CN111052445A

CN111052445A - Separator for nonaqueous electrolyte battery, and nonaqueous electrolyte battery using same

Info

Publication number: CN111052445A
Application number: CN201880049062.8A
Authority: CN
Inventors: 太田有纪; 岩崎秀治
Original assignee: Kuraray Co Ltd
Current assignee: Kuraray Co Ltd
Priority date: 2017-07-24
Filing date: 2018-07-10
Publication date: 2020-04-21
Also published as: KR20200019962A; WO2019021810A1; TW201909466A; JPWO2019021810A1

Abstract

One aspect of the present invention relates to a separation membrane for a nonaqueous electrolyte battery, characterized by comprising: a polymer compound having a carboxylate group in a molecule.

Description

Separator for nonaqueous electrolyte battery, and nonaqueous electrolyte battery using same

Technical Field

The present invention relates to a separator for a nonaqueous electrolyte battery and a nonaqueous electrolyte battery using the same.

Background

In recent years, mobile terminals such as mobile phones, notebook computers, tablet-type information terminal devices, and the like have been remarkably popularized. Lithium ion secondary batteries are often used as secondary batteries used as power sources for such mobile terminals. Since mobile terminals are required to be more comfortable to carry, miniaturization, thinning, weight reduction, and high performance have been rapidly advanced, and thus, mobile terminals are used in various applications. This trend continues, and batteries for mobile terminals are also required to be further reduced in size, thickness, weight, and performance.

Also, large-sized devices such as electric vehicles, hybrid vehicles, electric vehicles, and the like are increasingly prone to use nonaqueous electrolyte batteries. Therefore, high capacity and performance such as charge and discharge characteristics under a large current are required, but it is known that since a nonaqueous electrolyte battery is used, the risk of smoke generation, ignition, breakage, and the like is high as compared with an aqueous battery, and improvement in safety is required.

Nonaqueous electrolyte batteries such as lithium ion secondary batteries have the following structure: the positive electrode and the negative electrode were provided with a separator (separator) therebetween, and LiPF was used₆、LiBF₄An electrolyte solution in which a lithium salt such as LiTFSI (lithium bistrifluoromethanesulfonimide) or LiFSI (lithium difluorosulfonimide) is dissolved in an organic liquid such as ethylene carbonate is contained in a container.

This increases the risk of smoke generation due to temperature rise by external heat, overcharge, internal short circuit, external short circuit, and the like. In response to these problems, an external protection circuit is employed to prevent them to some extent. In addition, the temperature rise of the battery can be suppressed by utilizing the shutdown function of the spacer.

Conventionally, as a nonaqueous electrolyte battery separator, for example, a porous film of a polyolefin resin has been often used. The porous membrane is melted when the temperature inside the battery reaches about 120 ℃, and blocks the pores to cut off the current and/or ion flow, thereby playing a role of maintaining safety (shutdown function). However, when the temperature rises due to external heat or when a chemical reaction occurs in the battery as the temperature rises, the battery temperature continues to rise even if the shutdown function is activated, and the battery temperature may reach 150 ℃. In this case, an internal short circuit may occur due to shrinkage of the porous film, which may cause ignition or the like.

For this problem, the following is reported: by providing a coating layer highly filled with an inorganic filler on a porous film of a polyolefin resin, abnormal heat generation occurs, and short-circuiting between both electrodes can be prevented even when the temperature continues to rise above the shutdown temperature (for example, patent document 1).

However, when the particles and the binder material are laminated on the porous film, there is a problem that the internal resistance of the electric element increases to lower the output characteristics, or the capacity rapidly decreases with an increase in the charge-discharge cycle, resulting in a shorter cycle life. Further, stacking results in an increase in production cost and/or a decrease in productivity.

In addition to the above reports, from the viewpoint of safety, a polymer solid electrolyte has been proposed which is in a form in which an electrolyte is uniformly dissolved in a polymer (for example, patent document 2), and which has a lower ionic conductivity and is improved as compared with a liquid additive electrolyte, but has a practical problem.

As described above, it has been difficult to produce a separation film which is highly safe, suppresses an increase in internal resistance due to a spacer, improves battery characteristics such as battery capacity (in particular, reduces the resistance), and has high productivity.

The present invention has been made in view of the above-described problems, and an object thereof is to: provided are a separator for a nonaqueous electrolyte battery, which has high heat resistance, low resistance, and excellent productivity, and an electrical element (nonaqueous electrolyte battery) using the separator.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2007-280911

Patent document 2: japanese patent publication No. 4888366

Disclosure of Invention

The present inventors have conducted intensive studies to solve the above problems, and as a result, have found that: the above object is achieved by using a separation membrane having the following configuration, and the present invention has been completed by further studying based on this finding.

That is, one aspect of the present invention relates to a separator for a battery, comprising: the battery separator contains a polymer compound having a carboxylate group in the molecule.

According to the present invention, a safe and low-resistance separator for a nonaqueous electrolyte battery and an electrical element (nonaqueous electrolyte battery) using the same can be provided.

Detailed Description

Hereinafter, embodiments of the present invention will be described in detail, but the present invention is not limited to these embodiments.

In the present embodiment, the separator for a nonaqueous electrolyte battery (hereinafter, may be simply referred to as a separator) refers to: a membrane that separates a positive electrode and a negative electrode in a nonaqueous electrolyte battery and has an ion-transporting property (i.e., that allows ions to flow between the positive electrode and the negative electrode by flowing or holding an electrolytic solution).

(Polymer Compound)

The separation membrane of the present embodiment is characterized in that: the separation membrane as a whole contains a polymer compound having a carboxylate group in the molecule, that is, is formed of a polymer compound having a carboxylate group in the molecule. The polymer compound exhibits ion transport properties by having a carboxylate group in the molecule.

