Sodium-ion battery composite negative plate, preparation method thereof and sodium-ion battery

Abstract

The invention discloses a sodium-ion battery composite negative plate, a preparation method thereof and a sodium-ion battery. The sodium-ion battery composite negative plate is a composite negative plate of which the outer surface is provided with an Al2O3 protective layer after pre-sodium treatment. According to the composite negative plate of the sodium-ion battery, pre-sodium treatment and surface functionalization treatment can be efficiently realized by utilizing the synergistic effect of the pre-sodium treatment of the negative electrode and the coating of the protective layer, and the first efficiency, the energy density and the intrinsic safety of the sodium-ion battery are improved.

Description

Technical Field

[0001] The present application relates to the technical field of sodium ion batteries, and more specifically, to a sodium ion battery composite negative electrode sheet and a preparation method thereof, and a sodium ion battery. Background Art

[0002] The abundance of sodium in the Earth's crust is 2.64%, far higher than the 0.0065% of lithium. It is also widely distributed and simple to extract. Furthermore, because metallic sodium does not form a eutectic alloy with metallic aluminum, inexpensive aluminum foil can be used for both the positive and negative current collectors, replacing the more expensive copper negative current collector in lithium batteries. Therefore, sodium-ion batteries have the advantage of low cost. Furthermore, sodium-ion batteries have a high internal resistance, generate less heat during a short circuit, and have a low temperature rise. They exhibit high stability in tests such as overcharge, over-discharge, short circuit, needle puncture, and extrusion, thus offering the advantage of high safety. Furthermore, sodium-ion batteries utilize materials with more stable physical properties in their electrolyte and electrode materials, performing well within an operating temperature range of -40°C to 80°C. At -20°C, the capacity retention rate can reach 80%, significantly better than the 60% to 70% of lithium batteries. Sodium-ion batteries have the advantage of excellent low-temperature performance.

[0003] It can be seen that sodium-ion batteries are expected to be widely used in the future due to their rich sodium resource reserves and relatively low costs.

[0004] However, no matter what negative electrode material is used in sodium-ion batteries, the formation of the SEI film requires the consumption of a portion of the sodium ions from the positive electrode, affecting the capacity of the positive electrode material, such as the irreversible loss of active sodium caused during the charging and discharging process of the sodium-ion battery. Summary of the Invention

[0005] One purpose of the present application is to provide a composite negative electrode sheet for a sodium ion battery, which can at least solve the technical problem of irreversible active sodium loss caused by the sodium ion battery during the charge and discharge process in the prior art.

[0006] Another object of the present application is to provide a method for preparing a composite negative electrode sheet for a sodium ion battery, which can be used to prepare the above-mentioned composite negative electrode sheet for a sodium ion battery.

[0007] Another object of the present application is to provide a sodium ion battery, comprising the above-mentioned sodium ion battery composite negative electrode sheet, or comprising a sodium ion battery composite negative electrode sheet prepared according to the preparation method of the above-mentioned sodium ion battery composite negative electrode sheet.

[0008] In order to achieve the above objectives, this application provides the following technical solutions.

[0009] According to the sodium ion battery composite negative electrode sheet of the first embodiment of the present application, the composite negative electrode sheet is a pre-sodiumized negative electrode sheet; an Al2O3 protective layer is provided on the surface of the pre-sodiumized negative electrode sheet.

[0010] Optionally, the mass content of the Al2O3 protective layer is 5%-10%.

[0011] According to the second aspect of the present application, the preparation method of the composite negative electrode sheet of a sodium ion battery includes the following steps: S1, respectively mixing the negative electrode material with a conductive agent, a binder and a solvent, and preparing the negative electrode sheet of the sodium ion battery through coating and drying; S2, soaking the negative electrode sheet prepared in step S1 in a liquid pre-sodiumization reagent for pre-sodiumization, with a reaction time of 5 minutes to 20 minutes, rinsing the soaked negative electrode sheet with an ether solvent, and placing it in a vacuum oven until it is completely dried to obtain a pre-sodiumized negative electrode sheet; S3, mixing Al2O3 and PVDF to obtain a powder, adding a small molecule solvent, stirring and mixing to obtain a protective layer slurry; S4, evenly coating the protective layer slurry prepared in step S3 on the pre-sodiumized negative electrode sheet prepared in step S2, and then drying and rolling to obtain a finished composite negative electrode sheet.

[0012] Optionally, the negative electrode material in step S1 includes at least one of hard carbon, soft carbon, graphite, titanium-based material, and P / C; and / or the conductive agent includes at least one of carbon black, conductive graphite, VGCF, carbon nanotubes, and graphene; and / or the binder includes at least one of PI, PVDF, SBR, CMC, PPC, PEO, PVB, and PAA; and / or the solvent includes at least one of deionized water, NMP, ethanol, and DMC.

