Solvent composition for electrode-forming paste, electrode-forming paste, method for manufacturing electrode, and method for manufacturing secondary battery

Abstract

Provided is a solvent composition for an electrode-forming paste, the solvent composition having excellent crack resistance during manufacture of an electrode and being capable of reducing the solvent residue in the electrode.　The solvent composition for an electrode-forming paste comprises a solvent (A) having a boiling point of 180°C to 240°C, and has a Hansen solubility parameter hydrogen bond term δH of 4-11 (J / cm3) 0.5. The solvent (A) preferably has a solubility in water of 5 g / 100 g or more. The solvent (A) preferably comprises an ether skeleton and / or an ester skeleton.

Description

Solvent composition for electrode-forming paste, electrode-forming paste, electrode manufacturing method, and secondary battery manufacturing method

[0001] The present disclosure relates to a solvent composition for an electrode-forming paste, an electrode-forming paste, a method for manufacturing an electrode, and a method for manufacturing a secondary battery. More specifically, the present disclosure relates to a solvent composition used in a paste for forming an electrode, an electrode-forming paste using the solvent composition, a method for manufacturing an electrode using the electrode-forming paste, and a method for manufacturing a secondary battery using the electrode. This application claims priority from Japanese Patent Application No. 2024-068940, filed in Japan on April 22, 2024, the contents of which are incorporated herein by reference.

[0002] Electrodes for lithium ion batteries are formed by applying an electrode-forming paste to the surface of a current collector such as a metal foil and then drying it. The electrode-forming paste uses water as the main solvent (see, for example, Patent Documents 1 to 3). In recent years, there has been a demand for higher capacity in lithium ion batteries. To achieve this, thick electrode films must be formed.

[0003] To form a thick film, a relatively large amount of electrode-forming paste must be applied to the current collector, but this can lead to the problem of cracks occurring in the electrode, which destroys the uniform conductive network of the electrode, reducing the electrode's conductivity and shortening the battery life.

[0004] It is known that a water-soluble additive with a high boiling point having 2 to 20 oxygen atoms per molecule (e.g., 1,3-butylene glycol, propanediol, ethylene glycol, etc.) is used to improve the flexibility and adhesion of electrodes (see, for example, Patent Document 4).

[0005] International Publication No. 2010 / 008058 Japanese Patent Application Laid-Open No. 11-283630 Japanese Patent Application Laid-Open No. 2023-113925 International Publication No. 2013 / 115368

[0006] However, when the high-boiling-point water-soluble additive is used, cracks are unlikely to occur in the resulting electrode, but the high-boiling-point water-soluble additive may cause cracks in the electrode (especially if the density is 200 g / m) after vacuum drying. ２The residual solvent tends to remain in the electrolyte (thick film electrodes as mentioned above). The remaining solvent penetrates the electrolyte and reacts with lithium, deteriorating battery performance and making it difficult to increase capacity.

[0007] Therefore, an object of the present disclosure is to provide a solvent composition for an electrode-forming paste that has excellent crack resistance during electrode production and can reduce the amount of solvent remaining in the electrode.

[0008] The inventors of the present disclosure have presumed that the reason why cracks occur when forming a thick film electrode is that the coating film before drying used to form the electrode contains a large amount of solvent, and therefore, in the process of drying the coating film with hot air, the solvent evaporates quickly and drying begins from the edge of the coating film. Based on this finding, they have developed the technology of the present disclosure.

[0009] The present disclosure provides a solubility improvement agent having a boiling point of 180°C or higher and 240°C or lower, and a hydrogen bond term δH of the Hansen solubility parameter of 4 to 11 (J / cm ３ ) ０．５ The present invention provides a solvent composition for an electrode-forming paste, which comprises a solvent (A) represented by the formula:

[0010] The solvent (A) preferably has a solubility in water of 5 g / 100 g or more.

[0011] The solvent (A) preferably contains an ether skeleton and / or an ester skeleton.

[0012] The solvent (A) is preferably at least one selected from the group consisting of dipropylene glycol monomethyl ether, dipropylene glycol monopropyl ether, dipropylene glycol monobutyl ether, diethylene glycol monobutyl ether, triethylene glycol dimethyl ether, tripropylene glycol dimethyl ether, diethylene glycol butyl methyl ether, diethylene glycol diethyl ether, tetraethylene glycol dimethyl ether, dipropylene glycol methyl ether acetate, diethylene glycol monoethyl ether acetate, 1,3-butylene glycol diacetate, propylene glycol diacetate, α-terpineol, dihydroterpineol, and 3-hydroxy-3-methylbutyl acetate.

[0013] The present disclosure also provides an electrode-forming paste containing the above-mentioned solvent composition for an electrode-forming paste, water, an electrode active material, and a binder.

[0014] The content of the solvent composition for the electrode-forming paste is preferably 0.1 to 5.0 mass % relative to the total amount of the electrode-forming paste.

[0015] The present disclosure also provides an electrode-forming paste comprising an organic solvent, water, an electrode active material, and a binder, wherein the electrode-forming paste is applied to a copper foil in a film thickness of 600 μm and then hot-air dried at 110°C for 10 minutes to form a pre-dried film, which is measured by GC-MS to have a residual amount of the organic solvent of 50 ppm or more; and the pre-dried film is vacuum-dried at an absolute pressure of 1500 Pa or less for 300 minutes to form a dried film, which is measured by GC-MS to have a residual amount of the organic solvent of 40 ppm or less.

[0016] The present disclosure also provides a method for manufacturing an electrode having an electrode active material layer on a current collector, the method comprising the steps of applying the electrode-forming paste onto the current collector to form a coating film, evaporating the solvent from the coating film to form a pre-dried film, and vacuum-drying the pre-dried film to form the electrode active material layer.

