阅读说明：本技术 一种锂离子电池用隔膜及其制备方法 (Diaphragm for lithium ion battery and preparation method thereof ) 是由 王崇刚 欧小菊 赵艳方 陈杰 杨山 李载波 于 2020-12-31 设计创作，主要内容包括：本发明提供了一种锂离子电池用隔膜,包括基膜层、陶瓷层和粘结层；陶瓷层由水性陶瓷浆料涂覆而成,涂覆于基膜层的至少一面；水性陶瓷浆料包括陶瓷材料和第一水性粘结剂；粘结层由水性粘结层浆料涂覆而成,设置于隔膜的最外侧；水性粘结层浆料包括聚合物粒子和第二水性粘结剂；其中,第一水性粘结剂和/或第二水性粘结剂为聚合物锂盐。相比于现有技术,本发明的隔膜,在水性涂层中均引入聚合物锂盐作为水性粘结剂,不仅提高了涂层与基膜层之间的粘接性,且由于在涂层中引入了Li～+,使得涂层具有更高的极性和离子电导性,增加了隔膜的离子电导率,提供了电池的低温性能和循环寿命。(The invention provides a diaphragm for a lithium ion battery, which comprises a base film layer, a ceramic layer and a bonding layer; the ceramic layer is formed by coating water-based ceramic slurry and is coated on at least one surface of the base film layer; the aqueous ceramic slurry comprises a ceramic material and a first aqueous binder; the bonding layer is formed by coating aqueous bonding layer slurry and is arranged on the outermost side of the diaphragm; the aqueous bonding layer slurry comprises polymer particles and a second aqueous binder; wherein the first aqueous binder and/or the second aqueous binder is a polymer lithium salt. Compared with the prior art, the separator of the invention introduces polymer lithium salt into the water-based coatingThe water-based binder not only improves the adhesion between the coating and the base film layer, but also introduces Li into the coating + So that the coating has higher polarity and ionic conductivity, the ionic conductivity of the separator is increased, and the low-temperature performance and the cycle life of the battery are improved.)

1. A separator for a lithium ion battery, comprising:

a base film layer;

the ceramic layer is formed by coating water-based ceramic slurry and is coated on at least one surface of the base film layer; the aqueous ceramic slurry comprises a ceramic material and a first aqueous binder;

the bonding layer is formed by coating aqueous bonding layer slurry and is arranged on the outermost side of the diaphragm; the aqueous bonding layer slurry comprises polymer particles and a second aqueous binder;

wherein the first aqueous binder and/or the second aqueous binder is a polymeric lithium salt.

2. The separator according to claim 1, wherein the polymer lithium salt is selected from at least one of formula (a), formula (B), formula (C), and formula (D);

wherein R is₁-R₅Is independently selected from C_1-20Alkyl radical, C_1-10An alkoxy group.

3. The separator of claim 1, wherein the aqueous ceramic slurry further comprises a dispersant, a thickener, a wetting agent, and deionized water; 30-60 parts by weight of the ceramic material; 1-6 parts of first aqueous binder, 0-1.5 parts of dispersant, 0.1-2.5 parts of thickener, 0-0.1 part of wetting agent and 45-75 parts of deionized water.

4. The separator according to claim 3, wherein the ceramic material is at least one of silicon dioxide, aluminum oxide, zirconium dioxide, magnesium hydroxide, calcium oxide, boehmite, titanium dioxide, and barium sulfate; the dispersing agent is a nonionic dispersing agent, and the nonionic dispersing agent comprises at least one of polyethylene glycol, polyvinyl alcohol, polyethylene oxide, polyvinylpyrrolidone and a multi-branched alcohol modified surfactant; the wetting agent is at least one of polyether siloxane copolymer, tween-90, fluoroalkyl ethoxy alcohol ether, fatty alcohol-polyoxyethylene ether, butyl sodium naphthalene sulfonate, hydroxyethyl sodium sulfonate and sodium dodecyl sulfonate.

5. The separator of claim 1, wherein the aqueous tie-layer slurry further comprises a thickener, a defoamer, and deionized water; 5-20 parts of polymer particles, 0.5-3 parts of a second aqueous binder, 0.01-1 part of a thickening agent, 0.005-0.025 part of a defoaming agent and 70-95 parts of deionized water.

