JP7083696B2 - Non-water secondary battery - Google Patents

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, with the development of portable electronic devices such as mobile phones and notebook personal computers and the practical application of electric vehicles, a compact, lightweight, high-capacity, high-energy density non-aqueous secondary battery is required. Is becoming.

Currently, for example, a lithium ion battery is known as a non-aqueous secondary battery that can meet this demand, and lithium cobalt oxide (Li _x CoO ₂ ), lithium nickel oxide (Li _x NiO ₂ ), and nickel- are used as positive electrode active materials. Lithium cobalt-lithium manganate (NCM material represented by Li _x Ni _y1 Co _y2 Mn _y3 O ₂ : 0.9 <x <1.1, 0 <y1, y2, y3 <1, y1 + y2 + y3 = 1) A battery is configured by using a contained composite oxide or a composite or a mixture thereof, and using graphite or the like as a negative electrode active material. With the further development of equipment to which non-water secondary batteries are applied, further increase in capacity and energy density of non-water secondary batteries is required.

One of the methods for increasing the capacity and energy density of the non-aqueous secondary battery is to charge the positive electrode active material at a high voltage and use it. Further, a method of increasing the Ni ratio of the NCM material to increase the capacity is also being 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 electrolytic solution additive, an element added to a positive electrode material, a surface coating, an insulating material coating on a separator, and the like have been studied. In particular, the coating of the insulating material on the resin separator has the effect of preventing the battery from short-circuiting and suppressing the expansion of the short-circuited portion when a short-circuit occurs, and the demand for it has been increasing recently. 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 times or more and 1.6 times or less the total volume of voids in the positive electrode, the negative electrode, and the separator. Therefore, it has been proposed to suppress a decrease in capacity when charging and discharging are repeated, and to provide a battery having excellent cycle characteristics.

By the way, in the study by the present inventors, when a battery having a high energy density is used by increasing the Ni ratio of the NCM material, the effect becomes difficult to occur when the thickness of the separator insulating layer becomes thin, and the resin layer is melted. It was found that the effect of the insulating layer tends not to be exhibited at the time. Therefore, it is necessary to form an insulating layer that can contribute to safety even at a higher temperature.

On the other hand, batteries using solid electrolytes are also considered to be highly safe. The solid electrolyte itself is also a material having excellent heat resistance, and is expected to exhibit an effect equal to or higher than that of the above-mentioned insulating layer. However, there is a difficulty in operating the battery, and the formation of an interface between the active material and the solid electrolyte has become an issue. Therefore, in Patent Documents 2 to 4, it is also proposed to form a good interface by interposing an electrolytic solution at the interface and to improve the operating characteristics while exerting the effect of the insulating layer. In Section 2, it is also described that the solid electrolyte layer has a structure composed of a layered dense portion and a porous portion for holding the electrolytic solution, thereby preventing a short circuit due to dendrite during charging and discharging.

Japanese Unexamined Patent Publication No. 2010-113804 Japanese Unexamined Patent Publication No. 2013-232284 Japanese Unexamined Patent Publication No. 2017-11190 Japanese Unexamined Patent Publication No. 2008-243736

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 electrolytic solution is increased in order to increase the weight energy density and safety. It has become clear that when trying to limit the amount of energy, lithium dendrites are likely to be formed during charging, and the safety is likely to be impaired.

The present invention is intended to solve the above problems, and provides a non-aqueous secondary battery having a high weight energy density, excellent charge / discharge characteristics, and less likely to form lithium dendrites during charging. be.

The non-aqueous secondary battery of the present invention has an electrode body and a non-aqueous electrolytic solution 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, and the above. It has a porous insulating layer interposed between the positive electrode and the negative electrode, and 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 electrolytic solution in the battery container is the sum of the total 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 electrolytic solution. It is characterized by being 2% or more and 60% or less.

