.
`Sep. 7, 1999
`$371 Date:
`§ 102(e) Date: Sep. 7, 1999
`(87) PCT Pub. No.:: WO98/28812
`PCT Pub. Date: Jul. 2, 1998
`Foreign Application Priority Data
`(30)
`Dec. 20, 1996
`(DK)
`ceeesssesssssessssesesseessssceseneesnteeesnseesnes 1459/96
`(51)
`Int. Cl.
`Eeeeneeranareneeeeeecereeeeennaeeeeeeresereeeeseenee HOIM 6/22
`(52) US. Che oes 429/301; 429/303; 429/308;
`429/316; 29/623.1
`(58) Field of Search wo. 429/301, 303,
`429/306, 308, 316; 29/623.1
`.
`References Cited
`U.S. PATEN'! DOCUMENTS
`
`(56)
`
`O. Bohnke,
`et al, J. Electrochem. Soc., 139:7, pp.
`1862-1865, 1992 (Jul.).
`* cited by examiner
`Primary Examiner—Stephen Kalafut
`(74) Attorney, Agent, or Firm—Darby & Darby
`(57)
`ABSTRACT
`A lithium secondary battery with an electrolyte containing
`one or more alkai metal salts, one or more non-aqueous
`solvents and immobilized by a polymer selected from cel-
`lulose acetates, cellulose acetate butyrates, cellulose acetate
`propionates, polyvinylidene fluoride-hexafluoropropylenes
`and polyvinylpyrrolidone-vinyl acetates, the polymer pref-
`crably being uscd in an amount of at most 15% by weight
`based on the weight of the salts, solvents and polymerofthe
`electrolyte system, with the proviso that
`in the case of
`polyvinlidene fluoride-hexafluoropropylenes, the polymeris
`present in an amount of at most 12% by weight based on the
`weight of the salts, solvents and polymerof the electrolyte
`7/1975 Gillmanetal. .
`3,894,889
`system. The immobilized electrolyte does not cause prob-
`8/1993 Chuaet al.
`.
`5,240,790
`lems with respectto leakage from the cell compartment and
`3/1994 Gozdzetal. .
`5,296,318
`the elctrolyte also high conductivity
`implying
`a capacit
`11/1995 Williamsetal. .
`3,470,677
`
`
`5,589,295 implyingacapacity12/1996 Derzonetal. . € eletroly! $ dvity
`
`
`
`5,665,265
`9/1997 Ges et ale
`sesssessssssessnseeue 252/62.2
`_—‘Ulilization moreclosely approachingtheutilization observed
`5,681,357 * 10/1997 Eschbach et ale cesses 429/303 X
`for batteries using liquid electrolyte. The electrolyte is also
`5,962,168 * 10/1999 Denton vrrccecvccssseseeveeeeeveee 429/199 K_electrochemically stable.
`
`oe 429/317
`6,013,393 *
`1/2000 Taniuchi et al.
`6,027,836 * 10/2000 Okada el al. wee 429/306 X
`
`a2) United States Patent
`US 6,280,881 B1
`(10) Patent No.:
`Wendsjo etal.
`(45) Date of Patent:
`Aug. 28, 2001
`
`
`US006280881B1
`
`(54) LITHIUM SECONDARY BATTERY
`(75)
`Inventors: Asa Wendsjo, Odense C; Steen
`¥de-Andersen, Odense S, both of (DK)
`
`(73) Assignee: Danionics A/S, Odense S. (DK)
`
`6,051,342 *
`4/2000 Hamand et al. oo. 429/303
`FOREIGN PATENT DOCUMENTS
`0651455
`5/1995 (EP).
`0724305
`7/1996 (EP).
`0798791
`10/1997 (EP).
`WO 96/18215
`6/1996 (WO).
`WO 97/12409
`4/1997 (WO) .
`Subject to anydisclaimer, the term of this
`patent is extended or adjusted under 35
`OTHER PUBLICATIONS
`US.C. 154(b) by 0 days.
