阅读说明：本技术 一种高温性能优异的高电压锂离子电池 (High-voltage lithium ion battery with excellent high-temperature performance ) 是由 母英迪 王龙 廖波 曾长安 王海 李素丽 李俊义 徐延铭 于 2019-11-20 设计创作，主要内容包括：本发明属于锂离子电池技术领域,具体涉及一种高温性能优异的高电压锂离子电池,其包括正极片、负极片、置于正极片和负极片之间的隔膜,以及非水电解液；所述正极片包括正极集流体和涂覆在其上的包括正极活性物质、导电剂和正极粘结剂的混合层；所述负极片包括负极集流体和涂覆在其上的包括负极活性物质、导电剂和负极粘结剂的混合层；所述的高电压锂离子电池在4.4V高电压下60℃高温循环400次电芯容量保持率大于70％且电芯膨胀率(厚度变化率)小于10％。本发明通过电解液添加剂与负极粘结剂在正负极隔膜材料组合下联用后制备得到的锂离子电池能够有效改善高电压锂离子电池的高温循环和高温储存性能。(The invention belongs to the technical field of lithium ion batteries, and particularly relates to a high-voltage lithium ion battery with excellent high-temperature performance, which comprises a positive plate, a negative plate, a diaphragm arranged between the positive plate and the negative plate, and a non-aqueous electrolyte; the positive plate comprises a positive current collector and a mixed layer coated on the positive current collector and comprising a positive active material, a conductive agent and a positive binder; the negative plate comprises a negative current collector and a mixed layer coated on the negative current collector and comprising a negative active material, a conductive agent and a negative binder; the capacity retention rate of the cell of the high-voltage lithium ion battery is more than 70% and the expansion rate (thickness change rate) of the cell is less than 10% after the high-voltage lithium ion battery is cycled for 400 times at the high temperature of 60 ℃ under the high voltage of 4.4V. The lithium ion battery prepared by combining the electrolyte additive and the cathode binder under the combination of the anode and cathode diaphragm materials can effectively improve the high-temperature circulation and high-temperature storage performance of the high-voltage lithium ion battery.)

1. A high-voltage lithium ion battery comprises a positive plate, a negative plate, a diaphragm arranged between the positive plate and the negative plate, and a non-aqueous electrolyte; the positive plate comprises a positive current collector and a mixed layer coated on the positive current collector and comprising a positive active material, a conductive agent and a positive binder; the negative plate comprises a negative current collector and a mixed layer coated on the negative current collector and comprising a negative active material, a conductive agent and a negative binder;

the capacity retention rate of the cell of the high-voltage lithium ion battery is more than 70% and the expansion rate (thickness change rate) of the cell is less than 10% after the high-voltage lithium ion battery is cycled for 400 times at the high temperature of 60 ℃ under the high voltage of 4.4V.

2. The lithium ion battery of claim 1, wherein the high voltage lithium ion battery has a cell expansion (thickness change) of less than 10% when stored at a high temperature of 70 ℃ for 40 days at a high voltage of 4.4V.

3. The lithium ion battery of claim 1 or 2, wherein the high voltage lithium ion battery does not evolve lithium after 1C/1C cycle at 25 ℃ under 4.4V high voltage for 50 cycles of dissection.

4. The lithium ion battery of any one of claims 1-3, wherein the nonaqueous electrolytic solution comprises a nonaqueous organic solvent, a lithium salt, and an additive comprising one or a combination of 1,3, 6-hexanetricarbonitrile, fluoroethylene carbonate, 1, 3-propanesultone, ethylene sulfate, and lithium difluorophosphate.

5. The lithium ion battery according to any one of claims 1 to 4, wherein the positive active material is lithium cobaltate coated with two or more elements selected from Al, Mg, Mn and Cr, and the chemical formula of the positive active material is Li_xCo_{1-y1-y2-y3-y4}A_y1B_y2C_y3D_y4O₂(ii) a X is more than or equal to 0.95 and less than or equal to 1.05, y1 is more than or equal to 0.01 and less than or equal to 0.1, y2 is more than or equal to 0.01 and less than or equal to 0.1, y3 is more than or equal to 0.1, y4 is more than or equal to 0 and less than or equal to 0.1, A, B, C, D is selected from two or more elements of Al, Mg, Mn and Cr;

and/or the median particle diameter D of the lithium cobaltate subjected to doping coating treatment of two or more elements of Al, Mg, Mn and Cr₅₀10-17 μm, and a specific surface area BET of 0.15-0.45m²/g。

6. The lithium ion battery of any of claims 1-5, wherein the negative active material is graphite or a graphite composite containing 1-12 wt.% SiOx/C or Si/C.

7. The lithium ion battery of any of claims 1-6, wherein the separator comprises a substrate and a composite layer comprising inorganic particles and a polymer coated on the substrate;

wherein the thickness of the composite layer in the diaphragm is 1-5 μm;

wherein, the inorganic particles in the composite layer of the diaphragm are one or a mixture of more than two of alumina, titanium oxide, magnesium oxide, zirconium oxide and barium titanate.

