CA 02334240 2000-12-04 Sp ecification LITHIUM SECONDARY BATTERY USING GELLED POLYMERIC ELECTROLYTE Technical Field The present invention relates to a lithium secondary battery including spinel type lithium manganese oxide as a positive electrode active material and gelled polymeric electrolyte .as an ion conducting medium, and more particularly, it relates to improvement of a positive electrode for the purpose of providing ~a lithium secondary battery using a gelled polymeric electrolyte with large initial discharge capacity and good charge-discharge cycle performance. Background Art As an ion conducting; medium (electrolyte) of a lithium secondary battery, a liquid electrolyte (electrol;ytic solution) has been conventionally used because of its good ionic conductivity although it has problems of leakage and elution of an electrode material. When a liquid electrolyte is used as an ion conducting medium in a lithium secondary battery using lithium manganese oxide as a positive electrode active material, however, manganese included in the lithium manganese oxide is gradually eluted into the liquid electrolyte, resulting in causing a problem that the discharge capacity is degraded in a small number of charge-discharge cycles. When a solid electrolyte (such as a film and a foil) is used instead of a ~5 liquid electrolyte, the degradation of the discharge capacity due to the elution of 1 CA 02334240 2000-12-04 manganese into the electrolyte can be avoided. The ionic conductivity of the solid electrolyte is, however, generally lower than that of the liquid electrolyte, and a contact area between the electrolyte and the electrode is so small that the electric resistance (interface resistance) on the interface between the electrolyte and the electrode is large.. Therefore, the discharge capacity, at high rate lischarge in particular, is degraded. Accordingly, as an ion conducting medium for improving the disadvantages of and making the best use of the advantages of the liquid electrolyte and the solid electrolyte, a gelled electrolyte, particularly a gelled polymeric electrolyte that can be easily formed into a thin film and is inexpensive, has been recently proposed. A gelled polymeric electrolyte is a gelled substance obtained by impregnating a liquid electrolyte including a solute (electrolytic salt) and a solvent into a matrix of a polymer (resin). Since a gelled polymeric electrolyte: includes a liquid electrolyte, it has higher ionic conductivity than a solid electrolyte, and since the liquid electrolyte is fixed through gelation within the matrix of the gelled polymeric electrolyte, manganese is minimally eluted into the liquid electrolyte. When a gelled polymeric electrolyte is used, however, a contact area between the electrode and the electrolyte is smaller than in using a liquid electrolyte. Therefore, the electric resistance (interface resistance) on the interface between the electrode and the electrolyte is large as in using a solid electrolyte. As a result, the discharge capacity, at high rate discharge in particular, is degraded. Accordingly, an object of the invention is providing a lithium secondary battery using a gelled polymeric electrolyte with large initial discharge capacity 2 CA 02334240 2000-12-04 and good charge-discharge cycle performance. Disclosure of Invention The lithium secondary battery using a gelled polymeric electrolyte of this invention (present battery) comprises a positive electrode including a gelled polymeric electrolyte (A) and using spinel type lithium manganese oxide as an active material; a negative electrode; and a gelled polymeric electrolyte (B) in the shape of a film or sheet also serving as a separator, and the gelled polymeric electrolyte (A) and the gelled polymeric electrolyte (B) are made from a polymer of poly(alkylene oxide) series impregnated with a liquid electrolyte. Both the gelled polymeric electrolyte (A) included in the positive electrode and the gelled polymeric electrolyte (B) in the shape of a film or sheet also serving as a separator are the polymers of poly(alkylene oxide) series impregnated with a liquid electrolyte. Examples of the polymer of paly(alkylene oxide) series are polyethylene oxide), polypropylene oxide), a block copolymer of polyethylene oxide) and polystyrene, a block copolynner of polyethylene oxide) and polypropylene oxide, polyetherimide, polyethersmlfone, polysiloxane and polysulfone. From the viewpoint of the charge-discharge cycle performance, the block copolymer of polyethylene oxide) and polystyrene is particularly preferred. In particular, the polymer of poly(alkylene oxide) series used for the gelled polymeric electrolyte (B) preferably h;~s high mechanical strength and a large molecular weight. When, for example, polyethylene oxide) is used, the number average molecular weight Mn is preferably approximately two million through eight million. 3 CA 02334240 2000-12-04 Examples of the electrolyte used for impregnating the polymer of poly(alkylene oxide) series are LiCl04, LiCF3S03, LiPFs, LiBF4, LiSbFs, LiAsFs, LiN(C",FZr"+150~(CnF2n+~SO~;) (wherein m and n independently indicate an integer ranging between 1 and 5), and LiC(CpF2p+1SO~(CqFZQ+1SO~(C,FZ,.