Preparation method of silicon monoxide negative electrode material and external-pressure-free silicon-based solid-state battery

Abstract

The invention provides a preparation method of a silicon monoxide negative electrode material and an external-pressure-free silicon-based solid-state battery, low-volume-expansion silicon monoxide is used as a negative electrode, a polymer solid-state electrolyte with high ionic conductivity is used as an electrolyte, and a positive electrode is combined to finally assemble a soft package battery or a cylindrical battery. And the silicon monoxide negative electrode has a relatively low volume expansion effect and excellent electrode structure stability, so that the cycle life and the stability of the battery are favorably improved. The polymer solid electrolyte shows excellent stress buffering capability in a solid electrolyte system due to low Young modulus and excellent flexibility, and can effectively adapt to volume change of a silicon-based negative electrode in an electrochemical cycle process. The technology can help the silicon-based solid-state battery get rid of dependence on external pressure, and the technology is relatively simple, high in applicability and wide in application value.

Description

Technical Field

[0001] The present application relates to the technical field of lithium batteries, and particularly relates to a method for preparing a silicon suboxide negative electrode material and a non-external-pressure silicon-based solid-state battery thereof. Background Art

[0002] With the breakthrough development of sulfide solid electrolytes, their room-temperature ionic conductivity has been increased to 10 -3 -10 -2 S / cm magnitude, reaching the level of liquid electrolytes. Solid-state batteries based on such electrolytes have high energy density, intrinsic safety (no leakage, non-flammability), and wide-temperature operation characteristics (-20 - 80 °C), and are regarded as the core direction of the next-generation energy storage technology.

[0003] However, the existing sulfide inorganic solid electrolyte system mainly has the following three major technical bottlenecks: First, due to its high elastic modulus (>10 GPa), the contact impedance between the electrode and the electrolyte is large. To ensure close contact at the interface, a forming pressure of at least 50 MPa or more must be applied; second, when matching high specific-capacity negative electrodes (such as silicon-based materials with a theoretical specific capacity of up to 4200 mAh / g and lithium metal negative electrodes with 3860 mAh / g), the volume change of the electrode during the battery cycling process will destroy the interface stability. Therefore, external pressure needs to be applied for a long time to maintain good electrical contact; finally, sulfide all-solid-state batteries rely on expensive external pressure molds, which not only increase the manufacturing cost but also reduce the energy density of the entire system, severely restricting its industrialization process.

[0004] Compared with metal lithium negative electrodes with the risk of lithium dendrite growth (critical current density < 1 mA / cm 2 ), silicon-based negative electrodes fundamentally avoid the problem of lithium dendrite growth due to their alloying reaction mechanism (Li 22 Si5 phase change). However, traditional silicon-based materials still face three technical obstacles: 1) electrode pulverization failure caused by severe volume expansion (pure silicon > 300%); 2) uncontrollable solid electrolyte interface film (SEI) reconstruction process (interface impedance > 200 Ω·cm 2 ); 3) low intrinsic ion diffusion coefficient (D Li + <1×10 - 14 cm 2 / s) resulting in severe polarization. Summary of the Invention

[0005] The present application is made in view of the above problems, and its purpose is to solve the problem that silicon-based all-solid-state batteries in the prior art need to operate under external pressure conditions, and to provide a method for preparing a silicon suboxide negative electrode material and a non-external-pressure silicon-based solid-state battery thereof.

[0006] To achieve the above-mentioned invention object, the first aspect of the present application provides a preparation method of a silicon monoxide negative electrode material, comprising the following steps:

[0007] 1) Raw material treatment: Mix SiO x (0.5 ≤ x ≤ 1.5) powder and metal silicon powder in a molar ratio of 1:0.9 - 1.1, where the purity of SiO x ≥ 99.9%;

[0008] 2) High-temperature synthesis: Under vacuum or inert gas protection, heat up to 1100 - 1500 °C at a rate of 8 - 15 °C / min and hold for 1 - 10 h;

[0009] 3) Quenching treatment: Pass in an inert gas for rapid cooling, and the cooling rate ≥ 100 °C / min;

[0010] 4) Crushing and classification: Obtain a silicon monoxide negative electrode material with particles of 1 - 50 μm through air jet milling.

[0011] In any embodiment, the content of fine powder with particles ≤ 5 μm in the classified silicon monoxide negative electrode material < 10%, the specific surface area is 1 - 20 m 2 / g, and the tapped density ≥ 0.8 g / cm 3 .

[0012] The classified silicon monoxide negative electrode material is subjected to carbon coating or prelithiation treatment. The carbon layer thickness of the carbon-coated silicon monoxide negative electrode material is 1 - 50 nm; the prelithiation degree of the prelithiated silicon monoxide negative electrode material is 10 - 30%.

