Composite diaphragm, preparation method thereof and battery

Abstract

The present invention provides a composite diaphragm, comprising a base membrane and a composite coating located on at least one side of the base membrane, the composite coating comprising a lithium-intercalating oxide, a vapor-phase ceramic, and carboxylated lithium cellulose, wherein the particle size of the carboxylated lithium cellulose is larger than the particle size of the vapor-phase ceramic. The present invention further provides a battery, comprising the composite diaphragm described above. The present invention further provides a method for preparing the composite diaphragm, comprising: sequentially adding a solvent, a vapor-phase ceramic, a lithium-intercalating oxide, and carboxylated lithium cellulose, mixing to form a dispersion; adding an adhesive to the dispersion to form a coating slurry; and coating the coating slurry on at least one side of a base membrane, followed by drying to obtain a composite diaphragm comprising the composite coating.

Description

Technical Field

[0001] The present invention relates to the field of battery separators, and in particular to a high-heat-resistant and lithium-dendrite-resistant composite separator, a preparation method thereof, and a battery. Background Art

[0002] Lithium-ion batteries, with their high energy density, high power density, long cycle life, and lack of memory effect, have become the preferred power source for electric vehicles, wind and solar power generation, energy storage, and consumer electronics. Lithium-ion batteries primarily consist of positive and negative electrodes, an electrolyte, and a separator. The separator acts as a safety barrier, separating the positive and negative electrodes, insulating electrons, and transmitting lithium ions.

[0003] During the charge and discharge cycle, lithium reacts with the liquid electrolyte to continuously form a SEI (Solid Electrolyte Interphase) film, which consumes lithium ions and reduces the charge and discharge efficiency of the electrode material. As lithium dendrites grow, they consume electrolyte and lead to irreversible deposition of metallic lithium, reducing Coulombic efficiency and destroying the resulting solid electrolyte interphase (SEI) film. The rapid development of high-energy-density batteries means that batteries can store more energy for the same weight or volume. However, this increase in energy density exacerbates the formation of lithium dendrites. Continued growth can penetrate the separator, causing a battery short circuit and posing a significant safety hazard.

[0004] As an indispensable component of batteries, the properties of separators also affect the formation of lithium dendrites. Currently, most traditional separators have the following problems: (1) poor wettability with electrolyte, resulting in "dry areas" in the battery, which in turn causes excessive impedance or lithium deposition; (2) poor mechanical properties (mechanical strength, Young's modulus) that are insufficient to inhibit lithium dendrite growth; (3) poor thermal stability, etc. These unfavorable factors limit the application of separators in lithium metal batteries.

[0005] Based on this, there is an urgent need to develop a stable, high-performance composite diaphragm, its preparation technology and battery, which can fundamentally solve the problem of lithium dendrite growth, that is, inhibit the growth of lithium dendrites inside the battery to improve the battery stability, electrochemical performance and cycle life. Summary of the Invention

[0006] Based on the above-mentioned deficiencies in the prior art, the main purpose of the present invention is to provide a composite diaphragm and a preparation method thereof, and a battery, so as to improve the thermomechanical properties, mechanical strength and cycle performance of the composite diaphragm.

[0007] In a first aspect, some embodiments of the present invention provide a composite diaphragm comprising a base membrane and a composite coating located on at least one side of the base membrane, wherein the composite coating comprises lithium-embedded oxide, vapor-phase ceramics, and carboxylated cellulose lithium, wherein the particle size of the carboxylated cellulose lithium is larger than the particle size of the vapor-phase ceramics.

[0008] In some embodiments of the present invention, the material of the base film includes at least one of polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), and polyimide.

[0009] In some embodiments of the present invention, the composite coating is composed of 1 wt% to 30 wt% of lithium-intercalated oxide, 55 wt% to 70 wt% of fumed ceramic, and 1 wt% to 10 wt% of carboxylated lithium cellulose.

[0010] In some embodiments of the present invention, the composite coating includes lithium intercalation oxide, fumed ceramic, carboxylated lithium cellulose, and a binder.

[0011] In some embodiments of the present invention, the composite coating is composed of 1 wt% to 30 wt% of lithium-intercalated oxide, 55 wt% to 70 wt% of fumed ceramic, 1 wt% to 10 wt% of carboxylated lithium cellulose, and 1 wt% to 5 wt% of a binder.

[0012] In some embodiments of the present invention, the lithium-intercalated oxide includes at least one of SnO2, Fe2O3, Co3O4, NiO, CuO, Sb2O3, and CaO.

[0013] In some embodiments of the present invention, the fumed ceramic includes at least one of inorganic fumed alumina, fumed silica, fumed zirconia, and fumed titania.

[0014] In some embodiments of the present invention, the carboxylated lithium cellulose includes at least one of carboxylated lithium modified nanocellulose, carboxylated lithium modified cellulose nanowhiskers, carboxylated lithium modified cellulose nanofibrils, and carboxylated lithium modified microfibrillated cellulose.

[0015] In some embodiments of the present invention, the thermal decomposition temperature of carboxylated cellulose lithium is greater than 280°C.

[0016] In some embodiments of the present invention, the adhesive includes at least one of polyacrylamide, polybutyl methacrylate, polyhydroxyethyl methacrylate, styrene / acrylates, polyvinylidene fluoride, and polyvinyl alcohol.

[0017] In some embodiments of the present invention, the particle size of the lithium-intercalated oxide is D 50 ≤0.5μm; the particle size of the gas phase ceramic is D 50 ≤0.1μm; and / or the particle size of carboxylated cellulose lithium is D 50 ≤0.5μm.

[0018] In a second aspect, an embodiment of the present invention provides a battery, comprising the composite diaphragm provided by any embodiment of the first aspect.

[0019] In a third aspect, an embodiment of the present invention provides a method for preparing a composite diaphragm, comprising: sequentially adding a solvent, a dispersant, a vapor-phase ceramic, an embedded lithium oxide, and carboxylated cellulose lithium to mix to form a dispersion; adding an adhesive to the dispersion to form a coating slurry; and coating the coating slurry on at least one side of a base film, and obtaining a composite diaphragm including a composite coating after drying.

[0020] In some embodiments of the present invention, the particle size of the dispersion is D 50 <1μm, the maximum particle size of the dispersion is D max <3 μm, the particle size of the dispersion is based on the particle size of the material therein.

[0021] In some embodiments of the present invention, the particle size of the lithium-intercalated oxide is D 50 ≤0.5μm; the particle size of the gas phase ceramic is D 50 ≤0.1μm; and / or the particle size of carboxylated cellulose lithium is D 50 ≤0.5μm.

[0022] In some embodiments of the present invention, the amount of solvent added accounts for 50 wt% to 95 wt% of the coating slurry, and the solvent includes at least one of water, ethanol, acetone, NMP, and isopropyl alcohol.

[0023] In some embodiments of the present invention, the amount of the dispersant added is 0.0001 wt% to 1 wt% of the coating slurry, and the dispersant includes at least one of polyacrylic acid, polyoxyethylene ether, and sodium alkylbenzene sulfonate.

[0024] In some embodiments of the present invention, the amount of lithium intercalation oxide added is 10 wt% to 35 wt% of the coating slurry, and the lithium intercalation oxide includes at least one of SnO2, Fe2O3, Co3O4, NiO, CuO, Sb2O3, and CaO.

[0025] In some embodiments of the present invention, the amount of the fumed ceramic added accounts for 50 wt% to 75 wt% of the coating slurry, and the fumed ceramic includes at least one of inorganic fumed alumina, fumed silica, fumed zirconia, and fumed titania.

[0026] In some embodiments of the present invention, the added amount of carboxylated lithium cellulose accounts for 5 wt%~15wt% of the coating slurry, and the carboxylated lithium cellulose includes at least one of nanocellulose carboxylated lithium modified, cellulose nanowhisker carboxylated lithium modified, cellulose nanofibril carboxylated lithium modified, and microfibrillated cellulose carboxylated lithium modified.

[0027] In some embodiments of the present invention, in the step of coating the slurry on at least one side of the resin base film, the coating method includes at least one of roller coating, spin coating, dip coating, cast coating, and spray coating.

[0028] In some embodiments of the present invention, in the step of coating the slurry on at least one side of the resin base film, the coating thickness of the composite coating is in the range of 0.3 μm to 3 μm.

[0029] In some embodiments of the present invention, the base film includes a low closed-pore and high-breakage base film, and the thickness of the base film ranges from 3 μm to 20 μm.

[0030] The composite diaphragm provided by the present invention is coated on at least one side of a substrate by adding lithium-intercalated oxide, vapor-phase ceramics and carboxylated lithium cellulose to a composite coating. The co-addition of the aforementioned lithium-intercalated oxide, vapor-phase ceramics and carboxylated lithium cellulose produces a synergistic effect on the performance of the composite diaphragm, effectively improving the thermomechanical stability, heat resistance and mechanical strength of the composite diaphragm, inhibiting the formation of lithium dendrites, reducing the direct penetration of lithium dendrites through the diaphragm, and improving the electrochemical performance, capacity retention and cycle life of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0032] Figure 1 A schematic structural diagram of a composite partition provided in an embodiment of the present invention;

[0033] Figure 2 A process flow chart of a method for preparing a composite diaphragm provided in an embodiment of the present invention;

[0034] Figure 3 This is a scanning electron microscope image of the composite diaphragm provided in Example 1 of the present invention;

[0035] Figure 4 A schematic diagram of the dimensions of the test needle used in the nail penetration coefficient test method.

[0036] Icons: 100-composite diaphragm; 110-base film; 120-lithium-intercalated oxide; 130-vapor-phase ceramic; 140-carboxylated lithium cellulose; 150-adhesive; S210-step; S220-step; S230-step. DETAILED DESCRIPTION

[0037] To make the above and / or other purposes, effects, and features of the present invention more clearly understood, preferred embodiments are described in detail below:

[0038] like Figure 1 As shown, the main purpose of the present invention is to provide a composite separator 100, including a base film 110 and a composite coating located on at least one side of the base film 110, wherein the composite coating includes a lithium-intercalated oxide 120, a vapor-phase ceramic 130, and carboxylated lithium cellulose 140. In some embodiments, the composite coating further includes an adhesive 150.

[0039] In some embodiments, the base film 110 is made of at least one of polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), and polyimide. Alternatively, the base film is made of polyethylene or a composite of polyethylene and polypropylene.

[0040] As an example, the proportion of the lithium intercalation oxide 120 added to the composite coating is 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, or 40 wt%. Alternatively, the proportion of the lithium intercalation oxide 120 added to the composite coating is 1 wt% to 30 wt%.

[0041] As an example, the proportion of the fumed ceramic 130 added to the composite coating is 30 wt%, 35 wt%, 40 wt%, 45 wt%, 50 wt%, 55 wt%, 60 wt%, 65 wt%, 70 wt%, 75 wt%, or 80 wt%. Alternatively, the proportion of the fumed ceramic 130 added to the composite coating is 55 wt% to 70 wt%.

[0042] As an example, the proportion of carboxylated lithium cellulose 140 added to the composite coating is 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, or 30 wt%. Alternatively, the proportion of carboxylated lithium cellulose 140 added to the composite coating is 1 wt% to 10 wt%.

[0043] As an example, the adhesive 150 is added to the composite coating in an amount of 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 15 wt%, or 20 wt%. Alternatively, the adhesive 150 is added to the composite coating in an amount of 1 wt% to 5 wt%.

[0044] In some embodiments, the lithium-intercalation oxide 120 has poor heat resistance and is primarily responsible for capturing excess lithium ions, preventing the formation of lithium dendrites and inhibiting the further formation of existing dendrites. The vapor-phase ceramic 130 serves as the structural backbone of the composite coating, which is based on the requirements for heat resistance and liquid retention. Carboxylated lithium cellulose 140 provides skeletal support for the lithium-intercalation oxide 120 and vapor-phase ceramic 130, resulting in the composite coating having superior mechanical properties.

[0045] In some embodiments, the lithium intercalation oxide 120 includes at least one of SnO2, Fe2O3, Co3O4, NiO, CuO, Sb2O3, and CaO. In some embodiments, the lithium intercalation mechanism of the lithium intercalation oxide 120 is to undergo a decomposition-reduction reaction with active lithium ions to reduce the formation of lithium dendrites. The lithium intercalation oxide 120 reacts with active lithium ions to form a metal alloy LixZ (Z = Sn, Si, Ge, Fe, Co, Ni, Cu, Sb, etc.) and its corresponding oxide Li2O, which is beneficial to reducing the formation of lithium dendrites and inhibiting the formation of SEI film during battery cycling. The metal alloy LixZ has volume expansion and forms a uniform and dense interphase layer at the negative electrode. This interphase layer has good resistance to penetration by lithium dendrites, avoids short circuits within the battery, reduces battery heat generation, and improves the overall electrochemical performance and battery cycle life of the battery.

[0046] In some embodiments, the lithium intercalation oxide 120 is tin dioxide (SnO2), for example. It has a theoretical specific capacity of 782 mAh g⁻¹, a lithium storage potential of 0.6 V, and is readily available and non-toxic. Its lithium intercalation mechanism involves SnO2 first undergoing a conversion reaction with lithium ions, followed by a subsequent reaction between Sn and lithium ions to form a metal alloy. The reaction equation is shown below.

[0047]

[0048]

[0049] In some embodiments, the carboxylated lithium cellulose 140 includes at least one of nanocellulose carboxylated lithium modified, cellulose nanowhiskers carboxylated lithium modified, cellulose nanofibrils carboxylated lithium modified, and microfibrillated cellulose carboxylated lithium modified. Exemplarily, the thermal decomposition temperature of the carboxylated lithium cellulose 140 is 281° C., 282° C., 283° C., 284° C., 285° C., 286° C., 287° C., 288° C., 289° C., 290° C., 291° C., 295° C., 300° C., or 400° C. Alternatively, the thermal decomposition temperature of the carboxylated lithium cellulose 140 is >280° C.

[0050] In some embodiments, carboxylated lithium cellulose 140 is a carboxylated modification of conventional cellulose, in which the hydroxyl groups are replaced by lithium carboxylate to improve the processability of the cellulose and reduce its water absorption, thereby reducing the adverse factors caused by the moisture content in the battery cell. In addition, carboxylated lithium cellulose 140 provides lithium replenishment during the battery cycle and reduces the formation of lithium dendrites.

[0051] In some embodiments, carboxylated cellulose lithium 140 maintains a stable lithium concentration by providing the lithium salt it carries, reduces the concentration gradient of lithium ions, and reduces the formation of lithium dendrites. In some embodiments, carboxylated cellulose lithium 140 guides the uniform deposition of lithium ions through its grid-like skeleton structure, reducing the formation of spike-like lithium dendrites. In addition, in some embodiments, the fiber structure of carboxylated cellulose lithium 140 is conducive to the coating having a network skeleton structure, so that the gas-phase ceramic 130 particles and the lithium-intercalated oxide 120 particles are embedded in the modified fiber pores, thereby improving the porosity and structural strength of the diaphragm. When the diaphragm is under stress, the force exerted on a single point on the mesh structure in the diaphragm can be evenly diffused from the point to the surface. If lithium dendrites are generated, the mesh structure in the diaphragm can guide them to be evenly deposited, reducing the formation of spike-like lithium dendrites, effectively preventing the diaphragm from being pierced by lithium dendrites, and improving the cycle life of the battery. Furthermore, carboxylated cellulose lithium 140 has the advantages of high heat resistance and low density, which is conducive to the composite coating to achieve high heat resistance and light and thin structure, and reserves more space for battery materials.

[0052] In some embodiments, the fumed ceramic 130 includes at least one of inorganic fumed alumina, fumed silica, fumed zirconium oxide, and fumed titanium dioxide. As an example, in the preparation process of the fumed ceramic 130 by fumed synthesis, the original single particles of the ceramic are fused into an aggregate structure, the aggregate has a porous structure, and the particle size D of the aggregate is 50 is 80 nm, 85 nm, 90 nm, 95 nm, 96 nm, 97 nm, 98 nm or 99 nm. Optionally, the particle size of the aggregate is D 50 <100nm.

[0053] In some embodiments, the vapor-phase ceramic 130 has a high heat-resistant property. During the vapor-phase synthesis process, the original single particles of the ceramic are fused into an aggregate structure, and the porous structure of the aggregate has good liquid retention performance. Supported by the carboxylated lithium cellulose 140, the vapor-phase ceramic 130 is evenly dispersed in the fiber pore structure to resist the shrinkage of the composite diaphragm 100 due to temperature changes, thereby enhancing the mechanical strength of the diaphragm. The vapor-phase ceramic 130 has a large specific surface area and a particle size much smaller than that of conventional ceramics, which is the key to a thin and light coating. The vapor-phase ceramic 130 has good heat resistance. At the same thickness, ceramic particles are stacked in multiple layers to provide a stronger heat-resistant layer. There are pores between the original particles of the vapor-phase ceramic 130 in the heat-resistant layer, which improves the efficiency of the liquid retention rate. In addition, in some embodiments, in order to improve the effect of the high water absorption of the vapor-phase ceramic, the vapor-phase ceramic 130 is combined with the hydrophobic lithium-intercalated oxide 120 to improve the aforementioned effect.

[0054] In some embodiments, the adhesive 150 includes at least one of polyacrylamide, polybutyl methacrylate, polyhydroxyethyl methacrylate, styrene / acrylates, polyvinylidene fluoride, and polyvinyl alcohol. In some embodiments, the adhesive promotes adhesion between materials and between a material and the base film 110.

[0055] As an example, the particle size D of the lithium intercalation oxide 120 is 50 is 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm or 0.5 μm. Optionally, the particle size of the lithium-intercalated oxide 120 is D 50 ≤0.5μm.

[0056] As an example, the particle size D of the vapor-phase ceramic 130 is 50 is 0.001 μm, 0.01 μm, 0.05 μm, 0.06 μm, 0.07 μm, 0.08 μm, 0.09 μm or 0.1 μm. Optionally, the particle size of the vapor phase ceramic 130 is D 50 ≤0.1μm.

[0057] As an example, the particle size D of the carboxylated lithium cellulose 140 is 50 is 0.01 μm, 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm or 0.5 μm. Optionally, the particle size of the carboxylated lithium cellulose 140 is D 50 ≤0.5μm.

[0058] In some embodiments, the particle size of the intercalated lithium oxide 120 is larger than the particle size of the vapor-phase ceramic 130 particles. The purpose is that the intercalated lithium oxide 120 can preferentially capture excess and active lithium ions, undergo decomposition and reduction reactions with them, reduce the formation of lithium dendrites, and inhibit the SEI film. If lithium dendrites have already formed, the intercalated lithium oxide 120 reacts with the formed lithium dendrites to form a deposition layer with volume expansion (for example, the deposition layer after volume expansion forms a uniform interphase layer, which is evenly distributed on the negative electrode of the battery and forms a protective layer), and an additional protective wall is added to the diaphragm to preferentially resist lithium dendrite puncture. In addition, the particle size of the carboxylated cellulose lithium 140 is larger than the particle size of the vapor-phase ceramic 130 particles because the carboxylated cellulose lithium 140 needs to provide a large number of embedded attachment points for the vapor-phase ceramic 130, and the carboxylated cellulose lithium 140 forms a high-strength network structure to facilitate the provision of vapor-phase ceramic 130 particles filled in the aforementioned grid to resist thermal shrinkage and puncture, so as to achieve the purpose of the composite diaphragm 100 having high heat resistance and high mechanical strength.

[0059] Another object of the present invention is to provide a battery comprising the composite separator 100 as described above.

[0060] like Figure 2 As shown, another object of the present invention is to provide a method for preparing the composite diaphragm 100 as described above, comprising:

[0061] S210, adding a solvent, a dispersant, a vapor-phase ceramic 130, a lithium-intercalated oxide 120, and carboxylated cellulose lithium 140 in sequence and mixing to form a dispersion;

[0062] S220, adding the adhesive 150 to the dispersion to form a coating slurry; and

[0063] S230 , coating the coating slurry on at least one side of a base film 110 , and obtaining a composite diaphragm 100 including a composite coating after drying.

[0064] In some embodiments, in step S210, the materials are uniformly dispersed by stirring / ball milling to form a dispersion having good stability and a good particle size distribution. In some embodiments, the preparation process is a commonly used stirring, grinding, ultrasonication, etc. in the industry to achieve uniform mixing.

[0065] In some embodiments, in the aforementioned step S220 , other additives may be selectively added to the dispersion to form a coating slurry, such as a wetting agent. Optionally, the wetting agent includes at least one of silicone, alkylphenol polyoxyethylene ether, and succinic acid.

[0066] As an example, the particle size D of the dispersion is 50is 0.1 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm or 0.9 μm. Optionally, the particle size of the dispersion is D 50 <1μm. Maximum particle size D of the dispersion max is 1 μm, 2 μm or 2.5 μm. Optionally, the maximum particle size of the dispersion is D max <3μm, the particle size of the dispersion is based on the particle size of the material therein.

[0067] Illustratively, the amount of solvent added is 50 wt%, 60 wt%, 70 wt%, 80 wt%, 90 wt%, 91 wt%, 92 wt%, 93 wt%, 94 wt%, or 95 wt% of the dispersion. Alternatively, the amount of solvent added is 50 wt% to 95 wt% of the dispersion, and the solvent includes at least one of water, ethanol, acetone, NMP, and isopropyl alcohol.

[0068] Illustratively, the amount of the dispersant added is 0.0001 wt%, 0.0002 wt%, 0.0003 wt%, 0.0004 wt%, 0.0005 wt%, 0.0006 wt%, 0.0007 wt%, 0.0008 wt%, 0.0009 wt%, 0.001 wt%, 0.01 wt%, 0.1 wt%, or 1 wt% of the dispersion. Optionally, the amount of the dispersant added is 0.0001 wt% to 1 wt% of the dispersion, and the dispersant includes at least one of polyacrylic acid, polyoxyethylene ether, and sodium alkylbenzene sulfonate.

[0069] As an example, the amount of the lithium intercalation oxide 120 added is 5 wt%, 10 wt%, 20 wt%, 30 wt%, 31 wt%, 32 wt%, 33 wt%, 34 wt%, 35 wt%, or 40 wt% of the dispersion. Alternatively, the amount of the lithium intercalation oxide 120 added is 10 wt% to 35 wt% of the dispersion.

[0070] As an example, the amount of the vapor-phase ceramic 130 added is 40 wt%, 50 wt%, 60 wt%, 70 wt%, 75 wt%, or 80 wt% of the dispersion. Optionally, the amount of the vapor-phase ceramic 130 added is 50 wt% to 75 wt% of the dispersion.

[0071] For example, the amount of carboxylated cellulose lithium 140 added is 5 wt%, 10 wt%, 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt%, or 20 wt% of the dispersion. Alternatively, the amount of carboxylated cellulose lithium 140 added is 5 wt% to 15 wt% of the dispersion.

[0072] In some embodiments, in step S230 , the coating method includes at least one of roller coating, spin coating, dip coating, cast coating, and spray coating.

[0073] As an example, in step S230, the coating thickness of the composite coating ranges from 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, or 4 μm. Optionally, the coating thickness of the composite coating ranges from 0.3 μm to 3 μm.

[0074] In some embodiments, the base film 110 includes a low closed-pore, high-breakage base film 110. As an example, the thickness of the base film 110 ranges from 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 10 μm, 20 μm, or 30 μm. Optionally, the thickness of the base film 110 ranges from 3 μm to 20 μm. In some embodiments, the diaphragm has a high porosity, a high mechanical strength structure, good mechanical properties and Young's modulus. The large pore structure can enable the diaphragm to have better liquid absorption and retention and ionic conductivity, thereby facilitating the battery to have a higher capacity retention rate.

[0075] In some embodiments, the coating material is prepared into a coating slurry and coated on the base film 110 to obtain a composite separator 100. The composite separator 100 has the advantages of good thermomechanical properties, heat stability, mechanical strength, high porosity, ionic conductivity and good liquid retention. In addition, during battery cycling and lithium ion transmission, the composite separator 100 proposed in the present invention can uniformly deposit lithium ions, reduce electrolyte consumption, replenish lithium and inhibit the growth of lithium dendrites. If lithium dendrites are generated, the lithium-intercalated oxide 120 reacts with them to form a deposition layer with volume expansion, reducing the risk of lithium dendrites piercing the separator, thereby improving the cycle life and energy density of the battery.

[0076] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, all are conventional products that can be purchased commercially.

[0077] The following examples illustrate the above-mentioned embodiments of the present invention:

[0078] Table 1. Coating composition, coating orientation, and particle size of constituent materials of Examples and Comparative Examples

[0079]

[0080] Example 1

[0081] The separator of this embodiment has a base film 110 (comprising PE and PP materials) with a thickness of 7 μm and a coating thickness of 1.5 μm. The separator still meets the requirements for high heat resistance and strength, while also exhibiting excellent liquid absorption and retention. This improves battery safety and cycle performance, while also reserving space for battery materials and increasing the battery's energy density.

[0082] First, water solvent, 60 wt% fumed alumina, 30 wt% tin dioxide, and 5 wt% carboxylated cellulose lithium nanofiber (CNF) are added in sequence and mixed to form a dispersion. Next, 5 wt% of binder 150 (polyacrylamide) is added to the dispersion and mixed to form a coating slurry (also known as a composite coating). The aforementioned volume percentages are relative to the coating slurry. The particle size D of the fumed alumina is 1.5747 W / m2. 50 The particle size of tin dioxide is 0.1 μm. 50 The particle size D of carboxylated cellulose lithium CNF is 0.4 μm. 50 0.5μm.

[0083] Next, the coating slurry is rolled onto at least one side of the base film 110 and then dried to obtain the composite separator 100 .

