Preparation process of composite current collector, composite current collector and negative electrode-free sodium metal battery

Abstract

The application provides a preparation process of a composite current collector, a composite current collector and a sodium metal battery without negative electrode. The preparation process of the composite current collector comprises the following steps: mixing aromatic diamine, acrylic ester monomer and polyester polymer, then adding an initiator, and further adding a graphene solution to obtain a polymer solution; performing hydrothermal reaction on the polymer solution to obtain a three-dimensional porous flowable gel; and compositing the three-dimensional porous flowable gel on the current collector to obtain the composite current collector. In the preparation process, the aromatic diamine and the acrylic ester monomer are polymerized under the action of the initiator and the hydrothermal reaction, and the obtained polymer serves as a horizontal and vertical skeleton, the polyester polymer serves as an interlayer crosslinking agent, and the graphene serves as a sheet skeleton, so that the three-dimensional porous flowable gel can be composited on the current collector. The three-dimensional porous flowable gel can improve the specific capacity performance and the cycle performance of the sodium metal battery without negative electrode.

Description

Preparation process of composite current collectors, composite current collectors and sodium metal batteries without negative electrodes Technical Field

[0001] This invention relates to the field of materials preparation technology, and in particular to a preparation process of a composite current collector, the composite current collector, and a sodium metal battery without a negative electrode. Background Technology

[0002] As lithium-ion battery technology expands its application in consumer electronics, electric vehicles, and energy storage, the problem of insufficient lithium resources is becoming increasingly prominent. Sodium-based batteries are gaining attention due to the Earth's sufficiently high sodium abundance and hold a strategically important position in cost-sensitive applications such as energy storage. However, the low specific capacity of sodium-ion batteries limits their large-scale application.

[0003] In contrast, the sodium metal battery without a negative electrode has no sodium ion intercalation material on the negative electrode side, only a negative electrode current collector. After the initial charging process, it can work as the negative terminal of the sodium metal battery, thereby providing a higher operating voltage and significantly improving the volumetric energy density and gravimetric energy density due to the reduction in battery volume and weight.

[0004] However, sodium metal batteries without a negative electrode currently face two main problems: First, due to the limited amount of active sodium in the battery, the SEI film is constantly consuming sodium ions and undergoing rupture and reconstruction due to the volume change of deposited sodium metal, resulting in extremely rapid capacity decay. Second, during the repeated insertion and extraction of sodium ions, without the constraint of a negative electrode material, sodium ions tend to exhibit an uneven deposition pattern on the current collector, resulting in "dead sodium," which affects the capacity utilization and coulombic efficiency of the battery without a negative electrode.

[0005] Therefore, compared to electrodes with negative electrode active materials, sodium metal-free batteries suffer from more prominent sodium dendrite growth issues in their negative electrode current collectors, leading to problems such as rapid capacity decay and low coulombic efficiency. Thus, there is an urgent need for a new negative electrode current collector or a sodium metal-free battery to meet the demands for high-capacity and high-safety performance while further improving sodium dendrite growth, cycle life, and coulombic efficiency. Summary of the Invention

[0006] The purpose of this invention is to provide a preparation process for a composite current collector, a composite current collector, and a negative electrode-free sodium metal battery. This composite current collector can effectively suppress sodium dendrites and, while maintaining the high capacity of the negative electrode-free sodium metal battery, can also improve the cycle performance and coulombic efficiency of the battery.

[0007] To achieve the above objectives, the present invention provides a process for preparing a composite current collector, comprising the following steps:

[0008] (1) Mix aromatic diamine, acrylate monomers and polyester polymers, add initiator, and then add graphene solution to obtain polymer solution;

[0009] (2) The polymer solution is subjected to a hydrothermal reaction to obtain a three-dimensional porous flowable gel;

[0010] (3) The three-dimensional porous fluid gel is composited onto the current collector to obtain a composite current collector.

