WO2022257728A1

WO2022257728A1 - Separator and lithium ion battery comprising separator

Info

Publication number: WO2022257728A1
Application number: PCT/CN2022/093990
Authority: WO
Inventors: 张祖来; 李素丽; 贺飞; 李俊义; 唐伟超
Original assignee: 珠海冠宇电池股份有限公司
Priority date: 2021-06-07
Filing date: 2022-05-19
Publication date: 2022-12-15
Also published as: CN113206350A

Abstract

The present application provides a separator and a lithium-ion battery comprising said separator. The separator provided in the present application comprises a separator matrix, at least one functional surface of the separator matrix is provided with a coating area and a vacant area, and the coating area is provided with a gluing layer. In the separator of the present application, more electrolyte can be stored in a space that corresponds to a vacant area and that is between a separator and a pole piece, the residual liquid coefficient of a lithium-ion battery is improved, and the electrolyte may fully infiltrate the pole piece and the separator, thereby enabling the lithium-ion battery to have an excellent cycle performance.

Description

A separator and a lithium-ion battery comprising the separator

This application claims the priority of the Chinese patent application with the application number 202110633002.4 and the application title "a separator and a lithium-ion battery including the separator" submitted to the China Patent Office on June 07, 2021, the entire contents of which are incorporated by reference in this application.

technical field

The application belongs to the technical field of lithium ion batteries, and relates to a diaphragm and a lithium ion battery including the diaphragm.

Background technique

In recent years, lithium-ion batteries have been widely used in smartphones, tablet computers, smart wearables, power tools, and electric vehicles.

The amount of electrolyte held in a lithium-ion battery has an important impact on the electrical properties of the battery, such as battery internal resistance, high and low temperature discharge performance, and cycle performance. During the use of lithium-ion batteries, the electrolyte will be gradually consumed, and the cycle life of the battery will be greatly reduced.

Therefore, how to increase the liquid retention capacity of the lithium-ion battery so that the lithium-ion battery has excellent cycle performance is an urgent problem to be solved in this field.

Contents of the invention

The present application provides a separator. By limiting the composition and structure of the separator, the electrolyte can effectively infiltrate the surface of the separator and the pole piece, so that the battery has excellent cycle performance.

The present application also provides a lithium-ion battery, which has excellent cycle performance because the lithium-ion battery includes the separator as described above.

The present application provides a diaphragm, which includes a diaphragm base, at least one functional surface of the diaphragm base is provided with a coated area and a vacant area, and the coated area is provided with a glue layer.

The above-mentioned diaphragm, wherein, the area of the functional surface of the diaphragm substrate occupied by the glue coating layer is 5-97.5%.

The above-mentioned separator, wherein, the coating area includes N sub-coating areas, and the empty area includes M sub-empty areas, N≥1, M≥1;

Wherein, each of the sub-coating regions and each of the sub-vacant regions are alternately distributed along the first direction on the functional surface of the membrane substrate.

The membrane as described above, wherein the maximum dimension of each of the M sub-vacant areas in the first direction is 0.5-20 mm;

The maximum size of each sub-vacant area in the N sub-coating areas in the first direction is 0.5-20 mm.

Wherein, the sub-coating areas are distributed in the functional surface array of the diaphragm substrate, the area between the sub-coating areas of each adjacent column and the area between the sub-coating areas of each adjacent row is the sub-vacant area.

The above-mentioned diaphragm, wherein the maximum size of the sub-vacant regions distributed along the length direction of the diaphragm base in the length direction of the diaphragm base is 0.5-20 mm;

The maximum size of the sub-vacant areas distributed along the width direction of the diaphragm base in the width direction of the diaphragm base is 0.5-20 mm;

The maximum dimension of the sub-coating area in the length direction of the diaphragm base and the width direction of the diaphragm base is respectively 0.5-20 mm.

The above separator, wherein the distribution density of the sub-vacant areas is 25-1414/m ² .

The above-mentioned diaphragm, wherein at least a part of the vacant area communicates with the edge of the diaphragm base.

The above separator, wherein the thickness of the glue layer is 0.5-6 μm.

The present application also provides a lithium ion battery, including the separator as described above.