~.150~ (wherein p, q and r independently indicate an integer ranging between 1 and 5). examples of the solvent arE: ethylene carbonate, propylene carbonate, butylene carbonate, vi.nylene carbonate, dimethyl carbonate, diethyl carbonate, methylethyl carbonate, y -butyrolactone, sulfolane, 1,2-dimethoxyethane, 1,2- diethoxyethane, 1,2-ethox;ymethoxyethane, tetrahydrofuran, 2-methyl-1,3- dioxolane, 4-methyl-1,3-dioxolane, dimethyl ether, diethyl ether, ethyl acetate and methyl propionate. The liquid electrolyte preferably includes LiN(CmF2m+150~(CnF2"+~50~;1 (wherein m and n independently indicate an integer ranging between 1 aired 5) andlor LiC(CPFZP+1SO~(CqF2q+1SO~(C1.F2~1SO~ (wherein p, q and r independently indicate an integer ranging between 1 and 5) in a concentration of 0.1 through 2.0 mol/liter because the elution of manganese can be thus effectively suppressed during charge-discharge cycles. When another solute is used together with LiN(CmFZm+150~(C"FZ"+~SO~ (wherein m and n independently indicate an integer ranging between 1 and 5) andlor LiC(CPF2p+1SO~(CqF2q+150~(C,F2~.1SO~ (Where~.n p, q and r independently indicate an integer ranging between 1 and 5), the concentration of the solutes in the liquid electrolyte is prefi:rably lower than 2.0 mol/liter. In the case where the gelled polymeric electrolyte (A) and the gelled polymeric electrolyte (B) are made from the same material, a film of a polymer of poly(alkylene oxide) series is formed on a positive electrode by a casting method or the like, and part of the cast polymer of poly(alkylene oxide) series is allowed 4 CA 02334240 2000-12-04 to be included in the positive electrode at the same time. Subsequently, the polymer of poly(alkylene oxide) serves is impregnated with the same liquid electrolyte. In this manner, the film-like gelled polymeric electrolyte (B) also serving as the separator and the positive electrode including the gelled polymeric electrolyte (A) are preferably integrally fabricated because the fabrication can be thus eased and the contact resistance between the gelled polymeric electrolyte also serving as the separator and the positive electrode can be lowered. The spinel type lithium manganese oxide used as the active material of the positive electrode is lithium manganese oxide having a spinel structure belonging to the cubic system. A specific example of the spinel type lithium manganese oxide is LiM,~M:n2.X04 (wherein M is at least one element selected from the group consisting of Ni, Al, Mg, Fe and Co; and 0 <_ x <_ 0.5). Examples of the material for the negative electrode are a substance capable of electrochemically occluding and-discharging lithium ions and metallic lithium. Examples of the :substance capable of electrochemically occluding and discharging lithium ions .are a carbon material such as graphite (natural graphite and artifiicial graphite), coke and an organic baked substance; lithium alloy such as lithium - aluminum alloy, lithium- magnesium alloy, lithium - indium alloy, lithium - tin alloy, lithium - thallium alloy, lithium - lead alloy and lithium - bismuth alloy; and a metal oxide or metal sulfide including one of or two or more of tin, titanium., iron, molybdenum, niobium, vanadium and zinc. Since the present battery uses a positive electrode including a specific gelled polymeric electrolyte (A), the contact area between the positive electrode active material and the gelled polymeric electrolyte is large. Accordingly, the 5 CA 02334240 2005-02-07 present battery can attain large initial discharge capacity (at high rate discharge in particular). Also, since the present battery uses a specific gelled polymeric electrolyte (B) as the electrolyte, manganese included in spinel type lithium manganese oxide is minimally eluted, which can reduce the degradation of the discharge capacity derived from elution of manganese during charge- discharge cycles. Accordingly, the present battery can exhibit good charge- discharge cycle performance. According to an aspect of the present invention there is provided a lithium secondary battery comprising a positive electrode comprising a lithium manganese oxide spinet as the active material and a gelled polymeric electrolyte (A), a negative electrode, and a gelled polymeric electrolyte (B) in the shape of a film or sheet serving as a separator, the gelled polymeric electrolyte (A) and the gelled polymeric electrolyte (B) each being made from the same material which is a block copolymer of polyethylene oxide) and polystyrene impregnated with a liquid electrolyte. Brief Description of Drawing Figure 1 is a sectional view of a lithium secondary battery using a gelled polymeric electrolyte fabricated in an embodiment. Preferred Embodiments The present invention will now be described in detail on the basis of preferred embodiments thereof, and it is noted that the invention is not limited to the following embodiments but can be practiced with appropriate modification without departing from the scope of the invention. 6 CA 02334240 2005-02-07 Lithium nitrate (LiNO~, nickel nitrate (Ni(NO~~ and manganese acetate (Mn(CH3C00)~ were mixed in a molar ratio of 1:0.4:1.6, and the mixture was baked at 600 .degree.C for 24 hours in the air, thereby obtaining ~10.4~1.6~4- Then, the L11V1p.41Y1111.604 was crushed with a jet mill, so as to prepare a spinel type lithium manganese oxide powder with a median diameter of 10 a m. The spinel type lithium manganese oxide powder, a carbon powder 6a CA 02334240 2000-12-04 serving as a conductive agent and a poly(vinylidene fluoride) powder serving as a binder were mixed in a weight ratio of 85:10:5, and the mixture was kneaded with NMP (N-methyl-2-pyre.