[0013] Optionally, the liquid phase pre-sodiumization reagent in step S2 is a PAHs-Na-ether pre-sodiumization agent; and / or, the ether solvent is ethylene glycol dimethyl ether or tetraethylene glycol dimethyl ether.

[0014] Optionally, the weight ratio of Al2O3 to PVDF in the powder is 8:2; the weight ratio of the small molecule solvent to the powder is 9:1.

[0015] Optionally, the small molecule solvent is NMP or NEP; and / or the mass content of the small molecule solvent is 90-95%.

[0016] Optionally, in the liquid-phase pre-sodiumization reagent, the mass of sodium powder accounts for 0% to 3% of the mass of the liquid-phase pre-sodiumization reagent.

[0017] Optionally, during pre-sodiumization, the mass of sodium supplement per unit area is 0.02 mg / cm 2 ~0.15mg / cm 2, the drying temperature is 80℃~120℃.

[0018] The sodium ion battery according to the third embodiment of the present application includes any of the above-mentioned sodium ion battery composite negative electrode sheets, or includes a sodium ion battery composite negative electrode sheet prepared according to any of the above-mentioned methods for preparing a sodium ion battery composite negative electrode sheet.

[0019] According to the sodium ion battery composite negative electrode sheet of the embodiment of the present application, the method of pre-sodiumization of the negative electrode and coating of the Al2O3 protective layer can be used to achieve pre-sodiumization of the negative electrode of the sodium ion battery and preparation of the negative electrode protective layer. On the one hand, the negative electrode can be compensated for the irreversible active sodium loss caused by the battery charging and discharging process by pre-sodiumization; on the other hand, the Al2O3 protective layer effectively inhibits the decomposition of the electrolyte, thereby achieving high ICE and cycle stability. At the same time, the Al2O3 protective layer reduces the interface resistance and voltage drop, thereby increasing the reversible capacity; on the other hand, the synergistic effect of the negative electrode pre-sodiumization and the Al2O3 protective layer slurry can be used to achieve pre-sodiumization of the negative electrode of the sodium ion battery and in-situ preparation of the negative electrode protective layer.

[0020] Other features and advantages of the present application will become apparent from the following detailed description of exemplary embodiments of the present application with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the application and, together with the description, serve to explain the principles of the application.

[0022] Figure 1 is a comparison chart of power-off data according to the embodiment of the present application and the comparative example; Figure 2 It is a comparison chart of the capacity retention rates of the examples and comparative examples of the present application. DETAILED DESCRIPTION

[0023] Various exemplary embodiments of the present application will now be described in detail with reference to the accompanying drawings. It should be noted that unless otherwise specifically stated, the relative arrangements of components and steps, numerical expressions and numerical values ​​set forth in these embodiments do not limit the scope of the present application.

[0024] The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the present disclosure, its application, or uses.

[0025] Technologies, methods, and equipment known to ordinary technicians in the relevant art may not be discussed in detail, but where appropriate, the technologies, methods, and equipment should be considered part of the specification.

[0026] In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not limiting. Therefore, other examples of the exemplary embodiments may have different values.

[0027] It should be noted that like reference numerals and letters refer to like items in the following figures, and therefore, once an item is defined in one figure, it need not be further discussed in subsequent figures.

[0028] The following describes in detail the sodium ion battery composite negative electrode sheet according to the embodiment of the present application with reference to the accompanying drawings.

[0029] According to the embodiment of the present application, the composite negative electrode sheet of the sodium ion battery is a pre-sodiumized negative electrode sheet; an Al2O3 protective layer is provided on the surface of the pre-sodiumized negative electrode sheet.

[0030] That is to say, the negative electrode sheet is first pre-sodiumized, the pre-sodiumized negative electrode sheet is used as a matrix, and then an Al2O3 protective layer is set on the surface of the pre-sodiumized negative electrode sheet.

[0031] It is understandable that, on the one hand, sodium metal has natural advantages as the negative electrode of sodium ion batteries. The theoretical specific capacity of metallic sodium is 1166mAh / g, and the irreversible loss of active sodium caused by the battery charging and discharging process can be compensated by pre-sodiumization of the negative electrode; on the other hand, the Al2O3 protective layer effectively inhibits the decomposition of the electrolyte, thereby achieving high ICE and cycle stability. At the same time, the Al2O3 protective layer reduces the interface resistance and voltage drop, thereby increasing the reversible capacity; on the other hand, the synergistic effect of the negative electrode pre-sodiumization and the Al2O3 protective layer slurry can be utilized to achieve the pre-sodiumization of the negative electrode of the sodium ion battery and the in-situ preparation of the negative electrode protective layer.