`Patent Abstracts of Japan, 02020537, Jan. 24, 1990.
`
`(21) Appl. No.:—09/319,798 Patent Abstracts of Japan, 04267057, Sep. 22, 1992.
`(22) PCT Filed:
`Dec. 19, 1997
`Patent Abstracts of Japan, 04366563, Dec. 18, 1992.
`RU 2075799 (Uuniv. Sarat Tech. Techn,
`Inst.)
`
`(*) Notice:
`
`(WPI
`
`4
`
`18 Claims, No Drawings
`
`APPLE-1017
`
`APPLE-1017
`
`1
`
`

`

`US 6,280,881 B1
`
`1
`LITHIUM SECONDARY BATTERY
`
`This invention relates to a lithium secondarybattery, and
`particularly to the electrolyte used therein and to the prepa-
`ration of the battery.
`technology
`Recent developments in electrochemical
`have provided systems such as primary and sccondary
`lithium batteries of high specific energy per unit of volume,
`typically in the range 175-250 Wh/.
`Such secondary batteries are typically based on negative
`electrode structures of metallic lithium, alloys thereof or on
`carbonsof high lithium intercalation capacity. The positive
`electrode structures are typically based on transition metal
`oxides. The electrolyte comprises one or more non-aqueous
`solvents, and one or more lithium-salts.
`The fact that the electrolyte is a liquid at the battery
`operation temperature may cause safety problems such as
`electrolyte leakage from the cell compartment. Upon reac-
`tion with oxygen and water in the atmosphere, severe
`corrosion of the battery may occur.
`Several attempts have been made to solve this safety
`issueof lithium basedbatteries. The traditional approach has
`been solid polymer electrolytes, ic. electrolyte structures
`whichare based on ionic conduction within a solid polymer
`network. Such polymerelectrolytes provide batteries of high
`safety, as no electrolyte leakage can take place.
`Polymerelectrolytes are described in a numberof patents
`and patent applications, including the following:
`EP 724,305 A1 to Sony Corporation, which describes gel
`electrolytes of a polymer having a side chain to which at
`least one nitrile group is bonded.
`U.S. Pat. No. 5,240,790 to Alliant Techsystems Inc.,
`which covers a gelled electrolyte comprising
`polyacrylonitrile, preferably of a relative concentration of
`12-22 mole percent.
`USS. Pat. No. 5,589,295 to Derzon et al, which describes
`a thin film electrolyte with a polymeric gel-former selected
`from the group of polyacrylonitrile and polyvinylidenefluo-
`ride.
`The drawback of batteries based on such solid polymer
`electrolytes is reduced capacity and powercapability, espe-
`cially at low temperature. Compared to liquid electrolytes,
`the conductivity of solid polymer electrolytes is lower,
`mainly due to reduced ionic mobility. Further, the activation
`energy for the ionic migration process is higher than for the
`liquid electrolytes, implying strong conductivity variation
`with temperature and significantly reduced low-temperature
`performance. The capacity and powercapability are strongly
`dependent on the electrolyte conductivity; at low conduc-
`tivity high internal
`impedance implies high losses and
`reduced capacity acccssability.
`Therefore a need exists for secondary lithium batteries
`based on polymer electrolyte systems, which combine the
`demands for high safety and high conductivity.
`An object of the present inventionis to providea lithium
`secondary battery which avoids problems with respect to
`electrolyte leakage from the cell compartment but which
`also provides high conductivity sufficient for full capacity
`utilisation, i.e. which does not imply the same reduction in
`capacity utilisation comparedto lithium secondary batteries
`based on liquid electrolytes that is associated with known
`polymerelectrolytes.
