JP2021197309A - Lithium ion secondary battery - Google Patents

Abstract

To provide a lithium ion secondary battery which is high in the electric capacity achieved when being charged at a high speed, and which is arranged so that the occurrence of short circuit caused by lithium dendrite piercing a separator can be suppressed.SOLUTION: A lithium ion secondary battery comprises: a negative electrode in which a sulfur-modified polyacrylonitrile is used as a negative electrode active material; a separator composed of an unwoven fabric or a piece of paper; and a nonaqueous electrolyte containing a lithium salt.SELECTED DRAWING: None

Description

The present invention relates to a lithium ion secondary battery using sulfur-modified polyacrylonitrile as the negative electrode active material and non-woven fabric or paper as a separator interposed between the negative electrode and the positive electrode.

Lithium-ion secondary batteries have higher cell voltage and higher energy density than conventional nickel-hydrogen secondary batteries. Therefore, in addition to mobile devices such as smartphones, application to electronic devices such as hybrid vehicles, electric vehicles, stationary storage batteries, and notebook computers is being promoted. In a lithium ion secondary battery, a separator is interposed to insulate between the positive electrode and the negative electrode.
For example, Patent Document 1 and Patent Document 2 disclose a lithium ion secondary battery using a non-woven fabric as an inexpensive separator that easily holds a non-aqueous electrolytic solution.

Lithium-ion secondary batteries have problems such as high capacity, high output, long life, improved safety, and low cost, and electrode materials and electrolytic solutions are being actively developed.

For example, Patent Document 3 discloses a lithium ion secondary electrode using sulfur-modified polyacrylonitrile as a positive electrode material. Patent Document 4 proposes a secondary battery including a negative electrode using sulfur-modified polyacrylonitrile as a negative electrode active material, aluminum as a current collector, and a positive electrode using a lithium manganese-based composite oxide as a positive electrode active material. Has been done.

International Publication No. 2005/067079 Japanese Unexamined Patent Publication No. 2016-119212 International Publication No. 2010/0444437 Japanese Unexamined Patent Publication No. 2014-93626

The conventional lithium-ion secondary battery has a problem that the electric capacity that can be charged and discharged tends to decrease when high-speed charging and discharging are performed. In addition, lithium-ion secondary batteries that use non-woven fabric or paper as the separator have a problem of poor cycle life because the lithium dendrite generated on the electrodes due to repeated charging and discharging easily penetrates the non-woven fabric and causes a short circuit between the positive and negative electrodes. There is. An object of the present invention is to provide a lithium ion secondary battery capable of solving these problems.

As a result of diligent studies, the present inventors have found that the above problems can be solved by using a specific material for the negative electrode, and have completed the present invention.

That is, the present invention is a lithium ion secondary battery containing a non-aqueous electrolyte containing a lithium salt, using sulfur-modified polyacrylonitrile as the negative electrode active material for the negative electrode and non-woven fabric or paper as the separator.

In the lithium ion secondary battery of the present invention, the separator is preferably a non-woven fabric or paper having a thickness of 5 μm to 50 μm, a void ratio of 40% or more, and a Garley value of 100 seconds / 100 ml or less.

The lithium ion secondary battery of the present invention preferably has an average particle size of sulfur-modified polyacrylonitrile of 0.1 μm to 50 μm.

In the lithium ion secondary battery of the present invention, it is preferable that the non-aqueous electrolyte containing a lithium salt is a liquid non-aqueous electrolyte or a polymer gel-like non-aqueous electrolyte.

In the lithium ion secondary battery of the present invention, it is more preferable that the liquid non-aqueous electrolyte contains a cyclic carbonate compound.

In the lithium ion secondary battery of the present invention, it is more preferable that the liquid non-aqueous electrolyte further contains a chain carbonate compound.

According to the present invention, it is possible to provide a lithium ion secondary battery having an improved battery capacity during high-speed charging / discharging.

It is a vertical sectional view schematically showing an example of the structure of the coin-type battery of the lithium ion secondary battery of this invention. It is a schematic diagram which shows the basic structure of the cylindrical battery of the lithium ion secondary battery of this invention. It is a perspective view which shows the internal structure of the cylindrical battery of the lithium ion secondary battery of this invention as a cross section. It is an exploded perspective view which shows typically the laminated type electrode group inside the laminated type battery of the lithium ion secondary battery of this invention. It is an exploded perspective view schematically showing the laminated type battery of the lithium ion secondary battery of this invention. It is external top view which shows typically the laminated type battery of the lithium ion secondary battery of this invention.

The lithium ion secondary battery of the present invention has a negative electrode containing a sulfur-modified polyacrylonitrile, a non-woven fabric or paper as a separator, and a non-aqueous electrolyte containing a lithium salt.
Hereinafter, the lithium ion secondary battery of the present invention will be described in detail based on a preferred embodiment.

<Sulfur-modified polyacrylonitrile (SPAN)>
Sulfur-modified polyacrylonitrile (hereinafter referred to as "SPAN") can be produced by mixing a polyacrylonitrile compound and sulfur and modifying them in a non-oxidizing atmosphere by heat treatment at 250 ° C. to 600 ° C. The non-oxidizing atmosphere represents an atmosphere in which the oxygen concentration is less than 5% by volume, preferably less than 2% by volume, and more preferably substantially free of oxygen, for example, an inert gas atmosphere such as nitrogen, helium, or argon. , Sulfur gas atmosphere, etc.

The polyacrylonitrile compound may be a homopolymer of acrylonitrile or a copolymer of acrylonitrile and another monomer. When the content of acrylonitrile in the polyacrylonitrile compound is low, the capacity of the battery cannot be increased by the active material, and the battery performance is deteriorated. Therefore, the content of acrylonitrile in the copolymer of acrylonitrile and other monomers is at least 90% by mass. It is preferable to have a polyacrylonitrile homopolymer, and a polyacrylonitrile homopolymer is further preferable. Examples of other monomers include acrylic acid, vinyl acetate, N-vinylformamide, and N, N'-methylenebis (acrylamide).

It is preferable that the SPAN has a desired particle size by a method such as pulverization or granulation. The pulverization may be performed by dry pulverization performed in a gas or wet pulverization performed in a liquid such as water. Examples of the industrial crushing method include ball mills, roller mills, turbo mills, jet mills, cyclone mills, hammer mills, pin mills, rotary mills, vibration mills, planetary mills, attritors, bead mills and the like.

The crushed SPAN is preferably further classified. The classification method is not particularly limited, but is a dry classification method such as gravity classification, inertial classification, and centrifugal classification; a wet classification method such as sedimentation classification, mechanical classification, and hydraulic classification; vibration sieve, in-plane motion sieve, and the like. A classification method such as a sieving classification method using a sieving net can be adopted. Above all, the sieving classification method is preferable.
By carrying out the pulverization and classification steps, a SPAN with a particle size suitable for the present invention can be efficiently produced.