[0013] In any embodiment, the carbon coating includes vapor deposition coating and solid-phase coating:

[0014] 1) When using the vapor deposition method: The carbon source gas is acetylene or methane gas, the deposition pressure is 10 - 300 Pa, and the deposition temperature is controlled at 800 - 1100 °C;

[0015] 2) When using the solid-phase coating: The carbon precursor is medium-temperature pitch with a softening point of 120 - 180 °C. The carbonization process is divided into two stages: pre-carbonization at 650 - 750 °C for 1 - 5 h and high-temperature carbonization at 950 - 1050 °C for 1 - 5 h;

[0016] The prelithiation is to perform one of the chemical prelithiation method, electrochemical prelithiation method, lithium copper composite tape prelithiation method, and self-discharge prelithiation method on the classified silicon monoxide material or the carbon-coated silicon monoxide material.

[0017] A silicon monoxide negative electrode material-based silicon-based solid-state battery without external pressure, comprising a silicon monoxide negative electrode, a positive electrode, and a polymer solid electrolyte assembled to obtain a silicon-based solid-state battery in the form of a soft-pack battery or a cylindrical battery; the silicon monoxide negative electrode is obtained by wet-coating the electrode and dry-film electrode using the silicon monoxide negative electrode material described in any one of the above to obtain a silicon monoxide negative electrode; the polymer solid electrolyte is a lithium salt-containing electrolyte; the positive electrode is prepared from a positive electrode material.

[0018] In any embodiment, the volume expansion rate of the silicon monoxide negative electrode ≤ 200%, and the room-temperature ionic conductivity of the polymer solid electrolyte ≥ 1×10- 4 S / cm; the battery is assembled under the protection of dry air or an inert atmosphere, at a pressure of 0.5 - 1.2 MPa, and a forming temperature of 25 - 40 °C; the polymer solid electrolyte includes a polymer matrix and a lithium salt, and the molar ratio of the lithium salt to the repeating unit of the polymer matrix is 1:5 - 20, and the polymer matrix is a polymer macromolecule or a polymer monomer molecule; and the polymer solid electrolyte is prepared by a solution casting method, an in-situ polymerization method, a hot pressing method, or an electrospinning method.

[0019] In this application, a polymer macromolecule is used as the matrix, or a polymer monomer molecule is used, and the polymer monomer molecule undergoes an in-situ polymerization reaction during the treatment process to form a polymer macromolecule.

[0020] In any embodiment, the polymer solid electrolyte further includes at least one of a plasticizer, an electrolyte carrier, and a lithium salt additive; the polymer matrix in the polymer solid electrolyte is 25 - 60% of the total mass, the plasticizer is 3 - 60% of the total mass, and the lithium salt additive is 1 - 10% of the total mass. The electrolyte carrier is not included in the total mass calculation.

[0021] The lithium salt additive can stabilize the electrode / solid electrolyte interface, form a good SEI, and help widen the electrochemical window.

[0022] In any embodiment, the polymeric macromolecule is at least one of polyethylene oxide (PEO), polyvinylidene fluoride (PVDF), polyvinylidene fluoride - hexafluoropropylene copolymer (PVDF - HFP), polypropylene carbonate (PPC), polyacrylonitrile (PAN), and polymethyl methacrylate (PMMA); the polymer monomer molecule is at least one of ethylene carbonate (EC), propylene carbonate (PC), vinylene carbonate (VC), 1,3 - dioxolane (DOL), polyethylene glycol diacrylate (PEGDA), and polyethylene glycol diglycidyl ether (PEGDE); the lithium salt is at least one of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium perchlorate (LiClO4); the lithium salt additive is at least one of lithium difluorophosphate (LiPO2F2), lithium difluoro(oxalato)phosphate (LiDFOP), lithium difluoro(oxalato)borate (LiDFOB), lithium nitrate (LiNO3), and lithium tetrafluoroborate (LiBF4); the plasticizer is at least one of succinonitrile (SN), N - methylacetamide (NMA), urea, methyl carbamate (MC), acetamide, trifluoroacetamide (TFA), 1 - ethyl - 3 - methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM - TFSI), and polyethylene glycol dimethyl ether (PEGDME); the electrolyte carrier is at least one of glass fiber separator (GF / A or GF / D), polyimide separator (PI), polyacrylonitrile separator (PAN), and polyvinylidene fluoride separator (PVDF), and the porosity of the electrolyte carrier is 40 - 80%.

[0023] In any embodiment, the positive electrode material is at least one of ternary positive electrode, lithium cobaltate, lithium manganate, lithium iron phosphate, lithium nickel manganate, sulfur positive electrode, and lithium - rich manganese - based material; a coating layer is provided on the surface of the positive electrode material, and the coating layer is at least one of lithium niobate, boron, metal oxide, phosphate, carbon material, conductive polymer, and inorganic oxide solid electrolyte.

[0024] The coating layer can make the interface of the positive electrode material more stable, and the polymer is not easily decomposed, especially at high voltages.