6. The separator according to claim 5, wherein the polymer particles are any one of a copolymer of methyl methacrylate-methacrylic acid, a copolymer of methyl methacrylate-ethacrylic acid, a copolymer of methyl methacrylate-ethyl methacrylate, a copolymer of methyl methacrylate-butyl methacrylate, or a copolymer of methyl methacrylate-styrene; the defoaming agent is at least one of polyether emulsified silicone oil, a high-carbon alcohol fatty acid ester compound, polyoxyethylene polyoxypropylene pentaerythritol ether, polyoxyethylene polyoxypropylene amine ether and polyoxypropylene glycerol ether.

7. The separator according to any one of claims 3 to 6, wherein the thickener is at least one of lithium carboxymethyl cellulose, lithium alginate, sodium carboxymethyl cellulose, and sodium alginate.

8. The separator according to claim 1, wherein the ceramic layer is coated to a thickness of 0.3 to 5 μm and an areal density of 0.1 to 6g/m²(ii) a The coating thickness of the bonding layer is 0.3-3 mu m, and the surface density is 0.05-0.5 g/m²。

9. A preparation method of a diaphragm for a lithium ion battery is characterized by comprising the following steps:

preparing an aqueous ceramic slurry, wherein the aqueous ceramic slurry comprises a ceramic material and a first aqueous binder; then coating the water-based ceramic slurry on at least one surface of a base film layer, and drying to prepare a ceramic layer;

preparing an aqueous bonding layer slurry comprising polymer particles and a second aqueous binder; then coating the water-based bonding layer slurry on the outermost side of the diaphragm, and drying to prepare a bonding layer; wherein the first aqueous binder and/or the second aqueous binder is a polymeric lithium salt;

the preparation of the separator was completed.

10. The method for preparing the separator according to claim 9, wherein the aqueous ceramic slurry comprises 30 to 60 parts by weight of a ceramic material, 1 to 6 parts by weight of a lithium salt of a polymer, 0 to 1.5 parts by weight of a dispersant, 0.1 to 2.5 parts by weight of a thickener, 0 to 0.1 part by weight of a wetting agent, and 45 to 75 parts by weight of deionized water; the aqueous bonding layer slurry comprises, by weight, 5-20 parts of polymer particles, 0.5-3 parts of polymer lithium salt, 0.01-1 part of a thickening agent, 0.005-0.025 part of an antifoaming agent, and 70-95 parts of deionized water.

Technical Field

The invention relates to the field of lithium batteries, in particular to a diaphragm for a lithium ion battery and a preparation method thereof.

Background

The lithium ion battery diaphragm is an important component of the lithium ion battery, is arranged between the anode and the cathode of the battery, can prevent short circuit caused by direct contact of active substances of the anode and the cathode, can adsorb electrolyte and transmit lithium ions. The diaphragm plays an important role in the safety performance and the cycle performance of the battery, the internal resistance and the charge and discharge performance of the battery and the like. At present, the traditional battery separator is mainly made of polyolefin separator, PP or PE. Although such separators have certain mechanical and chemical stability and can generate closed pores at a certain temperature to prevent further short circuit of the lithium ion battery, the separators still cannot meet the ideal requirements. During the charge and discharge cycle of the lithium ion battery, the generated lithium dendrite may pierce through the diaphragm to cause short circuit, which affects the safety performance. In addition, the polyolefin film has lower surface energy and poorer wettability with electrolyte, and cannot be completely infiltrated with the electrolyte in a lithium battery, so that the internal resistance of the battery is increased, and the cycle performance of the battery is influenced.

In order to overcome the defects of the polyolefin film, in recent years, researchers have extensively studied and developed the surface modification of the lithium ion separator, and found that the most effective method is to coat the surface of the separator with an inorganic ceramic coating. The inorganic ceramic coating can reduce the thermal shrinkage rate of the diaphragm, improve the heat resistance of the diaphragm, and simultaneously can increase the liquid absorption of the diaphragm, thereby playing a great positive role in improving the performance of the lithium battery. However, both the inorganic ceramic coating and the adhesive which plays a role in bonding inevitably increase the resistance of the separator, increase the internal resistance of the battery, and limit the cycle life of the battery.