Specifically, the polymer compound is preferably a polymer compound containing a copolymer of at least 1 selected from the group consisting of vinyl alcohol, vinyl acetal, and vinyl ester. Here, the copolymer containing at least 1 selected from the group consisting of vinyl alcohol, vinyl acetal, and vinyl ester means: a copolymer having a structure derived from addition polymerization of at least 1 monomer selected from the group consisting of a vinyl alcohol monomer, a vinyl acetal monomer, and a vinyl ester monomer.

In the present embodiment, when a copolymer containing vinyl alcohol is used as the polymer compound, the saponification degree of the copolymer containing vinyl alcohol is not particularly limited, and is usually 50% or more, more preferably 80% or more, and still more preferably 95% or more. When the saponification degree is low, the alkali metal contained in the separator may be hydrolyzed, which is not preferable because the stability is poor.

As an example of the vinyl ester that can be used in the present embodiment, vinyl acetate is typically used from the viewpoint of good availability in the market and good impurity treatment efficiency in production. Further, examples thereof include: aliphatic vinyl esters such as vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, vinyl valerate, vinyl isovalerate, vinyl pivalate, vinyl decanoate, vinyl laurate, vinyl stearate, and vinyl neodecanoate; aromatic vinyl esters such as vinyl benzoate.

Examples of the vinyl acetal of the present embodiment include vinyl formal, vinyl butyral, and vinyl glyoxylic acid, and among them, vinyl glyoxylic acid which is inexpensive and can be easily produced is preferable.

The copolymerization mode of the copolymer of the present embodiment is not particularly limited, and examples thereof include random copolymerization, alternating copolymerization, block copolymerization, and graft copolymerization.

The method for producing the copolymer of the present embodiment is also not particularly limited, and any polymerization initiation method such as anionic polymerization, cationic polymerization, radical polymerization, or the like may be used, and any method such as solution polymerization, bulk polymerization, suspension polymerization, dispersion polymerization, or emulsion polymerization may be used as the method for producing the polymer.

The polymer compound of the present embodiment may be a copolymer of the above-mentioned vinyl alcohol, vinyl acetal and/or vinyl ester and another compound, and in this case, the other compound is not particularly limited as long as the effect of the present invention is not impaired, and examples thereof include α -olefin containing an alkyl group such as ethylene, 1-hexene, 1-dodecene, etc., α -olefin containing an alkyl group such as 2-acrylamido-2-methylpropanesulfonic acid, (3-acrylamidopropyl) trimethylammonium chloride, 6-acrylamidohexanoic acid, etc., acrylamide such as N-vinyl- ε -caprolactam, 1-vinyl-2-pyrrolidone, etc., α -olefin containing an alcohol such as 2-methyl-3-buten-2-ol, 3-hydroxy-3-methyl-1-butene, etc., α -olefin containing a silane such as trimethoxyvinylsilane, etc.

The average molecular weight of the copolymer of the present embodiment is preferably 5,000 to 250,000 in number average molecular weight. When the number average molecular weight of the copolymer is less than 5,000, the mechanical strength of the separator for a nonaqueous electrolyte battery may decrease. The number average molecular weight is more preferably 10,000 or more, and still more preferably 15,000 or more. On the other hand, when the number average molecular weight of the copolymer exceeds 250,000, the copolymer may aggregate in the aqueous coating solution or the viscosity stability of the aqueous coating solution may be lowered, and the separator for a nonaqueous electrolyte battery may have insufficient homogeneity and/or productivity. The number average molecular weight is more preferably 200,000 or less, and still more preferably 150,000 or less. The number average molecular weight of the copolymer in the present invention means: values measured by a Gel Permeation Chromatography (GPC) method using polyethylene oxide and polyethylene glycol as standard substances and an aqueous column as a column were used.

The polymer compound contained in the separation membrane of the present embodiment is characterized in that: has a carboxylate group in the molecule.

In the polymer compound having a carboxylate group of the present embodiment, it is desirable that the melting point which greatly changes the physical properties of the separator be 180 ℃ or higher. The separator of the present embodiment does not have a shutdown function, but the separator itself has heat resistance, and therefore, even if the battery internal temperature is 180 ℃ or higher, the shape and physical properties are not changed, short circuits are not caused, safety is high, and productivity can be improved because a heat-resistant coating agent is not required. It is more preferable to use a polymer compound having a carboxylate group with a melting point of 200 ℃ or higher. The upper limit of the melting point is not particularly limited, but is preferably 300 ℃ or less from the viewpoints of flexibility and strength of the separation film and productivity in producing the polymer compound.

In the present embodiment, the melting point can be adjusted to the above range by adjusting the molecular weight, crystallinity, saponification degree, and neutralization degree of the copolymer contained in the polymer compound having a carboxylate group, for example, but the method of adjusting the melting point is not limited thereto.

In the present embodiment, the method for measuring the melting point is not particularly limited, and the melting point can be measured by, for example, the method described in the examples described later.

In the present embodiment, the polymer compound contains a carboxylic acid forming a carboxylate group. Examples of the carboxylic acid include: unsaturated monocarboxylic acids such as acrylic acid, methacrylic acid, and crotonic acid; unsaturated dicarboxylic acids such as fumaric acid, itaconic acid, and maleic acid; glyoxylic acid and the like, and carboxylic acids are present in the polymer compound as monomer units derived from these. Among them, acrylic acid, methacrylic acid, maleic acid, and glyoxylic acid are preferred from the viewpoints of availability, polymerizability, and stability of the product. These carboxylic acids (monomers) may be used alone or in combination of two or more.

In the polymer compound of the present embodiment, the content ratio of the copolymer to the carboxylic acid (the amount of carboxylic acid (total amount of carboxylate group and carboxylic acid)) is preferably in the range of 100/1 to 1/100 in terms of a molar ratio. More preferably 50/100 or less, and still more preferably 80/100 or less. Further, it is more preferably 100/3 or more, and still more preferably 100/8 or more. The reason for this is that: as a water-soluble high molecular weight material, advantages such as hydrophilicity, water solubility, and affinity for metals and ions can be obtained. When the amount of the carboxylic acid is too small, the ion transportability is lowered; if the amount is too large, the flexibility of the separator film is reduced, and the separator film is likely to crack, and the thermal stability and the electrical stability are also reduced.

