阅读说明：本技术 一种正极片和包含该正极片的锂离子电池及其制备方法 (Positive plate, lithium ion battery comprising positive plate and preparation method of lithium ion battery ) 是由 李增鹏 刘成 任建国 于 2019-02-21 设计创作，主要内容包括：本发明公开了一种正极片和包含该正极片的锂离子电池及其制备方法。本发明提供的正极片中包括正极碱性添加剂。所述正极片的制备方法包括：制备正极浆料,所述正极浆料中含有正极碱性添加剂,将所述正极浆料涂布在正极集流片上,之后进行辊压,模切后得到正极片。本发明提供的锂离子电池包含上述正极片。所述锂离子电池的制备方法包括：(1)制备负极片；(2)对步骤(1)所述负极片、正极片和隔离膜进行叠片、焊接、入壳、装配,得到电芯；(3)将电解液注入步骤(2)所述电芯中,然后进行后处理工序,得到所述锂离子电池。本发明提供的电池能量密度高,循环性能好。(The invention discloses a positive plate, a lithium ion battery comprising the positive plate and a preparation method of the lithium ion battery. The positive plate provided by the invention comprises a positive alkaline additive. The preparation method of the positive plate comprises the following steps: preparing anode slurry, wherein the anode slurry contains an anode alkaline additive, coating the anode slurry on an anode current collector, rolling, and die-cutting to obtain an anode sheet. The lithium ion battery provided by the invention comprises the positive plate. The preparation method of the lithium ion battery comprises the following steps: (1) preparing a negative plate; (2) laminating, welding, encasing and assembling the negative plate, the positive plate and the isolating membrane in the step (1) to obtain a battery cell; (3) and (3) injecting electrolyte into the battery core in the step (2), and then performing a post-treatment process to obtain the lithium ion battery. The battery provided by the invention has high energy density and good cycle performance.)

1. The positive plate is characterized by comprising a positive alkaline additive.

2. The positive electrode sheet according to claim 1, wherein the positive electrode sheet comprises a positive electrode coating layer comprising a positive electrode active material and a positive electrode alkaline additive;

preferably, the positive electrode active material includes lithium iron phosphate;

the positive electrode alkaline additive comprises an inorganic additive and/or an organic additive, and is preferably a mixture of the inorganic additive and the organic additive;

preferably, the inorganic additive comprises Na₂CO₃、NaHCO₃、K₂CO₃、KHCO₃、Li₂CO₃Or LiHCO₃Any one or a combination of at least two of;

preferably, the organic additive comprises any one of hexamethyldisilazane, heptamethyldisiminosilane or lithium hexamethyldisilazide or a combination of at least two of the hexamethyldisilazane and the heptamethyldisiminosilane;

preferably, the mixture of the inorganic additive and the organic additive is composed of Na₂CO₃And hexamethyldisilazane or from NaHCO₃And hexamethyldisilazane;

preferably, the addition amount of the inorganic additive is 0.1-0.5% of the total mass of the positive electrode active material, the conductive agent and the binder;

preferably, the addition amount of the organic additive is 0.1-0.5% of the total mass of the positive electrode active material, the conductive agent and the binder;

preferably, the positive electrode active material is spherical lithium iron phosphate;

preferably, the gram capacity of the positive active material is 145-155 mAh/g;

preferably, the particle size distribution D50 of the positive electrode active material is 0.6-1.6 μm;

preferably, the specific surface area of the positive electrode active material is 11-15 m²/g；

Preferably, the positive electrode sheet further comprises a positive current collecting sheet for coating the positive coating;

preferably, the positive collector is a carbon-coated aluminum foil;

preferably, the positive electrode coating further comprises a conductive agent and a binder;

preferably, the conductive agent in the positive electrode coating comprises any one or a combination of at least two of conductive carbon black, conductive graphite and conductive carbon nanotubes, preferably a mixture of conductive carbon black, conductive graphite and conductive carbon nanotubes;

preferably, the binder in the positive electrode coating layer comprises polyvinylidene fluoride;

preferably, in the positive electrode coating, the mass percent of the positive electrode active substance is 95.5-96.5%, the mass percent of the conductive agent is 1.6-2.6%, and the mass percent of the binder is 1.6-2.2%, based on 100% of the total mass of the positive electrode active substance, the conductive agent and the binder;

preferably, when the conductive agent in the positive electrode coating is a mixture of conductive carbon black, conductive graphite and conductive carbon nanotubes, the mass ratio of the conductive carbon black to the conductive graphite to the conductive carbon nanotubes is (0.5-0.8): (0.6-1): (0.5-0.8).

