Sodium-ion battery positive electrode sheet and its preparation method, sodium-ion battery

Abstract

This invention provides a sodium-ion battery positive electrode sheet and its preparation method, as well as a sodium-ion battery. The sodium-ion battery positive electrode sheet includes a current collector and a positive electrode layer. The positive electrode layer includes a first electrode layer, a second electrode layer, and a third electrode layer. The first electrode layer is made of graphene, the second electrode layer is made of sodium-ion layered oxide, and the third electrode layer is made of a polyanionic salt compound containing sodium ions. Based on this application, the above-mentioned sodium-ion battery positive electrode sheet can improve the battery capacity and voltage, while also increasing battery safety, reducing battery internal resistance, and improving overall battery performance.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery technology, and more specifically, to a sodium-ion battery positive electrode sheet and its preparation method, and a sodium-ion battery. Background Technology

[0002] Currently, driving range is a crucial indicator for electric vehicles and a primary consideration for consumers. Improving battery pack capacity is a key research focus for most battery manufacturers. Since battery pack size is fixed, increasing capacity requires increasing the specific capacity of the cells and their operating voltage. Sodium-ion batteries are critical in electric vehicle systems; cell safety directly impacts vehicle safety. However, existing conventional sodium-ion batteries often suffer from issues such as low operating voltage, low specific capacity, or poor safety performance. Therefore, it is necessary to explore a new sodium-ion battery that offers higher operating voltage and specific capacity while maintaining strong safety performance. Summary of the Invention

[0003] The main objective of this invention is to provide a sodium-ion battery positive electrode sheet and its preparation method, as well as a sodium-ion battery, to solve the problems that conventional sodium-ion batteries in the prior art usually have, such as low operating voltage, low specific capacity, or poor safety performance.

[0004] To achieve the above objectives, according to one aspect of the present invention, a positive electrode sheet for a sodium-ion battery is provided, comprising a current collector and a positive electrode layer. The current collector has opposing first and second surfaces, and the positive electrode layer comprises: a first electrode layer disposed on the first surface and / or the second surface of the current collector; a second electrode layer disposed on the outer surface of at least one first electrode layer away from the current collector; and a third electrode layer disposed on the outer surface of at least one second electrode layer away from the current collector. The first electrode layer is made of graphene, the second electrode layer is made of sodium-ion layered oxide, and the third electrode layer is made of a polyanionic salt compound containing sodium ions.

[0005] Further, the thickness of the positive electrode layer is 200±10μm; preferably, the thickness of each first electrode layer is 20±5μm; preferably, the thickness ratio of the first electrode layer, the second electrode layer and the third electrode layer is 1∶2~6∶3~7.

[0006] Furthermore, in the structural formula of the polyanionic salt compound, the structural formula of the polyanionic salt compound is Na. x M y [X a O b]2, where element M is selected from Group IIA, Group IIIA, Group IVB, Group VB, Group VIB, Group VIIB, or Group VIII; element X is selected from Group IVA, Group VIA, Group VA, Group IIIA, or Group VIB; 2.8 < x < 3.2, 1.8 < y < 2.2, 0.8 < a < 1.2, 3 < b < 5; preferably, the structural formula of sodium ion layered oxide is Na c Z d O e In the formula, element Z is selected from one or more of Group IVB, Group VB, Group VIB, Group VIIB, Group VIII, and Group IB; 0.2 < c < 0.4, 0.2 < d < 0.4, 0.2 < e < 0.4; preferably, M is selected from one of Ti, V, Cr, Mn, Fe, Ni, Co, Ca, Mg, Al, or Nb, more preferably one of V, Cr, Mn, or Fe; X is selected from one of Si, S, P, As, B, Mo, W, or Ge, more preferably one of P, As, B, or Ge; preferably, in the structural formula of sodium ion layered oxide, Z is selected from one or more of Ti, V, Cr, Mn, Fe, Ni, Co, and Cu, more preferably one of Mn, Fe, Ni, Co, or Cu; more preferably, the polyanionic salt compound is Na3V2(PO4)3; the sodium ion layered oxide is Na[Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 O2; More preferably, the weight content of graphene in the first electrode layer is 85-89 wt%, the weight content of Na3V2(PO4)3 in the second electrode layer is 93.8-96.5 wt%, and the weight content of Na[Ni] in the third electrode layer is... 1 / 3 Fe 1 / 3 Mn 1 / 3 The weight content of O2 is 96.7–97.6 wt%.

[0007] Furthermore, the materials of the first electrode layer, the second electrode layer, and the third electrode layer each independently contain a binder; preferably, the binder is selected from one or more of polyvinylidene fluoride, a copolymer of polyhexafluoropropylene and polyvinylidene fluoride, polyvinyl acetate, polyvinyl alcohol, polyethylene oxide, polyvinylpyrrolidone, alkylated polyethylene oxide, polyvinyl ether, polymethyl methacrylate, ethyl polyacrylate, polytetrafluoroethylene, polyvinyl chloride, polyacrylonitrile, polyvinylpyridine, styrene-butadiene rubber, or acrylonitrile-butadiene rubber; preferably, the amount of binder in the first electrode layer is 1 to 10 wt% of the weight of graphene; preferably, the amount of binder in the second electrode layer is 0.1 to 2 wt% of the weight of sodium ion layered oxide; preferably, the amount of binder in the third electrode layer is 0.1 to 2 wt% of the weight of a polyanionic salt compound.