In view of the above, it is necessary to provide a technical solution to the above problems.

Disclosure of Invention

One object of the present invention is: the diaphragm for the lithium ion battery provided by the invention has the advantages that the performance of the diaphragm is ensured, the internal resistance of the lithium ion battery is reduced, and the cycle performance of the battery is improved.

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

a separator for a lithium ion battery, comprising:

a base film layer;

the ceramic layer is formed by coating water-based ceramic slurry and is coated on at least one surface of the base film layer; the aqueous ceramic slurry comprises a ceramic material and a first aqueous binder;

the bonding layer is formed by coating aqueous bonding layer slurry and is arranged on the outermost side of the diaphragm; the aqueous bonding layer slurry comprises polymer particles and a second aqueous binder;

wherein the first aqueous binder and/or the second aqueous binder is a polymeric lithium salt.

Preferably, the polymeric lithium salt is selected from at least one of formula (a), formula (B), formula (C) and formula (D);

wherein R is₁-R₅Is independently selected from C_1-20Alkyl radical, C_1-10An alkoxy group.

Preferably, the aqueous ceramic slurry further comprises a dispersant, a thickener, a wetting agent and deionized water; 30-60 parts by weight of the ceramic material; 1-6 parts of first aqueous binder, 0-1.5 parts of dispersant, 0.1-2.5 parts of thickener, 0-0.1 part of wetting agent and 45-75 parts of deionized water.

Preferably, the ceramic material is at least one of silicon dioxide, aluminum oxide, zirconium dioxide, magnesium hydroxide, calcium oxide, boehmite, titanium dioxide and barium sulfate; the dispersing agent is a nonionic dispersing agent, and the nonionic dispersing agent comprises at least one of polyethylene glycol, polyvinyl alcohol, polyethylene oxide, polyvinylpyrrolidone and a multi-branched alcohol modified surfactant; the wetting agent is at least one of polyether siloxane copolymer, tween-90, fluoroalkyl ethoxy alcohol ether, fatty alcohol-polyoxyethylene ether, butyl sodium naphthalene sulfonate, hydroxyethyl sodium sulfonate and sodium dodecyl sulfonate.

Preferably, the aqueous bonding layer slurry further comprises a thickener, a defoamer and deionized water; 5-20 parts of polymer particles, 0.5-3 parts of a second aqueous binder, 0.01-1 part of a thickening agent, 0.005-0.025 part of a defoaming agent and 70-95 parts of deionized water.

Preferably, the polymer particles are any one of a methyl methacrylate-methacrylic acid copolymer, a methyl methacrylate-ethacrylic acid copolymer, a methyl methacrylate-ethyl methacrylate copolymer, a methyl methacrylate-butyl methacrylate copolymer or a methyl methacrylate-styrene copolymer; the defoaming agent is at least one of polyether emulsified silicone oil, a high-carbon alcohol fatty acid ester compound, polyoxyethylene polyoxypropylene pentaerythritol ether, polyoxyethylene polyoxypropylene amine ether and polyoxypropylene glycerol ether.

Preferably, the thickener is at least one of lithium carboxymethyl cellulose, lithium alginate, sodium carboxymethyl cellulose and sodium alginate.

Preferably, the coating thickness of the ceramic layer is 0.3-5 μm, and the surface density is 0.1-6 g/m²(ii) a The coating thickness of the bonding layer is 0.3-3 mu m, and the surface density is 0.05-0.5 g/m²。

Another object of the present invention is to provide a method for preparing a separator for a lithium ion battery, including the steps of:

preparing an aqueous ceramic slurry, wherein the aqueous ceramic slurry comprises a ceramic material and a first aqueous binder; then coating the water-based ceramic slurry on at least one surface of a base film layer, and drying to prepare a ceramic layer;

preparing an aqueous bonding layer slurry comprising polymer particles and a second aqueous binder; then coating the water-based bonding layer slurry on the outermost side of the diaphragm, and drying to prepare a bonding layer; wherein the first aqueous binder and/or the second aqueous binder is a polymeric lithium salt;

the preparation of the separator was completed.