8. The lithium ion battery of any of claims 1-7, wherein the negative electrode binder is selected from polymers having a structure represented by formula 1:

in the formula 1, R₁Selected from H or an alkali metal atom, R₂Is selected from C_1-6Alkyl, x, y and z are the polymerization degree of the repeating unit, and the weight-average molecular weight of the polymer is 400000-800000;

preferably, R₁Selected from H, Li, K, R₂Is selected from-CH₃、-CH₂CH₃、-CH₂CH₂CH₃。

9. The lithium ion battery according to any one of claims 1 to 8, wherein the non-aqueous organic solvent is a mixture of at least one of cyclic carbonates, ethylene carbonate and propylene carbonate, and at least one of linear carbonates, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethyl propionate, propyl acetate, and the like, mixed in an arbitrary ratio.

10. The lithium ion battery of any one of claims 1 to 9, wherein the 1,3, 6-hexanetricarbonitrile is present in an amount of 1 to 5 wt.% of the total mass of the nonaqueous electrolytic solution;

the content of the fluoroethylene carbonate and the 1, 3-propane sultone is 8 to 22 wt.% of the total mass of the nonaqueous electrolyte;

the content of the lithium difluorophosphate and/or the ethylene sulfate is 0.2 to 4 wt.% of the total mass of the nonaqueous electrolyte;

the lithium salt of the non-aqueous electrolyte is lithium hexafluorophosphate, which accounts for 13-18 wt.% of the total mass of the electrolyte;

preferably, the nonaqueous electrolytic solution further comprises one or more of succinonitrile, adiponitrile, ethylene glycol bis (propionitrile) ether, lithium bis (fluorosulfonylimide), lithium bis (oxalato) borate and lithium difluoro (oxalato) borate; which accounts for 0-10 wt.% of the total mass of the electrolyte.

Technical Field

The invention belongs to the technical field of lithium ion batteries, and particularly relates to a high-voltage lithium ion battery with excellent high-temperature performance.

Background

In recent years, with the rapid development of electronic products such as smart phones, tablet computers, smart wearing and the like, in consideration of the difference between the service life and the working environment of the electronic products, the energy density of lithium ion batteries is required to be higher and higher by consumers, and the severe environment accompanied with global warming is increased, so that the lithium ion batteries are required to have excellent high-temperature performance such as high-temperature cycle and high-temperature storage in the face of special use areas such as india and africa.

At present, the energy density of the lithium ion battery is mainly improved by adopting a lithium cobaltate positive electrode material with high voltage of 4.4V or more and a high-capacity and high-compaction graphite negative electrode material. However, as the voltage of the lithium ion battery increases, a series of safety problems such as deterioration of high-temperature cycle performance of the high-voltage lithium ion battery, and high-temperature storage and air blowing are generated. One of the main factors causing these problems is the elution of metal ions from the positive electrode material. With the increase of temperature and voltage, the structural stability of the lithium cobaltate of the positive electrode is deteriorated, metal ions are dissolved out of the positive electrode and reduced and deposited on the surface of the negative electrode, so that the structure of an SEI (solid electrolyte interphase) film of the negative electrode is damaged, the impedance of the negative electrode and the thickness of the battery are increased continuously, and the capacity loss and the cycle performance of the battery are deteriorated. On the other hand, decomposition of the electrolyte at high temperature and high voltage. Under high temperature and high voltage, the electrolyte is easy to be oxidized and decomposed on the surface of the positive electrode to generate a large amount of gas, so that the battery is swelled and the electrode interface is damaged, and the high-temperature storage and high-temperature cycle performance of the battery are deteriorated. Meanwhile, the oxidation activity of the anode lithium cobaltate is higher under high temperature and high voltage, so that the side reaction between the anode and the electrolyte is further aggravated, and decomposition products of the electrolyte are continuously deposited on the surface of the anode, so that the internal resistance of the battery is increased, and the high-temperature circulation capacity retention rate and the residual capacity of a high-temperature storage battery core are reduced.

Based on the current situation, it is imperative to develop a high-voltage lithium ion battery with excellent high-temperature performance, so that the lithium ion battery has excellent high-temperature cycle and high-temperature storage performance to meet the requirements of consumers.

Disclosure of Invention

The invention aims to solve the problems of high-temperature storage gas generation, high-temperature cycle performance attenuation, battery internal resistance increase and the like of the conventional high-voltage lithium ion battery, and provides a high-voltage lithium ion battery with excellent high-temperature performance.

