Binder for granulation, active material granule using the same, and method for producing active material granule

Abstract

To provide an electrode having excellent cycle life characteristics.SOLUTION: An electrode for a non-aqueous electrolyte secondary battery includes a skeleton-forming agent including a silicate or a phosphate having a siloxane bond as a component, present on the surface of an active material layer and inside the active material layer, and the skeleton of the active material layer is formed by the skeleton-forming agent.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an electrode for a non-aqueous electrolyte secondary battery.

Background Art

[0002] The application fields of secondary batteries have expanded from electronic devices to automobiles, large-scale energy storage systems, etc., and its market size is expected to grow into an industry worth over 10 trillion yen. In particular, information and communication devices such as smartphones and tablet terminals have achieved remarkable popularity, and the global penetration rate has exceeded 30%.

[0003] In addition, the application range of secondary batteries has also expanded to power sources for next-generation automobiles such as electric vehicles (EVs) and plug-in hybrid vehicles (PHEVs). Also, secondary batteries have come to be used for household backup power supplies, storage of natural energy, load leveling, etc. since the Great East Japan Earthquake in 2011, and the uses of secondary batteries are expanding. Thus, secondary batteries are an indispensable existence also in the introduction of energy-saving technologies and new energy technologies.

[0004] Conventionally, alkaline secondary batteries such as nickel-cadmium batteries and nickel-metal hydride batteries were mainstream for secondary batteries, but due to characteristics such as small size, light weight, high voltage, and no memory effect, the use of non-aqueous electrolyte secondary batteries, particularly lithium secondary batteries (lithium-ion batteries), has been increasing. A non-aqueous electrolyte secondary battery is composed of a positive electrode, a negative electrode, a separator, an electrolytic solution or electrolyte, and an electric cell (housing case).

[0005] Electrodes such as the positive electrode and the negative electrode are composed of an active material, a conductive assistant, an organic polymer binder, and a current collector. Generally, an electrode is manufactured by mixing an active material, a conductive assistant, and an organic binder in a solvent to form a slurry, coating this on a current collector, and after drying, rolling it by roll pressing or the like.

[0006] Rolling the electrode after drying it is to shrink the volume of the active material layer of the electrode, that is, the coating layer composed of the active material, the conductive assistant, and the binder, so as to increase the contact area with the conductive assistant and the current collector. Thereby, a strong electronic conduction network of the active material layer is constructed, and the electronic conductivity is improved.

[0007] The binder is used to bind the active material to the active material, the active material to the conductive assistant, the active material to the current collector, the conductive assistant to the current collector, etc. The binder can be roughly classified into a "solution type" in which the binder is dissolved in a solvent to form a liquid, a "dispersion type (emulsion latex type)" in which the solid content is dispersed in a solvent, and a "reaction type" in which the binder precursor is reacted with heat or light.

[0008] In addition, the binder can be divided into an aqueous system and an organic solvent system according to the type of solvent. For example, polyvinylidene fluoride (PVdF) is a dissolution-type binder, and an organic solvent such as N-methyl-2-pyrrolidone (NMP) is used during the preparation of the electrode slurry. Styrene-butadiene rubber (SBR) is a dispersion-type binder, and SBR fine particles are dispersed in water for use. Polyimide (PI) is a reaction-type binder. The PI precursor is dissolved or dispersed in a solvent such as NMP, and heat treatment is performed to promote the imidization and cross-linking reactions to obtain tough PI.

[0009] Although it also varies depending on the molecular weight and substituents of the binder, etc., dissolution-type binders include polyvinylidene fluoride (PVdF), ethylene-vinyl acetate (EVA), etc. In addition, dispersion-type binders include styrene-butadiene rubber (SBR), polytetrafluoroethylene (PTFE), urethane rubber, polypropylene (PP), polyethylene (PE), polyvinyl acetate (PVAc), nitrocellulose, etc. Reaction-type binders include polyimide (PI), polyamide (PA), polyamideimide (PAI), polybenzimidazole (PBI), polybenzoxazole (PBO), etc.

[0010] In addition, organic solvent-based binders such as N-methyl-2-pyrrolidone (NMP) are considered to have a potential adverse impact on the environment. Therefore, it is required to recover them during electrode drying, which increases the electrode manufacturing cost. Also, organic solvent-based binders swell in high-temperature electrolytes, increasing the electrode resistance, making them difficult to use in high-temperature environments.

[0011] Water-based soluble binders are inferior in oxidation resistance or reduction resistance, and many of them are gradually decomposed by repeated charge and discharge, resulting in insufficient life characteristics. Also, due to their low ionic conductivity, they lack output characteristics. Dispersion binders have the advantage of being able to use water as a solvent, but their dispersion stability is easily impaired by the degree of acid or alkali (pH), moisture concentration, or environmental temperature, and segregation, aggregation, precipitation, etc. are likely to occur during the mixing of the electrode slurry. Also, the binder fine particles dispersed in water have a particle size of 1 to 800 nm, and when the moisture is vaporized by drying, the particles fuse together to form a film. Since this film has no electrical conductivity or ionic conductivity, even a slight difference in the amount used has a great impact on the output characteristics and life characteristics of the battery.

[0012] In the case of soluble or dispersion binders as described above, when combined with active materials that cause drastic volume changes during charge and discharge, such as sulfur (S), silicon (Si), tin (Sn), and aluminum (Al), stable life characteristics cannot be obtained, and the charge and discharge capacity becomes less than half after about several cycles.

[0013] On the other hand, reactive binders are excellent in all of heat resistance, binding property, and chemical resistance. In particular, PI exhibits high heat resistance and binding property, and even for active materials with large volume changes, stable life characteristics can be obtained, and the binder is less likely to swell in high-temperature electrolytes.

[0014] According to Non-Patent Document 1, it is disclosed that by combining PI with a high-strength current collector, deterioration of the current collector can be prevented and further life characteristics can be improved.

[0015] According to Patent Document 1, it is disclosed that a LiFePO4 / SiO-based lithium-ion secondary battery using PI for the positive and negative electrodes can be stably charged and discharged even at a high temperature of 120°C. On the other hand, when using PI, since it has excellent adhesion to the current collector, when combined with an active material with a large volume change, wrinkles or cracks may occur in the current collector during the initial charge and discharge. Therefore, it is necessary to use an iron foil or a stainless steel foil with high mechanical strength for the current collector.

[0016] In addition to the above organic binder, there are few reported examples in the field of non-aqueous electrolyte secondary batteries, but Patent Documents 2 to 4 disclose technologies using an inorganic binder for secondary battery electrodes. Patent Document 2 proposes an electrode mixture, an electrode, and a non-aqueous electrolyte secondary battery for a non-aqueous electrolyte secondary battery, which contains an amorphous carbon material containing an inorganic binder, a conductive agent, a binder, and a solvent, and has a viscosity in the range of 2000 mPa·s or more and 10000 mPa·s or less. It is also shown that in some cases, the decomposition reaction of the binder can be suppressed by including an inorganic binder.

[0017] Patent Documents 3 and 4 provide physically and chemically stable lithium-ion batteries using an inorganic binder. On the other hand, as described above, generally, an electrode is composed of an active material layer (a layer composed of an active material, a conductive assistant, and a binder) and a current collector, but there are cases where a layer different from the active material layer is provided on the active material layer.

[0018] For example, Patent Document 5 proposes a non-aqueous secondary battery using an electrode sheet having a layer mainly composed of a metal or semi-metal oxide and an auxiliary layer containing at least one layer of water-insoluble particles. The auxiliary layer provided on the electrode sheet is composed of water-insoluble conductive particles and a binder, and it is also possible to further mix particles that are substantially non-conductive. The particles that are substantially non-conductive are oxides, and oxides containing compounds that dissolve in both acidic and alkaline solutions are preferred. It is shown that the binder used for the auxiliary layer can be the same binder used when forming the electrode mixture.

[0019] Such secondary batteries include batteries of various shapes such as cylindrical, rectangular, and laminated types, which are widely popular. For relatively small-capacity batteries, the cylindrical type is adopted in terms of pressure resistance and ease of sealing, while for relatively large-capacity batteries, the rectangular type is adopted for ease of handling.

[0020] Also, focusing on the electrode structure of secondary batteries, broadly speaking, two types, namely the laminated type and the wound type, are used. That is, in a laminated-type battery, an electrode group in which positive electrodes and negative electrodes are alternately laminated via a separator is housed in a battery case. Many of the laminated-type batteries have a rectangular battery case. On the other hand, in a wound-type battery, a positive electrode and a negative electrode are wound in a spiral state while sandwiching a separator and are housed in a battery case. The battery cases of the wound type can be cylindrical or rectangular.

Prior Art Documents

Patent Documents

[0021]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Non-Patent Documents

[0022]

Non-Patent Document 1

Non-Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0023] As described above, when a thin copper foil or the like is used for the current collector, wrinkles, cracks, etc. occur, so it cannot be used as an electrode (see Fig. 19). On the other hand, if a high-strength iron foil or stainless steel foil is used for the current collector, even if the current collector is thin, it is possible to make it difficult for wrinkles, cracks, etc. to occur. However, since the current collector has very high strength and excellent toughness, the punching process of the electrode is difficult, and the active material layer may fall off or burrs may occur on the cut surface during cutting.

[0024] In addition, since PI is too excellent in chemical resistance, it is insoluble in almost all organic solvents. Therefore, for the preparation of the electrode slurry, polyamic acid (polyamide acid), which is a PI precursor, etc. is dissolved in NMP and used, and heat treatment is performed at 200 °C or higher to promote the imidization reaction (dehydration cyclization reaction) to obtain PI. Then, after the imidization reaction, a cross-linking reaction is caused by heat treatment at a higher temperature to obtain PI with high mechanical strength. From the viewpoint of electrode life, it is preferable to perform heat treatment at a high temperature to such an extent that PI is not carbonized. However, heat treatment at 200 °C or higher not only reduces the flexibility of the electrode and makes it difficult to handle, but also oxidation of the active material and the current collector surface cannot be avoided, which also causes irreversible capacity. In addition, heat treatment at a high temperature also leads to an increase in power consumption during electrode manufacturing.

[0025] There is also a PI binder dispersed in a solvent in a state where it is partially imidized to PI, but when using a pre-imidized one at the time of addition to the slurry, the electrode has poor adhesion strength and inferior life characteristics. In addition, many reaction-type binders such as PI absorb alkali metal ions during the initial charge, but cannot be taken out during discharge, which causes irreversible capacity. For example, depending on the molecular structure, PI has an irreversible capacity of 500 to 1000 mAh / g. Therefore, an electrode using a reaction-type binder has low initial charge-discharge efficiency and a large reduction in battery capacity.

[0026] By the way, in order to confirm the safety of the battery, a nail penetration test is being conducted. When a nail is pierced into a fully charged battery, heat generation exceeding 600 °C may be observed even in a battery of the nominal capacity 1 Ah class. Non-Patent Document 1 shows that a battery using an Si-based active material is greatly improved in the nail penetration safety of the battery. Further, it has been shown that a battery using an Si-based negative electrode and a heat-resistant nonwoven separator is further improved in safety.

[0027] In Non-Patent Document 2, this phenomenon has been studied, and it has been shown that when the electronic conductivity of the active material layer of the electrode is high, the heat generation temperature of the battery and the nail at the time of nail penetration becomes high, and when the electronic conductivity of the electrode active material layer is low, the heat generation temperature of the battery and the nail at the time of nail penetration also becomes low. That is, the electronic conductivity of the electrode active material layer greatly contributes to the nail penetration safety of the battery. When the electronic conductivity of the active material layer is high, the current value flowing through the nail becomes large, and the heat generation amount of the nail and the battery also increases. When the electronic conductivity is low, the current value flowing through the nail becomes small, and the heat generation amount per unit time decreases.

[0028] The alloy-based active material improves the electronic conductivity when alloyed with an alkali metal. For example, Si in the discharged state is a semiconductor and is in a state of low electronic conductivity, but Li in the charged state x Si alloy (0 < x ≤ 4.4) is a conductor and is in a state of high electronic conductivity. That is, in the Si-based negative electrode, it is considered that the Si-based active material in the short-circuited portion is delithiated due to an internal short circuit, the electronic conductivity of the electrode rapidly decreases, and the temperature rise of the battery can be suppressed by interrupting the current.

[0029] However, in an electrode having a large amount of conductive assistant in the active material layer or an electrode using a material in which a highly conductive material is coated or compounded with the active material, the electronic conductivity of the active material layer becomes high, and even if an Si-based material is used, the above-described current interruption mechanism hardly functions, and the temperature rise of the battery cannot be sufficiently suppressed. Therefore, in designing a battery that emphasizes safety, an electrode with a low conductivity of the active material layer must be used. Conversely, in an electrode composition that emphasizes safety, since the electronic conductivity is low, there is a high possibility of obtaining a low-output battery.

[0030] Even in a battery using an electrode with low electron conductivity in the active material layer, it is impossible to eliminate the instantaneous heat generation during internal short circuit. Therefore, if the binder carbonizes due to this heat generation, the electron conductivity of the electrode increases and the safety is impaired. No matter how excellent the heat resistance of the organic reactive binder is, the heat resistance temperature is limited to about 400 °C. When the temperature rise due to internal short circuit exceeds the heat resistance temperature of the binder, it carbonizes. Therefore, a binder that does not carbonize is required.

[0031] Also, in the active material, generally, a material with a small volume change is known to exhibit good life characteristics. For example, in the charge reaction of Si (Si + 4.4Li + + 4.4e - → Li 4.4 Si), a volume change of about 4 times occurs. In the charge reaction of SiO (SiO + 8.4Li + + 8.4e - → Li 4.4 Si + Li4SiO4), excluding the volume change for the initial formation of Li4SiO4, it is a volume change of about 2.7 times. Therefore, SiO exhibits excellent life characteristics compared to Si.

[0032] As another example, in a negative electrode using a mixture of Si and alumina, compared to a pure Si negative electrode, as the Si ratio decreases, the capacity decreases, but the life characteristics tend to improve. Alumina is inert to Li and does not contribute to the charge-discharge reaction, but it serves as a buffer for the volume change of Si and can reduce the volume change of the entire electrode.

[0033] For example, in the charge reaction of the Si negative electrode, according to the reaction of Equation 1 below, a volume change of about 4 times occurs compared to before charging, and the stress on the electrode binder also becomes about 4 times. Si + 4.4Li + + 4.4e - → Li 4.4 Si ····(Equation 1)

[0034] In the case of a negative electrode to which an equimolar amount of Al2O3 is added to Si, since Al2O3 is inert to Li, from a macroscopic perspective, the charging reaction is as shown in Equation (2). For such an electrode, compared with the electrode of pure Si, the volume change of the electrode is halved, so the stress on the electrode binder is also halved. Therefore, it is expected that for an electrode mixed with a material with a smaller volume change than Si, as the Si ratio decreases, the capacity decreases, but the life characteristics tend to be improved. 0.5Si + 0.5Al2O3 + 2.2Li + +2.2e - →0.5Li 4.4 Si + 0.5Al2O3 ····(Equation 2)

[0035] However, in actual life characteristics, although there is a slight life improvement effect, the deterioration rate of Si in each cycle does not change much. This is because, from a microscopic perspective, the volume change of the Si particles themselves is about 4 times, so the stress on the electrode binder remains the same as in Equation 1, and ultimately, stress concentrates at the binding part. In particular, for an electrode in which the electrode materials and the electrode material and the current collector are point-bonded with a binder, the bonding part intensively receives the stress due to the volume change, the binding property is lost, and the conductive network of the electrode is easily destroyed.

[0036] On the other hand, if the binder is surface-bonded, the binding part evenly disperses the stress, so the conductive network is less likely to be destroyed. However, since the binder inhibits the movement of ions, the output characteristics decrease. Depending on the type of binder, point bonding is likely to occur when the amount of binder is small, and surface bonding is likely to occur when the amount of binder is large.

[0037] Among several binders, at present, the binders that can stably charge and discharge alloy-based active materials are limited to reaction types such as PI. However, reaction-type binders use organic solvents during the production of the slurry, require a heat treatment process of 200 °C or higher, have a large irreversible capacity derived from the binder in the obtained electrode, and also have limitations in terms of safety.

[0038] In addition, it was difficult for the reactive binder alone to exhibit sufficient life characteristics, and it was necessary to combine it with SiO, high-strength current collector foil, etc. Organics have a low melting point, are easily soluble in organic solvents, and are flammable, while inorganics are known to have a high melting point, be insoluble in organic solvents, be incombustible, and have high thermal conductivity. Therefore, if a binder composed of inorganics can be used, there is a high possibility of obtaining an electrode with high heat resistance, excellent electrolyte resistance, and heat dissipation properties.

[0039] However, many conventional inorganic binders are not suitable for non-aqueous electrolyte secondary battery electrodes. Inorganic binders can be roughly classified into four types: silicate-based, phosphate-based, sol-based, and cement-based. Among these, the inventors of the present invention focused on silicate-based and phosphate-based binders, particularly alkali metal silicate-based binders, which have strong binding properties for all of metals, oxides, and carbon and heat resistance of 1000 °C or higher.

