Preparation process of negative-electrode-free sodium metal battery and negative-electrode-free sodium metal battery

Abstract

The invention provides a preparation process of a negative-electrode-free sodium metal battery and the negative-electrode-free sodium metal battery. The preparation process comprises the following steps: preparing a positive plate; mixing an acrylate monomer, a polyester polymer and an initiator to obtain a first mixture, adding an oxide solid electrolyte, mixing to obtain a second mixture, adding a liquid electrolyte into the second mixture, and mixing to obtain a third mixture; separating the positive plate and the negative current collector by using an isolating membrane, assembling the positive plate and the negative current collector into a naked battery cell, packaging, filling a third mixture, and sealing; and pressurizing and forming after heating polymerization. According to the invention, the solid electrolyte and the negative current collector are compounded, so that the problem of sodium dendrites existing in the negative-electrode-free sodium metal battery can be solved, and the circulation, the rate and the first coulombic efficiency of the negative-electrode-free sodium metal battery can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of material preparation, and in particular to a preparation process of a negative electrode-free sodium metal battery and a negative electrode-free sodium metal battery. Background Art

[0002] As the application of lithium-ion battery technology in consumer electronics, electric vehicles, energy storage and other markets gradually expands, the problem of insufficient lithium resources has also begun to emerge. Sodium-based batteries have gradually attracted attention because the earth has a sufficiently high abundance of sodium elements, and they have an important strategic position in application fields with high cost requirements such as energy storage. The large-scale application of sodium-ion batteries is limited by problems such as low specific capacity of sodium-ion batteries.

[0003] The negative electrode-free sodium metal battery does not have any sodium ion embedding material on the negative electrode side, only the negative electrode current collector, which can work as the negative terminal of the sodium metal battery after the initial charging process, thereby providing a higher operating voltage and significantly improving the volume energy density and mass energy density due to the reduction in battery volume and weight.

[0004] However, there are currently two major problems with negative electrode-free sodium metal batteries: First, due to the limited amount of active sodium in the battery, the SEI film is constantly consuming sodium ions and breaking and rebuilding as the volume of the deposited metallic sodium changes, resulting in extremely rapid capacity decay; second, in the process of repeated embedding and extraction of sodium ions, without the constraints of negative electrode materials, sodium ions are prone to uneven deposition on the current collector, resulting in "dead sodium", which affects the capacity and coulombic efficiency of the negative electrode-free battery.

[0005] Therefore, compared with electrodes with negative electrode active materials, the negative electrode current collector of negative electrode-free sodium metal batteries has a more prominent sodium dendrite growth problem, and the battery has problems such as fast capacity decay and low coulombic efficiency. Therefore, a new negative electrode current collector or negative electrode-free sodium metal battery is urgently needed to meet the needs of high capacity and high safety performance negative electrode-free sodium metal batteries, while further improving sodium dendrites, cycle and coulombic efficiency. Summary of the invention

[0006] The object of the present invention is to provide a preparation process of a negative electrode-free sodium metal battery and a negative electrode-free sodium metal battery, wherein the preparation process can effectively inhibit sodium dendrites and improve the cycle and rate performance of the battery while maintaining the high capacity of the negative electrode-free sodium metal battery.

[0007] To achieve the above object, the present invention provides a preparation process of a negative electrode-free sodium metal battery, comprising the steps of:

[0008] (1) preparing a positive electrode sheet;

[0009] (2) mixing an acrylic acid ester monomer, a polyester polymer and an initiator to obtain a first mixture, adding an oxide solid electrolyte to obtain a second mixture, and adding a liquid electrolyte to the second mixture to obtain a third mixture;

[0010] (3) using a separator to separate the positive electrode sheet and the negative electrode current collector, assembling them into a bare cell and packaging them, injecting the third mixture and sealing them;

[0011] (4) Heat polymerization followed by pressurization.

