CN117659912A - Binder composition, slurry composition, electrode, and secondary battery - Google Patents

Abstract

The invention provides a binder composition, a slurry composition, an electrode and a secondary battery. The binder composition comprises a polyalkylacrylate and a polysaccharide organic compound, wherein the content of the polysaccharide organic compound is 3-25 wt% of the polyalkylacrylate. The slurry composition for the secondary battery electrode prepared by the binder composition has good stability, can inhibit the expansion of the secondary battery electrode at high temperature caused by repeated charge and discharge, and enables the secondary battery to exert excellent high-temperature cycle characteristics.

Description

Binder composition, slurry composition, electrode, and secondary battery

Technical Field

The application relates to the technical field of new energy, in particular to a binder composition for a secondary battery electrode, a slurry composition for the secondary battery electrode, an electrode for a secondary battery and a secondary battery.

Background

The binder is one of important constituent materials of the secondary battery pole piece, is a high molecular compound for adhering active substances and conductive agents in the electrode pole piece to the electrode current collector, has the functions of enhancing the contact among the active materials, the conductive agents and the current collector and stabilizing the pole piece structure, and is an additional material with higher technical content in the lithium ion battery material. Studies have shown that although the binder is used in a small amount in the electrode sheet, the merits of the binder properties directly affect the capacity, life and cycle characteristics of the battery.

The binder for lithium ion batteries that was first commercialized was polyvinylidene fluoride (PVDF). However, such binders have the following disadvantages: a: poor electronic and ionic conductivity; b: is easy to be swelled by electrolyte, so that the adhesiveness of active substances on a current collector is poor; c: the mechanical property and elasticity are not ideal; d: lithium carbide is easy to form with metal lithium, and the service life and the cycle performance of the battery are affected; e: the humidity requirement for the environment is high when in storage and use.

With the continuous development of the lithium ion battery industry, the performance requirements of the binder are also continuously improved. The lithium ion battery with the novel structure needs to have excellent mechanical properties by the binder. The power lithium ion battery needs to have good electric conductivity of electrons and ions while the binder has good adhesion due to high discharge power. High energy density lithium ion batteries use positive and negative active materials with high specific capacity, and these materials have large volume changes during the process of lithium intercalation, and in order to maintain the stability of the electrode structure, the binder needs to have good elasticity to buffer the volume effect.

Disclosure of Invention

Problems to be solved by the invention

When the slurry composition is prepared using the binder composition of the above-mentioned existing binder material, the slurry composition may be excessively thickened, and the stability of the slurry composition may not be sufficiently ensured. In addition, when an electrode is manufactured using the above-mentioned conventional binder composition, there is also a problem that swelling of the electrode due to repeated charge and discharge cannot be suppressed. In addition, in an electrode obtained by using a conventional binder composition, the secondary battery cannot exhibit excellent high-temperature cycle characteristics.

Accordingly, there is room for improvement in the conventional binder composition described above in terms of ensuring stability of the slurry composition, suppressing electrode swelling due to repeated charge and discharge, and allowing the secondary battery to exhibit excellent high-temperature cycle characteristics.

Accordingly, an object of the present invention is to provide a binder composition for a secondary battery electrode, which can ensure good stability of a slurry composition for a secondary battery electrode, and can suppress swelling of the secondary battery electrode with repeated charge and discharge, thereby enabling the secondary battery to exhibit excellent high-temperature cycle characteristics.

Further, an object of the present invention is to provide a slurry composition for a secondary battery electrode, which is excellent in stability and can suppress swelling of the secondary battery electrode accompanying repeated charge and discharge, thereby enabling the secondary battery to exhibit excellent high-temperature cycle characteristics.

Further, the present application aims to provide the binder composition for secondary battery electrodes and the application of the slurry composition in the preparation of secondary battery electrodes or secondary batteries.

Further, an object of the present invention is to provide an electrode for a secondary battery capable of suppressing expansion accompanying repeated charge and discharge and enabling the secondary battery to exhibit excellent high-temperature cycle characteristics, and a method for manufacturing the same.

Further, an object of the present invention is to provide a positive electrode for a secondary battery that can suppress expansion accompanying repeated charge and discharge and can give the secondary battery excellent high-temperature cycle characteristics.

Further, an object of the present application is to provide a secondary battery having excellent high-temperature cycle characteristics.

Solution for solving the problem

The present inventors have conducted intensive studies in order to solve the above-mentioned problems. Then, the present inventors found that by using a binder composition containing a polyalkylacrylate and a polysaccharide organic compound, it is possible to secure stability of the slurry composition, suppress swelling of an electrode accompanying repeated charge and discharge, and improve cycle characteristics of a secondary battery, and completed the present application.

That is, the present application has an object of advantageously solving the above-described problems, and is characterized in that the binder composition for a secondary battery electrode of the present application comprises a polyalkylacrylate and a polysaccharide organic compound, and the content of the polysaccharide organic compound is 3 to 25 parts by mass per 100 parts by mass of the polyalkylacrylate. In this way, the polysaccharide organic substance can inhibit the gel of the polyalkyl acrylate in a solvent such as N-methylpyrrolidone (NMP), thereby enabling the preparation of a slurry composition excellent in stability. In addition, if a slurry composition containing the binder composition is used, an electrode that can suppress swelling accompanying repeated charge and discharge and can give a secondary battery excellent in high-temperature cycle characteristics can be produced.

Further, the present application has an object to advantageously solve the above-described problems, and is characterized by having an electrode composite layer formed using the above-described slurry composition for a secondary battery electrode. An electrode having an electrode composite layer obtained by using the above slurry composition can suppress swelling accompanying repeated charge and discharge, and can enable a secondary battery to exhibit excellent high-temperature cycle characteristics.

Further, the present application has an object to advantageously solve the above-mentioned problems, and is characterized by comprising a positive electrode composite material layer formed by using a slurry composition for a secondary battery electrode, wherein the density of the positive electrode composite material layer is 4.0g/cm ³ The above. The slurry composition was used to obtain a slurry having a density of 4.0g/cm ³ The positive electrode of the positive electrode composite material layer can suppress expansion accompanying repeated charge and discharge, can sufficiently increase the energy density of the secondary battery, and can enable the secondary battery to exhibit excellent high-temperature cycle characteristics.

In addition, in the present application, the "density" of the electrode composite layer can be calculated using the mass and thickness of the electrode composite layer per unit area.

Further, the present application has an object to advantageously solve the above-described problems, and a secondary battery of the present application is characterized by comprising the above-described electrode for a secondary battery or the above-described positive electrode for a secondary battery. The secondary battery having any one of the above-described electrodes in this way has excellent high-temperature cycle characteristics.

Further, the present application has an object to advantageously solve the above-described problems, and a method for manufacturing an electrode for a secondary battery according to the present application is characterized by comprising the steps of: a step of applying the secondary battery electrode slurry composition to a current collector, a step of drying the secondary battery electrode slurry composition applied to the current collector to form a pre-press electrode composite layer on the current collector, a step of pressing the pre-press electrode composite layer to obtain a post-press electrode composite layer, and a step of pressing the pre-press electrode composite layer at a temperature of 20 ℃ to 40 ℃. By adopting the above step using the above slurry composition, an electrode having a high density and capable of suppressing expansion accompanying repeated charge and discharge can be produced satisfactorily. Further, if the electrode is used, the secondary battery can exhibit excellent high-temperature cycle characteristics.

