Composite electrolyte negative electrode coating, preparation method thereof, negative electrode and battery

Abstract

The invention belongs to the technical field of batteries, and particularly relates to a composite electrolyte negative electrode coating, a preparation method thereof, a negative electrode and a battery. The composite electrolyte negative electrode coating comprises at least one or more polymer fibers, a polymer matrix, a ceramic solid electrolyte, a lithium salt and inert ceramic; the mass ratio of the polymer fiber to the polymer matrix to the inorganic ceramic solid electrolyte to the inert ceramic to the lithium salt is (1-2): (6-7): (1-1.2): (1-1.2): (0.5-1). The composite electrolyte negative electrode coating is prepared by taking the polymer fiber, the polymer matrix, the inorganic ceramic solid electrolyte and the inert ceramic as main raw materials, and when the composite electrolyte negative electrode coating is applied to a negative-electrode-free battery, the use amount of liquid electrolyte can be effectively reduced, dead lithium is adhered, the short-circuit risk of the battery is reduced, and the service life of the battery is prolonged. Therefore, the functions of improving the capacity retention ratio of the battery, delaying the capacity fading and the like are achieved, self-discharge can be avoided, and the safety is relatively good.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries, and in particular relates to a composite electrolyte negative electrode coating and a preparation method thereof, a negative electrode and a battery. Background Art

[0002] In the field of battery energy storage, dendrite growth and the formation of dead lithium during the negative electrode deposition process have always been key challenges facing lithium metal negative electrodes and a serious problem that limits the commercialization of lithium metal batteries. Due to its extremely high reactivity, lithium metal will be repeatedly plated and stripped during the charge and discharge process, gradually forming thorn-like protrusions on the surface of the lithium negative electrode, and exhibiting various morphologies, such as needle-like, moss-like, or tree-like structures. These lithium dendrites have the potential to penetrate the battery separator, which can easily cause the battery to short-circuit. More seriously, this short circuit is often accompanied by thermal runaway of the battery, and in some cases, it can even cause spontaneous combustion and explosion.

[0003] In addition, the growth of lithium dendrites will also cause the appearance of "dead lithium". When some branches of lithium dendrites react with the electrolyte, the dendrite structure will be destroyed, and the wrapped lithium dendrites may separate from the substrate, resulting in capacity loss and safety hazards. In lithium batteries, the formation of dead lithium is also related to the growth of lithium dendrites, compared with the parasitic lithium compounds produced by electrochemical reactions. The accumulation of dead lithium hinders the growth of Li + The migration of lithium metals accelerates the formation of lithium dendrites, reducing the battery's Coulombic efficiency. The dendritic structure also creates a larger surface area, increasing the extent of side reactions and leading to rapid depletion of lithium metal and electrolyte. Furthermore, side reactions also trigger the rapid degradation and breakage of lithium dendrites.

[0004] In recent years, researchers have proposed various strategies to improve the stability of lithium negative electrodes, including: (1) electrolyte modification and solid electrolytes; (2) construction of three-dimensional current collectors; (3) diaphragm modification strategies; (4) construction of artificial protective layers. Constructing an artificial protective layer on the surface of the lithium negative electrode is one of the effective strategies to improve the stability of the lithium negative electrode. Compared with electrolyte modification and solid electrolytes, the setting of the protective layer can also avoid consumption during long-term cycling. Compared with the three-dimensional current collector, the setting of the protective layer can regulate the nucleation and growth of lithium as much as possible without adding extra weight and volume, thus avoiding the formation of lithium dendrites. Compared with the diaphragm modification strategy, the construction of the protective layer is also simpler.

[0005] However, achieving uniform lithium deposition by providing a protective layer requires the protective layer to have multiple properties, and a single-component protective layer is difficult to excel in all aspects. Therefore, constructing a composite protective layer with multiple components has more prominent advantages. Summary of the Invention

[0006] The primary purpose of the present invention is to provide a composite electrolyte negative electrode coating and its preparation method, negative electrode and battery, so as to effectively reduce the amount of liquid electrolyte used, adhere dead lithium, reduce the risk of battery short circuit, and improve the safety of battery use.

[0007] To this end, the present invention provides the following technical solutions.

[0008] A first aspect of the present invention provides a composite electrolyte negative electrode coating comprising:

[0009] at least one or more polymer fibers;

[0010] at least one or more polymer matrices;

[0011] at least one or more inorganic ceramic solid electrolytes;

[0012] at least one or more lithium salts; and

[0013] At least one or more inert ceramics.

[0014] Furthermore, the polymer fiber is selected from at least one of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer, and aramid fiber.

[0015] Furthermore, the polymer matrix is selected from at least one of polyethylene oxide, polyacrylonitrile and polymethyl methacrylate.

[0016] Furthermore, the inorganic ceramic solid electrolyte is selected from at least one of lithium aluminum titanium phosphate, lithium aluminum germanium phosphate, lithium lanthanum zirconium oxide, lithium lanthanum zirconium titanium oxide, and lithium phosphorus sulfur chlorine;

[0017] Optionally, the inorganic ceramic solid electrolyte is lithium lanthanum zirconium titanium oxide.

[0018] Furthermore, the lithium salt is selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(trifluoromethylsulfonylamino)imide and lithium bis(fluoromethylsulfonylamino)imide.

[0019] Furthermore, the inert ceramic is selected from at least one of silicon dioxide, barium titanate, silicon nitride, aluminum oxide, titanium dioxide, and zirconium dioxide;

[0020] Optionally, the inert ceramic is silicon dioxide.