[0012] In the preparation process of the negative electrode-free sodium metal battery of the present invention, after the heating polymerization reaction, the acrylic ester monomer is polymerized and cross-linked with the polyester polymer to form a skeleton that wraps the oxide solid electrolyte to form an inorganic-organic composite solid electrolyte. After the heating polymerization, the pressurized formation is carried out. Under the action of external pressure, the solid composite solid electrolyte is fully in close contact with the solid negative electrode current collector, which can reduce the interface impedance and avoid the uneven deposition of sodium ions on the negative electrode current collector during repeated embedding and extraction, thereby reducing the loss of sodium ions. In addition, pressurization during formation can control the nucleation shape of sodium metal, enhance orientation, avoid the formation of sodium dendrites and make the deposition more uniform, thereby improving the first coulomb efficiency and capacity of the battery. The oxide solid electrolyte wrapped by the skeleton can improve the conductivity of the solid electrolyte. Therefore, the present invention combines the solid electrolyte and the negative electrode current collector, which can not only solve the sodium dendrite problem existing in the negative electrode-free sodium metal battery, but also improve the cycle, rate and first coulomb efficiency of the negative electrode-free sodium metal battery.

[0013] As a technical solution of the present invention, the acrylic acid ester monomer includes at least one of methyl methacrylate, ethyl methacrylate, methyl acrylate and ethyl acrylate, and the polyester polymer includes polyethylene glycol diacrylate (PEGDA) and / or polypropylene glycol diacrylate (PPGDA).

[0014] As a technical solution of the present invention, the mass ratio of the acrylic ester monomer to the polyester polymer is 1-5:1-5.

[0015] As a technical solution of the present invention, the sum of the masses of the acrylic ester monomer and the polyester polymer is m, the mass of the initiator is n, n / m is 0.001 to 0.010, and the initiator includes at least one of azobisisobutyronitrile, azobisisoheptanenitrile and dimethyl azobisisobutyrate.

[0016] As a technical solution of the present invention, the sum of the masses of the acrylate monomer and the polyester polymer is m, the mass of the oxide solid electrolyte is p, p / m is 0.10-0.50, and the oxide solid electrolyte includes at least one of LLZO, LATP, LAGP and LLTO.

[0017] As a technical solution of the present invention, the mass ratio of the liquid electrolyte to the second mixture is 1-9:1-9.

[0018] As a technical solution of the present invention, the liquid electrolyte includes a sodium salt and a non-aqueous organic solvent, the sodium salt includes at least one of sodium hexafluorophosphate, sodium difluorooxalatoborate, sodium tetrafluoroborate, sodium bisoxalatoborate, sodium perchlorate, sodium hexafluoroarsenate, sodium bis(fluorosulfonyl)imide, sodium trifluoromethylsulfonate and sodium bis(trifluoromethylsulfonyl)imide, and the non-aqueous organic solvent includes at least one of a carbonate, a carboxylate and a lactone.

[0019] As a technical solution of the present invention, the temperature of the heating polymerization is 40 to 90° C. and the time is 6 to 12 hours.

[0020] As a technical solution of the present invention, after the heating polymerization, the reaction mixture is allowed to stand for 36 to 60 hours at 200 to 1200 kPa for chemical formation.

[0021] The second aspect of the present invention provides a negative electrode-free sodium metal battery, comprising a positive electrode sheet, a separator, a negative electrode current collector and a solid electrolyte, wherein the solid electrolyte is at least composited on the surface of the negative electrode current collector. DETAILED DESCRIPTION

[0022] The negative electrode-free sodium metal battery of the present invention comprises a positive electrode sheet, a separator, a negative electrode current collector and a solid electrolyte, wherein the solid electrolyte is at least compounded on the surface of the negative electrode current collector. In other words, the solid electrolyte can be compounded on both surfaces of the separator in addition to being compounded on both surfaces of the negative electrode current collector.

[0023] The positive electrode sheet includes positive electrode active materials, positive electrode conductive agents and positive electrode binders. The positive electrode active materials include α-NaFeO2, NaCoO2, Na 0.7 [Fe 0.7 Mn 0.3 ]O2、Na(Mn 0.25 Fe 0.25 Co 0.25 Ni 0.25 )O2, NaMnO2, Na 0.5 [Fe 1 / 2 Mn 1 / 2 ]O2、Na 0.67 [Fe 1 / 2 Mn 1 / 2]O2, Na[Ni 0.35 Fe 0.40 Mn 0.25 ]O2, Na[Ni 0.30 Fe 0.45 Mn 0.25 ]O2, Na[Ni 0.25 Fe 0.50 Mn 0.25 ]O2, Na[Ni 0.20 Fe 0.55 Mn 0.25 ]O2、Na 0.67 [Mn 0.60 Ni 0.15 Fe 0.25 ]O2、Na[Li 0.05 (Ni 0.25 Fe 0.25 Mn 0.5 ) 0.95 ]O2, Na2FePO4F, Na4Fe2(CN)6, NaNi 0.33 Fe 0.33 Mn 0.33 At least one of O2, NaFePO4, Na2FeP2O7, Na2MnPO4F, NaCoPO4, Na3V2(PO4)3, NaCrO2 and Na2Fe2(SO4)3. The positive electrode active material includes not only the above materials but also the corresponding coating and doping materials. The positive electrode conductive agent includes at least one of conductive carbon black, conductive graphite, carbon fiber, carbon nanotubes and graphene. The positive electrode binder includes polyvinylidene fluoride. The mass ratio of the positive electrode active material, the positive electrode conductive agent and the positive electrode binder can be 90-98:1-5:1-5.