In the polymer compound of the present embodiment, active hydrogen of carbonyl acid generated from carboxylic acid reacts with a basic substance to form a salt, and the carboxylic acid forms a neutralized product. In the neutralization salt used in the present embodiment, a basic substance containing a monovalent or divalent metal and/or ammonia is preferably used as the basic substance from the viewpoint of ion transport properties of the separation membrane.

Examples of the basic substance that can be used in the present embodiment include: hydroxides of alkali metals such as ammonia, sodium hydroxide, potassium hydroxide, lithium hydroxide, calcium hydroxide, and magnesium hydroxide; carbonates of alkali metals such as sodium carbonate, potassium carbonate, calcium carbonate, and magnesium carbonate; acetates of alkali metals such as sodium acetate, potassium acetate, calcium acetate and the like; alkali metal phosphates such as trisodium phosphate, and the like. Among them, ammonia, lithium hydroxide, sodium hydroxide, and potassium hydroxide are preferable. In particular, ammonia, lithium hydroxide, and calcium carbonate are preferably used as the binder for the lithium ion secondary battery. The alkali substance containing a monovalent or divalent metal and/or ammonia may be used alone or in combination of two or more. The neutralized product may be prepared by using an alkaline substance such as a hydroxide containing an alkali metal or an alkaline earth metal such as sodium hydroxide or calcium hydroxide in combination as long as the neutralized product does not adversely affect the battery performance.

The degree of neutralization is not particularly limited, and it is generally desirable to use a substance that neutralizes 1 mole of carboxylic acid, preferably in the range of 0.1 to 1 mole, and more preferably in the range of 0.3 to 1 mole, in consideration of the ion transport property of the separation membrane. Such a neutralization degree is expected to contribute to improvement of low-temperature characteristics of the battery because the battery has excellent ion transport properties and low resistance. In addition, the flexibility of the separator can be maintained. That is, the amount of the carboxylate group is preferably 100/0.1 to 1/100 in a molar ratio with respect to the total monomer units constituting the polymer compound (copolymer). Further, it is more preferably 5/100 or less, and still more preferably 8/100 or less. Further, it is more preferably 100/0.3 or more, and still more preferably 100/0.5 or more.

In the present embodiment, the neutralization degree of the carboxylate may be as follows: the method of titration with a base, infrared spectroscopy, NMR spectroscopy, or the like is used, but in order to measure the degree of neutralization simply and accurately, titration with a base is preferably performed. The specific titration method is not particularly limited, and can be carried out by dissolving the compound in water containing a small amount of impurities such as ion-exchanged water and neutralizing the solution with an alkaline substance such as lithium hydroxide, sodium hydroxide or potassium hydroxide. The indicator for the neutralization point is not particularly limited, and an indicator such as phenolphthalein which indicates pH with a base can be used.

The introduction of the carboxylate group in the polymer compound of the present embodiment can be performed, for example, as follows: the reaction of the copolymer containing at least 1 selected from the group consisting of vinyl alcohol, vinyl acetal, and vinyl ester containing a carboxylic acid with the basic substance (the basic substance containing a monovalent or divalent metal and/or ammonia) as described above is performed. This reaction can be carried out according to a conventional method, but a method of carrying out the above reaction in the presence of water to obtain a neutralized product in the form of an aqueous solution is preferred because of its simplicity.

In the polymer compound of the present embodiment, the amount of the carboxylic acid modification is preferably about 1 to 35 mol%, more preferably about 5 to 20 mol%. Within such a range of the amount of carboxylic acid modification, the ionic conductivity is excellent and the electric resistance is suppressed to be low, and therefore, it is expected that the low-temperature characteristics of the battery can be improved. In addition, the flexibility of the separator can be maintained. The amount of carboxylic acid modification can be measured by titration with a base, by using an infrared spectrum or an NMR spectrum, or the like.

(separation film for nonaqueous electrolyte Battery)

The separator for a nonaqueous electrolyte battery of the present embodiment is a film containing the above-described polymer compound as a main component (formed of a polymer compound), and may contain a small amount of other components, additives, and the like as long as the effects of the present invention are not impaired, but is preferably a film made of the above-described polymer compound. The separator for a nonaqueous electrolyte battery of the present embodiment contains the above-described polymer compound in an amount of preferably 70% by mass or more, more preferably 75% by mass or more, and still more preferably 85% by mass or more, based on the entire components constituting the separator for a nonaqueous electrolyte battery. As the above-mentioned additives, various additives such as an antioxidant, an ultraviolet absorber, a lubricant, and an antiblocking agent may be added as necessary within a range (for example, 5% by mass or less) in which the effects of the present invention are not significantly inhibited.

The separator of the present embodiment is a porous membrane having pores through which ions in the nonaqueous electrolyte battery pass. The average pore diameter is usually 0.01 to 5 μm, preferably 0.02 to 3 μm, and more preferably 0.05 to 1 μm. If the pore diameter is too small, the liquid permeability of the electrolyte is poor, and the ion transport becomes difficult, resulting in high electric resistance. On the other hand, if the size is too large, the electrodes are likely to come into contact with each other, which causes a short circuit. The average pore diameter can be measured by the method described in examples. In the present embodiment, the average pore diameter of any one of the wide faces of the porous film is preferably within the above range, and more preferably, the average pore diameter of any one of the wide faces satisfies the above range.

The porosity of the separator of the present embodiment is usually 10 to 90% by weight, preferably 20 to 80% by weight, and particularly preferably 30 to 70% by weight. If the porosity is too low, the liquid permeability of the electrolyte is poor, and the transport of ions becomes difficult, resulting in high electrical resistance. On the other hand, if the porosity is too high, the strength of the film itself is lowered, and cracking is likely to occur, which causes short-circuiting. The porosity can be measured by the method described in examples.