`The present invention provides a lithium secondary bat-
`tery comprising an immobilized electrolyte containing one
`or more alkali metal salts, one or more non-aqueoussolvents
`and an immobilizing polymer, wherein the immobilizing
`polymeris selected from the group consisting of cellulose
`
`10
`
`15
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`2
`acetates, cellulose acetate butyrates, cellulose acetate
`propionates, polyvinylidene fluoride-hexafluoropropylenes
`and polyvinypyrrolidone-vinyl acetates, with the proviso
`that
`in the case of polyvinylidene fluoride-
`hexafluoropropylenes, the polymer is present in an amount
`of at most 12% by weight based on the weightofthe salts,
`solvents and polymerof the clectrolytc system.
`Surprisingly,
`it has been found that lithium secondary
`batteries which comprise as an electrolyte component an
`immobilising polymer selected from the group of cellulose
`acetates, cellulose acetate butyrates, cellulose acetate
`propionates, polyvinylidene fluoride-hexafluoropropylenes
`and polyvinylpyrrolidone-vinyl acetates does not cause
`problems with respect to electrolyte leakage from the cell
`compartment. Further, the electrolytes of such batteries have
`a high conductivity implying a capacity utilisation more
`closely approaching the utilisation observed for batteries
`using liquid electrolyte. Still further, the electrolytes of such
`batteries are electrochemically stable, ie. they are not oxi-
`dised or reduced even under the redox conditions observed
`in high voltage lithium batteries.
`Compared to the known technologyon polymerelectro-
`lyte based secondary batteries referred to above, the poly-
`mers used according to the invention are generally present in
`relatively small amounts, preferably at most 15% by weight
`based on the weight of the salts, solvents and polymerofthe
`electrolyte system,
`the
`According to one embodiment of the invention,
`cellulose polymers used according to the present invention
`will usually be present in an amount ranging from 0.1% to
`10% by weight of the complete electrolyte system, i.e. the
`total weightof salts, solvents and polymer, preferably 1% to
`8% by weight, more preferably 2% to 5% by weight.
`In another embodiment of the invention,
`the polyvi-
`nylidene fluoride-hexafluoropropylenes are present in an
`amount of from 1% to 12% by weight of the complete
`electrolyte system,
`i.c.
`the weight of salts, solvents and
`polymer, preferably 2 to 10% by weight, more preferably
`4% to 8% by weight. In a still further embodiment of the
`invention the polyvinylpyrrolidone-vinyl acetates will usu-
`ally be present in an amount from 1% to 15% by weight of
`the complete electrolyte system,i.e. the total weightof salts,
`solvents and polymer, preferably 3% to 12% by weight,
`more preferably 5% to 10% by weight.
`WO 97/12409 to Valence Technology describes “viscosi-
`fiers” tor electrolytes, which are selected trom the group of
`polyethylene oxide, polypropylene oxide, carboxymethyl-
`cellulose and polyvinylpyrrolidone. Although this patent
`specification describes the use of “viscosifiers” based on a
`cellulose compound and a polyvinylpyrrolidone, it does not
`describe the specific immobilising agents ccllulose acctates
`and polyvinylpyrrolidone-vinyl acetates used according to
`the present invention.
`U.S. Pat. No. 5,296,318 to Bell Communications
`Research discloses an electrolyte comprising a self-
`supporting film of a copolymer of vinylidene fluoride and
`hexafluoropropylene. Such copolymeris preferably present
`in the electrolyte in an amount corresponding to 30 to 80%
`of the electrolyte. Although the patent describes the use of
`polyvinylidene fluoride-hexafluoropropylene,
`it does not
`describe or suggest the use of this material in amounts as
`small as 12% or less by weight of the electrolyte system.
`The immobilizing properties of the polymers used
`according to the present invention may be improved by
`crosslinking.
`In a preferred embodiment, the immobilizing properties
`of the cellulose polymers used according to the invention are
`
`2
`
`

`

`US 6,280,881 B1
`
`3
`improved by crosslinking. In this embodiment, cellulose
`acetates, cellulose acetate butyrates and cellulose acetate
`propionates, preferably of high hydroxyl content,
`for
`example 3% by weight or more, are mixed with monomers
`or oligomers, which bear functional groups, and which can
`be crosslinked upon heat curing or upon exposure to
`UV-light or electron beams. Such monomers and polymers
`are preferably selected from urea formaldehyde, melamine
`and polyisocyanate polymers.
