JP2001202996A - Lithium-polymer secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium-polymer secondary battery having a superior cycle characteristics, and reliability, and high energy density. SOLUTION: The lithium-polymer secondary battery consists of a lithium- contained complex nitride expressed by general formula, Li(3-x)-yMxN (where M is at least one kind of transition metals selected from among a group of Co, Mn, Ni and Cu, 0.3<=x<=0.6, 0<=y<=3-x), a positive pole comprising conductive and polymer materials, a negative pole comprising conductive and polymer materials and a polymer-gel electrolyte, containing an organic electrolytic solution.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a secondary battery provided with a polymer electrolyte, and more particularly to a lithium polymer secondary battery having an improved negative electrode material.

[0002]

2. Description of the Related Art A lithium ion secondary battery using an organic electrolyte, a carbon material as a negative electrode material, and a lithium-containing composite oxide as a positive electrode material has a higher voltage and energy density than an aqueous secondary battery. Demand is growing rapidly because of its excellent low-temperature characteristics and excellent cycle stability. Also, a lithium polymer battery using a polymer gel electrolyte containing an organic electrolyte is being developed as a thin and lightweight new battery system.

As a polymer electrolyte battery, a battery using a polymer electrolyte comprising polyethylene oxide and an electrolyte salt has been proposed (Second International Meeting on Solid Elec).
trolytes, Extended Abstracts, p20-22 (1978), U.S. Pat. No. 4,303,748), and various studies have been made (for example, "Conductive Polymers", edited by Naoya Ogata, Kodansha (1990) and Polymer Electrolyte Reviews. , Vols.
1 and 2, Elsevier, London (1987,1989)). But,
These various polymer electrolyte materials have an ionic conductivity at room temperature of 10 ⁻⁴ to 10 ⁻⁵ S / cm.
Another approach to improve ionic conductivity is to include a solvent for the organic electrolyte as a plasticizer,
An electrolyte of a type that can easily achieve an ion conductivity of 0 ^-3 to / cm level has been proposed (J. Electrochem. Soc., 137,
1657 (1990), U.S. Pat.Nos. 5,085,952, 5,223,353
No. 5,275,750), which are called polymer gel electrolytes. A polymer battery using this polymer gel electrolyte is expected to have properties similar to those of a lithium ion secondary battery due to improvement in ionic conductivity.

However, in terms of capacity, since it is necessary to contain a polymer in the positive / negative electrode mixture, the amount (density) of the positive / negative electrode material capable of occluding and releasing lithium decreases.
Therefore, when the same positive and negative electrode materials are used, there is a problem that the energy density of the lithium polymer secondary battery is lower than that of the lithium ion secondary battery. When lithium metal with high capacity is used as the negative electrode material, dendrite-like precipitation occurs on the negative electrode during charging, and when charging and discharging are repeated, the precipitate may break through the polymer gel electrolyte and reach the positive electrode side, causing an internal short circuit. is there. In addition, the deposited lithium has a high specific activity due to its large specific surface area,
It reacts with the plasticizer (solvent) of the polymer gel electrolyte to deactivate it and lower the charge / discharge efficiency. For these reasons, lithium secondary batteries using lithium metal as the negative electrode material have problems of low reliability and short cycle life. At present, a battery using a carbon material capable of inserting and extracting lithium ions as a negative electrode material instead of lithium metal has been put to practical use. Normally, metallic lithium does not precipitate on the carbon material negative electrode, so there is no problem of internal short circuit due to dendrite. However, the theoretical capacity of graphite, which is a typical example of a carbon material, is 372 mAh / g, which is as small as about 1/10 of the theoretical capacity of Li metal alone.

As another negative electrode material, a nitride containing lithium is known as a high capacity material. The technology of using this lithium-containing composite nitride as a negative electrode material of a battery is relatively new, and a lithium nitride metal compound (same as lithium-containing composite nitride) is used as an electrode material of an electrochemical device.
(Japanese Patent Laid-Open No. 7-78609). A composite nitride of lithium and a transition metal Li _{(3-x) -y} M _x N (M is at least one transition metal selected from the group consisting of Co, Mn, Ni, and Cu) is a metal lithium Is usually not precipitated, so there is no problem of internal short circuit due to dendrite. Among them, the above-mentioned compound having an x value of about 0.1 to 0.6 has a reversible capacity of 500 to 800 mAh / g. It is a promising negative electrode material larger than the capacity.