[0032] Therefore, the sodium ion battery composite negative electrode sheet according to the embodiment of the present application can not only compensate for the irreversible loss of active sodium caused by the battery charging and discharging process, but also achieve high ICE and cycle stability, and there is a synergistic effect between the Al2O3 protective layer and the negative electrode pre-sodiumization.

[0033] According to one embodiment of the present application, the mass content of the Al2O3 protective layer is 5%-10%, for example, the mass content of the Al2O3 protective layer is 5%, 6%, 7%, 8%, 9%, 9.5% or 10%, etc. The use of the Al2O3 protective layer with the above content is beneficial to reducing the interface resistance and voltage drop while ensuring the proportion of the negative electrode active material in the negative electrode sheet. When making the Al2O3 protective layer, Al2O3 and PVDF can be mixed to obtain a powder, and then N-methylpyrrolidone is added to mix. At this time, the mass content of the Al2O3 protective layer is 10%. .

[0034] The present application also discloses a method for preparing a composite negative electrode sheet for a sodium ion battery, comprising the following steps: first, pre-sodiumizing the negative electrode sheet of the sodium ion battery to obtain a pre-sodiumized negative electrode sheet; second, providing an Al2O3 protective layer on the surface of the pre-sodiumized negative electrode sheet.

[0035] That is to say, the negative electrode sheet is first pre-sodiumized, and then an Al2O3 protective layer is provided on the surface. For example, the negative electrode sheet is first pre-sodiumized by liquid phase pre-sodiumization technology, and the liquid phase pre-sodiumization reagent is coated on the negative electrode sheet, and the pre-sodiumized negative electrode sheet is obtained after drying; then, the slurry containing the Al2O3 protective layer is evenly coated on the pre-sodiumized negative electrode sheet, dried, and rolled to obtain a finished composite negative electrode sheet.

[0036] Therefore, according to the preparation method of the sodium ion battery composite negative electrode sheet of the embodiment of the present application, the method of pre-sodiumization of the negative electrode and coating of the Al2O3 protective layer can be used to achieve the pre-sodiumization of the negative electrode of the sodium ion battery and the preparation of the negative electrode protective layer.

[0037] According to one embodiment of the present application, a composite negative electrode sheet for a sodium ion battery mainly includes the following steps: S1. The negative electrode material is uniformly mixed with a conductive agent, a binder, and a solvent, and the mixture is coated and dried to prepare a negative electrode sheet for a sodium ion battery. For example, when preparing the negative electrode sheet, the negative electrode material is uniformly mixed with a conductive agent, a binder, and a solvent, and the mixture is coated and dried to prepare the negative electrode sheet for a sodium ion battery. The above steps for preparing the negative electrode sheet have advantages such as ease of operation and improved production efficiency.

[0038] S2. Soak the negative electrode sheet prepared in step S1 in a liquid pre-sodiumization reagent for pre-sodiumization, with a reaction time of 5 minutes to 20 minutes. Rinse the soaked negative electrode sheet with an ether solvent and place it in a vacuum oven until completely dried to obtain a pre-sodiumized negative electrode sheet. For example, soak the prepared electrode sheet in a PAHs-Na-ether pre-sodiumization reagent for pre-sodiumization, with a reaction time of 5 minutes to 20 minutes. Then, rinse the soaked working electrode with an ether solvent and place it in a vacuum oven at 80°C until completely dried to obtain a pre-sodiumized negative electrode.

[0039] S3. Al2O3 and PVDF are mixed to obtain a powder, a small molecule solvent is added, and the mixture is stirred and mixed until uniformly mixed to obtain a protective layer slurry. That is, when providing an Al2O3 protective layer on the surface of a pre-sodiumized negative electrode sheet, the protective layer slurry can be first prepared by dissolving a certain amount of Al2O3 in a volatile small molecule solvent, such as N-ethylpyrrolidone or N-methylpyrrolidone, and fully dissolving to prepare a mixed solution. The small molecule solvent has a small molecular weight, for example, less than 500 g / mol, and is easy to disperse and volatilize.

[0040] S4. The protective layer slurry prepared in step S3 is evenly coated on the pre-sodiumized negative electrode sheet prepared in step S2, and then dried and rolled to obtain a finished composite negative electrode sheet.

[0041] In addition, in step S2, the negative electrode sheet can be pre-sodiumized by liquid-phase pre-sodiumization technology, and the liquid-phase pre-sodiumization reagent can be applied to the negative electrode sheet. In this embodiment, the liquid-phase pre-sodiumization technology belongs to the chemical pre-sodiumization method, which refers to the use of a strong reducing chemical sodiumization reagent to chemically supplement the sodium-ion battery negative electrode sheet. The liquid-phase pre-sodiumization technology has the advantages of controllable pre-sodiumization degree, conducive to the formation of a uniform SEI film, improved battery performance, universal applicability to a variety of sodium-ion battery negative electrode materials, simple and efficient process, etc.

