WO2022089127A1

WO2022089127A1 - Lithium ion battery

Info

Publication number: WO2022089127A1
Application number: PCT/CN2021/121196
Authority: WO
Inventors: 钱韫娴; 胡时光; 王勇; 刘中波
Original assignee: 深圳新宙邦科技股份有限公司
Priority date: 2020-10-30
Filing date: 2021-09-28
Publication date: 2022-05-05
Also published as: CN114464959A; CN114464959B

Abstract

The present invention relates to the technical field of lithium ion batteries, and disclosed is a lithium ion battery, wherein the lithium ion battery comprises a positive electrode, a negative electrode, a separator arranged between the positive electrode and the negative electrode, and a non-aqueous electrolyte; the separator comprises a substrate and a coating, wherein the coating is applied on at least one face of the substrate, and the coating comprises inorganic particles and/or PVDF; and the non-aqueous electrolyte comprises an organic solvent, a lithium salt, and a compound of formula (1). The lithium ion battery has a separator with a coating, which significantly improves the cycle performance and the fast charging performance of the battery while also ensuring the safety performance of the battery.

Description

Lithium Ion Battery

technical field

The invention relates to the technical field of lithium ion batteries, in particular to a lithium ion battery.

Background technique

Due to the advantages of high operating voltage, wide operating temperature range, high energy density and power density, no memory effect and long cycle life, lithium-ion batteries have been widely used in the field of 3C digital products such as mobile phones and notebook computers, as well as in the field of new energy vehicles. Applications. In recent years, with the continuous development of thin and light 3C digital products, the battery industry's requirements for high energy density of lithium-ion batteries are getting higher and higher. Therefore, it is urgent to improve the energy density of lithium-ion batteries.

While improving the energy density of lithium-ion batteries, it often brings serious safety problems. Among them, the separator has an important influence on the safety of the battery. If the battery shrinks and perforates the separator due to thermal runaway, the battery will short-circuit, posing a risk of fire and explosion. At present, most commercial lithium-ion battery separators are polyolefin separators, which thermally shrink at a temperature of 85°C or higher, posing a great safety hazard.

For this reason, many manufacturers use organic/inorganic composite separators, that is, coating inorganic particles on ordinary separators, thereby improving the thermal stability of the separators. In addition, there are also many manufacturers who use glue-coated separators with the hot-pressing process. The polyvinylidene fluoride (PVDF) coating of the glue-coated separators will fuse with the binder in the electrodes to improve the mechanical strength of the battery and prevent the battery from cycling. deformation during the process, thereby improving the safety performance of the battery.

However, in the case of high voltage, the inorganic particles (such as SiO ₂ , Al ₂ O ₃ , etc.) coated on the separator have more severe side reactions with the electrolyte than ordinary polyolefin separators, resulting in serious loss of cycle performance. It can be said that the use of organic or inorganic coated separators, to a certain extent, is the loss of battery performance in exchange for the improvement of safety performance. Therefore, how to reduce the negative impact on battery performance when using organic/inorganic coated separators is a problem that the lithium-ion battery industry needs to solve.

SUMMARY OF THE INVENTION

The purpose of the present invention is to overcome the problem of poor performance of lithium ion batteries using organic/inorganic coated separators in the prior art, and to provide a lithium ion battery that uses a separator with a coating to ensure that the battery At the same time of safety performance, it can also significantly improve the cycle performance and fast charging performance of the battery.

The inventors of the present invention have found through intensive research that when the separator of a lithium ion battery includes a substrate and a coating, the coating is coated on at least one side of the substrate, and the coating includes inorganic particles and/or PVDF, the non- When the compound represented by the formula (1) is added to the aqueous electrolyte, the cycle performance and fast charge performance of the lithium ion battery can be significantly improved, thereby completing the present invention.

Although the mechanism of action of the compound represented by formula (1) is not very clear, the inventors of the present invention speculate that the mechanism of action is that the inorganic particles of the separator usually contain active groups such as hydroxyl groups, which provide active sites for side reactions, As a result, side reactions occur with the electrolyte, resulting in capacity loss, and under high voltage conditions, these active sites will promote the dissolution of transition metal ions from the positive active material, which more significantly accelerates the side reactions of the electrolyte solution. The compound represented by the formula (1) reacts with these active groups, and the resulting product adheres to the surface of the inorganic particles, reducing its side reaction with the electrolyte, thereby improving the cycle stability of the battery.

In addition, the inventors of the present invention have further researched and found that lithium-ion batteries using PVDF coatings generally adopt a hot-pressing formation process. During the high-temperature formation process, the compound represented by formula (1) will form a block polymer with PVDF, which is beneficial to The migration of lithium ions increases the conductivity of lithium ions, thereby improving the fast charging performance and cycling performance of lithium ion batteries.