[0025] In any embodiment, the positive electrode or the negative electrode contains the following components in mass percentage: 60 - 95% active material, 1 - 20% conductive agent, 1 - 15% binder, and 3 - 30% solid electrolyte; the tap density of the positive electrode and the negative electrode is controlled at 0.8 - 4 g / cm 3, the rolling temperature is maintained at 50 - 120 °C; the environment for forming the positive electrode or negative electrode is one of an atmospheric environment, a dry air environment, and an inert gas atmosphere environment; the temperature of the atmospheric environment is 15 - 22 °C (average, day-night temperature difference 5 - 8 °C), the humidity is 20% - 60%, and the oxygen is about 21%; the dew point temperature of the dry air environment is lower than -20 °C; the inert gas in the inert gas atmosphere environment is one or more of argon, nitrogen, helium, krypton, and xenon, the dew point temperature is lower than -40 °C, the water content ≤ 20 ppm, the oxygen content ≤ 20 ppm, and the air pressure is maintained at 0.1 - 1.5 atm. The dry air environment is a drying room environment, and the inert gas atmosphere environment is a glove box environment.

[0026] Silicon monoxide in the negative electrode is the active material, the polymer solid electrolyte is the solid electrolyte, conductive carbon black and single-walled carbon nanotubes are the conductive agents, and sodium alginate is the binder; in the positive electrode, LiNi 0.8 Co 0.1 Mn 0.1 O2@B is the active material, the polymer solid electrolyte is the solid electrolyte, conductive carbon black is the conductive agent, and polyvinylidene fluoride is the binder.

[0027] In any embodiment, for the cylindrical battery, the winding forming process is adopted and carried out in a dry air or inert gas environment with a dew point temperature ≤ -40 °C; for the soft-pack battery, the stacking forming process is adopted and completed in a dry air or inert gas environment with a dew point temperature ≤ -40 °C; the inert gas is one or more of argon, nitrogen, helium, krypton, and xenon, the water content ≤ 20 ppm, and the oxygen content ≤ 20 ppm.

[0028] The advantages and beneficial effects of the present invention compared with the prior art are as follows:

[0029] 1) Through the carbon coating and prelithiation technologies, the present invention can obtain a silicon monoxide-based negative electrode material with high initial efficiency, low stress, and long cycle life, thereby improving the cycle stability and energy density of the silicon-based solid-state battery, and having the advantages of simple process, strong universality, and obvious effect. The initial coulombic efficiency of the carbon-coated silicon monoxide-based solid-state full battery can be increased from 60% to 70% or more, and the initial coulombic efficiency of the prelithiated silicon monoxide-based solid-state full battery can be increased to 80% or more.

[0030] 2) Through the collaborative design of the low-expansion silicon monoxide negative electrode and the flexible polymer electrolyte (elastic modulus 0.5 - 5 MPa), the present invention significantly reduces the volume expansion effect of the negative electrode, buffers the stress / strain generated at the interface due to the volume change of the electrode, eliminates the dependence of the silicon-based solid-state battery on the external pressure mold, and realizes the stable operation of the solid-state battery under the condition of no external pressure.

[0031] 3) The present invention proposes a technology of silicon monoxide negative electrode and polymer solid electrolyte, realizing a technical route for atmospheric pressure encapsulation of silicon-based solid-state batteries, and overcoming the challenge that traditional silicon-based solid-state batteries need to rely on external pressure molds in applications. The battery can operate stably in the form of a soft-pack battery or a cylindrical battery, which has important practical significance. Description of the Drawings

[0032] Figure 1 is the X-ray diffraction pattern of the silicon monoxide material in Example 1 of the present invention;

[0033] Figure 2 is the first charge-discharge curve of the full battery of silicon monoxide negative electrode || polymer solid electrolyte || ternary positive electrode in Example 1 of the present invention;

[0034] Figure 3 is the X-ray diffraction pattern of the carbon-coated silicon monoxide material in Example 2 of the present invention;

[0035] Figure 4 is the first charge-discharge curve of the full battery of carbon-coated silicon monoxide negative electrode || polymer solid electrolyte || ternary positive electrode in Example 2 of the present invention;

[0036] Figure 5 is the first 60-cycle capacity graph of the full battery of carbon-coated silicon monoxide composite negative electrode || polymer solid electrolyte || ternary positive electrode in Example 2 of the present invention;

[0037] Figure 6 is the first charge-discharge curve of the full battery of lithium hydride pre-lithiated silicon monoxide negative electrode || polymer solid electrolyte || ternary positive electrode in Example 3 of the present invention;

[0038] Figure 7 is the first 60-cycle capacity graph of the full battery of lithium hydride pre-lithiated silicon monoxide composite negative electrode || polymer solid electrolyte || ternary positive electrode in Example 3 of the present invention;

[0039] Figure 8 is the first charge-discharge curve of the full battery of silicon monoxide negative electrode || polymer solid electrolyte || ternary positive electrode in Comparative Example 1 of the present invention. Detailed Description of the Invention

[0040] Hereinafter, embodiments of a method for preparing a silicon monoxide negative electrode material and a non-external pressure silicon-based solid-state battery of the present application will be specifically described in detail with reference to the accompanying drawings as appropriate. However, there may be cases where unnecessary details are omitted. For example, there may be cases where details of well-known matters are omitted and repeated descriptions of actually identical structures are omitted. This is to prevent the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand the present application and are not intended to limit the subject matter recited in the claims.

