WO2024161673A1 - Electrode for nonaqueous electrolyte secondary battery and nonaqueous electrolyte secondary battery - Google Patents

Abstract

The present invention provides an electrode for a nonaqueous electrolyte secondary battery and a nonaqueous electrolyte secondary battery that can suppress a corrosion reaction in an aluminum current collecting layer and can further suppress decreases in battery capacity and an output characteristic upon employment of a water-based positive electrode manufacturing process. The present invention provides an electrode for a nonaqueous electrolyte secondary battery, the electrode including an electrode mixture layer present on the aluminum current collecting layer. This electrode is characterized in that an electrode mixture forming the electrode mixture layer includes an active material, a binder, and a protective film forming agent, the active material is capable of electrochemically intercalating and de-intercalating alkali metal ions or electrochemically alloying and dealloying alkali metal ions, the protective film forming agent includes an alkali silicate, and a protective film formed by the protective film forming agent is present on the surface of the aluminum current collecting layer.

Description

Electrode for non-aqueous electrolyte secondary battery and non-aqueous electrolyte secondary battery

The present invention relates to an electrode for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery.

Electric double-layer capacitors, lithium-ion secondary batteries, sodium-ion secondary batteries and other power storage devices have been developed as electrochemical devices to be installed in mobile phones, electric vehicles and the like. Of these, lithium-ion secondary batteries enable devices to be made smaller and lighter, have good charging and discharging efficiency and have high energy density, and are therefore used, for example, as power sources for mobile devices, notebook PCs, home appliances and even hybrid and electric vehicles. They are also attracting new attention as power storage devices for storing generated electricity when combined with natural energy systems such as solar and wind power generation.

The electrodes that make up a lithium-ion secondary battery are made up of active materials that absorb and release lithium ions to input and output energy, conductive assistants to ensure electrical conductivity within the electrode, binders to bond the active materials and conductive agents, and current collecting layers to connect to external circuits outside the battery. The characteristics of lithium-ion secondary batteries depend heavily on the electrodes, and are greatly influenced by the characteristics of each material itself and how the materials are combined.

In recent years, the uses of lithium-ion secondary batteries have expanded, and the market is expanding not only for electric vehicles but also as stationary storage batteries for disaster prevention and power business use, and there is a growing demand for batteries that not only have higher performance but also lower costs. In particular, to reduce the cost of secondary batteries, it is necessary to review not only the materials used to make the batteries but also the battery manufacturing process, and much research has been conducted on this issue.

For example, lithium transition metal oxides with a high nickel (Ni) content have been investigated in recent years as the positive electrode active material for lithium-ion secondary batteries in order to increase capacity. Increasing the capacity of the positive electrode active material improves the energy density per weight and reduces the amount of material used, making it possible to reduce battery costs. Meanwhile, electrodes are manufactured by turning the above-mentioned active material, conductive agent, and binder into a paint (slurry) using water or an organic solvent, and coating the positive electrode on an aluminum current collector layer, and the negative electrode on a copper or aluminum current collector layer. In this case, an organic solvent called N-methyl-N-pyrrolidone (NMP) is used to make the slurry for the positive electrode, and the final battery cost is affected not only by the cost of the organic solvent itself but also by the cost of recovery and purification.

In response to these issues, attempts have been made to reduce costs by replacing organic solvents with water in the manufacture of positive electrodes. However, when the positive electrode active material is dispersed in water, lithium ions are eluted from the active material into the water, and the pH of the slurry becomes strongly alkaline, at 10 or higher. When such a slurry is applied to an aluminum current collecting layer, a corrosion reaction between the aluminum and hydroxide ions progresses, and hydrogen gas is generated from the aluminum surface. As a result, hydrogen gas is mixed into the coating layer as air bubbles, which makes it impossible to obtain a smooth electrode. Furthermore, in such electrodes, the areas where the air bubbles were mixed in become voids after drying, and the electronic path in the electrode mixture layer is interrupted, increasing the battery resistance.

In order to overcome the above-mentioned problems, Patent Document 1 examines the addition of a neutralizing agent to the high pH slurry to neutralize it to a pH level at which corrosion of the aluminum current collecting layer does not occur.

However, these techniques for controlling the slurry pH through neutralization reactions induce the elution of lithium ions from the positive electrode active material, resulting in a decrease in battery capacity. In addition, it is necessary to add a neutralizing agent to the electrode mixture at a weight ratio of 1% or more, which also contributes to a decrease in energy density. Therefore, the above-mentioned slurry pH control through neutralization reactions has not been sufficiently studied to convert the organic solvent used in positive electrode production to an aqueous system.

International Publication No. 2016/052715

The present invention was developed in consideration of the above problems, and its purpose is to solve the problem of suppressing the corrosion reaction of the aluminum current collecting layer in the aqueous cathode manufacturing process, and further suppressing the decrease in battery capacity and output characteristics.

The inventors conducted extensive research to solve the above problems and discovered that by applying an aqueous slurry containing an alkaline silicate to the aluminum current collecting layer, it is possible to form a protective film on the aluminum current collecting layer that is corrosion-resistant to the high pH aqueous slurry, thereby preventing a decrease in battery capacity and output characteristics, and thus completing the present invention.

In order to achieve the above object, the present invention provides an electrode for a non-aqueous electrolyte secondary battery, comprising an electrode mixture layer on an aluminum current collecting layer,
The electrode mixture constituting the electrode mixture layer contains an active material, a binder, and a protective film forming agent,
the active material is an active material capable of electrochemically absorbing and desorbing alkali metal ions, or an active material capable of electrochemically alloying and dealloying alkali metal ions,
The protective film forming agent includes an alkali silicate,
The protective film formed by the protective film forming agent is present on the surface of the aluminum current collecting layer.

In the electrode for a non-aqueous electrolyte secondary battery of the present invention, it is preferable that the protective film forming agent contains at least an alkali silicate represented by M ₂ O.nSiO ₂ , where M contains at least one of Li, Na, and K, and n is 1.6 or more and 8.0 or less.

In the electrode for a non-aqueous electrolyte secondary battery of the present invention, the weight ratio of the protective film forming agent in the electrode mixture is preferably in the range of more than 0.1% and not more than 1%.

In the electrode for a nonaqueous electrolyte secondary battery of the present invention, it is preferable that the protective film on the surface of the aluminum current collecting layer contains at least a Si—O bond having a bond energy in the range of 102 to 107 eV in a Si2p3 _/2 spectrum, as determined by X-ray photoelectron spectroscopy (XPS) analysis using an X-ray source of MgKα rays.

In the electrode for a non-aqueous electrolyte secondary battery of the present invention, the aluminum current collecting layer is preferably pure aluminum or an alloy of aluminum and one or more additive elements.