3. A method for producing the positive electrode sheet according to claim 1, comprising the steps of:

preparing anode slurry, wherein the anode slurry contains an anode alkaline additive, coating the anode slurry on an anode current collector, rolling, and die-cutting to obtain the anode sheet.

4. The method for producing a positive electrode sheet according to claim 3, wherein the method for producing a positive electrode slurry comprises: mixing the positive active substance, the conductive agent, the binder, the positive alkaline additive and the organic solvent according to the formula ratio to obtain positive slurry;

preferably, the coating is a transfer coating;

preferably, the rolling is double-roll rolling;

preferably, before said rolling, baking is carried out;

preferably, the compaction density of the positive plate is 2.2-2.5 g/cm³Preferably 2.3g/cm³；

Preferably, the coating surface density of the positive plate is 360-370 g/m²Preferably 365g/m²。

5. A lithium ion battery comprising the positive electrode sheet according to claim 1 or 2.

6. The lithium ion battery according to claim 5, wherein the lithium ion battery comprises a positive electrode sheet, a negative electrode sheet, a separator for separating the positive electrode sheet from the negative electrode sheet, and an electrolyte, wherein the positive electrode sheet is the positive electrode sheet according to claim 1 or 2, the negative electrode sheet comprises a negative electrode coating layer, and the negative electrode coating layer comprises a negative electrode active material;

preferably, the negative active material is a silicon-based composite material;

preferably, the silicon-based composite material comprises a silica/carbon composite anode material;

preferably, the gram capacity of the negative electrode active material is 420-450 mAh/g;

preferably, the particle size distribution D50 of the negative electrode active material is 14-18 μm;

preferably, the specific surface area of the negative electrode active material is 1 to 2.5m²/g；

Preferably, the negative electrode sheet further comprises a negative current collector sheet for coating the negative electrode coating;

preferably, the negative current collector is a copper foil;

preferably, the negative electrode coating further comprises a conductive agent and a binder;

preferably, the conductive agent in the negative electrode coating layer includes conductive carbon black;

preferably, the binder in the negative electrode coating comprises carboxymethyl cellulose and/or styrene-butadiene rubber, preferably a mixture of carboxymethyl cellulose and styrene-butadiene rubber;

preferably, in the negative electrode coating, the mass percent of the negative electrode active material is 94.5-95.5%, the mass percent of the conductive agent is 1.3-2%, and the mass percent of the binder is 2.8-3.9% based on 100% of the total mass of the negative electrode active material, the conductive agent and the binder;

preferably, when the binder in the negative electrode coating is a mixture of carboxymethyl cellulose and styrene butadiene rubber, the mass ratio of the carboxymethyl cellulose to the styrene butadiene rubber is (1-1.4): (1.8-2.5).

7. The lithium ion battery according to claim 5 or 6, wherein the porosity of the separator is 40-45%;

preferably, the thickness of the isolation film is 10-15 μm, preferably 12 μm;

preferably, the electrolyte comprises an organic solvent and a lithium salt;

preferably, the organic solvent in the electrolyte comprises ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate;

preferably, in the electrolyte, the mass ratio of the ethylene carbonate to the dimethyl carbonate to the ethyl methyl carbonate is (10-20): 60-70): 10-20;

preferably, the electrolyte further comprises an additive;

preferably, the additive in the electrolyte is fluoroethylene carbonate;

preferably, in the electrolyte, the addition amount of the additive is 5-10% by mass of the organic solvent as 100%;

preferably, the lithium salt in the electrolyte is lithium hexafluorophosphate;

preferably, the concentration of the lithium salt in the electrolyte is 1.1-1.3 mol/L.

8. A method for preparing a lithium ion battery according to any of claims 5 to 7, characterized in that the method comprises the following steps:

(1) preparing negative electrode slurry, coating the negative electrode slurry on a negative electrode current collecting sheet, then rolling, and die-cutting to obtain a negative electrode sheet;

(2) laminating, welding, encasing and assembling the negative plate in the step (1), the positive plate in the claim 1 or 2 and the isolating membrane to obtain a battery cell;

(3) and (3) injecting electrolyte into the battery core in the step (2), and then performing a post-treatment process to obtain the lithium ion battery.

