CN110416467B

CN110416467B - Polymer diaphragm and preparation method and application thereof, and lithium ion battery and preparation method thereof

Info

Publication number: CN110416467B
Application number: CN201810402852.1A
Authority: CN
Inventors: 宣博文; 金丽娜; 曹晓东; 吴金祥; 单军; 胡刚; 何龙
Original assignee: BYD Co Ltd
Current assignee: BYD Co Ltd
Priority date: 2018-04-28
Filing date: 2018-04-28
Publication date: 2021-06-18
Anticipated expiration: 2038-04-28
Also published as: WO2019206283A1; CN110416467A; TW201946316A

Abstract

The invention discloses a polymer diaphragm and a preparation method thereof, and a lithium ion battery containing the polymer diaphragm and a preparation method thereof. The polymer diaphragm is used for the lithium ion battery and can be firmly bonded with the anode and the cathode of the lithium ion battery, so that the lithium ion battery has higher hardness and the lithium ion battery has good performance. When the preparation method is used for preparing the polar polymer binder solution, a low-boiling-point solvent or a high-boiling-point solvent with higher operation safety can be adopted, and when the high-boiling-point solvent is adopted, the operation safety can be improved, and the performance of the lithium ion battery cannot be obviously reduced.

Description

Polymer diaphragm and preparation method and application thereof, and lithium ion battery and preparation method thereof

Technical Field

The invention relates to a polymer diaphragm, a preparation method and application thereof, and also relates to a lithium ion battery adopting the polymer diaphragm and a preparation method thereof.

Background

The lithium ion battery mainly comprises a positive/negative electrode material, an electrolyte, a diaphragm and a battery shell packaging material. The diaphragm is an important component of the lithium ion battery and is used for separating the positive electrode from the negative electrode and preventing the internal short circuit of the battery; the diaphragm allows electrolyte ions to pass through freely, and the electrochemical charge and discharge process is completed. The performance of the diaphragm determines the interface structure, internal resistance and the like of the battery, directly influences the characteristics of the battery such as rate performance, cycle performance, safety performance (high temperature resistance) and the like, and the diaphragm with excellent performance plays an important role in improving the comprehensive performance of the battery.

The polyethylene and polypropylene microporous membrane prepared by the mechanical stretching method is a lithium ion battery diaphragm mainly used in commercial use at present due to the characteristics of low raw material price, simple preparation process, high mechanical strength, strong electrochemical stability and the like. However, the closed cell shrinkage of the commercial microporous membrane around the melting temperature causes a short circuit of the battery, which poses a risk of combustion and explosion at high temperatures; in addition, the polyolefin diaphragm has poor adsorbability to electrolyte and is not beneficial to the conduction of lithium ions in the charging and discharging processes.

At present, a porous membrane coated with polar polymers such as polyethers (e.g., polyethylene oxide), polyacrylonitriles, polyacrylates (e.g., polymethyl methacrylate and copolymers thereof), polyvinylidene fluorides (including polyvinylidene fluoride, and copolymers of vinylidene fluoride and hexafluoropropylene) and the like on both sides of a polyolefin microporous membrane is a main method for improving the performance of a separator for adsorbing an electrolyte and simultaneously reducing the shrinkage ratio of the microporous membrane near a melting temperature. The phase inversion method is one of the main methods for preparing a porous film, and mainly includes two forms: (1) solvent evaporation precipitation phase separation; (2) immersing in precipitation phase separation method.

In actual production, polyvinylidene fluoride (PVdF) coating technology has been widely used. Polyvinylidene fluoride (PVdF) coating technology adopts a solvent evaporation precipitation phase separation method to form pores on the surface of a polyolefin microporous membrane to obtain the PVdF porous membrane, and the specific operation process is as follows: polyvinylidene fluoride is dissolved or dispersed in acetone, and a certain amount of a pore-forming agent DMC (dimethyl carbonate) is added to form a slurry, and the slurry is coated on the surface of a polyolefin microporous membrane and dried. During the drying process, the latent solvent acetone is volatilized and the porogen DMC is evaporated to leave pores.

Disclosure of Invention

The existing polyvinylidene fluoride (PVdF) coating technology adopts low-boiling point acetone as a solvent, and the operation safety needs to be improved. In the research process, the inventor of the present invention finds that although the operation safety can be improved by using a high boiling point solvent instead of acetone, the performance of a lithium ion battery prepared by using a high boiling point solvent to prepare a polyvinylidene fluoride polymer solution is obviously reduced, and the reason may be found through research: the polyvinylidene fluoride polymer solution prepared by the high-boiling solvent has extremely strong permeability, and the polymer solution is easy to penetrate through the diaphragm to reach the other surface opposite to the coating surface, so that the polyvinylidene fluoride polymer is also brought into the pores of the diaphragm, and the polyvinylidene fluoride polymer carried into the diaphragm by the organic solvent usually remains in the pores of the diaphragm due to the fact that the fluidity and the permeability of the polyvinylidene fluoride polymer are far lower than those of the organic solvent, blocks the diaphragm, has adverse effects on the air permeability and the porosity of the diaphragm, improves the body impedance of the polymer diaphragm, reduces the ionic conductivity, and has adverse effects on the performance of the finally prepared lithium ion battery. Although the existing polyolefin separator generally forms a ceramic layer on the surface thereof to improve thermal stability of the separator and the ability to adsorb an electrolyte, it is difficult to block a polymer solution from penetrating the separator even with the polyolefin separator having the ceramic layer.

The present inventors have conducted intensive studies with respect to the problems occurring when a polyvinylidene fluoride polymer solution is prepared using a solvent having a high boiling point, and have found that: when a polyvinylidene fluoride polymer solution is prepared by using a high-boiling solvent, if a hydrophilic retardation layer is arranged between a porous base material (namely, a polyolefin porous membrane with a ceramic layer or without the ceramic layer) and a polyvinylidene fluoride polymer, the polyvinylidene fluoride polymer solution can be effectively inhibited from penetrating through the hydrophilic retardation layer to enter the porous base material, so that the amount of the polyvinylidene fluoride polymer entering the porous base material is effectively reduced, the air permeability and the porosity of a polymer diaphragm are improved, the body impedance of the polymer diaphragm is reduced, the ionic conductivity of the polymer diaphragm is improved, and the prepared lithium ion battery still has good performance. The present invention has been completed based on this finding.

According to a first aspect of the present invention, there is provided a polymer separator comprising a porous substrate, a hydrophilic retardation layer disposed between the porous substrate and the porous polar polymer bonding layer, and a porous polar polymer bonding layer having a pore diameter of 200nm to 20 μm.

According to a second aspect of the present invention, there is provided a method of preparing a polymer separator, the method comprising:

(1) applying a hydrophilic retardation slurry containing a dispersion medium, and hydrophilic inorganic particles and a binder dispersed in the dispersion medium, to at least one surface of a porous substrate to form a hydrophilic retardation coating, and optionally drying the hydrophilic retardation coating to form a hydrophilic retardation layer;

(2) coating a polar polymer binder solution on the surface of the hydrophilic retardation coating or the hydrophilic retardation layer to form a polar polymer binder coating, wherein the polar polymer binder solution contains an organic solvent, and a polar polymer binder and a pore-forming agent which are dispersed in the organic solvent;

(3) drying the hydrophilic retarding coating and the polar polymer binder coating to form a hydrophilic retarding layer and a porous polar polymer bonding layer, or drying the polar polymer binder coating to form a porous polar polymer bonding layer;

the pore-forming agent in the step (2) is a substance capable of forming gas under the drying condition in the step (3).

According to a third aspect of the present invention there is provided a polymeric separator produced by the process of the second aspect of the present invention.

According to a fourth aspect of the present invention there is provided the use of a polymer separator according to the first or third aspect of the present invention in a lithium ion battery.

According to a fifth aspect of the present invention, the present invention provides a lithium ion battery, which includes a positive electrode plate, a negative electrode plate and a polymer diaphragm, wherein the polymer diaphragm is the polymer diaphragm according to the first aspect or the third aspect of the present invention.

According to the preparation method of the polymer separator of the invention, when preparing the polar polymer binder solution, a low boiling point solvent (such as acetone) in the prior art can be adopted, a high boiling point solvent with higher operation safety can be adopted, and a mixture of the low boiling point solvent and the high boiling point solvent can be adopted. When the high-boiling-point solvent is adopted, the operation safety can be improved, and the performance of the lithium ion battery can not be obviously reduced.

Drawings

Fig. 1A and 1B are SEM topography pictures of the surface of the hydrophilic retardation layer of the polymer separator prepared in example 1-1, fig. 1A is a photograph magnified 500 times and fig. 1B is a photograph magnified 5000 times.

Fig. 2A and 2B are surface SEM topography pictures of the polymer separator prepared in example 2-1A, fig. 2A is a photograph at 500 x magnification, and fig. 2B is a photograph at 5000 x magnification.

Fig. 3A and 3B are surface SEM topography pictures of the polymer separator prepared in example 2-1B, fig. 3A is a photograph at 500 x magnification, and fig. 3B is a photograph at 5000 x magnification.

Fig. 4A and 4B are surface SEM topography pictures of the polymer separator prepared in comparative example 1, fig. 4A is a photograph magnified 500 times, and fig. 4B is a photograph magnified 5000 times.

Fig. 5A and 5B are surface SEM topography pictures of the polymer separator prepared in comparative example 3, fig. 5A is a photograph magnified 500 times, and fig. 5B is a photograph magnified 5000 times.

Fig. 6A and 6B are SEM morphology photographs of the polymer separator side (fig. 6A) and the positive electrode side (fig. 6B) after peeling the polymer separator prepared in example 2-1A from the positive electrode bonding contact surface.

Fig. 7A and 7B are SEM morphology photographs of the polymer separator side (fig. 7A) and the negative electrode side (fig. 7B) after peeling the polymer separator prepared in example 2-1A from the negative electrode bonding contact surface.

Fig. 8A and 8B are graphs showing peel strength test curves of the positive electrode and the polymer separator of the lithium ion batteries prepared in examples 2-1A (fig. 8A) and comparative example 1 (fig. 8B), respectively.

Fig. 9A and 9B are graphs of peel strength tests of the negative electrode and the polymer separator of the lithium ion batteries prepared in examples 2-1A (fig. 9A) and comparative example 1 (fig. 9B), respectively.

Detailed Description

The endpoints of the ranges and any values disclosed herein are not limited to the precise range or value, and such ranges or values should be understood to encompass values close to those ranges or values. For ranges of values, between the endpoints of each of the ranges and the individual points, and between the individual points may be combined with each other to give one or more new ranges of values, and these ranges of values should be considered as specifically disclosed herein.