[0040] The silicate-based may be, in addition to alkali metal silicates, silicates of guanidine compounds and silicates of ammonium compounds. The silicate-based inorganic binder is a compound having silicon (Si) and oxygen (O) with a siloxane bond (-Si-O-Si-) as the main molecular skeleton, which is different from an organic binder having a carbon-based skeleton (see Fig. 21a).

[0041] In addition, some of the Si sites in the siloxane bond may be substituted with transition metal elements such as Al, Zr, Ti, Mg, Mo, Sr, Ca, Zn, Ba, B, W, Ta, Ce, Hf, and Y.

[0042] Silicates include orthosilicates (A4SiO4), metasilicates (A2SiO3), pyrosilicates (A6Si2O7), disilicates (A2Si2O5), tetrasilicates (A2Si4O9) and other polysilicates, as well as many types such as A2Si2O5, A2Si3O7, A2Si4O9, etc., and these may be hydrates. Also, their structures can be broadly classified into crystalline silicates and amorphous silicates (A = alkali metal element or guanidine compound, ammonium compound). Such silicates tend to have a decreasing melting point as the proportion of A in the silicate increases, and at the same time show solubility in water.

[0043] Industrially, the proportion of A in the silicate can be continuously changed, and any salt can be adjusted. The general molecular formula of the silicate is represented in the form of A2O·nSiO2.

[0044] Due to this difference in molecular skeleton, it shows higher heat resistance and oxidation resistance than organic binders and is applied in various fields such as fire retardants, waterproof agents, bleaching agents, detergents, soaps, coating agents, sealing agents, and civil engineering ground strengthening agents. However, in the field of non-aqueous electrolyte secondary batteries, there are few reported examples.

[0045] The phosphate system may be aluminum phosphate salt, magnesium phosphate salt, or calcium phosphate salt in addition to aluminum phosphate salt.

[0046] Phosphate-based inorganic binders undergo a dehydration condensation reaction in which water is removed from the hydroxyl group upon heating to form a covalent bond between phosphorus and oxygen. This dehydration condensation reaction can occur at a maximum of six sites per molecule centered on a transition metal (M), resulting in a three-dimensionally polymerized transition metal phosphate. That is, it is a compound with phosphorus (P), oxygen (O), and transition metal (M) having an aluminophosphate bond as the main molecular skeleton, which is different from an organic binder having a carbon-based skeleton (see Fig. 21b).

[0047] Further, some of the transition metal sites may be substituted with transition metal elements such as Al, Mg, Ca, Cu, Fe, Ba, Ti, Mn, Mo, Mg, Si, Sr, Ca, Zn, Ba, B, W, Ta, Ce, Hf, Y.

[0048] Specifically, aluminum phosphate salts include primary aluminum phosphate salt (Al(H2PO4)3), aluminum hydrogen phosphate salt (Al2(H2PO4)3), and aluminum metaphosphate (Al(PO3)3). Magnesium phosphate salts include primary magnesium phosphate salt (Mg(H2PO4)3), magnesium hydrogen phosphate salt (MgHPO4), and magnesium metaphosphate (Mg(PO3)2). Calcium phosphate salts include primary calcium phosphate salt (Ca(H2PO4)3), calcium hydrogen phosphate salt (CaHPO4), tricalcium phosphate salt (Ca3(H2PO4)2), and calcium metaphosphate (Ca(PO3)2), and these may be hydrates. Their structures can be broadly classified into crystalline phosphates and amorphous phosphates.

[0049] Industrially, the ratio of M to P in the phosphate can be continuously varied, and any salt can be adjusted. The general molecular formula of the phosphate is represented in the form of M·nH x PO4 (where M = Al or Mg, Ca).

[0050] The sol system is a colloidal solution in which oxide fine particles are dispersed in water. The particle size of the oxide is 10 nm or more and 200 nm or less, and hydroxyl groups are present on its surface. For example, when the oxide is SiO2, siloxane bonds are formed by dehydration condensation. However, since these siloxane bonds are formed inside the oxide particles, the bonding force is weaker compared to silicate salts. Also, pH control is important, and there is a problem that it is difficult to maintain a stable sol state. In the present invention, since the sol system is difficult to penetrate into the active material layer, its use as a skeleton former is not preferred.

[0051] Patent Document 2 shows that when an inorganic binder is included in the binder, the decomposition reaction of the binder may be suppressed. This is because carbon materials (such as graphite, soft carbon, hard carbon, etc.) have a charge-discharge plateau potential around 0.1 V (vs. Li + / Li), and since the electrode has a strong reducing power, it is considered that the decomposition reaction is suppressed by an inorganic binder with excellent reduction resistance.

[0052] However, alloy-based materials have a higher charge-discharge plateau potential than carbon materials and a weaker reducing power than carbon-based electrodes. Therefore, the decomposition reaction of the binder hardly occurs. Therefore, even if the decomposition reaction of the binder is suppressed, the life characteristics of the alloy-based electrode are not significantly improved.

[0053] Also, Patent Document 2 shows that the inorganic binder contains inorganic particles, and the particle size of the inorganic particles is preferably 1 nm or more and 100 nm or less, more preferably 1 nm or more and 50 nm or less, and even more preferably 1 nm or more and 10 nm or less. By setting the particle size in this way, it is described that a binder with even better dispersibility and adhesion of the electrode binder can be obtained.

[0054] Since inorganic particles have a larger specific gravity than carbon materials, as the particle size of the inorganic particles increases, the precipitation rate of the particles increases, and the dispersibility and adhesion decrease. Therefore, it is effective to use particles of 100 nm or less. However, when drying after electrode coating, particles of 100 nm or less prevent the escape path of vaporized moisture, causing the coating film to foam, resulting in problems such as a decrease in the binding property with the current collector or difficulty in obtaining a uniform electrode. Also, such an electrode does not contain an organic binder with excellent flexibility, so it is brittle and breaks when the electrode is bent. Therefore, it is not suitable for wound-type batteries.

[0055] On the one hand, alloy-based active materials are known to have a higher capacity than conventional carbon-based active materials. For example, Si shows a high capacitance of 2800 - 4000 mAh / g, SiO shows 1300 - 2000 mAh / g, Sn shows 700 - 1000 mAh / g, and S shows 800 - 1500 mAh / g. Therefore, even a small error can cause a large variation in the electrode capacitance, which may deteriorate the life characteristics and output characteristics. In addition, the viscosity adjustment of the electrode slurry varies dramatically depending on the amount of solvent used, making it difficult to control.

[0056] Patent Document 3 and Patent Document 4 provide physically and chemically stable lithium-ion batteries using an inorganic binder. Examples of the electrodes describe a graphite negative electrode (graphite anode) and a LiCoO2 positive electrode (LiCoO2 cathode). In the graphite negative electrode, it is composed of 1.0 g of lithium hydroxide, 23.4 g of an inorganic binder (lithium polysilicate), and 45.0 g of graphite powder.

[0057] Therefore, when the total solid content of the active material, conductive assistant, and binder is 100% by mass, the active material is 64.8% by mass and the inorganic binder is 33.7% by mass.

[0058] In the LiCoO2 positive electrode, it is composed of 1.0 g of lithium hydroxide, 1.9 g of graphite powder, 2.9 g of C-100 carbon black, 24 g of an inorganic binder (lithium polysilicate), and 85.6 g of graphite powder.

[0059] Therefore, when the total solid content of the active material, conductive assistant, and binder is 100% by mass, the active material is 74.2% by mass and the inorganic binder is 20.8% by mass. Note that in Patent Document 3 and Patent Document 4, there is no description regarding inorganic particles, and inorganic particles are not included in the examples.

[0060] The above-mentioned Patent Documents 2 to 4 all aim to improve the decomposition reaction of the binder and the swelling caused by the electrolyte, which are difficult to achieve with conventional organic binders. By using an alloy material such as Si-based or Sn-based as the active material and a binder that is difficult to swell with the electrolyte, it seems possible to expand the operating temperature range of the electrode and achieve a higher capacity.

[0061] However, since the silicate-based binder is strongly alkaline and the phosphate-based binder is strongly acidic, the alloy-based active material dissolves during the preparation of the electrode slurry, generating hydrogen gas and causing the slurry to foam. In particular, since the temperature becomes high during electrode drying, the amount of hydrogen gas generated increases, making it impossible to manufacture a uniform electrode. In addition, if a current collector that is not resistant to alkali or acid is used, the current collector will deteriorate.

[0062] For example, when the Si active material comes into contact with an alkali metal silicate, the reaction Si + 2OH - + H2O → SiO3 - + 2H2↑ occurs. Therefore, at present, the only option is an active material that is resistant to alkali or acid, that is, a carbon-based material. In addition, a binder, which is one of the components of the electrode, is used to bind the active material to the active material, the active material to the conductive additive, the active material to the current collector, and the conductive additive to the current collector. However, since the current battery employs an organic binder such as PVdF or SBR, its thermal conductivity is lower than that of inorganic materials such as the active material, the conductive additive, and the current collector, making it difficult to transfer heat. In addition, compared with conventional organic binders, inorganic binders such as silicate-based and phosphate-based binders have a higher specific gravity. Therefore, when the total solid content of the active material, the conductive additive, and the binder is 100% by mass, the amount of binder used during electrode preparation must be 20% by mass or more to exhibit sufficient binding force. In particular, when a material with a large volume change is used, 30 - 70% by mass is required. As a result, the proportion of the active material in the electrode decreases, and the electrode energy density decreases.

[0063] As described above, the inventors of the present application initially conducted repeated studies on the application of silicate-based or phosphate-based binders. However, when silicate-based or phosphate-based binders were applied, it was found that there are many problems at present and they cannot be formed into practical electrodes. Therefore, the inventors conducted repeated studies so that they can be applied to electrodes, rather than using silicate-based or phosphate-based binders, and thus arrived at the present invention. The present invention can solve the above-described conventional problems and the problems newly discovered by the inventors.

Means for Solving the Problems

[0064] The skeleton forming agent according to the present invention is a skeleton forming agent used for an electrode of a non-aqueous electrolyte secondary battery, and is characterized by containing a silicate having a siloxane bond in its components or a phosphate having an aluminophosphate bond in its components. According to this configuration, by using a skeleton forming agent containing a silicate or a phosphate for the electrode, an electrode excellent in heat resistance, high strength, and improved cycle life characteristics can be obtained.

[0065] Further, in this skeleton forming agent, the silicate has a crystalline or amorphous structure represented by the general formula A2O·nSiO2, where A is at least one of Li, Na, K, triethanolammonium group, tetramethanolammonium group, tetraethanolammonium group, and guanidine group, and n is 0.5 or more and 5.0 or less.

[0066] Preferably, in this skeleton forming agent, A in the general formula is Li or Na, n is 1.6 or more and 3.9 or less, and more preferably 2.0 or more and 3.5 or less. From the viewpoint that A is excellent in mechanical strength, binding property, and abrasion resistance for skeleton formation, Na is preferable. Note that Li is excellent in input / output characteristics of the battery because a skeleton forming body having high ionic conductivity can be obtained. However, even when it is Na, if the number n of SiO2 exceeds 5.0, the binding property with the active material layer and the separator is inferior, and peeling and cracking are extremely likely to occur due to volume change of the electrode during charge and discharge and external factors such as a nail penetration test. Further, the viscosity becomes too low, and the dispersibility stability with the ceramics described later decreases.

[0067] Conversely, when n is less than 0.5, due to high viscosity, it becomes difficult for the skeleton former to penetrate or coat the electrode active material layer and the separator. In addition, when kneading with ceramics, the amount of heat generated increases.

[0068] The silicate is preferably amorphous. If it is an amorphous silicate, since it does not crack in a specific direction like a crystal, the life characteristics of the electrode are improved. In addition, since the resistance to hydrofluoric acid is improved, electrode disintegration due to hydrofluoric acid can be less likely to occur.

[0069] Normally, an amorphous solid consists of a disordered molecular arrangement and does not have a distinguishable crystal lattice. Also, the solubility of an amorphous solid is higher than that of a crystalline form and it does not have a definite melting point. Therefore, the absence of distinct peaks in the powder X-ray diffraction (XRD) pattern and the absence of an endothermic melting peak in the differential thermal analysis (DTA) curve or differential scanning calorimetry (DSC) curve indicate the amorphous form.

[0070] That is, an amorphous silicate shows a broad and typical peak, so-called halo pattern, within the diffraction angle (2θ) range of 15° to 40° by Cu-Kα line in XRD, without the sharp peaks which are characteristics of the crystalline form. More specifically, essentially, it shows the same XRD pattern as FIG. 17.

[0071] However, even if a halo pattern is obtained by XRD, not all of them are necessarily amorphous. However, that is only under the limited condition that the crystal grains are less than 5 nm according to the Scherrer equation shown in Equation 3. That is, when the crystal grains are 5 nm or more, the diffraction line does not become a broad pattern similar to the amorphous one. D(Å)=0.9λ / (β×cosθ) ····(Equation 3) (In the formula, D represents the size of the crystal grains, λ represents the wavelength of the X-ray tube, β represents the spread of the diffraction line due to the size of the crystal grains, and θ represents the diffraction angle)

[0072] Also, when changing from an amorphous state to a crystalline state, a large amount of heat is generated. By measuring this, it is also possible to determine the crystalline state of the silicate. Amorphous silicate can be obtained by heat-treating an electrode at a heating rate of 10 °C / h or more and a temperature of 80 °C or more and 600 °C or less.

[0073] Preferably, the solid content concentration of the silicate in this skeleton-forming agent is 0.1% by mass or more and 30% by mass or less. More preferably, it is 0.1% by mass or more and 15% by mass or less.

[0074] Also, this skeleton-forming agent further contains a surfactant, and the surfactant is 0.001% by mass or more and 5.0% by mass or less. According to this configuration, the lyophilicity of the skeleton-forming agent to the active material layer is improved, and the skeleton-forming agent uniformly penetrates into the active material layer. Therefore, a uniform skeleton is formed in the active material layer, and the cycle life characteristics are further improved. If it is less than 0.001% by mass, it is difficult for the skeleton-forming agent to penetrate into the active material layer containing a large amount of carbon-based materials such as graphite, hard carbon, and conductive aids. If it exceeds 5% by mass, a defoaming agent is required, and without a defoaming agent, the surface of the active material layer foams and it is difficult to form a strong skeleton.

[0075] Also, this skeleton-forming agent further contains alkali-resistant inorganic particles. According to this configuration, when the skeleton-forming agent is applied to the electrode, inorganic particles are laminated on the surface of the active material layer of the electrode, the active material layer is covered with a layer of inorganic particles, and inorganic particles also enter the active material layer.

[0076] Thereby, a strong skeleton can be formed in the active material layer, peeling and crack generation during drying can be suppressed, and pores are formed by the gaps between the inorganic particles to obtain good lyophilicity with the electrolyte. Also, an electrode excellent in heat resistance, high strength, and wear resistance is obtained by the layer of inorganic particles. Further, the layer of inorganic particles can replace the separator, and it becomes possible to configure a battery without using a separate separator.

[0077] Preferably, when the total solid content including the silicate and the alkali-resistant inorganic particles is 100% by mass, the silicate is 5% by mass or more and 80% by mass or less, and the alkali-resistant inorganic particles are 20% by mass or more and 95% by mass or less, and the median diameter (D 50 ) of the alkali-resistant inorganic particles is 0.2 μm or more and 20 μm or less.

[0078] Here, the median diameter (D 50 ) means the particle diameter on a volume basis in the laser diffraction / scattering particle size distribution measurement method. The laser diffraction / scattering particle size distribution measurement method is a method of measuring the particle size by utilizing the phenomenon that the light intensity distribution of the diffracted and scattered light differs depending on the particle size when laser light is applied to the particles.

[0079] When the above alkali-resistant inorganic particles are included in the skeleton-forming agent, the skeleton-forming agent is less likely to foam when dried at a high temperature. If the skeleton-forming agent foams, the binding property with the active material layer and the separator decreases, and it becomes difficult to obtain sufficient strength.

[0080] The reason for setting the median diameter (D 50 ) of the alkali-resistant inorganic particles to 0.2 μm or more and 20 μm or less is that pores are formed due to the gaps between the inorganic particles, and good lyophilicity with the electrolyte can be obtained. From the viewpoint of the output characteristics of the battery, it is more preferably 0.25 μm or more and 10 μm or less, and even more preferably 0.3 μm or more and 2 μm or less.

[0081] If the particle size of the inorganic particles is larger than this range, the thixotropy decreases and a tendency to exhibit dilatancy occurs, and the dispersion stability when the inorganic particles are added to the skeleton-forming agent decreases. Conversely, if the particle size is smaller than this range, when forming a skeleton with a thickness exceeding 2 μm, there is no escape path for the moisture vaporized during drying, the coating film foams, not only does the binding property with the current collector decrease, but it is also difficult to obtain a uniform electrode.

[0082] The reason why the above inorganic particles require alkali resistance is that silicate exhibits strong alkalinity (pH 12 or higher). In addition to the alkali resistance, it is desirable that this skeleton former be an inorganic particle excellent in solubility resistance in the electrolyte solution.

