CN110233221B

CN110233221B - Battery diaphragm and preparation method thereof, and lithium ion battery and preparation method thereof

Info

Publication number: CN110233221B
Application number: CN201810178960.5A
Authority: CN
Inventors: 胡家玲; 刘荣华; 单军; 何龙
Original assignee: BYD Co Ltd
Current assignee: BYD Co Ltd
Priority date: 2018-03-05
Filing date: 2018-03-05
Publication date: 2022-01-07
Anticipated expiration: 2038-03-05
Also published as: CN110233221A

Abstract

The invention discloses a battery diaphragm, a preparation method thereof and a lithium ion battery adopting the battery diaphragm, wherein the battery diaphragm comprises a polyolefin porous membrane layer, a non-conductive polymer fiber non-woven fabric layer, a first inorganic layer and a second inorganic layer; the polyolefin porous membrane layer is connected with the non-conductive polymer fiber non-woven fabric layer through a second inorganic layer; the first inorganic layer includes a second portion and optionally a first portion, the first portion being located on a surface of the non-conductive polymer fiber non-woven fabric layer, the second portion being located in at least a portion of the pores of the non-conductive polymer fiber non-woven fabric layer. The battery diaphragm of the invention has higher air permeability and strength, especially can still keep the shape at high temperature and has higher strength, thereby obviously improving the high-temperature safety performance and the high-low temperature storage performance of the lithium ion battery.

Description

Battery diaphragm and preparation method thereof, and lithium ion battery and preparation method thereof

Technical Field

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

Because of the characteristics of low raw material price, simple preparation process, high mechanical strength, strong electrochemical stability and the like, the polyolefin membrane prepared by the mechanical stretching method, such as polyethylene and polypropylene microporous membranes, is a lithium ion battery diaphragm mainly used in commercial use at present.

However, the above polyolefin films have a low rupture temperature, for example, about 140 ℃ for polyethylene films and about 160 ℃ for polypropylene films. When the battery is used improperly, the diaphragm is easy to shrink (wherein the shrinkage rate of the common polyethylene film at 180-200 ℃ reaches more than 80%), even melt, and the battery is short-circuited to cause serious safety accidents.

In view of the above disadvantages of the polyolefin film, researchers have developed an organic-inorganic composite separator, in which an inorganic ceramic layer is formed on the surface of the polyolefin separator, which can improve the safety performance of the battery at normal temperature, but it is still difficult to improve the high-temperature safety performance of the battery, because the inorganic ceramic layer is attached to the surface of the polyolefin porous film in the organic-inorganic composite separator, the inorganic ceramic layer has low strength, the polyolefin porous film shrinks or even melts at high temperature, and cannot maintain its original shape and strength, and the strength of the inorganic ceramic layer is also significantly reduced or even broken, resulting in significant reduction in the safety performance of the battery, or even serious safety accidents.

In addition, researchers have used non-conductive polymer (e.g., ethylene terephthalate) non-woven fabrics as base films to coat ceramic slurry to prepare separators, but lithium ion batteries using such separators have poor storage capacity and short service life during storage, particularly high temperature storage, and this may be due to the fact that the non-woven fabrics as the base films have large and numerous pores in the battery separators, resulting in very low strength of the battery separators, and self-discharge is very likely to occur during storage, particularly high temperature storage, resulting in not only weak storage capacity of the batteries, but also significantly shortened service life of the batteries.

In summary, with the expansion of the application field of lithium ion batteries, it is urgently needed to develop a separator with more excellent performance so as to improve the safety performance of the battery and improve other service performances of the battery.

Disclosure of Invention

The invention aims to overcome the problems that the existing organic-inorganic diaphragm taking polyolefin as a base film is easy to shrink or even melt at high temperature, so that the safety of a battery is poor, and the organic-inorganic diaphragm taking non-conductive polymer non-woven fabric as the base film has low strength, so that the low-temperature and high-temperature storage performance of the battery is poor, and provides a battery diaphragm which has higher strength, can keep the shape at high temperature and has higher strength, so that the high-temperature safety and the storage performance of the battery can be improved.

According to a first aspect of the present invention, there is provided a battery separator comprising a polyolefin porous membrane layer, a non-conductive polymer fiber nonwoven fabric layer, a first inorganic layer, and a second inorganic layer;

the polyolefin porous membrane layer and the non-conductive polymer fiber non-woven fabric layer are connected through the second inorganic layer;

the first inorganic layer includes a second portion and optionally a first portion, the first portion being located on a surface of the non-conductive polymer fiber nonwoven layer, the second portion being located in at least a portion of the pores of the non-conductive polymer fiber nonwoven layer.

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

s11, coating a first slurry containing a binder on at least one surface of the polyolefin porous membrane to form a binder slurry layer;

s12, laminating non-conductive polymer fiber non-woven fabric and the adhesive slurry layer and drying;

s13, applying a second slurry in which an inorganic substance is dispersed on the surface of a non-conductive polymer fiber nonwoven fabric to form a second slurry layer, and applying pressure to the second slurry layer to allow a part of the slurry in the second slurry layer to penetrate into the non-conductive polymer fiber nonwoven fabric layer to obtain a wet film;

s14, drying the wet film.

According to a third aspect of the present invention, there is provided a method for preparing a battery separator, the method comprising the steps of:

s21, providing a third slurry with inorganic matter dispersed therein;

s22, forming a third slurry layer on the surface of the first base film by using the third slurry;

s23, laminating the second base film and the third slurry layer to obtain a wet film;

s24, drying the wet film;

the first base film and the second base film are each a polyolefin porous film or a non-conductive polymer fiber non-woven fabric, and one of the first base film and the second base film is a polyolefin porous film and the other is a non-conductive polymer fiber non-woven fabric.

According to a fourth aspect of the invention there is provided a battery separator made by the method of the second or third aspect of the invention.

According to a fifth aspect of the present invention, there is provided a lithium ion battery comprising a positive electrode, a negative electrode and a separator, the separator being disposed between the positive electrode and the negative electrode, wherein the separator is the battery separator according to the first or fourth aspect of the present invention.

According to a sixth aspect of the present invention, there is provided a method of manufacturing a lithium ion battery, the method comprising:

(1) preparing a battery separator by the method of the second or third aspect of the invention;

(2) and arranging the battery diaphragm between the positive electrode and the negative electrode to form a battery pole core, and then packaging.

According to the battery separator of the present invention, compared to a separator obtained by using only a polyolefin porous film as a base film or only a non-conductive polymer non-woven fabric as a base film and forming an inorganic layer on the surface of the base film, the separator has improved strength, particularly, can maintain its shape at high temperature and has higher strength, thereby significantly improving high-temperature safety performance and high-low temperature storage performance of a lithium ion battery.

According to the battery separator of the present invention, the polyolefin porous film and the non-conductive polymer nonwoven fabric are connected through the inorganic layer, and the battery separator has improved air permeability as compared to a case where the polyolefin porous film and the non-conductive polymer nonwoven fabric are directly bonded through the binder.

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.

In the present invention, the term "optional" means optional, and may be understood as "containing or not containing" and "including or not including".

According to a first aspect of the present invention, there is provided a battery separator comprising a polyolefin porous membrane layer, a non-conductive polymer fiber nonwoven fabric layer, a first inorganic layer, and a second inorganic layer.

The polyolefin porous membrane layer may be a porous membrane capable of swelling the liquid electrolyte and transporting lithium ions. Preferably, the polymer in the polyolefin porous membrane layer is polyethylene and/or polypropylene. When the polymer in the polyolefin porous membrane layer is polyethylene and polypropylene, the polyolefin porous membrane layer may be a composite layer of polyethylene and polypropylene, and specific examples thereof may include, but are not limited to, PE/PP/PE composite porous membrane layers.

According to the battery separator of the present invention, the thickness of the polyolefin porous membrane layer may be 1 to 50 μm, for example: 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 25 μm, 26 μm, 27 μm, 28 μm, 29 μm, 30 μm, 31 μm, 32 μm, 33 μm, 34 μm, 35 μm, 36 μm, 37 μm, 38 μm, 39 μm, 40 μm, 41 μm, 42 μm, 43 μm, 44 μm, 45 μm, 46 μm, 47 μm, 48 μm, 49 μm, or 50 μm. According to the battery separator, even if the polyolefin porous film layer with small thickness is adopted, the separator has high strength. According to the battery separator of the present invention, in a preferred embodiment, the thickness of the polyolefin porous membrane layer is 5 to 20 μm, preferably 5 to 15 μm.

The polyolefin porous film may have a porosity of 30 to 50%, for example: 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, or 50%. Preferably, the polyolefin porous membrane has a porosity of 35 to 45%.

In the present invention, the porosity is determined by the following method:

the polyolefin porous film was cut into a circular piece having a diameter of 17mm, and the thickness (d) and the mass (M) were measured₀) Thereafter, the polyolefin porous membrane was immersed in n-butanol (BuOH) for 2 hours, taken out and the liquid on the surface of the membrane was blotted with filter paper, and the mass (M) of the wet polyolefin porous membrane was weighed to calculate the porosity according to the following formula:

wherein, P is the porosity,

M₀the quality of the dry film of the polyolefin porous film,

m is the quality of a wet film obtained by soaking polyolefin porous in n-butyl alcohol for 2 hours,

r is the radius of the polyolefin porous membrane,

d is the thickness of the polyolefin porous film,

ρ_BuOHis the density of n-butanol.

According to the battery separator of the present invention, the non-conductive polymer fiber non-woven fabric layer is preferably a non-woven fabric formed using high-strength polymer fibers. The polymer in the non-conductive polymer fiber non-woven fabric layer is preferably one or more of polyester (such as polyethylene terephthalate, polybutylene terephthalate), polyimide, polyetherimide and polyether ether ketone, and is more preferably polyethylene terephthalate and/or polybutylene terephthalate.

According to the battery diaphragm, the non-conductive polymer fiber non-woven fabric and the polyolefin porous membrane are compounded to be used as the base membrane, and compared with the method of singly adopting the non-conductive polymer fiber non-woven fabric as the base membrane, the thickness of the non-conductive polymer fiber non-woven fabric can be obviously reduced, so that the total thickness of the battery diaphragm is reduced. According to the battery separator of the present invention, the thickness of the non-conductive polymer fiber nonwoven fabric layer is preferably 5 to 20 μm, for example: 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, or 20 μm. More preferably, the non-conductive polymer fiber nonwoven layer has a thickness of 10 to 18 μm.

According to the battery separator of the present invention, the non-conductive polymer fiber non-woven fabric and the polyolefin porous membrane are compounded as the base membrane, and the separator can have higher strength even if the non-woven fabric having a smaller fiber diameter is used as compared with the case where the non-conductive polymer fiber non-woven fabric is used alone as the base membrane. According to the battery separator of the present invention, the diameter of the fibers in the non-conductive polymer fiber nonwoven fabric layer is preferably 0.5 to 5 μm, for example: 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 2 μm, 3 μm, 4 μm, or 5 μm. More preferably, the diameter of the fibers in the non-conductive polymer fiber nonwoven layer is 2-5 μm.