In order to achieve the purpose, the invention adopts the following technical scheme:

a high-voltage lithium ion battery comprises a positive plate, a negative plate, a diaphragm arranged between the positive plate and the negative plate, and a non-aqueous electrolyte; the positive plate comprises a positive current collector and a mixed layer coated on the positive current collector and comprising a positive active material, a conductive agent and a positive binder; the negative plate comprises a negative current collector and a mixed layer coated on the negative current collector and comprising a negative active material, a conductive agent and a negative binder;

the capacity retention rate of the cell of the high-voltage lithium ion battery is more than 70% and the expansion rate (thickness change rate) of the cell is less than 10% after the high-voltage lithium ion battery is cycled for 400 times at the high temperature of 60 ℃ under the high voltage of 4.4V.

As an improvement of the high-voltage lithium ion battery, the expansion rate (thickness change rate) of the core of the high-voltage lithium ion battery is less than 10 percent when the high-voltage lithium ion battery is stored for 40 days at the high temperature of 70 ℃ under the high voltage of 4.4V.

As an improvement of the high-voltage lithium ion battery, the high-voltage lithium ion battery does not separate lithium after 1C/1C cycle of 50 circles at normal temperature and 25 ℃ under 4.4V high voltage.

As an improvement of the high-voltage lithium ion battery, the nonaqueous electrolyte comprises a nonaqueous organic solvent, a lithium salt and an additive, wherein the additive comprises one or a combination of more of 1,3, 6-hexanetricarbonitrile, fluoroethylene carbonate, 1, 3-propane sultone, ethylene sulfate and lithium difluorophosphate. Wherein, 1,3, 6-hexanetricarbonitrile is used as an anode protective additive, fluoroethylene carbonate and 1, 3-propane sultone are used as cathode film forming additives, and ethylene sulfate and lithium difluorophosphate are used as low-impedance additives.

Illustratively, the additive includes a combination of 1,3, 6-hexanetricarbonitrile, fluoroethylene carbonate, lithium difluorophosphate; or, a combination of 1,3, 6-hexanetricarbonitrile, 1, 3-propanesultone, ethylene sulfate; or, a combination of 1,3, 6-hexanetricarbonitrile, fluoroethylene carbonate, ethylene sulfate; or, a combination of 1,3, 6-hexanetricarbonitrile, 1, 3-propanesultone, lithium difluorophosphate; or, a combination of 1,3, 6-hexanetricarbonitrile, fluoroethylene carbonate, 1, 3-propanesultone, ethylene sulfate; or, a combination of 1,3, 6-hexanetricarbonitrile, fluoroethylene carbonate, 1, 3-propanesultone, lithium difluorophosphate; or a combination of 1,3, 6-hexanetricarbonitrile, fluoroethylene carbonate, 1, 3-propanesultone, ethylene sulfate, lithium difluorophosphate.

As an improvement of the high voltage lithium ion battery of the present invention, the content of the 1,3, 6-hexanetricarbonitrile is 1 to 5 wt.%, for example, 1 wt.%, 1.5 wt.%, 2 wt.%, 2.5 wt.%, 3 wt.%, 3.5 wt.%, 4 wt.%, 4.5 wt.%, 5 wt.% of the total mass of the nonaqueous electrolytic solution.

As an improvement of the high voltage lithium ion battery of the present invention, the content of fluoroethylene carbonate and 1, 3-propane sultone is 8 to 22 wt.%, for example, 8 wt.%, 9 wt.%, 10 wt.%, 11 wt.%, 12 wt.%, 13 wt.%, 14 wt.%, 15 wt.%, 16 wt.%, 17 wt.%, 18 wt.%, 19 wt.%, 20 wt.%, 21 wt.%, 22 wt.% of the total mass of the nonaqueous electrolyte;

wherein the fluoroethylene carbonate is present in an amount of 4 to 18 wt.%, for example, 4 wt.%, 5 wt.%, 6 wt.%, 7 wt.%, 8 wt.%, 9 wt.%, 10 wt.%, 11 wt.%, 12 wt.%, 13 wt.%, 15 wt.%, 18 wt.%, based on the total mass of the nonaqueous electrolyte solution;

the content of the 1, 3-propane sultone is 4-16 wt.%, for example, 4 wt.%, 5 wt.%, 6 wt.%, 7 wt.%, 8 wt.%, 9 wt.%, 10 wt.%, 11 wt.%, 12 wt.%, 13 wt.%, 15 wt.%, 16 wt.% of the total mass of the nonaqueous electrolytic solution.

As an improvement of the high voltage lithium ion battery of the present invention, the content of lithium difluorophosphate and/or ethylene sulfate is 0.2 to 4 wt.%, e.g., 0.2 wt.%, 0.5 wt.%, 0.8 wt.%, 1 wt.%, 1.5 wt.%, 2 wt.%, 2.5 wt.%, 3 wt.%, 3.5 wt.%, 4 wt.% of the total mass of the nonaqueous electrolytic solution;

wherein the lithium difluorophosphate is present in an amount of 0.2 to 4 wt.%, e.g., 0.2 wt.%, 0.5 wt.%, 0.8 wt.%, 1 wt.%, 1.5 wt.%, 2 wt.%, 2.5 wt.%, 3 wt.%, 3.5 wt.%, 4 wt.%, based on the total mass of the nonaqueous electrolyte;

wherein the content of the ethylene sulfate is 0.2 to 4 wt.%, for example, 0.2 wt.%, 0.5 wt.%, 0.8 wt.%, 1 wt.%, 1.5 wt.%, 2 wt.%, 2.5 wt.%, 3 wt.%, 3.5 wt.%, 4 wt.% of the total mass of the nonaqueous electrolytic solution.

