Na2se@c composite sodium supplement, and preparation method and application thereof

Abstract

This invention discloses a Na2Se@C composite sodium supplement, its preparation method, and its application. The supplement comprises Na2Se and carbon coated on the surface of Na2Se, wherein the mass percentage of Na2Se is 80wt%–98wt%, and its particle size is 1–10μm. The preparation method includes the following steps: [The text abruptly ends here, so the translation stops.] x O y Selenium source and carbon are dried and purified before pretreatment, where x = 1, 2, y = 0, 2, 3, 4. The pretreated selenium source and carbon are thoroughly mixed, ground, and sieved at a mass ratio of 1:0.1 to 0.5 to obtain a mixture. The mixture is annealed in an inert gas atmosphere, heated to 500-900℃ and held at that temperature, and then cooled to obtain Na2Se@C composite sodium supplement. This invention can solve the problems of gas generation and inert substance residue in the sodium supplementation process of existing sodium supplements. The synthesis method is simple, safe, and efficient, and can improve the energy density of batteries.

Description

Technical Field

[0001] This invention relates to sodium-ion battery electrode materials, their preparation methods, and applications, specifically a Na2Se@C composite sodium supplement agent, its preparation method, and its applications. Background Technology

[0002] Sodium resources are abundant and widely distributed, making sodium-ion batteries a promising candidate for becoming one of the most popular next-generation energy storage systems. Sodium, like lithium, belongs to the alkali metal family, and its working mechanism is similar to that of lithium-ion batteries. During charging, an oxidation reaction occurs at the positive electrode, releasing sodium ions which migrate through the separator to the negative electrode. Electrons flow to the negative electrode via the external circuit, converting electrical energy into chemical energy. The discharge process is the reverse, converting chemical energy back into electrical energy. Developing sodium-ion batteries can alleviate lithium resource shortages and simultaneously expand the market for new rechargeable batteries.

[0003] Sodium-ion batteries offer significant cost advantages; however, the larger radius of sodium ions compared to lithium ions results in a lower sodium content in the positive electrode. Furthermore, the formation of the SEI (Sediment-Injection) in the negative electrode and side reactions during cycling consume substantial amounts of active sodium, leading to lower coulombic efficiency and consequently irreversible capacity loss and reduced energy density in sodium-ion batteries. Therefore, research on sodium replenishment has attracted considerable interest from researchers. Based on different replenishment methods, it can be categorized into negative electrode sodium replenishment, separator sodium replenishment, and positive electrode sodium replenishment. Negative electrode sodium replenishment typically involves directly rolling sodium powder or foil onto the surface of the electrode under pressure. This pre-added sodium source can compensate for the sodium consumed during battery cycling. However, this method is complex and difficult to manufacture, resulting in high costs. Excessive sodium metal addition can trigger sodium dendrite growth, posing safety concerns. Positive electrode sodium replenishment often involves mixing a sodium replenishing agent with the positive electrode material to form a slurry. During the first charge, the sodium replenishing agent is oxidized, releasing additional sodium ions to compensate for the active sodium consumed by the negative electrode.

[0004] Currently, sodium-ion batteries use positive electrode sodium replenishing agents such as NaN3, Na2O, Na3C6H5O7, Na2C6O6, and Na2CO3. During the sodium replenishment process, these agents generate various gases such as O2, N2, and CO2. This causes the battery to bulge and leaves residues inside the battery, resulting in useless "dead mass" and reducing the battery's energy density. Summary of the Invention

[0005] Objectives of this invention: The objective of this invention is to provide a Na2Se@C composite sodium replenisher that effectively replenishes sodium loss, produces no gas or leaves inert residue, and improves positive electrode conductivity and air stability. Another objective of this invention is to provide a simple, safe, efficient, and low-cost method for preparing the Na2Se@C composite sodium replenisher. This invention also provides an application of the Na2Se@C composite sodium replenisher in sodium-ion battery positive electrode materials.

[0006] Technical solution: The Na2Se@C composite sodium supplement of the present invention includes Na2Se and carbon coated on the surface of Na2Se, wherein the mass percentage of Na2Se is 80wt% to 98wt%.

[0007] Furthermore, the particle size of the Na2Se@C composite sodium supplement is 1–10 μm.