According to the battery separator of the present invention, the porosity of the non-conductive polymer fiber nonwoven fabric layer is preferably 35 to 70%, and may be, for example: 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, or 70%. According to the battery separator of the present invention, the porosity of the non-conductive polymer fiber nonwoven fabric layer is more preferably 40 to 65%, still more preferably 45 to 60%, still more preferably 50 to 55%.

According to the battery separator of the present invention, the inorganic substances in the first inorganic layer and the second inorganic layer are the same or different, and each may be Al₂O₃、SiO₂、BaSO₄、TiO₂、CuO、MgO、LiAlO₂、ZrO₂Carbon nanotube, BN, SiC, Si₃N₄、WC、BC、AlN、Fe₂O₃、BaTiO₃、MoS₂、α-V₂O₅、PbTiO₃、TiB₂、CaSiO₃One or more than two of molecular sieve, clay and kaolin. From the viewpoint of further improving the wettability of the battery separator and improving the service performance of a lithium ion battery using the separator, the inorganic material in each of the first inorganic layer and the second inorganic layer is preferably Al₂O₃And/or SiO₂。

According to the battery separator of the present invention, the inorganic substance in the first inorganic layer and the second inorganic layer is present in the form of particles. The average particle diameter of the inorganic particles in the first inorganic layer and the second inorganic layer may be 10nm to 3 μm, for example: 10nm, 20nm, 30nm, 40nm, 50nm, 100nm, 150nm, 200nm, 250nm, 300nm, 350nm, 400nm, 450nm, 500nm, 550nm, 600nm, 650nm, 700nm, 750nm, 800nm, 850nm, 900nm, 950nm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, or 3 μm. Preferably, the average particle diameter of the inorganic particles in the first inorganic layer and the second inorganic layer is each 20nm to 1 μm. More preferably, the average particle diameter of the inorganic particles in the first inorganic layer and the second inorganic layer is each 30nm to 800 nm. Further preferably, the average particle diameter of the inorganic particles in the first inorganic layer and the second inorganic layer is each 100nm to 400 nm. Still more preferably, the inorganic particles comprise first inorganic particles having an average particle size of 40 to 100nm and second inorganic particles having an average particle size of 300 to 400 nm. The weight ratio of the first inorganic particles to the second inorganic particles may be 0.1 to 10: 1, preferably 0.5 to 5: 1, more preferably 1-2: 1.

according to the battery separator of the present invention, the inorganic substances in the first inorganic layer and the second inorganic layer are each formed into an integral structure by a binder. The binder may be an oily binder, such as one or more of a polyurethane binder, an epoxy resin binder, a polyvinylidene fluoride binder, a polytetrafluoroethylene binder, and an acrylate-type binder.

In a preferred embodiment of the battery separator according to the present invention, the binder is a water-soluble binder. According to the preferred embodiment, not only is it more environmentally friendly, but the battery separator has higher gas permeability than when an oil-based binder is used, which may be due to: when the oil-based binder is used, the oil-based binder is easy to permeate into the polyolefin porous membrane to block the pores of the polyolefin porous membrane.

According to the preferred embodiment, preferred examples of the binder include, but are not limited to, one or more of polyvinyl alcohol (PVA), Polyoxyethylene Ether (PEO), water-soluble polyacrylate, and water-soluble compound-modified polyacrylate.

The "water-soluble polyacrylate" refers to polyacrylate having a water-soluble group in a molecular structure, for example, polyacrylate containing one or more of a hydroxyl group, an amide group and an ether bond in a molecular structure.

By "water-soluble compound modified polyacrylate" is meant that the polyacrylate together with a water-soluble compound, preferably interacting with the polyacrylate, forms a binder, for example: specific examples of the water-soluble compound that may be used as the crosslinking agent for the polyacrylate may include, but are not limited to, one or more of N-methylolacrylamide, N-hydroxyethylacrylamide, (N-methylol) methacrylamide, and (N-hydroxyethyl) methacrylamide.

According to the battery separator of the present invention, the first inorganic substance layer includes a second portion and optionally a first portion, the first portion is located on the surface of the non-conductive polymer fiber non-woven fabric layer, and the second portion is located in at least a part of the pores of the non-conductive polymer fiber non-woven fabric layer. When the first inorganic layer contains a first portion, the second portion is a unitary structure with the first portion.

According to the battery separator of the present invention, the thickness of the first portion of the first inorganic layer may be 0 to 5 μm. In a preferred embodiment, the first inorganic layer contains a first portion. In this preferred embodiment, the thickness of the first portion is preferably 0.1 to 5 μm, more preferably 1 to 4.5 μm, and still more preferably 2 to 4 μm.

According to the battery separator of the present invention, the polyolefin porous film layer and the non-conductive polymer fiber nonwoven fabric layer are joined by the second inorganic layer. Compared with the method that the polyolefin porous membrane and the non-conductive polymer fiber non-woven fabric layer are directly cemented by the binder, the air permeability of the battery diaphragm can be obviously improved. The content of the second inorganic layer may vary within a wide range. Generally, the weight ratio of the second inorganic layer to the first inorganic layer may be 1: 2.5-16, for example: 1: 2.5, 1: 3. 1: 3.5, 1: 4. 1: 4.5, 1: 5. 1: 5.5, 1: 6. 1: 6.5, 1: 7. 1: 7.5, 1: 8. 1: 8.5, 1: 9. 1: 9.5, 1: 10. 1: 10.5, 1: 11. 1: 11.5, 1: 12. 1: 12.5, 1: 13. 1: 13.5, 1: 14. 1: 14.5, and 1: 15. preferably, the weight ratio of the second inorganic layer to the first inorganic layer is 1: 3-12.

According to the battery separator of the present invention, the total amount of the inorganic substances in the first inorganic layer and the second inorganic layer may be 20 to 85 wt%, preferably 30 to 80 wt%, more preferably 35 to 78 wt%, further preferably 40 to 76 wt%, and still further preferably 45 to 75 wt%, based on the total amount of the battery separator.

According to the battery separator, the other surface of the polyolefin porous membrane layer can be a blank surface, or can be provided with an inorganic layer, and can be connected with another non-conductive polymer fiber non-woven fabric layer through the inorganic layer.

In one embodiment, the other surface of the polyolefin porous membrane layer is a blank surface. The battery separator according to this embodiment has the following structure: polyolefin porous membrane layer | second inorganic layer | non-conductive polymer fiber nonwoven layer | first inorganic layer.

In another embodiment, the other surface of the polyolefin porous membrane layer has a third inorganic layer. The battery separator according to this embodiment has the following structure: third inorganic layer | polyolefin porous membrane layer | second inorganic layer | non-conductive polymer fiber nonwoven layer | first inorganic layer.

In this embodiment, the inorganic material in the third inorganic layer may be Al₂O₃、SiO₂、BaSO₄、TiO₂、CuO、MgO、LiAlO₂、ZrO₂Carbon nanotube, BN, SiC, Si₃N₄、WC、BC、AlN、Fe₂O₃、BaTiO₃、MoS₂、α-V₂O₅、PbTiO₃、TiB₂、CaSiO₃One or more of molecular sieve, clay and kaolin, preferably Al₂O₃And/or SiO₂。

In this embodiment, the inorganic material in the third inorganic layer is present in the form of particles. The inorganic particles in the third inorganic layer may have an average particle diameter of 10nm to 3 μm, for example: 10nm, 20nm, 30nm, 40nm, 50nm, 100nm, 150nm, 200nm, 250nm, 300nm, 350nm, 400nm, 450nm, 500nm, 550nm, 600nm, 650nm, 700nm, 750nm, 800nm, 850nm, 900nm, 950nm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, or 3 μm. Preferably, the inorganic particles in the third inorganic layer have an average particle diameter of 20nm to 1 μm. More preferably, the inorganic particles in the third inorganic layer have an average particle diameter of 30nm to 800 nm. Further preferably, the inorganic particles in the third inorganic layer have an average particle diameter of 100nm to 400 nm. Still more preferably, the inorganic particles include first inorganic particles having an average particle diameter of 40 to 100nm and second inorganic particles having an average particle diameter of 300 to 400 nm. The weight ratio of the first inorganic particles to the second inorganic particles may be 0.1 to 10: 1, preferably 0.5 to 5: 1, more preferably 1-2: 1.

in this embodiment, the thickness of the third inorganic layer may be 0.3 to 5 μm, preferably 1 to 4.5 μm.

In this embodiment, the inorganic material in the third inorganic material layer is formed into an integral structure by a binder. The binder may be an oily binder, such as one or more of a polyurethane binder, an epoxy resin binder, a polyvinylidene fluoride binder, a polytetrafluoroethylene binder, and an acrylate-type binder. Preferably, the binder is a water-soluble binder, and preferred examples thereof include, but are not limited to, one or more of polyvinyl alcohol (PVA), Polyoxyethylene Ether (PEO), water-soluble polyacrylate, and water-soluble compound-modified polyacrylate.

In this preferred embodiment, the content of the third inorganic layer may be 5 to 50% by weight, preferably 10 to 48% by weight, more preferably 20 to 46% by weight, still more preferably 30 to 45% by weight, and still more preferably 35 to 40% by weight, based on the total amount of the battery separator.

In yet another embodiment, the other surface of the polyolefin porous membrane layer is joined to another non-conductive polymer fibrous nonwoven layer by an inorganic layer. The battery separator according to this embodiment has the following structure: first inorganic layer | non-conductive polymer fiber nonwoven layer | second inorganic layer | polyolefin porous film layer | second inorganic layer | non-conductive polymer fiber nonwoven layer | first inorganic layer. According to the separator of this embodiment, the non-conductive polymer fiber nonwoven fabric layer, the second inorganic layer, and the first inorganic layer located on both sides of the polyolefin porous membrane layer may be the same or different, and preferably, the same.

According to the battery separator of the present invention, the thickness of the battery separator may be conventionally selected, for example, 10 to 40 μm. The separator according to the present invention shows improved strength, i.e., higher strength with a smaller thickness. According to the battery separator of the present invention, the thickness of the battery separator is preferably 15 to 38 μm, more preferably 20 to 36 μm.

s14, drying the wet film.

According to the preparation method of the second aspect of the present invention, the binder in the first slurry may be an oily binder, such as one or two or more of a polyurethane binder, an epoxy resin binder, a polyvinylidene fluoride binder, a polytetrafluoroethylene binder, and an acrylate-type binder.

In a preferred embodiment, the binder in the first slurry is a water-soluble binder. According to the preferred embodiment, not only is the battery separator more environmentally friendly, but also the battery separator has higher gas permeability than when an oil-based binder is used.

According to this preferred embodiment, preferred examples of the binder in the first slurry include, but are not limited to, one or two or more of polyvinyl alcohol (PVA), Polyoxyethylene Ether (PEO), water-soluble polyacrylate, and water-soluble compound-modified polyacrylate.