The average particle size (D50) of SPAN is preferably 50 μm or less, more preferably 30 μm or less, still more preferably 20 μm or less. If the average particle size is too small, the handling property will deteriorate and side reactions will easily occur as the specific surface area of the particles increases, which will adversely affect the charge / discharge stability of the lithium ion secondary battery. It is preferable, 0.5 μm or more is more preferable, and 1 μm or more is further preferable.

The average particle size of the SPAN particle size is 50% particle size measured by the laser diffraction light scattering method. In the laser diffracted light scattering method, the particle size is a volume-based diameter, and the secondary particle size of SPAN is measured. When measuring the average particle size of SPAN by the laser diffraction light scattering method, SPAN is dispersed in a dispersion medium such as water or alcohol for measurement.

In the present invention, the shape of the SPAN may be fibrous. When a fibrous SPAN is used, the preferable average fiber diameter is 0.05 μm or more and 10 μm or less. It is preferable that the fiber diameter is small, but it is difficult to obtain an industrial product of polyacrylonitrile having an average fiber diameter of less than 0.05 μm as the polyacrylonitrile which is a raw material of SPAN. Further, when the average fiber diameter is larger than 10 μm, a large charge / discharge capacity may not be obtained. The average fiber diameter of the fibrous SPAN is preferably 0.1 μm to 5 μm, more preferably 0.15 μm to 2 μm, from the viewpoint of obtaining a larger charge / discharge capacity and making it easily available.

When the aspect ratio of the fibrous SPAN is expressed as fiber length / fiber diameter, the average aspect ratio of the fibrous SPAN is preferably 3 or more, more preferably 5 or more. When the aspect ratio is large, it is preferable that the fiber length is large because a large charge / discharge capacity can be obtained. However, if the fiber length is too large, the surface of the active material layer containing SPAN may not be smooth. The average fiber length of the fibrous SPAN is preferably 300 μm or less, more preferably 150 μm or less. From the same viewpoint, the average aspect ratio of the fibrous SPAN is preferably 5000 or less, more preferably 1000 or less. The fiber length and fiber diameter of the fibrous SPAN can be obtained from an image (SEM image) of a scanning electron microscope. The fiber length represents the length of the fiber, and the fiber diameter represents the diameter of the circle when the cross section orthogonal to the longitudinal direction of the fiber is circular, and when the cross section is not circular, the average of the minor axis and the major axis of the cross section. Represents. The measurement point of the fiber diameter in one fibrous SPAN can be arbitrarily performed.

The average aspect ratio of the fibrous SPAN is a value obtained by calculating the average fiber length / average fiber diameter, and the average fiber length and the average fiber diameter are the fiber diameter and the fiber length measured from the SEM images of 10 or more fibrous SPANs. Represents the number average value of.

The sulfur content in the SPAN is preferably 30% by mass to 55% by mass, more preferably 35% by mass to 50% by mass, because a large charge / discharge capacity and excellent cycle characteristics can be obtained.
In this specification, the sulfur content of SPAN represents a numerical value calculated from the result of elemental analysis using a CHN analyzer capable of analyzing sulfur and oxygen, for example, a vario MICRO cube manufactured by Elementer.

In the lithium ion secondary battery of the present invention, SPAN is used for the negative electrode as a negative electrode active material. The negative electrode can be manufactured according to a known method. For example, an electrode mixture paste containing a negative electrode active material, a binder and a conductive auxiliary agent is applied to a current collector by applying an electrode mixture paste slurryed with an organic solvent or water to the current collector and dried, whereby the electrode mixture is applied onto the current collector. A negative electrode having a layer formed can be manufactured.

The binder is not particularly limited, but a known binder can be used. Specific examples of the binder include, for example, styrene-butadiene rubber, butadiene rubber, acrylic nitrile-butadiene rubber, ethylene-propylene-diene rubber, styrene-isoprene rubber, fluororubber, polyethylene, polypropylene, polyacrylamide, polyamide, polyamideimide, and the like. Polyethylene, polyacrylonitrile, polyurethane, polyvinylidene fluoride, polytetrafluoroethylene, styrene-acrylic acid ester copolymer, ethylene-vinyl alcohol copolymer, polymethylmethacrylate, polyacrylate, polyvinyl alcohol, polyethylene oxide, polyvinylpyrrolidone, polyvinyl Examples thereof include ether, polyvinyl chloride, acrylic acid, polyacrylic acid, methyl cellulose, carboxymethyl cellulose, sodium carboxymethyl cellulose, cellulose nanofibers, starch and the like. Only one kind of binder may be used, or two or more kinds of binders may be used in combination.

The content of the binder is preferably 0.5 part by mass to 30 parts by mass with respect to 100 parts by mass of SPAN, and the stability of the electrode is improved, so that the content is more preferably 1 part by mass to 20 parts by mass. preferable.

As the conductive auxiliary agent, a known conductive auxiliary agent for the electrode can be used. Specific examples of conductive auxiliaries include natural graphite, artificial graphite, coal tar pitch, carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, roller black, and disc black. , Carbon nanotubes, carbon material such as Vapor Green Carbon Fiber (VGCF), flaky graphite, graphene, fullerene, needle coke; metal powders such as aluminum powder, nickel powder, titanium powder; zinc oxide, oxidation. Conductive metal oxides such as titanium; _{sulfides such as La 2} S ₃ , Sm ₂ S ₃ , Ce ₂ S ₃ and TiS ₂ can be mentioned.

The average particle size (D50) of the conductive auxiliary agent is preferably 0.0001 μm to 100 μm, and more preferably 0.001 μm to 50 μm.

The content of the conductive auxiliary agent is usually 0.1 part by mass to 50 parts by mass, preferably 0.5 part by mass to 30 parts by mass, and 1 part by mass to 100 parts by mass with respect to 100 parts by mass of the negative electrode active material. It is more preferably 20 parts by mass.

Examples of the solvent for preparing the electrode mixture paste for the negative electrode include propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, acetonitrile, and pro. Pionitrile, tetrahydrofuran, 2-methyltetrahydrofuran, dioxane, 1,3-dioxolane, nitromethane, N-methylpyrrolidone, N, N-dimethylformamide, dimethylacetamide, methylethylketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, N , N-dimethylaminopropylamine, polyethylene oxide, tetrahydrofuran, dimethyl sulfoxide, sulfolane, γ-butyrolactone, water, alcohol and the like. The amount of the solvent used can be adjusted according to the coating method selected when coating the electrode mixture paste. For example, in the case of coating by the doctor blade method, the total of the negative electrode active material, the binder and the conductive auxiliary agent. The amount is preferably 10 parts by mass to 300 parts by mass, and more preferably 20 parts by mass to 200 parts by mass with respect to 100 parts by mass.

The electrode mixture paste for the negative electrode contains, for example, other components such as a viscosity regulator, a reinforcing material, an antioxidant, a pH adjuster, and a dispersant, in addition to the above-mentioned components, as long as the effects of the present invention are not impaired. You may let it. As these other components, known ones can be used in known compounding ratios.