According to a first aspect of the present invention, there is provided a polymer separator comprising a porous substrate, a hydrophilic retardation layer and a porous polar polymer bonding layer, the hydrophilic retardation layer being disposed between the porous substrate and the porous polar polymer bonding layer.

The hydrophilic retardation layer is a retardation layer having hydrophilic properties. According to the polymer membrane of the present invention, the contact angle of the hydrophilic retardation layer with water may be 40 ° or less, for example, 1 °, 2 °, 3 °, 4 °, 5 °, 6 °, 7 °, 8 °, 9 °, 10 °, 11 °, 12 °, 13 °, 14 °, 15 °, 16 °, 17 °, 18 °, 19 °, 20 °, 21 °, 22 °, 23 °, 24 °, 25 °, 26 °, 27 °, 28 °, 29 °, 30 °, 31 °, 32 °, 33 °, 34 °, 35 °, 36 °, 37 °, 38 °, 39 °, or 40 °. Preferably, the contact angle of the hydrophilic retardation layer with water is 20 ° or less. When the contact angle of the hydrophilic retardation layer with water is less than 20 degrees, the performance of the polymer diaphragm can be improved more obviously, for example: the air permeability and the ionic conductivity of the polymer diaphragm are improved more obviously, so that the lithium ion battery adopting the polymer diaphragm shows more excellent performance. More preferably, the hydrophilic retardation layer has a contact angle with water of 2 to 18 °, preferably 5 to 15 °. The contact angle is measured by the method specified in the measurement of the contact angle between the GB/T30693-2014 plastic film and water.

The hydrophilic retardation layer contains a binder and hydrophilic inorganic particles bonded to each other by the binder.

The hydrophilic inorganic particles are preferably hydrophilic Al₂O₃Hydrophilic SiO₂Hydrophilic SnO₂Hydrophilic ZrO₂Hydrophilic TiO 2₂Hydrophilic SiC and hydrophilic Si₃N₄Hydrophilic CaO, hydrophilic MgO, hydrophilic ZnO, and hydrophilic BaTiO₃Hydrophilic LiAlO₂And hydrophilic BaSO₄One or more than two of them. More preferably, the hydrophilic inorganic particles are hydrophilic Al₂O₃And/or hydrophilic SiO₂. Further preferably, the hydrophilic inorganic particles are gas-phase hydrophilic SiO₂Precipitation method of hydrophilic SiO₂And vapor phase hydrophilic Al₂O₃One or more than two of them.

The hydrophilic inorganic particles may have a particle size of 1nm to 10 μm, preferably 1nm to 5 μm. From the viewpoint of further improving the gas permeability and ionic conductivity of the polymer separator and the performance of a lithium ion battery using the polymer separator, the particle size of the hydrophilic inorganic particles is more preferably 10nm to 1 μm, still more preferably 20nm to 800nm, and still more preferably 50nm to 350 nm. The particle size is the volume average particle size and is measured by a laser particle sizer.

The hydrophilic inorganic particles may have a specific surface area of 10 to 600m²(ii) in terms of/g. From the viewpoint of further improving the air permeability and ionic conductivity of the polymer separator and the performance of the lithium ion battery using the polymer separator, the specific surface area of the hydrophilic inorganic particles is preferably 100-500m²(ii)/g, more preferably 150-²(ii)/g, more preferably 200- & lt 400 & gt²(ii)/g, more preferably 250-²Per g, particularly preferably 300-²(ii) in terms of/g. The specific surface area is measured by the method specified in the method for measuring the specific surface area of the solid substance by using the GB/T19587-2004 gas adsorption BET method.

According to the polymer separator of the present invention, the content of the hydrophilic inorganic particles may be 50 to 95% by weight, preferably 70 to 95% by weight, more preferably 80 to 95% by weight, and still more preferably 85 to 95% by weight, based on the total amount of the hydrophilic retardation layer.

The binder serves to bind and fix the hydrophilic inorganic particles, and further improves the electrolyte adsorption capacity of the polymer separator. The binder is preferably one or more of an acrylate-based polymer, a styrene-acrylate copolymer, polyvinylidene fluoride, a vinylidene fluoride-hexafluoropropylene copolymer, an acrylonitrile-acrylate copolymer, a vinyl chloride-acrylate copolymer, and a butadiene-styrene copolymer.

According to the polymer separator of the present invention, the thickness of the hydrophilic retardation layer may be 0.1 to 3 μm, for example: 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2 μm, 2.1 μm, 2.2 μm, 2.3 μm, 2.4 μm, 2.5 μm, 2.6 μm, 2.7 μm, 2.8 μm, 2.9 μm, or 3 μm. Preferably, the thickness of the hydrophilic retardation layer is 0.1 to 1 μm, more preferably 0.3 to 0.8 μm.

According to the polymer separator of the present invention, the porous substrate contains a porous polymer layer, which can be used to swell the liquid electrolyte and transport lithium ions. Preferably, the porous polymer layer is a porous polyolefin layer, such as one or more of a porous Polyethylene (PE) layer, a Porous Polypropylene (PP) layer, a porous polyethylene and porous polypropylene composite layer. The porous polyethylene and porous polypropylene composite layer can be a PE/PP/PE composite substrate layer.

According to the polymer separator of the present invention, the thickness of the porous polymer layer may be 1 to 50 μm, preferably 5 to 20 μm, and more preferably 8 to 15 μm.

According to the polymer separator of the present invention, the porous substrate may further include a ceramic layer for improving thermal stability, mechanical properties, and electrolyte adsorption capacity of the porous polymer layer. The ceramic particles in the ceramic layer may be made of Al₂O₃、SiO₂、SnO₂、ZrO₂、TiO₂、SiC、Si₃N₄、CaO、MgO、ZnO、BaTiO₃、LiAlO₂And BaSO₄One or more than two of the ceramic particles are formed by sintering. Generally, the thickness of the ceramic layer may be 1 to 5 μm, preferably 1.5 to 3 μm. Preferably, the thickness of the ceramic layer is greater than the thickness of the hydrophilic retarding layer.

When the polymer separator according to the present invention includes a ceramic layer, the ceramic layer may be disposed between the porous polymer layer and the hydrophilic retardation layer, or the porous polymer layer may be disposed between the ceramic layer and the hydrophilic retardation layer, or a combination thereof.

According to the polymer separator, the porous polar polymer bonding layer is used for reducing the shrinkage ratio of the porous substrate near the melting temperature, plays a role in bonding, bonds the polymer separator and the positive electrode or the negative electrode of the battery together, and can also improve the electrolyte adsorption capacity of the porous substrate. The polar polymer in the porous polar polymer bonding layer may be a polar polymer capable of performing the above-described function, and specific examples thereof may include, but are not limited to, one or more of polyvinylidene fluoride (PVdF), a copolymer of vinylidene fluoride and hexafluoropropylene (P (VdF-HFP)), and a copolymer of vinylidene fluoride and an acrylate.

The thickness of the porous polar polymer adhesive layer may be 0.1 to 10 μm, preferably 0.2 to 5 μm, more preferably 0.7 to 3 μm, and further preferably 0.8 to 1.5 μm.

According to the polymer separator of the present invention, the pores in the porous polar polymer bonding layer include pores having a first pore size of 5 to 20 μm and pores having a second pore size of 200nm to 2 μm. Preferably, the first pore size is 5-10 μm and the second pore size is 200nm-2 μm. According to the invention, the porous polar polymer bonding layer in the polymer diaphragm has a two-stage pore diameter structure, the inventor of the invention finds that the large pore diameter can reduce the contact area between the polymer diaphragm and the positive and negative electrode surfaces and does not block the transmission of lithium ions, but the too large pore diameter can cause the poor strength of the bonding layer, the poor uniformity of the pore morphology on the bonding layer, and the poor conductivity and adhesion between the polymer diaphragm and the positive and negative electrodes; the small aperture can improve the uniformity of the pore morphology, ensure the strength of the bonding layer, further improve the conductivity and the adhesiveness between the polymer diaphragm and the anode and the cathode, but the too small adhesion can block the transmission of lithium ions and influence the performance of the battery. The porous polar polymer bonding layer provided by the application is combined to effectively solve the technical problem, and the battery performance is further improved.

Preferably, the porosity of the porous polar polymeric tie layer is 20-80%.

Preferably, the porous polar polymer bonding layer comprises through holes that pass through the porous polar polymer bonding layer.

In the invention, the pore diameter in the porous polar polymer bonding layer is qualitatively determined according to SEM images of the surface of the bonding layer; the porosity of the porous polar polymer bonding layer is obtained by immersing the diaphragm into n-butanol solvent with known density by adopting an n-butanol absorption method, and calculating the void volume occupied by liquid of the diaphragm by measuring the mass difference before and after the diaphragm is immersed to be used as the porosity of the diaphragm.

According to the polymer separator of the present invention, the hydrophilic retardation layer and the porous polar polymer adhesive layer may be provided on one surface of the porous substrate or on both surfaces of the porous substrate. Preferably, the porous polar polymeric tie layer is attached to a surface of the hydrophilic retardation layer.

The polymer separator according to the present invention, in one embodiment, is composed of a porous substrate, which is a porous polymer layer, a hydrophilicity-retarding layer, and a porous polar polymer adhesive layer. The hydrophilic retarding layer is attached to the surface of the porous substrate, and the porous polar polymer bonding layer is attached to the surface of the hydrophilic retarding layer. According to this embodiment, the hydrophilic retardation layer and the porous polar polymer adhesive layer may be sequentially provided on one surface of the porous substrate (i.e., the polymer separator has the structure of the porous polymer layer | hydrophilic retardation layer | porous polar polymer adhesive layer), or the hydrophilic retardation layer and the porous polar polymer adhesive layer may be sequentially provided on each of two opposite surfaces of the porous substrate (i.e., the polymer separator has the structure of the porous polar polymer adhesive layer | hydrophilic retardation layer | porous polymer layer | hydrophilic retardation layer | porous polar polymer adhesive layer).

According to the polymer separator of the present invention, in another embodiment, the polymer separator is composed of a porous substrate composed of a porous polymer layer and a ceramic layer, a hydrophilicity-retarding layer, and a porous polar polymer bonding layer. According to this embodiment, in one example, the ceramic layer is attached to a surface of the porous polymer layer, the hydrophilic retardation layer is attached to a surface of the ceramic layer, and the porous polar polymer bonding layer is attached to a surface of the hydrophilic retardation layer (i.e., the polymer separator has a structure of porous polymer layer | ceramic layer | hydrophilic retardation layer | porous polar polymer bonding layer). In another example, the porous polymer layer is attached to the surface of the ceramic layer, the hydrophilic blocking layer is attached to the surface of the porous polymer layer, and the porous polar polymer bonding layer is attached to the surface of the hydrophilic blocking layer (i.e., the polymer separator has a structure of the ceramic layer | porous polymer layer | hydrophilic blocking layer | porous polar polymer bonding layer). In yet another example, the ceramic layer is attached to a surface of the porous polymer layer, and the ceramic layer and the other surface of the porous polymer layer are each sequentially attached with a hydrophilicity-retarding layer and a porous polar polymer bonding layer (i.e., the polymer separator has a structure of porous polar polymer bonding layer | hydrophilicity-retarding layer | ceramic layer | hydrophilicity-retarding layer | porous polar polymer bonding layer |).