[0006]

However, in order to use a lithium-containing composite nitride having a higher capacity than the above-mentioned carbon material in a battery having a polymer gel electrolyte,
There were the following issues. That is, the lithium-containing composite nitride has insufficient charge / discharge cycle characteristics as compared with the carbon anode material. The reason is that the larger the reversible charge / discharge capacity, the larger the volume change due to expansion / contraction in charge / discharge. When the volume difference between charging and discharging is large, large strain is generated, cracks are generated and the nitride particles themselves are fined, and expansion and contraction include entanglement with the conductive agent in the electrode plate. As the electron conduction network is loosened or cut off, the portion that cannot participate in the electrochemical reaction increases, and the charge / discharge capacity decreases. In particular, in a battery using a polymer gel electrolyte, the degree of freedom of the form of the electrolyte is lower than in a solution system, so that the current collection network is significantly reduced and the cycle characteristics are significantly reduced.

An object of the present invention is to solve the above-mentioned conventional problems and to provide a lithium polymer secondary battery having excellent cycle characteristics and reliability and high energy density using a lithium-containing composite nitride as a negative electrode material. And

[0008]

In order to solve the above problems, a lithium polymer secondary battery of the present invention comprises a positive electrode comprising a main material, a conductive agent and a polymer material, which is a lithium-containing composite oxide, and a lithium-containing composite nitride. The main material,
A negative electrode composed of a conductive material and a polymer material, and a polymer gel electrolyte containing an organic electrolyte are provided. As a lithium-containing composite nitride, a general formula Li _{(3-x) -y} M _x N (M is C
At least one transition metal selected from the group consisting of o, Mn, Ni and Cu, x is a content of the transition metal, and y is a variable indicating a change in Li content that changes with charging and discharging. )
And the x value representing the content of the transition metal in the formula is 0.3
≦ x ≦ 0.6 is used. The y value is (3-x) -y = 0 when all Li is released, that is, y = 3
−x is the upper limit, and is in the range of 0 ≦ y ≦ 3-x. In addition,
It is possible to accumulate an amount of the y value exceeding 3-x by charging, but it is in the form of Li deposition.

The present invention focuses on the change in volume of a high-capacity lithium-containing composite nitride due to charge and discharge, and suppresses the change in volume by controlling the content of the transition metal to improve cycle characteristics. is there. In particular, the present invention solves the conventional problems of a polymer gel electrolyte battery by using a lithium-containing composite nitride having an appropriate composition as a negative electrode material, minimizing a change in volume thereof.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention relates to a negative electrode material of the general formula Li _{(3-x) -y} M _x N (M is at least one transition metal selected from the group consisting of Co, Mn, Ni and Cu). Using the lithium-containing composite nitride represented by the following formula, the value x in the above formula is set to 0.3 ≦ x ≦ 0.6. This lithium-containing composite nitride is a compound in which a transition metal atom is dissolved in lithium nitride Li ₃ N. The x value is determined at the time of synthesis. As a result of an experimental study, the amount that can be replaced is in the range of x ≦ 0.6 (unreacted transition metal remains when 6 <x),
In particular, the function as the main material of the battery is 0.1 ≦ x ≦ 0.
The range is 6. When x <0.1, almost no electrical conductivity was exhibited as in Li ₃ N, and it could not be used as the main material of the electrode.

The most suitable material for the battery according to the present invention using a polymer gel electrolyte is a lithium-containing composite nitride having an x value of 0.3 ≦ x ≦ 0.6. The specific reason for limiting the x value is as follows. That is, when a solution-based electrolyte is used, the lithium-containing composite nitride has an x value of 0.3.
Materials with 1 ≦ x ≦ 0.6 exhibit an electrode function capable of charge / discharge, but experimentally, when a material with x <0.3 constituted a battery with a polymer gel electrolyte, the results showed extremely poor cycle characteristics. When the thickness of the negative electrode plate was measured, it was found that the thickness change of the electrode plate due to charge and discharge was significantly large when x <0.3. Since these nitrides become amorphous when subjected to charge and discharge, the phenomenon cannot be captured from a change in lattice constant. However, at least in a region where the amount of substitution of the transition metal is small, that is, in a region where x <0.3, the transition state is low. It is presumed that the expansion and contraction of the crystal is promoted because the effect of relaxing the strain of the crystal due to the change in the valence of the metal is weakened. That is, in the range of 0.3 ≦ x ≦ 0.6 of the present invention, the valence change of the transition metal alleviates the crystal distortion, so that it is assumed that expansion and contraction are suppressed. Therefore, in a lithium polymer secondary battery using a polymer gel as an electrolyte, when a lithium-containing composite nitride is used for a negative electrode, a material having an x value in the above general formula in the range of 0.3 ≦ x ≦ 0.6 is used. It is necessary. In a polymer battery that does not include a liquid component having a lower degree of freedom in the form of an electrolyte, it is more important to select a material having such a small volume change.