[0008] The preparation method of the Na2Se@C composite sodium supplement of the present invention includes the following steps:

[0009] Step 1, for the chemical formula Na2Se x O y The selenium source and carbon were dried and purified pretreated, where x = 1, 2, y = 0, 2, 3, 4;

[0010] Step 2: The pretreated selenium source and carbon are thoroughly mixed, ground, and sieved at a mass ratio of 1:0.1 to 0.5 to obtain a mixture. The carbon in this ratio can fully reduce sodium selenite to Na2Se@C. Grinding and sieving make the sodium supplement particles have a moderate particle size and the best performance.

[0011] Step three involves annealing the mixture in an inert gas atmosphere, heating it to 500–900°C, holding it at that temperature, and then cooling it to obtain the Na₂Se@C composite sodium supplement. If the reaction temperature is below 500°C, carbon cannot fully reduce sodium selenite, resulting in a product rich in heterogeneous sodium diselenide. If the reaction temperature exceeds 900°C, the product decomposes, increasing energy consumption and causing uneven particle size. The inert gas atmosphere prevents the oxidative decomposition of carbon and the reaction products.

[0012] Na₂Se is a promising sodium supplement. However, as a reactive metal compound, Na₂Se readily reacts with water and oxygen in the air. Synthesizing it by reacting selenium powder with sodium metal in the presence of liquid ammonia is difficult due to the need for air isolation and the safety concerns posed by the use of liquid ammonia. This invention provides a simple, safe, and efficient method for synthesizing a Na₂Se@C composite sodium supplement. Furthermore, the carbon composite enhances the air stability of Na₂Se.

[0013] Further, the selenium source in step one is one or more of Na2SeO3·5H2O, Na2SeO4, Na2SeO4·10H2O, Na2SeO2, and Na2Se2.

[0014] Furthermore, the grinding in step two is performed using a planetary ball mill with a material-to-ball ratio of 1:1 to 10, a set rotation speed of 300 to 800 rpm, and a milling time of 6 to 12 hours. Ball mills, resonant mixers, and spiral mixers can be used. Uniform mixing ensures sufficient contact between sodium selenite and carbon, preparing for the next annealing step. Sieving ensures particle uniformity for optimal results.

[0015] Furthermore, the heating rate in step three is 1–5 °C / min.

[0016] Furthermore, the holding time in step three is 4–12 hours. If the reaction time is less than 4 hours, sodium selenite cannot completely generate sodium selenide; if the reaction time is more than 12 hours, it will cause the target product Na2Se@C particles to agglomerate and become too large and uneven, increasing the reaction energy consumption.

[0017] Furthermore, carbon is one or more of Ketjen black, acetylene black, conductive carbon black, activated carbon, graphite, carbon nanotubes, and graphene.

[0018] The present invention relates to the application of a Na2Se@C composite sodium supplement in the cathode material of sodium-ion batteries.

[0019] Furthermore, the mass ratio of Na2Se@C composite sodium replenisher to positive electrode active material in sodium-ion batteries is 1:4 to 99. This ratio ensures optimal sodium replenishment, allowing Na2Se@C to effectively compensate for lost active sodium and improve energy density.

[0020] The principle of this invention: Na₂Se can provide a high theoretical specific capacity of 675 mAh / g, and the sodium replenishment process does not generate additional gas or useless residues. The conductivity of solid selenium after sodium removal is approximately 10. -5 The S / cm further improves the conductivity of the composite cathode. Na₂Se has a high theoretical specific capacity, but it readily reacts with water and oxygen in the air. Combining it with carbon increases its air stability and conductivity. A Na₂Se@C composite sodium supplement is prepared using carbothermal reduction. Sodium selenite and carbon materials are thoroughly mixed, ground, and sieved in a specific ratio. Under high temperature and inert gas protection conditions, the reducing agent C reduces the O in sodium selenite to CO₂ gas, yielding Na₂Se and carbon coated on the surface of Na₂Se, i.e., the Na₂Se@C sodium supplement. Na₂Se@C is added to the cathode material of sodium-ion batteries. During charging, Na₂Se@C reacts to release sodium ions, replenishing the active sodium consumed in the formation of the SEI at the negative electrode. The polyselenides shuttling to the negative electrode can promote sodium ion transport, improve battery conductivity, inhibit dendrite growth, and contribute to improved cycle life.

[0021] Beneficial effects: Compared with the prior art, the present invention has the following significant features:

[0022] 1. In the synthesized Na2Se@C composite sodium supplement, Na2Se and C have a good synergistic effect. C improves the air stability of Na2Se and increases the energy density of the battery, which makes it possible for the large-scale application of Na2Se.

