Tin-carbon composite material and preparation method thereof

Abstract

The present invention discloses a tin-carbon composite material and a preparation method thereof. The tin-carbon composite material comprises a tin-based compound and a hollow carbon with nitrogen doping on the inner surface. The tin-based compound is uniformly distributed inside the nitrogen-doped hollow carbon on the inner surface, effectively suppressing the volume expansion of the tin-based compound during the sodium storage and de-sodium cycle and solving the crushing problem caused by uneven dispersion of active substances, thereby effectively enhancing the cycle life and safety performance of sodium ion batteries. The present invention greatly improves the energy density of sodium ion batteries by using a tin-based compound with high specific capacity.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium ion batteries, and in particular relates to a tin-carbon composite material and a preparation method thereof. Background Art

[0002] Currently, hard carbon has become the preferred material for sodium-ion battery anodes due to its advantages such as large interlayer spacing, abundant pores, low charge potential, small volume expansion rate, and high sodium storage capacity. However, although hard carbon exhibits good structural stability and long cycle life during sodium storage, its low operating voltage and theoretical specific capacity limit its application in high-energy density scenarios.

[0003] Tin-based compounds have attracted widespread attention due to their advantages such as controllable structure, high theoretical specific capacity, and low cost. However, in practical applications, tin-based compounds suffer from severe volume expansion, numerous side reactions, and poor electronic conductivity. Placing tin-based compounds with high volume expansion rates within hollow carbon is an effective structural design. However, unevenly dispersed tin-based compounds tend to aggregate, leading to stress concentration and pulverization of the active material during the sodium storage and de-sodium cycle, seriously affecting the electrochemical performance. Summary of the Invention

[0004] The purpose of the present invention is to provide a tin-carbon composite material. By doping nitrogen on the inner surface of hollow carbon, the tin-based compound is evenly anchored inside the hollow carbon, effectively suppressing the volume expansion of the tin-based compound during the sodium storage and de-sodium cycle and solving the crushing problem caused by uneven dispersion of active materials, thereby effectively enhancing the cycle life and safety performance of sodium ion batteries.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A tin-carbon composite material comprises a tin-based compound and hollow carbon with nitrogen doping on the inner surface, wherein the tin-based compound is uniformly distributed inside the hollow carbon with nitrogen doping on the inner surface.

[0007] The present invention also provides a method for preparing a tin-carbon composite material, comprising the following steps:

[0008] (1) adding ethyl orthosilicate to an ethanol aqueous solution and mixing uniformly, then sequentially adding dopamine, tris(hydroxymethyl)aminomethane buffer solution, phenolic resin, and ammonia water and mixing uniformly to obtain a mixture A;

[0009] (2) washing the mixture A obtained in step (1) with deionized water by centrifugation, drying, and then carbonizing at high temperature under nitrogen to obtain a mixture B;

[0010] (3) Soaking the mixture B in a sodium hydroxide solution, then centrifugally washing with deionized water and drying to obtain hollow carbon with nitrogen doped on the inner surface;

[0011] (4) adding the inner surface nitrogen-doped hollow carbon obtained in step (3) to an ethanol aqueous solution and mixing evenly, then adding a tin-containing substance and mixing evenly to obtain a mixture C;

[0012] (5) Adding a sulfur-containing or selenium-containing substance to the mixture C, mixing thoroughly and reacting at high temperature, washing with deionized water, and drying to obtain a tin-carbon composite material.

[0013] Preferably, in step (1), the mass ratio of ethanol to deionized water in the ethanol aqueous solution is 1:5 to 5:1; the mass ratio of tetraethyl orthosilicate to the ethanol aqueous solution is 1:10 to 1:30; the mass ratio of dopamine to tetraethyl orthosilicate is 1:1 to 1:10; the mass ratio of tris(hydroxymethylaminomethane) to tetraethyl orthosilicate in the tris(hydroxymethylaminomethane) buffer solution is 1:20 to 1:50; the mass ratio of phenolic resin to tetraethyl orthosilicate is 1:1 to 1:10; and the mass ratio of ammonia to tetraethyl orthosilicate in the ammonia solution is 1:3 to 1:10.

[0014] Preferably, in step (2), the temperature of the high-temperature carbonization is 500°C to 1000°C.

[0015] Preferably, in step (4), the mass ratio of ethanol to deionized water in the ethanol aqueous solution is 1:5 to 5:1; the mass ratio of the tin-containing substance to the inner surface nitrogen-doped hollow carbon is 1:5 to 5:1.

[0016] Preferably, in step (5), the mass ratio of the sulfur-containing substance to the inner surface nitrogen-doped hollow carbon is 1:5 to 5:1; the mass ratio of the selenium-containing substance to the inner surface nitrogen-doped hollow carbon is 1:5 to 5:1; and the temperature of the high-temperature reaction is 100°C to 200°C.

[0017] Preferably, the tin-containing substance is at least one of tin chloride, stannous octoate, stannous acetate, tin tetrachloride, and tin nitrate; the sulfur-containing substance is at least one of thiourea, thioacetamide, sodium sulfide, sodium sulfite, and sulfur powder; and the selenium-containing substance is at least one of selenium dioxide, selenium chloride, sodium selenite, and selenium powder.

[0018] The present invention also provides a method for preparing a tin-carbon composite material, comprising the following steps:

[0019] (1) adding a zeolite imidazolate framework material to an ethanol aqueous solution and mixing uniformly, then adding a phenolic resin and mixing thoroughly to obtain a mixture A;

[0020] (2) The mixture A was centrifugally washed with deionized water and dried, carbonized at high temperature under nitrogen, and then centrifuged with deionized water and dried to obtain hollow carbon with nitrogen doped on the inner surface;

[0021] (3) adding the inner surface nitrogen-doped hollow carbon obtained in step (2) to an ethanol aqueous solution and mixing evenly, then adding a tin-containing substance and mixing evenly to obtain a mixture B;

[0022] (4) Adding a sulfur- or selenium-containing substance to the mixture B and mixing thoroughly, reacting the mixture at a high temperature, and then washing with deionized water and drying the mixture to obtain a tin-carbon composite material.

[0023] Preferably, in step (1), the mass ratio of ethanol to deionized water in the ethanol aqueous solution is 1:5 to 5:1; the mass ratio of the zeolite imidazolate framework structure material to the ethanol aqueous solution is 1:10 to 1:30; and the mass ratio of the phenolic resin to the zeolite imidazolate framework structure material is 1:1 to 1:10.

[0024] Preferably, the zeolite imidazolate framework structural material is at least one of ZIF-8 and ZIF-68; the tin-containing substance is at least one of tin chloride, stannous octoate, stannous acetate, tin tetrachloride, and tin nitrate; the sulfur-containing substance is at least one of thiourea, thioacetamide, sodium sulfide, sodium sulfite, and sulfur powder; and the selenium-containing substance is at least one of selenium dioxide, selenium chloride, sodium selenite, and selenium powder.

[0025] Preferably, in step (2), the temperature of the high-temperature carbonization is 800°C to 1500°C.

[0026] Preferably, in step (3), the mass ratio of ethanol to deionized water in the ethanol aqueous solution is 1:5 to 5:1; the mass ratio of the tin-containing substance to the inner surface nitrogen-doped hollow carbon is 1:5 to 5:1.

[0027] Preferably, in step (4), the mass ratio of the sulfur-containing substance to the inner surface nitrogen-doped hollow carbon is 1:5 to 5:1; the mass ratio of the selenium-containing substance to the inner surface nitrogen-doped hollow carbon is 1:5 to 5:1; and the temperature of the high-temperature reaction is 100°C to 200°C.

[0028] The present invention also provides a negative electrode sheet comprising a negative electrode active material, a binder and a conductive agent, wherein the negative electrode active material is the above-mentioned tin-carbon composite material.

[0029] The present invention also provides a sodium ion battery, comprising a positive electrode sheet, a negative electrode sheet and a separator between the positive electrode sheet and the negative electrode sheet, wherein the negative electrode sheet is the negative electrode sheet described above.

[0030] The beneficial effects of the present invention are as follows: the present invention uses nitrogen doped inside the hollow carbon to uniformly anchor the tin-based compound inside the hollow carbon, effectively suppressing the volume expansion of the tin-based compound during the sodium storage and de-sodium cycle and solving the crushing problem caused by uneven dispersion of the active material, thereby effectively enhancing the cycle life and safety performance of the sodium ion battery; the present invention greatly improves the energy density of the sodium ion battery by using a tin-based compound with a high specific capacity. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 Schematic diagram of the structure of the tin-carbon composite material in one embodiment of the present invention;

[0032] Among them, 1-composite tin-carbon material, 11-tin-based compound, 12-inner surface nitrogen-doped hollow carbon. DETAILED DESCRIPTION

[0033] To make the technical solutions and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0034] According to a first aspect of the present invention, the present invention provides a tin-carbon composite material, which includes a tin-based compound and an inner surface nitrogen-doped hollow carbon, wherein the tin-based compound is uniformly distributed inside the inner surface nitrogen-doped hollow carbon.

