Positive electrode material, preparation method and application of binary high-nickel sodium-ion battery

Abstract

The present invention provides a binary high-nickel sodium-ion battery cathode material, a preparation method and an application thereof. The binary high-nickel sodium-ion battery cathode material includes a sodium-ion battery cathode particle material and a Ni-NaP layer coated on the surface of the cathode particle material. By mixing the sodium-ion battery cathode particle material, phosphate, and organic glue and sintering them, the binary high-nickel sodium-ion battery cathode material can be obtained, which can be applied to a sodium-ion battery cathode sheet and a sodium-ion battery. In the binary high-nickel sodium-ion battery cathode material prepared by the present invention, the Ni-NaP layer has strong conductivity, which helps to improve the surface conductivity of the particles, can increase the conductivity of the cathode material, and promotes the transport of ions between the cathode particles.

Description

Technical Field

[0001] The present invention relates to the field of sodium-ion batteries, and more particularly to a binary high-nickel sodium-ion battery cathode material, a preparation method and an application thereof. Background Art

[0002] Among various studied electrochemical energy storage technologies, lithium-ion batteries have obtained wide commercial applications due to their advantages of high energy density, high safety and low maintenance cost. However, when considering large-scale energy storage such as national power grids and communication base stations, the rising price and uneven distribution of lithium have forced people to seek other low-cost candidate systems. Under this background, sodium-ion batteries have received extensive attention from domestic and foreign researchers and have also become important substitutes for lithium-ion batteries in some application fields, especially in large-scale energy storage applications and low-speed electric vehicle application fields.

[0003] Sodium and lithium are homologous elements in the periodic table, and their working principles as batteries are extremely similar. Therefore, the research and development of sodium-ion batteries can refer to lithium-ion batteries. In addition, some materials that are not active in lithium-ion batteries may be more suitable for sodium-ion batteries, and new higher-performance materials can be developed.

[0004] However, compared with metallic lithium, sodium ions have poorer kinetic performance, and the insertion and extraction process is also accompanied by a more complex phase change process. Limited by the lower specific capacity, the application fields are greatly reduced. Therefore, how to develop a sodium-ion battery cathode material with high conductivity is one of the key problems in the development of sodium-ion batteries. Summary of the Invention

[0005] The purpose of the present invention is to provide a binary high-nickel sodium-ion battery cathode material, a preparation method and an application of a sodium-ion battery cathode to improve the conductivity of the sodium-ion battery cathode material.

[0006] In a first aspect, the present invention provides a binary high-nickel sodium-ion battery cathode material, including a sodium-ion battery cathode particle material and a Ni-NaP layer coated on the surface of the cathode particle material, and the Ni-NaP layer is obtained by sintering a mixture of an organic glue and a phosphate containing nickel and sodium.

[0007] In an alternative embodiment, the chemical formula is Na x Ni e M f O 2 @C|Ni-NaP; M is at least one of titanium, zirconium, chromium, yttrium, manganese, cobalt, zinc, scandium; where 0.5 ≤ x ≤ 1.2, 0.6 ≤ e < 1, e + f = 1; wherein the sodium-ion battery cathode particle material has a core-shell structure, and the core layer is Na x Ni e M f O2 , the shell is C, and the Ni-NaP layer is coated on the shell;

[0008] Preferably, where 0.6 ≤ x ≤ 0.9; 0.6 ≤ e < 0.9;

[0009] Preferably, the binary high-nickel sodium-ion battery cathode material is Na 0.64 Ni 0.65 M 0.35 O 2 @C|Ni-NaP, Na 0.71 Ni 0.65 M 0.35 @C|Ni-NaP, Na 0.78 Ni 0.68 M 0.32 O 2 @C|Ni-NaP, Na 0.86 Ni 0.78 M 0.22 O 2 @C|Ni-NaP, Na 0.88 Ni 0.84 M 0.16 O 2 @C|Ni-NaP, Na 0.81 Ni 0.89 M 0.11 @C|Ni-NaP, etc.

[0010] In a second aspect, the present invention provides a method for preparing a binary high-nickel sodium-ion battery cathode material, which comprises mixing sodium-ion battery cathode particle material, phosphate, and organic glue, and then sintering to obtain the binary high-nickel sodium-ion battery cathode material; the phosphate is one, two, or three of sodium phosphate, nickel phosphate, and sodium nickel phosphate.

[0011] In an alternative embodiment, the mass ratio of the sodium-ion battery cathode particle material, phosphate, and organic glue is 100: (0.05 - 20): (0.05 - 5);

[0012] Preferably, the mass ratio of the sodium-ion battery cathode particle material, phosphate, and organic glue is 100: (2 - 5): (0.05 - 0.5);

[0013] Preferably, the sintering temperature is 500 - 1000 °C, and the sintering time is 4 - 24 h;

[0014] Preferably, the sintering is carried out in an inert gas atmosphere;

[0015] Preferably, the sintering atmosphere is one of neon, argon, and nitrogen;

[0016] Preferably, the organic glue is at least one of guar gum, gum arabic, carrageenan, and styrene-butadiene rubber;

[0017] Preferably, after sintering, ball milling, water washing, drying, sieving, and demagnetization are carried out to obtain the cathode material for the binary high-nickel sodium-ion battery.

[0018] In an alternative embodiment, the preparation method of the sodium-ion battery cathode particle material includes:

[0019] Mix polyvinyl alcohol, water, nickel source solution, M-containing solution, and sodium source solution, and react to obtain a mixed gelatinous substance;

[0020] Perform evaporation, extrusion, swelling treatment, heating heat treatment, and post-treatment on the mixed gelatinous substance to obtain Na x Ni e M f O 2 @C particles.

[0021] In an alternative embodiment, polyvinyl alcohol and water are mixed and heated to 60 - 110 °C, and then nickel source solution, M-containing solution, and sodium source solution are added and mixed, and reacted to obtain a mixed gelatinous substance;

[0022] Preferably, the content of polyvinyl alcohol after mixing polyvinyl alcohol and water is 15 - 90%;

[0023] Preferably, the nickel source solution is obtained by mixing a nickel source and a citric acid solution or a citrate solution;

[0024] Preferably, the concentration of the citric acid solution is 0.05 - 1.8 mol / L;

[0025] Preferably, the nickel source is at least one of nickel oxalate, nickel formate, nickel nitrate, nickel sulfate, or nickel chloride;

[0026] Preferably, the M-containing solution is obtained by mixing an M source and a citric acid solution;

[0027] Preferably, the M source is at least one of sulfates, chlorides, or nitrates of titanium, zirconium, chromium, yttrium, manganese, cobalt, zinc, or scandium;

[0028] Preferably, the sodium source solution is at least one of sodium carbonate solution, sodium acetate solution, sodium oxalate solution, or sodium citrate solution.

[0029] In an alternative embodiment, the specific steps of the swelling treatment are: after evaporation and extrusion of the mixed gelatinous substance, it is soaked in a protonated solution and then taken out;

[0030] Preferably, the protonated solution is sodium chloride solution;

[0031] Preferably, the mass concentration of the protonated solution is 0.1 - 2%;

[0032] Preferably, the temperature of the protonation solution is 30 - 60 °C;

[0033] Preferably, the soaking time is 20 - 60 h;

[0034] Preferably, after taking out, the swollen mixed jelly is washed and dried.