[0011] In the preparation process of this invention, the polymer obtained by polymerizing aromatic diamines and acrylate monomers under the action of an initiator and hydrothermal reaction serves as the horizontal and vertical framework, the polyester polymer serves as the interlayer crosslinking agent, and graphene serves as the sheet framework, thereby composite a three-dimensional porous flowable gel on the current collector. The three-dimensional porous structure of the three-dimensional porous flowable gel can control the deposition size of sodium metal on the current collector, thereby suppressing its uneven deposition morphology and avoiding the generation of dead sodium. The graphene distributed in the three-dimensional porous structure has high mechanical properties and can suppress the volume change of deposited metallic sodium to prevent breakage during cycling. Therefore, the formed three-dimensional porous flowable gel can improve the specific capacity and cycle performance of a negative electrode-less sodium metal battery. The preparation process of the composite current collector provided by this invention is simple, highly feasible, and easy to realize for industrial production.

[0012] As one technical solution of the present invention, the aromatic diamine includes at least one of o-phenylenediamine, m-phenylenediamine and p-phenylenediamine, the acrylate 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).

[0013] As one technical solution of the present invention, the mass ratio of the aromatic diamine, the acrylate monomer and the polyester polymer is 1-5:1:4-10.

[0014] As one technical solution of the present invention, the sum of the masses of the aromatic diamine, the acrylate 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.

[0015] As one technical solution of the present invention, the sum of the masses of the aromatic diamine, the acrylate monomer and the polyester polymer is m, the mass of the graphene solution is p, p / m is 0.01 to 0.10, and the graphene solution is an aqueous solution with a graphene mass concentration of 3 to 10 mg / ml.

[0016] As one technical solution of the present invention, the temperature of the hydrothermal reaction is 70-100°C and the time is 5-15 hours.

[0017] As a technical solution of the present invention, the porosity of the three-dimensional porous fluid gel is 40-75%, and the viscosity is 5000-15000 cp.s.

[0018] As a technical solution of the present invention, the composite includes first extruding or coating onto the current collector and then hot pressing, wherein the hot pressing temperature is 250-450°C, the pressure is 100-300 MPa, and the hot pressing time is 5-30 seconds.

[0019] The second aspect of the present invention provides a composite current collector prepared by the aforementioned composite current collector preparation process, comprising a copper foil and a gel layer composited on the copper foil, wherein the thickness of the gel layer is 1 to 10 μm.

[0020] A third aspect of the present invention provides a negative electrode-free sodium metal battery, comprising a composite current collector, a separator and a positive electrode sheet stacked sequentially, wherein the composite current collector is a composite current collector prepared by the aforementioned composite current collector preparation process or the aforementioned composite current collector. Detailed Implementation

[0021] The composite current collector of this invention can be applied to sodium metal batteries without negative electrodes. It is applicable to both wound-type and stacked-type sodium metal batteries without negative electrodes. The sodium metal battery without negative electrodes comprises a composite current collector, a separator, and a positive electrode sheet stacked sequentially. These components are overlapped to form a laminate. Multiple laminates can be stacked to obtain a cell for a stacked sodium metal battery without negative electrodes, while a single laminate can be wound to obtain a cell for a wound sodium metal battery without negative electrodes. Sealing the cell in a packaging bag and filling it with electrolyte yields the sodium metal battery without negative electrodes.

[0022] The positive electrode can be a conventional solid-state battery electrode. It is prepared by mixing positive electrode active materials, positive electrode conductive agents, and positive electrode binders to form a positive electrode slurry, which is then coated onto aluminum foil, dried, and rolled to obtain the positive electrode sheet. Positive electrode active materials include α-NaFeO2, NaCoO2, and 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 / 2O2, 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 their 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 using NMP as the organic solvent. The mass ratio of the positive electrode active material, positive electrode conductive agent, and positive electrode binder can be 90–98:1–5:1–5.