Technical effects

According to the present invention, it is possible to provide a binder composition for a secondary battery electrode, which can ensure excellent stability of a slurry composition for a secondary battery electrode, and can suppress swelling of the secondary battery electrode accompanying repeated charge and discharge, thereby enabling the secondary battery to exhibit excellent high-temperature cycle characteristics.

Further, according to the present invention, it is possible to provide a slurry composition for a secondary battery electrode, which is excellent in stability and can suppress swelling of the secondary battery electrode accompanying repeated charge and discharge, thereby enabling the secondary battery to exhibit excellent high-temperature cycle characteristics.

Further, according to the present application, it is possible to provide an electrode for a secondary battery capable of suppressing expansion accompanying repeated charge and discharge and enabling the secondary battery to exhibit excellent high-temperature cycle characteristics, and a method for manufacturing the same.

Further, according to the present application, a secondary battery having excellent cycle characteristics can be provided.

Detailed Description

Other advantages and effects of the present application will become apparent to those skilled in the art from the present disclosure, when the following description of the embodiments is taken in conjunction with the accompanying drawings. The present application may be embodied or carried out in other specific embodiments, and the details of the present application may be modified or changed from various points of view and applications without departing from the spirit of the present application.

Here, the binder composition for a secondary battery electrode of the present application can be used for the preparation of a slurry composition for a secondary battery electrode. In addition, the paste composition for secondary battery electrodes of the present application can be used for the formation of electrodes of secondary batteries. The secondary battery electrode of the present application is characterized by having an electrode composite layer formed from the secondary battery electrode slurry composition of the present application. Further, the secondary battery of the present application is characterized by having the electrode for a secondary battery of the present application.

Binder composition for secondary battery electrode

The binder composition for a secondary battery electrode of the present application contains a polyalkylacrylate and a polysaccharide organic matter. The content of the polysaccharide organic substance is 3 to 25 parts by mass per 100 parts by mass of the polyalkylacrylate.

In addition, when the binder further contains an organic acid ester, the binder composition for a secondary battery electrode can be improved in adhesion and high-speed application properties, and the secondary battery can have good high-voltage cycle characteristics.

Further, according to the binder composition for a secondary battery electrode of the present application, it is possible to suppress gelation of the slurry composition for a secondary battery electrode and to improve dispersibility, and to impart excellent high-speed coatability to the slurry composition.

Polyacrylalkyl esters

The polyalkylacrylate is a component that functions as a binder, and is held in an electrode composite layer formed on a current collector using a slurry composition containing a binder composition so that components such as an electrode active material contained in the electrode composite layer do not separate from the electrode composite layer.

The polyalkyl acrylate contains acrylate monomer units, optionally containing alkylene structural units having 4 or more carbon atoms.

Acrylic ester monomer unit

The acrylate monomer capable of forming the acrylate monomer unit includes: alkyl acrylates such as methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, isobutyl acrylate, n-pentyl acrylate, isopentyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, lauryl acrylate, n-tetradecyl acrylate, stearyl acrylate; methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, isobutyl methacrylate, n-pentyl methacrylate, isopentyl methacrylate, hexyl methacrylate, heptyl methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, decyl methacrylate, lauryl methacrylate, n-tetradecyl methacrylate, stearyl methacrylate, glycidyl methacrylate and other alkyl methacrylates. Among these, from the viewpoint of ensuring dispersion stability of the slurry composition, the acrylic acid ester monomer is preferably an alkyl acrylate having 4 to 10 carbon atoms of an alkyl group bonded to a non-carbonyl oxygen atom, and among them, specifically, n-butyl acrylate and 2-ethylhexyl acrylate are preferable, and n-butyl acrylate is more preferable. These may be used singly or in combination of two or more.

The content of the acrylic acid ester monomer unit in the polyalkyl acrylate is 50 mass% or more, preferably 60 mass% or more, more preferably 70 mass% or more, and preferably 90 mass% or less, based on 100 mass% of the total repeating units in the polyalkyl acrylate. By setting the content of the acrylic acid ester monomer unit in the polyalkyl acrylate to 90 mass% or less, the solubility of the polyalkyl acrylate in an organic solvent such as NMP can be improved, and the dispersion stability of the slurry composition (for example, the positive electrode slurry composition) can be further improved. Further, by setting the content of the acrylic acid ester monomer unit in the polyalkyl acrylate to 10 mass% or more, the stability to the electrolyte of the composite material layer formed using the slurry composition can be improved, and the high-voltage cycle characteristics of the secondary battery manufactured using the obtained slurry composition can be improved.

Alkylene structural unit having 4 or more carbon atoms

The alkylene structural unit having 4 or more carbon atoms may be linear or branched, and from the viewpoint of improving the dispersion stability of the slurry composition and the battery characteristics of the secondary battery, the alkylene structural unit having 4 or more carbon atoms is preferably a linear, that is, a linear alkylene structural unit.

The method of introducing the alkylene structural unit having 4 or more carbon atoms into the polyalkyl acrylate is not particularly limited, and examples thereof include the following methods (1) and (2):

(1) Method for converting conjugated diene monomer units into alkylene structural units by preparing a polymer from a monomer composition comprising the conjugated diene monomer, and hydrogenating the polymer

(2) A method for producing a polymer from a monomer composition containing a 1-olefin monomer having 4 or more carbon atoms. Among these, the method of (1) is preferred because it is easy to produce a polyalkylacrylate.

Among them, examples of the conjugated diene monomer include conjugated diene compounds having 4 or more carbon atoms such as 1, 3-butadiene, isoprene, 2, 3-dimethyl-1, 3-butadiene, and 1, 3-pentadiene. Among them, 1, 3-butadiene is preferable. That is, the alkylene structural unit having 4 or more carbon atoms is preferably a structural unit (conjugated diene hydride unit) obtained by hydrogenating a conjugated diene monomer unit, more preferably a structural unit (1, 3-butadiene hydride unit) obtained by hydrogenating a 1, 3-butadiene monomer unit.

Examples of the 1-olefin monomer having 4 or more carbon atoms include 1-butene and 1-hexene.

These conjugated diene monomers and 1-olefin monomers having 4 or more carbon atoms may be used singly or in combination.

The content of the alkylene structural unit having 4 or more carbon atoms in the polyalkyl acrylate is preferably 20 mass% or less, more preferably 10 mass% or less, based on 100 mass% of the total repeating units (the total of the monomer units and the structural units) in the polyalkyl acrylate. When the content of the alkylene structural unit having 4 or more carbon atoms in the polyalkyl acrylate is within the above range, the dispersion stability of the slurry composition (for example, the slurry composition for positive electrode) and the battery characteristics of the secondary battery can be improved.

Process for preparing polyalkyl acrylate

The method for producing the polyalkylacrylate is not particularly limited, and may be produced by, for example, polymerizing a monomer composition containing the above-mentioned monomer to obtain a polymer, and optionally, hydrogenating the obtained polymer.

The content ratio of each monomer in the monomer composition of the present application can be determined based on the content ratio of each monomer unit and the structural unit (repeating unit) in the polyalkylacrylate.

The polymerization method is not particularly limited, and any of solution polymerization, suspension polymerization, bulk polymerization, emulsion polymerization, and the like may be used. In each polymerization method, a known emulsifier and a known polymerization initiator may be used as required.

