`
`
`PCT
`
`WORLD INTELLECTUAL PROPERTY ORGANIZATION
`International Bureau
`
`INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT)
`(51) International Patent Classification 5 :
`(11) International Publication Number:
`WO 93/21665
`HOIM 10/40
`(43) International Publication Date:
`28 October 1993(28.10.93)
`
`
`
`(21) International Application Number: PCT/US93/02368|(81) Designated States: CA, JP, European patent (AT, BE, CH,
`“5
`DE, DK, ES, FR, GB, GR, IE, IT, LU, MC, NL, PT,
`SE).
`
`Published
`With international search report.
`
`ow
`
`"6
`
`
`
`(22) International Filing Date:
`
`16 March 1993 (16.03.93)
`
`(30) Priority data:
`871,855
`
`21 April 1992 (21.04.92)
`
`US
`
`(71) Applicant: BELL COMMUNICATIONS RESEARCH,
`INC. [US/US]; 290 West Mount Pleasant Avenue, Li-
`vingston, NJ 07039-2729 (US).
`
`(72) Inventors; GUYOMARD, Dominique ; 16 Westminster
`Lane, Middletown, NJ 07748 (US). TARASCON,Jean,
`Marie ; 16 Davis Court, Martinsville, NJ 08836 (US).
`
`(74) Agents: WINTER, Richard, C.; PCT International, Inc.,
`Post Office Box 573, New Vernon, NJ 07976 (US)etal.
`
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`0.06
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`0.04
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`Current(mA)
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`(57) Abstract
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`3.8
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`4.0
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`4.2
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`4.4
`Voltage (V)
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`4.6
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`4.8
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`5.0
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`An electrolyte resistant to oxidation normally resulting from high voltage charging of a secondary battery comprising an
`Li, 4xMn0,intercalation positive electrode comprises a 0.5 M to 2 M solution of LiPF, dissolved in a mixture of non-
`aqueous dimethylcarbonate (DMC) and ethylene carbonate (EC) solvents wherein said solvents are present in a weight per-
`cent ratio range from about 95 DMC : 5 EC to 20 DMC : 80 EC.
`
`1
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`APPLE 1008
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`1
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`APPLE 1008
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`

`

`FOR THE PURPOSES OF INFORMATION ONLY
`
`Codes used to identify States party to the PCTon thefront pages of pamphlets publishing international
`applications under the PCT.
`
`Mongolia. Mauritania
`
`France
`Gabon
`United Kingdom
`Guinea
`Greece
`‘Hungary
`Ireland
`Maly -
`;
`Japan
`Democratic People’s Republic
`of Korea
`Republic of Korea
`Kazakhstan
`Licehtenstein
`Sri Lanka
`Luaxcmbourg
`Monivo
`Madagasear
`Mali
`
`AT
`AU
`BB
`BE
`BF
`BG
`BJ
`BR
`CA
`CF
`cG
`
`~ Austria
`Australia
`Barbados.
`Belgium
`Burkina Faso
`Bulgaria
`Benin
`Brazil
`Canada
`Central African Republic
`Congo
`Switecrland
`Cote d'Ivoire
`Cameroon
`Caechoslovakia
`Ceech Republic
`- Germany
`Denmark
`Spain
`Finland
`
`Malawi
`Netherlands
`Norway
`New Zealand
`Poland
`Portugal
`Romania
`Russian Federation.
`Sudan
`Sweden
`Slovak Republic
`Senegal
`Soviet Union
`Chad
`Tago
`Ukraine
`United States. of America
`Viet Nam
`
`a
`
`*
`
`2
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`€
`

`

`WO 93/21665
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`PCT/US93/02368
`
`HIGH-VOLTAGE-STABLE ELECTROLYTES FOR
`
`Lij4,Mn204/CARBON SECONDARY BATTERIES
`
`BACKGROUND OF THE INVENTION
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`This invention relates to non-aqueous electrolyte
`compositions for secondary (rechargeable) lithium battery cells
`and, more particularly,
`to electrolyte compositions that are
`capable of resisting decomposition normally resulting from
`oxidation which occurs in Li,,,Mn,0,
`/ carbon cells during
`recharging under conditions 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 rechargeable lithium batteries is to replace
`lithium metal with a material capable of reversibly
`intercalating lithium 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 Li* salt dissolved ina non-aqueous solvent
`or mixture of such solvents. Numerous such salts and solvents
`are known in the art, as evidenced in Canadian Patent
`Publication No. 2,022,191, dated 30 January 1991.
