Composite hard carbon negative electrode material, preparation method thereof and sodium ion battery

Abstract

The application provides a preparation method of a composite hard carbon negative electrode material, comprising the following steps: S1, SnCl4.5H2O is added into a suspension of microcrystalline graphite / phenolic resin hard carbon and uniformly stirred for 1h to obtain a mixed solution A; S2, the mixed solution A is placed in an autoclave for hydrothermal reaction, and after the reaction is completed, the SnO2@MG / PF hydrogel is obtained after being immersed and washed in deionized water; S3, the SnO2@MG / PF hydrogel is subjected to evaporation drying treatment under the protection of an inert gas, and then is placed in a high-temperature furnace for high-temperature treatment to obtain the composite hard carbon negative electrode material. After the phenolic resin hard carbon and the microcrystalline graphite are compounded and doped with a certain amount of tin dioxide, the obtained composite hard carbon negative electrode material can be used in a sodium ion battery, and the specific capacity, coulomb efficiency, rate and cycle performance of the sodium ion battery can be improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of sodium ion batteries, in particular to a composite hard carbon negative electrode material, a preparation method thereof and a sodium ion battery. BACKGROUND

[0002] In recent years, sodium ion batteries have developed rapidly and become a high-performance energy storage system. Sodium is abundant in nature, with a concentration nearly five orders of magnitude higher than lithium in seawater, accounting for 2.74% of the total mass of the earth's crust, and widely distributed. The abundance of this resource effectively reduces the cost of raw materials, making sodium ion batteries (SIB) gradually surpass lithium ion batteries (LIB) and become a more ideal energy storage option.

[0003] Similar to lithium, sodium also belongs to the first main group of elements and has similar chemical properties. Sodium ion batteries use a similar deintercalation mechanism as lithium ion batteries, that is, during the charging and discharging process, Na + ions migrate between the positive and negative electrodes to realize energy storage and release. However, compared with lithium, the relative atomic mass of sodium is higher, resulting in a relatively low theoretical specific capacity. At the same time, the radius of Na + ions is larger than that of Li + (Na + radius: 0.106 nm, Li + radius: 0.076 nm), making it more difficult for Na + to intercalate / deintercalate in the electrode material, thereby causing problems such as decreased cycle performance and specific capacity of the battery, which seriously restricts the large-scale development and commercialization of sodium ion batteries.

[0004] Current research focuses on finding alternative solutions for sodium ion battery negative electrode materials, which need to have high specific capacity and replaceability. Research objects include porous hard carbon, transition metal oxides, transition metal phosphides, and metal alloys. Traditional porous hard carbon has high capacity and high rate performance, but due to poor sodium storage structure, it is difficult to desolvate, resulting in low sodium storage capacity, obvious electrolyte side reactions, low initial coulombic efficiency, and low cycle coulombic efficiency. During the charging and discharging process under high rate and long cycle conditions, the rapid intercalation / deintercalation of sodium ions can cause the degradation of the microstructure and nanoscale structure of the negative electrode material, and the volume expansion can cause the negative electrode material to separate from the current collector, and the kinetic limitations related to the discontinuous electronic transfer structure of the electrode can also affect the stability. SUMMARY

[0005] In view of the problems existing in the prior art that graphite is used as a negative electrode material for sodium ion batteries, the present application obtains a composite hard carbon negative electrode material by compounding phenolic resin hard carbon and microcrystalline graphite and doping a certain amount of tin dioxide, which is used in a sodium ion battery, and can improve the specific capacity, coulombic efficiency, rate performance, and cycle performance of the sodium ion battery.

[0006] The first object of the present application is to provide a preparation method of a composite hard carbon negative electrode material, comprising the following steps:

[0007] S1 adding SnCl4 5H2O into a suspension of microcrystalline graphite / phenolic resin hard carbon and uniformly stirring for 1h to obtain a mixed solution A;

[0008] S2 placing the mixed solution A in an autoclave to perform a hydrothermal reaction, and after the reaction is completed, soaking and washing in deionized water to obtain SnO2@MG / PF hydrogel;

[0009] S3 performing evaporation drying treatment on the SnO2@MG / PF hydrogel under inert gas protection, and then placing it in a high-temperature furnace to perform high-temperature treatment, to obtain a composite hard carbon negative electrode material.