As an improvement of the high-voltage lithium ion battery, the nonaqueous electrolyte further comprises one or more of succinonitrile, adiponitrile, ethylene glycol bis (propionitrile) ether, lithium bis fluorosulfonylimide, lithium bis (oxalato) borate and lithium difluoro (oxalato) borate; which accounts for 0-10 wt.% of the total mass of the electrolyte.

Illustratively, the nonaqueous electrolyte comprises 7 wt.% of fluoroethylene carbonate, 5 wt.% of 1, 3-propanesulfonic lactone, 2 wt.% of 1,3, 6-hexanetricarbonitrile and 0.3 wt.% of lithium difluorophosphate based on the total mass of the nonaqueous electrolyte.

Illustratively, the nonaqueous electrolyte comprises 5 wt.% of fluoroethylene carbonate, 3 wt.% of 1, 3-propanesulfonic lactone, 0.5 wt.% of adiponitrile, 5 wt.% of 1,3, 6-hexanetrinitrile and 0.2 wt.% of lithium difluorophosphate based on the total mass of the nonaqueous electrolyte.

Illustratively, the nonaqueous electrolyte comprises 6 wt.% of fluoroethylene carbonate, 4 wt.% of 1, 3-propane sulfonic acid lactone, 1.5 wt.% of succinonitrile, 3 wt.% of 1,3, 6-hexane trinitrile and 1 wt.% of lithium difluorophosphate, based on the total mass of the nonaqueous electrolyte.

Illustratively, the nonaqueous electrolyte comprises 7 wt.% of fluoroethylene carbonate, 4 wt.% of 1, 3-propane sulfonic acid lactone, 1.5 wt.% of lithium bis-fluorosulfonylimide, 1.5 wt.% of 1,3, 6-hexanetricarbonitrile and 0.5 wt.% of lithium difluorophosphate based on the total mass of the nonaqueous electrolyte.

Illustratively, the nonaqueous electrolyte comprises 7 wt.% of fluoroethylene carbonate, 5 wt.% of 1, 3-propanesulfonic lactone, 0.5 wt.% of adiponitrile, 4 wt.% of 1,3, 6-hexanetrinitrile and 3 wt.% of lithium difluorophosphate based on the total mass of the nonaqueous electrolyte.

Illustratively, the nonaqueous electrolyte comprises 6 wt.% of fluoroethylene carbonate, 6 wt.% of 1, 3-propanesulfonic lactone, 2 wt.% of adiponitrile, 1 wt.% of 1,3, 6-hexanetrinitrile and 4 wt.% of lithium difluorophosphate based on the total mass of the nonaqueous electrolyte.

Illustratively, the nonaqueous electrolyte solution comprises 5 wt.% of fluoroethylene carbonate, 5 wt.% of 1, 3-propane sulfonic acid lactone, 0.5 wt.% of lithium bis (oxalato) borate, 3 wt.% of 1,3, 6-hexanetricarbonitrile and 0.8 wt.% of lithium difluorophosphate based on the total mass of the nonaqueous electrolyte solution.

Illustratively, the nonaqueous electrolyte solution comprises 8 wt.% of fluoroethylene carbonate, 6 wt.% of 1, 3-propanesulfonic acid lactone, 3 wt.% of adiponitrile, 4 wt.% of 1,3, 6-hexanetrinitrile, 1 wt.% of ethylene sulfate and 1 wt.% of lithium difluorophosphate based on the total mass of the nonaqueous electrolyte solution.

Illustratively, the nonaqueous electrolyte comprises 7 wt.% of fluoroethylene carbonate, 8 wt.% of 1, 3-propane sulfonic acid lactone, 3 wt.% of succinonitrile, 2 wt.% of 1,3, 6-hexane tricarbonitrile and 2 wt.% of lithium difluorophosphate based on the total mass of the nonaqueous electrolyte.

Illustratively, the nonaqueous electrolyte solution comprises 8 wt.% of fluoroethylene carbonate, 6 wt.% of 1, 3-propanesulfonic acid lactone, 3 wt.% of adiponitrile, 4 wt.% of 1,3, 6-hexanetrinitrile, 1 wt.% of ethylene sulfate and 1 wt.% of lithium difluorophosphate based on the total mass of the nonaqueous electrolyte solution.

As an improvement of the high voltage lithium ion battery of the present invention, the lithium salt of the nonaqueous electrolytic solution is lithium hexafluorophosphate, which accounts for 13 to 18 wt.%, for example, 13 wt.%, 14 wt.%, 15 wt.%, 16 wt.%, 17 wt.%, 18 wt.% of the total mass of the electrolytic solution.