[0021] Furthermore, in the above-mentioned composite electrolyte negative electrode coating, the mass ratio of the polymer fiber, polymer matrix, inorganic ceramic solid electrolyte, inert ceramic and lithium salt is (1-2): (6-7): (1-1.2): (1-1.2): (0.5-1).

[0022] A second aspect of the present invention provides a method for preparing a composite electrolyte negative electrode coating as described above, the method comprising the following steps:

[0023] S1: dissolving a lithium salt and a polymer matrix in a first organic solvent to obtain a solution A;

[0024] dissolving the polymer fiber in a second organic solvent to obtain a solution B;

[0025] S2: mixing the obtained solution A and solution B to obtain solution C;

[0026] S3: adding an inorganic ceramic solid electrolyte and an inert ceramic to the obtained solution C, stirring evenly to obtain a mixture;

[0027] S4: The mixed slurry is coated and dried to obtain the composite electrolyte negative electrode coating.

[0028] Furthermore, in the above step S1, the first organic solvent is selected from at least one of acetone, N-methyl-2-pyrrolidone, N,N-dimethylformamide, acetonitrile, dimethyl sulfoxide, and dimethylacetamide.

[0029] Furthermore, in the above step S1, the second organic solvent is selected from at least one of acetone, N-methyl-2-pyrrolidone, N,N-dimethylformamide, acetonitrile, dimethyl sulfoxide, and dimethylacetamide.

[0030] Furthermore, in the above step S2, the solution A and the solution B are mixed in a volume ratio of 1:1 to 1.2.

[0031] Furthermore, in the above step S4, the coating thickness is 1 to 4 μm.

[0032] Furthermore, in the above step S4, the drying conditions are: temperature: 60-90° C., time: 48 hours.

[0033] The third aspect of the present invention provides a negative electrode, comprising a negative electrode current collector and a composite electrolyte negative electrode coating as described above or a composite electrolyte negative electrode coating prepared by the preparation method of the composite electrolyte negative electrode coating as described above, wherein the negative electrode protective layer is arranged on the surface of the negative electrode current collector.

[0034] A fourth aspect of the present invention provides a battery comprising the negative electrode as described above.

[0035] By means of the above technical solution, the present invention has at least the following advantages:

[0036] The composite electrolyte negative electrode coating of the present invention is prepared with polymer fibers, polymer matrix, inorganic ceramic solid electrolyte and inert ceramic as main raw materials. The coating of the present invention is used on a negative electrode-free battery, which can effectively reduce the amount of liquid electrolyte, adhere to dead lithium, reduce the risk of battery short circuit, thereby achieving the functions of improving the capacity retention rate of the battery, delaying capacity decay, etc., and can also avoid self-discharge, with better safety. The main function of polymer fibers such as polyvinylidene fluoride PVDF, polyvinylidene fluoride-hexafluoropropylene copolymer PVDF-HFP, aramid fibers, etc. is to establish the skeleton of the coating and provide a certain accommodation space for the deposition of lithium atoms; the main function of polymer matrices such as polyethylene oxide PEO, polyacrylonitrile PAN, polymethyl methacrylate PMMA, etc. is to act as a cross-linking agent to link the skeleton with inert ceramics and inorganic ceramic solid electrolytes; organic solvents such as NMP, DMF, DMSO, DMAC, etc. are used as solvents to dissolve the raw materials, then mix them, and evaporate in the form of gas after coating; Organic ceramic solid electrolytes such as lithium aluminum titanium phosphate LATP, lithium aluminum germanium phosphate LAGP, lithium lanthanum zirconium oxide LLZO, lithium lanthanum zirconium titanium oxide LLZTO, lithium phosphorus sulfur chlorine LPSCL, etc. can improve ionic conductivity and be more lithium-friendly, preventing the production of more dead lithium; the role of inert fillers such as silicon dioxide SiO2, barium titanate BaTiO3, silicon nitride Si3N4, aluminum oxide Al2O3, titanium dioxide TiO2, zirconium dioxide ZrO2, etc. is to increase the mechanical strength of the coating on the one hand, and on the other hand, reduce the crystallinity of PEO, etc., improve the mobility of the chain segments, and increase more lithium ion transmission channels.

[0037] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention and implement it according to the contents of the specification, the following is a detailed description of the preferred embodiments of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is a charge and discharge curve of a battery assembled according to the method of Example 1 of the present invention;

[0039] Figure 2 This is a charge and discharge curve of a battery assembled according to the method of Example 4 of the present invention;

[0040] Figure 3 This is a charge and discharge curve of a battery assembled according to the method of Example 6 of the present invention;

[0041] Figure 4 This is a charge and discharge curve of a battery assembled according to the method of Example 7 of the present invention;

[0042] Figure 5 This is a charge and discharge curve of a battery assembled according to the method of Example 10 of the present invention;

[0043] Figure 6 This is the charge and discharge curve of the battery assembled according to the method of Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0044] In order to make the technical means, creative features, objectives and effects achieved by the present invention easier to understand, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0045] Unless otherwise specified, " scope " disclosed in the present invention is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and selected lower limit and upper limit define the boundary of special range.The scope that this mode limits can be to include end value or not include end value, and can be combined arbitrarily, and promptly any lower limit can form a scope with any upper limit combination.For example, if listed the scope of 60-120 and 80-110 for specific parameters, it is also expected to be understood that the scope of 60-110 and 80-120.In addition, if the minimum range value 1 and 2 listed, and if listed maximum range value 3,4 and 5, then the following scope can all be expected to: 13,1-4,1-5,2-3,2-4 and 2-5.

[0046] Unless otherwise specified, the numerical range "ab" in this disclosure is an abbreviation for any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is merely an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0047] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0048] Unless otherwise specified, all technical features and optional technical features of the present invention can be combined with each other to form a new technical solution.