[0035] In an alternative embodiment, the evaporation temperature is 80 - 110 °C, and evaporation stops when the water content of the mixed jelly ≤ 18%;

[0036] Preferably, the extruded mixed jelly is in a filamentous form;

[0037] Preferably, the temperature of the heat treatment with temperature increase is 500 - 1000 °C, the atmosphere is an oxygen-containing gas or oxygen, and the time is 0.5 - 2 h; Preferably: the atmosphere of the heat treatment with temperature increase is oxygen or air;

[0038] Preferably, the post-treatment includes annealing, ball milling, and sieving.

[0039] In a third aspect, the present invention provides an application of a binary high-nickel sodium-ion battery cathode material in a sodium-ion battery cathode sheet.

[0040] In a fourth aspect, the present invention provides a processing method of a sodium-ion battery cathode sheet, which is obtained by mixing a binary high-nickel sodium-ion battery cathode material, a binder, a conductive agent, and a solvent and then coating the mixture on a current collector;

[0041] Preferably, the binder includes one or more of polyacrylic acid (PAA), polyvinylidene fluoride (PVDF), carboxymethyl cellulose (CMC), and styrene-butadiene latex (SBR);

[0042] Preferably, the conductive agent includes one or more of acetylene black, Ketjen black, Super-P, carbon nanotubes, carbon nanofibers, activated carbon, and graphene;

[0043] Preferably, the solvent includes N-methylpyrrolidone (NMP);

[0044] Preferably, the mass ratio of the cathode material, the binder, and the conductive agent is (80 - 110) : (0.2 - 8) : (1 - 5);

[0045] Preferably, the mass ratio of the cathode material, the binder, and the conductive agent is 90 - 96 : 0.5 - 2 : 1 - 3;

[0046] Preferably, the processing includes drying and cold pressing.

[0047] The beneficial effects of the embodiments of the present invention include, for example:

[0048] In the cathode material of the binary high-nickel sodium-ion battery prepared by the present invention, the Ni-NaP layer has strong conductivity, which helps to improve the surface conductivity of the particles, can increase the conductivity of the cathode material, and promotes the ion transport between the cathode particles. In addition, the dense coating formed by the Ni-NaP layer has structural stability. On the premise of increasing the nickel content in the cathode material, it can minimize the direct contact between the electrolyte and nickel and M, thereby inhibiting the decomposition of the electrolyte on the surface of the cathode particle material, stabilizing the internal structure of the multi-layer cathode particles, and improving the intergranular cracks caused by long-cycle cycling under harsh conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can be obtained based on these drawings without creative efforts.

[0050] Figure 1 For Na in Example 3 0.78 Ni 0.68 M 0.32 @C|TEM image of the Ni-NaP cathode material;

[0051] Figure 2 For Na in Comparative Example 2 0.86 Ni 0.78 M 0.22 O 2 @C|TEM image of the cathode material. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0052] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. Usually, the components of the embodiments of the present invention described and illustrated herein can be arranged and designed in various different configurations.

[0053] Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0054] It should be noted that like reference numerals and letters refer to like items in the following figures, and thus, once an item is defined in one figure, it need not be further defined or explained in subsequent figures.

[0055] It should be noted that, without conflict, the features in the embodiments of the present invention may be combined with each other.

[0056] An embodiment of the present invention provides a binary high-nickel sodium-ion battery cathode material on the one hand, including sodium-ion battery cathode particle material and a Ni-NaP layer coated on the surface of the cathode particle material, and the Ni-NaP layer is obtained by sintering a mixture of an organic glue and a phosphate containing nickel and sodium.

[0057] In the binary high-nickel sodium-ion battery cathode material prepared in this embodiment, the Ni-NaP layer has strong conductivity, which helps to improve the surface conductivity of the particles, can increase the conductivity of the cathode material, and promotes the transport of ions between the cathode particles; in addition, the dense coating formed by the Ni-NaP layer has structural stability. On the premise of increasing the nickel content in the cathode material, it can minimize the direct contact between the electrolyte and nickel and M, thereby inhibiting the decomposition of the electrolyte on the surface of the cathode particle material, stabilizing the internal structure of the multi-layer cathode particles, and improving the intergranular cracks caused by long-cycle cycling under harsh conditions.

[0058] Further, the chemical formula is Na x Ni e M f O 2 @C|Ni-NaP; M is at least one of titanium, zirconium, chromium, yttrium, manganese, cobalt, zinc, and scandium; where 0.5 ≤ x ≤ 1.2, 0.6 ≤ e < 1, and e + f = 1; where the sodium-ion battery cathode particle material has a core-shell structure, where the core layer is Na x Ni e M f O 2 , the shell layer is C, and the Ni-NaP layer is coated on the shell layer;

[0059] Preferably, 0.6 ≤ x ≤ 0.9; 0.6 ≤ e < 0.9.

[0060] Preferably, the binary high-nickel sodium-ion battery cathode material is Na 0.64 Ni 0.65 M 0.35 O 2 @C|Ni-NaP, Na 0.71 Ni 0.65 M 0.35 @C|Ni-NaP, Na 0.78 Ni 0.68 M 0.32 O 2@C|Ni-NaP, Na 0.86 Ni 0.78 M 0.22 O 2 @C|Ni-NaP, Na 0.88 Ni 0.84 M 0.16 O 2 @C|Ni-NaP, Na 0.81 Ni 0.89 M 0.11 One of @C|Ni-NaP.

[0061] The Ni-NaP layer is coated on the shell layer, which improves the electrolyte decomposition on the surface of the cathode particle carbon, stabilizes the internal structure of the multi-layer lithium cathode particles, and can improve the intergranular cracks caused by long-term cycling under harsh conditions. The binary high-nickel sodium-ion cathode material is also double-coated, and the C layer and the Ni-NaP layer jointly stabilize Na x Ni e M f O 2 The internal structure of the particles.

[0062] The second aspect of the embodiments of the present invention provides a preparation method of a binary high-nickel sodium-ion battery cathode material. Mix the sodium-ion battery cathode particle material, phosphate, and organic glue, and sinter to obtain the binary high-nickel sodium-ion battery cathode material.

[0063] Furthermore, the mass ratio of the sodium-ion battery cathode particle material, phosphate, and organic glue is 100:(0.05 - 20):(0.05 - 5);

[0064] Preferably, the mass ratio of the sodium-ion battery cathode particle material, phosphate, and organic glue is 100:(2 - 5):(0.05 - 0.5);

[0065] Specifically, it can be 100:0.05:5, 100:10:5, 100:20:5, 100:5:0.05, 100:5:5;

[0066] Preferably, the phosphate is at least two of sodium phosphate, nickel phosphate, and sodium nickel phosphate;

[0067] Preferably, the sintering temperature is 500 - 1000 °C, specifically it can be 500 °C, 700 °C, 900 °C, 1000 °C, and the sintering time is 4 - 24 h, specifically it can be 4 h, 8 h, 12 h, 18 h, 24 h;

[0068] Preferably, the sintering is carried out in an inert gas atmosphere;

[0069] Preferably, the sintering atmosphere is one of neon, argon, and nitrogen;

[0070] Preferably, the organic glue is at least one of guar gum, gum arabic, carrageenan, and styrene-butadiene rubber;

[0071] Preferably, after sintering, ball milling, water washing, drying, sieving, and demagnetization are carried out to obtain the positive electrode material for the binary high-nickel sodium ion battery.

[0072] High-temperature sintering forms a dense Ni-NaP layer on the surface of the battery positive electrode particle material with the phosphate and the organic glue, improving the structural stability and conductivity of the composite positive electrode material, thereby enhancing the electrochemical performance of the battery.