[0024] The separator is not particularly limited and may be polypropylene, polyethylene, paper, glass fiber, fiber resin, non-woven fabric, etc. The negative electrode current collector may be copper foil.

[0025] The solid electrolyte includes a sodium salt and a polymer electrolyte, wherein the polymer electrolyte is formed by polymerizing an acrylate monomer and cross-linking with a polyester polymer to form a skeleton that wraps around an oxide solid electrolyte. The sodium salt includes at least one of sodium hexafluorophosphate, sodium difluorooxalate borate, sodium tetrafluoroborate, sodium bisoxalate borate, sodium perchlorate, sodium hexafluoroarsenate, sodium bis(fluorosulfonyl)imide, sodium trifluoromethylsulfonate and sodium bis(trifluoromethylsulfonyl)imide. The acrylate monomer includes at least one of methyl methacrylate, ethyl methacrylate, methyl acrylate and ethyl acrylate. The polyester polymer includes polyethylene glycol diacrylate and / or polypropylene glycol diacrylate. The oxide solid electrolyte includes at least one of LLZO, LATP, LAGP and LLTO.

[0026] The preparation process of the negative electrode-free sodium metal battery of the present invention comprises the following steps:

[0027] (1) preparing a positive electrode sheet;

[0028] (2) mixing an acrylic acid ester monomer, a polyester polymer and an initiator to obtain a first mixture, adding an oxide solid electrolyte to obtain a second mixture, and adding a liquid electrolyte to the second mixture to obtain a third mixture;

[0029] (3) using a separator to separate the positive electrode sheet and the negative electrode current collector, assembling them into a bare cell and packaging them, injecting the third mixture and sealing them;

[0030] (4) Heat polymerization followed by pressurization.

[0031] In step (1), the positive electrode sheet can be a conventional all-solid-state battery sheet. The positive electrode active material, positive electrode conductive agent and positive electrode binder are mixed to form a positive electrode slurry, which is then coated on an aluminum foil, dried and rolled to obtain a positive electrode sheet. The positive electrode active materials include α-NaFeO2, NaCoO2, Na 0.7 [Fe 0.7 Mn 0.3 ]O2、Na(Mn 0.25 Fe 0.25 Co 0.25 Ni 0.25 )O2, NaMnO2, Na 0.5 [Fe 1 / 2 Mn 1 / 2 ]O2、Na 0.67 [Fe 1 / 2 Mn 1 / 2 ]O2, Na[Ni 0.35 Fe 0.40 Mn 0.25 ]O2, Na[Ni 0.30 Fe 0.45 Mn 0.25 ]O2, Na[Ni 0.25 Fe 0.50 Mn 0.25 ]O2, Na[Ni 0.20 Fe 0.55 Mn 0.25 ]O2、Na 0.67 [Mn 0.60 Ni 0.15 Fe 0.25 ]O2、Na[Li 0.05 (Ni 0.25 Fe 0.25 Mn 0.5 ) 0.95 ]O2, Na2FePO4F, Na4Fe2(CN)6, NaNi0.33 Fe 0.33 Mn 0.33 At least one of O2, NaFePO4, Na2FeP2O7, Na2MnPO4F, NaCoPO4, Na3V2(PO4)3, NaCrO2 and Na2Fe2(SO4)3. The positive electrode active material includes not only the above materials but also the corresponding coating and doping materials. The positive electrode conductive agent includes at least one of conductive carbon black, conductive graphite, carbon fiber, carbon nanotubes and graphene. The positive electrode binder includes polyvinylidene fluoride. The positive electrode slurry is prepared by using NMP as an organic solvent. The mass ratio of the positive electrode active material, the positive electrode conductive agent and the positive electrode binder can be 90-98:1-5:1-5.

