WO2023098646A1

WO2023098646A1 - Separator and battery comprising same

Info

Publication number: WO2023098646A1
Application number: PCT/CN2022/134907
Authority: WO
Inventors: 张祖来; 李素丽; 艾新平; 李俊义
Original assignee: 珠海冠宇电池股份有限公司
Priority date: 2021-11-30
Filing date: 2022-11-29
Publication date: 2023-06-08
Also published as: CN114156599A

Abstract

The present disclosure provides a separator and a battery comprising same. The battery can have both high energy density and high safety. According to the present disclosure, by reasonably designing the composition of two polymers in a polymer layer in the battery separator, the prepared battery can effectively improve the safety performance of the battery while taking into account the energy density of the battery. Specifically, according to the present application, a first polymer is added to the polymer layer, the melting point of the first polymer is 100℃ to 130℃, the introduction of the first polymer can enable the separator to achieve pore closure before the temperature reaching 130℃, to isolate lithium ion shuttling between positive and negative electrodes in the battery, thereby achieving the purpose of improving safety; moreover, because the particle size of the first polymer is 0.1 μm to 10 μm, blending the first polymer with the second polymer does not additionally increase the thickness of the separator, thereby ensuring the energy density of the battery.

Description

A separator and a battery containing the separator

technical field

The disclosure belongs to the technical field of batteries, and relates to a diaphragm and a battery containing the diaphragm, in particular to a high-safety diaphragm and a battery containing the diaphragm.

Background technique

In recent years, batteries have been widely used in smartphones, tablet computers, smart wearables, power tools, and electric vehicles. With the wide application of batteries, consumers' demands on battery life and application environment continue to increase, which requires batteries to have a long cycle life while taking into account high safety performance.

At present, there are many safety hazards in the use of batteries. For example, when the temperature of the battery increases to a certain level, the internal temperature is out of control, which is prone to serious safety accidents, fire or even explosion. The study found that the main reason for the thermal runaway of the battery is that the heat resistance of the diaphragm is not enough, which causes the diaphragm to shrink easily at high temperature and cannot isolate the positive and negative electrodes of the battery; on the other hand, the closed cell temperature of the diaphragm is too high. High, the diaphragm cannot close the pores before thermal runaway, and cannot block the ion channels inside the battery in time.

Based on this situation, there is an urgent need to develop a separator for batteries with high safety. The commonly used improvement method in the prior art is, for example, by coating a heat-resistant layer on the surface of the separator, but the heat-resistant layer coated on the surface of the separator often leads to battery damage. The reduction of energy density cannot fundamentally solve the safety problem of the battery. Therefore, it is currently the top priority to be able to develop batteries with high safety without affecting the energy density of batteries.

Contents of the invention

The purpose of this disclosure is to solve the problems of potential safety hazards in the use of existing batteries, and the inability to balance battery energy density and safety performance, and provide a separator and a battery containing the separator, and the battery can take into account high energy density. and high security.

In order to achieve the above purpose, the present disclosure adopts the following technical solutions:

A diaphragm, the diaphragm includes a substrate, a heat-resistant layer and a polymer layer, the heat-resistant layer is arranged on the first surface of the substrate, the polymer layer is arranged on the substrate and the polymer layer on the second surface opposite to the first surface and/or on the surface of the heat-resistant layer;

Wherein, the polymer layer includes a first polymer and a second polymer;

The melting point of the first polymer is 100°C to 130°C;

The second polymer is selected from polytetrafluoroethylene, polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer (such as polyvinylidene fluoride-hexafluoropropylene copolymer), polyimide, polyacrylonitrile , polymethyl methacrylate, at least one of aramid resin and polyacrylic acid.

In the present disclosure, the "polyvinylidene fluoride-hexafluoropropylene copolymer" refers to hexafluoropropylene-modified polyvinylidene fluoride.

In an example, the particle size of the first polymer is 0.1 μm˜10 μm.