By "water-soluble compound modified polyacrylate" is meant that the polyacrylate together with a water-soluble compound, preferably interacting with the polyacrylate, forms a binder, for example: specific examples of the water-soluble compound that may be used as the crosslinking agent for the polyacrylate may include, but are not limited to, one or more of N-methylolacrylamide, N-hydroxyethylacrylamide, (N-methylol) methacrylamide, and (N-hydroxyethyl) methacrylamide. The water-soluble compound may be contained in an amount of 1 to 10 parts by weight with respect to 100 parts by weight of the polyacrylate.

According to the method of the second aspect of the present invention, the content of the binder in the first slurry is such that the first slurry has coating properties while achieving adhesion. Generally, the binder content of the first slurry may be 0.1 to 5 wt%, preferably 0.5 to 4 wt%, more preferably 1 to 3 wt%.

The dispersant of the first slurry may be selected according to the kind of the binder, so as to dissolve and disperse the binder. For example, when the binder in the first slurry is a water-soluble binder, the dispersion medium of the first slurry may be water.

According to the method of the second aspect of the invention, the content of the inorganic substance in the second slurry is such that the inorganic substance forms a stable dispersion. Generally, the content of the inorganic substance in the second slurry may be 5 to 50% by weight, preferably 10 to 40% by weight, more preferably 20 to 30% by weight.

The inorganic substance in the second slurry may be Al₂O₃、SiO₂、BaSO₄、TiO₂、CuO、MgO、LiAlO₂、ZrO₂Carbon nanotube, BN, SiC, Si₃N₄、WC、BC、AlN、Fe₂O₃、BaTiO₃、MoS₂、α-V₂O₅、PbTiO₃、TiB₂、CaSiO₃One or more of molecular sieve, clay and kaolin, preferably Al₂O₃And/or SiO₂。

In this embodiment, the inorganic material in the second slurry is present in the form of particles. The inorganic particles in the second slurry may have an average particle diameter of 10nm to 3 μm, for example: 10nm, 20nm, 30nm, 40nm, 50nm, 100nm, 150nm, 200nm, 250nm, 300nm, 350nm, 400nm, 450nm, 500nm, 550nm, 600nm, 650nm, 700nm, 750nm, 800nm, 850nm, 900nm, 950nm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, or 3 μm. Preferably, the inorganic particles in the second slurry have an average particle diameter of 20nm to 1 μm. More preferably, the inorganic particles in the second slurry have an average particle diameter of 30nm to 800 nm. Further preferably, the inorganic particles in the second slurry have an average particle diameter of 100nm to 400 nm. Still more preferably, the inorganic particles include first inorganic particles and second inorganic particles, the first inorganic particles have an average particle size of 40 to 100nm, the second inorganic particles have an average particle size of 300 to 400nm, and the weight ratio of the first inorganic particles to the second inorganic particles is preferably 0.1 to 10: 1, more preferably 0.5 to 5: 1, more preferably 1 to 2: 1.

the second slurry also contains a binder to bind the minerals into a unitary structure. The binder in the second slurry may be an oily binder, such as one or more of a polyurethane binder, an epoxy resin binder, a polyvinylidene fluoride binder, a polytetrafluoroethylene binder, and a polyacrylate-type binder.

In a preferred embodiment, the binder in the second slurry is a water-soluble binder. According to the preferred embodiment, not only is the battery separator more environmentally friendly, but also the battery separator has higher gas permeability than when an oil-based binder is used.

According to this preferred embodiment, preferred examples of the binder in the second slurry include, but are not limited to, one or two or more of polyvinyl alcohol (PVA), Polyoxyethylene Ether (PEO), water-soluble polyacrylate, and water-soluble compound-modified polyacrylate.

By "water-soluble compound modified polyacrylate" is meant that the polyacrylate together with a water-soluble compound, preferably interacting with the polyacrylate, forms a binder, for example: specific examples of the water-soluble compound that may be used as the crosslinking agent for the polyacrylate may include, but are not limited to, one or more of N-methylolacrylamide, N-hydroxyethylacrylamide, (N-methylol) methacrylamide, and (N-hydroxyethyl) methacrylamide. The water-soluble compound may be contained in an amount of 1 to 10 parts by weight, preferably 2 to 8 parts by weight, more preferably 3 to 6 parts by weight, relative to 100 parts by weight of the polyacrylate.

The binder content of the second slurry is such that the inorganic material is bonded to form a unitary structure. Generally, the binder content of the second slurry may be 0.05 to 10 wt%, preferably 1 to 8 wt%.

The dispersant of the second slurry may be selected according to the kind of the binder, so that the dispersant can dissolve the binder and form an inorganic substance into a stable dispersion. For example, when the binder is a water-soluble binder, the dispersant of the second slurry may be water.

The second slurry preferably further contains at least one coupling agent to improve the adhesion of the inorganic substance to the surface of the polyolefin porous membrane and/or the non-conductive polymer fiber nonwoven fabric. The coupling agent is preferably a silane coupling agent, and specific examples thereof may include, but are not limited to, one or more of 3-glycidoxypropyltrimethoxysilane, 3-aminopropyltriethoxysilane, gamma-methacryloxypropyltrimethoxysilane, N-beta- (aminoethyl) -gamma-aminopropyltrimethoxysilane, N-beta- (aminoethyl) -gamma-aminopropylmethyldimethoxysilane and vinyltrimethoxysilane. The amount of the coupling agent may be selected according to the content of the inorganic substance in the second slurry. Generally, the coupling agent may be used in an amount of 0.5 to 5 parts by weight, preferably 0.8 to 4 parts by weight, and more preferably 1 to 3 parts by weight, relative to 100 parts by weight of the inorganic substance in the second slurry.

The second slurry may further contain a dispersant to promote dispersion stability of the inorganic particles in the dispersion medium, and specific examples thereof may include, but are not limited to, polyvinyl alcohol (PVA) and/or sodium polyacrylate (PAANa). The amount of dispersant in the second slurry may be conventionally selected. Generally, the content of the dispersant may be 0.1 to 10 parts by weight, preferably 0.2 to 5 parts by weight, relative to 100 parts by weight of the inorganic substance.

The second slurry may also contain a thickener to further enhance the coatability of the second slurry. The thickener in the second slurry may be a cellulose-based thickener and/or a polyacrylate-based alkali-swellable thickener (e.g., a basf latex D thickener). The content of the thickener may be 0.1 to 10 parts by weight, preferably 0.5 to 5 parts by weight, and more preferably 0.8 to 3 parts by weight, relative to 100 parts by weight of the inorganic substance.

The third slurry may also contain a surfactant to further improve the stability of the third slurry. The surfactant may be an anionic surfactant, and specific examples thereof may include, but are not limited to, one or more of sodium dodecylbenzenesulfonate, sodium caprylate, sodium lauryl sulfate, and sodium stearate. The content of the surfactant may be 0.1 to 5 parts by weight, preferably 0.2 to 4 parts by weight, relative to 100 parts by weight of the inorganic substance.

The amount of the second slurry to be applied may be selected according to the content of inorganic substances expected to be introduced into the battery separator. Generally, the coating amount of the second slurry on the surface of the non-conductive polymer fiber nonwoven fabric is preferably such that the total amount of inorganic substances located in the surface and pores of the non-conductive polymer fiber nonwoven fabric and between the non-conductive polymer fiber nonwoven fabric and the polyolefin porous membrane in the finally prepared battery separator is 20 to 85% by weight, preferably 30 to 80% by weight, more preferably 35 to 78% by weight, further preferably 40 to 76% by weight, still further preferably 45 to 75% by weight.

According to the method of the second aspect of the present invention, in step S13, pressure may be applied to the second slurry layer by roll pressing, thereby causing at least a portion of the slurry in the second slurry layer to penetrate into the non-conductive polymer fiber nonwoven layer. By applying pressure to the second slurry layer, a portion of the slurry in the second slurry layer also permeates through the non-conductive polymeric fibrous nonwoven fabric layer, thereby leaving at least a portion of the inorganic substance between the non-conductive polymeric fibrous nonwoven fabric layer and the polyolefin porous membrane. The rolling condition is preferably such that in the finally prepared battery separator, the thickness of the inorganic layer on the surface of the non-conductive polymer fiber non-woven fabric is 0 to 5 μm (preferably 0.1 to 5 μm, more preferably 1 to 4.5 μm, and further preferably 2 to 4 μm), the weight ratio of the inorganic substance between the non-conductive polymer fiber non-woven fabric layer and the polyolefin porous film to the inorganic substance on the surface of the non-conductive polymer fiber non-woven fabric and in the pores is 1: 2.5 to 16, preferably 1: 3-12.

According to the method of the second aspect of the present invention, in steps S11 and S13, coating may be performed by a conventional method, such as: one or a combination of more than two of brushing, rolling and spraying. In steps S11 and S13, the coating may be performed once or twice or more.

According to the method of the second aspect of the present invention, in steps S12 and S14, the drying is performed to remove volatile substances in the slurry layer, so that the slurry layer loses fluidity and forms a layer having a fixed shape. Generally, the drying in step S12 and step S14 may each be performed at a temperature of 40-80 ℃, preferably at a temperature of 50-70 ℃. The drying may be performed under normal pressure (i.e., 1 atm), or under reduced pressure, and is not particularly limited. The duration of the drying can be selected according to the temperature at which the drying is carried out and can generally be from 1 to 60min, preferably from 5 to 40min, more preferably from 10 to 30 min.

According to the method of the second aspect of the invention, the polyolefin porous membrane may be a porous membrane capable of swelling the liquid electrolyte and transporting lithium ions. Preferably, the polymer in the polyolefin porous membrane layer is polyethylene and/or polypropylene. When the polymer in the polyolefin porous membrane layer is polyethylene and polypropylene, the polyolefin porous membrane layer may be a composite layer of polyethylene and polypropylene, and specific examples thereof may include, but are not limited to, a PE/PP/PE composite substrate layer.

The polyolefin porous membrane layer may have a thickness of 1 to 50 μm, for example: 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 25 μm, 26 μm, 27 μm, 28 μm, 29 μm, 30 μm, 31 μm, 32 μm, 33 μm, 34 μm, 35 μm, 36 μm, 37 μm, 38 μm, 39 μm, 40 μm, 41 μm, 42 μm, 43 μm, 44 μm, 45 μm, 46 μm, 47 μm, 48 μm, 49 μm, or 50 μm. In a preferred embodiment of the method according to the second aspect of the present invention, the thickness of the polyolefin porous membrane layer is 5 to 20 μm, such as 5 to 15 μm.

According to the method of the second aspect of the present invention, the non-conductive polymer fiber non-woven fabric layer is preferably a non-woven fabric formed using high-strength fibers. The polymer in the non-conductive polymer fiber non-woven fabric layer is preferably one or more of polyester (preferably polyethylene terephthalate, polybutylene terephthalate), polyimide, polyetherimide and polyether ether ketone.