Preferably, the aqueous ceramic slurry is prepared from 30-60 parts by weight of a ceramic material, 1-6 parts by weight of a polymer lithium salt, 0-1.5 parts by weight of a dispersant, 0.1-2.5 parts by weight of a thickener, 0-0.1 part by weight of a wetting agent and 45-75 parts by weight of deionized water; the aqueous bonding layer slurry comprises, by weight, 5-20 parts of polymer particles, 0.5-3 parts of polymer lithium salt, 0.01-1 part of a thickening agent, 0.005-0.025 part of an antifoaming agent, and 70-95 parts of deionized water.

Compared with the prior art, the invention has the beneficial effects that: the diaphragm provided by the invention adopts polymer lithium salt as the water-based binder in the ceramic layer and the bonding layer, thereby not only improving the adhesion between the coating and the base film layer, but also introducing Li in the coating⁺So that the coating has higher polarity and ionic conductivity, the ionic conductivity of the separator is increased, and the low-temperature performance and the cycle life of the battery are improved. Meanwhile, the diaphragm of the invention replaces organic solvent with aqueous solvent, and has the advantages of environmental protection, low cost, simple process and convenient continuous production.

Drawings

Fig. 1 is a schematic structural view of the separator of the present invention.

In the figure: 1-a base film layer; 2-a ceramic layer; 3-bonding layer.

Detailed Description

In order to make the technical solutions and advantages of the present invention clearer, the present invention and its advantages will be described in further detail below with reference to the following detailed description and the accompanying drawings, but the embodiments of the present invention are not limited thereto.

In the description of the present invention, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "fixed" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral part; can be mechanically or electrically connected; either directly or indirectly through intervening media, either internally or in any other relationship. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.

The standard parts used in the invention can be purchased from the market, the special-shaped parts can be customized according to the description of the specification and the accompanying drawings, the specific connection mode of each part adopts conventional means such as bolts, rivets, welding and the like mature in the prior art, the machines, the parts and equipment adopt conventional models in the prior art, and the circuit connection adopts the conventional connection mode in the prior art, so that the detailed description is omitted.

As shown in fig. 1, a separator for a lithium ion battery includes a base film layer 1, a ceramic layer 2, and an adhesive layer 3; the ceramic layer 2 is formed by coating water-based ceramic slurry and is coated on at least one surface of the base film layer 1; the aqueous ceramic slurry comprises a ceramic material and a first aqueous binder; the bonding layer 3 is formed by coating aqueous bonding layer 3 slurry and is arranged on the outermost side of the diaphragm; the aqueous bonding layer 3 slurry comprises polymer particles and a second aqueous binder; wherein the first aqueous binder and/or the second aqueous binder is a polymer lithium salt.

Further, the polymer lithium salt is selected from at least one of formula (A), formula (B), formula (C) and formula (D);

wherein R is₁-R₅Is independently selected from C_1-20Alkyl radical, C_1-10An alkoxy group.

Further, the aqueous ceramic slurry also comprises a dispersant, a thickening agent, a wetting agent and deionized water; 30-60 parts of a ceramic material; 1-6 parts of first aqueous binder, 0-1.5 parts of dispersant, 0.1-2.5 parts of thickener, 0-0.1 part of wetting agent and 45-75 parts of deionized water.

Further, the ceramic material is at least one of silicon dioxide, aluminum oxide, zirconium dioxide, magnesium hydroxide, calcium oxide, boehmite, titanium dioxide and barium sulfate; the dispersant is nonionic dispersant, and the nonionic dispersant comprises at least one of polyethylene glycol, polyvinyl alcohol, polyethylene oxide, polyvinylpyrrolidone and multi-branched alcohol modified surfactant; the wetting agent is at least one of polyether siloxane copolymer, tween-90, fluoroalkyl ethoxy alcohol ether, fatty alcohol-polyoxyethylene ether, butyl sodium naphthalene sulfonate, hydroxyethyl sodium sulfonate and sodium dodecyl sulfonate.

Further, the aqueous bonding layer 3 slurry also comprises a thickening agent, a defoaming agent and deionized water; 5-20 parts of polymer particles, 0.5-3 parts of a second aqueous binder, 0.01-1 part of a thickening agent, 0.005-0.025 part of a defoaming agent and 70-95 parts of deionized water.