In one example, the first polymer is at least one selected from polyethylene, polymethacrylic acid, polymethacrylate and polypropylene.

In one example, the polymethacrylate in the first polymer can be selected from polyalkylmethacrylate, such as polymethacrylate C _1-10 alkylester, exemplarily polymethylmethacrylate At least one of methyl acrylate, polyethyl methacrylate, poly-n-propyl methacrylate and polyisopropyl methacrylate.

In one example, the first polymer is selected from polyethylene, and the second polymer is selected from polyvinylidene fluoride-hexafluoropropylene copolymer; or, the first polymer is selected from polyethylene, and the The second polymer is selected from polymethyl methacrylate; or, the first polymer is selected from polypropylene, and the second polymer is selected from polyvinylidene fluoride-hexafluoropropylene copolymer; or, the first polymer is selected from polyvinylidene fluoride-hexafluoropropylene copolymer; A polymer is selected from polypropylene, and the second polymer is selected from polymethyl methacrylate; or, the first polymer is selected from polymethacrylic acid, and the second polymer is selected from polymethacrylic acid methyl ester; or, the first polymer is selected from polyethyl methacrylate, and the second polymer is selected from polyvinylidene fluoride-hexafluoropropylene copolymer; or, the first polymer is selected from poly N-propyl methacrylate, the second polymer is selected from polyvinylidene fluoride-hexafluoropropylene copolymer; or, the first polymer is selected from polyethylene, and the second polymer is selected from polyacrylonitrile .

In an example, the number average molecular weight of the first polymer is 50,000 Da to 500,000 Da.

In one example, the swelling degree of the first polymer is less than or equal to 5%; wherein, the swelling degree of the first polymer means that after the first polymer is soaked in a solvent at 60°C for 30 days, the first For the swelling of the polymer, the solvent is EC:EMC:DEC=1:1:1 (volume ratio).

In one example, the number average molecular weight of the second polymer is 100,000 Da to 1,500,000 Da.

In one example, the mass percentage of the first polymer in the entire polymer layer is 10%-90%, such as 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80% % or 90%.

In one example, the mass percentage of the second polymer in the entire polymer layer is 10%-90%, such as 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80% % or 90%.

In one example, both the first polymer and the second polymer can be prepared by methods known in the art, or purchased from commercial channels.

In an example, the thickness of the polymer layer is 0.5 μm˜10 μm, such as 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm or 10 μm.

In one example, the heat-resistant layer includes ceramic and adhesive.

Preferably, the mass of ceramics in the heat-resistant layer accounts for 20-99wt.% of the total mass of the heat-resistant layer, for example 20wt.%, 30wt.%, 40wt.%, 60wt.%, 80wt.%, 90wt.%, 95wt.%, 99wt.%, or any value within the range of the aforementioned pairwise values.

Preferably, the mass of the binder in the heat-resistant layer accounts for 1 to 80wt.% of the total mass of the heat-resistant layer, exemplarily 1wt.%, 5wt.%, 10wt.%, 20wt.%, 30wt.%. %, 50wt.%, 60wt.%, 80wt.%, or any value within the range of the aforementioned pairwise values.

In one example, the ceramic in the heat-resistant layer is selected from one, two or more of alumina, boehmite, magnesium oxide, boron nitride and magnesium hydroxide.

In one example, the binder in the heat-resistant layer is selected from polytetrafluoroethylene, polyvinylidene fluoride, hexafluoropropylene-vinylidene fluoride copolymer (such as polyvinylidene fluoride-hexafluoropropylene copolymer) , polyimide, polyacrylonitrile and polymethyl methacrylate, two or more.

In one example, the solvent used to prepare the heat-resistant layer and the polymer layer is selected from acetone, tetrahydrofuran, methylene chloride, chloroform, dimethylformamide, N-methyl-2-pyrrolidone, cyclohexane , methanol, ethanol, isopropanol and water.