[0041] The "range" disclosed in the present application is defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a specific range. The range defined in this way can include or exclude the end values and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 - 120 and 80 - 110 are listed for a specific parameter, ranges of 60 - 110 and 80 - 120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all contemplated: 1 - 3, 1 - 4, 1 - 5, 2 - 3, 2 - 4, and 2 - 5. In the present application, unless otherwise specified, the numerical range "a - b" represents an abbreviated representation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0 - 5" means that all real numbers between "0 - 5" are fully listed herein, and "0 - 5" is only an abbreviated representation of these numerical combinations. Additionally, when a certain parameter is expressed as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0042] If there is no special instruction, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0043] If there is no special instruction, all technical features and optional technical features of the present application can be combined with each other to form a new technical solution.

[0044] Unless otherwise specified, all steps of this application can be carried out sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method can include steps (a) and (b) carried out sequentially, or can also include steps (b) and (a) carried out sequentially. For example, when it is mentioned that the method may further include step (c), it means that step (c) can be added to the method in any order. For example, the method can include steps (a), (b) and (c), or can also include steps (a), (c) and (b), or can also include steps (c), (a) and (b), etc.

[0045] Unless otherwise specified, the terms "comprising" and "including" mentioned in this application mean open-ended, and can also be closed-ended. For example, the "comprising" and "including" can mean that other components not listed can also be included or contained, or can only include or contain the listed components.

[0046] Unless otherwise specified, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) while B is true (or exists); or both A and B are true (or exist).

[0047] Based on the problems faced by traditional silicon-based materials: the low intrinsic ion diffusion coefficient leads to severe polarization, the solid electrolyte interface membrane (SEI) reconstruction process is uncontrollable, and the electrode pulverization failure caused by severe volume expansion. This application studies that the anode with relatively good low-volume expansion materials and the polymer solid electrolyte which is a low-modulus flexible electrolyte alleviate the problems in two aspects; when the two are matched, the interface can buffer the stress / strain of the anode expansion due to the low expansion of the anode and the flexibility of the polymer electrolyte, rather than in the existing solid-state battery with a silicon anode and a sulfide solid electrolyte, where the hard sulfide solid and the expansion of silicon cause the interface to break away due to hard contact. This application fundamentally solves the problem of external pressure dependence.

[0048] This application uses silicon monoxide with a smaller volume expansion rate (<200%) and a more stable electrode structure as the anode, which can not only avoid the problem of lithium dendrite growth in solid-state batteries, but also alleviate the problem of external pressure dependence caused by large volume expansion. Synchronously using an elastic polymer solid electrolyte can adapt to the expansion stress of the silicon anode (Nature Communications, 2024, 15, 2263.). The polymer solid electrolyte has the lowest elastic modulus among various solid electrolytes, excellent flexibility and processing performance, and can avoid the problems of gaps appearing during electrolyte film formation and contact detachment at the electrode interface. Finally, the problem of the dependence of silicon-based solid-state batteries on external pressure is solved.

[0049] An embodiment of the present invention provides a silicon-based solid-state battery without an external pressure mold, and its preparation method is as follows:

[0050] Prepare silicon monoxide as the material, and further improve its performance through carbon coating or prelithiation treatment, and use it as the negative electrode of the silicon-based solid-state battery; select a polymer solid electrolyte containing a lithium salt as the electrolyte of the silicon-based solid-state battery, and enhance its ionic conductivity by introducing a plasticizer, or add a lithium salt additive to broaden its electrochemical window; assemble the above negative electrode, electrolyte material and positive electrode material to prepare a silicon-based solid-state battery in the form of a soft-pack battery or a cylindrical battery.

[0051] The present invention realizes a silicon-based solid-state battery without an external pressure mold by developing a silicon monoxide negative electrode material with high initial efficiency, low stress and long life, and combining a flexible polymer solid electrolyte with a low elastic modulus, so as to solve the problem of the dependence of the current silicon-based solid-state battery on the battery mold.

[0052] Further, the silicon monoxide material can be obtained as the initial silicon monoxide material through high-temperature deposition, pulverization and classification, and can be treated by carbon coating or prelithiation method to obtain carbon-coated silicon monoxide material and prelithiated silicon monoxide material. The silicon monoxide negative electrode not only has a high theoretical specific capacity, a low volume expansion rate and high electrode structure stability, but also has no risk of lithium dendrite growth, and has unique advantages different from silicon negative electrodes and lithium metal negative electrodes; the carbon-coated or prelithiated silicon monoxide material has higher stability and can improve the Coulomb efficiency of the first cycle of the battery.

[0053] Further, the type of the silicon monoxide-based negative electrode is one of a wet-coated electrode and a dry-film electrode. Different electrode preparation methods are different in cost, performance and production process. Selecting a suitable electrode preparation method can better optimize the battery performance.

[0054] Further, the materials for preparing the polymer solid electrolyte include polymer macromolecules or polymer monomer molecules, lithium salts, plasticizers, and electrolyte carriers. The macromolecules polymerized from polymer macromolecules or polymer monomer molecules provide continuous lithium ion transport channels; lithium salts can be used as lithium ion sources and can also enhance the stability of the solid electrolyte; plasticizers can improve the ionic conductivity of the solid electrolyte by reducing the activation energy of polymer chain segment movement; carriers can enhance the mechanical strength of the solid electrolyte and help the solid electrolyte to form. Through a multi-component cooperative regulation strategy, a solid electrolyte with high room-temperature ionic conductivity, a wide electrochemical stability window and excellent mechanical processability can be prepared.