[0035] Compared with hard carbon, the gram capacity of the tin-carbon composite material of the present invention is significantly improved, thereby improving the energy density of the sodium ion battery. When the tin-based compound is evenly dispersed in the hollow carbon, the hollow carbon not only effectively suppresses the volume expansion of the tin-based compound, but also avoids the problem of active material crushing caused by stress concentration due to uneven dispersion, thereby effectively improving the cycle life of the sodium ion battery. When the tin-based compound is both inside the hollow carbon and on the outer surface of the hollow carbon, the volume expansion of the tin compound on the outer surface of the hollow carbon during the sodium storage and sodium removal cycle causes the active material to crush, thereby affecting the performance of the electrochemical performance.

[0036] According to a second aspect of the present invention, the present invention further provides a method for preparing a tin-carbon composite material, comprising the following steps:

[0037] (1) adding ethyl orthosilicate to an ethanol aqueous solution and mixing uniformly, then sequentially adding dopamine, tris(hydroxymethyl)aminomethane buffer solution, phenolic resin, and ammonia water and mixing uniformly to obtain a mixture A;

[0038] (2) washing the mixture A obtained in step (1) with deionized water by centrifugation, drying, and then carbonizing at high temperature under nitrogen to obtain a mixture B;

[0039] (3) Soaking the mixture B in a sodium hydroxide solution, then centrifugally washing with deionized water and drying to obtain hollow carbon with nitrogen doped on the inner surface;

[0040] (4) adding the inner surface nitrogen-doped hollow carbon obtained in step (3) to an ethanol aqueous solution and mixing evenly, then adding a tin-containing substance and mixing evenly to obtain a mixture C;

[0041] (5) Adding a sulfur-containing or selenium-containing substance to the mixture C, mixing thoroughly and reacting at high temperature, washing with deionized water, and drying to obtain a tin-carbon composite material.

[0042] The reaction mechanism for preparing the tin-carbon composite material using the above-mentioned preparation method is as follows: ethyl orthosilicate is hydrolyzed to form silica, dopamine, which contains nitrogen in its molecule, is coated on the silica surface, tris(hydroxymethyl)aminomethane catalyzes the synthesis of polydopamine from dopamine, and phenolic resin is then coated on the polydopamine surface through non-covalent bonding forces with the polydopamine. Ammonia acts as a catalyst to completely hydrolyze the unhydrolyzed ethyl orthosilicate. After high-temperature carbonization, the polydopamine forms a nitrogen-doped carbon skeleton, while the phenolic resin forms an outer carbon skeleton. Sodium hydroxide then reacts with silica to form water-soluble sodium silicate. The sodium silicate dissolves in water to form a hollow carbon material, i.e., hollow carbon with nitrogen doped on the inner surface.

[0043] In one embodiment of the present invention, in step (1), the mass ratio of ethanol to deionized water in the ethanol aqueous solution is 1:5 to 5:1; specifically, it can be 1:5, 1:4, 1:3, 1:2, 1:1, 2:1, 3:1, 4:1, 5:1, and can include but are not limited to the listed values, preferably 1:1; when the mass ratio of ethanol to deionized water in the ethanol aqueous solution is controlled within the above range, it is beneficial to the dissolution of water-soluble dopamine, sodium silicate and alcohol-soluble ethyl orthosilicate and phenolic resin. If it is not within the above range, incomplete dissolution will occur, thereby resulting in the loss of raw materials and affecting the performance of the tin-carbon composite material in sodium ion batteries.

[0044] In one embodiment of the present invention, in step (1), the mass ratio of ethyl orthosilicate to ethanol aqueous solution is 1:10 to 1:30; specifically, it can be 1:10, 1:15, 1:20, or 1:30; it can include but is not limited to the values ​​listed, and is preferably 1:10; when the mass ratio of ethyl orthosilicate to ethanol aqueous solution is controlled within the above range, it is beneficial to the dissolution of ethyl orthosilicate; if there is too much ethyl orthosilicate, the dissolved concentration is too high, which is not conducive to the hydrolysis of ethyl orthosilicate; if there is too little ethyl orthosilicate, the concentration is too low, and the solvent is wasted.

[0045] In one embodiment according to the present invention, in step (1), the mass ratio of dopamine to tetraethyl orthosilicate is 1:1 to 1:10; specifically, it can be 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10; it can include but is not limited to the listed values, preferably 1:5; when the mass ratio of tetraethyl orthosilicate to ethanol aqueous solution is controlled within the above range, it is beneficial for dopamine to be coated on the surface of the silicon dioxide hydrolyzed by tetraethyl orthosilicate to a certain thickness. If the thickness is too small, it will lead to insufficient nitrogen; if the thickness is too large, the utilization efficiency of the nitrogen element is reduced.

[0046] In one embodiment of the present invention, in step (1), the mass ratio of tris(hydroxymethylaminomethane) to ethyl orthosilicate in the tris(hydroxymethylaminomethane) buffer solution is 1:20 to 1:50; specifically, it can be 1:20, 1:25, 1:30, 1:35, 1:40, 1:45, 1:50, and can include but are not limited to the listed values, preferably 1:35; when the mass ratio of tris(hydroxymethylaminomethane) to ethyl orthosilicate in the tris(hydroxymethylaminomethane) buffer solution is controlled within the above range, it is beneficial for dopamine to polymerize to form polydopamine; if the amount of tris(hydroxymethylaminomethane) is too little, the polymerization rate is slow; if the amount of tris(hydroxymethylaminomethane) is too much, more impurities are introduced.

[0047] In one embodiment according to the present invention, in step (1), the mass ratio of phenolic resin to tetraethyl orthosilicate is 1:1 to 1:10; specifically, it can be 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10; it can include but is not limited to the values ​​listed, and is preferably 1:5; when the mass ratio of phenolic resin to tetraethyl orthosilicate is controlled within the above range, it is beneficial for the phenolic resin to wrap a certain thickness on the surface of the silicon dioxide hydrolyzed by tetraethyl orthosilicate; if the thickness is too small, the carbon skeleton strength is insufficient; if the thickness is too large, it is not conducive to improving the energy density of the negative electrode.

[0048] In one embodiment of the present invention, in step (1), the mass ratio of ammonia in the ammonia water to ethyl orthosilicate is 1:3 to 1:10; specifically, it can be 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, or 1:10; it can include, but is not limited to, the values ​​listed above, and is preferably 1:7. When the mass ratio of ammonia in the ammonia water to ethyl orthosilicate is controlled within the above range, it is conducive to the complete hydrolysis of ethyl orthosilicate; if there is too little ammonia water, the hydrolysis rate is too slow; if there is too much ammonia water, the amount of ammonia water used is wasted.

[0049] In one embodiment of the present invention, in step (2), the high-temperature carbonization temperature is 500° C. to 1000° C.; specifically, it can be 500° C., 550° C., 600° C., 650° C., 700° C., 750° C., 800° C., 850° C., 900° C., 950° C., or 1000° C., preferably 500° C. When the carbonization temperature is controlled within the above range, it is beneficial to the carbonization of polydopamine and phenolic resin; if it is lower than this temperature, the carbonization is insufficient; if it is higher than this temperature, it is not conducive to the formation of pores in the carbon skeleton.

[0050] In one embodiment of the present invention, in step (4), the mass ratio of ethanol to deionized water in the ethanol aqueous solution is 1:5 to 5:1; specifically, it can be 1:5, 1:4, 1:3, 1:2, 1:1, 2:1, 3:1, 4:1, 5:1, and can include but are not limited to the listed values, preferably 1:1; when the mass ratio of ethanol to deionized water in the ethanol aqueous solution is controlled within the above range, it is conducive to the dissolution of water-soluble and alcohol-soluble substances.

[0051] In one embodiment of the present invention, in step (4), the mass ratio of the tin-containing substance to the inner surface nitrogen-doped hollow carbon is 1:5 to 5:1, specifically 1:5, 1:4, 1:3, 1:2, 1:1, 2:1, 3:1, 4:1, 5:1, and may include but not be limited to the listed values; preferably 1:1; when the mass ratio of the tin-containing substance to the inner surface nitrogen-doped hollow carbon is controlled within the above range, the tin-containing substance can be evenly distributed inside the inner surface nitrogen-doped hollow carbon, thereby improving the performance of the material.

