Diaphragm and preparation method thereof, battery and electric device

Abstract

The invention discloses a diaphragm, a preparation method of the diaphragm, a battery and a power utilization device. The solid electrolyte coating is arranged on one side, close to the positive pole piece, of the base membrane; and the functional film-forming additive coating is arranged on one side, close to the negative pole piece, of the base film. The solid electrolyte coating and the functional film-forming additive coating are arranged on the two sides of the base film respectively, and under the synergistic effect of the two coatings, the stability of a negative electrode SEI film (a solid electrolyte interface film) can be improved, direct contact between an electrolyte and a negative electrode interface is blocked, the stability of the electrolyte is improved, irreversible consumption of active lithium in the battery is reduced, and the service life of the battery is prolonged. Therefore, the manganese-based lithium ion battery can keep good high-temperature cycle performance and high-temperature storage performance at high temperature.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a diaphragm and a preparation method thereof, a battery, and an electrical device. Background Art

[0002] Lithium iron manganese phosphate, spinel lithium manganese oxide, lithium-rich manganese-based materials, etc. are several typical manganese-based positive electrode materials with great potential for promotion and application. However, under high-temperature conditions, manganese ions in lithium-ion batteries using manganese-based positive electrode materials will dissolve, causing the high-temperature cycle performance and high-temperature storage performance of the battery to deteriorate. Related technologies The main way to improve the high-temperature cycle performance and high-temperature storage performance of batteries is to solve the manganese dissolution of manganese-based positive electrode materials by adding functional molecules that can form positive electrode films to traditional liquid electrolytes or adding functional molecules that can complex with Mn ions to the electrolyte. Although this method can improve battery performance in the short term, after a long cycle process, the functional molecules will be exhausted, and the interfacial film involved in the formation will also lead to reduced stability under harsh conditions, and the high-temperature cycle performance and high-temperature storage performance of the battery cannot be maintained. Summary of the invention

[0003] The present invention aims to solve one of the technical problems in the related art at least to a certain extent. To this end, the present invention provides a diaphragm, which can enable a manganese-based lithium-ion battery to maintain good high-temperature cycle performance and high-temperature storage performance at high temperatures.

[0004] Specifically, the first aspect of the present invention provides a diaphragm, comprising:

[0005] Basement membrane;

[0006] A solid electrolyte coating, wherein the solid electrolyte coating is disposed on a side of the base film close to the positive electrode plate;

[0007] A functional film-forming additive coating is provided on a side of the base film close to the negative electrode plate.

[0008] The present invention sets a solid electrolyte coating and a functional film-forming additive coating on both sides of the base film. Under the synergistic effect of the two coatings, the stability of the negative electrode SEI film (solid electrolyte interface film) can be improved, the direct contact between the electrolyte and the negative electrode interface can be blocked, the stability of the electrolyte can be improved, and the irreversible consumption of active lithium inside the battery can be reduced, so that the manganese-based lithium-ion battery can maintain good high-temperature cycle performance and high-temperature storage performance at high temperatures. Compared with related technologies, the present invention proposes a new technical concept to improve the high-temperature cycle performance and high-temperature storage performance of manganese-based lithium-ion batteries.

[0009] According to some embodiments of the present invention, the thickness of the solid electrolyte coating is 0.5-6.0 μm. Optimizing the thickness of the solid electrolyte coating is beneficial to further improve the high temperature cycle performance and high temperature storage performance of the battery.

[0010] According to some embodiments of the present invention, the thickness of the solid electrolyte coating is 2.0-5.0 μm. Optimizing the thickness of the solid electrolyte coating is beneficial to further improve the high temperature cycle performance and high temperature storage performance of the battery.

[0011] According to some embodiments of the present invention, the thickness of the functional film-forming additive coating is 0.1-3.0 μm. Optimizing the thickness of the functional film-forming additive coating is beneficial to further improve the high-temperature cycle performance and high-temperature storage performance of the battery.

[0012] According to some embodiments of the present invention, the thickness of the functional film-forming additive coating is 0.5 to 2.5 μm. Optimizing the thickness of the functional film-forming additive coating is beneficial to further improve the high-temperature cycle performance and high-temperature storage performance of the battery.

[0013] According to some embodiments of the present invention, the thickness ratio of the solid electrolyte coating to the functional film-forming additive coating is (1.5-2.5): 1. Optimizing the thickness ratio of the solid electrolyte coating to the functional film-forming additive coating is beneficial to further improve the high-temperature cycle performance and high-temperature storage performance of the battery.

[0014] According to some embodiments of the present invention, the functional film-forming additive coating includes a functional film-forming additive, and the functional film-forming additive includes one or more of anhydrides, phosphates, sulfates, and lithium salts. The use of these functional film-forming additives is conducive to releasing the negative electrode SEI film modifier in real time according to the negative electrode interface requirements, blocking the direct contact between the electrolyte and the negative electrode interface, improving the stability of the electrolyte, and reducing the irreversible consumption of active lithium inside the battery, thereby improving the high temperature cycle performance and high temperature storage performance of the battery.

[0015] According to some embodiments of the present invention, the functional film-forming additive includes one or more of 2-methylmaleic anhydride, maleic anhydride, methylsuccinic anhydride, glutaric anhydride, succinic anhydride, adipic anhydride, triphenyl phosphate, triethyl diphosphate, pentafluorophenyl diphenyl phosphate, 1,3-propane sultone, 1,4-butane sultone, 1,3-propylene sultone, methanedisulfonic acid methylene ester, lithium difluorophosphate, lithium bis(fluorosulfonyl)imide, lithium dioxalatoborate, and lithium difluorooxalatoborate.

[0016] According to some embodiments of the present invention, the solid electrolyte coating includes a solid electrolyte, and the solid electrolyte includes one or more of lithium lanthanum zirconium oxide, lithium lanthanum zirconium tantalum oxide, lithium lanthanum zirconium niobium oxide, lithium lanthanum titanium oxide, and lithium aluminum titanium phosphate. The use of these solid electrolytes is conducive to reducing the manganese ion transmission channel on the diaphragm, blocking the migration of manganese ions from the positive terminal to the negative terminal, thereby reducing the deposition of manganese ions at the negative electrode interface, reducing the damage to the negative electrode SEI film, and improving the stability of the negative electrode SEI film.