[0010] Specifically, the preparation method of the phenolic resin hard carbon in step S1 is: uniformly mixing 0.2g of resorcinol, 0.3ml of ammonia water, 8ml of anhydrous ethanol and 48ml of deionized water to obtain a mixed solution a; then adding 0.28ml of formaldehyde solution to the mixed solution a, and uniformly stirring at 60℃ for 24h to obtain a phenolic resin-based precursor; high-temperature carbonizing the phenolic resin-based precursor at 1600℃ for 6h to obtain the phenolic resin hard carbon.

[0011] Specifically, the preparation method of the suspension of microcrystalline graphite / phenolic resin hard carbon in step S1 is: sequentially placing microcrystalline graphite and phenolic resin hard carbon in deionized water, and uniformly stirring at 25-45℃ for 6-8h to obtain the suspension of microcrystalline graphite / phenolic resin hard carbon.

[0012] Specifically, the concentration of the suspension of microcrystalline graphite / phenolic resin hard carbon in step S1 is 6mg / mL; and the size of the microcrystalline graphite is 200 mesh.

[0013] Specifically, the mass ratio of SnCl4 5H2O, microcrystalline graphite and phenolic resin hard carbon in step S1 is 3:2:3.

[0014] Specifically, the reaction temperature of the hydrothermal reaction in step S2 is 180-200℃, and the reaction time is 6-10h.

[0015] Specifically, the treatment temperature of the evaporation drying treatment in step S3 is 80-120℃, and the treatment time is 0.5-2h.

[0016] Specifically, the treatment temperature of the high-temperature treatment in step S3 is 1000-1200℃, the heating rate is 1-5℃ / min, and the treatment time is 6h.

[0017] Specifically, the inert gas in step S3 is any one of nitrogen, argon and helium.

[0018] The second object of the present application is to provide a composite hard carbon negative electrode material prepared by the above preparation method.

[0019] The second object of the present application is to provide a sodium ion battery composed of a positive electrode, a negative electrode, an electrolyte and a separator, wherein the negative electrode material used in the negative electrode is the composite hard carbon negative electrode material described above.

[0020] Compared with the prior art, the present application has the following beneficial effects:

[0021] Since the microcrystalline graphite itself has high electrical conductivity, the graphite lattice layer structure arranged by it is conducive to the rapid conduction of electrons in the plane; and the hard carbon formed by pyrolysis of phenolic resin can form more conductive channels in the structure, reduce the area of uneven electrical conductivity in the carbon material, and further improve the electrical conductivity of the entire material. After SnO2, as a semiconductor material, is compounded with the microcrystalline graphite / phenolic resin hard carbon material, it can form a close interface contact with the carbon material, and form a carbon-non-carbon hybrid nanoscale dispersed phase and a porous network structure on the surface of the material, thereby providing a larger specific surface area for the composite hard carbon negative electrode material and promoting the transmission of sodium ions in the charging and discharging process. In addition, SnO2 is doped in the porous composite hard carbon negative electrode material, which improves the specific capacity and electrical conductivity of the negative electrode material, and the unique structure can effectively inhibit the volume expansion change of the negative electrode sheet during the charging and discharging process, prevent agglomeration, reduce electrode material polarization and battery internal resistance, and improve the cycle stability and rate performance of the material. Through the synergistic effect among the microcrystalline graphite, the phenolic resin hard carbon and SnO2, the advantages of the three are fully utilized, and they are complementary in structure and properties. The composite hard carbon negative electrode material has the advantages of traditional hard carbon materials, and also has the advantages of nanodoped materials, has increased specific surface area and improved electrical conductivity, has excellent electrochemical performance, and also has enhanced thermal conductivity and structural stability, which indicates that it has great potential in the application fields of high capacity, high power and high safety. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 A structure schematic diagram of the composite hard carbon negative electrode material a1 provided for the embodiment 1 of the present application is shown in the figure.

[0023] Figure 2 A SEM diagram of the composite hard carbon negative electrode material a1 provided for the embodiment 1 of the present application is shown in the figure. DETAILED DESCRIPTION

[0024] With reference to the content in the embodiments of the present application, the technical solutions in the embodiments of the present application will be clearly and completely described. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all the other embodiments obtained by a person of ordinary skill in the art without creative effort belong to the scope of protection of the present application.