As an improvement of the high-voltage lithium ion battery, the positive active material is lithium cobaltate which is doped and coated by two or more elements of Al, Mg, Mn and Cr, and the chemical formula of the positive active material is Li_xCo_{1-y1-y2-y3-y4}A_y1B_y2C_y3D_y4O₂(ii) a X is more than or equal to 0.95 and less than or equal to 1.05, y1 is more than or equal to 0.01 and less than or equal to 0.1, y2 is more than or equal to 0.01 and less than or equal to 0.1, y3 is more than or equal to 0.1, y4 is more than or equal to 0 and less than or equal to 0.1, and A, B, C, D is selected from two or more elements of Al, Mg, Mn and Cr.

As an improvement of the high-voltage lithium ion battery, the lithium cobaltate which is doped and coated by two or more elements of Al, Mg, Mn and Cr has a median particle diameter D₅₀10-17 μm, and a specific surface area BET of 0.15-0.45m²/g。

As an improvement of the high voltage lithium ion battery of the present invention, the negative active material is graphite or a graphite composite material containing 1 to 12 wt.% SiOx/C or Si/C.

As an improvement of the high voltage lithium ion battery of the present invention, the separator includes a substrate and a composite layer including inorganic particles and a polymer coated on the substrate.

As an improvement of the high-voltage lithium ion battery, the thickness of the composite layer in the diaphragm is 1-5 μm.

In the improvement of the high-voltage lithium ion battery, the inorganic particles in the composite layer of the separator are one or a mixture of more than two of alumina, titania, magnesia, zirconia and barium titanate.

As an improvement of the high voltage lithium ion battery of the present invention, the mass ratio of the inorganic particles to the polymer is known in the art.

As an improvement of the high voltage lithium ion battery of the present invention, the negative electrode binder includes, but is not limited to, a polymer having a structure represented by formula 1:

in the formula 1, R₁Selected from H or an alkali metal atom, R₂Is selected from C_1-6Alkyl, x, y and z are the polymerization degrees of the repeating units, and the weight average molecular weight of the polymer is 400000-800000.

Illustratively, R₁Selected from H, Li, K, R₂Is selected from-CH₃、-CH₂CH₃、-CH₂CH₂CH₃。

As an improvement of the high-voltage lithium ion battery, the additive comprises one or a combination of more of 1,3, 6-hexanetricarbonitrile, fluoroethylene carbonate, 1, 3-propane sultone and lithium difluorophosphate; r in the structural formula shown in formula 1 of the negative electrode binder₁Selected from Li, R₂Is selected from-CH₃And the weight-average molecular weight is 550000.

Illustratively, the additive comprises 6 wt.% of fluoroethylene carbonate, 6 wt.% of 1, 3-propanesulfonic acid lactone, 1 wt.% of 1,3, 6-hexanetricarbonitrile and 4 wt.% of lithium difluorophosphate, based on the total mass of the nonaqueous electrolyte. R in the structural formula shown in formula 1 of the negative electrode binder₁Selected from Li, R₂Is selected from-CH₃And the weight-average molecular weight is 550000.

As an improvement of the high-voltage lithium ion battery, the additive comprises one or a combination of more of 1,3, 6-hexanetricarbonitrile, fluoroethylene carbonate, 1, 3-propane sultone and lithium difluorophosphate; r in the structural formula shown in formula 1 of the negative electrode binder₁Selected from H, R₂Is selected from-CH₃And a weight average molecular weight of 750000.

Illustratively, the additiveComprises 5 wt.% of fluoroethylene carbonate, 5 wt.% of 1, 3-propane sulfonic acid lactone, 3 wt.% of 1,3, 6-hexane trinitrile and 0.8 wt.% of lithium difluorophosphate based on the total mass of the nonaqueous electrolyte. R in the structural formula shown in formula 1 of the negative electrode binder₁Selected from H, R₂Is selected from-CH₃And a weight average molecular weight of 750000.

As an improvement of the high-voltage lithium ion battery, the additive comprises one or a combination of more of 1,3, 6-hexanetricarbonitrile, fluoroethylene carbonate, 1, 3-propane sultone and lithium difluorophosphate; r in the structural formula shown in formula 1 of the negative electrode binder₁Selected from Li, R₂Is selected from-CH₂CH₃The weight average molecular weight is 700000.

Illustratively, the additive comprises 8 wt.% of fluoroethylene carbonate, 6 wt.% of 1, 3-propanesulfonic acid lactone, 4 wt.% of 1,3, 6-hexanetricarbonitrile, 1 wt.% of ethylene sulfate, and 1 wt.% of lithium difluorophosphate, based on the total mass of the nonaqueous electrolyte. R in the structural formula shown in formula 1 of the negative electrode binder₁Selected from Li, R₂Is selected from-CH₂CH₃The weight average molecular weight is 700000.