[0055] Further, the method for preparing the polymer solid electrolyte is one of solution casting method, in-situ polymerization method, hot pressing method, and electrospinning method. Different methods for preparing solid electrolytes will result in differences in cost, performance, and production process in the battery system. Therefore, choosing a suitable preparation method is crucial for fully exerting the battery performance.

[0056] Further, the positive electrode system can be composed of an active material matrix and a surface functional modification layer: The positive electrode material is selected from one of ternary positive electrodes, lithium cobaltate, lithium manganate, lithium iron phosphate, lithium nickel manganate, sulfur positive electrode, and lithium-rich manganese-based materials. The surface functional modification layer is a coating layer of one of lithium niobate, amorphous boron-based coating, metal oxide, phosphate, carbon-based conductive network, conjugated polymer, or inorganic solid electrolyte. Different positive electrode materials have certain differences in cost and performance in the battery system. Therefore, choosing a suitable positive electrode material helps to optimize the overall performance of the battery. The surface functional modification layer of the positive electrode can not only improve the stability of the positive electrode material, but also improve the first-cycle Coulomb efficiency and extend the cycle life.

[0057] Further, by assembling the above-mentioned silicon monoxide-based negative electrode, polymer solid electrolyte, and positive electrode material, a silicon-based solid battery with a soft-pack battery structure and a cylindrical battery structure can be prepared. By this method, a silicon-based solid battery with a soft-pack battery structure or a cylindrical structure can be realized without an additional external pressure mold and can operate stably.

[0058] Further, the environment for forming the positive electrode and the negative electrode can be an atmospheric environment, a dry air environment, or an inert gas environment. In a dry air or inert gas environment, the dew point temperature should be lower than -20°C. By controlling the dryness of the atmosphere during the forming process, the side reactions that may be caused by the moisture in the gas during the electrode preparation process can be effectively reduced, thereby improving the stability and life of the electrode.

[0059] Further, the assembly environment of the soft-pack battery or the cylindrical battery should be a dry air or inert gas environment, and the dew point temperature of the environment should be lower than -40°C. During the battery preparation process, it is crucial to control the dryness of the atmosphere. A low dew point gas environment helps to reduce the side reactions caused by the moisture in the gas, thereby improving the overall stability and performance of the battery.

[0060] Examples

[0061] Hereinafter, examples of the present application will be described. The examples described below are exemplary and are only used to explain the present application and should not be construed as a limitation of the present application. For those techniques or conditions not specified in the examples, they shall be carried out according to the techniques or conditions described in the literature in the art or according to the product specifications. For the reagents or instruments not specified for the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0062] Example 1

[0063] In this embodiment, silicon monoxide is prepared using a vacuum high-temperature furnace, and the preparation process is as follows: Mix SiO2 powder (purity > 99.9%, D50 = 2 μm) and Si powder (purity > 99.5%, D50 = 1 μm) in a molar ratio of 1:1, evacuate in a high-temperature furnace, heat up to 1200 °C at a rate of 5 °C / min and hold for 6 h to obtain a silicon monoxide bulk material, and crush it to particles with D50 = 5 - 10 μm using an air-flow crusher (pressure 0.8 MPa). The X-ray diffraction pattern of silicon monoxide is as Figure 1 shown.

[0064] Weigh the following substances by mass ratio: polyethylene oxide (PEO, molecular weight = 600,000): lithium bis(trifluoromethanesulfonyl)imide (LiTFSI, purity 99.99%): lithium difluoro(oxalato)borate (purity 99.9%): succinonitrile (purity 99%) = 60:40:2:100. After weighing the above substances according to the ratio, dissolve and disperse the substances using acetonitrile solvent, stir overnight at 60 °C to form a homogeneous solution. The film preparation method of the polymer solid electrolyte uses the solution casting method, and pour the prepared solution onto a glass fiber separator. Subsequently, the polymer solid electrolyte film is preliminarily dried overnight at 60 °C to remove most of the acetonitrile solvent. Then, the film is further dried in a vacuum oven at 80 °C for 48 h to ensure complete removal of the residual acetonitrile solvent. Finally, the thickness of the completely dried electrolyte film is about 100 μm, and it is stored in a glove box filled with argon.

[0065] The process of preparing a silicon monoxide negative electrode using the wet coating method is as follows: Weigh the following substances by mass ratio: silicon monoxide (SiO): polymer solid electrolyte: conductive carbon black (Super P): single-walled carbon nanotubes (SWCNTs): sodium alginate (SA) = 75:15:2:1:7. After weighing the above substances according to the ratio, mix the substances using a Thinky disperser, and stir for a certain time to obtain a homogeneous slurry. Subsequently, use a scraper to coat the slurry on a copper foil. After coating, first blow-dry the solvent, and then transfer it to a vacuum oven and bake overnight at 120 °C to obtain a silicon monoxide negative electrode.