[0008] Furthermore, the materials of the second electrode layer and the third electrode layer each independently contain conductive carbon material; preferably, the carbon material is selected from one or more of carbon nanotubes, graphite, acetylene black, carbon black, nano-conductive carbon, vapor-grown carbon fiber, carbon black, acetylene black, conductive graphite, graphene, Ketjen black, or carbon fiber; preferably, the amount of carbon material in the second electrode layer is 0.1 to 1 wt% of the weight of the sodium ion layered oxide; preferably, the amount of carbon material in the third electrode layer is 0.1 to 1 wt% of the weight of the polyanionic salt compound.

[0009] Furthermore, the first electrode layer comprises 89–92 wt% graphene and 8–11 wt% polyvinylidene fluoride; the second electrode layer comprises 94–98 wt% sodium nickel iron manganese oxide, 1.8–2.1 wt% carbon nanotubes, and 1.8–2.1 wt% a copolymer of polyhexafluoropropylene and polyvinylidene fluoride; the third electrode layer comprises 96–98 wt% sodium vanadium phosphate, 0.4–0.6 wt% carbon nanotubes, 0.9–1.1 wt% carbon black, and 1.4–1.6 wt% polyvinylidene fluoride.

[0010] According to another aspect of the present invention, a method for preparing the aforementioned sodium-ion battery positive electrode sheet is provided. The method includes: providing a current collector having opposing first and second surfaces; disposing a first electrode layer on the first and / or second surfaces of the current collector; disposing a second electrode layer on the outer surface of at least one first electrode layer away from the current collector; and disposing a third electrode layer on the outer surface of at least one second electrode layer away from the current collector.

[0011] Further, the positive electrode layer is prepared by the following steps: Step S1, a first electrode slurry containing graphene and a binder is coated on at least one outer surface of the current collector, and after a first drying, a first electrode layer is formed; Step S2, a second electrode slurry containing sodium ion layered oxide, a binder, and carbon material is coated on the outer surface of the first electrode layer away from the current collector, and after a second drying, a second electrode layer is formed; Step S3, a third electrode slurry containing a polyanionic salt compound, a binder, and carbon material is coated on the outer surface of the second electrode layer away from the current collector, and after a third drying, a third electrode layer is formed; preferably, after step S3, the positive electrode layer is prepared by... The preparation method further includes a step of rolling the material obtained in step S3; preferably, the viscosity of the first electrode slurry at 25°C is controlled at 3000±1000cp; more preferably, the solid content of the first electrode slurry is 20-45%; preferably, the solid content of the second electrode slurry is 50-65%; preferably, the solid content of the third electrode slurry is 45-60%; preferably, the solvents in the first electrode slurry, the second electrode slurry and the third electrode slurry each independently include one or more of N-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, N,N-dimethylaminopropylamine, ethylene oxide or tetrahydrofuran.

[0012] According to another aspect of the present invention, a sodium-ion battery is provided, comprising a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode is the aforementioned sodium-ion battery positive electrode.

[0013] Further, the negative electrode includes a current collector and a negative electrode layer disposed on at least one outer surface of the current collector, wherein the active material of the negative electrode layer is selected from one or more of hard carbon, graphite, or soft carbon; preferably, the electrolyte includes a solvent and a sodium salt, wherein the solvent in the electrolyte is one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, or vinylene carbonate; and the sodium salt in the electrolyte is one or more of NaPF6, NaClO4, or NaBF4; more preferably, the electrolyte also includes an additive, wherein the additive is one or more of vinylene carbonate, ethylene vinylene carbonate, fluoroethylene carbonate, or vinyl sulfate.

[0014] Based on the above-mentioned sodium-ion battery positive electrode sheet, the battery capacity and battery voltage can be improved, while also increasing the battery safety performance, reducing the battery internal resistance, and improving the overall battery performance. Attached Figure Description

[0015] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0016] Figure 1 A schematic diagram of the structure of a sodium-ion battery positive electrode sheet in one embodiment of the present invention is shown;

[0017] Figure 2 A schematic diagram of the structure of a sodium-ion battery positive electrode sheet is shown in one embodiment of the present invention.

[0018] The above figures include the following reference numerals:

[0019] 10. Current collector; 20. Positive electrode layer; 21. First electrode layer; 22. Second electrode layer; 23. Third electrode layer. Detailed Implementation

[0020] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0021] As described in the background section of this application, conventional sodium-ion batteries in the prior art typically suffer from problems such as low operating voltage, low specific capacity, or poor safety performance. To address this issue, this application provides a positive electrode sheet for a sodium-ion battery, comprising a current collector 10 and a positive electrode layer 20. The current collector 10 has opposing first and second surfaces, and the positive electrode layer 20 includes a first electrode layer 21, a second electrode layer 22, and a third electrode layer 23. The first electrode layer 21 is disposed on the first surface and / or the second surface of the current collector 10; the second electrode layer 22 is disposed on the outer surface of at least one layer of the first electrode layer 21 away from the current collector 10; and the third electrode layer 23 is disposed on the outer surface of at least one layer of the second electrode layer 22 away from the current collector 10. The first electrode layer 21 is made of graphene, the second electrode layer 22 is made of sodium-ion layered oxide, and the third electrode layer 23 is made of a polyanionic salt compound containing sodium ions.