According to the method of the second aspect of the present invention, the non-conductive polymer fiber nonwoven fabric is compounded with the polyolefin porous membrane as the base membrane, so that the thickness of the non-conductive polymer fiber nonwoven fabric can be significantly reduced, thereby reducing the total thickness of the battery separator, as compared with the case where the non-conductive polymer fiber nonwoven fabric is used alone as the base membrane. According to the method of the second aspect of the invention, the thickness of the non-conductive polymer fiber nonwoven layer is preferably 5 to 20 μm, for example: 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, or 20 μm. More preferably, the non-conductive polymer fiber nonwoven layer has a thickness of 10 to 18 μm.

According to the method of the second aspect of the present invention, the non-conductive polymer fiber nonwoven fabric is compounded with the polyolefin porous film as the base film, and the separator can have higher strength even if the nonwoven fabric having a smaller fiber diameter is used as compared with the case where the non-conductive polymer fiber nonwoven fabric alone is used as the base film. According to the method of the second aspect of the invention, the diameter of the fibers in the non-conductive polymer fiber nonwoven layer is preferably 0.5 to 5 μm, for example: 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 2 μm, 3 μm, 4 μm, or 5 μm. More preferably, the diameter of the fibers in the non-conductive polymer fiber nonwoven layer is 2-5 μm.

According to the method of the second aspect of the invention, the porosity of the non-conductive polymer fiber nonwoven layer is preferably 35 to 70%, and may be, for example: 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, or 70%. The porosity of the non-conductive polymer fiber nonwoven fabric layer is more preferably 40 to 65%, still more preferably 45 to 60%, and still more preferably 50 to 55%.

According to the method of the second aspect of the present invention, the other surface of the polyolefin porous membrane layer may be a blank surface, or may have an inorganic layer, and may be connected to another non-conductive polymer fiber non-woven fabric layer through the inorganic layer.

In another embodiment, the other surface of the polyolefin porous membrane layer has a third inorganic layer. According to this embodiment, the second slurry may be applied to the other surface of the polyolefin porous film and dried to form the third inorganic layer on the other surface of the polyolefin porous film. The battery separator according to this embodiment has the following structure: third inorganic layer | polyolefin porous membrane layer | second inorganic layer | non-conductive polymer fiber nonwoven layer | first inorganic layer. In this embodiment, the coating amount of the second slurry on the surface of the polyolefin porous membrane layer is preferably such that the content of the third inorganic layer is 5 to 50% by weight, preferably 10 to 48% by weight, more preferably 20 to 46% by weight, still more preferably 30 to 45% by weight, and still more preferably 35 to 40% by weight, based on the total amount of the battery separator.

In yet another embodiment, the other surface of the polyolefin porous membrane layer is joined to another non-conductive polymer fibrous nonwoven layer by an inorganic layer. According to this embodiment, the steps S11 to S14 may be repeatedly performed on the other surface of the polyolefin porous membrane layer, thereby preparing a battery separator having the following structure: first inorganic layer | non-conductive polymer fiber nonwoven layer | second inorganic layer | polyolefin porous film layer | second inorganic layer | non-conductive polymer fiber nonwoven layer | first inorganic layer. According to the separator of this embodiment, the non-conductive polymer fiber nonwoven fabric layer, the second inorganic layer, and the first inorganic layer located on both sides of the polyolefin porous membrane layer may be the same or different, and preferably, the same.

According to the production method of the second aspect of the present invention, the thickness of the battery separator produced by the production method may be conventionally selected, for example, from 10 to 40 μm. The separator produced by the method according to the second aspect of the present invention exhibits improved strength, even with a small thickness. According to the production method of the second aspect of the present invention, the thickness of the battery separator produced by the production method is preferably 15 to 38 μm, more preferably 20 to 36 μm.

s21, providing a third slurry with inorganic matter dispersed therein;

s24, drying the wet film;

According to the method of the third aspect of the invention, the content of the inorganic substance in the third slurry is such that the inorganic substance forms a stable dispersion. Generally, the content of the inorganic substance in the third slurry may be 5 to 50% by weight, preferably 10 to 40% by weight, more preferably 20 to 30% by weight.

The inorganic substance in the third slurry may be Al₂O₃、SiO₂、BaSO₄、TiO₂、CuO、MgO、LiAlO₂、ZrO₂Carbon nanotube, BN, SiC, Si₃N₄、WC、BC、AlN、Fe₂O₃、BaTiO₃、MoS₂、α-V₂O₅、PbTiO₃、TiB₂、CaSiO₃One or more of molecular sieve, clay and kaolin, preferably Al₂O₃And/or SiO₂。

In this embodiment, the inorganic material in the third slurry is present in the form of particles. The inorganic particles in the third slurry may have an average particle diameter of 10nm to 3 μm, for example: 10nm, 20nm, 30nm, 40nm, 50nm, 100nm, 150nm, 200nm, 250nm, 300nm, 350nm, 400nm, 450nm, 500nm, 550nm, 600nm, 650nm, 700nm, 750nm, 800nm, 850nm, 900nm, 950nm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, or 3 μm. Preferably, the inorganic particles in the third slurry have an average particle diameter of 20nm to 1 μm. More preferably, the inorganic particles in the third slurry have an average particle diameter of 30nm to 800 nm. Further preferably, the inorganic particles in the third slurry have an average particle diameter of 100nm to 400 nm. Still more preferably, the inorganic particles include first inorganic particles having an average particle diameter of 40 to 100nm and second inorganic particles having an average particle diameter of 300 to 400 nm. The weight ratio of the first inorganic particles to the second inorganic particles may be 0.1 to 10: 1, preferably 0.5 to 5: 1, more preferably 1-2: 1.

the third slurry also contains a binder to bind the minerals into a unitary structure. The binder in the third slurry may be an oily binder, such as one or more of a polyurethane binder, an epoxy resin binder, a polyvinylidene fluoride binder, a polytetrafluoroethylene binder, and an acrylate-type binder.

In a preferred embodiment, the binder in the third slurry is a water-soluble binder. According to the preferred embodiment, not only is the battery separator more environmentally friendly, but also the battery separator has higher gas permeability than when an oil-based binder is used.

According to this preferred embodiment, preferred examples of the binder in the third slurry include, but are not limited to, one or two or more of polyvinyl alcohol (PVA), Polyoxyethylene Ether (PEO), water-soluble polyacrylate, and water-soluble compound-modified polyacrylate.

The binder content of the third slurry is such that the inorganic material is bonded to form a unitary structure. Generally, the concentration of the binder in the third slurry may be 0.05 to 10 wt%, preferably 1 to 8 wt%.

The dispersant of the third slurry may be selected according to the kind of the binder, so that the dispersant can dissolve the binder and form an inorganic substance into a stable dispersion. For example, when the binder is a water-soluble binder, the dispersant of the third slurry may be water.

The third slurry preferably further contains at least one coupling agent to improve the adhesion of the inorganic substance to the surface of the polyolefin porous membrane and/or the non-conductive polymer fiber nonwoven fabric. The coupling agent is preferably a silane coupling agent, and specific examples thereof may include, but are not limited to, one or more of 3-glycidoxypropyltrimethoxysilane, 3-aminopropyltriethoxysilane, gamma-methacryloxypropyltrimethoxysilane, N-beta- (aminoethyl) -gamma-aminopropyltrimethoxysilane, N-beta- (aminoethyl) -gamma-aminopropylmethyldimethoxysilane and vinyltrimethoxysilane. The amount of the coupling agent may be selected according to the content of the inorganic substance in the third slurry. Generally, the coupling agent may be used in an amount of 0.5 to 5 parts by weight, preferably 0.8 to 4 parts by weight, and more preferably 1 to 3 parts by weight, relative to 100 parts by weight of the inorganic substance in the third slurry.

The third slurry may further contain a dispersant to promote dispersion stability of the inorganic particles in the dispersion medium, and specific examples thereof may include, but are not limited to, polyvinyl alcohol (PVA) and/or sodium polyacrylate (PAANa). The amount of dispersant in the third slurry may be conventionally selected. Generally, the content of the dispersant may be 0.1 to 10 parts by weight, preferably 0.2 to 5 parts by weight, relative to 100 parts by weight of the inorganic substance.

The third slurry may also contain a thickener to further enhance the coatability of the third slurry. The thickener in the third slurry may be a cellulose-based thickener and/or a polyacrylate-based alkali-swellable thickener (e.g., a basf latex D thickener). The content of the thickener may be 0.1 to 10 parts by weight, preferably 0.5 to 5 parts by weight, and more preferably 0.8 to 3 parts by weight, relative to 100 parts by weight of the inorganic substance.

The amount of the third slurry to be applied may be selected according to the content of inorganic substances expected to be introduced into the battery separator. Generally, the coating amount of the third slurry on the surface of the non-conductive polymer fiber nonwoven fabric is preferably such that the total amount of inorganic substances located in the surface and pores of the non-conductive polymer fiber nonwoven fabric and between the non-conductive polymer fiber nonwoven fabric and the polyolefin porous membrane in the finally prepared battery separator is 20 to 85% by weight, preferably 30 to 80% by weight, more preferably 35 to 78% by weight, further preferably 40 to 76% by weight, still further preferably 45 to 75% by weight.

According to the method of the third aspect of the present invention, in step S22, the third slurry layer may be formed on the surface of the first base film by various methods, such as: one or a combination of more than two of dipping, spraying, brushing and rolling. In a preferred embodiment, the first base film is impregnated with the third slurry to form a third slurry layer on the surface of the first base film.

According to the method of the third aspect of the present invention, in step S23, the second base film is laminated with one surface of the first base film having the third slurry layer, thereby joining the polyolefin porous film and the non-conductive polymer fiber nonwoven fabric through the third slurry layer. In step S23, the third slurry layer for bonding to the second base film is preferably scraped off before the press bonding is performed, from the viewpoint of further improving the surface flatness of the battery separator to be produced. In step S23, the other surface of the first base film having the third slurry layer may be smoothed to improve the flatness of the inorganic layer formed on the surface of the non-conductive polymer fiber nonwoven fabric after drying.

According to the method of the third aspect of the present invention, when the first base film is a polyolefin porous film and the second base film is a non-conductive polymer fiber non-woven fabric, one or a combination of two or more of the following steps is further included:

s231, applying pressure to the third slurry layer to make part of the slurry in the third slurry layer penetrate through the non-conductive polymer fiber non-woven fabric and form a slurry layer on the surface of the non-conductive polymer fiber non-woven fabric;

and S232, forming a slurry layer on the surface of the non-conductive polymer fiber non-woven fabric by using the third slurry.

In step S231, pressure may be applied to the third slurry layer by roll pressing, so that a portion of the slurry in the third slurry layer penetrates into the non-conductive polymer fiber nonwoven fabric layer. By applying pressure to the third slurry layer, a portion of the slurry in the third slurry layer also penetrates through the non-conductive polymer fiber nonwoven layer, thereby forming a slurry layer on the surface of the non-conductive polymer fiber nonwoven layer.