In one example, the air permeability value of the membrane after baking in an oven at 130°C for 10 minutes is more than 10 times higher than that before baking; The air permeability increase value of the separator covered with the polymer layer of the first polymer baked in an oven at 130° C. for 10 minutes is more than 100 times higher.

In an example, the heat-resistant layer has a thickness of 0.5 μm˜5 μm, such as 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm or 5 μm.

In an example, the substrate has a thickness of 3 μm˜20 μm, such as 3 μm, 5 μm, 8 μm, 10 μm, 15 μm, 18 μm or 20 μm.

In one example, the substrate is selected from polyethylene, polypropylene, polyethylene and polypropylene composites, polyamide, polyethylene terephthalate, polybutylene terephthalate, polystyrene, at least one of polyparaphenylene.

The present disclosure also provides a battery including the above separator.

In one example, the battery further includes a positive electrode sheet, a negative electrode sheet, and the separator is placed between the positive electrode sheet and the negative electrode sheet.

In an example, the first surface of the substrate is close to the negative electrode sheet, and the second surface of the substrate opposite to the first surface is close to the positive electrode sheet.

In one example, the polymer layer of the separator is adjacent to the negative electrode sheet.

The inventors of the present invention have found that when the polymer layer of the separator is close to the negative electrode sheet, the cycle performance of the battery is further improved, which may be due to the fact that the polymer layer of the separator is easily separated from the The electrolyte solution swells, and the adhesion between the swollen polymer layer and the surface of the negative electrode is significantly enhanced, and the adhesion may come from van der Waals force, hydrogen bond and anchor effect.

The adhesive force between the polymer layer on the surface of the separator and the surface of the negative electrode can be 0.5N/m-20N/m, such as 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5 , 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20N/m.

In one example, the adhesive force between the polymer layer on the surface of the separator and the surface of the negative electrode is 1N/m˜10N/m.

In one example, the adhesive force between the polymer layer on the surface of the separator and the surface of the negative electrode is 1.2N/m˜8N/m.

In one example, the battery further includes a non-aqueous electrolyte, and the non-aqueous electrolyte includes a non-aqueous organic solvent.

In one example, the battery is, for example, a Li-ion battery.

In one example, the non-aqueous electrolytic solution further includes a lithium salt.

In one example, the lithium salt is selected from at least one of lithium bistrifluoromethylsulfonylimide, lithium bisfluorosulfonylimide and lithium hexafluorophosphate, and the lithium salt accounts for the total mass of the non-aqueous electrolyte 13 ~ 20wt.% of.

In one example, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer coated on one or both sides of the positive electrode current collector, and the positive electrode active material layer includes a positive electrode active material, a conductive agent and a binder. agent;

The positive electrode active material is selected from lithium cobalt oxide or lithium cobalt oxide that has been doped and coated with two or more elements in Al, Mg, Mn, Cr, Ti, and Zr. , Ti, Zr with two or more elements doped and coated with lithium cobalt oxide, the chemical formula is Li _x Co _{1-y1-y2-y3-y4} A _y1 B _y2 C _y3 D _y4 O ₂ ; 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 or more of Al, Mg, Mn, Cr, Ti, Zr Various elements.

In one example, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer coated on one or both sides of the negative electrode current collector, and the negative electrode active material layer includes a negative electrode active material, a conductive agent and a binding agent. agent;

The negative electrode active material is selected from graphite or graphite composite material containing 1-15wt% _SiOx /C or Si/C.

The beneficial effects of the present disclosure are:

The present disclosure provides a separator and a battery including the separator, and the battery can have both high energy density and high safety. In the disclosure, by rationally designing the composition of the two polymers in the polymer layer in the battery diaphragm, the prepared battery can effectively improve the safety performance of the battery while taking into account the energy density of the battery.