[0049] Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0050] Unless otherwise specified, the terms "include" and "comprising" used in the present invention may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0051] Unless otherwise specified, the term "or" is inclusive in this disclosure. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0052] Unless otherwise specified, for battery systems based on lithium-based negative electrodes, if dendrites and dead lithium are generated during the negative electrode deposition process, it will not only lead to rapid loss of active lithium and serious side reactions causing electrolyte dryness, but also easily cause safety accidents. Therefore, it is crucial to regulate the growth of negative electrode dendrites.

[0053] Embodiments of the present invention provide a composite electrolyte anode coating comprising: at least one or more polymer fibers; at least one or more polymer matrices; at least one or more inorganic ceramic solid electrolytes; and at least one or more inert ceramics. For example, the anode coating provided by embodiments of the present invention can be applied to the surface of an anode material or a cathode current collector to effectively inhibit dendrite growth and the formation of dead lithium.

[0054] Specifically, the polymer fiber can be selected from at least one of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), and aramid fiber. The main function of the selected material is to establish a skeleton of the coating and provide a certain amount of accommodation space for the deposition of lithium atoms.

[0055] In some embodiments, the polymer matrix can be selected from at least one of polyethylene oxide (PEO), polyacrylonitrile (PAN), and polymethyl methacrylate (PMMA). The addition of the polymer matrix primarily serves as a crosslinking agent, linking the polymer fiber skeleton with the inert ceramic and inorganic ceramic solid electrolyte.

[0056] In some exemplary embodiments, the inorganic ceramic solid electrolyte is selected from at least one of lithium aluminum titanium phosphate (LATP), lithium aluminum germanium phosphate (LAGP), lithium lanthanum zirconium oxide (LLZO), lithium lanthanum zirconium titanium oxide (LLZTO), and lithium phosphorus sulfur chlorine (LPSCL). Preferably, the inorganic ceramic solid electrolyte is lithium lanthanum zirconium titanium oxide (LLZTO). The addition of the inorganic ceramic solid electrolyte can improve ionic conductivity and make the battery more lithium-friendly, thereby preventing the generation of more dead lithium.

[0057] In some exemplary embodiments, the lithium salt is selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(trifluoromethylsulfonylamino)imide, and lithium bis(fluoromethylsulfonylamino)imide.

[0058] In some exemplary embodiments, the inert ceramic can be selected from at least one of silicon dioxide (SiO2), barium titanate (BaTiO3), silicon nitride (Si3N4), aluminum oxide (Al2O3), titanium dioxide (TiO2), and zirconium dioxide (ZrO2); preferably, the inert ceramic is silicon dioxide (SiO2). The inert ceramic can increase the mechanical strength of the coating while also reducing the crystallinity of PEO, improving the mobility of the chain segments and providing more lithium ion transport channels.

[0059] In some embodiments, the composite electrolyte negative electrode coating comprises the polymer fibers, polymer matrix, inorganic ceramic solid electrolyte, inert ceramic, and lithium salt in a weight percentage ratio of (1-2):(6-7):(1-1.2):(1-1.2):(0.5-1). The composite electrolyte negative electrode coating obtained with the above weight ratios is applied to the surface of a copper foil to obtain a coated copper foil, which is then assembled into a battery as a negative electrode sheet, thereby achieving higher electrochemical performance.

[0060] An embodiment of the present invention further provides a method for preparing a composite electrolyte negative electrode coating as described above, comprising the following steps: S1: dissolving a lithium salt and a polymer matrix in a first organic solvent to obtain solution A; and dissolving polymer fibers in a second organic solvent to obtain solution B. The first organic solvent is selected from at least one of acetone, N-methyl-2-pyrrolidone (NMP), N,N-dimethylformamide (DMF), acetonitrile (ACN), dimethyl sulfoxide (DMSO), and dimethylacetamide (DMAC). Solution A is obtained by adding the lithium salt and the polymer matrix to the first organic solvent and stirring until completely dissolved. A suitable stirring time can be, for example, 24 hours, 26 hours, or 28 hours, preferably 24 hours.

[0061] S2: Mixing the obtained solution A and solution B to obtain solution C; S3: Adding an inorganic ceramic solid electrolyte and an inert ceramic to the obtained solution C, stirring uniformly to obtain a mixture; S4: Applying and drying the mixed slurry to obtain the composite electrolyte negative electrode coating. The second organic solvent is selected from at least one of acetone, N-methyl-2-pyrrolidone (NMP), N,N-dimethylformamide (DMF), acetonitrile (ACN), dimethyl sulfoxide (DMSO), and dimethylacetamide (DMAC). Solution B is obtained by dissolving the polymer fiber in the second organic solvent, heating to 40-60°C, and stirring with a magnetic stirrer until dissolved.

[0062] Organic solvents can dissolve the raw materials, making it easier to mix them later. After coating, they are dried and the solvents evaporate in the form of gas. Therefore, the addition of solvents not only facilitates the mixing of the raw materials, but also does not affect the final performance of the coating.

[0063] In some embodiments, in step S2, solution A and solution B are mixed in a volume ratio of 1:1 to 1.2, for example, 1:1, 1:1.1 or 1:1.2, preferably 1:1.1.

[0064] In some embodiments, in step S4, the coating thickness is 1 to 4 μm, for example, 1 μm, 2 μm, 3 μm, or 4 μm, preferably 3 μm. A coating that is too thick will reduce the overall energy density of the anode-free system and increase the specific surface area. Although this will increase the capacity for lithium ions to a certain extent, it will also increase the consumption of electrolyte, thus losing the advantage of high energy density without anode. A coating that is too thin will not effectively inhibit the generation of dead lithium, thus reducing the overall electrochemical performance of the anode-free system. Therefore, the coating thickness of the present application is preferably 1 to 4 μm.

