is in a form
from which lithium ions can be reversibly extracted during
overcharging of the lithium ion battery cell; producing a positive
electrode using the cathode active material; producing an electrode
assembly using a negative electrode having an anode active
material, a separator, and the positive electrode; introducing an
electrolyte to the electrode assembly; and enclosing the electrode
assembly and the electrolyte with a housing.
8. The method of claim 7, comprising forming the lithium ion
battery cell up to a cutoff voltage, wherein the cutoff voltage is
lower than a voltage at which the overcharge protection additive
becomes active.
9. The method of claim 8, wherein the lithium ion battery cell is
formed up to the cutoff voltage such that lithium extraction during
charge occurs first from the lithium metal oxide, and then from the
overcharge protection additive in the event of an overcharge.
10. The method of claim 7, wherein the lithium metal oxide is
selected from the group consisting of lithium cobalt oxide, lithium
manganese oxide, lithium nickel manganese cobalt oxide, lithium
nickel cobalt aluminum oxide, and mixtures thereof, and the
overcharge protection additive comprises a lithium-rich layered
oxide or a high-voltage spinel.
11. The method of claim 7, wherein mixing the lithium metal oxide
and the overcharge protection additive comprises mixing the lithium
metal oxide and the overcharge protection additive with an
agitator.
12. The method of claim 7, comprising integrating a current
interrupt device (CID) in the lithium ion battery cell, wherein the
CID is configured to conduct current from terminals of the lithium
ion battery cell to the positive and negative electrodes of the
lithium ion battery cell until a pressure in the lithium ion
battery cell exceeds a threshold, the threshold being a pressure at
which the CID is configured to deform and break the electrical
connection between the terminals and the electrodes.
13. The method of claim 12, wherein the overcharge protection
additive is selected such that oxidation of the overcharge
protection additive results in gaseous products that facilitate
tripping of the CID before the lithium metal oxide or the
electrolyte undergo oxidative side-reactions.
14. The method of claim 13, wherein the lithium ion battery cell is
manufactured to exclude gassing additives in the electrolyte.
15. The method of claim 7, wherein the lithium ion battery cell is
manufactured to be substantially free of overcharge protection
electrolyte additives including polymeric film precursors, redox
shuttles, and gassing additives.
16. The method of claim 7, wherein introducing the electrolyte to
the electrode assembly and enclosing the electrode assembly and the
electrolyte with the housing comprise enclosing the electrode
assembly in a battery case and injecting the electrolyte into the
battery case.
17. The method of claim 7, wherein introducing the electrolyte to
the electrode assembly and enclosing the electrode assembly and the
electrolyte with the housing comprise enclosing the electrode
assembly in a pouch, injecting electrolyte into the pouch, and
sealing the pouch.
18. A method of manufacturing a battery cathode, comprising:
forming a mixture comprising a lithium metal oxide and an
overcharge protection additive, the lithium metal oxide of the
mixture being in an amount sufficient to provide a desired
operating capacity for a lithium ion battery cell, and the
overcharge protection additive of the mixture having a higher
operating voltage than the lithium metal oxide such that the
overcharge protection additive can undergo reversible lithium
removal during overcharging of the lithium ion battery cell; and
contacting the mixture with a current collector.
19. The method of claim 18, wherein the lithium metal oxide is
selected from the group consisting of lithium cobalt oxide, lithium
manganese oxide, lithium nickel manganese cobalt oxide, lithium
nickel cobalt aluminum oxide, lithium titanate, and mixtures
thereof.
20. The method of claim 18, wherein the overcharge protection
additive is selected from the group consisting of a Li-rich layered
oxide, a lithium oxide spinel, an olivine phosphate, and
combinations thereof.
21. The method of claim 18, wherein the overcharge protection
additive comprises a material of formula
xLi.sub.2M.sup.1O.sub.3(1-x)LiM.sup.2O.sub.2, wherein: M.sup.1 is
selected from the group consisting of Mn, Ti, and Zr; M.sup.2 is
selected from the group consisting of Mn, Ni, Co, Cr, and
combinations thereof; and x is greater than 0 and smaller than
1.
22. The method of claim 18, wherein the overcharge protection
additive comprises a material of formula
Li.sub.1+yMn.sub.2-yO.sub.4, wherein y is greater than 0 and at
most equal to 1/3.