[0023] There are no particular restrictions on the type of separator; it can be made of polypropylene, polyethylene, paper, glass fiber, fiber resin, non-woven fabric, etc.

[0024] The injected electrolyte comprises a sodium salt and a non-aqueous organic solvent. The sodium salt includes at least one of sodium hexafluorophosphate, sodium difluorooxalate borate, sodium tetrafluoroborate, sodium dioxalate borate, sodium perchlorate, sodium hexafluoroarsenate, sodium bis(fluorosulfonyl)imide, sodium trifluoromethanesulfonate, and sodium bis(trifluoromethanesulfonyl)imide. The non-aqueous organic solvent is selected from at least one of carbonate organic solvents, carboxylic acid ester organic solvents, and ether organic solvents. Specifically, the non-aqueous organic solvent may be, but is not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), amyl carbonate, vinyl carbonate (VC), dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), propylene carbonate (PC), butyl acetate (n-Ba), propyl propionate (n-PP), ethyl propionate (EP), ethyl butyrate (Eb), ethylene glycol dimethyl ether (DME), ethylene glycol diethyl ether (ECS), diethylene glycol dimethyl ether (DEGME), triethylene glycol dimethyl ether (TEGDME), tetraethylene glycol dimethyl ether (TEGDME), 1,3-dioxolane (DOL), tetrahydrofuran (THF), methyltetrahydrofuran (MTHF), diphenyl ether, and crown ether (CE).

[0025] The composite current collector includes a copper foil and a gel layer laminated on the copper foil. The thickness of the gel layer is 1–10 μm. For example, the thickness can be, but is not limited to, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, and 10 μm. A thinner gel layer can reduce the battery volume and weight, thereby increasing the battery's volumetric energy density and gravimetric energy density.

[0026] The preparation process of the composite current collector includes the following steps.

[0027] (1) Mix aromatic diamine, acrylate monomers and polyester polymers, add an initiator, and then add graphene solution to obtain a polymer solution.

[0028] (2) The polymer solution was subjected to a hydrothermal reaction to obtain a three-dimensional porous flowable gel.

[0029] (3) A composite current collector is obtained by combining a three-dimensional porous flowable gel with a current collector.

[0030] In step (1), the aromatic diamine includes at least one of o-phenylenediamine, m-phenylenediamine, and p-phenylenediamine. The acrylate monomers include at least one of methyl methacrylate, ethyl methacrylate, methyl acrylate, and ethyl acrylate. The polyester polymers include polyethylene glycol diacrylate (PEGDA) and / or polypropylene glycol diacrylate (PPGDA). The mass ratio of the aromatic diamine, acrylate monomers, and polyester polymers is 1 to 5:1:4 to 10. As an example, the mass ratio of the three can be, but is not limited to, 1:1:4, 1:1:7, 1:1:10, 3:1:4, 3:1:7, 3:1:10, 5:1:4, 5:1:7, and 5:1:10. The sum of the masses of the aromatic diamine, acrylate monomers, and polyester polymers is m, and the mass of the initiator is n, where n / m is 0.001 to 0.010. For example, n / m may be, but is not limited to, 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, or 0.010. The initiator includes at least one of azobisisobutyronitrile, azobisisoheptanenitrile, and dimethyl azobisisobutyrate. The mass of the graphene solution is p, where p / m is 0.01 to 0.10. For example, p / m may be, but is not limited to, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, or 0.10. The graphene solution is an aqueous solution with a graphene mass concentration of 3–10 mg / ml. For example, the concentration can be, but is not limited to, 3 mg / ml, 4 mg / ml, 5 mg / ml, 6 mg / ml, 7 mg / ml, 8 mg / ml, 9 mg / ml, and 10 mg / ml. By controlling the ratio of raw materials to regulate the degree of polymerization, the resulting three-dimensional porous flowable gel can possess a certain porosity and viscosity, facilitating subsequent gel processing and use. Maintaining a certain porosity allows control over the deposition size of sodium metal on the current collector, suppressing its uneven deposition morphology and avoiding the formation of dead sodium.