[0065] In some embodiments, in step S4, the drying temperature is 60-90°C, and the suitable drying temperature can be, for example, 60°C, 70°C, 80°C or 90°C, preferably 80°C; the drying time is ≥48h, for example, 48h, 50h or 52h, preferably 48h.

[0066] Embodiments of the present invention further provide a negative electrode comprising a negative electrode current collector and a composite electrolyte negative electrode coating as described above, or a composite electrolyte negative electrode coating prepared by the method for preparing a composite electrolyte negative electrode coating as described above, wherein the negative electrode protective layer is disposed on the surface of the negative electrode current collector. Exemplarily, the negative electrode current collector may be copper foil, aluminum foil, a composite current collector, or the like. Exemplarily, the negative electrode may also comprise a lithium metal negative electrode material, and the negative electrode protective layer is disposed on the surface of the negative electrode material or the negative electrode current collector that contacts the electrolyte to provide protection.

[0067] An embodiment of the present invention also provides a battery, comprising a negative electrode as described above. Exemplarily, the battery assembly method comprises: assembling a positive electrode, a separator, and the negative electrode of the above embodiment into a battery. Among them, the positive electrode material can be a ternary positive electrode (NCM), lithium cobalt oxide (LCO), lithium iron phosphate (LFP), lithium nickel manganese oxide (LNMO), lithium-rich manganese-based material (LMR), etc. The separator can be a PP or PE separator. The negative electrode is a negative electrode coated with a composite electrolyte negative electrode coating provided in an embodiment of the present application. The electrolyte can be an ether electrolyte, for example, the molar ratio of LiFSI:DME:TTE is 1:1.2:3.

[0068] The battery of this embodiment can reduce the generation of dendrites and dead lithium, thereby achieving functions such as improving the capacity retention rate of the battery and delaying capacity attenuation, and can also avoid self-discharge, thereby improving safety.

[0069] Unless otherwise specified, the PEO (CAS No. 68441-17-8), lithium salt (LiFSI) (CAS No. 90076-65-6), and PAN (polyacrylonitrile) (CAS No. 25014-41-9) described in the following examples were all purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. The aramid fiber was poly(m-phenylene isophthalamide) (CAS No. 39453-37-8) purchased from Taihe New Materials Group Co., Ltd. The electrolyte was an ether electrolyte 90076-65-6 purchased from Suzhou Duoduo Chemical Technology Co., Ltd. The separator was a PE membrane with an 11 μm base film, 2 μm ceramic coatings on both sides, and PVDF adhesive on both sides, purchased from Shenzhen Xingyuan Materials Technology Co., Ltd.

[0070] In order to verify the promoting effect of the negative electrode coating obtained in the following embodiments on the performance of the negative electrode-free lithium metal battery, lithium nickel cobalt manganese oxide (NCM) was used as the positive electrode material, aluminum foil was used as the current collector, lithium nickel cobalt manganese oxide (NCM), adhesive polyvinylidene fluoride (PVDF), conductive agent (conductive carbon, single-walled carbon nanotubes, multi-walled carbon nanotubes) and organic solvent N-methyl-2-pyrrolidone were used as raw materials to prepare the battery positive electrode, and metallic lithium was used as the negative electrode. Under the dew point condition of -40°C, the negative electrode coatings, electrolytes, battery positive electrodes, ceramic separators and negative electrodes prepared in the following Examples 1 to 11 and Comparative Examples 1 to 2 were respectively used to assemble a 15.7Ah negative electrode-free lithium metal soft pack battery for electrical performance testing. The specific test process and results are as follows:

[0071] Example 1:

[0072] PEO and lithium bis(fluorosulfonyl)imide salt were added to acetonitrile in a mass ratio of 1:9 and stirred for 24 hours until dissolved to obtain an acetonitrile solution of PEO / lithium salt. Aramid fiber (18% by mass) was added to the solvent DMSO, then heated to 50°C and stirred with a magnetic stirrer for 24 hours until dissolved to obtain an aramid fiber solution with a mass concentration of 18%. The above-mentioned acetonitrile solution of PEO / lithium salt and aramid fiber solution were mixed and stirred evenly in a volume ratio of 1:1 to obtain a mixed slurry. The obtained mixed slurry was coated on the surface of the negative electrode copper foil with a coating thickness of 3μm, and then placed in an oven for vacuum drying at a temperature of 80°C for 48 hours to obtain a negative electrode sheet coated with a porosity of 50%.

[0073] The obtained negative electrode sheet is die-cut and assembled into a negative electrode-free soft pack battery cell: the nickel cobalt manganese oxide (NCM) powder is baked under a dew point of -40°C. Then, NCM, adhesive polyvinylidene fluoride (PVDF), conductive carbon, single-walled carbon nanotubes, and multi-walled carbon nanotubes are added to the organic solvent N-methyl-2-pyrrolidone in a mass ratio of 96.6:1.5:1.2:0.5:0.2 to perform positive electrode homogenization. After stirring evenly, a uniform slurry is obtained. It should be noted that the amount of organic solvent N-methyl-2-pyrrolidone added needs to be controlled during the stirring process so that the viscosity of the obtained slurry is controlled between 5000-8000Mpa·s. After that, aluminum foil is transferred and baked at the same time to obtain a rolled electrode sheet. The rolled electrode sheet is then baked at 90°C for 24 hours to ensure that the organic solvent is completely removed. Next, the electrode sheet is rolled and cut to obtain a positive electrode sheet. The obtained positive electrode sheet, separator and negative electrode sheet were assembled into a 15.7Ah negative electrode-free soft pack battery cell, and then 24g of ether electrolyte was injected to test the electrochemical performance of the battery cell. See Table 1 and Figure 1 .