[0025] Unless otherwise defined, all technical and scientific terms used in the present application have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs. The terminology used in the description of the present application only for the purpose of describing specific embodiments and is not intended to limit the present application. The term "and / or" used in the present application includes any and all combinations of one or more related listed items.

[0026] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods. Unless otherwise specified, the materials, reagents, etc. used in the following examples can be obtained from commercial channels.

[0027] Example 1

[0028] The preparation method of the composite hard carbon negative material a1 involved in the present embodiment 1 includes the following steps:

[0029] (1) Preparation of phenolic resin hard carbon:

[0030] 0.2g of resorcinol, 0.3ml of ammonia water, 8ml of anhydrous ethanol and 48ml of deionized water were mixed uniformly to obtain a mixed solution a1; 0.28ml of formaldehyde solution was further added to the mixed solution a1, and uniform stirring was carried out at 60℃ for 24h to obtain a phenolic resin-based precursor a1; the phenolic resin-based precursor a1 was carbonized at 1600℃ for 6h to obtain the phenolic resin hard carbon prepared in example 1.

[0031] (2) Preparation of composite hard carbon negative material:

[0032] Step 1: 0.6g of microcrystalline graphite and 0.9g of phenolic resin hard carbon were placed in 250ml of deionized water, and uniform stirring was carried out at 25℃ for 6h to obtain a microcrystalline graphite / phenolic resin hard carbon suspension with a concentration of 6mg / mL. 0.9g of tin chloride pentahydrate (SnCl4·5H2O) was added to the microcrystalline graphite / phenolic resin hard carbon suspension as a precursor of SnO2, and uniform stirring was carried out for 1h to obtain a mixed solution A1 prepared in example 1.

[0033] Step 2: The mixed solution A1 was placed in an autoclave and hydrothermally reacted at 180℃ for 6h. After the reaction was completed, the product was immersed and washed in deionized water to remove excess Sn 4+cylindrical SnO2@MG / PF hydrogel prepared in Example 1.

[0034] Step 3: The cylindrical SnO2@MG / PF hydrogel prepared in Example 1 was placed in a vacuum drying oven and evaporated and dried at 100℃ for 1.5h under nitrogen protection, and then the evaporated and dried SnO2@MG / PF hydrogel was placed in a high-temperature furnace and heated to 1200℃ at a rate of 5℃ / min, and high-temperature treated for 6h to obtain the composite hard carbon negative electrode material a1 prepared in Example 1.

[0035] (3) Preparation of negative electrode sheet: After mixing and slurrying the composite hard carbon negative electrode material a1, the binder (CMC BH90) and the conductive agent SP at a mass ratio of 8:1:1, coating on the current collector aluminum foil, vacuum drying at 105℃ for 10h, and then pressing and forming after pressing at a pressure of 1MPa, the negative electrode sheet was prepared by punching.

[0036] Please refer to Figure 1 , Figure 1 The structural schematic diagram of the composite hard carbon negative electrode material a1 provided in Example 1 can be seen from Figure 1 , which can form more conductive channels in the structure by the compounding of microcrystalline graphite and phenolic resin hard carbon, and reduce the area of uneven conductivity in the carbon material. After the compounding of SnO2 as a semiconductor material with the microcrystalline graphite / phenolic resin hard carbon material, it can form a close interface contact with the carbon material, and form a carbon-non-carbon hybrid nanoscale dispersed phase and a porous network structure on the material surface, and SnO2 is doped in the pores. The unique structure formed by the present application can effectively inhibit the volume expansion change of the negative electrode sheet during the charging and discharging process, prevent agglomeration, reduce electrode material polarization and battery internal resistance, and improve the cycle stability and rate performance of the material. Figure 2 The SEM diagram of the composite hard carbon negative electrode material a1 provided in Example 1 of the present application can be seen from Figure 2 , which shows that the composite hard carbon negative electrode material a1 prepared according to the above method is in the form of particles, the particles are uniformly distributed, and there is no adhesion between the particles. Since the pore size is small and belongs to the micropore level, no macropores and defect structures are found.