In the production of the electrode mixture paste, when SPAN as a negative electrode active material, a binder and a conductive auxiliary agent are dispersed or dissolved in a solvent, all of them may be added to the solvent at once for dispersion treatment, or added separately. Distributed processing may be performed. It is preferable to sequentially add the binder, the conductive auxiliary agent, and the negative electrode active material to the solvent in this order to perform the dispersion treatment because these can be uniformly dispersed in the solvent. When the electrode mixture paste contains other components, the other components can be added all at once for dispersion treatment, but it is preferable to perform dispersion treatment for each addition of one of the other components.

The method of dispersion treatment is not particularly limited, but industrial methods include, for example, ordinary ball mills, sand mills, bead mills, cyclone mills, zero mills, pigment dispersers, grinders, ultrasonic dispersers, homogenizers, dispersers, and revolutions. A revolution mixer, a planetary mixer, a fill mix, a jet pacer, etc. can be used.

Examples of the current collector include conductive materials such as titanium, titanium alloy, aluminum, aluminum alloy, copper, nickel, stainless steel, nickel-plated steel, carbon, and conductive resin. Examples of the shape of the current collector include a foil shape, a plate shape, a net shape, a three-dimensional mesh shape, a foam shape, a non-woven fabric shape, and the like, and the current collector may be either porous or non-porous. Further, these conductive materials may be surface-treated in order to improve adhesion and electrical characteristics. Among these conductive materials, aluminum is preferable from the viewpoint of conductivity and price, and aluminum foil is particularly preferable. The thickness of the current collector is not particularly limited, but in the case of a foil, it is usually 5 μm to 30 μm.

The method of applying the electrode mixture paste of the negative electrode onto the current collector is not particularly limited, but for example, the die coater method, the comma coater method, the curtain coater method, the spray coater method, the gravure coater method, the flexo coater method, and the knife coater. A method, a doctor blade method, a reverse roll method, a brush coating method, a dip method, or the like can be used. The die coater method, the knife coater method, the doctor blade method and the comma coater method are preferable in that a good surface condition of the coating layer can be obtained according to the viscosity and the drying property of the electrode mixture paste.

The negative electrode mixture paste may be applied to one side of the current collector or both sides of the current collector. When it is applied to both sides of the current collector, it may be applied sequentially on one side at a time, or it may be applied on both sides at the same time. Further, it may be applied continuously to the surface of the current collector, intermittently, or in stripes. The thickness, length and width of the coating layer can be appropriately determined according to the size of the battery and the like.

The method for drying the electrode mixture paste of the negative electrode applied on the current collector is not particularly limited, and a known method can be used. Examples of the drying method include drying with warm air, hot air, and low humidity air, vacuum drying, and drying by irradiating far infrared rays, infrared rays, electron beams, or the like, which is left in a heating furnace or the like. These drying methods may be carried out in combination. The temperature for heating is generally about 50 ° C to 180 ° C, but conditions such as temperature are appropriately set according to the amount of the electrode mixture paste applied, the boiling point of the solvent used, the type of binder, and the like. be able to. By this drying, volatile components such as a solvent are volatilized from the coating film of the electrode mixture paste, and an electrode mixture layer is formed on the current collector.

Although SPAN is originally a lithium-free material, it can be pre-doped with lithium because it has an irreversible capacity. As a method of lithium-doping SPAN, for example, a method of assembling a semi-battery using metallic lithium at the counter electrode and inserting lithium by an electrolytic doping method of electrochemically doping lithium, or a method of attaching a metallic lithium foil to an electrode. After that, it is left in the electrolytic solution and is doped by utilizing the diffusion of lithium to the electrode. The method of inserting lithium by the pasting doping method, the active material and the lithium metal are mechanically collided and the lithium is inserted. Examples thereof include a mechanical dope method in which an electrode is immersed in a lithium naphthalenide solution and a chemical dope method in which lithium is inserted, but the present invention is not limited to these methods.

<Separator>
The separator forms a porous layer, has insulating properties, and suppresses a short circuit between a positive electrode and a negative electrode. The lithium ion secondary battery of the present invention is characterized in that a non-woven fabric or paper is used as the separator. And. Further, ceramic coating may be applied to one side or both sides of the separator.

The non-woven material represents a structure made by joining, entwining, or a combination of these fibers with a chemical, solvent, or a combination thereof without weaving or knitting the fibers, and represents the non-aqueous electrolyte of the present invention. Examples of the secondary battery include those that are arranged at a position between the positive electrode and the negative electrode and have a function as a separator.

As a method for producing a non-woven fabric, a known production method can be adopted, but in general, it has a two-step process of forming an integrated layer of fibers and a process of bonding the fibers of the integrated layer, each of which has two steps. At this stage, various manufacturing methods can be selected. For example, as a step of forming an integrated layer, for example, a dry method, a wet method, a spunbond method, a melt blow method, an electrospinning method, a force spinning method, a flash spinning method and the like can be mentioned. Examples of the step of bonding the fibers of the integrated layer include a thermal bond method, a chemical bond method, a needle punch method, a spunlace method (water flow entanglement method), a stitch bond method, a steam jet method and the like. When the electrospinning method, the force spinning method, or the flash spinning method is adopted, there may be no step of bonding the fibers of the integrated layer.

As the raw material of the non-woven fabric, a known substance that can be processed into a fiber can be used, and for example, polyethylene terephthalate fiber, polyolefin fiber, aramid fiber, glass fiber, cellulose fiber, polyacrylonitrile fiber, nylon fiber and the like can be used. Can be mentioned. In the lithium ion secondary battery of the present invention, the nonwoven fabric may be one using two or more kinds of fibers. Nonwoven fabrics containing polyethylene terephthalate fiber, polypropylene fiber, polyamide fiber, polyimide fiber, cellulose fiber, and polyacrylonitrile fiber are preferable, and polyethylene terephthalate fiber, cellulose fiber, and poly are preferable from the viewpoint of good thermal stability and easy availability as an industrial product. Nonwoven fabrics containing acrylonitrile fibers are more preferred. Further, the shape such as the fiber length and the thickness may be adjusted according to the purpose and use of the lithium ion secondary battery.

Paper represents a product produced by laminating plant fibers and other fibers, and examples of the plant fibers include cellulose and variants of cellulose (carboxymethyl cellulose, hydroxypropyl cellulose, etc.). Examples of other fibers include fibrous minerals, animal fibers, synthetic resin fibers and the like. Examples of the fibrous mineral include glass fiber, rock wool, fibrous silicate, ceramic wool, whiskers and the like. Animal fiber represents a fiber obtained from an animal, and examples of the animal from which the fiber can be obtained include sheep, silk moth, cocoon, Angora goat, cashmere goat, sardine, llama, alpaca, picuna, Angora rabbit, and spider. .. The synthetic resin fiber represents a fiber obtained from a synthetic resin, for example, polyolefin (polypropylene, polypropylene copolymer, etc.), polyester (polyethylene terephthalate, poethylene naphthalate, polybutylene terephthalate, etc.), polyacrylonitrile, polyaramid, polyamideimide. , Fibers obtained by using polyimide or the like.
The paper used in the present invention is preferably paper containing cellulose as a raw material, and paper obtained by pressure-bonding paper to a synthetic resin sheet such as polypropylene may be used.