~olidone) to give a paste. The paste was applied on a positive electrode collector (stainless steel plate) by a doctor blade method (to attain a thickness of 80 ,u m after drying), and the resultant was heated at 130.degree.C, thereby preparing a positive electrode (porous electrode) in the shape of a disk with a diameter of 10 nam. Preparation o_f ~ .,~gl ynol3~meric elPCtrnl_~k~te al-so raring as senar~ o Polyethylene glycol) ethyl ether acrylate (with a number average molecular weight Mn of 3~0; CH2=CH-COO-(CHZ CHZ 0)n-CH2 CH3) and a liquid electrolyte obtained by dissolving 1 M (mol/liter) of LiC104 in a mixed solvent including ethylene carbonate and dimethyl carbonate in a volume ratio of 2:3 were mixed in a 'weight ratio of 1:1. The mixture was applied on the positive electrode into a t~fiickness of 25 ,u m, and irradiated with electron beams with a beam irradiation apparatus with electron curtain system (having output power of 200 kV, exposure of 2 Mrad and a travel speed of an irradiated target of 1 mlmin.), thereby polymerizing the polyethylene glycol) ethyl ether acrylate. Thus, a gelled polymeric electrolyte film also serving as a separator was formed on one face of the positive electrode. It was confirmed through observation with a scanning electron microscope (SEM) that the gelled polymeric electrolyte had entered the inside of the positive electrode. Prenaratzon of negai;iy~ a . . rod . A graphite powder vvith an average particle size of 10 a m serving as a lithium ion occluding agent and poly(vinylidene fluoride) serving as a binder were mixed in a weight ratio of 95:5, and the mixture was kneaded with NMP to 7 CA 02334240 2000-12-04 give a paste. The paste was applied on a negative electrode collector (stainless steel plate) by the doctor blade method (to attain a thickness of 70 ,u m after drying), and the resultant was heated at 130.degree.C, thereby preparing a negative electrode in the shape of a disk with a diameter of 10 mm. Fabrication of Ltluum second~r~~ batte_r« using gelled ~,o]vmer;c electrolyte The negative electrode was placed on the gelled polymeric electrolyte film formed on one face of the positive electrode and the resultant was housed in a battery can, thereby fabricating a flat lithium secondary battery (present battery) A1 using the gelled polymeric electrolyte. The capacity ratio between the positive electrode and the negative electrode was set to 1:1.1, so as to control the battery capacity by the positive electrode capacity. In every battery described below, the capar:ity ratio between the positive electrode and the negative electrode was also set to 1:1.1. Figure 1 is a sectional view of the lithium secondary battery .A1 using the gelled polymeric electrolyte, and the battery A1 of Figure 1 comprises a positive electrode 1, a negative electrode 2, a gelled polymeric electrolytE; film 3 for separating these electrodes, a positive electrode can 4, a negative electrode can 5, a positive electrode collector G, a negative electrode collector ?, an insulating packing 8 and the like. The positive electrode 1 and thE~ negative electrode 2 opposing each other with the gelled polymeric electrolytic film 3 impregnated with a liquid electrolyte sandwiched therebetween are housed in the battery can formed by the positive electrode can 4 and the ne~~ative electrode can 5. The positive electrode 1 is connected to the positive elf>ctrode can 4 through the positive electrode collector G, and the negative electra~de 2 is connected to the negative electrode can 5 8 CA 02334240 2000-12-04 through the negative electrode collector 7, so that chemical energy generated within the battery can be taiken out as electric energy. Lithium nitrate, aluminum hydroxide (Al(OH)~ and manganese acetate were mixed in a molar ratio of 1:0.4:1.6, and the mixture was baked at 800.degree.C for 24 hours in the air, thereby obtaining LiAlo,4Mn1.6O4. The LiAlo.4Mno.s04 was crushed with a jet mill to ~;we a spinel type lithium manganese oxide powder with a median diameter of 10 ,u m. The spinel type lithium manganese oxide powder, a carbon powder serving as a conductive agent and a poly(vinylidene fluoride) powder serving a;~ a binder were mixed in a weight ratio of 85:10:5. The mixture was kneaded v~ith NMP to give a paste. The paste was applied on a positive electrode collector (stainless steel plate) by the doctor blade method (to attain a thickness of 80 ,u m after drying), and the resultant was heated at 130.degree.C. Thus, a positive elE;ctrode (porous electrode) in the shape of a disk with a diameter of 10 mm was prepared. Next, polyethylene glycol) ethyl ether acrylate (with a number average molecular weight Mn of 3'60; CHZ=CH-C00-(CHZ CHz O)n-CH2 CHI and a liquid electrolyte obtained by dissolving 1 M (mollliter) of LiC104 in a mixed solvent including ethylene carbonate and dimethyl carbonate in a volume ratio of 2:3 were mixed in a weight ratio of 1:1. The resultant was applied on the positive electrode into ;~ thickness of 25 a m, and irradiated with electron beams with a beam irradiaiaon apparatus with electron curtain system (having output power of 200 kV, exposure of 2 Mrad and a travel speed of an irradiated target of 1 m/min.), thereby polymerizing the polyethylene glycol) ethyl ether acrylate. Thus, a gelled polymeric electrolyte hlm also serving as a separator 9 CA 02334240 2000-12-04 was formed on one face of the positive electrode. It was confirmed through observation with a scanxiing electron microscope (SEM) that the gelled polymeric electrolyte had entered the inside of the positive electrode. Then, a negative electrode (the same as that prepared in Embodiment 1) was placed on the gelled polymeric electrolyte film formed on one face of the positive electrode and the resultant was housed in a battery can. Thus, a flat lithium secondary battery (present battery) A2 using the gelled polymeric electrolyte was fabricated. Fmho im n Lithium nitrate, magnesium acetate (Mg(CH3C00)~ and manganese acetate were mixed in a molar ratio of 1:0.4:1.6, and the mixture was baked at 700 .degree.C for 24 hours in the air, thereby obtaining LiMgo.4Mnl.s04- The ~g0.4~0.604 was crushed with a jet mill to give a spinel type lithium manganese oxide powder with a median diameter of 10 ,u m. The spinel type lithium manganese oxide powder, a carbon powder serving as a conductive agent and a poly(vinylidene ffuoxzde) powder serving as a binder were mixed in a weight ratio of 85:10:5. The mixture was kneaded with NMP to give a paste. The paste was applied on a positive electrode collector (stainless steel plate) by the doctor blade method (to attain a thickness of 80 a m after drying), and the resultant was heated at 130.degree.C. Thus, a positive electrode (porous electrode) in the shape of a disk with a diameter of 10 mm was prepared. Next, polyethylene glycol) ethyl ether acrylate (with a number average molecular weight Mn of 3Ei0; CH2=CH-COO-(CHZ CHZ O)n-CHZ CHI and a liquid electrolyte obtained by dissolving 1 M (mol/liter) of LiC104 in a mixed solvent including ethylene carbonate and dimethyl carbonate in a volume CA 02334240 2000-12-04 ratio of 2:3 were mixed in a~ weight ratio of l:l. The resultant was applied on the positive electrode into <i thickness of 25 ,u m, and irradiated with electron beams with a beam irradiation apparatus with electron curtain system (having output power of 200 kV, exposure of 2 Mrad and a travel speed of an irradiated target of 1 m/min.), thereby polymerizing the polyethylene glycol) ethyl ether acrylate. Thus, a gelled polymeric electrolyte elm also serving as a separator was formed on one face of the positive electrode. It was confirmed through observation with a scanning electron microscope (SE1VI) that the gelled polymeric electrolyte had entered the inside of the positive electrode. Then, a negative electrode (the same as that prepared in Embodiment 1) was placed on the gelled polymeric electrolyte film formed on one face of the positive electrode and the resultant was housed in a battery can. Thus, a flat lithium secondary battery (present battery) A3 using the gelled polymeric electrolyte was fabricated. Embodiment 4 Lithium nitrate, ferric nitrate (Fe(NO~~ and manganese acetate were mixed in a molar ratio of 1:0.4:1.6, and the mixture was baked at 700 for 24 hours in the air, thereby obtaining LiFeo,4lVly.s04. The LiFeo.4~o.s04 was crushed with a jet mill to give a spinel type lithium manganese oxide powder with a median diameter of 10 ~c m. The spinel type lithium manganese oxide powder, a carbon powder serving as a conductive agent and a poly(vinylidene fluoride) powder serving as a binder were mixed in a weight ratio of 85:10:5. The mixture was kneaded with NMP to give a paste. The paste was applied on a positive electrode collector (stainless steel plate) by the doctor blade method (to attain a thickness of 80 a m after drying), and the resultant was heated at 11 CA 02334240 2000-12-04 130.degree.C. Thus, a positive electrode (porous electrode) in the shape of a disk with a diameter of 10 mm was prepared. Next, polyethylene glycol) ethyl ether acrylate (with a number average molecular weight Mn of 360; CHZ=CH-COO -(CHZ CH2-O)n-CHZ (~H~ and a liquid electrolyte obtained by dissolving 1 M (mol/liter) of LiCl04 in ;a mixed solvent including ethylene carbonate and dimethyl carbonate in a volume ratio of 2:3 were mixed in a weight ratio of 1:1. The resultant was applied o~n the positive electrode into a thickness of 25 a m, and irradiated with electron beams with a beam irradiation apparatus with electron curtain system (having output power of 200 kV, exposure of 2 Mrad and a travel speed of an irradiated target of 1 m/min.), thereby polymerizing the polyethylene glycol) ethyl ether acrylate. Thus, a gelled polymeric electrolyte film also serving as a separator was formed on one face of the positive electrode. It was confirmed through observation with a scanning electron microscope (SEM) that the gelled polymeric electrolyte had entered the inside of the positive electrode. Then, a negative electrode (the same as that prepaxed in Embodiment 1) was placed on the gelled polymeric electrolyte film formed on one face of the positive electrode and the rEaultant was housed in a battery can. Thus, a flat lithium secondary battery (present battery) A4 using the gelled polymeric electrolyte was fabricated. Embodiment 5 Lithium nitrate, cobalt acetate (Co(CH3C00)~ and manganese acetate were mixed in a molar ratio ~of 1:0.4:1.6, and the mixture was baked at ?00.degree.C for 24 hours in the air, thereby obtaining LiCoo.4Mn1.604. The LiCoo.4Mnp.s04 was crushed with a jet mill to give a spinel type lithium manganese oxide powder 12 CA 02334240 2000-12-04 with a median diameter of 10 a m. The spinel type lithium manganese oxide powder, a carbon powder serving as a conductive agent and a poly(vinylidene fluoride) powder serving as a binder were mixed in a weight ratio of 85:10:5: The mixture was kneaded with NMP to give a paste. The paste was applied on a positive electrode collector (stainless steel plate) by the doctor blade method (to attain a thickness of 80 a m after drying), and the resultant was heated at 130.degree.C. Thus, a positive electrode (porous electrode) in the shape of a disk with a diameter of 10 mm was prepared. Next, polyethylene glycol) ethyl ether acrylate (with a number average molecular weight Mn of 360; CHZ=CH-COO -(CH2 CHZ-O)n-CH2 CHI and a liquid electrolyte obtained by dissolving 1 M (mol/liter) of LiC104 in ;~ mixed solvent including ethylene carbonate and dimethyl carbonate in a volume ratio of 2:3 were mixed in a weight ratio of 1:1. The resultant was applied on the positive electrode into a thickness of 25 ,u m, and irradiated with electron beams with a beam irradiation apparatus with electron curtain system (having output power of 200 kV, exposure of 2 Mrad and a travel speed of an irradiated target of 1 mlmin.), thereby polymerizing the polyethylene glycol) ethyl ether acrylate. Thus, a gelled polymeric electrolyte film also serving as a separator was farmed on one face of the positive electrode. It was confirmed through observation with a scanning electron microscope (SEM) that the gelled pvlym~eric electrolyte had entered the inside of the positive electro de. Then, a negative electrode (the same as that prepared in Embodiment 1) was placed on the gelled polymeric electrolyte film formed on one face of the positive electrode