A further preferred embodiment of the present invention will be described below. A preferred polymer of the polymer gel electrolyte of the present invention is a polymer having a skeleton of an alkylene oxide such as polyethylene oxide or polypropylene oxide or a derivative thereof. Alkylene oxide is a polymer material having a relatively low melting point, has a high solubility of a lithium salt, and has characteristics of being easy to handle. The problem of low ionic conductivity is solved by using an organic solvent as a plasticizer. Other preferred polymers of the polymer gel electrolyte of the present invention are two or three copolymers selected from the group consisting of vinylidene fluoride, propylene hexafluoride, ethylene tetrafluoride, and perfluoroalkyl vinyl ether. . Particularly preferred is a copolymer of vinylidene fluoride and propylene hexafluoride. This copolymer is excellent in chemical stability and can be thermally welded. Furthermore, a porous film is obtained by dissolving in a solvent such as tetrahydrofuran with a plasticizer such as a phthalate ester, casting and drying to produce a film, and then eluting the plasticizer with a solvent such as ether. . When an electrolytic solution is injected into the porous film, a gel electrolyte is obtained. Therefore, after an integrated electrode configuration is manufactured, the electrolytic solution can be finally injected and gelled.

Still another preferred polymer gel electrolyte polymer of the present invention is a polyacrylonitrile-based polymer having polyacrylonitrile or polyacrylonitrile as a main component and having a skeleton of a copolymer of methyl acrylate, vinylpyrrolidone, vinyl acetate and the like. It is. Further, it can be used as a polymer alloy with a fluorine resin, a polyolefin resin, a polyether resin, or the like. Polyacrylonitrile-based polymer is one of the most versatile polymer materials, and it is also possible to form a film by dissolving in a solvent such as dimethylformamide or heating and dissolving with an organic electrolyte solution. A nonwoven fabric-like porous body is impregnated with an organic electrolytic solution, heated and cooled to obtain a gel-like film, so that it is easy to handle, and furthermore, has a feature of being flame-retardant. Other preferred polymer gel electrolyte polymer of the present invention, polyethylene terephthalate, polybutylene terephthalate or a derivative thereof as a skeleton,
It is a polyester polymer which is a copolymer with ethyl methacrylate, styrene, vinyl acetate and the like. Further, it can be used as a polymer alloy with a fluorine resin, a polyolefin resin, a polyether resin, or the like. A polyester-based polymer is one of the most versatile polymer materials, and is capable of producing a film having excellent chemical stability, flexibility and high mechanical strength. A preferred polymer of the polymer gel electrolyte of the present invention is a copolymer of methacrylate and ethylene oxide. After casting a solution obtained by adding an organic electrolyte and a polymerization initiator to a solution of a mixture of ethyl methacrylate, dimethacrylethylene glycol, and a polyethylene oxide having a molecular weight of 10,000 or less on the positive and negative electrodes, the electrodes are irradiated with heat or ultraviolet rays. It is possible to form a gel electrolyte layer by directly polymerizing the above.

Since the lithium-containing composite nitride of the negative electrode has high reactivity with water and is degraded by water, it is preferable to use a highly dehydrated solvent for forming a paste or the like. The separator portion of the polymer gel electrolyte of the present invention preferably contains a structural reinforcing material such as a fine particle dispersant, a filler, and a nonwoven fabric. As the structural reinforcing material, any fine particles or fibrous materials that do not cause a chemical change with the organic electrolyte solution or the polymer material can be used, but the surface is made hydrophobic, for example, silica or alumina that has been subjected to silane coupling treatment. Can be used, ceramic fine particles having a particle size of about 1 μm or less, or fibers or nonwoven fabrics of olefin-based polymers such as polypropylene and polyethylene. The addition amount of the structural reinforcing material is not particularly limited, but is preferably in a range of up to 40% by weight of the polymer gel electrolyte separator.