[0022] To further explain, the first electrode layer 21 is disposed on the first surface and / or the second surface of the current collector 10. When the first electrode layer 21 is disposed on the first surface or the second surface of the current collector 10, as... Figure 1 The structure shown; when the first electrode layer 21 is disposed on the first and second surfaces of the current collector 10, as... Figure 2 The structure shown.

[0023] Based on the above-mentioned sodium-ion battery positive electrode sheet, the battery capacity and battery voltage can be improved, while also increasing the battery safety performance, reducing the battery internal resistance, and improving the overall battery performance.

[0024] Specifically, polyanionic salt compounds containing sodium ions exhibit high charge-discharge voltages and structural stability. While sodium-ion layered oxides possess relatively high specific capacity, their charge-discharge voltages are relatively low. Graphene, on the other hand, exhibits excellent electrical conductivity, with a carrier mobility of approximately 15000 cm⁻¹ at room temperature. 2 The value of graphene is / (V·s), which is more than 10 times that of silicon and more than twice that of indium antimonide (InSb), the material with the highest known carrier mobility. Under certain specific conditions, such as low temperatures, the carrier mobility of graphene can even reach 250,000 cm⁻¹. 2 / (V·s). Furthermore, the electron mobility of graphene is less affected by temperature changes; at any temperature between 50 and 500 K, the electron mobility of monolayer graphene remains at 15000 cm⁻¹. 2The conductivity is approximately / (V·s). This application selects graphene as the active material for the first electrode layer 21, which can improve the battery's conductivity, reduce its internal resistance, and enhance adhesion. The graphene material layer is placed on the current collector, which can significantly reduce the contact resistance between the two. This is because the resistance between a general material and the current collector is the highest; however, the graphene electrode layer greatly reduces this internal resistance and also increases the adhesion of the current collector, making it less prone to material loss and exhibiting excellent structural stability.

[0025] More importantly, this application selects graphene as the active material of the first electrode layer 21, sodium-ion layered oxide as the active material of the second electrode layer 22, and a sodium-ion-containing polyanionic salt compound as the active material of the third electrode layer 23, synergistically forming a complete positive electrode layer 20. This allows the battery to achieve a specific capacity of 140 mAh / g, a voltage of 1.5V-4.2V, and a capacity retention rate of over 93% after 1000 cycles at 25°C. Batteries assembled using the sodium-ion battery positive electrode sheet of this invention can achieve high specific capacity and also have excellent effects such as slow cycle decay and high first-cycle efficiency. It should be noted that the beneficial effects of the sodium-ion battery positive electrode sheet of this application are based on the above-mentioned specific multi-layer synergistic arrangement. If the positional relationship or materials of the electrode layers are different from those of this invention, the above effects cannot be obtained.

[0026] In a preferred embodiment, the D of the graphene material 50 The particle size is 10–65 nm, the porosity is 20–30%, and the specific surface area is 30 m². 2 / g~60m 2 / g.

[0027] Furthermore, this application does not impose any special limitations on the aforementioned current collector 10. Those skilled in the art can select a suitable current collector, such as aluminum foil, according to their own product needs. This application also does not impose any special limitations on the thickness (200±10μm) of the positive electrode layer 20 in the sodium-ion battery positive electrode sheet. Based on the aforementioned specific arrangement, this application effectively improves both battery capacity and battery voltage without changing the size of the battery and battery pack, while also increasing battery safety, reducing battery internal resistance, and improving overall battery performance. In a preferred embodiment, the thickness of the first electrode layer 21 is 20±5μm; the thickness ratio of the first electrode layer 21, the second electrode layer 22, and the third electrode layer 23 is 1:2 to 6:3 to 7. Based on this, the synergistic effect between the layers is better without changing the size of the battery and battery pack.

[0028] To further improve the operating voltage, specific capacity, and safety performance of sodium-ion batteries, in a preferred embodiment, the sodium-ion layered oxide has the structural formula Na. c Nd O e In the formula, N element is selected from one or more of Groups IVB, VB, VIB, VIIB, VIII, and IB; 0.2 < c < 0.4, 0.2 < d < 0.4, 0.2 < e < 0.4. The material of the third electrode layer 23 contains a sodium-containing polyanionic salt compound, and the structural formula of the sodium-containing polyanionic salt compound is Na. x M y [X a O b ]2, where the M element is selected from one of Group IIA, Group IIIA, Group IVB, Group VB, Group VIB, Group VIIB or Group VIII; the X element is selected from one of Group IVA, Group VIA, Group VA, Group IIIA or Group VIB; 2.8 < x < 3.2, 1.8 < y < 2.2, 0.8 < a < 1.2, 3 < b < 5. More preferably, in the structural formula of the polyanionic salt compound containing sodium ions, M is selected from one of Ti, V, Cr, Mn, Fe, Ni, Co, Ca, Mg, Al or Nb, more preferably one of V, Cr, Mn or Fe; X is selected from one of Si, S, P, As, B, Mo, W or Ge, more preferably one of P, As, B or Ge; in the structural formula of the sodium ion layered oxide, N is selected from one or more of Ti, V, Cr, Mn, Fe, Ni, Co, Cu, more preferably one of Mn, Fe, Ni, Co or Cu.