Specifically, the present application adds a first polymer to the polymer layer, and the melting point of the first polymer is between 100°C and 130°C. The introduction of the first polymer can make the membrane close before 130°C. , to isolate the shuttle of lithium ions between the positive and negative electrodes inside the battery to achieve the purpose of improving safety, and because the melting point of the polymer is above 100°C, it will not melt during the cell preparation process and affect the normal charge and discharge performance of the battery; at the same time , adding a second polymer to the polymer layer can improve the interfacial stability between the separator and the pole piece, and ensure that the battery has good cycle performance; by using the synergistic effect of the first polymer and the second polymer, the preparation The high-quality battery takes into account safety and cycle performance at the same time. Further, since the particle size of the first polymer is between 0.1 μm and 10 μm, by blending with the second polymer, the thickness of the separator will not be additionally increased, which ensures the energy density of the battery.

Detailed ways

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

The experimental methods used in the following examples are conventional methods unless otherwise specified; the reagents and materials used in the following examples can be obtained from commercial sources unless otherwise specified.

Comparative Examples 1-4 and Examples 1-8

The lithium-ion batteries of Comparative Examples 1-4 and Examples 1-8 were all prepared according to the following preparation methods, the only difference being that the composition of the polymer layer on the surface of the separator (the first polymer and the second polymer) was different, the specific difference As shown in Table 1, among them, in Comparative Examples 1-4 and Examples 1-8, the swelling degree of the first polymer is ≤5%.

(1) Preparation of positive electrode sheet

Mix the positive electrode active material LiCoO ₂ , the binder polyvinylidene fluoride (PVDF), and the conductive agent acetylene black at a weight ratio of 97:1.0:2.0, 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, Dry in an oven at 120° C. for 8 hours, and then roll and cut to obtain the desired positive electrode sheet.

(2) Negative sheet preparation

The artificial graphite negative electrode material with a mass proportion of 96%, the single-walled carbon nanotube (SWCNT) conductive agent with a mass proportion of 0.2%, the conductive carbon black (SP) conductive agent with a mass proportion of 1.0%, and the mass proportion A 1% sodium carboxymethylcellulose (CMC) binder and a 1.8% styrene-butadiene rubber (SBR) binder are made into a slurry by a wet process and coated on the negative electrode current collector copper foil The surface was dried (temperature: 85° C., time: 5 h), rolled and die-cut to obtain the negative electrode sheet.

(3) Preparation of non-aqueous electrolyte

In an argon-filled glove box (moisture <10ppm, oxygen <1ppm), ethylene carbonate (EC), propylene carbonate (PC), and propyl propionate (PP) were mixed in a mass ratio of 2:1.5:2 Mix evenly, slowly add 14wt.% LiPF ₆ based on the total mass of the non-aqueous electrolyte to the mixed solution, and stir evenly to obtain the non-aqueous electrolyte.

(4) Preparation of diaphragm

Polyethylene with a particle size of 1 μm, a melting point of 115° C., and a molecular weight of 300,000 Da was selected as the first polymer, and polyvinylidene fluoride-hexafluoropropylene copolymer was selected as the second polymer. The polyethylene particles and the polyvinylidene fluoride-hexafluoropropylene copolymer particles were respectively dispersed in the aqueous solution and mixed to obtain a dispersion liquid M including the first polymer and the second polymer.

The surface of one side of the polyethylene substrate with a thickness of 5 μm is coated with an aluminum oxide layer with a thickness of 2 μm (the composition is 92wt% aluminum oxide, 4wt% methacrylic acid, 4wt% polymethylcellulose sodium ), the surface of the other side of the polyethylene substrate and the surface of the aluminum oxide layer are each coated with a polymer layer with a thickness of 2 μm. Specifically, the dispersion M is coated with a thickness of A 5 μm polyethylene substrate and a 2 μm thick aluminum oxide layer on both sides were dried to obtain a separator with a 2 μm thick polymer layer on both sides.