[0017] In the step of forming the pre-dried film, the pre-dried film is preferably formed by drying under drying conditions such that the amount of the remaining organic solvent measured by GC-MS is 50 ppm or more.

[0018] In the step of forming the electrode active material layer, the electrode active material layer is preferably dried under drying conditions such that the amount of the remaining organic solvent measured by GC-MS method is 40 ppm or less to form the electrode active material layer.

[0019] The present disclosure also provides a method for producing a secondary battery, which comprises producing an electrode by the above-described method for producing an electrode, and using the obtained electrode to produce a secondary battery.

[0020] When used in an electrode-forming paste, the solvent composition for an electrode-forming paste of the present disclosure provides excellent crack resistance during electrode production and can reduce the amount of solvent remaining in the electrode.

[0021] [Solvent Composition for Electrode-Forming Paste] The solvent composition for electrode-forming paste of the present disclosure (sometimes simply referred to as "solvent composition") has a boiling point of 180°C or higher and 240°C or lower and a hydrogen bond term δH of the Hansen solubility parameter of 4 to 11 (J / cm ３ ) ０．５ In this specification, solvents having a boiling point of 180°C or more and 240°C or less and a hydrogen bond parameter δH of the Hansen solubility parameter of 4 to 11 (J / cm ３ ) ０．５ The solvent (A) may be referred to as “solvent (A).” Only one type of solvent (A) may be used, or two or more types may be used.

[0022] The solvent composition of the present disclosure contains the solvent (A), which prevents rapid evaporation of the solvent in the paste when the paste using the solvent composition is applied and dried, making it less likely to crack during drying. Furthermore, the solvent composition is more likely to volatilize during a further drying step, reducing the amount of solvent remaining on the electrode.

[0023] (Solvent (A)) The boiling point of solvent (A) is 180 to 240°C. The boiling point is preferably 230°C or lower, more preferably 220°C or lower. When the boiling point is 180°C or higher, rapid evaporation of the solvent is prevented when the paste is dried, and cracks are less likely to occur during drying. When the boiling point is 240°C or lower, the remaining solvent is easily evaporated when being removed, and the amount of remaining solvent is reduced.

[0024] The hydrogen bond term δH of the Hansen solubility parameter of the solvent (A) is 4 to 11 (J / cm ３ ) ０．５ The above δH is 4.5 (J / cm ３ ) ０．５ Preferably, 5 (J / cm ３ ) ０．５ Above, 6 (J / cm ３ ) ０．５ Above, 7 (J / cm ３ )０．５ or more, or 8 (J / cm ３ ) ０．５ The δH may be 10 (J / cm ３ ) ０．５ Preferably, it is 9 (J / cm ３ ) ０．５ Below, 8 (J / cm ３ ) ０．５ or less, or 7 (J / cm ３ ) ０．５ The δH may be 4 (J / cm ３ ) ０．５ or more (for example, 4 to 7 (J / cm ３ ) ０．５ ), the hydrogen bonding strength with water is not too high, and the remaining solvent is easily volatilized when being removed, and the amount of remaining solvent is reduced. ３ ) ０．５ or less (e.g., 8 to 11 (J / cm ３ ) ０．５ ), the hydrogen bonding strength with the water contained as a solvent in the paste is moderately high, resulting in excellent water solubility and preventing the rapid evaporation of water when the paste is dried, making it less likely to crack during drying, allowing for the formation of thick films. In this specification, the Hansen solubility parameter is referred to as the "SP value," and the hydrogen bonding parameter δH is sometimes simply referred to as "δH." The SP value and δH can be calculated using HSPiP (ver. 5.4) (Hansen Solubility Parameter in Practice) software.

[0025] The solubility of the solvent (A) in water (solubility in 100 g of water) is preferably 5 g / 100 g or more, more preferably 10 g / 100 g or more, and even more preferably 50 g / 100 g or more. When the solubility is 5 g / 100 g or more, separation from the water contained as a solvent in the paste is unlikely to occur when the paste is dried, making it easy to form a smooth electrode. In this specification, the solubility in 100 g of water may be referred to as "water solubility."

[0026] The solvent (A) preferably contains an ether skeleton and / or an ester skeleton. Examples of solvents containing an ether skeleton include polyalkylene glycols, (poly)alkylene glycol mono- or dialkyl ethers, polyalkylene glycol monoesters, and (poly)alkylene glycol alkyl ether monoesters. Examples of solvents containing an ester skeleton include (poly)alkylene glycol monoesters, (poly)alkylene glycol alkyl ether monoesters, (poly)alkylene glycol diesters, (poly)glycerin esters, and esterified products of terpineol or its hydrogenated derivatives. The carboxylic acid constituting the ester skeleton is preferably an aliphatic carboxylic acid. Furthermore, from the viewpoint of preferably having low reactivity with lithium, the solvent (A) preferably contains one or less hydroxy groups, and more preferably has no hydroxy groups.

[0027] Specific examples of the solvent (A) include (poly)alkylene glycol monoalkyl ethers such as dipropylene glycol monomethyl ether, dipropylene glycol monopropyl ether, dipropylene glycol monobutyl ether, and diethylene glycol monobutyl ether; (poly)alkylene glycol dialkyl ethers such as triethylene glycol dimethyl ether, tripropylene glycol dimethyl ether, diethylene glycol butyl methyl ether, diethylene glycol diethyl ether, and tetraethylene glycol dimethyl ether; (poly)alkylene glycol monoalkyl ether monoesters such as dipropylene glycol methyl ether acetate and diethylene glycol monoethyl ether acetate; (poly)alkylene glycol diesters such as 1,3-butylene glycol diacetate and propylene glycol diacetate; terpene alcohols such as α-terpineol and dihydroterpineol; and esters of terpene alcohols such as 3-hydroxy-3-methylbutyl acetate.