[0031] In step (2), the hydrothermal reaction temperature is 70–100°C. For example, the temperature may be, but is not limited to, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, or 100°C. The hydrothermal reaction time is 5–15 hours. For example, the time may be, but is not limited to, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, or 15 hours. Under hydrothermal conditions, aromatic diamines and acrylate monomers undergo polymerization. The porosity of the three-dimensional porous flowable gel is 40–75%. For example, the porosity may be, but is not limited to, 40%, 45%, 50%, 55%, 60%, 65%, 70%, or 75%. The viscosity ranges from 5000 to 15000 cp.s. For example, the viscosity can be, but is not limited to, 5000 cp.s, 6000 cp.s, 7000 cp.s, 8000 cp.s, 9000 cp.s, 10000 cp.s, 11000 cp.s, 12000 cp.s, 13000 cp.s, 14000 cp.s, and 15000 cp.s. The three-dimensional porous flowable gel has a low viscosity and a certain degree of flowability, which makes it easy to subsequently composite onto the current collector.

[0032] In step (3), the composite process includes first extruding or coating the three-dimensional porous flowable gel onto the current collector and then hot-pressing it. The hot-pressing temperature is 250–450°C. For example, the hot-pressing temperature can be, but is not limited to, 250°C, 280°C, 300°C, 320°C, 340°C, 360°C, 380°C, 400°C, 420°C, 440°C, or 450°C. The pressure is 100–300 MPa. For example, the pressure can be, but is not limited to, 100 MPa, 120 MPa, 150 MPa, 180 MPa, 200 MPa, 230 MPa, 250 MPa, 270 MPa, or 300 MPa. The hot-pressing time is 5–30 s. For example, the time can be, but is not limited to, 5 s, 10 s, 15 s, 20 s, 25 s, or 30 s. The current collector can be made of copper foil, and a three-dimensional porous flowable gel can be extruded or coated onto one or both sides of the current collector.

[0033] To better illustrate the purpose, technical solution, and beneficial effects of this invention, the invention will be further described below with reference to specific embodiments. It should be noted that the methods described below are further explanations of this invention and should not be construed as limiting it.

[0034] Example 1

[0035] This embodiment is a composite current collector. The composite current collector includes a copper foil and a gel layer laminated on the copper foil, the thickness of which is 7 μm.

[0036] The preparation process of this composite current collector includes the following steps:

[0037] (1) Mix o-phenylenediamine, methyl methacrylate and polyethylene glycol diacrylate in a mass ratio of 2:1:5 to obtain a first mixture. Add 0.5 wt.% of azobisisobutyronitrile to the first mixture and mix evenly. Then add 6 wt.% of graphene solution (an aqueous solution with a graphene concentration of 6 mg / ml) to the first mixture and mix evenly to obtain a polymer solution.

[0038] (2) The polymer solution was subjected to a hydrothermal reaction at 90°C for 8 hours to obtain a three-dimensional porous flowable gel with a porosity of 77% and a viscosity of 7000 cp.s.

[0039] (3) The three-dimensional porous flowable gel is extruded onto the surface of copper foil and then hot-pressed at 300℃ and 150MPa for 20s to obtain a composite current collector.

[0040] Example 2

[0041] This embodiment is a composite current collector. The composite current collector includes a copper foil and a gel layer laminated on the copper foil, the thickness of which is 8 μm.

[0042] The preparation process of this composite current collector includes the following steps:

[0043] (1) o-phenylenediamine, methyl methacrylate and polyethylene glycol diacrylate are mixed in a mass ratio of 5:1:9 to obtain a first mixture. 1.0 wt.% of azobisisobutyronitrile is added to the first mixture and mixed evenly. Then, 10.0 wt.% of graphene solution (an aqueous solution with a graphene concentration of 9 mg / ml) is added to the first mixture and mixed evenly to obtain a polymer solution.