[0066] The process of preparing a ternary positive electrode using the wet coating method is as follows: Weigh the following substances by mass ratio: boron-coated ternary positive electrode material LiNi 0.8 Co 0.1 Mn 0.1O2@B(NCM811@B): Polymer solid electrolyte: Conductive carbon black (SuperP): Polyvinylidene fluoride (PVDF) = 75:20:3:2. After weighing the above substances according to the ratio, the substances are mixed by a Thinky disperser. After stirring for a certain time, a uniform slurry is obtained. Subsequently, the slurry is coated on a carbon-coated aluminum foil using a doctor blade. After coating, the solvent is first dried by blowing air, and then it is transferred to a vacuum oven and baked overnight at 120 °C to obtain a ternary positive electrode.

[0067] After obtaining the silicon monoxide anode, the polymer solid electrolyte, and the ternary positive electrode, the following operations are carried out in a glove box (the gas atmosphere is argon, and the environmental dew point is lower than -40 °C): Assemble a flexible solid-state battery of silicon monoxide anode || polymer solid electrolyte || ternary positive electrode. The first-cycle charge-discharge curves of the silicon monoxide anode || polymer solid electrolyte || ternary positive electrode battery are as Figure 2 shown. The first-cycle charge capacity is 194.5 mAh / g, the discharge capacity is 132.9 mAh / g, and the first-cycle Coulombic efficiency is 68.3%. The flexible battery works normally in the first cycle, proving that the operation of this battery does not require an external pressure mold.

[0068] Example 2

[0069] In this example, the silicon monoxide is pretreated by the gas-phase carbon coating method to prepare carbon-coated silicon monoxide, and the preparation method is as follows: Place the classified silicon monoxide particles in a chemical vapor deposition furnace, introduce methane gas, and set the deposition temperature and deposition time to 950 °C and 1 h; then naturally cool down to obtain the carbon-coated silicon monoxide material. The X-ray diffraction pattern of the carbon-coated silicon monoxide is as Figure 3 shown. The silicon (111), (220), and (311) crystal plane peaks appear at 2Theta = 28.5°, 47.3°, and 56.2° positions, indicating that the silicon monoxide undergoes a disproportionation reaction at high temperature to form silicon and silicon dioxide.

[0070] The polymer solid electrolyte is prepared by the solution casting method, and its preparation process is the same as that of the polymer solid electrolyte in Example 1 above. The carbon-coated silicon monoxide anode is prepared by the wet coating method, and its preparation process is the same as that of the silicon monoxide anode in Example 1 above, only replacing the silicon monoxide material with the carbon-coated silicon monoxide material. The ternary positive electrode is prepared by the wet coating method, and its preparation process is the same as that of the ternary positive electrode in Example 1 above.

[0071] After obtaining the carbon-coated silicon monoxide anode, polymer solid electrolyte, and ternary cathode, the following operations are carried out in a dry chamber (the gas atmosphere is dry air, and the environmental dew point is lower than -40 °C): Assemble a soft-pack solid-state battery with a carbon-coated silicon monoxide anode || polymer solid electrolyte || ternary cathode. The first-cycle charge-discharge curve of the carbon-coated silicon monoxide anode || polymer solid electrolyte || ternary cathode battery is as Figure 4 shown. The first-cycle charge capacity is 205.6 mAh / g, the discharge capacity is 152.1 mAh / g, and the first-cycle Coulombic efficiency is 74%. The first 60-cycle charge-discharge curve of the full battery is as Figure 5 shown. After 60 cycles, the capacity is still 131.9 mAh / g, showing a high capacity retention rate. Compared with the battery in Example 1, the battery in this example releases more capacity, and at the same time, the first-cycle Coulombic efficiency is also improved, indicating that the carbon coating method improves the conductivity and electrochemical stability of the electrode.

[0072] Example 3

[0073] In this example, silicon monoxide is pretreated in the chemical prelithiation method to prepare lithium hydride prelithiated silicon monoxide. The preparation method is as follows: Lithium hydride and silicon monoxide are mixed according to a mass ratio of lithium hydride: silicon monoxide = 10:100. After mixing, they are placed in a box furnace and heated to 700 °C under a nitrogen atmosphere and held for 1 h to obtain lithium hydride prelithiated silicon monoxide.

[0074] The polymer solid electrolyte is prepared by the solution casting method, and its preparation process is the same as that of the polymer solid electrolyte in Example 1 above. The lithium hydride prelithiated silicon monoxide anode is prepared by the wet coating method, and its preparation process is the same as that of the silicon monoxide anode in Example 1 above, except that the silicon monoxide material is replaced with the lithium hydride prelithiated silicon monoxide material. The ternary cathode is prepared by the wet coating method, and its preparation process is the same as that of the ternary cathode in Example 1 above.