and the resultant was housed in a battery can. Thus, a flat lithium secondary battery (present battery) A5 using the gelled polymeric 13 CA 02334240 2000-12-04 electrolyte was fabricated. Embodiment 6 A block copolymer of polyethylene oxide) and polystyrene (with a copolymerization ratio of l.:l and a number average molecular weight Mn of approximately 300,000) wa.s dissolved in NMP to give a solution (with a solid content of 20 wt%). The solution was applied on one face of a positive electrode the same as that prepared in Embodiment 1 into a thickness of 25 ,u m, thereby forming a block copolymer film of polyethylene oxide) and polystyrene. This positive electrode was immersed in a liquid electrolyte obtained by dissolving 1 M of LiC104 in a mixed solvent including ethylene carbonate and dimethyl carbonate in a volume ratio of 2:3, so as to impregnate the block copolymer of polyethylene oxide) and polystyrene with the liquid electrolyte. Thus, a gelled polymeric electrolyte film also serving as a separator was formed on one face of the positive electrode. It was confirmed through observation with a scanning electron microscope that the gelled polymeric electrolyte had entered the inside of the positive electrode. next, a negative electrode (the same as that prepared in Embodiment 1) was placEed on the gelled polymeric electrolyte elm formed on one face of the positive electrode and the resultant was housed in a battery can. Thus, a flat lithium secondary battery (present battery) A6 using the gelled polymeric electrolyte was fabricated. ar ~ V ~'~,x m 1_e 1_ Aflat lithium secondary battery (comparative battery) 81 using a gelled polymeric electrolyte was f;~bricated in the same manner as in Embodiment 1 except for the following: Instead of the gelled polymeric electrolyte flm also serving as a separator, a liquid electrolyte obtained by dissolving 1 M of LiC104 14 CA 02334240 2000-12-04 in a mixed solvent including ethylene carbonate and dimethyl carbonate in a volume ratio of 2:3 and a polyethylene microporous film (separator) with a thickness of 25 ,u m were 'used, and the gelled polymeric electrolyte was not included in the positive electrode. C~na_rative Examnl_e 22 Poly(vinylidene fluoride) (with a number average molecular weight Mn of approximately 110,000) was dissolved in acetone to give a solution (with a solid content of 10 wt%). The solution was applied on one face of a positive electrode the same as that prepared in Embodiment 1 into a thickness of 25 a m, thereby forming a poly(vinylidene fluoride) film. The positive electrode was immersed in a liquid electrolyte obtained by dissolving 1 M of LiC104 in a mixed solvent including ethylene carbonate and dimethyl carbonate in a volume ratio of 2:3, so as to impregnate the poly(vinylidene fluoride) with the liquid electrolyte. Thus, a gelled polymeric electrolyte film also serving as a separator was formed on one face of the positive electrode. It was confirmed through observation with a scanning electron microscope that the gelled polymeric electrolyte had entered the inside of the positive electrode. Next, a negative electrode (the same as that prepared in Embodiment 1) was placed on the gelled polymeric electrolyte film formed on one face of the positive electrode and the resultant was housed in a battery can. Thus, a flat lithium secondary battery (comparative battery) B2 using the gelled polymeric electrolyte was prepared. ~parati_ve Fxam~rl, e~ A block copolymer of polyethylene oxide) and polystyrene (with a copolymerization ratio of 1:1 and a number average molecular weight Mn of approximately 300,000) wa:~ dissolved in NMP to give a solution (with a solid CA 02334240 2000-12-04 content of 20 wt%). The solution was formed by the casting method into a block copolymer film of poly(ethyl.ene oxide) and polystyrene with a thickness of 25 ,u m. Then, the film was immersed in a liquid electrolyte obtained by dissolving 1 M of LiC104 in a mixed solvent including ethylene carbonate and dimethyl carbonate in a volume ratio of 2:3, so as to impregnate the block copolymer of polyethylene oxide) and polystyrene with the liquid electrolyte by 100 wt%. Thus, a gelled polymeric electrolyte film also serving as a separator was formed. Next, the gelled polymeric electrolyte film was sandwiched between a positive electrode and a negative electrode the same as those prepared in Embodiment 1 (whereas the positive electrode was not impregnated with the gelled polymeric electrolyte), and the resultant was housed in a battery can. Thus, a flat lithium secondary battery (comparative battery) B3 using the gelled polymeric electrolyte was fabricated. Discharge ca aci .y of each ba .tery at 1 st anal 1 OOth ~«np~ With respect to each of the present batteries A1 through A6 and the comparative batteries B 1 tlurough B3, 100 charge-discharge cycles were run, in each cycle of which the battery was charged to 4.2 V at a current density of 100 a A/cm2 and discharged to 2.75 V at a current density of 100 a A/cm2 at 25.degree.C, thereby obtaining the discharge capacity (mAh) of the battery at the 1st and 100th cycles. The results acre shown in Table 1. 