[0037] Example 2

[0038] The preparation method of the composite hard carbon negative electrode material a2 involved in this embodiment 2 includes the following steps:

[0039] (1) Preparation of phenolic resin hard carbon:

[0040] Mixing 0.2 g of resorcinol, 0.3 ml of ammonia water, 8 ml of anhydrous ethanol and 48 ml of deionized water uniformly to obtain a mixed solution a1; then adding 0.28 ml of formaldehyde solution to the mixed solution a1, uniformly stirring at 60°C for 24 h to obtain a phenolic resin-based precursor a1; carbonizing the phenolic resin-based precursor a1 at 1600°C for 6 h to obtain the phenolic resin hard carbon prepared in Example 2.

[0041] (2) Preparation of composite hard carbon negative electrode material:

[0042] Step 1: Put 1 g of microcrystalline graphite and 1.5 g of phenolic resin hard carbon into 417 ml of deionized water, uniformly stir at 45°C for 8 h to obtain a microcrystalline graphite / phenolic resin hard carbon suspension with a concentration of 6 mg / mL. Add 1.5 g of SnCl4·5H2O to the microcrystalline graphite / phenolic resin hard carbon suspension, uniformly stir for 1 h to obtain a mixed solution A2 prepared in Example 2.

[0043] Step 2: Put the mixed solution A2 into an autoclave and hydrothermally react at 200°C for 10 h. After the reaction is completed, the product is soaked in deionized water for 48 h to remove excess Sn 4+ , to obtain the cylindrical SnO2@MG / PF hydrogel prepared in Example 2.

[0044] Step 3: Place the cylindrical SnO2@MG / PF hydrogel prepared in Example 2 in a vacuum drying oven, evaporate and dry at 120°C under argon protection for 2 h, then place the evaporated and dried SnO2@MG / PF hydrogel in a high-temperature furnace, heat to 1100°C at a rate of 3°C / min, and high-temperature treat for 6 h to obtain the composite hard carbon negative electrode material a2 prepared in Example 2.

[0045] (3) Preparation of negative electrode sheet: Mix the composite hard carbon negative electrode material a2, the binder (CMC BH90) and the conductive agent SP at a mass ratio of 8:1:1, coat on the current collector aluminum foil, vacuum dry at 105°C for 10 h, then press form under a pressure of 1 MPa, and then punch to prepare the negative electrode sheet.

[0046] Example 3

[0047] The preparation method of the composite hard carbon negative electrode material a3 involved in this example 3 includes the following steps:

[0048] (1) Preparation of phenolic resin hard carbon:

[0049] Mixing 0.2 g of resorcinol, 0.3 ml of ammonia water, 8 ml of anhydrous ethanol and 48 ml of deionized water uniformly to obtain a mixed solution a1; then adding 0.28 ml of formaldehyde solution to the mixed solution a1, uniformly stirring at 60°C for 24 h to obtain a phenolic resin-based precursor a1; carbonizing the phenolic resin-based precursor a1 at 1600°C for 6 h to obtain the phenolic resin hard carbon prepared in Example 3.

[0050] (2) Preparation of composite hard carbon negative electrode material:

[0051] Step 1: Put 0.8 g of microcrystalline graphite and 1.2 g of phenolic resin hard carbon into 334 ml of deionized water, uniformly stir at 30°C for 7 h to obtain a microcrystalline graphite / phenolic resin hard carbon suspension with a concentration of 6 mg / mL. Add 1.2 g of SnCl4·5H2O to the microcrystalline graphite / phenolic resin hard carbon suspension, uniformly stir for 1 h to obtain a mixed solution A3 prepared in Example 3.

[0052] Step 2: Put the mixed solution A3 into an autoclave, hydrothermal reaction at 185°C for 8 h, after the reaction is completed, the product is soaked in deionized water for 48 h, and the excess Sn 4+ is removed by washing to obtain a cylindrical SnO2@MG / PF hydrogel prepared in Example 3.

[0053] Step 3: Place the cylindrical SnO2@MG / PF hydrogel prepared in Example 3 in a vacuum drying oven, evaporate and dry at 90°C under argon protection for 1 h, then place the evaporated and dried SnO2@MG / PF hydrogel in a high-temperature furnace, heat to 1050°C at a rate of 2°C / min, and high-temperature treatment for 6 h to obtain a composite hard carbon negative electrode material a3 prepared in Example 3.