9. The method for preparing a lithium ion battery according to claim 8, wherein the method for preparing the negative electrode slurry according to the step (1) comprises: mixing the negative electrode active material, the conductive agent, the binder and the solvent according to the formula ratio to obtain negative electrode slurry;

preferably, in step (1), the solvent comprises water;

preferably, in step (1), the coating is transfer coating;

preferably, in the step (1), the rolling is a double-roll rolling;

preferably, in step (1), before the rolling, baking is performed;

preferably, in the step (1), the compacted density of the negative electrode sheet is 1.5-1.7 g/cm³Preferably 1.6g/cm³；

Preferably, in the step (1), the coating surface density of the negative plate is 140-150 g/m²Preferably 145g/m²；

Preferably, in the step (3), the post-treatment process comprises sealing, forming and grading.

10. Method for preparing a lithium-ion battery according to claim 8 or 9, characterized in that it comprises the following steps:

(1) mixing the positive active material lithium iron phosphate, a conductive agent, a binder and an organic solvent according to the formula ratio, adding a positive alkaline additive into the obtained mixed solution to obtain positive slurry, coating the positive slurry on a positive current collecting sheet by transfer coating, and carrying out the steps ofAfter baking, the mixture is rolled by a pair of rollers, and the compacted density of the mixture is 2.3g/cm after die cutting³The coating surface density is 365g/m²The positive electrode sheet of (1);

wherein the conductive agent is a mixture of conductive carbon black, conductive graphite and conductive carbon nanotubes, and the binder is polyvinylidene fluoride; the mass percent of the positive active substance is 95.5-96.5%, the mass percent of the conductive agent is 1.6-2.6%, and the mass percent of the binder is 1.6-2.2% based on 100% of the total mass of the positive active substance, the conductive agent and the binder; the mass ratio of the conductive carbon black to the conductive graphite to the conductive carbon nano tube is (0.5-0.8): (0.6-1): (0.5 to 0.8); the positive electrode alkaline additive is a mixture of an inorganic additive and an organic additive, the addition amount of the inorganic additive is 0.1-0.5% of the total mass of the positive electrode active substance, the conductive agent and the binder, and the addition amount of the organic additive is 0.1-0.5% of the total mass of the positive electrode active substance, the conductive agent and the binder;

(2) mixing the negative active material, the conductive agent, the binder and the solvent according to the formula ratio to obtain negative slurry, coating the negative slurry on a negative current collector by transfer coating, baking, rolling by a pair of rollers, and die-cutting to obtain the compact density of 1.6g/cm³The coating surface density is 145g/m²The negative electrode sheet of (1);

the negative active substance is a silicon oxide/carbon composite material, the conductive agent is conductive carbon black, and the binder is a mixture of carboxymethyl cellulose and styrene butadiene rubber; the mass percent of the negative electrode active material is 94.5-95.5%, the mass percent of the conductive agent is 1.3-2%, and the mass percent of the binder is 2.8-3.9% by taking the total mass of the negative electrode active material, the conductive agent and the binder as 100%; the mass ratio of the carboxymethyl cellulose to the styrene butadiene rubber is (1-1.4): (1.8-2.5);

(3) laminating, welding, entering a shell and assembling the positive plate in the step (1), the negative plate in the step (2) and the isolating membrane to obtain a battery cell;

(4) and (4) injecting the electrolyte into the battery cell in the step (3), and then sealing, forming and grading to obtain the lithium ion battery.

Technical Field

The invention belongs to the technical field of energy storage, relates to a pole piece, and particularly relates to a positive plate, a lithium ion battery comprising the positive plate and a preparation method of the lithium ion battery.

Background

Since the 21 st century, with the rapid development of global economy, the quality of life of people is continuously improved, and the problems of energy crisis and environmental pollution are accompanied. In such a severe situation, it has become a necessary trend to accelerate the development of new energy. With the continuous improvement and promotion of policies, the usage amount of new energy automobiles increases year by year, and as is well known, a power battery is the core of the new energy automobiles, and lithium iron phosphate power batteries are more and more favored due to better safety and long cycle life. The energy density of the existing lithium iron phosphate battery is low, and the endurance mileage of an electric automobile is seriously influenced; meanwhile, due to the reason of the lithium iron phosphate material, the conductivity of the lithium iron phosphate material is poor, the diffusion speed of lithium ions is low, the low-temperature performance is poor, and the popularization, the use and the operation of the electric automobile are seriously influenced under the condition of severe environment temperature. The commercial negative electrode material in the lithium iron phosphate lithium battery is mainly a carbon material, the theoretical specific capacity of the material is low and is about 372mAh/g, and the development of the lithium ion battery is greatly limited; the silicon-based negative electrode material has higher specific capacity, the theoretical capacity of the silicon-based material can reach more than 4200mAh/g, and the silicon-based negative electrode material has better lithium intercalation capability, and is more and more concerned by people due to the characteristic of high capacity of the material.