The amount of the binder to be blended in the slurry composition of the present application is preferably 0.1 part by mass or more, more preferably 0.5 part by mass or more, preferably 10 parts by mass or less, and even more preferably 5 parts by mass or less, per 100 parts by mass of the electrode active material, in terms of solid matter conversion. By setting the amount of the binder to 0.1 part by mass or more with respect to 100 parts by mass of the electrode active material, the adhesion between the electrode active materials, the electrode active material and the conductive material, and the electrode active material and the current collector can be improved, and therefore, when a secondary battery is produced, good cycle characteristics can be obtained, and the battery life can be prolonged. In addition, when an electrode obtained by using a slurry composition containing a binder is applied to a secondary battery, the electrode can ensure the diffusivity of an electrolyte solution and obtain good cycle characteristics by making the amount of the electrolyte solution 10 parts by mass or less.

In particular, when the slurry composition of the present application is used as a slurry composition for a positive electrode, the amount of the binder is preferably 0.1 part by mass or more, more preferably 0.5 part by mass or more, preferably 10 parts by mass or less, more preferably 5 parts by mass or less, per 100 parts by mass of the positive electrode active material, calculated as a solid matter conversion. By setting the amount of the binder to 0.1 part by mass or more with respect to 100 parts by mass of the positive electrode active material, the adhesion between the positive electrode active materials, the conductive material, and the current collector can be improved, and therefore, when a secondary battery is produced, good cycle characteristics can be obtained, and the battery life can be prolonged. In addition, when the amount of the binder is 10 parts by mass or less, the dispersibility of the electrolyte solution can be ensured and good cycle characteristics can be obtained when the positive electrode slurry composition obtained by using the slurry composition containing the binder is applied to a secondary battery.

Polysaccharide organic matter

The present inventors have found that polysaccharide organic substances can inhibit the gelation of polyalkyl acrylate in a slurry composition, thereby ensuring dispersibility of the slurry composition, and the reason for inhibiting gelation is not clear, and it is presumed that: in the case of a slurry composition using NMP as a solvent, for example, the polysaccharide organic substance can lower the surface energy of the slurry, improve the wettability of the polyalkylacrylate, and improve the dispersibility, thereby improving the adhesion with the electrode active material.

The polysaccharide organic matter comprises one or more of cellulose, hemicellulose, cellose, chitin, chitosan oligosaccharide, inulin, xylooligosaccharide, fructooligosaccharide, isomaltooligosaccharide, and maltodextrin.

The cellulose comprises one or more of methylcellulose, carboxymethyl cellulose, ethylcellulose, hydroxyethyl cellulose and hydroxypropyl cellulose. Preferably hydroxyethyl cellulose and/or hydroxypropyl cellulose, a further improved effect can be obtained.

The content of the polysaccharide organic substance is 3 to 25 parts by mass, preferably 3 to 20 parts by mass, more preferably 5 to 18 parts by mass or more, and particularly preferably 8 to 15 parts by mass, per 100 parts by mass of the polyalkylacrylate. If the content of the polysaccharide organic matter is less than 3 parts by mass, gelation of the slurry composition cannot be sufficiently suppressed, and further battery characteristics of the secondary battery are degraded. On the other hand, if the content of the polysaccharide organic compound exceeds 25 parts by mass, the dispersibility of the slurry composition is lowered, and further the adhesion of the electrode composite layer to the current collector cannot be ensured, and the battery characteristics (particularly, cycle characteristics) are lowered. Further, by setting the content of the polysaccharide organic compound to be within the above range, a slurry composition which can suppress gelation and is excellent in dispersibility in high-speed coating can be obtained.

Organic acid esters

The inventor further discovers that polysaccharide organic matters are easy to generate decomposition reaction in the battery circulation process under high temperature and high voltage, the interface between the positive electrode and the electrolyte is destroyed, and the decomposition of the polysaccharide organic matters can be obviously inhibited by adding organic acid ester.

Examples of the organic acid ester include fatty acid esters and citric acid esters. The organic acid ester may be used alone or in combination of 2 or more kinds at an arbitrary ratio.

The fatty acid ester is selected from one or more of diethyl adipate (A01), dipropyl adipate (A02), dibutyl adipate, dipentyl adipate, dihexyl adipate, diheptyl adipate, dioctyl adipate (A03), diethyl sebacate, dipropyl sebacate, dibutyl sebacate, dipentyl sebacate, dihexyl sebacate, diheptyl sebacate and dioctyl sebacate.

The citric acid ester comprises one or more of triethyl citrate, tributyl citrate (A04), acetyl tributyl citrate, isopropyl citrate, propylene glycol citrate polyoxyethylene polyoxypropylene ether monoester, alkyl glycoside monoester citrate and glyceryl stearate citric acid ester.

The content of the organic acid ester is 10 to 60 parts by mass, preferably 15 to 55 parts by mass, more preferably 20 to 50 parts by mass or more, particularly preferably 25 to 40 parts by mass, per 100 parts by mass of the polyalkylacrylate. If the content of the organic acid ester is within the above range, the high-temperature cycle characteristics of the secondary battery can be further improved.

Solvent(s)

The solvent of the adhesive composition of the present application is not particularly limited, and known solvents can be used. Among them, N-methylpyrrolidone (NMP) is preferably used as the solvent. In addition, the polymerization solvent contained in the monomer composition used in the preparation of the polyalkylacrylate can be made at least a part of the solvent of the adhesive composition without particular limitation.

Other ingredients

In addition to the above-described components, the adhesive composition of the present application may contain components such as a dispersion stabilizer, a tackifier (except for a tackifier corresponding to the dispersion stabilizer), a conductive material, a reinforcing material, a leveling agent, an electrolyte additive, and the like. These are not particularly limited as long as they have no effect on the battery reaction, and known components can be used. These components may be used alone in 1 kind, or may be used in combination in any ratio of 2 or more kinds.

Preparation of the adhesive composition

The method for producing the adhesive composition of the present application is not particularly limited, and the adhesive composition can be produced by, for example, mixing the above-described components. Specifically, the adhesive composition can be prepared by mixing the above-described components using a ball mill, a sand mill, a bead mill, a pigment dispersing machine, a grinding kneader, an ultrasonic dispersing machine, a homogenizer, a planetary mixer, a filemix, or the like.

Slurry composition for secondary battery electrode

The slurry composition for a secondary battery electrode of the present application contains an electrode active material and the binder composition of the present application described above. Further, since the slurry composition of the present application contains the binder composition of the present application, gelation can be suppressed, dispersibility is good, and excellent high-speed coatability can be exhibited.

Electrode active material

The electrode active material is a material that transfers electrons to the electrodes (positive electrode and negative electrode) of the secondary battery. As electrode active materials (positive electrode active materials, negative electrode active materials) of secondary batteries, materials that can absorb and release lithium ions are generally used.