[0032] In step (2), the acrylate monomer includes at least one of methyl methacrylate, ethyl methacrylate, methyl acrylate and ethyl acrylate. The polyester polymer includes polyethylene glycol diacrylate (PEGDA) and / or polypropylene glycol diacrylate (PPGDA). The mass ratio of the acrylate monomer to the polyester polymer is 1 to 5:1 to 5. As an example, the mass ratio of the two can be, but is not limited to, 1:1, 1:2, 1:3, 1:4, 1:5, 3:1, 3:2, 3:4, 3:5, 5:1, 5:2, 5:3, 5:4, 2:3, 4:5. The sum of the masses of the acrylic acid ester monomer and the polyester polymer is m, the mass of the initiator is n, n / m is 0.001 to 0.010, and as an example, n / m can be, but not limited to, 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, 0.010. The initiator includes at least one of azobisisobutyronitrile, azobisisoheptanenitrile and dimethyl azobisisobutyrate. The mass of the oxide solid electrolyte is p, and p / m is 0.10 to 0.50. As an example, p / m can be, but not limited to, 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45, 0.50. The oxide solid electrolyte includes at least one of LLZO, LATP, LAGP and LLTO.

[0033] The injected electrolyte includes sodium salt and non-aqueous organic solvent. The sodium salt includes at least one of sodium hexafluorophosphate, sodium difluorooxalate borate, sodium tetrafluoroborate, sodium bisoxalate borate, sodium perchlorate, sodium hexafluoroarsenate, sodium bis(fluorosulfonyl)imide, sodium trifluoromethylsulfonate and sodium bis(trifluoromethylsulfonyl)imide. The non-aqueous organic solvent is selected from at least one of carbonate, carboxylic acid ester and lactone. Specifically, the non-aqueous organic solvent may be, but is not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), pentyl carbonate, vinylene carbonate (VC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), propylene carbonate (PC), butyl acetate (n-Ba), γ-butyrolactone (γ-Bt), propyl propionate (n-PP), ethyl propionate (EP), and ethyl butyrate (Eb). The mass ratio of the liquid electrolyte to the second mixture is 1-9:1-9. As an example, the mass ratio of the two can be but is not limited to 1:1, 1:3, 1:5, 1:7, 1:9, 5:1, 5:3, 5:6, 5:7, 5:9, 9:1, 9:3, 9:5, 9:7, 9:8.

[0034] In step (3), the bare cell may be a wound cell or a laminated cell. The laminated cell is obtained by stacking a negative electrode current collector, a separator and a positive electrode sheet in sequence to obtain a laminate, and then stacking a plurality of laminates. A wound cell can be obtained by winding a single laminate. The bare cell is sealed in a packaging bag, injected with liquid, and sealed to obtain a negative electrode-free sodium metal battery precursor, and then polymerized and formed to form a solid electrolyte composited on the negative electrode current collector in the packaging bag. Since the third mixture is in a fluid state, it fills the inside of the packaging bag after injection, so the solid electrolyte formed after polymerization and formation not only exists on the surface of the negative electrode current collector, but also exists on the surface of the separator and the positive electrode sheet. However, in any case, the solid electrolyte can be composited on the negative electrode current collector. This composite structure not only solves the safety problem caused by the liquid electrolyte, but the presence of the solid electrolyte can also solve the sodium dendrite problem of the negative electrode-free sodium metal battery.

[0035] In step (4), the temperature of heating polymerization is 40-90°C. As an example, the temperature can be, but not limited to, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, and 90°C. The time is 6-12h. As an example, the time can be, but not limited to, 6h, 7h, 8h, 9h, 10h, 11h, and 12h. By heating, the acrylate monomer can be polymerized under the action of the initiator and cross-linked with the polyester polymer to form a skeleton that wraps the oxide solid electrolyte, that is, to form an inorganic-organic composite solid electrolyte. After heating polymerization, it is allowed to stand for 36-60h. As an example, the standing time can be, but not limited to, 36h, 40h, 44h, 48h, 50h, 54h, 58h, and 60h. The formation pressure is 200 to 1200 kPa. As an example, the pressure may be, but is not limited to, 200 kPa, 400 kPa, 600 kPa, 800 kPa, 1000 kPa, and 1200 kPa. The pressurization during formation can make the solid composite solid electrolyte fully and closely contact with the solid negative electrode current collector, thereby reducing the interface impedance and avoiding uneven deposition of sodium ions on the negative electrode current collector during repeated embedding and extraction.