In the electrode for a non-aqueous electrolyte secondary battery of the present invention, the active material is a lithium oxide represented by Li _x MO ₂ , LiM ₂ O ₄ , or Li ₄ M ₅ O ₁₂ (x is 1 to 2, and M is a transition metal) containing at least one transition metal;
A lithium polyanion compound represented by LiMPO ₄ (M is a transition metal) and containing at least one transition metal;
a lithium inorganic compound selected from a lithium sulfur compound, a lithium selenium compound, and a lithium fluoride compound;
A sodium oxide represented by _NaMO2 or _Na2MO3 (M is _a transition metal) and containing at least one transition metal;
a sodium polyanion compound represented by NaM ₂ (XO ₄ ) ₃ , NaMPO ₄ or NaM(SO ₄ ) ₂ (wherein M is a transition metal and X is one of sulfur, phosphorus and silicon) and containing at least one transition metal;
a sodium Prussian blue analogue compound represented by Na ₂ M[M′(CN) ₆ ] (M and M′ are transition metals) and containing at least one transition metal;
It is preferable that the compound is at least one selected from the group consisting of:

The non-aqueous electrolyte secondary battery of the present invention includes a positive electrode and a negative electrode, the positive electrode and the negative electrode being separated by an insulating layer, and at least one of the positive electrode and the negative electrode being an electrode for the non-aqueous electrolyte secondary battery of the present invention.

The present invention makes it possible to manufacture electrodes in an aqueous process using positive and negative electrode active material containing alkaline ions such as lithium and sodium while suppressing corrosion of the aluminum current collecting layer. Furthermore, even though the electrodes manufactured in an aqueous process are produced, it is possible to suppress the decrease in battery capacity and output characteristics. A non-aqueous electrolyte secondary battery using such electrodes can be provided at a lower cost than conventional batteries.

FIG. 1 is a set of photographs showing the results of visual observation of the surfaces of electrode mixture layers of (A) Comparative Example 2 and (B) Example 1, (C) Example 2, and (D) Example 3 produced based on the present invention. FIG. 2 is a photograph showing the results of visual observation of the surface of the electrode mixture layer of (E) Comparative Example 3, and (F) Example 4, (G) Example 5, and (H) Example 6 produced based on the present invention. FIG. 3 is a set of photographs showing the results of visual observation of the surfaces of the electrode mixture layers of (I) Comparative Example 4, and (J) Example 7, (K) Example 8, and (L) Example 9 produced based on the present invention. FIG. 4 (M) is a photograph showing the results of visual observation of the surface of the electrode mixture layer in Comparative Example 1. FIG. 5 shows SEM images of the surfaces of the electrode mixture layers of (A) Comparative Example 2, (B) Example 1, (C) Example 2, and (D) Example 3. FIG. 6 shows SEM images of the electrode mixture layer surfaces of (E) Comparative Example 3, (F) Example 4, (G) Example 5, and (H) Example 6. FIG. 7 shows SEM images of the electrode mixture layer surfaces of (I) Comparative Example 4, (J) Example 7, (K) Example 8, and (L) Example 9. FIG. 8 is an SEM observation image of the surface of the electrode mixture layer of Comparative Example 1 (M). FIG. 9 shows the results of XPS measurement of Si2p _3/2 spectrum on the surface of the aluminum current collecting layer in Comparative Example 1, Comparative Example 2, Example 1, and Example 1 after charging and discharging, and in Example 2 and Example 3. FIG. 10 shows the results of XPS measurement of Si2p _3/2 spectrum on the aluminum current collecting layer surface of Comparative Example 1, Comparative Example 3, Example 4, and Example 4 after charging and discharging, and of Examples 5 and 6. FIG. 11 shows the results of XPS measurement of Si2p _3/2 spectrum on the surface of the aluminum current collecting layer of Comparative Example 1, Comparative Example 4, Example 7, and Example 7 after charging and discharging, and of Examples 8 and 9.

The following provides a detailed explanation of the embodiments of the present invention, but the scope of the present invention is not limited to these explanations, and other than the examples below, appropriate modifications and implementations can be made without impairing the spirit of the present invention. Unless otherwise specified in this specification, "A to B" indicating a numerical range means "A or more, B or less." Furthermore, "mass" and "weight," "mass %" and "weight %" are treated as synonyms.

The positive and negative electrodes of the nonaqueous electrolyte secondary battery of the present invention contain a protective film forming agent, an active material capable of electrochemically absorbing and desorbing alkali ions, or an active material capable of electrochemically alloying and dealloying alkali metal ions, and a binder. The protective film forming agent contains an alkali silicate, and forms a protective film that suppresses corrosion reactions on the surface of the aluminum current collecting layer.

<Protective Film Forming Agent>
As the protective film forming agent, an alkali silicate represented by M ₂ O.nSiO ₂ can be used. Here, M is Li, Na, or K. The alkali species may be used alone or in combination of two or more. When two or more types are used in combination, the combination and mixing ratio of the alkali species can be selected arbitrarily. Moreover, n is 1.6 or more and 8.0 or less, and preferably 2.5 or more and 7.5 or less. It is preferable to use an aqueous solution in which the alkali silicate is dissolved in water, and the weight ratio of the alkali silicate in the aqueous solution is 10 to 80%.

<Aluminum current collecting layer>
As the material used for the aluminum current collecting layer, pure aluminum or an alloy containing aluminum and one or more additive elements can be used. As the pure aluminum, for example, materials such as A1050, A1070, A1085, A1100, A1235, 1N30, 1N90, and 1N99, which have an aluminum weight ratio of 99% or more as specified by the JIS standard, can be used. As the aluminum alloy, materials such as A3003, A3103, A3203, A3004, A3104, A3005, and A3105 of Al-Mn alloys and A8021 and A8079 of Al-Fe alloys can be used. As the form of the aluminum current collecting layer, any of rolled foils, punched foils, meshes, foams, and the like can be used, and the thickness is in the range of 1 μm to 2 mm. When using rolled foil, the thickness is preferably 5 to 20 μm. The aluminum current collecting layer may be surface-treated or coated with carbon, fluorine, tungsten, zirconium, or the like.

<Active material>
As an active material capable of electrochemically absorbing and desorbing alkali ions or an active material capable of electrochemically alloying and dealloying alkali ions, in the case of a positive electrode, lithium oxides or lithium polyanion compounds represented by LiCoO ₂ , LiMn _1-a Fe _a PO ₄ , LiNi _2-b Mn _b O ₄ , and Li _c Ni _d Mn _e Co _f M _1-d-e-f O ₂ can be used. In the above, it is possible to use the above-mentioned active material even if the ratio of the constituent elements is slightly different from the ratio described in the exemplified chemical formula. Here, M is one or more elements selected from the group consisting of Na, K, Al, Mg, Ti, Fe, V, Cr, Nb, Mo, W, Cu, Zn, Ga, In, Sn, Zr, Ru, and La,
0≦a≦1.0
0≦b≦2.0
0.8≦c≦2.0
0<d≦1.0
0≦e<1.0
0≦f<1.0
0<d+e+f≦1.0
In addition, lithium sulfur compounds, lithium selenium compounds, lithium fluoride compounds, etc. can be used. Sodium oxide, sodium polyanion compounds, and sodium Prussian blue analogues can also be used.