[0052] In one embodiment according to the present invention, in step (5), the mass ratio of the sulfur-containing substance to the inner surface nitrogen-doped hollow carbon is 1:5 to 5:1; specifically, it can be 1:5, 1:4, 1:3, 1:2, 1:1, 2:1, 3:1, 4:1, 5:1, and can include but are not limited to the listed values, preferably 1:1; when the mass ratio of the sulfur-containing substance to the inner surface nitrogen-doped hollow carbon is controlled within the above range, it is beneficial to the reaction between the sulfur-containing and tin-containing substances; if the sulfur-containing substance is too little, the sulfurization of the tin-containing substance is insufficient; if the sulfur-containing substance is too much, the amount of the sulfur-containing substance cannot be fully utilized.

[0053] In one embodiment of the present invention, in step (5), the mass ratio of the selenium-containing substance to the inner surface nitrogen-doped hollow carbon is 1:5 to 5:1; specifically, it can be 1:5, 1:4, 1:3, 1:2, 1:1, 2:1, 3:1, 4:1, 5:1, and can include but are not limited to the values ​​listed above, preferably 1:1; when the mass ratio of the selenium-containing substance to the inner surface nitrogen-doped hollow carbon is controlled within the above range, it is conducive to the reaction between the selenium-containing substance and the tin-containing substance. If the selenium-containing substance is too little, the selenization of the tin-containing substance is insufficient; if the selenium-containing substance is too much, the amount of the selenium-containing substance cannot be fully utilized.

[0054] In one embodiment of the present invention, in step (5), the temperature of the high-temperature reaction is 100°C to 200°C, specifically 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, preferably 150°C. When the reaction temperature is controlled within the above range, it is beneficial to the reaction of the sulfur- or selenium-containing substance with the tin-containing substance. If it is lower than this temperature, the reaction is incomplete. If it is higher than this range, the improvement of the reaction efficiency is not significant.

[0055] In one embodiment of the present invention, the tin-containing substance is at least one of tin chloride, stannous octoate, stannous acetate, tin tetrachloride, and tin nitrate; preferably tin chloride.

[0056] In one embodiment of the present invention, the sulfur-containing substance is at least one of thiourea, thioacetamide, sodium sulfide, sodium sulfite, and sulfur powder; preferably thiourea.

[0057] In one embodiment of the present invention, the selenium-containing substance is at least one of selenium dioxide, selenium chloride, sodium selenite, and selenium powder, preferably selenium dioxide.

[0058] According to a third aspect of the present invention, the present invention further provides a method for preparing a tin-carbon composite material, comprising the following steps:

[0059] (1) adding a zeolite imidazolate framework material to an ethanol aqueous solution and mixing uniformly, then adding a phenolic resin and mixing thoroughly to obtain a mixture A;

[0060] (2) The mixture A was centrifugally washed with deionized water and dried, carbonized at high temperature under nitrogen, and then centrifuged with deionized water and dried to obtain hollow carbon with nitrogen doped on the inner surface;

[0061] (3) adding the inner surface nitrogen-doped hollow carbon obtained in step (2) to an ethanol aqueous solution and mixing evenly, then adding a tin-containing substance and mixing evenly to obtain a mixture B;

[0062] (4) Adding a sulfur- or selenium-containing substance to the mixture B and mixing thoroughly, reacting the mixture at a high temperature, and then washing with deionized water and drying the mixture to obtain a tin-carbon composite material.

[0063] The reaction mechanism for preparing the tin-carbon composite material using the above-mentioned preparation method is as follows: the zinc element of the nitrogen-containing zeolite imidazolate framework volatilizes at high temperatures, forming a porous hollow carbon material with nitrogen doping on its outer surface. A phenolic resin can be coated on the surface of the zeolite imidazolate framework and, after high-temperature carbonization, coated on the outer surface of the nitrogen-doped hollow carbon material.

[0064] In one embodiment of the present invention, in step (1), the mass ratio of ethanol to deionized water in the ethanol aqueous solution is 1:5 to 5:1; specifically, it can be 1:5, 1:4, 1:3, 1:2, 1:1, 2:1, 3:1, 4:1, 5:1, and can include but are not limited to the listed values, preferably 1:1; when the mass ratio of ethanol to deionized water in the ethanol aqueous solution is controlled within the above range, it is beneficial to the dispersion of the zeolite imidazolate framework material and the dissolution of the phenolic resin; if it exceeds the above range, it is not conducive to the dispersion or dissolution of the above substances.

[0065] In one embodiment according to the present invention, in step (1), the mass ratio of the zeolite imidazolate framework structure material to the ethanol aqueous solution is 1:10 to 1:30; specifically, it can be 1:10, 1:15, 1:20, or 1:30; it can include but is not limited to the values ​​listed, and is preferably 1:10; controlling the mass ratio of the zeolite imidazolate framework structure material to the ethanol aqueous solution within the above range is beneficial to the dispersion of the zeolite imidazolate framework structure material; if it is lower than the above range, it is not conducive to dispersion; if it is higher than the above range, the efficiency is not greatly improved, resulting in waste of materials.

[0066] In one embodiment according to the present invention, in step (1), the mass ratio of the phenolic resin to the zeolite imidazolate skeleton structure material is 1:1 to 1:10; specifically, it can be 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10; it can include but is not limited to the listed values, preferably 1:6; controlling the mass ratio of the phenolic resin to the zeolite imidazolate skeleton structure material within the above range is conducive to the phenolic resin wrapping a certain thickness on the surface of the zeolite imidazolate skeleton structure material; if the thickness is too small, the carbon skeleton strength is insufficient; if the thickness is too large, it is not conducive to improving the energy density of the negative electrode.

[0067] In one embodiment of the present invention, the zeolite imidazolate framework structure material is at least one of ZIF-8 and ZIF-68, preferably ZIF-8; the zinc element of ZIF-8 and ZIF-68 can volatilize within 800-1500°C, and after high temperature, it is easy to form a porous and stable hollow carbon material; other zeolite imidazolate framework structure materials do not have much advantages in the above two aspects.

[0068] In one embodiment of the present invention, the tin-containing substance is at least one of tin chloride, stannous octoate, stannous acetate, tin tetrachloride, and tin nitrate; preferably tin chloride.

[0069] In one embodiment of the present invention, the sulfur-containing substance is at least one of thiourea, thioacetamide, sodium sulfide, sodium sulfite, and sulfur powder; preferably thiourea.

[0070] In one embodiment of the present invention, the selenium-containing substance is at least one of selenium dioxide, selenium chloride, sodium selenite, and selenium powder; preferably, selenium dioxide.

[0071] In one embodiment of the present invention, in step (2), the temperature of high-temperature carbonization is 800°C to 1500°C, specifically 800°C, 900°C, 1000°C, 1100°C, 1200°C, 1300°C, 1400°C, or 1500°C; preferably 1100°C; controlling the carbonization temperature within the above range is beneficial to the high-temperature carbonization of the phenolic resin and the volatilization of the zinc element; if it is lower than this temperature, it is not conducive to the volatilization of the zinc element; if it is higher than this temperature, it is not conducive to the formation of pores in the carbon material.

[0072] In one embodiment of the present invention, in step (3), the mass ratio of ethanol to deionized water in the ethanol aqueous solution is 1:5 to 5:1; specifically, it can be 1:5, 1:4, 1:3, 1:2, 1:1, 2:1, 3:1, 4:1, 5:1, and can include but are not limited to the listed values, preferably 1:1; when the mass ratio of ethanol to deionized water in the ethanol aqueous solution is controlled within the above range, it is conducive to the dissolution of water-soluble and alcohol-soluble substances.

[0073] In one embodiment of the present invention, in step (3), the mass ratio of the tin-containing substance to the inner surface nitrogen-doped hollow carbon is 1:5 to 5:1; specifically, it can be 1:5, 1:4, 1:3, 1:2, 1:1, 2:1, 3:1, 4:1, 5:1, and can include but are not limited to the listed values, preferably 1:1. When the mass ratio of the tin-containing substance to the inner surface nitrogen-doped hollow carbon is controlled within the above range, the tin-containing substance can be evenly distributed inside the inner surface nitrogen-doped hollow carbon, thereby improving the performance of the material.