Further, another embodiment of the non-aqueous secondary battery of the present invention has a plurality of electrode bodies conductively connected in series and a non-aqueous electrolytic solution in a battery container, and the electrode body is a positive electrode active material layer. It has a positive electrode having a positive electrode, a negative electrode having a negative electrode active material layer, and a porous insulating layer interposed between the positive electrode and the negative electrode, and the insulating layer contains 80% by mass or more of an inorganic insulator. It is contained in a proportion and has a pore ratio of 50% or less, and the mass of the non-aqueous electrolytic solution 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 characterized in that it is 2% or more and 60% or less with respect to the total and the total mass of the non-aqueous electrolytic solution.

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

In the non-aqueous secondary battery of the present invention, in order to improve heat resistance, an inorganic insulator is contained in a proportion of 80% by mass or more between the positive electrode having the positive electrode active material layer and the negative electrode having the negative electrode active material layer. A porous insulating layer contained therein is interposed.

The insulating layer may be an independent film instead of the conventional porous film made of resin or function as a separator together with the porous film made of resin, and may be a positive electrode active material layer or a negative electrode active material. It may be formed by coating on any surface or all surfaces of the layer and the porous film made of resin.

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

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

On the other hand, when the porosity of the insulating layer is 50% or less, the formation of lithium dendrite is suppressed, and safety can be enhanced. The porosity of the insulating layer is preferably 45% or less, more preferably 40% or less. On the other hand, if the porosity of the insulating layer becomes too low, the ionic conductivity decreases, the internal resistance increases, and the charge / discharge characteristics tend to decrease. Therefore, in order to obtain good charge / discharge characteristics, the insulating layer is required. The porosity of the above is preferably 5% or more, and more preferably 20% or more.

The content of the non-aqueous electrolyte solution is preferably as small as possible from the viewpoint of increasing the weight energy density, and the mass of the non-aqueous electrolyte solution 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 total and the total mass of the non-aqueous electrolytic solution. On the other hand, if the content of the non-aqueous electrolytic solution is too small, the ionic conductivity decreases, the internal resistance increases, and the charge / discharge characteristics tend to decrease. Therefore, the mass of the non-aqueous electrolytic solution is the positive electrode active material layer. , 10% or more, more preferably 25% or more, and 33% or more, based on the total mass of the negative electrode active material layer and the insulating layer and the total mass of the non-aqueous electrolytic solution. Most preferably.

As the inorganic insulator forming the insulating layer, insulating oxides, nitrides, sparingly soluble ionic crystals, covalently bonded crystals, clays, natural or artificial minerals and the like can be used, and Al ₂ O ₃ (alumina) can be used. , 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, mulite , Spinel, olivine, sericite, bentonite, etc. are exemplified. Among these, at least one selected from the group consisting of alumina, silica and boehmite is preferably used.

Further, the inorganic insulator may be a solid electrolyte, and 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-type structure, and Li _a La _b Zr _c MA _{d Oe} (where MA is Sc, Ti, V, Y, Nb, Hf). , Ta, Al, Si, Ga and Ge, at least one element selected from the group, 5 ≦ a ≦ 8, 2 ≦ b ≦ 4, 0 <c ≦ 2, 0 ≦ d <1, 11 <e. Specific examples thereof include compounds such as <13.).

Examples of the sulfide-based solid electrolyte include compounds 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 SP ₂ S ₅ system material, Li ₂ S-SiS ₂ system material, Li ₂ S-GeS ₂ system material, Li ₂ S-Al ₂ S ₃ system material, Li ₂ S-SiS ₂ -Li ₃ PO ₄ -based material, Li ₂ SP ₂ S ₅ -GeS ₂ -based material, Li ₂ S-Li ₂ OP ₂ S ₅ -SiS ₂ -based material, Li ₂ S Specific examples thereof include -GeS ₂ -P ₂ S ₅ -SiS ₂ system materials and Li ₂ S-SnS ₂ -P ₂ S ₅ -SiS ₂ system materials.

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

As LiX, LiCl and LiF are preferable, and it is particularly preferable that LiCl is present in the structure of the ionic conductor in a state of being incorporated. In other words, the sulfide-based solid electrolyte preferably contains lithium halide in a physically inseparable state rather than a simple mixture.