In order to increase the energy density of lithium iron phosphate lithium ion batteries, a great deal of research has been put into, and a corresponding effect has been achieved on the basis of, the research.

CN106450328A discloses a lithium iron phosphate battery, in which the positive electrode active material is lithium iron phosphate, the negative electrode active material is graphite, and the energy density of the battery is about 124 Wh/kg.

CN106374096A discloses a lithium iron phosphate battery, wherein the positive electrode adopts lithium iron phosphate active material, the negative electrode adopts mixture of natural graphite and mesocarbon microbeads, and the energy density of the obtained battery is about 159 Wh/kg.

CN106450436A discloses a low-temperature high-energy-density lithium iron phosphate battery, the mass percentage of each solid matter of the positive electrode is as follows: coated nanoscale lithium iron phosphate: 93.0% -95.5%; polyvinylidene fluoride: 3.5% -7.3%; oily carbon nanotubes: 1.0% -2.0%; the mass percentage of solid matters of the negative electrode is as follows: porous silicon carbon: 90.0% -93.5%; sodium carboxymethylcellulose: 1.5% -3.0%; adhesive: 3.0% -6.0%; SP type conductive carbon black: 0.5 to 1.2 percent; conductive carbon black of type C45: 0.5 to 1.5 percent; KS-6 type conductive graphite: 1.0 to 2.0 percent.

Although the above scheme can improve the cell energy density, some negative effects can be brought; under the condition of high energy density, the cycle life of the battery core can be influenced, and the electrolyte can generate chemical reaction inside the battery core to generate hydrofluoric acid, so that the effective Li can be reduced⁺The amount of the polymer is reduced, so that the capacity loss is caused, the stability of an SEI film is damaged, a certain attenuation or deterioration is generated on the battery cell, and the overall performance of the battery cell is influenced; therefore, the alkaline additive is added into the positive electrode to reduce the adverse effect of the positive electrode, and the battery cell environment is enabled to reach a stable system by neutralizing a certain acidic environment of the positive electrode.

In view of the above, it is desirable to provide a novel lithium ion battery to overcome the above drawbacks.

Disclosure of Invention

Aiming at the problems in the prior art, the invention aims to provide a positive plate, a lithium ion battery containing the positive plate and a preparation method of the lithium ion battery.

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

in a first aspect, the present invention provides a positive electrode sheet including a positive electrode alkaline additive.

In the positive plate provided by the invention, the alkaline additive of the positive electrode can obviously contribute to improving the cycle performance of the battery.

The following is a preferred technical solution of the present invention, but not a limitation to the technical solution provided by the present invention, and the technical objects and advantageous effects of the present invention can be better achieved and achieved by the following preferred technical solution.

According to a preferred technical scheme of the invention, the positive plate comprises a positive coating, and the positive coating comprises a positive active material and a positive alkaline additive.

Preferably, the positive electrode active material includes lithium iron phosphate.

The alkaline additive for the positive electrode comprises an inorganic additive and/or an organic additive, and is preferably a mixture of the inorganic additive and the organic additive. When the mixture of the inorganic additive and the organic additive is used, the cycle life of the battery cell can be better prolonged under the synergistic effect of the inorganic additive and the organic additive.

Preferably, the inorganic additive comprises Na₂CO₃、NaHCO₃、K₂CO₃、KHCO₃、Li₂CO₃Or LiHCO₃Any one or a combination of at least two of them. Typical but non-limiting combinations are: na (Na)₂CO₃And NaHCO₃A combination of (A), NaHCO₃And K₂CO₃Combination of (1), K₂CO₃And KHCO₃Combination of (1), Li₂CO₃And LiHCO₃Combinations of (a), (b), and the like.

Preferably, the organic additive comprises any one of Hexamethyldisilazane (HMDS), heptamethyldisiminosilane (H7DMS), or lithium hexamethyldisilazide, or a combination of at least two, typically but not limited to the following combinations: a combination of hexamethyldisilazane and heptamethyldisiminoalkane, a combination of heptamethyldisiminoalkane and lithium hexamethyldisilazide, a combination of hexamethyldisilazane and lithium hexamethyldisilazide, and the like.

Preferably, the mixture of the inorganic additive and the organic additive is composed of Na₂CO₃And hexamethyldisilazane or a mixture ofNaHCO₃And hexamethyldisilazane.