23. The method of claim 18, wherein the overcharge protection
additive comprises a material of formula LiMPO.sub.4, wherein M is
selected from the group consisting of Mn, Co, Ni, Fe, Zn, Cu, Ti,
Sn, Zr, V, Al, and mixtures thereof.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 13/664,210 entitled "CATHODE ACTIVE MATERIAL
FOR OVERCHARGE PROTECTION IN SECONDARY LITHIUM BATTERIES," filed on
Oct. 30, 2012 and which claims the benefit of priority from U.S.
Provisional Patent Application No. 61/555,261 entitled "CATHODE
ACTIVE MATERIAL FOR OVERCHARGE PROTECTION IN SECONDARY LITHIUM
BATTERIES," filed on Nov. 3, 2011, both of which are hereby
incorporated by reference in their entireties for all purposes.
BACKGROUND
[0002] Thermal runaway during overcharge in the lithium ion
batteries (LIB) is a safety concern in the automotive industry.
Layered metal oxide cathode materials, in particular, impose higher
risks of thermal runaway due to their exothermic oxidative
reactions with the electrolyte. Battery chargers usually operate at
a fixed current or at a fixed power. Consider the case of a fixed
current applied to a lithium ion battery containing a lithium metal
oxide. The total current leaving each electrode is the sum of all
the electrochemical reactions occurring in that electrode. The
reactions that may be occurring at the positive electrode during
overcharge include: (1) extraction of lithium ions from the lithium
metal oxide, (2) side reactions which generate only inert gaseous
species, and (3) side reactions which generate gas and/or species
which may continue to react after interruption of the current. The
relative rates of the reactions depend on the difference between
the local electrochemical potential and the redox potential for the
particular reaction, which is a function of the local reactant and
product concentrations. For the case of a lithium metal oxide, once
all of the lithium has been extracted at the redox potential of the
oxide, no further oxidation of the active material is possible.
Continued application of a charging current will then drive up the
cell voltage to potentials at which the side reactions occur at
rates sufficient to meet the applied current. That high voltage may
lead to unwanted side reactions which generate species that
continue to react after the current is interrupted or which
generate gas at too rapid a rate, potentially leading to thermal
runaway.
[0003] Traditionally, electrolyte additives have being employed for
the overcharge protection of commercial-grade lithium ion
batteries. Examples of such additives are redox shuttles which
bypass the overcharge current via a redox reaction between the
cathode and the anode. Such compounds usually have redox potentials
of 0.2-0.4 V higher than the end-of-charge potential of the
positive electrode, or cathode. In another approach, polymer
precursors, for instance aromatic compounds such as cyclohexyl
benzene and biphenyl are electrochemically oxidized and polymerized
thereafter on an overcharged positive electrode to form a passive
film that prevents the electrolyte from further reacting with the
positive electrode.
SUMMARY
[0004] In a first aspect, there is provided an electrode active
material comprising a lithium metal oxide and an overcharge
protection additive having an operating voltage higher than the
operating voltage of the lithium metal oxide.
[0005] In a second aspect, there is provided a lithium ion battery
comprising a positive electrode comprising a positive electrode
active material, a negative electrode comprising a negative
electrode active material, and an electrolyte. The positive
electrode active material comprises a lithium metal oxide and an
overcharge protection additive having an operating voltage higher
than an operating voltage of the lithium metal oxide.
[0006] In a third aspect, there is provided a method of
manufacturing a battery cathode, comprising: forming a mixture
comprising a lithium metal oxide and an overcharge protection
additive having an operating voltage higher than an operating
voltage of the lithium metal oxide, and contacting the mixture with
a current collector.
BRIEF DESCRIPTION OF THE FIGURES
[0007] FIG. 1 includes voltage and temperature plots comparing the
overcharge properties of the first type of overcharge-protected
pouch cells of Example (1) to those of reference cells without
overcharge protection additives.
[0008] FIG. 2 includes voltage and temperature plots comparing the
overcharge properties of the second type of overcharge-protected
pouch cells of Example (1) to those of reference cells without
overcharge protection additives.
[0009] FIG. 3 includes capacity-potential plots comparing the
capacity of the coin cells of Example (2) to that of a reference
cell without overcharge protection additives.