In the diaphragm of the present application, at least one functional surface of the diaphragm substrate is provided with a coating area and a vacant area, and the coating area is provided with a glue layer with a certain thickness, so that the space between the diaphragm and the pole piece corresponding to the vacant area can be Space to store more electrolyte, increase the residual liquid coefficient of the battery, and make the electrolyte fully infiltrate the diaphragm and pole pieces, so that the lithium-ion battery has excellent cycle performance.

The lithium-ion battery of the present application includes the diaphragm having the above-mentioned special composition and structure, so the lithium-ion battery has good wettability, and further has excellent cycle performance.

Description of drawings

FIG. 1 is a schematic diagram of a functional surface structure of a diaphragm substrate according to an embodiment of the present application;

Fig. 2 is a schematic diagram of the functional surface structure of the diaphragm matrix in another embodiment of the present application;

3 is a schematic cross-sectional view of a lithium-ion battery according to an embodiment of the present application;

4 is a schematic cross-sectional view of a lithium-ion battery according to another embodiment of the present application;

FIG. 5 is a schematic cross-sectional view of a lithium-ion battery according to yet another embodiment of the present application.

Explanation of reference signs:

A: sub-coating area;

B: sub-vacant area;

101: negative plate;

102: diaphragm;

103: positive plate;

104: glue layer;

105: diaphragm matrix;

105a: basement membrane;

105b: ceramic layer.

Detailed ways

The present application will be further described in detail below in conjunction with specific embodiments. It should be understood that the following examples are only for illustrating and explaining the present application, and should not be construed as limiting the protection scope of the present application. All technologies implemented based on the above contents of the application are covered within the scope of protection intended by the application.

The first aspect of the present application provides a diaphragm, including a diaphragm base, at least one functional surface of the diaphragm base is provided with a coating area and a vacant area, wherein the coating area is provided with a glue layer.

The functional surfaces of the membrane matrix refer to the two largest surfaces in the membrane matrix.

The vacant area mentioned above refers to the area where no material is applied on the functional surface of the diaphragm substrate. Since the glue layer has a certain thickness, the space corresponding to the vacant area between the diaphragm and the pole piece can store more Electrolyte, increase the liquid retention capacity of the battery, fully infiltrate the surface of the separator and the pole piece, and then make the lithium-ion battery have excellent cycle performance.

Furthermore, the adhesive layer arranged on the coating area on the functional surface of the separator base acts as an adhesive layer to ensure the tight adhesion between the pole piece and the separator, prevent the pole piece from falling off the battery body, and further ensure the safety performance of the battery. .

The inventors found that when the adhesive layer accounts for 5-97.5% of the functional surface area of the separator base, the liquid retention function brought by it can significantly improve the cycle performance of the lithium-ion battery.

The present application does not specifically limit the distribution of the coating area and the empty area on the functional surface of the diaphragm substrate, as long as the liquid retention function of the space corresponding to the empty area can be realized.

Figure 1 is a schematic diagram of the functional surface structure of the diaphragm substrate according to an embodiment of the present application. As shown in Figure 1, the coating area includes N sub-coating areas A, and the vacant area includes M sub-vacant areas B, N≥1, M≥1; Each sub-coating area A and each sub-empty area B are alternately distributed along the first direction on the functional surface of the membrane substrate.

The first direction in this application is not an absolute definition, and the first direction is not limited to the direction with a certain angle between the length direction and the width direction of the diaphragm base as shown in Figure 1, and can also be the direction consistent with the width direction of the diaphragm base Or the direction aligned with the length direction of the diaphragm base.

The present application does not limit the shape of the sub-coating area and the sub-vacancy area, which may be rectangular, circular, trapezoidal, rhombus, triangular, etc.

Further, in the embodiment shown in FIG. 1 , the maximum size of each sub-vacant area B in the first direction of the M sub-vacant areas B is 0.5-20 mm; each sub-vacant area B in the N sub-vacant areas B The largest dimension in the first direction is 0.5-20 mm.

When the sub-coating area and the sub-empty area are circular, the maximum size is the diameter of the circle; when the sub-coating area and the sub-empty area are rectangular, the maximum size is the width of the rectangle.