[0074] The results show that after 20 cycles at a charge rate of 0.1C, a charge cut-off voltage of 4.3V, a discharge rate of 0.1C, and a discharge cut-off voltage of 3V, the capacity retention rate is 87.1%.

[0075] Example 2:

[0076] PEO and lithium bis(fluorosulfonyl)imide salt were added to DMAC in a mass ratio of 1:9 and stirred for 24 hours until dissolved, yielding a PEO / lithium salt DMAC solution. Aramid fiber was added to the solvent DMSO, then heated to 50°C and stirred with a magnetic stirrer for 24 hours until dissolved, yielding an aramid fiber solution with a mass concentration of 18%. The PEO / lithium salt DMAC solution and the aramid fiber solution were mixed in a volume ratio of 1:1 and stirred evenly to yield a mixed slurry. The resulting mixed slurry was coated on the surface of the negative electrode copper foil to a coating thickness of 3μm, then vacuum-dried in an oven at 80°C for 48 hours to yield a coated negative electrode sheet with a porosity of 50%.

[0077] The obtained negative electrode sheets were assembled into negative electrode-free soft-pack cells in the same manner as in Example 1 and the electrochemical performance of the cells was tested. See Table 1.

[0078] The results show that after 17 cycles at a charge rate of 0.1C, a charge cut-off voltage of 4.3V, a discharge rate of 0.1C, and a discharge cut-off voltage of 3V, the capacity retention rate is 85.2%.

[0079] Example 3:

[0080] PAN and lithium bis(fluorosulfonyl)imide salt were added to acetonitrile in a mass ratio of 1:9 and stirred for 24 hours until dissolved to obtain an acetonitrile solution of PAN / lithium salt. Aramid fiber was added to the solvent DMSO, then heated to 50°C and stirred with a magnetic stirrer for 24 hours until dissolved to obtain an aramid fiber solution with a mass concentration of 18%. The above-mentioned acetonitrile solution of PEO / lithium salt and aramid fiber solution were mixed in a volume ratio of 1:1 and stirred evenly to obtain a mixed slurry. The obtained mixed slurry was coated on the surface of the negative electrode copper foil with a coating thickness of 3μm, and then placed in an oven at a temperature of 80°C for vacuum drying for 48 hours to obtain a negative electrode sheet coated with a porosity of 50%.

[0081] The obtained negative electrode sheets were assembled into negative electrode-free soft-pack cells in the same manner as in Example 1 and the electrochemical performance of the cells was tested. See Table 1.

[0082] The results show that after 20 cycles at a charge rate of 0.1C, a charge cut-off voltage of 4.3V, a discharge rate of 0.1C, and a discharge cut-off voltage of 3V, the capacity retention rate is 84.1%.

[0083] Example 4:

[0084] PEO and lithium bis(fluorosulfonyl)imide salt were added to acetonitrile in a mass ratio of 1:9 and stirred for 24 hours until dissolved to obtain an acetonitrile solution of PEO / lithium salt. Aramid fiber was added to the solvent DMSO, then heated to 50°C and stirred with a magnetic stirrer for 24 hours until dissolved to obtain an aramid fiber solution with a mass concentration of 18%. The above-mentioned acetonitrile solution of PEO / lithium salt and aramid fiber solution were mixed and stirred evenly in a volume ratio of 1:1.1 to obtain a mixed slurry. The obtained mixed slurry was coated on the surface of the negative electrode copper foil with a coating thickness of 3μm, and then placed in an oven at a temperature of 80°C for vacuum drying for 48 hours to obtain a negative electrode sheet coated with a porosity of 50%.

[0085] The obtained negative electrode sheets were assembled into negative electrode-free soft pack cells in the same manner as in Example 1 and the electrochemical performance of the cells was tested. Figure 2 .

[0086] The results show that after 20 cycles at a charge rate of 0.1C, a charge cut-off voltage of 4.3V, a discharge rate of 0.1C, and a discharge cut-off voltage of 3V, the capacity retention rate is 86.8%.

[0087] Example 5:

[0088] PEO and lithium bis(fluorosulfonyl)imide salt were added to acetonitrile in a mass ratio of 1:9 and stirred for 24 hours until dissolved to obtain an acetonitrile solution of PEO / lithium salt. Aramid fiber was added to the solvent DMSO, then heated to 50°C and stirred with a magnetic stirrer for 24 hours until dissolved to obtain an aramid fiber solution with a mass concentration of 18%. The above-mentioned acetonitrile solution of PEO / lithium salt and aramid fiber solution were mixed and stirred evenly in a volume ratio of 1:1.2 to obtain a mixed slurry. The obtained mixed slurry was coated on the surface of the negative electrode copper foil with a coating thickness of 3μm, and then placed in an oven at a temperature of 80°C for vacuum drying for 48 hours to obtain a negative electrode sheet coated with a porosity of 50%.

[0089] The obtained negative electrode sheets were assembled into negative electrode-free soft-pack cells in the same manner as in Example 1 and the electrochemical performance of the cells was tested. See Table 1.

[0090] The results show that after 19 cycles at a charge rate of 0.1C, a charge cut-off voltage of 4.3V, a discharge rate of 0.1C, and a discharge cut-off voltage of 3V, the capacity retention rate is 85.5%.