[0028] Among these, the solvent (A) is preferably at least one selected from the group consisting of tripropylene glycol dimethyl ether, dipropylene glycol methyl ether acetate, 1,3-butylene glycol diacetate, dipropylene glycol monopropyl ether, dipropylene glycol monomethyl ether, diethylene glycol diethyl ether, diethylene glycol monoethyl ether acetate, and diethylene glycol monobutyl ether.

[0029] The solvent composition may contain a solvent other than the solvent (A). Examples of the other solvent include a solvent other than the solvent (A) that has a boiling point of 300° C. or less (for example, 250 to 280° C.) and a δH of 4 to 13 (J / cm ３ ) ０．５ Examples of the solvent (B) include a solvent having a water solubility of 5 g / 100 g or more, more preferably 10 g / 100 g or more, and even more preferably 50 g / 100 g or more. Solvent (B) has excellent compatibility with solvent (A), and is easily able to form a homogeneous solution, and the amount of remaining solvent can be easily adjusted. One or more of the above other solvents may be used.

[0030] The solvent (B) preferably contains an ether skeleton and / or an ester skeleton. Examples of the solvent (B) include triethylene glycol butyl methyl ether, triethylene glycol monobutyl ether, triacetin, and dipropylene glycol dimethyl ether. In addition, the solvent (B) preferably has two or less hydroxy groups, from the viewpoint of preferably having low reactivity with lithium.

[0031] The content of the solvent (A) in the solvent composition is preferably 20% by mass or more, more preferably 30% by mass or more, and may be 50% by mass or more, 70% by mass or more, or 90% by mass or more, relative to the total amount (100% by mass) of the solvent composition. When the content is 20% by mass or more, rapid evaporation of the solvent is prevented when drying the paste, cracks are less likely to occur during drying, and the solvent composition is more likely to volatilize when removing the remaining solvent, thereby further reducing the amount of solvent remaining on the electrode.

[0032] The total content of solvent (A) and solvent (B) in the solvent composition is preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, particularly preferably 90% by mass or more, and may be 93% by mass or more, 96% by mass or more, 98% by mass or more, 99% by mass or more, or even 100% by mass, relative to the total amount (100% by mass) of the solvent composition. When the solvent composition does not contain solvent (B), the above content is the content of solvent (A).

[0033] The content of the compound having one or more groups selected from the group consisting of a hydroxy group, an amide group, and a ketone group in the solvent composition is preferably 40% by mass or less, and more preferably 10% by mass or less, relative to the total amount (100% by mass) of the solvent composition.

[0034] The solvent composition is a solvent composition for an electrode-forming paste, which is used in a paste for forming an electrode. The solvent composition can be produced by mixing the solvent (A) and, if necessary, other solvents. The mixing can be carried out by a known or conventional method.

[0035] The solvent composition for an electrode-forming paste according to the present disclosure, when used in an electrode-forming paste, can provide excellent crack resistance during electrode production and reduce the amount of solvent remaining in the electrode. Therefore, a thick-film electrode can be produced using the composition for an electrode-forming paste according to the present disclosure, thereby enabling the production of a high-capacity lithium-ion battery.

[0036] [Electrode Forming Paste] (First Electrode Forming Paste) An electrode forming paste can be produced using the solvent composition. The electrode forming paste contains, for example, the solvent composition, water, an electrode active material, and a binder. In this specification, an electrode forming paste containing the solvent composition, water, an electrode active material, and a binder may be referred to as a "first electrode forming paste." The first electrode forming paste may further contain a conductive additive.

[0037] The electrode active material may be a known or commonly used material. The electrode active material may be either a positive electrode active material or a negative electrode active material. Only one type of electrode active material may be used, or two or more types may be used.

[0038] Examples of the positive electrode active material include compounds containing lithium and transition metal elements, i.e., lithium transition metal composite oxides, such as lithium transition metal composite oxides having a layered structure, lithium transition metal composite oxides having a spinel structure, and lithium transition metal-containing phosphates having an olivine structure.

[0039] Specific examples of the lithium transition metal composite oxide include lithium cobalt-containing composite oxide, lithium manganese-containing composite oxide, lithium nickel-containing composite oxide, lithium titanium-containing composite oxide, lithium nickel manganese-containing composite oxide, lithium nickel cobalt manganese-containing composite oxide, and lithium nickel cobalt aluminum-containing composite oxide.

[0040] Examples of the lithium-cobalt-containing composite oxide include lithium cobalt oxide. Examples of the lithium-manganese-containing composite oxide include lithium manganese oxide. Examples of the lithium-nickel-containing composite oxide include lithium nickel oxide. Examples of the lithium-titanium-containing composite oxide include lithium titanate.

[0041] Examples of the negative electrode active material include metal Li, its alloys such as tin alloys, silicon alloys, and lead alloys, and Li Ｘ Fe２ O ３ , Li Ｘ Fe ３ O ４ , Li Ｘ WO ２ Examples of the carbonaceous material include metal oxides such as lithium titanate, lithium vanadate, and lithium silicate; conductive polymers such as polyacetylene and poly-p-phenylene; amorphous carbonaceous materials such as soft carbon and hard carbon; artificial graphite such as highly graphitized carbon materials; carbonaceous powders such as natural graphite; carbon black, mesophase carbon black, resin-baked carbon materials, vapor-grown carbon fibers, and carbon fibers.

[0042] As the conductive additive, known or commonly used ones can be used, for example, carbon materials such as carbon black (acetylene black, ketjen black, etc.), carbon fiber, graphite, etc. Only one type of the conductive additive may be used, or two or more types may be used.