[0036] In order to better illustrate the purpose, technical scheme and beneficial effects of the present invention, the present invention will be further described below in conjunction with specific embodiments. It should be noted that the following implementation method is a further explanation of the present invention and should not be used as a limitation of the present invention.

[0037] Example 1

[0038] This embodiment is a preparation process of a negative electrode-free sodium metal battery, which includes the following steps.

[0039] (1) Preparation of positive electrode

[0040] The maximum charging voltage is 4.2V. 0.25 Fe 0.25 Co 0.25 Ni 0.25 )O2, adhesive PVDF and conductive agent SuperP are evenly mixed in a mass ratio of 95:2:3 to form a positive electrode slurry with a certain viscosity. The mixed positive electrode slurry is coated on both sides of an aluminum foil, and then dried and rolled to obtain a positive electrode sheet.

[0041] (2) Methyl methacrylate and polyethylene glycol diacrylate are mixed in a mass ratio of 2:3, and 0.4 wt.% of azobisisobutyronitrile is added to the mixture to obtain a first mixture, and 45 wt.% of LLZO is added to the mixture to obtain a second mixture, and a liquid electrolyte is added to the second mixture to obtain a third mixture. The mass ratio of the liquid electrolyte to the second mixture is 5:2, the liquid electrolyte is 1M sodium hexafluorophosphate + non-aqueous organic solvent, and the non-aqueous organic solvent is a mixed solvent of EC and EMC in a volume ratio of 2:3.

[0042] (3) Using an isolation film to separate the positive electrode sheet and the copper foil, assembling them into a bare cell and then packaging them, pouring the third mixture and sealing them.

[0043] (4) The battery was polymerized at 75°C for 9 hours, left to stand for 48 hours, and then formed at 800 kPa.

[0044] Example 2

[0045] This embodiment is a preparation process of a negative electrode-free sodium metal battery, which includes the following steps.

[0046] (1) Preparation of positive electrode

[0047] The maximum charging voltage is 4.2V. 0.25 Fe 0.25 Co 0.25 Ni 0.25 )O2, adhesive PVDF and conductive agent SuperP are evenly mixed in a mass ratio of 95:2:3 to form a positive electrode slurry with a certain viscosity. The mixed positive electrode slurry is coated on both sides of an aluminum foil, and then dried and rolled to obtain a positive electrode sheet.

[0048] (2) Methyl methacrylate and polyethylene glycol diacrylate are mixed in a mass ratio of 5:2, and azobisisobutyronitrile accounting for 0.9 wt.% of the total mass of methyl methacrylate and polyethylene glycol diacrylate is added and mixed evenly to obtain a first mixture, and then LLZO accounting for 30 wt.% of the total mass of methyl methacrylate and polyethylene glycol diacrylate is added and mixed evenly to obtain a second mixture, and a liquid electrolyte is added to the second mixture and mixed to obtain a third mixture. The mass ratio of the liquid electrolyte to the second mixture is 8:1, the liquid electrolyte is 1M sodium hexafluorophosphate + non-aqueous organic solvent, and the non-aqueous organic solvent is a mixed solvent of EC and EMC in a volume ratio of 3:1.

[0049] (3) Using an isolation film to separate the positive electrode sheet and the copper foil, assembling them into a bare cell and then packaging them, pouring the third mixture and sealing them.

[0050] (4) The battery was polymerized at 75°C for 9 hours, left to stand for 48 hours, and then formed at 800 kPa.

[0051] Example 3

[0052] This embodiment is a preparation process of a negative electrode-free sodium metal battery, which includes the following steps.

[0053] (1) Preparation of positive electrode

[0054] The maximum charging voltage is 4.2V. 0.25 Fe 0.25 Co 0.25 Ni 0.25 )O2, adhesive PVDF and conductive agent SuperP are evenly mixed in a mass ratio of 95:2:3 to form a positive electrode slurry with a certain viscosity. The mixed positive electrode slurry is coated on both sides of an aluminum foil, and then dried and rolled to obtain a positive electrode sheet.