[0083] Examples of inorganic particles satisfying such conditions include oxides, hydroxides, nitrides, carbides, carbonate compounds, sulfate compounds, etc. of at least one or more elements selected from the group consisting of Al, Zr, Ti, Si, Mg, Mo, Sr, Ca, Zn, Ba, B, W, Ta, Ce, Hf, and Y. Among these, from the viewpoint of being a material that is less likely to undergo oxidative decomposition or reductive decomposition during charging and discharging of the battery and has a small irreversible capacity, it is preferable to contain Al2O3, ZrO2, TiO2, SiO2, CaO, MgO, CeO, Y2O3, AlN, WC, SiC, B4C, BN, TaC, TiC, TiB2, HfB2, Si3N4, TiN, CaCO3, MgSO4, Al2(SO4)3, CaSO4, ZrSiO4.

[0084] In addition, from the viewpoint of being a material with a small irreversible capacity of the battery, it is preferable to contain Al2O3, ZrO2, TiO2, SiO2, MgO, CeO, Y2O3, WC, SiC, B4C, TaC, TiC, Si3N4, TiN, CaCO3, MgSO4, CaSO4, ZrSiO4. With these materials, it is possible to suppress the large volume shrinkage of silicate generated during drying and to have sufficient strength even when dried at a low temperature.

[0085] On the other hand, the phosphate has a crystalline or amorphous structure represented by the general formula M·nH x PO4, where M is at least one of Al, Ca, and Mg, x is 0 or more and 2 or less, and n is 0.5 or more and 5 or less.

[0086] From the viewpoint of excellent mechanical strength, binding property, and wear resistance in skeleton formation, Al is preferable for M. From the viewpoint of excellent binding property in skeleton formation, x is preferably 1 to 2, more preferably 2. From the viewpoint of excellent mechanical strength, binding property, and wear resistance in skeleton formation, n is preferably 0.5 to 5.0, more preferably 2.5 to 3.5. Similar to the case of silicate, the phosphate is preferably amorphous.

[0087] Preferably, in this skeleton-forming agent, the solid content concentration of the phosphate is 0.1 mass% or more and 30 mass% or less. More preferably, it is 0.1 mass% or more and 15 mass% or less.

[0088] Also, this skeleton-forming agent contains a surfactant, and preferably, the surfactant is 0.001 mass% or more and 5.0 mass% or less.

[0089] Also, this skeleton-forming agent preferably further contains acid-resistant inorganic particles. According to this configuration, when the skeleton-forming agent is applied to the electrode, the inorganic particles are laminated on the surface of the active material layer of the electrode, the active material layer is covered with a layer of inorganic particles, and the inorganic particles also enter the active material layer.

[0090] Thereby, a strong skeleton can be formed in the active material layer, peeling and crack generation during drying can be suppressed, and pores are formed by the gaps between the inorganic particles, resulting in good liquid affinity with the electrolyte. Also, the layer of inorganic particles forms an electrode with excellent heat resistance, high strength, and excellent wear resistance. Further, the layer of inorganic particles serves as a separator, and it becomes possible to construct a battery without using a separate separator.

[0091] Preferably, in this skeleton-forming agent, when the total solid content including the phosphate and the acid-resistant inorganic particles is 100 mass%, the phosphate is 5 mass% or more and 80 mass% or less, the acid-resistant inorganic particles are 20 mass% or more and 95 mass% or less, and the median diameter (D 50 ) of the acid-resistant inorganic particles is 0.2 μm or more and 20 μm or less.

[0092] When the above-mentioned acid-resistant inorganic particles are included in the skeleton-forming agent, the skeleton-forming agent is less likely to foam when dried at a high temperature. If the skeleton-forming agent foams, the binding property with the active material layer and the separator decreases, and it becomes difficult to obtain sufficient strength. The median diameter (D 50 ) of the acid-resistant inorganic particles is preferably 0.2 μm or more and 20 μm or less.

[0093] The reason why the above-mentioned inorganic particles require acid resistance is that the phosphate exhibits strong acidity (pH 1 to 2). In addition to the acid resistance, it is desirable that this skeleton-forming agent is an inorganic particle excellent in solubility resistance in the electrolyte.

[0094] Examples of the inorganic particles satisfying such conditions include oxides, hydroxides, nitrides, carbides, carbonate compounds, sulfate compounds, etc. of at least one or more elements selected from the group consisting of Al, Zr, Ti, Si, Mo, Sr, Ba, B, W, Ta, Ce, Hf, and Y. Among these, from the viewpoint of being a material that is less likely to undergo oxidative decomposition or reduction decomposition during charging and discharging of the battery and has a small irreversible capacity, it is preferable to contain Al2O3, ZrO2, TiO2, SiO2, CeO, Y2O3, WC, SiC, B4C, BN, TaC, TiC, TiB2, HfB2, Si3N4, TiN, ZrSiO4.

[0095] In addition, from the viewpoint of being a material with a small irreversible capacity of the battery, it is preferable to contain Al2O3, ZrO2, TiO2, SiO2, CeO, Y2O3, WC, SiC, B4C, BN, TaC, TiC, Si3N4, TiN, ZrSiO4. With these materials, it is possible to suppress the large volume shrinkage of the phosphate generated during drying and to have sufficient strength even when dried at a low temperature.

[0096] In terms of battery life, input / output characteristics, irreversible capacity, moisture absorption resistance, heat resistance, etc., the silicate system is preferable between the silicate system and the phosphate system.

[0097] The electrode according to the present invention is an electrode for a non-aqueous electrolyte secondary battery, characterized in that the above-mentioned skeleton former is present at least on the surface of the active material layer. According to this configuration, a skeleton former containing silicate or phosphate constitutes the skeleton of the electrode, resulting in an electrode with excellent heat resistance, high strength, and improved cycle life characteristics. Also, in a case where a binder containing silicate or phosphate is used, an electrode cannot be formed, but by attaching the skeleton former to the surface of the active material layer, an electrode with excellent cycle life characteristics can be obtained.

[0098] Here, a non-aqueous electrolyte secondary battery is a secondary battery using an electrolyte that does not contain water as a main component, and examples include lithium secondary batteries (lithium ion batteries), sodium batteries (sodium ion batteries), potassium batteries (potassium ion batteries), and the like. Also, the electrode is not particularly limited as long as it is an electrode used in a non-aqueous electrolyte secondary battery, and the material and shape of the electrode are also not particularly limited.

[0099] Also, an electrode has a negative electrode and a positive electrode. First, regarding the negative electrode, the negative electrode active material used for the negative electrode is not particularly limited as long as it is a material capable of reversibly occluding and releasing alkali metal ions (such as lithium ions, sodium ions, potassium ions, etc.). For example, at least one or more elements selected from the group consisting of Li, Na, K, C, Mg, Al, Si, P, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Y, Zr, Nb, Mo, Pd, Ag, Cd, In, Sn, Sb, W, Pb, and Bi, an alloy, a composite, an oxide, a chalcogenide, or a halide using these elements may be used.

[0100] From the viewpoint that the discharge plateau region can be observed within the range of 0 to 1 V (vs. Li + / Li), at least one or more elements selected from the group consisting of Li, Na, K, C, Mg, Al, Si, Ti, Zn, Ge, Fe, Mn, Ag, Cu, In, Sn, and Pb, an allotrope, an alloy, or an oxide using these elements are preferable.

[0101] Furthermore, from the perspective of energy density, as elements, Al, Si, Zn, Ge, Ag, Sn, etc. are preferable. As alloys, combinations such as Si-Al, Al-Zn, Si-Mg, Si-La, Al-Ge, Si-Ge, Si-Ag, Si-Sn, Si-Ti, Si-Y, Si-Cr, Si-Ni, Si-Zr, Si-V, Si-Nb, Si-Mo, Zn-Sn, Ge-Ag, Ge-Sn, Ge-Sb, Ag-Sn, Ag-Ge, Sn-Sb, etc. are preferable. As oxides, Fe2O3, CuO, MnO2, NiO, Li4Ti5O 12 , H2Ti 12 O 25 , Na2Ti3O7, etc. are preferable. As alloys, they may be full solid solution type alloys, eutectic alloys, hypoeutectic alloys, hypereutectic alloys, peritectic alloys. Also, the surface of the active material particles may be coated with a material or ceramics having excellent electron conductivity. In addition, two or more of these materials capable of reversibly occluding and releasing lithium may be used.

[0102] The shape of the active material particles is not particularly limited and may be spherical, elliptical, prismatic, strip-shaped, fiber-shaped, flake-shaped, donut-shaped, or hollow-shaped. Materials capable of reversibly occluding and releasing alkali metal ions (lithium ions, sodium ions, potassium ions) are more preferably substances capable of occluding and releasing alkali metal ions during the initial charging process and compounds that decompose into solid electrolytes.

[0103] The solid electrolyte is not particularly limited as long as it is a substance having ion conductivity, but is preferably a solid electrolyte represented by LiαXβYγ. Here, in the formula, 0 < α ≤ 4, 0 ≤ β ≤ 2, 0 ≤ γ ≤ 5. The solid electrolyte also serves as a buffer material for materials capable of reversibly occluding and releasing alkali metal ions.

[0104] X is, for example, one or more of Si, Ti, Mg, Ca, Al, V, Ge, Zr, Mo, Ni, and Y is one or more of O, S, F, Cl, Br, I, P, B2O3, C2O4, CO3, PO4, S, CF3SO3, SO3. More specifically, for example, LiF, LiCl, LiBr, LiI, Li3N, LiPON, Li2C2O4, Li2CO3, LiAlCl4, Li2O, Li2S, LiSO4, Li2SO4, Li3PO4, Li3VO4, Li4GeO4, Li2Si2O5, Li2SiO3, Li4SiO4, Li4ZrO4, LiMoO4, LiAlF4, Li3Ni2, LiBF4, LiCF3SO3, NaF, NaCl, NaBr, NaI, Na3N, NaPON, Na2C2O4, Na2CO3, NaAlCl4, Na2O, Na2S, NaSO4, Na2SO4, Na3PO4, Na3VO4, Na4GeO4, Na2Si2O5, Na2SiO3, Na4SiO4, Na4ZrO4, NaMoO4, NaAlF4, Na3Ni2, NaBF4, NaCF3SO3, KF, KCl, KBr, KI, K3N, KPON, K2C2O4, K2CO3, KAlCl4, K2O, K2S, KSO4, K2SO4, K3PO4, K3VO4, K4GeO4, K2Si2O5, K2SiO3, K4SiO4, K4ZrO4, KMoO4, KAlF4, K3Ni2, KBF4, KCF3SO3, etc. can be mentioned, and one or more of these can be used.

[0105] Examples of substances that can occlude and release alkali metal ions and compounds that decompose into solid electrolytes include SiO, GeO, GeS, GeS2, SnO, SnO2, SnC2O4, SnO-P2O5, SnO-B2O3, SnS, SnS2, Sb2S3, SnF2, SnCl2, SnI2, SnI4, etc. Two or more of these may be used. However, substances that can occlude and release alkali metal ions and compounds that decompose into solid electrolytes are preferably pre-doped because the battery capacity will decrease extremely if not pre-doped before assembling the battery.

[0106] Regarding the pre-doping method, as described in patent documents (Japanese Patent Laid-Open No. 2015-088437) and non-patent documents (Chapter 3, Section 30, pp. 200-205, Technical Information Association, "Measurement and Analysis Data Collection of Lithium Secondary Battery Components"), known methods such as electrochemical methods, alkali metal pasting methods, and mechanical methods can be used. Although the reason is not clear, in the present invention, for the electrode subjected to skeleton formation, a particularly remarkable cycle life improvement effect is exhibited when it is Si, Si alloy, Si composite, Si oxide, or a mixture containing any one or more of these.

[0107] Regarding the particle size of the active material, when using an active material powder with a small particle size, the disintegration of the particles is reduced, and the life characteristics of the electrode tend to be improved. Also, the specific surface area increases, and the output characteristics tend to be improved. For example, according to non-patent documents ("Latest Technical Trends of Rare Metal-Free Secondary Batteries", Chapter 3, Section 1, Item 4, PP. 125-135, CMC Publishing, 2013), it is described that when the particle size of the active material becomes smaller, the initial discharge capacity increases and the cycle life is also improved, indicating that there is a correlation between the active material particle size and the initial charge-discharge efficiency and cycle life.

[0108] However, since nano-order active materials are difficult to handle, it is preferable to use them after granulation. For example, Japanese Patent No. 5525003 shows a negative electrode using nano-granules using any one or more granulation binders of polyimide, polybenzimidazole, styrene-butadiene rubber, polyvinylidene fluoride, carboxymethyl cellulose, and polyacrylic acid. By granulating nano-order active materials, the stress applied to the copper foil due to the expansion and contraction of the negative electrode active material can be relaxed, preventing deformation of the copper foil.

[0109] On the other hand, it is also conceivable to use the skeleton-forming agent of the present invention as a binder for granulating the above-described negative electrode active material. It is said that the smaller the particle size of the active material, the better the output characteristics and cycle characteristics. However, a powder composed of small particles is easy to burn, and scattering and aggregation are likely to occur, so it is difficult to handle. By using this granulating binder, combustion can be suppressed and handling becomes easier. In addition, as described above, the volume change of the active material can be alleviated. Also, the primary particles of the active material preferably have a median diameter (D 50 ) in the range of 0.01 μm to 10 μm, and the active material particles (secondary particles) after granulation preferably have a median diameter (D 50 ) in the range of 1 μm to 100 μm.

[0110] In addition, as a method for granulating the active material, known granulation methods can be applied. For example, fluidized bed granulation method, stirring granulation method, rolling granulation method, spray drying method, extrusion granulation method, rolling granulation method, and coating granulation method can be mentioned. Among these, the spray drying method and the fluidized bed granulation method are particularly preferred.

[0111] In the spray drying method, for example, a suspension in which the active material is dispersed in the skeleton-forming agent is sprayed from above into a greenhouse heated to 50 to 300 °C at a rate of 1 to 30 mL / min and an air pressure of 0.01 to 5 MPa to form agglomerated particles, and these are dried to obtain a granulated product.

[0112] In the fluidized bed granulation method, for example, the powder raw material is put into a fluidized bed granulation apparatus, and hot air heated to 50 to 300 °C is sent in from below to fluidize and mix the powder raw material (precursor of the granulated product). Then, water in which the skeleton-forming agent is dissolved is sprayed from above onto this mixed powder raw material by a nozzle at a rate of 1 to 30 mL / min and an air pressure of 0.01 to 5 MPa to form agglomerated particles, and these are dried to obtain a granulated product.

[0113] However, when using active materials with poor alkali resistance such as Si and Sn, there is a high possibility of reacting with the skeleton-forming agent to generate hydrogen gas and not being able to function as a negative electrode. Therefore, when using the skeleton-forming agent of the present invention, it is considered that by spraying the skeleton-forming agent onto the secondary particles previously granulated with the granulation organic binder and forming a skeleton on the granulated product, the generation of hydrogen gas can be minimized as much as possible.

[0114] In addition, as the granulation organic binder, known ones can be used. For example, a binder used for a positive electrode or a negative electrode may be used. However, from the viewpoints of chemical stability, heat resistance, reduction resistance, etc. of the granulated body, polybenzimidazole, styrene-butadiene rubber, polyvinylidene fluoride, carboxymethyl cellulose, polyvinyl alcohol, polyacrylic acid, cellulose nanofiber, polyimide, polyamide, and polyamideimide are preferable.

[0115] The amount of the granulation binder is not particularly limited as long as it can bind the active material particles, but it is preferably in the range of 0.1 to 30% by mass with respect to the granulated body. The granulated body may contain a conductive auxiliary for imparting electron conductivity as necessary in addition to the active material particles and the granulation binder. The skeleton-forming agent is preferably contained in the range of 0.2 to 30% by mass with respect to the granulated body. The granulated body thus obtained not only improves the cycle life characteristics but also improves the coating property of the slurry.

[0116] The conductive auxiliary for the negative electrode is not particularly limited as long as it has electron conductivity, and the above-described metals, carbon materials, conductive polymers, conductive glasses, etc. can be used. Specifically, acetylene black (AB), ketjen black (KB), furnace black (FB), thermal black, lamp black, channel black, roller black, disk black, carbon black (CB), carbon fiber (for example, vapor-grown carbon fiber named VGCF which is a registered trademark), carbon nanotube (CNT), carbon nanohorn, graphite, graphene, glassy carbon, amorphous carbon, etc. can be mentioned, and one or more of these may be used.

[0117] When the total of the active material, binder, and conductive assistant contained in the negative electrode is 100% by mass, it is preferable that the conductive assistant is contained in an amount of 0 to 20% by mass. That is, the conductive assistant is contained as needed. When it exceeds 20% by mass, since the proportion of the active material as a battery is small, the electrode capacity density tends to be low.

