A sodium-ion battery double-layer coated composite sodium supplement agent, its preparation method and application

Abstract

This invention discloses a sodium-ion battery double-layer coated composite sodium replenisher, its preparation method, and its application, relating to the field of new energy battery technology. The sodium replenisher consists of a core composite matrix and a double-layer outer shell. The core composite matrix is ​​αA∙(1-α)D; the double-layer outer shell surrounds the core composite matrix and includes a first coating layer E and a second coating layer G from the inside out. Wherein, A is Na… a Ni x M 1‑x O y D is Na b Π z This invention also discloses a method for preparing the sodium replenishing agent and its application in sodium-ion batteries. This sodium replenishing agent can compensate for the irreversible loss of active sodium in sodium-ion batteries, helping to improve the battery's energy density, increase coulombic efficiency and cycle life, and facilitate the large-scale promotion and application of sodium-ion batteries in energy storage fields requiring more than 10,000 cycles.

Description

Technical Field

[0001] This invention relates to the field of new energy battery technology, specifically to a sodium-ion battery double-layer coated composite sodium replenishing agent, its preparation method, and its application. Background Technology

[0002] Sodium-ion batteries offer advantages such as excellent low-temperature performance (-40℃), high safety, fast charging speed, high discharge rate (40C), and zero-voltage storage and transportation. Furthermore, the Earth's sodium resources are abundant, exceeding lithium reserves by more than 400 times. Therefore, developing sodium-ion batteries is a beneficial supplement and replacement for both lithium iron phosphate and ternary lithium-ion batteries. Due to their inherent advantages, sodium-ion batteries can be widely used in power tools, automotive start-stop systems, communication base stations, small-scale energy storage, large-scale energy storage, and passenger vehicles. As the cost of sodium-ion batteries further decreases, replacing lead-acid batteries used in two-wheeled vehicles and low-speed vehicles is an inevitable trend.

[0003] Currently, the market application of sodium-ion batteries is relatively slow due to their low energy density and poor cycle performance. One of the main reasons is that during the initial charging process, a solid electrolyte interphase (SEI) film forms on the negative electrode surface. While the formation of the SEI film is crucial for battery reliability, it causes the loss of some sodium ions, resulting in irreversible capacity loss and a decrease in coulombic efficiency, thus affecting the energy density of the sodium-ion battery. On the other hand, with the increase in the number of cycles, the layered oxide cathode material of the sodium-ion battery undergoes a phase transition, causing particle expansion and fragmentation, which consumes some active sodium ions, leading to a decrease in battery capacity and a reduction in the number of cycles. Therefore, improving the coulombic efficiency and cycle life of sodium-ion batteries is a key technical challenge. Summary of the Invention

[0004] To address the aforementioned technical problems, the present invention aims to provide a sodium-ion battery double-layer coated composite sodium replenishing agent, its preparation method, and its application. This sodium replenishing agent can compensate for the loss of irreversible active sodium in sodium-ion batteries, helping to improve the energy density of the battery, increase the battery coulombic efficiency and cycle life, and facilitate the large-scale promotion and application of sodium-ion batteries in energy storage fields requiring more than 10,000 cycles.

[0005] The technical solution of the present invention to solve the above technical problems is as follows: a sodium-ion battery double-layer coated composite sodium supplement is provided, which is composed of a core composite matrix and an outer double coating layer; the core composite matrix is ​​αA∙(1-α)D, 0<α<1; the outer double coating layer is wrapped around the core composite matrix and includes a first coating layer E and a second coating layer G from the inside to the outside.

[0006] Where A is Na aNi 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.

[0007] Furthermore, the granularity D of A in the kernel matrix 50 It is 3.5-15 μm.

[0008] Furthermore, the first coating layer E is at least one compound selected from elements Sb, Sn, Ce, Mg, Zr, Y, Ti, and Al. The aforementioned elements account for 0.05-1% of the total mass of the sodium-ion battery double-layer coating composite sodium replenisher.

[0009] Furthermore, 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.

[0010] Furthermore, the thickness of the first coating layer E is greater than 0 and less than or equal to 10 nm.

[0011] Furthermore, the second coating layer G is at least one compound of elements C, B, Ce, W, and P. The aforementioned elements account for 0.05-0.5% of the total mass of the sodium-ion battery double-layer coating composite sodium replenisher.

[0012] Furthermore, the second coating layer G is at least one selected from glucose, sucrose, boron oxide, boric acid, cerium oxide, tungsten oxide, ammonium tungstate, phosphorus oxide, ammonium hydrogen phosphate, ammonium phosphate, and carbon. Among these, boron oxide, tungsten oxide, phosphorus oxide, and carbon can be formed by sintering boric acid, ammonium tungstate, ammonium hydrogen phosphate, and glucose, respectively.

[0013] Furthermore, the thickness of the second coating layer G is greater than 0 and less than or equal to 5 nm.

[0014] This invention also provides a method for preparing the above-mentioned sodium-ion battery double-layer coated composite sodium replenishing agent, comprising the following steps:

[0015] (1) The nickel source, sodium source and dopant are ball-milled and mixed, and then sintered, crushed and sieved to obtain matrix A;

[0016] (2) The sodium source is mixed with the Π-containing substance, and after sintering, crushing and sieving, the matrix D is obtained;

[0017] (3) After mixing the matrix A obtained in step (1), the matrix D obtained in step (2) and the first coating layer E, the mixture is sintered, crushed and sieved to obtain a single-layer coated composite sodium supplement.

[0018] (4) The single-layer coated composite sodium supplement agent obtained in step (3) is mixed with the second coating layer G, and then sintered, crushed and sieved to obtain the sodium-ion battery double-layer coated composite sodium supplement agent.

[0019] Furthermore, in step (1), the nickel source is at least one of nickel oxide, nickel nitrate, and nickel oxalate;

[0020] 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;

[0021] In steps (1) and (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;

[0022] In step (2), the substance containing Π is at least one of nitrogen, elemental sulfur, elemental phosphorus, sodium bicarbonate, oxalic acid, and sodium hydroxide.

[0023] Among them, the dopant provides element M for component A in the core composite matrix.

[0024] Furthermore, in step (1), sintering is carried out at 650-800℃ for 6-15 h;

[0025] In step (2), sintering is carried out at 300-650℃ for 3-8 hours;

[0026] In step (3), sintering is carried out at 300-700℃ for 3-8 hours;

[0027] In step (4), sintering is carried out at 250-450℃ for 3-8 hours.

[0028] Furthermore, the sintering atmosphere is nitrogen, argon, or a mixture of nitrogen and argon.

[0029] This invention also provides the application of the above-mentioned sodium-ion battery double-layer coated composite sodium replenishing agent in sodium-ion batteries.

[0030] The present invention has the following beneficial effects:

[0031] 1. Sodium supplements, due to their high activity and large molar amount of sodium ions, readily react with moisture and gases in the air to form inactive NaOH and Na₂CO₃, leading to deterioration and increased impedance. This is especially true at high voltages above 4.0V, where structural instability is more likely, thus reducing the effectiveness of the sodium supplement. Therefore, the sodium supplement of this invention incorporates a dopant during solid-state sintering to maintain the stability of the crystal structure and prevent phase transformation.

[0032] 2. The sodium replenishing agent of this invention adopts two composite components: component A of the core matrix is ​​beneficial to the generation 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 enables sodium-ion batteries to continuously self-repair during long cycles, which helps to improve energy density and cycle number.

[0033] 3. The sodium replenishing agent of this invention, through a double-layer nano-uniform coating, effectively prevents the sodium replenishing agent from reacting with moisture and gases in the air, thereby stabilizing the sodium replenishing effect and reducing the impedance of the sodium replenishing agent. Furthermore, the double-layer coating effectively isolates the sodium replenishing agent from the electrolyte interface, preventing corrosion and damage to the sodium replenishing agent by the electrolyte. Therefore, adding the double-layer coated composite sodium replenishing agent of this invention to sodium-ion batteries can significantly improve the energy density, high-rate discharge, and cycle life of sodium-ion batteries. Attached Figure Description

[0034] Figure 1 This is a comparison chart of the charge-discharge curves of sodium-ion batteries assembled with sodium supplementation agent in Example 1 and Comparative Example 1.

[0035] Figure 2 This is a comparison graph showing the cycle curves of sodium-ion batteries assembled with sodium supplementation agents in Example 1 and Comparative Example 1.

[0036] Figure 3 This is a comparison graph showing the cycle curves of sodium-ion batteries assembled with and without sodium supplementation in Example 1. Detailed Implementation

[0037] The principles and features of this invention are described below. The examples given are for illustrative purposes only and are not intended to limit the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer should be followed. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0038] Example 1

[0039] A sodium-ion battery double-layer coated composite sodium replenisher consists of a core composite matrix and an outer double coating layer; the core composite matrix is ​​0.5Na. 2.0 Ni 0.9 Co 0.1 O2∙0.5Na3N; The outer shell is double-coated around the core composite matrix, and from the inside out it includes a first coating layer E and a second coating layer G;

[0040] The first coating layer E is aluminum oxide, with element Al accounting for 1% of the total mass of the sodium supplement and a thickness of 10 nm; the second coating layer G is boron oxide, with element B accounting for 0.1% of the total mass of the sodium supplement and a thickness of 3 nm.

[0041] The preparation method of this sodium-ion battery double-layer coated composite sodium supplement includes the following steps:

[0042] (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 under a nitrogen atmosphere, and then pulverized and sieved to obtain matrix A (Na 2.0 Ni 0.9 Co 0.01 O2);

[0043] (2) Under a pressure of 0.1 MPa, metallic sodium was sintered at 300°C for 3 h in a nitrogen atmosphere, and after crushing and sieving, matrix D (Na3N) was obtained.

[0044] (3) The matrix A obtained in step (1), the matrix D obtained in step (2) and the first coating layer E are mixed and sintered at 300°C for 5 h in a nitrogen atmosphere. After crushing and sieving, a single-layer coated composite sodium supplement is obtained.

[0045] (4) The single-layer composite coating sodium supplement agent obtained in step (3) is mixed with the second coating layer G and sintered at 250°C for 8 h under a nitrogen atmosphere. After crushing and sieving, the sodium-ion battery double-layer coating composite sodium supplement agent is obtained.

[0046] Example 2

[0047] A sodium-ion battery double-layer coated composite sodium replenisher consists of a core composite matrix and an outer double coating layer; the core composite matrix is ​​0.9Na2NiO2·0.1(0.5Na2S·0.5Na3P); the outer double coating layer is wrapped around the core composite matrix and includes a first coating layer E and a second coating layer G from the inside to the outside.

[0048] The first coating layer E is a mixture of Sb2O3, SnO2 and CeO2, with elements Sb, Sn and Ce accounting for 0.5% of the total mass of the sodium supplement and a thickness of 4 nm; the second coating layer G is carbon, with element C accounting for 0.5% of the total mass of the sodium supplement and a thickness of 5 nm.

[0049] The preparation method of this sodium-ion battery double-layer coated composite sodium supplement includes the following steps:

[0050] (1) Nickel oxide (15 μm) and nickel oxalate were mixed and sintered at 800 °C for 6 h under a nitrogen atmosphere. After crushing and sieving, matrix A (Na2NiO2) was obtained.

[0051] (2) Metallic sodium, elemental sulfur and elemental phosphorus are mixed and sintered at 650°C for 8 h under a pressure of 0.1 MPa. After crushing and sieving, matrix D (0.5Na2S·0.5Na3P) is obtained.

[0052] (3) Mix the matrix A obtained in step (1), the matrix D obtained in step (2) and the first coating layer E, sinter at 700°C for 3 h in a nitrogen atmosphere, and then crush and sieve to obtain a single-layer coated composite sodium supplement.

[0053] (4) The single-layer composite coating sodium supplement agent obtained in step (3) is mixed with the second coating layer G and sintered at 450°C for 3 h in a nitrogen atmosphere. After crushing and sieving, the sodium-ion battery double-layer coating composite sodium supplement agent is obtained.

[0054] Example 3

[0055] A sodium-ion battery double-layer coated composite sodium supplement consists of a core composite matrix and an outer double coating layer; the core composite matrix is ​​0.3Na2MoO3∙0.7Na2O; the outer double coating layer is wrapped around the core composite matrix and includes a first coating layer E and a second coating layer G from the inside to the outside.

[0056] The first coating layer E is a mixture of magnesium hydroxide, zirconium hydroxide, yttrium oxide and titanium oxide, with elements Mg, Zr, Y and Ti accounting for 0.1% of the total mass of the sodium supplement and a thickness of 3 nm; the second coating layer G is a mixture of cerium oxide, tungsten oxide and phosphorus oxide, with elements Ce, W and P accounting for 0.4% of the total mass of the sodium supplement and a thickness of 4 nm.

[0057] The preparation method of this sodium-ion battery double-layer coated composite sodium supplement includes the following steps:

[0058] (1) Sodium bicarbonate and molybdenum oxide (6 μm) were ball-milled and mixed, sintered at 700°C for 7 h under a nitrogen-argon mixed atmosphere, and then crushed and sieved to obtain matrix A (Na2MoO3).

[0059] (2) Sodium carbonate and sodium bicarbonate were mixed and decomposed at 550°C for 5 h under a nitrogen atmosphere, then crushed and sieved to obtain matrix D (Na2O).

[0060] (3) After mixing the matrix A obtained in step (1), the matrix D obtained in step (2) and the first coating layer E, sinter at 600°C for 5 h under a nitrogen atmosphere, and then crush and sieve to obtain a single-layer coated composite sodium supplement.

[0061] (4) The single-layer composite coating sodium supplement agent obtained in step (3) is mixed with the second coating layer G and sintered at 400°C for 5 h in a nitrogen atmosphere. After crushing and sieving, the sodium-ion battery double-layer coating composite sodium supplement agent is obtained.

[0062] Example 4

[0063] A sodium-ion battery double-layer coated composite sodium supplement consists of a core composite matrix and an outer double coating layer; the core composite matrix is ​​0.8Na8ZrO6·0.2Na2C2O4; the outer double coating layer is wrapped around the core composite matrix and includes a first coating layer E and a second coating layer G from the inside to the outside.

[0064] The first coating layer E is titanium oxide, with element Ti accounting for 0.05% of the total mass of the sodium supplement and a thickness of 1 nm; the second coating layer G is boron oxide, with element B accounting for 0.05% of the total mass of the sodium supplement and a thickness of 1 nm.

[0065] The preparation method of this sodium-ion battery double-layer coated composite sodium supplement includes the following steps:

[0066] (1) Sodium carbonate and zirconium oxide (8 μm) were ball-milled and mixed, sintered at 750°C for 10 h under an argon atmosphere, and then crushed and sieved to obtain matrix A (Na8ZrO6).

[0067] (2) Sodium hydroxide and oxalic acid were mixed and sintered at 600°C for 7 h under an argon atmosphere. After crushing and sieving, matrix D (Na2C2O4) was obtained.

[0068] (3) After mixing the matrix A obtained in step (1), the matrix D obtained in step (2) and the first coating layer E, sinter at 300°C for 3 h under an argon atmosphere, and after crushing and sieving, a single-layer composite coating sodium supplement is obtained.

[0069] (4) The single-layer composite coating sodium supplement agent obtained in step (3) is mixed with the second coating layer G and sintered at 250°C for 5 h in an argon atmosphere. After crushing and sieving, the sodium-ion battery double-layer coating composite sodium supplement agent is obtained.

[0070] Example 5

[0071] A sodium-ion battery double-layer coated composite sodium replenisher consists of a core composite matrix and an outer 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 is double-coated and wrapped around the core composite matrix, including the first coating layer E and the second coating layer G from the inside to the outside;

[0072] The first coating layer E is cerium oxide, with element Ce accounting for 0.1% of the total mass of the sodium supplement and a thickness of 8 nm; the second coating layer G is sucrose, with element C accounting for 0.4% of the total mass of the sodium supplement and a thickness of 3 nm.

[0073] The preparation method of this sodium-ion battery double-layer coated composite sodium supplement includes the following steps:

[0074] (1) Nickel oxide (5 μm), nickel nitrate, sodium oxide, ferrous oxide, manganese oxide and zinc oxide were ball-milled and mixed, and sintered at 710 °C for 13 h under nitrogen atmosphere. After crushing and sieving, matrix A (Na2Ni) was obtained. 0.7 Fe 0.1 Mn 0.05 Zn 0.15 O2);

[0075] (2) Sodium carbonate and bicarbonate were mixed and decomposed at 350°C for 4 h under a nitrogen atmosphere. After crushing and sieving, matrix D (Na2O) was obtained.

[0076] (3) After mixing the matrix A obtained in step (1), the matrix D obtained in step (2) and the first coating layer E, sinter at 390°C for 4 h under a nitrogen atmosphere, and then crush and sieve to obtain a single-layer coated composite sodium supplement.

[0077] (4) The single-layer composite coating sodium supplement agent obtained in step (3) is mixed with the second coating layer G and sintered at 400°C for 6 h under a nitrogen atmosphere. After crushing and sieving, the sodium-ion battery double-layer coating composite sodium supplement agent is obtained.

[0078] Example 6

[0079] A sodium-ion battery double-layer coated composite sodium replenisher consists of a core composite matrix and an outer 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 is double-coated around the core composite matrix, and from the inside out it includes a first coating layer E and a second coating layer G;

[0080] The first coating layer E is tin oxide, with Sn accounting for 0.25% of the total mass of the sodium supplement and a thickness of 9 nm; the second coating layer G is a mixture of tungsten oxide and phosphorus oxide, with W and P accounting for 0.25% of the total mass of the sodium supplement and a thickness of 2 nm.

[0081] The preparation method of this sodium-ion battery double-layer coated composite sodium supplement includes the following steps:

[0082] (1) Nickel nitrate (10 μm), sodium peroxide, zirconium hydroxide, boron oxide, ammonium fluoride and sodium fluoride were ball-milled and mixed, and sintered at 670℃ for 9 h under nitrogen atmosphere. After crushing and sieving, matrix A (Na2Ni) was obtained. 0.8 Zr 0.15 B 0.05 F 0.05 O 1.95 );

[0083] (2) Mix metallic sodium, elemental sulfur and elemental phosphorus, sinter at 600°C for 10 h under a pressure of 0.1 MPa, and then crush and sieve to obtain matrix D (0.3Na2S·0.7Na3P).

[0084] (3) After mixing the matrix A obtained in step (1), the matrix D obtained in step (2) and the first coating layer E, sinter at 350°C for 8 h under a nitrogen atmosphere, and then crush and sieve to obtain a single-layer coated composite sodium supplement.

[0085] (4) The single-layer composite coating sodium supplement agent obtained in step (3) is mixed with the second coating layer G and sintered at 300°C for 4 h under a nitrogen atmosphere. After crushing and sieving, the sodium-ion battery double-layer coating composite sodium supplement agent is obtained.

[0086] Comparative Example 1

[0087] A sodium supplement, which differs from Example 1 in that the core matrix does not contain Na3N.

[0088] Experimental Example 1

[0089] The performance of the sodium-ion battery sodium replenishing agents prepared in Examples 1-6 and Comparative Example 1 were tested using the following methods.

[0090] Sodium-ion button cell assembly: This involves adding sodium supplement and positive electrode material (NaNi). 0.25 Fe 0.35 Mn 0.40 O2), conductive carbon black, and PVDF binder were mixed in a mass ratio of 1:79:10:10 (for the control group without sodium supplementation, the mass ratio of positive electrode material, conductive carbon black, and PVDF binder was 80:10:10). NMP was added to form a uniform slurry, which was then coated onto aluminum foil. After drying and rolling, the mixture was cut into circular electrode sheets with a diameter of 14 mm. A sodium-ion battery was assembled using a CR2032 button cell. The separator was made of 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.

[0091] Sodium-ion battery test conditions: temperature 25±1℃, charge-discharge cycle voltage range 2.0-4.0 V, current 0.1 C (150 mAh / g), cycle test is conducted at 0.5 C charge 1 C discharge.

[0092] (1) The test results are shown in Table 1.

[0093] Table 1. Performance test results of sodium supplements

[0094]

[0095] As shown in Table 1, the sodium-ion battery supplements prepared in Examples 1-6 significantly improved the coulombic efficiency, rate discharge capacity, and cycle retention rate of the batteries after addition. For example, the coulombic efficiency was above 97%, and the 50-cycle retention rate was above 96%. This is because, after adding the sodium supplement, additional sodium ions migrate to the negative electrode surface during the first charge, forming an SEI film. The first component A of the core composite matrix of the sodium supplement in this invention has properties similar to the inorganic components of the SEI film, thus facilitating the formation of a high-density inorganic component layer, such as Na2CO3, NaF, and Na2O, inside the SEI film in contact with the negative electrode. Conversely, the second component D of the core composite matrix of the sodium supplement facilitates the formation of a low-density organic component layer, such as (CH2OCO2Na)2, RONa, and ROCO2Na, outside the SEI film in contact with the electrolyte. During repeated charge and discharge cycles, the inorganic and organic components maintain the stability of the SEI film and prevent its rupture and damage, thus enabling the sodium-ion battery to maintain long cycles.

[0096] (2) The charge-discharge curves and cycle curves of sodium-ion batteries assembled with sodium supplementation agent in Example 1, sodium supplementation agent in Comparative Example 1, and without sodium supplementation agent are shown in the figure below. Figure 1-3 As shown.

[0097] Depend on Figure 1-3 It can be seen that the sodium-ion battery with sodium supplementation agent of Example 1 has an initial coulombic efficiency and a 0.1 C discharge capacity of 98.2% and 154.8 mAh / g, respectively, and a 50-cycle retention rate of 97.31%. In contrast, the sodium-ion battery with sodium supplementation agent of Comparative Example 1 has an initial coulombic efficiency and a 0.1 C discharge capacity of 96.4% and 150.7 mAh / g, respectively, and a 50-cycle retention rate of 96.24%. Combined with the test data of the sodium-ion battery without sodium supplementation agent in Table 1, it is demonstrated that the two sodium supplementation agent components of the core composite matrix of this invention are superior to the single-component sodium supplementation agent and the sodium supplementation agent without sodium supplementation agent. Therefore, it can be concluded that the double-layer coated composite sodium supplementation agent of this invention can significantly improve the energy density and cycle performance of sodium-ion batteries.

[0098] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a sodium-ion battery double-layer coated composite sodium supplement agent, comprising the following steps: (1) Sodium carbonate and zirconium oxide are ball-milled and mixed, sintered at 750°C for 10 h under an argon atmosphere, and then crushed and sieved to obtain matrix A, wherein matrix A is Na8ZrO6; (2) Sodium hydroxide and oxalic acid are mixed and sintered at 600°C for 7 h under an argon atmosphere. After crushing and sieving, matrix D is obtained. The matrix D is Na2C2O4. (3) After mixing the matrix A obtained in step (1), the matrix D obtained in step (2) and the first coating layer E, sinter at 300°C for 3 h under an argon atmosphere, and after crushing and sieving, a single-layer composite coating sodium supplement is obtained. (4) The single-layer composite coating sodium supplement agent obtained in step (3) is mixed with the second coating layer G and sintered at 250°C for 5 h in an argon atmosphere. After crushing and sieving, the sodium-ion battery double-layer coating composite sodium supplement agent is obtained. The sodium-ion battery double-layer coated composite sodium supplement consists of a core composite matrix and an outer double coating layer; the core composite matrix is ​​0.8Na8ZrO6·0.2Na2C2O4; the outer double coating layer is wrapped around the core composite matrix and includes a first coating layer E and a second coating layer G from the inside to the outside. The first coating layer E is titanium oxide, with element Ti accounting for 0.05% of the total mass of the sodium supplement and a thickness of 1 nm; the second coating layer G is boron oxide, with element B accounting for 0.05% of the total mass of the sodium supplement and a thickness of 1 nm.

2. A method for preparing a sodium-ion battery double-layer coated composite sodium supplement agent, comprising the following steps: (1) Nickel oxide, nickel nitrate, sodium oxide, ferrous oxide, manganese oxide and zinc oxide are mixed by ball milling, sintered at 710°C for 13 h under nitrogen atmosphere, crushed and sieved to obtain a matrix A, the matrix A being Na2Ni 0.7 Fe 0.1 Mn 0.05 Zn 0.15 O2; (2) Sodium carbonate and bicarbonate are mixed and decomposed at 350°C for 4 h under a nitrogen atmosphere. After crushing and sieving, matrix D is obtained, wherein matrix D is Na2O. (3) After mixing the matrix A obtained in step (1), the matrix D obtained in step (2) and the first coating layer E, sinter at 390°C for 4 h under a nitrogen atmosphere, and then crush and sieve to obtain a single-layer coated composite sodium supplement. (4) The single-layer composite coating sodium supplement agent obtained in step (3) is mixed with the second coating layer G and sintered at 400°C for 6 h under a nitrogen atmosphere. After crushing and sieving, the sodium-ion battery double-layer coating composite sodium supplement agent is obtained. The sodium-ion battery double-layer coated composite sodium replenisher consists of a core composite matrix and an outer 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 is double-coated and wrapped around the core composite matrix, including the first coating layer E and the second coating layer G from the inside to the outside; The first coating layer E is cerium oxide, with element Ce accounting for 0.1% of the total mass of the sodium supplement and a thickness of 8 nm; the second coating layer G is sucrose, with element C accounting for 0.4% of the total mass of the sodium supplement and a thickness of 3 nm.

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