e
`United States Patent
`Huanget al.
`
`115
`
`[54] OVERCHARGE AND OVERDISCHARGE
`PROTECTION OF AMBIENT
`
`[75]
`
`[73] Assignee:
`
`TEMERATURE SECONDARY LITHIUM
`Inventors: Chen-kuo Huang, So. Pasadena;
`Subbarao Surampudi, Glendora; Alan
`‘
`.
`¥,Ati,G-dale:erald Halpert,
`The United States of America as
`represented by the Administrator of
`the National Aeronautics and Space
`Administration, Washington, D.C.
`[21] Appl. No.: 942,491
`“1.
`(22] Filed:
`Sep. 2, 1992
`[SU] mt. CLSessen neeenes HO1M 10/48
`[52] U.S. Ch. eeeeeceteeteeeetenereees 429/91; 429/191;
`429/194; 429/218
`[58] Field of Search ............... 429/191, 194, 218, 223,
`429/224, 91, 61, 90
`
`[56]
`
`.
`References Cited
`U.S. PATENT DOCUMENTS
` we 429/194
`
`LUIACAATA
`US005278000A
`[11] Patent Number:
`5,278,000
`{45} Date of Patent:
`Jan. 11, 1994
`
`5/1987 Uchiyamaet al... 429/194
`4,751,157
`
`
`ow. 429/194
`4,751,158 4/1988 Uchiyamaet al.
`8/1989 Abraham etal. ..
`4,857,423
`429/194
`4,911,996
`....
`« 429/194
`371990 Holleck et al.
`
`4,934,922
`6/1990 Abraham etal. ..
`we 429/50
`
`
`.. 429/194
`4,935,316 6/1990 Redney..........
`ote: 429/197
`4,965,150 10/1990 Dahn et al.
`
`ecceseeeeeeee 429/197
`4,983,476
`1/1991 Slane et al. ue
`1/1992 Toyoguchi wsccnccmecone 429/224
`5,084,366
`Primary Examiner—Anthony Skapars
`dttorney, Agent.orNaum—Thomas H. Jones; John H.
`usmuss;
`Guy
`M.
`Muller
`[57]
`ABSTRACT
`A cathode additive is provided for protecting an ambi-
`ent
`temperature secondary lithium cell
`from over-
`charging or overdischarging. The cathode additive is
`chosen to create an upper voltage plateau which is
`slightly higher than a characteristic charge cutoff volt-
`age of the cathode of the cell. The cathode additive
`additionally creates a lower voltage plateau which is
`slightly lower than the characteristic discharge cutoff
`voltage of the cell. Preferably the cathode additive is a
`transition metal oxide or a sulfide may, for example,
`include a mixture of LiyMn2O4 and Lio. ;MoO3.
`
`22 Claims, 3 Drawing Sheets
`
`VOLTAGE
`
`Li
`
`Vs.
`
`(VOLTS)
`
`-0.5
`
`0.0
`
`0.5
`
`1.0
`
`15
`
`2.0
`
`x in LiyMng0q4,
`
`x in Liy TiS2or x in Liy MoO?
`
`1
`
`APPLE-1026
`
`APPLE-1026
`
`1
`
`

`

`U.S. Patent
`
`Jan. 11, 1994
`
`Sheet 1 of 3
`
`5,278,000
`
`10
`CATHODE
`|
`¥
`L SSeS
`
`TAGE V
`
`s.
`
`REFEEN
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`OL
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`E V
`
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`R
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`EFE
`
`7
`c
`
`
`
`CHARGE ——>
`<— DISCHARGE
`STATE OF CHARGE OR DISCHARGE
`
`CATHODE
`
`
`
`le
`
`18
`
`20
`
`STATE OF CHARGE OR DISCHARGE
`
`FIG. 2
`
`ANODE
`_<—DISCHARGE CHARGE ——>
`
`
`
`
`
`2
`
`

`

`U.S. Patent
`
`Jan. 11, 1994
`
`Sheet 2 of3
`
`5,278,000
`
`17 sO00GOo-
`
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`3
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`

`

`U.S. Patent
`
`Jan. 11, 1994
`
`Sheet 3 of 3
`
`5,278,000
`
`ol O'l
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`2sNery
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`SO¢
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`