The total thickness of the polymer separator according to the present invention may be conventionally selected and may be generally 5 to 50 μm, preferably 8 to 30 μm, and more preferably 10 to 20 μm.

The polymer membrane has high air permeability. Generally, the polymer membrane according to the present invention has a Gurley value of 100-. Further preferably, the polymer membrane has a Gurley value of 150-350Sec/100mL, such as 200-300Sec/100 mL.

Compared with the ceramic layer used for improving the thermal stability and the electrolyte adsorption capacity of the existing polymer diaphragm, the hydrophilicity retardation layer in the polymer diaphragm provided by the invention has stronger hydrophilicity, and can effectively retard polar polymers from entering a porous base material in the preparation process. Compared with the existing polymer diaphragm, the polymer diaphragm provided by the invention has the advantages that the pore diameter of the pores in the porous polar polymer bonding layer is larger (the pore diameter in the porous polar polymer bonding layer of the existing polymer diaphragm is usually 0.5-1 μm, the pore diameter in the porous polar polymer bonding layer of the polymer diaphragm provided by the invention can be more than 3 μm and usually 3-10 μm), the porous polar polymer bonding layer is of a multilayer silk screen interweaved structure, and part of the surface of the hydrophilic retardation layer is exposed and visible through the multilayer silk screen interweaved structure; however, the porous polar polymer bonding layer in the existing polymer diaphragm is more compact and honeycomb-shaped.

(1) applying a hydrophilic retarding slurry to at least one surface of a porous substrate to form a hydrophilic retarding coating, and optionally drying the hydrophilic retarding coating to form a hydrophilic retarding layer;

(2) coating a polar polymer binder solution on the surface of the hydrophilic retardation coating or the hydrophilic retardation layer to form a polar polymer binder coating;

(3) and drying the hydrophilic retarding coating and the polar polymer binder coating to form a hydrophilic retarding layer and a porous polar polymer bonding layer, or drying the polar polymer binder coating to form a porous polar polymer bonding layer.

The porous substrate can be a porous polymer film, and can also be a composite film of the porous polymer film and a ceramic film. The porous polymer film is preferably a porous polyolefin film, more preferably a porous polyethylene film, a porous polypropylene film, a porous polyethylene and a porous polypropylene composite film. The porous polyethylene and polypropylene composite membrane can be a PE/PP/PE composite membrane. The ceramic in the ceramic film may be made of Al₂O₃、SiO₂、SnO₂、ZrO₂、TiO₂、SiC、Si₃N₄、CaO、MgO、ZnO、BaTiO₃、LiAlO₂And BaSO₄One or more than two of the ceramic particles are formed by sintering. In the composite membrane, the thickness of the porous polymer membrane may be 1 to 50 μm, preferably 5 to 20 μm, and more preferably 8 to 15 μm. The thickness of the ceramic film may be 1 to 5 μm, preferably 1.5 to 3 μm.

In the step (1), the hydrophilic retardation slurry contains a dispersion medium, and hydrophilic inorganic particles and a binder dispersed in the dispersion medium.

The hydrophilic inorganic particles may have a particle size of 1nm to 10 μm, preferably 1nm to 5 μm. From the viewpoint of further improving the gas permeability and ionic conductivity of the finally prepared polymer separator, and the performance of a lithium ion battery using the polymer separator, the particle size of the hydrophilic inorganic particles is more preferably 1nm to 2 μm, still more preferably 10nm to 1 μm, still more preferably 20nm to 800nm, and particularly preferably 50nm to 350 nm.

The hydrophilic inorganic particles may have a specific surface area of 10 to 600m²(ii) in terms of/g. From the viewpoint of further improving the air permeability and ionic conductivity of the finally prepared polymer separator and the performance of a lithium ion battery using the polymer separator, the specific surface area of the hydrophilic inorganic particles is preferably 100-500m²(ii)/g, more preferably 150-²(ii)/g, more preferably 200- & lt 400 & gt²(ii)/g, more preferably 250-²Per g, particularly preferably 300-²/g。

Specific examples of the hydrophilic inorganic particles may include, but are not limited to, hydrophilic Al₂O₃Hydrophilic SiO₂Hydrophilic SnO₂Hydrophilic ZrO₂Hydrophilic TiO 2₂Hydrophilic SiC and hydrophilic Si₃N₄Hydrophilic CaO, hydrophilic MgO, hydrophilic ZnO, and hydrophilic BaTiO₃Hydrophilic LiAlO₂And hydrophilic BaSO₄One or more than two of them. Preferably, the hydrophilic inorganic particles are hydrophilic Al₂O₃And/or hydrophilic SiO₂. More preferably, the hydrophilic inorganic particles are gas phase hydrophilic SiO₂Precipitation method of hydrophilic SiO₂And vapor phase hydrophilic Al₂O₃One or more than two of them.

In the hydrophilic retardation slurry, the binder is preferably one or more of an acrylate-based polymer, a styrene-acrylate copolymer, polyvinylidene fluoride, a vinylidene fluoride-hexafluoropropylene copolymer, an acrylonitrile-acrylate copolymer, a vinyl chloride-acrylate copolymer, and a butadiene-styrene copolymer.

In the hydrophilic retardation slurry, the dispersion medium may be selected according to the types of the hydrophilic inorganic particles and the binder, so that the hydrophilic inorganic particles and the binder form a uniform and stable slurry. Specific examples of the dispersion medium may include, but are not limited to, one or more of water, ethanol, isopropanol, cyclohexane, tetrahydrofuran, dichloromethane, and chloroform.

The hydrophilic retardation slurry may contain the hydrophilic inorganic particles in an amount of 50 to 95% by weight, preferably 70 to 95% by weight, more preferably 80 to 95% by weight, and still more preferably 85 to 95% by weight. The amount of the binder may be selected according to the amount of the hydrophilic inorganic particles so that the hydrophilic inorganic particles can be bound and fixed. Generally, the binder may be contained in the hydrophilic retardation slurry in an amount of 1 to 30 parts by weight, preferably 2 to 25 parts by weight, and more preferably 5 to 20 parts by weight, relative to 100 parts by weight of the hydrophilic inorganic particles.

The hydrophilic retarding slurry may also contain a dispersant to further increase the stability of the hydrophilic retarding slurry. The dispersant may be a common substance that can promote dispersibility of the inorganic particles in the liquid medium, and specific examples thereof may include, but are not limited to, polyvinyl alcohol (PVA) and/or sodium polyacrylate (PAANa). The amount of the dispersant may be conventionally selected. Generally, the dispersant may be used in an amount of 0.1 to 10 parts by weight, preferably 0.2 to 5 parts by weight, more preferably 0.3 to 2 parts by weight, relative to 100 parts by weight of the hydrophilic inorganic particles.

The hydrophilic retarding slurry may also contain a thickener to further enhance the coatability of the hydrophilic retarding slurry. The thickener may be a cellulose-based thickener and/or a polyacrylate-based alkali-swellable thickener (e.g., a basf latex D thickener). The thickener may be used in an amount of 0.1 to 10 parts by weight, preferably 0.5 to 5 parts by weight, and more preferably 0.8 to 2 parts by weight, relative to 100 parts by weight of the hydrophilic inorganic particles.

Preferably, the pH of the hydrophilic retarding slurry is adjusted to alkaline, preferably 8-10.

The solids content of the hydrophilic retardation slurry is preferably 2 to 30% by weight, more preferably 5 to 25% by weight.

The amount of the hydrophilic retarding slurry applied to the surface of the porous substrate can be selected according to the desired thickness of the hydrophilic retarding layer. Typically, the hydrophilic retarding slurry is applied in an amount such that the thickness of the hydrophilic retarding layer is from 0.1 to 3 μm, for example: 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2 μm, 2.1 μm, 2.2 μm, 2.3 μm, 2.4 μm, 2.5 μm, 2.6 μm, 2.7 μm, 2.8 μm, 2.9 μm, or 3 μm. Preferably, the hydrophilic retardation slurry is coated in such an amount that the thickness of the hydrophilic retardation layer is 0.1 to 1 μm, more preferably 0.3 to 0.8 μm.

In the step (1), the hydrophilic retardation coating may be dried to form a hydrophilic retardation layer and then coated with a polar polymer binder solution, or the hydrophilic retardation coating may be directly coated with a polar polymer binder solution on the surface of the hydrophilic retardation coating without being dried. Preferably, the hydrophilic retardation coating is dried to form a hydrophilic retardation layer, and then a polar polymer binder solution is applied, so that the air permeability and the ionic conductivity of the finally prepared polymer separator can be further improved, and the performance of a lithium ion battery using the polymer separator can be further improved.

In the step (1), the drying temperature may be 10 to 120 ℃. Preferably, the temperature of the drying is not higher than 100 ℃. More preferably, the drying temperature is not higher than 80 ℃, for example, 10-80 ℃, specifically 10 ℃, 15 ℃, 20 ℃, 25 ℃, 30 ℃, 35 ℃, 40 ℃, 45 ℃, 50 ℃, 55 ℃, 60 ℃, 65 ℃, 70 ℃, 75 ℃, or 80 ℃. Preferably, the temperature of the drying is 40-60 deg.C, such as 50-60 deg.C. In the step (1), the drying may be performed under normal pressure or under reduced pressure. Preferably, the drying is carried out at atmospheric pressure. The drying may be carried out in a forced air drying cabinet. In the step (1), the duration of the drying may be selected according to the temperature of the drying and the kind of the dispersant used. In general, the duration of the drying in step (1) may be from 0.1 to 24 hours, preferably from 5 to 18 hours, more preferably from 8 to 15 hours.

According to the method of the invention, the contact angle of the hydrophilic retardation layer with water may be 40 ° or less, e.g. 1 °, 2 °, 3 °, 4 °, 5 °, 6 °, 7 °, 8 °, 9 °, 10 °, 11 °, 12 °, 13 °, 14 °, 15 °, 16 °, 17 °, 18 °, 19 °, 20 °, 21 °, 22 °, 23 °, 24 °, 25 °, 26 °, 27 °, 28 °, 29 °, 30 °, 31 °, 32 °, 33 °, 34 °, 35 °, 36 °, 37 °, 38 °, 39 °, or 40 °. Preferably, the contact angle of the hydrophilic retardation layer with water is 20 ° or less. When the contact angle of the hydrophilic retardation layer with water is less than 20 degrees, the performance of the polymer diaphragm can be improved more obviously, for example: the air permeability and the ionic conductivity of the polymer diaphragm are improved more obviously, so that the lithium ion battery adopting the polymer diaphragm shows more excellent performance. More preferably, the hydrophilic retardation layer formed in step (1) has a contact angle with water of 2 to 18 °, more preferably 5 to 15 °.