[0043] The binder may be any known or commonly used binder, and examples thereof include acrylic resin, polyurethane resin, polyester resin, phenolic resin, epoxy resin, phenoxy resin, urea resin, melamine resin, alkyd resin, formaldehyde resin, silicone resin, fluororesin, cellulose resin such as carboxymethyl cellulose, synthetic rubber such as styrene-butadiene rubber and fluororubber, conductive resin such as polyaniline and polyacetylene, halogenated vinyl resin such as polyvinylidene fluoride (PVdF) and polytetrafluoroethylene (PTFE), polyalkylene oxide such as polyethylene oxide (PEO), etc. One or more of the binders may be used.

[0044] The content of the solvent composition in the electrode-forming paste is preferably 0.1 to 5.0 mass %, more preferably 0.3 to 3 mass %, relative to the total amount (100 mass %) of the electrode-forming paste. When the content is within the above range, rapid evaporation of the solvent is prevented when the paste is dried, cracks are less likely to occur during drying, and the solvent composition is more likely to volatilize when the remaining solvent is removed, further reducing the amount of solvent remaining in the electrode.

[0045] (Second Electrode-Forming Paste) The present disclosure also provides an electrode-forming paste comprising an organic solvent, water, an electrode active material, and a binder, the electrode-forming paste being coated on copper foil to a thickness of 600 μm and then hot-air-dried at 110°C for 10 minutes to form a pre-dried film, wherein the residual amount of the organic solvent is 50 ppm or more as measured by GC-MS; and the pre-dried film is vacuum-dried at an absolute pressure of 1500 Pa or less for 300 minutes to form a dried film, wherein the residual amount of the organic solvent is 40 ppm or less as measured by GC-MS. Note that, in this specification, the electrode-forming paste may be referred to as a "second electrode-forming paste." Also, in this specification, the organic solvent (including the solvent composition) and water may be collectively referred to as a "solvent." The second electrode-forming paste may further contain a conductive additive.

[0046] As the electrode active material, conductive additive, and binder in the second electrode-forming paste, those exemplified and explained above as those in the first electrode-forming paste can be used, respectively.

[0047] Examples of the organic solvent include alcohols such as methanol, ethanol, 1-propanol, 2-propanol, butanol, pentanol, hexanol, octanol, and diacetone alcohol; esters such as ethyl acetate, butyl acetate, ethyl lactate, propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, and γ-butyrolactone; ethers such as diethyl ether, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, and diethylene glycol monoethyl ether; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, acetylacetone, and cyclohexanone; amides such as dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone; and glycols such as ethylene glycol, diethylene glycol, and propylene glycol. One or more of the organic solvents may be used.

[0048] Furthermore, the solvent composition may be used as the organic solvent. When the solvent composition is used as the organic solvent, the second electrode-forming paste also corresponds to the first electrode-forming paste.

[0049] The electrode-forming paste is applied to a copper foil to a thickness of 600 μm, and the resulting pre-dried film is dried with hot air at 110°C for 10 minutes. The residual amount of the organic solvent measured by GC-MS is 50 ppm or more, preferably 100 ppm or more. If the residual amount is 50 ppm or more, cracks are less likely to occur in the pre-dried film and the electrode obtained thereafter, and warping and swelling of the edges are less likely to occur. Furthermore, it is preferable that the residual amount of the first electrode-forming paste be within the above range.

[0050] The electrode-forming paste has a residual organic solvent content of 40 ppm or less, preferably 30 ppm or less, and more preferably 20 ppm or less, as measured by GC-MS on the dried film obtained by vacuum-drying the pre-dried film at an absolute pressure of 1500 Pa or less for 300 minutes. If the residual content is 40 ppm or less, the amount of solvent remaining in the electrode is reduced. Furthermore, it is preferable that the residual content of the first electrode-forming paste be within the above range.

[0051] The content of the organic solvent in the electrode-forming paste is preferably 0.1 to 5.0 mass %, more preferably 0.3 to 3 mass %, relative to the total amount (100 mass %) of the electrode-forming paste. When the content is within the above range, rapid evaporation of the solvent is prevented when the paste is dried, cracks are less likely to occur during drying, and the solvent composition is more likely to volatilize when the remaining solvent is removed, further reducing the amount of solvent remaining on the electrode.

[0052] [Electrode] The electrode-forming paste (the first and second electrode-forming pastes) can be used to manufacture an electrode. The electrode may be either a positive electrode or a negative electrode, but a negative electrode is preferred.

[0053] The electrode includes, for example, at least a current collector and an electrode active material layer laminated (fixed) on the current collector. The electrode active material layer is a layer formed from the electrode-forming paste.

[0054] Known or commonly used current collectors can be used. Examples of materials constituting the current collector include stainless steel, aluminum, copper, aluminum, nickel, titanium, and alloys containing one or more of these. In the case of lithium ion batteries, aluminum is particularly preferred as a current collector for the positive electrode, and copper is particularly preferred as a current collector for the negative electrode.

[0055] The electrode can be manufactured by a manufacturing method including the steps of applying an electrode-forming paste (first or second electrode-forming paste) onto the current collector to form a coating film, evaporating water from the coating film to form a temporary dried film, and vacuum-drying the temporary dried film to form an electrode active material layer.

[0056] In the step of forming the pre-dried film, the pre-dried film is preferably formed by drying under drying conditions such that the amount of remaining organic solvent measured by GC-MS is 50 ppm or more (preferably 100 ppm or more). By performing drying under such drying conditions, the solvent can be evaporated slowly, the occurrence of warping and swelling at the edges can be suppressed, and the resulting electrode is less likely to crack.

[0057] The thickness of the applied film of the electrode-forming paste is, for example, 100 to 1000 μm. The applied film to obtain the pre-dried film is dried, for example, at a temperature of 70 to 150° C. (preferably 100 to 130° C.) for 30 seconds to 60 minutes (preferably 1 to 20 minutes).