(5) Preparation of lithium ion battery

The positive electrode sheet, separator, and negative electrode sheet prepared above were wound to obtain a bare battery without liquid injection (wherein the first surface of the polyethylene base material was close to the negative electrode sheet side, and the second surface of the polyethylene base material opposite to the first surface The two surfaces are close to the side of the positive electrode sheet); the bare cell is placed in the outer packaging foil, the above-mentioned prepared electrolyte is injected into the dried bare cell, and it is subjected to vacuum packaging, standing, formation, shaping, sorting and other processes , to obtain the desired Li-ion battery.

Table 1 Lithium-ion batteries prepared by Comparative Examples 1-4 and Examples 1-8

Electrochemical performance test is carried out to the battery obtained in the above-mentioned comparative examples and examples, and the relevant instructions are as follows:

Adhesion measurement method:

Place the batteries obtained in the above examples and comparative examples in an environment of (25±2)°C, and let them stand for 2-3 hours. When the battery body reaches (25±2)°C, charge the battery at a constant current of 0.7C, and The current is 0.05C. When the battery terminal voltage reaches the charging limit voltage, change to constant voltage charging until the charging current ≤ cut-off current, stop charging and put it aside for 5 minutes, dissect the fully charged battery, and choose a length of 30mm along the direction of the tab* 15mm wide diaphragm and negative electrode as a whole sample, the separator and the negative electrode at an angle of 180 degrees are tested on a universal stretching machine at a speed of 100mm/min and a test displacement of 50mm, and the test result is recorded as the adhesion between the diaphragm and the negative electrode N (unit N/m).

25°C cycle experiment:

Place the batteries obtained in the above examples and comparative examples in an environment of (25±2)°C, and let them stand for 2-3 hours. When the battery body reaches (25±2)°C, the cut-off current of the battery is 0.05 according to 1C constant current charging. C. After the battery is fully charged, put it aside for 5 minutes, and then discharge it at a constant current of 1C to a cut-off voltage of 3.0V. Record the highest discharge capacity of the first 3 cycles as the initial capacity Q. When the cycle reaches 1000 times, record the last discharge capacity of the battery Q ₁ , record the results as shown in Table 2.

The calculation formula used is as follows: capacity retention rate (%) = Q ₁ /Q × 100%;

150℃ thermal shock test:

Heat the batteries obtained in the above examples and comparative examples 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, and raise the temperature to (150±2)°C , keep the test for 60 minutes and end the test, record the battery status results as shown in Table 2.

Air permeability test:

Test the air permeability value of the diaphragm obtained in the above examples and comparative examples, which is the air permeability value G0 of the diaphragm before baking, and then place the diaphragm in an oven at a temperature of 130°C±2°C for 10 minutes, take out the diaphragm and test the air permeability value of the diaphragm, which is After baking, the air permeability value of the diaphragm is G1. The test method of the air permeability value refers to the national standard GB/T 36363-20183.2 air permeability test.

The calculation formula used therein is as follows: air permeability increase value G=G1-G0.

The performance test results of the diaphragm and lithium-ion battery of Table 2 Comparative Examples 1-4 and Examples 1-8

It can be seen from the results in Table 2: through the comparative examples and examples, it can be seen that the air permeability increase value G of the diaphragm of the embodiment is significantly improved after baking, indicating that the introduction of the polymer layer of the present application makes the diaphragm closed at high temperature. , making it impossible to shuttle between the positive and negative electrodes, improving battery safety performance. In addition, the present disclosure does not significantly increase the thickness of the separator, so the battery prepared by using the separator of the present disclosure can take into account both high energy density and high safety.

The embodiments of the present disclosure have been described above. However, the present disclosure is not limited to the above-mentioned embodiments. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present disclosure shall be included within the protection scope of the present disclosure.