[0118] The binder for the negative electrode may be one that is commonly used, for example, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), polyimide (PI), polyamide, polyamideimide, aramid, polyacrylic, styrene-butadiene rubber (SBR), ethylene-vinyl acetate copolymer (EVA), styrene-ethylene-butylene-styrene copolymer (SEBS), carboxymethyl cellulose (CMC), chitosan gum, polyvinyl alcohol (PVA), ethylene vinyl alcohol, polyvinyl butyral (PVB), ethylene vinyl alcohol, polyethylene (PE), polypropylene (PP), polyacrylic acid, lithium polyacrylate, sodium polyacrylate, potassium polyacrylate, ammonium polyacrylate, methyl polyacrylate, ethyl polyacrylate, polyacrylic acid amine, polyacrylic acid ester, epoxy resin, polyethylene terephthalate (PET), polybutylene terephthalate (PBT), nylon, vinyl chloride, silicone rubber, nitrile rubber, cyanoacrylate, urea resin, melamine resin, phenol resin, latex, polyurethane, silylated urethane, nitrocellulose, dextrin, polyvinyl pyrrolidone, vinyl acetate, polystyrene, chloropropylene, resorcinol resin, polyaromatic, modified silicone, methacrylic resin, polybutene, butyl rubber, 2-propenoic acid, cyanoacrylate, methyl methacrylate, glycidyl methacrylate, acrylic oligomer, 2-hydroxyethyl acrylate, alginic acid, starch, lacquer, sucrose, glue, casein, cellulose nanofiber and other organic materials may be used alone or in combination of two or more.

[0119] Alternatively, a mixture of these organic binders and inorganic binders may be used. The inorganic binder may be a silicate-based, phosphate-based, sol-based, cement-based, or the like. For example, lithium silicate, sodium silicate, potassium silicate, cesium silicate, guanidine silicate, ammonium silicate, silicofluoride salt, borate, lithium aluminate, sodium aluminate, potassium aluminate, aluminosilicate, lithium aluminate, sodium aluminate, potassium aluminate, polyaluminum chloride, polyaluminum sulfate, polyaluminum silicate sulfate, aluminum sulfate, aluminum nitrate, ammonium alum, lithium alum, sodium alum, potassium alum, chromium alum, iron alum, manganese alum, ammonium nickel sulfate, diatomaceous earth, polydizirconoxane, polytantaloxane, mullite, white carbon, silica sol, colloidal silica, fumed silica, alumina sol, colloidal alumina, fumed alumina, zirconia sol, colloidal zirconia, fumed zirconia, magnesia sol, colloidal magnesia, fumed magnesia, calcia sol, colloidal calcia, fumed calcia, titania sol, colloidal titania, fumed titania, zeolite, silicoaluminophosphate zeolite, sepiolite, montmorillonite, kaolin, saponite, aluminum phosphate salt, magnesium phosphate salt, calcium phosphate salt, iron phosphate salt, copper phosphate salt, zinc phosphate salt, titanium phosphate salt, manganese phosphate salt, barium phosphate salt, tin phosphate salt, low melting point glass, plaster, gypsum, magnesium cement, resarge cement, Portland cement, blast furnace cement, fly ash cement, silica cement, phosphate cement, concrete, solid electrolyte, and other inorganic materials may be used alone or in combination of two or more kinds.

[0120] Among these, from the viewpoints of binding property, resistance to electrolyte elution, redox resistance, energy density, etc., inorganic materials such as lithium silicate, sodium silicate, potassium silicate, guanidine silicate, ammonium silicate, silicofluoride salt, aluminosilicate, aluminum phosphate salt, magnesium phosphate salt, and calcium phosphate salt are preferable.

[0121] However, when manufacturing a negative electrode with an inorganic binder, since the specific gravity of the inorganic binder is large, the electrode energy density per unit weight tends to be low. Also, in an inorganic binder with strong acid or alkali, when a poor chemical resistance active material such as Si or Sn is included, hydrogen gas is generated during the mixing of the slurry, which not only makes it difficult to perform electrode coating, but also causes foaming in the heating and drying process and makes it impossible to manufacture a uniform electrode. Further, when using a current collector with poor chemical resistance, the current collector deteriorates.

[0122] Conventionally, when using an alloy-based negative electrode active material, for the negative electrode binder, from the viewpoint of suppressing the volume change of the active material accompanying charge and discharge and improving the cycle life characteristics of the battery, for example, PI has been considered preferable. However, in the present invention, since it is possible to suppress the volume change with a skeleton former, all of the above-mentioned commonly used ones can be used.

[0123] When the total of the active material, binder, and conductive assistant contained in the negative electrode is 100% by mass, it is preferable that the binder is contained in an amount of 0.1 to 60% by mass, and more preferably 0.5 to 30% by mass.

[0124] When the binder is less than 0.1% by mass, the mechanical strength of the electrode is low, so when forming the skeleton, the active material is likely to fall off, and the cycle life characteristics of the battery may deteriorate. On the other hand, when it exceeds 60% by mass, the ionic conductivity is low, the electrical resistance is high, and since the proportion of the active material as a battery is small, the electrode capacity density tends to be low.

[0125] The current collector used for the negative electrode is not particularly limited as long as it has electronic conductivity and can conduct electricity to the held negative electrode active material. For example, conductive materials such as C, Ti, Cr, Ni, Cu, Mo, Ru, Rh, Ta, W, Os, Ir, Pt, Al, Au, etc., and alloys containing two or more of these conductive materials (for example, stainless steel) can be used. When using materials other than the above-mentioned conductive materials, for example, a multi-layer structure of different metals such as iron coated with Cu or Ni may be used.

[0126] From the viewpoints of high electrical conductivity and good stability in the electrolyte, C, Ti, Cr, Au, Fe, Cu, Ni, stainless steel, etc. are preferable as the current collector, and further from the viewpoints of reduction resistance and material cost, C, Cu, Ni, stainless steel, etc. are preferable. When using iron for the current collector substrate, in order to prevent oxidation of the surface of the current collector substrate, it is preferably coated with Ni or Cu. In addition, since the volume change of the negative electrode material accompanying charge and discharge is large in the conventional alloy-based negative electrode, the current collector substrate has been preferably stainless steel or iron. However, in the present invention, since it is possible to relieve the stress applied to the current collector by the skeleton forming agent, all of the above-mentioned commonly used ones can be used.

[0127] The shape of the current collector includes linear, rod-shaped, plate-shaped, foil-shaped, and porous. Among these, it may be porous because the packing density can be increased and the skeleton forming agent can easily penetrate into the active material layer. Examples of the porous shape include mesh, woven fabric, non-woven fabric, embossed body, punched body, expanded body, or foam. Among these, the shape of the current collector substrate is preferably an embossed body or a foam because of good output characteristics.

[0128] Next, regarding the positive electrode, the active material used for the positive electrode is not particularly limited as long as it is a positive electrode active material used in a non-aqueous electrolyte secondary battery. Known electrodes including alkali metal transition metal oxide-based, vanadium-based, sulfur-based, solid solution-based (lithium excess-based, sodium excess-based, potassium excess-based), carbon-based, organic-based, etc. are used.

[0129] In the alkali metal transition metal oxide-based, for example, LiCoO2, Li0.9 Na 0.1 CoO2, LiNiO2, LiNi 0.5 Co 0.5 O2, LiNi 0.33 Mn 0.33 Co 0.33 O2, LiNi 0.5 Mn 0.2 Co 0.3 O2, LiNi 0.6 Mn 0.2 Co 0.2 O2, LiNi 0.8 Mn 0.1 Co 0.1 O2, Li(Ni,Co,Al)O2, LiMnO2, LiMn2O4, LiFePO4, LiFe 0.5 Mn 0.5 PO4, LiMnPO4, Li2MnSiO4, Li2FeSiO4, Li2(Mn,Fe)SiO4, Li2CoSiO4, Li2MgSiO4, Li2CaSiO4, Li2ZnSiO4, LiNb2O5, LiNbO2, LiFeO2, LiMgO2, LiCaO2, LiTiO2, LiTiS2, LiCrO2, LiRuO2, LiCuO2, LiZnO2, LiMoO2, LiMoS2, LiTaO2, LiWO2, NaCoO2, NaNiO2, NaNi 0.33 Mn 0.33 Co 0.33 O2, NaMnO2, NaMn2O4, NaFePO4, NaFe 0.5 Mn 0.5 PO4, NaMnPO4, Na2MnSiO4, Na2FeSiO4, Na2(Mn,Fe)SiO4, Na2CoSiO4, Na2MgSiO4, Na2CaSiO4, Na2ZnSiO4, NaNb2O5, NaNbO2, NaFeO2, NaMgO2, NaCaO2, NaTiO2, NaTiS2, NaCrO2, NaRuO2, NaCuO2, NaZnO2, NaMoO2, NaMoS2, NaTaO2, NaWO2, KCoO2, KNiO2, KNi 0.33 Mn 0.33 Co 0.33 O2, KMnO2, KMn2O4, KFePO4, KFe 0.5 Mn 0.5Examples include PO4, KMnPO4, K2MnSiO4, K2FeSiO4, K2(Mn,Fe)SiO4, K2CoSiO4, K2MgSiO4, K2CaSiO4, K2ZnSiO4, KNb2O5, KNbO2, KFeO2, KMgO2, KCaO2, KTiO2, KTiS2, KCrO2, KRuO2, KCuO2, KZnO2, KMoO2, KMoS2, KTaO2, KWO2, etc.

[0130] Examples of vanadium-based materials include LiV2O5, LiVO2, Li3VO4, Li3V2(PO4)3, NaV2O5, NaVO2, Na3VO4, Na3V2(PO4)3, KV2O5, KVO2, K3VO4, K3V2(PO4)3, etc. Examples of sulfur-based materials include sulfur, carbon sulfide, polysulfide, polysulfurized carbon, sulfur-modified polyacrylonitrile, disulfide compounds, sulfur-modified rubber, sulfur-modified pitch, sulfur-modified anthracene, metal sulfides, etc. Examples of solid solution systems include Li2MnO3-LiNiO2, Li2MnO3-LiMnO2, Li2MnO3-LiCoO2, Li2MnO3-Li(Ni,Mn)O2, Li2MnO3-Li(Ni,Co)O2, Li2MnO3-Li(Mn,Co)O2, Li2MnO3-Li(Ni,Mn,Co)O2, Na2MnO3-NaNiO2, Na2MnO3-NaMnO2, Na2MnO3-NaCoO2, Na2MnO3-Na(Ni,Mn)O2, Na2MnO3-Na(Ni,Co)O2, Na2MnO3-Na(Mn,Co)O2, Na2MnO3-Na(Ni,Mn,Co)O2, K2MnO3-KNiO2, K2MnO3-KMnO2, K2MnO3-KCoO2, K2MnO3-K(Ni,Mn)O2, K2MnO3-K(Ni,Co)O2, K2MnO3-K(Mn,Co)O2, K2MnO3-K(Ni,Mn,Co)O2, etc.

[0131] Examples of carbon-based materials include graphite, soft carbon, hard carbon, glassy carbon, etc. Examples of organic-based materials include rubic acid, tetracyanoquinodimethane, triquinoxalinylene, phenazine dioxide, trioxotrianthrylene, indigo carmine, nitronyl nitroxide radical compounds, radiarene-based compounds, aliphatic cyclic nitroxyl radicals, benzoquinones, and the like.

[0132] The above-described positive electrode active material may be used alone or in combination of two or more. From the viewpoint of energy density, for example, LiCoO2, LiMn2O4, LiFePO4, LiFe 0.5 Mn 0.5 PO4, LiMnPO4, LiNi 0.33 Mn 0.33 Co 0.33 O2, LiNi 0.5 Mn 0.2 Co 0.3 O2, LiNi 0.6 Mn 0.2 Co 0.2 O2, LiNi 0.8 Mn 0.1 Co 0.1 O2, Li(Ni,Co,Al)O2, solid solution systems, vanadium-based systems, sulfur-based systems are preferred. The shape of the active material particles is not particularly limited and may be spherical, elliptical, diced, strip-shaped, fibrous, flaky, doughnut-shaped, or hollow.

[0133] On the other hand, similar to the case of the negative electrode, it is also conceivable to use the skeleton former of the present invention as a binder for granulating the above-described positive electrode active material. In that case, the primary particles of the active material preferably have a median diameter (D 50 ) in the range of 0.01 μm to 10 μm, and the granulated active material particles (secondary particles) preferably have a median diameter (D 50 ) in the range of 1 μm to 100 μm. The granulation method of the active material is substantially the same as the granulation method of the negative electrode active material, and known granulation methods are applicable.

[0134] In addition, the conductive aid is not particularly limited as long as it has electron conductivity. Examples thereof include metals, carbon materials, conductive polymers, conductive glasses, etc. From the viewpoints of high electron conductivity and oxidation resistance, carbon materials are preferred. Specifically, acetylene black (AB), ketjen black (KB), furnace black (FB), thermal black, lamp black, channel black, roller black, disk black, carbon black (CB), carbon fiber (for example, vapor-grown carbon fiber named VGCF which is a registered trademark), carbon nanotube (CNT), carbon nanohorn, graphite, graphene, glassy carbon, amorphous carbon, etc. may be mentioned, and one or more of these may be used.

[0135] When the total of the active material, binder, and conductive aid contained in the positive electrode is 100% by mass, it is preferable that the conductive aid is contained in an amount of 0 to 20% by mass. That is, the conductive aid is contained as necessary. When it exceeds 20% by mass, since the proportion of the active material as a battery is small, the electrode capacity density tends to be low.

[0136] The binder for the positive electrode may be a commonly used one, for example, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), polyimide (PI), polyamide, polyamideimide, polyacrylic, styrene-butadiene rubber (SBR), ethylene-vinyl acetate copolymer (EVA), styrene-ethylene-butylene-styrene copolymer (SEBS), carboxymethyl cellulose (CMC), chitosan gum, polyvinyl alcohol (PVA), polyvinyl butyral (PVB), ethylene vinyl alcohol, polyethylene (PE), polypropylene (PP), polyacrylic acid, lithium polyacrylate, sodium polyacrylate, potassium polyacrylate, ammonium polyacrylate, methyl polyacrylate, ethyl polyacrylate, polyacrylic acid amine, polyacrylic acid ester, epoxy resin, polyethylene terephthalate (PET), polybutylene terephthalate (PBT), nylon, vinyl chloride, silicone rubber, nitrile rubber, cyanoacrylate, urea resin, melamine resin, phenolic resin, latex, polyurethane, silylated urethane, nitrocellulose, dextrin, polyvinyl pyrrolidone, vinyl acetate, polystyrene, chloropropylene, resorcinol resin, polyaromatic, modified silicone, methacrylic resin, polybutene, butyl rubber, 2-propenoic acid, cyanoacrylate, methyl methacrylate, glycidyl methacrylate, acrylic oligomer, 2-hydroxyethyl acrylate, polyacetal, alginic acid, starch, sucrose, lacquer, glue, casein, cellulose nanofiber and other organic materials may be used alone or in combination of two or more. Also, a mixture of these organic binders and inorganic binders may be used.

[0137] The inorganic binder may be, for example, a silicate-based, phosphate-based, sol-based, cement-based, etc. However, when manufacturing the positive electrode only with the inorganic binder, since the specific gravity of the inorganic binder is large, the electrode energy density per unit weight tends to be low.

[0138] Conventionally, when using sulfur-based, vanadium-based, or solid solution-based cathode active materials, a binder with high binding properties has been considered preferable for the positive electrode from the perspective of suppressing the volume change of the active material during charge and discharge and improving the cycle life characteristics of the battery. However, in the present invention, since it is possible to suppress the volume change with a skeleton-forming agent, all of the commonly used ones described above can be used.

[0139] When the total of the active material, binder, and conductive assistant contained in the positive electrode is 100% by mass, it is preferable that the binder is contained in an amount of 0.1 to 60% by mass. If the binder is less than 0.1% by mass, the mechanical strength of the electrode is low, so that the active material is likely to fall off during skeleton formation, and the cycle life characteristics of the battery may deteriorate. On the other hand, when it exceeds 60% by mass, the ionic conductivity is low, the electrical resistance is high, and the proportion of the active material as a battery is small, so that the electrode capacity density is likely to be low.

[0140] The current collector used for the positive electrode is not particularly limited as long as it has electron conductivity and can conduct electricity to the held cathode active material. For example, conductive substances such as C, Ti, Cr, Ni, Cu, Mo, Ru, Rh, Ta, W, Os, Ir, Pt, Au, Al, etc., and alloys containing two or more of these conductive substances (for example, stainless steel) can be used. When using something other than the above conductive substances, for example, a multi-layer structure of different metals such as iron coated with Al may be used. From the viewpoints of high electrical conductivity and good stability in the electrolyte, C, Ti, Cr, Au, Al, stainless steel, etc. are preferable as the current collector, and further, from the viewpoints of oxidation resistance and material cost, C, Al, stainless steel, etc. are preferable. More preferably, Al coated with carbon and stainless steel coated with carbon are preferable.

[0141] The shapes of the current collectors include linear, rod-shaped, plate-shaped, foil-shaped, and porous. Among these, the porous shape may be used because it can increase the packing density and the skeleton-forming agent can easily penetrate into the active material layer. Examples of the porous shape include mesh, woven fabric, non-woven fabric, embossed body, punched body, expanded body, or foam. Among these, the shape of the current collector substrate is preferably an embossed body or a foam because of good output characteristics.