Operations S231 and S232 may be used alone or in combination, so as to form a desired inorganic layer on the surface of the non-conductive polymer fiber nonwoven fabric.

The conditions of step S231 and/or step S232 are preferably such that in the finally prepared battery separator, the thickness of the inorganic layer on the surface of the non-conductive polymer fiber non-woven fabric is 0 to 5 μm (preferably 0.1 to 5 μm, more preferably 1 to 4.5 μm, and further preferably 2 to 4 μm), the weight ratio of the inorganic substance between the non-conductive polymer fiber non-woven fabric layer and the polyolefin porous membrane to the inorganic substance on the surface of the non-conductive polymer fiber non-woven fabric and in the pores is 1: 2.5 to 16, preferably 1: 3-12.

According to the method of the third aspect of the present invention, in step S24, the drying is performed to remove volatile substances in the slurry layer, so that the slurry layer loses fluidity and forms a layer having a fixed shape. Generally, in step S24, the drying may be performed at a temperature of 40-80 deg.C, preferably at a temperature of 50-70 deg.C. The drying may be performed under normal pressure (i.e., 1 atm), or under reduced pressure, and is not particularly limited. The duration of the drying can be selected according to the temperature at which the drying is carried out and can generally be from 1 to 60min, preferably from 5 to 40min, more preferably from 10 to 30 min.

According to the method of the third aspect of the invention, the polyolefin porous membrane may be a porous membrane capable of swelling the liquid electrolyte and transporting lithium ions. Preferably, the polymer in the polyolefin porous membrane layer is polyethylene and/or polypropylene. When the polymer in the polyolefin porous membrane layer is polyethylene and polypropylene, the polyolefin porous membrane layer may be a composite layer of polyethylene and polypropylene, and specific examples thereof may include, but are not limited to, a PE/PP/PE composite substrate layer.

The polyolefin porous membrane layer may have a thickness of 1 to 50 μm, for example: 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 25 μm, 26 μm, 27 μm, 28 μm, 29 μm, 30 μm, 31 μm, 32 μm, 33 μm, 34 μm, 35 μm, 36 μm, 37 μm, 38 μm, 39 μm, 40 μm, 41 μm, 42 μm, 43 μm, 44 μm, 45 μm, 46 μm, 47 μm, 48 μm, 49 μm, or 50 μm. In a preferred embodiment, the thickness of the polyolefin porous membrane layer is 5-20 μm, such as 5-15 μm.

According to the method of the third aspect of the present invention, the non-conductive polymer fiber non-woven fabric layer is preferably a non-woven fabric formed using high-strength fibers. The polymer in the non-conductive polymer fiber non-woven fabric layer is preferably one or more of polyester (preferably polyethylene terephthalate, polybutylene terephthalate), polyimide, polyetherimide and polyether ether ketone.

According to the method of the third aspect of the present invention, the non-conductive polymer fiber nonwoven fabric is combined with the polyolefin porous membrane as the base membrane, so that the thickness of the non-conductive polymer fiber nonwoven fabric can be significantly reduced, thereby reducing the total thickness of the battery separator, as compared with the case where the non-conductive polymer fiber nonwoven fabric is used alone as the base membrane. According to the method of the third aspect of the invention, the thickness of the non-conductive polymer fiber nonwoven layer is preferably 5 to 20 μm, for example: 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, or 20 μm. More preferably, the non-conductive polymer fiber nonwoven layer has a thickness of 10 to 18 μm.

According to the method of the third aspect of the present invention, the non-conductive polymer fiber nonwoven fabric is compounded with the polyolefin porous film as the base film, and the separator can have higher strength even if the nonwoven fabric having a smaller fiber diameter is used as compared with the case where the non-conductive polymer fiber nonwoven fabric alone is used as the base film. According to the method of the third aspect of the invention, the diameter of the fibers in the non-conductive polymer fiber nonwoven layer is preferably 0.5 to 5 μm, for example: 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 2 μm, 3 μm, 4 μm, or 5 μm. More preferably, the diameter of the fibers in the non-conductive polymer fiber nonwoven layer is 2-5 μm.

According to the method of the third aspect of the invention, the porosity of the non-conductive polymer fiber nonwoven layer is preferably 35 to 70%, and may be, for example: 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, or 70%. The porosity of the non-conductive polymer fiber nonwoven fabric layer is more preferably 40 to 65%, still more preferably 45 to 60%, and still more preferably 50 to 55%.

According to the method of the third aspect of the present invention, the other surface of the polyolefin porous membrane layer may be a blank surface, or may have an inorganic layer, and may be connected to another non-conductive polymer fiber non-woven fabric layer through the inorganic layer.

In another embodiment, the other surface of the polyolefin porous membrane layer has a third inorganic layer. According to this embodiment, the third slurry may be applied to the other surface of the polyolefin porous film and dried to form the third inorganic layer on the other surface of the polyolefin porous film. The battery separator according to this embodiment has the following structure: third inorganic layer | polyolefin porous membrane layer | second inorganic layer | non-conductive polymer fiber nonwoven layer | first inorganic layer. In this embodiment, the coating amount of the third slurry on the surface of the polyolefin porous membrane layer is preferably such that the content of the third inorganic layer is 5 to 50% by weight, preferably 10 to 48% by weight, more preferably 20 to 46% by weight, still more preferably 30 to 45% by weight, and still more preferably 35 to 40% by weight, based on the total amount of the battery separator.

In yet another embodiment, the other surface of the polyolefin porous membrane layer is joined to another non-conductive polymer fibrous nonwoven layer by an inorganic layer. According to this embodiment, the steps S21 to S24 may be repeatedly performed on the other surface of the polyolefin porous membrane layer, thereby preparing a battery separator having the following structure: first inorganic layer | non-conductive polymer fiber nonwoven layer | second inorganic layer | polyolefin porous film layer | second inorganic layer | non-conductive polymer fiber nonwoven layer | first inorganic layer. According to the separator of this embodiment, the non-conductive polymer fiber nonwoven fabric layer, the second inorganic layer, and the first inorganic layer located on both sides of the polyolefin porous membrane layer may be the same or different, and preferably, the same.

According to the production method of the third aspect of the present invention, the thickness of the battery separator produced by the production method may be conventionally selected, for example, from 10 to 40 μm. The separator produced by the method according to the third aspect of the present invention exhibits improved strength, even with a small thickness. According to the production method of the third aspect of the present invention, the thickness of the battery separator produced by the production method is preferably 15 to 38 μm, more preferably 20 to 36 μm.

According to the lithium ion battery provided by the invention, the battery diaphragm provided by the invention is adopted, so that the lithium ion battery has obviously improved high-temperature safety performance and high-low temperature storage performance. The positive electrode and the negative electrode may be conventional ones in lithium ion batteries, and are not particularly limited.

Generally, the positive electrode contains a positive electrode active material and a conductive agentAnd a binder. The positive electrode active material used includes any positive electrode material that can be used in a lithium ion battery, 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 electrode contains a negative electrode active material, a conductive agent, and a binder. The negative electrode active material may be one 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.

(2) and arranging the polymer diaphragm between the positive electrode and the negative electrode to form a battery pole core, and then packaging.

The step (2) may be performed by a conventional method in the technical field of lithium ion battery preparation, and the present invention is not particularly limited. In the step (2), the battery pole core can be filled with electrolyte, or can be directly packaged without being filled with electrolyte.

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

In the following examples and comparative examples, the particle size was measured as a volume average particle size using a laser particle sizer.

Examples 1-17 are intended to illustrate the invention.

Example 1

(1) Preparing a first slurry containing a binder

Polyoxyethylene ether (PEO, available from alatin, with a number average molecular weight of 100 ten thousand (GPC method)) was dispersed in water to form a first slurry containing a binder, the concentration of PEO in the first slurry being 1 wt%.

(2) Preparing a second slurry containing inorganic substances dispersed therein

2kg of aluminum oxide (volume average particle diameter of 400nm), 0.01kg of sodium polyacrylate (number average molecular weight of 9000, obtained from Yuanchang trade Co., Ltd., Guangzhou), and 0.024kg of sodium carboxymethylcellulose (1% by weight aqueous solution having a viscosity of 2500-.

After the mixture was stirred at 6000rpm for 1.5 hours, 0.02kg of 3-glycidoxypropyltrimethoxysilane was added thereto and the stirring was continued for 1.5 hours, and then 0.1kg of a polyacrylate binder containing N-methylolacrylamide (available from Shanghai Aigao, trademark: 1050 type, N-methylolacrylamide content 4% by weight based on the total amount of the binder) was added thereto and stirred at 3000rpm for 1.5 hours, followed by 0.08kg of sodium dodecylbenzenesulfonate and the stirring was continued at 3000rpm for 0.5 hours to obtain a second slurry.

(3) Making a diaphragm

The first slurry was coated on one surface of a polyethylene porous film (purchased from SK corporation, japan, and having a brand number of BD0701, a thickness of 7 μm, and a porosity of 38%) to form a first slurry layer. Then, a polyethylene terephthalate (PET) nonwoven fabric film (purchased from Mitsubishi paper, having a thickness of 10 μm, a porosity of 55%, and a fiber diameter of 2 to 5 μm) was laminated on the first slurry layer of the polyethylene porous film, and then air-dried at 60 ℃ and normal pressure (1 atm) for 10 min.

Next, the second slurry was coated on the surface of the PET nonwoven fabric to form a second slurry layer. Then, a part of the slurry in the second slurry layer was pressed into fiber pores of the PET nonwoven fabric by roll pressing to obtain a wet film.

Finally, the obtained wet film was dried at 60 ℃ and normal pressure (1 atm) for 10min to obtain a battery separator (total thickness: 22 μm) according to the present invention, which had a structure of: polyethylene porous film | second inorganic layer | PET nonwoven fabric film | first inorganic layer, the first inorganic layer including a first portion and a second portion, the first portion being located on a surface of the non-conductive polymer fiber nonwoven fabric layer, the second portion being located in at least a part of pores of the non-conductive polymer fiber nonwoven fabric layer, the second portion being of an integral structure with the first portion, the first portion having a thickness of 4 μm, a weight ratio of the second inorganic layer to the first inorganic layer being 1: 8; the total amount of inorganic substances in the first inorganic layer and the second inorganic layer was 70 wt% based on the total amount of the battery separator.

Example 2

A battery separator was prepared in the same manner as in example 1, except that the conditions for roll-pressing the second slurry layer were controlled such that the thickness of the first portion was 1 μm and the total thickness of the finally prepared battery separator was 19 μm.

Example 3

A battery separator was prepared in the same manner as in example 1, except that the concentration of PEO in the first slurry was 10 wt%.

Example 4

A battery separator was produced in the same manner as in example 1, except that the volume average particle diameter of alumina in the second slurry was 700 nm.

Example 5

A battery separator was produced in the same manner as in example 1, except that the volume average particle diameter of alumina in the second slurry was 40 nm.