The film thickness is not particularly limited, but is usually 1 to 100. mu.m, preferably 3 to 80 μm, and more preferably 5 to 50 μm. If the thickness is too large, the liquid permeability of the electrolyte is poor, and the ion transport becomes difficult, resulting in high resistance. On the other hand, if the thickness is too thin, the strength of the film itself is reduced, and the film is likely to be broken, which causes short-circuiting.

(method for producing separation film)

In the present embodiment, the method for producing a separation film comprising a polymer compound having a carboxylate group is not particularly limited as long as it can form a film, and can be produced, for example, by the following steps (1) to (5).

(1) Mixing an aqueous solution of a polymer compound having a carboxylate group with an inorganic powder, an organic material, an additive, or the like.

(2) And (3) a step of applying the aqueous solution obtained in the step (1) to a substrate to produce a sheet-like film.

(3) And (3) extracting and/or removing the inorganic powder and/or organic substance from the sheet-like film obtained in the step (2).

(4) And (4) rolling and drying the film obtained in the step (3) as required.

(5) And (4) peeling the film obtained in the step (4) from the substrate.

In the step (1), first, an aqueous solution (for example, a 10 wt% aqueous solution) containing the polymer compound of the present embodiment is prepared. The content of the inorganic powder, organic substance, additive, and the like is preferably 10 to 90 wt%, more preferably 20 to 80 wt%, and particularly preferably 30 to 70 wt% with respect to the polymer compound having a carboxylate group. If too small, the ion transport property is lowered, and therefore the resistance becomes high; if the amount is too large, the strength of the film itself is reduced, and the film is likely to be broken, and may not function as a separation film.

The inorganic powder used for producing the separation membrane containing a polymer compound of the present embodiment is preferably an inorganic fine powder, and specific examples thereof include silica, mica, talc, titanium oxide, alumina, ceramics, barium sulfate, synthetic zeolite, and the like, and these may be used singly or in combination of two or more kinds. The size of the inorganic powder may be such that the average pore diameter of the pores in the separation membrane is within the above range.

The organic material used for producing the separation membrane containing a polymer compound according to the present embodiment is not particularly limited as long as it is soluble in water and also soluble in an organic solvent such as alcohols, halogenated hydrocarbons, or aliphatic hydrocarbons, and polyethylene glycol is preferable from the viewpoint of cost and availability.

In addition to the copolymer having a polymer compound, the inorganic fine powder, and/or the organic material of the present embodiment, the additives described above may be added together within a range in which the effect of the present invention is not significantly suppressed.

The substrate used for coating is not particularly limited, and examples thereof include PET (polyethylene terephthalate), PTFE (polytetrafluoroethylene), PVC (polyvinyl chloride), and PE (polyethylene). In addition, a release agent or the like may be used to improve releasability.

(2) In the step (1), a sheet-like film is formed by using the aqueous solution obtained in the step (1) by a method such as a doctor blade method, a dip coating method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, a dipping method, a brush coating method, or the like. The coating amount may be set so that the thickness of the obtained separation film is within the above range.

(3) In the step (2), the organic substance and/or inorganic powder added in the step (1) is extracted and/or removed from the sheet-like film obtained in the step (2). Specifically, a method of extracting and/or removing the organic substance and/or the inorganic powder using a solvent capable of dissolving the organic substance and/or the inorganic powder and capable of insolubilizing the polymer compound of the present embodiment is exemplified. The solvent may be appropriately selected depending on the kind of the inorganic powder and/or organic substance, and examples thereof include alcohols, halogenated hydrocarbons, and aliphatic hydrocarbons.

(4) In the step (3), the sheet-like film obtained in the step (3), that is, the sheet-like film after extraction and/or removal, may be subjected to rolling and/or drying and removal of the solvent and the dissolving medium, if necessary. The method for drying the solvent (water) is not particularly limited, and examples thereof include: ventilating and drying by utilizing warm air, hot air and low-humidity air; vacuum drying; and drying with irradiation rays such as infrared rays, far infrared rays, and electron beams. The drying conditions may be adjusted so that the solvent is removed as quickly as possible within a speed range in which the film is not cracked due to stress concentration. In addition, the dried film may be rolled to improve surface smoothness. The rolling method may be a die pressing method or a roll pressing method.

(5) In the step, the film is peeled off from the substrate. Either of the step (5) and the step (4) may be performed first.

(nonaqueous electrolyte Battery)

The nonaqueous electrolyte battery of the present embodiment is characterized in that: comprising the above-mentioned separation membrane.

Examples of the nonaqueous electrolyte battery include a lithium ion battery, a sodium ion battery, a lithium sulfur battery, and an all-solid-state battery.

The nonaqueous electrolyte battery generally includes a negative electrode, a positive electrode, and an electrolytic solution in addition to the separator.

As the negative electrode, a negative electrode generally used for a nonaqueous electrolyte battery such as a lithium ion secondary battery can be used without particular limitation. For example, graphite, hard carbon, Si-based oxide, or the like can be used as the negative electrode active material. The negative electrode can be obtained by mixing the negative electrode active material, the conductive auxiliary described above, and a binder such as SBR, NBR, acrylic rubber, hydroxyethyl cellulose, carboxymethyl cellulose, polyvinylidene fluoride, or polyvinyl alcohol in water or the solvent having a boiling point of 100 ℃ or more and 300 ℃ or less at normal pressure to prepare a slurry for the negative electrode, coating the slurry for the negative electrode on a negative electrode current collector such as a copper foil, and drying the solvent.

