Preparation method of high-dispersed tin-hard carbon composite negative electrode material for sodium ion battery

Abstract

The application discloses a preparation method of a high-dispersion tin-hard carbon composite negative material for a sodium ion battery, and comprises the following steps: S1, hard carbon material pretreatment: taking porous hard carbon as raw material, adding a dopamine hydrochloride solution for pretreatment, and filtering to obtain pretreated hard carbon; S2, in-situ polymerization on the surface of the hard carbon: adding the pretreated hard carbon into a sodium hydroxide solution, and filtering to obtain hydrophilic hard carbon; S3, preparation of composite particles: adding the hydrophilic hard carbon into a SnCl2 or SnCl4 solution for sand milling and spray drying to obtain SnCl2-hard carbon or SnCl4-hard carbon composite particles; and S4, deposition of the tin-hard carbon composite material: adding the composite particles into a sodium borohydride hydrogen evolution reaction inhibition solution under an ice water bath condition, obtaining a Sn-hard carbon composite suspension, and filtering to obtain the tin-hard carbon composite material. The application has the characteristics of uniform deposition dispersion, good particle size and morphology adjustability, and strong process controllability.

Description

TECHNICAL FIELD

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

[0002] Lithium ion batteries have always been the main choice in the energy storage field due to their high energy density and relatively good cycle stability. However, because of the limited and uneven distribution of lithium resources, the large-scale application and cost of lithium ion batteries are limited. Sodium ion batteries gradually enter the field of vision due to their similar physical and chemical properties to lithium ion batteries. Sodium is abundant in the earth's crust, widely distributed, and low in cost, which makes sodium ion batteries have a significant advantage in resource sustainability.

[0003] Although sodium ion batteries have great potential in theory, they still face many challenges in practical application. At present, the research on the positive electrode materials of sodium ion batteries has made significant progress, and various materials with good electrochemical properties have been developed. However, the research on the negative electrode materials of sodium ion batteries is relatively lagging behind. The performance of the negative electrode material directly affects the capacity, cycle stability and charging efficiency of the battery. The ideal negative electrode material should have low charging and discharging platform, high specific capacity and good cycle stability. At present, although hard carbon has been commercialized, it still has some problems, such as low capacity (generally less than 350 mAh / g), low initial coulomb efficiency, poor rate performance, etc.

[0004] Alloy-based negative electrodes have high theoretical specific capacity. Among them, tin has high comprehensive advantages due to its low working voltage and high specific capacity (847 mAh / g), but its excessive volume expansion and poor material cycle performance hinder the in-depth study of tin negative electrodes.

[0005] The hard carbon material is combined with the high-capacity tin negative electrode material to comprehensively utilize the advantages of the hard carbon and tin, wherein the carbon material acts as a buffer substrate, can prevent particle aggregation, reduce volume expansion, and construct a conductive network, thereby significantly improving the electrochemical performance of the composite material. However, the traditional composite technology, such as the tin-hard carbon composite material prepared by using a mechanical ball milling method, often has difficulty in achieving uniform distribution of high specific capacity tin particles in the hard carbon matrix, not to mention achieving uniform distribution of tin particles in the interlayer and pores of the hard carbon. In addition, direct exposure of the alloy material to the electrolyte also easily causes re-agglomeration of the material, thereby causing the battery performance to decrease. The currently reported literature uses sodium borohydride to reduce stannous chloride in an aqueous solution, but because sodium borohydride reacts with water to produce hydrogen, even if the alkalinity of the aqueous solution is increased, it cannot completely eliminate this, which is obviously not conducive to industrial production. First, the generated hydrogen gas increases the risk of fire or even explosion, which obviously violates the principle of safe production; in addition, industrial equipment is often made of steel, and the generation of hydrogen causes hydrogen embrittlement of the steel, resulting in a decrease in the mechanical strength of the equipment, accelerating the aging of the instrument, and increasing the production cost. The method of the present application uses a co-solution of water and ethanol as the reaction system, which can inhibit the generation of hydrogen, which is very beneficial to the safety and sustainability of production. In terms of the morphology of the product, the reaction system in the literature causes tin to be generated only on the surface of the graphite due to the non-wetting of graphite and water, and it is difficult to reach the interlayer of the graphite. The present application modifies the surface of the hard carbon, utilizes the self-polymerization and adsorption properties of hydrochloric acid dopamine, realizes in-situ polymerization on the surface of the hard carbon, improves the wettability of the hard carbon, and enables the tin salt solution to penetrate into the interlayer or pores of the hard carbon. After subsequent drying, the tin salt is "locked" on the surface, interlayer and pores of the hard carbon. During the subsequent reduction reaction of tin ions, nano-tin is generated on the surface, interlayer and pores of the hard carbon, and a uniformly dispersed tin-hard carbon composite material is obtained.