[0054] (3) Preparation of negative electrode sheet: Mix the composite hard carbon negative electrode material a3, the binder (CMC BH90) and the conductive agent SP at a mass ratio of 8:1:1, coat on the current collector aluminum foil, vacuum dry at 105°C for 10 h, then press form under a pressure of 1 MPa, and then punch to prepare a negative electrode sheet.

[0055] Example 4

[0056] The preparation method of the composite hard carbon negative electrode material a4 involved in this example 4 includes the following steps:

[0057] (1) Preparation of phenolic resin hard carbon:

[0058] Mixing 0.2 g of resorcinol, 0.3 ml of ammonia water, 8 ml of anhydrous ethanol and 48 ml of deionized water uniformly to obtain a mixed solution a1; then adding 0.28 ml of formaldehyde solution to the mixed solution a1, uniformly stirring at 60°C for 24 h to obtain a phenolic resin-based precursor a1; carbonizing the phenolic resin-based precursor a1 at 1600°C for 6 h to obtain the phenolic resin hard carbon prepared in Example 4.

[0059] (2) Preparation of composite hard carbon negative electrode material:

[0060] Step 1: Put 0.6 g of microcrystalline graphite and 0.9 g of phenolic resin hard carbon into 250 ml of deionized water, uniformly stir at 30°C for 7 h to obtain a microcrystalline graphite / phenolic resin hard carbon suspension with a concentration of 6 mg / mL. Add 0.9 g of SnCl4·5H2O to the microcrystalline graphite / phenolic resin hard carbon suspension, uniformly stir for 1 h to obtain a mixed solution A4 prepared in Example 4.

[0061] Step 2: Put the mixed solution A4 into an autoclave and hydrothermally react at 185°C for 7 h. After the reaction is completed, the product is soaked in deionized water for 48 h to remove excess Sn 4+ , to obtain a cylindrical SnO2@MG / PF hydrogel prepared in Example 4.

[0062] Step 3: Place the cylindrical SnO2@MG / PF hydrogel prepared in Example 4 in a vacuum drying oven, evaporate and dry at 110°C for 0.5 h under helium protection, then place the evaporated and dried SnO2@MG / PF hydrogel in a high-temperature furnace, heat to 1200°C at a rate of 5°C / min, and high-temperature treat for 6 h to obtain a composite hard carbon negative electrode material a4 prepared in Example 4.

[0063] (3) Preparation of negative electrode sheet: Mix the composite hard carbon negative electrode material a4, the binder (CMC BH90) and the conductive agent SP at a mass ratio of 8:1:1, coat on the current collector aluminum foil, vacuum dry at 105°C for 10 h, then press form under a pressure of 1 MPa, and then punch to prepare a negative electrode sheet.

[0064] Comparative Example 1

[0065] The difference between Comparative Example 1 and Example 1 is that no microcrystalline graphite is added to the composite hard carbon negative electrode material obtained.

[0066] The preparation method of the composite hard carbon negative electrode material b1 involved in this comparative example 1 includes the following steps:

[0067] (1) Preparation of phenolic resin hard carbon:

[0068] Mixing 0.2 g of resorcinol, 0.3 ml of ammonia water, 8 ml of anhydrous ethanol and 48 ml of deionized water uniformly to obtain a mixed solution a1; then adding 0.28 ml of formaldehyde solution to the mixed solution a1, uniformly stirring at 60°C for 24 h to obtain a phenolic resin-based precursor a1; carbonizing the phenolic resin-based precursor a1 at 1600°C for 6 h to obtain the phenolic resin hard carbon prepared in Example 1.

[0069] (2) Preparation of composite hard carbon negative electrode material:

[0070] Step 1: Put 0.9 g of phenolic resin hard carbon into 150 ml of deionized water, uniformly stir at 25°C for 6 h to obtain a suspension of phenolic resin hard carbon with a concentration of 6 mg / mL. Add 0.9 g of SnCl4·5H2O as a precursor of SnO2 to the phenolic resin hard carbon suspension, uniformly stir for 1 h to obtain a mixed solution B1 prepared in Comparative Example 1.