In the step (2), the polar polymer binder solution contains an organic solvent, and a polar polymer binder and a pore-forming agent dispersed in the organic solvent.

The polar polymer binder may be one or more of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, and a copolymer of vinylidene fluoride and acrylate.

The organic solvent may be a low boiling point organic solvent (an organic solvent having a boiling point of less than 60 ℃), such as acetone; a high boiling point solvent, for example, a solvent having a boiling point of 60 ℃ or higher; it may also be a mixture of a low boiling point solvent and a high boiling point solvent. For the mixture of the low-boiling solvent and the high-boiling solvent, it is preferable to control the content of the low-boiling solvent to be not higher than the safety threshold at which the explosion occurs, from the viewpoint of further improving the safety of the operation.

In one embodiment, the organic solvent is a low boiling point solvent, preferably acetone. According to the embodiment, under the preferable conditions, the prepared polymer diaphragm and the lithium ion battery show more excellent performances, and particularly the lithium ion battery prepared by the polymer diaphragm shows obviously improved high-rate discharge performance and high-temperature performance. The preferred conditions include: the hydrophilic inorganic particles preferably have a particle diameter of 1nm to 2 μm, more preferably 10nm to 1 μm, further preferably 20nm to 800nm, still further preferably 50nm to 350nm, the contact angle of the hydrophilic retardation layer with water is preferably 20 ° or less, and the drying in step (2) is performed at a temperature of not higher than 60 ℃.

In another embodiment, the organic solvent is a high boiling point solvent, such as an organic solvent having a boiling point of 60 ℃ or higher (e.g., 60-260 ℃), preferably an organic solvent having a boiling point of 120 ℃ or higher (e.g., 120-260 ℃), and more preferably an organic solvent having a boiling point of 140 ℃ or higher (e.g., 140-260 ℃). Further preferably, the boiling point of the organic solvent is 145-260 ℃, such as 150-230 ℃. Specific examples of the organic solvent may include, but are not limited to, one or more of triethyl phosphate, N-methylpyrrolidone, N-dimethylacetamide, N-dimethylformamide, and dimethylsulfoxide. According to this embodiment, the operational safety can be improved.

In yet another embodiment, the organic solvent is a mixture of a low boiling point solvent and a high boiling point solvent. The low boiling point solvent and the high boiling point solvent are each the same as described above. In this embodiment, the content of the high-boiling solvent may be 0.1 to 99.9% by weight, preferably 20 to 90% by weight, more preferably 40 to 70% by weight, and still more preferably 45 to 55% by weight, based on the total amount of the organic solvent; the content of the low-boiling solvent may be 0.1 to 99.9% by weight, preferably 10 to 80% by weight, more preferably 30 to 60% by weight, and still more preferably 45 to 55% by weight.

The pore-forming agent is a substance capable of forming volatile gas under the drying condition in the step (3). And (3) adopting a substance capable of forming volatile gas under the drying condition in the step (3) as a pore-forming agent, and assisting pore formation on the basis of pore formation of the organic solvent during drying in the step (3). The pore-forming agent is preferably a substance that is solid at the application temperature and forms a volatile gas under dry conditions. The pore former is more preferably dry ice.

In the polar polymer binder solution, the weight ratio of the pore-forming agent may be 0.5 to 5 parts by weight, preferably 0.8 to 3 parts by weight, and more preferably 1 to 2 parts by weight, relative to 100 parts by weight of the organic solvent.

In step (2), the concentration of the polar polymeric binder in the polar polymeric binder solution is 1 to 30% by weight, preferably 2 to 25% by weight. The concentration of the polar polymer binder in the polar polymer binder solution is more preferably 5 to 20% by weight from the viewpoint of further improving the properties of the finally prepared polymer separator and the properties of a lithium ion battery using the polymer separator. Further preferably, the concentration of polar polymeric binder in the polar polymeric binder solution is a critical concentration (typically 8-15 wt%, preferably 10-12 wt%). The critical concentration is a concentration at which the polar polymer binder solution permeates the porous substrate, and the critical concentration is a concentration between a concentration at which the polar polymer binder solution permeates the porous substrate and a concentration at which the polar polymer binder solution does not permeate the porous substrate, wherein the polar polymer binder solution is applied to one surface of the porous substrate in an environment of 25 ℃, 1 standard atmospheric pressure, and RH 45% to 55%, and whether the polar polymer binder solution permeates the porous substrate within 1 hour is observed. When the concentration of the polar polymer binder is critical concentration, the polar polymer binder is in a gel state in a solution on a microscopic scale, and a single molecule is difficult to flow and diffuse, so that the interaction between polar polymer molecules can be enhanced, an ideal physical cross-linked network structure is formed in the solvent evaporation process, and the polymer diaphragm has more excellent air permeability and ionic conductivity, and a lithium ion battery adopting the polymer diaphragm has more excellent performance.

The amount of the polar polymer binder solution applied may be selected according to the desired thickness of the polar polymer adhesive layer. The polar polymer binder solution may be applied in such an amount that the thickness of the finally formed porous polar polymer adhesive layer is 0.1 to 10 μm, preferably 0.2 to 5 μm, more preferably 0.7 to 3 μm, and still more preferably 0.8 to 1.5 μm.

In the step (3), the drying may be performed at a temperature of not higher than 120 ℃. Preferably, the drying is carried out at a temperature not higher than 60 ℃, and may be from 10 to 60 ℃, for example: 10 deg.C, 15 deg.C, 20 deg.C, 25 deg.C, 30 deg.C, 35 deg.C, 40 deg.C, 45 deg.C, 50 deg.C, 55 deg.C, or 60 deg.C. The polar polymer bonding layer can have a more excellent pore structure by drying at the temperature of not higher than 60 ℃, so that the air permeability and the ionic conductivity of the finally prepared polymer diaphragm can be further improved, and the performance of a lithium ion battery adopting the polymer diaphragm is further improved. More preferably, the drying is carried out at a temperature of 20-55 ℃. Further preferably, the drying is carried out at a temperature of 30-45 ℃. The duration of the drying may be selected according to the temperature of the drying. Specifically, the duration of the drying may be 0.1 to 36 hours, preferably 5 to 30 hours, more preferably 8 to 24 hours, and further preferably 10 to 24 hours.

In the step (1) and the step (2), one or a combination of two or more of conventional coating methods such as a roll coating method, a spray coating method, a dip coating method, and a screen printing method may be employed.

According to the method of the present invention, in the prepared polymer separator, the hydrophilic retardation layer and the porous polar polymer adhesive layer may be formed on one side of the porous substrate, or the hydrophilic retardation layer and the porous polar polymer adhesive layer may be formed on both sides of the porous substrate.

According to the method of the present invention, in one embodiment, the finally prepared polymer separator is composed of a porous substrate, a hydrophilic retardation layer and a porous polar polymer bonding layer, the porous substrate is a porous polymer film, the hydrophilic retardation layer is attached to the surface of the porous substrate, and the porous polar polymer bonding layer is attached to the surface of the hydrophilic retardation layer. According to this embodiment, the hydrophilic retardation layer and the porous polar polymer adhesive layer may be sequentially provided on one surface of the porous substrate (i.e., the polymer separator has the structure of the porous polymer film hydrophilic retardation layer porous polar polymer adhesive layer), or the hydrophilic retardation layer and the porous polar polymer adhesive layer may be provided on each of two opposite surfaces of the porous substrate (i.e., the polymer separator has the structure of the porous polar polymer adhesive layer hydrophilic retardation layer porous polymer film hydrophilic retardation layer porous polar polymer adhesive layer).

According to the method of the present invention, in another embodiment, the finally prepared polymer separator is composed of a porous substrate, which is a composite film of a porous polymer film and a ceramic film, a hydrophilic retardation layer, and a porous polar polymer adhesive layer. According to this embodiment, in one example, the ceramic membrane is attached to the surface of the porous polymer membrane, the hydrophilic retardation layer is attached to the surface of the ceramic membrane, and the porous polar polymer bonding layer is attached to the surface of the hydrophilic retardation layer (i.e., the polymer membrane has a structure of porous polymer membrane | ceramic membrane | hydrophilic retardation layer | porous polar polymer bonding layer). In another example, the porous polymer film is attached to the surface of the ceramic layer, the hydrophilic retardation layer is attached to the surface of the porous polymer film, and the porous polar polymer bonding layer is attached to the surface of the hydrophilic retardation layer (i.e., the polymer separator has a structure of ceramic membrane | porous polymer membrane | hydrophilic retardation layer | porous polar polymer bonding layer). In yet another example, a ceramic membrane is attached to a surface of a porous polymer membrane, and the other surface of the ceramic membrane and the porous polymer membrane are each attached in sequence with a hydrophilic retardation layer and a porous polar polymer bonding layer (i.e., a polymer separator membrane has a structure of porous polar polymer bonding layer hydrophilic retardation layer ceramic membrane porous polymer membrane hydrophilic retardation layer porous polar polymer bonding layer).

The total thickness of the polymer separator prepared by the method according to the second aspect of the present invention may be conventionally selected and may be generally 5 to 50 μm, preferably 8 to 30 μm, and more preferably 10 to 20 μm.

The polymer membrane prepared by the method of the second aspect of the present invention has high gas permeability. Generally, the polymer membrane prepared by the method of the second aspect of the present invention has a Gurley value of 100-900Sec/100mL, preferably 120-600Sec/100mL, and more preferably 120-500Sec/100 mL. Further preferably, the polymer membrane prepared by the method of the second aspect of the present invention has a Gurley value of 150-350Sec/100mL, such as 200-300Sec/100 mL.

According to a fifth aspect of the present invention, the present invention provides a lithium ion battery, including a positive electrode plate, a negative electrode plate, and a polymer separator, wherein the polymer separator is the polymer separator according to the first aspect or the third aspect of the present invention.

The positive pole piece is prepared by mixing a positive pole material for the lithium ion battery, a conductive agent and a binder into slurry and coating the slurry on an aluminum foil. The positive electrode material used includes any positive electrode material that can be used in lithium ion batteries, for example, lithium cobalt oxide (LiCoO)₂) Lithium nickel oxide (LiNiO)₂) Lithium manganese oxide (LiMn)₂O₄) And lithium iron phosphate (LiFePO)₄) One or more than two of them. The negative pole piece is prepared by mixing a negative pole material for the lithium ion battery, a conductive agent and a binder into slurry and coating the slurry on a copper foil. The negative electrode material used includes any negative electrode material usable for lithium ion batteries, for example, one or two or more of graphite, soft carbon, and hard carbon.