[0029] In a preferred embodiment, the polyanionic salt compound containing sodium ions is Na3V2(PO4)3; the sodium ion layered oxide is Na[Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 O2. This results in better compatibility between the three electrode layers. Simultaneously, the active material of the second electrode layer 22 is Na[Ni]. 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 can increase the specific capacity of the battery, thereby increasing the battery capacity. In a preferred embodiment, Na[Ni] 1 / 3 Fe 1 / 3 Mn 1 / 3 D of O2 (sodium nickel iron manganate) 50 The particle size is greater than 4.32 μm and less than 11 μm, with a specific surface area of ​​0.9 ± 0.1 m². 2 / g, tap density ≥1.6g / cm³ 3The pH value is around 11.7, the material has good processing performance, a specific capacity of around 150 mAh / g, and a charge / discharge voltage of 1.5V-3.9V. The active material of the third electrode layer 23 is Na3V2(PO4)3, which has a charge / discharge mechanism very different from other cathode materials. During the first charge / discharge process, Na... + Extraction / intercalation leads to changes in the material structure. Based on this, the battery's operating voltage can be increased, the structure stabilized, and the battery's cycle performance improved. Moreover, this material is not only low-cost but also has good processability. In a preferred embodiment, the D of Na3V2(PO4)3 (sodium vanadium phosphate) 50 Particle size greater than 10 μm and less than 35 μm; specific surface area less than 0.7 ± 0.1 m². 2 / g, tap density ≥1.7g / cm³ 3 The pH value is around 11.9, the specific capacity is around 100 mAh / g, and the charge / discharge voltage is between 1.5V and 4.2V. Based on this, the sodium-ion battery positive electrode sheet described in this application can significantly improve the battery capacity and battery voltage, while also further increasing the battery's safety performance, reducing the battery's internal resistance, and improving the overall battery performance.

[0030] To further improve the overall performance of the battery, in a preferred embodiment, the graphene content in the first electrode layer 21 is 85-89 wt%, the Na3V2(PO4)3 content in the second electrode layer 22 is 93.8-96.5 wt%, and the Na[Ni] content in the third electrode layer 23 is... 1 / 3 Fe 1 / 3 Mn 1 / 3 The weight content of O2 is 96.7–97.6 wt%.

[0031] To further improve the uniformity of battery performance, in a preferred embodiment, the materials of the first electrode layer 21, the second electrode layer 22, and the third electrode layer 23 each independently contain a binder. Preferably, the binder is selected from one or more of polyvinylidene fluoride, a copolymer of polyhexafluoropropylene and polyvinylidene fluoride, polyvinyl acetate, polyvinyl alcohol, polyethylene oxide, polyvinylpyrrolidone, alkylated polyethylene oxide, polyvinyl ether, polymethyl methacrylate, ethyl polyacrylate, polytetrafluoroethylene, polyvinyl chloride, polyacrylonitrile, polyvinylpyridine, styrene-butadiene rubber, or acrylonitrile-butadiene rubber. Preferably, the amount of binder in the first electrode layer 21 is 1-10% of the weight of graphene. Preferably, the amount of binder in the second electrode layer 22 is 0.1-2% of the weight of sodium ion layered oxide. Preferably, the amount of binder in the third electrode layer 23 is 0.1-2% of the weight of a sodium-containing polyanionic salt compound.

[0032] To further improve the electrical performance of the battery, in a preferred embodiment, the materials of the second electrode layer 22 and the third electrode layer 23 each independently contain carbon material. Preferably, the carbon material is selected from one or more of carbon nanotubes, graphite, acetylene black, carbon black, nano-conductive carbon, vapor-grown carbon fibers, carbon black, acetylene black, conductive graphite, graphene, Ketjen black, or carbon fibers. Preferably, the amount of carbon material in the second electrode layer 22 is 0.1% to 1% of the weight of the sodium ion layered oxide. Preferably, the amount of carbon material in the third electrode layer 23 is 0.1% to 1% of the weight of the sodium ion-containing polyanionic salt compound.

[0033] To further improve the overall performance of the battery, in a preferred embodiment, the first electrode layer 21 comprises 89-92 wt% graphene and 8-11 wt% polyvinylidene fluoride; the second electrode layer 22 comprises 94-98 wt% sodium nickel iron manganese oxide, 1.8-2.1 wt% carbon nanotubes and 1.8-2.1 wt% a copolymer of polyhexafluoropropylene and polyvinylidene fluoride; and the third electrode layer 23 comprises 96-98 wt% sodium vanadium phosphate, 0.4-0.6 wt% carbon nanotubes, 0.9-1.1 wt% carbon black and 1.4-1.6 wt% polyvinylidene fluoride.

[0034] This application also provides a method for preparing the aforementioned sodium-ion battery positive electrode sheet. The method includes: providing a current collector 10 having a first surface and a second surface opposite to each other; disposing a first electrode layer 21 on the first surface and / or the second surface of the current collector 10; disposing a second electrode layer 22 on the outer surface of at least one first electrode layer 21 away from the current collector 10; and disposing a third electrode layer 23 on the outer surface of at least one second electrode layer 22 away from the current collector 10.

[0035] To further improve the performance uniformity of the positive electrode layer, in a preferred embodiment, the positive electrode layer 20 is prepared by the following steps: Step S1, a first electrode slurry containing graphene and a binder is coated on at least one outer surface of the current collector 10, and after a first drying, a first electrode layer 21 is formed; Step S2, a second electrode slurry containing sodium ion layered oxide, a binder, and carbon material is coated on the outer surface of the first electrode layer 21 away from the current collector 10, and after a second drying, a second electrode layer 22 is formed; Step S3, a third electrode slurry containing a polyanionic salt compound containing sodium ions, a binder, and carbon material is coated on the outer surface of the second electrode layer 22 away from the current collector 10, and after a third drying, a third electrode layer 23 is formed.