Fig. 2 is a schematic diagram of the surface structure of the diaphragm substrate in another embodiment of the present application. As shown in Fig. 2, the coating area includes N sub-coating areas A, and the vacant area includes M sub-vacant areas B, N≥1, M≥1; Among them, the sub-coating area A presents an array distribution on the functional surface of the diaphragm substrate, and the area between each adjacent sub-coating area A and the area between each adjacent row of sub-coating A areas is the sub-vacant area B .

In the embodiment shown in FIG. 2 , the distribution direction of sub-coating areas A in each row is consistent with the longitudinal direction of the diaphragm base, and the distribution direction of sub-coating areas A in each column is consistent with the width direction of the diaphragm base.

Further, in the embodiment shown in FIG. 2 , the maximum size of the sub-vacant areas B distributed along the length direction of the diaphragm base in the length direction of the diaphragm base is 0.5-20 mm; The maximum size of the sub-empty area B in the width direction of the diaphragm base is 0.5-20 mm; the maximum size of the sub-coating area A in the length direction of the diaphragm base and the width direction of the diaphragm base are respectively 0.5-20 mm.

In the embodiment shown in Figure 1 and Figure 2, in order to make the space corresponding to the vacant area between the functional surface of the diaphragm matrix and the pole piece can store more electrolyte, so that the battery has good wettability, it can be controlled The distribution density of sub-vacant areas is 25-1414/m ² .

In a specific embodiment, at least part of the vacant area communicates with the edge of the diaphragm base, so that the gas and heat generated by the battery at high temperature can be discharged from the battery body in time, and thermal runaway and battery bulging can be avoided. Appears to further improve the safety performance of the battery.

In a specific embodiment, the coating area can be connected to the central area of the cell and the edge of the cell, so that the pole piece and the separator can be tightly bonded, and the edge of the pole piece is not easy to warp.

It can be understood that the greater the thickness of the glue layer arranged on the coating area, the greater the space corresponding to the vacant area between the separator and the pole piece, which is conducive to the increase of the battery liquid storage capacity, so that the battery It has more excellent cycle performance, but the energy density of the battery is lower; the thickness of the glue layer on the coating area is smaller, and the space corresponding to the vacant area between the separator and the pole piece is smaller, Although the battery can obtain higher energy density, it is not conducive to the improvement of battery cycle performance. In order to make the battery take into account both energy density and cycle performance, the thickness of the adhesive layer can be controlled to be 0.5-6 μm.

The glue coating material of the glue layer can be selected from polyvinylidene fluoride, polyvinylidene fluoride-polyhexafluoropropylene copolymer, polyvinyl acetate, polyvinyl alcohol, polyvinyl ether, polyethylene, polyethylene oxide, alkanes Polyethylene oxide, polypropylene, polymethyl(meth)acrylate, polyethyl(meth)acrylate, polytetrafluoroethylene, polyvinyl chloride, polyacrylonitrile, polyimide, polyvinylpyridine , polyvinylpyrrolidone, styrene-butadiene rubber, polyvinylidene fluoride, acrylonitrile-butadiene rubber, ethylene-propylene-diene monomer (EPDM) rubber, sulfonated EPDM rubber, styrene-butene rubber , fluorine-containing rubber, styrene-butadiene rubber, carboxymethyl cellulose (CMC), starch, aramid resin, polyacrylic acid, hydroxypropyl cellulose, regenerated cellulose and mixtures thereof. The above gluing materials can make the diaphragm and the pole piece tightly adhered and not easy to fall off.

The inventors have found that when part of the vacant area is connected to the edge of the diaphragm matrix, adding ethyl propionate to the electrolyte can make the lithium-ion battery have both good low-temperature cycle performance and safety performance. The reason may be that propionate Ethyl ester is a solvent with low melting point and low viscosity. Adding an appropriate amount of ethyl propionate can make the electrolyte have higher ion conductivity at low temperature, so that the battery has better low-temperature cycle performance, and the lithium-ion battery can When working at high temperature, the gas produced by the vaporization of ethyl propionate can be discharged from the cell body along the area where the vacant area communicates with the edge of the diaphragm matrix, which can avoid the appearance of battery bulging and thermal runaway, and the gap between the diaphragm and the pole piece The space corresponding to the vacant area can store more electrolyte, so that the battery has a higher residual liquid coefficient, so that the lithium-ion battery has both good low-temperature cycle performance and safety performance. Preferably, the mass content of ethyl propionate in the electrolyte is 10%-50%.