[0073] Furthermore, the preparation method of the positive electrode particle material for the sodium ion battery includes:

[0074] Mix polyvinyl alcohol, water, a nickel source solution, an M-containing solution, and a sodium source solution, and react to obtain a mixed gelatinous substance;

[0075] Perform evaporation, extrusion, swelling treatment, heating treatment at an elevated temperature, and post-treatment on the mixed gelatinous substance to obtain Na x Ni e M f O 2 @C particles.

[0076] Furthermore, mix polyvinyl alcohol and water and heat them to 60 - 110 °C, specifically it can be 60 °C, 80 °C, 100 °C, 110 °C, add a nickel source solution, an M-containing solution, and a sodium source solution and mix them, and react to obtain a mixed gelatinous substance;

[0077] Preferably, the content of polyvinyl alcohol after mixing polyvinyl alcohol and water is 15 - 90%, specifically it can be 15%, 30%, 60%, 90%;

[0078] Preferably, the nickel source solution is obtained by mixing a nickel source and a citric acid solution or a citrate solution;

[0079] Preferably, the concentration of the citric acid solution is 0.05 - 1.8 mol / L, specifically it can be 0.05 mol / L, 0.1 mol / L, 0.5 mol / L, 1.0 mol / L, 1.5 mol / L, 1.8 mol / L;

[0080] Preferably, the nickel source is at least one of nickel oxalate, nickel formate, nickel nitrate, nickel sulfate, or nickel chloride;

[0081] Preferably, the M-containing solution is obtained by mixing an M source and a citric acid solution;

[0082] Preferably, the M source is at least one of sulfates, chlorides, or nitrates of titanium, zirconium, chromium, yttrium, manganese, cobalt, zinc, or scandium;

[0083] Preferably, the sodium source solution is at least one of sodium carbonate solution, sodium acetate solution, sodium oxalate solution or sodium citrate solution.

[0084] Polyvinyl alcohol is one of the carbon sources of the positive electrode particle material. Increasing the amount of polyvinyl alcohol in the solution will increase the solution viscosity, which is not conducive to obtaining a uniform mixed gel, and will increase the thickness of the C layer, hindering the diffusion of sodium ions to a certain extent.

[0085] Furthermore, the specific steps of the swelling treatment are as follows: after the mixed gel is evaporated and extruded, it is immersed in a protonated solution and then taken out;

[0086] Preferably, the protonated solution is sodium chloride solution;

[0087] Preferably, the mass concentration of the protonated solution is 0.1-2%, specifically it can be 0.1%, 0.5%, 1.0%, 2.0%;

[0088] Preferably, the temperature of the protonated solution is 30-60°C, specifically it can be 30°C, 40°C, 50°C, 60°C;

[0089] Preferably, the soaking time is 20-60h, specifically it can be 20h, 40h, 60h;

[0090] Preferably, after taking out, the swollen mixed gel is washed and dried.

[0091] To ensure that the mixed gel can be fully and evenly calcined, first, the mixed gel is turned into a silk-like gel. Different from the mixed gel piled up together, the heat absorption orientation degree of the cross-section of the silk-like gel is more consistent. Second, the silk-like gel can be swollen in the sodium chloride protonated solution to loosen the structure, thereby promoting the diffusion of oxygen into it during the heating process, occurring an oxidation reaction, and being fully calcined.

[0092] Furthermore, the evaporation temperature is 80-110°C, specifically it can be 80°C, 90°C, 100°C, 110°C. Evaporation stops when the water content of the mixed gel ≤ 18%. Controlling the evaporation degree is beneficial to obtaining a filamentous mixed gel forming;

[0093] Preferably, a filamentous mixed gel is obtained after extrusion;

[0094] Preferably, the temperature of the heat treatment during heating is 500-1000°C, specifically it can be 500°C, 700°C, 900°C, 1000°C, the atmosphere is air or oxygen, and the time is 0.5-2h, specifically it can be 0.5h, 1h, 2h;

[0095] Preferably, the post-treatment includes annealing, ball milling, and sieving.

[0096] The third aspect of the embodiments of the present invention provides an application of a binary high-nickel sodium-ion battery cathode material in a sodium-ion battery cathode sheet.

[0097] The fourth aspect of the embodiments of the present invention provides a processing method for a sodium-ion battery cathode sheet, which is obtained by mixing a binary high-nickel sodium-ion battery cathode material, a binder, a conductive agent, and a solvent and then coating the mixture on a current collector.

[0098] Preferably, the binder includes one or more of polyacrylic acid (PAA), polyvinylidene fluoride (PVDF), carboxymethyl cellulose (CMC), and styrene-butadiene latex (SBR);

[0099] Preferably, the conductive agent includes one or more of acetylene black, Ketjen black, Super-P, carbon nanotubes, carbon nanofibers, activated carbon, and graphene;

[0100] Preferably, the solvent includes NMP;

[0101] Preferably, the mass ratio of the cathode material, the binder, and the conductive agent is (80-110):(0.2-8):(1-5);

[0102] Preferably, the mass ratio of the cathode material, the binder, and the conductive agent is 90-96:0.5-2:1-3; specifically, it can be 93:0.5:1, 93:0.5:3, 93:0.5:2, 92:1:2, 92:2:2, 90:2:2, 96:2:2.

[0103] Preferably, the processing includes drying and cold pressing.

[0104] To achieve the above object, the features and properties of the present invention will be further described in detail below in combination with implementation cases.

[0105] Implementation cases

[0106] Implementation case 1

[0107] The binary high-nickel sodium-ion cathode material of this implementation case has the chemical formula Na 0.64 Ni 0.65 Mn 0.35 O 2 @C|Ni-NaP.

[0108] The preparation method of the binary high-nickel sodium-ion cathode material of this implementation case includes the following steps:

[0109] (1) Place polyvinyl alcohol in a heating reactor, inject deionized water, heat it to dissolve polyvinyl alcohol at 65 °C to obtain a solution containing 64.7% polyvinyl alcohol. Dissolve nickel oxalate and manganese sulfate in a solution containing 0.3 mol / L citric acid, then add a sodium source (the molar ratio of sodium, nickel, and manganese is 0.64:0.65:0.35), and stir to obtain a base solution. Inject the base solution and the polyvinyl alcohol solution (the solution containing 64.7% polyvinyl alcohol and the base solution are in a volume ratio of 10:0.5) into the reactor, mix and stir to obtain a mixed gel-like substance;

[0110] (2) Continuously heat the mixed gel-like substance at 95 °C until the water content in the mixed gel-like substance ≤ 18%, then send it to a temperature-resistant wire extruder, extrude a wire-like gel-like substance with a diameter of about 7 mm, and perform a swelling treatment (soak and stir in a 0.55% sodium chloride protonated solution at 55 °C for 24 h, take out the wire-like gel-like substance, rinse it with distilled water, and dry it in a ventilated place). Then send the wire-like gel-like substance to a heating furnace, heat it to 755 °C in an oxygen-containing atmosphere of 21% for 45 min, anneal it to room temperature, dry it, ball mill it, and sieve it to obtain Na 0.64 Ni 0.65 M 0.35 O 2 @C particles;

[0111] (3) Mix 500 g of Na 0.64 Ni 0.65 M 0.35 O 2 @C particles, 17.6 g of phosphate (a 1:1 mixture of sodium phosphate and nickel phosphate), and 0.9 g of styrene-butadiene rubber, mix and stir, heat and control the temperature to 640 °C and heat in an argon inert atmosphere for 10 h, anneal to room temperature, ball mill, wash with water, dry, sieve, and demagnetize to obtain Na 0.64 Ni 0.65 M 0.35 O 2 @C|Ni-NaP cathode material.