[0036] In a preferred embodiment, in order to further improve the structural stability of the product, after step S3, the preparation method further includes a step of rolling the material obtained in step S3.

[0037] To further improve the coating performance of the slurry, in a preferred embodiment, the viscosity of the first electrode slurry at 25°C is controlled at 3000±1000 cp; more preferably, the solid content of the first electrode slurry is 20-45%. Preferably, the solid content of the second electrode slurry is 50-65%. Preferably, the solid content of the third electrode slurry is 45-60%. To further improve the dispersion uniformity of the active material, preferably, the solvents in the first, second, and third electrode slurries each independently include one or more of N-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, N,N-dimethylaminopropylamine, ethylene oxide, or tetrahydrofuran.

[0038] This application also provides a sodium-ion battery, which includes a positive electrode, a negative electrode, and an electrolyte. The positive electrode is the aforementioned sodium-ion battery positive electrode; or it is a sodium-ion battery positive electrode prepared by the aforementioned preparation method.

[0039] Based on the reasons stated above, the battery capacity and voltage are improved, while also enhancing battery safety, reducing internal resistance, and improving overall battery performance. To further improve the battery's overall performance, in a preferred embodiment, the negative electrode includes a current collector and a negative electrode layer disposed on at least one outer surface of the current collector. The active material of the negative electrode layer is selected from one or more of hard carbon, graphite, or soft carbon. Preferably, the electrolyte includes a solvent and a sodium salt. The solvent in the electrolyte is one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, or vinylene carbonate. The sodium salt in the electrolyte is one or more of NaPF6, NaClO4, or NaBF4. More preferably, the electrolyte also includes an additive, which is one or more of vinylene carbonate, ethylene vinylene carbonate, fluoroethylene carbonate, or vinyl sulfate. The negative current collector is copper foil or aluminum foil.

[0040] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0041] Example 1

[0042] (1) Preparation of graphene slurry

[0043] Take 2000g of graphene powder and 200g of polyvinylidene fluoride and mix them together. Add N-methyl-2-pyrrolidone according to the solid content of graphene slurry of 45%. Mix the materials at a revolution speed of 25 rpm and a rotation speed of 3000 rpm. After mixing, stir evenly in a mixing pot to obtain graphene slurry. The viscosity of graphene slurry is controlled at 3000 cp.

[0044] (2) Preparation of sodium nickel ferromanganate slurry

[0045] First, take 10,000g of sodium nickel iron manganese oxide, 208.33g of carbon nanotubes, 208.33g of a copolymer of polyhexafluoropropylene and polyvinylidene fluoride, and mix them with solvent NMP (N-methyl-2-pyrrolidone). The solid content is controlled at 50%. After mixing, stir evenly in a mixing pot to obtain sodium nickel iron manganese oxide slurry.

[0046] (3) Preparation of sodium vanadium phosphate slurry

[0047] 10,000g of sodium vanadium phosphate, 51.5g of carbon nanotubes, 103.1g of conductive agent SP (carbon black), 154.6g of binder PVDF polymer (polyvinylidene fluoride) and solvent NMP (N-methyl-2-pyrrolidone) were mixed, with the solid content controlled at 50%. The mixture was stirred evenly in a mixing pot to obtain sodium vanadium phosphate slurry.

[0048] (4) Preparation of positive electrode

[0049] First, the mixed graphene slurry is uniformly sprayed onto the foil, and the electrode is dried at 110℃ for 5 minutes. Then, the obtained sodium nickel iron manganese slurry is uniformly sprayed onto the upper layer of the graphene, and the electrode is dried at 110℃ for 5 minutes. The obtained sodium vanadium phosphate slurry is uniformly sprayed onto the upper layer of the sodium nickel iron manganese slurry (sodium vanadium phosphate material is on the outermost layer), and the electrode is dried at 110℃ for 5 minutes. After drying, the electrode is rolled and die-cut to obtain the positive electrode. The graphene coating thickness: sodium nickel iron manganese slurry coating thickness: sodium vanadium phosphate coating thickness = 1:4:5, and the total coating thickness is 200 μm, of which the first coating layer is 20 μm, the second coating layer is 80 μm, and the third coating layer is 100 μm.

[0050] Example 2

[0051] The only difference from Example 1 is that the graphene coating thickness : sodium nickel iron manganese coating thickness : sodium vanadium phosphate coating thickness = 1 : 5 : 4, wherein the total coating thickness is 200 μm, the first coating layer is 20 μm, the second coating layer is 100 μm, and the third coating layer is 80 μm.

[0052] Example 3

[0053] The only difference from Example 1 is:

[0054] N-methyl-2-pyrrolidone was added according to the graphene slurry solid content of 20%.

[0055] The ratio of graphene coating thickness to sodium nickel iron manganese oxide coating thickness to sodium vanadium phosphate coating thickness is 1:4:5, with a total coating thickness of 200 μm, of which the first coating layer is 20 μm, the second coating layer is 80 μm, and the third coating layer is 100 μm.