[0091] Example 6:

[0092] PEO and lithium bis(fluorosulfonyl)imide salt were added to acetonitrile in a mass ratio of 1:9 and stirred for 24 hours until dissolved, yielding a PEO / lithium salt acetonitrile solution. Aramid fiber was added to the solvent DMSO, then heated to 50°C and stirred with a magnetic stirrer for 24 hours until dissolved, yielding an aramid fiber solution with a mass concentration of 18%. The PEO / lithium salt acetonitrile solution and the aramid fiber solution were mixed and stirred evenly in a volume ratio of 1:1.1, followed by the addition of 5% by mass of the solid electrolyte LLZTO to yield a mixed slurry. The resulting mixed slurry was coated on the surface of the negative electrode copper foil to a coating thickness of 3μm, and then dried in a vacuum oven at 80°C for 48 hours to yield a coated negative electrode sheet with a porosity of 50%.

[0093] The obtained negative electrode sheets were assembled into negative electrode-free soft pack cells in the same manner as in Example 1 and the electrochemical performance of the cells was tested. Figure 3 .

[0094] The results show that after 31 cycles at a charge rate of 0.1C, a charge cut-off voltage of 4.3V, a discharge rate of 0.1C, and a discharge cut-off voltage of 3V, the capacity retention rate is 87.2%.

[0095] Example 7:

[0096] PEO and lithium bis(fluorosulfonyl)imide salt were added to acetonitrile in a mass ratio of 1:9 and stirred for 24 hours until dissolved, yielding a PEO / lithium salt acetonitrile solution. Aramid fiber was added to the solvent DMSO, then heated to 50°C and stirred with a magnetic stirrer for 24 hours until dissolved, yielding an aramid fiber solution with a mass concentration of 18%. The PEO / lithium salt acetonitrile solution and the aramid fiber solution were mixed and stirred evenly in a volume ratio of 1:1.1. 5% by mass of inert ceramic SiO2 was then added and stirred evenly to yield a mixed slurry. The resulting mixed slurry was coated on the surface of the negative electrode copper foil to a coating thickness of 3μm. The coating was then dried in a vacuum oven at 80°C for 48 hours, yielding a coated negative electrode sheet with a porosity of 50%.

[0097] The obtained negative electrode sheets were assembled into negative electrode-free soft pack cells in the same manner as in Example 1 and the electrochemical performance of the cells was tested. Figure 4 .

[0098] The results show that after 30 cycles at a charge rate of 0.1C, a charge cut-off voltage of 4.3V, a discharge rate of 0.1C, and a discharge cut-off voltage of 3V, the capacity retention rate is 87.8%.

[0099] Example 8:

[0100] PEO and lithium bis(fluorosulfonyl)imide salt were added to acetonitrile in a mass ratio of 1:9 and stirred for 24 hours until dissolved, obtaining an acetonitrile solution of PEO / lithium salt. Aramid fiber was added to the solvent DMSO, then heated to 50°C and stirred with a magnetic stirrer for 24 hours until dissolved, obtaining an aramid fiber solution with a mass concentration of 18%. The above-mentioned acetonitrile solution of PEO / lithium salt and the aramid fiber solution were mixed and stirred evenly in a volume ratio of 1:1.1, and then a solid electrolyte LATP with a mass fraction of 5% was added and stirred evenly to obtain a mixed slurry. The obtained mixed slurry was coated on the surface of the negative electrode copper foil with a coating thickness of 3μm, and then placed in an oven at a temperature of 80°C and vacuum dried for 48 hours to obtain a coated negative electrode sheet with a porosity of 50%.

[0101] The obtained negative electrode sheets were assembled into negative electrode-free soft-pack cells in the same manner as in Example 1 and the electrochemical performance of the cells was tested. See Table 1.

[0102] The results show that after 25 cycles at a charge rate of 0.1C, a charge cut-off voltage of 4.3V, a discharge rate of 0.1C, and a discharge cut-off voltage of 3V, the capacity retention rate is 85.6%.

[0103] Example 9:

[0104] PEO and lithium bis(fluorosulfonyl)imide salt were added to acetonitrile in a mass ratio of 1:9 and stirred for 24 hours until dissolved, yielding a PEO / lithium salt acetonitrile solution. Aramid fiber was added to the solvent DMSO, then heated to 50°C and stirred with a magnetic stirrer for 24 hours until dissolved, yielding an aramid fiber solution with a mass concentration of 18%. The PEO / lithium salt acetonitrile solution and the aramid fiber solution were mixed and stirred evenly in a volume ratio of 1:1.1. A 5% mass fraction of inert filler Al2O3 was then added and stirred evenly to yield a mixed slurry. The resulting mixed slurry was coated on the surface of the negative electrode copper foil to a coating thickness of 3μm. The coating was then dried in a vacuum oven at 80°C for 48 hours, yielding a coated negative electrode sheet with a porosity of 50%.

[0105] The obtained negative electrode sheets were assembled into negative electrode-free soft-pack cells in the same manner as in Example 1 and the electrochemical performance of the cells was tested. See Table 1.

[0106] The results show that after 26 cycles at a charge rate of 0.1C, a charge cut-off voltage of 4.3V, a discharge rate of 0.1C, and a discharge cut-off voltage of 3V, the capacity retention rate is 85.9%.

[0107] Example 10:

[0108] PEO and lithium bis(fluorosulfonyl)imide salt were added to acetonitrile in a mass ratio of 1:9 and stirred for 24 hours until dissolved, yielding a PEO / lithium salt acetonitrile solution. Aramid fiber was added to the solvent DMSO, heated to 50°C, and magnetically stirred for 24 hours until dissolved, yielding an aramid fiber solution with a mass concentration of 18%. The PEO / lithium salt acetonitrile solution and the aramid fiber solution were mixed and stirred evenly in a volume ratio of 1:1.1. LLZTO solid electrolyte and SiO2 inert ceramic were then added and stirred evenly to yield a mixed slurry. The resulting mixed slurry was coated on the surface of the negative electrode copper foil to a coating thickness of 3μm. The coating was then dried in a vacuum oven at 80°C for 48 hours, yielding a coated negative electrode sheet with a porosity of 50%.