`
`The output voltage of a rechargeable lithium battery cell
`of this type is determined by the difference between the
`electrochemical potential of Li within the two intercalation
`
`electrodes of the cell. Therefore,
`
`in an effective cell the
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`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 electrode, carbon provides the
`best compromise between large specific capacity and good
`reversible cycling behavior. Such use of carbon, however,
`presents some detractions, such as loss of averagé output
`voltage andenergy density, as compared to lithium metal, since
`the voltage of a Li,Cg negative electrode is always greater than
`that of a pure lithium negative electrode.
`
`To compensate for the loss of voltage associated with the
`negative electrode, a strongly oxidizing intercalation material
`is preferably used as the positive electrode. Such an electrode
`material is the spinel phase Li,,,Mm0,, usually combined with a
`small amount of carbon black to improve electrical conductivity
`and provide the practical. composite electrode,
`that can
`reversibly intercalate lithiumat avoltage of 4.1 Vvs. Li. Use
`of such a strongly oxidizing intercalation material as positive
`electrode, however,
`introduces a further concern, namely,
`the _.
`risk of electrolyte decomposition from oxidation at the higher
`operating voltages, i.e. greater than about 4 V. For instance,
`since the voltage of the Li,,,Mn,0, / 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
`must be stable down to about 0 V with respect to a composite
`carbon negative electrode, e.g., petroleum coke combined with
`about 1-5% of each of carbon black {(Super-S) and an inert
`binder.
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`Presently-used intercalation electrolytes, e.g., a iM
`solution of LiClO, in a 50:50 mixture of ethylenecarbonate (EC)
`and diethoxyethane (DEE) such as described in U.S. Pat. No.
`
`5,110,696, when employed in a Lij,,Mn,0, / C cell, will begin to
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`PCT/US93/02368
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`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
`
`the available capacity of the cell at about
`cut~off voltage,
`55° Cc is only 75% of that at room temperature.
`
`When cells comprising these previously-available
`electrolytes are cycled to a voltage even slightly 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 discharging the cell, resulting in a continuous
`loss in the cell capacity over subsequent cycles. Further,
`if
`during each charge a small part of the 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.
`addition,
`the oxidation of the electrolyte often generates
`solid and gaseous byproducts,
`the solid of which build up a
`pasSivating layer on the particles of the active material,
`increasing the polarization of the cell and lowering the output
`voltage. Simultaneously, and more importantly,
`the gaseous
`byproducts increase the internal pressure of the cell,
`thereby
`increasing the risk of explosion and leading to unsafe and
`unacceptable operating conditions.
`
`In
`
`SUMMARY OF THE INVENTION
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`The present invention provides a class of electrolyte
`compositions that is exceptionally useful for minimizing
`electrolyte decomposition in secondary batteries comprising
`strongly oxidizing positive electrode materials. These
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`PCT/US93/02368
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`electrolytes are thereby uniquely capable of enhancing 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 investigations, we have discovered a group
`of electrolyte compositions whose range of effective stability
`extendsup to about 5.0 V at 55°C, as well as at room
`temperature (about 25°C).
`
`In selecting an improved electrolyte, a number of basic
`essential factors are considered. Ideally,
`the temperature
`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.e., between
`the meltingand boiling points, were determined, respectively,
`with a differential scanning calorimeter (Perkin-Elmer Model
`
`DSC-4) and by thermometry in a common laboratory 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 (Hewlett 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 of a potentiostatic mode coulometer
`(CNRS, Grenoble, France, Model "Mac-Pile", version A-3.01e/881)
`using a Lij,,Mn,0, 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 LiPFs, or LiPFg 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 inthe weight percent ratio range from
`about 95 DMC:5 EC to 33 DMC:67 EC. A preferred ratio of these
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`solvents is from about 80 DMC:20 EC to 20 DMC:80 EC.
`
`THE DRAWING
`
`The present invention will be described with reference to
`the accompanying drawing of which:
`
`1 depicts'a plot of cell current against charging
`FIG.