[0056] Example 4

[0057] The only difference from Example 1 is that the graphene coating thickness : sodium nickel iron manganese coating thickness : sodium vanadium phosphate coating thickness = 1 : 2 : 3, where the total coating thickness is 200 μm, the first coating layer is 33.3 μm, the second coating layer is 66.6 μm, and the third coating layer is 99.9 μm.

[0058] Example 5

[0059] The only difference from Example 1 is that the graphene coating thickness : sodium nickel iron manganese coating thickness : sodium vanadium phosphate coating thickness = 1 : 6 : 7, where the total coating thickness is 200 μm, the first coating layer is 14.28 μm, the second coating layer is 85.7 μm, and the third coating layer is 100 μm.

[0060] Example 6

[0061] The only difference from Example 1 is that the graphene coating thickness : sodium nickel iron manganese coating thickness : sodium vanadium phosphate coating thickness = 3 : 1 : 2, where the total coating thickness is 200 μm, the first coating layer is 99.9 μm, the second coating layer is 33.3 μm, and the third coating layer is 66.6 μm.

[0062] Example 7

[0063] The only difference from Example 1 is that Na[Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 and other mass fractions are replaced with Na[Ni] 1 / 3 Co 1 / 3 Mn 1 / 3 O2.

[0064] Example 8

[0065] The only difference from Example 1 is that Na3V2(PO4)3 is replaced by Na3Cr2(PO4)3 by mass.

[0066] Example 9

[0067] The only difference from Example 1 is that Na3V2(PO4)3 is replaced with Na3B2(PO4)3 by mass.

[0068] Example 10

[0069] The only difference from Example 1 is that Na3V2(PO4)3 is replaced by Na3Fe2(PO4)3 by mass.

[0070] Example 11

[0071] The only difference from Example 1 is that the weight content of Na3V2(PO4)3 is 85%.

[0072] Example 12

[0073] The only difference from Example 1 is that Na[Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 The O2 content is 90% by weight.

[0074] Example 13

[0075] The only difference from Example 1 is that the graphene content is 95% by weight.

[0076] Comparative Example 1

[0077] The positive electrode sheet was prepared using the slurry from Example 1.

[0078] First, the mixed graphene slurry is uniformly sprayed onto the foil, and the electrode is dried at 110℃ for 5 minutes. Then, the obtained sodium nickel iron manganese slurry is uniformly sprayed onto the upper layer of graphene, and the electrode is dried at 110℃ for 5 minutes. After drying, it is rolled and die-cut to obtain the positive electrode. The graphene coating thickness to sodium nickel iron manganese slurry coating thickness is 1:4, and the total coating thickness is 200 μm, of which the first coating layer is 40 μm and the second coating layer is 160 μm.

[0079] Comparative Example 2

[0080] Coating of the positive electrode sheet.

[0081] First, the graphene slurry mixed in Example 1 is uniformly sprayed onto the foil. The electrode is then dried at 110°C for 5 minutes. The obtained sodium vanadium phosphate slurry is uniformly sprayed onto the upper layer of the graphene material (sodium vanadium phosphate is on the outermost layer). The electrode is then dried at 110°C for 5 minutes. After drying, it is rolled and die-cut to obtain the positive electrode. The graphene coating thickness to sodium vanadium phosphate coating thickness is 1:5, and the total coating thickness is 200 μm, with the first coating layer being 34 μm and the second coating layer being 166 μm.

[0082] Comparative Example 3

[0083] Coating of the positive electrode sheet.

[0084] First, the mixed sodium nickel iron manganese slurry from Example 1 is uniformly sprayed onto the foil. The electrode is then dried at 110°C for 5 minutes. Next, the obtained sodium vanadium phosphate slurry is uniformly sprayed onto the upper layer of the sodium nickel iron manganese slurry (sodium vanadium phosphate is on the outermost layer). The electrode is then dried at 110°C for 5 minutes. After drying, the electrode is rolled and die-cut to obtain the positive electrode. The ratio of sodium nickel iron manganese slurry coating thickness to sodium vanadium phosphate coating thickness is 4:5, with a total coating thickness of 200 μm, of which the first coating layer is 88 μm and the second coating layer is 112 μm.

[0085] Comparative Example 4

[0086] Coating of the positive electrode sheet.

[0087] The sodium vanadium phosphate slurry obtained in Example 1 was uniformly sprayed onto the upper layer of the foil. The electrode was dried at a temperature of 110°C for 5 minutes. After drying, it was rolled and die-cut to obtain the positive electrode, wherein the total coating thickness was 200 μm.

[0088] Comparative Example 5

[0089] Coating of the positive electrode sheet.

[0090] The sodium nickel iron manganese slurry obtained in Example 1 was uniformly sprayed onto the upper layer of the foil. The electrode was dried at a temperature of 110°C for 5 minutes. After drying, it was rolled and die-cut to obtain the positive electrode, wherein the total coating thickness was 200 μm.

[0091] Test case

[0092] (1) Negative electrode sheet: The negative electrode material (hard carbon), binder CMC, conductive agent SP, and SBR emulsion are mixed with water at a ratio of 96.5:1.5:0.5:1.5, and the solid content is controlled at 40%. After mixing, the mixture is stirred evenly in a mixing pot to obtain a negative electrode slurry. The negative electrode slurry is coated on copper foil, and the coated copper foil is rolled and cut to obtain a negative electrode sheet.