In a specific embodiment, the separator base in the present application may be composed of a base film, or may be composed of a base film and a ceramic layer disposed on at least one functional surface of the base film.

The ceramic layer has good heat resistance, which can further avoid the occurrence of high-temperature thermal runaway of the battery.

Similarly, in consideration of both energy density and cycle performance of the lithium-ion battery, the thickness of the base film can be controlled to be 3-20 μm; and/or the thickness of the ceramic layer can be controlled to be 0.5-5 μm.

The base film of the present application can be selected from base film materials commonly used in the art, for example, can be selected from polyethylene, polypropylene, polyethylene and polypropylene composite materials, polyamide, polyethylene terephthalate, polyethylene terephthalate At least one of butylene formate, polystyrene, and poly-p-phenylenebenzobisoxazole.

The ceramic layer of the present application includes ceramic particles and a binder, and may further include a thickener.

Among them, the ceramic particles can be selected from one or more of alumina, boehmite, magnesium oxide and magnesium hydroxide; the binder can be selected from polyvinylidene fluoride (PVDF), polyvinylidene fluoride-polyhexafluoro Propylene copolymer (PVDF/HFP), polyvinyl acetate, polyvinyl alcohol, polyvinyl ether, polyethylene, polyethylene oxide, alkylated polyethylene oxide, polypropylene, poly(meth)acrylate ester, poly(meth)acrylate, polytetrafluoroethylene, polyvinyl chloride, polyacrylonitrile, polyimide, polyvinylpyridine, polyvinylpyrrolidone, styrene-butadiene rubber, polyvinylidene fluoride, Acrylonitrile-butadiene rubber, ethylene-propylene-diene monomer (EPDM) rubber, sulfonated EPDM rubber, styrene-butadiene rubber, styrene-butene rubber, fluorine-containing rubber, carboxymethyl cellulose (CMC), One or more of starch, hydroxypropyl cellulose, regenerated cellulose and mixtures thereof; the thickener can be carboxymethyl cellulose, carboxyethyl cellulose, free methyl cellulose, ethyl cellulose, One or two of benzyl cellulose, cellulose ether, polyethylene oxide, and modified polyacrylonitrile rubber.

Further, in order to make the ceramic layer can be better bonded on the base film and have excellent heat resistance, the ceramic layer can be made to include 50-99wt% ceramic particles, 1-50wt% bonding agent and 0-10wt% thickener.

The second aspect of the present application provides a lithium-ion battery, which includes the separator provided in the first aspect of the present application, and includes a positive electrode sheet, a negative electrode sheet, and an electrolyte in addition to the separator.

Fig. 3 is the lithium-ion battery interface schematic diagram of an embodiment of the present application, as shown in Fig. 3, lithium-ion battery comprises the positive electrode plate 103 of lamination arrangement, diaphragm 102 and negative electrode plate 101, and diaphragm 102 comprises diaphragm matrix 105 and is arranged on diaphragm matrix 105 is close to the adhesive layer 104 on the functional surface of the negative electrode sheet 101 .

In the lithium-ion battery shown in Figure 3, the adhesive layer 104 is only arranged on the functional surface of the diaphragm substrate 105 near the negative electrode sheet 101, in addition, the adhesive layer 104 can also be arranged only on the diaphragm substrate 105 near the positive electrode The functional surface of the sheet 103 or the two functional surfaces of the separator base near the positive electrode sheet 103 and the negative electrode sheet 101 are provided.

Figure 4 is a cross-sectional schematic view of a lithium-ion battery according to another embodiment of the present application. As shown in Figure 4, the lithium-ion battery includes a stacked positive electrode sheet 103, a separator 102 and a negative electrode sheet 101, and the separator 102 includes a separator base 105 and is respectively arranged on The separator base 105 is close to the functional surface of the negative electrode sheet 101 and the adhesive layer 104 of the separator base 105 is adjacent to the functional surface of the positive electrode sheet 103 .