[0044] (2) The polymer solution was subjected to a hydrothermal reaction at 90°C for 8 hours to obtain a three-dimensional porous flowable gel with a porosity of 60% and a viscosity of 8000 cp.s.

[0045] (3) The three-dimensional porous flowable gel is extruded onto the surface of copper foil and then hot-pressed at 300℃ and 150MPa for 20s to obtain a composite current collector.

[0046] Example 3

[0047] This embodiment is a composite current collector. The composite current collector includes a copper foil and a gel layer laminated on the copper foil, the thickness of which is 7 μm.

[0048] The preparation process of this composite current collector includes the following steps:

[0049] (1) Mix o-phenylenediamine, methyl methacrylate and polyethylene glycol diacrylate in a mass ratio of 1:1:7 to obtain a first mixture. Add 0.3 wt.% of azobisisobutyronitrile to the first mixture and mix evenly. Then add 3 wt.% of graphene solution (an aqueous solution with a graphene concentration of 4 mg / ml) to the first mixture and mix evenly to obtain a polymer solution.

[0050] (2) The polymer solution was subjected to a hydrothermal reaction at 90°C for 8 hours to obtain a three-dimensional porous flowable gel with a porosity of 65% and a viscosity of 5500 cp.s.

[0051] (3) The three-dimensional porous flowable gel is extruded onto the surface of copper foil and then hot-pressed at 300℃ and 150MPa for 20s to obtain a composite current collector.

[0052] Example 4

[0053] This embodiment is a composite current collector. The composite current collector includes a copper foil and a gel layer laminated on the copper foil, the thickness of which is 10 μm.

[0054] The preparation process of this composite current collector includes the following steps:

[0055] (1) Mix p-phenylenediamine, methyl acrylate and polypropylene glycol diacrylate in a mass ratio of 2:1:5 to obtain a first mixture. Add 0.5 wt.% of azobisisobutyronitrile to the first mixture and mix evenly. Then add 6 wt.% of graphene solution (an aqueous solution with a graphene concentration of 6 mg / ml) to the first mixture and mix evenly to obtain a polymer solution.

[0056] (2) The polymer solution was subjected to a hydrothermal reaction at 90°C for 8 hours to obtain a three-dimensional porous flowable gel with a porosity of 73% and a viscosity of 7500 cp.s.

[0057] (3) The three-dimensional porous flowable gel is extruded onto the surface of copper foil and then hot-pressed at 300℃ and 150MPa for 20s to obtain a composite current collector.

[0058] Example 5

[0059] This embodiment is a composite current collector. The composite current collector includes a copper foil and a gel layer laminated on the copper foil, the thickness of which is 9 μm.

[0060] The preparation process of this composite current collector includes the following steps:

[0061] (1) Mix o-phenylenediamine, methyl methacrylate and polyethylene glycol diacrylate in a mass ratio of 2:1:5 to obtain a first mixture. Add 0.5 wt.% of azobisisobutyronitrile to the first mixture and mix evenly. Then add 6 wt.% of graphene solution (an aqueous solution with a graphene concentration of 6 mg / ml) to the first mixture and mix evenly to obtain a polymer solution.

[0062] (2) The polymer solution was subjected to a hydrothermal reaction at 100°C for 6 hours to obtain a three-dimensional porous flowable gel with a porosity of 70% and a viscosity of 6000 cp.s.

[0063] (3) The three-dimensional porous flowable gel is extruded onto the surface of copper foil and then hot-pressed at 400℃ and 200MPa for 10s to obtain a composite current collector.

[0064] Comparative Example 1

[0065] This comparative example is a composite current collector. The composite current collector includes a copper foil and a gel layer laminated on the copper foil, the thickness of which is 9 μm.