[0093] (2) Positive electrode: Positive electrode prepared in Examples 4-5 and Comparative Examples 1-5;

[0094] (3) High-voltage electrolyte: Dissolve a certain amount of NaPF6 in ethylene carbonate, propylene carbonate and dimethyl carbonate in a volume ratio of 1:1:1, add additives (ethylene carbonate, fluoroethylene carbonate, ethylene sulfate or ethyleneethylene carbonate) to make the concentration of sodium salt NaPF6 1.15 mol / L, and make the additive account for 0.5% or 1.5% of the total mass. Stir until the electrolyte is completely clear to obtain the high-voltage electrolyte.

[0095] High-voltage electrolyte was used. The obtained positive and negative electrode sheets and separator were stacked in a Z-shape to obtain a bare cell. Then, aluminum-plastic film was used for encapsulation, followed by electrolyte injection to obtain a battery. The battery was then subjected to formation and capacity testing, and the battery performance was tested. The battery performance test results are shown in Table 1.

[0096] Table 1

[0097]

[0098]

[0099] As shown in Table 1, based on the comparison of different cathode materials, batteries were fabricated and tested. It was found that Example 1 was the best. With this spraying method, the battery specific capacity was significantly improved, and the voltage increased to 1.5V-4.2V. At the same time, the first efficiency was the best and relatively high. In addition, the capacity retention rate at 45℃ for 500 cycles was 93.5%, and the capacity retention rate at 25℃ for 1000 cycles was 94.6%, which was relatively high. Therefore, the overall performance was the best.

[0100] Actual experimental data shows that this invention can significantly improve the specific capacity and voltage of materials, while significantly reducing internal resistance and increasing cycle performance. Spraying graphene material onto the foil can greatly reduce contact internal resistance, as the resistance between materials and foil is generally the highest. After spraying graphene, the generation of internal resistance is greatly reduced, while the adhesion of the foil is increased, making it less prone to material detachment, resulting in excellent performance. The inner layer is coated with sodium nickel iron manganese oxide, and the outer layer with sodium vanadium phosphate, sprayed sequentially onto the foil. The mixture of the two materials can compensate for each other's shortcomings and leverage the advantages of each. Sodium vanadium phosphate has a relatively high voltage (up to 4.2V) and good cycle performance, but its specific capacity is relatively low. Sodium nickel iron manganese oxide has a high specific capacity and high initial efficiency, but its voltage is low. Therefore, the two materials can achieve excellent results.

[0101] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A sodium-ion battery positive electrode, comprising a current collector (10) and a positive electrode layer (20), characterized in that, The current collector (10) has opposing first and second surfaces, and the positive electrode layer (20) comprises: A first electrode layer (21) is disposed on the first surface and / or the second surface of the current collector (10); The second electrode layer (22) is disposed on the outer surface of the first electrode layer (21) away from the current collector (10) at least one layer; A third electrode layer (23) is disposed on the outer surface of at least one second electrode layer (22) away from the current collector (10); The first electrode layer (21) is made of graphene, the second electrode layer (22) is made of sodium ion layered oxide, and the third electrode layer (23) is made of a polyanionic salt compound containing sodium ions. The thickness ratio of the first electrode layer (21), the second electrode layer (22) and the third electrode layer (23) is 1:(2~6):(3~7); The polyanionic salt compound is Na3V2(PO4)3; The graphene content in the first electrode layer (21) is 85~89wt%, the sodium ion layered oxide content in the second electrode layer (22) is 93.8~96.5wt%, and the polyanionic salt compound content in the third electrode layer (23) is 96.7~97.6wt%.

2. The sodium-ion battery positive electrode sheet according to claim 1, characterized in that, The thickness of the positive electrode layer (20) is 200±10μm.

3. The sodium-ion battery positive electrode sheet according to claim 1, characterized in that, The thickness of each of the first electrode layers (21) is 20±5μm.

4. The sodium-ion battery positive electrode sheet according to claim 1, characterized in that, The chemical formula of the sodium ion layered oxide is Na. c Z d O e In the formula, the Z element is selected from one or more of Group IVB, Group VB, Group VIB, Group VIIB, Group VIII, and Group IB; 0.2 < c < 0.4, 0.2 < d < 0.4, 0.2 < e < 0.

4.

5. The sodium-ion battery positive electrode sheet according to claim 4, characterized in that, In the chemical formula of the sodium ion layered oxide, Z is selected from one or more of Ti, V, Cr, Mn, Fe, Ni, Co, and Cu.

6. The sodium-ion battery positive electrode sheet according to claim 4, characterized in that, The sodium ion layered oxide is Na[Ni] 1 / 3 Fe 1 / 3 Mn 1 / 3 O2.

7. The sodium-ion battery positive electrode sheet according to any one of claims 1 to 3, characterized in that, The materials of the first electrode layer (21), the second electrode layer (22) and the third electrode layer (23) also each independently contain a binder.

8. The sodium-ion battery positive electrode sheet according to claim 7, characterized in that, The adhesive is selected from one or more of the following: polyvinylidene fluoride, a copolymer of polyhexafluoropropylene and polyvinylidene fluoride, polyvinyl acetate, polyvinyl alcohol, polyethylene oxide, polyvinylpyrrolidone, alkylated polyethylene oxide, polyvinyl ether, polymethyl methacrylate, ethyl polyacrylate, polytetrafluoroethylene, polyvinyl chloride, polyacrylonitrile, polyvinylpyridine, styrene-butadiene rubber, or acrylonitrile-butadiene rubber.