`

`1
`
`5,278,000
`
`OVERCHARGE AND OVERDISCHARGE
`PROTECTION OF AMBIENT TEMPERATURE
`SECONDARYLITHIUM CELLS
`
`ORIGIN OF THE INVENTION
`
`The invention described herein was madein the per-
`formance of work under a NASAcontract, and is sub-
`ject to the provisions of Public Law 96-517 (35 U.S.C.
`Section 202) in which the Contractor has elected not to
`retaintitle.
`
`2
`battery terminal voltage, as in the case ofa battery with
`cells which exhibit cell voltage as a function of charge
`and discharge.
`In cells which exhibit a voltage plateau in the charge
`and discharge behavior, the battery terminal voltage
`can provide an indication ofthe status of the cells. For
`example, if the discharge cutoff voltage is 10 volts (1
`volt per cell), upon discharge, the battery terminal volt-
`age will be less than 10 volts only if one or more of the
`cell voltages are less than 1 volt each. In suchcase, to
`avoid discharge abuse ofthe cell, one can measure the
`terminal voltage and terminate the currentif the overall
`voltageindicates overdischarge. However,this solution
`is not practical for many applications, and is not applica-
`ble for batteries with changing cell voltages, as de-
`scribed above.
`Exemplary patented systems directed to overcharge
`or overdischarge protection include U.S. Pat. No.
`4,935,316 to Redey, which specifically addresses over-
`Manyapplications require the use of secondary,i.e.,
`discharge protection of a cell system having plateau
`rechargeable, battery cells having more than twocells
`potentials for both anode and cathode. The method of
`connected in series. The individual cells in the battery
`Redey exploits a family of allay materials which are
`may be subjected to inadvertent overcharging or over-
`addedto the parent anode material to adjust the cathode
`discharging during cycling. Cells subjected to over-
`and anoderelative capacity. overdischarge protectionis
`charge or overdischargelose capacity irreversibly. Fur-
`achieved either by reducing or terminating the operat-
`ther, repeated overcharge and overdischarge ofcells
`ing current or, for deeply discharged cells, by using a
`results in possible venting or exploding ofcells. In par-
`Li+ —Li? shuttling mechanism. However, for batteries
`ticular, state of the art secondary lithium cells are very
`where either the cathode or anode material does not
`sensitive to overcharge and overdischarge. A mecha-
`haveaflat potential versus Li with composition change,
`nism to prevent both the overcharge and overdischarge
`the method of Redeyis noteffective.
`of such cells is highly desirable for practical applica-
`In U.S. Pat. No. 4,935,316, an anode additive is em-
`tions. Previously, electrolyte additives such as dimethyl
`ferrocene, dibutyl] ferrocene, etc., were examined as
`ployed for high temperature batteries.
`possible candidates for protecting cells from over-
`U.S. Pat. No. 4,857,423 to Abraham etal. features the
`charge. However, such electrolyte additives only pro-
`use of redox reagents, such as ferrocene, butylferro-
`tect cells from overcharge and do noteffectively pro-
`cene, etc., which are dissolved in nonaqueouselectro-
`tect the cells from overdischarge. Further, electrolyte
`lytes to provide overchargeprotection for cells having
`additives are effective at only very low rates of over-
`alkali metal negative electrodes. The method of Abra-
`charge. Moreover, electrolyte additives are not effec-
`ham et al. does not address overdischarging. Moreover,
`tive in solid state batteries or polymeric electrolyte
`for solid state batteries,
`the approach described by
`batteries, since additives to such batteries are not mo-
`Abraham et al. does not even provide overcharge pro-
`bile, unlike additives in a liquid electrolyte battery.
`tection.
`Battery voltage indicators have also been proposed
`for protecting cells from overcharge and overdischarge
`by either terminating or reducing applied current.
`However, for multicell batteries, such external voltage
`indicators are not always effective, and a built-in over-
`charge and overdischarge protection mechanism may
`be necessary.
`Specifically, built-in protection is preferable in cells
`of the type where cell voltage, which is governed by
`the difference of cathode and anodepotential, does not
`show a plateau, FIG. 1, but instead changes as a func-
`tion of charge and discharge state, FIG. 2. The latter
`occurs in, for example, Li—TiS>cells. In such cells, the
`terminal battery voltage may not necessarily reflect the
`actual individual cell status, even though some of the
`cells are being overcharged or overdischarged.
`Toillustrate, consider a secondary battery consisting
`of 10 cells in series where the discharge cutoff voltage
`is 10 volts (1 volt per cell) and the overcharge cutoff
`voltage is 27 volts (2.7 volts per cell). Upon discharge,
`the terminal voltage of the battery can be 10 volts with-
`out everycell being 1 volt. In other words, eight cells
`can each beat | volt, with the remaining twocells being
`1.2 volts and 0.8 volt, respectively. Although the cell
`which has reached 0.8 volt is being overdischarged,this
`overdischarge is not detected by simply measuring the
`
`STATEMENTOF THE INVENTION
`From the foregoing,it can be appreciated thatthere is
`a need to prevent overcharging and overdischarging of
`secondarylithium cells, particularly solid state second-
`ary lithium cells.
`This object, and the general purposes of the inven-
`tion, may be achieved by the provision of a cathode
`additive for incorporating into a cathode of a lithium
`cell for preventing overcharging and overdischarging
`of the cell. The cathode additive is chosen to yield an
`upper voltage plateau slightly higher than a charge
`cutoff voltage of the cathode and for yielding a lower
`voltage plateau slightly lower than a discharge cutoff
`voltage of the cathode. By providing such upper and
`lower plateaus, any increase or decrease of the cell
`voltage to above or below the base cathode voltage
`range is achieved through action of the additive, rather
`than the base cathode material. In this manner,the base
`cathode material
`is protected from overcharge and
`overdischarge. In other words, the additive acts as the
`sink/source system for the electroactive species (lith-
`ium) to control the cell voltage both during overcharge
`and overdischarge. The cathode additive also functions
`as an end of discharge or end of charge indicator.
`
`TECHNICAL FIELD
`
`Thepresent invention generally relates to preventing
`overcharging and over-discharging of secondary bat-
`tery cells, in particular, ambient temperature secondary
`lithium ceils.
`
`RELATED ART
`
`40
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`5
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`