[0112] A method for preparing a sodium-ion battery cathode sheet, comprising the following steps:

[0113] Mix the Na 0.64 Ni 0.65 M 0.35 O 2 @C|Ni-NaP cathode material, binder polyvinylidene fluoride (PVDF), and conductive agent carbon nanofibers in a mass ratio of 95:1:1.5, mix and stir, add solvent NMP, coat it on a current collector to obtain an electrode sheet, dry it, cold press it, and prepare a sodium cathode sheet.

[0114] Implementation Case 2

[0115] The binary high-nickel sodium-ion cathode material of this embodiment has the chemical formula Na 0.71 Ni 0.65 Mn 0.35 O 2 @C|Ni-NaP.

[0116] The preparation method of the binary high-nickel sodium-ion cathode material of this embodiment includes the following steps:

[0117] (1) Place polyvinyl alcohol in a heating reactor, inject deionized water, heat it to dissolve polyvinyl alcohol at 65 °C to obtain a solution containing 64.7% polyvinyl alcohol. Dissolve nickel oxalate and manganese sulfate in a solution containing 0.3 mol / L citric acid, then add a sodium source (the molar ratio of sodium, nickel, and manganese is 0.71:0.65:0.35), stir to obtain a base solution. Inject the base solution and the polyvinyl alcohol solution (the solution containing 64.7% polyvinyl alcohol and the base solution are in a volume ratio of 10:0.5) into the reactor, mix and stir to obtain a mixed gelatinous substance;

[0118] (2) Continuously heat the mixed gelatinous substance at 95 °C until the water content in the mixed gelatinous substance ≤ 18%, then send it to a temperature-resistant wire extruder, extrude to obtain a wire-like gelatinous substance with a diameter of about 7 mm, and perform a swelling treatment (soak and stir in a 0.55% sodium chloride protonated solution at 55 °C for 24 h, take out the wire-like gelatinous substance, rinse it with distilled water, and dry it in a ventilated place). Then send the wire-like gelatinous substance to a heating furnace, heat it to 755 °C in an oxygen atmosphere containing 21% for 45 min, anneal it to room temperature, dry it, ball-mill it, and screen it to obtain Na 0.71 Ni 0.65 Mn 0.35 O 2 @C particles;

[0119] (3) Mix 500 g of Na 0.71 Ni 0.65 Mn 0.35 O 2 @C particles, 17.6 g of phosphate (obtained by mixing sodium phosphate and nickel phosphate in a 1:1 ratio), and 0.9 g of styrene-butadiene rubber, stir, heat and control the temperature at 640 °C in an argon inert atmosphere for 10 h, anneal it to room temperature, ball-mill it, wash it with water, dry it, screen it, and demagnetize it to obtain Na 0.71 Ni 0.65 Mn 0.35 O 2 @C|Ni-NaP cathode material.

[0120] A preparation method of a sodium-ion battery cathode sheet includes the following steps:

[0121] Place Na 0.71 Ni 0.65 Mn 0.35O 2 The Ni-NaP cathode material, binder polyvinylidene fluoride (PVDF), and conductive agent carbon nanofibers are mixed, stirred, and added with solvent NMP in a mass ratio of 95:1:1.5, coated on a current collector to obtain a pole piece, dried, cold-pressed, and a sodium cathode piece is prepared.

[0122] Implementation Case 3

[0123] The binary high-nickel sodium ion cathode material of this implementation case has the chemical formula Na 0.78 Ni 0.68 Mn 0.32 O 2 @C|Ni-NaP.

[0124] The preparation method of the binary high-nickel sodium ion cathode material of this implementation case includes the following steps:

[0125] (1) Place polyvinyl alcohol in a heating reactor, inject deionized water, heat to dissolve polyvinyl alcohol at 87 °C to obtain a solution containing 64.7% polyvinyl alcohol. Dissolve nickel oxalate and manganese sulfate in a solution containing 0.3 Mol / L citric acid, then add a sodium source (the molar ratio of sodium, nickel, and manganese is 0.78:0.68:0.32), stir to obtain a base solution. Inject the base solution and polyvinyl alcohol solution (the solution containing 64.7% polyvinyl alcohol and the base solution in a volume ratio of 10:0.5) into the reactor, mix and stir to obtain a mixed jelly-like substance;

[0126] (2) Continuously heat the mixed jelly-like substance at 95 °C until the water content in the mixed jelly-like substance ≤ 18%, then send it to a temperature-resistant wire extruder, extrude to obtain a wire jelly-like substance with a diameter of about 7 mm, and perform a swelling treatment (soak and stir in a 1.0% sodium chloride protonated solution at 50 °C for 36 h, take out the wire jelly-like substance, rinse it with distilled water, and dry it in a ventilated place). Then send the wire jelly-like substance to a heating furnace, heat it to 840 °C in an oxygen atmosphere containing 21% for 40 min, anneal it to room temperature, dry it, ball-mill it, and sieve it to obtain Na 0.78 Ni 0.68 Mn 0.32 O 2 @C particles;

[0127] (3) Mix 500 g of Na 0.78 Ni 0.68 Mn 0.32 O 2 @C particles, 17.6 g of phosphate (a 1:1 mixture of sodium phosphate and nickel phosphate), and 0.9 g of styrene-butadiene rubber, stir, heat and control the temperature at 640 °C in an argon inert atmosphere for 10 h, anneal to room temperature, ball-mill, wash with water, dry, sieve, and demagnetize to obtain Na 0.78 Ni 0.68 Mn0.32 O 2 @C|Ni-NaP cathode material, see the TEM image in Figure 1 。

[0128] A method for preparing a positive electrode sheet of a sodium-ion battery, comprising the following steps:

[0129] Mix, stir, and add the solvent NMP to Na 0.78 Ni 0.68 Mn 0.32 O 2 @C|Ni-NaP cathode material, binder polyvinylidene fluoride (PVDF), and conductive agent carbon nanofibers in a mass ratio of 93:1.5:2, coat the mixture on a current collector to obtain an electrode sheet, and dry and cold press to obtain a sodium positive electrode sheet.

[0130] Implementation Case 4

[0131] The binary high-nickel sodium-ion cathode material of this implementation case has the chemical formula Na 0.86 Ni 0.78 Mn 0.22 O 2 @C|Ni-NaP.

[0132] The preparation method of the binary high-nickel sodium-ion cathode material of this implementation case comprises the following steps:

[0133] (1) Place polyvinyl alcohol in a heating reaction kettle, inject deionized water, heat it to dissolve polyvinyl alcohol at 82 °C to obtain a solution containing 64.7% polyvinyl alcohol. Dissolve nickel oxalate and manganese sulfate in a solution containing 0.3 mol / L citric acid, then add a sodium source (the molar ratio of sodium, nickel, and manganese is 0.86:0.78:0.22), stir to obtain a base solution. Inject the base solution and the polyvinyl alcohol solution (the solution containing 64.7% polyvinyl alcohol and the base solution in a volume ratio of 10:0.5) into the reaction kettle, mix and stir to obtain a mixed gel;

[0134] (2) Continuously heat the mixed gel at 95 °C until the water content in the mixed gel ≤ 18%, then send it to a temperature-resistant wire extruder, extrude to obtain a wire-like gel with a diameter of about 7 mm, and perform a swelling treatment (soak and stir in a 1.0% sodium chloride protonated solution at 50 °C for 36 h, take out the wire-like gel, rinse it with distilled water, dry it in a ventilated place), then send the wire-like gel to a heating furnace, heat it to 840 °C in an oxygen atmosphere containing 21% for 40 min, anneal it to room temperature, dry, ball mill, and screen to obtain Na 0.86 Ni 0.78 Mn 0.22 O 2 @C particles;

[0135] (3) Take 500 g of Na0.86 Ni 0.78 Mn 0.22 O 2 @C particles, 17.6 g of phosphate (obtained by mixing sodium phosphate and nickel phosphate in a 1:1 ratio), 0.9 g of styrene-butadiene rubber are mixed and stirred, heated, and the temperature is controlled at 640 °C and heated in an argon inert atmosphere for 10 h, annealed to room temperature, ball-milled, washed with water, dried, sieved, and demagnetized to obtain Na 0.86 Ni 0.78 Mn 0.22 O 2 @C|Ni-NaP cathode material for sodium-ion batteries.