[0142] Also, this electrode is an electrode for a non-aqueous electrolyte secondary battery, and the above-mentioned skeleton-forming agent is present at least in the active material layer. According to this configuration, by applying the skeleton-forming agent to the electrode or the like, the skeleton-forming agent penetrates into the active material layer and forms a strong skeleton in the active material layer. Thereby, the volume change of the electrode is alleviated and the insulation property of the electrode surface is improved.

[0143] Also, in this electrode, the above-mentioned skeleton-forming agent is present in the active material layer, and there are gaps between the active materials in the active material layer. According to this configuration, by applying the skeleton-forming agent to the electrode or the like, the skeleton-forming agent penetrates into the active material layer. Therefore, the gaps between the active materials in the active material layer are not completely filled with the skeleton-forming agent, and the gaps between the active materials remain. Thereby, the expansion and contraction of the active material during charge and discharge are allowed, and the occurrence of wrinkles, cracks, etc. in the current collector of the electrode is suppressed.

[0144] Also, this electrode has a layer containing the alkali-resistant inorganic particles on the surface of the layer of the silicate-based skeleton-forming agent. According to this configuration, by providing the layer of inorganic particles, a strong skeleton can be formed and the occurrence of peeling and cracks during drying can be suppressed. In addition, the layer of inorganic particles can serve as a separator, and it is possible to construct a battery without using a separate separator. When the skeleton-forming agent is a phosphate-based one, a layer containing acid-resistant inorganic particles is used.

[0145] Preferably, for this one-sided coated electrode, the amount of the skeleton-forming agent per unit area is 0.01 mg / cm 2 or more and 3 mg / cm 2is as follows, or the amount of the skeleton former per unit area of the double-sided coated electrode is 0.02 mg / cm 2 or more and 6 mg / cm 2 or less. More preferably, the amount of the skeleton former per unit area of the single-sided coated electrode is 0.05 mg / cm 2 or more and 3 mg / cm 2 or less, or the amount of the skeleton former per unit area of the double-sided coated electrode is 0.1 mg / cm 2 or more and 6 mg / cm 2 or less.

[0146] Further, this electrode includes an active material capable of alloying with an alkali metal or an active material capable of occluding an alkali metal ion, an organic binder, and the skeleton former.

[0147] Preferably, when the total solid content of the active material, conductive assistant, binder, and skeleton former of this electrode is 100% by mass, the skeleton former is preferably 0.1% by mass or more and 30% by mass or less, more preferably 0.2% by mass or more and 20% by mass or less, and still more preferably 0.5% by mass or more and 10% by mass or less.

[0148] The separator according to the present invention is a separator for a non-aqueous electrolyte secondary battery, and is characterized in that the above-mentioned skeleton former is present at least on the surface.

[0149] According to this configuration, a separator with high strength, excellent heat resistance, and improved cycle life characteristics is obtained. Here, a separator generally used for a non-aqueous electrolyte secondary battery can be used. Also, the material of the separator is not particularly limited. A separator coated or filled with a ceramic layer so as not to melt down due to local heat generation during short circuit may be used. Further, the shape of the separator includes a microporous membrane, woven fabric, non-woven fabric, and compacted powder, and the shape is not particularly limited.

[0150] By applying a skeleton-forming agent to the separator, local heat generation during a short circuit can melt down the separator substrate, suppressing the short circuit of the battery. Also, when the battery is charged, oxidation of the separator on the positive electrode side can be suppressed, thereby suppressing the self-discharge of the battery. In addition, since the heat resistance of the separator is improved, the safety against nail penetration and overcharging is improved.

[0151] In addition, the silicate-based skeleton-forming agent may contain inorganic particles such as ceramics having alkali resistance. In that case, the particle size of the ceramics is preferably in the range of 0.2 to 20 μm, more preferably in the range of 0.25 to 10 μm. However, in the case of the phosphate-based one, inorganic particles such as ceramics having acid resistance may be contained. In that case, it is the same as the silicate-based one.

[0152] Alternatively, a separator in which a skeleton-forming agent is applied and filled to the ceramic layer of an existing ceramic-coated separator to improve heat resistance may be used.

[0153] The porosity of the separator is preferably 30% or more, and more preferably 40% or more and 90% or less from the viewpoints of alkali metal ion conductivity and dendrite resistance characteristics. Also, the air permeability obtained by the Gurley test method is preferably 3000 seconds / 100 cc or less. Here, the porosity is a value calculated by the formula: porosity (%) = 100 - (apparent density of the separator / true density of the solid content of the constituent material) × 100. Also, the Gurley air permeability is the air permeability resistance by the Gurley tester method defined in JIS P 8117.

[0154] Preferably, for the separator with single-sided coating, the skeleton-forming agent per unit area is 0.01 mg / cm 2 or more and 3 mg / cm 2 or less, or for the separator with double-sided coating, the skeleton-forming agent per unit area is 0.02 mg / cm 2 or more and 6 mg / cm 2 or less.

[0155] The method for manufacturing an electrode according to the present invention is a method for manufacturing an electrode of a non-aqueous electrolyte secondary battery, and includes a step A of applying a skeleton former containing a silicate having a siloxane bond or a skeleton former containing a phosphate to the surface of the active material layer of the electrode, and a step B of drying the electrode. According to this configuration, by using a skeleton former in the manufacture of the electrode, an electrode excellent in heat resistance, high strength, and improved cycle life characteristics can be manufactured.

[0156] Also, in this method for manufacturing an electrode, in the step A, the skeleton former penetrates from the surface to the inside of the active material layer.

[0157] Also, in this method for manufacturing an electrode, the step A is a step of impregnating the electrode into a tank containing the skeleton former.

[0158] Preferably, in this method for manufacturing an electrode, the solid content concentration of the silicate or phosphate in the skeleton former is 0.1 to 30 parts by mass, and the step B is a step of performing heat treatment at a temperature of 60°C or higher. When drying at a temperature lower than 60°C, the binding strength between the electrode and the separator is low, and the moisture of these cannot be sufficiently removed, so it becomes difficult to obtain stable life characteristics when assembling the battery.

[0159] Here, the method for manufacturing an electrode is, for example, a method in which an active material, a binder, and a conductive assistant added as necessary are mixed and slurried, applied to a current collector, pre-dried, and then water in which a skeleton former is dissolved is filled into the active material layer, and heat treatment is performed at 60°C or higher to obtain an electrode. That is, an electrode obtained by the slurry coating method is filled with a skeleton former in the active material layer and heat-treated to obtain an electrode. The pre-drying is not particularly limited as long as it is a method capable of volatilizing and removing the solvent in the slurry. For example, a method of performing heat treatment in an atmosphere at a temperature of 50 to 200°C in the air can be mentioned.

[0160] In addition, this heat treatment is preferably carried out at 80°C or higher, more preferably 100°C or higher, and desirably 110°C or higher, because the heat treatment time can be shortened as the temperature increases and the strength of the skeleton-forming agent is improved. The upper limit temperature of the heat treatment is not particularly limited as long as the current collector does not melt. For example, it may be raised up to about 1000°C, which is the melting point of copper. In the case of conventional electrodes, the upper limit temperature was estimated to be much lower than 1000°C because the electrode binder might carbonize or the current collector might soften. However, in the present invention, since the skeleton-forming agent exhibits excellent heat resistance and is stronger than the strength of the current collector, the upper limit temperature is 1000°C.

[0161] Also, the heat treatment can be performed by holding for 0.5 to 100 hours. The atmosphere for the heat treatment may be in the air, but it is preferably treated in a non-oxidizing atmosphere to prevent oxidation of the current collector. The non-oxidizing atmosphere means an environment where the abundance of oxygen gas is less than that in the air. For example, it may be a reduced-pressure environment, a vacuum environment, a hydrogen gas atmosphere, a nitrogen gas atmosphere, a noble gas atmosphere, etc.

[0162] In the case of an electrode using a material with irreversible capacity, it is preferable to cancel the irreversible capacity by lithium doping. The method of lithium doping is not particularly limited. For example, (i) a method of doping lithium into the electrode active material by forming a local cell by attaching metallic lithium to a portion of the electrode current collector where there is no active material layer and injecting electrolyte; (ii) a method of doping lithium into the electrode active material by attaching metallic lithium to the active material layer on the electrode current collector and injecting electrolyte to cause forced short circuit; (iii) a method of doping lithium into the electrode active material by forming a film of metallic lithium on the active material layer by vapor deposition or sputtering and performing a solid-phase reaction; (iv) a method of electrochemically doping lithium into the electrode in the electrolyte before battery assembly; (v) a method of doping lithium into the active material by adding metallic lithium to the active material powder and performing a mixing process, etc.

[0163] As other methods for manufacturing the electrode, for example, a method of forming and integrating an active material layer on a current collector using a chemical plating method, a sputtering method, a vapor deposition method, a gas deposition method, etc. with an active material or an active material precursor may be used. However, from the viewpoints of the lyophilicity of the skeleton former and the electrode manufacturing cost, the slurry coating method is preferable.

[0164] The battery according to the present invention is characterized by including the above electrode or the above separator. According to this configuration, a battery excellent in cycle life characteristics and having good safety can be obtained.

[0165] For example, in the case of a battery using the above electrode (positive electrode or negative electrode), a battery structure in which the positive electrode and the negative electrode are joined via a separator and sealed in a state of being immersed in an electrolytic solution can be considered. Note that the battery structure is not limited to this, and it can be applied to existing battery forms and structures such as laminated batteries and wound batteries.

[0166] In addition, the electrolyte used in this battery may be a liquid or a solid capable of moving alkali metal ions from the positive electrode to the negative electrode or from the negative electrode to the positive electrode, and the same electrolyte as that used in known non-aqueous electrolyte secondary batteries can be used. Examples include electrolytic solutions, gel electrolytes, solid electrolytes, ionic liquids, and molten salts. Here, the electrolytic solution refers to a state in which an electrolyte is dissolved in a solvent.

[0167] Since the electrolyte needs to contain alkali metal ions, the electrolyte salt is not particularly limited as long as it is used in a non-aqueous electrolyte secondary battery, but alkali metal salts such as lithium salts, sodium salts, and potassium salts are preferred. Examples of such alkali metal salts include lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), lithium trifluoromethanesulfonate (LiCF3SO4), lithium bis(trifluoromethanesulfonyl)imide (LiN(SO2CF3)2), lithium bis(pentafluoroethanesulfonyl)imide (LiN(SO2C2F5)2), lithium bis(oxalato)borate (LiBC4O8), sodium hexafluorophosphate, sodium perchlorate, sodium tetrafluoroborate, sodium trifluoromethanesulfonate, and sodium trifluoromethanesulfonimide, potassium hexafluorophosphate, potassium perchlorate, potassium tetrafluoroborate, potassium trifluoromethanesulfonate, and potassium trifluoromethanesulfonimide. At least one or more selected from the group consisting of these can be used.

[0168] As the solvent of the electrolyte, for example, propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), γ-butyrolactone (GBL), methyl-γ-butyrolactone, methyl lactone, 2-methyltetrahydrofuran, 1,3-dioxolane (DOL), 4-methyl-1,3-dioxolane, 1,2-dimethoxyethane, 1,2-diethoxyethane, diethyl ether, furan, dimethyl furan, tetrahydrofuran (THF), methyltetrahydrofuran (MeTHF), tetrahydropyran (THP), dioxane (DIOX), crown ether, dimethoxymethane (DMM), dimethoxyethane (DME), diglyme, triglyme, tetraglyme, methyl acetate (MA), ethyl acetate (EA), propyl acetate, isopropyl acetate, butyl acetate, methyl fluoroacetate, ethyl trifluoroacetate, methyl propionate, ethyl propionate, propyl propionate, methyl formate, ethyl formate, propyl formate, ethyl butyrate, propyl butyrate, propyl methyl butyrate, vinyl acetate, methyl cyanoacetate, γ-valerolactone, σ-valerolactone, ε-caprolactone, γ-hexalactone, γ-undecalactone, trimethyl phosphate (TMP), triethyl phosphate (TEP), tri-n-propyl phosphate, trioctyl phosphate, triphenyl phosphate, N,At least one selected from the group consisting of N-dimethylformamide (DMF), ethylenediamine, pyridine, N-methylimidazole, dimethyl sulfate, dimethyl sulfite, dipropyl sulfite, ethylene sulfite, dimethyl sulfone, ethyl methyl sulfone, diphenyl sulfone, sulfolane, methyl sulfolane, methyl methanesulfonate, methyl benzenesulfonate, methyl trifluoromethanesulfonate, propane sulfone, butane sulfone, dimethyl sulfoxide, diphenyl disulfide, dimethyl sulfide, diethyl sulfide, acetonitrile, propanenitrile, adiponitrile, valeronitrile, glutaronitrile, malononitrile, succinonitrile, pimelonitrile, suberonitrile, isobutyronitrile, biphenyl, succinic anhydride, t-butylbenzene, naphthalene, cyclohexylbenzene, benzotriazole, thiophene, toluene, methyl ethyl ketone, benzene, fluorobenzene, hexafluorobenzene, nitromethane, N,N-dimethylformamide, dimethyl sulfoxide, vinylene carbonate (VC), vinyl ethylene carbonate (EVC), fluoroethylene carbonate (FEC), and ethylene sulfite (ES) can be used.

[0169] Ionic liquids and molten salts are classified into pyridine-based, alicyclic amine-based, aliphatic amine-based, etc. according to the type of cation (positive ion). By selecting the type of anion (negative ion) to be combined with this, various ionic liquids or molten salts can be synthesized. Examples of cations include ammonium-based such as imidazolium salts and pyridinium salts, phosphonium-based ions, inorganic ions, etc. Examples of anions employed include halogen-based such as bromide ions and triflate, boron-based such as tetraphenylborate, phosphorus-based such as hexafluorophosphate, etc.

[0170] Ionic liquids and molten salts can be obtained by known synthesis methods, for example, by combining cations such as imidazolinium with anions such as Br−, Cl−, BF4−, PF6−, (CF3SO2)2N−, CF3SO3−, FeCl4−. Ionic liquids and molten salts can function as electrolytes without adding an electrolyte.

[0171] The electrical device according to the present invention is characterized by including the battery described above.

[0172] Examples of electrical appliances include irons, frothers, all-in-one computers, clothes dryers, medical devices, intercoms, wearable terminals, video devices, air conditioners, air circulators, gardening machines, motorcycles, ovens, music players, music recorders, warm air heaters, toys, car components, flashlights, speakers, car navigation systems, cassette stoves, household storage batteries, caregiving machines, humidifiers, dryers, fuel dispensers, water dispensers, suction machines, safes, glue guns, mobile phones, portable information devices, air purifiers, air-conditioned clothing, game machines, fluorescent lamps, lint removers, cordless phones, coffee makers, coffee warmers, ice crushers, kotatsu, copiers, hair styling tools, shavers, lawn mowers, automobiles, lighting fixtures, dehumidifiers, sealers, shredders, automated external defibrillators, rice cookers, stereos, stoves, speakers, trouser presses, smartphones, rice polishers, washing machines, toilet seats with a cleaning function, sensors, fans, submarines, blowers, vacuum cleaners, tablets, body fat scales, fishing gear, digital cameras, TVs, TV receivers, video games, displays, disc changers, desktop computers, railways, TVs, electric carpets, electric stands, electric stoves, electric kettles, electric blankets, calculators, electric carts, electric wheelchairs, power tools, electric vehicles, electric floats, electric toothbrushes, telephones, electric bicycles, electric insect killers, electromagnetic cookers, electronic notebooks, electronic musical instruments, electronic locks, electronic cards, microwave ovens, electronic mosquito repellents, electronic cigarettes, telephones, toasters, hair dryers, transceivers, watches, drones, food waste processors, laptop computers, incandescent bulbs, soldering irons, panel heaters, halogen heaters, fermenters, bread makers, hybrid vehicles, computers, computer peripherals, hair clippers, panel heaters, video cameras, video decks, airplanes, emergency lights, emergency storage batteries, ships, beauty devices, printers, copiers, grinders, sprayers, facsimiles, forklifts, plug-in hybrid vehicles, projectors, hair dryers, hair irons, headphones, disaster prevention devices, crime prevention devices, home theaters, hot sandwich makers, hot plates, pumps, aroma diffusers, massage machines, mixers, mills, movie players, monitors, mochi pounding machines, water heaters, floor heating panels, radios, radio cassettes, lanterns, remote control cars, laminators, remote controls, ranges, water coolers, refrigerators, cool air fans, air conditioners, robotsExamples include word processors, GPS, etc.

Advantages of the Invention

[0173] By using the skeleton forming agent according to the present invention as an electrode, unlike the case of using it as a binder, the occurrence of wrinkles, cracks, etc. can be suppressed. In addition, better life characteristics can be obtained than before. Also, even when the electron conductivity of the active material layer is high, the heat generation due to internal short circuit can be reduced.

Brief Description of the Drawings

[0174]

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Embodiments for Carrying Out the Invention

[0175] Hereinafter, an embodiment according to the present invention will be described with reference to the drawings, but the present invention is not limited to this embodiment. In particular, in this embodiment, an electrode of a lithium secondary battery (lithium ion battery) will be described as an example, but the present invention is not limited thereto. Further, as the skeleton forming agent, an aqueous solution of an alkali metal silicate containing mainly Na2O·3SiO2 will be described as an example, but it is not limited thereto.