Thus, the present invention provides a lithium ion battery, the lithium ion battery includes a positive electrode, a negative electrode, a separator placed between the positive electrode and the negative electrode, and a non-aqueous electrolyte,

The separator includes a substrate and a coating, the coating is applied to at least one side of the substrate, and the coating contains inorganic particles and/or PVDF.

The non-aqueous electrolyte solution contains an organic solvent, a lithium salt and a compound represented by the formula (1),

In formula (1), R ₁ is a hydrocarbylene group having 2 to 20 carbon atoms, and the hydrocarbylene group contains one or more of a chain alkyl group, a cycloalkyl group and an aromatic group.

R ₂ is one of an amine group, a group represented by the following formula (2), and a group represented by the following formula (3);

R ₃ is one of an alkyl group having 1-10 carbon atoms, an ether group having 1-10 carbon atoms, an aryl group having 1-10 carbon atoms and an unsaturated hydrocarbon group having 2-10 carbon atoms, and R The hydrogen in ₃ can be optionally substituted by halogen.

Wherein, R ₄ is one of an alkyl group having 1 to 6 carbon atoms and an ester group having 3 to 10 carbon atoms, and * represents a bonding position.

Preferably, R ₁ is a hydrocarbylene group having 3-15 carbon atoms, and the hydrocarbylene group contains one or more of a chain alkyl group, a cycloalkyl group and an aromatic group.

Preferably, R ₁ is one of the hydrocarbylene groups represented by the following structure, * represents the position of bonding,

Preferably, R ₄ is one of an alkyl group with 1-3 carbon atoms and an ester group with 3-5 carbon atoms;

Preferably, R ₂ is one of the groups represented by the following structures, * represents the position of binding,

Preferably, the halogen is fluorine.

Preferably, R ₃ is one of the groups represented by the following structures, * represents the position of binding,

Preferably, the compound represented by formula (1) is selected from one or more compounds having the following structures:

Preferably, in the non-aqueous electrolyte, the content of the compound represented by formula (1) is 0.001% by weight or more; more preferably, in the non-aqueous electrolyte, the content of the compound represented by formula (1) is 0.001- 1 wt%.

Preferably, the substrate is one or more of a porous polymer film, a single-layer or multi-layer porous polymer film laminate, and a porous non-woven fabric.

Preferably, the porous polymer film is a polyolefin porous polymer film.

Preferably, the non-woven fabric is one or more of glass fiber non-woven fabric, synthetic fiber non-woven fabric and ceramic fiber paper.

Preferably, the thickness of the coating is 0.5-3 μm.

Preferably, the inorganic particles are inorganic particles that do not undergo oxidation and/or reduction reactions within the battery operating voltage range; more preferably, the inorganic particles are one of Al ₂ O ₃ particles, SiO ₂ particles and AlOOH particles one or more.

Preferably, the particle size of the inorganic particles is 0.2-3 μm.

Preferably, the active material of the positive electrode is LiNixCoyMzO ₂ , wherein M is selected from Mn and/or Al, and 0≤x≤1, 0≤y≤0.5, 0≤z≤0.5, and x+y+z≤1.

Preferably, the organic solvent is one or more of cyclic carbonate, linear carbonate, carboxylate and ether.

Preferably, the cyclic carbonate includes one or more of ethylene carbonate, vinylene carbonate, propylene carbonate and butylene carbonate.

Preferably, the linear carbonate includes one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate and propyl methyl carbonate.

Preferably, the carboxylic acid esters include methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, methyl butyrate, methyl isobutyrate, methyl trimethyl acetate and ethyl trimethyl acetate one or more of the esters.

Preferably, the ethers include ethylene glycol dimethyl ether, 1,3-dioxolane and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether one or more of.

More preferably, the organic solvent is a mixture of ethylene carbonate and diethyl carbonate.

Preferably, the lithium salt is selected from LiPF ₆ , LiBF ₄ , LiPO ₂ F ₂ , LiTFSI, LiBOB, LiDFOB, LiTFSI, LiSbF ₆ , LiAsF ₆ , LiN(SO ₂ CF ₃ ) ₂ , LiC(SO ₂ CF ₃ ) ₃ and one or more of LiN(SO ₂ F) ₂ ; more preferably, the lithium salt is LiPF ₆ .

Preferably, the content of the lithium salt in the non-aqueous electrolyte of the lithium ion battery is 0.5-3.5 mol/L; more preferably, the content of the lithium salt in the non-aqueous electrolyte of the lithium ion battery is 0.7-3.5 mol/L 1.5mol/L.

Preferably, the non-aqueous electrolyte further contains additives, the additives are cyclic carbonate compounds with fluorine atoms, cyclic carbonate compounds with carbon-carbon unsaturated bonds, cyclic sulfonates One or more of compounds and nitrile compounds.

Preferably, the cyclic carbonate compound having a fluorine atom is fluoroethylene carbonate and/or difluoroethylene carbonate.