[0058] In the step of forming the electrode active material layer (dried film), the electrode active material layer is preferably formed by drying under drying conditions such that the amount of the remaining organic solvent measured by GC-MS is 40 ppm or less (preferably 20 ppm or less). By performing drying under such drying conditions, the organic solvent is less likely to remain in the resulting electrode active material layer and electrode.

[0059] The vacuum drying of the pre-dried film to obtain the electrode active material layer is carried out, for example, at a pressure of 800 to 5000 Pa (preferably 1300 to 3000 Pa) (absolute pressure) and a temperature of 70 to 150°C (preferably 80 to 120°C) for 2 to 72 hours (preferably 5 to 24 hours).

[0060] In this manner, an electrode can be manufactured.

[0061] The thickness of the electrode is, for example, 100 to 350 μm, preferably 150 to 300 μm, and more preferably 200 to 250 μm. Since the electrode-forming paste of the present disclosure has a small amount of residual solvent, cracks are unlikely to occur even in a thick film having a thickness of 100 μm or more (particularly 200 μm or more).

[0062] [Secondary Battery] A secondary battery can be manufactured using the above-mentioned electrode. In this specification, the term "secondary battery" encompasses reusable storage batteries (secondary batteries) and storage elements in general. Examples of secondary batteries include lithium secondary batteries (lithium ion batteries), nickel-metal hydride batteries, lithium ion capacitors, and electric double layer capacitors. The lithium ion battery includes, for example, at least a positive electrode, a negative electrode, and an electrolyte. The lithium ion battery may further include a separator.

[0063] The positive electrode and / or the negative electrode may be obtained using the first or second electrode-forming paste. Also, the positive electrode or the negative electrode may be a known or commonly used electrode for a secondary battery.

[0064] The electrolyte can be any known or commonly used electrolyte for secondary batteries. The electrolyte may be in a liquid, sol, or solid state at room temperature (25°C). The electrolyte includes, for example, a supporting salt and a solvent. The supporting salt dissociates in the solvent to generate charge carrier ions, which in lithium-ion batteries generate lithium ions. The charge carrier ions are typically cations such as lithium ions, calcium ions, and magnesium ions, but may also be anions such as fluoride ions. Specific examples of the supporting salt include fluorine-containing lithium salts such as LiPF6 and LiBF4. Examples of the solvent include non-aqueous solvents such as aprotic solvents such as carbonates, ethers, esters, nitriles, sulfones, and lactones. When the solvent is non-aqueous, the electrolyte becomes a non-aqueous electrolytic solution.

[0065] The electrolyte may contain other components in addition to the supporting salt and the solvent, such as film-forming agents such as lithium bis(oxalato)borate (LiBOB) and vinylene carbonate (VC), and gas generating agents such as biphenyl (BP) and cyclohexylbenzene (CHB).

[0066] The secondary battery can be used for known or conventional secondary battery applications, but is preferably used in applications requiring excellent high-rate characteristics (high-rate output characteristics and high-rate cycle characteristics), i.e., applications requiring high power density. Specifically, it can be preferably used, for example, as a power source (driving power source) for a motor mounted on a vehicle. The type of vehicle is not particularly limited, but examples include plug-in hybrid vehicles (PHVs), hybrid vehicles (HVs), and electric vehicles (EVs). The secondary battery may be used in the form of a battery pack in which multiple batteries are connected in series and / or parallel.

[0067] Each aspect disclosed in this specification can be combined with any other feature disclosed in this specification. Each configuration and combination thereof in each embodiment is an example, and addition, omission, substitution, and other modifications of configurations are possible as appropriate within the scope of the spirit of this disclosure. Furthermore, each invention according to this disclosure is not limited by the embodiments or the following examples.

[0068] Hereinafter, one embodiment of the present disclosure will be described in more detail based on examples.

[0069] Preparation Examples (Preparation of Solvent Compositions) Various solvents were added to give the compositions (unit: mass %) shown in Table 1, and stirred until they were compatible, thereby obtaining solvent compositions 1 to 15.

[0070]

[0071] The solvents shown in Table 1 are as follows. The δH values ​​were calculated using HSPiP (ver. 5.4) (Hansen Solubility Parameter in Practice) software. (Solvent (A)) MTPOM: Trade name "Hisorb MTPOM", manufactured by Toho Chemical Industry Co., Ltd., tripropylene glycol dimethyl ether, boiling point 215°C, δH 4.52 (J / cm ３ ) ０．５ , water solubility 23.6 g / 100 g DPMA: dipropylene glycol methyl ether acetate, manufactured by Daicel Corporation, boiling point 213°C, δH 5.78 (J / cm ３ ) ０．５, water solubility 19 g / 100 g 1,3-BGDA: 1,3-butylene glycol diacetate, manufactured by Daicel Corporation, boiling point 232°C, δH 7.21 (J / cm ３ ) ０．５ , water solubility 5g / 100g PFDG: Nippon Nyukazai Co., Ltd., dipropylene glycol monopropyl ether, boiling point 212°C, δH 8.35 (J / cm ３ ) ０．５ , water solubility 15 g / 100 g MFDG: Nippon Nyukazai Co., Ltd., dipropylene glycol monomethyl ether, boiling point 190°C, δH 9.85 (J / cm ３ ) ０．５ , water solubility 100g / 100g or more EDE: trade name "Hisorb EDE", manufactured by Toho Chemical Industry Co., Ltd., diethylene glycol diethyl ether, boiling point 189°C, δH 5.61 (J / cm ３ ) ０．５ , water solubility 100g / 100g or more DB: Trade name "Hisorb DB", manufactured by Toho Chemical Industry Co., Ltd., diethylene glycol monobutyl ether, boiling point 230°C, δH 10.46 (J / cm ３ ) ０．５ , water solubility 100g / 100g or more (Other solvents) 1,3-BG: 1,3-butylene glycol manufactured by Daicel Corporation, boiling point 208°C, δH 19.78 (J / cm ３ ) ０．５ , water solubility 100 g / 100 g or more DMM: dipropylene glycol dimethyl ether, manufactured by Daicel Corporation, boiling point 175°C, δH 4.68 (J / cm ３ ) ０．５ , water solubility 53 g / 100 g EDG: diethylene glycol monoethyl ether, manufactured by Daicel Corporation, boiling point 202°C, δH 11.99 (J / cm ３ ) ０．５ , water solubility 100g / 100g or more BTM: Trade name "Hisorb BTM", manufactured by Toho Chemical Industry Co., Ltd., triethylene glycol butyl methyl ether, boiling point 261°C, δH 5.89 (J / cm ３ ) ０．５ , water solubility 100g / 100g or more BTG: Triethylene glycol monobutyl ether, manufactured by Nippon Nyukazai Co., Ltd., boiling point 276°C, δH 9.14 (J / cm３ ) ０．５ , water solubility 100g / 100g or more DRA-150: Trade name "DRA-150", manufactured by Daicel Corporation, triacetin, boiling point 260°C, δH 8.67 (J / cm ３ ) ０．５ , water solubility 8g / 100g

[0072] Examples 1 to 7 and Comparative Examples 1 to 8 (Preparation of paste for forming negative secondary battery electrode) Graphite (trade name "MAGE3", manufactured by Resonac Holdings Co., Ltd.) as a negative electrode active material, a 1 wt % aqueous solution of carboxymethyl cellulose (trade name "CMC2200", manufactured by Daicel Miraize Co., Ltd.) as a thickener, a solvent composition, and SBR (trade name "JSR104", manufactured by JSR Corporation) were mixed in a mixer to obtain the composition (unit: parts by mass) shown in Table 2, thereby obtaining a paste for forming a negative secondary battery electrode.

[0073]

[0074] <Evaluation> The negative secondary battery electrode-forming pastes obtained in the Examples and Comparative Examples were evaluated as follows. The results are shown in Table 2.

[0075] (1) Crack Resistance The negative electrode secondary battery electrode-forming pastes obtained in the Examples and Comparative Examples were applied to copper foil using an automatic coater to a coating thickness setting of 400 to 600 μm, and then dried at 110°C for 10 minutes at atmospheric pressure to obtain a negative electrode for crack resistance evaluation. Using a cylindrical mandrel bending tester manufactured by BEVS, the prepared negative electrode pieces were fixed with the main clamp, and after rotating the handle 180°, the crack resistance was evaluated from the minimum diameter of the mandrel at which the electrode began to crack or peel from the copper foil. A mandrel with a minimum diameter smaller than or equal to that of Comparative Example 1 was marked with a circle, and a larger diameter was marked with an X. Good crack resistance indicates that the electrode is highly flexible and suitable for thicker films.

[0076] (2) Residual Solvent Properties The negative electrode secondary battery electrode-forming paste obtained in the examples and comparative examples was coated on copper foil using an automatic coater so that the coating thickness setting was 600 μm, dried at 110 ° C. for 10 minutes at atmospheric pressure, and then vacuum dried at 110 ° C. for 5 hours to remove the residual solvent, thereby obtaining a negative electrode for evaluating residual solvent properties. The obtained negative electrode was placed in a headspace container and the mass (W) was accurately weighed, and analysis was carried out using headspace (trade name "HS-20", manufactured by Shimadzu Corporation) and GC / MS (manufactured by Shimadzu Corporation, trade name "GC / MS-QP2010 Ultra", column: DB-5MS 30 m - 0.25 mm, I.D - 0.25 μm). Then, from a separately prepared calibration curve, the content of residual solvent in the negative electrode (Ws) was determined. From these, the residual solvent concentration was calculated according to the following formula. Residual solvent concentration of 20 ppm or less was evaluated as ◯, more than 20 ppm but not more than 40 ppm was evaluated as △, and more than 40 ppm was evaluated as ×. Residual solvent concentration (ppm) = Ws / W × 100 × 10000

[0077] As shown in Table 2, when a paste for forming a secondary battery electrode obtained using a solvent composition containing solvent (A) was used (Examples), the negative electrode had excellent crack resistance and little residual solvent. On the other hand, when a paste for forming a secondary battery electrode obtained using another solvent instead of solvent (A) was used, the amount of residual solvent tended to be large (Comparative Examples 1 to 3, 5 to 8). Furthermore, when a paste for forming a secondary battery electrode obtained using another solvent instead of solvent (A) was used, cracks were more likely to occur during drying due to rapid drying of the solvent (Comparative Example 4).