[0176] —First Embodiment— [1. Method for manufacturing an electrode] First, as an example of this embodiment, a method for manufacturing an electrode of a lithium secondary battery will be described. Note that the electrode includes a negative electrode and a positive electrode. The negative electrode and the positive electrode are mainly different only in the current collector and the active material, and the manufacturing methods are the same. Therefore, the method for manufacturing the negative electrode will be described, and the method for manufacturing the positive electrode will be omitted as appropriate.

[0177] The negative electrode is manufactured by applying an electrode material to a copper foil. First, for example, a rolled copper foil with a thickness of 10 μm is manufactured, and a copper foil wound in a roll in advance is prepared. Further, the electrode material of the negative electrode is obtained by firing a carbon precursor to graphitize artificial graphite and mixing it with a binder, a conductive assistant, etc. to make it into a paste form. In this embodiment, as an example, PVdF is used as the binder and acetylene black (AB) is used as the conductive assistant. Then, the electrode material is coated on the surface of the copper foil, and after drying, pressure adjustment treatment is performed to complete the negative electrode body.

[0178] The positive electrode is manufactured by applying an electrode material to an aluminum foil. Note that the electrode material of the positive electrode is obtained by mixing a lithium-transition metal oxide with a binder, a conductive assistant, etc. to make it into a paste form. In this embodiment, as an example, PVdF is used as the binder and AB is used as the conductive assistant. Hereinafter, the positive electrode body and the negative electrode body are collectively referred to as the electrode body, the copper foil and the aluminum foil are collectively referred to as the current collector, and the electrode material coated on the current collector may be referred to as the active material layer.

[0179] On the other hand, in this embodiment, a skeleton former used for the electrode body is prepared in advance. The skeleton former is obtained by purifying Na2O·3SiO2, which is an alkali metal silicate having a siloxane bond, by a dry or wet method, and adjusting it with water. For example, in the dry method, it is obtained by the following formula 4, and in the wet method, it is obtained by the following formula 5. At this time, a surfactant is mixed. As an example of the skeleton former of this embodiment, the solid content concentration of Na2O·3SiO2 in the skeleton former is 5% by mass, and the surfactant is 0.04% by mass. Na2CO3 + 3SiO2 → Na2O·3SiO2 + CO2↑ ····(Formula 4) 2NaOH + 3SiO2 → Na2O·3SiO2 + H2O ····(Equation 5)

[0180] Then, a skeleton former is coated on the surface of each electrode body to coat the active material layer. The coating method of the skeleton former includes methods such as impregnating the electrode body in a tank storing the skeleton former, dropping or applying the skeleton former on the surface of the electrode body, spray coating, screen printing, curtain coating, spin coating, gravure coating, die coating, etc. The skeleton former coated on the surface of the electrode body penetrates into the interior of the active material layer and enters the gaps between the active material and the conductive assistant. Then, the electrode body is dried by hot air, heating, etc. at 110°C to 160°C to cure the skeleton former. Thereby, the skeleton former forms the skeleton of the active material layer.

[0181] Finally, each electrode body, that is, the negative electrode body and the positive electrode body, are cut into desired sizes, and the electrodes with skeleton formation are completed.

[0182] Also, the above-described method for manufacturing an electrode can be realized by a manufacturing apparatus. The current collector wound in a roll shape is sent out, the electrode material is coated on the current collector in the active material layer coating apparatus, the electrode material is dried by hot air in the first drying apparatus, the skeleton former is coated on the surface of the electrode body in the skeleton former coating apparatus, the skeleton former is dried and cured by hot air in the second drying apparatus, and then wound in a roll shape again. Finally, the electrode wound in a roll shape is cut into a desired size.

[0183] According to the above-described method for manufacturing an electrode, electrodes with high strength, excellent heat resistance, and improved cycle life characteristics can be continuously manufactured. Also, by using a silicate having a siloxane bond as a skeleton former instead of a binder, wrinkles, cracks, etc. do not occur in the copper foil, cracks, warping of the active material layer, and expansion due to the generated gas do not occur, and it can be used as an electrode.

[0184] Further, the positive electrode and the negative electrode obtained as described above are joined via a separator and sealed in a state of being immersed in an electrolytic solution, thereby forming a lithium secondary battery. According to the lithium secondary battery having this structure, it can function as a lithium secondary battery with good safety. The structure of the lithium secondary battery is not particularly limited, and it can be applied to existing battery forms and structures such as laminated batteries and wound batteries.

[0185] [2. Configuration of Electrodes] The negative electrode for a non-aqueous electrolyte secondary battery manufactured by the above manufacturing process includes a current collector of copper foil and an active material layer containing an active material, a conductive assistant, and a binder on its surface. Further, the surface of the active material layer is coated with a cured skeleton former, and a cured skeleton former also exists inside the active material layer. Further, the skeleton former inside the active material layer exists in the gaps between these so as to cover the active material, the conductive assistant, and the binder. Further, as an example, the density of the skeleton former in the active material layer is 0.7 mg / cm 2 and it is preferably in the range of 0.1 mg to 3 mg / cm 2 .

[0186] Further, the positive electrode includes a current collector of aluminum foil and an active material layer containing an active material, a conductive assistant, and a binder on its surface. Further, the surface of the active material layer is coated with a cured skeleton former, and a cured skeleton former also exists inside the active material layer. Further, the skeleton former inside the active material layer exists in the gaps between these so as to cover the active material, the conductive assistant, and the binder. Further, as an example, the density of the skeleton former in the active material layer is 0.5 mg / cm 2 and it is preferably 2 set to 0.1 mg to 3 mg / cm.

[0187] The electrode of this embodiment is high-strength, has excellent heat resistance, and has improved cycle life characteristics. Also, as shown in the nail penetration test results described later, the nail penetration safety is also improved. Further, since the skeleton forming agent is applied to the surface of the electrode by coating or impregnation, the skeleton forming agent exists in the gaps so as to cover the active material, the conductive assistant, and the binder inside the active material layer. That is, when the skeleton forming agent is kneaded with the binder and used, the skeleton forming agent exists substantially without gaps inside the active material layer, whereas in the electrode of this embodiment, a certain gap exists inside the active material layer. Thereby, expansion and contraction of the electrode can be tolerated, and the occurrence of wrinkles, cracks, etc. in the current collector can be suppressed.

[0188] [3. Configuration of Skeleton Forming Agent] As described above, the solid content concentration of Na2O·3SiO2, which is an alkali metal silicate having a siloxane bond, of the skeleton forming agent of this embodiment is 7.5% by mass, the surfactant is 0.09% by mass, and the rest is water. The surfactant is not essential, but it improves the lyophilicity to the active material layer and allows the skeleton forming agent to uniformly penetrate the active material layer.

[0189] Also, although the skeleton forming agent of this embodiment uses sodium alkali metal silicate Na2O·3SiO2 as the silicate, it is not limited thereto, and instead of Na, Li, K, triethanolammonium group, tetramethanolammonium group, tetraethanolammonium group, and guanidine group may be used.

[0190] The reason for using Na is that Na has high strength and excellent cycle life characteristics. Also, it is possible to use Na and Li in combination, and using Li improves ion conductivity. In this case, it is preferable that Li < Na, and in this way, a skeleton forming agent that retains a certain strength and has good ion conductivity is obtained. More specifically, when the total of Na and Li is 100 mol%, it is preferable that Na is in the range of 51 to 99% and Li is in the range of 1 to 49%, and it is more preferable that Na is in the range of 70 to 98% and Li is in the range of 2 to 30%.

[0191] In addition, the skeleton-forming agent of the present embodiment has a coefficient of SiO2 of 3, but is not limited thereto, and may be 0.5 or more and 5.0 or less, preferably 2.0 or more and 4.5 or less, and more preferably 2.2 or more and 3.8 or less.

[0192] In addition, the skeleton-forming agent of the present embodiment can also be used for coating existing electrodes. By doing so, an electrode with high strength, excellent heat resistance, and improved cycle life characteristics can be obtained.

[0193] In addition, the skeleton-forming agent of the present embodiment can also be used by coating the surface of the separator. By doing so, a separator with high strength, excellent heat resistance, and improved cycle life characteristics can be obtained.

[0194] [4. Examples] Hereinafter, in the present embodiment, examples in which various parameters such as the solid content concentration and skeleton density of the skeleton-forming agent are changed, and their tests, results, and effects will be described.

[0195] [Examination of the number of n in Na2O·nSiO2 and skeleton density] (Examples 1 to 18 and Comparative Example 1) Using Si-C granulated bodies as the electrode active material, under the conditions of 0.2C-rate, cut-off potential of 0.01V to 1.2V (vs. Li+ / Li), and 30°C, the solid content concentration of Na2O·nSiO2 of the skeleton-forming agent was changed from 0 mass% to 20 mass%, and the value of n was changed to 2.0, 2.5, and 3.0. This is a test on the cycle life characteristics. The Si-C granulated bodies (D 50 = 9.8μm) are composed of Si (D 50 = 1.1μm) and artificial graphite (D 50 = 1μm) (Si: artificial graphite = 29:71 mass%) and a granulation aid, and are produced by spray-drying a suspension at a feed rate of 6g / min, a spray pressure of 0.1MPa, and a drying temperature of 80 to 180°C.

[0196] A granulation aid was used, which was polyvinyl alcohol (PVA, Poval 1400). PVA is contained at 1% by mass based on 100% by mass of the solid content composed of Si, artificial graphite, and PVA. Note that D 50 The value of D indicates the median diameter measured by the laser diffraction / scattering particle size distribution measurement method.

[0197] The test electrode (1.4 mAh / cm 2 ) was prepared by coating and pressing a slurry composed of Si-C granulated bodies, AB, vapor-grown carbon fibers (VGCF), copper flakes, and PVdF (solid content ratio: 85:3:1:1:10% by mass) onto a copper foil, immersing it in an aqueous solution in which a predetermined skeleton former was dissolved, and then heat-treating it at 160°C. A metal lithium foil was used as the counter electrode. A glass nonwoven fabric (manufactured by Toyo Roshi Kaisha, Ltd., GA-100) and a polyethylene (PE) microporous membrane (20 μm) were used as the separator. As the electrolyte, 1.0 M LiPF6 / (EC:DEC = 50:50 vol%, + 1% by mass of vinylene carbonate) was used.

[0198] Table 1 shows the solid content concentrations of the skeleton formers and the values of n in Na2O·nSiO2 for Examples 1 to 18 and Comparative Example 1. The inorganic skeleton former was prepared by formulating a mixture composed of Na2CO3 and SiO2 to have the composition shown in Table 1 below, heating and melting it at 1000°C or higher, cooling it, and then dissolving it in water.

[0199]

Table 1

[0200] Figure 4 is a graph showing the cycle life characteristics of Examples 1 to 18 and Comparative Example 1. As is clear from Figure 4, the negative electrodes (Examples 1 to 18) coated with the skeleton former have significantly improved life characteristics compared to the uncoated negative electrode (Comparative Example 1). Among these, the solid content concentration of Na2O·nSiO2 showed particularly excellent cycle life characteristics in the range of 2 to 10% by mass. The value of n in Na2O·nSiO2 showed particularly excellent cycle life characteristics at 3.0.

[0201] FIG. 5 is a graph showing the relationship between the density (skeletal density) of the skeletal formation bodies of Examples 1 to 18 and Comparative Example 1 and the discharge capacity at each cycle. As is clear from FIG. 5, in the electrode using the Si—C granulated body (Si: artificial graphite = 29:71% by mass) as the active material, when the skeletal density is 0.04 to 3.15 mg / cm 2 it can be seen that a sufficient discharge capacity can be obtained. More preferably, the skeletal density is 0.1 to 2.5 mg / cm 2 .

[0202] (Examples 19 to 36 and Comparative Example 2) In Examples 19 to 36 and Comparative Example 2, as the active material, the composition of the Si—C granulated body was changed from Si: artificial graphite = 29:71% by mass to 46:54% by mass, and the capacity density of the test electrode was 1.2 mAh / cm 2 In addition, it is the same as the previous test (Examples 1 to 18 and Comparative Example 1). Table 2 shows the solid content concentration of the skeletal formation agent and the value of n of Na2O·nSiO2 in Examples 19 to 36 and Comparative Example 2, respectively.

[0203]

Table 2

[0204] FIG. 6 is a graph showing the cycle life characteristics of Examples 19 to 36 and Comparative Example 2. As is clear from FIG. 6, the negative electrodes (Examples 19 to 36) coated with the skeletal formation agent have greatly improved life characteristics compared to the uncoated negative electrode (Comparative Example 2). Among these, the solid content concentration of Na2O·nSiO2 showed particularly excellent cycle life characteristics in the range of 2 to 10% by mass. The value of n in Na2O·nSiO2 showed particularly excellent cycle life characteristics at 3.0.

[0205] FIG. 7 is a graph showing the relationship between the density (skeletal density) of the skeletal formation bodies of Examples 19 to 36 and Comparative Example 2 and the discharge capacity at each cycle. As is clear from FIG. 7, in the electrode using the Si—C granulated body (Si: artificial graphite = 46:54% by mass) as the active material, when the skeletal density is 0.03 to 3.45 mg / cm 2It can be seen that a sufficient discharge capacity can be obtained in this case. More preferably, the skeletal density is 0.1 to 2.5 mg / cm 2 is obtained.

[0206] (Examples 37 to 40 and Comparative Example 3) In Examples 37 to 40, the active material is Si (D 50 = 1.1 μm), the skeleton former is Li 0.05 Na 1.95 O·3SiO2, the capacity density of the test electrode is 3.0 mAh / cm 2 The charge and discharge test was carried out under the conditions of 0.1 C-rate and a cut-off potential of 0.01 V to 1.4 V (vs. Li+ / Li), and was the same as the previous test (Examples 1 to 18 and Comparative Example 1). Table 3 shows the solid content concentration of the skeleton former and the skeletal density of the electrode for Examples 37 to 40 and Comparative Example 3. The inorganic skeleton former was prepared by mixing Li2CO3, Na2CO3, and SiO2 to have the composition shown in Table 3, heating and melting at 1000 °C or higher, cooling, and then dissolving in water.

[0207]

Table 3

[0208] Figure 8 is a graph showing the cycle life characteristics of Examples 37 to 40 and Comparative Example 3. As is clear from Figure 8, the negative electrodes (Examples 37 to 40) coated with the skeleton former had an initial discharge capacity exceeding 1800 mAh / g, while the uncoated negative electrode (Comparative Example 3) had a discharge capacity of 56.7 mAh / g. A dramatic improvement in cycle life characteristics was shown as compared with the negative electrode (Examples 37 to 40) coated with the skeleton former and the uncoated negative electrode (Comparative Example 3). Among these, the solid content concentration of Li 0.05 Na 1.95 O·3SiO2 showed particularly excellent cycle life characteristics in the range of 0.5 to 2.5 mass%. In the electrode using Si as the active material, it was found that a discharge capacity exceeding 2000 mAh / g can be obtained when the skeletal density is 0.12 to 0.90 mg / cm 2 .

[0209] Next, the batteries after charge and discharge (after 20 cycles) of Examples 37 to 40 and Comparative Example 3 were disassembled, and the test electrodes were observed. As a result, in Comparative Example 3, the active material layer was peeled off from the current collector, whereas in Examples 37 to 40, there was no peeling from the current collector, and no wrinkles or cracks were observed in the current collector. From these results, it was clarified that the electrode coated and filled with the skeleton former had improved adhesion between the active material layer and the current collector and improved electrode performance.

[0210] <Examination of Surfactant> (Examples 41 and 42) In Example 41, as the electrode active material, Si-C granulated bodies (Si: artificial graphite = 29:71% by mass) were used, and as the skeleton former, the solid content concentration of Na2O·nSiO2 was 6% by mass, the value of n was 2.5, and the skeleton density was 0.84 mg / cm 2 The other conditions were the same as those in Example 10.

[0211] In Example 42, 0.05% by mass of a nonionic surfactant (registered trademark: Triton X-100) was added as the skeleton former, and the other conditions were the same as those in Example 41.

[0212] FIG. 9 is a graph showing a comparison of the cycle life characteristics of an electrode (Example 41) in which no surfactant was added to the skeleton former and an electrode (Example 42) in which a surfactant was added to the skeleton former. As is clear from FIG. 9, it can be seen that the cycle life characteristics are improved by adding a surfactant. This is because the surfactant improves the lyophilicity of the skeleton former to the active material layer, and a uniform skeleton is formed in the active material layer. Further, although a nonionic surfactant is used as the surfactant in the present embodiment, the surfactant is not limited thereto, and an anionic surfactant, a cationic surfactant, an amphoteric surfactant, or a nonionic surfactant may be used.