[0023] 2. The synthesis method of Na2Se@C composite sodium supplement is simple, safe and efficient, changing the existing complex synthesis process. No difficult-to-degrade waste is generated during the synthesis process, which is green and environmentally friendly and can be mass-produced.

[0024] 3. Na2Se@C composite sodium replenisher has excellent sodium replenishment effect in sodium-ion battery applications, which can effectively improve the energy density and cycle life of sodium-ion batteries. It can solve the problems of gas generation and inert substance residue in the sodium replenishment process of existing sodium replenishers, and promote the commercialization of sodium-ion batteries. Attached Figure Description

[0025] Figure 1 The X-ray diffraction pattern of the Na2Se@C composite sodium supplement of Example 1 of the present invention is shown below.

[0026] Figure 2 This is a scanning electron microscope image of the Na2Se@C composite sodium supplement of Example 1 of the present invention;

[0027] Figure 3 The first charge-discharge curve of the Na2Se@C composite sodium supplement in Example 1 of this invention;

[0028] Figure 4 A comparison chart of the cycle performance of sodium-ion batteries with the Na2Se@C composite sodium supplement agent of Example 1 of this invention. Detailed Implementation

[0029] Unless otherwise specified, all materials and reagents used in the following embodiments are commercially available. Experimental methods not specifically described in the embodiments are generally performed under standard conditions or as recommended by the manufacturer.

[0030] Example 1

[0031] The preparation method of Na2Se@C compound sodium supplement includes the following steps:

[0032] Sodium selenite and carbon were dried and purified before pretreatment. 1g of sodium selenite and 0.1g of acetylene black were weighed and placed in a planetary ball mill at a material-to-ball ratio of 1:5. After adding milling beads, the mixture was continuously milled at 500 rpm for 10 hours to obtain a homogeneous mixture. The mixture was then passed through a 1500-mesh sieve. Subsequently, the mixture was transferred to a tube furnace, and under an argon atmosphere, the furnace temperature was raised to 800℃ at a heating rate of 5℃ / min. After holding at this temperature for 10 hours, it was naturally cooled to room temperature to obtain the target product, Na₂Se@C composite sodium supplement.

[0033] Figure 1 The X-ray diffraction pattern of the prepared Na2Se@C composite sodium supplement shows that the diffraction peaks correspond to the standard card, confirming the synthesis of Na2Se.

[0034] Figure 2 This is a scanning electron microscope image.

[0035] Example 2

[0036] The preparation method of Na2Se@C compound sodium supplement includes the following steps:

[0037] Na₂SeO₄ and carbon were dried and purified before pretreatment. 1g of Na₂SeO₄ and 0.5g of Ketjen Black were weighed and placed in a planetary ball mill with a material-to-ball ratio of 1:1. After adding milling beads, the mixture was milled at 300 rpm for 6 hours to obtain a homogeneous mixture. The mixture was then passed through a 1500-mesh sieve. Subsequently, the mixture was transferred to a tube furnace, and under an argon atmosphere, the furnace temperature was raised to 500℃ at a heating rate of 1℃ / min. After holding at this temperature for 4 hours, it was naturally cooled to room temperature to obtain the target product, Na₂Se@C composite sodium supplement.

[0038] Example 3

[0039] The preparation method of Na2Se@C compound sodium supplement includes the following steps:

[0040] Na₂SeO₂ and carbon were dried and purified before pretreatment. 1g of Na₂SeO₂ and 0.2g of graphite were weighed and placed in a planetary ball mill with a material-to-ball ratio of 1:3. After adding milling beads, the mixture was milled at 400 rpm for 7 hours to obtain a homogeneous mixture. The mixture was then passed through a 1500-mesh sieve. Subsequently, the mixture was transferred to a tube furnace, and under an argon atmosphere, the furnace temperature was raised to 600℃ at a heating rate of 2℃ / min. After holding at this temperature for 6 hours, the mixture was naturally cooled to room temperature to obtain the target product, Na₂Se@C composite sodium supplement.

[0041] Example 4

[0042] The preparation method of Na2Se@C compound sodium supplement includes the following steps:

[0043] Na₂Se₂ and carbon were dried and purified before pretreatment. 1g of Na₂Se₂ and 0.3g of conductive carbon black were weighed and placed in a planetary ball mill at a material-to-ball ratio of 1:7. After adding milling beads, the mixture was milled at 600 rpm for 9 hours to obtain a homogeneous mixture. The mixture was then passed through a 1500-mesh sieve. Subsequently, the mixture was transferred to a tube furnace, and under an argon atmosphere, the furnace temperature was raised to 700℃ at a heating rate of 3℃ / min. After holding at this temperature for 8 hours, the mixture was naturally cooled to room temperature to obtain the target product, Na₂Se@C composite sodium supplement.