[0078] Variations of the present invention are described below. [Appendix 1] A solubility liquid having a boiling point of 180°C or higher and 240°C or lower and a hydrogen bond term δH of the Hansen solubility parameter of 4 to 11 (J / cm ３ ) ０．５[Appendix 2] The solvent composition for an electrode-forming paste according to Appendix 1, wherein the boiling point of the solvent (A) is 180°C or higher and 230°C or lower. [Appendix 3] The solvent composition for an electrode-forming paste according to Appendix 1 or 2, wherein the boiling point of the solvent (A) is 180°C or higher and 220°C or lower. [Appendix 4] The hydrogen bond term δH of the Hansen solubility parameter of the solvent (A) is 4.5 (J / cm ３ ) ０．５ The solvent composition for an electrode-forming paste according to any one of Supplementary Notes 1 to 3, wherein the hydrogen bond term δH of the Hansen solubility parameter of the solvent (A) is 5 (J / cm ３ ) ０．５ The solvent composition for an electrode-forming paste according to any one of claims 1 to 4, wherein the hydrogen bond term δH of the Hansen solubility parameter of the solvent (A) is 6 (J / cm ３ ) ０．５ The solvent composition for an electrode-forming paste according to any one of claims 1 to 5, wherein the hydrogen bond term δH of the Hansen solubility parameter of the solvent (A) is 7 (J / cm ３ ) ０．５ The solvent composition for an electrode-forming paste according to any one of claims 1 to 6, wherein the hydrogen bond term δH of the Hansen solubility parameter of the solvent (A) is 8 (J / cm ３ ) ０．５ The solvent composition for an electrode-forming paste according to any one of Supplementary Notes 1 to 7, wherein the hydrogen bond term δH of the Hansen solubility parameter of the solvent (A) is 10 (J / cm ３ ) ０．５ The solvent composition for an electrode-forming paste according to any one of claims 1 to 8, wherein the hydrogen bond term δH of the Hansen solubility parameter of the solvent (A) is 9 (J / cm ３ ) ０．５ The solvent composition for an electrode-forming paste according to any one of claims 1 to 9, wherein the hydrogen bond term δH of the Hansen solubility parameter of the solvent (A) is 8 (J / cm ３ ) ０．５The solvent composition for an electrode-forming paste according to any one of claims 1 to 10, wherein the hydrogen bond term δH of the Hansen solubility parameter of the solvent (A) is 7 (J / cm ３ ) ０．５The solvent composition for an electrode-forming paste according to any one of Appendices 1 to 11, wherein the solvent (A) has a solubility in water of 5 g / 100 g or more. [Appendix 13] The solvent composition for an electrode-forming paste according to any one of Appendices 1 to 12, wherein the solvent (A) has a solubility in water of 5 g / 100 g or more. [Appendix 14] The solvent composition for an electrode-forming paste according to any one of Appendices 1 to 13, wherein the solvent (A) has a solubility in water of 10 g / 100 g or more. [Appendix 15] The solvent composition for an electrode-forming paste according to any one of Appendices 1 to 14, wherein the solvent (A) has a solubility in water of 50 g / 100 g or more. [Appendix 16] The solvent composition for an electrode-forming paste according to any one of Appendices 1 to 15, wherein the solvent (A) contains an ether skeleton and / or an ester skeleton. [Appendix 17] The solvent composition for an electrode-forming paste according to any one of Appendices 1 to 16, wherein the solvent (A) is one or more selected from the group consisting of dipropylene glycol monomethyl ether, dipropylene glycol monopropyl ether, dipropylene glycol monobutyl ether, diethylene glycol monobutyl ether, triethylene glycol dimethyl ether, tripropylene glycol dimethyl ether, diethylene glycol butyl methyl ether, diethylene glycol diethyl ether, tetraethylene glycol dimethyl ether, dipropylene glycol methyl ether acetate, diethylene glycol monoethyl ether acetate, 1,3-butylene glycol diacetate, propylene glycol diacetate, α-terpineol, dihydroterpineol, and 3-hydroxy-3-methylbutyl acetate. [Appendix 18] The solvent composition for an electrode-forming paste according to any one of Appendices 1 to 17, wherein the solvent (A) is one or more selected from the group consisting of tripropylene glycol dimethyl ether, dipropylene glycol methyl ether acetate, 1,3-butylene glycol diacetate, dipropylene glycol monopropyl ether, dipropylene glycol monomethyl ether, diethylene glycol diethyl ether, diethylene glycol monoethyl ether acetate, and diethylene glycol monobutyl ether.[Appendix 19] The solvent composition for an electrode-forming paste according to any one of Appendices 1 to 18, wherein the content of the solvent (A) is 20% by mass or more, relative to the total amount (100% by mass) of the solvent composition. [Appendix 20] The solvent composition for an electrode-forming paste according to any one of Appendices 1 to 19, wherein the content of the solvent (A) is 30% by mass or more, relative to the total amount (100% by mass) of the solvent composition. [Appendix 21] The solvent composition for an electrode-forming paste according to any one of Appendices 1 to 20, wherein the content of the solvent (A) is 50% by mass or more, relative to the total amount (100% by mass) of the solvent composition. [Appendix 22] The solvent composition for an electrode-forming paste according to any one of Appendices 1 to 21, wherein the content of the solvent (A) is 70% by mass or more, relative to the total amount (100% by mass) of the solvent composition. [Appendix 23] The solvent composition for an electrode-forming paste according to any one of Appendices 1 to 22, wherein the content of the solvent (A) is 90% by mass or more relative to the total amount (100% by mass) of the solvent composition. [Appendix 24] An electrode-forming paste comprising the solvent composition for an electrode-forming paste according to any one of Appendices 1 to 23, water, an electrode active material, and a binder. [Appendix 25] The electrode-forming paste according to Appendices 24, wherein the content of the solvent composition for an electrode-forming paste is 0.1 to 5.0% by mass relative to the total amount of the electrode-forming paste. [Appendix 26] The electrode-forming paste according to Appendices 24 or 25, wherein the content of the solvent composition for an electrode-forming paste is 0.3 to 3% by mass relative to the total amount of the electrode-forming paste. [Appendix 27] An electrode-forming paste comprising an organic solvent, water, an electrode active material, and a binder, wherein the electrode-forming paste is applied to a copper foil in a thickness of 600 μm and hot-air-dried at 110°C for 10 minutes to form a pre-dried film, the amount of the remaining organic solvent being 50 ppm or more as measured by GC-MS, and the pre-dried film is vacuum-dried at an absolute pressure of 1500 Pa or less for 300 minutes to form a dried film, the amount of the remaining organic solvent being 40 ppm or less as measured by GC-MS. [Appendix 28] The electrode-forming paste according to Appendices 27, wherein the electrode-forming paste is applied to a copper foil in a thickness of 600 μm and hot-air-dried at 110°C for 10 minutes to form a pre-dried film, the amount of the remaining organic solvent being 100 ppm or more as measured by GC-MS.[Appendix 29] The electrode-forming paste according to Appendices 27 or 28, wherein the residual amount of the organic solvent is 30 ppm or less when measured by GC-MS after the pre-dried film is vacuum-dried at an absolute pressure of 1500 Pa or less for 300 minutes. [Appendix 30] The electrode-forming paste according to any one of Appendices 27 to 29, wherein the residual amount of the organic solvent is 20 ppm or less when measured by GC-MS after the pre-dried film is vacuum-dried at an absolute pressure of 1500 Pa or less for 300 minutes. [Appendix 31] The electrode-forming paste according to any one of Appendices 27 to 30, wherein the content of the organic solvent is 0.1 to 5.0 mass% with respect to the total amount (100 mass%) of the electrode-forming paste. [Appendix 32] The electrode-forming paste according to any one of Appendices 27 to 31, wherein the content of the organic solvent is 0.3 to 3 mass% with respect to the total amount (100 mass%) of the electrode-forming paste. [Appendix 33] A method for manufacturing an electrode having an electrode active material layer on a current collector, comprising the steps of: applying the electrode-forming paste according to any one of Appendices 27 to 32 onto the current collector to form a coating film; evaporating water from the coating film to form a pre-dried film; and vacuum-drying the pre-dried film to form the electrode active material layer. [Appendix 34] A method for manufacturing an electrode according to Appendices 33, wherein in the step of forming the pre-dried film, the pre-dried film is dried under drying conditions such that the remaining amount of the organic solvent measured by GC-MS is 50 ppm or more to form the pre-dried film. [Appendix 35] A method for manufacturing an electrode according to Appendices 33 or 34, wherein in the step of forming the pre-dried film, the pre-dried film is dried under drying conditions such that the remaining amount of the organic solvent measured by GC-MS is 100 ppm or more to form the pre-dried film. [Appendix 36] The method for manufacturing an electrode according to any one of Appendices 33 to 35, wherein, in the step of forming the electrode active material layer, the electrode active material layer is dried under drying conditions such that the amount of the remaining organic solvent measured by GC-MS is 40 ppm or less to form an electrode active material layer. [Appendix 37] The method for manufacturing an electrode according to any one of Appendices 33 to 36, wherein, in the step of forming the electrode active material layer, the electrode active material layer is dried under drying conditions such that the amount of the remaining organic solvent measured by GC-MS is 20 ppm or less to form an electrode active material layer.[Supplementary Note 38] A method for producing a secondary battery, comprising producing an electrode by the method for producing an electrode according to any one of Supplementary Notes 33 to 37, and using the obtained electrode to produce a secondary battery.