[0084] The composite separator 100 is used to prepare a battery, wherein the separator coating faces the negative electrode side of the battery.

[0085] In addition, if Figure 3 As shown, it is a scanning electron microscope image of the composite membrane provided in Example 1. It can be seen from the figure that the coating of the composite membrane contains particles and fibers, and the gas-phase ceramic 130 particles and the lithium-intercalated oxide 120 particles are filled in the network structure of the modified fibers.

[0086] Example 2

[0087] The preparation method of this embodiment is substantially the same as that of embodiment 1, except that the lithium-intercalated oxide 120 tin dioxide, fumed alumina, and carboxylated lithium cellulose CNF in the coating account for 25 wt%, 60 wt%, and 10 wt%, respectively.

[0088] Example 3

[0089] The preparation method of this embodiment is substantially the same as that of embodiment 1, except that the lithium-intercalated oxide 120 tin dioxide, fumed alumina, and carboxylated lithium cellulose CNF in the coating account for 35 wt%, 50 wt%, and 15 wt%, respectively.

[0090] Example 4

[0091] The preparation method of this embodiment is substantially the same as that of embodiment 1, except that the lithium-intercalated oxide 120 tin dioxide, fumed alumina, and carboxylated cellulose lithium CNF in the coating account for 15 wt%, 70 wt%, and 10 wt%, respectively.

[0092] Example 5

[0093] The preparation method of this embodiment is substantially the same as that of embodiment 1, except that the lithium-intercalated oxide 120 tin dioxide, fumed alumina, and carboxylated cellulose lithium CNF in the coating account for 10 wt%, 75 wt%, and 10 wt%, respectively.

[0094] Example 6

[0095] The preparation method of this embodiment is substantially the same as that of embodiment 1, except that the lithium-intercalated oxide 120 tin dioxide, fumed silica, and carboxylated cellulose lithium CNC (Lithium Carboxylated Cellulose Nanocrystals) in the coating account for 35 wt%, 50 wt%, and 10 wt%, respectively.

[0096] Example 7

[0097] The preparation method and coating of this embodiment are exactly the same as those of Example 2, except that after the battery is manufactured, the diaphragm coating faces the side where the positive electrode is located.

[0098] Comparative Example 1

[0099] The preparation method of this embodiment is substantially the same as that of embodiment 2, except that the addition ratio of fumed alumina in the coating is 95 wt %, and no lithium storage oxide and no carboxylated cellulose lithium 140 are contained.

[0100] Comparative Example 2

[0101] The preparation method of this embodiment is substantially the same as that of Comparative Example 2, except that the coating contains 35 wt % of tin dioxide and 60 wt % of fumed alumina as lithium-intercalated oxide 120, and does not contain carboxylated lithium cellulose 140.

[0102] Comparative Example 3

[0103] The preparation method of this embodiment is substantially the same as that of Comparative Example 2, except that the cellulose is unmodified (eg, CNC) and does not contain carboxyl lithium groups.

[0104] Comparative Example 4

[0105] This embodiment is prepared in the same manner and with the same coating materials as in embodiment 2, except that the particle size D of tin dioxide is 50 The particle size of fumed alumina is 0.3 μm. 50The particle size D50 of carboxylated cellulose lithium 140 is 0.5 μm.

[0106] Comparative Example 5

[0107] The preparation method and coating materials of this embodiment are the same as those of embodiment 2, except that the particle size of tin dioxide is D 50 0.4μm, fumed alumina D 50 0.3μm, carboxylated cellulose lithium 140 particle size D 50 0.2μm.

[0108] Test method:

[0109] 1. Raw materials and slurry test items

[0110] (1) Particle size: Use Mastersizer 3000 laser particle size analyzer to test. Take a sample and add it to the test equipment so that its brightness reaches the test range. Measure the sample particle size and take the average value of three tests.

[0111] 2. Diaphragm test items

[0112] (2) Thickness: The measuring tool used is a Mahr Millimar thickness gauge. First, the surface of the composite membrane 100 sample is kept flat. Then, the thickness of the composite membrane 100 sample is randomly measured at 5 to 10 points along the longitudinal direction (MD). Then, the obtained measurement results are averaged to measure the thickness of the composite membrane 100 sample.

[0113] (3) Puncture strength: Cut three test samples from the composite diaphragm 100 sample, where the length and width of each test sample are not less than 5 cm*5 cm. Fix the test sample on the sample table and use a puncture needle with a diameter (φ) of 1.65 mm and a needle tip (SR) of 0.5 mm and an electronic puncture strength tester to measure. After the test is completed, take the average value of the three test results to obtain the puncture strength of the composite diaphragm 100 sample.

[0114] (4) Liquid absorption rate and liquid retention rate: Cut three test samples with a length and width of 100 mm*100 mm from the composite diaphragm 100 sample and weigh the initial weight of each test sample (m0). Place the test sample in the electrolyte and soak it for 1 hour, then take it out and wipe the electrolyte on the surface of the test sample with a dust-free cloth. Then weigh the liquid absorption weight of the test sample (m1). Spread the weighed test sample flat and let it stand at room temperature for 1 hour. Then weigh the liquid retention weight of the test sample (m2). Among them: the liquid absorption rate of the test sample = ((m1-m0)) / m0*100%; and the liquid retention rate = ((m2-m0)) / m0*100%. Finally, take the average value of the above three groups of experimental data to measure the liquid absorption rate and liquid retention rate of the composite diaphragm 100 sample.

[0115] (5) Moisture content: Weigh three membrane samples of approximately 0.1 g each and seal them in sample bottles. Place the sealed sample bottles in a heating furnace at 150°C for 300 s. Test the moisture content using a Karl Fischer moisture analyzer. After the test, take the average of the three sample measurements.

[0116] (6) Membrane rupture temperature: Using the rising temperature internal resistance method, a circular membrane sample with a diameter of φ50 mm is cut and sealed in a mold filled with a conductive liquid. The mold containing the sample is placed in an oven and the temperature is increased at a rate of 5°C / min. The change in the internal resistance in the mold with temperature is recorded during the heating process. The closed cell temperature Tc is the starting temperature at which the internal resistance begins to increase significantly; the membrane rupture temperature Tb is the temperature at which the internal resistance begins to decrease significantly.

[0117] (7) Thermal shrinkage: Cut the sample to be tested into a size of 100 mm × 100 mm, mark the MD and TD directions, sandwich two layers of thick glass plates, and bake in an oven at 180°C for 1 hour. After taking it out, use an optical projector to measure the length after shrinkage in the MD / TD directions. The specific shrinkage rate calculation formula is as follows:

[0118] Transverse shrinkage MD: ΔM=(M1-M2) / M1×100%;

[0119] Longitudinal shrinkage TD: ΔT = (T1-T2) / T1 × 100%;

[0120] In the above calculation formula, M1, T1 are the initial lengths (in mm); M2, T2 are the final lengths (in mm). The greater the thermal shrinkage, the worse the heat resistance of the separator.

[0121] (8) Nail penetration coefficient: Use a hot nail penetration tester (model: EL-EQ-048). Cut the sample larger than the test mold (40 mm diameter) and secure it to the test mold with a clamp, keeping the surface as flat as possible and the force applied evenly. Test conditions: needle temperature: 250°C, needle size: 0.2 mm, distance: -0.1 mm, dwell time: 10 s.

[0122] The diameter of the ruptured membrane was measured using a digital microscope and marked as X in mm.

[0123] Test needle size as Figure 4 As shown in the figure, the top diameter of the test needle is 5 mm and the needle diameter is 0.2 mm. The nail penetration coefficient is X / 215, and the calculation formula is as follows:

[0124]

[0125]

[0126]

[0127] (9) Scanning electron microscopy (SEM): A test sample with a length and width of 0.5 cm*0.5 cm was cut from the composite diaphragm 100 sample and attached to the sample stage with conductive adhesive. The test sample was then placed in an ion sputtering instrument for gold spraying. Finally, the gold-sprayed test sample was scanned using a scanning electron microscope to capture the coating morphology on the test sample.

[0128] 3. Battery performance test

[0129] (1) Cycling performance: The separator is configured with the positive electrode and the negative electrode to make a full battery, and the electrochemical performance is tested. The capacity retention rate is recorded after 800 cycles.

[0130] All test results are shown in the following table:

[0131] Table 2. Test results

[0132]

[0133] First, as can be seen from Tables 1 and 2, Examples 1-7 generally outperform the comparative examples in terms of thermal shrinkage, film rupture temperature, needle puncture strength, liquid absorption rate, liquid retention rate, and battery capacity retention in both the MD and TD directions. Notably, after 800 cycles, the battery capacity retention rates of Examples 1, 2, 3, and 6 all remained above 92% or higher, indicating that these batteries exhibit superior electrochemical performance and cycle life.

[0134] Next, the following describes an embodiment (using carboxylated lithium cellulose 140, lithium intercalation oxide 120, and fumed ceramic 130 to be added to the coating), in which a synergistic effect is observed, that is, the composite membrane 100 has significantly better film rupture temperature, needle puncture strength, liquid absorption rate, liquid retention rate, and battery capacity retention characteristics than the comparative example. Specifically, in Comparative Examples 1 to 3, it can be seen that in Comparative Example 1, the composite membrane 100 containing fumed alumina and no lithium intercalation oxide 120 and no carboxylated lithium cellulose 140 has a rupture temperature of 151°C. In Comparative Example 2, the composite membrane 100 containing fumed alumina and tin dioxide and no carboxylated lithium cellulose 140 has a rupture temperature of 146°C. In Comparative Example 3, the composite membrane 100 containing fumed alumina, tin dioxide, and unmodified CNC has a rupture temperature of 182°C. Theoretically, when carboxylated lithium cellulose 140, lithium intercalation oxide 120, and fumed ceramic 130 are simultaneously added to the composite coating, the observed membrane rupture temperature is theoretically between 146°C and 182°C. However, in Examples 2-7, the membrane rupture temperatures were all above 185°C or even higher, indicating that carboxylated lithium cellulose 140 (carboxylated lithium modified cellulose), lithium intercalation oxide 120, and fumed ceramic 130 have a synergistic effect on the membrane rupture temperature of the composite separator 100.

[0135] Next, as can be seen in Comparative Examples 1-3, the needle puncture strength of the composite membrane 100 observed in Comparative Example 1 was 490 (gf), the needle puncture strength of the composite membrane 100 observed in Comparative Example 2 was 484 (gf), and the needle puncture strength of the composite membrane 100 observed in Comparative Example 3 was 551 (gf). Theoretically, if carboxylated lithium cellulose 140, lithium intercalation oxide 120, and fumed ceramic 130 were added to the composite coating simultaneously, the observed needle puncture strength would be between 484 (gf) and 551 (gf). However, in Examples 2, 3, 4, 5, and 7, the needle puncture strength was above 556 (gf) or even higher, indicating that the carboxylated lithium cellulose 140 (carboxylated lithium modified cellulose), lithium intercalation oxide 120, and fumed ceramic 130 produced a synergistic effect on the needle puncture strength of the composite membrane 100.

[0136] Next, as can be seen in Comparative Examples 1-3, the liquid absorption rate of the composite separator 100 was observed to be 92% in Comparative Example 1, 90% in Comparative Example 2, and 92% in Comparative Example 3. Theoretically, if carboxylated lithium cellulose 140, lithium intercalation oxide 120, and fumed ceramic 130 were added simultaneously to the composite coating, the observed liquid absorption rate would be between 90% and 92%. However, in Examples 2, 4, 5, and 7, the liquid absorption rates were all above 93% or even higher, indicating that the carboxylated lithium cellulose 140 (carboxylated lithium modified cellulose), lithium intercalation oxide 120, and fumed ceramic 130 had a synergistic effect on the liquid absorption rate of the composite separator 100.

[0137] Next, as can be seen in Comparative Examples 1-3, the liquid retention rate of the composite separator 100 was observed to be 91% in Comparative Example 1, 88% in Comparative Example 2, and 92% in Comparative Example 3. Theoretically, if carboxylated lithium cellulose 140, lithium intercalation oxide 120, and fumed ceramic 130 were added simultaneously to the composite coating, the observed liquid retention rate would be between 88% and 92%. However, in Examples 4 and 5, the liquid retention rates were both above 96% or even higher, indicating that the carboxylated lithium cellulose 140 (carboxylated lithium modified cellulose), lithium intercalation oxide 120, and fumed ceramic 130 had a synergistic effect on the liquid retention rate of the composite separator 100.

[0138] Next, as can be seen in Comparative Examples 1-3, the battery capacity retention rate of the composite separator 100 was observed to be 85% in Comparative Example 1, 90% in Comparative Example 2, and 88% in Comparative Example 3. Theoretically, if carboxylated lithium cellulose 140, lithium intercalation oxide 120, and fumed ceramic 130 were added to the composite coating simultaneously, the observed battery capacity retention rate would be between 85% and 90%. However, in Examples 1, 2, 3, and 6, the battery capacity retention rates were all above 92% or even higher, indicating that the carboxylated lithium cellulose 140 (carboxylated lithium modified cellulose), lithium intercalation oxide 120, and fumed ceramic 130 had a synergistic effect on the battery capacity retention rate of the composite separator 100.

[0139] In addition, the following examples (using carboxylated lithium cellulose 140, lithium intercalation oxide 120, and fumed ceramic 130 co-added to the coating, and with specific particle sizes) show that the composite separator 100 exhibits significantly better thermal shrinkage characteristics, membrane rupture temperature, needle puncture strength, liquid absorption rate, liquid retention rate, and battery capacity retention characteristics than the comparative examples. Specifically, in Comparative Examples 4 and 5, even though the preparation methods and coating materials of Comparative Examples 4 and 5 are substantially the same as those of Example 2, the difference is that the particle size of the lithium intercalation oxide 120 is not larger than that of the fumed ceramic 130 and / or the particle size of the carboxylated lithium cellulose 140 is not larger than that of the fumed ceramic 130. Consequently, it is observed that the thermal shrinkage of the composite separator 100 is significantly higher than that of the examples, and the heat resistance is poor. In detail, when the coating thickness is the same, the increase in the particle size of the vapor-phase ceramic 130 will reduce the superposition of the heat-resistant layer, affect the comprehensive physical properties of the composite diaphragm 100, and make the heat resistance, mechanical strength, liquid absorption and liquid retention of the diaphragm worse, while affecting the electrochemical performance of the battery, the capacity retention rate after a certain number of battery cycles and the cycle life.

[0140] Based on the measurement results of Comparative Examples 4 and 5, in other words, if the particle size of the lithium intercalation oxide 120 is not larger than that of the vapor-phase ceramic 130 (i.e., if the particle size requirements of the coating material of the present invention are not met), the lithium intercalation oxide 120 cannot preferentially capture free lithium ions on the negative electrode and react with them to form a metal alloy, thereby reducing the formation of the aforementioned metal alloy with specific volume expansion. When the formation of the aforementioned metal alloy as a protective layer is reduced, when lithium dendrites form, the separator, lacking the aforementioned metal alloy as a protective layer, will be directly subjected to stress, and there is a risk of lithium dendrites piercing the separator, affecting the battery's capacity retention and cycling stability. In addition, if the particle size of the carboxylated lithium cellulose 140 is not larger than the particle size of the vapor phase ceramic 130 (that is, the particle size conditions of the coating material of the present invention are not met), the small particle size of the carboxylated lithium cellulose 140 is dispersed and buried in the vapor phase ceramic 130, which is not conducive to the carboxylated lithium cellulose 140 forming a grid structure for filling the vapor phase ceramic 130 particles, and thus lacks a stable supporting role in the coating, affecting the mechanical strength of the composite diaphragm 100.

[0141] Furthermore, it can be seen from Example 2 and Comparative Example 4 that a small difference in particle size between the lithium-intercalating oxide 120 and the fumed aluminum oxide will affect the capacity retention rate of the battery after a certain number of cycles.

[0142] In addition, it is supplemented that, as can be seen from Examples 2 to 5, the vapor-phase ceramic 130 provides the composite diaphragm 100 with heat resistance and liquid retention. Due to the small particle size of the vapor-phase ceramic 130, multiple layers of heat-resistant particles are superimposed in the same coating thickness, and are filled in the modified fiber skeleton. Its original particle size is smaller, and after forming aggregates, there are still a large number of pores between the particles to provide the coating with air permeability, liquid absorption and liquid retention properties. As the proportion of vapor-phase ceramic 130 increases, the diaphragm's heat resistance, membrane rupture temperature, liquid absorption rate, and liquid retention rate are better. The vapor-phase ceramic 130 is combined with the hydrophobic lithium-intercalated oxide 120, and the moisture content is greatly reduced, reducing the risk of battery energy decay.

[0143] It is additionally noted that, as can be seen from Examples 1 to 6, a high ratio of the lithium-intercalated oxide 120 reduces heat resistance, while significantly improving the capacity retention rate of the battery.

[0144] It can be seen from Example 2 and Example 7 that the same diaphragm coating has a good capacity retention rate for the negative electrode. In contrast, after the diaphragm coating is set towards the positive electrode, it is observed that the capacity retention rate of the battery is significantly reduced after a certain number of cycles. It is explained that during the discharge of the battery, the lithium embedded oxide 120 alleviates the problem of insufficient lithium embedded sites on the negative electrode during the discharge process. As the lithium ion concentration increases, the lithium embedded oxide 120 reacts with the free lithium ions on the negative electrode to form a metal alloy and its corresponding oxide, and the metal alloy forms a protective layer on the surface of the negative electrode through its specific volume expansion, inhibiting the continued formation of lithium dendrites and inhibiting the SEI film. The metal alloy (LixZ) has a certain volume expansion property and forms a uniform and dense interphase layer at the negative electrode. This interphase layer has good puncture resistance, avoids internal short circuit of the battery, reduces battery heat generation, and improves the battery's safety performance, electrochemical properties, battery cycle stability and cycle life.

[0145] It can be seen from Examples 1 and 3 that although the proportion of vapor-phase ceramic 130 is reduced, which affects the liquid absorption rate and liquid retention rate of the composite diaphragm 100, the capacity retention rate of the battery still maintains an advantage as the proportion of carboxylated cellulose lithium 140 increases. Carboxylated cellulose lithium 140 reduces the concentration difference of lithium ions and reduces the formation of lithium dendrites by replenishing lithium. During the charging process, carboxylated cellulose lithium 140 adjusts the lithium ion concentration gradient by providing its lithium ions, avoiding the risk of lithium dendrite formation due to the continuous increase of positive electrode lithium ion concentration and the gradual decrease of negative electrode lithium ion concentration.

[0146] The increase in the proportion of added carboxylated cellulose lithium 140 has an effect on improving the mechanical strength of the composite diaphragm 100, which provides fibrous grid support. In addition, the vapor-phase ceramic 130 particles are filled in the aforementioned fibrous network structure like nails, which improves the overall mechanical strength of the composite diaphragm 100. When the composite diaphragm 100 is subjected to force, the aforementioned fibrous grid structure is similar to a dynamic functional layer, which realizes the conversion of the force point from point to surface, weakens the local force, and strengthens the mechanical strength of the composite diaphragm 100. When the composite diaphragm 100 is heated, the vapor-phase ceramic 130 particles filled in the aforementioned fibrous network structure exert excellent heat resistance, inhibiting the thermal shrinkage of the fiber mesh surface and the entire coating. Therefore, the ratio of vapor-phase ceramic 130 to carboxylated cellulose lithium 140 in the coating is reduced, which will affect the mechanical strength, heat resistance and liquid retention of the composite diaphragm 100.