The lithium ion battery of the present invention may or may not contain an electrolyte solution. The electrolyte is well known to those skilled in the art and contains a lithium salt and an organic solvent. The lithium salt may be a dissociable lithium salt, and may be, for example, selected from lithium hexafluorophosphate (LiPF)₆) Lithium perchlorate (LiClO)₄) And lithium tetrafluoroborate (LiBF)₄) One or more than two of them. The organic solvent may be one or more selected from Ethylene Carbonate (EC), Propylene Carbonate (PC), dimethyl carbonate (DMC), Ethyl Methyl Carbonate (EMC), diethyl carbonate (DEC) and Vinylene Carbonate (VC). Preferably, the concentration of the lithium salt in the electrolyte may be 0.8 to 1.5 mol/L.

The lithium ion battery according to the present invention may be prepared by a method comprising the steps of:

s1, preparing a polymer separator by the method according to the second aspect of the present invention;

and S2, arranging the polymer diaphragm between the positive pole piece and the negative pole piece to form a battery pole core, and then packaging.

Step S2 can be performed by a conventional method in the technical field of lithium ion battery preparation, and the present invention is not particularly limited thereto. In step S2, the battery pole core may be filled with the electrolyte, or may be directly packaged without being filled with the electrolyte.

The present invention will be described in detail with reference to examples, but the scope of the present invention is not limited thereto.

The following examples and comparative examples relate to the following test methods.

(1) The areal density is determined gravimetrically.

(2) The contact angle between the hydrophilic retardation layer and water is determined by the method specified in the GB/T30693-2014 plastic film contact angle measurement.

(3) The particle size is determined by a laser particle sizer and is a volume average particle size.

(4) Specific surface area the method specified in GB/T19587-2004 gas adsorption BET method for determining the specific surface area of a solid substance was used.

Examples 1-1 to 1-4 were used to prepare a hydrophilic retardation layer according to the present invention.

Examples 1 to 1

Hydrophilic silica (specific surface area 380 m) prepared by gas phase method²(ii)/g, particle size 80nm, from alatin), acrylate binder (P1005, from shanghai advanced chemical company, ltd.), dispersant (PVA, from alatin), dispersant (PAANa, from showa and electrician), carboxymethyl cellulose (CMC, from xylonite) as thickener, in a solid content of 95: 5: 0.4: 0.4: 1.5 (weight ratio) is dispersed in water, the solid content is controlled to be 8 weight percent, the pH value of the slurry is adjusted to be 8.5, and the slurry is stirred uniformly to form hydrophilic retardation slurry. The hydrophilic retardation slurry is coated on two sides of a single-sided ceramic diaphragm (a 9 mu mPE +2 mu m ceramic layer, wherein the ceramic particles in the ceramic layer are micron-sized aluminum oxide ceramic particles and are purchased from Shandong China, the same below) by a gravure roll coating method, and the diaphragm with the hydrophilic retardation layer is obtained after drying for 12 hours at 55 ℃, wherein the thickness of the hydrophilic retardation layer is 0.5 mu m, and the contact angle between the hydrophilic retardation layer and water is 7 degrees. FIG. 1A and FIG. 1BFIG. 1B shows SEM topography of the hydrophilic retardation layer

Examples 1 to 2

Hydrophilic silica (specific surface area 370 m) prepared by precipitation²Per g, particle size 150nm, from alatin), acrylate binder (P1005, from shanghai advanced chemical industries, ltd), dispersant (PVA), dispersant (PAANa), thickener latex D (from basf) at a solids content of 95: 8: 0.4: 0.4: 1.0 (weight ratio) in water, controlling the solid content of the slurry to be 6 weight percent, adjusting the pH value of the slurry to be 9.6, and uniformly stirring to form the hydrophilic retardation slurry. And (3) coating the hydrophilic retardation slurry on two sides of the single-sided ceramic diaphragm by a gravure roll coating method, and drying at 50 ℃ for 14 hours to obtain the diaphragm with the hydrophilic retardation layer, wherein the thickness of the hydrophilic retardation layer is 0.7 mu m, and the contact angle between the hydrophilic retardation layer and water is 11 degrees.

Examples 1 to 3

Hydrophilic aluminum oxide (specific surface area is 350 m) prepared by gas phase method²(ii)/g, particle size 200nm, from alatin), acrylate binder (P2010, from shanghai chemical co., ltd), dispersant (PVA), dispersant (PAANa), thickener latex D (from basf) at a solids content of 95: 10: 0.4: 0.4: 1.4 (weight ratio) in water, controlling the solid content of the slurry to be 22 weight percent, adjusting the pH value of the slurry to be 8.2, and uniformly stirring to form the hydrophilic retardation slurry. And (3) coating the hydrophilic retardation slurry on two sides of the single-sided ceramic diaphragm by a spraying method, and drying at 50 ℃ for 8 hours to obtain the diaphragm with the hydrophilic retardation layer, wherein the thickness of the hydrophilic retardation layer is 0.6 mu m, and the contact angle between the hydrophilic retardation layer and water is 13 degrees.

Examples 1 to 4

Hydrophilic alumina (specific surface area of 320 m) prepared by gas phase method²(ii)/g, particle size 320nm, from alatin), acrylate binder (P2010, from shanghai chemical co., ltd), dispersant (PVA), dispersant (PAANa), thickener latex D (from basf) at a solids content of 95: 12: 0.4: 0.4: 0.8 (weight ratio) was dispersed in water, and the solid content of the slurry was controlled to 15% by weightThe pH value of the node slurry is 9.5, and the node slurry is uniformly stirred to form hydrophilic retardation slurry. And (3) coating the hydrophilic retardation slurry on two sides of the single-sided ceramic diaphragm by a gravure roll coating method, and drying at 50 ℃ for 12 hours to obtain the diaphragm with the hydrophilic retardation layer, wherein the thickness of the hydrophilic retardation layer is 0.8 mu m, and the contact angle between the hydrophilic retardation layer and water is 12 degrees.

The following examples were used to prepare polymer separators according to the present invention as well as lithium ion batteries.

Example 2-1A

(1) P (VdF-HFP) powder (Kynar powerflex LBG powder, available from arkema, same below) was dissolved in N, N-dimethylformamide with the concentration of P (VdF-HFP) controlled to the critical concentration (10 wt%), and stirred uniformly. The temperature of the solution formed by stirring was lowered to 20 ℃, and dry ice was added in an amount of 1 part by weight relative to 100 parts by weight of N, N-dimethylformamide, to obtain a polar polymer binder solution.

A polar polymer binder solution was coated on the surfaces of the hydrophilic retardation layers on both sides of the separator having the hydrophilic retardation layer prepared in example 1-1 by a gravure roll coating method, and air-dried at 45 ℃ for 10 hours to form a porous polar polymer adhesive layer, thereby obtaining a polymer separator according to the present invention.

(2) Subjecting LiCoO to condensation₂PVDF binder and carbon black according to the mass ratio of 100: 0.8: 0.5 mixing into slurry, coating on aluminum foil, and drying to obtain LiCoO with thickness of 0.114mm₂And (3) a positive pole piece.

Styrene Butadiene Rubber (SBR) and carboxymethyl cellulose (CMC) are dispersed in water, and the mass ratio of the Styrene Butadiene Rubber (SBR) to the artificial graphite and the conductive agent is 2.5: 1.5: 90: 6 stirring at room temperature (25 ℃) for 3.5 hours at high speed, coating the stirred material on copper foil and drying to prepare the graphite negative pole piece with the thickness of 0.135 mm.

(3) In a drying room, LiCoO is added₂Preparing the CSL454187 LiCoO type by winding the positive pole piece, the graphite negative pole piece and the polymer diaphragm prepared in the step (2)₂Filling electrolyte into the graphite soft package lithium ion battery pole core, and then packaging to obtain the lithium ion battery; wherein the original ceramic surface faces the anode and the electrolyteThe electrolyte in the electrolyte is lithium hexafluorophosphate, the concentration of the lithium hexafluorophosphate is 1mol/L, and the organic solvent is EC, EMC and DEC according to the weight ratio of 1: 1: 1 mixing the obtained mixed solution.

Example 2-1B

Example 2-1B a lithium ion battery was manufactured in the same manner as in example 2-1A, except that, in the step (1), a polar polymer binder solution was coated on the surface of the hydrophilic retardation layer on both sides of the separator having the hydrophilic retardation layer, which was manufactured in example 1-3, in a dip coating method, in which the separator having the hydrophilic retardation layer was dipped in the polar polymer binder solution for 30 seconds.

Example 2-2A

Example 2-2A lithium ion battery was manufactured in the same manner as in example 2-1A, except that a polymer separator was manufactured by the following method: p (VdF-HFP) powder was dissolved in N-methylpyrrolidone, and the concentration of P (VdF-HFP) was controlled to be the critical concentration (12% by weight), and the mixture was stirred uniformly. The temperature of the solution formed by stirring was lowered to 20 ℃, and dry ice was added in an amount of 1.5 parts by weight relative to 100 parts by weight of N-methylpyrrolidone, to obtain a polar polymer binder solution. A polar polymer binder solution was coated on the surfaces of the hydrophilic retardation layers on both sides of the separator having the hydrophilic retardation layer prepared in example 1-2, respectively, by a gravure roll coating method, and air-dried at 35 ℃ for 24 hours to form a porous polar polymer adhesive layer, thereby obtaining a polymer separator according to the present invention.

Examples 2 to 2B

Example 2-2B a lithium ion battery was manufactured in the same manner as in example 2-2A, except that, in the step (1), a polar polymer binder solution was coated on the surface of the hydrophilic retardation layer on both sides of the separator having the hydrophilic retardation layer, which was manufactured in example 1-4, in a dip coating method, in which the separator having the hydrophilic retardation layer was dipped in the polar polymer binder solution for 30 seconds.

Examples 2 to 3A

Examples 2-3A lithium ion battery was manufactured in the same manner as in example 2-1A, except that a polymer separator was manufactured by the following method: p (VdF-HFP) powder was dissolved in triethyl phosphate, and the concentration of P (VdF-HFP) was controlled to be the critical concentration (12% by weight), and the mixture was stirred uniformly. The temperature of the solution formed by stirring was lowered to 20 c, and dry ice was added in an amount of 1.8 parts by weight relative to 100 parts by weight of triethyl phosphate to obtain a polar polymer binder solution. A polar polymer binder solution was coated on the surfaces of the hydrophilic retardation layers on both sides of the separator having the hydrophilic retardation layer prepared in example 1-2 by a gravure roll coating method, and air-dried at 30 ℃ for 24 hours to form a porous polar polymer adhesive layer, thereby obtaining a polymer separator according to the present invention.