`

`5,278,000
`
`3
`the
`In accordance with a preferred embodiment,
`cathode additiveis a transition metal oxide or sulfide. In
`particular, the cathode additive may include Li,Mn2O,,
`LixMoO2, LixCoO», LixNiO2, and Lix,MyMn.,)O4,
`wherein M is Co, Cr, or Fe, wherein x indicates a range
`of lithium titration, and y indicates a range of metal
`titration. Considering Li,Mn7Q4, for example, if titra-
`tion occurs until half of the Mn2O4 molecules include a
`lithium atom,
`then x=0.5. Typically, x ranges from
`slightly greater than 0 to 1 or 2, but may be higher as
`desired. In LixMyMng.,)O4, y can range anywherebe-
`tween O and2. In one embodiment, the cathode additive
`comprises a mixture of LizMyO4 and Lio.;MoO2. In the
`preferred embodiment, the additive is employed with a
`multicell
`lithium battery of the type employing Li-
`—TiS2. However, the cathode additive is also effective
`in other secondary lithium cells such as Li—MoS:,
`Li—NbSe3, Li—V20s, Li—MnQ3, and LixC-LixCoO2
`cells.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`The objects and features of the present invention,
`which are believed to be novel, are set forth with partic-
`ularity in the appended claims. The present invention,
`both as to its organization and manner of operation,
`together with further objects and advantages, may best
`be understood by reference to the following descrip-
`tion, taken in connection with the accompanying draw-
`ings.
`FIG. 1 is a schematic diagram representing cell volt-
`age as a function of cell charge or dischargestate for a
`cell exhibiting a plateau voltage;
`FIG. 2 is a schematic diagram of cell voltage as a
`function of cell charge or discharge state for a cell
`exhibiting a nonplateau voltage,i.e., a voltage changing
`with the amount of charge or discharge;
`FIG. 3 is a coulometric titration curve for a mixture
`cathode additive compound provided in accordance
`with the invention; and
`FIG. 4 is a coulometric titration curve for an ideal
`single component cathodeadditive.
`DETAILED DESCRIPTION OF THE
`INVENTION
`
`The following description is provided to enable any
`person skilled in the art to make and use the invention
`and sets forth the best modes contemplated by the in-
`ventors of carrying out their invention. Various modifi-
`cations, however, will remain readily apparent to those
`skilled in the art, since the generic principles of the
`present invention have been defined herein specifically
`to provide overcharging and overdischarging protec-
`tion for an ambient temperature secondarylithium cell.
`Referring to FIGS. 3 and 4, the characteristics of
`preferred cathode additives will be described and exem-
`plary additives set forth. The cathode additives are
`selected for incorporating directly into the cathode of a
`secondary,i.e. rechargeable, lithium cell. The base cath-
`ode material, such as TiS2, is a powder, and the cathode
`additive is also a powder. During fabrication of the
`battery cell, the additive powder is merely mixed with
`the base cathode powder. To properly prevent over-
`charging, the cathode additive operates to produce an
`upper voltage plateau which is slightly higher than a
`charge cutoff voltage of the base cathode material of
`the secondarylithium cell. Considering, for example, a
`lithium cell of the type Li—TiS2, which has a recom-
`mended upper charge cutoff voltage of 2.7 volts, a suit-
`
`4
`able cathode additive provides an upper voltage plateau
`of 2.7 volts or slightly higher.
`the cathode additive
`To prevent overdischarging,