[0055] (2) Methyl methacrylate and polyethylene glycol diacrylate are mixed in a mass ratio of 1:1, and 0.2 wt.% of azobisisobutyronitrile is added to the mixture to obtain a first mixture, and 50 wt.% of LLZO is added to the mixture to obtain a second mixture, and a liquid electrolyte is added to the second mixture to obtain a third mixture. The mass ratio of the liquid electrolyte to the second mixture is 2:7, the liquid electrolyte is 1M sodium hexafluorophosphate + non-aqueous organic solvent, and the non-aqueous organic solvent is a mixed solvent of EC and EMC in a volume ratio of 2:3.

[0056] (3) Using an isolation film to separate the positive electrode sheet and the copper foil, assembling them into a bare cell and then packaging them, pouring the third mixture and sealing them.

[0057] (4) The battery was polymerized at 75°C for 9 hours, left to stand for 48 hours, and then formed at 800 kPa.

[0058] Example 4

[0059] This embodiment is a preparation process of a negative electrode-free sodium metal battery, which includes the following steps.

[0060] (1) Preparation of positive electrode

[0061] The highest charging voltage is 4.2V. 0.35 Fe 0.40 Mn 0.25]O2, adhesive PVDF and conductive agent SuperP are mixed evenly in a mass ratio of 96:3:1 to form a positive electrode slurry with a certain viscosity. The mixed positive electrode slurry is coated on both sides of the aluminum foil, and then dried and rolled to obtain a positive electrode sheet.

[0062] (2) Ethyl acrylate and polypropylene glycol diacrylate are mixed in a mass ratio of 2:3, 0.4 wt.% of azobisisoheptanenitrile accounting for the total mass of ethyl acrylate and polypropylene glycol diacrylate is added and mixed evenly to obtain a first mixture, and 45 wt.% of LLTO accounting for the total mass of ethyl acrylate and polypropylene glycol diacrylate is added and mixed evenly to obtain a second mixture, and a liquid electrolyte is added to the second mixture and mixed to obtain a third mixture. The mass ratio of the liquid electrolyte to the second mixture is 5:2, the liquid electrolyte is 1M sodium hexafluorophosphate + non-aqueous organic solvent, and the non-aqueous organic solvent is a mixed solvent of EC and EMC in a volume ratio of 2:3.

[0063] (3) Using an isolation film to separate the positive electrode sheet and the copper foil, assembling them into a bare cell and then packaging them, pouring the third mixture and sealing them.

[0064] (4) The battery was polymerized at 75°C for 9 hours, left to stand for 48 hours, and then formed at 800 kPa.

[0065] Example 5

[0066] This embodiment is a preparation process of a negative electrode-free sodium metal battery, which includes the following steps.

[0067] (1) Preparation of positive electrode

[0068] The maximum charging voltage is 4.2V. 0.25 Fe 0.25 Co 0.25 Ni 0.25 )O2, adhesive PVDF and conductive agent SuperP are evenly mixed in a mass ratio of 95:2:3 to form a positive electrode slurry with a certain viscosity. The mixed positive electrode slurry is coated on both sides of an aluminum foil, and then dried and rolled to obtain a positive electrode sheet.

[0069] (2) Methyl methacrylate and polyethylene glycol diacrylate are mixed in a mass ratio of 2:3, and 0.4 wt.% of azobisisobutyronitrile is added to the mixture to obtain a first mixture, and 45 wt.% of LLZO is added to the mixture to obtain a second mixture, and a liquid electrolyte is added to the second mixture to obtain a third mixture. The mass ratio of the liquid electrolyte to the second mixture is 5:2, the liquid electrolyte is 1M sodium hexafluorophosphate + non-aqueous organic solvent, and the non-aqueous organic solvent is a mixed solvent of EC and EMC in a volume ratio of 2:3.

[0070] (3) Using an isolation film to separate the positive electrode sheet and the copper foil, assembling them into a bare cell and then packaging them, pouring the third mixture and sealing them.

[0071] (4) The battery was polymerized at 90°C for 7 hours, left to stand for 40 hours, and then formed at 1000 kPa.

[0072] Comparative Example 1

[0073] This comparative example is a preparation process of a negative electrode-free sodium metal battery, which includes the following steps.

[0074] (1) Preparation of positive electrode

[0075] The maximum charging voltage is 4.2V. 0.25 Fe 0.25 Co 0.25 Ni 0.25 )O2, adhesive PVDF and conductive agent SuperP are evenly mixed in a mass ratio of 95:2:3 to form a positive electrode slurry with a certain viscosity. The mixed positive electrode slurry is coated on both sides of an aluminum foil, and then dried and rolled to obtain a positive electrode sheet.