Examples 2 to 3B

Examples 2-3B a lithium ion battery was manufactured in the same manner as in examples 2-3A, except that, in the step (1), a polar polymer binder solution was coated on the surface of the hydrophilic retardation layer on both sides of the separator having the hydrophilic retardation layer manufactured in examples 1-3 by a dip coating method, in which the separator having the hydrophilic retardation layer was dipped in the polar polymer binder solution for 30 seconds.

Comparative example 1

A polymer separator and a lithium ion battery were manufactured in the same manner as in example 2-1A, except that, in step (1), the separator having the hydrophilic retardation layer was replaced with the single-sided ceramic separator (9 μmPE +2 μm ceramic layer) in example 1-1, i.e., the polar polymer binder solution was directly coated on both side surfaces of the single-sided ceramic separator, and N, N-dimethylformamide was replaced with acetone of an equal weight, to obtain a polymer separator (which did not have a hydrophilic retardation layer).

Comparative example 2

A polymer separator and a lithium ion battery were manufactured in the same manner as in examples 2-3B, except that, in the preparation of the polymer separator, the separator having the hydrophilic retardation layer was replaced with the single-sided ceramic separator (9 μmPE +2 μm ceramic layer) in examples 1-3, i.e., the polar polymer binder solution was directly coated on both side surfaces of the single-sided ceramic separator, and triethyl phosphate was replaced with equal weights of acetone, to obtain a polymer separator (which did not have the hydrophilic retardation layer).

Comparative example 3

A polymer separator and a lithium ion battery were prepared in the same manner as in example 2-1A, except that the polar polymer binder solution did not contain dry ice.

Comparative example 4

A polymer separator and a lithium ion battery were manufactured in the same manner as in example 2-1A, except that, in the preparation of the polymer separator, the separator having a hydrophilic retardation layer was replaced with the single-sided ceramic separator (9 μmPE +2 μm ceramic layer) in example 1-3, i.e., a polar polymer binder solution was directly applied to both side surfaces of the single-sided ceramic separator, to obtain a polymer separator (which did not have a hydrophilic retardation layer).

Example 3

A polymer separator and a lithium ion battery were produced in the same manner as in example 2-1B, except that, in the step (1), the air-blast drying was not carried out at 35 ℃ for 20 hours, but at 120 ℃ for 8 hours.

Example 4

A polymer separator and a lithium ion battery were manufactured in the same manner as in example 2-1B, except that the concentration of P (VdF-HFP) was controlled to be 4 wt% (non-critical concentration) when preparing the polar polymer binder solution.

Example 5

A polymer separator and a lithium ion battery were manufactured in the same manner as in example 2-1B, except that the concentration of P (VdF-HFP) was controlled to be 22 wt% (non-critical concentration) when preparing the polar polymer binder solution.

Example 6

A polymer separator and a lithium ion battery were manufactured in the same manner as in example 2-1B, except that N, N-dimethylformamide was replaced with acetone of equal weight in the preparation of the polar polymer binder solution.

Example 7

A polymer separator and a lithium ion battery were manufactured in the same manner as in example 2-1B, except that, in the preparation of the polar polymer binder solution, N-dimethylformamide was replaced with a mixed solution of acetone and N, N-dimethylformamide in an equal weight ratio of 1: 1.

example 8

A separator having a hydrophilic retardation layer was produced in the same manner as in example 1-1, except that in the step (1), quartz (specific surface area: 10 m) for hydrophilic silica was used in the vapor phase method²G, the particle diameter is 10 mu m), thereby obtaining the diaphragm with the hydrophilic retardation layer, and the contact angle between the formed hydrophilic retardation layer and water is 38 degrees; a polymer separator and a lithium ion battery were manufactured in the same manner as in example 2-1A, except that the separator having a hydrophilic retardation layer, which was manufactured in example 8, was used.

Example 9

A separator having a hydrophilic retardation layer was produced in the same manner as in examples 1 to 3, except that the vapor-phase hydrophilic alumina was alumina by the alumina alkoxide method (specific surface area: 130 m)²G, the particle diameter is 5 mu m), thereby obtaining the diaphragm with the hydrophilic retardation layer, and the contact angle between the formed hydrophilic retardation layer and water is 32 degrees; a polymer separator and a lithium ion battery were manufactured in the same manner as in example 2-1B, except that the separator having a hydrophilic retardation layer, which was manufactured in example 9, was used.

Example 10

Example 10 a lithium ion battery was manufactured in the same manner as in example 2-1B, except that, in the step (1), a polar polymer binder solution was applied to the surfaces of the hydrophilic retardation layers on both sides of the separator having the hydrophilic retardation layer manufactured in example 1-3 by a spray coating method.

Example 11

A polymer separator and a lithium ion battery were manufactured in the same manner as in example 10, except that the hydrophilic retardation slurry was coated on both sides of the single-sided ceramic separator in the same manner as in example 10 and then dried, but after spraying the polar polymer binder solution directly in the manner of example 10, the polymer separator was dried in the same manner as in example 10, thereby obtaining a polymer separator.

Test example

(1) Observation of surface morphology of polymer membrane:

the microscopic morphology of the polymer separators prepared in each example and comparative example was observed using a scanning electron microscope (SEM, JEOL, JSM-7600 FE).

Fig. 2A and 2B show SEM morphology photographs of the polymer separator prepared in example 2-1A, and fig. 3A and 3B show SEM morphology photographs of the polymer separator prepared in example 2-1B.

As can be seen from fig. 2A, 2B, 3A and 3B, the method of the present invention can prepare a porous polar polymer bonding layer with excellent porosity, and the surface of the prepared porous polar polymer bonding layer has a porous membrane layer. Fig. 4A and 4B show SEM morphology photographs of the polymer separator prepared in comparative example 1, and fig. 5A and 5B show SEM morphology photographs of the polymer separator prepared in comparative example 3.

As can be seen by comparing fig. 2A and 2B with fig. 4A and 4B, the pores in the porous polar polymer adhesive layer of the surface of the polymer separator according to the present invention include pores having a first pore size of 5 to 20 μm and pores having a second pore size of 200nm to 2 μm, and a part of the surface of the hydrophilic retardation layer is exposed to the view through the multi-layered wire mesh woven structure; the porous polar polymer bonding layer in the polymer separator prepared in comparative example 1 was dense and honeycomb-like.

As can be seen from comparing fig. 2A and 2B with fig. 5A and 5B, the pores in the porous polar polymer bonding layer of the polymer separator prepared by the method of the present invention include pores having a first pore size of 5 to 20 μm and pores having a second pore size of 200nm to 2 μm.

(2) Polymer membrane gas permeability (Gurley value) and apparent porosity test

The test was carried out using an air permeability apparatus of type Gurley 4110N. The time for 100mL of air to pass through a 1.0 square inch area of a polymeric septum at 1 standard atmosphere was tested.

The results of the test for the gas permeability of the polymer separator are shown in table 1.

As can be seen from the results of table 1, the polymer separator according to the present invention showed better gas permeability.

The apparent porosity of the polymer separator is calculated according to the following formula:

in the above formula, ρ M is an apparent density, ρ f is an areal density, ρ P is a bulk density, and d is a thickness of the polymer separator.

As can be seen from the data of table 1, the polymer separator according to the present invention has a high apparent porosity.

(3) Polymer membrane heat shrinkage test

Isothermal heat treatment is carried out on the polymer diaphragm (the area is 5mm multiplied by 5mm) for 2h and 1h by utilizing a constant temperature oven at the temperature of 90 ℃ and 120 ℃ respectively, and the temperature resistance of the polymer diaphragm is represented.

The experimental results are listed in table 1, and it can be understood from the results of table 1 that the polymer separator according to the present invention has a lower thermal shrinkage rate.

(4) Tensile Strength test of Polymer membranes

Measured using a universal mechanical tester according to the method specified in GB/T13022-.

The experimental results are shown in table 1, and it can be understood from the results of table 1 that the polymer separator according to the present invention has a high tensile strength.

(5) Polymer membrane puncture strength test

The diameter of the steel needle was 1 mm as determined by the method specified in GB/T1004-.

The experimental results are shown in table 1, and it can be seen from table 1 that the polymer separator according to the present invention has high puncture strength.

TABLE 1

¹: thickness of polymer separator²: single-side surface density of polar polymer coating on two surfaces of polymer diaphragm

(6) Polymer membrane ionic conductivity test

The test is carried out by adopting an alternating current impedance method, and the specific operation steps are as follows.

Cutting the polymer diaphragm into a wafer with the diameter of 17mm, drying, overlapping three layers, placing between two Stainless Steel (SS) electrodes, absorbing enough electrolyte (lithium hexafluorophosphate is used as electrolyte, the concentration of the lithium hexafluorophosphate is 1mol/L, organic solvent is mixed liquid obtained by mixing EC, EMC and DEC according to the weight ratio of 1: 1: 1), sealing in a 2016 type button cell, performing an alternating current impedance experiment by adopting an electrochemical workstation (CHI 660C), wherein the frequency range of an alternating current signal is 0.01Hz to 1MHz, the amplitude of a sine wave potential is 5mV, the intersection point of a linear axis and a real axis is the bulk resistance of the polymer diaphragm, and calculating the ionic conductivity of the polymer diaphragm by adopting the following formula:

σ＝L/(A·R)，

wherein L represents the thickness of the gel polymer electrolyte,

a is the contact area of the stainless steel plate and the polymer diaphragm,

r is the bulk resistance of the polymer electrolyte.

The bulk impedance and ionic conductivity of the polymer separator are shown in table 2.

As can be seen from table 2, the polymer separator according to the present invention exhibited excellent ionic conductivity.

TABLE 2

(7) Polymer separator testing for positive and negative electrode adhesion and peel strength

Dissecting the prepared lithium ion battery (subjected to 85 ℃, 4h and 1MPa hot pressing) in a full-electric state, measuring the peeling mechanical strength of the lithium ion battery by adopting a universal mechanical testing machine, and measuring the standard reference GBT 2792-2014 adhesive tape peeling strength; and the obtained positive and negative pole pieces and the diaphragm are photographed. Fig. 6A and 6B and fig. 7A and 7B respectively show SEM morphology photographs after peeling the positive electrode and the negative electrode of the lithium ion battery prepared in example 2-1A from the polymer separator, fig. 8A and 9A respectively show peel strength test graphs of the positive electrode and the negative electrode of the lithium ion battery prepared in example 2-1A, and fig. 8B and 9B respectively show peel strength test graphs of the positive electrode and the negative electrode of the lithium ion battery prepared in comparative example 1 for comparison.

As can be seen from fig. 6A and 6B and fig. 7A and 7B: after the lithium ion battery prepared by the polymer diaphragm is stripped, the porous polar polymer bonding layer of the polymer diaphragm is adhered to the anode material; part of the negative electrode material is adhered to the polymer separator.