In the present invention, the separator insulates between the positive electrode and the negative electrode to prevent a short circuit, has ion permeability for carrying out a battery reaction via the separator, and has an active material layer that contributes to the battery reaction in the battery. It is preferable to adjust the thickness of the non-woven fabric or paper so that the volume efficiency of the non-woven fabric or paper is high. Specifically, the thickness of the nonwoven fabric or paper used as the separator is preferably 5 μm or more and 50 μm or less. By making the thickness of the non-woven fabric or paper 5 μm or more, the insulating function can be enhanced and the non-woven fabric or paper can hold the required amount of the non-aqueous electrolytic solution. By reducing the thickness of the non-woven fabric or paper to 50 μm or less, the influence on the battery capacity and battery characteristics can be reduced.

The porosity of the separator is based on the volume, and the porosity is preferably 40% or more so that the function of holding the electrolytic solution can be obtained. The upper limit is preferably 80% or less so as to prevent a short circuit between the positive and negative electrodes.

The Garley value of the separator is an index relating to a woven fabric or a non-woven fabric, and in this specification, it represents a value measured according to JIS P8117. The smaller this garley value, the higher the breathability. In the lithium ion secondary battery of the present invention, the Garley value of the separator is preferably 100 seconds / 100 ml or less, more preferably 50 seconds / 100 ml or less, in order to enhance the ion diffusivity in the separator.

<Positive electrode>
The positive electrode used in the lithium ion secondary battery of the present invention contains a positive electrode active material, a binder and a conductive auxiliary agent.

Examples of the positive electrode active material that can be used in the lithium ion secondary battery of the present invention include a composite oxide containing lithium.

The lithium-containing composite oxide is selected from the group consisting of a lithium transition metal composite oxide, a lithium transition metal silicate compound, and a lithium transition metal sulfate compound. The transition metal contained in these compounds is not particularly limited, but aluminum, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, and copper have good charge / discharge stability of the lithium ion secondary battery. Zinc, magnesium, gallium, zirconium, niobium, boron, calcium, molybdenum, and tungsten are preferable, and aluminum, vanadium, titanium, chromium, manganese, iron, cobalt, nickel, and copper are preferable because the effects of the present invention become remarkable. , Aluminum, manganese, iron, cobalt, and nickel are preferred because the effects of the present invention are even more pronounced.

Examples of the lithium transition metal composite oxide include LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , a compound represented by the following general formula (1), and a compound represented by the following general formula (2).
Li _a Ni _b Co _c M1 _d O ₂ (1)
Li _{(1 + x)} Mn _(2-x-y) M1 _y O ₄ (2)
In the formula, a, b, c and d have 0.9 ≦ a ≦ 1.2, 0.3 <b <1, 0 ≦ c ≦ 0.5, 0 ≦ d ≦ 0.5, b + c + d = 1. Satisfaction, x satisfies 0 ≦ x <0.5, and y satisfies 0 ≦ y <0.5. M1 is preferably at least one selected from the group consisting of aluminum, titanium, vanadium, chromium, manganese, iron, copper, zinc, magnesium, gallium, zirconium, niobium, boron, calcium, molybdenum, and tungsten.

Specific examples of the compound represented by the general formula (1) or the compound represented by the general formula (2) include, for example, LiMn ₂ O ₄ , LiNi _0.5 Co _0.2 Mn _0.3 O ₂ , LiNi _0.8 Co _0.1 Mn _0.1 O ₂ , LiNi _0.5 Mn _1.5 O ₄ , LiNi _0.80 Co _0.15 Al _0.05 O ₂ , LiNi _0.80 Co _0.17 Al _0.03 O ₂ , LiNi _0.90 Co _0.05 Al _0.05 O ₂ , LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiNi _0.6 Co _0.2 Mn _0.2 O ₂ , LiNi _0.9 Co _0.05 Mn _0.05 O ₂ , LiMn _1.8 Al _0.2 O ₄ , Li _1.1 Mn _1.8 Mg _0.1 O ₄ , Li _1.1 Mn _1. Examples thereof _{include 85} Al _0.05 O ₄ , Li ₂ MnO _{3- LiMO 2} (M = cobalt, nickel, manganese) and the like.

The lithium transition metal composite oxide that can be used for the positive electrode of the present invention has good charge / discharge stability, and therefore, for example, LiCoO ₂ , LiMn ₂ O ₄ , LiNi _1/3 Co _1/3 Mn _1/3. O ₂ , LiNi _0.5 Co _0.2 Mn _0.3 O ₂ , LiNi _0.6 Co _0.2 Mn _0.2 O ₂ , LiNi _0.8 Co _0.1 Mn _0.1 O ₂ , LiNi _{0 8.8} Co _0.15 Al _0.05 O ₂ is preferable.

Examples of the lithium transition metal phosphoric acid compound of the present invention include compounds represented by the following general formula (3).
Li _h M2 _j (PO ₄ ) _{kF l} (3)
In the formula, h is 0 <h ≦ 3, j is 0.5 ≦ j ≦ 2, k is 1 ≦ k ≦ 3, and l is 0 ≦ l ≦ 1. M2 is at least one of iron, cobalt, nickel, manganese, copper, titanium, tungsten, molybdenum, chromium, vanadium, or vanadium monoxide (II), and has good charge / discharge stability, so iron and cobalt. , Nickel, manganese, copper, vanadium, or vanadium monoxide (II) is more preferred. Further, a part of M2 may be replaced with one or more other metals such as aluminum, zinc, magnesium, zirconium, gallium and niobium.

Specific examples of the lithium-transition metal phosphate compound, for _{example, LiFePO 4, LiMn X Fe 1} -X PO 4, LiCuPO 4, LiNiPO 4, LiCoPO 4, LiMnPO 4, LiVOPO 4, Li 2 FePO 4, Li 2 NiPO ₄ , Li ₂ CoPO ₄ , Li ₂ MnPO ₄ , Li ₂ NiPO ₄ F, Li ₂ CoPO ₄ F, Li ₂ MnPO ₄ F, Li ₂ FePO ₄ F, Li ₃ V ₂ (PO ₄ ) ₃ , _{Li Mn 7 / 8} Fe _1/8 PO ₄ , LiMn _2/3 Fe _1/3 PO ₄ , LiFe _0.9 Mn _0.1 PO ₄ , LiFe _0.2 Mn _0.8 PO ₄ , LiFe _0.15 Mn _0.75 Mg Examples thereof include _0.1 PO ₄ , LiFe _0.19 Mn _0.75 Zr _0.03 PO _4.