[0010] FIG. 4 includes voltage and temperature plots comparing the
overcharge properties of the first type of overcharge-protected
prismatic cells of Example (3) to those of reference cells without
overcharge protection additives.
[0011] FIG. 5 includes voltage and temperature plots comparing the
overcharge properties of the second type of overcharge-protected
prismatic cells of Example (3) to those of reference cells without
overcharge protection additives.
[0012] FIG. 6 is a cross-sectional view of an example lithium ion
battery.
DEFINITIONS
[0013] As intended herein, the terms "a" and "an" include singular
as well as plural references unless the context clearly dictates
otherwise. For example, the term "a lithium metal oxide" can
include one or more such oxides.
[0014] As intended herein, the terms "approximately" and "about"
and similar terms are intended to have a broad meaning in harmony
with the common and accepted usage in the art to which the subject
matter of this disclosure pertains. It should be understood by
those of skill in the art who review this disclosure that these
terms are intended to allow a description of certain features
described and claimed without restricting the scope of these
features to precise numerical ranges provided.
[0015] Accordingly, these terms should be interpreted as indicating
that insubstantial or inconsequential modifications or alterations
of the subject matter described and claimed are considered to be
within the scope of the invention as recited in the appended
claims.
[0016] It should be noted that the term "example" as used herein to
describe various embodiments is intended to indicate that such
embodiments are possible examples, representations, and/or
illustrations of possible embodiments (and such term is not
intended to connote that such embodiments are necessarily
extraordinary or superlative examples).
DETAILED DESCRIPTION
[0017] The present invention is based on the discovery of novel
electrode active materials for electrochemical cell electrodes.
Such materials include a lithium metal oxide and an overcharge
protection additive having an operating voltage higher than the
lithium metal oxide. Also provided are methods, electrodes, cells
and systems employing such electrode materials that can promote
improved battery performance, safety and/or longevity. These
materials, methods, electrodes, cells, and systems are beneficial
in a variety of battery applications. For example, the materials
can serve as cathode active materials in the positive electrode of
lithium cells. When subjected to overcharge, such electrodes have
been found to exhibit delayed voltage and temperature increases as
compared to electrodes containing traditional materials. This
advantageous feature can protect a cell by delaying deleterious
overcharge-associated phenomena such as electrolyte oxidation and
thermal runaway.
[0018] Without being bound to any particular theory, it is believed
that, in the event of an overcharge, the protection additive
accepts surplus current and prevents sharp potential excursions in
electrode potential, leading instead to a gentler, plateau-like
voltage curve as the battery is charged beyond full capacity. In
some instances, oxygen gas may also be released during the
oxidation of the overcharge protection additive, and this evolution
of gas may facilitate the activation of a current interrupt device
(CID) in the cell. Some overcharge protection additives can also
undergo reversible lithium removal during overcharge, i.e. they can
intercalate and de-intercalate lithium ions and that in turn
contributes to the battery capacity and energy. By contrast,
traditional overcharge protection electrolyte additives do not
contribute to the capacity of the battery and, when activated by
overcharge events, tend to undergo irreversible reactions having
adverse effects on the battery performance.
[0019] In one aspect, there is provided an electrochemical cell
electrode with overcharge protection. The active material of the
electrode includes a lithium ion oxide from which energy storage or
release is obtained by oxidation or reduction accompanied by
lithium ion insertion or removal. An additive that possesses a
higher operating voltage than the lithium metal oxide is also
included in the active material. In some embodiments, the additive
will provide a change in the behavior of open voltage of the
electrode (as measured, for example, against a lithium metal)
electrode)Li.sup.+/Li.sup.0. As the electrode is charged above the
desired state of charge (SOC), the change in voltage is more
gradual than as found in an electrode without the additive. In
representative embodiments, the change in temperature associated
with overcharge is also more gradual than in an unprotected
electrode.
[0020] As a result, the additive performs the function of reducing
and/or delaying overcharge-induced temperature and/or voltage
increases as compared to those exhibited by unprotected electrodes.