`In another preferred embodiment of the invention, the
`electrolyte of the lithtum secondary battery comprises, in
`addition to the immobilising polymer, one or more solvents
`selected from organic carbonates,
`lactones, esters and
`glymes, more preferably selected from the groupsof:
`(a) alicyclic carbonates represented by the following general
`formula:
`
`(=0)—O—CR,R.-{CR;R,], —CR.R,—O—,
`
`wherein each of R,, R,, R3, Ry, R; and R, independently
`represents hydrogen or a C,—-C, alkyl group and m is 0
`or 1, preferably ethylene carbonate or propylene car-
`bonate;
`(b) aliphatic carbonates represented by the general formula
`R[OC(O)],OR,;, wherein each of R, and R, indepen-
`dently represents a C,—C, alkyl group, and p is an integer
`equal to 1 or 2, preferably dimethyl carbonate or diethyl
`carbonate;
`(c) lactones in the form of cyclic esters represented by the
`general formula:
`
`{CRisRic]-
`C(=0)
`CReRyo— CRRi
`CRi3Ri4—O:
`
`10
`
`15
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`4
`polyethylene, polypropylene, polycarbonate, cellulose or
`cellulose derivate, or made from a glass fibre material e.g.
`boronsilicate glass fibre material.
`The separator acts as a matrix which confines the physical
`dimensionsof the electrolyte system, thereby enabling the
`production of thin, self-sustaining and uniform electrolyte
`membrancs. The scparator is preferably a woven or non-
`wovenstructure having a pore size in the range of 10x10 nm
`to 1x1 mm and a thickness of 10-100 um, preferably 10-25
`um. More specifically, the size of the pores can be as in a
`microporousfilm (e.g. a Celgard separator) or up to 1x1 mm
`as in a woven net having a meshofthis size.
`The present invention also provides a simple and eco-
`nomically advantageous method for the preparation of the
`lithium secondarybattery of the invention. In general terms,
`this method comprise the steps of preparing the immobilized
`electrolyte by mixing the solvents (where more than one
`solventis used), dissolving the salt(s) in the solvent mixture,
`adding an immobilizing agentto the solution, and optionally
`crosslinking the immobilizing agent.
`Thus according to another aspect the present invention
`provides a method for the preparation of a lithium secondary
`battery as defined above, comprising the steps of:
`mixing the solvents in case the electrolyte comprises more
`than onc solvent,
`dissolving the salt(s)
`organic electrolyte,
`adding the immobilizing polymer and optionally mono-
`mers or oligomers having one or more polymerisable
`functional groups, to the organic electrolyte,
`if monomers or oligomers are added, inducing polymeri-
`sation of these monomers or oligomers,
`sandwiching the immobilized organic electrolyte between
`a positive electrode laminate and a negative electrode
`laminate to form the battery.
`Optionally the battery is wound or folded as it is known
`in the art.
`
`in the solvent(s) to provide an
`
`EXAMPLE1
`
`wherein each of Ro, R15, Ry, Ryo, Ris, Ry, Rys and Ry.
`independently represents hydrogen or a C,_, alkyl
`group and r is 0 or 1, preferably y-valerolactone or
`y-butyrolactone;
`(d) esters represented by the formula R,,[C(O)JOR,.