_{LiFePO 4} , LiCuPO ₄ , LiNiPO ₄ , LiCoPO ₄ , LiMnPO ₄ , and LiVOPO ₄ are preferable, and LiFePO ₄ , LiNiPO ₄ , LiCoPO ₄ , and LiMnPO ₄ are more preferable because of good charge / discharge stability.

In the lithium ion secondary battery of the present invention, the positive electrode active material preferably has a desired particle size by a method such as pulverization or granulation, and is further preferably classified. Examples of the method for crushing and classifying include the same methods described in the method for crushing and classifying SPAN.

The average particle size (D50) of the positive electrode active material is preferably 0.1 μm to 50 μm, more preferably 0.5 μm to 30 μm, and even more preferably 1 μm to 20 μm. If it exceeds 50 μm, a uniform and smooth electrode mixture layer may not be obtained, and if it is smaller than 0.1 μm, the handling property is poor, and the specific surface area becomes large and side reactions are likely to occur, resulting in charge / discharge stability. May have an adverse effect.

The positive electrode used in the lithium ion secondary battery of the present invention can be manufactured according to a known method. For example, a compound containing a composite oxide containing lithium as a positive electrode active material, a binder, and a conductive auxiliary agent is applied to a current collector and dried by applying an electrode mixture paste slurryed with an organic solvent or water to a current collector. , A positive electrode having an electrode mixture layer formed on a current collector can be manufactured.

The binder used for the positive electrode may be the same as that described above, but because of its good charge / discharge stability, polyvinylidene fluoride, polyimide, polyacrylonitrile, polytetrafluoroethylene, polyacrylic acid, and sodium carboxymethyl cellulose can be used. Is preferable.

The content of the binder is preferably 0.5 part by mass to 30 parts by mass, and more preferably 1 part by mass to 20 parts by mass with respect to 100 parts by mass of the positive electrode active material.

Examples of the conductive auxiliary agent used for the positive electrode include the same as those described above.

The content of the conductive auxiliary agent is preferably 0.1 part by mass to 50 parts by mass, more preferably 0.5 part by mass to 30 parts by mass, and 1 part by mass to 1 part by mass with respect to 100 parts by mass of the positive electrode active material. 20 parts by mass is more preferable.

As the solvent for preparing the electrode mixture paste for the positive electrode, the same solvent as the solvent for preparing the electrode mixture paste for the negative electrode can be used. The amount of the solvent used can be adjusted according to the coating method selected when coating the electrode mixture paste. For example, in the case of coating by the doctor blade method, the total of the positive electrode active material, the binder and the conductive auxiliary agent. The amount is preferably 10 parts by mass to 300 parts by mass, and more preferably 20 parts by mass to 200 parts by mass with respect to 100 parts by mass.

The positive electrode mixture paste contains, for example, other components such as a viscosity regulator, a reinforcing material, an antioxidant, a pH adjuster, and a dispersant, in addition to the above-mentioned components, as long as the effects of the present invention are not impaired. You may let it. As these other components, known ones can be used in known compounding ratios.

In the production of the electrode mixture paste, when the positive electrode active material, the binder and the conductive auxiliary agent are dispersed or dissolved in the solvent, all of them may be added to the solvent at once for dispersion treatment or separately added for dispersion treatment. You may. It is preferable to sequentially add the binder, the conductive auxiliary agent, and the positive electrode active material to the solvent in this order to perform the dispersion treatment because these can be uniformly dispersed in the solvent. When the electrode mixture paste contains other components, the other components can be added all at once for dispersion treatment, but it is preferable to perform dispersion treatment for each addition of one of the other components.

Examples of the dispersion treatment method and the current collector in the production of the electrode mixture paste include the same as those described above.

The method of applying the electrode mixture paste of the positive electrode on the current collector and the method of drying the electrode mixture paste are the method of applying the electrode mixture paste of the negative electrode on the current collector and the method of drying the electrode mixture paste. It can be used in the same way as described as the method.

<Non-water electrolyte>
The non-aqueous electrolyte containing a lithium salt is a liquid non-aqueous electrolyte obtained by dissolving a lithium salt in an organic solvent, or as a solvent or a dispersion medium, a polymer gel obtained by dissolving a polymer compound in an organic solvent and gelling. Examples thereof include a high molecular weight gel-like non-aqueous electrolyte obtained by dissolving or dispersing a lithium salt.

The above lithium salt is not particularly limited, and a known lithium salt that can be used as a lithium salt for a lithium ion secondary battery can be used. Specific examples of lithium salts include, for example, LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) _2. , LiN (SO ₂ F) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiB (CF ₃ SO ₃ ) ₄ , LiB (C ₂ O ₄ ) ₂ , LiBF ₂ (C ₂ O ₄ ), LiSbF ₆ , LiSiF ₅ , LiSCN, LiClO ₄ , LiCl, LiF, LiBr, LiI, _{LiAlF 4} , LiAlCl ₄ , LiPO ₂ F ₂ , and derivatives thereof, and examples thereof include LiPF ₆ , LiBF ₄ , LiClO ₄ , LiCF ₃ SO ₃ , LiN ( CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (SO ₂ F) ₂ , LiPO ₂ F ₂ , LiC (CF ₃ SO ₂ ) ₃ and derivatives of LiCF ₃ SO ₃ and LiC (CF) ₃ SO ₂ ) It is preferable to use at least one selected from the group consisting of _{3 derivatives.}

If the concentration of the lithium salt in the non-aqueous electrolyte is too low, sufficient current density may not be obtained, while if it is too high, the stability of the non-aqueous electrolyte may be impaired. Therefore, the concentration of the lithium salt is preferably 0.5 mol / L to 7 mol / L, more preferably 0.8 mol / L to 1.8 mol / L.

<Liquid non-aqueous electrolyte>
When a liquid non-aqueous electrolyte is used as the non-aqueous electrolyte, it preferably contains at least one compound selected from cyclic carbonate compounds.
Examples of the cyclic carbonate compound include saturation of ethylene carbonate, 1,2-propylene carbonate, 1,3-propylene carbonate, 1,2-butylene carbonate, 1,3-butylene carbonate, 1,1,-dimethylethylene carbonate and the like. Examples thereof include unsaturated cyclic carbonate compounds such as cyclic carbonate compounds, vinylene carbonates, vinylethylene carbonates, propyridene carbonates, ethyleneethylidene carbonates and ethyleneisopropyridene carbonates. In these cyclic carbonate compounds, a part of hydrogen atom may be replaced with a fluorine atom.