Without being bound to any particular theory, it is believed that,
when a battery is overcharged, the oxidation of the protection
additive prevents the ignition or explosion of the battery that may
be induced by the overcharging. In addition, reversible ion removal
enables the additive to contribute to the cell capacity and energy
without the disadvantage of deteriorating battery performance that
is found in the case of traditional overcharge protection
additives.
[0021] The lithium metal oxide may be any of those finding use in
lithium ion batteries. Typical classes of lithium metal oxides
include those of formula LiMO.sub.2, where M represents one or more
metals, for instance transition metals such as Sc, Ti, V, Co, Mn,
Fe, Co, Ni, Cu, Zn, and Al. Lithium metal oxides commonly found in
battery electrodes include lithium cobalt oxides (e.g.
LiCoO.sub.2), lithium nickel oxides (e.g. LiNiO.sub.2), lithium
manganese oxides (e.g. LiMnO.sub.2), lithium nickel manganese
cobalt oxides (e.g. LiNi.sub.1/3Mn.sub.1/3Co.sub.1/3O.sub.2, also
known as NMC), and other oxides comprising other metals partially
substituting for Mn, Ni, and Co, such as
LiNi.sub.0.80Co.sub.0.15A.sub.0.05O.sub.2. Other representative
oxides finding use in battery electrodes include lithium nickel
cobalt aluminum oxides, lithium titanates, lithium iron oxides, and
lithium vanadium oxides.
[0022] The overcharge protection additive may be chosen from among
the many materials known to exhibit an operating voltage higher
than lithium metal oxides commonly found in battery electrodes.
Example overcharge protection additives include the class of
compounds known as metal oxide composite materials. Well-known
composite materials are those represented in two-component notation
as xLi.sub.2M.sup.1O.sub.3(1-x)LiM.sup.2O.sub.2, where M.sup.1
represents one or more of Mn, Ti, Zr, M.sup.2 represents one or
more of Mn, Ni, Co, and Cr, and x is greater than 0 and smaller
than 1. Exemplary among them are manganese oxide composite
materials, also known as "Li-rich layered oxides," which can be
represented as xLi.sub.2MnO.sub.3(1-x)LiM.sup.2O.sub.2(0<x<1)
and are believed to include a layered Li.sub.2MnO.sub.3 component
structurally integrated with a layered LiM.sup.1O.sub.2 component.
Also included is the class of Li-rich layered oxides which can be
represented as xLi2M.sup.1O.sub.3(1-x)LiM.sup.2.sub.2O.sub.4
(0<x<1) and are believed to feature a layered
Li.sub.2M.sup.1O.sub.3 component structurally integrated with a
spinel LiM.sup.2.sub.2O.sub.4 component, such as
xLi.sub.2MnO.sub.3(1-x)Li.sub.1+.delta.Mn.sub.2-.delta.O.sub.4
(0<.delta.<0.33). Both the above types of manganese oxide
composite materials undergo reversible lithium abstraction upon
oxidation, thereby contributing to battery capacity.
[0023] Spinels provide another exemplary class of overcharge
protection additives that can undergo reversible lithium
abstraction upon oxidation. Chief among them are high-voltage
spinels ("HVS"), for instance those of formula
LiM.sup.2.sub.2O.sub.4 where, as disclosed above, M.sup.2 may be
one or more of Mn, Ni, Co, and Cr, such as lithium manganese oxide
spinel of formula LiMn.sub.2O.sub.4. Other spinels have somewhat
more complex formulas, such as
Li.sub.1+x[M.sup.1.sub.yMn.sub.(2-y)]O.sub.4, where M.sup.1 is one
or more of Mn, Ni, and Mg. The additive may also be chosen from
among lithium metal phosphates. Commonly known phosphates include
those of formula LiM.sup.3PO.sub.4, wherein M.sup.3 where M.sup.3
represents one or more metals, for instance transition metals such
as Fe, Mn, Co, Ni, Sc, Ti, V, Co, Cu, Zn, and Al. Some such
compounds crystallize in the olivine, disordered olivine, or
modified olivine structure types. Representative olivine lithium
metal phosphates (olivine phosphates) include those of formula
Li.sub.xM.sup.3PO.sub.4, where x is greater or equal to zero and
smaller or equal to 1, and M is one or more of Fe, Mn, Co, and Ni.