Positive electrode active material

The positive electrode active material may include a compound capable of intercalating and deintercalating lithium, and in particular, may include one or more composite oxides of lithium and a metal selected from cobalt, manganese, nickel, and combinations thereof. As a specific example, a compound represented by one of the chemical formulas may be used. Li (Li) _a A _1-b X _b D ₂ (0.90≤a≤1.8，0≤b≤0.5)；Li _a A _1-b X _b O _2-c D _c (0.90≤a≤1.8，0≤b≤0.5，0≤c≤0.05)；Li _a E _1-b X _b O _2-c D _c (0.90≤a≤1.8，0≤b≤0.5，0≤c≤0.05)；Li _a E _2-b X _b O _4-c Dc(0.90≤a≤1.8，0≤b≤0.5，0≤c≤0.05)；Li _a Ni _1-b-c Co _b X _c D _α (0.90≤a≤1.8，0≤b≤0.5，0≤c≤0.5，0＜α≤2)；Li _a Ni _1-b-c Co _b XcO _2-α T _α (0.90≤a≤1.8，0≤b≤0.5，0≤c≤0.05，0＜α＜2)；Li _a Ni _1-b-c Co _b X _c O _2-α T ₂ (0.90≤a≤1.8，0≤b≤0.5，0≤c≤0.05，0＜α＜2)；Li _a Ni _1-b-c Mn _b X _c D _α (0.90≤a≤1.8，0≤b≤0.5，0≤c≤0.05，0＜α≤2)；Li _a Ni _{1-b- c} Mn _b X _c O _2-α T _α (0.90≤a≤1.8，0≤b≤0.5，0≤c≤0.05，0＜α＜2)；Li _a Ni _1-b-c Mn _b X _c O _2-α T ₂ (0.90≤a≤1.8，0≤b≤0.5，0≤c≤0.05，0＜α＜2)；Li _a Ni _b E _c G _d O ₂ (0.90≤a≤1.8，0≤b≤0.9，0≤c≤0.5，0.001≤d≤0.1)；Li _a Ni _b Co _c Mn _d G _e O ₂ (0.90≤a≤1.8，0≤b≤0.9，0≤c≤0.5，0≤d≤0.5，0.001≤e≤0.1)；Li _a NiG _b O ₂ (0.90≤a≤1.8，0.001≤b≤0.1)；Li _a CoG _b O ₂ (0.90≤a≤1.8，0.001≤b≤0.1)；Li _a Mn _1-b G _b O ₂ (0.90≤a≤1.8，0.001≤b≤0.1)；Li _a Mn ₂ G _b O ₄ (0.90≤a≤1.8，0.001≤b≤0.1)；Li _a Mn _1-g G _g PO ₄ (0.90≤a≤1.8，0≤g≤0.5)；QO ₂ ；QS ₂ ；LiQS ₂ ；V ₂ O ₅ ；LiV ₂ O ₅ ；LiZO ₂ ；LiNiVO ₄ ；Li ₍₃ - _f) J2(PO ₄ ) ₃ (0≤f≤2)；Li _(3-f) Fe ₂ (PO ₄ ) ₃ (0≤f≤2)；Li _a FePO ₄ (0.90≤a≤1.8)。

In the chemical formula, A is selected from Ni, co, mn and combinations thereof; x is selected from Al, ni, co, mn, cr, fe, nb, mg, sr, V, rare earth elements, and combinations thereof; d is selected from O, F, S, P and combinations thereof; e is selected from Co, mn, and combinations thereof; t is selected from F, S, P and combinations thereof; g is selected from Al, cr, mn, fe, nb, mg, la, ce, sr, V and combinations thereof; q is selected from Ti, mo, mn, and combinations thereof; z is selected from Cr, V, fe, sc, Y and combinations thereof; j is selected from V, cr, mn, co, ni, cu and combinations thereof.

The compound may have a coating layer on the surface, or may be mixed with another compound having a coating layer. The coating layer may include at least one coating element compound selected from the group consisting of an oxide of a coating element, a hydroxide of a coating element, a oxyhydroxide of a coating element, an oxycarbonate of a coating element, and a hydroxycarbonate of a coating element. The compound used for the coating layer may be amorphous or crystalline. The coating elements included in the coating layer may include Mg, al, co, K, na, ca, si, ti, V, sn, ge, ga, B, as, nb, zr or a mixture thereof. The coating layer may be provided by a method of using these elements in a compound without adversely affecting the properties of the positive electrode active material, for example, the method may include any coating method (e.g., spraying, dipping, etc.), but since it is well known to those skilled in the relevant art, it is not described in more detail.

Negative electrode active material

As the negative electrode active material, a material which can reversibly intercalate/deintercalate lithium ions, lithium metal, a lithium metal alloy, a material which can dope/dedope lithium, or a transition metal oxide can be used.

The material that reversibly intercalates/deintercalates lithium ions may include a carbon material, i.e., a carbon-based anode active material conventionally used in rechargeable lithium batteries. Examples of the carbon-based anode active material may include crystalline carbon, amorphous carbon, or a mixture thereof. The crystalline carbon may be amorphous (without a specific shape), plate-like, spherical or fibrous natural graphite or artificial graphite. The amorphous carbon may be soft carbon, hard carbon, mesophase pitch carbonized product, sintered coke, or the like.

The lithium metal alloy includes an alloy of lithium and a metal selected from Na, K, rb, cs, fr, be, mg, ca, sr, si, sb, pb, in, zn, ba, ra, ge, A1 and Sn.

The material capable of doping/dedoping lithium may be Si, siO _x (0 < x < 2), si-Q alloy (wherein Q is an element selected from alkali metals, alkaline earth metals, group 13 elements, group 14 elements, group 15 elements, group 16 elements, transition metals, rare earth elements, and combinations thereof, but is not Si), si-carbon composite, sn, snO ₂ An Sn-R alloy (wherein R is an element selected from the group consisting of alkali metals, alkaline earth metals, group 13 elements, group 14 elements, group 15 elements, group 16 elements, transition metals, rare earth elements, and combinations thereof, but is not Sn), an Sn-carbon composite, and the like, and And at least one of these materials may be mixed with SiO ₂ Mixing. The elements Q and R may be selected from Mg, ca, sr, ba, ra, sc, Y, ti, zr, hf, rf, V, nb, ta, db, cr, mo, W, sg, tc, re, bh, fe, pb, ru, os, hs, rh, ir, pd, pt, cu, ag, au, zn, cd, B, A, ga, sn, in, ge, P, as, sb, bi, S, se, te, po and combinations thereof.

The transition metal oxide includes lithium titanium oxide.

Adhesive composition

As the binder composition that can be blended in the slurry composition, the binder composition for a secondary battery electrode of the present application containing the above-described polyalkylacrylate, polysaccharide organic matter, optional organic acid ester, and solvent can be used.

The content of the binder composition is not particularly limited, and may be, for example, the following amounts: the polyalkylacrylate is preferably 0.5 parts by mass or more, and preferably 5.0 parts by mass or less, more preferably 3.0 parts by mass or less, per 100 parts by mass of the electrode active material, in terms of solid matter conversion.

Furthermore, the polyalkyl acrylate, polysaccharide organic, and optionally organic acid ester in the slurry composition are components contained in the binder composition, and the suitable ratio of these components is the same as the suitable ratio of the components in the binder composition.

Preparation of slurry compositions

The slurry composition can be prepared by adding a solvent such as NMP to the above components as necessary and mixing the components. Specifically, the slurry composition can be prepared by mixing the above-described components and the solvent medium using a ball mill, a sand mill, a bead mill, a pigment dispersing machine, a grinding mixer, an ultrasonic dispersing machine, a homogenizer, a planetary mixer, a filemix, or the like. The mixing of the above components can be usually carried out at a temperature ranging from room temperature to 80℃for 10 minutes to several hours.

Properties of the slurry composition

Viscosity of the mixture

The viscosity of the slurry composition is preferably 3000 pa.s or more, preferably 8000pa.s or less, more preferably 700 pa.s or less, and still more preferably 600 mpa.s or less. By setting the viscosity of the slurry composition to the above range, the dispersibility of the slurry composition can be ensured, the gelation can be sufficiently suppressed, and the high-speed application property can be improved.