[0044] Example 5

[0045] The preparation method of Na2Se@C compound sodium supplement includes the following steps:

[0046] Sodium selenite and carbon were dried and purified before pretreatment. 1g of sodium selenite and 0.4g of carbon nanotubes were weighed and placed in a planetary ball mill at a material-to-ball ratio of 1:10. After adding milling beads, the mixture was milled at 800 rpm for 12 hours to obtain a homogeneous mixture. The mixture was then passed through a 1500-mesh sieve. Subsequently, the mixture was transferred to a tube furnace, and under an argon atmosphere, the furnace temperature was raised to 900℃ at a heating rate of 4℃ / min. After holding at this temperature for 12 hours, the mixture was naturally cooled to room temperature to obtain the target product, Na₂Se@C composite sodium supplement.

[0047] Example 6

[0048] The remaining steps in this embodiment are the same as in Example 1, except that sodium selenite is replaced sequentially with Na2SeO4, Na2SeO2, and Na2Se2 to obtain the target product Na2Se@C composite sodium supplement.

[0049] Comparative Example 1

[0050] The preparation method of Na2Se@C compound sodium supplement includes the following steps:

[0051] Unlike Example 1, Comparative Example 1 did not undergo ball milling. 1g of sodium selenite and 0.1g of acetylene black were weighed and thoroughly mixed. The mixture was transferred to a tube furnace, and under an argon atmosphere, the furnace temperature was raised to 800°C at a heating rate of 5°C / min. After holding at this temperature for 10 hours, the mixture was allowed to cool naturally to room temperature to obtain the target product, Na2Se@C composite sodium supplement.

[0052] Comparative Example 2

[0053] The preparation method of Na2Se@C compound sodium supplement includes the following steps:

[0054] Unlike Example 1, 1g of sodium selenite and 0.6g of acetylene black were weighed and placed in a planetary ball mill at a material-to-ball ratio of 1:5. After adding milling beads, the mixture was continuously milled at 500 rpm for 10 hours to obtain a homogeneous mixture. The mixture was then passed through a 1500-mesh sieve. Subsequently, the mixture was transferred to a tube furnace, and the furnace temperature was raised to 800°C at a heating rate of 5°C / min under an argon atmosphere. After holding at this temperature for 10 hours, the mixture was naturally cooled to room temperature to obtain the target product, Na2Se@C composite sodium supplement.

[0055] Comparative Example 3

[0056] The preparation method of Na2Se@C compound sodium supplement includes the following steps:

[0057] Unlike Example 1, the annealing temperature was 400℃, and the holding time was 3 hours. 1 g of sodium selenite and 0.1 g of acetylene black were weighed and placed in a planetary ball mill at a material-to-ball ratio of 1:5. After adding milling beads, the mixture was continuously milled at 500 rpm for 10 hours to obtain a homogeneous mixture. The mixture was then passed through a 1500-mesh sieve. Subsequently, the mixture was transferred to a tube furnace, and under an argon atmosphere, the furnace temperature was raised to 400℃ at a heating rate of 5℃ / min. After holding at this temperature for 3 hours, the mixture was naturally cooled to room temperature to obtain the target product, Na2Se@C composite sodium supplement.

[0058] Comparative Example 4

[0059] The preparation method of Na2Se@C compound sodium supplement includes the following steps:

[0060] Unlike Example 1, the annealing temperature was 1000℃ and the holding time was 13h. 1g of sodium selenite and 0.1g of acetylene black were weighed and placed in a planetary ball mill at a material-to-ball ratio of 1:5. After adding milling beads, the mixture was continuously milled at 500rpm for 10h to obtain a homogeneous mixture. The mixture was then passed through a 1500-mesh sieve. Subsequently, the mixture was transferred to a tube furnace, and under an argon atmosphere, the furnace temperature was raised to 1000℃ at a heating rate of 5℃ / min. After holding at this temperature for 13h, the mixture was naturally cooled to room temperature to obtain the target product, Na2Se@C composite sodium supplement.