[0074] In one embodiment of the present invention, in step (4), the mass ratio of the sulfur-containing substance to the inner surface nitrogen-doped hollow carbon is 1:5 to 5:1; specifically, it can be 1:5, 1:4, 1:3, 1:2, 1:1, 2:1, 3:1, 4:1, 5:1, and can include but are not limited to the values ​​listed above, preferably 1:1. When the mass ratio of the sulfur-containing substance to the inner surface nitrogen-doped hollow carbon is controlled within the above range, the reaction between the sulfur-containing substance and the tin-containing substance is facilitated; if the sulfur-containing substance is too little, the tin-containing substance is not fully vulcanized; if the sulfur-containing substance is too much, the amount of the sulfur-containing substance cannot be fully utilized.

[0075] In one embodiment of the present invention, in step (4), the mass ratio of the selenium-containing substance to the inner surface nitrogen-doped hollow carbon is 1:5 to 5:1; specifically, it can be 1:5, 1:4, 1:3, 1:2, 1:1, 2:1, 3:1, 4:1, 5:1, and can include but are not limited to the listed values, preferably 1:1. When the mass ratio of the selenium-containing substance to the inner surface nitrogen-doped hollow carbon is controlled within the above range, it is beneficial to the reaction between the selenium-containing substance and the tin-containing substance. If the selenium-containing substance is too little, the selenization of the tin-containing substance is insufficient; if the selenium-containing substance is too much, the amount of the selenium-containing substance cannot be fully utilized.

[0076] In one embodiment of the present invention, in step (4), the temperature of the high-temperature reaction is 100°C to 200°C; specifically, it can be 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, or 200°C, preferably 150°C. When the reaction temperature is controlled within the above range, the reaction between the sulfur- or selenium-containing substance and the tin-containing substance is facilitated. If the temperature is lower than the above range, the reaction is incomplete; if the temperature is higher than the above range, the improvement in reaction efficiency is not significant.

[0077] According to a fourth aspect of the present invention, the present invention further provides a negative electrode sheet comprising a negative electrode active material, a binder and a conductive agent, wherein the negative electrode active material is the above-mentioned tin-carbon composite material.

[0078] The present invention also provides a method for preparing the aforementioned negative electrode sheet, comprising the steps of: uniformly mixing a negative electrode active material, a binder, and a conductive agent in a weight ratio of (92-94):(3-4):(3-4) in an appropriate amount of deionized water to obtain a negative electrode slurry; then coating the negative electrode slurry on a negative electrode current collector, drying, and roller-pressing to obtain the negative electrode sheet. The binder is at least one of polyvinyl alcohol, polyacrylic acid, sodium polyacrylate, sodium alginate, styrene-butadiene rubber, and sodium carboxymethyl cellulose; and the conductive agent is at least one of acetylene black, carbon black, Ketjen black, graphene, carbon nanotubes, and carbon nanofibers. The negative electrode current collector may be made of carbon-coated foil, metal foil, or composite foil, preferably aluminum foil.

[0079] According to the fifth aspect of the present invention, the present invention also provides a sodium ion battery, comprising a positive electrode sheet, a negative electrode sheet and a separator between the positive electrode sheet and the negative electrode sheet, wherein the negative electrode sheet is the above-mentioned negative electrode sheet.

[0080] The present invention also provides a method for preparing the above-mentioned sodium ion battery, which comprises the following steps: stacking or winding a negative electrode sheet, a separator, and a positive electrode sheet in order to obtain a battery cell, placing the battery cell in a packaging shell, adding an electrolyte and encapsulating the battery cell, and obtaining a sodium ion battery after processes such as formation, hot and cold pressing, and capacity separation.

[0081] The positive electrode sheet can be produced by the following method: uniformly mixing a positive electrode active material, a conductive agent, a binder, and N-methylpyrrolidone to obtain a positive electrode slurry. The positive electrode slurry is then coated on a positive electrode current collector, dried, and rolled to obtain the positive electrode sheet. The positive electrode active material is at least one of a transition metal oxide, a Prussian blue compound, and a polyanionic compound; the conductive agent is at least one of carbon nanotubes, acetylene black, Ketjen black, carbon black, graphene, and carbon nanofibers; the binder is at least one of polyvinylidene fluoride, polyacrylic acid, polyimide, sodium polyacrylate, styrene-butadiene rubber, sodium alginate, and nitrile rubber; and the positive electrode current collector can be made of carbon-coated foil, metal foil, or composite foil, preferably aluminum foil.

[0082] The separator may be a single-layer or multi-layer separator of at least one of glass fiber, polypropylene, polyethylene, non-woven fabric and polyvinylidene fluoride.

[0083] The electrolyte includes an organic solvent and an electrolyte sodium salt. Preferably, the organic solvent can be at least one of diethyl carbonate, ethyl methyl carbonate, propylene carbonate, and ethylene carbonate; and the electrolyte sodium salt can be at least one of NaClO4, Na(CH3)C6H4SO3, NaSO3CF3, NaPF6, and NaBCl4.

[0084] The present invention will be further described below through specific examples.

[0085] Example 1

[0086] An embodiment of the present invention provides a tin-carbon composite material 1 , which includes a tin-based compound 11 and an inner-surface nitrogen-doped hollow carbon 12 , wherein the tin-based compound 11 is uniformly distributed inside the inner-surface nitrogen-doped hollow carbon 12 .

[0087] This embodiment also provides a method for preparing the above-mentioned tin-carbon composite material, and the specific steps are as follows:

[0088] (1) Weigh ethanol and deionized water, mix ethanol and deionized water in a mass ratio of 1:1, and mechanically stir at 200 r / min for 3 minutes. Then, add tetraethyl orthosilicate (the mass ratio of tetraethyl orthosilicate to ethanol aqueous solution is 1:10). After mechanically stirring at 1000 r / min for 20 minutes, add dopamine (the mass ratio of dopamine to tetraethyl orthosilicate is 1:1). After mechanically stirring at 500 r / min for 20 minutes, add tris(hydroxymethyl)aminomethane buffer solution (the mass ratio of tris(hydroxymethyl)aminomethane to tetraethyl orthosilicate is 1:20). Mechanically stir at 500 r / min for 10 hours. Add phenolic resin (the mass ratio of phenolic resin to tetraethyl orthosilicate is 1:1). Mechanically stir at 500 r / min for 30 minutes. Add ammonia water (the mass ratio of ammonia in the ammonia water to tetraethyl orthosilicate is 1:3). Mechanically stir at 500 r / min at 70°C for 5 hours to obtain a mixture A.

[0089] (2) Mixture A was centrifugally washed with deionized water and then dried, calcined under nitrogen, and heated to 500°C at a rate of 5°C / min and kept at that temperature for 6 h to obtain mixture B;

[0090] (3) Soaking the mixture B in a 3 mol / L sodium hydroxide solution, then centrifugally washing with deionized water and drying to obtain hollow carbon with nitrogen doped on the inner surface;

[0091] (4) adding the inner surface nitrogen-doped hollow carbon to an ethanol aqueous solution, wherein ethanol and deionized water are mixed at a mass ratio of 1:1, and the mass ratio of the inner surface nitrogen-doped hollow carbon to the ethanol aqueous solution is 1:1, and mechanically stirring at 500 r / min for 20 minutes, adding tin chloride, and the mass ratio of tin chloride to the inner surface nitrogen-doped hollow carbon is 1:5, and mechanically stirring at 1000 r / min for 60 minutes to obtain a mixture C;

[0092] (5) Thiourea was added to the mixture C, with a mass ratio of thiourea to the inner surface nitrogen-doped hollow carbon being 1:5. After mechanical stirring at 1000 r / min for 60 minutes, the mixture was placed in an autoclave and reacted at 100° C. for 10 hours. The mixture was then centrifuged and washed with deionized water and dried to obtain a tin-carbon composite material.

[0093] This embodiment also provides a method for preparing a negative electrode sheet, comprising the following steps: uniformly mixing a tin-carbon composite material, sodium polyacrylate, and carbon black in a weight ratio of 94:3:3 in an appropriate amount of deionized water to obtain a negative electrode slurry. The negative electrode slurry is then coated on aluminum foil, and the negative electrode sheet is obtained after baking and roller pressing.

[0094] This embodiment also provides a method for preparing a positive electrode sheet, which specifically includes: mixing sodium iron phosphate, polyvinylidene fluoride, and carbon black in a weight ratio of 92:4:4 in an appropriate amount of NMP to obtain a positive electrode slurry; then coating the positive electrode slurry on a carbon-coated aluminum foil, and obtaining a positive electrode sheet after drying and rolling.

[0095] This embodiment also provides a method for preparing a sodium ion battery, the specific steps of which include: stacking a polypropylene film, a negative electrode sheet, and a positive electrode sheet in order, placing the battery cell in a packaging shell, and adding an electrolyte (propylene carbonate + NaPF 6) The battery is then packaged and processed through processes such as formation, hot and cold pressing, and capacity division to produce a sodium-ion battery.

[0096] Example 2

[0097] The method for preparing the tin-carbon composite material in this embodiment is different from the method for preparing the tin-carbon composite material in Example 1. The rest is the same as in Example 1 and will not be repeated here. The specific steps of this embodiment include the following steps:

[0098] (1) Weigh ethanol and deionized water, mix ethanol and deionized water in a mass ratio of 1:1, and mechanically stir at 200 r / min for 3 minutes. Then, add tetraethyl orthosilicate (the mass ratio of tetraethyl orthosilicate to ethanol aqueous solution is 1:10). After mechanically stirring at 1000 r / min for 20 minutes, add dopamine (the mass ratio of dopamine to tetraethyl orthosilicate is 1:3). After mechanically stirring at 500 r / min for 20 minutes, add tris(hydroxymethyl)aminomethane buffer solution (the mass ratio of tris(hydroxymethyl)aminomethane to tetraethyl orthosilicate is 1:30), and mechanically stir at 500 r / min for 10 hours. Then add phenolic resin (the mass ratio of phenolic resin to tetraethyl orthosilicate is 1:3), and mechanically stir at 500 r / min for 30 minutes. Then add ammonia water (the mass ratio of ammonia in the ammonia water to tetraethyl orthosilicate is 1:5), and mechanically stir at 500 r / min at 70°C for 5 hours to obtain a mixture A.

[0099] (2) Mixture A was centrifugally washed with deionized water and then dried, and calcined under nitrogen, heating to 600°C at a rate of 5°C / min and holding for 6 h to obtain mixture B;

[0100] (3) Soaking the mixture B in a 3 mol / L sodium hydroxide solution, then centrifugally washing with deionized water and drying to obtain hollow carbon with nitrogen doped on the inner surface;

[0101] (4) adding the inner surface nitrogen-doped hollow carbon to an ethanol aqueous solution, wherein ethanol and deionized water are mixed in a mass ratio of 1:1, and the mass ratio of the inner surface nitrogen-doped hollow carbon to the ethanol aqueous solution is 1:1, and mechanically stirring is performed at 500 r / min for 20 minutes, adding tin chloride, and the mass ratio of tin chloride to the inner surface nitrogen-doped hollow carbon is 1:3, and mechanically stirring is performed at 1000 r / min for 60 minutes to obtain a mixture C;

[0102] (5) Thiourea was added to the mixture C in a mass ratio of thiourea to the inner surface nitrogen-doped hollow carbon of 1:3. After mechanical stirring at 1000 r / min for 60 minutes, the mixture was placed in an autoclave and reacted at 120° C. for 10 hours. The mixture was then centrifuged and washed with deionized water and dried to obtain a tin-carbon composite material.

[0103] Example 3

[0104] The method for preparing the tin-carbon composite material in this embodiment is different from the method for preparing the tin-carbon composite material in Example 1. The rest is the same as in Example 1 and will not be repeated here. The specific steps of this embodiment include the following steps:

[0105] (1) Weigh ethanol and deionized water, mix ethanol and deionized water in a mass ratio of 1:1, and mechanically stir at 200 r / min for 3 minutes. Then, add tetraethyl orthosilicate (the mass ratio of tetraethyl orthosilicate to ethanol aqueous solution is 1:10). After mechanically stirring at 1000 r / min for 20 minutes, add dopamine (the mass ratio of dopamine to tetraethyl orthosilicate is 1:5). After mechanically stirring at 500 r / min for 20 minutes, add tris(hydroxymethyl)aminomethane buffer solution (the mass ratio of tris(hydroxymethyl)aminomethane to tetraethyl orthosilicate is 1:35). Mechanically stir at 500 r / min for 10 hours. Add phenolic resin (the mass ratio of phenolic resin to tetraethyl orthosilicate is 1:5). Mechanically stir at 500 r / min for 30 minutes. Add ammonia water (the mass ratio of ammonia in the ammonia water to tetraethyl orthosilicate is 1:7). Mechanically stir at 500 r / min at 70°C for 5 hours to obtain a mixture A.

[0106] (2) Mixture A was centrifugally washed with deionized water and then dried, and calcined under nitrogen, heating to 700°C at a rate of 5°C / min and holding for 6 h to obtain mixture B;

[0107] (3) Soaking the mixture B in a 3 mol / L sodium hydroxide solution, then centrifugally washing with deionized water and drying to obtain hollow carbon with nitrogen doped on the inner surface;

[0108] (4) adding the inner surface nitrogen-doped hollow carbon to an ethanol aqueous solution, wherein the ethanol and deionized water are mixed at a mass ratio of 1:1, and the mass ratio of the inner surface nitrogen-doped hollow carbon to the ethanol aqueous solution is 1:1, and mechanically stirring is performed at 500 r / min for 20 minutes, adding tin chloride, and the mass ratio of tin chloride to the inner surface nitrogen-doped hollow carbon is 1:1, and mechanically stirring is performed at 1000 r / min for 60 minutes to obtain a mixture C;

[0109] (5) Thiourea was added to the mixture C in a mass ratio of thiourea to the inner surface nitrogen-doped hollow carbon of 1:1. After mechanical stirring at 1000 r / min for 60 minutes, the mixture was placed in an autoclave and reacted at 150° C. for 10 hours. The mixture was then centrifuged and washed with deionized water and dried to obtain a tin-carbon composite material.

[0110] Example 4

[0111] The method for preparing the tin-carbon composite material in this embodiment is different from the method for preparing the tin-carbon composite material in Example 1. The rest is the same as in Example 1 and will not be repeated here. The specific steps of this embodiment include the following steps:

[0112] (1) Ethanol and deionized water were weighed, and the ethanol and deionized water were mixed in a mass ratio of 1:1, and mechanically stirred at 200 r / min for 3 minutes. Then, tetraethyl orthosilicate was added, and the mass ratio of tetraethyl orthosilicate to ethanol aqueous solution was 1:10. After mechanically stirring at 1000 r / min for 20 minutes, dopamine was added, and the mass ratio of dopamine to tetraethyl orthosilicate was 1:7. After mechanically stirring at 500 r / min for 20 minutes, tris(hydroxymethyl)aminomethane buffer solution was added, and the mass ratio of tris(hydroxymethyl)aminomethane to tetraethyl orthosilicate was 1:40. The mixture was mechanically stirred at 500 r / min for 10 hours. Phenolic resin was added, and the mass ratio of phenolic resin to tetraethyl orthosilicate was 1:7. The mixture was mechanically stirred at 500 r / min for 30 minutes. Ammonia water was added, and the mass ratio of ammonia in the ammonia water to tetraethyl orthosilicate was 1:9. The mixture was mechanically stirred at 500 r / min at 70°C for 5 hours to obtain a mixture A.

[0113] (2) Mixture A was centrifugally washed with deionized water and then dried, and calcined under nitrogen, heating to 800°C at a rate of 5°C / min and holding for 6 h to obtain mixture B;

[0114] (3) Soaking the mixture B in a 3 mol / L sodium hydroxide solution, then centrifugally washing with deionized water and drying to obtain hollow carbon with nitrogen doped on the inner surface;

[0115] (4) adding the inner surface nitrogen-doped hollow carbon to an ethanol aqueous solution, wherein ethanol and deionized water are mixed at a mass ratio of 1:1, and the mass ratio of the inner surface nitrogen-doped hollow carbon to the ethanol aqueous solution is 1:1, and mechanically stirring is performed at 500 r / min for 20 minutes, adding tin chloride, and the mass ratio of tin chloride to the inner surface nitrogen-doped hollow carbon is 3:1, and mechanically stirring is performed at 1000 r / min for 60 minutes to obtain a mixture C;

[0116] (5) Thiourea was added to the mixture C in a mass ratio of thiourea to the inner surface nitrogen-doped hollow carbon of 1:1. After mechanical stirring at 1000 r / min for 60 minutes, the mixture was placed in an autoclave and reacted at 180° C. for 10 hours. The mixture was then centrifuged and washed with deionized water and dried to obtain a tin-carbon composite material.