Preferably, the cyclic carbonate compound with carbon-carbon unsaturated bond is one or more of vinylene carbonate, vinyl ethylene carbonate, vinyl ethylene carbonate and vinylene methyl carbonate kind.

Preferably, the cyclic sulfonate compound is 1,3-propane sultone and/or propylene sulfite.

Preferably, the nitrile compounds are succinonitrile, adiponitrile, ethylene glycol bis(propionitrile) ether, hexanetrinitrile, adiponitrile, pimeliconitrile, suberonitrile, azelonitrile and sebacic acid one or more of nitriles.

More preferably, the additive is fluoroethylene carbonate and/or succinonitrile.

Preferably, the content of the additive is 0.1-5 wt % of the total weight of the non-aqueous electrolyte of the lithium ion battery.

Preferably, the active material of the negative electrode is one or more of a metal material, a carbon-based negative electrode material and a non-carbon-based negative electrode material.

Preferably, the metallic material includes metallic lithium.

Preferably, the carbon-based negative electrode material includes one or more of graphite-based carbon materials, hard carbon materials and soft carbon materials.

Preferably, the non-carbon-based negative electrode material includes one or more of silicon-based, tin-based, antimony-based, aluminum-based and transition metal compounds.

More preferably, the active material of the negative electrode is artificial graphite.

Through the above technical solutions, the lithium ion battery provided by the present invention adopts a separator including a substrate and a coating, which can ensure that the battery has excellent safety performance. By adding the compound represented by formula (1) to the non-aqueous electrolyte, the high temperature and normal temperature cycle performance of the battery can be ensured, the capacity retention rate and cycle stability of the lithium ion battery can be improved, and the fast charging performance of the battery can be improved.

Detailed ways

The endpoints of ranges and any values disclosed herein are not limited to the precise ranges or values, which are to be understood to encompass values proximate to those ranges or values. For ranges of values, the endpoints of each range, the endpoints of each range and the individual point values, and the individual point values can be combined with each other to yield one or more new ranges of values that Ranges should be considered as specifically disclosed herein.

The present invention provides a lithium ion battery, wherein the lithium ion battery comprises a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte, the separator comprises a substrate and a coating layer, and the coating layer is coated Distributed on at least one side of the substrate, and the coating layer includes inorganic particles and/or PVDF; the non-aqueous electrolyte contains an organic solvent, a lithium salt and a compound represented by formula (1),

According to the present invention, preferably, R ₁ is a hydrocarbylene group with 3-15 carbon atoms, and the hydrocarbylene group contains one or more of a chain alkyl group, a cycloalkyl group and an aromatic group; more preferably, R ₁ is one of the hydrocarbylene groups represented by the following structure, * represents the position of bonding,

According to the present invention, R ₂ is one of an amino group, a group represented by the following formula (2), and a group represented by the following formula (3).

Preferably, in formula (3), R ₄ is one of an alkyl group with 1-3 carbon atoms and an ester group with 3-5 carbon atoms.

More preferably, R ₂ is one of the groups represented by the following structure, * represents the position of binding,

According to the present invention, R ₃ is one of an alkyl group with 1-10 carbon atoms, an ether group with 1-10 carbon atoms, an aryl group with 1-10 carbon atoms and an unsaturated hydrocarbon group with 2-10 carbon atoms species, and the hydrogen in _R3 may be optionally substituted by halogen.

As a C1-C10 alkyl group, a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a neobutyl group, a t-butyl group etc. are mentioned, for example.

Examples of the group in which hydrogen in the alkyl group having 1 to 10 carbon atoms is substituted by halogen include, for example, groups in which at least one hydrogen in each of the alkyl groups listed above is substituted with a halogen, and each of the alkyl groups listed above is preferred. A group in which one of the hydrogens is replaced by a halogen.

Examples of the unsaturated hydrocarbon group having 2 to 10 carbon atoms include a vinyl group, a propenyl group, an allyl group, a propynyl group, a propargyl group, a methyl vinyl group, and a methallyl group.

Examples of groups in which hydrogen in an unsaturated hydrocarbon group having 2 to 10 carbon atoms is substituted with halogen include, for example, groups in which at least one hydrogen in each of the unsaturated hydrocarbon groups listed above is substituted with halogen, and the above-mentioned groups are preferred. A group in which one hydrogen in each of the listed unsaturated hydrocarbon groups is replaced by a halogen.

Preferably, the halogen is F, Cl, Br or I; more preferably, the halogen is F, Cl or Br; further preferably, the halogen is F or Cl; particularly preferably, the halogen is F .