`[OR9], wherein each of R,7, R,, and R,, independently
`According to a still further aspect, the present invention
`represent hydrogen or a C,—-C, alkyl group, and t is 0 or
`also provides the use of a polymer selected from the group
`an integer equal to 1 or 2, preferably an acetate, more
`preferably (2-methoxyethyl)-acetate or ethyl acetate;
`consisting of cellulose acetates, cellulose acetate butyrates,
`(ec) glymes represented by the general
`formula
`cellulose acetate propionates, polyvinylidene fluoride-
`hexafluoropropylenes and polyvinypyrrolidone-vinyl
`R3,0(R2,0),,R5., in which each of R55 and R,» indepen-
`acetates as immobilizing agentfor an electrolyte in a lithium
`dently represents a C,., alkyl group, R,,
`is
`—(CR3R5,CR>5R26)— wherein each of R53, Roa, Ros
`secondary battery, with the proviso that
`in the case of
`and R,, independently represents hydrogen or a C,-C,
`polyvinylidene fluoride-hexafluoropropylenes, the polymer
`
`alkyl group, andnis an integer from 2 to 6, preferably 3, is present in an amountof at most 12% by weight based on
`Rs and R,, preferably being methyl groups, R53, R3,,
`the weight of the salts, solvents and polymerofthe electro-
`lyte system.
`R,, and R,, preferably being hydrogen or C,-C, alkyl
`invention is illustrated by the following
`groups, more preferably hydrogen.
`The present
`Such solvents may contribute furtherto the clectrochem1-
`non-limiting cxamples together with a comparative
`cal stability and ionic conductivity of the electrolyte of the
`example.
`battery.
`Any salt commonly employed as an ion-conductivesalt in
`batteries may be used in the electrolyte system according to
`the invention. Preferably, however, the salt is an alkali metal
`salt of ClO,, CF,;SO,°, AsF,-, PF;~ or BF,, or any
`mixture of such alkali metal or ammonium salts, more
`preferably LiAsF,, LiCF,SO.3, LiPF, or LiBF, or any mix-
`ture thereof. Those salts are preferably present in the elec-
`trolyle solvents in a concentration from 0.01M to 2.5M,
`more preferably 0.1M to 1.5M.
`In a preferred embodimentof the battery of the invention
`the electrolyte is incorporated into a porous separator.
`Thus the immobilized electrolyte according to the inven-
`tion is optionally incorporated into a separator which is a
`porous structure made from a polymer, preferably
`
`A lithium secondarybattery was prepared from a negative
`electrode laminate of a polymer bound carbon coated onto a
`copper current collector, a positive electrode laminate of a
`polymer bound lithium manganese oxide spinel coated onto
`an aluminium current collector, and an electrolyte sand-
`wiched between the electrode laminates.
`
`The carbon was R-LIBA-A (product of Timcal,
`Switzerland). The lithium magnesium oxide spinel was
`prepared by a solid state reaction at 800° C. from Li,CO,
`and MnO, and had a specific capacity of 120 mAh/g. In the
`case of both electrodes, the polymeric binder was EPDM
`(ethylene propylene diene polymethylene).
`
`60
`
`65
`
`3
`
`

`

`US 6,280,881 B1
`
`6
`butyrates, cellulose acetate propionates, and polyvinylidene
`fluoride-hexafluoropropylenes with the proviso that in the
`case of polyvinylidene fluoride-hexafluoropropylenes, the
`polymer is present in an amount or at most 12% by weight
`based on the weightof the salts, solvents and polymerof the
`electrolyte system.
`2. A lithium sccondary battery according to claim 1,
`wherein the immobilizing polymer is present in an amount
`of at most 15% by weight based on the weight ofthe salts,
`solvents and polymerof the electrolyte system.
`3. A lithium secondary battery according to claim 1,
`wherein the polymeris selected from the group consisting of
`cellulose acetates, cellulose acetate butyrates and cellulose
`acetate propionates.
`4. A lithium secondary battery according to claim 3,
`wherein the polymeris present in an amountof from 0.1%
`to 10% by weight based an the weightof the salts, solvents
`and polymer of the electrolyte system.
`5. A lithium secondary battery according to claim 3,
`wherein the cellulose polymer has a hydroxyl content of 3%
`by weight or more.
`6. A lithtum secondary battery according to claim 1,
`wherein the polymer is mixed with monomersor oligomers
`selected from urea formaldehyde, melamine and polyisocy-
`anate polymers.