Claims

A diaphragm, the diaphragm includes a substrate, a heat-resistant layer and a polymer layer, the heat-resistant layer is arranged on the first surface of the substrate, the polymer layer is arranged on the substrate and the polymer layer The second surface opposite to the first surface and/or the surface of the heat-resistant layer; characterized in that,

the polymer layer includes a first polymer and a second polymer;

The melting point of the first polymer is 100°C to 130°C;

The second polymer is selected from polytetrafluoroethylene, polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyimide, polyacrylonitrile, polymethyl methacrylate, aramid resin and polyacrylic acid at least one of the
The separator according to claim 1, wherein the particle diameter of the first polymer is 0.1 μm˜10 μm.
The separator according to claim 1 or 2, wherein the first polymer is selected from at least one of polyethylene, polymethacrylic acid, polymethacrylate and polypropylene;

Preferably, the polymethacrylate is selected from at least one of polymethylmethacrylate, polyethylmethacrylate, polyn-propylmethacrylate and polyisopropylmethacrylate.
The diaphragm according to any one of claims 1-3, wherein the first polymer is selected from polyethylene, and the second polymer is selected from polyvinylidene fluoride-hexafluoropropylene copolymer; or, The first polymer is selected from polyethylene, and the second polymer is selected from polymethyl methacrylate; or, the first polymer is selected from polypropylene, and the second polymer is selected from polyvinylidene fluoride Ethylene-hexafluoropropylene copolymer; or, the first polymer is selected from polypropylene, and the second polymer is selected from polymethyl methacrylate.
The diaphragm according to any one of claims 1-3, wherein the first polymer is selected from polymethacrylic acid, and the second polymer is selected from polymethyl methacrylate; or, the The first polymer is selected from polyethyl methacrylate, and the second polymer is selected from polyvinylidene fluoride-hexafluoropropylene copolymer; or, the first polymer is selected from poly-n-propyl methacrylate, The second polymer is selected from polyvinylidene fluoride-hexafluoropropylene copolymer; or, the first polymer is selected from polyethylene, and the second polymer is selected from polyacrylonitrile.
The separator according to any one of claims 1-5, characterized in that, the number average molecular weight of the first polymer is 50,000 Da to 500,000 Da;

And/or, the number average molecular weight of the second polymer is 100,000 Da to 1,500,000 Da.
The separator according to any one of claims 1-6, characterized in that, the mass percentage of the first polymer in the entire polymer layer is 10% to 90%;

And/or, the mass percentage of the second polymer in the entire polymer layer is 10%-90%.
The membrane according to any one of claims 1-7, characterized in that the swelling degree of the first polymer is less than or equal to 5%.
The separator according to any one of claims 1-8, characterized in that, the thickness of the polymer layer is 0.5 μm˜10 μm.
The diaphragm according to any one of claims 1-9, wherein the heat-resistant layer comprises ceramics and a binder, and the mass of ceramics in the heat-resistant layer accounts for 20-20% of the total mass of the heat-resistant layer. 99wt.%, the mass of the binder in the heat-resistant layer accounts for 1-80wt.% of the total mass of the heat-resistant layer.
The membrane according to any one of claims 1-10, characterized in that the air permeability value of the membrane after baking in an oven at 130°C for 10 minutes is more than 10 times higher than that before baking.
The membrane according to any one of claims 1-11, characterized in that, the air permeability increase value of the membrane when baked in an oven at 130° C. for 10 minutes is compared to that of the membrane not coated with the polymer layer containing the first polymer The air permeability increase value of the diaphragm baked in an oven at 130°C for 10 minutes was more than 100 times higher.
The separator according to any one of claims 1-12, characterized in that, the thickness of the heat-resistant layer is 0.5 μm to 5 μm; and/or,

The thickness of the substrate is 3 μm to 20 μm.
A battery, characterized in that the battery comprises the separator according to any one of claims 1-13.
The battery according to claim 14, wherein the battery further comprises a positive electrode sheet, a negative electrode sheet, and the separator is placed between the positive electrode sheet and the negative electrode sheet;

Preferably, the polymer layer of the separator is close to the negative electrode sheet; and/or,

The adhesive force between the polymer layer on the surface of the separator and the surface of the negative electrode is 0.5N/m˜20N/m.