Example 6

A battery separator was prepared in the same manner as in example 1, except that, in the second slurry, alumina was large-particle alumina and small-particle alumina in a weight ratio of 1: 1, wherein the volume average particle diameter of the small alumina particles is 40nm, and the volume average particle diameter of the large alumina particles is 400 nm.

Comparative example 1

The second slurry prepared in example 1 was coated on one side surface of a polyethylene porous membrane (same as in example 1) to form a first slurry layer, and then air-dried at 60 ℃ and normal pressure (1 atm) for 10min to obtain a battery separator having an inorganic layer, the battery separator having a structure of: polyethylene porous membrane | inorganic layer, the thickness of the inorganic layer is 4 μm.

Comparative example 2

The first slurry was coated on one surface of the polyethylene porous membrane (same as example 1) to form a first slurry layer. Then, a PET nonwoven fabric film (same as example 1) was press-bonded on the first slurry layer of the polyethylene porous film, and then air-dried at 60 ℃ and normal pressure (1 atm) for 10min to obtain a battery separator having a structure of: polyethylene porous film | PET nonwoven fabric film.

Comparative example 3

The second slurry (same as example 1) was coated on the surface of the PET nonwoven fabric (same as example 1) to form a second slurry layer. Then, a part of the slurry in the second slurry layer was pressed into fiber pores of the PET nonwoven fabric by roll pressing to obtain a wet film. The obtained wet film was dried at 60 ℃ and normal pressure (1 atm) for 10min to obtain a battery separator having a structure of: PET non-woven fabric film | inorganic layer having a thickness of 4 μm.

Comparative example 4

A battery separator was prepared in the same manner as in example 1, except that the PET nonwoven fabric film was replaced with a polyethylene porous film (same as in example 1), to obtain a battery separator having a structure of: polyethylene porous membrane | second inorganic layer | polyethylene porous membrane | first inorganic layer, the first inorganic layer includes first portion and second portion, the first portion is located the surface of polyethylene porous membrane, the second portion is located at least partial pore space of polyethylene porous membrane, the second portion is structure as an organic whole with the first portion, the thickness of first portion is 4 μm, the weight ratio of second inorganic layer to first inorganic layer is 1: 8; the total amount of inorganic substances in the first inorganic layer and the second inorganic layer was 70 wt% based on the total amount of the battery separator.

Comparative example 5

A battery separator was prepared in the same manner as in example 1, except that the polyethylene porous film was replaced with a PET nonwoven fabric film (same as in example 1), to obtain a battery separator having a structure of: PET nonwoven film second inorganic layer PET nonwoven film first inorganic layer, the first inorganic layer including a first portion located on a surface of the PET nonwoven film and a second portion located in at least a part of pores of the PET nonwoven film, the second portion being of an integral structure with the first portion, the first portion having a thickness of 4 μm, a weight ratio of the second inorganic layer to the first inorganic layer being 1: 8; the total amount of inorganic substances in the first inorganic layer and the second inorganic layer was 70 wt% based on the total amount of the battery separator.

Example 7

A battery separator was prepared in the same manner as in example 1, except that the polyoxyethylene ether in the first slurry was replaced with an equal weight of vinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP, available from akram, under the trademark LBG), to prepare a battery separator according to the present invention.

Example 8

The PET nonwoven fabric film (same as in example 1) was immersed in the second slurry (same as in example 1) for 0.5 hour and then taken out. After the slurry on one side surface of the PET nonwoven fabric film was scraped off with a doctor blade, a polyethylene porous film (same as in example 1) was laminated on the scraped-off surface, and then dried in a forced air drying oven at 60 ℃ and normal pressure (1 atm) for 10min to obtain a battery separator (total thickness: 22 μm) according to the present invention, which had a structure: polyethylene porous film | second inorganic layer | PET nonwoven fabric film | first inorganic layer, the first inorganic layer including a first portion and a second portion, the first portion being located on a surface of the non-conductive polymer fiber nonwoven fabric layer, the second portion being located in at least a part of pores of the non-conductive polymer fiber nonwoven fabric layer, the second portion being of an integral structure with the first portion, the first portion having a thickness of 4 μm, a weight ratio of the second inorganic layer to the first inorganic layer being 1: 12; the total amount of inorganic matter in the first inorganic layer and the second inorganic layer was 75 wt% based on the total amount of the battery separator.

Example 9

The second slurry (same as example 1) was coated on one surface of the polyethylene porous membrane (same as example 1) to form a second slurry layer. A PET nonwoven fabric film (same as example 1) was laminated on the surface of the second slurry layer and part of the slurry in the second slurry layer was allowed to pass through the PET nonwoven fabric film and form a slurry layer on the surface of the PET nonwoven fabric film layer, which was dried in a forced air drying oven at 60 ℃ and normal pressure (1 atm standard atmospheric pressure) for 10min to obtain a battery separator (total thickness 21 μm) according to the present invention, which had a structure of: polyethylene porous film | second inorganic layer | PET nonwoven fabric film | first inorganic layer, the first inorganic layer including a first portion and a second portion, the first portion being located on a surface of the non-conductive polymer fiber nonwoven fabric layer, the second portion being located in at least a part of pores of the non-conductive polymer fiber nonwoven fabric layer, the second portion being of an integral structure with the first portion, the first portion having a thickness of 4 μm, a weight ratio of the second inorganic layer to the first inorganic layer being 1: 3; the total amount of inorganic substances in the first inorganic layer and the second inorganic layer was 70 wt% based on the total amount of the battery separator.

Example 10

(1) Preparing a first slurry containing a binder

Polyvinyl alcohol (PVA, available from alatin, having a number average molecular weight of 10 ten thousand (GPC method)) was dispersed in water to form a first slurry containing a binder, the concentration of PVA in the first slurry being 2.5 wt%.

(2) Preparing a second slurry containing inorganic substances dispersed therein

2kg of silica (volume average particle diameter of 100nm), 0.1kg of sodium polyacrylate (number average molecular weight of 9000, available from Yuanchuan trade Co., Ltd., Guangzhou), and 0.05kg of sodium carboxymethylcellulose (1% by weight aqueous solution having a viscosity of 3000 mPa. multidot.S, available from Xinxiang and Toyoda Power Material Ltd., trade name of BTT-3000) were uniformly mixed with water to obtain a mixture having a silica content of 20% by weight.

After stirring the mixture at 6000rpm for 2 hours, 0.05kg of 3-glycidoxypropyltrimethoxysilane was added and stirring was continued for 2 hours, and then 0.5kg of a polyacrylate binder containing N-methylolacrylamide (obtained from Aladdin and having an N-methylolacrylamide content of 5% by weight based on the total amount of the binder) was added and stirred at 3000rpm for 2 hours, followed by 0.005kg of sodium dodecylbenzenesulfonate and stirring was continued at 3000rpm for 0.5 hours to obtain a second slurry.

(3) Making a diaphragm

The first slurry was coated on one surface of a polypropylene porous membrane (purchased from celegard, 12 μm in thickness, 40% in porosity) to form a first slurry layer. Then, a PET nonwoven fabric film (purchased from Mitsubishi paper, having a thickness of 15 μm, a porosity of 50%, and a fiber diameter of 2 to 5 μm) was laminated on the first slurry layer of the polypropylene porous film, and then dried in a forced air drying oven at 50 ℃ and normal pressure (1 atm) for 20 min.

Next, the second slurry was coated on the surface of the PET nonwoven fabric to form a second slurry layer. Then, a part of the slurry in the second slurry layer was pressed into fiber pores of the PET nonwoven fabric by roll pressing to obtain a wet film. The resulting wet film was dried in a forced air drying oven at 50 ℃ for 20 min.

The other side surface of the polypropylene porous membrane of the film obtained by drying was coated with the second slurry, and then dried in a forced air drying oven at 50 ℃ for 20min to obtain a battery separator (total thickness: 31 μm) according to the present invention, which had a structure of: third inorganic layer | polypropylene porous film | second inorganic layer | PET nonwoven fabric film | first inorganic layer, the first inorganic layer including a first portion located on a surface of the non-conductive polymer fiber nonwoven fabric layer and a second portion located in at least a part of pores of the non-conductive polymer fiber nonwoven fabric layer, the second portion being of an integral structure with the first portion, the first portion having a thickness of 3 μm, and a weight ratio of the second inorganic layer to the first inorganic layer being 1: 12. the thickness of the third inorganic layer is 1 μm; the total amount of inorganic substances in the first inorganic layer and the second inorganic layer was 45 wt%, and the content of the third inorganic layer was 40 wt%, based on the total amount of the battery separator.

Example 11

The PET nonwoven fabric film (same as in example 10) was immersed in the second slurry (same as in example 10) for 0.5 hour and then taken out. After the slurry on one side surface of the PET nonwoven fabric film was scraped off with a spatula, a polypropylene porous film (same as in example 10) was laminated on the scraped-off surface, and then dried in a 60 ℃ forced air drying oven for 10 min. Then, after coating the second slurry on the other side surface of the polypropylene porous membrane, it was dried in a forced air drying oven at 50 ℃ for 20min to obtain a battery separator (total thickness: 32 μm) according to the present invention, which had a structure of: third inorganic layer | polypropylene porous film | second inorganic layer | PET nonwoven fabric film | first inorganic layer, the first inorganic layer including a first portion located on a surface of the non-conductive polymer fiber nonwoven fabric layer and a second portion located in at least a part of pores of the non-conductive polymer fiber nonwoven fabric layer, the second portion being of an integral structure with the first portion, the first portion having a thickness of 3 μm, and a weight ratio of the second inorganic layer to the first inorganic layer being 1: 12. the thickness of the third inorganic layer is 1 μm; the total amount of inorganic substances in the first inorganic layer and the second inorganic layer was 45 wt%, and the content of the third inorganic layer was 40 wt%, based on the total amount of the battery separator.

The separators prepared in examples 1 to 11 and comparative examples 1 to 5 were tested for their properties by the following methods, and the results are listed in table 1.

(1) Permeability (gurley) test

The membrane was cut to an area of 6.45cm²The smaller the value of the time (s/100mL) required for 100mL of gas (air) to permeate the membrane sample, as measured by the Gurley-4110 Grignard meter, the better the gas permeability, wherein the pressure was 12.39cm (height of water column).

(2) Test of Peel Strength

A diaphragm sample of 40mm multiplied by 100mm is cut, two sides of the diaphragm are respectively fixed on a fixed clamp and a movable clamp by using adhesive tapes, the tensile force required for peeling a PET non-woven fabric layer and a polyolefin film in the diaphragm by reverse stretching at 180 ℃ is measured, and the larger the required tensile force is, the higher the peeling strength of the composite film is, and the higher the bonding strength is.

(3) Mechanical property test at normal temperature

And (3) adopting a Shenzhen Junrui universal testing machine (which is calibrated) to measure the tensile property and the needling strength of the lithium ion battery diaphragm, wherein the testing temperature is 25 ℃, and the diameter of the adopted steel needle is 3mm when the needling experiment is carried out.