Further, the polymer particles are any one of a methyl methacrylate-methacrylic acid copolymer, a methyl methacrylate-ethacrylic acid copolymer, a methyl methacrylate-ethyl methacrylate copolymer, a methyl methacrylate-butyl methacrylate copolymer or a methyl methacrylate-styrene copolymer; the defoaming agent is at least one of polyether emulsified silicone oil, high-alcohol fatty acid ester compound, polyoxyethylene polyoxypropylene pentaerythritol ether, polyoxyethylene polyoxypropylene amine ether and polyoxypropylene glycerol ether.

Further, the thickener is at least one of lithium carboxymethyl cellulose, lithium alginate, sodium carboxymethyl cellulose and sodium alginate.

Further, the coating thickness of the ceramic layer 2 is 0.3 to 5 μm, and the surface density is 0.1 to 6g/m²(ii) a The coating thickness of the bonding layer 3 is 0.3-3 μm, and the surface density is 0.05-0.5 g/m²。

The specific preparation method of the diaphragm comprises the following steps:

mixing, stirring and dispersing 30-60 parts by weight of a ceramic material, 1-6 parts by weight of a polymer lithium salt, 0-1.5 parts by weight of a dispersing agent, 0.1-2.5 parts by weight of a thickening agent, 0-0.1 part by weight of a wetting agent and 45-75 parts by weight of deionized water for 10-150 min to obtain a water-based ceramic slurry, coating at least one surface of a base film layer 1 with the water-based ceramic slurry, and drying to prepare a ceramic layer 2;

mixing, stirring and dispersing 5-20 parts by weight of polymer particles, 0.5-3 parts by weight of polymer lithium salt, 0.01-1 part by weight of thickening agent, 0.005-0.025 part by weight of defoaming agent and 70-95 parts by weight of deionized water for 10-120 min to obtain aqueous bonding layer 3 slurry, coating the aqueous bonding layer 3 slurry on the outermost side of the diaphragm, and drying to prepare a bonding layer 3; the preparation of the separator was completed.

And preparing the lithium ion battery by using the obtained diaphragm.

Example 1

A lithium ion battery comprises a positive plate, a negative plate and a diaphragm arranged between the positive plate and the negative plate at intervals, wherein the diaphragm is the diaphragm for the lithium ion battery. In the embodiment, the active material of the positive plate is lithium cobaltate, the active material of the negative plate is artificial graphite, the soft package lithium battery is assembled by sequentially completing the processes of stirring, coating, rolling, slitting, winding and top sealing of positive and negative electrode material slurry, and then the soft package lithium battery is placed in a vacuum oven at 80 ℃ to be baked for 12-24 hours; and when the mixed water content of the negative plate of the bare cell is less than 150ppm, performing automatic liquid injection, high-temperature standing, negative pressure formation, sealing welding, capacity grading, detection and other processes on the soft package lithium battery, and finally obtaining the soft package lithium battery.

The specific preparation method of the diaphragm comprises the following steps:

(a) preparing water-based ceramic slurry: adding 38 parts of alumina, 0.13 part of polyethylene glycol, 0.69 part of lithium alginate, 2.91 parts of polymer lithium salt A and 0.025 part of sodium hydroxyethyl sulfonate into 62 parts of deionized water, and stirring and dispersing at a low speed for 2 hours to obtain high-temperature-resistant water-based ceramic slurry;

(b) preparing aqueous bonding layer 3 slurry: adding 11 parts of polymethyl methacrylate-polystyrene copolymer particles, 0.05 part of lithium alginate, 1.5 parts of polymer lithium salt A and 0.01 part of polyether emulsified silicone oil defoaming agent into 85 parts of deionized water, and mixing and stirring for 60min to obtain aqueous bonding layer 3 slurry;

the structure of the polymer lithium salt a is shown below:

wherein R is₁、R₂Are all-C₂H₅；

(c) Coating: coating the water-based ceramic slurry prepared in the step a on one side of a 7-micron polyethylene microporous membrane in a gravure coating mode to obtain a semi-finished ceramic coating diaphragm; and c, coating the water-based bonding layer 3 slurry prepared in the step b on two sides of the ceramic coating semi-finished diaphragm in a gravure roll coating mode to finally obtain the composite diaphragm coated with the water-based ceramic layer 2 and the water-based bonding layer 3. In the obtained composite separator, the thickness of the ceramic layer 2 was 2 μm, and the single-layer thickness of the adhesive layer 3 was 0.5 μm.