Concentration of solid content

The solid content concentration of the slurry composition is preferably 55 mass% or more, more preferably 57 mass% or more, further preferably 60 mass% or more, preferably 85 mass% or less, more preferably 83 mass% or less, and particularly preferably 80 mass% or less. If the solid content concentration of the slurry composition is 55 mass% or more, uniform coating can be performed in high-speed coating due to the proper fluidity of the slurry composition, and furthermore, drying efficiency when the slurry composition is dried to obtain an electrode composite layer is ensured. On the other hand, if the solid content concentration of the slurry composition is 85 mass% or less, the dispersibility of the slurry composition improves, and further, cracking of the coating film can be suppressed because smooth coating can be performed in high-speed coating.

Electrode for secondary battery

The above-described paste composition for secondary battery electrodes (paste composition for negative electrode and paste composition for positive electrode) prepared using the binder composition for secondary battery electrode of the present application can be used for the production of electrodes for secondary battery (negative electrode and positive electrode).

Specifically, the secondary battery electrode of the present application includes a current collector, and an electrode composite layer formed on the current collector, and the electrode composite layer is generally formed from a dried product of the above-described secondary battery electrode slurry composition. The electrode composite layer preferably contains an electrode active material, the above-mentioned polyalkylacrylate, a polysaccharide organic material, and optionally an organic acid ester. The components contained in the electrode composite layer are components contained in the slurry composition, and the appropriate presence ratio of these components is the same as the appropriate presence ratio of the components in the slurry composition.

Further, the secondary battery electrode has an electrode composite layer excellent in layer thickness uniformity and adhesion to a current collector, and therefore can exhibit excellent battery characteristics.

Method for manufacturing electrode for secondary battery

The electrode for a secondary battery of the present application can be produced, for example, by the following steps: and a step (coating step) of coating the secondary battery electrode slurry composition on a current collector, and a step (drying step) of drying the secondary battery electrode slurry composition coated on the current collector to form an electrode composite layer on the current collector.

Coating process

The method of applying the slurry composition to the current collector is not particularly limited, and a known method can be used. Specifically, as the coating method, a doctor blade coating method, a dipping method, a reverse roll coating method, a direct roll coating method, a gravure method, an extrusion method, a brush coating method, or the like can be used. In this case, the slurry composition may be applied to only one side of the current collector, or may be applied to both sides. The thickness of the slurry film on the current collector before drying after coating can be appropriately set according to the thickness of the electrode composite material layer to be dried.

Here, as the current collector to which the slurry composition is applied, a material having conductivity and electrochemical durability can be used. Specifically, as the current collector, for example, a current collector formed of iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, platinum, or the like may be used. Among them, copper foil is particularly preferable as a current collector for the negative electrode. Further, as the current collector for the positive electrode, aluminum foil is particularly preferable. The above materials may be used alone in 1 kind, or may be used in combination in any ratio of 2 or more kinds.

Drying process

The method for drying the slurry composition on the current collector is not particularly limited, and known methods can be used, and examples thereof include: drying with warm air, hot air, and low humidity air; vacuum drying; drying method by irradiation with infrared ray, electron beam, etc. By drying the slurry composition on the current collector in this manner, an electrode composite layer can be formed on the current collector, and an electrode for a secondary battery having the current collector and the electrode composite layer can be obtained.

After the drying step, the electrode composite layer may be subjected to a pressing treatment using a die press, a roll press, or the like. By the pressurizing treatment, the adhesion of the electrode composite layer to the current collector can be improved.

The method for manufacturing the electrode for a secondary battery of the present application preferably includes the steps of: a step of applying the secondary battery electrode slurry composition to a current collector, a step of drying the secondary battery electrode slurry composition applied to the current collector to form a pre-press electrode composite layer on the current collector, a step of pressing the pre-press electrode composite layer to obtain a post-press electrode composite layer, and a step of pressing the pre-press electrode composite layer at a temperature of 20 ℃ to 40 ℃. By using the above-described manufacturing method, an electrode having high density and capable of suppressing expansion accompanying repeated charge and discharge can be manufactured satisfactorily. Further, if the electrode is used, the secondary battery can exhibit excellent high-temperature cycle characteristics.

Secondary battery

The secondary battery of the present application has a positive electrode, a negative electrode, an electrolyte, and a separator, and the electrode for a secondary battery of the present application is used as at least one of the positive electrode and the negative electrode. Further, the secondary battery of the present application has the electrode for a secondary battery of the present application, and therefore, is excellent in high-temperature expansion and high-temperature cycle battery characteristics.

Electrode

As described above, the electrode for a secondary battery of the present application can be used as at least one of a positive electrode and a negative electrode. That is, the positive electrode of the secondary battery may be an electrode of the present application, the negative electrode may be another known negative electrode, the negative electrode of the secondary battery may be an electrode of the present application, the positive electrode may be another known positive electrode, or both the positive electrode and the negative electrode of the secondary battery may be electrodes of the present application.

The electrode for a secondary battery of the present invention is a negative electrode for a secondary batteryIn the case of (2), the density of the negative electrode composite material layer of the negative electrode is preferably 1.7g/cm ³ The above is more preferably 1.8g/cm ³ The above. The upper limit of the density of the negative electrode composite material layer is not particularly limited, but is usually 2.0g/cm ³ The following is given.

In the case where the electrode for a secondary battery of the present invention is a positive electrode for a secondary battery, the density of the positive electrode composite material layer of the positive electrode is preferably 4.0g/cm ³ The above is more preferably 4.1g/cm ³ The above. The upper limit of the density of the positive electrode composite material layer is not particularly limited, but is usually 4.6g/cm ³ The following is given.

If the density of the electrode composite layer (positive electrode composite layer or negative electrode composite layer) is the above lower limit value or more, the energy density of the secondary battery can be sufficiently improved. In addition, when the density of the electrode composite layer is increased, the electrolyte may become difficult to penetrate the electrode composite layer, and thus the battery characteristics may be degraded. However, since the electrode of the present invention is formed using the slurry composition containing the binder composition of the present invention, even when the electrode composite layer is densified and the electrolyte is difficult to permeate, the electrode of the present invention can sufficiently ensure excellent battery characteristics (particularly cycle characteristics) of the secondary battery.

Electrolyte solution

As the electrolyte solution, an organic electrolyte solution in which a supporting electrolyte is dissolved in an organic solvent can be generally used. As the supporting electrolyte, for example, a lithium salt can be used in a lithium ion secondary battery. Examples of the lithium salt include LiPF ₆ 、LiAsF ₆ 、LiBF ₄ 、LiSbF ₆ 、LiAlCl4、LiClO ₄ 、CF ₃ SO ₃ Li、C ₄ F ₉ SO ₃ Li、CF ₃ COOLi、(CF ₃ CO) ₂ NLi、(CF ₃ SO ₂ ) ₂ NLi、(C ₂ F ₅ SO ₂ ) NLi, etc. Wherein, liPF ₆ 、LiClO ₄ 、CF ₃ SO ₃ Li is preferable because it is easily dissolved in a solvent and exhibits a high dissociation degree. In addition, the electrolyte may be used alone or in combination of 1 kind More than 2. Since the support electrolyte having a higher dissociation degree generally tends to have a higher lithium ion conductivity, the lithium ion conductivity can be adjusted according to the type of the support electrolyte.