Particularly preferably, R ₃ is one of the groups represented by the following structure, * represents the position of binding,

According to the present invention, it is particularly preferred that the compound represented by formula (1) is selected from one or more compounds having the following structures:

According to the present invention, the compound represented by the formula (1) can be obtained by those skilled in the art through organic synthesis. For example, it can be synthesized according to the following synthetic route:

As a synthesis method, a base can be used as an acid binding agent, and the compound represented by the formula (1) is obtained by amidation reaction of the primary amine as the compound A and the acid chloride as the compound B.

As the conditions of the amidation reaction, the conditions commonly used in the art can be adopted, for example, the molar ratio to the acid chloride of compound B can be 1:0.9-1.2; The molar ratio of amine to base can be, for example, 1:1-3; the reaction temperature can be room temperature, and the time can be more than 1 hour, preferably 1-24 hours.

In addition, after the completion of the reaction, purification can be carried out according to conventional purification methods in the art, which will not be repeated here.

According to the present invention, in the non-aqueous electrolyte of the lithium ion battery, the content of the compound represented by the formula (1) is 0.001% by weight; preferably, in the non-aqueous electrolyte of the lithium ion battery, the compound represented by the formula (1) The content of the compound is 0.001-1% by weight; more preferably, the content of the compound represented by formula (1) in the non-aqueous electrolyte of the lithium ion battery is 0.2-0.5% by weight. If the content of the compound represented by formula (1) is lower than the above range, the improvement effect on the performance of the lithium ion battery is not obvious; if it exceeds the above range, the further improvement effect on the performance of the lithium ion battery is limited.

According to the present invention, the separator comprises a substrate and a coating, the coating is applied to at least one side of the substrate, preferably, the coating is applied to both sides of the substrate.

According to the present invention, the coating may contain inorganic particles and/or PVDF, for example, the coating may contain inorganic particles, may contain PVDF, or may contain both inorganic particles and PVDF.

According to the present invention, the substrate can be various conventional membrane substrate materials in the field, for example, can be porous polymer film and porous non-woven fabric.

The porous polymer film may be used in a single layer, or may be a laminate of single or multi-layer porous polymer films.

In the present invention, preferably, the porous polymer film is a polyolefin porous polymer film. As the polyolefin, for example, it can be polyethylene, polypropylene, etc., and can be various polyolefin materials conventional in the field. special restrictions.

In the present invention, preferably, the non-woven fabric can be various non-woven fabrics used in the field for lithium ion battery separators, without particular limitations, such as glass fiber non-woven fabrics, synthetic fiber non-woven fabrics and ceramic non-woven fabrics. One or more of fiber paper.

According to the present invention, the thickness of the coating on the substrate can be the conventional thickness of the membrane coating in the field, preferably, the thickness of the coating is 0.5-3 μm, more preferably, the thickness of the coating is 0.5-2.5 μm, further preferably, the thickness of the coating is 1.5-2.5 μm. By limiting the thickness of the coating to the above range, the safety performance of the battery can be ensured.

According to the present invention, the inorganic particles may be various inorganic particles used in the field for coating lithium ion battery separators, as long as the inorganic particles do not undergo oxidation and/or reduction reactions within the operating voltage range of the lithium ion battery. Preferably, the inorganic particles are one or more of Al ₂ O ₃ particles, SiO ₂ particles and AlOOH particles; more preferably, the inorganic particles are Al ₂ O ₃ particles.

In the present invention, the particle size of the inorganic particles is not particularly limited, and can be the size commonly used for coating separators in the field. Preferably, the particle size of the inorganic particles is 0.1-5 μm; more preferably, The particle size of the inorganic particles is 0.2-3 μm; further preferably, the particle size of the inorganic particles is 0.2-0.5 μm.

According to the present invention, the preparation of the separator is not particularly limited, and can be carried out according to various methods commonly used in the art to prepare a separator by coating. For example, the coating material can be dispersed in a solvent to obtain a coating slurry, and then the coating slurry can be coated on the material used as the diaphragm substrate by a conventional coating method in the art, and then processed by drying and other processes, and then the coating slurry can be A coated separator was obtained.

In addition, in order to ensure the cohesiveness of the coating, materials such as conventional binders may also be added to the coating slurry, which will not be repeated here.

According to the present invention, the active material of the positive electrode is not particularly limited. Preferably, the active material of the positive electrode is LiNixCoyMzO ₂ , wherein M is selected from Mn and/or Al, and 0≤x≤1, 0≤y≤0.5 , 0≤z≤0.5, x+y+z≤1.

As the above positive active material, for example, where x and z can be 0, the positive active material is LiCoO ₂ ; for example, the x can be 0.8, y and z can be 0.1, M can be Mn, then the The positive electrode active material is LiNi _0.8 Co _0.1 Mn _0.1 O ₂ . As long as the above relationship is satisfied, it will not be repeated here.

According to the present invention, the organic solvent can be various organic solvents commonly used in the field to prepare non-aqueous electrolytes for lithium ion batteries, without particular limitations, for example, cyclic carbonates, linear carbonates, carboxylic acids can be used One or more of esters and ethers are used as organic solvents.