[0006] The liquid phase reaction can achieve uniform distribution of the product due to the uniformity of the solution, and the surface morphology, particle size distribution and crystal form of the product can be controlled by controlling the reaction conditions. Through the chemical reduction reaction in the liquid phase, tin can be deposited in the interlayer, pores and surface of the hard carbon. In the process of preparing tin, it is crucial to select an appropriate reducing agent due to the high reduction potential of tin. Different reducing agents can reduce different valence state tin ions, and can realize synthesis at normal temperature and pressure, reducing energy consumption. The traditional synthesis method of nano-tin is often very complex and is accompanied by agglomeration of nano-tin. In the synthesis process of the tin-hard carbon composite negative electrode, the hard carbon is not wetted in the aqueous solvent, which causes the reaction to generate tin only at the interface between the hard carbon and the solvent, and the agglomeration is more serious, which cannot achieve high dispersion of the composite material. SUMMARY

[0007] The application aims to provide a preparation method of a high-dispersion tin-hard carbon composite negative electrode material for sodium ion batteries, which has the characteristics of uniform deposition, good particle size and morphology adjustability, and strong process controllability.

[0008] The application can be implemented by the following technical solutions:

[0009] The application discloses a preparation method of a high-dispersion tin-hard carbon composite negative electrode material for sodium ion batteries, comprising the following steps:

[0010] S1, hard carbon material pretreatment: taking porous hard carbon as raw material, adding a dopamine hydrochloride solution for pretreatment, filtering after fully mixing, and obtaining pretreated hard carbon;

[0011] S2, in-situ polymerization on the surface of hard carbon: adding the pretreated hard carbon into a sodium hydroxide solution to realize in-situ polymerization of the dopamine hydrochloride on the surface of the pretreated hard carbon, stirring to make the polymerization layer completely cover the surface of the hard carbon, and then filtering to obtain hydrophilic hard carbon;

[0012] S3, preparation of composite particles: adding the hydrophilic hard carbon into a SnCl2 or SnCl4 solution for sand milling to make Sn 2+ or Sn 4+ fully penetrate into the interlayer or open pores of the hard carbon, continuously stirring to obtain a suspension dispersion liquid, and then spray drying the dispersion liquid to obtain SnCl2-hard carbon or SnCl4-hard carbon composite particles, which can lock the tin element on the outer surface and internal pores of the hard carbon, and is more conducive to improving the deposition efficiency and uniform distribution of the expensive tin element on the outer surface and internal pores of the hard carbon in the subsequent steps;

[0013] S4, deposition of tin-hard carbon composite material: under the condition of ice water bath, the composite particles are added into a sodium borohydride hydrogen evolution reaction inhibition solution under stirring, Sn generated by the reaction is uniformly deposited on the outer surface and internal pores of the hard carbon, a Sn-hard carbon composite suspension liquid is obtained, after filtration, the residual solvent and tin salt are removed by repeatedly washing and filtering with deionized water, and finally, the tin-hard carbon composite material is obtained by drying at 60-100 DEG C.

[0014] Step S4 ensures the uniform distribution of tin on the inner and outer surfaces of the hard carbon, and maximizes the complete reaction of the tin salt to improve the yield, and the tin-hard carbon composite material is obtained after the reaction is completed. The reaction greatly inhibits and slows down the hydrogen evolution side reaction of the active protons on the water molecules due to the ice water low temperature condition and the ethanol dilution aqueous solvent, avoids the powder and liquid spraying caused by the violent hydrogen evolution side reaction, and improves the utilization efficiency of sodium borohydride as a reducing agent, and the specific equation is:

[0015] 4Sn 2+ +BH4 - +8OH - →4Sn+MO2- + 6H 2 O

[0016] or 2Sn 4+ + BH 4 - + 8OH - → 2Sn + MO 2 - + 6H 2 O

[0017] In the present application, by surface modification of hard carbon, the wettability of hard carbon in solvent is enhanced, so that the reaction can be carried out in the interlayer of hard carbon or even in the open pores, realizing the deep dispersion of tin and forming tin-hard carbon composite negative electrode with excellent electrochemical performance.