The positive electrode and the negative electrode used in the present invention comprise a positive electrode material capable of electrochemically and reversibly absorbing and releasing lithium ions and a mixture layer in which a conductive agent, a polymer material and the like are added to the above-mentioned negative electrode material, respectively. It is produced by coating on the surface of the electric body. The conductive agent for a negative electrode used in the present invention may be any material as long as it is an electron conductive material. For example, graphite such as natural graphite (flaky graphite, etc.), artificial graphite, expanded graphite, acetylene black, Ketjen black, channel black, furnace black, lamp black,
Carbon blacks such as thermal black, carbon fiber,
Conductive fibers such as metal fibers, metal powders such as copper and nickel, and organic conductive materials such as polyphenylene derivatives can be included alone or as a mixture thereof. Among these conductive agents, artificial graphite, acetylene black and carbon fiber are particularly preferred. The addition amount of the conductive agent is not particularly limited, but is preferably 1 to 50% by weight, and particularly preferably 1 to 30% by weight based on the negative electrode material. Since the negative electrode material of the present invention itself has electronic conductivity, it is possible to function as a battery without adding a conductive agent. The current collector for the negative electrode used in the present invention may be any electronic conductor that does not cause a chemical change in the configured battery. For example, in addition to stainless steel, nickel, copper, titanium, carbon, conductive resin, and the like, a material obtained by treating the surface of copper or stainless steel with carbon, nickel, or titanium is used. In particular,
Copper or copper alloys are preferred. In addition, it is desirable to make the current collector surface uneven by surface treatment. As the shape, in addition to a foil, a film, a sheet, a net, a punched material, a lath body, a porous body, a foamed body, a molded body of a fiber group, and the like are used. The thickness is not particularly limited, but is 1 to 5
One having a thickness of 00 μm is used.

As the positive electrode material of the present invention, a lithium-containing transition metal oxide can be used. For example, Li _x Co
O ₂ , Li _x NiO ₂ , Li _x MnO ₂ , Li _x Co _y Ni _1-y
O ₂ , Li _x Co _y M _1-y O _z , Li _x Ni _{1- y My} O _z , Li _x
Mn ₂ O ₄ , Li _x Mn _2-y MyO ₄ (M = Na, Mg, S
c, Y, Mn, Fe, Co, Ni, Cu, Zn, Al,
At least one of Cr, Pb, Sb and B, x = 0
1.2, y = 0 to 0.9, z = 2.0 to 2.3). Here, the above-mentioned x value is a value before the start of charge / discharge, and increases / decreases due to charge / discharge. In addition, from normal charge such as a lithium-containing transition metal compound (from the direction of Li release)
When a positive electrode material is used, the nitride material of the present invention is a negative electrode material that normally starts from discharge.
Chemical conversion treatment is required. It is also possible to use other positive electrode materials such as transition metal chalcogenides, lithium compounds of vanadium oxides, lithium compounds of niobium oxides, conjugated polymers using organic conductive substances, and Chevrel phase compounds. In the case of a positive electrode material such as manganese dioxide or vanadium pentoxide, which starts from a normal discharge, it is not necessary to perform a chemical conversion treatment, which is advantageous in production. It is also possible to use a mixture of a plurality of different positive electrode materials. The average particle size of the particles of the positive electrode material is not particularly limited, but is preferably 1 to 30 μm.

The conductive agent for the positive electrode used in the present invention may be any electronic conductive material which does not cause a chemical change at the charge / discharge potential of the positive electrode material used. For example, graphites such as natural graphite (flaky graphite, etc.), artificial graphite, acetylene black, Ketjen black, channel black, furnace black, lamp black,
Carbon blacks such as thermal black, carbon fiber,
Conductive fibers such as metal fibers, metal powders such as aluminum, conductive whiskers such as zinc oxide and potassium titanate, conductive metal oxides such as titanium oxide, and organic conductive materials such as polyphenylene derivatives alone. Alternatively, they can be included as a mixture thereof. Among these conductive agents, artificial graphite and acetylene black are particularly preferred. The addition amount of the conductive agent is not particularly limited, but is preferably 1 to 50% by weight, and particularly preferably 1 to 30% by weight based on the positive electrode material. For carbon and graphite, 2 to 15% by weight is particularly preferred. The positive electrode current collector used in the present invention may be any electronic conductor that does not cause a chemical change in the charge and discharge potential of the positive electrode material used. For example, in addition to stainless steel, aluminum, titanium, carbon, conductive resin, and the like, a material obtained by treating the surface of aluminum or stainless steel with carbon or titanium is used. Particularly, aluminum or an aluminum alloy is preferable. The surface of these materials can be oxidized and used. In addition, it is desirable to make the current collector surface uneven by surface treatment. As the shape, in addition to a foil, a film, a sheet, a net, a punched material, a lath body, a porous body, a foamed body, a fiber group, a molded body of a nonwoven fabric body, or the like is used. The thickness is not particularly limited,
Those having a thickness of 1 to 500 μm are used.