`7. A lithium secondary battery according to claim 6,
`wherein the polymer is crosslinked upon exposure to heat,
`light or electron radiation.
`8. A lithium sccondary battery according to claim 1,
`wherein the polymer
`is polyvinylidene fluoride-
`hexafluoropropylene.
`9. A lithtum secondary battery according to claim 8,
`wherein the polymeris present in an amount of from 1% to
`12% based on the weightof the salts, solvents and polymer
`of the electrolyte system.
`10. A lithium secondary battery according to claim 1,
`wherein the polymeris present in an amount of from 1% to
`15% by weight based on the weightof the salts, solvents and
`polymer of the electrolyte system.
`11. A lithium secondary battery according to claim 1,
`wherein the electrolyte comprises one or more of the fol-
`lowing solvents (a) to (€):
`(a) alicyclic carbonates represented by the following
`general formula:
`
`C(=0)—O—CR,R,{CR5R,],—CR5R,,—O—,
`
`
`
`wherein each of R,, R,, R;, Ry, Rs and R,; independently
`represents hydrogen or a C,-C, alkyl group and mis an 0
`or 1;
`(b) aliphatic carbonates represented by the gencral for-
`mula R[OC(O)],ORg,, wherein each of R; and Rg
`independently represents a C,—C, alkyl group, and p is
`an integer equal to 1 or 2;
`(c) lactonesin the form of cyclic esters represented bythe
`general formula:
`
`
`C(0)—CRoRyo —CRyRia
`TCR,sRi6],—CRisRisO
`
`A lithium secondary battery was prepared following the
`same procedure as described in the above example 1,
`however, 8% of polyvinylpyrrolidone-vinyl acetate was
`substituted for the 3% CAB of example 1.
`Upon nail penetration (@=5 mm, F=6000N) the battery
`short-circuited, however, no leakage of electrolyte was
`observed on the surface of the battery upon visual inspec-
`tion.
`wherein each of Ro, Rio, Raz, Ryo, Ris, Rua, Ry5 and
`Whatis claimed is:
`R,. independently represents hydrogen or a C,_5
`alkyl group andris 0 or 1;
`1. A lithium secondary battery comprising an immobilized
`(d) esters represented by the formula R,,[C(O)JOR,,
`electrolyte containing one or more alkali metal salts, one or
`more non-aqueous solvents and an immobilizing polymer,
`[OR,o], Wherein each of R,,, Ry, and Ry. indepen-
`wherein the immobilizing polymer is selected from the
`dently represents hydrogen or a C,—-C, alkyl group, and
`group consisting of cellulose acetates, cellulose acetate
`t is 0 or an integer equal to 1 or 2;
`
`5
`The electrolyte was prepared by:
`mixing equimolar amounts of propylene carbonate (PC)
`and cthylene carbonate (EC)
`adding LiBF, to obtain a 1M solution of LIBF, in PC/EC
`adding cellulose acetate butyrate (CAB)to the solution to
`obtain a 3% by weight solution of CAB in 1M LiBF,
`in PC/EC.
`
`incorporating the above CAB electrolyte in a microporous
`polyethylene separator
`The battery prepared had an active electrode area of 365
`cm’ and, subsequent to charging to 4.2V, an internal imped-
`ance of 49 mQ at 1 kHz. When cycled between 4.2V and
`2.5V at 500 mA,the battery displayed an initial capacity of
`358 mAh. After 400 cycles, the capacity was 299 mAh, say
`84% of the initial capacity. At 1.25 A discharge rate, an
`initial capacity of 210 mAh wasobserved.
`Upon nail penetration (0=5 mm, F=6000N) the battery
`short-circuited, however, no leakage of electrolyte was
`observed on the surface of the battery upon visual inspec-
`tion.
`
`Comparative Example
`
`A lithium secondary battery was prepared following the
`same procedure as described in the above example 1,
`however, 1M LIBF, in PC/EC was used, i.e. no cellulose
`acetate butyrate was added to the electrolyte solution.