In the embodiment shown in FIG. 3 and FIG. 4 , the diaphragm base 105 only includes a base film, in addition, the diaphragm base 105 may also include a base film and a ceramic layer disposed on at least one functional surface of the base film.

Figure 5 is a cross-sectional schematic diagram of a lithium-ion battery according to another embodiment of the present application. As shown in Figure 5, the lithium-ion battery includes a stacked positive electrode sheet 103, a diaphragm 102, and a negative electrode sheet 101, wherein the diaphragm 102 includes a stacked adhesive coating Layer 104, diaphragm base body 105, adhesive layer 104, the lithium ion battery shown in Figure 5, diaphragm base body 105 comprises base film 105a and is arranged on base film 105a the ceramic layer 105b near the functional surface of negative plate 101, and ceramic layer 105b is not limited to It can also be arranged on the functional surface of the base film 105a near the negative electrode sheet 101, or it can be arranged on the functional surface of the base film 105a near the positive electrode sheet 103, or the functional surface of the base film 105a near the negative electrode sheet 101 and the functional surface near the positive electrode sheet 103 are both The specific setting method can be determined according to the energy density and safety performance requirements of the lithium-ion battery.

The positive electrode sheet of the present application includes a positive electrode current collector and a positive electrode active material layer disposed on at least one functional surface of the positive electrode current collector. The positive electrode active material layer generally includes a positive electrode active material, a conductive agent and a binder.

Lithium-containing compounds such as lithium oxides, lithium phosphorus oxides, lithium sulfides, or intercalation compounds containing lithium are suitable as positive electrode active materials capable of intercalating and deintercalating lithium, and examples include lithium metal composite oxides. Metal elements constituting the lithium metal composite oxide are, for example, selected from Mg, Al, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Y, Zr, Sn, Sb , W, Pb and Bi at least one. Among them, at least one selected from Co, Ni, Mn and Al is preferably contained. Examples of suitable lithium metal composite oxides include lithium metal composite oxides containing Co, Ni, and Mn, and lithium metal composite oxides containing Co, Ni, and Al. Preferably, the positive electrode active material is selected from lithium cobaltate or lithium cobaltate that has been doped and coated with two or more elements in Al, Mg, Mn, Cr, Ti, Zr, wherein, after Al, Mg, Mn, The chemical formula of lithium cobaltate coated with two or more elements in Cr, Ti, Zr is Li _x Co _{1-y1-y2-y3-y4} A _y1 B _y2 C _y3 D _y4 O ₂ , and 0.95≤ x≤1.05, 0.01≤y1≤0.1, 0.01≤y2≤0.1, 0≤y3≤0.1, 0≤y4≤0.1, A, B, C, D are selected from two of Al, Mg, Mn, Cr, Ti, Zr One or more elements, the median particle size D50 of lithium cobalt oxide coated with two or more elements in Al, Mg, Mn, Cr, Ti, Zr is 10-17 μm, and the specific surface area BET is 0.15 ~0.45 m ² /g.

The negative electrode sheet of the present application includes a negative electrode current collector and a negative electrode active material layer disposed on at least one functional surface of the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material, a conductive agent and a binder.

The negative electrode active material contained in the negative electrode active material layer is not particularly limited as long as it is a material capable of absorbing and releasing lithium ions. For example, carbon materials, lithium metal, metals capable of forming alloys with lithium, or metals containing such metals are exemplified. alloy compounds, etc. As the carbon material, graphites such as natural graphite, non-graphitizable carbon, and artificial graphite, and cokes can be used. As the alloy compound, at least one metal that can form an alloy with lithium can be used. As an element capable of forming an alloy with lithium, silicon and tin are preferable, and silicon oxide, tin oxide, and the like bonded to oxygen can also be used. In addition, a mixture of the above-mentioned carbon material and a compound of silicon or tin can be used. In addition to the above, one having a higher charging and discharging potential with respect to metal lithium such as lithium titanate than carbon materials and the like may be used. Preferably, the negative electrode active material is selected from graphite or a graphite composite material containing 1-12 wt% of SiOx or Si.