[0061] Comparative Example 5

[0062] The preparation method of Na2Se@C compound sodium supplement includes the following steps:

[0063] Unlike Example 1, the target product was Na₂Se. 1g of sodium selenite and 0.08g of acetylene black were weighed and placed in a planetary ball mill at a material-to-ball ratio of 1:5. After adding milling beads, the mixture was continuously milled at 500 rpm for 10 hours to obtain a homogeneous mixture. The mixture was then passed through a 1500-mesh sieve. Subsequently, the mixture was transferred to a tube furnace, and under an argon atmosphere, the furnace temperature was raised to 800°C at a heating rate of 5°C / min. After holding at this temperature for 10 hours, the mixture was allowed to cool naturally to room temperature to obtain the target product, Na₂Se, a sodium supplement.

[0064] Using the Na2Se@C composite sodium supplement obtained from the above embodiments and comparative examples as electrode materials, battery electrode sheets were prepared and assembled into button cells (CR2032) for testing, including the following steps:

[0065] The Na2Se@C composite sodium supplement obtained in the above embodiments and comparative examples was mixed with polyvinylidene fluoride (PVDF) binder and acetylene black conductive agent at a mass ratio of 80:10:10. Then, 1-methyl-2-pyrrolidone (NMP) was added and stirred until a slurry was formed, which was then uniformly coated onto the surface of aluminum foil. After drying at 85°C for 12 hours, the mixture was pressed using a roller press and slit into electrode sheets. The prepared electrode sheets were assembled into button batteries (CR2032) for testing. Metallic sodium was used as the counter electrode, 1.0M NaClO4 (EC:PC = 3:7) was used as the electrolyte, and a glass fiber separator was used. After the assembled batteries were placed for 24 hours, charge-discharge tests were conducted at 25°C in a voltage range of 1.2-4V. The electrochemical performance test results of the Na2Se@C composite sodium supplement obtained in each embodiment and comparative example are shown in Table 1. Figure 3 As shown, within a voltage range of 1.2-4V, the Na2Se@C prepared in Example 1, as an electrode material, has a charge specific capacity of 455mAh / g and a discharge specific capacity of only 66.2mAh / g.

[0066] Table 1 Electrochemical performance test results

[0067]

[0068]

[0069] Table 2 Electrochemical performance test results of Example 6

[0070] Selenium source <![CDATA[Charge specific capacity / mAh·g -1 > <![CDATA[Discharge specific capacity / mAh·g -1 > <![CDATA[Na2SeO4]]> 445.3 56.3 <![CDATA[Na2SeO2]]> 438.4 67.3 <![CDATA[Na2Se2]]> 423.6 52.7

[0071] According to Table 1, Table 2 and Figure 3The results show that the Na2Se@C composite sodium supplement of the present invention exhibits excellent electrochemical performance as an electrode material, with the Na2Se@C composite sodium supplement prepared by reacting sodium selenite with carbon in Example 1 showing the best performance. Within a voltage range of 1.2-4V, the battery using the Na2Se@C composite sodium supplement as an electrode material achieves a charging specific capacity of 455 mAh / g and a discharging specific capacity of only 66.2 mAh / g. A comparison between Example 1 and Comparative Example 1 shows that ball milling significantly reduces the particle size, which helps accelerate the migration of ions and electrons during the electrochemical reaction, significantly improving its kinetics.

[0072] Using the Na2Se@C composite sodium supplement obtained in Example 1 as the experimental group and the Na2S@C composite sodium supplement as the control group, a verification experiment was conducted to assess the improvement in battery charge-discharge performance. The charge-discharge capacity of the prepared batteries is shown in Table 2. The battery preparation includes the following steps:

[0073] Application examples

[0074] The Na₂Se@C obtained in Example 1 was uniformly mixed with sodium vanadium phosphate at a mass ratio of 5:95 to serve as the electrode active material. This mixture was then combined with a binder, polyvinylidene fluoride (PVDF), and a conductive agent, acetylene black, at a ratio of 80:10:10. 1-Methyl-2-pyrrolidone (NMP) was added and stirred until a slurry was formed. This slurry was then uniformly coated onto the surface of aluminum foil and dried at 85°C for 12 hours to obtain an electrode sheet. The electrode sheet was then pressed using a roller press and dried at 90°C for 8 hours before being slit to produce sodium-ion battery positive electrode sheets.

[0075] The fabricated electrode sheets were assembled into button cells (CR2032) for testing. Hard carbon was used as the negative electrode, 1.0M NaClO4 (EC:PC = 3:7) was used as the electrolyte, and a glass fiber separator was used. After 24 hours of incubation, the assembled cells were subjected to constant current charge-discharge cycle testing at 0.5C in a room temperature environment of 25℃, with a voltage range of 1.2–4V. The test results are as follows. Figure 4 As shown, after adding the Na2Se@C composite sodium supplement, the first-cycle discharge specific capacity of the sodium-ion battery increased from 78.45 mAh / g to 103.5 mAh / g. After 200 cycles at 0.5C, it maintained a discharge specific capacity of 90.1 mAh / g.