The cyclic carbonate used as the organic solvent for non-aqueous electrolysis of lithium ion batteries may include one or more of ethylene carbonate, vinylene carbonate, propylene carbonate and butylene carbonate.

The linear carbonate as the organic solvent for non-aqueous electrolysis of the lithium ion battery may include one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate and propyl methyl carbonate.

The carboxylate used as the organic solvent for non-aqueous electrolysis of lithium ion batteries may include methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, methyl butyrate, methyl isobutyrate, and trimethyl acetic acid One or more of methyl ester and ethyl trimethylacetate.

The ethers as organic solvents for non-aqueous electrolysis of lithium ion batteries may include ethylene glycol dimethyl ether, 1,3-dioxolane, and 1,1,2,2-tetrafluoroethyl-2,2,3 , one or more of 3-tetrafluoropropyl ether.

In a particularly preferred embodiment of the present invention, the organic solvent is a mixture of ethylene carbonate and diethyl carbonate. By using the above three compounds as organic solvents, the conductivity, viscosity and safety of the electrolyte can be balanced, so that the electrolyte can achieve better comprehensive performance.

In the present invention, the lithium salt can be various lithium salts commonly used in the field to prepare lithium ion batteries, and there is no particular limitation. For example, LiPF ₆ , LiBF ₄ , LiPO ₂ F ₂ , LiTFSI, LiBOB, LiDFOB, One or more of LiTFSI, LiSbF ₆ , LiAsF ₆ , LiN(SO ₂ CF ₃ ) ₂ , LiC(SO ₂ CF ₃ ) ₃ and LiN(SO ₂ F) ₂ . In the present invention, preferably, the lithium salt is LiPF ₆ .

In the present invention, the content of the lithium salt may be the usual content in the non-aqueous electrolyte of lithium ion batteries in the art, and is not particularly limited. For example, the content of the lithium salt in the non-aqueous electrolyte of the lithium ion battery may be 0.5-3.5 mol/L; preferably, the content of the lithium salt in the non-aqueous electrolyte of the lithium ion battery is 0.7-1.5 mol/L. When the content of the lithium salt is within this range, not only good battery performance can be achieved, but also the cost of the electrolyte can be effectively controlled.

According to the present invention, the non-aqueous electrolyte for lithium ion batteries may further contain various additives commonly used in the art to improve the performance of lithium ion batteries, for example, the additives may be selected from cyclic carbonate compounds with fluorine atoms , one or more of cyclic carbonate compounds, cyclic sulfonate compounds and nitrile compounds having carbon-carbon unsaturated bonds.

According to the present invention, in the non-aqueous electrolyte of the lithium ion battery, the content of the additive may be the conventional content of various additives in the lithium ion battery in the art. For example, the content of the additive may be 0.1-5% by weight of the total mass of the non-aqueous electrolyte of the lithium ion battery; preferably, the content of the additive may be 2% of the total mass of the non-aqueous electrolyte of the lithium ion battery -5 wt%.

According to the present invention, the active material of the negative electrode material can be selected from various materials commonly used in the negative electrode active material of lithium ion batteries in the art, without special limitation, for example, the active material of the negative electrode can be a metal material, a carbon-based active material One or more of negative electrode materials and non-carbon-based negative electrode materials. Wherein, preferably, the metal material includes metal lithium; the carbon-based negative electrode material includes one or more of graphite-based carbon materials, hard carbon materials and soft carbon materials; the non-carbon-based negative electrode material includes silicon-based , one or more of tin-based, antimony-based, aluminum-based and transition metal compounds. More preferably, the active material of the negative electrode is artificial graphite.

In the present invention, the preparation of the positive electrode and the negative electrode of the lithium ion battery can be carried out according to the method commonly used in the art for preparing the positive electrode and the negative electrode of the lithium ion battery, and there is no particular limitation. For example, the active materials of the positive and negative electrodes may be mixed with a conductive agent, a binder, etc., and the resulting mixture may be dispersed in a solvent to prepare a slurry, and then the resulting slurry may be coated on a current collector and dried and rolled and so on. The materials and substances commonly used in the art can be used for the conductive agent, solvent, current collector, etc., which will not be repeated here.

In the present invention, the preparation of the lithium ion battery can be carried out by the "sandwich" method commonly used in the art. For example, a separator is placed between the positive plate and the negative plate coated with the active material, and then the whole is wound, Then, the coiled body is flattened and placed in a packaging bag to be vacuum-baked and dried to obtain a battery cell. Then, the electrolyte is injected into the battery core, vacuum-sealed and left to stand for formation. This method is a conventional method in the field and will not be repeated here.

The present invention will be described in detail through the following examples, but the present invention is not limited to the following examples.