Preferably, the inorganic additive is added in an amount of 0.1 to 0.5%, for example, 0.1%, 0.2%, 0.3%, 0.4%, or 0.5% by mass of the total mass of the positive electrode active material, the conductive agent, and the binder, but the inorganic additive is not limited to the above-mentioned values, and other values not listed in the above-mentioned range are also applicable. In the invention, if the addition amount of the inorganic additive is too much, some side reactions of the electrolyte can be caused, and simultaneously, too much impurities in the additive can be introduced; if the amount of the inorganic additive added is too small, the effect of the additive is adversely affected. Within the preferable range of 0.1-0.5%, the inorganic additive can have the effects of small dosage and quick effect in the electrolyte.

Preferably, the organic additive is added in an amount of 0.1 to 0.5%, for example, 0.1%, 0.2%, 0.3%, 0.4%, or 0.5% by mass of the total mass of the positive electrode active material, the conductive agent, and the binder, but the organic additive is not limited to the above-mentioned values, and other values not listed in the above-mentioned range are also applicable. In the invention, if the addition amount of the organic additive is too much, some side reactions of the electrolyte can be caused, and simultaneously, too much impurities in the additive can be introduced; if the amount of the organic additive added is too small, the effect of the additive is adversely affected. Within the preferable range of 0.1-0.5%, the organic additive can have the effects of small dosage and quick effect in the electrolyte.

Preferably, the positive electrode active material is spherical lithium iron phosphate.

Preferably, the gram capacity of the positive electrode active material is 145 to 155mAh/g, for example, 145mAh/g, 147mAh/g, 149mAh/g, 151mAh/g, 153mAh/g, or 155mAh/g, but is not limited to the recited values, and other values not recited in the numerical range are also applicable.

Preferably, the particle size distribution D50 of the positive electrode active material is 0.6 to 1.6 μm, for example, D50 is 0.6 μm, 0.8 μm, 1.0 μm, 1.2 μm, 1.4 μm, or 1.6 μm, but is not limited to the values listed, and other values not listed in the numerical range are also applicable. In the invention, if the D50 of the positive active material is too large, the transmission of lithium ions can be influenced by the too large lithium iron phosphate material with smaller conductivity, and the compaction of a pole piece can be influenced by the too large lithium iron phosphate material; if the D50 of the positive electrode active material is too small, the specific surface area of the material is too large, partial agglomeration is likely to occur, and the electrical properties of the cell are affected.

Preferably, the specific surface area of the positive electrode active material is 11-15 m²G, e.g. 11m²/g、12m²/g、13m²/g、14m²G or 15m²And/g, but are not limited to, the recited values, and other values not recited within the range of values are equally applicable.

Preferably, the positive electrode sheet further includes a positive electrode current collecting sheet for coating the positive electrode coating layer.

Preferably, the positive current collector is a carbon-coated aluminum foil.

Preferably, the positive electrode coating further comprises a conductive agent and a binder.

Preferably, the conductive agent in the positive electrode coating layer includes any one or a combination of at least two of conductive carbon black, conductive graphite, and conductive Carbon Nanotubes (CNTs), preferably a mixture of conductive carbon black, conductive graphite, and conductive carbon nanotubes. Wherein, SuperP (SP) can be selected as the conductive carbon black, and KS-6 can be selected as the conductive graphite.

Preferably, the binder in the positive electrode coating includes polyvinylidene fluoride (PVDF).

Preferably, the mass percentage of the positive electrode active material in the positive electrode coating layer is 95.5 to 96.5%, for example, 95.5%, 95.7%, 95.9%, 96.1%, 96.3%, or 96.5%, based on 100% by mass of the total of the positive electrode active material, the conductive agent, and the binder, but is not limited to the recited values, and other values not recited in the range of the values are also applicable; the conductive agent is 1.6-2.6% by mass, such as 1.6%, 1.8%, 2.0%, 2.2%, 2.4% or 2.6%, but not limited to the recited values, and other values not recited in the range of values are also applicable; the mass percentage of the binder is 1.6 to 2.2%, for example, 1.6%, 1.8%, 2.0%, or 2.2%, but is not limited to the recited values, and other values not recited in the above range are also applicable.

Preferably, when the conductive agent in the positive electrode coating is a mixture of conductive carbon black, conductive graphite and conductive carbon nanotubes, the mass ratio of the conductive carbon black to the conductive graphite to the conductive carbon nanotubes is (0.5-0.8): (0.6-1): (0.5 to 0.8), for example, 0.5:0.6:0.5, 0.6:0.7:0.6, 0.7:1:0.8, 0.8:0.8:0.7, 0.8:1:0.8, etc., but the numerical values are not limited to the enumerated values, and other numerical values not enumerated within the numerical range are also applicable.