[0042] In this embodiment, an Al2O3 protective layer is provided on the surface of the pre-sodiumized negative electrode sheet in the above manner, which has the advantages of easy operation and improved uniformity of the protective layer.

[0043] In some specific embodiments of the present application, the negative electrode material in step S1 includes at least one of hard carbon, soft carbon, graphite, titanium-based materials, and P / C (phosphorus / carbon composite materials); and / or the conductive agent includes at least one of carbon black, conductive graphite, VGCF, carbon nanotubes, and graphene; and / or the binder includes at least one of PI (polyimide), PVDF, SBR, CMC, PPC, PEO, PVB, and PAA; and / or the solvent includes at least one of deionized water, NMP, ethanol, and DMC. As can be seen, the material selection range of the embodiments of the present application is relatively broad and has universal applicability.

[0044] According to one embodiment of the present application, the liquid-phase pre-sodiumization reagent in step S2 is a PAHs-Na-ether pre-sodiumization agent, which has the advantage of good sodium replenishment; and / or the ether solvent is ethylene glycol dimethyl ether or tetraethylene glycol dimethyl ether, which has the advantages of good cleaning effect and high efficiency. In addition, in this embodiment, the pre-sodiumization method of immersing the negative electrode sheet in the PAHs-Na-ether pre-sodiumization agent has the advantages of convenient operation and conducive to the formation of a uniform artificial SEI film.

[0045] In some specific embodiments of the present application, the weight ratio of Al2O3 to PVDF in the powder is 8:2, which facilitates the formation of a uniform Al2O3 protective layer and can ensure reduced interfacial resistance and voltage drop. The weight ratio of the small molecule solvent to the powder is 9:1, which can improve the uniformity and stability of the protective layer slurry.

[0046] According to one embodiment of the present application, the small molecule solvent is NMP (N-methyl-2-pyrrolidone) or NEP (N-ethylpyrrolidone); and / or, the mass content of the small molecule solvent is 90%-95%, for example, the mass content of the small molecule solvent is 90%, 91%, 92%, 93%, 94% or 95%, etc. In this embodiment, the use of the above-mentioned type and content of small molecule solvents is conducive to forming a protective layer slurry with better dispersion stability.

[0047] In some specific embodiments of the application, in liquid phase pre-sodiumization reagent, the quality of sodium powder is 0%~3% of the quality of liquid phase pre-sodiumization reagent.For example, the quality of sodium powder is 0%, 0.5%, 0.8%, 1.0%, 1.2%, 1.5%, 1.8%, 2.0%, 2.5% or 3.0% etc. of the quality of liquid phase pre-sodiumization reagent, by adopting above-mentioned quality proportion, be conducive to controlling pre-sodiumization efficiency.In addition, it is understandable that, when the quality of sodium powder is 0%, sodium powder is not separately added in liquid phase pre-sodiumization reagent.

[0048] According to one embodiment of the present application, during pre-sodiumization, the mass of sodium supplement per unit area is 0.02 mg / cm 2 ~0.15mg / cm 2 ; and / or, the drying temperature is 80°C to 120°C. In this embodiment, during pre-sodiumization, the mass of sodium supplement per unit area is 0.02 mg / cm 2 ~0.15mg / cm 2 For example, the mass of sodium per unit area is 0.02 mg / cm 2 , 0.05mg / cm 2 , 0.08mg / cm 2 , 0.10mg / cm 2 , 0.11mg / cm 2 , 0.12mg / cm 2 or 0.15 mg / cm 2 Etc., which can effectively compensate for the sodium content lost due to cycle failure; the drying temperature is 80℃, 82℃, 85℃, 90℃, 95℃, 100℃, 110℃ or 120℃, etc., which can avoid waste of resources under the premise of sufficient drying.

[0049] The present application also discloses a sodium ion battery, comprising the sodium ion battery composite negative electrode sheet of any of the above embodiments, or comprising a sodium ion battery composite negative electrode sheet prepared according to the preparation method of the sodium ion battery composite negative electrode sheet of any of the above embodiments.

[0050] For example, a sodium ion battery composite negative electrode can be produced by the following preparation process.

[0051] S1. Preparation of negative electrode sheet The negative electrode material, conductive agent and binder were mixed in a homogenizer at a mass ratio of 8:1:1 and processed for 10 min to 15 min to obtain a uniform electrode slurry, which was then scraped onto an aluminum foil current collector and transferred to an 80°C to 120°C forced air drying oven for drying for 8 h to 12 h to obtain a negative electrode sheet.

[0052] In step S1, the negative electrode material of the sodium ion battery includes at least one of traditional sodium ion battery negative electrode materials such as hard carbon, soft carbon, graphite, titanium-based materials, P / C, etc., and the binder includes at least one of PI, PVDF, SBR, CMC, PPC, PEO, PVB, PAA, etc.