In the following preparation examples, examples and comparative examples, unless otherwise specified, the materials used are all commercially available products.

Preparation Examples 1-7: Preparation of Compounds

At 25°C, the raw material compound A and raw material compound B in Table 1 were respectively subjected to amidation reaction at a molar ratio of 1:1 for 10 hours, and triethylamine was used as an acid binding agent (the ratio of triethylamine and raw material compound A) in the reaction. The molar ratio is 1.5:1). After the reaction, the compound 1, the compound 2, the compound 3, the compound 4, the compound 6, the compound 7 and the compound 12 are obtained by purification by column chromatography.

Table 1

Preparation Example 8: Preparation of PVDF Coated Separator

PVDF was added to acetone in an amount of 5% by weight relative to acetone, and dissolved at 50 ° C for 12 hours to prepare PVDF slurry; the PVDF slurry was coated on one side of Celgard2400 separator (thickness: 20 μm), and then After drying in an oven at 60 °C for 12 h, the thickness of the dried coating was 2 μm.

Preparation Example ₉ : Preparation of _Al2O3 Coated Separator

PVDF was added to acetone in an amount of 5% by weight relative to acetone, and dissolved at 50 ° C for 12 hours to prepare a PVDF mixed solution; Al ₂ O ₃ particles (particle size of 0.2 μm) were added to the PVDF mixed solution, Among them, the weight ratio of Al ₂ O ₃ particles to PVDF was 9:1, and Al ₂ O ₃ slurry was prepared; the Al ₂ O ₃ slurry was coated on one side of the Celgard2400 separator (thickness: 20 μm), and then the After drying in an oven at 60 °C for 12 h, the thickness of the coating after drying was 2 μm.

Preparation Example 10: Preparation of PVDF Coating + Al ₂ O ₃ Coating Separator

The PVDF slurry and Al ₂ O ₃ slurry prepared by the methods in Preparation Example 8 and Preparation Example 9 were coated on both sides of a Celgard2400 separator (thickness of 20 μm), and then dried in an oven at 60 ° C for 12 h, and then dried. The coating thickness on the latter two sides is 2 μm.

Test Example 1: High temperature cycle performance test

The lithium-ion batteries prepared in the following examples and comparative examples were placed in an oven with a constant temperature of 45°C, charged to 4.2V (or 4.45V) at a constant current of 0.7C, and then charged at a constant voltage until the current dropped to 0.03C, and then Discharge to 3.0V at a constant current of 1C, cycle 400 times, record the first and last discharge capacities, and calculate the capacity retention rate of high-temperature cycles as follows:

Capacity retention rate (%)=discharge capacity of the last cycle/discharge capacity of the first cycle×100%.

Test example 2: normal temperature 3C fast charge cycle test

The lithium-ion batteries prepared in the following examples and comparative examples were placed in an incubator at 25°C, charged to 4.2V (or 4.45V) at a constant current of 3C, and then charged at a constant voltage until the current dropped to 0.03C, and then charged at a constant current of 3C to 0.03C. The current constant current discharge to 3.0V, so cycle 200 times, record the first constant current charge capacity and total charge capacity, record the first discharge capacity and the last discharge capacity, calculate the 3C constant current charge as follows Proportion and capacity retention rate:

Constant current charging ratio (%) = constant current charging capacity/total charging capacity × 100%;

Capacity retention ratio (%)=last discharge capacity/first discharge capacity×100%.

Example 1

1) Preparation of electrolyte

Mix ethylene carbonate (EC) and diethyl carbonate (DEC) in a weight ratio of EC:DEC=3:7, then add lithium hexafluorophosphate (LiPF ₆ ) to the resulting mixture to a molar concentration of 1 mol/L, and then add an electrolyte solution 0.2% by weight of compound 2 in total mass;

2) Preparation of positive electrode

The positive active material LiCoO ₂ , the conductive agent conductive carbon black Super-P, and the binder polyvinylidene fluoride (PVDF) were uniformly mixed in a weight ratio of 93:4:3, and then dispersed in N-methyl-2- In pyrrolidone (NMP), the positive electrode slurry is obtained; the positive electrode slurry is uniformly coated on both sides of the aluminum foil, dried, calendered and vacuum-dried, and the aluminum lead wire is welded with an ultrasonic welder to obtain the positive electrode. The thickness is 110±2 μm.

3) Preparation of negative electrode

The negative active material artificial graphite, the conductive agent conductive carbon black Super-P, and the binders styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) are mixed uniformly in a weight ratio of 94:1:2.5:2.5, and then the The mixture is dispersed in deionized water to obtain a negative electrode slurry; the negative electrode slurry is coated on both sides of the copper foil, dried, calendered and vacuum dried, and the nickel lead wire is welded with an ultrasonic welder to obtain a negative electrode, a polar plate The thickness is 126 ± 2 μm.