[0018] Specifically, in the present application, by modifying the surface of hard carbon, using the self-polymerization and adsorption properties of dopamine hydrochloride under alkaline conditions, a polydopamine hydrochloride film with high adhesion and adsorption is generated on the surface of hard carbon, realizing uniform and dense in-situ polymerization and improving the wettability of hard carbon. During the process of coating hard carbon with dopamine hydrochloride, the benzene ring structure and phenolic group in dopamine hydrochloride molecule are first adsorbed on the surface of the charged functional groups on the surface of hard carbon through electrostatic interaction. Then, under alkaline conditions, dopamine hydrochloride undergoes redox reaction to form a polydopamine hydrochloride film, which is coated on the surface of hard carbon. Polydopamine hydrochloride is a material with high hydrophilicity, which is mainly due to the rich functional groups such as catechol and amino groups in its molecular structure. These functional groups enable polydopamine hydrochloride to form hydrogen bonds with water molecules, thus exhibiting strong hydrophilicity, allowing tin salt solution to penetrate into the interlayer or interlayer of hard carbon. During subsequent spray drying, tin salt can be "locked" on the surface, interlayer and interlayer of hard carbon. The reducing agent reduces tin ions to tin nanoparticles, and the morphology and size of the generated tin nanoparticles are controlled by adjusting the reaction conditions, resulting in a highly dispersed tin-hard carbon composite material. The obtained composite negative electrode realizes high specific capacity due to the presence of tin, while carbon provides a buffer space for sodium intercalation into tin, improving the conductivity of tin, thus obtaining a high-performance tin-hard carbon composite negative electrode.

[0019] Further, the preparation method of the sodium borohydride hydrogen evolution reaction inhibition solution is as follows: under ice water bath conditions, an aqueous-ethanol solution of sodium hydroxide is prepared, sodium borohydride is added to the above solution, and the mass fraction of sodium borohydride in the solution is controlled to be 0.1-1%, and the uniform sodium borohydride hydrogen evolution reaction inhibition solution is obtained by stirring.

[0020] Further, in step S1, the concentration of the dopamine hydrochloride solution is 1-5 mg / mL, and a polydopamine hydrophilic layer is formed on the hard carbon surface; specifically, an increase in monomer concentration generally increases the polymerization growth rate and conversion rate, thereby increasing the molecular weight. This is because the higher the monomer concentration, the more monomer molecules are available for reaction, thereby increasing the likelihood of polymerization. When the monomer concentration is insufficient, it is insufficient to completely cover the hard carbon surface, and when the monomer concentration is too high, the thickness of the polymerization layer is increased, thereby possibly occupying the internal space of Sn deposition.

[0021] Further, in step S2, the concentration of the sodium hydroxide solution is 0.05-0.5 mol / L. Specifically, the concentration of sodium hydroxide affects the reaction rate of dopamine polymerization. Within a certain concentration range, as the concentration of sodium hydroxide increases, the polymerization reaction rate may increase, and excessive polymerization may result in an excessively thick polymerization layer, thereby possibly occupying the internal space of Sn deposition.

[0022] Further, in step 3, the mass ratio of hard carbon to tin is 0.01-0.3, and the concentration of tin salt is 0.01-1 mol / L; specifically, the concentration of tin salt affects the subsequent processability. A lower tin salt concentration reduces the spray drying efficiency, resulting in higher energy consumption, and a higher concentration may result in less liquid in the system, blocking the nozzle device of the spray drying equipment.

[0023] Further, in step S3, the sanding time is 30-60 min, and the rotation speed is 1000-1500 r / min, to enable tin ions to fully penetrate into the interlayer or open pores of the hard carbon. Specifically, too low a rotation speed will slow down the slurry flow and easily block the pipe opening.

[0024] Further, in the sodium borohydride hydrogen evolution reaction inhibition solution, the molar ratio of sodium borohydride to tin salt is 1-3, to ensure that the tin salt is completely reduced and fully precipitated; the volume ratio of water to ethanol is 0.2-0.5; specifically, the hydroxyl group in the water molecule is more active than the hydroxyl group in the ethanol molecule, and water molecules form a large number of hydrogen bonds. This large range of hydrogen bonds has a certain effect of dispersing the negative charge on the oxygen atom, which is manifested as the polarity of water molecules being significantly stronger than that of ethanol. Therefore, the reaction between sodium borohydride and water is more intense, while the reaction between sodium borohydride and ethanol is relatively stable, and thus the addition of ethanol can inhibit hydrogen production.