[0017] The second aspect of the present invention provides a method for preparing the diaphragm according to the first aspect of the present invention, comprising the following steps:

[0018] After mixing the solid electrolyte, the binder and the solvent, the mixture is applied on the side of the base film close to the positive electrode plate;

[0019] After mixing the functional film-forming additive and the solvent, the mixture is applied on the side of the base film close to the negative electrode plate;

[0020] After drying, the separator is obtained.

[0021] The method for preparing the diaphragm of the present invention has simple process flow, low raw material cost, good reproducibility and is suitable for large-scale industrial promotion.

[0022] The third aspect of the present invention provides a battery, comprising the separator according to the first aspect of the present invention or the separator obtained by the method according to the second aspect of the present invention.

[0023] According to some embodiments of the present invention, the battery further comprises a positive electrode sheet and a negative electrode sheet, the solid electrolyte coating of the diaphragm is close to the positive electrode sheet, and the functional film-forming additive coating of the diaphragm is close to the negative electrode sheet.

[0024] According to some embodiments of the present invention, the positive electrode plate includes a positive electrode current collector and a positive electrode coating disposed on at least one surface of the positive electrode current collector, and the positive electrode coating includes a positive electrode active material, a solid electrolyte, a conductive agent and a binder.

[0025] Applying the diaphragm of the present invention to a battery can improve the stability of the negative electrode SEI film and improve the high temperature performance of the battery; at the same time, by physically doping the positive electrode coating with a solid electrolyte, the dissolution of manganese ions can be inhibited, the stability of the positive electrode active material can be improved, the content of free manganese ions in the electrolyte can be reduced, and the stability of the negative electrode SEI film can be improved. Thus, the high temperature storage performance and high temperature cycle performance of the battery are improved through "double protection".

[0026] According to some embodiments of the present invention, the solid electrolyte includes one or more of lithium lanthanum zirconium oxide, lithium lanthanum zirconium tantalum oxide, lithium lanthanum zirconium niobium oxide, lithium lanthanum titanium oxide, and lithium aluminum titanium phosphate. The use of these solid electrolytes is conducive to inhibiting the dissolution of manganese ions in the positive electrode active material, improving the stability of the positive electrode active material, reducing the content of free manganese ions in the electrolyte, and improving the stability of the negative electrode SEI film.

[0027] According to some embodiments of the present invention, the amount of the solid electrolyte added to the positive electrode coating is 0.1 wt% to 5 wt%. Optimizing the amount of the solid electrolyte added to the positive electrode coating is beneficial to inhibiting the dissolution of manganese ions in the positive electrode active material.

[0028] According to some embodiments of the present invention, the positive electrode active material includes a manganese-based positive electrode material; preferably, the manganese-based positive electrode material includes one or more of lithium iron manganese phosphate, lithium-rich manganese-based materials, and lithium manganate. Manganese-based positive electrode materials have the problem of manganese dissolution under high temperature conditions. The use of the separator and / or positive electrode coating of the present invention in a manganese-based lithium-ion battery is conducive to improving its high-temperature storage performance and high-temperature cycle performance.

[0029] A fourth aspect of the present invention provides an electrical device comprising the battery of the third aspect of the present invention.

[0030] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 Schematic diagram of the structure of the diaphragm of some embodiments of the present invention.

[0032] Figure 2 Schematic diagram of the internal structure of batteries according to some embodiments of the present invention.

[0033] Figure 3 It is a schematic diagram of the structure of the positive electrode sheet of some embodiments of the present invention.

[0034] Figure 4 It is a scanning electron microscope (SEM) image of the diaphragm containing the solid electrolyte coating prepared in Comparative Example 8.

[0035] Figure 5 This is an energy dispersive X-ray spectrometer (EDS) scanning spectrum of the diaphragm containing a solid electrolyte coating prepared in Comparative Example 8.

[0036] Figure 6 It is a comparison chart of the cycle performance of the LMR / graphite battery of Comparative Example 5 and Example 9 at 45°C. DETAILED DESCRIPTION

[0037] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0038] Lithium iron manganese phosphate, spinel lithium manganese oxide, lithium-rich manganese-based materials, etc. are several typical manganese-based positive electrode materials with great potential for promotion and application. However, under high-temperature conditions, manganese ions in lithium-ion batteries using manganese-based positive electrode materials will dissolve, causing the high-temperature cycle performance and high-temperature storage performance of the battery to deteriorate. Related technologies The main way to improve the high-temperature cycle performance and high-temperature storage performance of batteries is to solve the manganese dissolution of manganese-based positive electrode materials by adding functional molecules that can form positive electrode films to traditional liquid electrolytes or adding functional molecules that can complex with Mn ions to the electrolyte. Although this method can improve battery performance in the short term, after a long cycle process, the functional molecules will be exhausted, and the interfacial film involved in the formation will also lead to reduced stability under harsh conditions, and the high-temperature cycle performance and high-temperature storage performance of the battery cannot be maintained.

[0039] In order to improve the high-temperature cycle performance and high-temperature storage performance of manganese-based lithium-ion batteries, the present invention respectively arranges a solid electrolyte coating and a functional film-forming additive coating on both sides of the base membrane. Under the synergistic effect of these two coatings, the stability of the negative electrode SEI film (solid electrolyte interface film) can be improved, the direct contact between the electrolyte and the negative electrode interface can be blocked, the stability of the electrolyte can be improved, and the irreversible consumption of active lithium inside the battery can be reduced, so that the manganese-based lithium-ion battery can maintain good high-temperature cycle performance and high-temperature storage performance at high temperatures.

[0040] Specifically, Figure 1 As shown, the first aspect of the present invention provides a diaphragm, comprising:

[0041] Basement membrane;

[0042] A solid electrolyte coating, wherein the solid electrolyte coating is disposed on a side of the base film close to the positive electrode plate;

[0043] A functional film-forming additive coating is provided on a side of the base film close to the negative electrode plate.