[0213] <Nail Penetration Safety> (Examples 43 and Comparative Example 4) Tests were conducted on the safety of a battery using a negative electrode with a skeleton-forming agent. The test method was a nail penetration test in which a nail was inserted into a battery model to examine the state of smoke emission and ignition of the battery model. For the test, a 1.1 Ah battery model with a negative electrode, a separator, and a positive electrode laminated in an aluminum laminate casing and filled with an electrolyte was used. The positive electrode (4.2 mAh / cm 2 ) was prepared by applying a slurry composed of LiNi 0.33 Co 0.33 Mn 0.33 O2, AB, and PVdF onto an aluminum foil (20 μm), adjusting the pressure, and then heat-treating at 160 °C. The negative electrode (4.6 mAh / cm 2 ) was prepared by applying a slurry composed of artificial graphite (D 50 = 20 μm), AB, and an acrylic binder onto a copper foil (10 μm), adjusting the pressure, and then heat-treating at 160 °C.

[0214] Example 43 was prepared by immersing the negative electrode in an aqueous solution in which a skeleton-forming agent was dissolved and then heat-treating at 150 °C as shown in Figure 2. The skeleton-forming agent was an aqueous solution composed of Na2O·3SiO2 and a nonionic surfactant (registered trademark: Triton X-100), with a solid content concentration of Na2O·3SiO2 of 6 mass% and a solid content concentration of the surfactant of 0.05 mass%. The skeleton density of the electrode was 0.9 mg / cm 2 per side. In this test, since the positive electrode and the negative electrode were prepared by double-sided coating, the skeleton density on both sides was 1.8 mg / cm 2 . Also, a battery using a negative electrode without applying the skeleton-forming agent was used as Comparative Example 4.

[0215] As the electrolyte, 1 M LiPF6 / ethylene carbonate (EC):diethyl carbonate (DEC) = 50:50 vol%, + 1 mass% vinylene carbonate was used. As the separator, a polypropylene (PP) microporous membrane (23 μm) was used. In the nail penetration test, this battery model was charged to 4.2 V at a 0.1 C-rate, and then a iron nail (φ3 mm, round) was pierced through the center of the battery at a speed of 1 mm / sec in a 25 °C environment until it penetrated, and the battery voltage, the nail temperature, and the temperature of the casing were measured.

[0216] In the conventional battery model (Comparative Example 4) using a negative electrode without a skeleton former, when nail penetration was performed, the battery voltage dropped to 0 V, and a large amount of smoke was generated. This is because of the heat generation when a short circuit occurred inside the battery model, and the separator melted down.

[0217] On the other hand, the battery model (Example 43) using an artificial graphite negative electrode with a skeleton former maintained a voltage of 3 V or more even when nail penetration was performed, there was no generation of smoke, the temperature of the casing and the nail was also 50°C or less, and almost no heat generation due to short circuit occurred. This is presumably because the skeleton existing inside the active material layer of the negative electrode coats the active material and the like to block the movement of electrons and suppress short circuits.

[0218] <Electrode peeling test> (Example 43 and Comparative Example 4) A peeling test of the negative electrodes used in the batteries of Example 43 and Comparative Example 4 was conducted. The peeling test was carried out in accordance with JIS K685. An adhesive tape (Scotch, No. 845, Book Tape) was pressure-bonded to the active material layer of the negative electrode with a 1 kg roller, and evaluated under the conditions of a pulling speed of 300 mm / min and an angle of 180° in an environment of 25°C. Fig. 16 shows photographs of the negative electrodes and the adhesive tape of Example 43 and Comparative Example 4 after the peeling test. As is clear from Fig. 16, in the negative electrode of Comparative Example 4 that did not use a skeleton former, an active material layer peeled off adhered to the adhesive tape, but in the negative electrode of Example 43 that used a skeleton former, the active material layer hardly adhered to the adhesive tape. It was shown that the peeling strength was improved.

[0219] <Examination of negative electrode active material> (Examples 44 to 59 and Comparative Examples 5 to 20) Using various negative electrode active materials shown in Table 4, the effects with and without a skeleton former were compared. Examples 44 to 59 were prepared by coating a slurry composed of the negative electrode active material, AB, and PVdF shown in Table 4 on a copper foil (10 μm), adjusting the pressure, then coating and impregnating the active material layer with a skeleton former using a spray gun, and heat-treating at 160°C. The solid content ratio of the electrode slurry was 88% by mass of the electrode active material, 4% by mass of AB, and 8% by mass of PVdF.

[0220] The bone-forming agent is Li 0.05 Na 1.95 An aqueous solution composed of O·3SiO2 and a nonionic surfactant (registered trademark: Triton X-100), where the solid content concentration of Li 0.05 Na 1.95 O·3SiO2 is 7.5% by mass and the solid content concentration of the surfactant is 0.03% by mass was used. In this test, the test electrode was fabricated by single-sided coating.

[0221] The test battery used lithium metal as the counter electrode, and as the electrolyte, 1M LiPF6 / ethylene carbonate (EC): diethyl carbonate (DEC) = 50:50 vol%, + 1% by mass of vinylene carbonate was used. A polypropylene (PP / PE / PP) three-layer microporous membrane (25 μm) was used as the separator. The charge-discharge test was carried out at a current density of 0.1 mA / cm 2 with a test environmental temperature of 30 °C. The cut-off potential, the active material density (single-sided) of the electrode, the electrode thickness, and the skeleton density (single-sided) are as shown in Table 4.

[0222] Table 5 is a table showing the cycle life characteristic test results of each electrode (Examples 44 to 59) having bone formation. Table 6 is a table showing the cycle life characteristic test results of each electrode (Comparative Examples 5 to 20) that did not have bone formation for comparison. As is clear from comparing Table 5 and Table 6, the electrodes using Si, SiO, Ge, In, and Fe2O3 as the active material showed excellent cycle life characteristics by using the bone-forming agent. Among these, the electrodes using Si as the active material (Examples 56 and Comparative Example 17) showed particularly significant differences. This is presumably because a strong bone-forming agent was constructed in the active material layer, suppressing the destruction of the electronic conduction network accompanying volume changes.

[0223] On the other hand, for Ag, Ag2O, Sb, Sb2S3, SnO2, CuO, NiO, artificial graphite, and hard carbon, no significant difference in cycle life characteristics was observed with or without the bone-forming agent. These active materials are thought to have shown no clear difference under the test conditions because they have a smaller volume change compared to Si, SiO, Ge, In, and Fe2O3.

[0224] However, in the case of Sn, the cycle life characteristics deteriorated when a skeleton forming agent was used. This is presumably because Sn has a high dissolution rate when added to the skeleton forming agent and cannot maintain the shape of the active material, resulting in capacity degradation.

[0225]

Table 4

[0226]

Table 5

[0227]

Table 6

[0228] <Examination of the mixing ratio of Si and graphite> (Examples 60 to 63 and Comparative Examples 21 to 24) In an electrode using a mixture of Si (1 μm) and artificial graphite (19 μm) as the negative electrode active material, the presence or absence of the effect of skeleton formation was compared. Examples 60 to 63 were prepared by coating a slurry composed of the negative electrode active material, AB, and PVdF shown in Table 7 on a copper foil (10 μm), adjusting the pressure, coating and impregnating the active material layer with a skeleton forming agent using a spray gun, and heat-treating at 160°C.

[0229] Also, for comparison, electrodes without coating and impregnation with a skeleton forming agent were prepared (Comparative Examples 21 to 24). The solid content ratio of the electrode slurry was 88% by mass of the electrode active material, 4% by mass of AB, and 8% by mass of PVdF. The skeleton forming agent was an aqueous solution composed of 0.05 Na 1.95 Li 0.05 Na 1.95 O·3SiO2 and a nonionic surfactant (registered trademark: Triton X-100), and an aqueous solution with a solid content concentration of 7.5% by mass of Li

[0230] The test battery used lithium metal as the counter electrode and 1M LiPF6 / ethylene carbonate (EC):diethyl carbonate (DEC) = 50:50 vol%, + vinylene carbonate 1 mass% as the electrolyte. A polypropylene (PP / PE / PP) three-layer microporous membrane (25μm) was used as the separator. The charge / discharge test was performed with a current density of 0.1C-rate, a test environment temperature of 30°C, and a cut-off potential of 0.0 to 1.4V (vs. Li+ / Li). The skeletal density (one side) is as shown in Table 8. The capacity density of the test electrode was 3.0mAh / cm 2 It was decided.

[0231] Fig. 10 is a graph showing a comparison of cycle life characteristics of Examples 60 to 63 in which a skeletal forming agent was applied and Comparative Examples 21 to 24 in which a skeletal forming agent was not applied. As is clear from Fig. 10, when the total amount of active material contained in the negative electrode is taken as 100 mass%, electrodes with Si of 10 mass% or less (Example 60, Example 61, Comparative Example 21, Comparative Example 22) did not show a significant change, but electrodes with Si of 20 mass% or more (Example 62, Example 63, Comparative Example 23, Comparative Example 24) clearly showed an improvement in life characteristics. In particular, electrodes with Si of 50 mass% (Example 63 and Comparative Example 24) showed an overwhelming improvement in life characteristics by forming a skeletal structure.

[0232] [Table 7]

[0233] [Table 8]

[0234] <Study of various positive electrode materials> Using each cathode active material, the effects at the coating amount of the skeleton former were compared. The test electrodes were prepared by coating a slurry composed of the cathode active material, AB, and PVdF shown in Table 9 on an aluminum foil (20 μm), adjusting the pressure, impregnating the skeleton former into the active material layer using a spray gun, and heat-treating at 170 °C. The solid content ratio of the electrode slurry was 90% by mass of the electrode active material, 5% by mass of AB, and 5% by mass of PVdF.

[0235] The skeleton formers used in Examples 64 to 72 were aqueous solutions composed of Na2O·2.8SiO2 and a nonionic surfactant (registered trademark: Triton X-100), with a solid content concentration of Na2O·3SiO2 of 5.5% by mass and a solid content concentration of the surfactant of 0.03% by mass. The skeleton formers used in Examples 73 to 81 were aqueous solutions composed of Na2O·2.8SiO2 and a nonionic surfactant (registered trademark: Triton X-100), with a solid content concentration of Na2O·3SiO2 of 1.1% by mass and a solid content concentration of the surfactant of 0.03% by mass.

[0236] Table 9 shows the skeleton density and cut-off potential per one side of the electrodes of Examples 64 to 81. However, for Example 72 and Example 81, only the first charge was charged up to 4.6 V.

[0237] In this test, the test electrode was fabricated by single-sided coating so that the electrode capacity was 2.0 mAh / cm 2 For the test battery, lithium metal was used as the counter electrode, and 1 M LiPF6 / ethylene carbonate (EC):diethyl carbonate (DEC) = 50:50 vol% was used as the electrolyte. A polypropylene (PP / PE / PP) three-layer microporous membrane (25 μm) was used as the separator. The charge-discharge test was carried out at a test environmental temperature of 30 °C and a charge-discharge rate of 0.1 C-rate up to 1 to 10 cycles.

[0238] Table 10 is a table showing the cycle life characteristic test results of Examples 64 to 81. As is clear from Table 10, the cathodes (Examples 64 to 72) having a skeleton density exceeding 0.5 mg / cm 2 were compared with those having a skeleton density of 0.5 mg / cm 2It can be seen that the discharge capacity is lower compared to the positive electrodes (Examples 73 to 81) having the following skeletal densities. In the positive electrode, the skeletal density (one-sided) is preferably 0.5 mg / cm 2 It has been found to be as follows.

[0239] [Table 9]

[0240] [Table 10]

[0241] <High-temperature durability of positive electrode> (Examples 82 to 84 and Comparative Examples 21 to 23) Example 82 is the same as Example 74 except that the electrode capacity is changed to 1.0 mAh / cm 2 and the skeletal density is changed to 0.06 mg / cm 2 . Example 83 is the same as Example 76 except that the electrode capacity is changed to 1.0 mAh / cm 2 and the skeletal density is changed to 0.07 mg / cm 2 . Example 84 is the same as Example 81 except that the electrode capacity is changed to 1.0 mAh / cm 2 and the skeletal density is changed to 0.11 mg / cm 2 . Comparative Example 21 is the same as Example 74 except that the electrode capacity is 1.0 mAh / cm 2 and no skeletal former is provided. Comparative Example 22 is the same as Example 76 except that the electrode capacity is 1.0 mAh / cm 2 and no skeletal former is provided. Comparative Example 23 is the same as Example 81 except that the electrode capacity is 1.0 mAh / cm 2 and no skeletal former is provided.

[0242] Using each of the positive electrodes of Examples 82 to 84 and Comparative Examples 21 to 23, full batteries were fabricated. The negative electrode (2 mAh / cm 2) was prepared by coating a slurry composed of SiO, AB, and polyimide (PI) on a copper foil (40 μm), adjusting the pressure, and then performing heat treatment at 300°C. The solid content ratio of the negative electrode slurry was 79% by mass of the electrode active material, 3% by mass of AB, and 18% by mass of PI. Note that, before assembling into the battery, the negative electrode electrochemically compensates for the irreversible capacity portion of Li.

[0243] As the electrolyte for the test battery, 1 M LiPF6 / ethylene carbonate (EC):diethyl carbonate (DEC) = 50:50 vol%, + 1% by mass of vinylene carbonate was used. As the separator, a glass nonwoven fabric (manufactured by Toyo Roshi Kaisha, Ltd., GA-100) was used. For the charge-discharge test, the test environment temperature was set to 80°C, and after repeating 10-cycle charge-discharge at a current density of 0.1 C-rate, 30-cycle charge-discharge was performed at 1 C-rate. The cut-off potential was 4.15 V to 2.0 V for Examples 82 and Comparative Example 21, 4.15 to 2.0 V for Examples 83 and Comparative Example 22, and 4.25 V to 2.0 V for Examples 84 and Comparative Example 23.

[0244] Figure 11 is a graph showing a comparison of the cycle life characteristics of Examples 82 to 84 coated with the skeleton former and Comparative Examples 21 to 23 not coated with the skeleton former. As is clear from Figure 11, it can be seen that the cycle life characteristics of Examples 82 to 84 coated with the skeleton former are improved compared to Comparative Examples 21 to 23. When the PVdF binder is exposed to a high-temperature electrolyte, it absorbs the electrolyte and swells, increasing the electrode resistance. However, by using an electrode (Examples 82 to 84) coated with a skeleton former having excellent swelling resistance, it is considered that the swelling of the binder is suppressed even in a high-temperature electrolyte of 80°C. In addition, it is considered that the decomposition of the electrolyte is also suppressed by the application of the skeleton former to the positive electrode active material layer, contributing to the improvement effect of the cycle life characteristics.

[0245] [5. Effects of the Present Embodiment] According to the above-described embodiments, the following effects are achieved. By using a skeleton-forming agent containing A2O·3SiO2 (A = Na, Li) for the electrode, an electrode with excellent heat resistance, high strength, and improved cycle life characteristics is obtained. Further, a tough current collector is not essential, and the occurrence of wrinkles, cracks, etc. in the current collector can be suppressed. Further, it is not necessary to use a binder with a large irreversible capacity. Further, even if the electronic conductivity of the active material layer is high, heat generation due to internal short circuit can be reduced. Further, it has heat resistance exceeding 1000°C and the skeleton-forming agent does not carbonize. Even in an electrode using an alloy-based material with a large volume change and a binder with low adhesive strength, good life characteristics can be obtained. Further, even when in contact with a high-temperature electrolytic solution, swelling of the active material layer is small.

[0246] - Second Embodiment - [1. Configuration of Skeleton-Forming Agent and Electrode] Next, a second embodiment of the present invention will be described. The difference between the second embodiment and the first embodiment is mainly that the skeleton-forming agent contains ceramics. Fig. 12 shows a cross-sectional image of the electrode of the second embodiment. The skeleton-forming agent of the second embodiment contains ceramic powder or solid electrolyte powder with excellent alkali resistance.

[0247] Fig. 3 shows an example of the manufacturing process. By applying the skeleton-forming agent of the second embodiment to the surface of the electrode body, alumina in the skeleton-forming agent is laminated on the surface of the active material layer to form an electrically insulating ceramic layer or solid electrolyte layer, and the skeleton-forming agent penetrates into the active material layer.

[0248] Thereby, a strong skeleton can be formed, peeling and crack generation during drying can be suppressed, and pores are formed by the gaps between inorganic particles to obtain good liquid affinity with the electrolytic solution. Further, the ceramic layer serves as a separator, and it is possible to configure a battery without using a separate separator.

[0249] [2. Examples] Next, in the second embodiment, examples in which various changes are made to the composition, etc. of the skeleton-forming agent will be described.

[0250] <Examination of the Ratio of Na2O·3SiO2 and α-Al2O3> (Examples 85 to 87 and Comparative Example 23) Table 11 shows the solid content composition of the skeleton-forming agents used in Examples 85 to 87. Also, an electrode using polyimide (PI) as the skeleton-forming agent was fabricated (Comparative Example 23). For α-Al2O3, a powder with a median diameter (D 50 ) of 0.95 μm was used as measured by the laser diffraction / scattering particle size distribution measurement method. The solid content concentration of the skeleton-forming agent was set to 10% by mass when the solid content of Na2O·3SiO2 and α-Al2O3 was 100% by mass.