4) Preparation of cells

The PVDF-coated separator prepared in the above Preparation Example 8 was placed between the positive electrode and the negative electrode, and then the sandwich structure composed of the positive electrode, the negative electrode and the separator was wound, and the wound body was flattened and placed in an aluminum foil packaging bag. Bake under vacuum for 48h to obtain the cell to be injected;

5) Liquid injection and formation of cells

In a glove box with water and oxygen content less than 10 ppm, inject the electrolyte prepared in step 1) into the battery cell prepared in step 4), and let it stand for 24h after vacuum packaging;

Then hot-pressing is carried out according to the following steps: temperature 75°C, pressure 0.8MPa, 0.1C constant current charging for 45min, 0.2C constant current charging for 30min, then 0.5C constant current charging for 75min, secondary vacuum sealing, and then further charging at 0.2C Current constant current and constant voltage charge to cut-off voltage 4.45V, cut-off current 0.03C, and constant current discharge to 3.0V at 0.2C current.

Examples 2-18 and Comparative Examples 1-4

Carry out according to the method of embodiment 1, the difference is:

The type and amount of the compound represented by formula (1) added to the non-aqueous electrolyte are different, the type of separator, the type of positive active material, the cut-off voltage, and the type and amount of additives are different.

The specific content is shown in Table 2.

The results of Examples 1-18 and Comparative Examples 1-4 are shown in Table 3.

Table 2

Note: / indicates that the corresponding substances are not added, the % in Table 2 are all weight %, FEC is fluoroethylene carbonate; SN is succinonitrile.

table 3

Combining Table 2 and Table 3, it can be seen from the results of Examples and Comparative Examples that in lithium-ion batteries containing inorganic particles Al ₂ O ₃ and/or PVDF-coated separators, when the non-aqueous electrolyte further contains this When the compound represented by the formula (1) is provided in the invention, the high-temperature cycle capacity retention rate, the capacity retention rate at normal temperature and the constant current charging ratio of the lithium ion battery can be significantly improved.

It can be seen from the results of Examples 3-9 that, within the scope of the present invention, with the increase of the content of the compound represented by formula (1), the performance of the lithium ion battery is gradually improved.

It can be seen from the results of Examples 10-11 and Example 18 that on the basis of adding the compound represented by the formula (1) to the non-aqueous electrolyte of the lithium ion battery, other additives are further added, which can be combined with the compound represented by the formula (1). The compounds work together to further improve the high-temperature cycle capacity retention rate, the capacity retention rate at room temperature, and the constant current charging ratio of lithium-ion batteries, thereby improving the performance of lithium-ion batteries.

From the results of Example 1-2 and Example 12-15, it can be seen that among the compounds represented by formula (1) provided by the present invention, compounds 2, 3, 4, 6, 7, 12, etc. all have the same effect as compound 1 .

The preferred embodiments of the present invention have been described above in detail, however, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, a variety of simple modifications can be made to the technical solutions of the present invention, including combining various technical features in any other suitable manner. These simple modifications and combinations should also be regarded as the content disclosed in the present invention. All belong to the protection scope of the present invention.

Claims

A lithium ion battery, characterized in that the lithium ion battery comprises a positive electrode, a negative electrode, a separator placed between the positive electrode and the negative electrode, and a non-aqueous electrolyte,

The separator includes a substrate and a coating, the coating is applied to at least one side of the substrate, and the coating contains inorganic particles and/or PVDF;

The non-aqueous electrolyte solution contains an organic solvent, a lithium salt and a compound represented by the formula (1),

In formula (1), R 1 is a hydrocarbylene group with 2-20 carbon atoms, and the hydrocarbylene group contains one or more of a chain alkyl group, a cycloalkyl group and an aromatic group;

R 2 is one of an amine group, a group represented by the following formula (2), and a group represented by the following formula (3);

R 3 is one of an alkyl group having 1-10 carbon atoms, an ether group having 1-10 carbon atoms, an aryl group having 1-10 carbon atoms and an unsaturated hydrocarbon group having 2-10 carbon atoms, and R The hydrogen in 3 can be optionally substituted by halogen;

Wherein, R 4 is one of an alkyl group having 1 to 6 carbon atoms and an ester group having 3 to 10 carbon atoms, and * represents a bonding position.
The lithium ion battery according to claim 1, wherein R 1 is a hydrocarbylene group having 3 to 15 carbon atoms, and the hydrocarbylene group contains one or more of a chain alkyl group, a cycloalkyl group and an aromatic group kind;

Preferably, R 1 is one of the hydrocarbylene groups represented by the following structure, * represents the position of bonding,

Preferably, R 4 is one of an alkyl group with 1-3 carbon atoms and an ester group with 3-5 carbon atoms;

Preferably, R 2 is one of the groups represented by the following structures, * represents the position of binding,

Preferably, the halogen is fluorine;