[0075] After obtaining the lithium hydride prelithiated silicon monoxide anode, polymer solid electrolyte, and ternary cathode, the following operations are carried out in a dry chamber (the gas atmosphere is dry air, and the environmental dew point is lower than -40 °C): Assemble a soft-pack solid-state battery with a lithium hydride prelithiated silicon monoxide anode || polymer solid electrolyte || ternary cathode. The first-cycle charge-discharge curve of the lithium hydride prelithiated silicon monoxide anode || polymer solid electrolyte || ternary cathode battery is as Figure 6 shown. The first-cycle charge capacity is 210.3 mAh / g, the discharge capacity is 174.2 mAh / g, and the first-cycle Coulombic efficiency is 82.8%. The first 60-cycle charge-discharge curve of the full battery is as Figure 7As shown, after 60 cycles, the capacity is still 146.8 mAh / g, with a relatively high capacity retention rate. Compared with the battery in Example 2, the battery in this example has a higher reversible capacity, and at the same time, the Coulombic efficiency of the first cycle is also significantly improved, indicating that the prelithiation method solves the problem of low Coulombic efficiency of the first cycle of the silicon suboxide electrode.

[0076] Comparative Example 1

[0077] In this Comparative Example 1, the plasticizer component of the polymer solid electrolyte will be reduced to compare the performance of solid-state batteries at different conductivities. The preparation method of the polymer solid electrolyte is the same as that of the polymer solid electrolyte in Example 1 above, and only the mass ratio of substances needs to be adjusted. The mass ratio is as follows: Polyethylene oxide (PEO, molecular weight = 600,000): Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI, purity 99.99%): Lithium difluoro(oxalato)borate (purity 99%): Succinonitrile (purity 99%) = 60:40:2:11. Other operations are the same as in Example 1. The first-cycle charge-discharge curve of the silicon suboxide negative electrode || polymer solid electrolyte || ternary positive electrode battery is as Figure 8 shown. The first-cycle charge capacity is 193.9 mAh / g, the discharge capacity is 123.5 mAh / g, the first-cycle Coulombic efficiency is 63.7%, and there is obvious polarization in the voltage curve. This result shows that too low conductivity of the solid electrolyte will significantly reduce the battery performance.

[0078] Example 1 is the silicon suboxide after grading; Comparative Example 1 uses a polymer solid electrolyte with a low content of succinonitrile, has a lower conductivity, and the assembled battery has obvious electrochemical polarization and releases less capacity.

[0079] Example 2 is carbon-coated silicon suboxide, which enhances the conductivity of silicon suboxide, improves the interface, and to a certain extent, the carbon coating layer reduces the expansion of silicon suboxide, can improve the Coulombic efficiency of the first cycle, and improve the battery cycling performance; Example 3 is the prelithiated silicon suboxide material, which completely solves the problem of low Coulombic efficiency of the first cycle of silicon suboxide and improves the energy density of the battery.

[0080] It should be noted that this application is not limited to the above embodiments. The above embodiments are only examples, and embodiments with the same structure and the same effect as the technical idea within the technical solution scope of this application are included in the technical scope of this application. In addition, within the scope of not departing from the main idea of this application, various deformations that those skilled in the art can think of are applied to the embodiments, and other ways constructed by combining some constituent elements in the embodiments are also included in the scope of this application.

Claims

1. A method for preparing a silicon oxide negative electrode material, characterized in that: The following steps are involved: 1) Raw material processing: SiO x (0.5≤x≤1.5) powder and metal silicon powder are mixed in a molar ratio of 1:0.9-1.1, wherein SiO x Purity ≥99.9%; 2) High temperature synthesis: under vacuum or inert gas protection, heat up to 1100-1500℃ at 8-15℃ / min and keep warm for 1-10h; 3) Rapid cooling: Rapid cooling by passing inert gas, cooling rate ≥ 100℃ / min; 4) Crushing and classification: The silicon oxide negative electrode material with particles of 1-50 μm is obtained by air flow crushing.

2. The method for preparing a silicon oxide negative electrode material according to claim 1, characterized in that: The content of fine powder with particles ≤5 μm in the classified silicon oxide negative electrode material is less than 10%, and the specific surface area is 1-20 m 2 / g, tap density ≥0.8g / cm 3 . The graded silicon 2 oxide negative electrode material is subjected to carbon coating or pre-lithiation treatment, the carbon layer thickness of the carbon-coated silicon 2 oxide negative electrode material is 1-50 nm; the pre-lithiation degree of the pre-lithiation silicon 2 oxide negative electrode material is 10-30%.

3. The method for preparing a silicon oxide negative electrode material according to claim 1, characterized in that: The carbon coating includes vapor deposition coating and solid phase coating: 1) When the vapor deposition method is used: the carbon source gas is acetylene or methane gas, the deposition pressure is 10-300 Pa, and the deposition temperature is controlled at 800-1100°C; 2) When solid phase coating is used: the carbon precursor is medium temperature asphalt with a softening point of 120-180°C, and the carbonization process is divided into two stages: pre-carbonization at 650-750°C for 1-5h and high temperature carbonization at 950-1050°C for 1-5h; The pre-lithiation is to subject the graded silicon dioxide material or carbon-coated silicon dioxide material to one of chemical pre-lithiation, electrochemical pre-lithiation, lithium-copper composite belt pre-lithiation and self-discharge pre-lithiation.