[0136] A method for preparing a cathode sheet for a sodium-ion battery, comprising the following steps:

[0137] Mix Na 0.86 Ni 0.78 Mn 0.22 O 2 @C|Ni-NaP cathode material, binder polyvinylidene fluoride (PVDF), and conductive agent carbon nanofibers are mixed, stirred, and added with solvent NMP in a mass ratio of 94:1:2, coated on a current collector to obtain a cathode sheet, dried, and cold-pressed to obtain a sodium cathode sheet.

[0138] Example 5

[0139] The binary high-nickel sodium-ion cathode material of this example has the chemical formula Na 0.88 Ni 0.84 Mn 0.16 O 2 @C|Ni-NaP.

[0140] The preparation method of the binary high-nickel sodium-ion cathode material of this example comprises the following steps:

[0141] (1) Place polyvinyl alcohol in a heating reactor, inject deionized water, heat to dissolve polyvinyl alcohol at 82 °C to obtain a solution containing 64.7% polyvinyl alcohol. Dissolve nickel oxalate and manganese sulfate in a solution containing 0.3 mol / L citric acid, then add a sodium source (the molar ratio of sodium, nickel, and manganese is 0.88:0.84:0.16), stir to obtain a base solution. Inject the base solution and the polyvinyl alcohol solution (the solution containing 64.7% polyvinyl alcohol and the base solution are in a volume ratio of 10:1.2) into the reactor, mix and stir to obtain a mixed gel-like substance;

[0142] (2) Continuously heat the mixed jelly at 96 °C until the water content in the mixed jelly ≤ 18%, then send it to a temperature-resistant wire extruder, extrude to obtain a wire jelly with a diameter of about 7 mm, and perform a swelling treatment (soak and stir in a 1.0% sodium chloride protonation solution at 50 °C for 36 h, take out the wire jelly, rinse it clean with distilled water, and dry it in a ventilated place). Then send the wire jelly to a heating furnace, heat it to 840 °C in an oxygen-containing atmosphere of 21% for 40 min, anneal it to room temperature, dry it, ball mill it, and screen it to obtain Na 0.88 Ni 0.84 Mn 0.16 O 2 @C particles;

[0143] (3) Mix 500 g of Na 0.88 Ni 0.84 Mn 0.16 O 2 @C particles, 17.6 g of phosphate (a 1:1 mixture of sodium phosphate and nickel phosphate), and 0.9 g of styrene-butadiene rubber, mix and stir, heat and control the temperature at 640 °C in an argon inert atmosphere for 10 h, anneal to room temperature, ball mill, wash with water, dry, screen, and demagnetize to obtain Na 0.88 Ni 0.84 Mn 0.16 O 2 @C|Ni-NaP cathode material.

[0144] A method for preparing a positive electrode sheet of a sodium-ion battery, comprising the following steps:

[0145] Mix the Na 0.88 Ni 0.84 Mn 0.16 O 2 @C|Ni-NaP cathode material, binder polyvinylidene fluoride (PVDF), and conductive agent carbon nanofibers in a mass ratio of 96:1.2:2.5, mix and stir, add solvent NMP, coat on a current collector to obtain a positive electrode sheet, dry, cold press, and prepare a sodium positive electrode sheet.

[0146] Example 6

[0147] The binary high-nickel sodium-ion cathode material of this example has the chemical formula Na 0.81 Ni 0.89 Mn 0.11 O 2 @C|Ni-NaP.

[0148] The method for preparing the binary high-nickel sodium-ion cathode material of this example comprises the following steps:

[0149] (1) Place polyvinyl alcohol in a heating reactor, inject deionized water, heat it at 94 °C until the polyvinyl alcohol dissolves to obtain a solution containing 64.7% polyvinyl alcohol. Dissolve nickel oxalate and manganese sulfate in a solution containing 0.66 mol / L citric acid, then add a sodium source (the molar ratio of sodium, nickel, and manganese is 0.81:0.89:0.11), and stir to obtain a base solution. Inject the base solution and the polyvinyl alcohol solution (the solution containing 64.7% polyvinyl alcohol and the base solution are in a volume ratio of 10:1.2) into the reactor, mix and stir to obtain a mixed gel-like substance;

[0150] (2) Continuously heat the mixed gel-like substance at 96 °C until the water content in the mixed gel-like substance ≤ 18%, then send it to a temperature-resistant wire extruder, extrude to obtain a wire-like gel-like substance with a diameter of about 7 mm, and perform a swelling treatment (soak and stir in a 1.3% sodium chloride protonated solution at 35 °C for 48 h, take out the wire-like gel-like substance, rinse it with distilled water, and dry it in a ventilated place). Then send the wire-like gel-like substance to a heating furnace, heat it to 840 °C in an oxygen-containing atmosphere of 21% for heat treatment for 40 min, anneal it to room temperature, dry it, ball mill it, and sieve it to obtain Na 0.81 Ni 0.89 Mn 0.11 O 2 @C particles;

[0151] (3) Mix 500 g of Na 0.81 Ni 0.89 Mn 0.11 O 2 @C particles, 17.6 g of phosphate (a 1:1 mixture of sodium phosphate and nickel phosphate), and 0.9 g of styrene-butadiene rubber, stir, heat and control the temperature to 640 °C and heat in an argon inert atmosphere for 10 h, anneal to room temperature, ball mill, wash with water, dry, sieve, and demagnetize to obtain Na 0.81 Ni 0.89 Mn 0.11 O 2 @C|Ni-NaP cathode material.

[0152] A method for preparing a positive electrode sheet of a sodium-ion battery, comprising the following steps:

[0153] Mix the Na 0.81 Ni 0.89 Mn 0.11 O 2 @C|Ni-NaP cathode material, binder polyvinylidene fluoride (PVDF), and conductive agent carbon nanofibers in a mass ratio of 96:2:2, stir, add the solvent NMP, coat it on a current collector to obtain an electrode sheet, dry, cold press, and prepare a sodium positive electrode sheet.

[0154] Example 7

[0155] The binary high-nickel sodium-ion cathode material of this embodiment has the chemical formula Na 0.81 Ni 0.89 C O0.11 O 2 @C|Ni-NaP.