[0076] Application of comparative examples

[0077] Weigh 1g of sodium sulfite and 0.1g of acetylene black, place them in a planetary ball mill with a material-to-ball ratio of 1:5, add milling beads, and continuously ball mill at 500rpm for 10h to obtain a uniformly mixed mixture. Pass the mixture through a 1500-mesh sieve and transfer it to a tube furnace. In an argon atmosphere, raise the furnace temperature to 800℃ at a heating rate of 5℃ / min, hold for 10h, and then allow it to cool naturally to room temperature to obtain Na2S@C sodium supplement.

[0078] The Na2S@C obtained from the control group was uniformly mixed with sodium vanadium phosphate at a mass ratio of 5:95 to serve as the electrode active material. This mixture was then combined with polyvinylidene fluoride (PVDF) as a binder and acetylene black as a conductive agent at a ratio of 80:10:10. 1-Methyl-2-pyrrolidone (NMP) was added and stirred until a slurry was formed. This slurry was then uniformly coated onto the surface of aluminum foil and dried at 85°C for 12 hours to obtain the electrode sheet. The electrode sheet was then pressed using a roller press and dried at 90°C for 8 hours before being slit to produce the positive electrode sheet for sodium-ion batteries.

[0079] The fabricated electrode sheets were assembled into button cells (CR2032) for testing. Hard carbon was used as the negative electrode, 1.0M NaClO4 (EC:PC = 3:7) was used as the electrolyte, and a glass fiber separator was used. After being placed for 24 hours, the assembled cells were subjected to constant current charge-discharge cycle tests at a rate of 0.5C at room temperature (25°C), with a voltage range of 1.2–4V.

[0080] Table 3 Battery charge / discharge capacity

[0081] serial number <![CDATA[Initial charging specific capacity / mAh·g -1 > <![CDATA[Initial cycle discharge specific capacity / mAh·g -1 > Application examples 121.7 103.5 Application of comparative examples 106.0 98.4

[0082] From Table 3 and Figure 4 It is known that the Na2Se@C composite sodium supplement can remove excess active sodium ions in a full cell, and exhibits excellent sodium supplementation effect in practical applications.

Claims

1. A method for preparing a Na2Se@C composite sodium supplement agent for sodium-ion battery cathode materials, characterized in that, Includes the following steps: Step 1: Dry and purify the selenium source and carbon. The selenium source is one or more of Na2SeO3·5H2O, Na2SeO4, Na2SeO4·10H2O, Na2SeO2, and Na2Se2. Step 2: The pretreated selenium source and carbon are thoroughly mixed, ground, and sieved at a mass ratio of 1:0.1~0.5 to obtain a mixture; Step 3: Anneal the mixture in an inert gas atmosphere, heat it to 500~900℃ and hold it at that temperature, then cool it to obtain Na2Se@C composite sodium supplement; The heat preservation time in step three is 4~12 hours; The Na2Se@C composite sodium supplement includes Na2Se and carbon coated on the surface of Na2Se, wherein the mass percentage of Na2Se is 80wt%~98wt%.

2. The preparation method of the Na2Se@C composite sodium supplement agent for sodium-ion battery cathode material according to claim 1, characterized in that, The particle size of the Na2Se@C composite sodium supplement is 1~10μm.

3. The preparation method of the Na2Se@C composite sodium supplement agent for sodium-ion battery cathode material according to claim 1, characterized in that, The grinding in step two is performed using a planetary ball mill with a material-to-ball ratio of 1:1 to 10 and a set rotation speed of 300 to 800 rpm. -1 The ball milling time is 6~12 hours.

4. The preparation method of the Na2Se@C composite sodium supplement agent for sodium-ion battery cathode material according to claim 1, characterized in that, The heating rate in step three is 1~5℃ / min.

5. The preparation method of the Na2Se@C composite sodium supplement agent for sodium-ion battery cathode material according to claim 1, characterized in that, The carbon is one or more of conductive carbon black, activated carbon, graphite, carbon nanotubes, and graphene.

6. The preparation method of the Na2Se@C composite sodium supplement agent for sodium-ion battery cathode material according to claim 1, characterized in that, The mass ratio of the Na2Se@C composite sodium supplement agent to the cathode material in the sodium-ion battery cathode material is 1:4~99.

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