Example 2

Different from example 1 is the preparation of the separator. The specific preparation method of the separator of the embodiment is as follows:

(a) preparing water-based ceramic slurry: adding 38 parts of alumina, 0.13 part of polyethylene glycol, 0.69 part of lithium alginate, 2.91 parts of polymer lithium salt A and 0.025 part of sodium hydroxyethyl sulfonate into 62 parts of deionized water, and stirring and dispersing at a low speed for 2 hours to obtain high-temperature-resistant water-based ceramic slurry;

(b) preparing aqueous bonding layer 3 slurry: adding 12 parts of polymethyl methacrylate-polystyrene copolymer particles, 0.06 part of lithium carboxymethyl cellulose, 1.3 parts of polymer lithium salt B and 0.01 part of polyether emulsified silicone oil defoaming agent into 87 parts of deionized water, and mixing and stirring for 60min to obtain aqueous bonding layer 3 slurry;

the structure of the polymer lithium salt A, B is shown below:

wherein R is₁、R₂Are all-C₂H₅；R₃、R₄Are all-CH₃。

The rest is the same as embodiment 1, and the description is omitted here.

Example 3

Different from example 1 is the preparation of the separator. The specific preparation method of the separator of the embodiment is as follows:

(a) preparing water-based ceramic slurry: adding 37.5 parts of alumina, 0.69 part of lithium carboxymethyl cellulose and 2.98 parts of polymer lithium salt B into 63 parts of deionized water, stirring at a low speed, and dispersing for 2 hours to obtain high-temperature-resistant water-based ceramic slurry;

(b) preparing aqueous bonding layer 3 slurry: adding 12 parts of polymethyl methacrylate-polystyrene copolymer particles, 0.06 part of lithium carboxymethyl cellulose, 1.3 parts of polymer lithium salt B and 0.01 part of polyether emulsified silicone oil defoaming agent into 87 parts of deionized water, and mixing and stirring for 60min to obtain aqueous bonding layer 3 slurry;

the structure of the polymer lithium salt B is shown below:

wherein R is₁、R₂Are all-C₂H₅；R₃、R₄Are all-CH₃。

The rest is the same as embodiment 1, and the description is omitted here.

Example 4

Different from example 1 is the preparation of the separator. The specific preparation method of the separator of the embodiment is as follows:

(a) preparing water-based ceramic slurry: adding 37.5 parts of alumina, 0.69 part of lithium carboxymethyl cellulose and 2.98 parts of polymer lithium salt B into 63 parts of deionized water, stirring at a low speed, and dispersing for 2 hours to obtain high-temperature-resistant water-based ceramic slurry;

(b) preparing aqueous bonding layer 3 slurry: adding 12 parts of polymethyl methacrylate-polystyrene copolymer particles, 0.05 part of sodium carboxymethylcellulose, 1.7 parts of polymer lithium salt C and 0.01 part of polyether emulsified silicone oil defoaming agent into 84 parts of deionized water, and mixing and stirring for 60min to obtain aqueous bonding layer 3 slurry;

the structure of the polymer lithium salt C is shown below:

wherein R is₁、R₂Are all-C₂H₅；R₃、R₄Are all-CH₃。

The rest is the same as embodiment 1, and the description is omitted here.

Example 5

Different from example 1 is the preparation of the separator. The specific preparation method of the separator of the embodiment is as follows:

(a) preparing water-based ceramic slurry: adding 35 parts of alumina, 0.75 part of sodium carboxymethylcellulose and 2.8 parts of polymer lithium salt C into 65 parts of deionized water, stirring at a low speed, and dispersing for 2 hours to obtain high-temperature-resistant water-based ceramic slurry;

(b) preparing aqueous bonding layer 3 slurry: adding 12 parts of polymethyl methacrylate-polystyrene copolymer particles, 0.05 part of sodium carboxymethylcellulose, 1.7 parts of polymer lithium salt C and 0.01 part of polyether emulsified silicone oil defoaming agent into 84 parts of deionized water, and mixing and stirring for 60min to obtain aqueous bonding layer 3 slurry;

the structure of the polymer lithium salt C is shown below:

wherein R is₃、R₄Are all-CH₃。

The rest is the same as embodiment 1, and the description is omitted here.