(4) Heat shrinkage test

Cutting the diaphragm into a sample of 6cm multiplied by 6cm, placing the sample in an oven, baking the sample at 120 ℃, 140 ℃, 160 ℃ and 180 ℃ for 1h, measuring the length and width of the sample, and calculating the thermal shrinkage rate according to the following formula:

the heat shrinkage rate was (1-length of sample after heat shrinkage/6) × 100%.

(5) Measurement of ion conductivity

Using the AC impedance test, specifically, the separators were each cut into a circular piece having a diameter of 17mm, dried in a vacuum oven at 80 ℃ for 24 hours, and then placed between two Stainless Steel (SS) electrodes to absorb a sufficient amount of an electrolyte containing 32.5% by weight of Ethylene Carbonate (EC), 32.5% by weight of Ethyl Methyl Carbonate (EMC), 32.5% by weight of dimethyl carbonate (DMC), 2.5% by weight of Vinylene Carbonate (VC), and 1mol/L of LiPF₆(lithium hexafluorophosphate)), sealing in a 2016 type button cell, performing an alternating current impedance experiment, wherein the intersection point of a linear axis and a real axis is the bulk resistance of the electrolyte, and calculating the ionic conductivity (sigma) by adopting the following formula:

σ＝L/A·R

wherein L is the thickness (cm) of the diaphragm,

a is the contact area (cm) of the stainless steel plate and the diaphragm²)，

R is the bulk resistance (mS) of the electrolyte.

(6) High temperature strength

Cutting the diaphragm into a sample of 15cm multiplied by 10cm, placing the sample in an oven, baking the sample for 1h at 180 ℃, cutting the sample into a sample strip of 10cm multiplied by 1cm after cooling, and then measuring the tensile property of the lithium ion battery diaphragm by adopting a Shenzhen Junrui universal tester (both calibrated), wherein the test temperature is 25 ℃.

As can be seen from the results of table 1, the separator according to the present invention not only has good air permeability and normal temperature mechanical properties, but also maintains good strength and low shrinkage at high temperature.

Examples 12 to 17

Lithium ion batteries were prepared using the following methods with the separators prepared in examples 1 and 7 to 11, respectively.

(1) 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.

(2) In a drying room, LiCoO is added₂Preparing CSL454187 type LiCoO by winding a positive pole piece, a graphite negative pole piece and a diaphragm₂Filling electrolyte into the graphite soft package lithium ion battery pole core, and then packaging to obtain the lithium ion battery; wherein, the 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.

Comparative examples 6 to 10

Lithium ion batteries were fabricated in the same manner as in examples 12 to 17, except that the separators were the separators fabricated in comparative examples 1 to 5, respectively.

The performance of the lithium ion batteries prepared in examples 12 to 17 and comparative examples 6 to 10 was measured by the following method.

(1) 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 a 25 ℃ cycle performance test 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.

TABLE 2

¹: a polyethylene porous film (same as in example 1) was used as a separator (same below)

The test results in table 2 show that: the lithium ion battery according to the present invention shows excellent cycle performance.

Specifically, as can be seen from comparison of example 12 with comparative examples 7, 8 and 10, the lithium ion battery using the separator of the present invention has a higher capacity retention rate at normal temperature and thus has more excellent cycle performance at normal temperature.

(3) Battery self-discharge test

The lithium ion batteries after capacity grading prepared in the examples and the comparative examples were subjected to a self-discharge performance test using a (BK 6016, guangzhou langqi) lithium ion battery performance test cabinet, the specific method being as follows.

(1) After the state of charge (SOC) of 70% was obtained and aged at room temperature (25 ℃ C.) for 3 days, the Open Circuit Voltage (OCV) of the lithium ion battery was measured₁)；

(2) Aging the lithium ion battery aged at normal temperature at high temperature (45 deg.C) for 3 days, and measuring Open Circuit Voltage (OCV) of the lithium ion battery₂)；

(3) The voltage drop of the cell was calculated using the following formula, and the results are listed in table 3: voltage drop equal to OCV₁-OCV₂。

TABLE 3

Numbering	Source of membrane	Voltage drop (mV)
			Example 12	Example 1	10.8
Comparative example	/	10.7
			Comparative example 6	Comparative example 1	11.2
Comparative example 7	Comparative example 2	11.5
			Comparative example 8	Comparative example 3	33.8
Comparative example 9	Comparative example 4	10.8
			Comparative example 10	Comparative example 5	32.5
Example 13	Example 7	10.4
			Example 14	Example 8	10.7
Example 15	Example 9	10.6
			Example 16	Example 10	11.2
Example 17	Example 11	10.3

The larger the voltage drop value is, the higher the self-discharge degree of the lithium ion battery is, and the storage performance of the battery is not good. As can be seen from the results of table 3, the voltage drop according to the present invention is small, showing excellent storage properties. Comparing example 12 with comparative examples 8 and 10, it can be seen that the lithium ion battery using the separator of the present invention has a significantly lower voltage drop and thus more excellent storage properties.

(4) 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 4. As can be seen from Table 4: the lithium ion battery provided by the invention has high capacity recovery rate after high-temperature storage. As can be seen from comparison of example 12 with comparative examples 8 and 10, the lithium ion battery using the separator of the present invention showed a higher capacity recovery rate, indicating that the lithium ion battery had more excellent high temperature storage properties.

TABLE 4

Numbering	Source of membrane	Rate of capacity recovery
			Example 12	Example 1	0.99
Comparative example	/	0.97
			Comparative example 6	Comparative example 1	0.97
Comparative example 7	Comparative example 2	0.97
			Comparative example 8	Comparative example 3	0.92
Comparative example 9	Comparative example 4	0.96
			Comparative example 10	Comparative example 5	0.93
Example 13	Example 7	0.95
			Example 14	Example 8	0.99
Example 15	Example 9	0.98
			Example 16	Example 10	0.99
Example 17	Example 11	0.99

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 battery separator comprising a polyolefin porous membrane layer, a non-conductive polymer fiber nonwoven fabric layer, a first inorganic layer, and a second inorganic layer;

the first inorganic layer comprises a second portion, or the first inorganic layer comprises a second portion and a first portion, the first portion is positioned on the surface of the non-conductive polymer fiber non-woven fabric layer, the second portion is positioned in at least part of the pores of the non-conductive polymer fiber non-woven fabric layer;

the inorganic substances in the first inorganic layer and the second inorganic layer are each formed into an integral structure by a binder.

2. The battery separator according to claim 1, wherein the non-conductive polymer fiber nonwoven fabric layer has a porosity of 35-70%.

3. The battery separator of claim 1 wherein the fibers in the non-conductive polymeric fiber nonwoven layer have a diameter of 0.5-5 μm.

4. The battery separator of any of claims 1-3, wherein the polymer in the non-conductive polymer fiber nonwoven layer is one or more of polyester, polyimide, polyetherimide, and polyetheretherketone.

5. The battery separator of any of claims 1-3, wherein the polymer in the non-conductive polymer fiber nonwoven layer is polyethylene terephthalate and/or polybutylene terephthalate.

6. The battery separator according to any of claims 1-3, wherein the non-conductive polymer fiber nonwoven fabric layer has a thickness of 5-20 μm.

7. The battery separator according to claim 1, wherein the thickness of the polyolefin porous membrane layer is 1 to 50 μm.

8. The battery separator according to claim 7, wherein the thickness of the polyolefin porous membrane layer is 5-20 μm.

9. The battery separator according to claim 1, wherein the polyolefin porous membrane layer has a porosity of 30-50%.

10. The battery separator according to any of claims 1 and 7-9, wherein the polyolefin in the polyolefin porous membrane layer is polyethylene and/or polypropylene.

11. The battery separator of claim 1 wherein the second inorganic layer is a unitary structure with the first inorganic layer.

12. The battery separator according to claim 11, wherein the inorganic substance in the first inorganic layer and the second inorganic layer is the same or different, and each is Al₂O₃、SiO₂、BaSO₄、TiO₂、CuO、MgO、LiAlO₂、ZrO₂Carbon nanotube, BN, SiC, Si₃N₄、WC、BC、AlN、Fe₂O₃、BaTiO₃、MoS₂、α-V₂O₅、PbTiO₃、TiB₂、CaSiO₃Molecular sieve, clayOne or more than two of earth and kaolin.

13. The battery separator according to any one of claims 1, 11 and 12, wherein the inorganic substance in the first inorganic layer and the second inorganic layer is present in the form of particles having an average particle diameter of 10nm to 3 μm.

14. The battery separator according to claim 13, wherein the particles have an average particle size of 20nm to 1 μm.

15. The battery separator according to claim 14, wherein the particles have an average particle size of 30nm to 800 nm.

16. The battery separator according to claim 15, wherein the average particle diameter of the particles is 100nm to 400 nm.

17. The battery separator according to claim 13, wherein the particles comprise first inorganic particles and second inorganic particles, the first inorganic particles having an average particle size of 40-100nm, and the second inorganic particles having an average particle size of 300-400 nm.

18. The battery separator according to claim 17, wherein the weight ratio of the first inorganic particles to the second inorganic particles is 0.1-10: 1.

19. the battery separator according to claim 18, wherein the weight ratio of the first inorganic particles to the second inorganic particles is 0.5-5: 1.

20. the battery separator according to claim 19, wherein the weight ratio of the first inorganic particles to the second inorganic particles is 1-2: 1.

21. the battery separator of claim 1 wherein said binder is a water soluble binder.

22. The battery separator according to claim 21, wherein the binder is one or more of polyvinyl alcohol, polyoxyethylene ether, water-soluble polyacrylate, and water-soluble compound-modified polyacrylate.

23. The battery separator of any of claims 1, 11, and 12, wherein the thickness of the first portion is 0-5 μ ι η.

24. The battery separator of claim 1 wherein the first inorganic layer contains a first portion.

25. The battery separator of claim 24 wherein the thickness of the first portion is 0.1-5 μ ι η.

26. The battery separator of claim 25 wherein the thickness of the first portion is 1-4.5 μ ι η.

27. The battery separator of claim 26 wherein the thickness of the first portion is 2-4 μ ι η.

28. The battery separator of any of claims 24-27 wherein the first portion and the second portion are a unitary structure.

29. The battery separator of any of claims 1, 11, and 12, wherein the weight ratio of the second inorganic layer to the first inorganic layer is 1: 2.5-16.

30. The battery separator of claim 29 wherein the weight ratio of the second inorganic layer to the first inorganic layer is 1: 3-12.

31. The battery separator according to any of claims 1, 11 and 12, wherein the total amount of inorganic substances in the first inorganic layer and the second inorganic layer is 20-85 wt% based on the total amount of the battery separator.

32. The battery separator according to claim 31, wherein the total amount of inorganic substances in the first inorganic layer and the second inorganic layer is 30-80 wt% based on the total amount of the battery separator.

33. The battery separator according to claim 32, wherein the total amount of inorganic matter in the first inorganic layer and the second inorganic layer is 35-78 wt% based on the total amount of the battery separator.