As the organic solvent used in the electrolyte solution, there is no particular limitation as long as it can dissolve the supporting electrolyte, and for example, in a lithium ion secondary battery, carbonates such as dimethyl carbonate (DMC), ethylene Carbonate (EC), diethyl carbonate (DEC), propylene Carbonate (PC), butylene Carbonate (BC), and ethylmethyl carbonate (EMC) can be preferably used; esters such as gamma-butyrolactone, methyl formate, ethyl acetate, propyl propionate, and ethyl propionate; ethers such as 1, 2-dimethoxyethane and tetrahydrofuran; sulfolane, dimethyl sulfoxide and other sulfur-containing compounds. In addition, a mixture of these solvents may be used. Among them, carbonates are preferable because of their high dielectric constant and wide stable potential region. Since the lithium ion conductivity tends to be higher as the viscosity of the solvent used is lower, the lithium ion conductivity can be adjusted according to the kind of the solvent.

In addition, the concentration of the electrolyte in the electrolyte solution can be appropriately adjusted.

In addition, at least one of ethylene glycol bis (propionitrile) ether, 1,2, 3-tris (cyanoethoxy) propane, bis (cyanoethyl) sulfone, or lithium difluorophosphate may be preferably added to the electrolyte. When lithium difluorophosphate, including ethylene glycol bis (propionitrile) ether, 1,2, 3-tris (cyanoethoxy) propane, bis (cyanoethyl) sulfone or lithium difluorophosphate, is added to the electrolyte, the decomposition reaction of the polyalkyl acrylate with the charge and discharge process can be suppressed, thereby further improving the high-temperature expansion and high-temperature cycle characteristics of the secondary battery.

The content of ethylene glycol bis (propionitrile) ether, 1,2, 3-tris (cyanoethoxy) propane, bis (cyanoethyl) sulfone or lithium difluorophosphate is 5 to 40 parts by mass, and the content of ethylene glycol bis (propionitrile) ether, 1,2, 3-tris (cyanoethoxy) propane, bis (cyanoethyl) sulfone or lithium difluorophosphate is preferably 7 parts by mass or more, more preferably 10 parts by mass or more, particularly preferably 15 parts by mass or more, preferably 35 parts by mass or less, more preferably 30 parts by mass or less, particularly preferably 25 parts by mass or less, relative to 100 parts by mass of lithium hexafluorophosphate. If the content of ethylene glycol bis (propionitrile) ether, 1,2, 3-tris (cyanoethoxy) propane, bis (cyanoethyl) sulfone or lithium difluorophosphate is within the above-described range, the high-temperature expansion and high-temperature cycle characteristics of the secondary battery can be further improved.

Diaphragm

From the viewpoint of being able to make the film thickness of the whole separator thin, thereby being able to increase the ratio of electrode active materials in the secondary battery and to increase the capacity per unit volume, microporous films formed of polyolefin-based resins (polyethylene, polypropylene, polybutylene, polyvinyl chloride) are preferred.

Method for manufacturing secondary battery

The secondary battery may be manufactured by, for example, the following means: the positive electrode and the negative electrode are stacked with a separator interposed therebetween, and wound, folded, or the like as necessary in accordance with the shape of the battery, and placed in a battery container, and an electrolyte is injected into the battery container to seal the battery container. In order to prevent pressure rise and overcharge and discharge in the secondary battery, an overcurrent preventing element such as a fuse or PTC element, a porous metal mesh, a guide plate, or the like may be provided as necessary. The shape of the secondary battery may be any of coin type, button type, sheet type, cylinder type, square type, flat type, and the like, for example.

Examples

The present application is specifically described below based on examples, but the present application is not limited to these examples. In the following description, "%" and "parts" indicating amounts are mass standards unless otherwise specified.

In examples and comparative examples, the stability of the slurry composition, the coating uniformity, and the high-speed coatability; and the high-temperature expansion and high-temperature cycle characteristics of the secondary battery were evaluated by the following methods, respectively.

(1) Slurry stability

The slurry stability of the slurry composition for positive electrode was evaluated based on the rate of change in viscosity of the slurry composition for positive electrode.

Specifically, a B-type viscometer (product of Dong machine industry Co., ltd. "RB-80L") was used at a temperature of 25℃and a rotation speed of 6%The viscosity (. Eta.1) of the freshly prepared positive electrode slurry composition was measured at 0rpm for a rotation time of 60 seconds. Then, the positive electrode slurry composition was stored at 25℃for 5 days, and then was subjected to the above-mentioned viscosity (. Eta. ₁ ) The measurement of (c) was performed in the same manner, and the viscosity (. Eta.) of the positive electrode slurry composition after storage was measured ₂ ). The resulting viscosity (. Eta.) was used ₁ ) Sum (eta) ₂ ) The viscosity change Δη is obtained based on the following equation.

Viscosity change Δη (%) = (|η) ₁ -η ₂ |/η ₁ )×100％

Then, the slurry stability of the slurry composition for positive electrode was evaluated according to the following criteria. The smaller the viscosity change Δη, the more excellent the slurry stability of the positive electrode slurry composition, and the better the dispersion state of the conductive material contained in the positive electrode slurry composition can be maintained. A, B, C in the column of slurry stability in table 4 represents:

A: the viscosity change Δη is less than 20%.

B: the viscosity change Deltaeta is 20% or more and less than 50%.

C: the viscosity change Deltaeta is more than 50%.

(2) Coating uniformity

The pressed positive electrode was cut to a size of 10cm×10 cm. Then, the cut positive electrode surface was visually checked, and the coating uniformity was evaluated based on the number of irregularities (aggregates) on the positive electrode surface. The less the irregularities (aggregates) on the positive electrode surface that are visually observed, the more uniform the positive electrode slurry can be applied, and the more excellent the application uniformity. A, B, C in the column of coating uniformity in table 4 represents:

a: the irregularities (aggregates) on the positive electrode surface could not be visually confirmed.

B: the roughness (aggregates) of the positive electrode surface was visually confirmed to be less than 3.

C: the irregularities (aggregates) on the positive electrode surface were visually confirmed to be 3 or more.

(3) High speed coatability

The slurry composition was discharged from the die onto an aluminum foil (thickness: 15mm, organic solvent treatment was performed) moving at a speed of 30 m/min in the horizontal direction using a die coater to apply the slurry composition. After coating, the electrode composite layer was dried at 120℃for 5 minutes to form an electrode composite layer having a thickness of 70. Mu.m, on an aluminum foil. The obtained electrodes (electrode composite layer + aluminum foil) were punched with a punching tool having a diameter of 16mm to prepare 10 circular electrodes, and the weight was measured and calculated for the electrode composite layer in each circular electrode. Then, a value obtained by subtracting the minimum value from the maximum value of the weight of the 10 electrode composite layers was calculated, a value obtained by dividing the value by the average value of the maximum value and the minimum value was calculated, and a deviation (%) obtained by multiplying the value by 100 was calculated, and was evaluated according to the following criteria. The smaller the value of the deviation, the more uniform the coating amount at the time of high-speed coating can be said to be. A, B, C, D in the high speed coating column in table 4 represents:

A: the deviation is less than 1.5%

B: the deviation is more than 1.5% and less than 3.0%

C: the deviation is more than 3.0% and less than 5.0%

D: the deviation degree is above 5.0%

(4) Expansion suppression of positive electrode

The lithium ion secondary battery thus produced was allowed to stand at 25℃for 24 hours, and then was charged and discharged at 4.65V and 1C and 3.0V and 1C in the 25℃environment. Next, in an environment of 60 ℃, the charge and discharge operations were repeated for 50 cycles with charge of 4.65V, 1C and discharge of 3.0V, 1C. Then, the battery in a charged state was disassembled by charging at 1C in an environment of 25 ℃, the positive electrode was taken out, and the thickness d1 of the positive electrode composite material layer was measured. The thickness of the positive electrode composite layer before the lithium ion secondary battery was produced was d0, and the thickness change rate represented by Δd= { (d 1-d 0)/d 0) } ×100 (%) was obtained and evaluated according to the following criteria. The smaller the thickness change rate Δd, the less the positive electrode expands after cycling. A, B, C, D in the column of the high temperature expansion in Table 4 represents:

a: the thickness change rate Deltad is less than 6%

B: the thickness change rate Deltad is more than 6% and less than 8%

C: the thickness change rate Deltad is 8 to less than 10%

D: a thickness change rate Δd of 10% or more

(5) Cycle characteristics of secondary battery

After the lithium ion secondary battery thus produced was allowed to stand at 25℃for 24 hours, the charge and discharge operations were performed at 25℃with charge of 4.65V and 1C and discharge of 3.0V and 1C, and the initial capacity C0 was measured. Next, the charge and discharge operations were repeated for 300 cycles at 45 ℃ with the charge of 4.65V and 1C and the discharge of 3.0V and 1C, and the capacity C1 after 300 cycles was measured. Then, from the initial capacity C0 and the capacity C1 after 300 cycles, the capacity retention Δc= (C1/C0) ×100 (%) was calculated and evaluated according to the following criteria. The higher the value of the capacity retention Δc, the smaller the decrease in discharge capacity, and the more excellent the cycle characteristics. A, B, C, D in the column of the high temperature cycle in Table 4 represents:

a: the capacity retention DeltaC is 90% or more

B: the capacity retention rate DeltaC is more than 85% and less than 90%

C: the capacity retention rate DeltaC is 80% or more and less than 85%

D: the capacity retention DeltaC is less than 80%

The components of the adhesive compositions used in the examples and comparative examples of the present application are shown in Table 1, and each of the components is commercially available.

Adhesive composition Components represented by tables 1B01 to B10

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The codes corresponding to the binder composition components in table 1 represent the substances shown in table 2 below: table 2 substances represented by codes in Table 1

The preparation methods of the electrolytes in the examples and comparative examples of the present application are as follows:

the weight ratio of the ethylene carbonate to the propylene carbonate to the ethyl propionate to the propyl propionate is 2:2:2:4, 3% of fluoroethylene carbonate and 3% of 1, 3-propane sultone are mixed with each other, and lithium hexafluorophosphate is dissolved so as to reach a concentration of 13 mass%. Then, according to Table 3, ethylene glycol bis (propionitrile) ether, 1,2, 3-tris (cyanoethoxy) propane, bis (cyanoethyl) sulfone or lithium difluorophosphate, which were shown in Table 3, were added to the above base electrolyte to form example electrolytes. The content of ethylene glycol bis (propionitrile) ether, 1,2, 3-tris (cyanoethoxy) propane, bis (cyanoethyl) sulfone or lithium difluorophosphate is 5 to 40 parts by mass relative to 100 parts by mass of the lithium hexafluorophosphate. The electrolytes used in the following examples and comparative examples are shown in table 3.

Composition of electrolytes represented by tables 3E01 to E08

Example 1

Slurry composition for positive electrode and positive electrode production

LiCoO as a positive electrode active material was stirred with a double planetary mixer ₂ 96 parts of carbon black as a positive electrode conductive material, 2.0 parts of a positive electrode binder composition (B01), 2 parts of N-methylpyrrolidone (NMP), and an appropriate amount of N-methylpyrrolidone (NMP), to prepare a positive electrode slurry composition;

As a current collector, an aluminum foil having a thickness of 9 μm was prepared, and the coating amount of the aluminum foil after drying was 25mg/cm on both sides of the aluminum foil ² The above-mentioned slurry composition for positive electrode was applied and dried at 60℃for 20 minutes, and after drying at 120℃for 20 minutes, the resultant was heat-treated at 150℃for 2 hours to obtain a positive electrode raw film; rolling the positive electrode raw film by a roll squeezer at 25 ℃ to obtain the product with the density of 4.15g/cm ³ A sheet-like positive electrode comprising a positive electrode active material layer and an aluminum foil, which was cut into a sheet-like positive electrode having a width of 4.8mm and a lengthThe degree is 50cm, and the aluminum leads are connected.

Slurry composition for negative electrode and production of negative electrode

98 parts of spherical artificial graphite (particle size: 12 μm) as a negative electrode active material, 1 part of styrene butadiene rubber (particle size: 180nm, glass transition temperature: -40 ℃) as a binder, 1 part of carboxymethyl as a thickener, and a proper amount of water were stirred by a double planetary mixer to prepare a slurry composition for a negative electrode;

as a current collector, a copper foil having a thickness of 5 μm was prepared, and the coating amount after drying was 10mg/cm on both sides of the copper foil ² The above-mentioned slurry composition for negative electrode was applied, dried at 60℃for 20 minutes, dried at 120℃for 20 minutes, and then heat-treated at 150℃for 2 hours to obtain a negative electrode raw film; the negative electrode raw film was rolled by a roll press to obtain a negative electrode raw film having a density of 1.8g/cm ³ The sheet-like negative electrode composed of the negative electrode active material layer and copper foil was cut into a sheet-like negative electrode having a width of 5.0mm and a length of 52cm, and a nickel lead was connected.

The obtained sheet-like positive electrode and sheet-like negative electrode were wound with a separator (a microporous membrane made of polyethylene having a thickness of 7 μm) interposed therebetween with a core having a diameter of 20mm, and the wound body was compressed at a speed of 10 mm/sec from one direction until a thickness of 4.5mm was reached, and the ratio of the major diameter to the minor diameter of the substantially oval was 7.7.

Electrolyte preparation

The weight ratio of the ethylene carbonate to the propylene carbonate to the ethyl propionate to the propyl propionate is 2: 3% of fluoroethylene carbonate and 3% of 1, 3-propane sultone were mixed in a 2:2:4 mixture, and lithium hexafluorophosphate was dissolved so as to reach a concentration of 13 mass%, to obtain an electrolyte used in this example.

The electrode plate group was housed in a predetermined aluminum laminate case together with 3.2g of an electrolyte, and then a negative electrode lead and a positive electrode lead were connected to predetermined portions, and then the opening of the case was sealed by heat, thereby completing a secondary battery. The high temperature storage and cycle characteristics of the resulting battery are shown in table 4.

Examples 2 to 25

The same procedure as in example 1 was conducted except that the binder compositions and electrolytic solutions for positive electrode were changed as shown in tables 1, 2 and 3 and described above. The results are shown in Table 4.

Comparative examples 1 to 6

The same procedure as in example 1 was conducted except that the binder compositions and electrolytic solutions for positive electrode were changed as shown in tables 1, 2 and 3 and described above. The results are shown in Table 4.

Table 4 binder compositions, electrolytes and related properties used in examples, comparative examples

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From tables 1, 2 and 3, it is known that: in the examples satisfying the requirements of the present application, all the evaluation items gave good results in good balance.