[0066] The preparation process of this composite current collector includes the following steps:

[0067] (1) o-phenylenediamine, methyl methacrylate and polyethylene glycol diacrylate are mixed in a mass ratio of 2:1:5 to obtain a first mixture. Azobisisobutyronitrile (AIO) accounting for 0.5 wt.% of the first mixture is added and mixed evenly to obtain a polymer solution.

[0068] (2) The polymer solution was subjected to a hydrothermal reaction at 90°C for 8 hours to obtain a three-dimensional porous flowable gel with a porosity of 45% and a viscosity of 10000 cp.s.

[0069] (3) The three-dimensional porous flowable gel is extruded onto the surface of copper foil and then hot-pressed at 300℃ and 150MPa for 20s to obtain a composite current collector.

[0070] Comparative Example 2

[0071] This comparative example is a composite current collector. The composite current collector includes a copper foil and a gel layer laminated on the copper foil, the gel layer having a thickness of 11 μm. The preparation process of this composite current collector includes the following steps:

[0072] (1) Mix o-phenylenediamine and methyl methacrylate at a mass ratio of 2:1 to obtain a first mixture. Add 0.5 wt.% of azobisisobutyronitrile to the first mixture and mix evenly. Then add 6 wt.% of graphene solution (an aqueous solution with a graphene concentration of 6 mg / ml) to the first mixture and mix evenly to obtain a polymer solution.

[0073] (2) The polymer solution was subjected to a hydrothermal reaction at 90°C for 8 hours to obtain a three-dimensional porous flowable gel with a porosity of 40% and a viscosity of 9200 cp.s.

[0074] (3) The three-dimensional porous flowable gel is extruded onto the surface of copper foil and then hot-pressed at 300℃ and 150MPa for 20s to obtain a composite current collector.

[0075] The composite current collectors from Examples 1-5 and Comparative Examples 1-2 were assembled into a negative electrode-free sodium metal battery, and the assembly process is as follows. The electrochemical performance of the prepared negative electrode-free sodium metal battery was tested under the following conditions, and the test results are shown in Table 1.

[0076] (I) Preparation of sodium metal batteries without negative electrodes

[0077] Using a cutting machine, the composite current collectors of Examples 1-5 and Comparative Examples 1-2 were cut into samples to serve as negative electrode current collectors, with the gel layer facing the positive electrode direction. A sodium vanadium phosphate positive electrode sheet (sodium vanadium phosphate loading of 16 mg·cm⁻¹) was used. 2 A sodium metal battery without a negative electrode was assembled using NaFP6 / diethylene glycol dimethyl ether (DEGDME) as the counter electrode, 1M NaFP6 / diethylene glycol dimethyl ether (DEGDME) as the electrolyte, and a porous monolayer polypropylene membrane as the separator in a glove box (high-purity argon atmosphere, where the oxygen and water content are both less than 0.1ppm).

[0078] (II) Electrochemical Performance Testing

[0079] 1. First Coulomb efficiency test

[0080] The sodium metal battery without a negative electrode is subjected to aging, formation, sealing and capacity testing using conventional methods. The charging capacity during the formation process is denoted as C1, the charging capacity during the capacity testing process is denoted as C2, and the discharging capacity during the capacity testing process is denoted as C0.

[0081] First Coulomb efficiency = C0 / (C1+C2)×100%

[0082] 2. Room temperature cycling performance test

[0083] The sodium metal battery without a negative electrode was placed in an environment of 25°C and charged at a constant current of 1C to 4.0V, then charged at a constant voltage to 0.05C, and then discharged at a constant current of 1C to 2.0V. This cycle was repeated for 500 cycles. The discharge capacity of the first cycle and the discharge capacity of the last cycle were recorded. The capacity retention rate of the room temperature cycle was calculated according to the following formula.