`Operates to provide a lower voltage plateau which is
`slightly lower than a discharge cutoff voltage of the
`cathode material. Thus, for the Li—TiS) lithium cell,
`which has a discharge voltage cutoff of approximately
`1.7 voits, the additive provides a lower voltage plateau
`of approximately 1.7 volts or slightly less.
`A suitable cathode additive having the above-
`described characteristics is a mixture of Li,Mn2O4 and
`Li,MoO>.Asindicated above,the x indicates a range of
`lithium titration which essentially sets forth the ratio of
`MoQ; or Mn204 molecules to LiMoO, and LiMn204
`molecules, respectively. FIG. 3 illustrates a coulometric
`titration curve of lithium with respect to the Lix;Mn2O4
`and LixMoQ2 compounds. FIG. 3 also provides the
`coulometric titration curve oflithium with respect to
`the Li—TiS2 cathode. As can be seen from FIG. 3,
`maximum titration oflithium into TiS», occurs with one
`lithium per TiS: molecule. At that maximum titration,
`the lithium cell has a minimum voltage of approxi-
`mately 1.7 volts. As noted above, this is the discharge
`cutoff voltage for the Li—TiS)lithium cell. An attempt
`to discharge the lithium cell below about 1.5 volts re-
`sults in an irreversible intercalation of lithium into the
`Li—TiS», and a further reduction of electrolyte salts
`used in the lithium cell. However, with the addition of
`LixMoOzto the Li—TiS2 cathode, overdischarge pro-
`tection is achieved. As can be seen from FIG.3, the
`titration oflithium into LiyMoO}yields a lower voltage
`plateau of approximately 1.6 volts,i.e., a voltage plateau
`slightly below the 1.7-volt discharge cutoff voltage of
`the Li—TiS:cell. By providing a lower voltage plateau
`below the cutoff voltage of Li—TiS2, an attempt to
`lower the voltage of the lithium cell below 1.7 volts is
`effectuated through titration of lithium into the Li,.
`MoO>rather than the Li—TiS2, thus protecting the
`cathode andelectrolytes.
`FIG. 3 also provides the titration curve of lithium
`into Li,Mn2QOq4. An attempt to chargethe cell to a volt-
`age higher than approximately 3 volts results in oxida-
`tive degradation of the electrolyte solvent. As can be
`seen, LixMn2O4 provides an upper voltage plateau
`slightly above the recommended 2.7-volt upper charge
`cutoff voltage of the Li—TiSp cell. As such, the Li,
`Mn2O4 compoundprevents an increase in voltage above
`2.7 volts from damaging the Li—TiS>cell. Any attempt
`to increase the voltage above 2.7 volts is effectuated
`through titration of lithium into LixMn204, thus pro-
`tecting the entire cell.
`Thus, FIG.3 illustrates the operating voltage range
`of the Li—TiS2 and the voltage protection window of
`the additive material. During overcharge (>2.7 volts),
`the additive material activates to maintain the cell volt-
`age locked at the upper voltage plateau of the additive.
`During overdischarge (<1.7 volts), the additive also
`activates to maintain the cell voltage locked at the
`lower voltage plateau of the additive. The Li—Li,.
`Mn2O4 system exhibits a voltage plateau around 2.9
`volts (versus Li), and the Li-Li,MoO}system exhibits
`a voltage plateau around 1.6 volts (versus Li). An addi-
`tive containing these two compoundsprotects the cell
`from both overcharge and overdischarge.
`FIG. 4 provides the coulimetric titration curve of
`lithium into TiS2, and into an ideal cathode additive
`compound, representing as ABy. The ideal cathode
`additive compoundnot only provides an uppervoltage
`
`= 5
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`20
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`