[0109] The obtained negative electrode sheets were assembled into negative electrode-free soft pack cells in the same manner as in Example 1 and the electrochemical performance of the cells was tested. Figure 5 .

[0110] The results show that after 53 cycles at a charge rate of 0.1C, a charge cut-off voltage of 4.3V, a discharge rate of 0.1C, and a discharge cut-off voltage of 3V, the capacity retention rate is 88.6%.

[0111] Example 11:

[0112] PEO and lithium bis(fluorosulfonyl)imide salt were added to acetonitrile in a mass ratio of 1:9 and stirred for 24 hours until dissolved, yielding a PEO / lithium salt acetonitrile solution. Aramid fiber was added to the solvent DMSO, heated to 50°C, and magnetically stirred for 24 hours until dissolved, yielding an aramid fiber solution with a mass concentration of 18%. The PEO / lithium salt acetonitrile solution and the aramid fiber solution were mixed and stirred evenly in a volume ratio of 1:1.1. LLZTO, a solid electrolyte, and Al2O3, an inert ceramic, were then added and stirred evenly to yield a mixed slurry. The resulting mixed slurry was coated on the surface of the negative electrode copper foil to a coating thickness of 3μm. The coating was then dried in a vacuum oven at 80°C for 48 hours, yielding a coated negative electrode sheet with a porosity of 50%.

[0113] The obtained negative electrode sheets were assembled into negative electrode-free soft-pack cells in the same manner as in Example 1 and the electrochemical performance of the cells was tested. See Table 1.

[0114] The results show that after 35 cycles at a charge rate of 0.1C, a charge cut-off voltage of 4.3V, a discharge rate of 0.1C, and a discharge cut-off voltage of 3V, the capacity retention rate is 87.2%.

[0115] Comparative Example 1:

[0116] The only difference between this comparative example and Example 1 is that no coating is performed on the surface of the negative electrode copper foil, that is, the negative electrode plate is a smooth copper foil, and the rest is consistent with Example 1.

[0117] The negative electrode plate smooth copper foil was assembled into a negative electrode-free soft pack battery cell in the same manner as in Example 1 and the electrochemical performance of the battery cell was tested. See Table 1 and Figure 6 .

[0118] The results show that after 15 cycles of constant current charging at a charge rate of 0.1C and a charge cut-off voltage of 4.3V, and a discharge rate of 1C and a discharge cut-off voltage of 3V, the capacity retention rate is 76.8%.

[0119] Comparative Example 2:

[0120] The only difference between this comparative example and Example 1 is that the amount of electrolyte added during the assembly of the negative electrode-free soft-pack battery cell is 36 g, and the rest is consistent with Comparative Example 1.

[0121] The negative electrode plate smooth copper foil was assembled into a negative electrode-free soft pack battery cell in the manner of Example 1 and the electrochemical performance of the battery cell was tested. See Table 1.

[0122] The results show that after 15 cycles of constant current charging at a charge rate of 0.1C and a charge cut-off voltage of 4.3V, and a discharge rate of 1C and a discharge cut-off voltage of 3V, the capacity retention rate is 86.4%.

[0123] Comparative Example 3:

[0124] The only difference between this comparative example and Example 1 is that the thickness of the negative electrode coating is 2 μm. Other details are consistent with Example 1, see Table 1.

[0125] The results show that after 15 cycles of constant current charging at a charge rate of 0.1C and a charge cut-off voltage of 4.3V, and a discharge rate of 1C and a discharge cut-off voltage of 3V, the capacity retention rate is 83.4%.

[0126] Comparative Example 4:

[0127] The only difference between this comparative example and Example 1 is that the thickness of the negative electrode coating is 4 μm. Other details are consistent with Example 1, see Table 1.

[0128] The results show that after 15 cycles of constant current charging at a charge rate of 0.1C and a charge cut-off voltage of 4.3V, and a discharge rate of 1C and a discharge cut-off voltage of 3V, the capacity retention rate is 86.6%.

[0129] Comparative Example 5:

[0130] The only difference between this comparative example and Example 1 is that the porosity of the negative electrode coating is 40%. Other details are consistent with Example 1, see Table 1.

[0131] The results show that after 20 cycles of constant current charging at a charge rate of 0.1C and a charge cut-off voltage of 4.3V, and a discharge rate of 1C and a discharge cut-off voltage of 3V, the capacity retention rate is 80.63%.

[0132] Comparative Example 6:

[0133] The only difference between this comparative example and Example 1 is that the porosity of the negative electrode coating is 60%. Other details are consistent with Example 1, see Table 1.

[0134] The results show that after 20 cycles of constant current charging at a charge rate of 0.1C and a charge cut-off voltage of 4.3V, and a discharge rate of 1C and a discharge cut-off voltage of 3V, the capacity retention rate is 82.98%.

[0135] Table 1 Electrochemical performance of batteries corresponding to each embodiment and comparative example From the results in Table 1, it can be seen that the difference between Example 2 and Example 1 is that the solvent is replaced by DMAC.

