JP2019200868A - Nonaqueous secondary battery - Google Patents

Abstract

To provide a nonaqueous secondary battery which has high weight energy density, has an excellent charge-discharge behavior, and in which a lithium dendrite is hardly formed during charging.SOLUTION: In a nonaqueous secondary battery having an electrode body and a nonaqueous electrolyte in a battery container, the electrode body is structured by a positive electrode having a positive electrode active material layer, a negative electrode having a negative electrode active material layer, and a porosity insulation layer inserted between the positive electrode and the negative electrode and containing an inorganic insulation body of 80 mass% or more. A vacancy ratio of the insulation layer is 50% or less, a mass of the nonaqueous electrolyte is 2% or more 60% or less for a total sum of a mass of the positive electrode active material layer, the negative electrode active material layer, and the insulation layer and the total sum of the mass of the nonaqueous electrolyte.SELECTED DRAWING: None

Description

  The present invention relates to a non-aqueous secondary battery provided with a porous insulating layer mainly composed of an inorganic insulator as a separator.

  In recent years, along with the development of portable electronic devices such as mobile phones and notebook personal computers, and the practical application of electric vehicles, non-aqueous secondary batteries with small size, light weight, high capacity and high energy density are required. It is becoming.

Currently, lithium ion batteries, for example, are known as non-aqueous secondary batteries that can meet this requirement, and the positive electrode active materials include lithium cobaltate (Li _x CoO ₂ ), lithium nickelate (Li _x NiO ₂ ), nickel- cobalt - lithium manganate _{(Li x Ni y1 Co y2 Mn} y3 O 2: 0.9 <x <1.1,0 <y1, y2, y3 <1, y1 + y2 + y3 = NCM material represented by 1) lithium such as A battery is constituted by using the composite oxide or a composite or a mixture thereof and using graphite or the like as the negative electrode active material. And with the further development of the application equipment of a non-aqueous secondary battery, further higher capacity and higher energy density of the non-aqueous secondary battery are required.

  One technique for increasing the capacity and energy density of a non-aqueous secondary battery is to charge and use a positive electrode active material at a high voltage. A method of increasing the capacity by increasing the Ni ratio of the NCM material has also been studied. On the other hand, the safety of the battery tends to decrease as the capacity and voltage increase.

  Conventionally, as a method for improving safety, an additive for electrolytic solution, an additive element for a positive electrode material, a surface coating, an insulating material coating for a separator, and the like have been studied. In particular, the insulating material coating on the resin separator has an effect of suppressing the expansion of the short-circuited part when the battery is difficult to be short-circuited and a short-circuit occurs, and the demand has recently increased. For example, in Patent Document 1, in a lithium ion battery using a separator containing a heat-resistant material, the amount of electrolytic solution is 0.9 to 1.6 times the total volume of voids in the positive electrode, the negative electrode, and the separator. Thus, it has been proposed to provide a battery having excellent cycle characteristics by suppressing a decrease in capacity when charging and discharging are repeated.

By the way, in the study by the present inventors, when using a battery having a high energy density by increasing the Ni ratio of the NCM material or the like, the effect becomes difficult to occur when the separator insulating layer is thinned, and the resin layer is melted. In this case, it was found that the effect of the insulating layer tended not to appear. Therefore, it is necessary to form an insulating layer that can contribute to safety even at higher temperatures.

On the other hand, a battery using a solid electrolyte is also considered to be highly safe. The solid electrolyte itself is also a material excellent in heat resistance, and is expected to exhibit an effect equivalent to or higher than that of the insulating layer. However, the operation of the battery is difficult, and the formation of the interface between the active material and the solid electrolyte is a problem. Therefore, in Patent Documents 2 to 4 and the like, it has also been proposed to improve the operating characteristics while forming an excellent interface and exhibiting the effect of the insulating layer by interposing an electrolytic solution at the interface. 2 describes that the solid electrolyte layer has a structure composed of a layered dense portion and a porous portion for holding an electrolytic solution, thereby preventing a short circuit due to dendrite during charging and discharging.

JP 2010-113804 A JP 2013-232284 A JP 2017-1111890 A JP 2008-243736 A

  However, according to the study of the present inventor, in a non-aqueous secondary battery using a porous insulating layer mainly composed of an inorganic insulator as a separator, the amount of electrolyte is increased in order to increase the weight energy density or increase the safety. It was clarified that lithium dendrite tends to be formed during charging, and the safety tends to be impaired.

The present invention is intended to solve the above problems, and provides a non-aqueous secondary battery that has high weight energy density, excellent charge / discharge characteristics, and is highly resistant to lithium dendrite formation during charging. is there.

  The non-aqueous secondary battery of the present invention has an electrode body and a non-aqueous electrolyte in a battery container, and the electrode body includes a positive electrode having a positive electrode active material layer, a negative electrode having a negative electrode active material layer, A porous insulating layer interposed between the positive electrode and the negative electrode, the insulating layer containing an inorganic insulator in a proportion of 80% by mass or more, and a porosity of 50% or less The mass of the non-aqueous electrolyte in the battery container is the sum of the mass of the positive electrode active material layer, the negative electrode active material layer and the insulating layer of the electrode body, and the total mass of the non-aqueous electrolyte solution. It is characterized by being 2% or more and 60% or less.

  Another embodiment of the non-aqueous secondary battery of the present invention has a plurality of electrode bodies electrically connected in series and a non-aqueous electrolyte in a battery container, the electrode body comprising a positive electrode active material layer A negative electrode having a negative electrode active material layer, and a porous insulating layer interposed between the positive electrode and the negative electrode, wherein the insulating layer comprises 80% by mass or more of an inorganic insulator. And the mass of the non-aqueous electrolyte in the battery container is the mass of the positive electrode active material layer, the negative electrode active material layer, and the insulating layer of each electrode body. It is 2% or more and 60% or less with respect to the sum total of the total and the mass of the non-aqueous electrolyte.