The conductive agent should not be particularly limited as long as it does not cause side reactions in the internal environment of the battery and does not cause chemical changes in the battery, and has excellent conductivity. The conductive agent can generally be graphite or conductive carbon or carbon nanotubes, and for example can be but not limited to one selected from the group consisting of: graphite, such as natural graphite or artificial graphite; carbon black, such as carbon black, acetylene Black, Ketjen black, Denka black, thermal black, channel black, furnace black, lamp black, and thermal black; carbon with a crystal structure of graphene or graphite conductive fibers such as carbon fibers and metal fibers; carbon fluoride; metal powders such as aluminum and nickel powders; conductive whiskers such as zinc oxide and potassium titanate; conductive oxides such as titanium oxide; conductive polymers substances, such as polyphenylene derivatives; and mixtures of two or more thereof.

The electrolytic solution of the present application includes a non-aqueous organic solvent, an additive and a lithium salt.

The non-aqueous organic solvent is at least one selected from ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propyl propionate, propyl acetate and ethyl propionate.

Additives are selected from ethylene carbonate, fluoroethylene carbonate, 1,3-propane sultone, ethylene glycol bis(propionitrile) ether, 1,2,3-tris(2-cyanoethoxy)propane , at least one of lithium bisoxalate borate and lithium difluorooxalate borate, the additive accounts for 0-10wt% of the total mass of the electrolyte.

The lithium salt is selected from at least one of lithium bistrifluoromethanesulfonyl imide, lithium bisfluorosulfonyl imide and lithium hexafluorophosphate, and the lithium salt accounts for 10-20 wt% of the total mass of the electrolytic solution.

By controlling the composition of the positive and negative plates, the diaphragm, and the electrolyte, the lithium-ion battery of the present application can be made to work normally at a high voltage of 4.45V or above for the cut-off voltage of charging.

The lithium-ion battery provided by the present application will be further described in detail through specific examples below. Apparently, the following embodiments are only some of the embodiments of the present application, but not all of them. All other embodiments obtained by those skilled in the art based on the technical solutions and the given embodiments in the present application without creative efforts are within the protection scope of the present application.

Embodiment 1-11 and comparative example 1

Refer to Figure 5 for the structure of the lithium-ion battery of Examples 1-11 and Comparative Example 1 of the present application, refer to Figure 1 for the structure of the functional surface of the diaphragm matrix of Examples 1-7 and Examples 9-11, and refer to Figure 1 for the functional surface of the diaphragm matrix of Example 8 Referring to Figure 2, the functional surface of the diaphragm substrate of Comparative Example 1 is all covered with a glue layer.

The separators and lithium-ion batteries of Examples 1-11 of the present application and Comparative Example 1 were prepared according to the following methods, the difference is only in the selection of separators and electrolytes, and the specific differences are shown in Table 1.

1. Preparation of positive electrode sheet 103

Mix the positive electrode active material LiCoO ₂ , the binder polyvinylidene fluoride (PVDF), and the conductive agent acetylene black at a mass ratio of 97:1.5:1.5, add N-methylpyrrolidone (NMP), and stir under the action of a vacuum mixer. Until the mixed system becomes a positive electrode slurry with uniform fluidity; the positive electrode slurry is evenly coated on an aluminum foil with a thickness of 10 μm; after the above-mentioned coated aluminum foil is baked in an oven with 5 different temperature gradients, Drying in an oven at 120° C. for 8 hours, and then rolling and cutting to obtain the desired positive electrode sheet 103 .

2. Preparation of negative electrode sheet 101

Negative electrode active material artificial graphite, conductive agent single-walled carbon nanotube (SWCNT), conductive agent conductive carbon black (SP), binder carboxymethyl cellulose sodium (CMC-Na), binder styrene-butadiene rubber (SBR ) were mixed according to a mass ratio of 96.9:0.1:0.9:0.8:1.3, and a negative electrode slurry with uniform fluidity was prepared by a wet process, coated on the surface of a copper foil with a thickness of 6 μm, and dried (temperature: 85°C , time: 5h), rolling and die-cutting to obtain the negative electrode sheet 101 .