(1) As is clear from examples 1 to 25, by compounding the polyalkylacrylate and the polysaccharide organic compound in the amount ratio disclosed in the present application, the gel inhibition and the improvement of the dispersibility of the slurry composition obtained by using the binder composition were achieved, and the secondary battery excellent in the high-temperature expansion and the high-temperature cycle characteristics was obtained.

(2) As is clear from comparative examples 1 to 8 and comparative example 3, the binder used, when comprising the polyalkylacrylate and polysaccharide organic compound having the above-described characteristics disclosed in the present application, can significantly improve at least the stability, coating uniformity and high-speed coating property of the slurry composition, and the high-temperature expansion and high-temperature cycle performance of the secondary battery having the composite material layer formed of the slurry composition.

(3) As is clear from comparative examples 1 to 5 and comparative examples 1 to 2, the content of the suitable polysaccharide organic compound has a certain effect of improving the stability and coatability of the slurry composition and the battery performance of the secondary battery.

(4) As is clear from comparative examples 5 to 8, the binder used contains an organic acid ester, which can further improve the stability, coating uniformity and high-speed coating property of the slurry composition, and the high-temperature expansion property of the secondary battery having the composite material layer formed of the slurry composition is further improved.

(5) Comparative example 3 and examples 11 to 15 show that when the electrolyte contains ethylene glycol bis (propionitrile) ether, 1,2, 3-tris (cyanoethoxy) propane, bis (cyanoethyl) sulfone or lithium difluorophosphate, the high-temperature cycle performance of the secondary battery can be further improved.

The foregoing embodiments are merely illustrative of the principles of the present application and their effectiveness, and are not intended to limit the application. Modifications and variations may be made to the above-described embodiments by those of ordinary skill in the art without departing from the spirit and scope of the present application. Accordingly, it is intended that all equivalent modifications and variations which may be accomplished by persons skilled in the art without departing from the spirit and technical spirit of the disclosure be covered by the claims of this application.

Claims (10)

1. A binder composition for secondary battery electrodes, characterized by: the binder composition comprises a polyalkylacrylate and a polysaccharide organic compound, wherein the content of the polysaccharide organic compound is 3-25 wt% of the polyalkylacrylate.

2. The binder composition for secondary battery electrodes according to claim 1, wherein: the content of polysaccharide organic matters is 3-20wt%, preferably 5-18wt%, more preferably 8-15wt% of the polyalkylacrylate;

and/or the polysaccharide organic matter comprises one or more of cellulose, hemicellulose, cellose, chitin, chitosan oligosaccharide, inulin, xylooligosaccharide, fructooligosaccharide, maltooligosaccharide, isomaltooligosaccharide and maltodextrin, preferably, the cellulose comprises one or more of methylcellulose, carboxymethyl cellulose, ethyl cellulose, hydroxyethyl cellulose and hydroxypropyl cellulose;

and/or the content ratio of the acrylate monomer units in the polyalkyl acrylate is more than 50wt%, preferably 50-90 wt% of the total repeating units in the polyalkyl acrylate;

and/or the polyalkyl acrylate further comprises an alkylene structural unit having 4 or more carbon atoms, preferably, the content of the alkylene structural unit having 4 or more carbon atoms is 20wt% or less, more preferably 10wt% or less of the total repeating units in the polyalkyl acrylate;

And/or the polyalkyl acrylate comprises one or more of octyl polyacrylate, polymethyl methacrylate, decyl polyacrylate, butyl polyacrylate and lauryl polyacrylate;

and/or, the binder composition further comprises an organic acid ester;

and/or the adhesive composition further comprises a solvent comprising N-methylpyrrolidone.

3. The binder composition for secondary battery electrodes according to claim 2, wherein: the organic acid ester comprises fatty acid ester and/or citric acid ester; preferably, the fatty acid ester comprises one or more of diethyl adipate, dipropyl adipate, dibutyl adipate, dipentyl adipate, dihexyl adipate, diheptyl adipate, dioctyl adipate, diethyl sebacate, dipropyl sebacate, dibutyl sebacate, dipentyl sebacate, dihexyl sebacate, diheptyl sebacate and dioctyl sebacate, and the citric acid ester comprises one or more of triethyl citrate, tributyl citrate, acetyl tributyl citrate, isopropyl citrate, propylene glycol polyoxyethylene polyoxypropylene ether monoester citrate, alkyl glycoside monoester citrate and glyceryl stearate citric acid ester;

And/or the content of the organic acid ester is 10 to 60wt%, preferably 15 to 55wt%, more preferably 20 to 50wt%, particularly preferably 25 to 40wt% of the polyalkylacrylate.

4. A slurry composition for secondary battery electrodes, characterized by: the slurry composition comprising an electrode active material and the binder composition for a secondary battery electrode according to any one of claims 1 to 3.

5. The slurry composition for secondary battery electrodes according to claim 4, wherein: the binder composition is added in an amount such that the content of the polyalkylacrylate in the slurry composition is 0.5wt% or more, preferably 0.5wt% to 5wt%, more preferably 0.5wt% to 3wt% of the electrode active material;

and/or the solid content concentration in the slurry composition is 55wt% to 85wt%, preferably 57wt% to 83wt%, more preferably 60wt% to 80wt%;

and/or the viscosity of the slurry composition is 3000mpa·s or more, preferably 3000mpa·s to 8000pa·s, more preferably 3000mpa·s to 7000pa·s, and particularly preferably 3000mpa·s to 6000pa·s.

6. Use of the binder composition according to any one of claims 1 to 3 or the slurry composition according to any one of claims 4 to 5 for the preparation of an electrode for a secondary battery or a secondary battery.

7. An electrode for a secondary battery, comprising a current collector, characterized in that: further comprising an electrode composite layer formed on the current collector using the slurry composition for a secondary battery electrode according to claim 4 or 5.

8. The electrode for a secondary battery according to claim 7, wherein: the current collector is a positive electrode current collector, the electrode composite material layer is a positive electrode composite material layer formed on the positive electrode current collector, and the density of the positive electrode composite material layer is 4.0g/cm ³ The above is preferably 4.1g/cm ³ The above;

alternatively, the current collector is a negative electrode current collector, the electrode composite layer is a negative electrode composite layer formed on the negative electrode current collector, and its density is 1.7g/cm ³ The above is preferably 1.8g/cm ³ The above.

9. A method for manufacturing an electrode for a secondary battery, comprising:

coating the slurry composition for a secondary battery electrode according to claim 4 or 5 on a current collector;

drying the slurry composition for secondary battery electrode coated on the current collector to form a pre-press electrode composite material layer on the current collector;

pressing the electrode composite material layer before pressing to obtain a pressed electrode composite material layer;

Wherein the pressing temperature is 20 ℃ or higher and 40 ℃ or lower.

10. A secondary battery comprising a positive electrode, a negative electrode, an electrolyte and a separator, characterized in that: at least one of the positive electrode and the negative electrode is the electrode for a secondary battery according to claim 7 or 8;

preferably, the electrolyte of the secondary battery includes a solvent, lithium hexafluorophosphate, and an additive including at least one of ethylene glycol bis (propionitrile) ether, 1,2, 3-tris (cyanoethoxy) propane, bis (cyanoethyl) sulfone, lithium difluorophosphate;

more preferably, the content of the additive is 5 to 40wt%, still more preferably 7 to 35wt%, still more preferably 10 to 30wt%, particularly preferably 15 to 25wt% of the lithium hexafluorophosphate.