[0076] (2) Methyl methacrylate and polyethylene glycol diacrylate are mixed in a mass ratio of 2:3, 0.4 wt.% of azobisisobutyronitrile is added to the mixture to obtain a first mixture, and a liquid electrolyte is added to the first mixture to obtain a second mixture. The mass ratio of the liquid electrolyte to the first mixture is 5:2, the liquid electrolyte is 1M sodium hexafluorophosphate + non-aqueous organic solvent, and the non-aqueous organic solvent is a mixed solvent of EC and EMC in a volume ratio of 2:3.

[0077] (3) Using an isolation film to separate the positive electrode sheet and the copper foil, assembling them into a bare cell and then packaging them, pouring the third mixture and sealing them.

[0078] (4) The battery was polymerized at 75°C for 9 hours, left to stand for 48 hours, and then formed at 800 kPa.

[0079] Comparative Example 2

[0080] This comparative example is a preparation process of a negative electrode-free sodium metal battery, which includes the following steps.

[0081] (1) Preparation of positive electrode

[0082] The maximum charging voltage is 4.2V. 0.25 Fe 0.25 Co 0.25 Ni 0.25 )O2, adhesive PVDF and conductive agent SuperP are evenly mixed in a mass ratio of 95:2:3 to form a positive electrode slurry with a certain viscosity. The mixed positive electrode slurry is coated on both sides of an aluminum foil, and then dried and rolled to obtain a positive electrode sheet.

[0083] (2) Methyl methacrylate and polyethylene glycol diacrylate are mixed in a mass ratio of 2:3, and 0.4 wt.% of azobisisobutyronitrile is added to the mixture to obtain a first mixture, and 45 wt.% of LLZO is added to the mixture to obtain a second mixture, and a liquid electrolyte is added to the second mixture to obtain a third mixture. The mass ratio of the liquid electrolyte to the second mixture is 5:2, the liquid electrolyte is 1M sodium hexafluorophosphate + non-aqueous organic solvent, and the non-aqueous organic solvent is a mixed solvent of EC and EMC in a volume ratio of 2:3.

[0084] (3) Using an isolation film to separate the positive electrode sheet and the copper foil, assembling them into a bare cell and then packaging them, pouring the third mixture and sealing them.

[0085] (4) The battery was polymerized at 75°C for 9 hours, left to stand for 48 hours, and then formed at normal pressure.

[0086] The electrochemical performance of the negative electrode-free sodium metal batteries prepared in Examples 1 to 5 and Comparative Examples 1 to 2 was tested under the following test conditions. The test results are shown in Table 1.

[0087] (1) First Coulomb efficiency test

[0088] The negative electrode-free sodium metal battery is subjected to aging, formation, sealing, and capacity division steps according to conventional means, wherein the charging capacity during the formation process is recorded as C1, the charging capacity during the capacity division process is recorded as C2, and the discharge capacity during the capacity division process is recorded as C0.

[0089] First coulomb efficiency = C0 / (C1+C2)×100%

[0090] (2) Normal temperature cycle performance test

[0091] A negative electrode-free sodium metal battery was placed in an environment of 25°C, charged at a constant current of 1C to 4.0V, then charged at a constant voltage to a current of 0.05C, and then discharged at a constant current of 1C to 2.0V. This cycle was repeated for 500 cycles, and the discharge capacity of the first cycle and the last cycle were recorded. The capacity retention rate of the room temperature cycle was calculated according to the following formula.

[0092] Capacity retention rate = discharge capacity of the last cycle / discharge capacity of the first cycle × 100%

[0093] (3) Rate performance test

[0094] The negative electrode-free sodium metal battery was charged to 4.0V at a constant current of 0.5C, then charged to a current of 0.05C at a constant voltage, and then discharged to 2.0V at a constant current, and the discharge capacity was recorded as C0. The battery was then charged to 4.0V using the above method, and then discharged at a current of 3C, and the discharge capacity was recorded as C1.