`voltage at room temperature for a secondary cell comprising a
`positive Li intercalation electrode and an electrolyte of LiClO,
`in 50:50 EC:DEE;
`
`2 depicts comparative plots of cell current against
`FIG.
`charging voltage at room temperature and at 55° C for secondary
`cells comprising a positive Li intercalation electrode and an
`electrolyte of LiClO, in 50:50 EC:DEE;
`
`3 depicts comparative plots of cell current against
`FIG.
`charging voltage at room temperature for secondary cells
`comprising a positive Li intercalation electrode and respective
`electrolytes of LiClO, in 50:50 EC:DEE and LiPFg in 67:33
`DMC:EC; and
`
`4 depicts comparative plots of cell current against
`FIG.
`charging voltage at 55° C for secondary cells comprising a
`positive Li intercalation electrode and respective electrolytes
`of LiClO, in 50:50 EC:DEE and LiPF, in 67:33 DMC:EC.
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`DESCRIPTION OF THE INVENTION
`
`350
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`Our investigations covered the vast range of combinations
`of currently known Li-bearing electrolyte salts and non-aqueous
`solvents, and the more commonly employed positive intercalation
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`electrode materials. The salts included LiAsF,, LiBF,, LiCF3S03,
`LiCl0,, LiN(CF,S03)3, and LiPF,. The solvents included
`diethylcarbonate, diethoxyethane, dimethylcarbonate, ethylene
`carbonate, and propylene carbonate. The test electrode
`compositions comprised LiCo0z, Li,,,Mn,0,, LiNiO,, Mn0,, and
`V20s.
`.
`
`‘The initial scanning of meltingto boiling ranges of
`solutions of the various salts in the solvents and mixtures
`
`thereof indicated that 1M to 2M solutions provided 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 conductivityproperty of
`the candidate electrolytes indicated a widely disparate range
`of about 3 to 12 mS (milliSiemens or millimhos) 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 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 this
`criterion,
`the list of prospective candidate compositions
`rapidly narrowed to those comprising the solvent combination of
`dimethylcarbonate and ethylene carbonate. Further, the salt
`components were limited toLiPF, and some mixtures of LiPF, and
`LiBF,.
`
`The ultimate series of tests was conducted on these
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`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 potentiostatic mode at a scan rate of 40 mV/hr
`to test candidate electrolyte compositions against 10mg, 1 cm?
`samples of selected electrode material. This enabled the
`continuous plotting of coulometric measurements of charging
`
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`PCT/US93/02368
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`voltage against cell current. From such curves the onset of
`electrolyte oxidation can be readily identified. This procedure
`can be seen with reference to FIG.
`1 which plots the
`characteristic curve for the mentioned prior LiClO, / EC + DEE
`electrolyte 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 Lij,,Mn20, 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.
`
`The effect of cell operating temperature is also
`2 which
`indicated from such plots, as can be observed from FIG.
`depicts results of a test of the prior LiClO, electrolyte
`solution at the higher end of the ambient temperature range,
`about 55°C. With the dotted room temperature curve of FIC. 1 as
`a reference, one may readily see that the kinetics governing the
`electrolyte oxidation reaction lead to a lower electrolyte
`breakdown voltage as a result of increased temperature. The
`initiation 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 Vv
`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 range,
`oxidation resistant electrolyte for a LiMn,0, positive electrode
`intercalation battery cell, particularly one utilizing the
`preferred Lij,,Mn,0,
`(0 < x < 1) electrode, may be realized in a
`0.5M to 2M solution of LiPFg, or LiPFg with up to about an equal
`amount of LiBFy added,
`in _a mixture of dimethylcarbonate (DMC)
`and ethylene carbonate (EC) within the weight percent ratio
`range from about 95 DMC:5 EC to 20 DMC:80 EC. Ina preferred
`such electrolyte solution the solvent ratio range is about
`80 DMC:20 EC to 20 DMC:80 EC. An optimum composition for
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`operation at room temperature 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 essentially of an
`approximately1.5M 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 LiPFg and LiBF, in a solvent mixture of about 50 DMC:50 EC.