In the case of the negative _electrode , a lithium titanium oxide, typified by the compound represented by _{Li4Ti5O12 ,} can be used. In _{addition, transition metal oxides such as CuO, Cu2O, MnO2, MoO3, V2O5, CrO3, MoO3 , Fe2O3 , Ni2O3 , and CoO3 can be used .}

In addition, active materials doped with elements such as aluminum, boron, fluorine, chromium, zirconium, molybdenum, magnesium, _sodium , and iron, and active material particles whose surfaces are treated or coated with carbon, _Al2O3 , _Li3PO4 , _LiNbO3 , _TiO2 , _{SiO2 ,} etc. can also be used.

The active material may be one of the above materials, or two or more of them may be used in combination. At least two materials selected from the materials usable for the positive electrode may be used in combination for the positive electrode, and at least two materials selected from the materials usable for the negative electrode may be used in combination for the negative electrode. The mixture ratio of the materials constituting the active material may be any ratio.

There are no particular limitations on the equipment used to mix multiple materials, but for example, in the case of rotary mixers, the following can be used: cylindrical mixer, twin cylindrical mixer, double cone mixer, upright cube mixer, hoe-shaped mixer; in the case of stationary mixers, the following can be used: spiral mixer, ribbon mixer, Muller mixer, helical flight mixer, Pugmil mixer, fluidization mixer, etc.

The active material is preferably in a particulate form, in which case the particle size is preferably about 100 nm to 50 μm, and more preferably in the range of 200 nm to 20 μm. If the particle size is less than 100 nm, it is likely to be difficult to disperse the slurry, and if the particle size exceeds 50 μm, the battery characteristics are likely to deteriorate.

In the nonaqueous electrolyte secondary battery of the present invention, at least one of the positive electrode and the negative electrode is an electrode of the present invention. When either the positive electrode or the negative electrode is not an electrode of the present invention, suitable active materials for use in the electrode include graphite, non-graphitizable carbon, easily graphitizable carbon, lithium, etc.

<Binder>
The positive and negative electrodes for the non-aqueous electrolyte secondary battery of the present invention are provided with a binder. The binder is preferably contained in the electrodes at a weight ratio of 0.1% to 20%. More preferably, the binder is contained in the electrodes at a weight ratio of 0.5% to 10%. If the weight ratio of the binder is small, the adhesive strength decreases and the battery life decreases. If the weight ratio is large, the battery resistance increases.

As the binder, an aqueous emulsion solution, an aqueous polymer solution, an aqueous polymer dispersion, etc. can be used. As the emulsion, synthetic resin emulsions such as "polyacrylic acid copolymer resin emulsion", "conjugated diene polymer emulsion", and "fluorine-containing copolymer emulsion" can be preferably used. As the aqueous polymer solution, "water-soluble polyacrylic acid copolymer" can be used. As the aqueous polymer dispersion, "aqueous dispersion of fluorine-containing copolymer" can be used. These are resin-based solutions developed for battery applications.

"Polyacrylic acid copolymer resin emulsion" refers to an emulsion of a copolymer resin obtained by emulsion polymerization of acrylic acid monomer and other reactive monomers in water. Examples of the other reactive monomers include vinylidene fluoride monomer; styrene monomer; ethylenically unsaturated monomers containing a nitrile group, such as acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, crotononitrile, α-ethylacrylonitrile, α-cyanoacrylate, vinylidene cyanide, fumaronitrile, and other α,β-unsaturated nitrile monomers; monofunctional monomers such as methacrylic acid and acrylic acid, fumaric acid, maleic acid, itaconic acid, citraconic acid, mesaconic acid, glutaconic acid, 1,2,3,6-tetrahydrophthalic acid, 3-methyl-1,2,3,6-tetrahydrophthalic acid, 4-methyl-1,2,3,6-tetrahydrophthalic acid, methyl-3,6-endomethylene ... Examples of the other reactive monomers include ethylenically unsaturated monomers containing carboxylic acids, such as trihydrophthalic acid, exo-3,6-epoxy-1,2,3,6-tetrahydrophthalic acid, and himic acid; anhydrides of the ethylenically unsaturated monomers containing carboxylic acids; saponification products of the anhydrides; ethylenically unsaturated monomers containing ketone groups, such as methyl vinyl ketone, ethyl vinyl ketone, isopropyl vinyl ketone, isobutyl vinyl ketone, t-butyl vinyl ketone, and hexyl vinyl ketone; ethylenically unsaturated monomers containing organic acid vinyl ester groups, such as vinyl acetate, vinyl propionate, vinyl butyrate, trimethyl vinyl acetate, vinyl caproate, vinyl caprylate, vinyl laurate, vinyl palmitate, and vinyl stearate; and the like. One type of other reactive monomer may be used, or two or more types may be used in combination.

Also, by substituting the terminals of the polyacrylic acid copolymer resin with specific functional groups, it is possible to produce a modified product capable of reacting with specific monomers, etc. Examples of modified products include epoxy modified products, carboxy modified products, isocyanate modified products, and hydrogen modified products.

As the "conjugated diene polymer emulsion", an emulsion of styrene butadiene copolymer rubber can be suitably used. The emulsion of styrene butadiene copolymer rubber is a particle of a copolymer of styrene and butadiene, and has a copolymer component derived from styrene and a copolymer component derived from butadiene. The content of the copolymer component derived from styrene is preferably 50 to 80 mol % based on the total copolymer components constituting the styrene butadiene copolymer. The content of the copolymer component derived from butadiene is preferably 20 to 50 mol % based on the total copolymer components.

The styrene-butadiene copolymer may have other reactive monomers in addition to the copolymerization components derived from styrene and the copolymerization components derived from butadiene. As the other reactive monomers, for example, those mentioned above as components of the emulsion of the polyacrylic acid copolymer resin can be used.

When the styrene-butadiene copolymer has the other reactive monomer, the content of the other reactive monomer is preferably 1 to 30 mol% based on the total copolymerization components constituting the styrene-butadiene copolymer. The styrene-butadiene copolymer may be any of a random copolymer, a block copolymer, and a graft copolymer. The styrene-butadiene copolymer may also be carboxy-modified.