[0084] Capacity retention rate = (Discharge capacity in the last cycle / Discharge capacity in the first cycle) × 100%

[0085] Table 1. Electrochemical performance test results of Examples 1-5 and Comparative Examples 1-2

[0086] Example First-time Coulomb Efficiency / % Capacity Retention Rate after 500 Cycles / % Example 1 88.6 9 0.2 Example 2 88.0 8 9.9 Example 3 89.0 9 0.8 Example 4 88.5 9 0.1 Example 5 88.3 9 0.3 Comparative Example 1 82.5 7 5.5 Comparative Example 2 81.8 7 6.0 surface

[0087] As shown in Table 1, a three-dimensional porous fluid gel was obtained by polymerizing aromatic diamines and acrylate monomers as the longitudinal and transverse framework, using polyester polymers as interlayer crosslinking agents, and graphene as the sheet-like framework. When this gel was composited onto a current collector, the resulting electrodeless sodium metal battery exhibited high coulombic efficiency and excellent cycle performance. This is likely because the three-dimensional porous structure of the fluid gel can control the deposition size of sodium metal on the current collector, suppressing its uneven deposition morphology and avoiding the formation of dead sodium. The graphene distributed within the three-dimensional porous structure possesses high mechanical properties, which can suppress the volume change of deposited sodium metal and prevent breakage during cycling. Therefore, it can improve the specific capacity and cycle performance of the electrodeless sodium metal battery.

[0088] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, it is not limited to those listed in the embodiments. Those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A process for preparing a composite current collector, characterized in that, The steps include: (1) mixing aromatic diamine, acrylate monomer and polyester polymer, adding an initiator, and then adding graphene solution to obtain a polymer solution, wherein the mass ratio of aromatic diamine, acrylate monomer and polyester polymer is 1~5:1:4~10; (2) subjecting the polymer solution to a hydrothermal reaction to obtain a three-dimensional porous flowable gel; (3) compositing the three-dimensional porous flowable gel onto a current collector to obtain a composite current collector.

2. The preparation process of the composite current collector according to claim 1, characterized in that, The aromatic diamine includes at least one of o-phenylenediamine, m-phenylenediamine, and p-phenylenediamine; the acrylate monomers include at least one of methyl methacrylate, ethyl methacrylate, methyl acrylate, and ethyl acrylate; and the polyester polymers include polyethylene glycol diacrylate and / or polypropylene glycol diacrylate.

3. The preparation process of the composite current collector according to claim 1, characterized in that, The sum of the masses of the aromatic diamine, the acrylate monomer, and the polyester polymer is m, the mass of the initiator is n, and n / m is 0.001~0.

010. The initiator includes at least one of azobisisobutyronitrile, azobisisoheptanenitrile, and dimethyl azobisisobutyrate.

4. The preparation process of the composite current collector according to claim 1, characterized in that, The sum of the masses of the aromatic diamine, the acrylate monomer, and the polyester polymer is m, the mass of the graphene solution is p, p / m is 0.01~0.10, and the graphene solution is an aqueous solution with a graphene mass concentration of 3~10 mg / ml.

5. The preparation process of the composite current collector according to claim 1, characterized in that, The hydrothermal reaction is carried out at a temperature of 70-100℃ for 5-15 hours.

6. The preparation process of the composite current collector according to claim 1, characterized in that, The porosity of the three-dimensional porous flowable gel is 40-75%, and the viscosity is 5000-15000 cp.s.

7. The preparation process of the composite current collector according to claim 1, characterized in that, The composite process involves first extruding or coating the current collector and then hot-pressing it. The hot-pressing temperature is 250~450℃, the pressure is 100~300Mpa, and the hot-pressing time is 5~30s.

8. The composite current collector prepared by the preparation process of the composite current collector according to any one of claims 1 to 7, characterized in that, It includes a copper foil and a gel layer laminated on the copper foil, wherein the thickness of the gel layer is 1~10μm.

9. A sodium metal battery without a negative electrode, characterized in that, It includes a composite current collector, a separator, and a positive electrode sheet stacked sequentially, wherein the composite current collector is a composite current collector prepared by the preparation process of the composite current collector according to any one of claims 1 to 7 or the composite current collector according to claim 8.