[0053] S2. Pre-sodium treatment of negative electrode sheets The prepared electrode is immersed in a PAHs-Na-ether pre-sodiumization agent for pre-sodiumization, and the reaction time is 5 min to 20 min.

[0054] The soaked working electrode was rinsed clean with ether solvent and placed in a vacuum oven at 80°C until completely dried to obtain a pre-sodiumized negative electrode.

[0055] In the liquid phase pre-sodiumization reagent of step S2, the mass of sodium powder accounts for 0% to 3% of the mass of the slurry. In addition, during pre-sodiumization, the mass of sodium supplemented per unit area is 0.02 mg / cm 2 ~0.15mg / cm 2 , the drying temperature is 80℃~100℃.

[0056] Preparation of S3 and Al2O3 solution A certain amount of Al2O3 and a binder are dissolved in a volatile small molecule solvent and fully dissolved to prepare a mixed solution.

[0057] In step S3, the mass content of Al2O3 is 5% to 10%; the mass content of the small molecule solvent is 90% to 95%.

[0058] S4. Apply the mixed solution on the pre-sodiumized negative electrode sheet and dry it to obtain a sodium ion battery composite negative electrode sheet.

[0059] S5. Assemble the composite negative electrode sheet, glass fiber separator and metallic sodium into a two-electrode system in a CR2032 button battery and conduct electrochemical performance testing.

[0060] Among them, 1M sodium hexafluorophosphate (NaPF) was dissolved in ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) (EC / EMC / DMC=1, vol. %) as the electrolyte.

[0061] Moreover, the entire battery assembly process is carried out in an anhydrous and oxygen-free inert gas glove box (water and oxygen content are <0.01ppm respectively).

[0062] The sodium ion battery composite negative electrode prepared according to the preparation method of the sodium ion battery composite negative electrode sheet of the embodiment of the present application can not only compensate for the irreversible active sodium loss caused by the battery charging and discharging process by pre-sodiumization of the negative electrode, but also effectively inhibit the decomposition of the electrolyte through the Al2O3 protective layer, thereby achieving high ICE and cycle stability, reducing the interface resistance and voltage drop, and thus increasing the reversible capacity.

[0063] The sodium ion battery composite negative electrode sheet and its preparation method, and the sodium ion battery of the embodiment of the present application are described in detail below in conjunction with specific implementation methods.

[0064] Example 1 (1) Preparation of negative electrode sheet The hard carbon material, conductive agent (SP) and binder (CMC and SBR) were mixed in a homogenizer at a mass ratio of 8:1:1 and processed for 15 minutes to obtain a uniform electrode slurry, which was then scraped onto an aluminum foil current collector and transferred to a 110°C forced air drying oven for drying for 12 hours to obtain a negative electrode sheet, which was then cut into circular electrode sheets with a diameter of 10 mm.

[0065] Among them, the formula of the negative electrode sheet is: the mass contents of hard carbon material, conductive agent, CMC and SBR are 80%, 10%, 5% and 5% respectively.

[0066] (2) Pre-sodium treatment of negative electrode sheets The electrode was immersed in 4-methoxybiphenyl-Na-tetraethylene glycol dimethyl ether pre-sodiumization agent for pre-sodiumization, and the reaction time was 5 minutes.

[0067] The soaked working electrode was rinsed with ethylene glycol dimethyl ether and placed in a vacuum oven at 80° C. until completely dried to obtain a pre-sodiumized negative electrode sheet.

[0068] (3) Preparation of protective layer slurry Al2O3 and PVDF were mixed in a weight ratio of 8:2 to obtain a powder, N-methylpyrrolidone was added (the weight ratio of N-methylpyrrolidone to the powder was 9:1), and the mixture was stirred and mixed to obtain a protective layer slurry.

[0069] (4) Apply protective layer The protective layer slurry was coated on the pre-sodiumized negative electrode sheet and dried at 80°C. The coating amount of the protective liquid was controlled to be 0.1 mg / cm 2 , and obtain a sodium ion battery composite negative electrode sheet.

[0070] (5) Assemble the buckle A composite negative electrode sheet, glass fiber separator, and sodium metal were assembled into a two-electrode system in a CR2032 button cell for electrochemical performance testing. The electrolyte consisted of 1M sodium hexafluorophosphate (NaPF) dissolved in ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) (EC / EMC / DMC = 1, vol. %). The entire battery assembly process was performed in an anhydrous and oxygen-free inert gas glove box (water and oxygen contents < 0.01 ppm, respectively).

[0071] (6) Assembling soft pack batteries According to the general preparation method of sodium-ion batteries, a sodium-layered oxide positive electrode system (positive electrode: binder: conductive agent = 94%:3%:3%), conventional sodium-ion battery electrolyte, separator, etc. are assembled into a monolithic soft-pack battery; and conventional testing equipment is used for testing.

