Slurry for battery diaphragm, battery diaphragm, application of battery diaphragm and lithium ion battery

Abstract

The invention relates to the technical field of lithium ion batteries, and discloses slurry for a battery diaphragm, the battery diaphragm, application of the battery diaphragm and a lithium ion battery. The slurry contains a main agent and an auxiliary agent, and the main agent contains an oxygen adsorbent and an oxygen fixing agent; the oxygen adsorbent is a zeolite molecular sieve, and the oxygen fixing agent is oxygen-deficient titanium dioxide; the content mass ratio of the oxygen adsorbent to the oxygen fixing agent is 1: (0.1-10). The slurry provided by the invention is coated on a diaphragm, so that oxygen in a battery can be reduced, the problem of battery expansion caused by gas production of a lithium-rich nickel-based lithium supplementing agent is solved, the safety risk of the battery is reduced, and the cycle life and the safety of the battery are improved.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to a slurry for battery separators, battery separators and their applications, and lithium-ion batteries. Background Technology

[0002] With the rapid development of new energy vehicles and energy storage power stations, higher requirements have been placed on the energy density, cycle life, and safety performance of lithium-ion batteries. Lithium-rich nickel-based materials (such as LiNiO2-based materials, or LNO for short) used in lithium iron phosphate batteries serve as efficient lithium replenishers, effectively supplementing the lithium ions consumed during the first charge and discharge process due to the formation of the SEI film, thereby improving the overall capacity and cycle life of the battery.

[0003] However, LNO easily releases oxygen during battery storage and charging / discharging, leading to increased internal pressure, expansion and deformation, and even safety issues. Currently, research on LNO gas generation mainly focuses on cathode material coating and electrolyte additives, with less attention paid to the functional design of the separator.

[0004] As a key component of lithium-ion batteries, the separator can greatly mitigate the safety hazards caused by gas production by introducing a specific functional coating on its surface to adsorb and fix oxygen. Summary of the Invention

[0005] The purpose of this invention is to overcome the problem that the gas generation of lithium-rich nickel-based lithium replenishing agents in the prior art can easily lead to battery expansion and safety risks.

[0006] To achieve the above objectives, a first aspect of the present invention provides a slurry for battery separators, the slurry containing a main agent and an auxiliary agent, wherein the main agent contains an oxygen adsorbent and an oxygen-fixing agent; the oxygen adsorbent is a zeolite molecular sieve, and the oxygen-fixing agent is oxygen-deficient titanium dioxide; the mass ratio of the oxygen adsorbent to the oxygen-fixing agent is 1:0.1-10; based on the total solid mass of the slurry, the total content of the oxygen adsorbent and the oxygen-fixing agent is 90-99.5 wt%; the oxygen-deficient titanium dioxide has the structural formula TiO2. 2-x , of which 0.2 <x<0.5。

[0007] A second aspect of the present invention provides a battery separator comprising a base film and a coating applied to at least one surface of the base film; The coating is formed from the slurry for battery separators described in the first aspect.

[0008] The third aspect of the present invention provides the application of the battery separator described in the second aspect in the field of lithium-ion battery technology.

[0009] A fourth aspect of the present invention provides a lithium-ion battery comprising: a positive electrode, a negative electrode, a separator, and an electrolyte; wherein the separator is the battery separator described in the second aspect.

[0010] The battery separator slurry provided by this invention, when coated onto a base membrane, can adsorb and fix oxygen inside the battery. This slurry contains an oxygen adsorbent and an oxygen-fixing agent, wherein the adsorbent is a zeolite molecular sieve and the oxygen-fixing agent is TiO₂. 2-x The slurry has a solid content of 34-37 wt% and is suitable for coating various base films. The slurry provided by this invention, when coated on a separator, can reduce oxygen inside the battery, solve the battery expansion problem caused by gas generation from lithium-rich nickel-based lithium replenishing agents, reduce battery safety risks, and improve battery cycle life and safety. Detailed Implementation

[0011] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0012] As previously described, a first aspect of the present invention provides a slurry for battery separators, the slurry containing a main agent and an auxiliary agent, wherein the main agent contains an oxygen adsorbent and an oxygen-fixing agent; the oxygen adsorbent is a zeolite molecular sieve, and the oxygen-fixing agent is oxygen-deficient titanium dioxide; the mass ratio of the oxygen adsorbent to the oxygen-fixing agent is 1:0.1-10; based on the total solid mass of the slurry, the total content of the oxygen adsorbent and the oxygen-fixing agent is 90-99.5 wt%; the oxygen-deficient titanium dioxide has the structural formula TiO2. 2-x , of which 0.2 <x<0.5。

[0013] According to a particularly preferred embodiment, the mass ratio of the oxygen adsorbent to the oxygen fixative is 1:0.5-2. The inventors have discovered that, in this preferred embodiment, the battery separator formed from the slurry enables the adsorption and fixation processes to work synergistically, achieving optimal oxygen removal.