[0095] Capacity retention rate = C1 / C0*100%

[0096] Table 1 Electrochemical performance test results of Examples 1 to 5 and Comparative Examples 1 to 2

[0097]

[0098] From the results in Table 1, it can be seen that the inorganic-organic composite solid electrolyte formed by polymerizing acrylic monomers and then cross-linking with polyester polymers to form a skeleton that wraps the oxide solid electrolyte can make the prepared negative electrode-free sodium metal battery have higher first coulomb efficiency, cycle performance and rate performance after pressurized formation and composited on the negative electrode current collector. This is because the oxide solid electrolyte wrapped by the skeleton can improve the conductivity of the solid electrolyte, thereby improving the rate performance. After polymerization and pressurized formation, the solid composite solid electrolyte is fully in close contact with the solid negative electrode current collector, which can reduce the interface impedance and avoid the uneven deposition of sodium ions on the negative electrode current collector during repeated insertion and extraction, thereby reducing the loss of sodium ions. In addition, pressurization during formation can control the shape of sodium metal nucleation, enhance orientation, avoid the formation of sodium dendrites and make the deposition more uniform, so the first coulomb efficiency and capacity of the battery can be improved.

[0099] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention is described in detail with reference to the preferred embodiments, it is not limited to those listed in the embodiments. Those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A preparation process for a negative electrode-free sodium metal battery, characterized in that: Includes steps: (1) preparing a positive electrode sheet; (2) mixing an acrylic acid ester monomer, a polyester polymer and an initiator to obtain a first mixture, adding an oxide solid electrolyte to obtain a second mixture, and adding a liquid electrolyte to the second mixture to obtain a third mixture; (3) using a separator to separate the positive electrode sheet and the negative electrode current collector, assembling them into a bare cell and then packaging them, pouring the third mixture and sealing them; (4) Heat polymerization followed by pressurization.

2. The preparation process of the negative electrode-free sodium metal battery according to claim 1, characterized in that: The acrylic acid ester monomer includes at least one of methyl methacrylate, ethyl methacrylate, methyl acrylate and ethyl acrylate, and the polyester polymer includes polyethylene glycol diacrylate and / or polypropylene glycol diacrylate.

3. The preparation process of the negative electrode-free sodium metal battery according to claim 1, characterized in that: The mass ratio of the acrylic ester monomer to the polyester polymer is 1-5:1-5.

4. The preparation process of the negative electrode-free sodium metal battery according to claim 1, characterized in that: The sum of the masses of the acrylic acid ester monomer and the polyester polymer is m, the mass of the initiator is n, n / m is 0.001-0.010, and the initiator includes at least one of azobisisobutyronitrile, azobisisoheptanenitrile and dimethyl azobisisobutyrate.

5. The preparation process of the negative electrode-free sodium metal battery according to claim 1, characterized in that: The sum of the masses of the acrylic ester monomer and the polyester polymer is m, the mass of the oxide solid electrolyte is p, p / m is 0.10-0.50, and the oxide solid electrolyte includes at least one of LLZO, LATP, LAGP and LLTO.

6. The preparation process of the negative electrode-free sodium metal battery according to claim 1, characterized in that: The mass ratio of the liquid electrolyte to the second mixture is 1-9:1-9.

7. The preparation process of the negative electrode-free sodium metal battery according to claim 1, characterized in that: The liquid electrolyte includes a sodium salt and a non-aqueous organic solvent, wherein the sodium salt includes at least one of sodium hexafluorophosphate, sodium difluorooxalatoborate, sodium tetrafluoroborate, sodium bisoxalatoborate, sodium perchlorate, sodium hexafluoroarsenate, sodium bis(fluorosulfonyl)imide, sodium trifluoromethylsulfonate and sodium bis(trifluoromethylsulfonyl)imide, and the non-aqueous organic solvent includes at least one of carbonate, carboxylate and lactone.

8. The process for preparing a negative electrode-free sodium metal battery according to claim 1, characterized in that: The temperature of the heating polymerization is 40 to 90° C., and the time is 6 to 12 hours.

9. The process for preparing a negative electrode-free sodium metal battery according to claim 1, characterized in that: After the heating polymerization, the mixture is allowed to stand for 36 to 60 hours at 200 to 1200 kPa for chemical formation.

10. The negative electrode-free sodium metal battery prepared by the process for preparing a negative electrode-free sodium metal battery according to any one of claims 1 to 9, characterized in that: The invention comprises a positive electrode sheet, a separator, a negative electrode current collector and a solid electrolyte, wherein the solid electrolyte is at least compounded on the surface of the negative electrode current collector.

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