In a second aspect, the present invention provides a method for producing a positive electrode sheet according to the first aspect, the method comprising the steps of:

preparing anode slurry, wherein the anode slurry contains an anode alkaline additive, coating the anode slurry on an anode current collector, rolling, and die-cutting to obtain the anode sheet.

As a preferred embodiment of the present invention, the method for preparing the positive electrode slurry includes: and mixing the positive active substance, the conductive agent, the binder, the positive alkaline additive and the organic solvent according to the formula ratio to obtain positive slurry.

Here, the organic solvent may be selected according to the prior art, for example, N-methylpyrrolidone (NMP) or the like is used.

Preferably, the coating is a transfer coating.

Preferably, the rolling is a counter-roll rolling.

Preferably, baking is performed prior to said rolling.

Preferably, the compaction density of the positive plate is 2.2-2.5 g/cm³E.g. 2.2g/cm³、2.2g/cm³、2.3g/cm³、2.4g/cm³Or 2.5g/cm³Etc., but are not limited to the recited values, and other values not recited within the range of the recited values are also applicable, preferably 2.3g/cm³。

Preferably, the coating surface density of the positive plate is 360-370 g/m²E.g. 360g/m²、362g/m²、364g/m²、366g/m²、368g/m²Or 370g/m²And the like, but not limited to the enumerated values, and other unrecited values within the numerical range are also applicable, and preferably 365g/m²。

In a third aspect, the present invention provides a lithium ion battery comprising the positive electrode sheet according to the first aspect.

As a preferred technical solution of the present invention, the lithium ion battery includes a positive plate, a negative plate, an isolation film for isolating the positive plate from the negative plate, and an electrolyte, the positive plate is the positive plate of the first aspect, the negative plate includes a negative electrode coating, and the negative electrode coating includes a negative electrode active material.

After the battery cell in the lithium ion battery provided by the invention is cycled for 1000 weeks, the retention rate of the battery cell can reach 85.5%, the battery cell shows better cycle performance, and the development requirement of an electric automobile can be met.

In addition, in the lithium ion battery provided by the invention, the mutual matching of the anode, the cathode and the isolating membrane plays an important role in improving the performance of the battery.

Preferably, the negative active material is a silicon-based composite material.

Preferably, the silicon-based composite material comprises a silicon oxide/carbon composite anode material (SiOx/C,0 < x < 2).

Preferably, the negative electrode active material has a gram capacity of 420 to 450mAh/g, for example, 420mAh/g, 430mAh/g, 440mAh/g, or 450mAh/g, but is not limited to the recited values, and other values not recited in the range of the recited values are also applicable.

Preferably, the particle size distribution D50 of the negative electrode active material is 14 to 18 μm, for example, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, etc., but is not limited to the values listed, and other values not listed within the range of the values are also applicable. In the present invention, if the D50 of the negative electrode active material is too large, the diffusion path of lithium ions is long, and the kinetics of the diffusion process is relatively difficult; if the D50 of the negative active material is too small, the material surface defects of the small particles are so large that the intercalated lithium ions cannot be efficiently extracted during discharge, increasing the irreversible effect.

Preferably, the specific surface area of the negative electrode active material is 1 to 2.5m²G, e.g. 1m²/g、1.2m²/g、1.4m²/g、1.6m²/g、1.8m²/g、2m²/g、2.3m²G or 2.5m²And/g, but are not limited to, the recited values, and other values not recited within the range of values are equally applicable.

Preferably, the negative electrode sheet further comprises a negative current collector sheet for coating the negative electrode coating.

Preferably, the anode current collecting sheet is a copper foil.

Preferably, the negative electrode coating further comprises a conductive agent and a binder.

Preferably, the conductive agent in the negative electrode coating layer includes conductive carbon black. The conductive carbon black can be SuperP (SP).

Preferably, the binder in the negative electrode coating layer includes carboxymethyl cellulose (CMC) and/or styrene-butadiene rubber (SBR), preferably a mixture of carboxymethyl cellulose and styrene-butadiene rubber.