[0251]

Table 11

[0252] The negative electrode (4.0 mAh / cm 2 ) was prepared by coating a slurry composed of SiO, carbon black (CB), and an acrylic binder on a copper foil (10 μm), adjusting the pressure, and then coating and impregnating the active material layer with the skeleton-forming agent shown in Table 11 using a spray gun, followed by heat treatment at 160°C. The skeleton density of the electrode was 3.0 mg / cm per side 2 . The solid content ratio of the negative electrode slurry was 90% by mass of SiO, 5% by mass of CB, and 5% by mass of the acrylic binder. Note that the negative electrode electrochemically compensates for the irreversible capacity portion of Li before being assembled into the battery.

[0253] The positive electrode (2.0 mAh / cm 2 ) was prepared by coating a slurry composed of LiFePO4, CB, and an acrylic binder on an aluminum foil (20 μm), adjusting the pressure, and then heat treating at 160°C. The solid content ratio of the positive electrode slurry was 91% by mass of LiFePO4, 5% by mass of CB, and 4% by mass of the acrylic binder. As the electrolyte for the test battery, 1 M LiPF6 / ethylene carbonate (EC):diethyl carbonate (DEC) = 50:50 vol%, + 1% by mass of vinylene carbonate was used.

[0254] In this test, a separator was not used. The charge-discharge test was carried out at a test environmental temperature of 60°C and a charge-discharge current density of 0.1 C-rate. The cut-off potential was set at 4.0V to 2.5V.

[0255] Fig. 13 shows the initial charge-discharge curves of the test batteries of Examples 85 to 87. It can be seen that it functions as a battery without using a separator. Note that in Comparative Example 23, no battery test was conducted. The reason is that the electrode resistance increased due to coating the active material layer with PI, and Li ions could not be electrochemically doped.

[0256] <Examination of the alkaline-resistant ceramic particle size> As shown in Table 12, by changing the particle size of α-Al2O3, the skeleton-forming agent was applied and dried on the surface of the electrode body, and the coating property, fresh liquid property, binding property, foaming state, aggregation state, and sedimentation state were observed. As the skeleton-forming agent, it is an aqueous solution composed of Li 0.05 Na 1.95 O·3SiO2 and α-Al2O3. When the solid content concentration of the skeleton-forming agent is 100% by mass for the solid content of Li 0.05 Na 1.95 O·3SiO2 and α-Al2O3, it contains 25% by mass. Note that the particle size of the inorganic particles shown in Table 12 means the median diameter (D 50 ) measured by the laser diffraction / scattering particle size distribution measurement method. As shown in Table 12, it can be seen that in the second embodiment, the particle size of the ceramics is preferably in the range of 0.2 to 20 μm.

[0257]

Table 12

[0258] [3. Effects of this embodiment] According to the above-described embodiment, the following effects are obtained. The skeleton-forming agent used in the first embodiment and the powder excellent in alkali resistance (D 50By applying (with a particle size of 0.2 to 20 μm) to the electrode surface, a strong skeleton can be formed in the active material layer, peeling during drying and the generation of cracks can be suppressed, and pores are formed due to the gaps between the inorganic particles, resulting in good liquid affinity with the electrolyte. Further, the ceramic layer serves as a separator, and it becomes possible to construct a battery without using a separate separator.

[0259] - Other Embodiments - <Skeleton Formation of Active Material Granules> (Examples 88 to 93) This is a test on the manufacturing method of Si granules to which a skeleton forming agent is applied. The Si granules are composed of Si (D 50 = 1 μm), AB, VGCF, and PI. A suspension composed of these is spray-dried under the conditions of a liquid feeding rate of 5 g / min, a spraying pressure of 0.1 MPa, and a drying temperature of 80 to 180 °C, and D 50 is produced to be 5 to 8 μm. The solid content ratio of the suspension is as shown in Table 13.

[0260] Next, the Si granules to which the skeleton forming agent is applied are transferred into a fluidized bed with the granules obtained by spray drying, and the skeleton forming agent (Li 0.2 Na 1.8 O·nSiO2) adjusted to a solid content concentration of 0.5 mass% is used for particle coating. The skeleton forming agent is adjusted to be 1 mass% when the granules obtained by spray drying and the skeleton forming agent are set to 100 mass%.

[0261] Fig. 14 shows SEM images of the Si granules (Examples 88 to 93) to which the obtained skeleton forming agent is applied. In Example 88, the amount of PI contained in the suspension is small, and it is difficult to obtain spherical granules. However, it was found that as the amount of PI increases, spherical granules are more easily obtained. Also, it was found that adding fibrous particles such as VGCF makes it easier to form sea urchin-shaped granules.

[0262] [Table 13]

[0263] <Aluminum phosphate-based skeleton former (Example 94)> The test electrode (4.0 mAh / cm 2 ) was prepared by coating a slurry composed of Si (1 μm), CB, and a PVdF binder on a copper foil (40 μm), adjusting the pressure, coating and impregnating the skeleton former on the active material layer using a spray gun, and heat-treating at 300°C. As the skeleton former, aluminum phosphate (Al2O3·3P2O5) was dissolved in water and adjusted to a solid content of 5% by mass. The skeleton density of the electrode is 2.0 mg / cm per side 2 . The solid content ratio of the negative electrode slurry was 90% by mass of Si, 4% by mass of CB, and 8% by mass of the PVdF binder.

[0264] The test battery used metallic Li as the counter electrode, and as the electrolyte, 1 M LiPF6 / ethylene carbonate (EC):diethyl carbonate (DEC) = 50:50 vol%, + 1% by mass of vinylene carbonate was used. As the separator, a glass nonwoven fabric (manufactured by Toyo Roshi Kaisha, Ltd., GA-100) was used. The charge-discharge test was carried out at a test environment temperature of 30°C, and charged and discharged at current densities of 0.1 C-rate, 0.5 C-rate, and 1.0 C-rate. The cut-off potential was set to 1.0 V to 0.01 V. Fig. 15 shows the charge-discharge curves at each rate of Example 94. It was found that even when using aluminum phosphate (Al2O3·3P2O5) as the skeleton former, a stable reversible capacity was exhibited.

[0265] <Evaluation as a binder> (Comparative Example 24) This is a test using a skeleton former as a binder. As the binder, water was added to adjust the solid content concentration of an alkali metal silicate (Li 0.05 Na 1.95 O·2.8SiO2) to 40% by mass. The test negative electrode (2 mAh / cm 2 ) was Si (D 50A slurry composed of Si (particle size = 1μm), carbon black, and an inorganic binder was applied to a copper foil (10μm) and heat-treated at 150°C. The solid content ratio of the electrode slurry was 19% by mass of Si, 4% by mass of CB, and 76% by mass of the binder.

[0266] (Comparative Example 25) Comparative Example 25 is the same as Comparative Example 24, except that the binder was changed from an alkali metal silicate to primary aluminum phosphate (Al2O3·3P2O5). Commercially available reagents (manufactured by Aesar) were used for the aluminum phosphate salts.

[0267] (Reference Example 1) As the binder, an alkali metal silicate (Li 0.05 Na 1.95 O·2.8SiO2) and α-Al2O3 (D 50 = 3μm) were mixed so that the ratio was 50:50% by mass, and water was added to adjust the solid content concentration of this mixture to 40% by mass. Other conditions were the same as those in Comparative Example 24.

[0268] (Reference Example 2) As the binder, aluminum phosphate (Al2O3·3P2O5) and α-Al2O3 (D 50 = 3μm) were mixed so that the ratio was 50:50% by mass, and water was added to adjust the solid content concentration of this mixture to 40% by mass. Other conditions were the same as those in Comparative Example 25.

[0269] In Comparative Example 25, Si and the alkali metal silicate reacted during the mixing of the slurry, generating hydrogen gas and causing the slurry to foam. Also, in Comparative Example 25 and Comparative Example 26, when pre-drying was performed at 80°C, the active material layer swelled and a uniform electrode could not be obtained. Furthermore, when the electrodes of Comparative Example 25 and Comparative Example 26 were heat-treated at 150°C, the active material layer greatly shrank in volume, cracks occurred in the active material layer, and it peeled off from the current collector.

[0270] On the one hand, in Reference Example 1, when the slurry was mixed, Si reacted with the alkali metal silicate to generate hydrogen gas and the slurry foamed, but during the preliminary drying at 80 °C, the active material layer did not expand. Furthermore, when this electrode was heat-treated at 150 °C, compared with Comparative Example 25, volume shrinkage was suppressed and there were no cracks in the active material layer or peeling from the current collector.

[0271] In Reference Example 2, since hydrogen gas was not generated during the mixing of the slurry, the slurry did not foam, and even during the preliminary drying at 80 °C, the active material layer did not expand. Furthermore, when this electrode was heat-treated at 150 °C, compared with Comparative Example 25, there were no cracks in the active material layer or peeling from the current collector.

[0272] The reason why the active material layer expanded at 80 °C in Comparative Example 25 and Comparative Example 26 is considered to be that when the slurry was dried, the vaporized gas (water vapor) was trapped in the active material layer, causing the active material layer to swell. Furthermore, at 150 °C, it is considered that large volume shrinkage derived from the alkali metal silicate or aluminum phosphate salt caused cracks in the active material layer and the active material layer peeled off from the current collector.

[0273] On the other hand, Reference Example 1 and Reference Example 2 contain non-binder Al2O3 as a binder, and it is considered that gas was discharged from between the Al2O3 particles during electrode drying, and the active material layer did not swell. Furthermore, at 150 °C, it is considered that Al2O3 suppressed the volume shrinkage of the alkali metal silicate or aluminum phosphate salt and prevented cracks in the active material layer and peeling from the current collector.

[0274] These phenomena are, for example, when mochi is heated, the water vapor inside expands while being trapped in the mochi, but in cookies mainly composed of flour, the water vapor can escape from the gaps in the flour, making it less likely for the mochi-like expansion to occur, which is the same.

[0275] Charge and discharge tests were carried out using the electrodes of Reference Example 1 and Reference Example 2. As the electrolyte, a half-cell was fabricated with 1 M LiPF6 / EC:DEC = 50:50 vol.%, + VC 1 mass %), as the separator, a laminate of a polyolefin microporous membrane (20 μm) and a glass nonwoven fabric (GA-100), and metallic Li as the counter electrode. The charge and discharge tests were carried out at an environmental temperature of 30 °C, a current density of 0.25 C-rate, and a cut-off potential of 1.5 V to 0.01 V.

[0276] When comparing the initial charge and discharge efficiencies, the alkali metal silicate-based (Reference Example 1) was 71% and the aluminum phosphate salt-based (Reference Example 2) was 67%. The alkali metal silicate-based had better initial charge and discharge efficiency. This means that the alkali metal silicate has a smaller irreversible capacity than aluminum phosphate.

[0277] Fig. 18 shows the cycle life characteristics of Reference Example 1 and an electrode photograph (current collector side) after 200 cycles. The capacity retention rate after 100 cycles was 78% with respect to the initial discharge capacity of 2609 mAh / g. It is considered that a strong inorganic binder (alkali metal silicate) skeleton was formed in the active material layer, making it difficult for the conductive network to be destroyed by the expansion and contraction of Si, showing excellent capacity retention. The reason why a thin copper foil could be used without causing distortion is thought to be that the strength of the inorganic binder (alkali metal silicate) is higher than that of copper.

[0278] <Confirmation analysis of inorganic skeleton former> (Reference Example 3) This is a test to confirm whether the skeleton former has penetrated into the electrode. The simulated electrode is Al2O3 (D 50A slurry composed of α-Al2O3 (average particle size: 9 μm), AB, and PVdF binder was applied to a copper foil (10 μm), and after adjusting the pressure, a skeleton former was coated and impregnated into the active material layer using a spray gun, and then heat-treated at 150 °C to produce the electrode. As the skeleton former, an alkali metal silicate (Na2O·3SiO) was dissolved in water and adjusted to a solid content of 8% by mass. Note that no surfactant was added. The solid content ratio of the simulated electrode slurry was 85% by mass of α-Al2O3, 5% by mass of CB, and 10% by mass of PVdF binder.

[0279] (Reference Example 4) Reference Example 4 is the same as Reference Example 3 except that, for comparison, the electrode was not coated and impregnated with a skeleton former. Fig. 20 shows the glow discharge optical emission spectroscopy (GDS) results of Reference Example 3 and Reference Example 4. The GDS measurement conditions were a measurement diameter of 4 mmφ and a Ne gas pressure of 2000 Pa. The measurement wavelengths were 121 nm for H, 685 nm for F, 130 nm for O, 156 nm for C, 396 nm for Al, and 251 nm for Si. The horizontal axis represents the sputtering time, which is an index corresponding to the depth direction of the active material layer (the direction from the electrode surface to the current collector). The vertical axis represents the emission intensity, which is an index corresponding to the element content rate. As is clear from Fig. 20, the presence of Si could not be confirmed in Reference Example 4, whereas in Reference Example 3, although the presence of Si was not constant from the surface to the inside, it was confirmed that Si was present in the deep layer. From this result, it was proved that by applying the skeleton former to the electrode surface, the skeleton former can penetrate into the active material layer.

[0280] As described above, the preferred embodiments of the present invention have been described with reference to the drawings. However, various additions, changes, or deletions are possible without departing from the spirit of the present invention. For example, various concentrations and ratios such as the solid content concentration of the alkali metal silicate as the skeleton former are not limited to the numerical values of the above-described embodiments. Further, in the above-described embodiments, the alkali metal silicate is not limited to A2O·3SiO2 (A = Li, Na) where A is Li or Na, and the coefficient of SiO2 is also not limited to 2 to 3. Further, the skeleton former is not limited to aluminum monophosphate (Al2O3·3P2O5) as the phosphate, and the coefficient of P2O5 is also not limited to 3. Therefore, such things are also included within the scope of the present invention.

Claims

1. A granulation binder used in granulating active materials, The component contains a silicate having a siloxane bond or a phosphate having an aluminophosphate bond, The silicate has a structure represented by the general formula A2O.nSiO2, A is at least one of Li, Na, K, a triethanolammonium group, a tetramethanolammonium group, a tetraethanolammonium group, and a granidine group, and n is 1.6 or more and 3.9 or less. Binding agent for granulation.

2. A granulation binder used in granulating active materials, The component contains a silicate having a siloxane bond or a phosphate having an aluminophosphate bond, The silicate or the phosphate has an amorphous structure; Binding agent for granulation.

3. In the above general formula, A is Li or Na; n is 2.0 or more and 3.5 or less; The granulation binder according to claim 1.

4. The active material is an active material containing a Si-based material. The granulation binder according to any one of claims 1 to 3.

5. A granulation binder according to any one of claims 1 to 3 and an active material, Active material granules.

6. The surface of the active material is coated with the granulation binder. The active material granule according to claim 5 .

7. The particles of the active material have a median diameter (D 50 ) in the range of 1 μm to 100 μm; The active material granule according to claim 5 .

8. The primary particles of the active material before granulation with the granulation binder have a median diameter (D 50 ) in the range of 0.01 μm to 10 μm; The active material granule according to claim 5 .

9. The active material includes a Si-based material. The active material granule according to any one of claims 5 to 8.

10. The active material further includes a carbon-based material. The active material granule according to claim 9 .

11. A method for producing an active material granule, A step A of dispersing an active material in a granulation binder containing a silicate having a siloxane bond or a phosphate having an aluminophosphate bond as a component to obtain a suspension; A step B of spraying the suspension to obtain aggregated particles; and a step C of drying the agglomerated particles, The silicate has a structure represented by the general formula A2O.nSiO2, A is at least one of Li, Na, K, a triethanolammonium group, a tetramethanolammonium group, a tetraethanolammonium group, and a granidine group, and n is 1.6 or more and 3.9 or less. A method for producing active material granules.

12. A method for producing an active material granule, A step A of dispersing an active material in a granulation binder containing a silicate having a siloxane bond or a phosphate having an aluminophosphate bond as a component to obtain a suspension; A step B of spraying the suspension to obtain aggregated particles; and a step C of drying the agglomerated particles, The silicate or the phosphate has an amorphous structure; A method for producing active material granules.

13. A method for producing an active material granule, A step A of fluidizing and mixing the active material at a predetermined temperature to obtain primary granules; A step B of spraying a granulation binder containing a silicate having a siloxane bond or a phosphate having an aluminophosphate bond as a component onto the primary granules to obtain an aggregate; and a step C of drying the agglomerate, The silicate has a structure represented by the general formula A2O.nSiO2, A is at least one of Li, Na, K, a triethanolammonium group, a tetramethanolammonium group, a tetraethanolammonium group, and a granidine group, and n is 1.6 or more and 3.9 or less. A method for producing active material granules.

14. A method for producing an active material granule, A step A of fluidizing and mixing the active material at a predetermined temperature to obtain primary granules; A step B of spraying a granulation binder containing a silicate having a siloxane bond or a phosphate having an aluminophosphate bond as a component onto the primary granules to obtain an aggregate; and a step C of drying the agglomerate, The silicate or the phosphate has an amorphous structure; A method for producing active material granules.

15. The step A is a step of further adding an organic binder and mixing it with the active material to obtain primary granules. The method for producing an active material granule according to claim 13 or 14.

16. The active material includes a Si-based material. The method for producing an active material granule according to any one of claims 11 to 14.

17. The active material further includes a carbon-based material. The method for producing an active material granule according to claim 16.

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