As can be seen from fig. 8A and 8B, the polymer separator according to the present invention has high adhesion to both the positive electrode and the negative electrode of the lithium ion battery.

(8) Hardness test of lithium ion batteries

The test results are listed in table 3. As shown in table 3, the lithium ion battery according to the present invention has high hardness.

TABLE 3

(9) Test of normal temperature cycle performance of battery

The lithium ion batteries after capacity grading, prepared in the examples and the comparative examples, were subjected to 25 ℃ cycle performance testing using a (Guangzhou Lanqi, BK6016) lithium ion battery performance test cabinet, the specific method being as follows.

The battery is charged to 4.40V cut-off at 0.7C and 0.2C respectively; standing for 10min, and cooling to 3.0V at 0.7C or 0.2C, and circulating. The test results in table 4 show that: the lithium ion battery according to the present invention exhibits more excellent cycle performance.

TABLE 4

(10) High temperature cycle performance test of battery

The lithium ion batteries after capacity grading obtained in the examples and the comparative examples were tested for cycle performance at 45 ℃ by using a (Guangzhou Lanqi, BK6016) lithium ion battery performance test cabinet. The test method comprises the following steps: cut off the battery charging to 4.40V at 0.7C; standing for 10min, and cooling to 3.0V at 0.7C, and circulating. The cycling results are shown in Table 5.

The test result shows that: the lithium ion battery according to the present invention exhibits more excellent high temperature cycle performance. It can be seen that the polymer separator according to the present invention is advantageous in improving the high-temperature performance of a battery.

TABLE 5

(11) Battery rate capability test

The lithium ion batteries after capacity grading obtained in the examples and the comparative examples are subjected to rate discharge performance testing by adopting a (BK 6016, Guangzhou Lanqi) lithium ion battery performance testing cabinet. The specific test method is as follows.

The cell was charged to 4.40V with a constant current and voltage of 0.5C (1C-2640 mA), the cutoff current was 0.02C, left for 5min, discharged to 3.0V with 0.2C/0.5C/1C/2C/3C/4C, and the discharge capacity was recorded.

The results of the rate discharge test are shown in Table 6. The test result shows that the lithium ion battery provided by the invention has good rate discharge performance.

TABLE 6

(12) Battery high temperature storage performance test

The lithium ion batteries obtained in the examples and comparative examples were subjected to a storage performance test at 85 ℃ for 4 hours. The test method is as follows.

1) The battery was charged to 4.40V at 0.5C with a (guangzhou langqi, BK6016) li-ion battery performance test cabinet, cut-off at 0.02C; standing for 5min, discharging to 3.0V at 0.2C, and recording the discharge capacity before discharge;

2) the cell was charged to 4.40V at 0.5C, cut off at 0.02C; testing the voltage, the internal resistance and the thickness before standing for 1 h;

3) the battery is placed into an oven at 85 ℃ for storage for 4 h;

4) testing the thickness immediately after storage, and testing the cooling thickness, the post-voltage and the post-internal resistance after placing for 2 hours at normal temperature;

5) discharging the battery to 3.0V at 0.2C;

6) fully charged at 0.5C, left stand for 5min, discharged to 3.0V at 0.2C, the recovered capacity was recorded, and the capacity recovery ratio (recovered capacity divided by previous capacity) was calculated.

The test results are shown in Table 7. As can be seen from Table 7: the lithium ion battery provided by the invention has better capacity retention rate and capacity recovery rate after high-temperature storage. It can be seen that the polymer separator according to the present invention is advantageous in improving the high-temperature performance of a battery.

TABLE 7

Numbering	Recovery capacity (mAh)	Capacity recovery ratio (%)
			Example 2-1A	2587	98.0
Example 2-1B	2573	97.5
			Example 2-2A	2575	97.6
Examples 2 to 2B	2576	97.6
			Examples 2 to 3A	2582	97.8
Examples 2 to 3B	2581	97.7
			Comparative example 1	2267	87.2
Comparative example 2	2281	89.7
			Comparative example 3	2283	89.8
Comparative example 4	2151	81.5
			Example 3	2314	87.7
Example 4	2217	84.0
			Example 5	2236	84.7
Example 6	2573	97.5
			Example 7	2577	97.6
Example 8	2202	83.4
			Example 9	2237	84.7
Example 10	2252	85.3
			Example 11	2224	84.2

Comparing example 2-1A with comparative example 1 and comparative example 4, and comparing example 2-3B with comparative example 2, it can be seen that by providing a hydrophilic retardation layer, the prepared lithium ion battery has good rate discharge performance, and particularly shows significantly improved discharge performance under high rate discharge conditions, even when a polar polymer solution is prepared using a high boiling point solvent.

Comparing example 2-1B with example 3, it can be seen that drying the polar polymer binder coating at a temperature of not higher than 60 ℃ can significantly improve the air permeability and ionic conductivity of the prepared polymer separator, and significantly improve various properties of the finally prepared lithium ion battery. Comparing example 2-1B with examples 4 and 5, it can be seen that controlling the concentration of the polar polymer in the polar polymer binder solution to be the critical concentration can significantly improve the air permeability and ionic conductivity of the prepared polymer separator, and significantly improve various properties of the finally prepared lithium ion battery. Comparing examples 2-1A and 2-1B with examples 8 and 9, respectively, it can be seen that making the contact angle of the hydrophilic retardation layer with water not higher than 20 ° further improves the properties of the finally prepared lithium ion battery. Comparing example 10 with example 11, it can be seen that the hydrophilic retardation coating is dried and then coated with a polar polymer binder solution to form a polar polymer bonding layer, which can further improve the air permeability and ionic conductivity of the prepared polymer separator, thereby improving various properties of the finally prepared lithium ion battery.

The preferred embodiments of the present invention have been described above in detail, but the present invention is not limited thereto. Within the scope of the technical idea of the invention, many simple modifications can be made to the technical solution of the invention, including combinations of various technical features in any other suitable way, and these simple modifications and combinations should also be regarded as the disclosure of the invention, and all fall within the scope of the invention.

Claims

1. A lithium ion battery comprises a positive pole piece, a negative pole piece and a polymer diaphragm, wherein the positive pole material in the positive pole piece comprises one or more than two of cobalt lithium oxide, nickel lithium oxide, manganese lithium oxide and lithium iron phosphate, the negative pole material in the negative pole piece comprises one or more than two of graphite, soft carbon and hard carbon,

the polymer diaphragm is characterized by comprising a porous substrate, a hydrophilic blocking layer and a porous polar polymer bonding layer, wherein the hydrophilic blocking layer is arranged between the porous substrate and the porous polar polymer bonding layer, the water contact angle of the hydrophilic blocking layer is less than 20 degrees, the hydrophilic blocking layer comprises an adhesive and hydrophilic inorganic particles, the hydrophilic inorganic particles are mutually bonded through the adhesive, the adhesive is one or more than two of acrylate polymer, styrene-acrylate copolymer, polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, acrylonitrile-acrylate copolymer, vinyl chloride-acrylate copolymer and butadiene-styrene copolymer, and the porous polar polymer bonding layer comprises polar polymer, the polar polymer is one or more than two of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene and a copolymer of vinylidene fluoride and acrylate, and the pore diameter of the porous polar polymer bonding layer is 200nm-20 mu m.

2. The lithium ion battery of claim 1, wherein the pores in the porous polar polymer tie layer comprise pores having a first pore size of 5-20 μ ι η and pores having a second pore size of 200nm-2 μ ι η.

3. The lithium ion battery of claim 2, wherein the first pore size is 5-10 μ ι η and the second pore size is 200nm-2 μ ι η.

4. The lithium ion battery of any of claims 1-3, wherein the porous polar polymeric tie layer has a porosity of 20-80%.

5. The lithium ion battery of any of claims 1-3, wherein the porous polar polymeric tie layer comprises through-holes that extend through the porous polar polymeric tie layer.

6. The lithium ion battery of claim 1, wherein the hydrophilic retardation layer has a water contact angle of 2-18 °.

7. The lithium ion battery of claim 1, wherein the hydrophilic inorganic particles are hydrophilic Al₂O₃Hydrophilic SiO₂Hydrophilic SnO₂Hydrophilic ZrO₂Hydrophilic TiO 2₂Hydrophilic SiC and hydrophilic Si₃N₄Hydrophilic CaO, hydrophilic MgO, hydrophilic ZnO, and hydrophilic BaTiO₃Hydrophilic LiAlO₂And hydrophilic BaSO₄One or more than two of them.

8. The lithium ion battery according to claim 1, wherein the hydrophilic inorganic particles have a particle size of 1nm to 10 μm.

9. The lithium ion battery of claim 8, wherein the hydrophilic inorganic particles have a particle size of 1nm to 5 μ ι η.

10. The lithium ion battery of claim 9, wherein the hydrophilic inorganic particles have a particle size of 1nm to 2 μ ι η.

11. The lithium ion battery of claim 10, wherein the hydrophilic inorganic particles have a particle size of 10nm to 1 μ ι η.

12. The lithium ion battery of claim 11, wherein the hydrophilic inorganic particles have a particle size of 20nm to 800 nm.

13. The lithium ion battery of claim 12, wherein the hydrophilic inorganic particles have a particle size of 50nm to 350 nm.

14. The lithium ion battery of any of claims 1 and 7-13, wherein the hydrophilic inorganic particles have a specific surface area of 10-600m²/g。

15. The lithium ion battery of claim 14, wherein the hydrophilic inorganic particles have a specific surface area of 100-500m²/g。

16. The lithium ion battery of claim 15, wherein the hydrophilic inorganic particles have a specific surface area of 150-400m²/g。

17. The lithium ion battery of any of claims 1 and 6-13, wherein the hydrophilic particles are present in an amount of 50-95 wt.%, based on the total amount of the hydrophilic retardation layer.

18. The lithium ion battery of claim 17, wherein the hydrophilic particles are present in an amount of 70-95 wt.% based on the total amount of the hydrophilic retardation layer.

19. The lithium ion battery of claim 18, wherein the hydrophilic particles are present in an amount of 80-95 wt.% based on the total amount of the hydrophilic retardation layer.

20. The lithium ion battery of any of claims 1 and 6-13, wherein the hydrophilic blocking layer has a thickness of 0.1-3 μ ι η.

21. The lithium ion battery of claim 20, wherein the hydrophilic blocking layer has a thickness of 0.1-1 μ ι η.

22. The lithium ion battery of claim 21, wherein the hydrophilic blocking layer has a thickness of 0.3-0.8 μ ι η.

23. The lithium ion battery of any of claims 1-3, wherein the porous polar polymeric tie layer has a thickness of 0.1-10 μm.