In the improvement of the high-voltage lithium ion battery, the non-aqueous organic solvent is a mixture of at least one of cyclic carbonates and at least one of linear carbonates and linear carboxylic acid esters in any proportion, the cyclic carbonates are ethylene carbonate and propylene carbonate, and the linear carbonates and linear carboxylic acid esters are dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethyl propionate, propyl acetate and other compounds.

As an improvement of the high voltage lithium ion battery of the present invention, the charge cut-off voltage of the lithium ion battery is 4.4V or more.

Compared with the prior art, the invention has the advantages that:

1. the lithium ion battery prepared by combining the electrolyte additive and the cathode binder under the combination of the anode and cathode diaphragm materials can effectively improve the high-temperature circulation and high-temperature storage performance of the high-voltage lithium ion battery.

2. According to the invention, the additive is added into the electrolyte and combined with the cathode binder, so that the interface impedance of the battery can be obviously reduced, and the problem of overlarge cell expansion caused by internal resistance increase in the circulation process of the lithium ion battery can be solved.

Detailed Description

The preparation method of the present invention will be described in further detail with reference to specific examples. It is to be understood that the following examples are only illustrative and explanatory of the present invention and should not be construed as limiting the scope of the present invention. All the technologies realized based on the above-mentioned contents of the present invention are covered in the protection scope of the present invention.

The experimental methods used in the following examples are all conventional methods unless otherwise specified; reagents, materials and the like used in the following examples are commercially available unless otherwise specified.

Example 1

Preparing a positive plate: the chemical formula of 4.4V lithium cobaltate is Li_1.02Co_0.6Al_0.1Mg_0.1Mn_0.1Cr_0.1O₂Mixing polyvinylidene fluoride (PVDF) serving as a positive binder and acetylene black serving as a conductive agent according to a weight ratio of 96.5:2:1.5, adding N-methylpyrrolidone (NMP), and stirring under the action of a vacuum stirrer until a mixed system becomes positive slurry with uniform fluidity; uniformly coating the positive electrode slurry on an aluminum foil with the thickness of 9-12 mu m; baking the coated aluminum foil in 5 sections of baking ovens with different temperature gradients, drying the aluminum foil in a baking oven at the temperature of 100-130 ℃ for 4-10h, and then rolling and slitting to obtain the required positive plate.

Preparing a negative plate: mixing negative active material artificial graphite, conductive carbon black, and negative binder (R in formula 1)₁Selected from K, R₂Is selected from-CH₂CH₃Weight average molecular weight of 500000) in an appropriate amount of deionized water, and fully stirring and mixing to form uniform negative electrode slurry; and uniformly coating the negative electrode slurry on a copper foil of a negative current collector, and drying, rolling and slitting to obtain a negative plate.

Preparing a diaphragm: a polyethylene separator having a thickness of 7 μm was coated with a 3 μm thick composite layer of a mixture of titanium oxide and polyvinylidene fluoride.

Preparation of nonaqueous electrolyte: ethylene Carbonate (EC), Propylene Carbonate (PC), diethyl carbonate (DEC) and Propyl Propionate (PP) were mixed uniformly in a weight ratio of 20:20:15:45 in an argon-filled glove box (moisture < 10ppm, oxygen < 1ppm), and 13 wt.% of LiPF based on the total weight of the nonaqueous electrolyte was slowly added to the mixed solution₆Stirring until the mixture is completely dissolved, then adding 7 wt.% of fluoroethylene carbonate, 5 wt.% of 1, 3-propanesulfonic acid lactone, 2 wt.% of 1,3, 6-hexanetricarbonitrile and 0.3 wt.% of lithium difluorophosphate in sequence based on the total mass of the nonaqueous electrolyte, and uniformly mixing to obtain the lithium ion battery electrolyte of example 1.

Preparing a high-voltage lithium ion battery: and winding the prepared positive plate, the diaphragm and the prepared negative plate to obtain a naked battery cell, and packaging the battery cell into an aluminum plastic film bag formed in a stamping manner in advance. And (3) after the packaged battery is dried at 85 ℃, injecting the prepared nonaqueous electrolytic solution into the dried battery, and finishing the preparation of the lithium ion battery after the battery is laid aside, formed and sealed for the second time.

Example 2

Unlike example 1, the chemical formula of the active material in the positive electrode sheet was Li_0.99Co_0.8Al_0.1Cr_0.1O₂. The rest is the same as in example 1.

Example 3

Unlike example 1, 5 wt.% fluoroethylene carbonate, 3 wt.% 1, 3-propanesulfonic lactone, 0.5 wt.% adiponitrile, 5 wt.% 1,3, 6-hexanetrinitrile, and 0.2 wt.% lithium difluorophosphate were added to the electrolyte preparation, based on the total mass of the nonaqueous electrolyte. The rest is the same as in example 1.