[0147] As can be seen from the Examples and Comparative Example 1, the vapor-phase ceramic 130 has significant advantages in heat resistance and liquid retention, but when used alone, it has the disadvantage of high moisture content, which affects battery performance. Comparative Example 2 shows that the addition of the lithium-intercalating oxide 120 improves the high moisture content and increases the battery capacity retention rate. Comparative Example 3 shows that even if the particle size of the coating material meets the aforementioned conditions, the use of cellulose that has not been modified with lithium carboxylates, where the presence of a large number of hydroxyl groups causes high moisture content, and the lack of the lithium replenishment effect of the carboxylated lithium cellulose 140, affects battery cycling performance and still fails to achieve the desired effect of the present invention.

[0148] The above contents involving common knowledge are not described in detail and can be understood by those skilled in the art.

[0149] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Anyone skilled in the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by one of ordinary skill in the art without departing from the spirit and technical principles disclosed herein are intended to be covered by the claims of the present invention.

Claims

1. A composite diaphragm, characterized in that: The invention comprises a base film and a composite coating located on at least one side of the base film, wherein the composite coating comprises a lithium-intercalated oxide, a vapor-phase ceramic, and carboxylated cellulose lithium, wherein the particle size of the carboxylated cellulose lithium is larger than that of the vapor-phase ceramic, the particle size of the lithium-intercalated oxide is larger than that of the vapor-phase ceramic, and the particle size of the vapor-phase ceramic is D 50 ≤0.1μm.

2. The composite diaphragm according to claim 1, characterized in that The material of the base film includes at least one of polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET) and polyimide.

3. The composite diaphragm according to claim 1, wherein The composite coating is composed of 1 wt% to 30 wt% of lithium-intercalated oxide, 55 wt% to 70 wt% of vapor-phase ceramics and 1 wt% to 10 wt% of carboxylated lithium cellulose.

4. The composite diaphragm according to claim 1, characterized in that The composite coating further includes an adhesive.

5. The composite diaphragm according to claim 4, wherein The composite coating is composed of 1 wt% to 30 wt% of lithium-embedded oxide, 55 wt% to 70 wt% of vapor-phase ceramics, 1 wt% to 10 wt% of carboxylated lithium cellulose, and 1 wt% to 5 wt% of an adhesive.

6. The composite diaphragm according to claim 1, characterized in that The lithium-intercalated oxide includes at least one of SnO2, Fe2O3, Co3O4, NiO, CuO, Sb2O3, and CaO.

7. The composite diaphragm according to claim 1, characterized in that The fumed ceramic includes at least one of inorganic fumed alumina, fumed silica, fumed zirconia, and fumed titania.

8. The composite diaphragm according to claim 1, characterized in that The carboxylated lithium cellulose includes at least one of carboxylated lithium modified nanocellulose, carboxylated lithium modified cellulose nanowhiskers, carboxylated lithium modified cellulose nanofibrils, and carboxylated lithium modified microfibrillated cellulose.

9. The composite diaphragm according to claim 1, characterized in that The thermal decomposition temperature of the carboxylated lithium cellulose is greater than 280°C.

10. The composite diaphragm according to claim 4, characterized in that The adhesive includes at least one of polyacrylamide, polybutyl methacrylate, polyhydroxyethyl methacrylate, styrene / acrylates, polyvinylidene fluoride and polyvinyl alcohol.

11. The composite diaphragm according to claim 1, characterized in that The particle size of the lithium-intercalated oxide is D 50 ≤0.5μm; and / or the particle size of carboxylated cellulose lithium is D 50 ≤0.5μm.

12. A battery, characterized in that: Comprising the composite diaphragm according to any one of claims 1 to 11.

13. A method for preparing a composite diaphragm according to any one of claims 1 to 11, characterized in that: include: adding a solvent, a dispersant, a vapor-phase ceramic, a lithium-intercalated oxide, and carboxylated lithium cellulose in sequence, and mixing to form a dispersion; adding a binder to the dispersion to form a coating slurry; and The coating slurry is coated on at least one side of the base film, and a composite diaphragm including a composite coating layer is obtained after drying.

14. The preparation method according to claim 13, characterized in that The particle size of the dispersion is D 50 <1μm, the maximum particle size of the dispersion is D max <3 μm, the particle size of the dispersion is based on the particle size of the material therein.

15. The preparation method according to claim 13, characterized in that The particle size of the lithium-intercalated oxide is D 50 ≤0.5μm; and / or the particle size of carboxylated cellulose lithium is D 50 ≤0.5μm.

16. The preparation method according to claim 13, wherein The added amount of the solvent accounts for 50 wt% to 95 wt% of the coating slurry, and the solvent includes at least one of water, ethanol, acetone, NMP, and isopropyl alcohol.

17. The preparation method according to claim 13, characterized in that The added amount of the dispersant accounts for 0.0001 wt% to 1 wt% of the coating slurry, and the dispersant includes at least one of polyacrylic acid, polyoxyethylene ether, and sodium alkylbenzene sulfonate.

18. The preparation method according to claim 13, wherein The added amount of the lithium intercalation oxide accounts for 10 wt% to 35 wt% of the coating slurry, and the lithium intercalation oxide includes at least one of SnO2, Fe2O3, Co3O4, NiO, CuO, Sb2O3, and CaO.

19. The preparation method according to claim 13, characterized in that The added amount of the fumed ceramic accounts for 50 wt% to 75 wt% of the coating slurry, and the fumed ceramic includes at least one of inorganic fumed alumina, fumed silica, fumed zirconia, and fumed titania.

20. The preparation method according to claim 13, characterized in that The added amount of the carboxylated lithium cellulose accounts for 5 wt% to 15 wt% of the coating slurry, and the carboxylated lithium cellulose includes at least one of nanocellulose carboxylated lithium modified, cellulose nanowhisker carboxylated lithium modified, cellulose nanofibril carboxylated lithium modified, and microfibrillated cellulose carboxylated lithium modified.

21. The preparation method according to claim 13, characterized in that In the step of coating the slurry on at least one side of the resin base film, the coating method includes at least one of roller coating, spin coating, dip coating, cast coating, and spray coating.

22. The preparation method according to claim 13, wherein In the step of coating the slurry on at least one side of the resin base film, the coating thickness of the composite coating is in the range of 0.3 μm to 3 μm.

23. The preparation method according to claim 13, wherein The base film includes a low closed-pore and high-breakage base film, and the thickness of the base film ranges from 3 μm to 20 μm.

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