`5,278,000
`
`5
`plateau of exactly 2.7 volts and a lower voltage plateau
`of exactly 1.7 volts, but achieves a sharp transition from
`the upper voltage to the lower voltage. The upper and
`lower voltage plateaus are separated by about 1000
`millivolts. The upper voltage plateau is slightly higher
`than the charge cutoff voltage for the cathode material,
`and the lower voltage plateau is slightly lower than the
`discharge cutoff voltage of the cathode material. Of
`course,
`the ideal additive is capable of undergoing a
`reversible reaction with lithium, is a good electron and
`lithium ion conductor, andis stable in combination with
`the cathode active material and the electrolyte.
`Generally, any transition metal oxide or sulfide is a
`candidate for use as a cathode additive. In particular,
`transition metal oxides such as LixMn2O4, LixMoO:,
`Li,CoO2, LixNiO2 and Lix,MyMnq.»)O4, wherein M is
`Co, Cr, or Fe are effective. Such cathode additives are
`effective in a wide variety of secondary lithium cells,
`including Li—MoS2, Li—NbSe3, Li—V20s, and Li-
`—Mn0O:, etc. Preferably, the additive is added to the
`cathode to a concentration of between 1% and 15% by
`weight. As described above with respect to FIG. 3, a
`combination of LizMn204 and Lio. ;MoQ2 provides an
`effective overcharge and overdischarge production for
`Li—Ti&)lithium cells. Any of the cathode additives
`described herein maybeeffective in a single cell lithium
`battery. However, these additives are particularly desir-
`able in multicell lithium batteries wherein the additiveis
`added to the cathode of each cell of the multicell bat-
`tery.
`Althoughillustrated with respect to Li—TiS>lithium
`systems, suitable cathode additives can be selected for
`protecting other secondary lithium systems such as
`Li—MoS>. Li—NbSe3, Li—V20s, Li—MnQhz, and Li,.
`C—LixCoO2.
`Those skilled in the art will appreciate that various
`adaptations and modifications of the just-described pre-
`ferred embodiment can be configured without depart-
`ing from the scope and spirit of the invention. There-
`fore, it is to be understood that, within the scope of the
`appended claims, the invention may be practiced other
`than as specifically described herein.
`Weclaim:
`1. In a secondary lithium cell susceptible to over-
`charging or overdischarging, the improvement being:
`a cathode additive for incorporating into a cathode of
`the cell, the cathode having a charge cutoff voltage
`and a discharge cutoff voltage, the cathode addi-
`tive yielding an upper voltage plateau within the
`cell upon the application of an overcharge voltage
`to the cell, said upper voltage plateau beingslightly
`higher than the charge cutoff voltage of the cath-
`ode and yielding a lower voltage plateau within the
`cell upon the application of an overdischarge volt-
`age to the cell, said lower voltage plateau being
`slightly lower than the discharge cutoff voltage
`plateau of the cathode.
`2. The improvement of claim 1, wherein the additive
`is a transition metal oxide.
`3. The improvementof claim 1, wherein the additive
`is a sulfide.
`4. The improvement of claim 2, wherein the cathode
`additive is selected from a group consisting of Li,.
`Mn20q, LixMoQ2, LixCoO2, LixNiO2, and LixMyMnq.
`y)O4, wherein M is Co, Cr, or Fe.
`5. The improvement of claim 1, wherein the cathode
`additive is a mixture of LigMn204 and Lio ;MoO3.
`
`10
`
`5_
`
`45
`
`6
`6. The improvementof claim 1, wherein the second-
`ary lithium cell is selected from a group consisting of
`Li—TiS2, Li—MoS2, Li—NbSe3, Li—V20s, Li—M-
`nOQz, and Li,C—Li,CoO3.
`7. The improvementof claim 1, wherein the second-