Example 6

Different from example 1 is the preparation of the separator. The specific preparation method of the separator of the embodiment is as follows:

(a) preparing water-based ceramic slurry: adding 35 parts of alumina, 0.75 part of sodium carboxymethylcellulose and 2.8 parts of polymer lithium salt C into 65 parts of deionized water, stirring at a low speed, and dispersing for 2 hours to obtain high-temperature-resistant water-based ceramic slurry;

(b) preparing aqueous bonding layer 3 slurry: adding 13 parts of polymethyl methacrylate-polystyrene copolymer particles, 0.17 part of lithium alginate, 1.9 parts of polymer lithium salt D and 0.01 part of polyether emulsified silicone oil defoaming agent into 85 parts of deionized water, and mixing and stirring for 60min to obtain aqueous bonding layer 3 slurry;

the structure of the polymer lithium salt C, D is shown below:

wherein R is₃、R₄Are all-CH₃；R₁、R₂、R₅Are all-C₂H₅。

The rest is the same as embodiment 1, and the description is omitted here.

Example 7

Different from example 1 is the preparation of the separator. The specific preparation method of the separator of the embodiment is as follows:

(a) preparing water-based ceramic slurry: adding 38 parts of alumina, 0.78 part of lithium alginate and 2.5 parts of polymer lithium salt D into 66 parts of deionized water, stirring at a low speed, and dispersing for 2 hours to obtain high-temperature-resistant water-based ceramic slurry;

(b) preparing aqueous bonding layer 3 slurry: adding 13 parts of polymethyl methacrylate-polystyrene copolymer particles, 0.17 part of lithium alginate, 1.9 parts of polymer lithium salt D and 0.01 part of polyether emulsified silicone oil defoaming agent into 85 parts of deionized water, and mixing and stirring for 60min to obtain aqueous bonding layer 3 slurry;

the structure of polymer lithium salt D is shown below:

wherein R is₁、R₂、R₅Are all-C₂H₅。

The rest is the same as embodiment 1, and the description is omitted here.

Example 8

Different from example 1 is the preparation of the separator. The specific preparation method of the separator of the embodiment is as follows:

(a) preparing water-based ceramic slurry: adding 39 parts of alumina, 0.69 part of sodium alginate and 2.5 parts of polymer lithium salt D into 61 parts of deionized water, stirring at a low speed, and dispersing for 2 hours to obtain high-temperature-resistant water-based ceramic slurry;

(b) preparing aqueous bonding layer 3 slurry: adding 13 parts of polymethyl methacrylate-polystyrene copolymer particles, 0.19 part of sodium alginate, 1.8 parts of polymer lithium salt D and 0.01 part of polyether emulsified silicone oil defoaming agent into 87 parts of deionized water, and mixing and stirring for 60min to obtain aqueous bonding layer 3 slurry;

the structure of polymer lithium salt D is shown below:

wherein R is₁、R₂、R₅Are all-C₂H₅。

The rest is the same as embodiment 1, and the description is omitted here.

Comparative example 1

The difference from example 1 is: in the comparative example, the aqueous ceramic slurry is added with polyacrylic acid binder, and the thickening agent is sodium alginate.

The rest is the same as embodiment 1, and the description is omitted here.

Comparative example 2

The difference from example 1 is: in the comparative example, the aqueous bonding layer 3 slurry is added with a polyacrylic acid binder, and the thickening agent is sodium alginate.

The rest is the same as embodiment 1, and the description is omitted here.

Comparative example 3

The difference from example 1 is: in the comparative example, the aqueous ceramic slurry and the aqueous bonding layer 3 slurry are both added with polyacrylic acid type binders, and the thickening agent is sodium alginate.