24. The lithium ion battery of claim 23, wherein the porous polar polymer tie layer has a thickness of 0.2-5 μ ι η.

25. The lithium ion battery of claim 24, wherein the porous polar polymer tie layer has a thickness of 0.7-3 μ ι η.

26. The lithium ion battery of claim 25, wherein the porous polar polymer tie layer has a thickness of 0.8-1.5 μ ι η.

27. The lithium ion battery of claim 1, wherein the porous substrate comprises a porous polymer layer.

28. The lithium ion battery of claim 27, wherein the porous polymer layer is a porous polyolefin layer.

29. The lithium ion battery of claim 28, wherein the porous polymer layer is one or more of a porous polyethylene layer, a porous polypropylene layer, a porous polyethylene and porous polypropylene composite layer.

30. The lithium ion battery of claim 27, wherein the porous substrate further comprises a ceramic layer disposed between the porous polymer layer and the hydrophilic blocking layer; and/or

The porous polymer layer is disposed between the ceramic layer and the hydrophilic retarding layer.

31. The lithium ion battery of claim 30, wherein the ceramic layer has a thickness of 1-5 μ ι η.

32. The lithium ion battery of claim 31, wherein the ceramic layer has a thickness of 1.5-3 μ ι η.

33. The lithium ion battery of any of claims 1-3, 6-13, and 27-32, wherein the polymer separator has a Gurley value of 100 and 900Sec/100 mL.

34. The lithium ion battery of claim 33, wherein the polymer separator has a Gurley of 120-600Sec/100 mL.

35. The lithium ion battery of claim 34, wherein the polymer separator has a Gurley of 120-500Sec/100 mL.

36. The lithium ion battery of claim 35, wherein the polymer separator has a Gurley of 150-350Sec/100 mL.

37. A method of making a lithium ion battery, the method comprising:

s1, preparing the polymer diaphragm by adopting the following method, wherein the method comprises the following steps:

(1) coating a hydrophilic retardation slurry on at least one surface of a porous substrate to form a hydrophilic retardation coating, the hydrophilic retardation slurry containing a dispersion medium, and hydrophilic inorganic particles and a binder dispersed in the dispersion medium, and drying the hydrophilic retardation coating to form a hydrophilic retardation layer having a water contact angle of 20 ° or less, the binder being one or more of an acrylate-based polymer, a styrene-acrylate copolymer, polyvinylidene fluoride, a vinylidene fluoride-hexafluoropropylene copolymer, an acrylonitrile-acrylate copolymer, a vinyl chloride-acrylate copolymer, and a butadiene-styrene copolymer;

(2) coating a polar polymer binder solution on the surface of the hydrophilic retardation layer to form a polar polymer binder coating, wherein the polar polymer binder solution contains an organic solvent, and a polar polymer binder and a pore-forming agent which are dispersed in the organic solvent, the polar polymer binder is one or more of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, and a copolymer of vinylidene fluoride and acrylate, and the boiling point of the organic solvent is 60-260 ℃;

(3) drying the polar polymer binder coating to form a porous polar polymer binding layer;

s2, arranging the polymer diaphragm between a positive pole piece and a negative pole piece, forming a battery pole core, and then packaging, wherein the positive pole material in the positive pole piece comprises one or more than two of cobalt lithium oxide, nickel lithium oxide, manganese lithium oxide and lithium iron phosphate, and the negative pole material in the negative pole piece comprises one or more than two of graphite, soft carbon and hard carbon.

38. A method of making a lithium ion battery, the method comprising:

(1) coating a hydrophilic retardation slurry on at least one surface of a porous substrate to form a hydrophilic retardation coating, the hydrophilic retardation slurry containing a dispersion medium, and hydrophilic inorganic particles dispersed in the dispersion medium, and a binder, the hydrophilic retardation layer having a water contact angle of 20 ° or less, the binder being one or more of an acrylate-based polymer, a styrene-acrylate copolymer, polyvinylidene fluoride, a vinylidene fluoride-hexafluoropropylene copolymer, an acrylonitrile-acrylate copolymer, a vinyl chloride-acrylate copolymer, and a butadiene-styrene copolymer;

(2) coating a polar polymer binder solution on the surface of the hydrophilic retardation coating to form a polar polymer binder coating, wherein the polar polymer binder solution contains an organic solvent, and a polar polymer binder and a pore-forming agent which are dispersed in the organic solvent, the polar polymer binder is one or more of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, and a copolymer of vinylidene fluoride and acrylate, and the boiling point of the organic solvent is 60-260 ℃;

(3) drying the hydrophilic retardation coating and the polar polymer binder coating to form a hydrophilic retardation layer and a porous polar polymer bonding layer, wherein the water contact angle of the hydrophilic retardation layer is below 20 degrees;

39. The method of claim 37 or 38, wherein the pore-forming agent of step (2) is a substance that forms a volatile gas under the drying conditions of step (3).

40. The method of claim 37 or 38, wherein the hydrophilic retardation layer has a water contact angle of 20 ° or less.

41. The method of claim 40, wherein the hydrophilic retardation layer has a water contact angle of 2-18 °.

42. The method of claim 37 or 38, wherein the hydrophilic retardation slurry is applied in an amount such that the thickness of the finally formed hydrophilic retardation layer is 0.1-3 μm.

43. The method of claim 42, wherein the hydrophilic retardation slurry is applied in an amount such that the thickness of the finally formed hydrophilic retardation layer is 0.1-1 μm.

44. The method of claim 43, wherein the hydrophilic retardation slurry is applied in an amount such that the thickness of the finally formed hydrophilic retardation layer is 0.3-0.8 μm.

45. The method of claim 37 or 38, wherein the hydrophilic inorganic particles are hydrophilic Al₂O₃Hydrophilic SiO₂Hydrophilic SnO₂Hydrophilic ZrO₂Hydrophilic TiO 2₂Hydrophilic SiC and hydrophilic Si₃N₄Hydrophilic CaO, hydrophilic MgO, hydrophilic ZnO, and hydrophilic BaTiO₃Hydrophilic LiAlO₂And hydrophilic BaSO₄One or more than two of them.

46. The method of claim 37 or 38, wherein the hydrophilic retarding slurry has a hydrophilic inorganic particle content of 50-95 wt%.

47. The method of claim 46, wherein the hydrophilic retarding slurry has a hydrophilic inorganic particle content of 70-95 wt%.

48. The method of claim 47, wherein the hydrophilic retarding slurry has a hydrophilic inorganic particle content of 80-95 wt%.

49. The method as claimed in claim 37 or 38, wherein the binder is contained in an amount of 1-30 parts by weight with respect to 100 parts by weight of the hydrophilic inorganic particles.

50. The method of claim 37 or 38, wherein the hydrophilic inorganic particles have a particle size of 1nm to 10 μ ι η.

51. The method of claim 50, wherein the hydrophilic inorganic particles have a particle size of 1nm to 5 μm.

52. The method of claim 51, wherein the hydrophilic inorganic particles have a particle size of 1nm to 2 μm.

53. The method of claim 52, wherein the hydrophilic inorganic particles have a particle size of 10nm to 1 μm.

54. The method of claim 53, wherein the hydrophilic inorganic particles have a particle size of 20nm to 800 nm.

55. The method of claim 54, wherein the hydrophilic inorganic particles have a particle size of 50nm to 350 nm.

56. The method of claim 37 or 38, wherein the hydrophilic inorganic particles have a specific surface area of 10-600m²/g。

57. The method as claimed in claim 56, wherein the hydrophilic inorganic particles have a specific surface area of 100-500m²/g。

58. The method as claimed in claim 57, wherein the hydrophilic inorganic particles have a specific surface area of 150-400m²/g。

59. The method according to claim 37 or 38, wherein the dispersion medium is one or more of water, ethanol, isopropanol, cyclohexane, tetrahydrofuran, dichloromethane, and chloroform.

60. The method of claim 37 or 38, wherein the polar polymer is present in the polar polymer binder solution at a concentration of 1-30 wt%.

61. The method of claim 60, wherein the polar polymer binder solution has a polar polymer concentration of 2-25 wt.%.

62. The method of claim 61, wherein the polar polymer binder solution has a polar polymer concentration of 5-20 wt.%.

63. The method of claim 37 or 38, wherein the concentration of polar polymer in the polar polymer binder solution is a critical concentration.

64. The method according to claim 37 or 38, wherein the organic solvent has a boiling point of 120 ℃ or higher.

65. The method according to claim 64, wherein the organic solvent has a boiling point of 140 ℃ or higher.

66. The method as claimed in claim 65, wherein the organic solvent has a boiling point of 150-230 ℃.

67. The method according to claim 37 or 38, wherein the organic solvent is one or more of triethyl phosphate, N-methylpyrrolidone, N-dimethylacetamide, N-dimethylformamide, and dimethylsulfoxide.

68. The method of claim 37 or 38, wherein the pore former is dry ice.

69. The method as set forth in claim 37 or 38, wherein the pore-forming agent is 0.5 to 5 parts by weight with respect to 100 parts by weight of the organic solvent.

70. The method of claim 69, wherein the pore former is present in an amount of 0.8 to 3 parts by weight per 100 parts by weight of organic solvent.

71. The method of claim 70, wherein the pore former is present in an amount of 1 to 2 parts by weight per 100 parts by weight of organic solvent.

72. The method of claim 37 or 38, wherein the polar polymer binder solution is applied in an amount such that the porous polar polymer bonding layer has a thickness of 0.1-10 μ ι η.

73. The method of claim 72, wherein the polar polymer binder solution is applied in an amount such that the porous polar polymer bonding layer has a thickness of 0.2-5 μm.

74. The method of claim 73, wherein the polar polymer binder solution is applied in an amount such that the porous polar polymer bonding layer has a thickness of 0.7-3 μm.

75. The method of claim 74, wherein the polar polymer binder solution is applied in an amount such that the porous polar polymer bonding layer has a thickness of 0.8-1.5 μm.

76. The method according to claim 37 or 38, wherein in step (2), the drying is performed at a temperature of not higher than 120 ℃.

77. The method of claim 76, wherein in step (2), the drying is carried out at a temperature of not greater than 60 ℃.

78. The method of claim 77, wherein in step (2), the drying is performed at a temperature of 20-55 ℃.

79. The method of claim 78, wherein the duration of drying is 0.1-36 hours.

80. The method of claim 37 or 38, wherein the porous substrate is a porous polymer membrane, or a composite membrane of a porous polymer membrane and a ceramic membrane.

81. The method of claim 80, wherein the porous polymer membrane is a polyolefin membrane.

82. The method of claim 81, wherein the porous polymer film is a porous polyethylene film, a porous polypropylene film, or a porous polyethylene and porous polypropylene composite film.

83. The method according to claim 80, wherein the ceramic membrane has a thickness of 1-5 μm.

84. The method according to claim 83, wherein the ceramic membrane has a thickness of 1.5-3 μm.