[0072] Example 2 (1) Preparation of negative electrode sheet The soft carbon material, conductive agent (SP) and binder (CMC, SBR) were mixed in a homogenizer at a mass ratio of 8:1:1 and processed for 15 minutes to obtain a uniform electrode slurry, which was then scraped onto an aluminum foil current collector and transferred to a 110°C forced air drying oven for drying for 12 hours to obtain a negative electrode sheet, which was then cut into circular electrode sheets with a diameter of 10 mm.

[0073] Among them, the formula of the negative electrode sheet is: the mass contents of soft carbon material, conductive agent, CMC, and SBR are 80%, 10%, 5%, and 5% respectively.

[0074] (2) Pre-sodium treatment of negative electrode sheets The electrode was immersed in 4-methoxybiphenyl-Na-tetraethylene glycol dimethyl ether pre-sodiumization agent for pre-sodiumization, and the reaction time was 10 minutes.

[0075] The soaked working electrode was rinsed with ethylene glycol dimethyl ether and placed in a vacuum oven at 80° C. until completely dried to obtain a pre-sodiumized negative electrode sheet.

[0076] (3) Preparation of protective layer slurry Al2O3 and PVDF were mixed in a weight ratio of 8:2 to obtain a powder, N-methylpyrrolidone was added (the weight ratio of N-methylpyrrolidone to the powder was 9:1), and the mixture was stirred and mixed to obtain a protective layer slurry.

[0077] (4) Apply protective layer The protective layer slurry was coated on the pre-sodiumized negative electrode sheet and dried at 80°C. The coating amount of the protective liquid was controlled to be 0.2 mg / cm 2 , and obtain a sodium ion battery composite negative electrode sheet.

[0078] (5) Assemble the buckle A two-electrode system composed of a composite anode sheet, a glass fiber separator, and sodium metal was assembled in a CR2032 button cell for electrochemical performance testing. The electrolyte consisted of 1M sodium hexafluorophosphate (NaPF) dissolved in ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) (EC / EMC / DMC = 1, vol. %). The entire battery assembly process was performed in an anhydrous and oxygen-free inert gas glove box (water and oxygen contents <0.01 ppm, respectively).

[0079] (6) Assembling soft pack batteries Following the general sodium-ion battery preparation method, a sodium-ion layered oxide cathode system (cathode: binder: conductive agent = 94%:3%:3%), conventional sodium-ion battery electrolyte, and separator were assembled into a monolithic soft-pack battery. Testing was performed using conventional testing equipment.

[0080] Example 3 (1) Preparation of negative electrode sheet The P / C material, conductive agent (SP) and binder (CMC and SBR) were mixed in a homogenizer at a mass ratio of 8:1:1 and processed for 15 minutes to obtain a uniform electrode slurry, which was then scraped onto an aluminum foil current collector and transferred to a 110°C forced air drying oven for drying for 12 hours to obtain a negative electrode sheet, which was then cut into circular electrode sheets with a diameter of 10 mm.

[0081] Among them, the formula of the negative electrode sheet is: the mass contents of P / C material, conductive agent, CMC and SBR are 80%, 10%, 5% and 5% respectively.

[0082] (2) Pre-sodium treatment of negative electrode sheets The electrode was immersed in 4-methoxybiphenyl-Na-tetraethylene glycol dimethyl ether pre-sodiumization agent for pre-sodiumization, and the reaction time was 15 minutes.

[0083] The soaked working electrode was rinsed with ethylene glycol dimethyl ether and placed in a vacuum oven at 80° C. until completely dried to obtain a pre-sodiumized negative electrode sheet.

[0084] (3) Preparation of protective layer slurry Al2O3 and PVDF were mixed in a weight ratio of 8:2 to obtain a powder, N-methylpyrrolidone was added (the weight ratio of N-methylpyrrolidone to the powder was 9:1), and the mixture was stirred and mixed to obtain a protective layer slurry.

[0085] (4) Apply protective layer The protective layer slurry was coated on the pre-sodiumized negative electrode sheet and dried at 80°C. The coating amount of the protective liquid was controlled to be 0.2 mg / cm 2 , and obtain a sodium ion battery composite negative electrode sheet.

[0086] (5) Assemble the buckle A two-electrode system composed of a composite anode sheet, a glass fiber separator, and sodium metal was assembled in a CR2032 button cell for electrochemical performance testing. The electrolyte consisted of 1M sodium hexafluorophosphate (NaPF) dissolved in ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) (EC / EMC / DMC = 1, vol. %). The entire battery assembly process was performed in an anhydrous and oxygen-free inert gas glove box (water and oxygen contents <0.01 ppm, respectively).