Styrene-butadiene copolymer rubber emulsion is an emulsion of rubber particles obtained by emulsion polymerization of styrene monomer, butadiene monomer, and, if necessary, other reactive monomers in water, and is sometimes called latex or synthetic rubber latex.

In place of styrene-butadiene copolymer rubber, butadiene rubber (BR), isoprene rubber (IR), chloroprene rubber (CR), nitrile rubber (NBR), butyl rubber (IIR), ethylene propylene rubber (EPDM), natural rubber (NR), etc. can also be used.

A "fluorine-containing copolymer" is a copolymer that contains at least one polymer of a fluorine-containing monomer in the molecule. Examples of fluorine-containing copolymers include copolymers of polyvinylidene fluoride (PVDF) and polyvinyl alcohol (PVA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), polyvinylidene fluoride-hexafluoropropylene (PVdF-co-HFP), ethylene-tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), propylene-tetrafluoroethylene copolymer, and ethylene-chlorotrifluoroethylene copolymer (ECTFE).

A "fluorine-containing copolymer emulsion" is an emulsion of a copolymer resin obtained by emulsion polymerization in water of one type of fluorine-containing monomer and another reactive monomer, or two or more types of fluorine-containing monomers. A "water dispersion of a fluorine-containing copolymer" is an aqueous solution of a copolymer resin obtained by copolymerizing one type of fluorine-containing monomer and another reactive monomer, or two or more types of fluorine-containing monomers, or a dispersion in which the copolymer resin is dispersed in water.

Other reactive monomers include PVA, hexafluoropropylene, ethylene, propylene, etc.

The content (solids concentration) of polyacrylic acid copolymer resin, styrene butadiene copolymer rubber, or fluorine-containing copolymer in the polyacrylic acid copolymer resin emulsion, styrene butadiene copolymer rubber emulsion, fluorine-containing copolymer emulsion, or fluorine-containing copolymer aqueous dispersion is preferably 0.1 to 80% by weight, and more preferably 0.5 to 65% by weight.

The solids concentration of the binder is preferably 0.5 to 95% by mass, and more preferably 1.0 to 85% by mass. The solids concentration is the mass ratio of the binder to the mass of the aqueous solution containing the binder.

<Slurry (electrode mixture slurry)>
The slurry (electrode mixture slurry) for producing the electrode for a non-aqueous electrolyte secondary battery of the present invention contains a protective film forming agent, an active material, and a binder, and uses water as a solvent.

When the active material used for the positive and negative electrodes is mixed with water to prepare a slurry, alkaline ions are eluted from the active material structure, forming lithium hydroxide in the aqueous solution, and the pH becomes 10 or more. If a binder is added to such a high pH slurry and applied to an aluminum current collecting layer, a corrosion reaction occurs on the surface of the aluminum current collecting layer, and a smooth electrode cannot be obtained. However, in an electrode containing the protective film forming agent of the present invention, a corrosion-resistant protective film is formed on the surface of the aluminum current collecting layer, making it possible to suppress the corrosion reaction despite the high pH slurry. Therefore, it is no longer necessary to prepare an electrode with a slurry using a conventional organic solvent, and the cost of recovering and recycling the organic solvent and the cost of the solvent itself are not required, resulting in a reduction in battery costs. In addition, in the case of production using a water-based system, the conventional method of neutralizing a high pH slurry to a pH level at which corrosion of the aluminum current collecting layer does not occur by adding a neutralizing agent induces alkaline ion elution from the active material, resulting in a reduction in battery capacity. The appropriate amount of neutralizing agent to be added had to be adjusted depending on the type and amount of active material. However, in the present invention, a technology in which a protective film is formed on the surface of the current collecting layer using a protective film forming agent contained in the electrode mixture has the advantage that the amount added can be kept constant regardless of the type of active material, etc.

The slurry for producing the electrode for the non-aqueous electrolyte secondary battery of the present invention preferably has a total solids concentration of 50 to 95% by weight, excluding water, including the active material, binder, protective film forming agent, etc. If the water content is low, the slurry viscosity will be high, resulting in variation in the coating thickness, etc. If the water content is high, the time required for drying will be long and the coating speed will be reduced.

The slurry can be prepared, for example, by the following two methods.
[Method 1]
The active material, water-soluble thickener, etc. are mixed in powder form, water is added, and the mixture is kneaded. Then, a protective film forming agent is added, and the mixture is further kneaded. Finally, a binder is added, and the mixture is kneaded.
[Method 2]
An aqueous solution containing a water-soluble thickener and a water-soluble polymer binder is prepared in advance at a predetermined weight percentage. Then, an active material is added to this aqueous solution and kneaded. Finally, a protective film forming agent is added and kneaded.

　With these methods, it is possible to disperse the protective film forming agent in advance in the electrode mixture slurry. Furthermore, by uniformly dispersing the protective film forming agent, a uniform protective film can be formed on the surface of the aluminum current collecting layer. Note that the silica component contained in the protective film forming agent does not contribute to the battery capacity, so in terms of energy density, it is preferable to add a small amount. Therefore, in order to uniformly disperse the protective film forming agent in the electrode mixture slurry and form a uniform protective film on the surface of the aluminum current collecting layer while maintaining battery performance, it is preferable that the weight ratio of the protective film forming agent in the electrode mixture is in the range of more than 0.1% and 1% or less.

In the above, the mixing or kneading method may be, for example, mixing using various grinders, mixers, stirrers, etc., or dispersion using ultrasonic waves. Specific examples include processing methods using shear force or collision such as mixers, high-speed rotary mixers, shear mixers, blenders, ultrasonic homogenizers, high-pressure homogenizers, and ball mills; and methods using Waring blenders, flash mixers, turbulizers, etc. These methods may also be used in appropriate combination.

The slurry may contain a conductive additive to ensure electrical conductivity. Adding a conductive additive reduces the internal resistance of the battery. There are no particular limitations on the conductive additive, and examples of the conductive additive include metals, carbon materials, conductive polymers, and conductive glass. Of these, carbon materials are preferred, and examples of the conductive additive include nanocarbons such as carbon nanotubes, carbon nanofibers, carbon nanohorns, and fullerenes; acetylene black, furnace black, thermal black, channel black, ketjen black, vulcan, graphene, vapor-grown carbon fiber (VGCF), and graphite. Acetylene black, ketjen black, VGCF, and carbon nanotubes are more preferred. The carbon nanotubes may be single-walled, double-walled, or multi-walled carbon nanotubes. The conductive additive may be used alone or in combination of two or more types. The conductive additive may be treated with an acid or alkali to improve hydrophilicity. There are no particular limitations on the shape, size, or specific surface area of the conductive additive. Any one may be selected depending on the amount added.