Preferably, the mass percentage of the negative electrode active material in the negative electrode coating is 94.5 to 95.5%, for example, 94.5%, 94.7%, 94.9%, 95.1%, 95.3%, or 95.5%, based on 100% by mass of the total of the negative electrode active material, the conductive agent, and the binder, but is not limited to the recited values, and other values not recited in the range of the values are also applicable; the conductive agent is 1.3 to 2% by mass, for example, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, or 2%, but not limited to the recited values, and other values not recited in the range of the values are also applicable; the mass percentage of the binder is 2.8 to 3.9%, for example, 2.8%, 3.0%, 3.1%, 3.3%, 3.5%, 3.7%, or 3.9%, but is not limited to the values listed, and other values not listed in the numerical range are also applicable.

Preferably, when the binder in the negative electrode coating is a mixture of carboxymethyl cellulose and styrene butadiene rubber, the mass ratio of the carboxymethyl cellulose to the styrene butadiene rubber is (1-1.4): (1.8 to 2.5), for example, 1:2.5, 1:2, 1:1.8, 1.2:2.5, 1.4:2 or 1.4:1.8, etc., but not limited to the values listed, and other values not listed in the numerical range are also applicable.

In a preferred embodiment of the present invention, the separator has a porosity of 40 to 45%, for example, 40%, 41%, 42%, 43%, 44%, or 45%, but the separator is not limited to the above-mentioned values, and other values not shown in the above-mentioned numerical range are also applicable.

Preferably, the thickness of the separator is 10 to 15 μm, for example, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, or 15 μm, but is not limited to the values listed, and other values not listed in the range of the values are also applicable, and 12 μm is preferable.

Preferably, the electrolyte contains an organic solvent and a lithium salt.

Preferably, the organic solvent in the electrolyte solution includes Ethylene Carbonate (EC), Ethyl Methyl Carbonate (EMC), and dimethyl carbonate (DMC).

Preferably, the mass ratio of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate in the electrolyte is (10-20): (60-70): (10-20), for example, 20:60:20, 15:70:15, 10:70:20, 20:65:15, 20:70:10, etc., but the electrolyte is not limited to the recited values, and other values not recited in the numerical range are also applicable.

Preferably, the electrolyte further comprises an additive.

Preferably, the additive in the electrolyte is fluoroethylene carbonate (FEC).

Preferably, the additive is added in an amount of 5 to 10%, for example, 5%, 6%, 7%, 8%, 9%, or 10% by mass of the organic solvent based on 100% by mass of the electrolyte, but the additive is not limited to the recited values, and other values not recited in the above range are also applicable.

Preferably, the lithium salt in the electrolyte is lithium hexafluorophosphate.

Preferably, the concentration of the lithium salt in the electrolyte is 1.1 to 1.3mol/L, such as 1.1mol/L, 1.15mol/L, 1.2mol/L, 1.25mol/L, or 1.3mol/L, but not limited to the recited values, and other values not recited in the numerical range are also applicable.

In a fourth aspect, the present invention provides a method for preparing the lithium ion battery according to the third aspect, wherein the method comprises the following steps:

(1) preparing negative electrode slurry, coating the negative electrode slurry on a negative electrode current collecting sheet, then rolling, and die-cutting to obtain a negative electrode sheet;

(2) laminating, welding, encasing and assembling the negative plate in the step (1), the positive plate in the first aspect and the isolating membrane to obtain a battery cell;

(3) and (3) injecting electrolyte into the battery core in the step (2), and then performing a post-treatment process to obtain the lithium ion battery.

The preparation method provided by the invention has the advantages of short flow, easy operation and low cost, and is suitable for industrial large-scale production.

As a preferred embodiment of the present invention, the method for preparing the negative electrode slurry in step (1) includes: and mixing the negative electrode active material, the conductive agent, the binder and the solvent according to the formula ratio to obtain negative electrode slurry.

Preferably, in step (1), the solvent comprises water.

Preferably, in step (1), the coating is transfer coating.

Preferably, in the step (1), the rolling is a roll rolling.

Preferably, in step (1), before the rolling, baking is performed.

Preferably, in the step (1), the compacted density of the negative electrode sheet is 1.5-1.7 g/cm³E.g. 1.5g/cm³、1.6g/cm³Or 1.7g/cm³Etc., but are not limited to the recited values, and other values not recited within the range of the recited values are also applicable, preferably 1.6g/cm³。

Preferably, in the step (1), the coating surface density of the negative plate is 140-150 g/m²E.g. 140g/m²、142g/m²、144g/m²、146g/m²、148g/m²Or 150g/m²Etc., but are not limited to the recited values, and other values not recited within the range of the recited values are also applicable, preferably 145g/m²。

Preferably, in the step (3), the post-treatment process comprises sealing, forming and grading.