`
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`The outstanding oxidation resistant characteristics of
`the preferred electrolyte compositions may be observed, with
`reference to the earlier-noted LiClO, composition,
`in FIG. 3 at
`room temperature and in FIG. 4 at 55°C. The negligible current
`increase, after the reversible Li intercalations, at voltages
`up to about 5 V vs. Li indicates this remarkable stability which
`enables enhanced cell capacity not only in the "rocking chair"
`
`cells comprising negative electrodes of carbon, e.g., petroleum
`coke, but also in Li negative electrode cells. Such a lithium
`metal cell utilizing a Lij,,Mn,0, positive electrode may be
`reasonably expected to achieve normal operating ranges of about
`
`4.3 to 5.1 V.
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`The efficacy of the new electrolyte compositions was
`confirmed in common Swagelock cell recycling tests. For
`example, test cells were assembled with positive electrodes
`comprising Li,,,Mn,0, which, according to usual practice,
`typically included about 3-10% carbon (Super-S graphite) to
`improve electrical conductivity and about 1-5% of an inert
`binder, such as polytetrafluoroethylene. 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 electrolyte of
`1M LiPF, in 95 DMC:5 EC and a carbon (graphite or petroleum
`coke) negative electrode were repeatedly charged and discharge
`over two hours cycles at about 25° Cc and 55° C and at charging
`cut-off voltages of 4.9 V and 4.5 V, respectively. Even at this
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`the voltage
`cycling rate and high charging voltage,
`polarization was unusually small, confirming the high ionic
`conductivity of the electrolyte, and there was no significant
`loss of cell capacity, verifying the high voltage Stability of
`the electrolyte. The ability of the electrolyte to extend the
`cycle life of the batteries was amply demonstrated by the
`remarkable fact that the cell capacities after 500 cycles was
`only about 10% less than after 5 cycles.
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`The electrolyte solutions we have discovered may be
`employed in practical batteries with any of the various
`immobilizing means that have found utility in prior cells.
`addition to being used to saturate the porous separator
`these
`elements normally disposed between the cell electrodes,
`new electrolytes solutions may be included in the form of gelled
`or thickened compositions or they may be introduced into
`polymeric matrices as a secondary plasticizer. Such
`- applications and other variants of this type will be apparent to
`‘the skilled artisan and are intended to be nonetheless included
`within the scope of the present invention as recited in the
`appended claims.
`
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`. What is claimed is:
`
`A high-voltage-stable electrolyte for a lithiated
`1.
`intercalation secondary battery comprising a solution of a
`lithium compound in a non-aqueous. solvent
`
`‘ws,
`
`characterized in that
`said electrolyte consists essentially of an approximately 0.5
`to 2M solution of a solute selected from the class consisting
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`of:
`
`-
`a) LiPFe; and
`b) mixtures of LiPFs with up to about equal mole parts of
`LIBF4,
`|
`dissolved in a mixture of non-aqueous 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.
`
`2.
`
`An electrolyte according to claim 1
`characterized ‘in that.
`“Said solvents are present in a weight. percent ratio range from
`about 80 DMC:20 EC to 20 DMC:80 EC.
`
`3. An electrolyte according to claim 1
`characterized in that
`
`said electrolyte solution 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,g in a solvent
`mixture of about 67 DMC:33 EC; and
`c)
`1M to 2M solutions of approximately equal parts of LiPF,
`and LiBFy, in a solvent mixture of about 50 DMC:50 EC.
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`PCT/US93/02368
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`A secondary battery comprising a negative electrode, a
`4.
`positive electrode, and an electrolyte comprising a solution of
`a lithium compound in a non-aqueous solvent
`characterized in that
`said electrolyte consists essentially of an approximately 0.5
`to 2M solution of a solute selected from the class consisting
`of:
`
`a) LiPF,e; and
`b) mixtures of LiPF, with up to about equal mole parts of
`LIBF4,
`dissolved in a mixture of non-aqueous 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.
`
`5.
`
`A battery according to claim 4
`characterized in that
`said positive electrode comprises an intercalation compound
`combined with about 3-10 weight percent carbon black and about _
`1-5 weight percent inert binder.
`
`6.
`
`A battery according to claim 4
`characterized in that
`said positive electrode intercalation compound consists
`essentially of Li,,,Mn,0, wherein x is in the range of 0 to
`about 1.