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.

As the inorganic insulator, these may be used alone or in combination of two or more.

The shape of the inorganic insulator may be a sheet-like material or a particle-like material. In the case of particulate matter (inorganic particles), the average particle size of the particles used to form the insulating layer is preferably 2 μm or less, and more preferably 1.5 μm or less, in order to prevent short circuits due to the formation of lithium dendrites. It is desirable, and most preferably 1 μm or less. On the other hand, if the average particle size becomes too small, the particle size becomes bulky, and the strength of the insulating layer and the homogeneity tend to decrease. Therefore, the average particle size is preferably 0.01 μm or more, and 0. It is more preferably 1 μm or more, and most preferably 0.2 μm or more.

Further, in order to make the insulating layer more dense, it is preferable to use a combination of inorganic particles having different particle sizes. This can be expected to improve the strength of the insulating layer. For example, when two types of particle size inorganic particles are used in combination, DL / DS is 1.2, where DL is the average particle size of the particles with the larger particle size and DS is the average particle size of the particles with the smaller particle size. The above is preferable, 1.5 or more is more preferable, 2 or more is most preferable, while 5 or less is preferable, and 3 or less is more preferable.

For the average particle size, for example, a laser scattering particle size distribution meter (for example, “LA-920” manufactured by HORIBA) is used to disperse the inorganic particles in a medium that does not dissolve the inorganic particles or swell the inorganic particles. It can be specified as the number average particle size measured by the process.

The porous insulating layer can be formed by applying a slurry for forming an insulating layer containing the inorganic particles and drying the slurry. Further, the inorganic particles can be integrated into a sheet-like material of an inorganic insulator by sintering the inorganic particles with each other.
A thickener may be used for the slurry for forming the insulating layer. By using the thickener, the viscosity of the slurry for forming the insulating layer can be adjusted in a suitable range, the dispersion of the inorganic particles can be made uniform, and an excellent dispersed state can be stably maintained.

The thickener may be one that does not have side effects such as agglomeration of inorganic particles in the slurry for forming an insulating layer and can adjust the slurry to the required viscosity, but has a high thickening effect by adding a small amount. The one is preferable. Further, the thickener is preferably one that can be satisfactorily dissolved or dispersed in the dispersion medium used for the slurry. If a large amount of undissolved components or aggregates of the thickener are present in the slurry, the dispersion of the inorganic particles becomes non-uniform, and the inorganic particles are formed in the insulating layer formed by applying the slurry to a substrate or the like and drying it. Distribution becomes non-uniform. Therefore, the heat resistance of the insulating layer is lowered, and as a result, the reliability and heat resistance of the non-aqueous secondary battery may be lowered.

Specific examples of the thickener include synthetic polymers such as polyethylene glycol, polysaccharide acid, polyvinyl alcohol, and vinylmethyl ether-maleic anhydride copolymer; cellulose derivatives such as carboxymethyl cellulose, hydroxyethyl cellulose, and hydroxypropyl cellulose; xanthan gum. , Welan gum, gellan gum, guar gum, natural polysaccharides such as carrageenan and the like. These may be used alone or in combination of two or more.

The content of the thickener in the slurry for forming the insulating layer is preferably 10% by volume or less, preferably 5% by volume, based on the total volume of the solid content (components excluding the dispersion medium; hereinafter the same) in the slurry. It is more preferably less than or equal to 1% by volume or less. Further, the content of the thickener in the slurry for forming the insulating layer is preferably 0.1% by volume or more based on the total volume of the solid content in the slurry.

Further, it is preferable to use a dispersant for the slurry for forming the insulating layer. 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 slurry for forming an insulating layer is further improved and the aggregation of these inorganic particles can be prevented. Therefore, it becomes possible to maintain a good dispersed state of the inorganic particles more stably.

Specific examples of the dispersant include various anionic, cationic, and nonionic surfactants; polycarboxylic acid, polyacrylic acid, polymethacrylic acid, amino acids (aspartic acid, etc.), polycarboxylate, and polyacrylic acid. Polymer-based dispersants such as salts and polymethacrylates; and the like can be used. As the dispersant, one of the above-exemplified ones may be used alone, or two or more of them may be used in combination.

Among these dispersants, an ion-dissociable acid group (carboxyl group, sulfonic acid group, amino acid group, maleic acid group, etc.) or an ion-dissociable acid base (carboxylic acid base) has a strong effect of dispersing fine particles. , Sulphonic acid base, maleic acid base, etc.) are preferable, and aspartic acid, polycarboxylic acid salt, polyacrylic acid salt, and polymethacrylic acid salt are more preferable. When the polymer-based dispersant is a salt (having an acid-base), it is preferably an ammonium salt.

The content of the dispersant in the slurry for forming the insulating layer is preferably 0.1 part by mass or more, and more preferably 0.3 part by mass or more with respect to 100 parts by mass of the insulating fine particles. However, if the amount of the dispersant is too large, the ratio of other components in the insulating layer may decrease, and the effect of these components may be reduced. Therefore, the content of the dispersant in the slurry for forming the insulating layer 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 slurry for forming the insulating layer, a binder is provided in the insulating layer for the purpose of adhering the inorganic particles to each other, the inorganic particles and other components described later, or adhering the insulating layer and the base material. Can be contained. The type of binder is not particularly limited as long as it is electrochemically stable inside the non-aqueous secondary battery and stable with respect to the electrolytic solution of the non-aqueous secondary battery. Further, among the above-mentioned thickeners, those having a function as a binder can be used in combination with the thickener and the binder.

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. (Meta) acrylic acid copolymers such as; fluororubber; styrene-butadiene rubber (SBR); polyvinyl alcohol (PVA); polyvinyl butyral (PVB); polyvinylpyrrolidone (PVP); polyN-vinylacetamide; crosslinked acrylic resin ; Polypolymer; epoxy resin; etc. are used. These binders may be used alone or in combination of two or more.

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 lower is preferable. More preferred.

Examples of the dispersion medium of the slurry for forming an insulating layer include those containing water as a main component 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 a main component are preferable.

The porous insulating layer is interposed between the positive electrode having the positive electrode active material layer and the negative electrode having the negative electrode active material layer to form an electrode body composed of a laminated body 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 composed of a positive electrode active material and a negative electrode active material, a binder, a conductive auxiliary agent, and the like, respectively, and can be formed on a current collector such as a metal foil.

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. Examples thereof include a lithium-containing composite oxide having a _spinel structure such as _{5/3 O4} ; a lithium-containing composite oxide having an olivine structure such as LiFePO ₄ ; an oxide having the above oxide as a basic composition and being replaced with various elements. Only one of these may be used, or two or more thereof may be used in combination.

Conductive auxiliaries related to the positive electrode active material layer include, for example, natural graphite (scaly graphite, etc.), graphite such as artificial graphite; acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, etc. It is preferable to use carbon materials such as carbon blacks; carbon fibers; and conductive fibers such as metal fibers; carbon fluoride; metal powders such as aluminum; zinc oxide; conductivity such as potassium titanate. Sexual 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 related to the positive electrode active material layer include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), polyvinylpyrrolidone (PVP) and the like.

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 and dedoped with lithium ions, for example, graphite, thermally decomposed carbons, cokes, glassy carbon, fired organic polymer compounds, and mesocarbon microbeads. , Carbon fiber, carbonaceous materials such as activated carbon. Further, 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, and the like, as well as lithium-aluminum and lithium-lead. , Lithium-indium, lithium-gallium, lithium-indium-gallium, and the like. Some of these exemplified negative electrode active materials do not contain lithium at the time of manufacture, but they are in a state of containing lithium at the time of charging.

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

For the positive and negative electrodes, for example, an active material and a binder, and if necessary, a conductive auxiliary agent and the like are dispersed or dissolved in a solvent such as NMP or water to form a paste-like or slurry-like composition, which is used to collect electricity. It can be manufactured by applying it to one or both sides of the body, drying it, and then pressing it if necessary.

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

The porosity of the positive electrode active material layer and the negative electrode active material layer can be adjusted, for example, by changing the pressing treatment conditions. When an insulating layer is formed on the surface of the positive electrode active material layer or the negative electrode active material layer, the effect on charge / discharge characteristics is achieved by applying the insulating layer forming slurry on the active material layer after the press treatment. It is preferable because it is possible to form a thinner and stronger insulating layer.

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

The non-aqueous electrolyte solution is formed 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 flame-retardant solvent 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (HCF ₂ CF ₂ -O-CH ₂ CF ₂ CF). _2H : Fluorinated ether such as fluorinated rate 67%) and phosphoric acid ester 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 (TMP) Phosphate, Tris (Trifluoroethyl) Phosphate (TFEP): (CF ₃ CH ₂ O) ₃ P = O, Triphenyl Phosphate (TPP): (C ₆ H ₅ O) ₃ P = O, ethyldiethylphosphonoacetate (EDPA): (C ₂ H ₅ O) ₂ (P = O) -CH ₂ (C = O) OC ₂ H ₅ ], derivatives of each of the above compounds, etc. may be used. preferable.

In addition, dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), dipropyl carbonate (DPC), 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, methyl acetate , 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 and the like having a flash point of 100 ° C. or higher can also be used.

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

The above-mentioned solvent may be used alone or in combination of two or more, and it is desirable to use a phosphoric acid ester such as a flame-retardant fluorinated ether or trimethyl phosphate or a cyclic ester. In particular, it is desirable to use fluorinated ether. As the fluorinated ether, it is more desirable to use a solvent having a fluorination rate of 50% or more because the 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%, more preferably less than 80%. When fluorinated ether is used, it is desirable to use a chain ester together. Specific examples thereof include dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), dipropyl carbonate (DPC), propyl propionate, ethyl propionate, sevaconitrile, pimeronitrile, and glutaronitrile. ..

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

Examples of the inorganic lithium salt include 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 acid Li, LiAlCl ₄ , LiCl, LiBr. , LiI, chloroborane Li, Li 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 , and LiC _n1 F. _{2n1 + 1} SO ₃ (2≤n1≤7), LiN (Rf ₁ OSO ₂ ) ₂ [However, Rf ₁ is a fluoroalkyl group. ], LiN (FSO ₂ ) ₂ , etc., and these may be used 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 is high in combination with a flame-retardant solvent, and the battery characteristics can be further improved.

The concentration of the electrolyte salt in the non-aqueous electrolyte solution is, for example, preferably 0.2 to 3.0 mol / dm ³ , more preferably 0.5 to 1.5 mol / dm ³ , and 0. It is more preferably 9 to 1.3 mol / dm ³ .

Further, the non-aqueous electrolytic solution may appropriately contain the following additives for the purpose of improving the charge / discharge cycle characteristics, high temperature storage characteristics, prevention of overcharging and the like. Examples of the additive include anhydrous acid, sulfonic acid ester, dinitrile, 1,3-propanesarton, diphenyl disulfide, cyclohexylbenzene, vinylene carbonate (VC), biphenyl, fluorobenzene, t-butylbenzene, and cyclic fluorinated carbonate. [Trifluorochloropropylene carbonate (TFPC), fluoroethylene carbonate (FEC), etc.] or chain fluorinated carbonate [trifluorodimethyl carbonate (TFDMC), trifluorodiethyl carbonate (TFDEC), trifluoroethylmethyl carbonate (TFEMC) ) Etc.], 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, and 1, 8-Dicyanooctane, 1,9-Dicyanononane, 1,10-Dicyanodecane, 1,12-Dicyanododecane, Tetramethylsuccinonitrile, 2-Methylglutaronitrile, 4-Dicyanopentane, 2,6-Dicyanoheptan, Examples thereof include dinitriles such as 2,7-dicyanooctane, 2,8-dicyanononane, 1,6-dicyanodecane and 1,2-dicyanobenzene. Further, some of these dinitriles and the like may be fluorinated.

The concentration of the compound having two or more nitrile groups in the molecule in the non-aqueous electrolytic solution is preferably 0.1% by mass or more, more preferably 2% by mass or more, most preferably 10% by mass or more, and 50. It is preferably mass% or less, more preferably 30 mass% or less, and most preferably 20 mass% or less.

The temperature of the battery during charging is not particularly limited, but it is desirable to operate the battery 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, the more difficult it is for a short circuit to occur even if the amount of the electrolytic solution is small, and the ionic conductivity of the electrolytic solution is increased to improve the charge / discharge characteristics of the battery. However, in order to prevent evaporation of the electrolytic solution, the temperature of the battery during charging is preferably 200 ° C. or lower, more preferably 170 ° C. or lower, and most preferably 150 ° C. or lower.

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 high, a short circuit of the battery due to the formation of lithium dendrite is likely to occur even when the charging depth is shallow. However, by using a mixed solvent of fluorinated ether and chain ester as the solvent of the electrolytic 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, in addition to forming a battery by using the electrode body alone, it is also possible to form a battery in which a plurality of the electrode bodies are conductively connected in series and housed in a battery container to multiply the voltage by n. It is possible. That is, in a non-aqueous secondary battery having a plurality of electrodes connected in series and a non-aqueous electrolytic solution in the battery container, the total mass of the non-aqueous electrolytic solutions in the battery container is the sum of the masses of the respective electrode bodies. 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 becomes similar to that of a battery using the electrode body alone. It is a non-aqueous secondary battery that is high in quality, has excellent charge / discharge characteristics, is less likely to form lithium dendrites during charging, and is highly safe, and its operating voltage is increased according to the number of electrodes connected in series. It is also possible to configure a water secondary battery.

Examples of the non-aqueous secondary battery of the present invention include a tubular shape (square tubular shape, cylindrical shape, etc.) using a steel can, an aluminum can, or the like as a battery container (exterior body), a coin shape, or the like. Further, a soft package battery using a laminated film on which metal is vapor-deposited as a battery container can also be used.

In the case of a battery having a shape such as a square cylinder or a coin, or a flat battery having a laminated film as a battery container, the battery is pressurized in the thickness direction in order to improve the charge / discharge characteristics of the battery. Charging and discharging may be performed in the state. The pressure applied to the battery container is preferably 0.001 kgf / cm ² or more, and more preferably 0.01 kgf / cm ² or more. On the other hand, if the pressure is too high, the characteristics tend 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
[Preparation of positive electrode]
First, LiNi _0.5 Co _0.2 Mn _0.3 O ₂ (hereinafter “NCM523”), which is a positive electrode active material,: 100 parts by mass, acetylene black, which is a conductive auxiliary agent: 3.2 parts by mass, and a binder. A certain PVDF: 3.2 parts by mass (provided with a solid content as an NMP solution) was mixed with NMP as a solvent so as to be uniform 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. After that, a pressing process 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 cut so as to have a length of 30 mm and a width of 30 mm while leaving the tab welded portion to prepare a positive electrode. Further, the active material of the tab welded portion of the positive electrode was removed, and the tab was welded to the tab welded portion to form a lead portion.

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

[Formation of an insulating layer on the positive electrode]
The slurry for forming an insulating layer was applied onto the active material layer of the positive electrode that had been pressed, 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.

[Manufacturing of negative electrode]
100 parts by mass of graphite as a negative electrode active material, VGCF (gas phase carbon fiber) as a conductive auxiliary agent: 2 parts by mass, CMC as a solvent: 1 part by mass (supplying solid content as 1% by mass of 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 coating amount was 11.4 mg / cm ² as the solid content of the composition, dried, and then pressed. The thickness of the negative electrode active material layer was adjusted so that the total thickness was 88 μm, and the negative electrode was prepared by cutting so that the length was 32 mm and the width was 32 mm, leaving the tab welded portion. Further, a tab was welded to the tab welded portion of the negative electrode to form a lead portion.

[Preparation of non-aqueous electrolyte solution]
0.1 mol in 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). A non-aqueous electrolyte solution was prepared by dissolving LiN (FSO ₂ ) ₂ .

[Battery assembly]
The positive electrode and the negative electrode were laminated with an insulating layer interposed therebetween to prepare an electrode body having a three-layer structure of a positive electrode / an insulating layer / a negative electrode. The obtained electrode body is housed in an exterior body made of an aluminum laminated film, 0.1 ml of the non-aqueous electrolytic solution is injected onto the insulating layer of the positive electrode, and the pressure is reduced to impregnate the electrolytic solution, and then normal pressure is applied. A non-aqueous secondary battery was produced by sealing with. The mass of the non-aqueous electrolytic solution in this battery was 34% of the total mass of the positive electrode active material layer, the negative electrode active material layer and the insulating layer and the total mass of the non-aqueous electrolytic solution.

A glass plate is placed on the side surface of the created battery via a 3.5 cm square silicon rubber, and while applying a load of 150 g and pressurizing, 2.5 mA (rate equivalent to 1 / 10C) under a temperature environment of 25 ° C. ) Constant current-constant voltage charging, which charges up to 4.2V with a constant current and then charges at a constant voltage of 4.2V, and constant current discharge, which discharges to 3V with a constant current of 2.5mA, at that time. The charge / discharge characteristics were evaluated by measuring the discharge capacity of. In the charge / discharge, the pressure applied to the side surface of the exterior body was 0.015 kgf / cm ² .

Example 2
The charging / discharging characteristics were evaluated in the same manner as in Example 1 except that the charging / discharging of the battery was carried out 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 electrolytic solution to the total of the total 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 electrolytic solution was 30%.

Example 5
A non-aqueous secondary battery was produced in the same manner as in Example 1 except that the amount of the non-aqueous electrolytic solution was 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 electrolytic solution to the total of the total 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 electrolytic solution was 30%.

Example 6
Two sets of electrodes having a three-layer structure of positive electrode / insulating layer / negative electrode are produced, and the negative electrode of one electrode body and the positive electrode of the other electrode body are overlapped with each other to form 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 insulating layer 2 and the negative electrode 2 are laminated in this order, and tabs are welded to the positive electrode 1 and the negative electrode 2 to form lead portions, whereby the two sets of electrode bodies are formed. A laminate was produced.

This was carried out except that the laminated body of the two sets of electrodes was housed in an exterior body made of an aluminum laminated film, and 0.1 ml of a non-aqueous electrolytic solution was injected between the insulating layer of each electrode body and the counter electrode. 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 solution to the sum of the total 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 electrolytic solution is 34%. Met.

The manufactured non-aqueous secondary battery is charged to 8.4V with a constant current of 2.5mA, and then charged with a constant voltage of 8.4V. Constant current-constant voltage charging and constant current of 2.5mA. A constant current discharge was performed to discharge to 6 V, and the discharge capacity at that time was measured to evaluate the charge / discharge characteristics. In the charge / discharge, the pressure applied to the side surface of the exterior body was 0.015 kgf / cm ² .

Comparative Example 1
By using alumina having an average particle diameter of 0.5 μm, an insulating layer having a thickness of 12.5 μm and a pore ratio of 55% was formed on the positive electrode active material layer, but not in the same manner as in Example 1. A water secondary battery was prepared, 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 electrolytic solution to the total of the total 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 electrolytic solution 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 electrolytic solution was 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 electrolytic solution to the total of the total 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 electrolytic solution 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 electrolytic solution 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 electrolytic solution to the total of the total 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 electrolytic solution was 1%.

Comparative Example 4
A non-aqueous 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 non-aqueous electrolyte solution. Then, the charge / discharge characteristics were evaluated in the same manner as in Example 1.

Reference example 1
The charge / discharge characteristics were evaluated in the same manner as in Comparative Example 1 except that the side surface of the exterior body was charged / discharged without being pressurized.

Table 1 shows the configuration of each battery, and Table 2 shows the evaluation results of charge / discharge characteristics. The weight energy density of each battery is the total mass of the positive electrode mixture layer and the insulating layer of the electrode body housed in the exterior body, and the portion of the negative electrode mixture layer facing the positive electrode mixture layer, and non-water. It is a value calculated by assuming that the operating voltage (average discharge voltage) of each electrode body of each battery is 3.7 V based on the total with the mass of the electrolytic solution and the measured discharge capacity of the battery.

An insulating layer containing an inorganic insulator in a proportion of 80% by mass or more and having a pore ratio of 50% or less is used as a separator, and the proportion of the mass of the non-aqueous electrolyte solution in the battery container is determined by the positive electrode active material layer and the negative electrode. The non-aqueous secondary battery of the present invention having a range of 2% or more and 60% or less with respect to the total mass of the active material layer and the insulating layer and the mass of the non-aqueous electrolytic solution has a high weight energy density. In addition to having excellent charge / discharge characteristics, the formation of lithium dendrites during charging was suppressed, and the battery could be made highly safe.

On the other hand, in the battery of Comparative Example 1 in which the porosity of the insulating layer is larger than 50%, the discharge capacity is 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 was 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 electrolytic solution was large. On the contrary, in the battery of Comparative Example 3 in which the weight energy density of the battery is low and the amount of the non-aqueous electrolyte solution is too small, the ionic conductivity is lowered and the internal resistance is increased, so that the battery cannot be discharged.

Further, the battery of Comparative Example 2 in which fluorinated ether, which is a flame-retardant solvent, is contained in the total solvent at a mass ratio of 30% or more and a non-aqueous electrolyte solution is formed by a mixed solvent with a chain ester (MEC) is used. A discharge capacity equivalent to that of the battery of Comparative Example 4 in which a non-aqueous electrolyte solution is composed of a mixed solvent of a general-purpose cyclic carbonate and a chain carbonate can be obtained, and the above-mentioned electrolyte solution composition containing a flame-retardant solvent shall be obtained. Therefore, it can be seen that the electrolytic solution can be made flame-retardant without deteriorating the charge / discharge characteristics.

Further, the discharge capacity of the batteries of Examples 1 to 6 in which a constant pressure is applied to the side surface of the exterior body is larger than that of the battery of Reference Example 1 in which the side surface of the exterior body is charged and discharged without pressurizing. 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 exterior body during charging and discharging.

Further, as is clear from the evaluation results of the battery of Example 6, since the amount of the electrolytic solution is small in the non-aqueous secondary battery of the present invention, a plurality of electrode bodies are conductive in series inside the battery container. Even if they are 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 electrolytic solution 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 electrolytic solution in the battery container is 25 with respect to the total 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 electrolytic solution. A non-aqueous secondary battery characterized by being% or more and 60% or less. A non-aqueous secondary battery having a plurality of electrode bodies conductively connected in series and a non-aqueous electrolytic solution 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 electrolytic solution in the battery container is the sum of the total 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 electrolytic solution. A non-aqueous secondary battery characterized by being 25 % or more and 60% or less. The non-aqueous secondary battery according to claim 1 or 2, wherein the thickness of the insulating layer is 20 μm or less. The non-aqueous secondary battery according to any one of claims 1 to 3, wherein the inorganic insulator is an inorganic particle. The non-aqueous secondary battery according to claim 4, wherein the inorganic particles are oxide particles or solid electrolyte particles. The non-aqueous secondary battery according to claim 4 or 5, wherein the average particle size of the inorganic particles is 2 μm or less. The non-aqueous secondary battery according to any one of claims 1 to 6, wherein the non-aqueous electrolyte solution contains a flame-retardant solvent. The non-aqueous secondary battery according to claim 7, wherein the non-aqueous electrolytic solution contains a flame-retardant solvent and a chain ester. The non-aqueous secondary battery according to claim 7 or 8, wherein the non-aqueous electrolyte solution contains a fluorinated ether as the flame-retardant solvent. The non-aqueous secondary battery according to claim 9, wherein the ratio of the fluorinated ether to the total solvent is 30% or more by mass ratio.