As a further preferable technical scheme of the preparation method of the lithium ion battery, the method comprises the following steps:

(1) mixing the positive active material lithium iron phosphate, a conductive agent, a binder and an organic solvent according to the formula ratio, adding a positive alkaline additive into the obtained mixed solution to obtain positive slurry, coating the positive slurry on a positive current collecting sheet by transfer coating, baking, rolling by a pair of rollers, and die-cutting to obtain the lithium iron phosphate with the compacted density of 2.3g/cm³The coating surface density is 365g/m²The positive electrode sheet of (1);

wherein the conductive agent is a mixture of conductive carbon black, conductive graphite and conductive carbon nanotubes, and the binder is polyvinylidene fluoride; the mass percent of the positive active substance is 95.5-96.5%, the mass percent of the conductive agent is 1.6-2.6%, and the mass percent of the binder is 1.6-2.2% based on 100% of the total mass of the positive active substance, the conductive agent and the binder; the mass ratio of the conductive carbon black to the conductive graphite to the conductive carbon nano tube is (0.5-0.8): (0.6-1): (0.5 to 0.8); the positive electrode alkaline additive is a mixture of an inorganic additive and an organic additive, the addition amount of the inorganic additive is 0.1-0.5% of the total mass of the positive electrode active substance, the conductive agent and the binder, and the addition amount of the organic additive is 0.1-0.5% of the total mass of the positive electrode active substance, the conductive agent and the binder;

(2) mixing the negative active material, the conductive agent, the binder and the solvent according to the formula ratio to obtain negative slurry, coating the negative slurry on a negative current collector by transfer coating, baking, rolling by a pair of rollers, and die-cutting to obtain the compact density of 1.6g/cm³The coating surface density is 145g/m²The negative electrode sheet of (1);

the negative active substance is a silicon oxide/carbon composite material, the conductive agent is conductive carbon black, and the binder is a mixture of carboxymethyl cellulose and styrene butadiene rubber; the mass percent of the negative electrode active material is 94.5-95.5%, the mass percent of the conductive agent is 1.3-2%, and the mass percent of the binder is 2.8-3.9% by taking the total mass of the negative electrode active material, the conductive agent and the binder as 100%; the mass ratio of the carboxymethyl cellulose to the styrene butadiene rubber is (1-1.4): (1.8-2.5);

(3) laminating, welding, entering a shell and assembling the positive plate in the step (1), the negative plate in the step (2) and the isolating membrane to obtain a battery cell;

(4) and (4) injecting the electrolyte into the battery cell in the step (3), and then sealing, forming and grading to obtain the lithium ion battery.

In the above further preferred technical scheme, the positive active material lithium iron phosphate, the negative active material silicon oxide/carbon composite material and the positive alkaline additive are matched with each other, which greatly helps to improve the energy density and cycle life of the battery.

Compared with the prior art, the invention has the following beneficial effects:

(1) the alkaline additive is added into the positive plate provided by the invention, so that the cycle performance of the battery can be obviously improved.

(2) The lithium ion battery provided by the invention has the advantages that the main materials of the battery, such as the positive plate, the negative plate, the isolating membrane, the electrolyte and the like, are optimized, so that the positive plate, the negative plate, the isolating membrane, the electrolyte and the like are better matched with each other, the obtained lithium ion battery has higher energy density, and the battery core shows better cycle performance. According to the invention, when the inorganic additive and the organic additive are simultaneously added into the positive electrode, the cycle life of the battery cell can be better prolonged under the synergistic effect of the inorganic additive and the organic additive. The energy density of the lithium ion battery provided by the invention can reach more than 180Wh/kg, and the cycle retention rate after 1000 cycles can reach 85.5%. According to the invention, when the additive is added into the electrolyte, the low-temperature performance of the battery cell can be better improved.

(3) The preparation method of the positive plate and the preparation method of the lithium ion battery provided by the invention have the advantages of short flow, easiness in operation and low cost, and are suitable for industrial large-scale production.

Drawings

Fig. 1 is an SEM image of a spherical lithium iron phosphate material used in example 1 of the present invention;

FIG. 2 is an SEM photograph of a silica/carbon composite material used in example 1 of the present invention.

Detailed Description

In order to better illustrate the present invention and facilitate the understanding of the technical solutions of the present invention, the present invention is further described in detail below. The following examples are merely illustrative of the present invention and do not represent or limit the scope of the claims, which are defined by the claims.

The following are typical but non-limiting examples of the invention: