Double-layer coated composite sodium supplementing agent for sodium ion battery as well as preparation method and application of double-layer coated composite sodium supplementing agent

Abstract

The invention discloses a sodium ion battery double-layer coated composite sodium supplementing agent and a preparation method and application thereof, and relates to the technical field of new energy batteries, the sodium supplementing agent is composed of an inner core composite matrix and a shell double-coating layer; the core composite matrix is alpha A (1-alpha) D; the shell double-coating layer wraps the outer part of the inner core composite matrix and comprises a first coating layer E and a second coating layer G from inside to outside; wherein A is Na Ni < x > M < 1-x > O < y >, and D is N pi < z >. The invention also discloses a preparation method of the sodium supplementing agent and application of the sodium supplementing agent in a sodium ion battery. The sodium supplementing agent can compensate the loss of irreversible active sodium in the sodium-ion battery, is beneficial to improving the energy density of the battery, realizes the increase of the coulombic efficiency and the cycle index of the battery, and is beneficial to large-scale popularization and application of the sodium-ion battery in the field of energy storage requiring more than 10,000 cycles.

Description

Technical Field

[0001] The present invention relates to the technical field of new energy batteries, and in particular to a double-layer coated composite sodium supplement for sodium ion batteries, and a preparation method and application thereof. Background Art

[0002] Sodium-ion batteries have the advantages of excellent low-temperature (-40°C) performance, high safety, fast charging speed, high discharge rate (40C), zero-voltage storage and transportation; at the same time, the earth's sodium resources are abundant, more than 400 times the reserves of lithium. Therefore, the development of sodium-ion batteries is a favorable supplement and replacement for lithium iron phosphate lithium-ion batteries and ternary lithium-ion batteries. Due to the inherent advantages of sodium-ion batteries, they can be widely used in power tools, car start-stop, communication base stations, small energy storage, large energy storage and passenger cars in the future. With the further reduction of the cost of sodium-ion batteries, it is an inevitable trend to replace lead-acid batteries used in two-wheeled vehicles and low-speed vehicles.

[0003] At present, due to the shortcomings of low energy density and poor cycle performance of sodium-ion batteries, the market application of sodium-ion batteries is relatively slow. One of the main reasons is that during the initial charging process of sodium-ion batteries, a layer of solid electrolyte interface (SEI) film will react on the surface of the negative electrode. Although the formation of the SEI film is particularly critical to the reliability of the battery, it causes the loss of some sodium ions, resulting in irreversible capacity loss and a decrease in coulombic efficiency, which affects the energy density of the sodium-ion battery. On the other hand, as the number of cycles increases, the layered oxide positive electrode material of the sodium-ion battery undergoes a phase transition, causing the particles to expand and crush, resulting in the consumption of some active sodium ions, resulting in a decrease in battery capacity and a decrease in the number of cycles. Therefore, improving the coulombic efficiency and cycle number of sodium-ion batteries is a key technical problem. Summary of the invention

[0004] In order to solve the above technical problems, the purpose of the present invention is to provide a double-layer coated composite sodium supplement for sodium ion batteries and a preparation method and application thereof, wherein the sodium supplement can compensate for the loss of irreversible active sodium in sodium ion batteries, help to improve the energy density of the battery, achieve an increase in the coulombic efficiency and the number of cycles of the battery, and facilitate the large-scale promotion and application of sodium ion batteries in the field of energy storage requiring more than 10,000 cycles.

[0005] The technical solution of the present invention to solve the above technical problems is as follows: a double-layer coated composite sodium supplement for sodium ion batteries is provided, which is composed of a core composite matrix and an outer shell double coating layer; the core composite matrix is ​​αA∙(1-α)D, 0<α<1; the outer shell double coating layer is wrapped outside the core composite matrix, and includes a first coating layer E and a second coating layer G from inside to outside; Where A is Na a Nix M 1-x O y , 2≤a≤8, 0≤x≤1, 1.95≤y≤6, M is at least one of Cu, Co, Fe, Mn, Zn, Zr, Mo, B and F; D is Na b Π z , 2≤b≤3, 1≤z≤2, Π is at least one of C, O, S, N and P.

[0006] Furthermore, the particle size D of A in the core matrix 50 3.5-15 μm.

[0007] Furthermore, the first coating layer E is at least one of the compounds of elements Sb, Sn, Ce, Mg, Zr, Y, Ti and Al. The above elements account for 0.05-1% of the total mass ratio of the double-layer coated composite sodium supplement for sodium ion batteries.

[0008] Further, the first coating layer E is at least one of antimony oxide, tin oxide, cerium oxide, magnesium oxide, magnesium hydroxide, zirconium oxide, zirconium hydroxide, yttrium oxide, titanium oxide, aluminum oxide and aluminum hydroxide.

[0009] Furthermore, the thickness of the first coating layer E is greater than 0 and less than or equal to 10 nm.

[0010] Furthermore, the second coating layer G is at least one of the compounds of elements C, B, Ce, W and P. The above elements account for 0.05-0.5% of the total mass ratio of the double-layer coated composite sodium supplement for sodium ion batteries.

[0011] Further, the second coating layer G is at least one of glucose, sucrose, boron oxide, boric acid, cerium oxide, tungsten oxide, ammonium tungstate, phosphorus oxide, ammonium hydrogen phosphate, ammonium phosphate and carbon. Among them, boron oxide, tungsten oxide, phosphorus oxide and carbon can be formed by sintering boric acid, ammonium tungstate, ammonium hydrogen phosphate and glucose respectively.

[0012] Furthermore, the thickness of the second coating layer G is greater than 0 and less than or equal to 5 nm.

[0013] The present invention also provides a method for preparing the double-layer coated composite sodium supplement for sodium ion batteries, comprising the following steps: (1) The nickel source, the sodium source and the dopant are ball-milled and mixed, and then sintered, crushed and sieved to obtain a matrix A; (2) mixing the sodium source and the II-containing substance, sintering, crushing and screening to obtain a matrix D; (3) mixing the matrix A obtained in step (1), the matrix D obtained in step (2) and the first coating layer E, sintering, crushing and screening to obtain a single-layer coated composite sodium supplement; (4) The single-layer coated composite sodium supplement agent obtained in step (3) is mixed with the second coating layer G, and the mixture is sintered, crushed and sieved to obtain a double-layer coated composite sodium supplement agent for sodium ion batteries.

[0014] Furthermore, in step (1), the nickel source is at least one of nickel oxide, nickel nitrate and nickel oxalate; In step (1), the dopant is at least one of copper oxide, copper hydroxide, cobalt oxide, cobalt hydroxide, iron oxide, iron hydroxide, manganese oxide, manganese hydroxide, zinc oxide, zinc hydroxide, zirconium oxide, zirconium hydroxide, molybdenum oxide, ammonium molybdate, boron oxide, boric acid, ammonium fluoride and sodium fluoride; In step (1) and step (2), the sodium source is independently selected from at least one of metallic sodium, sodium hydroxide, sodium carbonate, sodium bicarbonate, sodium peroxide and sodium oxide; In step (2), the II-containing substance is at least one of nitrogen, elemental sulfur, elemental phosphorus, sodium bicarbonate, oxalic acid and sodium hydroxide.

[0015] The dopant provides element M for component A in the core composite matrix.

[0016] Furthermore, in step (1), sintering is performed at 650-800°C for 6-15 hours; In step (2), sintering at 300-650°C for 3-8 h; In step (3), sintering at 300-700°C for 3-8 hours; In step (4), sinter at 250-450°C for 3-8 h.

[0017] Furthermore, the sintering atmosphere is nitrogen, argon or a nitrogen-argon mixed gas.

[0018] The present invention also provides application of the double-layer coated composite sodium supplement for sodium ion batteries in sodium ion batteries.

[0019] The present invention has the following beneficial effects: 1. Due to its high activity and large sodium ion molar mass, the sodium supplement agent is easy to react with moisture and gas in the air to form inactive NaOH and Na2CO3, which leads to deterioration of the sodium supplement agent and increased impedance; especially at high voltages above 4.0V, it is more likely to cause structural instability, thereby reducing the use effect of the sodium supplement agent. Therefore, the sodium supplement agent of the present invention is added with a dopant during solid phase sintering to maintain the stability of the sodium supplement agent crystal structure and prevent phase structure transformation.

[0020] 2. The sodium supplement of the present invention adopts two composite components, namely, component A of the core matrix is ​​beneficial to the formation of inorganic components in the SEI film, and component D of the core matrix is ​​beneficial to the growth of organic components in the SEI film. The synergistic effect of components A and D can realize the continuous self-repair of sodium ion batteries in long cycles, which is helpful to improve the energy density and the number of cycles.

[0021] 3. The sodium supplement agent of the present invention can effectively prevent the sodium supplement agent from reacting with moisture and gas in the air through double-layer nano-uniform coating, thereby stabilizing the sodium supplement effect of the sodium supplement agent and reducing the impedance of the sodium supplement agent. Furthermore, the double-layer coating layer can effectively isolate the sodium supplement agent from the electrolyte interface to prevent the electrolyte from corroding and damaging the sodium supplement agent. Therefore, adding the double-layer coated composite sodium supplement agent of the present invention to the sodium ion battery can significantly improve the energy density, high-rate discharge and cycle life of the sodium ion battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 A comparison chart of charge and discharge curves of sodium ion batteries assembled with sodium supplement agents of Example 1 and Comparative Example 1; Figure 2 A comparison chart of the cycle curves of sodium ion batteries assembled with sodium supplement agents in Example 1 and Comparative Example 1; Figure 3 This is a comparison chart of the cycle curves of the sodium ion battery assembled with the sodium supplement agent in Example 1 and without the addition of the sodium supplement agent. DETAILED DESCRIPTION

[0023] The principles and features of the present invention are described below, and the examples are only used to explain the present invention and are not used to limit the scope of the present invention. If no specific conditions are specified in the embodiments, they are carried out according to normal conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be purchased commercially.

[0024] Example 1 A double-layer coated composite sodium supplement for sodium ion batteries, comprising a core composite matrix and an outer shell double coating layer; the core composite matrix is ​​0.5Na 2.0 Ni 0.9 Co 0.1 O2∙0.5Na3N; the outer shell double coating layer is wrapped around the outside of the inner core composite matrix, including a first coating layer E and a second coating layer G from the inside to the outside; Among them, the first coating layer E is aluminum oxide, the element Al accounts for 1% of the total mass ratio of the sodium supplement agent, and the thickness is 10 nm; the second coating layer G is boron oxide, the element B accounts for 0.1% of the total mass ratio of the sodium supplement agent, and the thickness is 3 nm.

[0025] The preparation method of the double-layer coated composite sodium supplement for sodium ion batteries comprises the following steps: (1) Nickel oxide (3.5 μm), sodium oxide, and cobalt oxide (50 nm) were ball-milled and mixed, sintered at 650 °C for 15 h in a nitrogen atmosphere, and crushed and sieved to obtain matrix A (Na 2.0 Ni 0.9 Co 0.01 O2); (2) Under a pressure of 0.1 MPa, metallic sodium was sintered at 300 °C for 3 h in a nitrogen atmosphere, and then crushed and sieved to obtain matrix D (Na3N); (3) mixing the substrate A obtained in step (1), the substrate D obtained in step (2) and the first coating layer E, sintering at 300° C. for 5 h in a nitrogen atmosphere, and crushing and sieving to obtain a single-layer coated composite sodium supplement; (4) The single-layer composite coated sodium supplement agent obtained in step (3) is mixed with the second coating layer G, sintered at 250° C. for 8 h under a nitrogen atmosphere, and crushed and sieved to obtain a double-layer coated composite sodium supplement agent for sodium ion batteries.

[0026] Example 2 A double-layer coated composite sodium supplement for sodium ion batteries, comprising a core composite matrix and an outer shell double coating layer; the core composite matrix is ​​0.9Na2NiO2·0.1(0.5Na2S·0.5Na3P); the outer shell double coating layer is wrapped outside the core composite matrix, and includes a first coating layer E and a second coating layer G from inside to outside; Among them, the first coating layer E is a mixture of Sb2O3, SnO2 and CeO2, the elements Sb, Sn and Ce account for 0.5% of the total mass ratio of the sodium supplement agent, and the thickness is 4 nm; the second coating layer G is carbon, the element C accounts for 0.5% of the total mass ratio of the sodium supplement agent, and the thickness is 5 nm.

[0027] The preparation method of the double-layer coated composite sodium supplement for sodium ion batteries comprises the following steps: (1) Nickel oxide (15 μm) and nickel oxalate were mixed, sintered at 800 °C for 6 h in a nitrogen atmosphere, and then crushed and sieved to obtain matrix A (Na2NiO2); (2) Sodium metal, elemental sulfur and elemental phosphorus were mixed, sintered at 650°C for 8 h under a pressure of 0.1 MPa, and crushed and sieved to obtain matrix D (0.5Na2S·0.5Na3P); (3) mixing the substrate A obtained in step (1), the substrate D obtained in step (2) and the first coating layer E, sintering at 700° C. for 3 h in a nitrogen atmosphere, and crushing and sieving to obtain a single-layer coated composite sodium supplement; (4) The single-layer composite coated sodium supplement agent obtained in step (3) is mixed with the second coating layer G, sintered at 450° C. for 3 h under a nitrogen atmosphere, and crushed and sieved to obtain a double-layer coated composite sodium supplement agent for sodium ion batteries.

[0028] Example 3 A double-layer coated composite sodium supplement for sodium ion batteries, comprising a core composite matrix and an outer shell double coating layer; the core composite matrix is ​​0.3Na2MoO3∙0.7Na2O; the outer shell double coating layer is wrapped outside the core composite matrix, and includes a first coating layer E and a second coating layer G from inside to outside; Among them, the first coating layer E is a mixture of magnesium hydroxide, zirconium hydroxide, yttrium oxide and titanium oxide, the elements Mg, Zr, Y and Ti account for 0.1% of the total mass ratio of the sodium supplement agent, and the thickness is 3 nm; the second coating layer G is a mixture of cerium oxide, tungsten oxide and phosphorus oxide, the elements Ce, W and P account for 0.4% of the total mass ratio of the sodium supplement agent, and the thickness is 4 nm.

[0029] The preparation method of the double-layer coated composite sodium supplement for sodium ion batteries comprises the following steps: (1) Sodium bicarbonate and molybdenum oxide (6 μm) were ball-milled and mixed, sintered at 700 °C for 7 h in a nitrogen-argon mixed atmosphere, and crushed and sieved to obtain matrix A (Na2MoO3); (2) Sodium carbonate and sodium bicarbonate were mixed, decomposed at 550 °C for 5 h under a nitrogen atmosphere, crushed and sieved to obtain matrix D (Na2O); (3) mixing the substrate A obtained in step (1), the substrate D obtained in step (2) and the first coating layer E, sintering at 600° C. for 5 h in a nitrogen atmosphere, and crushing and sieving to obtain a single-layer coated composite sodium supplement; (4) The single-layer composite coated sodium supplement agent obtained in step (3) is mixed with the second coating layer G, sintered at 400° C. for 5 h under a nitrogen atmosphere, and crushed and sieved to obtain a double-layer coated composite sodium supplement agent for sodium ion batteries.

[0030] Example 4 A double-layer coated composite sodium supplement for sodium ion batteries, comprising a core composite matrix and an outer shell double coating layer; the core composite matrix is ​​0.8Na8ZrO6·0.2Na2C2O4; the outer shell double coating layer is wrapped outside the core composite matrix, and includes a first coating layer E and a second coating layer G from inside to outside; Among them, the first coating layer E is titanium oxide, the element Ti accounts for 0.05% of the total mass ratio of the sodium supplement agent, and the thickness is 1 nm; the second coating layer G is boron oxide, the element B accounts for 0.05% of the total mass ratio of the sodium supplement agent, and the thickness is 1 nm.

[0031] The preparation method of the double-layer coated composite sodium supplement for sodium ion batteries comprises the following steps: (1) Sodium carbonate and zirconium oxide (8 μm) were ball-milled and mixed, sintered at 750 °C for 10 h in an argon atmosphere, and crushed and sieved to obtain matrix A (Na8ZrO6); (2) Sodium hydroxide and oxalic acid were mixed, sintered at 600 °C for 7 h in an argon atmosphere, and then crushed and sieved to obtain matrix D (Na2C2O4); (3) mixing the substrate A obtained in step (1), the substrate D obtained in step (2) and the first coating layer E, sintering at 300° C. for 3 h in an argon atmosphere, and crushing and sieving to obtain a single-layer composite coated sodium supplement; (4) The single-layer composite coated sodium supplement agent obtained in step (3) is mixed with the second coating layer G, sintered at 250° C. for 5 h under an argon atmosphere, and crushed and sieved to obtain a double-layer coated composite sodium supplement agent for sodium ion batteries.

[0032] Example 5 A double-layer coated composite sodium supplement for sodium ion batteries, comprising a core composite matrix and an outer shell double coating layer; the core composite matrix is ​​0.1Na2Ni 0.7 Fe 0.1 Mn 0.05 Zn 0.15 O2·0.9Na2O; the outer shell double coating layer is wrapped around the outside of the inner core composite matrix, including a first coating layer E and a second coating layer G from the inside to the outside; Among them, the first coating layer E is cerium oxide, the element Ce accounts for 0.1% of the total mass ratio of the sodium supplement agent, and the thickness is 8 nm; the second coating layer G is sucrose, the element C accounts for 0.4% of the total mass ratio of the sodium supplement agent, and the thickness is 3 nm.

[0033] The preparation method of the double-layer coated composite sodium supplement for sodium ion batteries comprises the following steps: (1) Nickel oxide (5 μm), nickel nitrate, sodium oxide, ferrous oxide, manganese oxide and zinc oxide were ball-milled and mixed, sintered at 710 °C for 13 h in a nitrogen atmosphere, and crushed and sieved to obtain matrix A (Na2Ni 0.7 Fe 0.1 Mn 0.05 Zn 0.15 O2); (2) Sodium carbonate and bicarbonate are mixed, decomposed at 350 °C for 4 h in a nitrogen atmosphere, and then crushed and sieved to obtain matrix D (Na2O); (3) mixing the substrate A obtained in step (1), the substrate D obtained in step (2) and the first coating layer E, sintering at 390° C. for 4 h in a nitrogen atmosphere, and crushing and sieving to obtain a single-layer coated composite sodium supplement; (4) The single-layer composite coated sodium supplement agent obtained in step (3) is mixed with the second coating layer G, sintered at 400° C. for 6 h in a nitrogen atmosphere, and crushed and sieved to obtain a double-layer coated composite sodium supplement agent for sodium ion batteries.

[0034] Example 6 A double-layer coated composite sodium supplement for sodium ion batteries, comprising a core composite matrix and an outer shell double coating layer; the core composite matrix is ​​0.9Na2Ni 0.8 Zr 0.15 B 0.05 F 0.05 O 1.95 ·0.1(0.3Na2S·0.7Na3P); the outer shell double coating layer is wrapped around the outside of the inner core composite matrix, including the first coating layer E and the second coating layer G from the inside to the outside; Among them, the first coating layer E is tin oxide, the element Sn accounts for 0.25% of the total mass ratio of the sodium supplement agent, and the thickness is 9 nm; the second coating layer G is a mixture of tungsten oxide and phosphorus oxide, the elements W and P account for 0.25% of the total mass ratio of the sodium supplement agent, and the thickness is 2 nm.

[0035] The preparation method of the double-layer coated composite sodium supplement for sodium ion batteries comprises the following steps: (1) Nickel nitrate (10 μm), sodium peroxide, zirconium hydroxide, boron oxide, ammonium fluoride and sodium fluoride were ball-milled and mixed, sintered at 670 °C for 9 h in a nitrogen atmosphere, and crushed and sieved to obtain matrix A (Na2Ni 0.8 Zr 0.15 B 0.05 F 0.05 O 1.95 ); (2) Sodium metal, elemental sulfur and elemental phosphorus were mixed, sintered at 600 °C for 10 h under a pressure of 0.1 MPa, and crushed and sieved to obtain matrix D (0.3Na2S·0.7Na3P); (3) mixing the substrate A obtained in step (1), the substrate D obtained in step (2) and the first coating layer E, sintering at 350° C. for 8 h in a nitrogen atmosphere, and crushing and sieving to obtain a single-layer coated composite sodium supplement; (4) The single-layer composite coated sodium supplement agent obtained in step (3) is mixed with the second coating layer G, sintered at 300° C. for 4 h in a nitrogen atmosphere, and crushed and sieved to obtain a double-layer coated composite sodium supplement agent for sodium ion batteries.

[0036] Comparative Example 1 A sodium supplement, which is different from Example 1 in that the inner core matrix does not contain Na3N.

[0037] Test Example 1 The performance of the sodium ion battery sodium supplement prepared in the above Examples 1-6 and Comparative Example 1 was tested using the following method.

[0038] Sodium ion button cell assembly: Sodium supplement, positive electrode material (NaNi 0.25 Fe 0.35 Mn 0.40O2), conductive carbon black and binder PVDF were mixed in a mass ratio of 1:79:10:10 (the mass ratio of positive electrode material, conductive carbon black and binder PVDF in the control group without sodium supplement was 80:10:10), NMP was added to make a uniform slurry and coated on aluminum foil, and then cut into a circular electrode with a diameter of 14 mm after drying and roller pressing. CR2032 button cells were used to assemble sodium ion batteries, the diaphragm was glass fiber, the electrolyte was a 1 mol / L NaPF6 solution with EC / PC / DEC as the solvent, and the negative electrode was a sodium sheet.

[0039] Sodium ion battery test conditions: temperature is 25±1℃, the voltage range of the charge and discharge cycle is 2.0-4.0 V, the current size is 0.1 C (150 mAh / g), and the cycle test is carried out at 0.5 C charging and 1 C discharging.

[0040] (1) The test results are shown in Table 1.

[0041] Table 1 Performance test results of sodium supplement

[0042] As can be seen from Table 1, after the sodium ion battery sodium supplement prepared in Examples 1-6 is added to the battery, its coulombic efficiency, rate discharge capacity and cycle retention rate are significantly improved. For example, the coulombic efficiency is above 97%, and the 50-week cycle retention rate is above 96%. This is because after the addition of the sodium supplement, during the first charging process, the sodium supplement releases additional sodium ions to migrate to the negative electrode surface to form an SEI film. The first component A of the core composite matrix of the sodium supplement of the present invention has similar properties to the inorganic components of the SEI film, so it is conducive to the high-density inorganic component layer formed inside the SEI film in contact with the negative electrode, such as Na2CO3, NaF and Na2O, while the second component D of the core composite matrix of the sodium supplement is conducive to the formation of a low-density organic component layer outside the SEI film in contact with the electrolyte, such as (CH2OCO2Na)2, RONa and ROCO2Na. During multiple charge and discharge cycles, the inorganic component layer and the organic component layer can maintain the stability of the SEI film and prevent the SEI film from rupturing and being damaged, thus enabling the sodium-ion battery to maintain a long cycle.

[0043] (2) The charge-discharge curves and cycle curves of the sodium ion battery assembled with the sodium supplement agent in Example 1, the sodium supplement agent in Comparative Example 1, and the sodium ion battery assembled without adding the sodium supplement agent are shown in the figure below: Figure 1-3 shown.

[0044] Depend on Figure 1-3It can be seen that the first coulombic efficiency and 0.1 C discharge capacity of the sodium ion battery with the sodium supplement in Example 1 are 98.2% and 154.8 mAh / g, respectively, and the 50-week cycle retention rate is 97.31%; while the first coulombic efficiency and 0.1 C discharge capacity of the sodium ion battery with the sodium supplement in Comparative Example 1 are 96.4% and 150.7 mAh / g, respectively, and the 50-week cycle retention rate is 96.24%. Combined with the test data of the sodium ion battery without the addition of the sodium supplement in Table 1, it is proved that the two sodium supplement components of the core composite matrix of the present invention are better than the single-component sodium supplement and the sodium supplement without the addition. It can be seen that the double-layer coated composite sodium supplement of the present invention can significantly improve the energy density and cycle performance of the sodium ion battery.

[0045] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modification, equivalent substitution or improvement made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A double-layer coated composite sodium supplement for sodium ion batteries, characterized in that: It consists of a core composite matrix and an outer shell double coating layer; the core composite matrix is ​​αA∙(1-α)D, 0<α<1; The outer shell double coating layer is wrapped around the outside of the inner core composite matrix, and includes a first coating layer E and a second coating layer G from the inside to the outside; Where A is Na a Ni x M 1-x O y , 2≤a≤8, 0≤x≤1, 1.95≤y≤6, M is at least one of Cu, Co, Fe, Mn, Zn, Zr, Mo, B and F; D is Na b Π z , 2≤b≤3, 1≤z≤2, Π is at least one of C, O, S, N and P.

2. The double-layer coated composite sodium supplement for sodium ion batteries according to claim 1, characterized in that: The particle size D of A in the core composite matrix 50 3.5-15 μm.

3. The double-layer coated composite sodium supplement for sodium ion batteries according to claim 1, characterized in that: The first coating layer E is at least one of compounds of the elements Sb, Sn, Ce, Mg, Zr, Y, Ti and Al.

4. The double-layer coated composite sodium supplement for sodium ion batteries according to claim 1, characterized in that: The thickness of the first coating layer E is greater than 0 and less than or equal to 10 nm.

5. The double-layer coated composite sodium supplement for sodium ion batteries according to claim 1, characterized in that: The second coating layer G is at least one of compounds of elements C, B, Ce, W and P.

6. The double-layer coated composite sodium supplement for sodium ion batteries according to claim 1, characterized in that: The thickness of the second coating layer G is greater than 0 and less than or equal to 5 nm.

7. The method for preparing the double-layer coated composite sodium supplement for sodium ion batteries according to any one of claims 1 to 6, characterized in that: The following steps are involved: (1) The nickel source, the sodium source and the dopant are ball-milled and mixed, and then sintered, crushed and sieved to obtain a matrix A; (2) mixing the sodium source and the II-containing substance, sintering, crushing and screening to obtain a matrix D; (3) mixing the matrix A obtained in step (1), the matrix D obtained in step (2) and the first coating layer E, sintering, crushing and screening to obtain a single-layer coated composite sodium supplement; (4) The single-layer coated composite sodium supplement agent obtained in step (3) and the second coating layer G are mixed, sintered, crushed and sieved to obtain a double-layer coated composite sodium supplement agent for sodium ion batteries.

8. The method for preparing a double-layer coated composite sodium supplement for sodium ion batteries according to claim 7, characterized in that: In step (1), the nickel source is at least one of nickel oxide, nickel nitrate and nickel oxalate; In step (1), the dopant is at least one of copper oxide, copper hydroxide, cobalt oxide, cobalt hydroxide, iron oxide, iron hydroxide, manganese oxide, manganese hydroxide, zinc oxide, zinc hydroxide, zirconium oxide, zirconium hydroxide, molybdenum oxide, ammonium molybdate, boron oxide, boric acid, ammonium fluoride and sodium fluoride; In step (1) and step (2), the sodium source is independently selected from at least one of metallic sodium, sodium hydroxide, sodium carbonate, sodium bicarbonate, sodium peroxide and sodium oxide; In step (2), the II-containing substance is at least one of nitrogen, elemental sulfur, elemental phosphorus, sodium bicarbonate, oxalic acid and sodium hydroxide.

9. The method for preparing a double-layer coated composite sodium supplement for sodium ion batteries according to claim 7, characterized in that: In step (1), sintering at 650-800°C for 6-15 h; In step (2), sintering at 300-650°C for 3-8 h; In step (3), sintering at 300-700°C for 3-8 hours; In step (4), sinter at 250-450°C for 3-8 h.

10. Use of the double-layer coated composite sodium supplement for sodium ion batteries according to any one of claims 1 to 6 in sodium ion batteries.

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