[0025] Further, in step S3, the spray drying conditions are as follows: the inlet air temperature during spray drying is 100-200°C, to ensure an effective drying process; and the outlet air temperature is 50-90°C.

[0026] Further, in step S1, the mixing method is one or more than two of stirring, ultrasonic, ball milling, and oscillation.

[0027] Further, in steps S1 and S2, the filtering method is one or more of centrifugation, suction filtration, and filtration.

[0028] The tin-hard carbon composite material obtained by the present application has different effects compared to traditional methods, but overall has good electrochemical performance. The reason for achieving better results is that:

[0029] (1) The proportion of the obtained tin-hard carbon composite material is different, and the composite material with a higher carbon proportion has better conductivity and provides a larger buffer space for tin expansion, and has better cycle stability.

[0030] (2) The concentration of tin salt affects the distribution and dispersity of tin in the carbon material. Lower tin salt concentration may lead to uneven distribution of tin, while higher concentration may lead to excessive aggregation of tin. Poor dispersity of tin will affect the electrochemical performance of the composite, such as capacity and cycle stability.

[0031] (3) The effect of sodium borohydride varies with the amount used, and the amount of sodium borohydride has an important effect on the reduction efficiency of tin and the morphology of the composite. An appropriate amount of sodium borohydride can ensure the complete reduction of tin ions, but excessive amount may cause side reactions or lead to excessive deposition of tin, affecting the morphology and structure of the material.

[0032] The present application discloses a preparation method of a high-dispersion sodium-ion battery tin-hard carbon composite negative electrode material, which has the following beneficial effects:

[0033] First, the deposition is uniform. Since hard carbon has a porous and interlayer structure, Sn cannot usually be deposited inside the voids in traditional liquid-phase synthesis methods, which is a bottleneck for Sn deposition on hard carbon. In the present application, the hard carbon is surface-modified before the reaction. The self-polymerization and adsorption properties of hydrochloric acid dopamine under alkaline conditions are used to generate a poly-dopamine hydrochloride film with high adhesion and adsorption on the surface of the hard carbon, achieving uniform in-situ polymerization and improving the wettability of the hard carbon. The poly-dopamine hydrochloride film does not need to be dense, and a thin layer is sufficient, even thinner is better, mainly to uniformly improve the hydrophilicity of the outer surface of the hard carbon and the inner surface of the pore. During the process of coating the hard carbon with hydrochloric acid dopamine, the benzene ring structure and phenolic group in the hydrochloric acid dopamine molecule are first adsorbed on the charged functional groups on the surface of the hard carbon through electrostatic interaction. Then, under alkaline conditions, the hydrochloric acid dopamine undergoes a polymerization reaction to form a poly-dopamine hydrochloride film, which coats the surface of the hard carbon. Poly-dopamine hydrochloride is a material with high hydrophilicity, which is mainly due to the rich functional groups such as catechol and amino groups in its molecular structure. These functional groups enable poly-dopamine hydrochloride to form hydrogen bonds with water molecules, thereby exhibiting strong hydrophilicity, allowing the tin salt solution to penetrate into the interlayer or interlayer of the hard carbon. During subsequent spray drying, the tin salt can be "locked" on the surface, interlayer and interlayer of the hard carbon. The subsequent reducing agent reduces the tin ions in-situ to tin nanoparticles, obtaining a tin-hard carbon composite negative electrode material that can be deposited in the interlayer and open pores of the hard carbon.