[0117] Example 5

[0118] The method for preparing the tin-carbon composite material in this embodiment is different from the method for preparing the tin-carbon composite material in Example 1. The rest is the same as in Example 1 and will not be repeated here. The specific steps of this embodiment include the following steps:

[0119] (1) Ethanol and deionized water were weighed, and the ethanol and deionized water were mixed in a mass ratio of 1:1, and mechanically stirred at 200 r / min for 3 minutes. Then, tetraethyl orthosilicate was added, and the mass ratio of tetraethyl orthosilicate to ethanol aqueous solution was 1:10. After mechanically stirring at 1000 r / min for 20 minutes, dopamine was added, and the mass ratio of dopamine to tetraethyl orthosilicate was 1:10. After mechanically stirring at 500 r / min for 20 minutes, tris(hydroxymethyl)aminomethane) buffer solution was added, and the mass ratio of tris(hydroxymethyl)aminomethane to tetraethyl orthosilicate was 1:50. The mixture was mechanically stirred at 500 r / min for 10 hours. Phenolic resin was added, and the mass ratio of phenolic resin to tetraethyl orthosilicate was 1:10. The mixture was mechanically stirred at 500 r / min for 30 minutes. Ammonia water was added, and the mass ratio of ammonia in the ammonia water to tetraethyl orthosilicate was 1:10. The mixture was mechanically stirred at 500 r / min at 70°C for 5 hours to obtain a mixture A.

[0120] (2) Mixture A was centrifugally washed with deionized water and then dried, and calcined under nitrogen, heating to 1000°C at a rate of 5°C / min and holding for 6 h to obtain mixture B;

[0121] (3) Soaking the mixture B in a 3 mol / L sodium hydroxide solution, then centrifugally washing with deionized water and drying to obtain hollow carbon with nitrogen doped on the inner surface;

[0122] (4) adding the inner surface nitrogen-doped hollow carbon to an ethanol aqueous solution, wherein ethanol and deionized water are mixed at a mass ratio of 1:1, and the mass ratio of the inner surface nitrogen-doped hollow carbon to the ethanol aqueous solution is 1:1, and mechanically stirring at 500 r / min for 20 minutes, adding tin chloride, and the mass ratio of tin chloride to the inner surface nitrogen-doped hollow carbon is 5:1, and mechanically stirring at 1000 r / min for 60 minutes to obtain a mixture C;

[0123] (5) Thiourea was added to the mixture C, with the mass ratio of thiourea to the inner surface nitrogen-doped hollow carbon being 5:1. After mechanical stirring at 1000 r / min for 60 minutes, the mixture was placed in an autoclave and reacted at 200° C. for 10 hours. The mixture was then centrifuged and washed with deionized water and dried to obtain a tin-carbon composite material.

[0124] Example 6

[0125] The method for preparing the tin-carbon composite material in this embodiment is different from the method for preparing the tin-carbon composite material in Example 1. The rest is the same as in Example 1 and will not be repeated here. The specific steps of this embodiment include the following steps:

[0126] (1) Ethanol and deionized water were weighed, and the ethanol and deionized water were mixed in a mass ratio of 1:1, and mechanically stirred at 200 r / min for 3 minutes. ZIF-8 was then added, and the mass ratio of ZIF-8 to ethanol-water solution was 1:10. The mixture was mechanically stirred at 1000 r / min for 20 minutes. Phenolic resin was added, and the mass ratio of phenolic resin to ZIF-8 was 1:1. The mixture was mechanically stirred at 500 r / min for 30 minutes to obtain a mixture A.

[0127] (2) Mixture A was centrifugally washed with deionized water, dried, calcined under nitrogen, heated to 800°C at 5°C / min, kept at this temperature for 6 hours, and then centrifugally washed with deionized water and dried to obtain hollow carbon with nitrogen doped on the inner surface;

[0128] (3) adding the inner surface nitrogen-doped hollow carbon obtained in step (2) to an ethanol aqueous solution, mixing ethanol and deionized water in a mass ratio of 1:1, the mass ratio of the inner surface nitrogen-doped hollow carbon to the ethanol aqueous solution being 1:1, and mechanically stirring at 500 r / min for 20 minutes, adding tin chloride, the mass ratio of tin chloride to the inner surface nitrogen-doped hollow carbon being 1:5, and mechanically stirring at 1000 r / min for 60 minutes to obtain a mixture B

[0129] (4) Thiourea was added to the mixture B, with a mass ratio of thiourea to the inner surface nitrogen-doped hollow carbon being 1:5. The mixture was mechanically stirred at 1000 r / min for 60 minutes, placed in an autoclave, reacted at 100° C. for 10 hours, and then centrifuged and washed with deionized water and dried to obtain a tin-carbon composite material.

[0130] Example 7

[0131] The method for preparing the tin-carbon composite material in this embodiment is different from the method for preparing the tin-carbon composite material in Example 6. The rest is the same as in Example 6 and will not be repeated here. The specific steps of this embodiment include the following steps:

[0132] (1) Ethanol and deionized water were weighed, and the ethanol and deionized water were mixed in a mass ratio of 1:1, and mechanically stirred at 200 r / min for 3 minutes. ZIF-8 was then added, and the mass ratio of ZIF-8 to ethanol-water solution was 1:10. The mixture was mechanically stirred at 1000 r / min for 20 minutes. Phenolic resin was added, and the mass ratio of phenolic resin to ZIF-8 was 1:3. The mixture was mechanically stirred at 500 r / min for 30 minutes to obtain a mixture A.

[0133] (2) Mixture A was centrifugally washed with deionized water, dried, calcined under nitrogen, heated to 950°C at 5°C / min, kept at this temperature for 6 hours, and then centrifugally washed with deionized water and dried to obtain hollow carbon with nitrogen doped on the inner surface;

[0134] (3) adding the inner surface nitrogen-doped hollow carbon obtained in step (2) to an ethanol aqueous solution, mixing ethanol and deionized water in a mass ratio of 1:1, the mass ratio of the inner surface nitrogen-doped hollow carbon to the ethanol aqueous solution being 1:1, and mechanically stirring at 500 r / min for 20 minutes, adding tin chloride, the mass ratio of tin chloride to the inner surface nitrogen-doped hollow carbon being 1:3, and mechanically stirring at 1000 r / min for 60 minutes to obtain a mixture B

[0135] (4) Thiourea was added to the mixture B, with a mass ratio of thiourea to the inner surface nitrogen-doped hollow carbon being 1:3. The mixture was mechanically stirred at 1000 r / min for 60 minutes, placed in an autoclave, reacted at 120° C. for 10 hours, and then centrifuged and washed with deionized water and dried to obtain a tin-carbon composite material.

[0136] Example 8

[0137] The method for preparing the tin-carbon composite material in this embodiment is different from the method for preparing the tin-carbon composite material in Example 6. The rest is the same as in Example 6 and will not be repeated here. The specific steps of this embodiment include the following steps:

[0138] (1) Ethanol and deionized water were weighed, and the ethanol and deionized water were mixed in a mass ratio of 1:1, and mechanically stirred at 200 r / min for 3 minutes. ZIF-8 was then added, and the mass ratio of ZIF-8 to ethanol-water solution was 1:10. The mixture was mechanically stirred at 1000 r / min for 20 minutes. Phenolic resin was added, and the mass ratio of phenolic resin to ZIF-8 was 1:6. The mixture was mechanically stirred at 500 r / min for 30 minutes to obtain a mixture A.

[0139] (2) Mixture A was centrifugally washed with deionized water, dried, calcined under nitrogen, heated to 1100°C at 5°C / min, kept warm for 6 hours, and then centrifugally washed with deionized water and dried to obtain hollow carbon with nitrogen doped on the inner surface;

[0140] (3) adding the inner surface nitrogen-doped hollow carbon obtained in step (2) to an ethanol aqueous solution, mixing ethanol and deionized water in a mass ratio of 1:1, the mass ratio of the inner surface nitrogen-doped hollow carbon to the ethanol aqueous solution being 1:1, and mechanically stirring at 500 r / min for 20 minutes, adding tin chloride, the mass ratio of tin chloride to the inner surface nitrogen-doped hollow carbon being 1:1, and mechanically stirring at 1000 r / min for 60 minutes to obtain a mixture B

[0141] (4) Thiourea was added to the mixture B, with the mass ratio of thiourea to the inner surface nitrogen-doped hollow carbon being 1:1. The mixture was mechanically stirred at 1000 r / min for 60 minutes, placed in an autoclave, reacted at 150° C. for 10 hours, and then centrifuged and washed with deionized water and dried to obtain a tin-carbon composite material.

[0142] Example 9

[0143] The method for preparing the tin-carbon composite material in this embodiment is different from the method for preparing the tin-carbon composite material in Example 6. The rest is the same as in Example 6 and will not be repeated here. The specific steps of this embodiment include the following steps:

[0144] (1) Ethanol and deionized water were weighed, and the ethanol and deionized water were mixed in a mass ratio of 1:1, and mechanically stirred at 200 r / min for 3 minutes. ZIF-8 was then added, and the mass ratio of ZIF-8 to ethanol-water solution was 1:10. The mixture was mechanically stirred at 1000 r / min for 20 minutes. Phenolic resin was added, and the mass ratio of phenolic resin to ZIF-8 was 1:8. The mixture was mechanically stirred at 500 r / min for 30 minutes to obtain a mixture A.