16 CA 02334240 2000-12-04 Table I Discharge capacity (mAh) 1st cycle 100th cycle Present battery A1 2.2 l,g Present battery A2 2.2 2.0 Present battery A3 2.1 1,g Present battery A4 2.1 l,g Present battery A5 2.2 2.0 Present battery A6 2.2 2.0 Comparative battery B 2.2 1.2 1 Comparative battery B2 2.2 1.2 Comparative battery B3 1.9 1.7 As is shown in TablE~ 1, the discharge capacity at the 100th cycle is larger in the present batteries A1 Through A8 than in the comparative batteries B 1 and B2. Also, the discharge capacity at the 1st cycle is larger in the present batteries A1 through A6 than in the comparative battery B3. It is understood from the results that the invention provides a lithium secondary battery using a gelled polymeric electrolyte with large initial discharge capacity and good charge-discharge cycle performance. The discharge capacity at the 100th cycle of the comparative battery B1 was small probably because manganese was eluted into the liquid electrolyte, and the discharge capacity at the 100th cycle of the comparative battery B2 was small probably because manganese was eluted into the liquid electrolyte impregnated into the gelled polymeric electrolyte film also serving as the separator. Furthermore, the discharge capacity at the 1st cycle of the comparative battery B3 is small probably because a contact area between the positive electrode and the electrolyte was so small that the contact resistance on the interface vvas large. Embodiment 7 I7 CA 02334240 2000-12-04 Preparation of nosit:ive electrode Lithium nitrate and manganese dioxide were mixed in a molar ratio of 1:2, and the mixture was baked at 600.degree.C for 24 hours in the air, thereby obtaining LiMn2O4. The LiMnZO4 was crushed with a jet mill to give a spinel type lithium manganese oxide powder with a median diameter of 10 a m. The spinel type lithium manganese oxide powder, a carbon powder serving as a conductive agent, a poly(vinylidene fluoride) powder serving as a binder and a block copolymer of polly(ethylene oxide) and polystyrene (with a copolymerization ratio of 1:1 and a number average molecular weight Mn of approximately 300,000) were mixed in a weight ratio of 85:10:3:2. The resultant mixture was kneaded with NMP to give a pastes the paste was applied on a positive electrode collecaor (aluminum plate) by the doctor blade method (to attain a thickness of 80 ,u m after drying), and the resultant was heated at 130.degree.C. Thus, a positive electrode (porous electrode) in the shape of a disk with a diameter of 10 mm was prepared. The positive electrode was immersed in a liquid electrolyte obtained b;y dissolving 1 M of LiN(CZFbS0~2 in a mixed solvent including ethylene carbonate and diethyl carbonate in a volume ratio of 1:1, so as to impregnate the block copolymer of polyethylene oxide) and polystyrene with the liquid electrolyte. Preparation of ge l i ~ol3rm ru .l . . olyte also ~ex~rin~ aura ~or A block copolymer of polyethylene oxide) and polystyrene (with a copolymerization ratio of 1.;1 and a number average molecular weight Mn of approximately 300,000) was dissolved in NMP to give a 20 wt% solution. The solution was formed by the casting method into a block copolymer film of polyethylene oxide) and polystyrene with a thickness of 25 a m. Next, the 18 CA 02334240 2000-12-04 film was immersed in a liquid electrolyte obtained by dissolving 1 M of LiN(CZF6SO~2 in a mixed solvent including ethylene carbonate and diethyl carbonate in a volume ratio of 1:1, so as to impregnate the block copolymer of polyethylene oxide) and pol.ystyxene with the liquid electrolyte. Thus, a gelled polymeric electrolyte film also serving as a separator was prepared. _ Fabrication of Lth~ium sPCO_n_d_a__ry~T u~in~ gelled poyme_ric ~,trolvt~ The gelled polymeric electrolyte film also serving as a separator was sandwiched between the positive electrode and a negative electrode (the same as that prepared in Embodiment 1) and the resultant was housed in a battery can. Thus, a flat lithium secondary battery (present battery) A7 using the gelled polymeric electrolyte was fabricated. Embodiment 8 A flat lithium secondary battery (present battery) A8 using a gelled polymeric electrolyte was fabricated in the same manner as in Embodiment 7 except that a liquid electrolyte obtained by dissolving 1 M of LiN(CF3S0~2 in a mixed solvent including ethylene carbonate and diethyl carbonate in a volume ratio of 1:1 was used as the liquid electrolyte for impregnating the block copolymer of polyethylene oxide) and polystyrene in the preparation of the positive electrode and the gelled polymeric electrolyte film also serving as the sep arator. Embodiment 9 A flat lithium secondary battery (present battery) A9 using a gelled polymeric electrolyte was fabricated in the same manner as in Embodiment 7 except that a liquid electrolyte obtained by dissolving 1 M of 19 CA 02334240 2000-12-04 LiN(CF3S0~(C4F9S0~ in a mixed solvent including ethylene carbonate and diethyl carbonate in a volume ratio of 1:1 was used as the liquid electrolyte for impregnating the block copolymer of polyethylene oxide) and polystyrene in the preparation of the positive electrode and the gelled polymeric electrolyte film also serving as the separator. Fmbo im n . 10 A flat lithium secondary battery (present battery) A10 using a gelled polymeric electrolyte was fabricated in the same manner as in Embodiment 7 except that a liquid electrolyte obtained by dissolving 1 M of LiN(C4F9S0~2 in a mixed solvent including ethylene carbonate and diethyl carbonate in a volume ratio of 1:1 was used as the liquid electrolyte for impregnating the block copolymer of polyethylene oxide) and polystyrene in the preparation of the positive electrode and the gelled polymeric electrolyte elm also serving as the sep arator. Embodiment 11 A flat lithium secondary battery (present battery) A11 using a gelled polymeric electrolyte was fabricated in the same manner as in Embodiment 7 except that a liquid electrolyte obtained by dissolving 1 M of LiC(CF3S0~3 in a mixed solvent including ethylene carbonate and diethyl carbonate in a volume ratio of 1:1 was used as the liquid electrolyte for impregnating the block copolymer of polyethylene oxide) and polystyrene in the preparation of the positive electrode and the gelled polymeric electrolyte film also serving as the sep arator. ~:mbodiment 12 A flat lithium secondary battery (present battery) A12 using a gelled CA 02334240 2000-12-04 polymeric electrolyte was fabricated in the same manner