[0044] The solid electrolyte coating is close to the positive electrode plate, and the functional film-forming additive coating is close to the negative electrode plate. This setting cannot be reversed, otherwise it will have a negative impact on the negative electrode plate and cause degradation of the battery's high temperature performance.

[0045] Experimental verification shows that the solid electrolyte coating and the functional film-forming additive coating work together to improve the stability of the negative electrode SEI film. Although the high-temperature performance of the battery is improved by coating the solid electrolyte coating or the functional film-forming additive coating only on one side of the base film, the improvement effect is far less than that of the present invention; even coating the solid electrolyte coating on both sides of the base film at the same time is not conducive to improving the high-temperature performance of the battery.

[0046] The present invention has no particular limitation on the material of the base film, and one or more of polypropylene (PP) and polyethylene (PE) may be used. The thickness of the base film may generally be 6-10 μm, such as 6 μm, 7 μm, 8 μm, 9 μm or 10 μm.

[0047] In some embodiments, the thickness of the solid electrolyte coating may be 0.5 to 6.0 μm. Optimizing the thickness of the solid electrolyte coating is beneficial to further improve the high temperature cycle performance and high temperature storage performance of the battery.

[0048] In some specific embodiments, the thickness of the solid electrolyte coating may be 0.5 μm, 1.0 μm, 1.5 μm, 2.0 μm, 2.5 μm, 3.0 μm, 3.5 μm, 4.0 μm, 4.5 μm, 5.0 μm, 5.5 μm or 6.0 μm.

[0049] In some specific embodiments, the solid electrolyte coating may have a thickness of 2.0 to 5.0 μm.

[0050] In some embodiments, the thickness of the functional film-forming additive coating may be 0.1 to 3.0 μm. Optimizing the thickness of the functional film-forming additive coating is beneficial to further improve the high-temperature cycle performance and high-temperature storage performance of the battery.

[0051] In some specific embodiments, the functional film-forming additive coating may have a thickness of 0.1 μm, 0.5 μm, 1.0 μm, 1.5 μm, 2.0 μm, 2.5 μm, or 3.0 μm.

[0052] In some specific embodiments, the thickness of the functional film-forming additive coating layer may be 0.5-2.5 μm.

[0053] In some embodiments, the thickness ratio of the solid electrolyte coating to the functional film-forming additive coating may be (1.5-2.5): 1. Optimizing the thickness ratio of the solid electrolyte coating to the functional film-forming additive coating is beneficial to further improve the high-temperature cycle performance and high-temperature storage performance of the battery.

[0054] In some specific embodiments, the thickness ratio of the solid electrolyte coating to the functional film-forming additive coating may be 1.5:1, 1.8:1, 2:1, 2.2:1 or 2.5:1.

[0055] In some embodiments, the functional film-forming additive coating includes a functional film-forming additive, and the functional film-forming additive includes one or more of anhydrides, phosphates, sulfates, and lithium salts. The functional film-forming additives of the present invention are easily reduced and decomposed to form a film at the negative electrode, thereby improving the structural stability of the negative electrode SEI film. The use of these functional film-forming additives is conducive to the real-time release of the negative electrode SEI film modifier according to the negative electrode interface requirements, blocking the direct contact between the electrolyte and the negative electrode interface, improving the stability of the electrolyte, and reducing the irreversible consumption of active lithium inside the battery, thereby improving the high temperature cycle performance and high temperature storage performance of the battery.

[0056] In some specific embodiments, the functional film-forming additive includes one or more of 2-methylmaleic anhydride, maleic anhydride, methylsuccinic anhydride, glutaric anhydride, succinic anhydride, adipic anhydride, triphenyl phosphate, triethyl diphosphate, pentafluorophenyl diphenyl phosphate, 1,3-propane sultone, 1,4-butane sultone, 1,3-propylene sultone, methanedisulfonic acid methylene ester, lithium difluorophosphate, lithium bis(fluorosulfonyl)imide, lithium dioxalatoborate, and lithium difluorooxalatoborate.

[0057] According to some embodiments of the present invention, the solid electrolyte coating includes a solid electrolyte, and the solid electrolyte includes one or more of lithium lanthanum zirconium oxide (LLZO), lithium lanthanum zirconium tantalum oxide (LLZTO), lithium lanthanum zirconium niobium oxide (LLZNO), lithium lanthanum titanium oxide (LLTO), and lithium aluminum titanium phosphate (LATP). The use of these solid electrolytes is conducive to reducing the manganese ion transmission channel on the diaphragm, blocking the migration of manganese ions from the positive terminal to the negative terminal, thereby reducing the deposition of manganese ions at the negative electrode interface, reducing the damage to the negative electrode SEI film, and improving the stability of the negative electrode SEI film.

[0058] The second aspect of the present invention provides a method for preparing the diaphragm according to the first aspect of the present invention, comprising the following steps:

[0059] After mixing the solid electrolyte, the binder and the solvent, the mixture is applied on the side of the base film close to the positive electrode plate;

[0060] After mixing the functional film-forming additive and the solvent, the mixture is applied on the side of the base film close to the negative electrode plate;

[0061] After drying, the separator is obtained.

[0062] The method for preparing the diaphragm of the present invention has simple process flow, low raw material cost, good reproducibility and is suitable for large-scale industrial promotion.

[0063] According to some embodiments of the present invention, the coating includes spray coating, dip coating, roller coating, and die coating. These coating methods are beneficial to improving the distribution uniformity and performance of the coating, thereby improving the high temperature cycle performance and high temperature storage performance of the battery.

[0064] In some embodiments, the binder includes one or more of sodium alginate, styrene-butadiene rubber, sodium polyacrylate, sodium polycarboxymethyl cellulose, polyacrylic acid, polyethyl acrylate, polymethacrylic acid, water-soluble unsaturated resin SR-1B, polyurethane, polyvinyl alcohol, carboxymethyl chitosan, and acrylamide.

[0065] In some embodiments, the mass ratio of the solid electrolyte to the binder ranges from 97:3 to 99:1, for example: 97:3, 98:2, 99:1.