The slurry may contain a thickener to ensure dispersion and viscosity stability. Examples of thickeners include water-soluble polymers such as sodium carboxymethylcellulose, alginic acid, polyacrylic acid, guar gum, and xanthan gum. Of these, alkali metal salts and ammonium salts of carboxymethylcellulose, alginic acid, and polyacrylic acid are preferred because they have excellent dispersion and viscosity stability. These thickeners may be used alone or in combination of two or more types.

The water used to prepare the slurry is not particularly limited, and any commonly used water can be used. For example, tap water, distilled water, ion-exchanged water, pure water, ultrapure water, etc. can be used. Among these, ion-exchanged water, pure water, and ultrapure water are preferred.

The water may contain an organic solvent (hydrophilic organic solvent) that is uniformly miscible with water. Examples of hydrophilic organic solvents include N-methyl-2-pyrrolidone; dimethyl sulfoxide; alcohols such as methanol, ethanol, 2-propanol (IPA), isopropanol, n-butanol, and t-butanol; ketones such as acetone and methyl ethyl ketone (MEK); ethers such as 1,4-dioxane and tetrahydrofuran (THF); N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), acetonitrile, and ethyl acetate. One type of hydrophilic organic solvent may be used, or two or more types may be used. However, from the viewpoints of safety, environmental impact, and ease of handling, it is preferable to use only water without using an organic solvent.

The mixing ratio of water to organic solvent may be appropriately determined taking into consideration the type of organic solvent, the affinity between water and organic solvent, etc.

The weight ratio of each component in the solid content of the slurry is preferably, for example, 74.0 to 99.3% active material, 0.5 to 10.0% binder, 0.001 to 1.0% protective film forming agent, 0.1 to 10.0% conductive aid, and 0.1 to 5.0% thickener, assuming the total weight of the active material, binder, protective film forming agent, conductive aid, and thickener to be 100%.

<Method of manufacturing electrode for non-aqueous electrolyte secondary battery>
The electrode for a non-aqueous electrolyte secondary battery of the present invention can be manufactured, for example, by applying the above-mentioned slurry to the surface of a current collector layer, drying, and press molding. This makes it possible to manufacture an electrode for a non-aqueous electrolyte secondary battery in which an electrode mixture layer exists on the current collector layer. The electrode mixture layer is the coating layer part of the electrode after the slurry is applied to a current collector layer such as a foil and dried, and is a combination of an active material, a binder, a protective film forming agent, a conductive assistant, and a thickener. In addition, the electrode manufactured by the present invention has a protective film formed on the surface of the aluminum current collector layer.

Examples of the coating method include a method using a knife coater, a comma coater, a die coater, etc. The current collecting layer can be made of pure aluminum foil or an alloy foil made of aluminum and one or more metals.

The amount of the slurry applied to the current collecting layer can be set, for example, so that the thickness of the electrode mixture layer after drying is in the range of 0.01 to 0.40 mm, preferably 0.02 to 0.25 mm.

The temperature in the drying process can be set appropriately within the range of, for example, 35 to 150°C, preferably 40 to 135°C. The drying method can be selected from hot air drying, air drying, infrared drying, reduced pressure drying, hot plate drying, etc. In the case of reduced pressure drying, the temperature can be set arbitrarily from the above values.

The non-aqueous electrolyte secondary battery electrodes thus obtained may be used as the positive and negative electrodes of the secondary battery.

<Electrode for non-aqueous electrolyte secondary battery>
The obtained electrode for a non-aqueous electrolyte secondary battery has the following characteristics: A corrosion-resistant protective film is formed on the surface of the aluminum current collecting layer by the alkali silicate, which is a protective film forming agent; The electrode is a smooth electrode with no void defects of 50 μm or more in the electrode mixture layer containing the active material and binder. With such an electrode, even an electrode made from an aqueous slurry has excellent output characteristics. It is possible to obtain a battery having the above structure.

The reason for this improved output characteristic is believed to be that the protective film forming agent forms a corrosion-resistant protective film on the surface of the aluminum current collecting layer, thereby suppressing the corrosion reaction during electrode production. In an electrode that does not contain a protective film forming agent, no protective film is formed on the surface of the aluminum current collecting layer, so when a high pH slurry is applied, a corrosion reaction occurs on the surface of the aluminum current collecting layer. Hydrogen gas generated during the corrosion reaction diffuses into the electrode mixture layer, and after drying, the areas where hydrogen gas was present become void defects. These voids break the electronic connection between the active materials in the electrode mixture, resulting in an increase in resistance. In the electrode according to the present invention, the protective film suppresses the corrosion reaction, so excellent output characteristics can be obtained.

<Protective film>
The protective film on the surface of the aluminum current collecting layer of the electrode for a non-aqueous electrolyte secondary battery obtained by the present invention is characterized by having Si-O bonds. In addition, since the protective film having Si-O bonds is water-insoluble, it effectively protects the surface of the aluminum current collecting layer and suppresses corrosion of aluminum caused by high pH slurry. Furthermore, when applied as an electrode for a non-aqueous electrolyte secondary battery, the protective film must be stable against charge and discharge reactions. To determine whether the electrode has a protective film and whether the electrode mixture layer has no pore defects of 50 μm or more, analysis by X-ray photoelectron spectroscopy (XPS) and scanning electron microscope (SEM) can be used. If clear Si-O bonds are not obtained by XPS, pore defects of 50 μm or more are formed in the electrode mixture layer due to corrosion reactions, the smoothness of the electrode is impaired, and the output characteristics of the battery are reduced.

<XPS Measurement>
The protective film on the surface of the aluminum current collecting layer is measured by XPS using an X-ray photoelectron spectrometer. The sample for measurement is the aluminum current collecting layer remaining after the composite layer of the prepared electrode is peeled off with pure water. MgKα radiation is used as the XPS radiation source to analyze the Si2p _3/2 spectrum.

The presence or absence of a protective film having Si-O bonds can be determined by whether or not a clear peak is detected in the range of 102 to 107 eV in the XPS measurement.

<SEM Observation>
The surface observation of the electrode mixture layer by SEM is carried out using a scanning electron microscope. The prepared electrode is used as a sample for observation.
The presence or absence of void defects of 50 μm or more in the electrode mixture layer formed by the corrosion reaction can be identified by observing the mixture surface.

<Nonaqueous electrolyte secondary battery>
The nonaqueous electrolyte secondary battery of the present invention is a secondary battery comprising a positive electrode and a negative electrode, and containing an electrolyte between the positive electrode and the negative electrode, wherein at least one of the positive electrode and the negative electrode is an electrode of the present invention. It is.

In non-aqueous electrolyte secondary batteries, a separator is placed between the positive and negative electrodes to prevent short circuits between the electrodes. The current collecting layers of the positive and negative electrodes are connected to an external device. Charging and discharging are switched on and off by operating this device.