As the binder for the positive and negative electrodes, the same polymer as that usually used for the separator portion is used as the binder, but this improves the strength of the electrode and the adhesive strength between the electrode and the current collector. Therefore, it is also possible to use another binder in combination. For example, polyethylene, polypropylene, polytetrafluoroethylene, polyvinylidene fluoride, styrene butadiene rubber, tetrafluoroethylene-hexafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer Polymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer, polychlorotrifluoroethylene, vinylidene fluoride-pentafluoropropylene copolymer Coalesce, propylene-
Tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, vinylidene fluoride-perfluoromethylvinyl ether-tetrafluoroethylene copolymer, ethylene- Acrylic acid copolymer or (Na ⁺ ) ion crosslinked product of the above material, ethylene-methacrylic acid copolymer or (Na ⁺ ) ion crosslinked product of the above material, ethylene-methyl acrylate copolymer or (Na ⁺ ) ⁺ ) Ion cross-linked,
Examples include an ethylene-methyl methacrylate copolymer or a (Na ⁺ ) ion cross-linked product of the above-mentioned materials, and these materials can be used alone or as a mixture.

The structure of the negative electrode plate and the positive electrode plate in the present invention is as follows.
It is preferable that the negative electrode mixture surface exists at least on the surface opposite to the positive electrode mixture surface. The non-aqueous electrolyte used for the polymer electrolyte of the present invention comprises a solvent and a lithium salt dissolved in the solvent. Examples of the non-aqueous solvent that also acts as a plasticizer include, for example, cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and vinylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and dipropyl carbonate. Chain carbonates such as carbonate, methyl formate, methyl acetate, methyl propionate, aliphatic carboxylic acid esters such as ethyl propionate,
γ-lactones such as γ-butyrolactone, 1,2-dimethoxyethane, 1,2-diethoxyethane, chain ethers such as ethoxymethoxyethane, tetrahydrofuran, cyclic ethers such as 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolan, formamide, acetamide, dimethylformamide, dioxolan, acetonitrile, propylnitrile, nitromethane, ethyl monoglyme, phosphoric acid triester,
Trimethoxymethane, dioxolane derivative, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, 3-methyl-2-oxazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ethyl ether, 1,3-propane sultone, Aprotic organic solvents such as anisole, dimethylsulfoxide, N-methylpyrrolidone, and the like;
These may be used alone or in combination of two or more. Among them, a mixed system of a cyclic carbonate and a chain carbonate or a mixed system of a cyclic carbonate, a chain carbonate and an aliphatic carboxylic acid ester is preferable.

As a lithium salt dissolved in these solvents,
Is, for example, LiClO_Four, LiBF_Four, LiPF₆, Li
AlCl_Four, LiSbF₆, LiSCN, LiCl, Li
CF_ThreeSO_Three, LiCF_ThreeCO_Two, Li (CF_ThreeSO_Two)_Two,
LiAsF₆, LiN (CF _ThreeSO_Two)_Two, LiB_TenC
l_Ten, Lower aliphatic lithium carboxylate, LiCl, Li
Br, LiI, lithium chloroborane, tetraphenylboron
Lithium acid, imides and the like can be mentioned.
A single or a combination of two or more
Can be used, but especially LiPF₆Can contain
Is more preferable. Particularly preferred non-aqueous electrolyte in the present invention
Degradation is based on ethylene carbonate and ethyl methyl carbonate.
LiPF as a supporting salt₆including
Electrolyte. The amount of these electrolytes added in the battery is
Although not particularly limited, the amount of the positive electrode material and the negative electrode material and the
The required amount can be used depending on the size. Supporting electrolysis
The amount of the dissolved non-aqueous solvent is not particularly limited,
0.2 to 2 mol / l is preferred. In particular, 0.5-1.
More preferably, it is 5 mol / l.

It is also effective to add another compound to the electrolyte for the purpose of improving the discharge and charge / discharge characteristics. For example,
Triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, pyridine, hexaphosphoric triamide, nitrobenzene derivative,
Crown ethers, quaternary ammonium salts, ethylene glycol dialkyl ether and the like can be mentioned. The shape of the battery can be any of a coin type, a button type, a sheet type, a laminated type, a cylindrical type, a flat type, a square type, and a large type used for electric vehicles. The lithium polymer secondary battery of the present invention can be used for a portable information terminal, a portable electronic device, a small household electric power storage device, a motorcycle, an electric vehicle, a hybrid electric vehicle, etc., but is not particularly limited thereto. Absent.

