.
`
`United States Patent
`Guyomard etal.
`
`115)
`
`US005192629A
`(11) Patent Number:
`[45] Date of Patent:
`
`5,192,629
`Mar. 9, 1993
`
`[54] HIGH-VOLTAGE-STABLE ELECTROLYTES
`FOR Lh +.©MN204/CARBON SECONDARY
`BATTERIES
`
`4,904,552 2/1990 Furukawaetal. ............0100 429/197
`5,079,109
`1/1992 Takami etal. ......
`ww 429/197
`
`5,110,696 5/1992 Shokoohi etal. ...
`se 429/218
`
`[75]
`
`Inventors: Dominique Guyomard, Middletown;
`.
`Jean-Marie Tarascon, Martinsville,
`both of N.J,
`
`[73]
`
`Assignee:
`
`Bell Communications Research, Inc.,
`Livingston, N.J.
`
`(21)
`
`[22]
`
`[51]
`[52]
`[58]
`
`[56]
`
`Appl. No.: 871,855
`
`Apr. 21, 1992
`Filed:
`Unt, C15 ccecccccscssseenasesssscseenecsscrenes HOIM 10/40
`WLS. CD. ceesccceetecsnsesetseeseenesess 429/197; 429/224
`Field of Search .....
`«. 429/197, 194, 199, 196,
`429/218, 224
`
`
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`FOREIGN PATENT DOCUMENTS
`2022191
`1/1991 Canada .
`
`Primary Examiner—Anthony Skapars
`Attorney, Agent, or Firm—Leonard C. Suchyta; Lionel
`N. White
`
`ABSTRACT
`[57]
`An electrolyte resistant to oxidation normally resulting
`from high voltage charging of a secondary battery com-
`prising a Lij.,Mn2O, intercalation positive electrode
`comprises a 0.5M to 2M solution of LiPF¢ dissolved in
`a mixture of non-aqeuous dimethylcarbonate (DMC)
`and ethylene carbonate (EC) solvents wherein said
`solvents are present in a weight percent ratio range
`from about 95 DMC:5 EC to 20 DMC:80 EC.
`
`4,419,423 12/1983 Leger .....sescscsessrecesseseress 429/199 X
`4,874,680 10/1989 Koshiba et al.
`.......sccscssser 429/197
`
`19 Claims, 4 Drawing Sheets
`
`0.10
`
`0.04
`
`0.02
`
`
`
`Current(mA)
`
`3.8
`
`4.0
`
`4.2
`
`4.4
`
`4.6
`
`4.8
`
`5.0
`
`Voltage (V)
`
`APPLE-1016
`
`APPLE-1016
`
`1
`
`

`

`U.S. Patent
`
`Mar. 9, 1993
`
`Sheet 1 of 4
`
`5,192,629
`
`
`
`Voltage(V)
`
`46485.0
`
`4.4
`
`av
`
`t
`
`°+
`
`oO
`°— &)
`©
`
`FIG.1
`
`©
`=
`©
`
`co
`oO
`©
`
`co
`Oo
`©
`
`w+
`Oo
`©
`
`A
`Oo
`©
`
`(yuu) juEUIND
`
`2
`
`

`

`U.S. Patent
`
`Mar. 9, 1993
`
`Sheet 2 of 4
`
`5,192,629
`
`(V)
`
`Voltage
`
`©
`
`Oo
`
`©
`
`©
`
`co
`
`©
`
`wt
`
`©
`
`A
`
`©
`
`(yw) jueuND
`
`FIG.2
`
`3
`
`

`

`U.S. Patent
`
`Mar. 9, 1993
`
`Sheet 3 of 4
`
`5,192,629
`
`(V)
`
`Voltage
`
`Oo
`™
`©
`
`©
`o
`©
`
`©
`°
`©
`
`wv
`©
`©
`
`WN
`°
`©
`
`(Wu) jueuND
`
`FIG.3
`
`4
`
`

`

`U.S. Patent
`
`Mar. 9, 1993
`
`Sheet 4 of 4
`
`5,192,629
`
`(V)
`
`Voltage
`
`(\Wuu) JUBLIND
`
`FIG.4
`
`5
`
`

`

`1
`
`5,192,629
`
`HIGH-VOLTAGE-STABLE ELECTROLYTES FOR
`LI) 4..©MN204/CARBON SECONDARY BATTERIES
`
`BACKGROUND OF THE INVENTION
`This invention relates to non-aqueous electrolyte
`compositions for secondary (rechargeable) lithium bat-
`tery cells and, more particularly, to electrolyte compo-
`sitions that are capable of resisting decomposition nor-
`mally resulting from oxidation which occurs in Lii+x-
`Mn204/carbon cells during recharging under condi-
`tions of greater than about 4.5 V or 55° C.
`The advantages generally provided by rechargeable
`lithium batteries are often significantly overshadowed
`by dangers of the reactivity of lithium in cells which
`comprise lithium metal as the negative electrode. A
`more advanced and inherently safer approach to re-
`chargeable lithium batteries is to replace lithium metal
`with a material capable of reversibly intercalating lith-
`ium ions, thereby providing the so-called “rocking-
`chair”battery in which lithium ions “rock” between the
`intercalation electrodes during the charging/recharging
`cycles. Such a Li metal-free “rocking-chair” battery
`may thus be viewed as comprising two lithium-ion-
`absorbing electrode “sponges” separated by a lithium-
`ion conducting electrolyte usually comprising a Lit
`salt dissolved in a non-aqueous solvent or mixture of
`such solvents. Numerous such salts and solvents are
`knownin the art, as evidenced in Canadian Patent Pub-
`lication No. 2,022,191, dated Jan. 30, 1991.
`.
`The output voltage of a rechargeablelithium battery
`cell of this type is determined by the difference between
`the electrochemical potential of Li within the two inter-
`calation electrodes ofthe cell. Therefore, in an effective
`cell the positive and negative electrode materials should
`be able to intercalate lithium at high and low voltages,
`respectively. Among the alternative materials that can
`effectively replace lithium metal as the negative elec-
`trode, carbon provides the best compromise between
`large specific capacity and good reversible cycling be-
`havior. Such use of carbon, however, presents some
`detractions, such as loss of average output voltage and
`energy density, as compared to lithium metal, since the
`voltage of a Li,C¢ negative electrode is always greater
`than that of a pure lithium negative electrode.
`To compensatefor the loss of voltage associated with
`the negative electrode, a strongly oxidizing intercala-
`tion material is preferably used as the positive electrode.
`Such an electrode material is the spinel phase Li: +x.
`Mn204, usually combined with a small amountof car-
`bon black to improve electrical conductivity and pro-
`vide the practical composite electrode, that can revers-
`ibly intercalate lithium at a voltage of 4.1 V vs. Li. Use
`of such a strongly oxidizing intercalation material as
`positive electrode, however, introduces a further con-
`cern, namely,
`the risk of electrolyte decomposition
`from oxidation at the higher operating voltages,
`ice.
`greater than about 4 V.For instance, since the voltage
`of the Li14x,Mn204/Li couple is about 4.1 V, one
`should charge the cell up to a voltage of about 4.5 V in
`order to take full advantage of this redox system. As a
`result, the electrolyte in such a cell must be stable over
`a voltage window extending above 4.5 V to about 5.0 V.
`Also, when used in the noted “rocking chair”cells, the
`electrolyte compositions mustbe stable down to about0
`V with respect to a composite carbon negative elec-
`
`2
`trode, e.g., petroleum coke combined with about 1-5%
`of each of carbon black (Super-S) and an inert binder.
`Presently-used intercalation electrolytes, e.g., a 1M
`solution of LiCiO, in a 50:50 mixture of ethylene car-
`bonate (EC) and diethoxyethane (DEE) such as de-
`scribed in U.S. Pat. No. 5,110,696, when employed in a
`Lij4xMn204 /C cell, will begin to oxidize at about 4.5
`V at room temperature and as low as about 4.3 V at
`temperatures in the range of 55° C. Thus, to operate
`such a cell in the higher temperature ambient, one must
`reduce the charging cut-off voltage to a level below
`about 4.3 V in order to avoid electrolyte oxidation.
`Because of this lower cut-off voltage,
`the available
`capacity of the cell at about 55° C.is only 75% of that
`at room temperature.
`When cells comprising these previously-available
`electrolytes are cycled to a voltage evenslightly greater
`than 4.3 V, electrolyte oxidation occurs. Although
`small, this oxidation can jeopardize the capacity, cycle
`life, and safety of the battery cell. For example, the
`electrode oxidation reaction consumes part of the
`charging current which is then not recovered when
`dischargingthe cell, resulting in a continuous loss in the
`cell capacity over subsequentcycles. Further,if during
`each charge a small part ofthe electrolyte is consumed,
`excess electrolyte must be included when the cell is
`assembled. This in turn results in less active material for
`a constant volume battery body and consequently less
`initial capacity. In addition, the oxidation of the electro-
`lyte often generates solid and gaseous byproducts, the
`solid of which build up a passivating layer on the parti-
`cles of the active material, increasing the polarization of
`the cell and lowering the output voltage. Simulta-
`neously, and more importantly, the gaseous byproducts
`increase the internal pressure of the cell, thereby in-
`creasing the risk of explosion and leading to unsafe and
`unacceptable operating conditions.
`SUMMARYOF THE INVENTION
`Thepresent invention provides a class of electrolyte
`compositions thatis exceptionally useful for minimizing
`electrolyte decomposition in secondary batteries com-
`prising strongly oxidizing positive electrode materials.
`These electrolytes are thereby uniquely capable of en-
`hancing the cycle life and improving the temperature
`performance of practical “rocking chair”cells. In our
`search for such an effective electrolyte, we examined
`literally hundreds of compositions, since the catalytic
`activity of the desirable positive electrode materials can
`not be predicted. As a result of these extensive investi-
`gations, we have discovered a group of electrolyte
`compositions whose range of effective stability extends
`up to about 5.0 V at 55° C., as well as at room tempera-
`ture (about 25° C.).
`In selecting an improved electrolyte, a number of
`basic essential factors are considered. Ideally, the tem-
`perature range of fluidity should be broad, the ionic
`conductivity should be high, and the charging cut-off
`voltage which avoids electrolyte oxidation should be
`high. In our selection process, the fluid temperature
`ranges of the compositions, i.c., between the melting
`and boiling points, were determined,respectively, with
`a differential
`scanning calorimeter
`(Perkin-Elmer
`Model DSC-4) and by thermometry in a commonlabo-
`ratory reflux apparatus. Next, the ionic conductivity of
`the different electrolyte compositions was measured
`over a wide practical temperature range (—25° C.to 65°
`C.) using a high frequency impedance analyzer (Hewl-
`
`20
`
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`

`5,192,629
`
`3
`ett Packard Model HP4129A, 5 Hz-10 MHz).Finally,
`the stability of the electrolytes against oxidation was
`determined over varying temperature and charging
`voltage ranges by means ofa potentiostatic mode cou-
`lometer (CNRS, Grenoble, France, Model “Mac-Pile”,
`version A-3.0le/881) using a LiMn2O, electrode to
`simulate activity to be expected in a practical cell. From
`these determinations, we have. discovered that
`the
`above-noted exceptional electrolyte results are obtained
`from a composition of about a 0.5M to 2M solution of 10
`LiPF¢, or LiPF¢ to which up to about an equal amount
`of LiBF, has been added, dissolved in a mixture of
`dimethylcarbonate (DMC) and ethylene carbonate
`(EC) wherein these solvent components are present in
`the weight percent ratio range from about 95 DMC:5 15
`EC to 33 DMC:67 EC.A preferred ratio of these sol-
`vents is from about 80 DMC:20 EC to 20 DMC:80 EC.
`
`THE DRAWING
`
`4
`this criterion, the list of prospective candidate composi-
`tions rapidly narrowed to those comprising the solvent
`combination of dimethylcarbonate and ethylene car-
`bonate. Further, the salt components were limited to
`LiPF¢ and some mixtures of LiPF¢ and LiBF4.
`The ultimate series of tests was conducted on these
`remaining compositions to determine their ability to
`withstand oxidation (decomposition) under recharging
`voltages in excess of about 4.5 V. The CNRS “Mac-
`Pile” data acquisition system was operated in the poten-
`tiostatic mode at a scan rate of 40 mV/hr to test candi-
`date electrolyte compositions against 10 mg,
`1 cm?
`samples of selected electrode material. This enabled the
`continuous plotting of coulometric measurements of
`charging voltage againstcell current. From such curves
`the onset of electrolyte oxidation can be readily identi-
`fied. This procedure can be seen with reference to FIG.
`1 whichplots the characteristic curve for the mentioned
`prior LiClO4/EC +DEEelectrolyte at 25° C. The
`peaking at about 4.05 and 4.15 V vs. Li corresponds to
`the reversible removal of Li from the spinel structure of
`a LiMn20«positive cell electrode, while the rapid non-
`reversing increase in current beginning at about 4.5 V
`vs. Li heralds the onset of electrolyte oxidation at that
`charging level.
`Theeffect of cell operating temperatureis also indi-
`cated from such plots, as can be observed from FIG. 2
`which depicts results of a test of the prior LiClO, elec-
`trolyte solution at the higher end of the ambient temper-
`ature range, about 55° C. With the dotted room temper-
`ature curve of FIG. 1 as a reference, one may readily
`see that the kinetics governing the electrolyte oxidation
`reaction lead to a lowerelectrolyte breakdown voltage
`as a result of increased temperature. Theinitiation of
`electrolyte oxidation at about 4.3 V vs. Li, and at even
`lower voltage during later recharge cycles, indicates
`that the charging cut-off voltage must be limited to
`about 4.1 V vs. Li for practical operation at the higher
`temperature. As a result of this limitation, the available
`cell capacity is, at best, only about 75% of that at room
`temperature.
`From this electrolyte oxidation screening, we have
`discovered that an exceptional, wide temperature
`Tange, oxidation resistant electrolyte for a LiMn2O4
`positive electrode intercalation battery cell, particularly
`one utilizing the preferred Li}+,Mn204 (0< x <1)
`electrode, may be realized in a 0.5M to 2M solution of
`LiPF¢, or LiPF¢ with up to about an equal amount of
`LiBF,4added, in a mixture of dimethylcarbonate (YMC)
`and ethylene carbonate (EC) within the weight percent
`ratio range from about 95 DMC:5 EC to 20 DMC:80
`EC.In a preferred such electrolyte solution the solvent
`ratio range is about 80 DMC:20 EC to 20 DMC:80 EC.
`An optimum composition for operation at room temper-
`ature and below is an approximately 1M LiPF¢ solution
`in a solvent mixture of about 33 DMC:67 EC, while a
`battery operating at higher temperatures in the range of
`55° C. optimally utilizes an electrolyte consisting essen-
`tially of an approximately 1.5M LiPF¢ solution in a
`solvent combination of about 67 DMC:33 EC . An
`additionally useful electrolyte consists essentially of an
`approximately 1M to 2M solution of equal parts of
`LiPF, and LiBF, in a solvent mixture of about 50
`DMC:50 EC.
`The outstanding oxidation resistant characteristics of
`the preferred electrolyte compositions may be ob-
`served, with reference to the earlier-noted LiCiO4 com-
`position, in FIG. 3 at room temperature and in FIG. 4 at
`
`The present invention will be described with refer- 20
`ence to the accompanying drawing of which:
`FIG.1 depicts a plot ofcell current against charging
`voltage at room temperature for a secondary cell com-
`prising a positive Li intercalation electrode and an elec-
`trolyte of LiClO, in 50:50 EC:DEE;
`FIG. 2 depicts comparative plots of cell current
`against charging voltage at room temperature and at 55°
`C. for secondary cells comprising a positive Li interca-
`lation electrode and an electrolyte of LiC]O4 in 50:50
`EC:DEE;
`FIG. 3 depicts comparative plots of cell current
`against charging voltage at room temperature for sec-
`ondary cells comprising a positive Li intercalation elec-
`trode and respective electrolytes of LiClO, in 50:50
`EC:DEEand LiPF¢in 67:33 DMC:EC; and
`FIG. 4 depicts comparative plots of cell current
`against charging voltage at 55° C. for secondary cells
`comprising a positive Li intercalation electrode and
`respective electrolytes of LiClO4 in 50:50 EC:DEE and
`LiPF¢ in 67:33 DMC:EC.
`
`25
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`
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`
`DESCRIPTION OF THE INVENTION
`
`Our investigations covered the vast range of combi-
`nations of currently known Li-bearing electrolyte salts
`and non-aqueous solvents, and the more commonly 45
`employed positive intercalation electrode materials.
`Thesalts included LiAsF6, LiBF4, LiCF3SO3, LiCiO«,
`LiN(CF3S02)2, and LiPFs. The solvents included
`diethylcarbonate, diethoxyethane, dimethylcarbonate,
`ethylene carbonate, and propylene carbonate. The test 50
`electrode compositions comprised LiCoO2, LiMn2O,,
`.
`LiNiO2, MnO2, and V20s.
`Theinitial scanning of melting to boiling ranges of
`solutions of the various salts in the solvents and mix-
`tures thereof indicated that 1M to 2M solutions pro- 55
`vided generally good utility from about —40° C. to 130°
`C. Subsequent testing for effective electrolytes was
`conducted with these solutions in the projected battery
`cell “working range” of about —25° C. to 65° C.
`Screening of the important ionic conductivity prop- 60
`erty of the candidate electrolytes indicated a widely
`disparate range of about 3 to 12 mS (milliSiemens or
`millimohs) per cm. From an evaluation of the efficacy
`of a prior functional “rocking chair” battery electrolyte
`composition comprising a 1M solution of LiClO, in a 65
`50:50 percent ratio mixture of ethylene carbonate and
`diethoxyethane, a minimum threshold conductivity for
`this selection process was set at about 10 mS/cm. Upon
`
`7
`
`7
`
`

`

`5
`55° C. The negligible current increase, after the revers-
`ible Li intercalations, at voltages up to about 5 V vs. Li
`indicates this remarkable stability which enables en-
`hanced cell capacity not only in the “rocking chair”
`cells comprising negative electrodes of carbon, ¢.g.,
`petroleum coke,but also in Li negative electrode cells.
`Such a lithium metal cell utilizing a Li; +.Mn2O« posi-
`tive electrode may be reasonably expected to achieve
`normal operating ranges of about 4.3 to 5.1 V.
`Theefficacy of the new electrolyte compositions was
`confirmed in common Swagelock cell recycling tests.
`For example, test cells were assembled with positive
`electrodes comprising Lij..Mn20,4 which, according
`to usual practice, typically included about 3-10% car-
`bon (Super-S graphite) to improve electrical conductiv-
`ity and about 1-5% of an inert binder, such as polytetra-
`fluoroethylene. In the course of these test we noted that
`it was preferable to favor lower carbon content in the
`range of about 4-7%, since the electrolyte oxidation
`tendency was additionally reduced. A set of such test
`cells with the separator element comprising an electro-
`lyte of IM LiPF¢ in 95 DMC:5 EC and a carbon (graph-
`ite or petroleum coke) negative electrode were repeat-
`edly charged and discharge cver two hours cycles at
`about 25° C. and 55° C. and at charging cut-off voltages
`of 4.9 V and 4.5 V, respectively. Even at this cycling
`rate and high charging voltage, the voltage polarization
`was unusually small, confirming the high ionic conduc-
`tivity of the electrolyte, and there was no significant
`loss ofcell capacity, verifying the high voltage stability
`of the electrolyte. The ability of the electrolyte to ex-
`tend the cycle life of the batteries was amply demon-
`strated by the remarkable fact that the cell capacities
`after 500 cycles was only about 10% less than after 5
`cycles.
`Theelectrolyte solutions we have discovered may be
`employed in practical batteries with any of the various
`immobilizing means that have found utility in prior
`cells. In addition to being used to saturate the porous
`separator elements normally disposed between the cell
`electrodes,
`these new electrolytes solutions may be
`included in the form of gelled or thickened composi-
`tions or they may be introduced into polymeric matrices
`as a secondary plasticizer. Such applications and other
`variants of this type will be apparent to theskilled arti-
`san and are intended to be nonetheless included within
`the scope of the present invention as recited in the ap-
`pended claims.
`Whatis claimed is:
`1. A high-voltage-stable electrolyte for a lithiated
`intercalation secondary battery, said electrolyte consist-
`ing essentially of about a 0.5 to 2M solution ofa solute
`selected from the class consisting of:
`a) LiPFe; and
`b) mixtures of LiPF¢ with up to about equal mole
`parts of LIBF4,
`dissolved in a mixture of non-aqueous dimethylcarbon-
`ate (DMC) and ethylene carbonate (EC) solvents
`wherein said solvents are present in a weight percent
`ratio range from about 95 DMC:5 EC to 20 DMC:80
`EC.
`2. An electrolyte according to claim 1 for a secondary
`battery comprising a negative electrode and a positive
`intercalation electrode wherein the intercalation com-
`pound consists essentially of Li, ,x.MnzO4 wherein x is
`in the range of 0 to about1.
`
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`3. An electrolyte according to claim 2 wherein said
`solvents are present in a weight percent ratio range
`from about 80 DMC:20 EC to 20 DMC:80 EC.
`4. An electrolyte according to claim 3 selected from
`the group consisting of:
`a) an approximately 1Msolution of LiPF¢in a solvent
`mixture of about 33 DMC:67 EC;
`b) an approximately 1.5M solution of LiPF¢ in a sol-
`vent mixture of about 67 DMC:33 EC; and
`c) 1M to 2M solutions of approximately equal parts of
`LiPFand LiBF, in a solvent mixture of about 50
`DMC:50 EC.
`S. A lithiated intercalation secondary battery com-
`prising a positive electrode, a negative electrode, and an
`electrolyte consisting essentially of about a 0.5M to 2M
`solution of a solute selected from the class consisting of:
`a) LiPFe, and
`b) mixtures of LiPF¢ with up to about equal mole
`parts of LIBF,,
`dissolved in a mixture of non-aqueous dimethylcarbon-
`ate (DMC) and ethylene carbonate (EC) solvents
`wherein said solvents are present in a weight percent
`ratio range from about 95 DMC:5 EC to 20 DMC:80
`EC.
`6. A battery according to claim 5 wherein said posi-
`tive electrode comprises an intercalation compound
`combined with about 3-10 weight percent carbon black
`and about 1-5 weight percentinert binder.
`7. A battery according to claim 6 wherein said carbon
`black is present in about a 4-7 weight percentratio.
`8. A battery according to claim 6 wherein said inter-
`calation compound consists essentially of Li; +.Mn204
`wherein x is in the range of 0 to about 1.
`9. A battery according to claim 8 wherein said sol-
`vents are present in a weight percent ratio range from
`about 80 DMC:20 EC to 20 DMC:80 EC.
`10. A battery according to claim 8 wherein said elec-
`trolyte is selected from the group consisting of:
`a) an approximately 1M solution of LiPF¢in a solvent
`mixture of about 33 DMC:67 EC;
`b) an approximately 1.5M solution of LiPF¢in a sol-
`vent mixture of about 67 DMC:33 EC; and
`c) IM to 2M solutions of approximately equal parts of
`LiPF¢ and LiBF, in a solvent mixture of about 50
`DMC:50 EC.
`11. A battery according to claim 8 wherein said nega-
`tive electrode consists essentially of a material selected
`from the group consisting of carbon andlithium metal.
`12. A battery according to claim 8 wherein said nega-
`tive electrode consists essentially of carbon and said
`electrolyte consists essentially of an approximately 1M
`to 1.5M solution of LiPF¢ in a solvent mixture of about
`67 DMC:33 EC to about 33 DMC:67 EC.
`13. A secondary battery comprising a negative elec-
`trode, a lithium intercalated positive electrode, and an
`electrolyte comprising a solution of a lithium salt in a
`non-aqueous solvent characterized in that said electro-
`lyte consists essentially of an approximately 0.5 to 2M
`solution of a solute selected from the class consisting of:
`a) LiPF¢; and
`b) mixtures of LiPF¢ with up to about equal mole
`parts of LIBF4,
`dissolved in a mixture of non-aqueous dimethylcarbon-
`ate (DMC) and ethylene carbonate (EC) solvents
`wherein said solvents are present in a weight percent
`ratio range from about 95 DMC:5 EC to 20 DMC:80
`EC,
`
`8
`
`

`

`7
`14. A battery according to claim 13 characterized in
`that said positive electrode comprises an intercalation
`compound combined with about 3-10 weight percent
`carbon black and about 1-5 weight percentinert binder.
`15. A battery according to claim 14 characterized in
`that said carbon black is present in about a 4-7 weight
`percent ratio.
`16. A battery according to claim 14 characterized in
`that said positive electrode intercalation compound
`consists essentially of LI14xMn204 wherein x is in the
`range of Oto about 1.
`17. A battery according to claim 14 characterized in
`that said electrolyte is selected from the group consist-
`ing of:
`a) an approximately 1M solution of LiPF¢in a solvent
`mixture of about 33 DMC:67 EC;
`
`8
`b) an approximately 1.5M solution of LiPF¢ in a sol-
`vent mixture of about 67 DMC:33 EC; and
`c) 1M to 2M solutionsof approximately equal parts of
`LiPF¢ and LiBF, in a solvent mixture of about 50
`DMC:50 EC.
`18. A battery according to claim 14 characterized in
`that said negative electrode consists essentially of a
`material selected from the group consisting of carbon
`and lithium metal.
`19. A battery according to claim 14 characterized in
`that said negative electrode consists essentially of car-
`bon and said electrolyte consists essentially of an ap-
`proximately 1M to 1.5M solution of LiPF¢ in a solvent
`mixture of about 67 DMC:33 EC to about 33 DMC:67
`EC.
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`30
`
`35
`
`45
`
`35
`
`65
`
`9
`
`

`

`Adverse Decisions In Interference
`Patent No. 5,192,629, Dominique Guyomard, Jean-Marie Tarascon, HIGH-VOLTAGE-STABLE
`ELECTROLYTES FOR LI1+XMN204/CARBON SECONDARY BATTERIES,Interference No.
`103,568, final judgment adverse to the patentees rendered May 14, 1997, as to claims 1-19.
`(Official Gazette June 2, 1998)
`
`10
`
`10
`
`