[0014] According to a particularly preferred embodiment, the solid content of the slurry for the battery separator is 34-37 wt%. In this preferred embodiment, the slurry for the battery separator has good coating and leveling properties, and can form a coating with a sufficient content of functional substances.

[0015] According to a particularly preferred embodiment, the D of the zeolite molecular sieve 50The particle size is 0.5-2.0 μm. In this preferred embodiment, the zeolite molecular sieve has a stable and large specific surface area and a porous structure, which can physically adsorb oxygen molecules; therefore, it is beneficial to form a dense and porous microstructure in the coating, which not only ensures oxygen transport channels but also provides a sufficient reaction interface.

[0016] Particularly preferred is the D of the oxygen-deficient titanium dioxide. 50 The particle size is 0.1-1.0 μm. In this preferred embodiment, the oxygen vacancies present in the oxygen-deficient titanium dioxide have high chemical activity and can undergo coordination reactions with oxygen to fix it.

[0017] Preferably, the additive contains a binder and a dispersant.

[0018] Preferably, the adhesive is selected from at least one of polyvinylidene fluoride, polyacrylate, styrene-butadiene rubber, and polyamide.

[0019] Preferably, the dispersant is selected from at least one of sodium carboxymethyl cellulose, polyvinyl alcohol, and polyvinylpyrrolidone.

[0020] In a preferred embodiment, the content of the binder is 0.5-6 wt% and the content of the dispersant is 0.5-2 wt%, based on the total solid mass of the slurry.

[0021] As previously stated, a second aspect of the present invention provides a battery separator comprising a base film and a coating applied to at least one surface of the base film; The coating is formed from the slurry for battery separators described in the first aspect.

[0022] Preferably, the battery separator is prepared by a method comprising the following steps: (1) In the presence of a solvent, an oxygen adsorbent, an oxygen fixative, a binder, and a dispersant are mixed to obtain the slurry for the battery separator; (2) The battery separator is coated on the base film with a slurry and dried to obtain the battery separator.

[0023] Preferably, the mixing is carried out under stirring conditions.

[0024] More preferably, the stirring conditions include: a rotation speed of 1200-1600 rpm and a stirring time of 30-60 min.

[0025] According to a particularly preferred embodiment, the preparation steps of the battery separator further include: in step (1), the oxygen adsorbent and the oxygen fixative are premixed, then a first part of the solvent and dispersant are added and stirred for 30-60 minutes, then a binder is added and stirred for 30-60 minutes, and finally another part of the solvent is added and stirred for 30-60 minutes to obtain the slurry for the battery separator.

[0026] More preferably, based on the total mass of the oxygen adsorbent and the oxygen fixative, the amount of the first portion of solvent is 180-220g.

[0027] More preferably, the amount of the other portion of solvent is controlled so that the solid content of the slurry for battery separator is 34-37 wt%.

[0028] Preferably, the drying conditions include a temperature of 50-60°C and a time of 2-5 minutes.

[0029] Preferably, the base film is selected from at least one of polyethylene film, polypropylene film, polyethylene / polypropylene composite film, and polyimide film.

[0030] In a preferred embodiment, the thickness of the base film is 5-10 μm, and the thickness of the coating is 1-4 μm.

[0031] Preferably, the coating method is microgravure transfer coating.

[0032] According to a particularly preferred embodiment, the preparation step of the battery separator further includes: in step (2), coating the battery separator on both sides of the base film with a slurry.

[0033] As previously stated, the third aspect of the present invention provides the application of the battery separator described in the second aspect in the field of lithium-ion battery technology.

[0034] As previously described, a fourth aspect of the present invention provides a lithium-ion battery comprising: a positive electrode, a negative electrode, a separator, and an electrolyte; wherein the separator is the battery separator described in the second aspect.

[0035] The present invention will be described in detail below through embodiments. Unless otherwise specified, all instruments and materials used in the following embodiments are commercially available products.

[0036] Zeolite molecular sieve: purchased from Jianlong Micro-Nano New Materials Co., Ltd., grade ZSM-5.

[0037] TiO 1.75 TiO 1.8 All were purchased from Taizhou Aites Optical Materials Co., Ltd.

[0038] Sodium carboxymethyl cellulose: purity 99 wt%.

[0039] N-Methylpyrrolidone: purity 99.5 wt%.

[0040] Polyvinylidene fluoride: purity 99wt%.

[0041] Polyethylene (PE) porous base film: purchased from Enjie Company, brand name ND.

[0042] Lithium iron phosphate cathode: purchased from Yuneng New Energy Battery Materials Co., Ltd., grade CN-5.

[0043] Graphite anode: purchased from Yu Rong Lithium New Materials Technology Co., Ltd.