[0087] (6) Assembling soft pack batteries According to the general preparation method of sodium-ion batteries, a sodium-layered oxide positive electrode system (positive electrode: binder: conductive agent = 94%:3%:3%), conventional sodium-ion battery electrolyte, separator, etc. are assembled into a monolithic soft-pack battery; and conventional testing equipment is used for testing.

[0088] Example 4 (1) Graphite material, conductive agent (SP) and binder (CMC and SBR) were mixed in a homogenizer at a mass ratio of 8:1:1 and processed for 15 minutes to obtain a uniform electrode slurry. The slurry was then scraped onto an aluminum foil current collector and transferred to a 110°C forced air drying oven for 12 hours to obtain a negative electrode sheet. The electrode sheet was cut into a circular electrode sheet with a diameter of 10 mm.

[0089] Among them, the formula of the negative electrode sheet is: the mass content of graphite material, conductive agent, CMC and SBR are 80%, 10%, 5% and 5% respectively.

[0090] (2) Pre-sodium treatment of negative electrode sheets The electrode was immersed in 4-methoxybiphenyl-Na-tetraethylene glycol dimethyl ether pre-sodiumization agent for pre-sodiumization, and the reaction time was 20 minutes.

[0091] The soaked working electrode was rinsed with ethylene glycol dimethyl ether and placed in a vacuum oven at 80° C. until completely dried to obtain a pre-sodiumized negative electrode sheet.

[0092] (3) Preparation of protective layer slurry Al2O3 and PVDF were mixed in a weight ratio of 8:2 to obtain a powder, N-methylpyrrolidone was added (the weight ratio of N-methylpyrrolidone to the powder was 9:1), and the mixture was stirred and mixed to obtain a protective layer slurry.

[0093] (4) Apply protective layer The protective layer slurry was coated on the pre-sodiumized negative electrode sheet and dried at 80°C. The coating amount of the protective liquid was controlled to be 0.2 mg / cm 2 , and obtain a sodium ion battery composite negative electrode sheet.

[0094] (5) Assemble the buckle A two-electrode system composed of a composite anode sheet, a glass fiber separator, and sodium metal was assembled in a CR2032 button cell for electrochemical performance testing. The electrolyte consisted of 1M sodium hexafluorophosphate (NaPF) dissolved in ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) (EC / EMC / DMC = 1, vol. %). The entire battery assembly process was performed in an anhydrous and oxygen-free inert gas glove box (water and oxygen contents <0.01 ppm, respectively).

[0095] (6) Assembling soft pack batteries According to the general preparation method of sodium ion batteries, a sodium layered oxide positive electrode system (positive electrode: binder: conductive agent = 94%: 3%: 3%), conventional sodium ion battery electrolyte, separator, etc. are assembled into a single-chip soft-pack battery; conventional testing equipment is used for testing. control group (1) The hard carbon negative electrode material, conductive agent (SP) and binder (CMC and SBR) were mixed in a homogenizer at a mass ratio of 8:1:1 and processed for 15 minutes to obtain a uniform electrode slurry. The slurry was then scraped onto an aluminum foil current collector and transferred to a 110°C forced air drying oven for 12 hours to obtain a negative electrode sheet. The electrode sheet was cut into a circular electrode sheet with a diameter of 10 mm.

[0096] Among them, the formula of the negative electrode sheet is: the mass content of negative electrode material, conductive agent, CMC and SBR are 80%, 10%, 5% and 5% respectively.

[0097] (2) Assemble the buckle A two-electrode system composed of a composite anode sheet, a glass fiber separator, and sodium metal was assembled in a CR2032 button cell for electrochemical performance testing. The electrolyte consisted of 1M sodium hexafluorophosphate (NaPF) dissolved in ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) (EC / EMC / DMC = 1, vol. %). The entire battery assembly process was performed in an anhydrous and oxygen-free inert gas glove box (water and oxygen contents <0.01 ppm, respectively).

[0098] (3) Assembling soft pack batteries According to the general preparation method of sodium-ion batteries, a sodium-layered oxide positive electrode system (positive electrode: binder: conductive agent = 94%:3%:3%), conventional sodium-ion battery electrolyte, separator, etc. are assembled into a monolithic soft-pack battery; and conventional testing equipment is used for testing.

[0099] The test results of the above embodiments and comparative examples are shown in Table 1 below.

[0100] Table 1 Through Table 1 and Figure 1 It can be seen that at a current density of 0.1 A / g, the single negative electrode in the control group has a lower charge and discharge platform and an initial efficiency of 87.9%. After the negative electrode sheets in Examples 1 to 4 are compounded, the ICE of the negative electrode is significantly increased to 92%, and the charge and discharge platform does not change significantly.