[0071] Step 2: Put the mixed solution B1 into an autoclave and hydrothermally react at 180°C for 6 h. After the reaction is completed, the product is immersed and washed in deionized water to remove excess Sn 4+ , to obtain SnO2@PF hydrogel prepared in Comparative Example 1.

[0072] Step 3: Put the SnO2@PF hydrogel prepared in Example 1 into a vacuum drying oven, evaporate and dry at 100°C under nitrogen protection for 1.5 h, then put the evaporated and dried SnO2@PF hydrogel into a high-temperature furnace, heat to 1200°C at a rate of 5°C / min, and high-temperature treat for 6 h to obtain the composite hard carbon negative electrode material b1 prepared in Comparative Example 1.

[0073] (3) Preparation of negative electrode sheet: Mix the composite negative electrode material b1, the binder (CMC BH90) and the conductive agent SP at a mass ratio of 8:1:1, coat on the current collector aluminum foil, vacuum dry at 105°C for 10 h, then press form under a pressure of 1 MPa, and then punch to prepare the negative electrode sheet.

[0074] Comparative Example 2

[0075] The difference between Comparative Example 1 and Example 1 is that no phenolic resin hard carbon is added to the composite negative electrode material obtained.

[0076] The preparation method of the composite negative electrode material b2 involved in this comparative example 2 includes the following steps:

[0077] Step 1: 0.6 g of microcrystalline graphite was placed in 100 ml of deionized water and stirred uniformly at 25°C for 6 h to obtain a microcrystalline graphite suspension with a concentration of 6 mg / mL. 0.6 g of tin chloride pentahydrate (SnCl4·5H2O) as a precursor of SnO2 was added to the microcrystalline graphite suspension and stirred uniformly for 1 h to obtain a mixed solution B2 prepared in Comparative Example 2.

[0078] Step 2: The mixed solution B2 was placed in an autoclave and hydrothermally reacted at 180°C for 6 h. After the reaction was completed, the product was immersed and washed in deionized water to remove excess Sn 4+ , to obtain SnO2@MG hydrogel prepared in Comparative Example 2.

[0079] Step 3: The SnO2@MG hydrogel prepared in Comparative Example 2 was placed in a vacuum drying oven and evaporated and dried at 100°C under nitrogen protection for 1.5 h. Subsequently, the evaporated and dried SnO2@MG hydrogel was placed in a high-temperature furnace and heated to 1200°C at a rate of 5°C / min, and high-temperature treated for 6 h to obtain a composite negative electrode material b2 prepared in Comparative Example 2.

[0080] (3) Negative electrode sheet preparation: The composite negative electrode material b2, binder (CMC BH90), and conductive agent SP were mixed and slurried in a mass ratio of 8:1:1 and then coated on a current collector aluminum foil. After vacuum drying at 105°C for 10 h, the product was pressed into shape at a pressure of 1 MPa and then punched into a negative electrode sheet.

[0081] Performance test

[0082] The negative electrode sheets prepared in Examples 1-4 and Comparative Examples 1-2 were used as the negative electrode, the positive electrode was metal sodium, and the electrolyte was 1 mol / L of NaPF6 or NaClO4. After the processes of liquid injection and packaging, sodium ion batteries were prepared. The 0.1C rate first inverse specific capacity test and the first coulombic efficiency test were carried out at 25°C. After 50 cycles at 0.1C rate, the charge specific capacity at 50 cycles was measured. The specific results are shown in Table 1 below.

[0083] Table 1

[0084]

[0085] As can be seen from Table 1, the sodium ion batteries prepared in Examples 1-4 still have a specific capacity of about 200 mAh / g after 50 cycles, and the capacity attenuation rate is less than 12%. In addition, the first coulombic efficiency and the rate performance are significantly improved compared with Comparative Examples 1-2. It can be seen that the sodium ion batteries prepared in Examples 1-4 all have high specific capacity, high first efficiency, high rate, and long cycle stability.