[0022]

The present invention will be described in more detail with reference to the following examples. However, the present invention is not limited to these examples.

Example 1 [Method of Synthesizing Negative Electrode Material] A predetermined amount of lithium nitride and a transition metal powder were mixed, placed in a porcelain crucible, and placed in a nitrogen atmosphere at 700.degree.
By heating at 8 ° C. for 8 hours, a target compound lithium-containing composite nitride in which a transition metal was dissolved in lithium nitride as a solidified product was obtained. The coagulated product was pulverized by a ball mill and classified by a sieve to obtain particles of 45 μm or less. In this embodiment, Co is used as a transition metal, and the above-mentioned x value is 0.1, 0.2, 0.3, 0.
Six types of lithium-containing composite nitrides of 4, 0.5, and 0.6 were synthesized, respectively.

[Method of Manufacturing Flat-Type Lithium Polymer Secondary Battery] FIG. 1 is a sectional view of a flat-type nonaqueous electrolyte battery.
Represents a battery case made of a laminate film of a resin film and an aluminum film. This battery case 1
In the inside, a negative electrode 3 sandwiching a copper negative electrode lead 2, a positive electrode 5 and an aluminum positive electrode lead 6 arranged outside a separator portion 4 of a polymer gel electrolyte made of a polymer material, an electrolytic solution and a structural reinforcing material outside the negative electrode 3. Is housed. A lead portion welding seal 7 is provided at a lead-out portion of the leads 2 and 6. The battery manufacturing method will be described in more detail. The electrolyte polymer material was prepared by mixing polyvinylidene fluoride with polyethylene oxide (PEO) having a molecular weight of 800,000 to 2,000,000 to form a polymer alloy, and this was dissolved in a mixed solvent of ethylene carbonate and ethyl methyl carbonate (hereinafter, this solution). To PEO
Solution). Then, a paste obtained by mixing and dispersing nitride particles as a negative electrode material and carbon black as a conductive agent in a PEO solution is applied to a copper core material as a negative electrode current collector, and after volatile components are removed by drying, a predetermined size is obtained. By cutting, a negative electrode plate was produced. The positive electrode plate is prepared by applying a paste in which a lithium-containing composite oxide of the positive electrode material and carbon black of the conductive agent are similarly mixed and dispersed in a PEO solution to an aluminum core material serving as a positive electrode current collector, and processed similarly. Produced. The separator section is formed by heating and dissolving PEO in an organic electrolyte solution, impregnating the same with a polypropylene nonwoven fabric as a structural reinforcing material, and then cooling to form a gel electrolyte layer.
The positive electrode plate, the separator part, and the negative electrode plate were laminated and pressed to form an electrode group, placed in the battery case 1, and then the laminated film at the opening was heat-welded to obtain a flat battery. If the gelation or bonding of the electrode and the separator is insufficient, a heating step may be incorporated before the sealing.

The organic electrolytic solution is prepared by mixing a solvent mixture of ethylene carbonate and ethyl methyl carbonate at a volume ratio of 1: 1 with lithium hexafluorophosphate (LiPF) as an electrolyte.
₆ ) was dissolved at a concentration of 1.0 mol / dm ³ . In this example, a lithium-cobalt composite oxide (LiCoO ₂ ) was used as a positive electrode material. The lithium-containing composite nitride of the negative electrode is in a so-called Li occlusion state in a charged state at the time of synthesis, and the LiCoO _{2 of the} positive electrode is in a so-called Li occlusion state in an initial state of a discharged state. For this reason, a battery cannot be constituted as it is. It is necessary to desorb Li from either the positive or negative electrode material and combine the batteries in a Li-released state. Therefore, here, a positive electrode material obtained by extracting Li from the LiCoO ₂ of the positive electrode by acid treatment in advance, and a product equivalent to the composition formula Li _0.5 CoO ₂ were used at the time of manufacturing the battery. The flat lithium polymer secondary battery shown in FIG. 1 was fabricated using a material equivalent to Li _0.5 CoO _{2 for the} cathode material and a nitride of the six compositions using Co as the transition metal for the anode material. Then, the battery characteristics were compared. Charging and discharging were performed at a constant current of 100 mA, and the charging and discharging were terminated at 4.1 V and 2.0 V, respectively, for 50 cycles.