The rest is the same as embodiment 1, and the description is omitted here.

Performance testing

The separators and batteries manufactured in examples 1 to 8 and comparative examples 1 to 3 were subjected to the relevant performance tests:

(1) and (3) ion conductivity test:

and (3) putting the diaphragm into the electrolyte with the temperature of 23 +/-2 ℃, keeping the sealing, and soaking for 2 h. And injecting the electrolyte into the resistance testing mold, connecting the resistance testing mold with the electrochemical workstation, and setting testing parameters. Sequentially placing 1 layer of diaphragm, testing its impedance spectrum, placing another layer, testing its impedance spectrum until 4 layers are placed, measuring four impedance spectrograms, and respectively reading resistance values R of 1-4 layers from the impedance spectrograms₁、R₂、R₃And R₄. Wherein σ ═ d/(R × S). σ: ionic conductivity; d: the thickness of the single-layer separator; r: a resistance value; s: the membrane area was tested.

(2) And (3) testing the normal-temperature cycle performance: at 25 ℃, the battery after capacity grading is charged to 4.48V at constant current and constant voltage of 0.7C, the current is cut off at 0.05C, then the battery is discharged to 3.0V at constant current of 0.5C, and the capacity retention rate at 500 weeks is calculated after the battery is charged and discharged for 500 cycles according to the cycle, wherein the calculation formula is as follows:

the 500-week cycle capacity retention ratio (%) (300-week cycle discharge capacity/first-cycle discharge capacity) × 100%.

(3) And (3) testing low-temperature discharge performance: discharging the soft package battery cell at 0.5C to 3.0V at 25 ℃ for 5 min; charging to 4.48V at 0.2C, changing to 4.48V constant voltage charging when the cell voltage reaches 4.48V, and standing for 5min until the charging current is less than or equal to the given cutoff current of 0.05C; transferring the fully charged core into a high-low temperature box, setting the temperature to be 20 ℃ below zero, and standing for 120min after the temperature of the incubator reaches; discharging at 0.2C to stop voltage of 3.0V, and standing for 5 min; then the temperature of the high-low temperature box is adjusted to 25 +/-3 ℃, and the box is placed for 60min after the temperature of the box is reached; charging to 4.48V at 0.2C, and changing to 4.48V constant-voltage charging when the cell voltage reaches 4.48V until the charging current is less than or equal to the given cutoff current of 0.05C; standing for 5 min; the capacity retention rate of 3.0V discharged at the low temperature of-20 ℃ is calculated. The calculation formula is as follows:

capacity retention (%) of 3.0V at 20 ℃ (discharge capacity from-20 ℃ to 3.0V/discharge capacity from 25 ℃ to 3.0V) × 100%.

(4) And (3) rate performance test: discharging the soft package battery cell at 0.5C to 3.0V at 25 ℃ for 5 min; charging to 4.48V at 0.2C, changing to 4.48V constant voltage charging when the cell voltage reaches 4.48V until the charging current is less than or equal to the given cutoff current of 0.05C, standing for 5min, and testing the discharge capacities of 0.2C and 3.0C respectively;

discharge capacity retention (%) at 25 ℃ &3.0C [ (& 3.0C discharge capacity to 3.0V/25 ℃ &0.2C discharge capacity to 3.0V) × 100%.

The test results of the above properties are shown in table 1:

TABLE 1

As can be seen from comparison of the test results of examples 1 to 8 and comparative examples 1 to 3 in Table 1:

the addition of the adhesive of the invention can obviously improve the ion conductivity of the diaphragm and the rate capability and the cycle performance of the battery using the diaphragm.

In conclusion, the polymer lithium salt binder is introduced into the aqueous coating, the ceramic layer 2 and the aqueous bonding layer 3 are sequentially coated on the base film, and the composite diaphragm can improve the cycle performance, the low-temperature performance and the rate performance of the lithium battery.

Variations and modifications to the above-described embodiments may also occur to those skilled in the art, which fall within the scope of the invention as disclosed and taught herein. Therefore, the present invention is not limited to the above-mentioned embodiments, and any obvious improvement, replacement or modification made by those skilled in the art based on the present invention is within the protection scope of the present invention. Furthermore, although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.