[0101] In addition, according to Table 1 and Figure 2 It can be seen that after 150 cycles, the capacity retention rate is increased from 84% to 98%, indicating that after the composite treatment in Examples 1 to 4, the negative electrode has better cycle stability and effectively reduces the irreversible capacity during the first discharge process.

[0102] In summary, according to the sodium ion battery composite negative electrode sheet and its preparation method of the embodiment of the present application, the method of pre-sodiumization of the negative electrode and coating of the Al2O3 protective layer can be utilized, and the synergistic effect of pre-sodiumization of the negative electrode and coating of the protective layer is also utilized, which not only realizes the pre-sodiumization of the sodium ion battery negative electrode and the preparation of the negative electrode protective layer, but also improves the initial efficiency, energy density and intrinsic safety of the sodium ion battery. In addition, the preparation method of the sodium ion battery composite negative electrode sheet of the embodiment of the present application can also adopt liquid phase pre-sodiumization technology, which can efficiently realize pre-sodiumization and surface functionalization treatment, and has the advantages of uniform and controllable reaction, and easy industrial preparation.

[0103] Although some specific embodiments of the present application have been described in detail by way of examples, it should be understood by those skilled in the art that the above examples are for illustration only and are not intended to limit the scope of the present application. It should be understood by those skilled in the art that the above embodiments may be modified without departing from the scope and spirit of the present application. The scope of the present application is defined by the appended claims.

Claims

1. A composite negative electrode sheet for a sodium ion battery, characterized in that: The composite negative electrode sheet is a pre-sodiumized negative electrode sheet; an Al2O3 protective layer is provided on the surface of the pre-sodiumized negative electrode sheet.

2. The sodium ion battery composite negative electrode sheet according to claim 1, characterized in that: The mass content of the Al2O3 protective layer is 5%-10%.

3. A method for preparing a composite negative electrode sheet for a sodium ion battery, characterized in that: The following steps are involved: S1. Mixing the negative electrode material with the conductive agent, the binder and the solvent respectively, and coating and drying to obtain a negative electrode sheet for a sodium ion battery; S2. Soaking the negative electrode sheet prepared in step S1 in a liquid pre-sodiumization reagent for pre-sodiumization for a reaction time of 5 min to 20 min, rinsing the soaked negative electrode sheet with an ether solvent, and placing it in a vacuum oven until completely dried to obtain a pre-sodiumized negative electrode sheet; S3, mixing Al2O3 and PVDF to obtain a powder, adding a small molecule solvent, stirring and mixing uniformly to obtain a protective layer slurry; S4. The protective layer slurry prepared in step S3 is evenly coated on the pre-sodiumized negative electrode sheet prepared in step S2, and then dried and rolled to obtain a finished composite negative electrode sheet.

4. The method for preparing a composite negative electrode sheet for a sodium ion battery according to claim 3, wherein: The negative electrode material in step S1 includes at least one of hard carbon, soft carbon, graphite, titanium-based material, and P / C; and / or, The conductive agent includes at least one of carbon black, conductive graphite, VGCF, carbon nanotubes and graphene; and / or, The binder includes at least one of PI, PVDF, SBR, CMC, PPC, PEO, PVB, and PAA; and / or The solvent includes at least one of deionized water, NMP, ethanol, and DMC.

5. The method for preparing a composite negative electrode sheet for a sodium ion battery according to claim 3, wherein: The liquid phase pre-sodiumization reagent in step S2 is a PAHs-Na-ether pre-sodiumization agent; and / or the ether solvent is ethylene glycol dimethyl ether or tetraethylene glycol dimethyl ether.

6. The method for preparing a composite negative electrode sheet for a sodium ion battery according to claim 3, wherein: The weight ratio of Al2O3 to PVDF in the powder is 8:2; the weight ratio of the small molecule solvent to the powder is 9:

1.

7. The method for preparing a composite negative electrode sheet for a sodium ion battery according to claim 3, wherein: The small molecule solvent is NMP or NEP; and / or the mass content of the small molecule solvent is 90%-95%.

8. The method for preparing a composite negative electrode sheet for a sodium ion battery according to claim 3, wherein: In the liquid-phase pre-sodiumization reagent, the mass of the sodium powder accounts for 0% to 3% of the mass of the liquid-phase pre-sodiumization reagent.

9. The method for preparing a composite negative electrode sheet for a sodium ion battery according to any one of claims 3 to 8, characterized in that: During pre-sodiumization, the sodium mass per unit area is 0.02 mg / cm 2 ~0.15mg / cm 2 , and / or, the drying temperature is 80℃~120℃.

10. A sodium ion battery, characterized in that: The invention relates to a sodium ion battery composite negative electrode sheet according to claim 1 or 2, or a sodium ion battery composite negative electrode sheet prepared by the method for preparing a sodium ion battery composite negative electrode sheet according to any one of claims 3 to 9.

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