3. Preparation of electrolyte

In a glove box filled with argon (moisture <10ppm, oxygen <1ppm), ethylene carbonate (EC), propylene carbonate (PC), and propyl propionate (PP) were mixed in a mass ratio of 1.5:1:2 Mix well, slowly add 13wt% LiPF6 based _on the total mass of the electrolyte, 10-50wt% ethyl propionate based on the total mass of the electrolyte (the specific amount of ethyl propionate is shown in Table 1) and additives to the mixed solution (3wt% of 1,3-propane sultone, 5wt% of fluoroethylene carbonate, 2wt% of ethylene glycol bis(propionitrile) ether, 1wt% of 1,2,3-three (2-cyanoethyl Oxygen) propane and 0.5wt% ethylene carbonate), stirred evenly to obtain electrolyte solution.

4. Preparation of diaphragm 102

Be that the ceramic layer 105b of 2 μm is coated on the functional surface near the negative electrode sheet 101 of the base film 105a with a thickness of 5 μm, the function surface near the positive electrode sheet 103 of the base film 105a and the ceramic layer 105b are near the function of the negative electrode sheet 101 Each surface is coated with an adhesive layer 104 with a thickness of 1 μm. The specific coating method of the adhesive layer is shown in Table 1. Wherein, the base film is selected from polyethylene, the ceramic layer includes 92wt% aluminum oxide, 4wt% methacrylic acid, and 4wt% polymethylcellulose sodium according to the mass percentage, and the glue layer is selected from polyvinylidene fluoride- Hexafluoropropylene copolymer.

5. Preparation of Li-ion battery

The positive electrode sheet 103, separator 102, and negative electrode sheet 101 prepared above are wound to obtain a bare cell without liquid injection; the bare cell is placed in the outer packaging foil, and the above-mentioned prepared electrolyte is injected into the dried In the bare cell, after vacuum packaging, standing, forming, shaping, sorting and other processes, the required lithium-ion battery is obtained.

Table 1

Wherein, in embodiment 8, the width of the sub-vacant area along the length direction of the functional surface of the diaphragm base body and the width of the sub-vacant area along the width direction of the functional surface of the diaphragm base body are both 1.

Test case

The lithium ion battery of embodiment 1-11 and comparative example 1 is carried out the test of following performance:

1. High-rate cycle performance at room temperature

Test method: Put the lithium-ion battery in an environment of (25±2)°C, and let it stand for 2-3 hours. When the temperature of the battery body reaches (25±2)°C, the cut-off current of the battery is 0.05C according to 3C constant current charging. , After the battery is fully charged, leave it on hold for 5 minutes, and then discharge it at a constant current of 3C to a cut-off voltage of 3.0V. Record the highest discharge capacity of the first three cycles as the initial capacity Q. When the cycle reaches 400 times, record the last discharge capacity Q of the battery. _1. Calculate the 25°C 3C cycle capacity retention rate of the battery according to the following formula:

25°C 3C cycle capacity retention (%)=Q ₁ /Q×100%;

The record results of 25°C 3C cycle capacity retention are shown in Table 2.

2. Safety performance

Test method: 150°C thermal shock test for lithium-ion batteries. The test method is to heat the lithium-ion battery with a convection method or a circulating hot air box at an initial temperature of 25±3°C, with a temperature change rate of 5±2°C/min. Raise the temperature to 150±2°C, keep it for 30 minutes, and then end the test. Observe whether the battery catches fire or explodes. Record the results as shown in Table 2.

3. Low temperature cycle performance

Test method: Discharge the lithium-ion battery at an ambient temperature of 25±3°C to 3.0V at 0.2C, and leave it for 5 minutes; charge it at 0.7C, and when the battery terminal voltage reaches the charging limit voltage, change to constant voltage charging until Charging current ≤ cut-off current, stop charging, put aside for 5 minutes, discharge to 3.0V at 0.2C, record this discharge capacity as room temperature capacity Q ₂ . Then the battery is charged at 0.7C. When the terminal voltage of the battery reaches the charging limit voltage, it is changed to constant voltage charging until the charging current is less than or equal to the cut-off current, and the charging is stopped; the fully charged battery is kept at -20±2℃ After resting for 4 hours, discharge at a current of 0.2C to a cut-off voltage of 3.0V, record the discharge capacity Q ₃ , and calculate the cycle capacity retention rate of the battery at -20°C according to the following calculation formula:

-20°C cycle capacity retention (%)=Q ₃ /Q ₂ ×100%;

The record results of the cycle capacity retention at -20°C are shown in Table 2.