When the cyclic carbonate compound is contained as the non-aqueous electrolyte, it is preferable to further contain the chain carbonate compound because the viscosity is lowered and the ionic conductivity is improved. Examples of the chain carbonate compound include saturated chain carbonate compounds such as dimethyl carbonate, ethylmethyl carbonate, diethyl carbonate, and dipropyl carbonate, dipropargyl carbonate, propargyl methyl carbonate, ethylpropargyl carbonate, and bis (1-methylpropargyl) carbonate. , An unsaturated chain carbonate compound such as bis (1-dimethylpropargyl) carbonate. In these chain carbonate compounds, a part of hydrogen atom may be replaced with a fluorine atom.

The liquid non-aqueous electrolyte is a mixture of propylene carbonate, a mixed solvent of ethylene carbonate and dimethyl carbonate, a mixed solvent of ethylene carbonate and ethylmethyl carbonate, and a mixed solvent of ethylene carbonate and diethyl carbonate from the viewpoint of the performance and storage stability of the lithium ion secondary battery. A mixed solvent, a mixed solvent of propylene carbonate and dimethyl carbonate, a mixed solvent of propylene carbonate and diethyl carbonate, a mixed solvent of propylene carbonate, ethylene carbonate and ethylmethyl carbonate are preferable, and a mixed solvent of propylene carbonate, an ethylene carbonate and ethylmethylcarbonate, and ethylene are preferable. A mixed solvent of carbonate and diethyl carbonate, a mixed solvent of propylene carbonate and diethyl carbonate, and a mixed solvent of propylene carbonate, ethylene carbonate and ethylmethyl carbonate are more preferable.

When the liquid non-aqueous electrolyte contains a chain carbonate compound, the mixing ratio of the cyclic carbonate compound and the chain carbonate compound is 100 parts by volume of the cyclic carbonate compound and 10 parts by volume to 1,000 parts by volume of the chain carbonate compound. It is preferably a part. If the amount of the chain carbonate compound is less than 10 parts by volume, the performance of the lithium ion secondary battery may be deteriorated, and if it exceeds 1,000 parts by volume, the charge / discharge stability of the lithium ion secondary battery is lowered. In some cases.

The liquid non-aqueous electrolyte may contain an organic solvent usually used for the non-aqueous electrolyte of a lithium ion secondary battery. Specific examples thereof include saturated cyclic ester compounds, sulfoxide compounds, sulfon compounds, amide compounds, chain ether compounds, cyclic ether compounds, saturated chain ester compounds and the like. Only one kind of these organic solvents may be added, or two or more kinds may be added and used.

Examples of the saturated cyclic ester compound include γ-butyrolactone, γ-valerolactone, γ-caprolactone, δ-hexanolactone, and δ-octanolactone.

Examples of the sulfoxide compound include dimethyl sulfoxide, diethyl sulfoxide, dipropyl sulfoxide, diphenyl sulfoxide, thiophene and the like.

Examples of the sulfone compound include dimethyl sulfone, diethyl sulfone, dipropyl sulfone, diphenyl sulfone, sulfolane (also referred to as tetramethylene sulfone), 3-methyl sulfolane, 3,4-dimethyl sulfolane, 3,4-diphenylmethyl sulfolane, and the like. Examples thereof include sulfolane, 3-methylsulfolen, 3-ethylsulfolen, 3-bromomethylsulfolen and the like. Among these, sulfolane and tetramethylsulfolane are preferable.

Examples of the amide compound include N-methylpyrrolidone, dimethylformamide, dimethylacetamide and the like.

Examples of the chain ether compound and the cyclic ether compound include dimethoxyethane, ethoxymethoxy ethane, diethoxy ethane, tetrahydrofuran, dioxolan, dioxane, 1,2-bis (methoxycarbonyloxy) ethane, and 1,2-bis (ethoxycarbonyl). Oxy) ethane, 1,2-bis (ethoxycarbonyloxy) propane, ethylene glycol bis (trifluoroethyl) ether, propylene glycol bis (trifluoroethyl) ether, ethylene glycol bis (trifluoromethyl) ether, diethylene glycol bis (tri) Fluoroethyl) ether and the like can be mentioned, and among these, dioxolane is preferable.

The saturated chain ester compound is preferably a monoester compound or a diester compound having a total number of carbon atoms in the molecule of 2 to 8, and specific compounds include, for example, methyl formate, ethyl formate, methyl acetate, and acetate. Ethyl, propyl acetate, isobutyl acetate, butyl acetate, methyl propionate, ethyl propionate, methyl butyrate, methyl isobutyrate, methyl trimethylacetate, ethyl trimethylacetate, methyl malonate, ethyl malonate, methyl succinate, ethyl succinate, Methyl 3-methoxypropionate, ethyl 3-methoxypropionate, ethylene glycol diacetyl, propylene glycol diacetyl and the like can be mentioned, including methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, isobutyl acetate, butyl acetate and methyl propionate. , And ethyl propionate are preferred.

As other organic solvents, for example, acetonitrile, propionitrile, nitromethane, derivatives thereof, and various ionic liquids can also be used.

<Polymer gel-like non-aqueous electrolyte>
Examples of the polymer that can be used as the polymer gel include polyethylene oxide, polypropylene oxide, polyvinyl chloride, polyacrylonitrile, polymethylmethacrylate, polyethylene, polyvinylidene fluoride, polyhexafluoropropylene, and polystyrene sulfonic acid. The organic solvent that dissolves and gels the polymer, the compounding ratio of the lithium salt and the polymer gel, and the method for producing the polymer gel are not particularly limited, and the organic solvent known in the present technology, the known lithium salt, and the known materials are known. The manufacturing method of can be adopted.

In the lithium ion secondary battery of the present invention, the form of the non-aqueous electrolyte is not particularly limited, but it is preferable to use a liquid non-aqueous electrolyte because the manufacturing process is simple, and it is preferable to use a cyclic carbonate and a chain. It is more preferable to use a combination of carbonates.

The non-aqueous electrolyte may further contain known electrolyte additives such as an electrode film forming agent, an antioxidant, a flame retardant, and an overcharge inhibitor in order to improve battery life and safety. When the electrolyte additive is used, the concentration is preferably 0.01% by mass to 10% by mass, more preferably 0.1% by mass to 5% by mass, based on the non-aqueous electrolyte. If it is less than 0.01% by mass, the addition effect may not be exhibited, and if it exceeds 10% by mass, the characteristics of the lithium ion secondary battery may be adversely affected.

<External packaging>
The shape of the lithium ion secondary battery of the present invention is not particularly limited, and can be a battery having various shapes such as a coin type battery, a cylindrical type battery, a square type battery, and a laminated type battery, and is made of metal as an external packaging member. A manufacturing container or a laminated film can be used. The thickness of the outer packaging member is usually 0.5 mm or less, preferably 0.3 mm or less. Examples of the shape of the external packaging member include a flat type (thin type), a square type, a cylindrical type, a coin type, and a button type. Further, the lithium ion secondary battery of the present invention can also be applied to a wound battery in which separators are simultaneously or sequentially cast and laminated on electrodes, and a positive electrode, a negative electrode and two layers of separators are laminated and wound in a layered manner. Is.