Example 4

Different from the embodiment 1, the electrolyte is prepared by adding 6 wt.% fluoroethylene carbonate, 6 wt.% 1, 3-propanesulfonic lactone, 2 wt.% adiponitrile, 1 wt.% 1,3, 6-hexanetrinitrile and 4 wt.% difluorophosphoric acid based on the total mass of the non-aqueous electrolyteAnd (3) lithium. R in the structural formula shown in formula 1 of the negative electrode binder₁Selected from Li, R₂Is selected from-CH₃And the weight-average molecular weight is 550000. The rest is the same as in example 1.

Example 5

Different from the embodiment 1, the electrolyte is prepared by adding 6 wt.% fluoroethylene carbonate, 4 wt.% 1, 3-propane sulfonic lactone, 1.5 wt.% succinonitrile, 3 wt.% 1,3, 6-hexane trinitrile and 1 wt.% lithium difluorophosphate based on the total mass of the non-aqueous electrolyte. The rest is the same as in example 1.

Example 6

Different from the embodiment 1, 7 wt.% of fluoroethylene carbonate, 4 wt.% of 1, 3-propane sulfonic acid lactone, 1.5 wt.% of lithium bis-fluorosulfonylimide, 1.5 wt.% of 1,3, 6-hexanetricarbonitrile and 0.5 wt.% of lithium difluorophosphate are added in the preparation of the electrolyte. The rest is the same as in example 1.

Example 7

Different from the embodiment 1, 7 wt.% of fluoroethylene carbonate, 5 wt.% of 1, 3-propane sulfonic lactone, 0.5 wt.% of adiponitrile, 4 wt.% of 1,3, 6-hexane trinitrile and 3 wt.% of lithium difluorophosphate are added in the preparation of the electrolyte. The rest is the same as in example 1.

Example 8

Unlike example 1, 5 wt.% of fluoroethylene carbonate, 5 wt.% of 1, 3-propanesulfonic lactone, 0.5 wt.% of lithium bis (oxalato) borate, 3 wt.% of 1,3, 6-hexanetricarbonitrile, and 0.8 wt.% of lithium difluorophosphate were added to the electrolyte preparation, based on the total mass of the nonaqueous electrolyte. R in the structural formula shown in formula 1 of the negative electrode binder₁Selected from H, R₂Is selected from-CH₃And a weight average molecular weight of 750000. The rest is the same as in example 1.

Example 9

Different from the embodiment 1, 7 wt.% of fluoroethylene carbonate, 8 wt.% of 1, 3-propane sulfonic lactone, 3 wt.% of succinonitrile, 2 wt.% of 1,3, 6-hexane trinitrile and 2 wt.% of lithium difluorophosphate are added in the preparation of the electrolyte. The rest is the same as in example 1.

Example 10

In contrast to example 1, 8 wt.% fluoroethylene carbonate, 6 wt.% 1, 3-propanesulfonic acid lactone, 3 wt.% adiponitrile, 4 wt.% 1,3, 6-hexanetrinitrile, 1 wt.% ethylene sulfate, and 1 wt.% lithium difluorophosphate were added to the electrolyte preparation, based on the total mass of the nonaqueous electrolyte. R in the structural formula shown in formula 1 of the negative electrode binder₁Selected from Li, R₂Is selected from-CH₂CH₃The weight average molecular weight is 700000. The rest is the same as in example 1.

Comparative example 1

Unlike example 1, the active material used in the preparation of the positive electrode sheet had a chemical formula of Li_0.95CoO₂. The rest is the same as in example 1.

Comparative example 2

Unlike example 1, 5 wt.% fluoroethylene carbonate, 1 wt.% 1, 3-propanesulfonic lactone, and 1 wt.% adiponitrile, based on the total mass of the nonaqueous electrolyte, were added to the electrolyte preparation. The rest is the same as in example 1.

Comparative example 3

Unlike example 1,3 wt.% of 1, 3-propanesulfonic lactone, 1 wt.% of succinonitrile, and 1 wt.% of 1,3, 6-hexanetricarbonitrile were added to the preparation of the electrolyte, based on the total mass of the nonaqueous electrolyte. The rest is the same as in example 1.

Comparative example 4

Unlike example 1, the active material used in the preparation of the positive electrode sheet had a chemical formula of Li_0.97Co_0.9Mn_0.1O₂The electrolyte was prepared by adding 2 wt.% of 1, 3-propanesulfonic lactone, 2 wt.% of adiponitrile, 1.5 wt.% of lithium difluorophosphate, based on the total mass of the nonaqueous electrolyte, and the rest was the same as in example 1.

Comparative example 5

The difference from example 1 was that 2.5 wt.% of 1, 3-propanesulfonic acid lactone and 3.5 wt.% of fluoroethylene carbonate, based on the total mass of the nonaqueous electrolytic solution, were added to the preparation of the electrolytic solution, and the rest was the same as example 1.