[0044] Electrolyte: Purchased from Faenlet New Energy Technology Co., Ltd., brand name Y01.

[0045] Nano-alumina: Purchased from Silicon Labs Technology Co., Ltd., grade 25SN.

[0046] Example 1 (1) The zeolite molecular sieve (i.e., oxygen adsorbent) and TiO2 are combined. 1.75 (i.e., oxygen-fixing agent) is used as a premixed functional material; the first part of N-methylpyrrolidone (NMP, i.e., solvent) is added, sodium carboxymethyl cellulose (i.e., dispersant) is added, and the mixture is dispersed by high-speed stirring for 30 minutes (1500 rpm); polyvinylidene fluoride (PVDF, i.e., binder) is added, and the mixture is dispersed by high-speed stirring for 60 minutes (1200 rpm); another part of N-methylpyrrolidone (NMP, i.e. solvent) is added, and the solid content of the slurry is adjusted to 35.5 wt%. After high-speed dispersion for 30 minutes (1500 rpm), the slurry for battery separators is obtained. (2) Select a porous polyethylene (PE) base film and use a microgravure transfer coating method to coat the battery separator slurry on both sides of the PE base film; after drying (temperature is 55℃, time is 2min), a functional coating with a thickness of 2μm is formed on the base film surface to obtain the battery separator.

[0047] The specific types and amounts of raw materials and process parameters in this embodiment are shown in Table 1.

[0048] Examples 2-6 The method of Example 1 is followed, except that the types and amounts of raw materials and process parameters of the other examples are different, as shown in Table 1.

[0049] In Table 1, the amount of solvent used is indicated by "+" to represent the amount of solvent in the first part and the amount of solvent in the other part. For example, in Example 1, "200+163.4" means that the amount of solvent used in the first part is 200g and the amount of solvent used in the other part is 163.4g.

[0050] Table 1

[0051] Comparative Example 1 The procedure was carried out according to Example 1, except that the oxygen-fixing agent TiO2 was not added. 1.75 The dosage of the oxygen adsorbent zeolite molecular sieve has been adjusted from "95g" to "190g". Specifically, (1) Mix 190g of zeolite molecular sieve (i.e. oxygen adsorbent) with the first part of N-methylpyrrolidone (NMP, i.e. solvent), add sodium carboxymethyl cellulose (i.e. dispersant), and disperse at high speed for 30min (1500rpm); add polyvinylidene fluoride (PVDF, i.e. binder), and disperse at high speed for 60min (1200rpm); add another part of N-methylpyrrolidone (NMP, i.e. solvent), adjust the solid content of the slurry to 35.5wt%, disperse at high speed for 30min (1500rpm), and obtain the slurry for battery separator; The remaining steps are the same as in Example 1, resulting in a conventional ceramic battery separator.

[0052] Comparative Example 2 The method was carried out according to Example 1, except that the total content of oxygen adsorbent and oxygen fixative was 80 wt%. Specifically, (1) Mix 80g of zeolite molecular sieve (i.e., oxygen adsorbent) and 80g of TiO2. 1.75 (i.e., oxygen-fixing agent) is used as a premixed functional material; the first part of N-methylpyrrolidone (NMP, i.e., solvent) and 35g of nano-alumina powder are added, and sodium carboxymethyl cellulose (i.e., dispersant) is added. The mixture is then stirred and dispersed at high speed for 30min (1500rpm); polyvinylidene fluoride (PVDF, i.e., binder) is added, and the mixture is stirred and dispersed at high speed for 60min (1200rpm); another part of N-methylpyrrolidone (NMP, i.e., solvent) is added, and the solid content of the slurry is adjusted to 35.5wt%. After high-speed dispersion for 30min (1500rpm), the slurry for battery separators is obtained. The remaining steps are the same as in Example 1, to obtain the battery separator.

[0053] Comparative Example 3 The process was carried out according to the method of Example 1, except that the mass ratio of oxygen adsorbent to oxygen fixative was 1:12, the total amount of oxygen adsorbent and oxygen fixative remained unchanged, and the remaining steps were the same as in Example 1, to obtain the battery separator.

[0054] Comparative Example 4 The procedure was carried out according to Example 1, except that the oxygen-fixing agent TiO2 was used. 1.75 Replace with an equal mass of "oxygen-fixing agent TiO2" 1.8 The total amount of oxygen adsorbent and oxygen fixative remains unchanged, and the remaining steps are the same as in Example 1 to obtain the battery separator.

[0055] Application Example 1: Preparation of Lithium-ion Batteries A lithium-ion battery was assembled from a lithium iron phosphate cathode, a graphite anode, an electrolyte, and the battery separator prepared in Example 1.

[0056] Application Examples 2-6 The method of Application Example 1 was followed, except that the battery separator prepared in Example 1 was replaced with the battery separator prepared in Examples 2, 3, 4, 5, and 6, respectively.