[0066] In some embodiments, the solvent includes one or more of water, N-methylpyrrolidone, N-ethylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, 1,2-dimethoxyethane, dimethyl sulfoxide, tetrahydrofuran, ethanol, ethylene glycol, ethylene glycol dimethyl ether, diethyl isopropyl carbonate, and ethyl methyl carbonate.

[0067] In some embodiments, the drying process is carried out at 40°C-80°C for 3min-15min. In some specific embodiments, the temperature of the drying process can be 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, etc., or can be a range composed of any of the above values. In some specific embodiments, the drying time can be 3min, 5min, 7min, 10min, 12min, 15min, etc., or can be a range composed of any of the above values. Thus, it helps to fix the coating on the base film to ensure that the coating is evenly distributed and not easy to fall off.

[0068] The third aspect of the present invention provides a battery, comprising the separator according to the first aspect of the present invention or the separator obtained by the method according to the second aspect of the present invention.

[0069] In some embodiments, Figure 2 As shown, the battery further comprises a positive electrode sheet and a negative electrode sheet, the solid electrolyte coating of the separator is close to the positive electrode sheet, and the functional film-forming additive coating of the separator is close to the negative electrode sheet; the positive electrode sheet (such as Figure 3 ) includes a positive electrode current collector and a positive electrode coating disposed on at least one surface of the positive electrode current collector, wherein the positive electrode coating includes a positive electrode active material, a solid electrolyte, a conductive agent and a binder.

[0070] Applying the separator of the present invention to a battery can improve the stability of the negative electrode SEI film and the high-temperature performance of the battery; at the same time, by physically doping the positive electrode coating with a solid electrolyte, the dissolution of manganese ions can be inhibited, the stability of the positive electrode active material can be improved, the content of free manganese ions in the electrolyte can be reduced, and the stability of the negative electrode SEI film can be improved. Thus, the high-temperature storage performance and high-temperature cycling performance of the battery are improved through "double protection".

[0071] In some embodiments, the solid electrolyte includes one or more of lithium lanthanum zirconium oxide (LLZO), lithium lanthanum zirconium tantalum oxide (LLZTO), lithium lanthanum zirconium niobium oxide (LLZNO), lithium lanthanum titanium oxide (LLTO), and lithium aluminum titanium phosphate (LATP). Using these solid electrolytes is beneficial to inhibiting the dissolution of manganese ions in the positive electrode active material, improving the stability of the positive electrode active material, reducing the content of free manganese ions in the electrolyte, and improving the stability of the negative electrode SEI film.

[0072] In some embodiments, the addition amount of the solid electrolyte in the positive electrode coating can be 0.1 wt% to 5 wt%. Optimizing the addition amount of the solid electrolyte in the positive electrode coating is beneficial to inhibiting the dissolution of manganese ions in the positive electrode active material.

[0073] In some specific embodiments, the addition amount of the solid electrolyte in the positive electrode coating can be 0.1 wt%, 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, or 5 wt%.

[0074] In some embodiments, the positive electrode active material includes a manganese-based positive electrode material. The manganese-based positive electrode material has a problem of manganese dissolution under high-temperature conditions. Using the separator and / or positive electrode coating of the present invention in a manganese-based lithium-ion battery is beneficial to improving its high-temperature storage performance and high-temperature cycling performance.

[0075] In some specific embodiments, the manganese-based positive electrode material includes one or more of lithium iron manganese phosphate, lithium-rich manganese-based material (xLi2MnO3·(1 - x)LiMO2, 0 < x < 1, M = Ni, Co, Mn and other transition metals and their combinations), and lithium manganese oxide (LiMn2O4).

[0076] In some embodiments, the conductive agent includes one or more of carbon black, conductive graphite, carbon fiber, carbon nanotube, and graphene.

[0077] In some embodiments, the binder includes one or more of polyvinylidene fluoride homopolymer (such as 5130, HSV900) and polyvinylidene fluoride copolymer (such as Solef 5130, etc.).

[0078] The scheme of the present invention will be explained below in conjunction with the embodiments. It will be appreciated by those skilled in the art that the following embodiments are only used to illustrate the present invention and should not be considered as limiting the scope of the present invention. Where specific techniques or conditions are not indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. The reagents or instruments used are not indicated by the manufacturer and are all conventional products that can be obtained commercially.

[0079] Comparative Example 1

[0080] (1) Positive electrode preparation:

[0081] 96.0wt% lithium manganese iron phosphate (LiMn 0.8 Fe 0.2 PO4, LMFP), 1.0wt% conductive carbon black, 1.0wt% conductive carbon nanotubes (CNT), and 2.0wt% polyvinylidene fluoride (PVDF) are uniformly mixed. After the positive electrode slurry is vacuum stirred evenly, the positive electrode slurry is coated on a clean aluminum foil with a coating machine, and then vacuum dried at 120°C for 12h. The dried electrode sheet is rolled with a roller machine and then cut into sheets to obtain the required battery positive electrode sheet.

[0082] (2) Negative electrode preparation:

[0083] 95.0wt% graphite, 1.5wt% carboxymethyl cellulose (CMC), 1.0wt% conductive carbon black and 2.5wt% styrene-butadiene rubber (SBR) were uniformly mixed. After the negative electrode slurry was vacuum stirred evenly, the negative electrode slurry was coated on a clean copper foil with a coating machine, and then vacuum dried at 120°C for 12h. The dried electrode sheet was rolled with a roller machine and then cut into pieces to obtain the required battery negative electrode sheet.

[0084] (3) Preparation of electrolyte:

[0085] Ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) were mixed at a ratio of 1:1.5:1.5 (mass ratio), and then a certain amount of LiPF6 was added to the mixed solvent system and mixed evenly to ensure that the lithium salt concentration in the electrolyte was 1 mol / L, which was used as electrolyte D1.

[0086] (4) Preparation of soft pack batteries:

[0087] The prepared positive and negative electrode sheets are wound or stacked with conventional 7μm polyethylene (PE) separators, and then packaged with aluminum-plastic film to obtain non-liquid-injected battery cells. The above-mentioned electrolyte is added to a glove box filled with argon or nitrogen where the moisture and oxygen are both less than 10ppm to obtain a soft-pack battery.

[0088] Comparative Example 2

[0089] The positive and negative electrode sheets, electrolyte preparation and soft-pack battery preparation process are the same as those in comparative example 1, except that the electrolyte of comparative example 2 is electrolyte D1 with 2-methylmaleic anhydride added, wherein the ratio of the total added mass to the mass of electrolyte D1 is 1.0%, namely electrolyte D2.

[0090] Comparative Example 3

[0091] The positive and negative electrode sheets, the soft-pack battery preparation process, the electrolyte and the separator used are the same as those in Comparative Example 1. The difference is that the positive electrode active material used in Comparative Example 3 is LiMn2O4, and its proportion in the positive electrode slurry remains unchanged.

[0092] Comparative Example 4

[0093] The positive and negative electrode sheets, the soft pack battery preparation process, and the used separator are the same as those in Comparative Example 1, except that the positive electrode active material used in Comparative Example 4 is LiMn2O4, and its proportion in the positive electrode slurry remains unchanged. At the same time, the used electrolyte is the same as that in Comparative Example 2, which is electrolyte D2.

[0094] Comparative Example 5

[0095] The positive and negative electrode sheets, the soft pack battery preparation process, the electrolyte and the separator used are the same as those in Comparative Example 1, except that the positive electrode active material used in Comparative Example 5 is a lithium-rich manganese-based active material (Li 1.2 Mn 0.56 Co 0.12 Ni 0.12 O2, LMR), and its proportion in the positive electrode slurry remains unchanged.

[0096] Comparative Example 6

[0097] The positive and negative electrode sheets, the soft pack battery preparation process, and the separator used are the same as those in Comparative Example 1, except that the positive electrode active material used in Comparative Example 6 is a lithium-rich manganese-based active material (Li 1.2 Mn 0.56 Co 0.12 Ni 0.12 O2, LMR), and its proportion in the positive electrode slurry remains unchanged. At the same time, the electrolyte used is the same as that of Comparative Example 2, namely, electrolyte D2.

[0098] Comparative Example 7

[0099] The negative electrode sheet, the soft pack battery preparation process, the electrolyte and the separator used are the same as those in Comparative Example 1, except that 95.0wt% LMFP, 1.0wt% lithium aluminum titanium phosphate (Li 1.3 Al 0.3 Ti 1.7(PO4)3, LATP), 1.0wt% conductive carbon black, 1.0wt% conductive carbon nanotubes (CNT) and 2.0wt% polyvinylidene fluoride (PVDF) are uniformly mixed. After the positive electrode slurry is vacuum stirred evenly, the positive electrode slurry is coated on a clean aluminum foil with a coating machine, and then vacuum dried at 120°C for 12h. The dried electrode sheet is rolled with a roller machine and then cut into sheets to obtain the required battery positive electrode sheet.

[0100] Comparative Example 8

[0101] The positive and negative electrode sheets, the soft pack battery preparation process, and the electrolyte used are the same as those in Comparative Example 1, except that the diaphragm used is modified with a solid electrolyte near the positive electrode side (such as Figure 4 and Figure 5 ), specifically, the solid electrolyte (LATP), the binder polyvinylidene fluoride (PVDF), and the solvent N-methylpyrrolidone (NMP) were mixed and dispersed evenly at a mass ratio of 100:1:300, and then sprayed on the side of the polypropylene base film close to the positive electrode sheet, and dried at 60°C for 15 minutes to obtain a diaphragm. The thickness of the solid electrolyte coating is 4μm.

[0102] Comparative Example 9

[0103] The positive and negative pole pieces, the soft-pack battery preparation process, and the electrolyte used are the same as those of Comparative Example 1, except that the functional film-forming additive is used to modify the side of the separator near the negative electrode. Specifically, the functional film-forming additive triphenyl phosphate and dimethyl carbonate solvent are mixed and dispersed evenly in a mass ratio of 2:98, and then sprayed on the side of the base film near the negative pole piece, and vacuum dried at 30°C to obtain the separator. The thickness of the functional film-forming additive coating is 2μm.

[0104] Example 1

[0105] The positive and negative electrode sheets, the soft-pack battery preparation process, and the electrolyte used are the same as those of Comparative Example 1, except that the separator used is modified by a solid electrolyte coating and a functional film-forming additive coating, respectively, wherein the solid electrolyte coating is prepared in the same manner as Comparative Example 8 and is in contact with the positive electrode side; the functional film-forming additive coating is prepared in the same manner as Comparative Example 9 and is in contact with the negative electrode side. The thickness of the solid electrolyte coating is 4 μm. The thickness of the functional film-forming additive coating is 2 μm.

[0106] Example 2

[0107] The negative electrode sheet, the soft pack battery preparation process, and the electrolyte used are the same as those in Example 1, except that 95.5wt% LMFP, 0.5wt% LATP, 1.0wt% conductive carbon black, 1.0wt% conductive carbon nanotubes (CNT), and 2.0wt% polyvinylidene fluoride (PVDF) are uniformly mixed. After the positive electrode slurry is vacuum stirred evenly, the positive electrode slurry is applied to a clean aluminum foil with a coating machine, and then vacuum dried at 120°C for 12h. The dried electrode sheet is rolled with a roller machine and then cut into pieces to obtain the required battery positive electrode sheet.

[0108] Example 3

[0109] The negative electrode sheet, soft pack battery preparation process, electrolyte, and separator are the same as those in Example 1, except that 95.0wt% LMFP, 1.0wt% LATP, 1.0wt% conductive carbon black, 1.0wt% conductive carbon nanotube (CNT), and 2.0wt% polyvinylidene fluoride (PVDF) are uniformly mixed. After the positive electrode slurry is vacuum stirred evenly, the positive electrode slurry is applied to a clean aluminum foil with a coating machine, and then vacuum dried at 120°C for 12h. The dried electrode sheet is rolled with a roller machine and then cut into pieces to obtain the required battery positive electrode sheet.

[0110] Example 4

[0111] The negative electrode sheet, soft pack battery preparation process, electrolyte, and separator are the same as those in Example 1, except that 93.0wt% LMFP, 3.0wt% LATP, 1.0wt% conductive carbon black, 1.0wt% conductive carbon nanotube (CNT), and 2.0wt% polyvinylidene fluoride (PVDF) are uniformly mixed. After the positive electrode slurry is vacuum stirred evenly, the positive electrode slurry is applied to a clean aluminum foil with a coating machine, and then vacuum dried at 120°C for 12h. The dried electrode sheet is rolled with a roller machine and then cut into pieces to obtain the required battery positive electrode sheet.

[0112] Example 5

[0113] The negative electrode sheet, soft pack battery preparation process, electrolyte, and separator are the same as those in Example 1, except that 91.0wt% LMFP, 5.0wt% LATP, 1.0wt% conductive carbon black, 1.0wt% conductive carbon nanotube (CNT), and 2.0wt% polyvinylidene fluoride (PVDF) are uniformly mixed. After the positive electrode slurry is vacuum stirred evenly, the positive electrode slurry is applied to a clean aluminum foil with a coating machine, and then vacuum dried at 120°C for 12h. The dried electrode sheet is rolled with a roller machine and then cut into pieces to obtain the required battery positive electrode sheet.

[0114] Comparative Example 10

[0115] The negative electrode sheet, soft pack battery preparation process, electrolyte and separator used are the same as those of comparative example 3, except that 95.0wt% LiMn2O4, 1.0wt% lithium lanthanum zirconium oxide (LLZO, LiLaZrO4), 1.0wt% conductive carbon black, 1.0wt% conductive carbon nanotube (CNT) and 2.0wt% polyvinylidene fluoride (PVDF) are uniformly mixed. After the positive electrode slurry is vacuum stirred evenly, the positive electrode slurry is applied to a clean aluminum foil with a coating machine, and then vacuum dried at 120°C for 12h. The dried electrode sheet is rolled with a roller machine and cut into sheets to obtain the required battery positive electrode sheet.

[0116] Comparative Example 11

[0117] The positive and negative pole pieces, the soft-pack battery preparation process, and the electrolyte used are the same as those of Comparative Example 3, except that the separator used is modified with a solid electrolyte near the positive electrode side. Specifically, the solid electrolyte (LLZO), the binder polyvinylidene fluoride (PVDF), and the solvent N-methylpyrrolidone (NMP) are mixed and dispersed uniformly at a mass ratio of 100:1:300, and then sprayed on the side of the polypropylene base film near the positive pole piece, and dried at 60°C for 15 minutes to obtain the separator. The thickness of the solid electrolyte coating is 4μm.

[0118] Comparative Example 12

[0119] The positive and negative pole pieces, the soft-pack battery preparation process, and the electrolyte used are the same as those of Comparative Example 3, except that the functional film-forming additive is used to modify the side of the separator near the negative electrode. Specifically, the functional film-forming additive lithium bis(fluorosulfonyl)imide and dimethyl carbonate solvent are mixed and dispersed evenly in a mass ratio of 2:98, and then sprayed on the side of the base film near the negative pole piece, and vacuum dried at 30°C to obtain the separator. The thickness of the functional film-forming additive coating is 2 μm.

[0120] Example 6

[0121] The positive and negative electrode sheets, the soft-pack battery preparation process, and the electrolyte used are the same as those of Comparative Example 3, except that the separator used is modified by a solid electrolyte coating and a functional film-forming additive coating, respectively, wherein the solid electrolyte coating is prepared in the same manner as Comparative Example 11 and is in contact with the positive electrode side; the functional film-forming additive coating is prepared in the same manner as Comparative Example 12 and is in contact with the negative electrode side. The thickness of the solid electrolyte coating is 4 μm. The thickness of the functional film-forming additive coating is 2 μm.

[0122] Example 7

[0123] The negative electrode sheet, soft pack battery preparation process, and the electrolyte used are the same as those of Comparative Example 3, except that 95.0wt% LiMn2O4, 1.0wt% LLZO, 1.0wt% conductive carbon black, 1.0wt% conductive carbon nanotubes (CNT), and 2.0wt% polyvinylidene fluoride (PVDF) are uniformly mixed. After the positive electrode slurry is vacuum stirred evenly, the positive electrode slurry is coated on a clean aluminum foil with a coating machine, and then vacuum dried at 120°C for 12h. The dried electrode sheet is rolled with a roller machine and then cut into pieces to obtain the required battery positive electrode sheet;

[0124] The difference is that the separator used is modified by a solid electrolyte coating and a functional film-forming additive coating, respectively, wherein the solid electrolyte coating is prepared in the same manner as in Comparative Example 11 and is in contact with the positive electrode side; the functional film-forming additive coating is prepared in the same manner as in Comparative Example 12 and is in contact with the negative electrode side. The thickness of the solid electrolyte coating is 4 μm. The thickness of the functional film-forming additive coating is 2 μm.

[0125] Comparative Example 13

[0126] The negative electrode sheet, the soft pack battery preparation process, the electrolyte and the separator used are the same as those in Comparative Example 5, except that 95.0wt% LMR, 1.0wt% lithium lanthanum zirconium tantalum oxide (LLZTO, Li 6.5 Ln3Z 1.5 Ta 0.5 O 12 ), 1.0wt% conductive carbon black, 1.0wt% conductive carbon nanotubes (CNT) and 2.0wt% polyvinylidene fluoride (PVDF) are uniformly mixed. After the positive electrode slurry is vacuum stirred evenly, the positive electrode slurry is coated on a clean aluminum foil with a coating machine, and then vacuum dried at 120°C for 12h. The dried electrode sheet is rolled with a roller machine and then cut into sheets to obtain the required battery positive electrode sheet.

[0127] Comparative Example 14

[0128] The positive and negative pole pieces, the soft-pack battery preparation process, and the electrolyte used are the same as those of Comparative Example 5, except that the separator used is modified with a solid electrolyte near the positive electrode side. Specifically, the solid electrolyte (LLZTO), the binder polyvinylidene fluoride (PVDF), and the solvent N-methylpyrrolidone (NMP) are mixed and dispersed uniformly at a mass ratio of 100:1:300, and then sprayed on the side of the polypropylene base film near the positive pole piece, and dried at 60°C for 15 minutes to obtain the separator. The thickness of the solid electrolyte coating is 4μm.

[0129] Comparative Example 15

[0130] The positive and negative pole pieces, the soft-pack battery preparation process, and the electrolyte used are the same as those of Comparative Example 5, except that the functional film-forming additive is used to modify the side of the separator near the negative electrode. Specifically, the functional film-forming additive 2-methylmaleic anhydride and dimethyl carbonate solvent are mixed and dispersed evenly in a mass ratio of 2:98, and then sprayed on the side of the base film near the negative pole piece, and vacuum dried at 30°C to obtain the separator. The thickness of the functional film-forming additive coating is 2μm.

[0131] Comparative Example 16

[0132] The positive and negative electrode sheets, the soft-pack battery preparation process, and the electrolyte used are the same as those of Comparative Example 5, except that both sides of the separator used are modified with solid electrolytes, wherein the solid electrolyte coating is prepared in the same manner as in Comparative Example 14, and is in contact with the positive and negative electrode sides, respectively. The thickness of the solid electrolyte coating near the positive and negative electrodes is 4 μm and 2 μm, respectively.

[0133] Example 8

[0134] The positive and negative electrode sheets, the soft-pack battery preparation process, and the electrolyte used are the same as those of Comparative Example 5, except that the separator used is modified by a solid electrolyte coating and a functional film-forming additive coating, respectively, wherein the solid electrolyte coating is prepared in the same manner as Comparative Example 14 and contacts the positive electrode side; the functional film-forming additive coating is prepared in the same manner as Comparative Example 15 and contacts the negative electrode side. The thickness of the solid electrolyte coating is 4 μm. The thickness of the functional film-forming additive coating is 2 μm.

[0135] Example 9

[0136] The negative electrode sheet, soft pack battery preparation process, and the electrolyte used are the same as those of Comparative Example 5, except that 95.0wt% LMR, 1.0wt% LLZTO, 1.0wt% conductive carbon black, 1.0wt% conductive carbon nanotubes (CNT), and 2.0wt% polyvinylidene fluoride (PVDF) are uniformly mixed. After the positive electrode slurry is vacuum stirred evenly, the positive electrode slurry is coated on a clean aluminum foil with a coating machine, and then vacuum dried at 120°C for 12h. The dried electrode sheet is rolled with a roller machine and then cut into pieces to obtain the required battery positive electrode sheet;

[0137] The difference is that the separator used is modified by a solid electrolyte coating and a functional film-forming additive coating, respectively, wherein the solid electrolyte coating is prepared in the same manner as in Comparative Example 14 and is in contact with the positive electrode side; the functional film-forming additive coating is prepared in the same manner as in Comparative Example 15 and is in contact with the negative electrode side. The thickness of the solid electrolyte coating is 4 μm. The thickness of the functional film-forming additive coating is 2 μm.

[0138] Example 10

[0139] A soft pack battery was prepared according to the method of Example 8, except that the thickness of the solid electrolyte coating was 2 μm and the thickness of the functional film-forming additive coating was 2 μm, and the thickness ratio of the two was 1:1.

[0140] Embodiment 11

[0141] A soft-pack battery was prepared according to the method of Example 8, except that the thickness of the solid electrolyte coating was 4.5 μm and the thickness of the functional film-forming additive coating was 1.5 μm, and the thickness ratio of the two was 3:1.

[0142] Example 12

[0143] A soft-pack battery was prepared according to the method of Example 8, except that the thickness of the solid electrolyte coating was 0.3 μm.

[0144] Embodiment 13

[0145] A soft-pack battery was prepared according to the method of Example 8, except that the thickness of the solid electrolyte coating was 7 μm.

[0146] Embodiment 14

[0147] A soft-pack battery was prepared according to the method of Example 8, except that the thickness of the functional film-forming additive coating was 0.05 μm.

[0148] Embodiment 15

[0149] A soft-pack battery was prepared according to the method of Example 8, except that the thickness of the functional film-forming additive coating was 4 μm.

[0150] The above-mentioned embodiments and comparative examples were subjected to high temperature cycle performance test and high temperature storage performance test respectively.

[0151] High-temperature storage test steps: first, cycle the battery at a rate of 1C for 5 weeks at room temperature, then place the fully charged battery in a 60°C constant temperature explosion-proof oven for 14 days, calculate the expansion rate of the battery before and after high-temperature storage (expansion rate = (battery thickness after high-temperature storage - thickness before high-temperature storage) / thickness before high-temperature storage × 100%), and after high-temperature storage, cycle the battery at room temperature for 5 weeks for a capacity recovery test, and calculate the battery's capacity retention rate and recovery rate (capacity retention rate = discharge capacity at room temperature in the first week / discharge capacity of the battery before storage, capacity recovery rate = discharge capacity at room temperature in the fifth week / discharge capacity of the battery before storage).

[0152] The specific steps of the 45°C cycle test are as follows: at 45°C, with a charge and discharge current of 1C, the LMFP / graphite, LiMn2O4 / graphite, and LMR / graphite soft-pack batteries are cycled for 100 cycles at 2.2-4.35V, 2.75-4.35V, and 2.2-4.55V voltage ranges, respectively, and the capacity retention rate after the battery cycle is calculated (capacity retention rate = discharge capacity at the 100th week / discharge capacity of the battery at the 1st week). The test results are shown in Table 1 below. The cycle performance comparison of Comparative Example 5 and Example 9 is shown in the figure below. Figure 6 shown.