[0156] The preparation method of the binary high-nickel sodium-ion cathode material of this embodiment includes the following steps:

[0157] (1) Place polyvinyl alcohol in a heating reactor, inject deionized water, heat it to dissolve polyvinyl alcohol at 60 °C to obtain a solution containing 90% polyvinyl alcohol. Dissolve nickel oxalate and cobalt chloride in a solution containing 1.8 mol / L citric acid, then add a sodium source (the molar ratio of sodium, nickel, and cobalt is 0.81:0.89:0.11), stir to obtain a base solution. Inject the base solution and the polyvinyl alcohol solution (the solution containing 90% polyvinyl alcohol and the base solution are in a volume ratio of 10:1.2) into the reactor, mix and stir to obtain a mixed jelly-like substance;

[0158] (2) Continuously heat the mixed jelly-like substance at 80 °C until the water content in the mixed jelly-like substance ≤ 18%, then send it to a temperature-resistant wire extruder, extrude to obtain a wire jelly-like substance with a diameter of about 7 mm, and perform a swelling treatment (soak and stir in a 0.13% sodium chloride protonated solution at 60 °C for 20 h, take out the wire jelly-like substance, rinse it with distilled water, dry it in a ventilated place), then send the wire jelly-like substance to a heating furnace, heat it to 1000 °C under an oxygen atmosphere containing 21% for heat treatment for 30 min, anneal it to room temperature, dry, ball mill, and screen to obtain Na 0.81 Ni 0.89 C O0.11 O 2 @C particles;

[0159] (3) Mix 500 g of Na 0.81 Ni 0.89 C O0.11 O 2 @C particles, 50 g of phosphate (a mixture of sodium phosphate and nickel phosphate in a ratio of 2:1), and 25 g of styrene-butadiene rubber, mix and stir, heat and control the temperature to 1000 °C and heat in an argon inert atmosphere for 4 h, anneal to room temperature, ball mill, wash with water, dry, screen, and demagnetize to obtain Na 0.81 Ni 0.89 C O0.11 O 2 @C|Ni-NaP cathode material.

[0160] A preparation method of a sodium-ion battery cathode sheet includes the following steps:

[0161] Put Na 0.81 Ni 0.89 Mn 0.11 O2 The Ni-NaP cathode material, binder polyvinylidene fluoride (PVDF), and conductive agent carbon nanofibers are mixed, stirred, and added with solvent NMP in a mass ratio of 80:0.5:5, coated on a current collector to obtain a pole piece, dried, cold-pressed, and a sodium cathode piece is prepared.

[0162] Example 8

[0163] The binary high-nickel sodium ion cathode material in this example has the chemical formula Na 0.81 Ni 0.89 Ti 0.11 O 2 @C|Ni-NaP.

[0164] The preparation method of the binary high-nickel sodium ion cathode material in this example includes the following steps:

[0165] (1) Place polyvinyl alcohol in a heating reactor, inject deionized water, heat to dissolve polyvinyl alcohol at 110 °C to obtain a solution containing 15% polyvinyl alcohol. Dissolve nickel oxalate and titanium nitrate in a solution containing 0.05 mol / L citric acid, then add a sodium source (the molar ratio of sodium, nickel, and titanium is 0.81:0.89:0.11), stir to obtain a base solution. Inject the base solution and the polyvinyl alcohol solution (the solution containing 15% polyvinyl alcohol and the base solution are in a volume ratio of 10:1.2) into the reactor, mix and stir to obtain a mixed gelatinous substance;

[0166] (2) Continuously heat the mixed gelatinous substance at 110 °C until the water content in the mixed gelatinous substance ≤ 18%, then send it to a temperature-resistant wire extruder, extrude to obtain a wire gelatinous substance with a diameter of about 7 mm, and perform a swelling treatment (soak and stir in a 2.0% sodium chloride protonation solution at 30 °C for 60 h, take out the wire gelatinous substance, rinse it with distilled water, and dry it in a ventilated place). Then send the wire gelatinous substance to a heating furnace, heat it to 500 °C under an oxygen atmosphere containing 21% for heat treatment for 120 min, anneal it to room temperature, dry it, ball mill it, and screen it to obtain Na 0.81 Ni 0.89 Ti 0.11 O 2 @C particles;

[0167] (3) Mix 500 g of Na 0.81 Ni 0.89 Ti 0.11 O 2 @C particles, 0.25 g of phosphate (obtained by mixing sodium phosphate and nickel phosphate in a ratio of 1:2), and 0.25 g of styrene-butadiene rubber, stir, heat and control the temperature at 500 °C under an argon inert atmosphere for 24 h, anneal to room temperature, ball mill, wash with water, dry, screen, and demagnetize to obtain Na 0.81 Ni 0.89 Ti0.11 O 2 @C|Ni-NaP cathode material.

[0168] A method for preparing a positive electrode sheet of a sodium-ion battery, comprising the following steps:

[0169] Mix Na 0.81 Ni 0.89 Ti 0.11 O 2 @C|Ni-NaP cathode material, binder polyvinylidene fluoride (PVDF), and conductive agent carbon nanofibers in a mass ratio of 110:8:1, stir, add solvent NMP, coat on a current collector to obtain an electrode sheet, dry, cold press, and prepare a sodium positive electrode sheet.

[0170] Comparative Example 1

[0171] The binary high-nickel sodium-ion cathode material of this comparative example has the chemical formula Na 0.64 Ni 0.65 Mn 0.35 O 2 @C|Ni-NaP.

[0172] The preparation method of the binary high-nickel sodium-ion cathode material of this comparative example comprises the following steps:

[0173] (1) Place polyvinyl alcohol in a heating reaction kettle, inject deionized water, heat to dissolve polyvinyl alcohol at 65 °C to obtain a solution containing 64.7% polyvinyl alcohol. Dissolve nickel oxalate and manganese sulfate in a solution containing 0.3 mol / L citric acid, then add a sodium source (the molar ratio of sodium, nickel, and manganese is 0.64:0.65:0.35), stir to obtain a base solution. Inject the base solution and the polyvinyl alcohol solution (the solution containing 64.7% polyvinyl alcohol and the base solution are in a volume ratio of 10:0.5) into the reaction kettle, mix and stir to obtain a mixed gel;

[0174] (2) Continuously heat the mixed gel at 95 °C until the water content in the mixed gel ≤ 18%, then send it to a temperature-resistant wire extruder, extrude to obtain a wire gel with a diameter of about 7 mm. Send the wire gel to a heating furnace, heat it to 755 °C in an oxygen atmosphere containing 21% for 45 min, anneal to room temperature, dry, ball mill, and screen to obtain Na 0.64 Ni 0.65 M 0.35 O 2 @C particles;

[0175] (3) Take 500 g of Na 0.64 Ni 0.65 M 0.35 O 2@C particles, 17.6 g of phosphate (a 1:1 mixture of sodium phosphate and nickel phosphate), and 0.9 g of styrene-butadiene rubber are mixed and stirred, heated to 640 °C under an argon inert atmosphere for 10 h, annealed to room temperature, ball-milled, washed with water, dried, sieved, and demagnetized to obtain Na 0.64 Ni 0.65 M 0.35 O 2 @C|Ni-NaP cathode material.

[0176] A method for preparing a sodium-ion battery cathode sheet, comprising the following steps:

[0177] Mix Na 0.64 Ni 0.65 M 0.35 O 2 @C|Ni-NaP cathode material, binder polyvinylidene fluoride (PVDF), and conductive agent carbon nanofibers are mixed, stirred, and added with solvent NMP according to a mass ratio of 95:1:1.5, coated on a current collector to obtain a cathode sheet, dried, and cold-pressed to obtain a sodium cathode sheet.

[0178] Comparative Example 2

[0179] The binary high-nickel sodium-ion cathode material of this comparative example has the chemical formula Na 0.86 Ni 0.78 Mn 0.22 O 2 @C.