Table 2

As can be seen from the data in Table 2, the lithium-ion battery of the present application has excellent cycle performance and safety performance at high-rate charging and low temperature, while in Comparative Example 1, the adhesive layer is completely covered on the diaphragm substrate, and the lithium-ion battery The cycle performance and safety performance of the high-rate charge and low temperature of the battery are inferior to those of the lithium-ion batteries of Examples 1-11 of the present application. And by comparative example 1, embodiment 4, embodiment 6,

It can be seen from Example 9, Example 10 and Example 11 that when the composition and structure of the separator are consistent, adding ethyl propionate to the electrolyte is beneficial to the high-rate charging of lithium-ion batteries and the cycle performance at low temperatures improvement. As can be seen from the comparison of Examples 1, 4, 6 and Examples 10, 11, when the content of ethyl propionate in the electrolyte was less than 10%, the low-temperature cycle performance of the battery decreased, and when ethyl propionate in the electrolyte When the ester content is greater than 50%, the high-rate charging and low-temperature cycle performance of the electrolyte are obviously improved, but the safety performance of the battery is obviously reduced.

The above embodiments are only used to illustrate the technical solutions of the present application, and are not intended to limit them; although the application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: it can still be applied to the foregoing embodiments The technical solutions described in the examples are modified, or some or all of the technical features are equivalently replaced; and these modifications or replacements do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the application.

Claims

A diaphragm, wherein the diaphragm includes a diaphragm base, at least one functional surface of the diaphragm base is provided with a coating area and a vacant area, and the coating area is provided with a glue layer.
The diaphragm according to claim 1, wherein the adhesive layer accounts for 5-97.5% of the area of the functional surface of the diaphragm base.
The separator according to claim 1 or 2, wherein the coating area includes N sub-coating areas, and the empty area includes M sub-empty areas, N≥1, M≥1;

Wherein, each of the sub-coating regions and each of the sub-vacant regions are alternately distributed along the first direction on the functional surface of the membrane substrate.
The membrane according to claim 3, wherein the maximum dimension of each of the M sub-vacant areas in the first direction is 0.5-20 mm;

The maximum size of each sub-vacant area in the N sub-coating areas in the first direction is 0.5-20 mm.
The separator according to claim 1 or 2, wherein the coating area includes N sub-coating areas, and the empty area includes M sub-empty areas, N≥1, M≥1;

Wherein, the sub-coating areas are distributed in the functional surface array of the diaphragm substrate, the area between the sub-coating areas of each adjacent column and the area between the sub-coating areas of each adjacent row is the sub-vacant area.
The diaphragm according to claim 5, wherein the maximum dimension of the sub-vacant regions distributed along the length direction of the diaphragm base in the length direction of the diaphragm base is 0.5-20 mm;

The maximum size of the sub-vacant areas distributed along the width direction of the diaphragm base in the width direction of the diaphragm base is 0.5-20 mm;

The maximum dimension of the sub-coating area in the length direction of the diaphragm base and the width direction of the diaphragm base is respectively 0.5-20 mm.
The membrane according to any one of claims 3-6, wherein the distribution density of the sub-vacant areas is 25-1414/m 2 .
The membrane according to claim 1 or 2, wherein at least a partial area of the empty space communicates with an edge of the membrane base.
The separator according to claim 1 or 2, wherein the thickness of the adhesive layer is 0.5-6 μm.
The diaphragm according to any one of claims 1-9, wherein the diaphragm substrate is composed of a base film and a ceramic layer arranged on at least one functional surface of the base film.
The separator according to claim 10, wherein the base film has a thickness of 3-20 μm.
The separator according to claim 10 or 11, wherein the thickness of the ceramic layer is 0.5-5 μm.
The separator according to any one of claims 10-12, wherein the ceramic layer comprises 50-99wt% of ceramic particles, 1-50wt% of binder and 0-10wt% of thickening agent.
A lithium ion battery, comprising the separator according to any one of claims 1-13.
The lithium ion battery according to claim 14, wherein the lithium ion battery further comprises an electrolyte, and the electrolyte includes ethyl propionate.
The lithium ion battery according to claim 15, wherein the mass content of ethyl propionate in the electrolyte is 10%-50%.