FIG. 2 compares the cycle characteristics of the above-mentioned lithium polymer secondary batteries using lithium-containing composite nitrides having six types of x values. For example,
In the battery using x = 0.4 in FIG. 2, that is, a lithium-containing composite nitride having a composition of Li _2.6 Co _0.4 N (using Li _0.5 CoO ₂ from which Li was desorbed for the positive electrode), about 4 g of the positive electrode material was used.
Filled and an initial capacity of 540 mAh has been obtained. At this time, the filling amount of the lithium-containing composite nitride as the negative electrode material was about 0.8 g. This battery is 5
Since the capacity at the 0th cycle was 499 mAh, the cycle deterioration rate was 0.152% / cycle. The cycle deterioration rate used here is from the initial capacity of 540 mAh to 50.
A value obtained by dividing the amount of capacity reduction obtained by subtracting the capacity of 499 mAh at the cycle from the initial capacity of 540 mAh and the number of cycles of 50 is expressed as a percentage, and is a so-called capacity reduction rate based on the initial capacity per cycle. As is clear from FIG. 2, the cycle reversibility is excellent in the range of 0.3 ≦ x ≦ 0.6. The cycle deterioration rate at this time was 0.642 for the batteries using lithium-containing composite nitrides of x = 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6, respectively. %, 0.537%, 0.181%,
0.152%, 0.139%, and 0.147%.

Example 2 A vinylidene fluoride-6-fluoropropylene copolymer was used as a polymer material, and a lithium-containing composite nitride material for a negative electrode and carbon black as a conductive material were combined with vinylidene fluoride as a binder and an electrolyte polymer. -6 mixed with fluorinated propylene copolymer, and the solvent N-methyl-
A paste obtained by mixing and dispersing in a solution of 2-pyrrolidone was applied to a copper core material serving as a negative electrode current collector, dried, and then cut into a predetermined size, whereby a negative electrode plate 3 was obtained. The positive electrode 5 is prepared by mixing and dispersing Li _0.5 CoO _{2 as a} positive electrode material and carbon black as a conductive agent in a solution of vinylidene fluoride-6-propylene copolymer, N-methyl-2-pyrrolidone, and dibutyl phthalate. It was produced by coating on an aluminum core material as a current collector and processing the same. The separator part 4 is subjected to a hydrophobic treatment as a structural reinforcing material with vinylidene fluoride-6-propylene copolymer, and silicon oxide fine particles are dispersed in a similar solution to form a paste.
Obtained by coating and drying. After welding the positive electrode plate, the separator part, and the negative electrode plate with a heat roller, the plasticizer dibutyl phthalate was eluted in diethyl ether to obtain a porous polymer electrode group. After this electrode group was placed in the battery case, the same organic electrolyte as in Example 1 was injected to form a gel polymer electrolyte. Finally, the laminated film in the opening was heat-welded to obtain a completed battery. Also in this example, for comparative study, as in Example 1, a battery was prototyped using lithium-containing composite nitrides having six types of x values. The solvent N-methyl-2-pyrrolidone used was highly dehydrated in consideration of the deterioration of the lithium-containing composite nitride due to moisture.

Example 3 Polyacrylonitrile was used as a polymer material and dissolved in dimethylformamide as a solvent. A paste obtained by mixing and dispersing a lithium-containing composite nitride and carbon black as a conductive material in this polyacrylonitrile solution was applied to a copper core material as a negative electrode current collector to produce a negative electrode. Example 1 was repeated except that the above-mentioned polyacrylonitrile solution was used instead of the PEO solution of Example 1.
In the same manner as in the above, a positive electrode of Li _0.5 CoO ₂ was produced. next,
The positive plate is acetone or ethanol and the negative plate is dehydrated N
Each was washed with -methyl-2-pyrrolidone to remove dimethylformamide. A positive electrode plate 5, a separator portion, and a negative electrode plate were laminated to form an electrode group using a non-woven film made of polyacrylonitrile for the separator portion, and an electrode group was prepared. The same organic electrolyte solution as in Example 1 was injected, and then sandwiched between hot plates. After heating, compression, and cooling, the electrode group was integrated and the electrolyte was gelled, and inserted into the battery case 1 and sealed to obtain a completed battery. For comparison, a battery was prototyped using lithium-containing composite nitrides having six types of x-values as in Example 1. The solvent dimethylformamide used was highly dehydrated in consideration of the deterioration of the lithium-containing composite nitride due to moisture.