Examples of non-aqueous electrolyte secondary batteries include lithium ion secondary batteries, lithium ion capacitors, sodium ion secondary batteries, and sodium ion capacitors, and also include other secondary batteries.

Non-aqueous electrolyte secondary batteries have high performance and can be used as safe power storage devices. Therefore, the secondary batteries may be installed in small electronic devices such as mobile phones, notebook computers, personal digital assistants, video cameras, and digital cameras, mobile devices (vehicles) such as electric bicycles, electric automobiles, and trains, power generation devices such as thermal power plants, wind power plants, hydroelectric power plants, nuclear power plants, and geothermal power plants, natural energy storage systems, and the like.

The nonaqueous electrolyte secondary battery of the present invention is preferably a lithium ion secondary battery. The positive or negative electrode active material used in the secondary battery contains lithium in the active material structure.

The nonaqueous electrolyte secondary battery of the present invention is equipped with the electrodes of the present invention, and therefore exhibits particularly high battery characteristics, including high battery capacity and output characteristics, compared to nonaqueous electrolyte secondary batteries equipped with electrodes obtained from conventional aqueous slurries that do not contain a protective film-forming agent.

In the nonaqueous electrolyte secondary battery of the present invention, either the positive electrode or the negative electrode may be the electrode of the present invention, and if one of the positive and negative electrodes is the electrode of the present invention, the other electrode may be manufactured from either an aqueous slurry or an organic solvent slurry.

The nonaqueous electrolyte secondary battery of the present invention may be in the form of a cylinder in which rectangular electrodes and a separator are stacked and wound into a wound body, a laminated type in which electrodes are wrapped in separators and stacked and packaged in an aluminum laminate pouch, or a coin type in which electrode pellets and a separator are stacked. The exterior case may be made of stainless steel, aluminum, or the like.

<Electrolytes>
As the electrolyte, lithium salts or lithium inorganic compounds having lithium ion conductivity are used. Lithium salts soluble in non-aqueous solvents can be used in the form of electrolytic solutions or gel-like, rubber-like, or sheet-like polymer electrolytes prepared by mixing with organic polymers. When using lithium inorganic compounds as the electrolyte, they can be used by forming them with a pressure press or a binder.

<Non-aqueous solvent>
Examples of non-aqueous solvents used in the non-aqueous electrolyte solution include cyclic carbonates such as propylene carbonate, ethylene carbonate, vinylene carbonate, and butylene carbonate; chain carbonates such as diethyl carbonate, dimethyl carbonate, and ethyl methyl carbonate; cyclic ethers such as tetrahydrofuran, 2-methyltetrahydrofuran, and 3-dioxolane; chain ethers such as diethoxyethane and dimethoxyethane; sulfone-based solvents such as sulfolane, ethyl isopropyl sulfone, dimethyl sulfone, and di-normal propyl sulfone; chain esters such as methyl formate, methyl acetate, and methyl propionate; cyclic esters such as γ-butyrolactone and γ-valerolactone; and acetonitrile.

These non-aqueous solvents may be used alone or in a mixture of two or more. When preparing a mixed solvent, a combination of a cyclic carbonate and a chain carbonate is preferred. The cyclic carbonate dissolves lithium salts at a high concentration, and the chain carbonate can reduce the viscosity of the electrolyte without reducing the solubility of the lithium salt, so this combination makes it possible to obtain an electrolyte with high ionic conductivity. In addition, these mixed solvents have high oxidation-reduction resistance, and are therefore preferred in that there is little concern about continuous electrolysis within the operating voltage range of lithium-ion batteries.

The non-aqueous solvent used in the non-aqueous electrolyte may be an ionic liquid. An ionic liquid is a molten salt formed by combining a cation and an anion, and means a salt that exists in a liquid state over a wide temperature range including room temperature. The ionic liquid may be formed by appropriately combining at least one of the following cations and at least one of the following anions.

The cation of this ionic liquid is not particularly limited as long as it allows the movement of lithium ions in the electrolyte and enables charging and discharging of the electricity storage device, and examples include imidazolium, pyridinium, pyrrolidinium, piperidinium, tetraalkylammonium, pyrazolium, and tetraalkylphosphonium.

Examples of the imidazolium include 1-ethyl-3-methylimidazolium [EMIm ⁺ ], 1-butyl-3-methylimidazolium, 1-ethyl-2,3-dimethylimidazolium, 1-allyl-3-methylimidazolium, 1-allyl-3-ethylimidazolium, 1-allyl-3-butylimidazolium, and 1,3-diallylimidazolium.

Examples of the pyridinium include 1-propylpyridinium, 1-butylpyridinium, 1-allylpyridinium, 1-ethyl-3-(hydroxymethyl)pyridinium, and 1-ethyl-3-methylpyridinium.

Examples of the pyrrolidinium include N-methyl-N-propylpyrrolidinium [MPPyr ⁺ ], N-methyl-N-butylpyrrolidinium, N-methyl-N-methoxymethylpyrrolidinium, N-allyl-N-methylpyrrolidinium, and N-allyl-N-propylpyrrolidinium.

Examples of the piperidinium include N-methyl-N-propylpiperidinium, N-methyl-N-butylpiperidinium, N-methyl-N-methoxymethylpiperidinium, and N-allyl-N-propylpiperidinium.

Examples of the tetraalkylammonium include N,N,N-trimethyl-N-propylammonium and methyltrioctylammonium.

Examples of the pyrazolium include 1-ethyl-2,3,5-trimethylpyrazolium, 1-propyl-2,3,5-trimethylpyrazolium, 1-butyl-2,3,5-trimethylpyrazolium, and 1-allyl-2,3,5-trimethylpyrazolium.

Examples of the tetraalkylphosphonium include P-butyl-P,P,P-triethylphosphonium and P,P,P-triethyl-P-(2-methoxyethyl)phosphonium.

The anions that are combined with these cations to form the ionic liquid may be any anion that allows the movement of lithium ions in the electrolyte and enables charging and discharging of the electricity storage device. For example, BF ₄ ⁻ , PF ₆ ⁻ , SbF ₆ ⁻ , NO ₃ ⁻ , CF ₃ SO ₃ ⁻ , (FSO ₂ ) ₂ N ⁻ [bis(fluorosulfonyl)imide anion; FSI ⁻ ], (CF ₃ SO ₂ ) ₂ N ⁻ [bis(trifluoromethylsulfonyl)imide; TFSI ⁻ ], (C 2 F ₅ SO ₂ ) ₂ N ⁻ , (CF ₃ SO ₂ ) ₃ C ⁻ , CF ₃ CO ₂ ⁻ , C ₃ F ₇ CO ₂ ⁻ , CH ₃ CO ₂ ⁻ , (CN) ₂ N ⁻ , etc. These anions may be contained in combination of two or more kinds.

The lithium salt used in the non-aqueous electrolyte is not particularly limited, and examples thereof include fluoride-based lithium salts such as LiPF ₆ , LiBF ₄ , and LiAsF ₆ , halide-based lithium salts such as LiClO ₄ , LiCl, LiBr, and LiI, and sulfonate-based lithium salts such as LiN(CF ₃ SO ₂ ) ₂ (LiTFSI) and LiN(FSO ₂ ) ₂ (LiFSI). The lithium salt may be used alone or in a mixture of two or more kinds. The concentration of the lithium salt in the non-aqueous electrolyte is 0.3 to 2.5 mol/dm ³ .

When the above-mentioned non-aqueous electrolyte solution is mixed with an organic polymer compound and used as a gel-like, rubber-like, or solid sheet-like electrolyte, examples of the organic polymer compound that can be used include polyethylene oxide, polypropylene oxide, polyvinyl alcohol, polyvinyl butyral, polyvinylpyrrolidone, polyvinylidene carbonate, polyacrylonitrile, and PVDF-HFP.

The non-aqueous electrolyte may contain additives to suppress continuous redox decomposition on the positive and negative electrodes. Examples of additives include vinylene carbonate, fluoroethylene carbonate, ethylene sulfide, 1,3-propane sultone, 1,3-propene sultone, lithium bisoxalate borate, and lithium difluorooxalate borate. The content of the additive is preferably in the range of 10 to 0.1% by weight of the non-aqueous electrolyte. If the content is too high, it is undesirable because it leads to an increase in the resistance of the secondary battery. These additives form a film on the electrodes to protect the electrode surfaces, and this protective effect mitigates the continuous redox decomposition reaction of the electrolyte on each electrode, which is effective in improving the lifespan.

<Separator>
In the non-aqueous electrolyte secondary battery of the present invention, a separator is provided between the positive electrode and the negative electrode to prevent short circuit between them. Examples of the separator include porous films containing polyethylene, polypropylene, cellulose, polyvinylidene fluoride (PVDF), polyimide, alumina, silica, etc. In order to form a porous film, holes can be provided by stretching a polymer film, or a fiber or granular polymer or inorganic compound can be molded using a press or a binder. A coating layer may be provided on one or both sides of the separator. The coating layer is a layer of several nm to several μm made of alumina, zirconia, silica, aramid, PVDF, etc., and is effective in preventing short circuit by improving heat resistance and strength.

The present invention will be explained in more detail based on examples and comparative examples, but the present invention is not limited to these.

<Preparation of Positive Electrode Slurry Using Water as Solvent>
The positive electrode active material was 94.8 to 95.2% by weight, the conductive assistant was 2% by weight of carbon black, the protective film forming agent was 0.0 to 0.4% by weight of lithium silicate, the thickener was 0.55% by weight of carboxymethylcellulose Na (CMC-Na), and the binder was 2.25% by weight of acrylic emulsion. The slurry was mixed with water as a solvent to prepare the slurry. The positive electrode active material was LiNi _0.8 Mn _0.1 Co _0.1 O _2. The protective film forming agent, lithium silicate, is represented by the chemical formula Li ₂ O.nSiO ₂ , and three types of n were used: 3.5, 4.5, and 7.5. The detailed weight composition of the electrode mixture is shown in Table 1.

<Measurement of pH of electrode slurry>
The pH of the resulting electrode slurry was measured by immersing a pH meter in the slurry for 10 minutes. The results are shown in Table 1.

<Preparation of electrodes using electrode slurry>
The obtained electrode slurry was applied by a doctor blade method to one side of a 15 μm thick pure aluminum foil (material A1085) so that the active material coverage was 20.0 mg/cm ² to prepare an electrode. The dried electrode was then pressed with a roll press machine so that the positive electrode mixture density was 3.4 g/cc.

<Evaluation of electrode corrosion state>
To evaluate the corrosion state of the electrode obtained above, the surface of the electrode mixture layer was observed visually and with an SEM (FlexSEM 1000II, Hitachi High-Tech). The SEM observation was performed at 100x magnification. Photographs showing the results of the visual observation are shown in Figs. 1 to 4, and SEM observation images are shown in Figs. 5 to 8. The presence or absence of corrosion was evaluated according to the following criteria.

Corrosion present: In the SEM observation area, there is one or more void defects having a diameter of 50 μm or more on the surface of the electrode mixture layer, or there is exposure of the aluminum current collecting layer when visually confirmed from the surface of the electrode mixture layer.
No corrosion: There are no pore defects with a diameter of 50 μm or more on the surface of the electrode mixture layer in the observation area, and there is no exposure of the aluminum current collecting layer when visually confirmed from the surface of the electrode mixture layer.

The results are shown in Table 2. In Comparative Examples 1 to 4 (indicated by (M), (A), (E), and (I) in the figure), hydrogen gas was generated due to the corrosion reaction of aluminum, and pore defects were formed in the electrode mixture, and the aluminum current collecting layer was exposed. In Examples 1 to 9, no pore defects or exposed aluminum current collecting layer were observed in the electrode mixture, and smooth electrodes were obtained.

<Evaluation of the presence of protective film components on the surface of the aluminum current collecting layer>
In order to evaluate the presence of components having Si-O bonds originating from the protective film forming agent on the surface of the aluminum current collecting layer of the electrode obtained above, analysis was performed using an XPS (JEOL, JPS-9010MC) MgKα radiation source. The mixture layer of the prepared electrode was peeled off with pure water to prepare a sample. The electrode for which the battery capacity and output characteristics were evaluated was taken out by dismantling and disassembling from the lithium ion battery described later, and the electrode mixture layer was peeled off with pure water in the same manner as above to prepare a sample. The presence or absence of components originating from the protective film forming agent was evaluated by the presence or absence of a bond peak in the range of 102 to 107 eV in the Si2p _3/2 spectrum.

The results are shown in Table 2 and Figures 9 to 11. In Examples 1 to 9, the results of XPS measurement showed that a bond peak was clearly observed in the aforementioned range of 102 to 107 eV, confirming the presence of components having Si-O bonds. On the other hand, in Comparative Examples 1 to 4, the corresponding bond peak was scarce or absent, so it cannot be said that the aforementioned components were sufficiently present on the aluminum current collecting layer, and this, together with the results of SEM observation and visual observation, supports the fact that the formation of a protective film was insufficient or nonexistent.