Exemplary among such olivines are lithium iron phosphate
(LiFePO.sub.4), lithium manganese phosphate (LiMnPO.sub.4), lithium
cobalt phosphate (LiCoPO.sub.4) and lithium nickel phosphate
(LiNiPO.sub.4).
[0024] In representative embodiments, there is provided a positive
electrode active material that includes an operating amount of a
lithium metal oxide sufficient to provide a desired operating
capacity, and a selected amount of an overcharge protection
additive having an operating voltage higher than the lithium metal
oxide. The metal oxide and protection additive may be a physical
mixture or, for instance, form a solution together with or without
the other components of the electrode. There are no specific
restrictions on the amount of protection additive present, which
may vary on the basis of the operating capacity and amount of
overcharge protection desired. Example additive concentration
ranges, expressed as a fraction of the weight of the positive
electrode material, include from about 1 to about 20 weight %, from
about 5 to about 15 wt %, and about 7.5 to about 12.5 wt %. Other
example additive concentration ranges include from about 1 to about
30 wt %, from about 5 to about 20 wt %, and about 7.5 to about 15
wt %. In some instances, the positive electrode material may be
prepared by co-synthesizing or physically mixing an amount of the
lithium metal oxide with the additive in a proportion that is
consistent with the state of charge for which one is seeking
indication, or in order to provide the desired capacity and voltage
for overcharge protection. In one or more embodiments, physical
mixtures of these compounds are used for overcharge protection.
[0025] In at least some instances involving physical mixing of the
lithium metal oxide with an overcharge protection additive, the
additive is added in a form from which lithium can be extracted at
the desired voltage to function as overcharge protection agent. In
certain lithium ion cells, the cell is assembled in a discharged
state, and the lithium that is inserted into the positive electrode
during discharge is typically the lithium that was initially
extracted from the positive electrode during charge. In such an
instance, typically all of the lithium that is cycled during use of
the battery originates from the starting positive electrode. If the
overcharge protection additive in the positive electrode additive
is in the lithiated state in the original mixture, lithium
extraction during charge occurs first from the lithium metal oxide,
and then from the additive in the event of an overcharge.
[0026] As an example of an embodiment employing a protective
additive, a method is provided to prevent an electrochemical cell
from catastrophic failure in the event of accidental overcharge.
Often cells are made with a current-interrupt device (CID). The CID
is designed so that it conducts current from the cell terminal to
the cell electrodes during normal operation. If the pressure in the
cell exceeds a certain threshold, the CID deforms, breaking the
electrical connection and thus interrupting the current, thereby
protecting the cell against further overcharge, which could
generate dangerous amounts of gas.
[0027] The cell may generate gas during overcharge because the
electrolyte or electrode materials are oxidized at potentials
beyond the normal operating voltages to produce gaseous products.
It is these gaseous products that create the increased pressure
that trips the CID. However, in some situations, the species
produced during the period of overcharge may continue to react
after the current is interrupted. This continuing reaction may
further generate heat and gas, leading to thermal runaway, popping
of safety vents or even bursting of the cell cap or case. The risk
of cell venting is particularly acute if the rate of gas generation
is very rapid, in which case the pressure of the cell may rise
somewhat above the CID trip pressure in the time that it takes for
the CID to activate. Several methods of enabling safe tripping of a
CID are known in the art. For example, gassing additives such as
biphenyl may be mixed into the electrolyte to generate gas at a
potential lower than that at which undesirable reactions begin to
occur. However, these additives do not contribute to, and may
negatively impact, cell energy or power during normal operation of
the cell.
[0028] In certain embodiments herein, the overcharge protection
additive of the positive electrode material releases gas in the
event of an overcharge, thereby reaching the CID trip pressure
prior before unwanted overcharge-induced reactions take place. An
amount of overcharge protection additive is added to positive
electrodes in which the primary active material is a lithium metal
oxide. During normal operation, the additive will not be active. If
the positive electrode is charged above the redox potential of
additive, it will be oxidized. As a result, the cell potential will
grow more slowly than it would without the additive. The oxidation
of the additive may also generate gaseous products, inducing the
CID to trip before the lithium metal oxide or the electrolyte
undergoes oxidative side-reactions.