Comparative example 6

Unlike example 1, 4 wt.% of 1, 3-propanesulfonic lactone and 1.3 wt.% of lithium difluorophosphate were added to the preparation of the electrolyte, based on the total mass of the nonaqueous electrolyte, and the rest was the same as in example 1.

Comparative example 7

Different from the embodiment 1, the negative active material is artificial graphite, conductive carbon black, negative binder Styrene Butadiene Rubber (SBR) and thickener carboxymethylcellulose sodium (CMC) in a mass ratio of 96.4:0.5:1.6: 1.5. The rest is the same as in example 1.

The lithium ion batteries obtained in the above comparative examples and examples were subjected to electrochemical performance tests, and the following descriptions were made:

60 ℃ high temperature cycling experiment:

the batteries obtained in the examples 1 to 10 and the comparative examples 1 to 7 are placed in a (60 +/-2) DEG C environment and are kept stand for 2 to 3 hours, when the battery body reaches (60 +/-2) DEG C, the cut-off current of the battery is 0.05C according to 1C constant current charging, the battery is kept stand for 5 minutes after being fully charged, the battery is discharged to the cut-off voltage of 3.0V at a constant current of 0.7C, the highest discharge capacity of the previous 3 cycles is recorded as an initial capacity Q, and when the cycles reach the required times, the last discharge capacity Q of the battery is recorded₁(ii) a Recording the initial thickness T of the battery cell, and recording the thickness of the battery cell which is selected and circulated to 400 weeks as T₀. The results are reported in Table 1.

The calculation formula used therein is as follows:

capacity retention (%) ═ Q₁/Q×100％

Thickness change rate (%) - (T)₀-T)/T×100％。

High temperature storage experiment:

the batteries obtained in examples 1 to 10 and comparative examples 1 to 7 were subjected to a charge-discharge cycle test at room temperature for 3 times at a charge-discharge rate of 0.5C, and then charged to a full charge state at a rate of 0.5C, and the maximum discharge capacity Q and the battery thickness T of the previous 3 times at 0.5C cycles were recorded, respectively. The fully charged battery was stored at 70 ℃ for 40 days, and the battery thickness T after 40 days was recorded₀And 0.5C discharge capacity Q₁Then, the cell was charged and discharged 3 times at a rate of 0.5C at room temperature, and the maximum discharge capacity Q was recorded for 3 cycles₂And calculating to obtain experimental data such as the thickness change rate, the capacity retention rate, the capacity recovery rate and the like of the battery stored at high temperature, and recording the results as shown in table 1.

The calculation formula used therein is as follows:

thickness change rate (%) - (T)₀-T)/T×100％

Capacity retention (%) ═ Q₁/Q×100％

Capacity recovery rate (%) ═ Q₂/Q×100％。

Normal temperature cycle dissection experiment:

the batteries obtained in examples 1 to 10 and comparative examples 1 to 7 were placed in an environment of (25. + -.2) ℃ and left for 2 to 3 hours, when the battery body reached (25. + -.2) DEG C, the battery was charged at a constant current of 0.05C according to a constant current of 1C, left for 5 minutes after being fully charged, and then discharged at a constant current of 1C to a cut-off voltage of 3.0V, and the cycle was repeated 50 times, and the conditions of the electrode sheet were observed by full electrolysis, and the results were recorded as shown in Table 1.

TABLE 1 high temperature cycling and high temperature storage test results for examples 1-10 and comparative examples 1-7

As can be seen from the results of table 1:

as can be seen from comparison of example 3 with comparative examples 2 to 4, the battery of example 1, which contains fluoroethylene carbonate, 1, 3-propane sultone, 1,3, 6-hexanetricarbonitrile, and lithium difluorophosphate together, has better high-temperature cycle properties and high-temperature storage electrical properties. Further, by comparing each example with comparative examples 1 to 7, it can be found that the performances of high-temperature cycle, high-temperature storage, normal-temperature cycle dissection and the like of the high-voltage lithium ion battery can be obviously improved after the positive electrode doping coating, the negative electrode binder addition, and the optimized combination of the additive fluoroethylene carbonate, 1,3, 6-hexanetricarbonitrile and lithium difluorophosphate in the electrolyte in the battery system are combined.

In summary, the non-aqueous electrolyte for the high-voltage lithium ion battery provided by the invention contains additives of fluoroethylene carbonate, 1, 3-propane sultone, 1,3, 6-hexanetricarbonitrile and lithium difluorophosphate, and further can be optimally combined with various additives of succinonitrile, adiponitrile, ethylene glycol bis (propionitrile) ether, lithium bis (fluorosulfonyl) imide, lithium bis (oxalato) borate, lithium difluorooxalato borate and the like, and the high-voltage lithium ion battery can have excellent high-temperature cycle and high-temperature storage electrical performance and form excellent interface to reduce impedance through the synergistic effect of the additives and the combination with a negative electrode binder, so that the high-voltage lithium ion battery can be free of lithium precipitation through normal-temperature cycle dissection.

The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiment. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.