[0153] Table 1 Performance test results of batteries prepared in comparative examples and examples

[0154]

[0155]

[0156] It can be seen from the data in Table 1 that compared with comparative examples 1-6 in which a functional film-forming additive is added to the electrolyte, the present invention respectively arranges a solid electrolyte coating and a functional film-forming additive coating on both sides of the base membrane. Under the synergistic effect of the two coatings, the stability of the negative electrode SEI film (solid electrolyte interface film) is improved, the direct contact between the electrolyte and the negative electrode interface is blocked, the stability of the electrolyte is improved, and the irreversible consumption of active lithium inside the battery is reduced, so that the manganese-based lithium-ion battery maintains good high-temperature performance at high temperatures, and significantly improves the high-temperature storage performance and high-temperature cycle performance.

[0157] From the data of Comparative Examples 1 and 2, Comparative Examples 3 and 4, and Comparative Examples 5 and 6 after high-temperature storage in the table, it can be seen that adding a certain amount of high-temperature electrolyte additives to the electrolyte is beneficial to the improvement of the high-temperature performance of the battery. As can be seen from Comparative Examples 7 and 1, the mixing of a certain solid electrolyte with the lithium iron manganese phosphate positive electrode slurry is beneficial to the high-temperature performance of the battery; Comparative Examples 8 and 9 use composite diaphragms, and compared with Comparative Example 1, the high-temperature performance of the battery is improved to a certain extent through the modification of different interface coatings; as can be seen from Example 2, Comparative Example 1, and Comparative Examples 7-9, the lithium iron manganese phosphate battery with 1.0% LATP mixed in the positive electrode slurry and using a composite diaphragm with different coatings on both sides has better high-temperature characteristics. Example 7 and Example 9 are compared with Comparative Examples 10-12 and Comparative Examples 13-15, respectively. It can be seen that the mixing of the slurry with solid electrolytes and the modification of the diaphragm are beneficial to the improvement of the high-temperature storage performance of lithium manganese oxide and lithium-rich manganese-based batteries, respectively. At the same time, from Figure 6 The cycle curves of the LMR / graphite batteries of Comparative Example 5 and Example 9 at 45°C further confirmed that the method of the present invention is beneficial to improving the high temperature performance of lithium-ion batteries with manganese-based positive electrode materials.

[0158] The terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of this application, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0159] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, unless they are contradictory.

[0160] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A diaphragm, characterized in that: include: Basement membrane; A solid electrolyte coating, wherein the solid electrolyte coating is disposed on a side of the base film close to the positive electrode plate; A functional film-forming additive coating is provided on a side of the base film close to the negative electrode plate.

2. The diaphragm according to claim 1, characterized in that The thickness of the solid electrolyte coating is 0.5-6.0 μm.

3. The diaphragm according to claim 2, characterized in that The thickness of the solid electrolyte coating is 2.0-5.0 μm.

4. The diaphragm according to any one of claims 1 to 3, characterized in that: The thickness of the functional film-forming additive coating is 0.1-3.0 μm.

5. The diaphragm according to claim 4, characterized in that The thickness of the functional film-forming additive coating is 0.5 to 2.5 μm.

6. The diaphragm according to any one of claims 1 to 3, characterized in that: The thickness ratio of the solid electrolyte coating to the functional film-forming additive coating is (1.5-2.5):

1.

7. The diaphragm according to any one of claims 1 to 3, characterized in that: The functional film-forming additive coating includes a functional film-forming additive, and the functional film-forming additive includes one or more of anhydrides, phosphates, sulfates, and lithium salts.

8. The diaphragm according to claim 7, characterized in that The functional film-forming additives include one or more of 2-methylmaleic anhydride, maleic anhydride, methylsuccinic anhydride, glutaric anhydride, succinic anhydride, adipic anhydride, triphenyl phosphate, triethyl diphosphate, pentafluorophenyl diphenyl phosphate, 1,3-propane sultone, 1,4-butane sultone, 1,3-propylene sultone, methanedisulfonic acid methylene ester, lithium difluorophosphate, lithium bis(fluorosulfonyl)imide, lithium dioxalatoborate, and lithium difluorooxalatoborate.

9. The diaphragm according to any one of claims 1 to 3, characterized in that: The solid electrolyte coating includes a solid electrolyte, and the solid electrolyte includes one or more of lithium lanthanum zirconium oxide, lithium lanthanum zirconium tantalum oxide, lithium lanthanum zirconium niobium oxide, lithium lanthanum titanium oxide, and lithium aluminum titanium phosphate.

10. A method for preparing the diaphragm according to any one of claims 1 to 9, characterized in that: The following steps are involved: After mixing the solid electrolyte, the binder and the solvent, the mixture is applied on the side of the base film close to the positive electrode plate; After mixing the functional film-forming additive and the solvent, the mixture is applied on the side of the base film close to the negative electrode plate; After drying, the separator is obtained.

11. A battery, characterized in that: A diaphragm comprising any one of claims 1 to 9 or a diaphragm obtained by the method of claim 10.

12. The battery according to claim 11, characterized in that It also includes a positive electrode sheet and a negative electrode sheet, wherein the solid electrolyte coating of the diaphragm is close to the positive electrode sheet, and the functional film-forming additive coating of the diaphragm is close to the negative electrode sheet.

13. The battery according to claim 12, characterized in that The positive electrode sheet includes a positive electrode current collector and a positive electrode coating disposed on at least one surface of the positive electrode current collector, wherein the positive electrode coating includes a positive electrode active material, a solid electrolyte, a conductive agent, and a binder.

14. The battery according to claim 13, characterized in that The solid electrolyte includes one or more of lithium lanthanum zirconium oxide, lithium lanthanum zirconium tantalum oxide, lithium lanthanum zirconium niobium oxide, lithium lanthanum titanium oxide, and lithium aluminum titanium phosphate.

15. The battery according to claim 13, characterized in that The solid electrolyte is added in an amount of 0.1 wt % to 5 wt % in the positive electrode coating.

16. The battery according to claim 13, characterized in that The positive electrode active material includes a manganese-based positive electrode material; the manganese-based positive electrode material includes one or more of lithium iron manganese phosphate, lithium-rich manganese-based material, and lithium manganate.

17. An electrical device, characterized in that: A battery comprising the battery according to any one of claims 11 to 16.

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