`
`A battery according to claim 6 wherein said solvents are
`7.
`present in a weight percent ratio range from about 80 DMC:20 FC
`to 20 DMC:80 EC.
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`8. A battery according to claim 4
`characterized in that
`said electrolyte 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 solvent
`mixture of about 67 DMC:33 EC; and
`
`c) 1M to 2M solutions of approximately equal parts of LiPF,
`and LiBF, in a solvent mixture of about 50 DMC:50 EC.
`
`*)
`
`<
`
`9. A battery according to claim 4
`characterized in that
`said negative electrode consists essentially of a material
`selected from the group consisting of carbon and lithium metal.
`
`10. A battery according to claim 4
`: characterized in that
`said negative 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. >
`|
`: a
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`4.64.85.0
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`4.4
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`
`
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`WO 93/21665
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`

`

` A.
`
`
`te
`
`Documentation searched otherthan minimum documentationto the extentthat suchdocuments are included in the fields searched
`
`Electronic data base consulted during the international search (name of data base and, where practicable, search terms used)
`
`
`INTERNATIONAL SEARCH. REPORT
`International application No.
`PCT/US93/02368
`
`
`CLASSIFICATION OF SUBJECT MATTER
`
`IPC(5)
`:HOIM 10/40
`US CL :429/197, 224
`Accordingto International Patent Classification (IPC) or to both nationalclassification and IPC
`B.
`FIELDS SEARCHED
`
`Minimum documentation searched (classification system followed by classification symbols)
`
`U.S.
`:
`
`429/197, 224; 429/194, 196, 199, 218
`
`
`
`
`DOCUMENTS CONSIDERED TO BE RELEVANT
`C.
`Category*
`Citation of document,
`with
`indication, where appropriate,of the relevant passages
`
`
`
`
`
`US, A, 4,419,423 (LEGER) 06 December 1983.
`
`US, A, 4,874,680 (KOSHIBA) 17 October 1989.
`
`US, A, 4,904,552 (FURUKAWAETAL.) 27 February 1990.
`
`US, A, 5,079,109 (TAKAMI ET AL.) 07 January 1992.
`
`Relevant to claim No.
`
`
`
`
`
`
`
`US, A, 5,110,696 (SHOKOOHI ET AL.) 05 May 1992.
`
`“xe
`
`*o°
`
`
`
`[] Furtherdocuments are listed in the continuation of Box C. C]
`See patent family annex.
`
`.
`Specialcategories ofcited documents:
`“T°
`Interdocumentpublishedafter the international filing dateor priority
`wae
`dateand not inconflictwith theapplicationbutcited to underatandthe
`
`
`to bepartofparticularrelevance
`principleortheory undertyingtheinveation
`“AY
`documentdefining the general state ofthe art which is not considered
`saci
`‘
`'
`‘
`
`
`.
`.
`.
`.
`.
`.
`document of particular relevance; the claimed invention cannot be
`Ee
`earlier documentpublished on or after the international filing date
`comidered novel or cannot be consideredto. involvean inventivestep
`
`
`
`
`“LY
`documentwhich may throw doubts oa priority clain(s) or which ia
`whea thedocument is taken aloos
`cited to establish the publication date of another citation or other =|,
`.
`.
`.
`.
`special reason(aespecified)
`XY
`document of particular relevance; the claimed invention cannot be
`
`
`considered to involve aa inventive atep when the document is
`document referring to an oral disclosure, use, exhibition or other
`combinedwith one or more othersuchdocuments, such combination
`
`
`means
`being obviousta a person skilled in the art
`theprioritydateclaimed
`documentmemberofthesamepatentfamily
`*p*
`*&
`documentpublished priorto the international filing datebut later than
`f
`
`
`
`
`
`meES IUNES
`Date of the actual completion ofthe international search
`Date of
`
`
`
`
`
` 18 MAY 1993
`
`
` Nameand mailing address of the ISA/US
`Authorized officer
`Commissioner of Patents and Trademarks
`
`Box PCT
`Washington, D.C. 20231
`Facsimile No. NOT APPLICABLE
`
`
`Form PCT/ISA/210 (secondsheet)(July 1992)
`
`Lf
`
`19
`
`19
`
`