Example 4 As a polymer material, a polyester polymer which is a copolymer of polybutylene terephthalate and ethyl methacrylate was used and dissolved in ethyl acetate. A lithium-containing composite nitride and a conductive agent were added to this polymer solution to prepare a paste, which was applied to a copper core material and dried to produce a negative electrode 7. A Li _0.5 CoO ₂ positive electrode was produced in the same manner as in Example 1 except that the above polymer solution was used instead of the PEO solution of Example 1. The separator portion was made porous by impregnating a polyester-based polymer with a nonwoven fabric made of polypropylene as a structural reinforcing material, and then removing the solvent by drying. A positive electrode plate, a separator part, and a negative electrode plate are laminated to form an electrode group. The same organic electrolytic solution as in Example 1 is injected, and then sandwiched between a hot plate, heated, compressed, and cooled to integrate the electrode group and electrolyze. The solution was gelled, inserted into a battery case, and sealed to obtain a completed battery. For comparison, a battery was prototyped using lithium-containing composite nitrides having six types of x-values as in Example 1. Ethyl acetate used as the solvent was highly dehydrated in consideration of deterioration of the lithium-containing composite nitride due to moisture.

The various batteries having different x values in Examples 2 to 4 were charged and discharged under the same conditions as in Example 1.
Similarly, the cycle deterioration rate up to the 50th cycle was determined. FIG. 3 shows x values (horizontal axis) of the polymer batteries of Examples 1 to 4.
And the cycle deterioration rate (vertical axis). Each of the polymer gel electrolytes used in the above examples was 10 ⁻³ S / c.
It had an ionic conductivity of m level. In the above embodiment, Co is used as the transition metal species to be substituted.
Similar effects were obtained when Mn, Ni, or Cu was used instead of o, and when these were used in combination.

[0031]

As described above, according to the present invention, a high energy density lithium polymer secondary battery having excellent cycle characteristics and reliability can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic longitudinal sectional view of a lithium polymer secondary battery according to an embodiment of the present invention.

FIG. 2 is a diagram comparing cycle characteristics of the lithium polymer secondary battery of the present invention.

FIG. 3 is a diagram comparing the cycle deterioration rates of the lithium polymer secondary battery of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Battery case 2 Negative electrode lead 3 Negative electrode 4 Polymer gel electrolyte separator part 5 Positive electrode 6 Positive electrode lead 7 Lead welding seal

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Masaki Hasegawa 1-1, Matsushita-cho, Moriguchi-shi, Osaka Matsushita Battery Industry Co., Ltd. (72) Inventor Shuji Tsutsumi 1-1, Matsushita-cho, Moriguchi-shi, Osaka Matsushita Battery (72) Inventor Yoji Sakurai 2-3-1 Otemachi, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (72) Inventor Sou Arai 2-3-1 Otemachi, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation F-term (reference)

Claims (6)

[Claims] 1. The general formula Li _{(3-x) -y} M _x N (M is Co, M
at least one transition metal selected from the group consisting of n, Ni and Cu, 0.3 ≦ x ≦ 0.6, 0 ≦ y ≦ 3-x)
A negative electrode composed of a lithium-containing composite nitride, a conductive material and a polymer material represented by the following; a positive electrode composed of a lithium-containing composite oxide, a conductive material and a polymer material; and a polymer gel electrolyte containing an organic electrolytic solution. A lithium polymer secondary battery characterized by the above-mentioned. 2. The lithium polymer secondary battery according to claim 1, wherein the polymer material of the positive and negative electrodes and the polymer of the polymer gel electrolyte are polymers having a polyalkylene oxide or a derivative thereof as a skeleton. 3. The polymer material of the positive and negative electrodes and the polymer of the polymer gel electrolyte are two or three selected from the group consisting of vinylidene fluoride, propylene hexafluoride, ethylene tetrafluoride, and perfluoroalkyl vinyl ether. The lithium polymer secondary battery according to claim 1, which is a copolymer of the following. 4. The lithium polymer secondary battery according to claim 1, wherein the polymer material of the positive and negative electrodes and the polymer of the polymer gel electrolyte are polymers having polyacrylonitrile or a copolymer thereof as a skeleton. 5. The polymer material of the positive and negative electrodes and the polymer of the polymer gel electrolyte are polyester polymers having a skeleton of polyester or a derivative thereof.
4. The lithium polymer secondary battery according to 4. 6. The polymer gel electrolyte contains one or more structural reinforcing materials selected from the group consisting of hydrophobically treated ceramic fine particles, fibers of a polyolefin resin, and nonwoven fabrics. 6. The lithium polymer secondary battery according to any one of 5.