[0136] Group First-cycle Coulomb efficiency% Number of cycles Capacity retention rate% Example 1 91.21 20 87.1 Example 2 91.13 17 85.2 Example 3 90.89 20 84.1 Example 4 91.42 20 86.8 Example 5 90.98 19 85.5 Example 6 92.64 31 87.2 Example 7 92.54 30 87.8 Example 8 92.63 25 85.6 Example 9 92.15 26 85.9 Example 10 92.55 53 88.6 Example 11 92.37 35 87.2 Comparative Example 1 90.88 15 76.8 Comparative Example 2 91.05 15 86.4 Comparative Example 3 90.67 15 83.4 Comparative Example 4 91.24 15 86.6 Comparative Example 5 91.54 20 80.63 Comparative Example 6 91.76 20 82.98

[0137] The capacity retention after 17 cycles was lower than that of Example 1 after 20 cycles, indicating that using acetonitrile as a solvent can improve battery performance. Examples 3-5 differ from Example 1 in the polymer matrix or solution mixing ratio. While maintaining essentially the same number of cycles, the capacity retention rates are essentially the same. This result demonstrates that varying the polymer matrix or solution mixing ratio has little impact on battery performance. Compared to Example 1, Examples 6-11 show significant improvements in battery performance, demonstrating that adding an inorganic ceramic solid electrolyte and / or an inert ceramic to the coating can improve battery performance. Compared to Example 6, Example 11 maintains a similar capacity retention rate to Example 6 after 35 cycles. This result demonstrates that the addition of the inert ceramic Al2O3 to Example 6 significantly improves the electrochemical performance of the battery. Example 10, which differs from Example 11 solely by replacing the inert ceramic with SiO2, achieves significantly higher battery performance than Example 11, demonstrating that the combination of the solid electrolyte LLZTO and the inert ceramic SiO2 yields optimal battery performance. In terms of coating thickness and porosity, the coating thicknesses in Comparative Examples 3 and 4 were 2 μm and 4 μm, respectively, and the resulting battery performance was lower than that in Example 1. The porosities in Comparative Examples 5 and 6 were 40% and 60%, respectively, and the resulting battery performance was lower than that in Example 1. Based on the above results, it can be seen that the optimal coating thickness of the present invention is 3 μm, and the optimal porosity is 50%.

[0138] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as a preferred embodiment as above, it is not intended to limit the present invention. Any technician familiar with this profession can make slight changes or modifications to equivalent embodiments of the methods and technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A composite electrolyte negative electrode coating, characterized in that: include: at least one or more polymer fibers; at least one or more polymer matrices; at least one or more inorganic ceramic solid electrolytes; at least one or more lithium salts; as well as at least one or more inert ceramics; The mass ratio of the polymer fiber, the polymer matrix, the inorganic ceramic solid electrolyte, the inert ceramic and the lithium salt is (1-2): (6-7): (1-1.2): (1-1.2): (0.5-1).

2. The composite electrolyte negative electrode coating according to claim 1, characterized in that The polymer fiber is selected from at least one of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer, and aramid fiber.

3. The composite electrolyte negative electrode coating according to claim 1, characterized in that The polymer matrix is selected from at least one of polyethylene oxide, polyacrylonitrile and polymethyl methacrylate.

4. The composite electrolyte negative electrode coating according to claim 1, characterized in that The inorganic ceramic solid electrolyte is selected from at least one of lithium aluminum titanium phosphate, lithium aluminum germanium phosphate, lithium lanthanum zirconium oxide, lithium lanthanum zirconium titanium oxide, and lithium phosphorus sulfur chloride; Optionally, the inorganic ceramic solid electrolyte is lithium lanthanum zirconium titanium oxide.

5. The composite electrolyte negative electrode coating according to claim 1, characterized in that: The lithium salt is selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(trifluoromethylsulfonylamino)imide and lithium bis(fluoromethylsulfonylamino)imide.

6. The composite electrolyte negative electrode coating according to claim 1, characterized in that The inert ceramic is selected from at least one of silicon dioxide, barium titanate, silicon nitride, aluminum oxide, titanium dioxide, and zirconium dioxide; Optionally, the inert ceramic is silicon dioxide.

7. The method for preparing a composite electrolyte negative electrode coating according to any one of claims 1 to 6, characterized in that: The method comprises the following steps: S1: dissolving a lithium salt and a polymer matrix in a first organic solvent to obtain a solution A; dissolving the polymer fiber in a second organic solvent to obtain a solution B; S2: mixing the obtained solution A and solution B to obtain solution C; S3: adding an inorganic ceramic solid electrolyte and an inert ceramic to the obtained solution C, stirring evenly to obtain a mixture; S4: The mixed slurry is coated and dried to obtain the composite electrolyte negative electrode coating.

8. The preparation method according to claim 7, characterized in that In step S1, the first organic solvent is selected from at least one of acetone, N-methyl-2-pyrrolidone, N,N-dimethylformamide, acetonitrile, dimethyl sulfoxide, and dimethylacetamide; the second organic solvent is selected from at least one of acetone, N-methyl-2-pyrrolidone, N,N-dimethylformamide, acetonitrile, dimethyl sulfoxide, and dimethylacetamide; In step S2, the solution A and the solution B are mixed in a volume ratio of 1:1 to 1.2; In step S4, the coating thickness is 1 to 4 μm; the drying conditions are: temperature: 60 to 90° C., time: 48 hours.

9. A negative electrode, characterized in that It comprises a negative electrode current collector and a composite electrolyte negative electrode coating according to any one of claims 1 to 6 or a composite electrolyte negative electrode coating prepared by the preparation method of the composite electrolyte negative electrode coating according to claim 7 or 8, wherein the negative electrode protective layer is arranged on the surface of the negative electrode current collector.

10. A battery, characterized in that: The negative electrode according to claim 9 is included.

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