4. A silicon-based solid-state battery without external pressure having a silicon iodine negative electrode material, comprising a silicon iodine negative electrode sheet, a positive electrode and a polymer solid electrolyte assembled to obtain a silicon-based solid-state battery in the form of a soft-pack battery or a cylindrical battery; the silicon iodine negative electrode is obtained by wet coating an electrode and a dry thin film electrode using the silicon iodine negative electrode material according to any one of claims 1 to 3; the polymer solid electrolyte is a lithium salt-containing electrolyte; the positive electrode is prepared from the positive electrode material.

5. The external pressure-free silicon-based solid-state battery according to claim 4, characterized in that: The volume expansion rate of the silicon oxide negative electrode is ≤200%, and the room temperature ionic conductivity of the polymer solid electrolyte is ≥1×10- 4 S / cm; the battery is assembled under the protection of dry air or inert atmosphere, at a pressure of 0.5-1.2MPa and a molding temperature of 25-40°C; the polymer solid electrolyte comprises a polymer matrix and a lithium salt, wherein the molar ratio of the lithium salt to the polymer matrix is ​​1:5-20, and the polymer matrix is ​​a polymer macromolecule or a polymer monomer molecule; and the polymer solid electrolyte is prepared by solution casting, in-situ polymerization, hot pressing or electrospinning.

6. The non-external pressure silicon-based solid-state battery according to claim 4 or 5, characterized in that: The polymer solid electrolyte also includes at least one of a plasticizer, an electrolyte carrier and a lithium salt additive; in the polymer solid electrolyte, the polymer matrix accounts for 25-60% of the total mass, the plasticizer accounts for 3-60% of the total mass, and the lithium salt additive accounts for 1-10% of the total mass.

7. The non-external pressure silicon-based solid-state battery according to claim 6, characterized in that: The polymer macromolecule is at least one of polyethylene oxide (PEO), polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polypropylene carbonate (PPC), polyacrylonitrile (PAN), and polymethyl methacrylate (PMMA); the polymer monomer molecule is at least one of ethylene carbonate (EC), propylene carbonate (PC), vinylene carbonate (VC), 1,3-dioxolane (DOL), polyethylene glycol diacrylate (PEGDA), and polyethylene glycol diglycidyl ether (PEGDE); the lithium salt is at least one of lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium bisfluorosulfonyl imide (LiFSI), and lithium perchlorate (LiClO4); the lithium salt additive is lithium difluorophosphate (Li The invention relates to a novel nanostructured carbon nanotube film, wherein the nanostructured carbon nanotube film is selected from the group consisting of lithium phosphate (PO2F2), lithium difluorobis(oxalate) phosphate (LiDFOP), lithium difluorooxalate borate (LiDFOB), lithium nitrate (LiNO3) and lithium tetrafluoroborate (LiBF4); the plasticizer is selected from the group consisting of succinonitrile (SN), N-methylacetamide (NMA), urea, methyl carbamate (MC), acetamide, trifluoroacetamide (TFA), 1-ethyl-3-methylimidazole bis(trifluoromethanesulfonyl)imide salt (EMIM-TFSI) and polyethylene glycol dimethyl ether (PEGDME); the electrolyte carrier is selected from the group consisting of glass fiber membrane (GF / A or GF / D), polyimide membrane (PI), polyacrylonitrile membrane (PAN) and polyvinylidene fluoride membrane (PVDF), and the porosity of the electrolyte carrier is 40-80%.

8. The non-external pressure silicon-based solid-state battery according to claim 4, characterized in that: The positive electrode material is at least one of a ternary positive electrode, lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, lithium nickel manganese oxide, a sulfur positive electrode, and a lithium-rich manganese-based material; the surface of the positive electrode material is provided with a coating layer, and the coating layer is at least one of lithium niobate, boron, metal oxide, phosphate, carbon material, conductive polymer, and inorganic oxide solid electrolyte.

9. The non-external pressure silicon-based solid-state battery according to claim 4, characterized in that: The positive electrode or negative electrode comprises the following components in percentage by weight: 60-95% active material, 1-20% conductive agent, 1-15% binder and 3-30% solid electrolyte; the compaction density of the positive electrode and the negative electrode is controlled at 0.8-4g / cm 3 , the rolling temperature is maintained at 50-120°C; the environment for forming the positive electrode or the negative electrode is one of an atmospheric environment, a dry air environment, and an inert atmosphere environment; the dew point temperature of the dry air environment and the inert atmosphere environment is lower than -20°C, the inert gas is one or more of argon, nitrogen, helium, krypton and xenon, the water content is ≤20ppm, the oxygen content is ≤20ppm, and the air pressure is maintained at 0.1-1.5atm.

10. The non-external pressure silicon-based solid-state battery according to claim 4, characterized in that: The cylindrical battery adopts a winding molding process in a dry air or inert gas environment with a dew point temperature of ≤-40°C; the soft-pack battery adopts a stacking molding process in a dry air or inert gas environment with a dew point temperature of ≤-40°C; the inert gas is one or more of argon, nitrogen, helium, krypton and xenon, the water content is ≤20ppm, and the oxygen content is ≤20ppm.

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