Claims

1. The boiling point is 180°C or more and 240°C or less, and the hydrogen bond parameter δH of the Hansen solubility parameter is 4 to 11 (J / cm ３ ) ０．５ A solvent composition for an electrode-forming paste, comprising a solvent (A) comprising:

2. The solvent composition for an electrode-forming paste according to claim 1, wherein the solvent (A) has a solubility in water of 5 g / 100 g or more.

3. The solvent composition for an electrode-forming paste according to claim 1 or 2, wherein the solvent (A) contains an ether skeleton and / or an ester skeleton.

4. The solvent composition for an electrode-forming paste according to claim 1 or 2, wherein the solvent (A) is one or more selected from the group consisting of dipropylene glycol monomethyl ether, dipropylene glycol monopropyl ether, dipropylene glycol monobutyl ether, diethylene glycol monobutyl ether, triethylene glycol dimethyl ether, tripropylene glycol dimethyl ether, diethylene glycol butyl methyl ether, diethylene glycol diethyl ether, tetraethylene glycol dimethyl ether, dipropylene glycol methyl ether acetate, diethylene glycol monoethyl ether acetate, 1,3-butylene glycol diacetate, propylene glycol diacetate, α-terpineol, dihydroterpineol, and 3-hydroxy-3-methylbutyl acetate.

5. An electrode-forming paste comprising the solvent composition for an electrode-forming paste according to claim 1, water, an electrode active material, and a binder.

6. The electrode-forming paste according to claim 5, wherein the content of the solvent composition for the electrode-forming paste is 0.1 to 5.0 mass % relative to the total amount of the electrode-forming paste.

7. An electrode-forming paste comprising an organic solvent, water, an electrode active material, and a binder, wherein the electrode-forming paste is applied to a copper foil in a film thickness of 600 μm, and the pre-dried film is dried with hot air at 110°C for 10 minutes, and the residual amount of the organic solvent is measured by GC-MS to find 50 ppm or more; and the pre-dried film is vacuum-dried at an absolute pressure of 1500 Pa or less for 300 minutes, and the residual amount of the organic solvent is measured by GC-MS to find 40 ppm or less.

8. A method for manufacturing an electrode having an electrode active material layer on a current collector, comprising the steps of: applying the electrode-forming paste according to claim 7 onto the current collector to form a coating film; evaporating water from the coating film to form a temporary dried film; and vacuum-drying the temporary dried film to form the electrode active material layer.

9. The method for manufacturing an electrode according to claim 8, wherein in the step of forming the pre-dried film, the pre-dried film is dried under drying conditions such that the amount of the remaining organic solvent measured by GC-MS is 50 ppm or more to form the pre-dried film.

10. The method for manufacturing an electrode according to claim 8, wherein in the step of forming the electrode active material layer, the electrode active material layer is dried under drying conditions such that the amount of the remaining organic solvent measured by GC-MS is 40 ppm or less to form the electrode active material layer.

11. A method for producing a secondary battery, comprising producing an electrode by the method for producing an electrode according to claim 8, and using the obtained electrode to produce a secondary battery.

Images