as in Embodiment 7 except that a liquid electrolyte obtained by dissolving 1 M of LiC(CF3S0~}2(C4F9S0~ in a mixed solvent including ethylene carbonate and diethyl carbonate in a volume ratio of 1:1 was used as the liquid electrolyte for impregnating the block copolymer ofpoly(ethylene oxide) and polystyrene in the preparation of the positivE~ electrode and the gelled polymeric electrolyte film also serving as the separator. Embodim n 1 A flat lithium secondary battery (present battery) A13 using a gelled polymeric electrolyte was i:abricated in the same manner as in Embodiment 7 except that a liquid electrolyte obtained by dissolving 1 M of LiC(CF3SO~(C4F9SO~2 in a mixed solvent including ethylene carbonate and diethyl carbonate in a volume ratio of 1:1 was used as the liquid electrolyte for impregnating the block copolymer of polyethylene oxide) and polystyrene in the preparation of the positive electrode and the gelled polymeric electrolyte film also serving as the separator. Embodimen 14 A flat lithium secondary battery (present battery) A14 using a gelled polymeric electrolyte was fabricated in the same manner as in Embodiment 7 except that a liquid electrolyte obtained by dissolving 1 M of LiC(C4F9S0~3 in a mixed solvent including ethylene carbonate and diethyl carbonate in a volume ratio of 1:1 was used as the liquid electrolyte for impregnating the block copolymer of polyethylene oxide) and polystyrene in the preparation of the positive electrode and the gelled polymeric electrolyte film also serving as the separator. 21 CA 02334240 2000-12-04 Embodi_m n . 1 A flat lithium secondary battery (present battery) A15 using a gelled polymeric electrolyte was fabricated in the same manner as in Embodiment 7 except that a liquid electrolyte obtained by dissolving 1 M of LiN(CF3S0~(CSF11S0~ in a mixed solvent including ethylene carbonate and diethyl carbonate in a volume ratio of 1:1 was used as the liquid electrolyte for impregnating the block copolymer of polyethylene oxide) and polystyrene in the preparation of the positive electrode and the gelled polymeric electrolyte film also serving as the separator. Embodiment 1_6 A flat lithium secondary battery (present battery) A16 using a gelled polymeric electrolyte was fabricated in the same manner as in Embodiment 7 except that a liquid electrolyte obtained by dissolving 0.1 M of LiPFs and 0.9 M of LiN(CZF6S0~2 in a mixed solvent including ethylene carbonate and diethyl carbonate in a volume ratio of 1:1 was used as the liquid electrolyte for impregnating the block copolymer of polyethylene oxide) and polystyrene in the preparation of the positive electrode and the gelled polymeric electrolyte film also serving as the separator. Embodiment 17 A flat lithium secondary battery (present battery) A17 using a gelled polymeric electrolyte was fabricated in the same manner as in Embodiment 7 except that a liquid electrolyte obtained by dissolving 0.5 M of LiPFs and 0.5 M of LiN(CZF6S0~2 in a mixed solvent including ethylene carbonate and diethyl carbonate in a volume ratio of l:l was used as the liquid electrolyte for impregnating the block copolymer of polyethylene oxide) and polystyrene in the 22 CA 02334240 2000-12-04 preparation of the positive. electrode and the gelled polymeric electrolyte film also serving as the separator. Embodim n ~ 18 A flat lithium secondary battery (present battery) A18 using a gelled polymeric electrolyte was fabricated in the same manner as in Embodiment 7 except that a liquid electrolyte obtained by dissolving 0.9 M of LiPFs and 0.1 M of LiN(CZF650~2 in a mixed solvent including ethylene carbonate and diethyl carbonate in a volume ratio of 1:1 was used as the liquid electrolyte for impregnating the block copolymer of polyethylene oxide) and polystyrene in the preparation of the positive electrode and the gelled polymeric electrolyte film also serving as the separator. Embodiment t A flat lithium secondary battery (present battery) A19 using a gelled polymeric electrolyte was fabricated in the same manner as in Embodiment 7 except that a liquid electrolyte obtained by dissolving 1 M of LiC104 in a mixed solvent including ethylene carbonate and diethyl carbonate in a volume ratio of 1:1 was used as the liquid electrolyte for impregnating the block copolymer of polyethylene oxide) and polystyrene in the preparation of the positive electrode and the gelled polymeric electrolyte elm also serving as the separator. Embodiment ?0 A flat lithium secondary battery (present battery) A20 using a gelled polymeric electrolyte was fabricated in the same manner as in Embodiment 7 except that a liquid electrolyte obtained by dissolving 1 M of LiBF4 in a mixed solvent including ethylene carbonate and diethyl carbonate in a volume ratio of 1:1 was used as the liquid electrolyte for impregnating the block copolymer of 23 CA 02334240 2000-12-04 polyethylene oxide) and pollystyrene in the preparation of the positive electrode and the gelled polymeric electrolyte film also serving as the separator. 'F:mbodim n 21 A flat lithium secondary battery (present battery) A21 using a gelled polymeric electrolyte was fabricated in the same manner as in Embodiment 7 except that a liquid electrolyte obtained by dissolving 1 M of LiPFs in a mixed solvent including ethylene carbonate and diethyl carbonate in a volume ratio of 1:1 was used as the liquid electrolyte ~or impregnating the block copolymer of polyethylene oxide) and polystyrene in the preparation of the positive electrode and the gelled polymeric electrolyte film also serving as the separator. C'O~pa_rative Examnl 4 Aflat lithium secondary battery (comparative battery) B4 using a gelled polymeric electrolyte was fabricated in the same manner as in Embodiment 3 except that a liquid electrolyte obtained by dissolving 1 M of LiC104 in a mixed solvent including ethylene carbonate and diethyl carbonate in a volume ratio of 1:1 and a polyethylene micr~oporous t~lm (separator) with a thickness of 25 ,u m were used instead of the gelled polymeric electrolyte film also serving as the separator and that the gelled polymeric electrolyte was not included in the positive electrode. omna_rative Exam ln_~ ~. 