`ary lithium cell is a liquid electrolyte cell.
`8. The improvement of claim 1, wherein the second-
`ary lithium cell is a solid state cell.
`9. The improvementof claim 8, wherein the second-
`ary lithium cell is a polymeric electrolyte cell.
`10. The improvementof claim 1, wherein the upper
`and lowerplateaus are separated by at least 1000 milli-
`volts.
`11. The improvementof claim 1, wherein the additive
`is an electron and lithium ion conductor.
`12. The improvementofclaim 1, wherein the additive
`is a single compound additive which creates a sharp
`transition between the upper and lower voltage pla-
`teaus.
`
`13. The improvementof claim 1, wherein the additive
`is incorporated into the cathode to a concentration of
`less than 15% by weight.
`14. In a multicell rechargeable lithium battery suscep-
`tible to over-charging and overdischarging,
`the im-
`provementbeing:
`a cathode additive for incorporating into a cathode of
`each cell of the multicell battery, said cathode
`additive selected from a group consisting of Li,.
`Mn204, LixMoO2, LixCoO2, LixNiOz, and Li,.
`MyMnq2.yj04, wherein M is Co, Cr, or Fe, said
`secondarylithium cell being ofa type selected from
`a group consisting of Li—TiS2, Li—MOS:,
`Li—NbSe3, Li—V20s, Li—MnOz,and Li,C—Li,.
`CoO, each cathode having a charge cutoff voltage
`and a discharge cutoff voltage, the cathode addi-
`tive yielding an upper voltage plateau within each
`respective cell upon the application of an over-
`charge voltage to the respective cell, said upper
`voltage plateau being slightly higher than the
`charge cutoff voltage of the cathode ofthe respec-
`tive cell and yielding a lower voltage plateau
`within each respective cell upon the application of
`an over-discharge voltage to the respective cell,
`said lower voltage plateau being slightly lower
`than the discharge cutoff voltage plateau of the
`cathode of the respective cell.
`15. The improvementof claim 14, wherein the cath-
`ode additive is a mixture of LizMn204 and Lip.1.MoQ).
`16. The improvement of claim 14, wherein the sec-
`ondarylithium cell is a solid state cell.
`17. The improvement of claim 16, wherein the sec-
`ondary lithium cell is a polymericelectrolyte cell.
`18. The improvementof claim 14, wherein the upper
`and lowerplateaus are separated byat least 1000 milli-
`volts.
`19. The improvementof claim 14, wherein the addi-
`tive is an electron and lithium ion conductor.
`20. The improvementof claim 14, wherein the addi-
`tive is a single compound additive which creates a sharp
`transition between the upper and lower voltage pla-
`teaus.
`
`65
`
`21. The improvementof claim 14, wherein the addi-
`tive is incorporated into the cathodeto a concentration
`of less than 15% by weight.
`22. In a multicell rechargeable solid state lithium
`battery susceptible to over-charging and overdischarg-
`ing, the improvementbeing:
`
`7
`
`

`

`3,278,000
`
`7
`a cathode additive for incorporating into a cathode of
`each cell of the multicell battery, said cathode
`additive being a mixture of LigMn204 and Lip.
`I1MoO3, said secondary lithium cell being a Li-
`—TiS2 cell, each cathode having a charge cutoff
`voltage of about 2.7 volts and a discharge cutoff
`voltage of about 1.7 volts, the cathode additive
`
`8
`yielding an upper voltage plateau of about 2.9 volts
`within each respective cell upon the application of
`an overcharge voltage to the respective cell, and
`yielding a lower voltage plateau of about 1.6 volts
`within each respective cell upon the application of
`an overdischarge voltage to the respective cell.
`*
`*
`*£
`&
`&
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`60
`
`65
`
`8
`
`