Examples of the metal container include those made of stainless steel, aluminum, an aluminum alloy, or the like. The aluminum alloy is preferably an alloy containing elements such as magnesium, zinc and silicon. By reducing the content of transition metals such as iron, copper, nickel, and chromium to 1% or less in aluminum or an aluminum alloy, long-term reliability and heat dissipation in a high temperature environment can be dramatically improved.

As the laminated film, a multilayer film having a metal layer between resin films can be used. The metal layer is preferably an aluminum foil or an aluminum alloy foil for weight reduction. As the resin film, for example, a polymer material such as polypropylene, polyethylene, nylon, or polyethylene terephthalate can be used. The laminated film can be sealed by heat fusion to form an exterior member.

FIG. 1 shows an example of a coin-type battery of a lithium-ion secondary battery of the present invention, FIGS. 2 and 3 show an example of a cylindrical battery, and FIGS. 4 to 6 show an example of a laminated battery. be.

In the coin-type lithium ion secondary battery 10 shown in FIG. 1, 1 is a positive electrode capable of emitting lithium ions, 1a is a positive electrode current collector, 2 is a negative electrode capable of storing and releasing lithium ions released from the positive electrode, and 2a is a negative electrode collection. The electric body, 3 is a non-aqueous electrolyte, 4 is a positive electrode case made of stainless steel, 5 is a negative electrode case made of stainless steel, 6 is a gasket made of polypropylene, and 7 is a separator.
In the examples described later, a coin-type lithium ion secondary battery will be used, but the present invention is not limited thereto.

In the cylindrical lithium ion secondary battery 10'shown in FIGS. 2 and 3, 11 is a negative electrode, 12 is a negative electrode current collector, 13 is a positive electrode, 14 is a positive electrode current collector, 15 is a non-aqueous electrolyte, and 16 is a separator. 17 is a positive electrode terminal, 18 is a negative electrode terminal, 19 is a negative electrode plate, 20 is a negative electrode lead, 21 is a positive electrode plate, 22 is a positive electrode lead, 23 is a case, 24 is an insulating plate, 25 is a gasket, 26 is a safety valve, and 27 is a PTC. It is an element.

FIG. 4 is an exploded perspective view schematically showing the electrode group 29 of the laminated lithium ion secondary battery 28. The electrode group 29 has, for example, a structure in which a sheet-shaped negative electrode 11, a sheet-shaped positive electrode 13, and a sheet-shaped separator 16 for partitioning the negative electrode 11 and the positive electrode 13 are alternately laminated. Reference numeral 17 is a positive electrode terminal and 18 is a negative electrode terminal.

FIG. 5 is an exploded perspective view schematically showing the laminated lithium ion secondary battery 28, and FIG. 6 is an external plan view schematically showing the laminated lithium ion secondary battery 28. 17 is a positive electrode terminal, 18 is a negative electrode terminal, 29 is an electrode group, 30 is a case-side laminated film, and 31 is a lid-side laminated film.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments. As long as it does not deviate from the gist of the present invention, it can be carried out in various forms with modifications, improvements, etc. that can be made by those skilled in the art.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. The present invention is not limited to these examples.

[Production Example 1] Production of SPAN negative electrode 200 parts by mass of sulfur (manufactured by Sigma Aldrich, particle diameter 200 μm, powder) and 100 parts by mass of polyacrylonitrile powder (manufactured by Sigma Aldrich, classified using a sieve having an opening diameter of 30 μm) are mixed. After putting the resulting mixture into an alumina tanman tube, the opening of the alumina tanman tube was covered with a rubber stopper to which a thermocouple, a gas introduction tube and a gas discharge tube were attached. The mixture was heated at a heating rate of 5 ° C./min while introducing argon gas into the alumina tanman tube at a flow rate of 100 cc / min, and the heating was stopped when the temperature reached 360 ° C., but the temperature rose to 400 ° C. did. After cooling to room temperature by natural cooling, the reaction product was taken out from the alumina tanman tube. The obtained reaction product was heated to remove elemental sulfur and then pulverized to obtain SPAN. The average particle size of the obtained SPAN was 6 μm, and the sulfur content was 37% by mass.

Next, the manufactured SPAN was used as a negative electrode active material to manufacture a SPAN negative electrode.
SPAN 90.0 parts by mass, acetylene black as a conductive auxiliary agent (manufactured by Denka Co., Ltd.) 5.0 parts by mass, styrene-butadiene rubber as a binder (40% by mass aqueous dispersion, manufactured by Nippon Zeon Co., Ltd.) 3.0 mass Add 2.0 parts by mass (solid content) and 2.0 parts by mass of sodium carboxymethyl cellulose (manufactured by Daicel FineChem Co., Ltd.) to 110 parts by mass of water as a solvent, and use a rotation / revolution mixer to rotate 1600 rpm and 800 rpm. The composition for forming an electrode mixture layer was prepared by mixing under the above conditions for 60 minutes.

The obtained composition for forming an electrode mixture layer is applied to one side of a current collector made of a carbon-coated aluminum foil (thickness 22 μm) by a doctor blade method, and allowed to stand at 90 ° C. for 1 hour to dry. After that, it was press-molded. Then, the electrode was cut to a predetermined size and vacuum dried at 140 ° C. for 24 hours immediately before use to prepare a SPAN negative electrode.

[Production Example 2] Production of Graphite Negative Electrode 90.0 parts by mass of artificial graphite as a negative electrode active material, 5.0 parts by mass of acetylene black (manufactured by Denka Co., Ltd.) as a conductive auxiliary agent, and styrene-butadiene rubber (40) as a binder. Mass% water dispersion, 3.0 parts by mass (solid content) manufactured by Nippon Zeon Co., Ltd., and 2.0 parts by mass of sodium carboxymethyl cellulose (manufactured by Daicel FineChem Co., Ltd.) are added to 100 parts by mass of water as a solvent. , These were mixed for 60 minutes under the conditions of revolution 1600 rpm and rotation 800 rpm using a rotation / revolution mixer to prepare a composition for forming an electrode mixture layer. This composition for forming an electrode mixture layer was applied to one side of a current collector made of a copper foil (thickness 10 μm) by a doctor blade method, allowed to stand at 90 ° C. for 1 hour, dried, and then press-molded. Then, the electrode was cut into a predetermined size and vacuum dried at 140 ° C. for 24 hours immediately before use to prepare a graphite negative electrode.

[Production Example 3] Production of positive electrode LiNi _1/3 Co _1/3 Mn _1/3 O ₂ 90.0 parts by mass as positive electrode active material, 5.0 mass of acetylene black (manufactured by Denka Co., Ltd.) as a conductive auxiliary agent Add 5.0 parts by mass of polyvinylidene fluoride as a binder to 50 parts by mass of N-methylpyrrolidone as a solvent, and mix these with a rotation / revolution mixer under the conditions of revolution 1600 rpm and rotation 800 rpm for 60 minutes. Then, a composition for forming an electrode mixture layer was prepared. This composition for forming an electrode mixture layer was applied to one side of a current collector made of an aluminum foil (thickness 20 μm) by a doctor blade method, dried at 90 ° C., and then press-molded. Then, the electrode was cut to a predetermined size, and immediately before use, it was vacuum dried at 150 ° C. for 24 hours to prepare a positive electrode.