[0145] (2) The mixture A was centrifugally washed with deionized water, dried, calcined under nitrogen, heated to 1300°C at 5°C / min, kept at this temperature for 6 hours, and then centrifugally washed with deionized water and dried to obtain hollow carbon with nitrogen doped on the inner surface;

[0146] (3) adding the inner surface nitrogen-doped hollow carbon obtained in step (2) to an ethanol aqueous solution, mixing ethanol and deionized water in a mass ratio of 1:1, the mass ratio of the inner surface nitrogen-doped hollow carbon to the ethanol aqueous solution being 1:1, and mechanically stirring at 500 r / min for 20 minutes, adding tin chloride, the mass ratio of tin chloride to the inner surface nitrogen-doped hollow carbon being 3:1, and mechanically stirring at 1000 r / min for 60 minutes to obtain a mixture B

[0147] (4) Thiourea was added to the mixture B, with a mass ratio of thiourea to the inner surface nitrogen-doped hollow carbon being 3:1. The mixture was mechanically stirred at 1000 r / min for 60 minutes, placed in an autoclave, reacted at 170° C. for 10 hours, and then centrifuged and washed with deionized water and dried to obtain a tin-carbon composite material.

[0148] Example 10

[0149] The method for preparing the tin-carbon composite material in this embodiment is different from the method for preparing the tin-carbon composite material in Example 6. The rest is the same as in Example 6 and will not be repeated here. The specific steps of this embodiment include the following steps:

[0150] (1) Ethanol and deionized water were weighed, and the ethanol and deionized water were mixed in a mass ratio of 1:1, and mechanically stirred at 200 r / min for 3 minutes. ZIF-8 was then added, and the mass ratio of ZIF-8 to ethanol-water solution was 1:10. The mixture was mechanically stirred at 1000 r / min for 20 minutes. Phenolic resin was added, and the mass ratio of phenolic resin to ZIF-8 was 1:10. The mixture was mechanically stirred at 500 r / min for 30 minutes to obtain a mixture A.

[0151] (2) Mixture A was centrifugally washed with deionized water, dried, calcined under nitrogen, heated to 1500°C at 5°C / min, kept at this temperature for 6 hours, and then centrifugally washed with deionized water and dried to obtain hollow carbon with nitrogen doped on the inner surface;

[0152] (3) adding the inner surface nitrogen-doped hollow carbon obtained in step (2) to an ethanol aqueous solution, mixing ethanol and deionized water in a mass ratio of 1:1, the mass ratio of the inner surface nitrogen-doped hollow carbon to the ethanol aqueous solution being 1:1, and mechanically stirring at 500 r / min for 20 minutes, adding tin chloride, the mass ratio of tin chloride to the inner surface nitrogen-doped hollow carbon being 5:1, and mechanically stirring at 1000 r / min for 60 minutes to obtain a mixture B

[0153] (4) Thiourea was added to the mixture B, with a mass ratio of thiourea to the inner surface nitrogen-doped hollow carbon being 5:1. The mixture was mechanically stirred at 1000 r / min for 60 minutes, placed in an autoclave, reacted at 200° C. for 10 hours, and then centrifuged and washed with deionized water and dried to obtain a tin-carbon composite material.

[0154] Comparative Example 1

[0155] The difference between this comparative example and Example 1 and Example 6 is that hard carbon is directly used as the negative electrode active material to prepare the negative electrode sheet, and the specific steps include:

[0156] Hard carbon, sodium polyacrylate, and carbon black were mixed uniformly in a suitable amount of deionized water at a weight ratio of 94:3:3 to obtain a negative electrode slurry. The negative electrode slurry was then coated on aluminum foil, baked, and rolled to obtain a negative electrode sheet.

[0157] Comparative Example 2

[0158] The method for preparing the tin-carbon composite material in this comparative example is different from the method for preparing the tin-carbon composite material in Example 1. The rest is the same as in Example 1 and will not be repeated here. The specific steps of this comparative example include the following steps:

[0159] (1) Ethanol and deionized water were weighed, and the ethanol and deionized water were mixed in a mass ratio of 1:1, and mechanically stirred at 200 r / min for 3 minutes. Then, ethyl orthosilicate was added, and the mass ratio of ethyl orthosilicate to ethanol aqueous solution was 1:10. The mixture was mechanically stirred at 1000 r / min for 20 minutes. Phenolic resin was added, and the mass ratio of phenolic resin to ethyl orthosilicate was 1:1. The mixture was mechanically stirred at 500 r / min for 30 minutes. Ammonia water was added, and the mass ratio of ammonia in the ammonia water to ethyl orthosilicate was 1:3. The mixture was mechanically stirred at 500 r / min at 70°C for 5 hours to obtain a mixture A.

[0160] (2) Mixture A was centrifugally washed with deionized water and then dried; calcined under nitrogen at a temperature of 5°C / min to 500°C and kept at that temperature for 6 hours to obtain mixture B;

[0161] (3) Soaking the mixture B in a 3 mol / L sodium hydroxide solution, washing it with deionized water by centrifugation, and drying it to obtain hollow carbon;

[0162] (4) adding the hollow carbon to an ethanol aqueous solution, wherein the ethanol and deionized water are mixed in a mass ratio of 1:1, the mass ratio of the hollow carbon to the ethanol aqueous solution is 1:1, and mechanically stirring at 500 r / min for 20 minutes, adding tin chloride, the mass ratio of tin chloride to the hollow carbon is 1:5, and mechanically stirring at 1000 r / min for 60 minutes to obtain a mixture C;

[0163] (5) Thiourea was added to the mixture C in a mass ratio of thiourea to hollow carbon of 1:5. The mixture was mechanically stirred at 1000 r / min for 60 minutes, placed in an autoclave, reacted at 100° C. for 10 hours, and then centrifuged and washed with deionized water and dried to obtain a tin-carbon composite material.

[0164] Comparative Example 3

[0165] The method for preparing the tin-carbon composite material in this comparative example is different from the method for preparing the tin-carbon composite material in Example 6. The rest is the same as in Example 6 and will not be repeated here. The specific steps of this comparative example include the following steps:

[0166] (1) ZIF-8 was calcined under nitrogen, heated at 5°C / min to 950°C, kept at this temperature for 6 h, washed by centrifugation with deionized water, and then dried to obtain nitrogen-doped hollow carbon;

[0167] (2) adding the nitrogen-doped hollow carbon to an ethanol aqueous solution, wherein the ethanol and deionized water are mixed in a mass ratio of 1:1, the mass ratio of the nitrogen-doped hollow carbon to the ethanol aqueous solution is 1:1, and mechanically stirring at 500 r / min for 20 minutes, adding tin chloride, the mass ratio of tin chloride to the nitrogen-doped hollow carbon is 1:3, and mechanically stirring at 1000 r / min for 60 minutes to obtain a mixture B;

[0168] (3) Thiourea was added to the mixture B in a mass ratio of thiourea to nitrogen-doped hollow carbon of 1:3. The mixture was mechanically stirred at 1000 r / min for 60 minutes, placed in an autoclave, reacted at 120° C. for 10 hours, and then centrifuged and washed with deionized water and dried to obtain a tin-carbon composite material.

[0169] Test section

[0170] (1) Negative electrode active material gram capacity test:

[0171] The negative electrode sheet and fiber separator were placed sequentially into a steel shell. After dripping an electrolyte solution (1M NaPF6, EC:DEC = 1:1), the sodium sheet was placed on top of the fiber separator. A gasket, spring, and steel shell were then added in that order to create a button cell. At 25°C, the button cell was discharged at 0.01C to 0V, allowed to rest for 5 minutes, and then charged at 0.03C to 2V and allowed to rest for 5 minutes. This constituted one charge-discharge cycle. The gram capacity of the negative electrode active material = the charge capacity of the first cycle / the weight of the negative electrode active material.

[0172] (2) Cycle performance test of sodium ion batteries:

[0173] At 25°C, charge the sodium-ion battery at a constant current of 1C to the upper cutoff voltage limit, then charge it at a constant voltage to a current of 0.2C. After standing for 5 minutes, discharge it at a constant current of 1C to the lower cutoff voltage limit and stand for 5 minutes. This constitutes one charge-discharge cycle, and the discharge capacity at this time is the initial capacity of the sodium-ion battery. Perform the battery charge-discharge test 500 times according to the above steps to obtain the discharge capacity at the 500th cycle. The capacity retention rate of the sodium-ion battery after the 500th cycle at 25°C = discharge capacity at the 500th cycle / discharge capacity at the first cycle × 100%.