9. The sodium-ion battery positive electrode sheet according to claim 8, characterized in that, The amount of binder in the first electrode layer (21) is 1 to 10 wt% of the weight of the graphene.

10. The sodium-ion battery positive electrode sheet according to claim 8, characterized in that, The amount of binder used in the second electrode layer (22) is 0.1 to 2 wt% of the weight of the sodium ion layered oxide.

11. The sodium-ion battery positive electrode sheet according to claim 8, characterized in that, The amount of binder in the third electrode layer (23) is 0.1 to 2 wt% of the weight of the polyanionic salt compound.

12. The sodium-ion battery positive electrode sheet according to claim 7, characterized in that, The materials of the second electrode layer (22) and the third electrode layer (23) also independently contain conductive carbon materials.

13. The sodium-ion battery positive electrode sheet according to claim 12, characterized in that, The carbon material is selected from one or more of carbon nanotubes, graphite, carbon black, graphene, or carbon fiber.

14. The sodium-ion battery positive electrode sheet according to claim 13, characterized in that, The carbon black is acetylene black and / or Ketjen black; the graphite is conductive graphite; and the carbon fiber is vapor-grown carbon fiber.

15. The sodium-ion battery positive electrode sheet according to claim 12, characterized in that, The amount of carbon material used in the second electrode layer (22) is 0.1 to 1 wt% of the weight of the sodium ion layered oxide.

16. The sodium-ion battery positive electrode sheet according to claim 12, characterized in that, The amount of carbon material used in the third electrode layer (23) is 0.1 to 1 wt% of the weight of the polyanionic salt compound.

17. The sodium-ion battery positive electrode sheet according to any one of claims 1 to 3, characterized in that, The material of the first electrode layer (21) includes 89-92 wt% graphene and 8-11 wt% polyvinylidene fluoride; The second electrode layer (22) comprises 94-98 wt% sodium nickel iron manganese oxide, 1.8-2.1 wt% carbon nanotubes and 1.8-2.1 wt% a copolymer of polyhexafluoropropylene and polyvinylidene fluoride; The third electrode layer (23) comprises 96-98 wt% sodium vanadium phosphate, 0.4-0.6 wt% carbon nanotubes, 0.9-1.1 wt% carbon black and 1.4-1.6 wt% polyvinylidene fluoride.

18. A method for preparing a sodium-ion battery positive electrode sheet according to any one of claims 1 to 17, characterized in that, The preparation method includes: A current collector (10) is provided, having opposing first and second surfaces; A first electrode layer (21) is disposed on the first surface and / or the second surface of the current collector (10); A second electrode layer (22) is disposed on the outer surface of the first electrode layer (21) away from the current collector (10). A third electrode layer (23) is disposed on the outer surface of the second electrode layer (22) away from the current collector (10).

19. The preparation method according to claim 18, characterized in that, The positive electrode layer (20) is prepared by the following steps: Step S1: A first electrode slurry containing graphene and binder is applied to at least one outer surface of the current collector (10), and after drying, a first electrode layer (21) is formed. Step S2 involves coating a second electrode slurry containing sodium ion layered oxide, binder, and carbon material onto the outer surface of the first electrode layer (21) away from the current collector (10), and then drying it to form a second electrode layer (22). Step S3 involves coating a third electrode slurry containing a polyanionic salt compound, a binder, and a carbon material onto the outer surface of the second electrode layer (22) away from the current collector (10), and then drying it to form the third electrode layer (23).

20. The preparation method according to claim 19, characterized in that, After step S3, the preparation method further includes a step of rolling the material obtained in step S3.

21. The preparation method according to claim 19, characterized in that, The viscosity of the first electrode slurry at 25°C is controlled at 3000±1000cp.

22. The preparation method according to claim 21, characterized in that, The solid content of the first electrode slurry is 20-45%.

23. The preparation method according to claim 19, characterized in that, The solid content of the second electrode slurry is 50-65%.

24. The preparation method according to claim 19, characterized in that, The solid content of the third electrode slurry is 45-60%.

25. The preparation method according to claim 19, characterized in that, The solvents in the first electrode slurry, the second electrode slurry, and the third electrode slurry each independently include one or more of N-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, N,N-dimethylaminopropylamine, ethylene oxide, or tetrahydrofuran.

26. A sodium-ion battery, said sodium-ion battery comprising a positive electrode, a negative electrode, and an electrolyte, characterized in that, The positive electrode is the sodium-ion battery positive electrode as described in any one of claims 1-17.

27. The sodium-ion battery according to claim 26, characterized in that, The negative electrode sheet includes a current collector and a negative electrode layer disposed on at least one outer surface of the current collector, wherein the active material of the negative electrode layer is selected from one or more of hard carbon, graphite or soft carbon.

28. The sodium-ion battery according to claim 26, characterized in that, The electrolyte comprises a solvent and a sodium salt. The solvent in the electrolyte is one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, or vinylene carbonate. The sodium salt in the electrolyte is one or more of NaPF6, NaClO4, or NaBF4.

29. The sodium-ion battery according to claim 28, characterized in that, The electrolyte also includes additives, which are one or more of vinylene carbonate, ethylene vinylene carbonate, fluoroethylene carbonate, or ethylene sulfate.

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