[Example 1-1] Manufacture of lithium ion secondary battery A A non-woven fabric (cellulose, thickness 25 μm, void ratio 60%, Garley value 10 seconds / 100 ml) is sandwiched between a positive electrode, a SPAN negative electrode, a positive electrode and a negative electrode in a case. Retained. _{As the non-aqueous electrolytic solution, a non-aqueous electrolytic solution adjusted so that LiPF 6} has a concentration of 1.0 mol / L is sealed in a mixed solvent consisting of 30% by volume of ethylene carbonate and 70% by volume of ethylmethyl carbonate. The case was sealed and sealed using a caulking machine to prepare a coin-shaped lithium ion secondary battery A having a diameter of 20 mm and a thickness of 3.2 mm. The capacity of the battery was 2.0 mAh. A schematic diagram of this coin-shaped lithium ion secondary battery is shown in FIG.

[Comparative Example 1-1] Examples of Production of Lithium Ion Secondary Battery B Except that the non-woven fabric was changed to a microporous membrane separator (polypropylene, thickness 25 μm, void ratio 40%, Garley value 200 seconds / 100 ml). A lithium ion secondary battery B was produced by carrying out the same procedure as in 1-1. The capacity of the battery was 2.0 mAh.

[Comparative Example 1-2] Manufacture of Lithium Ion Secondary Battery C Lithium ion secondary battery C is manufactured by carrying out the same procedure as in Example 1-1 except that the SPAN negative electrode is changed to a graphite negative electrode as the negative electrode. did. The capacity of the battery was 2.1 mAh.

[Comparative Example 1-3] Manufacture of Lithium Ion Secondary Battery D As a negative electrode, a SPAN negative electrode is used as a graphite negative electrode, and as a separator, a non-woven fabric is used as a microporous membrane separator (polypropylene, thickness 25 μm, void ratio 40%, Garley value 200 seconds / A lithium ion secondary battery D was produced by carrying out the same procedure as in Example 1-1 except that the value was changed to 100 ml). The capacity of the battery was 2.1 mAh.

The following evaluations were performed using the lithium ion secondary batteries A to D produced in Examples 1 and Comparative Examples 1 to 3.

<Rate characteristics>
The prepared lithium ion secondary battery is placed in a constant temperature bath at 25 ° C., and the charge / discharge test is continuously performed 5 times under the conditions shown in Table 1 for the charge rate 0.1C, the discharge rate 0.1C, the charge termination voltage and the discharge termination voltage. Then, the charge / discharge test was continuously performed 10 times under the conditions shown in Table 1 for the charge rate of 0.1 C, the discharge rate of 3.0 C, the charge end voltage and the discharge end voltage, and the charge rate was 0. .1C, discharge rate 0.1C, charge termination voltage and discharge termination voltage are subjected to three consecutive charge / discharge tests under the conditions shown in Table 1, and a total of 18 charge / discharge tests are performed to measure the discharge capacity. did. Table 1 shows the 5th and 15th discharge capacities and their discharge capacity ratios (rate characteristics). The unit of discharge capacity is mAh.

<Charging / discharging test>
(1) The prepared lithium ion secondary battery is placed in a constant temperature bath at 25 ° C., and a charge / discharge test is performed under the conditions shown in Table 2 for a charge rate of 0.1C, a discharge rate of 0.1C, a charge termination voltage and a discharge termination voltage. Was carried out continuously for 5 cycles.
(2) After the treatment of (1), the lithium ion secondary battery is placed in a constant temperature bath at 25 ° C., and the charge rate 1.0C, the discharge rate 1.0C, the charge termination voltage and the discharge termination voltage are shown in Table 2. The charge / discharge test was carried out continuously for 500 cycles under the conditions, and the discharge capacities after 5 cycles and after 500 cycles were measured.
(3) The discharge capacity after 500 cycles and the discharge capacity after 5 cycles were introduced into the following formula to calculate the discharge capacity retention rate (%). These discharge capacity retention rates (%) are shown in Table 2 below.
Discharge capacity retention rate (%) = (Discharge capacity after 500 cycles / Discharge capacity after 5 cycles) x 100

In Comparative Example 2-2 in Table 1 and Comparative Example 3-2 in Table 2, a short circuit occurred and an accurate evaluation could not be performed. Further, from Comparative Examples 2-1 to 2-3 in Table 1 and Comparative Examples 3-1 to 3-3 in Table 2, both the rate characteristics and the discharge capacity retention rate were not satisfactory. On the other hand, it was confirmed that the lithium ion secondary battery of the present invention can maintain the rate characteristics and the discharge capacity retention rate at a high level.

1 Positive electrode 1a Positive electrode current collector 2 Negative electrode 2a Negative electrode current collector 3 Non-aqueous electrolyte 4 Positive electrode case 5 Negative electrode case 6 Gasket 7 Separator 10 Coin-type lithium ion secondary battery 10'Cylindrical lithium ion secondary battery 11 Negative electrode 12 Negative electrode collection Electrode 13 Positive electrode 14 Positive electrode collector 15 Non-aqueous electrolyte 16 Separator 17 Positive electrode terminal 18 Negative electrode terminal
19 Negative electrode plate 20 Negative electrode lead 21 Positive electrode plate 22 Positive electrode lead 23 Case 24 Insulation plate 25 Gasket 26 Safety valve 27 PTC element 28 Laminated lithium ion secondary battery 29 Electrode group 30 Case side laminated film 31 Lid side laminated film

Claims (6)

A lithium ion secondary battery comprising a non-aqueous electrolyte containing a lithium salt, using sulfur-modified polyacrylonitrile as the negative electrode active material for the negative electrode, and using non-woven fabric or paper as the separator. The lithium ion secondary battery according to claim 1, wherein the separator is a non-woven fabric or paper having a thickness of 5 μm to 50 μm, a porosity of 40% or more, and a Garley value of 100 seconds / 100 ml or less. The lithium ion secondary battery according to claim 1 or 2, wherein the sulfur-modified polyacrylonitrile has an average particle size of 0.1 μm to 50 μm. The lithium ion secondary battery according to any one of claims 1 to 3, wherein the non-aqueous electrolyte containing a lithium salt is a liquid non-aqueous electrolyte or a polymer gel non-aqueous electrolyte. The lithium ion secondary battery according to claim 4, wherein the liquid non-aqueous electrolyte contains a cyclic carbonate compound. The lithium ion secondary battery according to claim 5, wherein the liquid non-aqueous electrolyte further contains a chain carbonate compound.

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