[0174] The test results of Examples 1 to 10 and Comparative Examples 1 to 3 are shown in Table 1:

[0175] Table 1

[0176]

[0177] From the test results of Examples 1 to 5 and Comparative Example 1, and the test results of Examples 6 to 10 and Comparative Example 1, it can be seen that compared with hard carbon, the gram capacity of the tin-carbon composite material of the present invention is significantly improved, thereby improving the energy density of the sodium ion battery. Furthermore, from the test results of Examples 1 to 5 and Comparative Example 2, and the test results of Examples 6 to 10 and Comparative Example 3, it can be seen that when the tin-based compound is evenly dispersed in the hollow carbon, the hollow carbon not only effectively suppresses the volume expansion of the tin-based compound, but also avoids the problem of active material crushing caused by stress concentration due to uneven dispersion, thereby effectively improving the cycle life of the sodium ion battery. When the tin-based compound is both inside the hollow carbon and on the outer surface of the hollow carbon, the volume expansion of the tin compound on the outer surface of the hollow carbon during the sodium storage and de-sodium cycle causes the active material to crush, thereby affecting the performance of the electrochemical performance.

[0178] Based on the disclosure and teachings of the above description, those skilled in the art will be able to make changes and modifications to the above embodiments. Therefore, the present invention is not limited to the above specific embodiments. Any obvious improvements, substitutions, or modifications made by those skilled in the art based on the present invention fall within the scope of protection of the present invention. In addition, although certain specific terms are used in this description, these terms are only for convenience of description and do not constitute any limitation to the present invention.

Claims

1. A tin-carbon composite material, characterized in that The tin-carbon composite material includes a tin-based compound and an inner-surface nitrogen-doped hollow carbon, wherein the tin-based compound is uniformly distributed inside the inner-surface nitrogen-doped hollow carbon. The inner-surface nitrogen-doped hollow carbon can be prepared in the following two ways: first, after mixing ethyl orthosilicate, dopamine, trishydroxymethylaminomethane, phenolic resin and ammonia water, carbonizing the mixture at high temperature and then treating the mixture with sodium hydroxide to obtain the inner-surface nitrogen-doped hollow carbon; second, after mixing a zeolite imidazole ester skeleton structure material and a phenolic resin, carbonizing the mixture at high temperature to obtain the inner-surface nitrogen-doped hollow carbon; the inner-surface nitrogen-doped hollow carbon is added to a tin-containing substance and mixed, and then a sulfur-containing substance or a selenium-containing substance is added to react to obtain the tin-carbon composite material.

2. A method for preparing the tin-carbon composite material according to claim 1, characterized in that: The following steps are involved: (1) adding ethyl orthosilicate to an ethanol aqueous solution and mixing uniformly, then sequentially adding dopamine, tris(hydroxymethyl)aminomethane buffer solution, phenolic resin, and ammonia water and mixing uniformly to obtain a mixture A; (2) The mixture A obtained in step (1) is centrifugally washed with deionized water, dried, and then carbonized at high temperature under nitrogen to obtain a mixture B; (3) Soaking the mixture B in a sodium hydroxide solution, then centrifugally washing with deionized water and drying to obtain hollow carbon with nitrogen doped on the inner surface; (4) adding the inner surface nitrogen-doped hollow carbon obtained in step (3) to an ethanol aqueous solution and mixing uniformly, then adding a tin-containing substance and mixing uniformly to obtain a mixture C; (5) Adding a sulfur-containing substance or a selenium-containing substance to the mixture C, mixing thoroughly and reacting at high temperature, washing with deionized water, and drying to obtain a tin-carbon composite material.

3. The method for preparing the tin-carbon composite material according to claim 2, wherein: In step (1), the mass ratio of ethanol to deionized water in the ethanol aqueous solution is 1:5 to 5:1; the mass ratio of tetraethyl orthosilicate to the ethanol aqueous solution is 1:10 to 1:30; the mass ratio of dopamine to tetraethyl orthosilicate is 1:1 to 1:10; the mass ratio of tris(hydroxymethylaminomethane) to tetraethyl orthosilicate in the tris(hydroxymethylaminomethane) buffer solution is 1:20 to 1:50; the mass ratio of phenolic resin to tetraethyl orthosilicate is 1:1 to 1:10; and the mass ratio of ammonia to tetraethyl orthosilicate in the ammonia water is 1:3 to 1:

10.

4. The method for preparing the tin-carbon composite material according to claim 2, wherein: In step (2), the temperature of the high-temperature carbonization is 500°C to 1000°C.

5. The method for preparing the tin-carbon composite material according to claim 2, wherein: In step (4), the mass ratio of ethanol to deionized water in the ethanol aqueous solution is 1:5 to 5:1; the mass ratio of the tin-containing substance to the inner surface nitrogen-doped hollow carbon is 1:5 to 5:

1.

6. The method for preparing the tin-carbon composite material according to claim 2, wherein: In step (5), the mass ratio of the sulfur-containing substance to the inner surface nitrogen-doped hollow carbon is 1:5 to 5:1; the mass ratio of the selenium-containing substance to the inner surface nitrogen-doped hollow carbon is 1:5 to 5:1; and the temperature of the high-temperature reaction is 100°C to 200°C.

7. The method for preparing the tin-carbon composite material according to claim 2, characterized in that: The tin-containing substance is at least one of tin chloride, stannous octoate, stannous acetate, tin tetrachloride, and tin nitrate; the sulfur-containing substance is at least one of thiourea, thioacetamide, sodium sulfide, sodium sulfite, and sulfur powder; and the selenium-containing substance is at least one of selenium dioxide, selenium chloride, sodium selenite, and selenium powder.

8. A method for preparing the tin-carbon composite material according to claim 1, characterized in that: The following steps are involved: (1) adding a zeolite imidazolate framework material to an ethanol aqueous solution and mixing uniformly, then adding a phenolic resin and mixing thoroughly to obtain a mixture A; (2) The mixture A is centrifugally washed with deionized water and dried, carbonized at high temperature under nitrogen, and then centrifugally washed with deionized water and dried to obtain hollow carbon with nitrogen doped on the inner surface; (3) adding the inner surface nitrogen-doped hollow carbon obtained in step (2) to an ethanol aqueous solution and mixing uniformly, then adding a tin-containing substance and mixing uniformly to obtain a mixture B; (4) Add a sulfur-containing substance or a selenium-containing substance to the mixture B, mix thoroughly, react at high temperature, and then wash with deionized water and dry to obtain a tin-carbon composite material.

9. The method for preparing the tin-carbon composite material according to claim 8, characterized in that: In step (1), the mass ratio of ethanol to deionized water in the ethanol aqueous solution is 1:5 to 5:1; the mass ratio of the zeolite imidazolate framework structure material to the ethanol aqueous solution is 1:10 to 1:30; and the mass ratio of the phenolic resin to the zeolite imidazolate framework structure material is 1:1 to 1:

10.

10. The method for preparing the tin-carbon composite material according to claim 8, characterized in that: The zeolite imidazolate framework structural material is at least one of ZIF-8 and ZIF-68; the tin-containing substance is at least one of tin chloride, stannous octoate, stannous acetate, tin tetrachloride, and tin nitrate; the sulfur-containing substance is at least one of thiourea, thioacetamide, sodium sulfide, sodium sulfite, and sulfur powder; and the selenium-containing substance is at least one of selenium dioxide, selenium chloride, sodium selenite, and selenium powder.

11. The method for preparing the tin-carbon composite material according to claim 8, characterized in that: In step (2), the temperature of the high-temperature carbonization is 800°C to 1500°C.

12. The method for preparing the tin-carbon composite material according to claim 8, characterized in that: In step (3), the mass ratio of ethanol to deionized water in the ethanol aqueous solution is 1:5 to 5:1; the mass ratio of the tin-containing substance to the inner surface nitrogen-doped hollow carbon is 1:5 to 5:

1.

13. The method for preparing the tin-carbon composite material according to claim 8, characterized in that: In step (4), the mass ratio of the sulfur-containing substance to the inner surface nitrogen-doped hollow carbon is 1:5 to 5:1; the mass ratio of the selenium-containing substance to the inner surface nitrogen-doped hollow carbon is 1:5 to 5:1; and the temperature of the high temperature reaction is 100°C to 200°C.

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