[0057] Comparative Application Example 1 The method was carried out in accordance with Application Example 1, except that the battery separator prepared in Example 1 was replaced with the conventional ceramic battery separator prepared in Comparative Example 1.

[0058] Comparative Application Example 2 The method was carried out in accordance with Application Example 1, except that the battery separator prepared in Example 1 was replaced with the battery separator prepared in Comparative Example 2.

[0059] Comparative Application Example 3 The method was carried out in accordance with Application Example 1, except that the battery separator prepared in Example 1 was replaced with the battery separator prepared in Comparative Example 3.

[0060] Comparative Application Example 4 The method was carried out in accordance with Application Example 1, except that the battery separator prepared in Example 1 was replaced with the battery separator prepared in Comparative Example 4.

[0061] Test case Storage gas production test: The batteries prepared by each application example and the comparative application example were subjected to cycle test in a charge-discharge tester. Specifically: (1) The batteries were charged and discharged 3 times at a rate of 0.1C within a voltage range of 2.5-3.65V to fully activate the batteries; (2) The batteries were charged to 3.65V at 0.5C and stored at 55℃ for 14 days. The battery thickness after cycle was tested and the volume expansion rate was calculated.

[0062] Cyclic performance test: Batteries prepared for each application example and comparative application example were subjected to cyclic testing in a charge-discharge tester. Specifically, (1) the batteries were charged and discharged 3 times at a rate of 0.1C within a voltage range of 2.5-3.65V to fully activate them; (2) the batteries were charged and discharged 500 times at a rate of 1C within a voltage range of 2.5-3.65V. The test results are shown in Table 2.

[0063] The formula for calculating the discharge energy retention rate is: Discharge energy retention rate = (Discharge energy of the Nth cycle / Discharge energy of the initial cycle) × 100%.

[0064] The formula for calculating the volume expansion rate is: Volume expansion rate = (Battery thickness after cycle - Battery thickness before cycle) / Battery thickness before cycle × 100%.

[0065] Table 2

[0066] As can be seen from the results in Table 2, the lithium-ion battery provided by the present invention exhibits a better discharge energy retention rate and maintains a lower gas production rate after 500 cycles, indicating that the battery separator provided by the present invention has the function of suppressing battery gas production, thereby improving the cycle and safety performance of the battery.

[0067] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A slurry for battery separators, characterized in that, The slurry contains a main agent and auxiliary agents. The main agent contains an oxygen adsorbent and an oxygen fixative. The oxygen adsorbent is a zeolite molecular sieve, and the oxygen fixative is oxygen-deficient titanium dioxide. The mass ratio of the oxygen adsorbent to the oxygen fixative is 1:0.1-10. Based on the total solid mass of the slurry, the total content of the oxygen adsorbent and the oxygen fixative is 90-99.5 wt%. The oxygen-deficient titanium dioxide has the structural formula TiO2. 2-x , of which 0.2 <x<0.5。 2. The slurry for battery separators according to claim 1, characterized in that, The mass ratio of the oxygen adsorbent to the oxygen fixative is 1:0.5-2.

3. The slurry for battery separators according to claim 1, characterized in that, The solid content of the slurry used for the battery separator is 34-37 wt%.

4. The slurry for battery separators according to claim 1, characterized in that, The D of the zeolite molecular sieve 50 The particle size is 0.5-2.0 μm; And / or, the D of the oxygen-deficient titanium dioxide 50 The particle size is 0.1-1.0 μm.

5. The slurry for battery separators according to any one of claims 1-4, characterized in that, The additives contain binders and dispersants; And / or, the adhesive is selected from at least one of polyvinylidene fluoride, polyacrylate, styrene-butadiene rubber, and polyamide; And / or, the dispersant is selected from at least one of sodium carboxymethyl cellulose, polyvinyl alcohol, and polyvinylpyrrolidone.

6. The slurry for battery separators according to claim 5, characterized in that, Based on the total solids mass of the slurry, the content of the binder is 0.5-6 wt%, and the content of the dispersant is 0.5-2 wt%.

7. A battery separator, characterized in that, The diaphragm includes a base membrane and a coating applied to at least one surface of the base membrane; The coating is formed from the slurry for battery separators as described in any one of claims 1-6.

8. The battery separator according to claim 7, characterized in that, The base film is selected from at least one of polyethylene film, polypropylene film, polyethylene / polypropylene composite film, and polyimide film; And / or, the thickness of the base film is 5-10 μm, and the thickness of the coating is 1-4 μm.

9. The application of the battery separator according to claim 7 or 8 in the field of lithium-ion battery technology.

10. A lithium-ion battery, characterized in that, The lithium-ion battery includes: a positive electrode, a negative electrode, a separator, and an electrolyte; the separator is the battery separator as described in claim 7 or 8.

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