[0180] The preparation method of the binary high-nickel sodium-ion cathode material of this comparative example comprises the following steps:

[0181] (1) Polyvinyl alcohol is placed in a heating reaction kettle, deionized water is injected, and it is heated to dissolve polyvinyl alcohol at 82 °C to obtain a solution containing 64.7% polyvinyl alcohol. Nickel oxalate and manganese sulfate are dissolved in a solution containing 0.3 mol / L citric acid, and then a sodium source (the molar ratio of sodium, nickel, and manganese is 0.86:0.78:0.22) is added and stirred to obtain a base solution. The base solution and the polyvinyl alcohol solution (the solution containing 64.7% polyvinyl alcohol and the base solution are in a volume ratio of 10:0.5) are injected into the reaction kettle, mixed, and stirred to obtain a mixed gel;

[0182] (2) The mixed gel is continuously heated at 95 °C until the water content in the mixed gel ≤ 18%, and then sent to a temperature-resistant wire extruder to extrude a wire-like gel with a diameter of about 7 mm. It is subjected to a swelling treatment (soaked and stirred in a 1.0% sodium chloride protonation solution at 50 °C for 36 h, the wire-like gel is taken out, rinsed with distilled water, and dried in a ventilated place), and then the wire-like gel is sent to a heating furnace. It is heated to 840 °C in an oxygen atmosphere containing 21% for 40 min, annealed to room temperature, dried, ball-milled, and sieved to obtain Na0.86 Ni 0.78 Mn 0.22 O 2 @C particles, see the TEM image in Figure 2 。

[0183] A method for preparing a positive electrode sheet of a sodium-ion battery, comprising the following steps:

[0184] Mix Na 0.86 Ni 0.78 Mn 0.22 O 2 @C cathode material, binder polyvinylidene fluoride (PVDF), and conductive agent carbon nanofibers in a mass ratio of 94:1:2, mix, stir, add solvent NMP, coat on a current collector to obtain an electrode sheet, dry, cold press, and prepare a sodium cathode sheet.

[0185] Comparative Example 3

[0186] The binary high-nickel sodium-ion cathode material of this comparative example has the chemical formula Na 0.81 Ni 0.89 Mn 0.11 O 2 @C.

[0187] The preparation method of the binary high-nickel sodium-ion cathode material of this embodiment comprises the following steps:

[0188] (1) Place polyvinyl alcohol in a heating reactor, inject deionized water, heat to dissolve polyvinyl alcohol at 94 °C to obtain a solution containing 64.7% polyvinyl alcohol. Dissolve nickel oxalate and manganese sulfate in a solution containing 0.66 mol / L citric acid, then add a sodium source (the molar ratio of sodium, nickel, and manganese is 0.81:0.89:0.11), stir to obtain a base solution. Inject the base solution and the polyvinyl alcohol solution (the solution containing 64.7% polyvinyl alcohol and the base solution are in a volume ratio of 10:1.2) into the reactor, mix and stir to obtain a mixed gel;

[0189] (2) Continuously heat the mixed gel at 96 °C until the water content in the mixed gel ≤ 18%, then send it to a temperature-resistant wire extruder, extrude to obtain a wire-like gel with a diameter of about 7 mm, and perform a swelling treatment (soak and stir in a 1.3% sodium chloride protonated solution at 35 °C for 48 h, take out the wire-like gel, rinse it with distilled water, dry it in a ventilated place), then send the wire-like gel to a heating furnace, heat it to 840 °C under an oxygen atmosphere containing 21% for 40 min, anneal to room temperature, dry, ball mill, and screen to obtain Na 0.81 Ni 0.89 Mn 0.11 O 2 @C particles.

[0190] A preparation method for the positive electrode sheet of a sodium-ion battery, comprising the following steps:

[0191] Mix Na 0.88 Ni 0.84 Mn 0.16 O 2 @C positive electrode material, binder polyvinylidene fluoride (PVDF), and conductive agent carbon nanofibers are mixed at a mass ratio of 96:2:2, stirred, solvent NMP is added, and then coated on a current collector to obtain an electrode sheet, which is dried, cold-pressed to obtain a sodium positive electrode sheet.

[0192] Testing of the negative electrode material, electrode sheet, and battery in the implementation cases and comparative cases:

[0193] 1. Use a specific surface area tester to measure the specific surface area of the positive electrode material, a laser particle size analyzer to measure the median particle size D50 of the positive electrode material, and a density meter to measure the tap density.

[0194] 2. The positive electrode sheets prepared in the implementation cases and comparative cases are placed in a vacuum oven for drying (80°C, 3 h); and then punched into circular sheets with a diameter of 12 mm. In a half-cell, the positive electrode uses the dried electrode sheet, the positive electrode uses a sodium sheet as the counter electrode, the separator is a PP and PE composite separator, and the electrolyte: 1M NaPF 6 in EC, DMC, DEC (volume ratio 1:1:1).

[0195] 3. Use a CT2001A battery testing system to test the prepared half-cell, with a cut-off voltage of 2.8 - 4.1V. First, charge at a constant current of 0.1C to 4.1V, then charge at a constant voltage of 4.1V until the current ≤ 0.05C, and perform a discharge performance test at 0.1C.

[0196] Table 1 Specific surface area, particle size, and tap density of the positive electrode materials in the implementation cases and comparative cases

[0197]

[0198] The specific surface areas of the binary high-nickel sodium-ion positive electrode materials prepared in Implementation Cases 1 - 6 are shown in Table 1. The D50 of the binary high-nickel sodium-ion positive electrode material is 3.45 - 3.58 μm, the specific surface area is 2.28 - 2.54 m 2 / g, and the tap density is 3.13 - 3.55 g / cm 3 .

[0199] Table 2 Electrical properties of the batteries prepared in the implementation cases and Comparative Cases 1 - 3

[0200]

[0201] As can be seen from the test results in Table 2, the initial discharge specific capacities of the half-cells prepared in Examples 1-6 and Comparative Examples 1-3 are respectively between 132.2 and 149.3 mAh / g. The discharge specific capacities of Example 1 and Comparative Example 1 are not much different, but the initial Coulombic efficiency and the capacity retention rates at the 150th and 500th cycles of Comparative Example 1 are lower than those of Example 1, indicating that the swelling treatment is beneficial to improving the performance of the cathode material. The initial Coulombic efficiency and the capacity retention rates at the 150th and 500th cycles of Comparative Examples 2 and 3 are lower than those of Examples 1-6, indicating that the Ni-NaP layer structure obtained by adding a modified coating in Examples 1-6 improves the surface conductivity of the cathode particles and has strong structural stability.

[0202] The above is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed by the present invention should be covered by the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. A cathode material for a binary high-nickel sodium-ion battery, characterized in that, it includes cathode particle materials for a sodium-ion battery and a Ni-NaP layer coated on the surface of the cathode particle materials. The Ni-NaP layer is obtained by sintering after mixing an organic glue with a phosphate containing nickel and sodium. The organic glue is at least one of guar gum, gum arabic, carrageenan, and styrene-butadiene rubber.

2. The cathode material for a binary high-nickel sodium-ion battery according to claim 1, characterized in that, The chemical formula is Na x Ni e M f O 2 @C|Ni-NaP; wherein M is at least one of titanium, zirconium, chromium, yttrium, manganese, cobalt, zinc, and scandium; where 0.5 ≤ x ≤ 1.2, 0.6 ≤ e < 1, and e + f = 1; wherein the sodium-ion battery cathode particle material has a core-shell structure, wherein the core layer is Na x Ni e M f O 2 , the shell layer is C, and the Ni-NaP layer is coated on the shell layer.

3. The cathode material for a binary high-nickel sodium-ion battery according to claim 2, characterized in that, where 0.6 ≤ x ≤ 0.9; 0.6 ≤ e < 0.