As the positive electrode, a positive electrode generally used for a nonaqueous electrolyte battery such as a lithium ion secondary battery can be used without particular limitation. For example, as the positive electrode active material, there can be used: TiS₂、TiS₃Amorphous MoS₃、Cu₂V₂O₃Amorphous V₂O-P₂O₅、MoO₃、V₂O₅、V₆O₁₃And transition metal oxides; LiCoO₂、LiNiO₂、LiMnO₂、LiMn₂O₄And lithium-containing composite metal oxides. The positive electrode can be prepared by mixing the positive electrode active material, the conductive auxiliary agent described above, and a binder such as SBR, NBR, acrylic rubber, hydroxyethyl cellulose, carboxymethyl cellulose, polyvinylidene fluoride, or polyvinyl alcohol in water or a solvent having a boiling point of 100 ℃ or more and 300 ℃ or less at normal pressure to prepare a slurry for a positive electrode, applying the slurry for a positive electrode to a positive electrode current collector such as aluminum, and drying the solvent.

In the nonaqueous electrolyte battery of the present embodiment, an electrolyte solution in which an electrolyte is dissolved in a solvent may be used. The electrolyte solution may be in a liquid state or a gel state as long as it can be used for a nonaqueous electrolyte battery such as a normal lithium ion secondary battery, and an electrolyte solution that functions as a battery may be appropriately selected depending on the kind of the negative electrode active material and the positive electrode active material. As a specific electrolyte, for example, any of conventionally known lithium salts can be used, and examples thereof include: LiClO₄、LiBF₆、LiPF₆、LiCF₃SO₃、LiCF₃CO₂、LiAsF₆、LiSbF₆、LiB₁₀Cl₁₀、LiAlC₁₄、LiCl、LiBr、LiB(C₂H₅)₄、CF₃SO₃Li、CH₃SO₃Li、LiCF₃SO₃、LiC₄F₉SO₃、Li(CF₃SO₂)₂And lithium N, lower aliphatic carboxylates.

The solvent (electrolyte solvent) for dissolving the electrolyte is not particularly limited. Specific examples thereof include: carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, and diethyl carbonate; lactones such as γ -butyrolactone; ethers such as trimethyl orthoformate, ethylene glycol dimethyl ether, diethyl ether, ethylene glycol diethyl ether, tetrahydrofuran, and 2-methyltetrahydrofuran; sulfoxides such as dimethyl sulfoxide; oxolanyls such as 1, 3-dioxolane and 4-methyl-1, 3-dioxolane; nitrogen-containing compounds such as acetonitrile and nitromethane; organic acid esters such as methyl formate, methyl acetate, ethyl acetate, butyl acetate, methyl propionate, and ethyl propionate; inorganic acid esters such as triethyl phosphate, dimethyl carbonate, and diethyl carbonate; diethylene glycol dimethyl ethers; triethylene glycol dimethyl ethers; sulfolanes; oxazolidinones such as 3-methyl-2-oxazolidinone; sultones such as 1, 3-propane sultone, 1, 4-butane sultone, and naphthalene sultone, and these may be used alone or in combination of two or more. When a gel-like electrolyte is used, a nitrile polymer, an acrylic polymer, a fluorine polymer, an alkylene oxide polymer, or the like may be added as a gelling agent.

In particular, by using a polymer compound having a copolymer containing vinyl alcohol, vinyl acetal, and/or vinyl ester, which is the same material as the separator of the present embodiment, as a binder used for the negative electrode and the positive electrode, it is possible to prevent the electrode position from shifting from the separator and the active material from falling off, and thus it is possible to expect improvement in productivity.

The method for producing the nonaqueous electrolyte battery of the present embodiment is not particularly limited, and the following production method can be exemplified. That is, the negative electrode and the positive electrode are stacked with the separator of the present invention interposed therebetween, and are wound or bent in accordance with the battery shape and placed in a battery container, and an electrolyte solution is injected and sealed. The shape of the battery may be any of known coin, button, sheet, cylinder, square, flat, and the like.

The nonaqueous electrolyte battery of the present embodiment is a battery in which heat resistance (safety) and battery characteristics are improved at the same time, and is useful for various applications. For example, the battery is very useful as a battery for a mobile terminal which is required to be small, thin, light, and high in performance.

The present invention discloses the above-described embodiments, and the main techniques thereof are summarized as follows.

According to this configuration, it is considered that: a separation membrane for a nonaqueous electrolyte battery having ion-transporting properties can be provided, and battery characteristics can be improved.

In the above separator for a nonaqueous electrolyte battery, it is preferable that: the polymer compound has a copolymer containing at least 1 selected from the group consisting of vinyl alcohol, vinyl acetal, and vinyl ester.

In the separator for a nonaqueous electrolyte battery, it is preferable that: the separator for a nonaqueous electrolyte battery is a porous film, and more preferably: the porosity of the separator for a nonaqueous electrolyte battery is 10% or more. Accordingly, it is considered that: the liquid permeability of the electrolyte of the separation membrane becomes good, so that the transmission of ions becomes easy, so that the resistance can be suppressed.

Another aspect of the present invention relates to a nonaqueous electrolyte battery characterized by comprising: the separator for a nonaqueous electrolyte battery described above. According to this configuration, a nonaqueous electrolyte battery which is safe, has a long life, and has excellent battery characteristics can be provided.

Examples

Examples of the present invention will be described below, but the present invention is not limited to these examples.

(example 1)

640g of vinyl acetate, 240.4g of methanol and 0.88g of acrylic acid were charged into a reactor equipped with a stirrer, a reflux condenser, an argon inlet and an initiator addition port, and then the inside of the system was replaced with nitrogen for 30 minutes while bubbling nitrogen. Separately, a methanol solution (concentration: 20 wt%) of acrylic acid was prepared as a sequential addition solution of a comonomer (hereinafter, referred to as a delayed solution), and argon bubbling was performed for 30 minutes. After the temperature rise of the reactor was started, 0.15g of 2, 2' -azobisisobutyronitrile was added to start the polymerization when the internal temperature reached 60 ℃. During the polymerization, the prepared delay solution was added dropwise to the system so that the monomer composition (molar ratio of vinyl acetate to acrylic acid) in the polymerization solution was kept constant. After polymerization at 60 ℃ for 210 minutes, cooling was carried out to stop the polymerization. Subsequently, unreacted monomers were removed while adding methanol at 30 ℃ under reduced pressure to obtain a methanol solution of acrylic acid-modified polyvinyl acetate. Then, methanol was added to the methanol solution of polyvinyl acetate to adjust the concentration to 25% by weight, and 20.4g of a methanol solution of sodium hydroxide (concentration: 18.0% by weight) and 79.6g of methanol were added to 400g of the methanol solution of polyvinyl acetate, followed by saponification at 40 ℃. After adding sodium hydroxide methanol solution for several minutes, a gelled product was formed, and therefore, this was pulverized by a pulverizer and left to stand at 40 ℃ for 60 minutes to be saponified. The resultant pulverized gel was repeatedly washed with methanol and then vacuum-dried at 40 ℃ overnight, thereby synthesizing the objective copolymer. The copolymerization mode is random polymerization. The carboxylic acid modification amount of the obtained copolymer was 5.0 mol%. Further, 0.5 equivalent of lithium hydroxide was added to the carboxylic acid unit in the polymer, thereby preparing a neutralized salt of the above copolymer.

< measurement of melting Point of Polymer Compound having carboxylate group >

Differential scanning calorimetry was performed using a thermal analyzer (manufactured by YAMATO science). The melting point was 220 ℃ as a result of measurement at a measurement temperature range of 50 ℃ to 1000 ℃ and a temperature rise rate of 10 ℃/min. The results are shown in table 1 below.

< preparation of coating liquid for separation film >

To 100g of a 10 wt% aqueous solution of the vinyl alcohol/acrylic acid copolymer obtained above, 0.5 equivalent of lithium hydroxide to the carboxylic acid units in the polymer was added, and the mixture was heated and stirred at 80 ℃ for 2 hours. Then, the mixture was cooled to room temperature, and polyethylene glycol (molecular weight 600, Wako pure chemical industries, Ltd.) was added in an amount of 50 wt% in terms of solid content to prepare a separator coating solution (a coating solution of a neutralized salt of a copolymer of vinyl alcohol and an ethylenically unsaturated carboxylic acid) having a solid content concentration of 10 wt% in an aqueous solution.

< preparation of separation film >

The separator coating solution prepared above was applied to a fluororesin film (manufactured by ESCO corporation) as a base material by using a bar coater (T101, manufactured by sontail industries). Before drying, the polyethylene glycol was extracted by dipping in isopropyl alcohol (IPA) together with the substrate. The separator dried at room temperature was peeled from the substrate, and then vacuum-dried at room temperature, and used as a separator. The thickness of the resulting separation film was 31 μm.

The porosity and pore diameter of the obtained separation membrane were determined by the following methods, and the results are shown in table 1.

< calculation of void fraction >

The thickness and mass of the test piece punched out to a specified size (17 mm) were measured, and the porosity of the porous film was calculated according to the following equation.

Porosity {1- (theoretical volume of spacer/apparent volume of spacer) } × 100

Theoretical volume of spacer (mass of spacer)/(theoretical density)

Apparent volume of spacer (thickness) x (spacer area)

Here, the theoretical density generally refers to the specific gravity of the polymer.

< pore diameter >

The diameters of the 100 openings observed in the scanning electron micrograph were averaged and calculated. As the observation surface, a wide-mouth surface located on the opposite side of the surface in contact with the substrate when the porous film was produced was observed.

< production of negative electrode for Battery >

The electrode slurry was prepared as follows: an electrode coating slurry was prepared by charging 96 parts by weight of artificial graphite (FSN-1, manufactured by sequoia china) as an active material for a negative electrode into a special container, 2 parts by weight of an SBR latex aqueous solution (TRD2001, manufactured by JSR corporation, 48.3 wt%) as a binder in terms of solid content, 1 part by weight of CMC-Na (sodium carboxymethylcellulose; CelogenBSH-6, manufactured by first industrial pharmaceutical corporation, 10 wt%) as a thickener in terms of solid content, and 1 part by weight of Super-P (manufactured by timal corporation) as a conductive aid (conductivity-imparting agent) in terms of solid content, and kneading the mixture with a planetary mixer (ARE-250, manufactured by shinky). The composition ratio of the active material to the binder in the slurry is graphite powder in terms of solid components: conductive auxiliary agent: SBR: CMC-Na is 96: 1: 2: 1 (weight ratio).

< production of negative electrode for Battery >

The obtained slurry was coated on a copper foil (CST8G, manufactured by fuda foil powder industries, ltd.) as a current collector by a bar coater (T101, manufactured by songi industries, ltd.), primarily dried at room temperature (24.5 ℃) and then subjected to a rolling treatment by a roll press (manufactured by baoquan industries, ltd.). Then, the electrode was punched out to give a battery electrode (phi 14mm), and then subjected to secondary drying at 140 ℃ for 3 hours under reduced pressure to give an electrode for a coin battery.

< preparation of Battery >

The coated electrode for a battery obtained above was transferred to a glove box (manufactured by Kabushiki Kaisha) under an argon atmosphere. A lithium metal foil (thickness 0.2mm, 16mm) was used as the positive electrode. A coin cell (2032 type) was produced by using the separator obtained in the above as a spacer and injecting a mixed solvent system (1M-LiPF6, EC/EMC 3/7 vol%, VC2 wt%) of lithium hexafluorophosphate (LiPF6) added with Vinylene Carbonate (VC) to Ethylene Carbonate (EC) and Ethyl Methyl Carbonate (EMC) as an electrolyte solution.

< measurement of resistance >

Using the coin cell manufactured as described above, ac impedance measurement was performed using an impedance measuring device (potentiostat/galvanostat (SI1287, manufactured by SOLARTRON corporation)) and a frequency response analyzer (FRA, manufactured by power transmission force corporation). The coin cells were placed in a thermostatic bath at 25 ℃ and-20 ℃ and the impedance curve of the test cells was measured by the alternating current impedance method at a frequency of 0.01-106Hz and a voltage amplitude of 10 mV. For the measured impedance curve, on a complex plane (koll diagram) designated by the components of resistance (Z axis, real axis) and capacitance (Z axis, imaginary axis), the diameter of the arc-shaped portion when represented by a line including the arc-shaped portion was calculated as the interface resistance (Rin) with the separation membrane, and the value of the component axis of resistance (Z axis, real axis) when the component axis of capacitance (Z axis, imaginary axis) was 0 was calculated as the solution resistance (Rso 1). The results are shown in Table 1.

(example 2)

370g of water and 100g of commercially available polyvinyl alcohol (M115, manufactured by Kokura, Ltd.) were charged into a reactor equipped with a stirrer, a reflux condenser, a nitrogen gas inlet, and an initiator addition port, and the polyvinyl alcohol was dissolved by heating at 95 ℃ with stirring, and then cooled to room temperature. To this aqueous solution, 0.5 equivalents (N) of sulfuric acid was added to bring the pH to 3.0. After 9.9g of acrylic acid was added thereto with stirring, the resulting aqueous solution was heated to 70 ℃ while bubbling nitrogen gas therethrough, and further, nitrogen gas was bubbled at 70 ℃ for 30 minutes, thereby carrying out nitrogen substitution. After the nitrogen substitution, 80.7g of an aqueous potassium persulfate solution (concentration: 2.5% by weight) was added dropwise to the aqueous solution over 1.5 hours. After all the components were added, the temperature was raised to 75 ℃ and further stirred for 1 hour, and then the mixture was cooled to room temperature. The membrane was frozen with liquid nitrogen, pulverized with a centrifugal pulverizer, and vacuum-dried at 40 ℃ overnight, whereby the objective copolymer was obtained. The copolymerization mode is block polymerization. The modification amount of the ethylenically unsaturated carboxylic acid of the obtained copolymer was 6.0 mol%. Further, 0.5 equivalent of lithium hydroxide to the carboxylic acid unit in the polymer was added, thereby preparing a neutralized salt of the above copolymer.

The melting point was measured by the same method as in example 1. A separator coating solution was prepared at a solid content concentration of 10 wt% in the aqueous solution, and a separator and a battery were prepared in the same manner as in example 1. The thickness of the obtained separation film was 30 μm. The porosity and pore diameter were determined by the same method as in example 1, and the resistance was measured. The results are shown in table 1 below.

(example 3)

100g of commercially available polyvinyl alcohol (28-98 s, manufactured by Korea corporation) was irradiated with an electron beam (30 kGy). Then, 33.4g of acrylic acid and 466.6g of methanol were fed into a reactor equipped with a stirrer, a reflux condenser, a nitrogen inlet and a port for adding particles, and the inside of the system was replaced with nitrogen for 30 minutes while bubbling nitrogen. 100g of polyvinyl alcohol after electron irradiation was added thereto, and the mixture was heated and refluxed for 300 minutes while being stirred to disperse the particles in the solution, thereby carrying out graft polymerization. Then, the particles were recovered by filtration and dried under vacuum at 40 ℃ overnight, whereby the objective copolymer was obtained. The copolymerization mode is graft polymerization. The modification amount of the ethylenically unsaturated carboxylic acid of the obtained copolymer was 7.3 mol%. Further, 0.5 equivalent of lithium hydroxide to the carboxylic acid unit in the polymer was added, thereby preparing a neutralized salt of the above copolymer.

(example 4)

The synthesis of a target copolymer was carried out in the same manner as in example 2 except that 20g of acrylic acid and 150g of an aqueous potassium persulfate solution (concentration: 2.5% by weight) were added. The copolymerization mode is block polymerization. The carboxylic acid modification amount of the obtained copolymer was 12.0 mol%. Further, 0.5 equivalent of lithium hydroxide to the carboxylic acid unit in the polymer was added, thereby preparing a neutralized salt of the above copolymer.

The melting point was measured by the same method as in example 1. A separator coating solution was prepared at a solid content concentration of 10 wt% in the aqueous solution, and a separator and a battery were prepared in the same manner as in example 1. The thickness of the resulting separation film was 31 μm. The porosity and pore diameter were determined by the same method as in example 1, and the resistance was measured. The results are shown in table 1 below.

(example 5)

A neutralized salt was prepared in the same manner as in example 4, except that 02 equivalents of lithium hydroxide and 0.3 equivalents of sodium hydroxide were added to 100g of the 10 wt% aqueous solution of the vinyl alcohol-acrylic acid copolymer prepared in example 4, based on the carboxylic acid units in the polymer.

The melting point was measured by the same method as in example 1. A separator coating solution was prepared at a solid content concentration of 10 wt% in the aqueous solution, and a separator and a battery were prepared in the same manner as in example 1. The thickness of the resulting separation film was 29 μm. The porosity and pore diameter were determined by the same method as in example 1, and the resistance was measured. The results are shown in table 1 below.

(example 6)

A neutralized salt of a copolymer was prepared in the same manner as in example 4, except that 1.0 equivalent of lithium hydroxide was added to the carboxylic acid unit in the polymer.

(example 7)

A neutralized salt of a copolymer was prepared in the same manner as in example 4, except that 0.2 equivalents of lithium hydroxide was added to the carboxylic acid units in the polymer.