  According to the present invention, it is possible to provide a non-aqueous secondary battery that has a high weight energy density and excellent charge / discharge characteristics, and that is difficult to form lithium dendrite during charging and has high safety.

  In the nonaqueous secondary battery of the present invention, in order to improve heat resistance, an inorganic insulator is added at a ratio of 80% by mass or more between a positive electrode having a positive electrode active material layer and a negative electrode having a negative electrode active material layer. A porous insulating layer is contained.

  The insulating layer functions as a separator in place of a conventional resin porous film or together with a resin porous film, and may be an independent film. Also, a positive electrode active material layer, a negative electrode active material It may be formed by coating or the like on any or all surfaces of the layer and the resin porous film.

  In order to increase the weight energy density of the battery, it is conceivable to reduce the proportion of components other than the active material, such as a non-aqueous electrolyte, in addition to using a high-capacity active material. According to the above studies, it was found that when the porous insulating layer is used as a separator, as the amount of the electrolyte decreases, lithium dendrites are more easily formed during charging and short-circuiting is more likely.

  Specifically, the mass of the non-aqueous electrolyte in the battery container is 60% or less with respect to the total of the mass of the positive electrode active material layer, the negative electrode active material layer, and the insulating layer and the mass of the non-aqueous electrolyte. In this case, it has been found that short-circuiting due to lithium dendrite formation is likely to occur.

  On the other hand, when the porosity of the insulating layer is 50% or less, formation of lithium dendrite is suppressed, and safety can be improved. The porosity of the insulating layer is preferably 45% or less, and more preferably 40% or less. On the other hand, if the porosity of the insulating layer is too low, the ionic conductivity is lowered, the internal resistance is increased, and the charge / discharge characteristics are liable to be lowered. The porosity is preferably 5% or more, and more preferably 20% or more.

  The content of the non-aqueous electrolyte is preferably as small as possible from the viewpoint of increasing the weight energy density, and the mass of the non-aqueous electrolyte in the battery container is the mass of the positive electrode active material layer, the negative electrode active material layer, and the insulating layer. It is preferably 50% or less, more preferably 45% or less, and most preferably 40% or less with respect to the sum of the total and the mass of the non-aqueous electrolyte. On the other hand, if the content of the non-aqueous electrolyte is too low, the ionic conductivity is lowered, the internal resistance is increased, and the charge / discharge characteristics are easily lowered. The total mass of the negative electrode active material layer and the insulating layer and the total mass of the non-aqueous electrolyte is preferably 10% or more, more preferably 25% or more, and 33% or more. Most preferably it is.

As the inorganic insulator forming the insulating layer, insulating oxides, nitrides, sparingly soluble ionic crystals, covalent bonding crystals, clay, natural or artificial minerals, and the like can be used. Al ₂ O ₃ (alumina) , SiO ₂ (silica), TiO ₂ , BaTiO ₃ , ZrO ₂ , aluminum nitride, silicon nitride, calcium fluoride, barium fluoride, barium sulfate, silicon, diamond, talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite , Spinel, olivine, sericite, bentonite and the like. Among these, at least one selected from the group consisting of alumina, silica and boehmite is preferably used.

  The inorganic insulator may be a solid electrolyte. For example, an oxide-based solid electrolyte or a sulfide-based solid electrolyte can be used.

Examples of the oxide-based solid electrolyte include a solid electrolyte having a garnet structure, and Li _a La _b Zr _c MA _d O _e (where MA is Sc, Ti, V, Y, Nb, Hf , Ta, Al, Si, Ga and Ge, at least one element selected from the group consisting of 5 ≦ a ≦ 8, 2 ≦ b ≦ 4, 0 <c ≦ 2, 0 ≦ d <1, 11 <e <13.) And the like are specifically exemplified.

Examples of the sulfide-based solid electrolyte include a compound containing Li, MB (where MB is at least one element selected from the group consisting of P, Si, Ge, Al, and B), and S. Li ₂ S—P ₂ S ₅ based material, Li ₂ S—SiS ₂ based material, Li ₂ S—GeS ₂ based material, Li ₂ S—Al ₂ S ₃ based material, Li _{2 S-SiS} 2 _-Li 3 PO ₄ based _{material, Li 2 S-P 2 S} 5 -GeS 2 based _{materials, Li 2 S-Li 2 O} -P 2 S 5 -SiS 2 based materials, _Li 2 S -GeS ₂ -P ₂ S ₅ -SiS ₂ based _materials, such as _{Li 2 S-SnS 2 -P 2} S 5 -SiS 2 based materials are specifically exemplified.

  The sulfide-based solid electrolyte preferably contains LiX (X is a halogen element) in addition to the ionic conductor. In order to improve chemical stability, the ionic conductor has an anion structure having an ortho composition. It is preferable to have (PS43-structure, SiS44-structure, GeS44-structure, AlS33-structure, BS33-structure) as a main component of the anion. The ratio of the anion structure of the ortho composition is preferably 50 mol% or more in the solid electrolyte, more preferably 70 mol% or more, and particularly preferably 90 mol% or more.

  As LiX, LiCl and LiF are preferable, and it is particularly preferable that LiCl is present in a state in which LiCl is incorporated into the structure of the ion conductor. In other words, the sulfide-based solid electrolyte is preferably not a simple mixture but contains lithium halide in a physically inseparable state.

The sulfide-based solid electrolyte may be a crystalline material or an amorphous material. Further, it may be glass or crystallized glass (glass ceramics). The Li ion conductivity of the sulfide-based solid electrolyte at 25 ° C. is preferably 1 × 10 ⁻⁴ S / cm or more, and more preferably 1 × 10 ⁻³ S / cm or more.

  These inorganic insulators may be used alone or in combination of two or more.

  The shape of the inorganic insulator may be a sheet or a particulate. In the case of particulate matter (inorganic particles), the average particle size of the particles used for forming the insulating layer is preferably 2 μm or less and more preferably 1.5 μm or less in order to prevent short circuit due to the formation of lithium dendrite. Desirably, the thickness is most desirably 1 μm or less. On the other hand, if the average particle size is too small, the average particle size is preferably 0.01 μm or more because the bulkiness is increased, and the strength of the insulating layer and the homogeneity are easily decreased. It is more preferably 1 μm or more, and most preferably 0.2 μm or more.

  In order to make the insulating layer denser, it is preferable to use a combination of inorganic particles having different particle sizes. Thereby, the strength improvement of an insulating layer can be expected. For example, when two types of inorganic particles are used in combination, DL / DS is 1.2 when the average particle size of the larger particle is DL and the average particle size of the smaller particle is DS. Preferably, it is 1.5 or more, more preferably 2 or more, most preferably 5 or less, and more preferably 3 or less.

  The average particle size is determined by, for example, using a laser scattering particle size distribution meter (for example, “LA-920” manufactured by HORIBA) to disperse the inorganic particles in a medium in which the inorganic particles are not dissolved or the inorganic particles do not swell. And can be defined as the number average particle diameter measured.

The porous insulating layer can be formed by applying a slurry for forming an insulating layer containing the inorganic particles and drying the slurry. Alternatively, the inorganic particles can be integrated by sintering or the like to form an inorganic insulator sheet.
A thickener may be used in the insulating layer forming slurry. By using a thickener, the viscosity of the insulating layer forming slurry is adjusted to a suitable range, the dispersion of the inorganic particles is made uniform, and an excellent dispersion state can be stably maintained.

  Any thickening agent may be used as long as it has no side effects such as agglomeration of inorganic particles in the slurry for forming the insulating layer and the slurry can be adjusted to the required viscosity, but has a high thickening effect with a small amount of addition. Those are preferred. Moreover, it is preferable that a thickener can melt | dissolve or disperse | distribute favorably with respect to the dispersion medium used for a slurry. If there are many undissolved parts or aggregates of the thickener in the slurry, the dispersion of the inorganic particles becomes uneven, and the inorganic particles are formed in the insulating layer formed by applying the slurry to a substrate and drying. Distribution is non-uniform. Therefore, the heat resistance of the insulating layer is lowered, and as a result, the reliability and heat resistance of the nonaqueous secondary battery may be lowered.

  Specific examples of thickeners include synthetic polymers such as polyethylene glycol, polyacrylic acid, polyvinyl alcohol, vinyl methyl ether-maleic anhydride copolymer; cellulose derivatives such as carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose; xanthan gum Natural polysaccharides such as welan gum, gellan gum, guar gum and carrageenan. These may be used alone or in combination of two or more.

  The content of the thickener in the insulating layer forming slurry is preferably 10% by volume or less, and preferably 5% by volume, based on the total volume of solids in the slurry (components excluding the dispersion medium; the same shall apply hereinafter). More preferably, it is more preferably 1% by volume or less. Moreover, it is preferable that content of the thickener in the slurry for insulating layer formation is 0.1 volume% or more in the total volume of the solid content in a slurry.

  Moreover, it is preferable to use a dispersing agent for the insulating layer forming slurry. By using the dispersant, for example, the dispersant adheres to the surface of the inorganic particles, so that the dispersibility of the inorganic particles in the insulating layer forming slurry is further improved, and aggregation of these inorganic particles can be prevented. And a good dispersion state of the inorganic particles can be maintained more stably.

  Specific examples of the dispersant include various anionic, cationic, and nonionic surfactants; polycarboxylic acid, polyacrylic acid, polymethacrylic acid, amino acids (such as aspartic acid), polycarboxylic acid salts, and polyacrylic acid. Polymeric dispersants such as salts and polymethacrylates can be used. As the dispersant, those exemplified above may be used alone or in combination of two or more.

  Among these dispersants, since the action of dispersing fine particles is strong, ion dissociable acid groups (carboxyl group, sulfonic acid group, amino acid group, maleic acid group, etc.) or ion dissociable acid bases (carboxylate bases) , Sulfonate groups, maleate groups, and the like), and aspartic acid, polycarboxylates, polyacrylates, and polymethacrylates are more preferable. When the polymer dispersant is a salt (having an acid base), an ammonium salt is preferable.

  The content of the dispersant in the insulating layer forming slurry is preferably 0.1 parts by mass or more, and more preferably 0.3 parts by mass or more with respect to 100 parts by mass of the insulating fine particles. However, if the amount of the dispersing agent is excessively increased, the ratio of other components in the insulating layer is lowered, and there is a possibility that the effect due to them is reduced. Therefore, the content of the dispersant in the insulating layer forming slurry is preferably 5 parts by mass or less and more preferably 1 part by mass or less with respect to 100 parts by mass of the insulating fine particles.

  In the insulating layer forming slurry, in the formed insulating layer, a binder is added for the purpose of adhering inorganic particles to each other, inorganic particles and other components described later, or adhering the insulating layer and the substrate. It can be included. The type of the binder is not particularly limited as long as it is electrochemically stable inside the non-aqueous secondary battery and stable with respect to the electrolyte of the non-aqueous secondary battery. Moreover, about the thing which also has a function as a binder among the said thickeners, a thickener and a binder can also be combined.

  Specific examples of the binder include, for example, an ethylene-vinyl acetate copolymer (EVA, having a structural unit derived from vinyl acetate of 20 to 35 mol%); an ethylene-ethyl acrylate copolymer, an ethylene-ethyl methacrylate copolymer. (Meth) acrylic acid copolymer such as: fluorinated rubber; styrene-butadiene rubber (SBR); polyvinyl alcohol (PVA); polyvinyl butyral (PVB); polyvinyl pyrrolidone (PVP); poly N-vinylacetamide; Polyurethane, epoxy resin, etc. are used. These binders may be used individually by 1 type, and may use 2 or more types together.

  Among these, a (meth) acrylic acid copolymer having self-crosslinking property is more preferable, and a (meth) acrylic acid copolymer having self-crosslinking property and having a glass transition temperature (Tg) of −20 ° C. or less. Further preferred.

  Examples of the dispersion medium for the insulating layer forming slurry include water-based components and organic solvents (aromatic hydrocarbons such as toluene; furans such as tetrahydrofuran; ketones such as methyl ethyl ketone and methyl isobutyl ketone; etc.). However, those containing water as the main component are preferred.

  The porous insulating layer is interposed between a positive electrode having a positive electrode active material layer and a negative electrode having a negative electrode active material layer, thereby forming an electrode body composed of a laminate of the positive electrode, the insulating layer, and the negative electrode. . The positive electrode active material layer and the negative electrode active material layer are each composed of a positive electrode active material and a negative electrode active material, a binder, a conductive auxiliary agent, and the like, and can be formed on a current collector such as a metal foil, for example.

Examples of the positive electrode active material include lithium cobalt oxides such as LiCoO ₂ ; lithium manganese oxides such as LiMnO ₂ and Li ₂ MnO ₃ ; lithium nickel oxides such as LiNiO ₂ ; LiMn ₂ O ₄ and Li _4/3 Ti _5/3 O ₄ and other spinel-structured lithium-containing composite oxides; LiFePO ₄ and other olivine-structured lithium-containing composite oxides; oxides obtained by substituting the above-mentioned oxides with various elements; Only one of these may be used, or two or more may be used in combination.

  Examples of the conductive auxiliary agent related to the positive electrode active material layer include graphites such as natural graphite (eg, scaly graphite) and artificial graphite; acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and the like. It is preferable to use carbon materials such as carbon blacks; carbon fibers; and conductive fibers such as metal fibers; carbon fluorides; metal powders such as aluminum; zinc oxide; Conductive whiskers; conductive metal oxides such as titanium oxide; organic conductive materials such as polyphenylene derivatives; and the like can also be used.

  Examples of the binder relating to the positive electrode active material layer include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), and polyvinylpyrrolidone (PVP).

  As the positive electrode current collector, an aluminum foil, a punching metal, a net, an expanded metal, or the like can be used, but an aluminum foil is usually used. The thickness of the positive electrode current collector is preferably 10 to 30 μm.

  The negative electrode active material may be any material that can be doped / undoped with lithium ions. For example, graphite, pyrolytic carbons, cokes, glassy carbon, a fired body of an organic polymer compound, mesocarbon microbeads Carbonaceous materials such as carbon fiber and activated carbon. Moreover, lithium or a lithium-containing compound can also be used as the negative electrode active material. Examples of the lithium-containing compound include tin oxide, silicon oxide, nickel-silicon alloy, magnesium-silicon alloy, tungsten oxide, lithium iron composite oxide, lithium-aluminum, and lithium-lead. , Lithium-indium, lithium-gallium, lithium-indium-gallium, and other lithium alloys. Some of these exemplary negative electrode active materials do not contain lithium at the time of manufacture, but are in a state containing lithium at the time of charging.

  As the binder related to the negative electrode active material layer, the same binder as the various binders exemplified above as the binder related to the positive electrode active material layer can be used. The same applies to the conductive assistant.

The positive electrode and the negative electrode are, for example, an active material and a binder, and further, if necessary, a conductive additive or the like dispersed or dissolved in a solvent such as NMP or water to obtain a paste-like or slurry-like composition. After applying to one side or both sides of the body and drying, it can be produced through a step of pressing as required.

  The porosity of the positive electrode active material layer and the negative electrode active material layer is preferably 22% or more, and more preferably 25% or more in order to facilitate impregnation with the electrolyte and improve charge / discharge characteristics. Most preferably, it is 28% or more. On the other hand, when an insulating layer is formed on the active material layer, the porosity of the active material layer is desirably 35% or less in order to prevent the slurry for forming the insulating layer from entering the active material layer. 32% or less is more desirable, and 29% or less is most desirable.

  Adjustment of the porosity of a positive electrode active material layer and a negative electrode active material layer can be performed by changing the conditions of a press process, for example. In the case where an insulating layer is formed on the surface of the positive electrode active material layer or the negative electrode active material layer, the insulating layer forming slurry is applied on the active material layer after the press treatment, thereby affecting the charge / discharge characteristics. Is preferable, and a thinner and stronger insulating layer can be formed.

  The non-aqueous secondary battery of the present invention is produced by housing the electrode body and the non-aqueous electrolyte in a battery container.

  The non-aqueous electrolyte is configured by dissolving an electrolyte salt such as an inorganic lithium salt or an organic lithium salt in an organic solvent.

Examples of the organic solvent include 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (HCF ₂ CF ₂ —O—CH ₂ CF ₂ CF) which is a flame retardant solvent. Fluorinated ethers such as ₂ H: fluorination rate 67%) and phosphate esters such as trimethyl phosphate are preferably used. More specifically, fluorinated ether [Rf ₂ —OR ₄ (where Rf ₂ is an alkyl group containing fluorine, and R ₄ is an organic group which may contain fluorine], phosphate ester [Trimethyl phosphate (TMP), Tris (trifluoroethyl) phosphate (TFEP): (CF ₃ CH ₂ O) ₃ P═O, Triphenyl phosphate (TPP): (C ₆ H ₅ O) ₃ P = O, ethyl diethylphosphonoacetate _{(EDPA) :( C 2 H 5} O) 2 (P = O) -CH 2 (C = O) OC 2 H 5] or, the use of such derivatives of the respective compounds preferable.

  Also, dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), dipropyl carbonate (DPC), 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, methyl formate , Methyl acetate, propyl propionate, dinitrile (such as sebaconitrile) and derivatives thereof can also be used.

  Ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), γ-butyrolactone having a flash point of 100 ° C. or higher can also be used.

  In addition, aprotic organic solvents such as 1,3-propane sultone, dimethyl sulfoxide, formamide, dimethylformamide, acetonitrile, nitromethane, sulfolane, 3-methyl-2-oxazolidinone, and propylene carbonate derivatives can also be used.

  The above-described solvents may be used alone or in combination of two or more, and it is desirable to use a flame retardant fluorinated ether, a phosphate ester such as trimethyl phosphate, or a cyclic ester. In particular, it is desirable to use a fluorinated ether. As the fluorinated ether, it is more desirable to use a solvent having a fluorination rate of 50% or more because flame retardancy is enhanced. On the other hand, from the viewpoint of the solubility of the lithium salt in the electrolytic solution, the fluorination rate is preferably less than 90%, and more preferably less than 80%. When using a fluorinated ether, it is desirable to use a chain ester together. Specific examples include dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), dipropyl carbonate (DPC), propyl propionate, ethyl propionate, sebacononitrile, pimelonitrile, and glutaronitrile. .

  A combination of a fluorinated ether and the above chain ester is more desirable. In order to reduce side reactions, the ratio of the fluorinated ether in the total solvent is preferably 30% or more, more preferably 50% or more, and most preferably 60% or more in terms of mass ratio. On the other hand, 90% or less is desirable in order not to deteriorate the charge / discharge characteristics.

Examples of the inorganic lithium _{salt, LiClO 4, LiBF 4, LiPF} 6, LiCF 3 SO 3, LiCF 3 CO 2, LiAsF 6, LiSbF 6, LiB 10 Cl 10, lower aliphatic carboxylic acids _Li, LiAlCl 4, LiCl, LiBr , LiI, chloroborane Li, lithium tetraphenylborate and the like, and these may be used alone or in combination of two or more.

Examples of the organic lithium salt include LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , Li ₂ C ₂ F ₄ (SO ₃ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiC _n1 F _{2n1 + 1} SO ₃ (2 ≦ n1 ≦ 7), LiN (Rf ₁ OSO ₂ ) ₂ [wherein Rf ₁ is a fluoroalkyl group. ], It includes LiN _{(FSO 2) 2} and the like, may be used those either alone, or in combination of two or more.

Among these lithium salts, it is particularly desirable to use LiN (FSO ₂ ) ₂ . This is because the solubility in the combination with the flame retardant solvent is high, and the battery characteristics can be further improved.

The concentration of the electrolyte salt in the nonaqueous electrolyte solution, for example, is preferably 0.2~3.0mol / dm ^3, more preferably from 0.5~1.5mol / dm ^3, 0. More preferably, it is 9-1.3 mol / dm ³ .

  In addition, the non-aqueous electrolyte may appropriately contain the following additives for the purpose of improving charge / discharge cycle characteristics, high-temperature storage characteristics, and safety such as overcharge prevention. Examples of the additive include anhydride, sulfonate ester, dinitrile, 1,3-propane sultone, diphenyl disulfide, cyclohexylbenzene, vinylene carbonate (VC), biphenyl, fluorobenzene, t-butylbenzene, and cyclic fluorinated carbonate. [Trifluoropropylene carbonate (TFPC), fluoroethylene carbonate (FEC), etc.] or chain fluorinated carbonate [trifluorodimethyl carbonate (TFDMC), trifluorodiethyl carbonate (TFDEC), trifluoroethyl methyl carbonate (TFEMC) ) Etc.].

  Additives that are highly effective in improving charge / discharge cycle characteristics under high voltage are compounds having two or more nitrile groups in the molecule. Examples of the compound having two or more nitrile groups in the molecule include succinonitrile, glutaronitrile, adiponitrile, 1,5-dicyanopentane, 1,6-dicyanohexane, 1,7-dicyanoheptane, 1, 8-dicyanooctane, 1,9-dicyanononane, 1,10-dicyanodecane, 1,12-dicyanododecane, tetramethylsuccinonitrile, 2-methylglutaronitrile, 4-dicyanopentane, 2,6-dicyanoheptane, Examples include dinitriles such as 2,7-dicyanooctane, 2,8-dicyanononane, 1,6-dicyanodecane and 1,2-dicyanobenzene. Some of these dinitriles may be fluorinated.

  The concentration of the compound having two or more nitrile groups in the molecule in the non-aqueous electrolyte is preferably 0.1% by mass or more, more preferably 2% by mass or more, and most preferably 10% by mass or more. % By mass or less is desirable, 30% by mass or less is more desirable, and 20% by mass or less is most desirable.

  The temperature of the battery during charging is not particularly limited, but it is desirable to operate at a temperature higher than room temperature, preferably 25 ° C. or higher, more preferably 30 ° C. or higher, and most preferably 45 ° C. or higher. This is because the higher the temperature is, the more difficult the short circuit occurs even when the amount of the electrolytic solution is reduced, and the ionic conductivity of the electrolytic solution is further increased to improve the charge / discharge characteristics of the battery. However, in order to prevent the electrolyte from evaporating, the temperature of the battery during charging is desirably 200 ° C. or less, more desirably 170 ° C. or less, and most desirably 150 ° C. or less.

  The charging voltage of the battery is preferably 4.2 V or higher, and more preferably 4.35 V or higher. When the charging voltage is increased, short-circuiting of the battery due to the formation of lithium dendrite is likely to occur even when the charging depth is shallow, but by using a mixed solvent of a fluorinated ether and a chain ester as a solvent for the electrolyte solution, 4. Even at a higher charging voltage of 45 V or higher, it is possible to prevent a short circuit due to the formation of lithium dendrite.

  In the present invention, besides using the electrode body alone to constitute a battery, a plurality of the electrode bodies are conductively connected in series and accommodated in a battery container to constitute a battery having a voltage multiplied by n. Is possible. That is, in a nonaqueous secondary battery having a plurality of electrode bodies electrically connected in series and a nonaqueous electrolyte solution in a battery container, the total mass of the nonaqueous electrolyte solution in the battery container is By adjusting the total mass of the positive electrode active material layer, the negative electrode active material layer, and the insulating layer to be 2% or more and 60% or less, the weight energy density is similar to that of the battery using the electrode body alone. It is a non-aqueous secondary battery that is high and has excellent charge / discharge characteristics, and is difficult to form lithium dendrites during charging, and has high safety, and the operating voltage is increased according to the number of electrode bodies connected in series. It is also possible to constitute a water secondary battery.

  Examples of the form of the non-aqueous secondary battery of the present invention include a tubular shape (such as a rectangular tube shape or a cylindrical shape) using a steel can or an aluminum can as a battery container (exterior body), a coin shape, or the like. Moreover, it can also be set as the soft package battery which used the laminated film which vapor-deposited the metal as a battery container.

In addition, in the case of a battery having a shape such as a rectangular tube shape or a coin shape, or a flat battery having a laminate film as a battery container, the battery was pressurized in the thickness direction in order to enhance the charge / discharge characteristics of the battery. You may charge / discharge in a state. Pressure applied to the battery container, 0.001kgf / cm ² or more is desirable, 0.01 kgf / cm ² or more is more preferable. On the other hand, if the pressure is too high, the characteristics are liable to deteriorate, so the pressure applied to the battery container is preferably 10,000 kgf / cm ² or less.

  Hereinafter, the present invention will be described in detail based on examples. However, the following examples do not limit the present invention.

Example 1
[Production of positive electrode]
First, LiNi _0.5 Co _0.2 Mn _0.3 O ₂ (hereinafter referred to as “NCM523”) as a positive electrode active material: 100 parts by mass, acetylene black as a conductive auxiliary agent: 3.2 parts by mass, and a binder A certain PVDF: 3.2 parts by mass (supplying a solid content as an NMP solution) was mixed with NMP as a solvent uniformly to prepare a paste-like positive electrode mixture composition. Next, the obtained composition was applied to one side of a current collector made of an aluminum foil having a thickness of 20 μm so that the coating amount was 19.5 mg / cm ² as the solid content of the composition and dried. Thereafter, a press treatment was performed to adjust the thickness of the positive electrode active material layer so that the total thickness was 60 μm, and the positive electrode was manufactured by cutting to a length of 30 mm and a width of 30 mm leaving a tab weld. Further, the active material in the tab welded portion of the positive electrode was removed, and a tab was welded to the tab welded portion to form a lead portion.

[Preparation of insulating layer forming slurry]
After adding ion-exchanged water: 154 ml and aspartic acid: 10 g and stirring. Alumina (Al ₂ O ₃ ): 385 g having an average particle size of 0.5 μm was added, and further stirred for 10 hours to prepare a dispersion. While this was cooled, a bead mill treatment was performed to prepare a finely pulverized slurry. After removing coarse particles in the slurry using a mesh having an opening of 5 μm, ion exchange water was added to prepare a dispersion containing water: 48% by mass, aspartic acid: 1% by mass, and alumina: 51% by mass. . 3 parts by mass of ethylene / vinyl acetate copolymer emulsion was added to 100 parts by weight of the slurry and stirred for 6 hours to obtain an insulating layer forming slurry.

[Formation of insulating layer on positive electrode]
The insulating layer forming slurry was applied on the positive electrode active material layer subjected to the press treatment and dried at 120 ° C. for 10 minutes. By roll-pressing the dried coating film, an insulating layer having an alumina content of 98% by mass, a thickness of 10 μm, and a porosity of 45% was formed on the positive electrode active material layer.

(Production of negative electrode)
100 parts by mass of graphite as a negative electrode active material, VGCF (vapor phase grown carbon fiber) as a conductive auxiliary agent: 2 parts by weight, CMC as a binder: 1 part by mass (a solid content is supplied as a 1% by mass aqueous solution) SBR: 1 part by mass was mixed with ion-exchanged water as a solvent to prepare a paste-like negative electrode mixture composition. Next, the obtained composition was applied to one side of a copper foil having a thickness of 16.5 μm so that the amount applied was 11.4 mg / cm ² as the solid content of the composition, and then dried, followed by press treatment. The thickness of the negative electrode active material layer was adjusted so that the total thickness would be 88 μm, and the negative electrode was fabricated by cutting to a length of 32 mm and a width of 32 mm leaving the tab weld. Further, a tab was welded to the tab weld portion of the negative electrode to form a lead portion.

(Preparation of non-aqueous electrolyte)
To 100 g of a mixed solvent having a mass ratio of 1: 3 of methyl ethyl carbonate (MEC) and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (HFE), 0.1 mol of LiN (FSO ₂ ) ₂ was dissolved to prepare a non-aqueous electrolyte.

[Assembling the battery]
The positive electrode and the negative electrode were overlapped with an insulating layer interposed therebetween to produce an electrode body having a three-layer structure of positive electrode / insulating layer / negative electrode. The obtained electrode body is housed in an outer package made of an aluminum laminate film, 0.1 ml of the nonaqueous electrolyte solution is injected onto the positive electrode insulating layer, and the electrolyte solution is impregnated by reducing the pressure, and then the atmospheric pressure is increased. Sealing was performed to prepare a non-aqueous secondary battery. The mass of the non-aqueous electrolyte in this battery was 34% with respect to the total of the mass of the positive electrode active material layer, the negative electrode active material layer and the insulating layer and the mass of the non-aqueous electrolyte.

A glass plate is placed on the side of the produced battery via a 3.5 cm square silicon rubber, and the pressure is applied under a load of 150 g and a pressure of 2.5 mA (a rate equivalent to 1/10 C) at a temperature of 25 ° C. ) To a constant current of 4.2), then a constant current-constant voltage charge to charge at a constant voltage of 4.2V, and a constant current discharge to discharge to 3V at a constant current of 2.5 mA. The discharge capacity was measured to evaluate the charge / discharge characteristics. In addition, in the said charging / discharging, the pressure applied to the side surface of an exterior body was 0.015 kgf / cm < ² >.

Example 2
The charge / discharge characteristics were evaluated in the same manner as in Example 1 except that the battery was charged / discharged in a temperature environment of 45 ° C.

Example 3
The charge / discharge characteristics were evaluated in the same manner as in Example 1 except that the pressure applied to the side surface of the exterior body was 0.006 kgf / cm ² .

Example 4
A non-aqueous secondary battery was produced in the same manner as in Example 1 except that the thickness of the insulating layer formed on the positive electrode active material layer was 20 μm and the porosity was 49%. The charge / discharge characteristics were evaluated. The ratio of the mass of the non-aqueous electrolyte to the total of the mass of the positive electrode active material layer, the negative electrode active material layer, and the insulating layer of this battery and the mass of the non-aqueous electrolyte was 30%.

Example 5
A nonaqueous secondary battery was produced in the same manner as in Example 1 except that the amount of the nonaqueous electrolyte was changed to 0.08 ml, and the charge / discharge characteristics were evaluated in the same manner as in Example 2. In this battery, the ratio of the mass of the non-aqueous electrolyte to the total of the mass of the positive electrode active material layer, the negative electrode active material layer, and the insulating layer and the mass of the non-aqueous electrolyte was 30%.

Example 6
Two sets of electrode bodies having a three-layer structure of positive electrode / insulating layer / negative electrode are prepared, the negative electrode of one electrode body and the positive electrode of the other electrode body are overlapped, and positive electrode 1 / insulating layer 1 / negative electrode 1 / positive electrode 2 / Two sets of electrode bodies are conductively connected in series so that the order of lamination of insulating layer 2 / negative electrode 2 is established, and lead portions are formed by welding tabs to positive electrode 1 and negative electrode 2, respectively. A laminate was produced.

  Implementation was performed except that the laminate of the two sets of electrode bodies was housed in an exterior body made of an aluminum laminate film, and 0.1 ml of nonaqueous electrolyte was injected between the insulating layer and the counter electrode of each electrode body. A non-aqueous secondary battery was produced in the same manner as in Example 1. In this battery, the ratio of the mass of the non-aqueous electrolyte to the total of the mass of the positive electrode active material layer, the negative electrode active material layer, and the insulating layer of each electrode body and the mass of the non-aqueous electrolyte is 34%. Met.

The produced non-aqueous secondary battery is charged to 8.4 V at a constant current of 2.5 mA and further charged at a constant voltage of 8.4 V, and at a constant current of 2.5 mA. A constant current discharge was performed to 6V, and the discharge capacity at that time was measured to evaluate the charge / discharge characteristics. In addition, in the said charging / discharging, the pressure applied to the side surface of an exterior body was 0.015 kgf / cm < ² >.

Comparative Example 1
By using alumina having an average particle diameter of 0.5 μm, a non-conductive layer having a thickness of 12.5 μm and a porosity of 55% was formed on the positive electrode active material layer in the same manner as in Example 1. A water secondary battery was produced, and charge / discharge characteristics were evaluated in the same manner as in Example 1. In this battery, the ratio of the mass of the non-aqueous electrolyte to the total of the mass of the positive electrode active material layer, the negative electrode active material layer, and the insulating layer and the mass of the non-aqueous electrolyte was 34%.

Comparative Example 2
A non-aqueous secondary battery was produced in the same manner as in Example 1 except that the amount of the non-aqueous electrolyte was changed to 0.5 ml, and the charge / discharge characteristics were evaluated in the same manner as in Example 1. In this battery, the ratio of the mass of the non-aqueous electrolyte to the total of the mass of the positive electrode active material layer, the negative electrode active material layer, and the insulating layer and the mass of the non-aqueous electrolyte was 73%.

Comparative Example 3
A non-aqueous secondary battery was produced in the same manner as in Example 1 except that the amount of the non-aqueous electrolyte was 0.002 ml, and the charge / discharge characteristics were evaluated in the same manner as in Example 1. In this battery, the ratio of the mass of the non-aqueous electrolyte to the total of the mass of the positive electrode active material layer, the negative electrode active material layer, and the insulating layer and the mass of the non-aqueous electrolyte was 1%.

Comparative Example 4
A nonaqueous secondary battery was produced in the same manner as in Comparative Example 2 except that a mixed solvent having a mass ratio of ethylene carbonate (EC) and methyl ethyl carbonate (MEC) of 1: 3 was used for the preparation of the nonaqueous electrolyte. In the same manner as in Example 1, the charge / discharge characteristics were evaluated.

Reference example 1
The charge / discharge characteristics were evaluated in the same manner as in Comparative Example 1 except that charge / discharge was performed without applying pressure to the side surface of the outer package.

  Table 1 shows the configuration of each battery, and Table 2 shows the evaluation results of the charge / discharge characteristics. The weight energy density of each battery is the sum of the masses of the positive electrode mixture layer and insulating layer of the electrode body accommodated in the outer package, the portion of the negative electrode mixture layer facing the positive electrode mixture layer, and non-aqueous Based on the total of the electrolyte solution mass and the measured discharge capacity of the battery, this is a value obtained by calculation assuming that the operating voltage (average discharge voltage) of each electrode body of each battery is 3.7V.

  An insulating layer containing an inorganic insulator in a proportion of 80% by mass or more and having a porosity of 50% or less is used as a separator, and the proportion of the mass of the non-aqueous electrolyte in the battery container is defined as a positive electrode active material layer, a negative electrode In the non-aqueous secondary battery of the present invention in which the total mass of the active material layer and the insulating layer and the total mass of the non-aqueous electrolyte solution are in the range of 2% to 60%, the weight energy density is high, And while being excellent in charging / discharging characteristic, formation of lithium dendrite at the time of charge was suppressed, and it was able to be set as a highly safe battery.

  On the other hand, in the battery of Comparative Example 1 in which the porosity of the insulating layer was greater than 50%, the discharge capacity was low due to a short circuit due to the formation of lithium dendrite during charging. Further, in the battery of Comparative Example 2 in which the amount of the non-aqueous electrolyte solution is too large, there was no short circuit due to the formation of lithium dendrite during charging, and the same discharge capacity as in Example 1 was obtained, but the weight of the electrolyte solution was large. In contrast, the battery of Comparative Example 3 in which the weight energy density of the battery was low and the amount of the non-aqueous electrolyte solution was too small, the ionic conductivity was lowered, the internal resistance was increased, and discharge was impossible.

  In addition, the battery of Comparative Example 2 that contains 30% or more of the fluorinated ether, which is a flame-retardant solvent, in a mass ratio in the total solvent, and constituted a non-aqueous electrolyte with a mixed solvent with a chain ester (MEC) is A discharge capacity equivalent to that of the battery of Comparative Example 4 in which a non-aqueous electrolyte is configured with a mixed solvent of general-purpose cyclic carbonate and chain carbonate is obtained, and the above-described electrolyte configuration containing a flame retardant solvent is used. Thus, it is understood that the electrolyte solution can be made flame retardant without deteriorating the charge / discharge characteristics.

  Furthermore, the batteries of Examples 1 to 6 in which a certain pressure was applied to the side surface of the outer package had a larger discharge capacity than the battery of Reference Example 1 in which charging and discharging were performed without pressurizing the side surface of the outer package. It can be seen that, in the non-aqueous secondary battery of the present invention, it is desirable to pressurize the side surface of the outer package during charging and discharging.

  Further, as is clear from the evaluation results of the battery of Example 6, in the non-aqueous secondary battery of the present invention, since the amount of the electrolyte solution is reduced, a plurality of electrode bodies are electrically connected in series inside the battery container. Even if connected, charging and discharging can be performed without causing an internal short circuit.

Claims (10)

A non-aqueous secondary battery having an electrode body and a non-aqueous electrolyte in a battery container,
The electrode body has a positive electrode having a positive electrode active material layer, a negative electrode having a negative electrode active material layer, and a porous insulating layer interposed between the positive electrode and the negative electrode,
The insulating layer contains an inorganic insulator in a proportion of 80% by mass or more and has a porosity of 50% or less,
The mass of the non-aqueous electrolyte in the battery container is 2 with respect to the sum of the mass of the positive electrode active material layer, the negative electrode active material layer and the insulating layer of the electrode body and the mass of the non-aqueous electrolyte. % Non-aqueous secondary battery characterized by being not less than 60% and not more than 60%. A non-aqueous secondary battery having a plurality of electrode bodies electrically connected in series and a non-aqueous electrolyte in a battery container,
The electrode body has a positive electrode having a positive electrode active material layer, a negative electrode having a negative electrode active material layer, and a porous insulating layer interposed between the positive electrode and the negative electrode,
The insulating layer contains an inorganic insulator in a proportion of 80% by mass or more and has a porosity of 50% or less,
The mass of the non-aqueous electrolyte in the battery container is the sum of the mass of the positive electrode active material layer, the negative electrode active material layer and the insulating layer of each electrode body, and the total mass of the non-aqueous electrolyte solution. A nonaqueous secondary battery characterized by being 2% or more and 60% or less.   The non-aqueous secondary battery according to claim 1, wherein the insulating layer has a thickness of 20 μm or less.   The non-aqueous secondary battery according to claim 1, wherein the inorganic insulator is inorganic particles.   The nonaqueous secondary battery according to claim 4, wherein the inorganic particles are oxide particles or solid electrolyte particles.   6. The non-aqueous secondary battery according to claim 4, wherein the inorganic particles have an average particle diameter of 2 μm or less.   The non-aqueous secondary battery according to claim 1, wherein the non-aqueous electrolyte contains a flame retardant solvent.   The non-aqueous secondary battery according to claim 7, wherein the non-aqueous electrolyte contains a flame retardant solvent and a chain ester.   The nonaqueous secondary battery according to claim 7 or 8, wherein the nonaqueous electrolytic solution contains a fluorinated ether as the flame retardant solvent.   The non-aqueous secondary battery according to claim 9, wherein a ratio of the fluorinated ether in the total solvent is 30% or more by mass ratio.