9.

4. A preparation method for the cathode material for a binary high-nickel sodium-ion battery according to any one of claims 1-3, characterized in that, mix the cathode particle materials for the sodium-ion battery, phosphate, and organic glue, and sinter to obtain the cathode material for the binary high-nickel sodium-ion battery; the phosphate includes nickel salt and sodium salt.

5. The preparation method for the cathode material for a binary high-nickel sodium-ion battery according to claim 4, characterized in that, the mass ratio of the cathode particle materials for the sodium-ion battery, phosphate, and organic glue is 100:(0.05 - 20):(0.05 - 5).

6. The preparation method for the cathode material for a binary high-nickel sodium-ion battery according to claim 5, characterized in that, the mass ratio of the cathode particle materials for the sodium-ion battery, phosphate, and organic glue is 100:(2 - 5):(0.05 - 0.5).

7. The preparation method for the cathode material for a binary high-nickel sodium-ion battery according to claim 5, characterized in that, the sintering temperature is 500 - 1000 °C, and the sintering time is 4 - 24 h.

8. The preparation method for the cathode material for a binary high-nickel sodium-ion battery according to claim 5, characterized in that, the phosphate includes at least two of sodium phosphate, nickel phosphate, and sodium nickel phosphate.

9. The preparation method for the cathode material for a binary high-nickel sodium-ion battery according to claim 5, characterized in that, the sintering is carried out in an inert gas atmosphere.

10. The preparation method for the cathode material for a binary high-nickel sodium-ion battery according to claim 5, characterized in that, the sintering atmosphere is one of neon, argon, and nitrogen.

11. The preparation method for the cathode material for a binary high-nickel sodium-ion battery according to claim 5, characterized in that, carry out ball milling, water washing, drying, sieving, and demagnetization after sintering to obtain the cathode material for the binary high-nickel sodium-ion battery.

12. The preparation method for the cathode material for a binary high-nickel sodium-ion battery according to claim 4, characterized in that, the preparation method for the cathode particle materials for the sodium-ion battery includes: mix polyvinyl alcohol, water, nickel source solution, M-containing solution, and sodium source solution, and react to obtain a mixed jelly-like substance; The mixed jelly-like substance is subjected to evaporation, extrusion, swelling treatment, heat treatment with temperature increase, and post-treatment to obtain Na x Ni e M f O 2 @C particles.

13. The preparation method for the cathode material for a binary high-nickel sodium-ion battery according to claim 12, characterized in that, mix polyvinyl alcohol and water and heat to 60 - 110 °C, add nickel source solution, M-containing solution, and sodium source solution to mix and react to obtain a mixed jelly-like substance.

14. The preparation method of the binary high-nickel sodium-ion battery cathode material according to claim 13, characterized in that the content of polyvinyl alcohol is 15 - 90% after mixing polyvinyl alcohol and water.

15. The preparation method of the binary high-nickel sodium-ion battery cathode material according to claim 13, characterized in that the nickel source solution is obtained by mixing a nickel source and a citric acid solution or a citrate solution.

16. The preparation method of the binary high-nickel sodium-ion battery cathode material according to claim 15, characterized in that the concentration of the citric acid solution is 0.05 - 1.8 mol / L.

17. The preparation method of the binary high-nickel sodium-ion battery cathode material according to claim 13, characterized in that the nickel source is at least one of nickel oxalate, nickel formate, nickel nitrate, nickel sulfate or nickel chloride.

18. The preparation method of the binary high-nickel sodium-ion battery cathode material according to claim 13, characterized in that the solution containing M is obtained by mixing an M source and a citric acid solution.

19. The preparation method of the binary high-nickel sodium-ion battery cathode material according to claim 13, characterized in that the M source is at least one of sulfates, chlorides, nitrates of titanium, zirconium, chromium, yttrium, manganese, cobalt, zinc, scandium.

20. The preparation method of the binary high-nickel sodium-ion battery cathode material according to claim 13, characterized in that the sodium source solution is at least one of sodium carbonate solution, sodium acetate solution, sodium oxalate solution or sodium citrate solution.

21. The preparation method of the binary high-nickel sodium-ion battery cathode material according to claim 12, characterized in that the specific steps of the swelling treatment are: after evaporating and extruding the mixed colloid, it is soaked in a protonated solution and then taken out.

22. The preparation method of the binary high-nickel sodium-ion battery cathode material according to claim 21, characterized in that the protonated solution is sodium chloride solution.

23. The preparation method of the binary high-nickel sodium-ion battery cathode material according to claim 21, characterized in that the mass concentration of the protonated solution is 0.1 - 2%.

24. The preparation method of the binary high-nickel sodium-ion battery cathode material according to claim 21, characterized in that the temperature of the protonated solution is 30 - 60 °C.

25. The preparation method of the binary high-nickel sodium-ion battery cathode material according to claim 21, characterized in that the soaking time is 20 - 60 h.

26. The preparation method of the binary high-nickel sodium-ion battery cathode material according to claim 21, characterized in that after taking out, the swollen mixed colloid is washed and dried.

27. The preparation method of the binary high-nickel sodium-ion battery cathode material according to claim 12, characterized in that the temperature of the evaporation is 80 - 110 °C, and the evaporation is stopped when the water content of the mixed colloid ≤ 18%.

28. The preparation method of the binary high-nickel sodium-ion battery cathode material according to claim 27, characterized in that the extruded product is a filamentous mixed colloid.

29. The preparation method of the binary high-nickel sodium-ion battery cathode material according to claim 27, characterized in that The temperature of the heating heat treatment is 500 - 1000 °C, the atmosphere is an oxygen-containing gas or oxygen, and the time is 0.5 - 2 h.

30. The preparation method of the binary high-nickel sodium-ion battery cathode material according to claim 29, characterized in that, the atmosphere of the heating heat treatment is oxygen or air.

31. The preparation method of the binary high-nickel sodium-ion battery cathode material according to claim 27, characterized in that, the post-treatment includes annealing, ball milling and sieving.

32. A sodium-ion battery cathode sheet, characterized in that, it includes the binary high-nickel sodium-ion battery cathode material according to any one of claims 1 - 3.

33. A preparation method of the sodium-ion battery cathode sheet according to claim 32, characterized in that, the binary high-nickel sodium-ion battery cathode material, binder, conductive agent and solvent are mixed and then coated on a current collector, and processed to obtain the sodium-ion battery cathode sheet.

34. The preparation method of the sodium-ion battery cathode sheet according to claim 33, characterized in that, the binder includes one or more of polyacrylic acid, polyvinylidene fluoride, carboxymethyl cellulose and styrene-butadiene latex.

35. The preparation method of the sodium-ion battery cathode sheet according to claim 33, characterized in that, the conductive agent includes one or more of acetylene black, Ketjen black, Super-P, carbon nanotubes, carbon nanofibers, activated carbon and graphene.

36. The preparation method of the sodium-ion battery cathode sheet according to claim 33, characterized in that, the solvent includes N-methylpyrrolidone.

37. The preparation method of the sodium-ion battery cathode sheet according to claim 33, characterized in that, the mass ratio of the cathode material, binder and conductive agent is (80 - 110) : (0.2 - 8) : (1 - 5).

38. The preparation method of the sodium-ion battery cathode sheet according to claim 33, characterized in that, the mass ratio of the cathode material, binder and conductive agent is (90 - 96) : (0.5 - 2) : (1 - 3).

39. The preparation method of the sodium-ion battery cathode sheet according to claim 33, characterized in that, the processing includes drying and cold pressing.

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