<Evaluation of battery capacity and output characteristics>
The non-aqueous electrolyte secondary battery electrode obtained above was used as the positive electrode of the battery to fabricate a lithium ion secondary battery having the following configuration. The positive electrode was processed to a size of 12 mmΦ, and the negative electrode was processed to a size of 13 mmΦ. Using these electrodes, a CR2032 type coin cell was fabricated in an argon atmosphere with a dew point of -60°C. The materials used are as follows:

Positive electrode: the positive electrode for the non-aqueous electrolyte Negative electrode: lithium metal Electrolyte: 1.0 M _LiPF6 , an electrolyte, was dissolved in a non-aqueous solvent, ethylene carbonate (EC) and dimethyl carbonate (DMC), mixed in a volume ratio of 3:7, to be used as the electrolyte (hereinafter referred to as 1.0 M _LiPF6 /EC:DMC [3:7 volume ratio]).
Separator: Polyethylene porous film

[Measurement conditions]
The battery capacity and output characteristics were evaluated using the lithium ion secondary battery prepared above by the following method. First, an evaluation sample was placed in a 25°C thermostatic chamber, and charged at a constant current up to 4.3V at a 10-hour rate (0.1C) current value, and constant voltage charging was performed to hold the voltage after the battery voltage reached 4.3V. The constant voltage charging was performed until the current value attenuated to 0.01C. Thereafter, constant current discharge was performed at a current value of 0.1C or 3C, and each capacity was measured when the battery voltage reached 3.0V. Here, the capacity obtained at a current of 0.1C is the battery capacity, and the capacity obtained at a current of 3C is the battery capacity obtained in the output test. The capacity retention rate was calculated by comparing the value of the 3C capacity with the 0.1C capacity. The battery capacity was calculated by dividing the actual capacity value (mAh) obtained by the amount of positive electrode active material (g). The results are shown in Table 2.

As shown in Tables 1 and 2 and Figures 1 to 11, in Examples 1 to 3, Examples 4 to 6, and Examples 7 to 9, which contain 0.2 wt%, 0.3 wt%, and 0.4 wt% lithium silicate as a protective film forming agent, respectively, a protective film is formed on the surface of the aluminum current collecting layer of the electrode, and the corrosion reaction can be suppressed even if an electrode is produced by applying an electrode slurry having a high pH exceeding pH 11 to the aluminum current collecting layer. As shown in the XPS measurement results of the Si2p _3/2 spectrum on the aluminum current collecting layer surface in Figures 9 to 11, in Examples 1 to 3, Examples 4 to 6, and Examples 7 to 9, a peak derived from the Si-O bond was clearly observed in the range of 102 to 107 eV, and it was confirmed that a protective film was formed on the aluminum current collecting layer surface. Figures 9 to 11 further show the XPS measurement results of the aluminum current collecting layer surface after charging and discharging for Examples 1, 4, and 7. In these examples, the Si-O bond peak was clearly observed even after charging and discharging, and it was confirmed that the protective film was stable against the charging and discharging reaction. On the other hand, it was confirmed that a corrosion reaction occurred in Comparative Example 1, which did not have a protective film forming agent. In Comparative Examples 2, 3, and 4, in which the amount of the protective film forming agent was 0.1% by weight, the corrosion was reduced compared to Comparative Example 1, but the corrosion reaction occurred, and it was confirmed that the protective film formation was insufficient. As shown in Table 2, by using an electrode mixture containing a protective film forming agent, the electrode according to the present invention having a protective film suppresses or reduces the corrosion reaction, thereby maintaining the electronic connection in the electrode mixture, and it became possible to obtain a high battery capacity and output characteristics compared to the comparative examples.

The above examples show that the electrode mixture slurry prepared using lithium oxide or the like according to the present invention as an active material and water as a solvent contains a protective film forming agent, and a protective film is formed on the surface of the aluminum current collecting layer, making it possible to suppress corrosion of the aluminum current collecting layer during electrode preparation, and the resulting electrode has high battery capacity and output characteristics. The present invention makes it possible to change from the conventional electrode manufacturing process using organic solvents to one using water, which is expected to reduce the cost of secondary battery electrodes and, ultimately, secondary batteries.

The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present invention is defined by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims.

Claims (7)

1. An electrode for a non-aqueous electrolyte secondary battery, comprising an electrode mixture layer on an aluminum current collecting layer,
   The electrode mixture constituting the electrode mixture layer contains an active material, a binder, and a protective film forming agent,
   the active material is an active material capable of electrochemically absorbing and desorbing alkali metal ions, or an active material capable of electrochemically alloying and dealloying alkali metal ions,
   The protective film forming agent includes an alkali silicate,
   a protective film formed by the protective film forming agent on a surface of the aluminum current collecting layer;
2. 2. The electrode for a non-aqueous electrolyte secondary battery according to claim ₁ , wherein the protective film forming agent contains at least an alkali silicate represented by _M2O.nSiO2 , in which M includes at least one of Li, Na, and K, and n is 1.6 or more and 8.0 or less.
3. The electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein the weight ratio of the protective film forming agent in the electrode mixture is in the range of more than 0.1% and not more than 1%.
4. 2. The electrode for a nonaqueous electrolyte secondary battery according to claim 1, wherein the protective film present on the surface of the aluminum current collecting layer at least contains a Si—O bond having a bond energy in the range of 102 to 107 eV in a Si2p3 _/2 spectrum, as determined by X-ray photoelectron spectroscopy (XPS) analysis using an X-ray source of MgKα radiation.
5. The electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein the aluminum current collecting layer is pure aluminum or an alloy of aluminum and one or more additive elements.
6. The active material is
   A lithium oxide represented by Li _x MO ₂ , LiM ₂ O ₄ , or Li ₄ M ₅ O ₁₂ (x is 1 to 2, and M is a transition metal) containing at least one transition metal;
   A lithium polyanion compound represented by LiMPO ₄ (M is a transition metal) and containing at least one transition metal;
   a lithium inorganic compound selected from a lithium sulfur compound, a lithium selenium compound, and a lithium fluoride compound;
   A sodium oxide represented by _NaMO2 or _Na2MO3 (M is _a transition metal) and containing at least one transition metal;
   a sodium polyanion compound represented by NaM ₂ (XO ₄ ) ₃ , NaMPO ₄ or NaM(SO ₄ ) ₂ (wherein M is a transition metal and X is one of sulfur, phosphorus and silicon) and containing at least one transition metal;
   a sodium Prussian blue analogue compound represented by Na ₂ M[M′(CN) ₆ ] (M and M′ are transition metals) and containing at least one transition metal;
   2. The electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein the electrode is at least one selected from the following:
7. 7. A non-aqueous electrolyte secondary battery comprising a positive electrode and a negative electrode, the positive electrode and the negative electrode being separated by an insulating layer, and at least one of the positive electrode and the negative electrode being the electrode for a non-aqueous electrolyte secondary battery according to claim 1.
   
   

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