[0029] In one aspect, a positive electrode including an above
described positive electrode active material is provided. An
example method of producing such a positive electrode according
will now be described. First, a lithium metal oxide, an overcharge
protection additive, a conducting agent, a binder, and a solvent
are mixed to prepare a positive electrode active material
composition. The positive electrode active material composition can
be coated directly on an aluminum collector and dried to prepare a
cathode plate. Alternatively, the composition can be cast on a
separate support to form a cathode active material film, which film
is then peeled from the separate support and laminated on an
aluminum collector to prepare a positive electrode plate. One
commonly used conducting agent is carbon black. Examples binders
include vinylidene fluoride/hexafluoropropylene copolymers,
polyvinylidenefluoride (PVDF), polyacrylonitrile,
polymethylmethacrylate, polytetrafluoroethylene, and combinations
thereof. The binder may also be a styrene butadiene rubber-based
polymer. Example solvents include N-methylpyrrolidone (NMP),
acetone, water, and the like.
[0030] A lithium battery including an above described positive
electrode is also provided. A method of producing one such battery
will now be described. First, a positive electrode including an
above described cathode active material composition is prepared.
Then, a negative electrode active material, a conducting agent, a
binder, and a solvent are mixed to prepare a negative electrode
active material composition. The anode active material composition
can be coated directly on a copper collector to obtain an anode
plate. Alternatively, the negative electrode active material
composition can be cast on a separate support to form an anode
active material film, which film is then peeled from the separate
support and laminated on a copper collector to obtain a negative
electrode plate.
[0031] Non-limiting examples of suitable negative electrode active
materials include lithium metal, lithium alloys, and carbonaceous
materials (such as graphite). In the negative electrode active
material composition, the conducting agent, the binder, and the
solvent may be the same as used in the cathode. In some cases, a
plasticizer may be added to the cathode active material composition
and the anode active material composition to form pores in the
electrode plates.
[0032] The cathode and the anode can be separated by a separator.
The separator can be any separator that is commonly used in lithium
batteries. A suitable separator may have low resistance to ion
movement of the electrolyte and high electrolyte retaining
capability. Non-limiting examples of suitable separators include
glass fibers, polyester, teflon, polyethylene, polypropylene,
polytetrafluoroethylene (PTFE) and combinations thereof, each of
which can be a woven or non-woven fabric. Foldable separators
formed of polyethylene or polypropylene can be used in lithium ion
batteries. On the other hand, separators having high organic
electrolyte retaining capabilities can be used in lithium ion
polymer batteries. A method of preparing a separator will now be
described.
[0033] A polymer resin, a filler, and a solvent are mixed to
prepare a separator composition. The separator composition can be
coated directly on an electrode and dried to form a separator film.
Alternatively, the separator composition can be cast on a support
and dried to form a separator composition film, which film is then
peeled from the separate support and laminated on an electrode. The
polymer resin is not limited and can be any material used as a
binder for an electrode plate. Non-limiting examples of suitable
polymer resins include vinylidenefluoride/hexafluoropropylene
copolymers, polyvinylidenefluoride, polyacrylonitrile,
polymethylmethacrylate, and combinations thereof.
[0034] As shown in FIG. 6, an example lithium battery 3 includes an
electrode assembly 4 which includes a positive electrode 5,
negative electrode 6 and a separator 7 between the cathode 5 and
anode 6. The electrode assembly 4 is enclosed in a battery case 8,
which is sealed with a cap plate 11 and gasket 12. An organic
electrolyte is then injected into the battery to complete a lithium
ion battery. Alternatively, the battery assembly can be stacked to
form a bi-cell structure, and then impregnated with an organic
electrolyte. The obtained product is then placed in a pouch and
sealed, thus completing a lithium ion polymer battery.
[0035] The organic electrolyte used in these lithium batteries can
include a lithium salt and a mixed organic solvent including a high
permittivity solvent and a low boiling point solvent. The high
permittivity solvent can be any solvent used in the art.
Non-limiting examples of suitable high permittivity solvents
include cyclic carbonates (such as ethylene carbonate, propylene
carbonate, and butylene carbonate), and gammabutyrolactone. The low
boiling point solvent can be any solvent used in the art.
Non-limiting examples of suitable low boiling point solvents
include linear carbonates (such as dimethyl carbonate, ethylmethyl
carbonate, diethyl carbonate, and dipropyl carbonate),
dimethoxyethane, diethoxyethane, and fatty acid ester derivatives.
The lithium salt can be any lithium salt used in lithium ion
batteries. Non-limiting examples of suitable lithium salts include
LiClO.sub.4, LiCF.sub.3SO.sub.3, LiPF.sub.6, LiN(CF.sub.3SO.sub.2),
LiBF.sub.4, LiC(CF.sub.3SO.sub.2).sub.3,
LiN(C.sub.2F.sub.5SO.sub.2).sub.2 and combinations thereof. In the
organic electrolyte, the concentration of the lithium salt usually
ranges from about 0.5 to about 2 M.
[0036] As noted above, traditional overcharge protection
electrolyte additives do not contribute to the capacity of the
battery and are designed or tend to undergo irreversible reactions
having adverse effects on the battery performance. By contrast, the
inclusion in a cell of an overcharge protection additive capable of
reversible ion removal renders such electrolyte additives
superfluous while providing protection without sacrificing battery
capacity. As a result, in a further aspect, there are provided
electrochemical cells substantially free of overcharge protection
electrolyte additives such as polymeric film precursors, redox
shuttles, and gassing additives. By "substantially free" is meant
that a cell contains no overcharge-protecting electrolyte additives
at all or in amounts too small to afford meaningful protection
against overcharge. Example concentration ranges in such a
substantially free electrolyte include less than about 1 wt %, less
than 0.5% wt %, less than 0.1 wt %, and less than 0.01 wt % of the
protection additive(s). Overcharge protection is instead effected
by adding an amount of overcharge protection additive to a positive
electrode in which the primary active material is a lithium metal
oxide. In some embodiments, the additive can also undergo
reversible lithium removal during overcharge. In addition, an
additive that produces oxygen when oxidized may be chosen.
[0037] It is important to note that the construction and
arrangement of electrodes and electrochemical cells as shown in the
examples above is illustrative only. Although only a few
embodiments have been described in detail in this disclosure, those
skilled in the art who review this disclosure will readily
appreciate that many modifications are possible (e.g., variations
in sizes, dimensions, structures, shapes and proportions of the
various elements, values of parameters, mounting arrangements, use
of materials, colors, orientations, etc.) without materially
departing from the novel teachings and advantages of the subject
matter described herein. For example, elements shown as integrally
formed may be constructed of multiple parts or elements, the
position of elements may be reversed or otherwise varied, and the
nature or number of discrete elements or positions may be altered
or varied. The order or sequence of any process or method steps may
be varied or re-sequenced according to alternative embodiments.
Other substitutions, modifications, changes and omissions may also
be made in the design, operating conditions and arrangement of the
various exemplary embodiments without departing from the scope of
the present invention.
EXAMPLES
Example (1)
NMC Pouch Cells with Li-Rich Layered Oxide or High-Voltage Spinel
as Overcharge Protection Additives
[0038] In order to measure beneficial effects imparted by
overcharge protection additives, reference pouch cells having a
capacity of 1.25 Ah were first built, as follows. A reference
cathode active material composition was formed containing 95 wt %
NMC, 3 wt % conductive carbon and 2 wt % of PVDF binder and cast as
an NMP slurry on aluminum foil, followed by drying and calendaring.
The foil coated with the dried mixture was then folded and pressed
to obtain the desired electrode density and thickness. The
resulting electrode was slitted and stacked with a cell separator
and a lithium negative electrode, to obtain a pouch cell that was
ultrasonically welded, filled with an electrolyte containing NMP
and LiPF6 and vacuum-sealed.
[0039] A first type of Li-rich layered oxide overcharge-protected
pouch cells were then built with the same ingredients as the
reference pouch cells, with the exception of the NMC which was
substituted with a mixture including 90 wt % NMC and 10 wt % of the
Li-rich layered oxide
xLi.sub.2MnO.sub.3(1-x)LiNi.sub.1/3Mn.sub.1/3CO.sub.1/3O.sub.2
(0<x<1) as overcharge protection additive. A second type of
overcharge-protected pouch cells were also made where the NMC was
substituted with a mixture including 90 wt % NMC and 10 wt % of a
high-voltage spinel of formula LiMn.sub.1.5Ni.sub.0.5O.sub.4 as
overcharge protection additive.
[0040] Overcharge-protected cells of the first type were
overcharged up to 5.4-5.5 Volts (as measured against
Li.sup.+/Li.sup.0)and their temperature and voltage in the course
of charging were measured and plotted, as illustrated in FIG. 1.
The protected cells (High Voltage Cathode 1-1 and 1-2) showed a
delay in the onset of overcharge- induced voltage increases as
compared to the reference cells. This improvement was most
prominent when the cells were charged beyond 150% SOC. Whereas the
reference cells (Reference Cathode) exhibited a rapid surge in
potential, the overcharge-protected cells showed a slower increase
until a charge of about 175% SOC was reached. The
overcharge-protected cells also exhibited a delay in the onset of
overcharge-induced temperature increases. Overcharge-protected
cells of the second type (High Voltage Cathode 2-1 and 2-2) were
also compared to the reference cells, as illustrated in FIG. 2.
Here, too, a delay in the insurgence of overcharged-induced voltage
and temperature increases was found.
Example (2)
Coin Cells with Li-Rich Layered Oxide
[0041] A reference coin cell was built as follows. A cathode active
material composition was formed containing 94 wt % NMC, 3 wt %
conductive carbon, and 3 wt % PVDF binder, which were blended and
mixed in NMP, to form a slurry. The slurry was cast on an aluminum
substrate and the NMP was removed under vacuum. Discs having a
diameter of 0.5 in were then punched and reference coin cells made
using lithium as counter electrode. Coin cells with overcharge
protection were then made with the same ingredients as the
reference coin cell, the only difference being in the cathode
active material composition containing 84 wt % NMC and 10 wt % of
the Li-rich layered oxide
xLi.sub.2MnO.sub.3(1-x)LiMnO.sub.2(0<x<1) as overcharge
protection additive.
[0042] Coin cells of both types were formed up to the normal cutoff
voltage (4.3 V) and discharged to 2.5 V. The cells were then
overcharged to 5 V, as illustrated in FIG. 3. Cells with the
overcharge protection additive ("10% Li Excess") exhibited a slower
voltage increase rate that was indicative of lithium extraction.
Such lithium extraction could also be inferred from the higher
specific capacity (mAh/g) of the cells with the additive, as
calculated on the basis of the overall amount of electrode active
material in a cell (NMC+additive).
Example (3)
Prismatic Cells
[0043] The applicability of the overcharge-protected materials to
large batteries suited to automotive applications was tested, as
follows. The reference cathode active material composition of
Example (1) was included in the cathode of prismatic reference
cells having a capacity of 32 Ah. Then, a first type of Li-rich
layered oxide overcharge-protected prismatic cells were built with
the cathode active material substituting the NMC of the reference
cells with the mixture including 90 wt % NMC and 10 wt % of the
Li-rich layered oxide
xLi.sub.2MnO.sub.3(1-x)LiNi.sub.1/3Mn.sub.1/3Co.sub.1/3O.sub.2
(0<x<1) as overcharge protection additive. A second type of
overcharge-protected prismatic cells were also made where the NMC
was substituted with a mixture including 90 wt % NMC and 10 wt % of
the high-voltage spinel of formula LiMn.sub.1.5Ni.sub.0.5O.sub.4 as
overcharge protection additive.
[0044] Overcharge-protected prismatic cells of the first type were
overcharged up to 5.1-5.2 Volts (as measured against
Li.sup.+/Li.sup.0) and their temperature and voltage in the course
of charging were measured and plotted, as illustrated in FIG. 4.
Similarly to what was found in Example (1), the protected cells
(High Voltage Cathode 1-1 and 1-2) showed a delay in the onset of
overcharge-induced voltage increases as compared to the reference
cells. This improvement became apparent when the cells were
overcharged at 130% SOC and higher. Gentler, slower
overcharge-induced temperature increases were also observed, as
seen in the temperature plots at 180% SOC and higher.
Overcharge-protected prismatic cells of the second type were also
compared to the reference cell, as illustrated in FIG. 5. Here,
too, a delay in the insurgence of overcharged-induced voltage and
temperature increases was observed in the protected cells (High
Voltage Cathode 2-1 and 2-2).
* * * * *