[0086] It can be seen that through the synergistic effect among microcrystalline graphite, phenolic resin hard carbon and SnO2, the respective advantages of the three are fully utilized, and the composite hard carbon material with a unique carbon-non-carbon hybrid structure is constructed. After SnO2, as a semiconductor material, is compounded with the microcrystalline graphite / phenolic resin hard carbon material, it can form a close interface contact with the carbon material, and form a carbon-non-carbon hybrid nanoscale dispersed phase and a porous network structure on the surface of the material, thereby providing a larger specific surface area for the composite hard carbon negative electrode material and promoting the transmission of sodium ions during the charging and discharging process. In addition, SnO2 is doped in the porous composite hard carbon negative electrode material, further improving the specific capacity and conductivity of the negative electrode material. The prepared composite hard carbon negative electrode material has the advantages of traditional hard carbon materials, and the thermal conductivity, specific capacity, cycle stability and rate performance are also significantly improved.

[0087] Meanwhile, the contents not described in detail in the specification all belong to the prior art known to those skilled in the art.

[0088] It should be noted that in this paper, relationship terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between the entities or operations. Moreover, the term "include", "contain" or any other variant thereof is intended to cover non-exclusive inclusion, so that the process, method, article or equipment including a series of elements not only includes those elements, but also includes other elements not explicitly listed or inherent to such process, method, article or equipment.

[0089] Although the embodiments of the present application have been shown and described, it can be understood by those skilled in the art that various changes, modifications, replacements and variations can be made to the embodiments without departing from the principles and spirits of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a composite hard carbon negative electrode material, characterized in that: The following steps are involved: S1: Add SnCl4·5H2O to the suspension of microcrystalline graphite / phenolic resin hard carbon and stir evenly for 1 h to obtain a mixed solution A; S2: placing the mixed solution A in an autoclave for hydrothermal reaction, and then soaking and washing in deionized water to obtain SnO2@MG / PF hydrogel; S3 evaporates and dries the SnO2@MG / PF hydrogel under the protection of inert gas, and then places it in a high-temperature furnace for high-temperature treatment to obtain a composite hard carbon negative electrode material.

2. The preparation method according to claim 1, characterized in that The preparation method of the phenolic resin hard carbon described in step S1 is: 0.2g of resorcinol, 0.3ml of ammonia water, 8ml of anhydrous ethanol and 48ml of deionized water are mixed uniformly to obtain a mixed solution a; then 0.28ml of formaldehyde solution is added to the mixed solution a, and the mixture is stirred uniformly at 60°C for 24h to obtain a phenolic resin-based precursor; the phenolic resin-based precursor is carbonized at a high temperature of 1600°C for 6h to obtain a phenolic resin hard carbon.

3. The preparation method according to claim 1, characterized in that The preparation method of the microcrystalline graphite / phenolic resin hard carbon suspension in step S1 is: placing microcrystalline graphite and phenolic resin hard carbon in deionized water in sequence, and stirring uniformly at 25-45° C. for 6-8 hours to obtain a microcrystalline graphite / phenolic resin hard carbon suspension.

4. The preparation method according to claim 1, characterized in that The concentration of the suspension of microcrystalline graphite / phenolic resin hard carbon in step S1 is 6 mg / mL; the size of the microcrystalline graphite is 200 mesh.

5. The preparation method according to claim 1, characterized in that In step S1, the mass ratio of SnCl4·5H2O, microcrystalline graphite and phenolic resin hard carbon is 3:2:

3.

6. The preparation method according to claim 1, characterized in that The reaction temperature of the hydrothermal reaction in step S2 is 180-200° C., and the reaction time is 6-10 hours.

7. The preparation method according to claim 1, characterized in that The treatment temperature of the evaporation drying treatment in step S3 is 80-120° C., and the treatment time is 0.5-2 h; the treatment temperature of the high temperature treatment is 1000-1200° C., the heating rate is 1-5° C. / min, and the treatment time is 6 h.

8. The preparation method according to claim 1, characterized in that The inert gas in step S3 is any one of nitrogen, argon and helium.

9. A composite hard carbon negative electrode material prepared by the preparation method according to any one of claims 1 to 8.

10. A sodium ion battery, comprising a positive electrode, a negative electrode, an electrolyte and a separator, characterized in that: The negative electrode material used in the negative electrode is the composite hard carbon negative electrode material according to claim 9.

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