(example 8)

100g of commercially available polyvinyl alcohol (Elvanol 71-30, made by Korea corporation) was irradiated with an electron beam (30 kGy). Then, 25g of methacrylic acid and 475g of methanol were fed into a reactor equipped with a stirrer, a reflux condenser, a nitrogen inlet and a particle addition port, and the inside of the system was replaced with nitrogen for 30 minutes while bubbling nitrogen. 100g of polyvinyl alcohol after electron beam irradiation was added thereto, and the mixture was heated and refluxed for 300 minutes while being stirred to disperse the particles in the solution, thereby graft-polymerizing. Then, the particles were recovered by filtration and dried under vacuum at 40 ℃ overnight, whereby the objective copolymer was obtained. The copolymerization mode is graft polymerization. The modification amount of the ethylenically unsaturated carboxylic acid of the obtained copolymer was 7.0 mol%. Further, 0.5 equivalent of lithium hydroxide to the carboxylic acid unit in the polymer was added, thereby preparing a neutralized salt of the copolymer.

(example 9)

The synthesis of the objective copolymer was carried out in the same manner as in example 5 except that 100g of methacrylic acid and 400g of methanol were added. The copolymerization mode is graft polymerization. The modification amount of the ethylenically unsaturated carboxylic acid of the obtained copolymer was 34.0 mol%. Further, 0.5 equivalent of lithium hydroxide to the carboxylic acid unit in the polymer was added, thereby preparing a neutralized salt of the copolymer.

Comparative example 1

A copolymer was obtained in the same manner as in example 1, except that lithium hydroxide was not added. The copolymerization mode is random polymerization. Next, the melting point was measured by the same method as in example 1. A separator coating solution having a solid content concentration of 10 wt% was prepared in the same manner as in example 1, and a separator and a battery were prepared in the same manner as in example 1. The thickness of the obtained separation film was 30 μm. The porosity and pore diameter were determined by the same method as in example 1, and the resistance was measured. The results are shown in table 1 below.

Comparative example 2

A copolymer was obtained in the same manner as in example 2, except that lithium hydroxide was not added. Next, the melting point was measured by the same method as in example 1. Then, a separator coating solution was prepared in the same manner as in example 1, with the solid content concentration of the aqueous solution being 10 wt%, and a separator and a battery were prepared in the same manner as in example 1. The thickness of the obtained separation film was 30 μm. The porosity and pore diameter were determined by the same method as in example 1, and the resistance was measured. The results are shown in table 1 below.

Comparative example 3

A copolymer was obtained in the same manner as in example 3, except that lithium hydroxide was not added. The copolymerization mode is block polymerization. Next, the melting point was measured by the same method as in example 1. Then, a separator coating solution was prepared in the same manner as in example 1, with the solid content concentration of the aqueous solution being 10 wt%, and a separator and a battery were prepared in the same manner as in example 1. The thickness of the resulting separation film was 29 μm. The porosity and pore diameter were determined by the same method as in example 1, and the resistance was measured. The results are shown in table 1 below.

Comparative example 4

A separator coating solution was prepared in the same manner as in example 1 except that commercially available polyvinyl alcohol (28-98 s, manufactured by Korea Co., Ltd., saponification degree: 98, block polymerization) was used as the polymer compound, and a separator and a battery were prepared in the same manner as in example 1, except that the solid content concentration of the aqueous solution was 10 wt%. The thickness of the obtained separation film was 30 μm. The porosity and pore diameter were determined by the same method as in example 1, and the resistance was measured. The melting point of polyvinyl alcohol was measured in the same manner as in example 1. The results are shown in table 1 below.

Comparative example 5

A battery was produced in the same manner as in example 1 except that a commercially available polypropylene-based separator (Celgard #2400, film thickness: 25 μm, manufactured by POLYPORE) was used as the separation film. The porosity and pore diameter were determined by the same method as in example 1, and the resistance was measured. In addition, the melting point of Celgard was measured by the same method as in example 1. The results are shown in table 1 below.

(examination)

The following are explicitly stated: in examples 1 to 9, since the polymer compound constituting the separation film has a carboxylate group, the resistance was reduced even at low temperatures. On the other hand, the following are clear: the polymers containing carboxylic acid but no salt (comparative examples 1 to 3) and the polymer containing no carboxylic acid itself (comparative example 4) had high electric resistance both at normal temperature and at low temperature. The following is also clear: the separator of the present invention exhibited superior resistance characteristics when compared to the separator of one of the common parts (comparative example 5). The reason is presumed to be: the polymer compound contains a carboxylate group to facilitate ion transport in the separation membrane. The following is also clear: the compound shown in example is also superior in heat resistance to the general-purpose spacer shown in comparative example 5.

The application is based on Japanese patent application laid-open at 7, 24 and 2017, namely application No. 2017-142571, and the content of the application is included in the application.

The present invention has been described in detail with reference to specific examples and the like for the purpose of illustrating the invention, but it should be understood that those skilled in the art can easily modify and/or improve the above-described embodiments. Therefore, a modified embodiment or an improved embodiment that a person skilled in the art carries out is to be construed as being included in the scope of the claims as long as the modified embodiment or the improved embodiment does not depart from the scope of the claims described in the claims.

Industrial applicability

The present invention has wide industrial applicability in the technical field of nonaqueous electrolyte batteries such as lithium ion secondary batteries.

Claims

1. A separation membrane for a nonaqueous electrolyte battery, characterized by comprising:

a polymer compound having a carboxylate group in a molecule.

2. The separation membrane for a nonaqueous electrolyte battery according to claim 1, characterized in that:

the polymer compound has a copolymer containing at least 1 selected from the group consisting of vinyl alcohol, vinyl acetal, and vinyl ester.

3. The separation membrane for a nonaqueous electrolyte battery according to claim 1 or 2, characterized in that:

the separator for a nonaqueous electrolyte battery is a porous film.

4. The separation membrane for a nonaqueous electrolyte battery according to claim 3, characterized in that:

the porosity of the separator for a nonaqueous electrolyte battery is 10% or more.

5. A nonaqueous electrolyte battery characterized by comprising:

the separator for a nonaqueous electrolyte battery according to any one of claims 1 to 4.