5 Aflat lithium secondary battery (comparative battery) B5 using a gelled polymeric electrolyte was fabricated in the same manner as in Embodiment 3 except that a liquid electrolyte obtained by dissolving 1 M of Li.BF4 in a mixed solvent including ethylene carbonate and diethyl carbonate in a volume ratio of 1:1 and a polyethylene microporous film (separator) with a thickness of 25 a m 24 CA 02334240 2000-12-04 were used instead of the gelled polymeric electrolyte film also serving as the separator and that the gelled polymeric electrolyte was not included in the positive electrode. Comnarativ Fx mnl 6 A flat lithium secondary battery (comparative battery) B6 using a gelled polymeric electrolyte was fabricated in the same manner as in Embodiment 3 except that a liquid electrolyte obtained by dissolving 1 M of LiPFs in a mixed solvent including ethylene c;arbonate and diethyl carbonate in a volume ratio of 1:1 and a polyethylene microporous hlm (separator) with a thickness of 25 ,u m were used instead of the gelled polymeric electrolyte film also serving as the separator and that the gellled polymeric electrolyte was not included in the positive electrode. C'y ratio Fx m~~ Aflat lithium secondary battery (comparative battery) B7 using a gelled polymeric electrolyte was fabricated in the same manner as in Embodiment 3 except that a liquid electrolyte obtained by dissolving 1 M of LiN(CZF~S0~2 in a mixed solvent including ethylene carbonate and diethyl carbonate in a volume ratio of 1:1 and a polyethylE;ne microporous film (separator) with a thickness of a m were used instead of the gelled polymeric electrolyte film also serving as 20 the separator and that the 3;elled polymeric electrolyte was not included in the positive electrode. Discharge ca aci~y of battery at 1 and 100 ~h~3, With respect to each of the present batteries A7 through A21 and the comparative batteries B4 through B7, 100 charge-discharge cycles were run 25 under the aforementioned conditions, thereby obtaining the discharge capacity CA 02334240 2000-12-04 (mAh) at the lst and 100th cycles. The results are shown in Table 2. Table 2 Discharge capacity (mAh) 1st cycle 100th cycle Present battery A7 2.4 2.2 Present battery A8 2.4 2.2 Present battery A9 2.4 2.1 Present battery A10 2.4 2.2 Present battery A11 2.4 2.2 Present battery A12 2.4 2.1 Present battery A13 2.4 2.2 Present battery A14 2.4 2.2 Present battery A15 2.4 2.0 Present battery A16 2.4 2.2 Present battery A17 2.4 2.0 Present battery Al8 2.4 l.g Present battery A19 2.4 1.7 Present battery A20 2.4 1.5 Present battery A21 2.4 1.6 Comparative battery B4 2.4 1.2 Comparative battery B5 2.4 1.1 Comparative battery B6 2.4 1.2 Comp arative b attery 2.4 1.2 B 7 As is shown in Table 2, the discharge capacity at the 100th cycle is larger in the present batteries A7 through A21 using the gelled polymeric electrolyte film also serving as the separator because of a smaller amount of manganese eluted during the charge-discharge cycles than in the comparative batteries B4 through B7 using the liquud electrolyte. Among the present batteries A7 through A21, the discharge capacity at the 100th cycle is particularly large in the present batteries A7 through A18. Accordingly, it is understood that the solute of the liquid electrolyte used for the impregnation is preferably 26 CA 02334240 2000-12-04 LiN(CmF2m+,SO~(C"F2~+1SO?) (wherein m and n independently indicate an integer ranging between 1 and 5) or LiC(CpF~,+iSO~(CqFZq+~SO~(C1.F2~.iS0~ (wherein p, q and r independently indicate an integer ranging between 1 and 5). ~,ycle perfo_rman~P _ Seven kinds of lithium secondary batteries (present batteries) A22 through A28 each using a gelled polymeric electrolyte were fabricated in the same manner as in Embodiiment 7 except that a liquid electrolyte obtained by dissolving 0.05 M, 0.1 M, O.,i M, 1.5 M, 2.0 M, 2.5 M or 3.0 M of LiN(C2F6S0~2 in a mixed solvent including ethylene carbonate and diethyl carbonate in a volume ratio of 1:1 was used as the liquid electrolyte for impregnating the block copolymer of polyethylene oxide) and polystyrene in the fabrication of the positive electrode and the gelled polymeric electrolyte elm also serving as the separator. Subsequently, with respect to each of the batteries, 100 charge- discharge cycles were rum under the aforementioned conditions, thereby obtaining the discharge capacity (mAh) at the 1st and 100th cycles. The results are shown in Table 3. Table 3 also shows the discharge capacity at the 1st and 100th cycles of the present battery A7 listed in Table 2. 27 CA 02334240 2000-12-04 Table 3 Concentration of L:iN(C2F6S0~2 Discharge capacity (mAh) in liquid electrolyte 1st cycle 100th cycle Present battery A22 0.05 2.4 1.3 Present battery A23 0.1 2.4 1.6 Present battery A24 0.5 2.4 l,g Present battery A7 1.0 2.4 2.2 Present battery A25 1.5 2.4 2.0 Present battery A26 2.0 2.4 1.6 Present battery A27 2.5 2.4 1.3 Present battery A28 3.0 2.4 1.3 It is understood from Table 3 that the liquid electrolyte preferably includes 0.1 through 2.0 M Of LiN(C2F6SO~2. It was also confirmed that a concentration of 0.1 through 2.0 M is preferred in using any of other liquid electrolytes according to this invention represented by LiN(CmF2m+~SO~(CnF2"+ISOy or L~.C(CPF~,+1SO~(CqF2q+1SO~(C,F~..,.1SO~. Industrial Applicability The invention provides a lithium secondary battery using a gelled polymeric electrolyte with .large initial discharge capacity and good charge- discharge cycle performance. 28