34. The battery separator according to claim 33, wherein the total amount of inorganic substances in the first inorganic layer and the second inorganic layer is 40-76 wt% based on the total amount of the battery separator.

35. The battery separator according to claim 34, wherein the total amount of inorganic matter in the first inorganic layer and the second inorganic layer is 45-75 wt% based on the total amount of the battery separator.

36. A method of making the battery separator of claim 1, comprising the steps of:

s14, drying the wet film.

37. The production method according to claim 36, wherein the binder is a water-soluble binder.

38. The production method according to claim 37, wherein the binder is one or more of polyvinyl alcohol, polyoxyethylene ether, water-soluble polyacrylate, and water-soluble compound-modified polyacrylate.

39. A method of making the battery separator of claim 1, comprising the steps of:

s21, providing a third slurry with inorganic matter dispersed therein;

s24, drying the wet film;

the first base film and the second base film are each a polyolefin porous film or a non-conductive polymer fiber non-woven fabric, and one of the first base film and the second base film is a polyolefin porous film and the other is a non-conductive polymer fiber non-woven fabric,

when the first base film is a polyolefin porous film and the second base film is a non-conductive polymer fiber non-woven fabric, the method further comprises one or both of the following steps:

40. The method according to claim 36, wherein the content of the inorganic substance in the second slurry is 5 to 50% by weight.

41. The production method according to claim 39, wherein the content of the inorganic substance in the third slurry is 5 to 50% by weight.

42. The production method according to claim 40, wherein the content of the inorganic substance in the second slurry is 10 to 40% by weight.

43. The production method according to claim 41, wherein the content of the inorganic substance in the third slurry is 10 to 40% by weight.

44. The production method according to claim 42, wherein the content of the inorganic substance in the second slurry is 20 to 30% by weight.

45. The method according to claim 43, wherein the content of the inorganic substance in the third slurry is 20 to 30% by weight.

46. The production method according to claim 36, wherein the inorganic substance in the second slurry is present in the form of particles having an average particle diameter of 10nm to 3 μm.

47. The production method according to claim 39, wherein the inorganic substance in the third slurry is present in the form of particles having an average particle diameter of 10nm to 3 μm.

48. The production method according to claim 46, wherein the average particle diameter of the particles is 20nm to 1 μm.

49. The production method according to claim 47, wherein the average particle diameter of the particles is 20nm to 1 μm.

50. The production method according to claim 48, wherein the average particle diameter of the particles is 30nm to 800 nm.

51. The production method according to claim 49, wherein the average particle diameter of the particles is 30nm to 800 nm.

52. The production method according to claim 50, wherein the average particle diameter of the particles is 100nm to 400 nm.

53. The production method according to claim 51, wherein the average particle diameter of the particles is 100nm to 400 nm.

54. The production method according to claim 46 or 47, wherein the particles comprise first inorganic particles having an average particle diameter of 40 to 100nm and second inorganic particles having an average particle diameter of 300-400 nm.

55. The method of claim 54, wherein the weight ratio of the first inorganic particles to the second inorganic particles is from 0.1 to 10: 1.

56. the method of claim 55, wherein the weight ratio of the first inorganic particles to the second inorganic particles is from 0.5 to 5: 1.

57. the method of claim 56, wherein the weight ratio of the first inorganic particles to the second inorganic particles is from 1-2: 1.

58. the method according to claim 36, wherein the inorganic substance in the second slurry is Al₂O₃、SiO₂、BaSO₄、TiO₂、CuO、MgO、LiAlO₂、ZrO₂Carbon nanotube, BN, SiC, Si₃N₄、WC、BC、AlN、Fe₂O₃、BaTiO₃、MoS₂、α-V₂O₅、PbTiO₃、TiB₂、CaSiO₃One or more than two of molecular sieve, clay and kaolin.

59. The method according to claim 39, wherein the inorganic substance in the third slurry is Al₂O₃、SiO₂、BaSO₄、TiO₂、CuO、MgO、LiAlO₂、ZrO₂Carbon nanotube, BN, SiC, Si₃N₄、WC、BC、AlN、Fe₂O₃、BaTiO₃、MoS₂、α-V₂O₅、PbTiO₃、TiB₂、CaSiO₃One or more than two of molecular sieve, clay and kaolin.

60. The production method according to claim 36, wherein the second slurry is applied in such an amount that the total amount of inorganic substances located in the surface and pores of the non-conductive polymer fiber non-woven fabric and between the non-conductive polymer fiber non-woven fabric and the polyolefin porous membrane in the finally produced battery separator is 20 to 85 wt% based on the total weight of the composite separator.

61. The production method according to claim 39, wherein the third slurry is applied in such an amount that the total amount of inorganic substances located in the surface and pores of the non-conductive polymer fiber non-woven fabric and between the non-conductive polymer fiber non-woven fabric and the polyolefin porous membrane in the finally produced battery separator is 20 to 85% by weight based on the total weight of the composite separator.

62. The production method according to claim 60, wherein the second slurry is applied in such an amount that the total amount of inorganic substances located in the surface and pores of the non-conductive polymer fiber non-woven fabric and between the non-conductive polymer fiber non-woven fabric and the polyolefin porous membrane in the finally produced battery separator is 30 to 80% by weight based on the total weight of the composite separator.

63. The production method according to claim 61, wherein the third slurry is applied in such an amount that the total amount of inorganic substances located in the surface and pores of the non-conductive polymer fiber non-woven fabric and between the non-conductive polymer fiber non-woven fabric and the polyolefin porous membrane in the finally produced battery separator is 30 to 80 wt% based on the total weight of the composite separator.

64. The production method according to claim 62, wherein the second slurry is applied in such an amount that the total amount of inorganic substances located in the surface and pores of the non-conductive polymer fiber non-woven fabric and between the non-conductive polymer fiber non-woven fabric and the polyolefin porous membrane in the finally produced battery separator is 35 to 78 wt% based on the total weight of the composite separator.

65. The production method according to claim 63, wherein the third slurry is applied in such an amount that the total amount of inorganic substances located in the surface and pores of the non-conductive polymer fiber non-woven fabric and between the non-conductive polymer fiber non-woven fabric and the polyolefin porous membrane in the finally produced battery separator is 35 to 78 wt% based on the total weight of the composite separator.

66. The production method according to claim 64, wherein the second slurry is applied in such an amount that the total amount of inorganic substances located in the surface and pores of the non-conductive polymer fiber non-woven fabric and between the non-conductive polymer fiber non-woven fabric and the polyolefin porous membrane in the finally produced battery separator is 40 to 76% by weight based on the total weight of the composite separator.

67. The production method according to claim 65, wherein the third slurry is applied in such an amount that the total amount of inorganic substances located in the surface and pores of the non-conductive polymer fiber non-woven fabric and between the non-conductive polymer fiber non-woven fabric and the polyolefin porous membrane in the finally produced battery separator is 40 to 76% by weight based on the total weight of the composite separator.

68. The production method according to claim 66, wherein the second slurry is applied in such an amount that the total amount of inorganic substances located in the surface and pores of the non-conductive polymer fiber non-woven fabric and between the non-conductive polymer fiber non-woven fabric and the polyolefin porous membrane in the finally produced battery separator is 45 to 75 wt% based on the total weight of the composite separator.

69. The production method according to claim 67, wherein the third slurry is applied in such an amount that the total amount of inorganic substances located in the surface and pores of the non-conductive polymer fiber non-woven fabric and between the non-conductive polymer fiber non-woven fabric and the polyolefin porous membrane in the finally produced battery separator is 45 to 75 wt% based on the total weight of the composite separator.

70. The production method according to any one of claims 36 to 39, wherein in the finally produced battery separator, at least a part of the inorganic substance is present in the pores of the non-conductive polymer fiber nonwoven fabric and between the non-conductive polymer fiber nonwoven fabric layer and the polyolefin porous membrane, or at least a part of the inorganic substance is present in the pores of the non-conductive polymer fiber nonwoven fabric, between the non-conductive polymer fiber nonwoven fabric layer and the polyolefin porous membrane, and on the surface of the non-conductive polymer fiber nonwoven fabric.

71. The production method of claim 70, wherein the inorganic layer on the surface of the non-conductive polymer fiber nonwoven fabric has a thickness of 0 to 5 μm.

72. The production method as claimed in claim 71, wherein the inorganic layer on the surface of the non-conductive polymer fiber nonwoven fabric has a thickness of 0.1 to 5 μm.

73. The method of claim 72, wherein the inorganic layer on the surface of the non-conductive polymer fiber nonwoven fabric has a thickness of 1 to 4.5 μm.

74. The method of claim 73, wherein the inorganic layer on the surface of the non-conductive polymer fiber nonwoven fabric has a thickness of 2 to 4 μm.

75. The production method according to claim 70, wherein the weight ratio of the inorganic substance between the non-conductive polymer fiber non-woven fabric layer and the polyolefin porous membrane to the inorganic substance on the surface and in the pores of the non-conductive polymer fiber non-woven fabric layer is 1: 2.5-16.

76. The production method according to claim 75, wherein the weight ratio of the inorganic substance between the non-conductive polymer fiber non-woven fabric layer and the polyolefin porous membrane to the inorganic substance on the surface and in the pores of the non-conductive polymer fiber non-woven fabric layer is 1: 3-12.

77. The production method according to any one of claims 36 to 39, wherein the polymer in the non-conductive polymer fiber nonwoven fabric layer is one or more of polyester, polyimide, polyetherimide and polyetheretherketone.

78. The method of claim 77, wherein the polymer in the non-conductive polymer fiber non-woven fabric layer is polyethylene terephthalate and/or polybutylene terephthalate.

79. The production method as claimed in any one of claims 36 to 39, wherein the thickness of the non-conductive polymer fiber nonwoven fabric layer is 5 to 20 μm.

80. The production method as claimed in any one of claims 36 to 39, wherein the non-conductive polymer fiber nonwoven layer has a porosity of 35 to 70%.

81. The production method as claimed in any one of claims 36 to 39, wherein the diameter of the fibers in the non-conductive polymer fiber nonwoven fabric layer is 0.5 to 5 μm.

82. The production method according to any one of claims 36 to 39, wherein the thickness of the polyolefin porous membrane layer is 1 to 50 μm.

83. The production method according to claim 82, wherein the thickness of the polyolefin porous membrane layer is 5 to 20 μm.

84. The production method according to any one of claims 36 to 39, wherein the polyolefin porous membrane layer has a porosity of 30 to 50%.

85. The production method according to any one of claims 36 to 39, wherein the polyolefin in the polyolefin porous membrane layer is polyethylene and/or polypropylene.

86. A lithium ion battery comprising a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, wherein the separator is the battery separator of any one of claims 1-35.

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

(1) preparing a battery separator using the method of any one of claims 36-85;

(2) and arranging the diaphragm between the positive electrode and the negative electrode to form a battery pole core, and then packaging.