Preferably, R 3 is one of the groups represented by the following structures, * represents the position of binding,
The lithium ion battery according to claim 1 or 2, wherein the compound represented by formula (1) is selected from one or more of compounds having the following structures:
The lithium ion battery according to any one of claims 1 to 3, wherein, in the non-aqueous electrolyte, the content of the compound represented by the formula (1) is 0.001% by weight or more;

Preferably, in the non-aqueous electrolyte solution, the content of the compound represented by formula (1) is 0.001-1% by weight.
The lithium ion battery according to any one of claims 1-3, wherein the substrate is one or more of a porous polymer film, a single-layer or multi-layer porous polymer film laminate, and a porous nonwoven fabric kind;

Preferably, the porous polymer film is a polyolefin porous polymer film;

Preferably, the non-woven fabric is one or more of glass fiber non-woven fabric, synthetic fiber non-woven fabric and ceramic fiber paper;

Preferably, the thickness of the coating is 0.5-3 μm;

Preferably, the inorganic particles are inorganic particles that do not undergo oxidation and/or reduction reactions within the operating voltage range of the lithium-ion battery;

More preferably, the inorganic particles are one or more of Al 2 O 3 particles, SiO 2 particles and AlOOH particles;

Preferably, the particle size of the inorganic particles is 0.2-3 μm.
The lithium ion battery according to any one of claims 1-3, wherein the active material of the positive electrode is LiNixCoyMzO 2 , wherein M is selected from Mn and/or Al, and 0≤x≤1, 0≤y≤ 0.5, 0≤z≤0.5, x+y+z≤1.
The lithium ion battery according to any one of claims 1-3, wherein the organic solvent is one or more of cyclic carbonate, linear carbonate, carboxylate and ether;

Preferably, the cyclic carbonate includes one or more of ethylene carbonate, vinylene carbonate, propylene carbonate and butylene carbonate;

Preferably, the linear carbonate comprises one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate and propyl methyl carbonate;

Preferably, the carboxylic acid esters include methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, methyl butyrate, methyl isobutyrate, methyl trimethyl acetate and ethyl trimethyl acetate one or more of the esters;

Preferably, the ethers include ethylene glycol dimethyl ether, 1,3-dioxolane and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether one or more of;

More preferably, the organic solvent is a mixture of ethylene carbonate and diethyl carbonate.
The lithium ion battery according to any one of claims 1-3, wherein the lithium salt is selected from LiPF 6 , LiBF 4 , LiPO 2 F 2 , LiTFSI, LiBOB, LiDFOB, LiTFSI, LiSbF 6 , LiAsF 6 , One or more of LiN(SO 2 CF 3 ) 2 , LiC(SO 2 CF 3 ) 3 and LiN(SO 2 F) 2 ;

Preferably, the lithium salt is LiPF 6 ;

Preferably, the content of the lithium salt in the non-aqueous electrolyte of the lithium ion battery is 0.5-3.5 mol/L;

More preferably, the content of the lithium salt in the non-aqueous electrolyte of the lithium ion battery is 0.7-1.5 mol/L.
The lithium ion battery according to any one of claims 1 to 3, wherein the non-aqueous electrolyte further contains an additive, and the additive is a cyclic carbonate compound having a fluorine atom, a carbon-carbon One or more of cyclic carbonate compounds, cyclic sulfonate compounds and nitrile compounds with saturated bonds;

Preferably, the cyclic carbonate compound having a fluorine atom is fluoroethylene carbonate and/or difluoroethylene carbonate;

Preferably, the cyclic carbonate compound with carbon-carbon unsaturated bond is one or more of vinylene carbonate, vinyl ethylene carbonate, vinyl ethylene carbonate and vinylene methyl carbonate kind;

Preferably, the cyclic sulfonate compound is 1,3-propane sultone and/or propylene sulfite;

Preferably, the nitrile compounds are succinonitrile, adiponitrile, ethylene glycol bis(propionitrile) ether, hexanetrinitrile, adiponitrile, pimeliconitrile, suberonitrile, azelonitrile and sebacic acid one or more of nitriles;

More preferably, the additive is fluoroethylene carbonate and/or succinonitrile;

Preferably, the content of the additive is 0.1-5 wt % of the total weight of the non-aqueous electrolyte of the lithium ion battery.
The lithium ion battery according to any one of claims 1-3, wherein the active material of the negative electrode is one or more of a metal material, a carbon-based negative electrode material, and a non-carbon-based negative electrode material;

Preferably, the metal material includes metallic lithium;

Preferably, the carbon-based negative electrode material includes one or more of graphite-based carbon materials, hard carbon materials and soft carbon materials;

Preferably, the non-carbon-based negative electrode material includes one or more of silicon-based, tin-based, antimony-based, aluminum-based and transition metal compounds;

More preferably, the active material of the negative electrode is artificial graphite.