`Such a battery, based on the same electrodes as in
`example 1 and having the same dimensioanl characteristics
`as the battery of example 1, had an internal impedance of 49
`mQ at | kHz. When cycled between 4.2V and 2.5V at 500
`mA,the battery displayed an initial capacity of 408 mAh.
`After 400 cycles, the capacity was 343 mAh,say 84% ofthe
`initial capacity. At 1.25 A dischargerate, an initial capacity
`of 360 mAh wasobserved.
`
`Upon nail penetration (@=5 mm, F=6000N) the battery
`short-circuited. Leakage of electrolyte was observed on the
`surface of the battery upon visual inspection.
`
`EXAMPLE2
`
`A lithium secondary battery was prepared following the
`same procedure as described in the above example 1,
`however,
`6% of polyvinylidene fluoride-
`hexafluoropropylene was substituted for the 3% CAB of
`example 1.
`Upon nail penetration (0=5 mm, F=6000N) the battery
`short-circuited, however, no leakage of electrolyte was
`observed on the surface of the battery upon visual inspec-
`tion.
`
`10
`
`15
`
`30
`
`35
`
`40
`
`45
`
`50
`
`EXAMPLE 3
`
`55
`
`60
`
`65
`
`4
`
`

`

`US 6,280,881 B1
`
`7
`(c) glymes represented by the general formula R,0
`(R,,0),,R5., in which each of R,, and R,, indepen-
`dently represents a C,_, alkyl groups, R,,
`is
`—(CR,3R3,CR25R>5)— wherein each of Ry3, Ro4, Ros
`and R,, independently represents hydrogen or a C,-C,
`alkyl groups, and n is an integer from 2 to 6.
`12. A lithium sccondary battery according to claim 1,
`wherein the electrolyte comprises one or moresalts selected
`from the group of alkali metal or ammonium salts of ClO”,
`CF,S0,°, AsF,”, PF,” or BF,-.
`13. A battery according to claim 12, wherein the salts are
`present in the electrolyte solvent(s) in a concentration from
`0.01M to 2.5M.
`
`14. A lithium secondary battery according to claim 1,
`wherein the electrolyte is confined in a separator consisting
`of a porous structure made of a polymer or made of a glass
`fibre material.
`
`15. A lithium secondary battery according to claim 14,
`wherein the separator is a woven or non-woven structure
`having a pore size in the range of 10x10 nm to 1x1 mm.
`16. A lithium secondary battery according to claim 14,
`wherein the separator has a thickness of 10-100 sam.
`17. A method for the preparation of a lithium secondary
`battery according to claim 1, comprising the steps of:
`mixing the solvents in casc the clectrolyte compriscs more
`than one solvent,
`
`dissolving the salt(s)
`organic electrolyte,
`
`8
`in the solvent(s) to provide an
`
`10
`
`15
`
`adding the immobilizing polymer and optionally mono-
`mers or oligomers having one or more polymerisable
`functional groups, to the organic electrolyte,
`
`if monomers or oligomers are added, inducing polymeri-
`sation of these monomers or oligomers,
`
`sandwiching the immobilized organic electrolyte between
`a positive electrode laminate and a negative electrode
`laminate to form the battery.
`18. A method of immobilizing an electrolyte in a lithium
`secondary battery comprising an electrolyte system which
`includes salts, solvents and polymer, said method compris-
`ing combining the electrolyte with a polymer selected from
`the group consisting of ccllulose acctates, ccllulose acctate
`butyrates, cellulose acetate propionates and polyvinylidene
`fluoride-hexafluoropropylenes with the proviso that when
`the
`polymer
`is polyvinylidene
`fluoride-
`hexafluoropropylenes, the polymer is present in an amount
`of at most 12% by weight based on the weightofthe salts,
`solvents and polymerof the electrolyte system.
`*
`% eR Ok
`
`5
`
`