[0034] Second, the particle size and morphology are good, and the concentration of the reactant is controlled to adjust. The concentration of sodium borohydride can control the nucleation and growth rate of tin particles in the liquid phase. When the concentration of sodium borohydride is low, the reduction rate of tin ions is slow, resulting in the formation of a small amount of crystal nucleus, and then forming larger particles in the diffusion growth stage. At this time, due to the slow reaction rate, new small crystal nuclei will continue to be generated in the solution, and the particles obtained by spray drying are hard carbon composites with tin ions enriched on the inner and outer surfaces, so these crystal nuclei have enough time and sufficient tin ion supply to grow, resulting in a larger particle size of the obtained powder. On the contrary, when the concentration of sodium borohydride is high, more tin ions participate in nucleation in a short time, resulting in the formation of a large number of crystal nuclei instantaneously, consuming the tin ions in the solution, thereby limiting the further growth of nanoparticles, and reducing the average particle size of tin. In addition, too high a temperature will change the composition of the reaction system solution, resulting in defects in the Sn deposition layer, reducing the adhesion of the Sn deposition layer, and easily falling off from the carbon matrix during repeated charging and discharging; at the same time, high temperature is also easy to cause Sn metal grain growth too large, making the Sn deposition layer become fragile and easy to break; therefore, the impedance increases and the performance deteriorates. Too low a temperature will slow down the reaction rate, making the Sn deposition layer grow slowly, or even stop, resulting in poor surface quality. In addition, low temperature will also cause the adhesion of the coating to be insufficient, and the peeling phenomenon is easy to occur. Therefore, it is necessary to control the temperature in the appropriate range to obtain an ideal Sn deposition layer. The obtained composite negative electrode realizes high specific capacity due to the presence of tin, and the carbon provides a buffer space for sodium intercalation of tin, and improves the conductivity of tin, so that a high-performance tin-hard carbon composite negative electrode is obtained.

[0035] Third, the process operation is controllable. Compared with the reported method, sodium borohydride is used to reduce stannous chloride in aqueous solution. Because sodium borohydride and water will hydrolyze to produce hydrogen, this reaction cannot be completely inhibited even by increasing the alkalinity of the aqueous solution, which is obviously not conducive to industrial production. First, the hydrogen produced by the reaction will increase the risk of fire or even explosion, which has a major safety hazard. In addition, industrial equipment is often made of metal, and the presence of hydrogen will cause hydrogen embrittlement of the metal material, resulting in a decrease in the mechanical strength of the equipment, accelerating the aging of the instrument, and causing the container or pipeline to be damaged. In the present application, water and ethanol are used as co-solvents. The hydroxyl group in the water molecule is more active than the hydroxyl group in the ethanol molecule. Water molecules form a large number of hydrogen bonds. This wide range of hydrogen bonds has the effect of dispersing the negative charge on the oxygen atom, which is manifested as the polarity of the water molecule being significantly stronger than that of ethanol. Therefore, the reaction of sodium borohydride with water is more intense, while the reaction with ethanol is relatively stable, so the addition of ethanol can inhibit hydrogen production. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 XRD pattern of Example 1;

[0037] Figure 2The charge-discharge curves for Example 2 are obtained under a current density of 100 mA / g.

[0038] Figure 3 Example 3 shows the CV test curves performed at a scan rate of 0.05 mV / s and a voltage range of 0.01-1.5 V.

[0039] Figure 4 The cycling performance curve of Example 4 at a current density of 1000 mA / g;

[0040] Figure 5 The charge-discharge curves for the first three weeks of charging and discharging at a current density of 100 mA / g are for Example 5.

[0041] Figure 6 Example 6 shows the rate charge-discharge curves at current densities of 0.1C, 0.5C, 1C, 2C, 5C, and 10C (1C = 847 mA / g). Detailed Implementation

[0042] To enable those skilled in the art to better understand the technical solution of the present invention, the product of the present invention will be further described in detail below with reference to embodiments.

[0043] This invention discloses a method for preparing a highly dispersed tin-hard carbon composite anode material for sodium-ion batteries, comprising the following steps:

[0044] S1. Hard carbon material pretreatment: Porous hard carbon is used as raw material. Dopamine hydrochloride solution is added for pretreatment. After thorough mixing, the mixture is filtered out to obtain pretreated hard carbon.

[0045] S2. In-situ polymerization on hard carbon surface: Pretreated hard carbon is added to sodium hydroxide solution to achieve in-situ polymerization of dopamine hydrochloride on the surface of pretreated hard carbon. Stirring makes the polymer layer completely cover the surface of hard carbon, and then filtering out to obtain hydrophilic hard carbon.

[0046] S3. Preparation of composite particles: Hydrophilic hard carbon is added to SnCl2 or SnCl4 solution and milled to make Sn... 2+ or Sn 4+ The particles are fully penetrated into the interlayer or open pores of hard carbon, and a suspension is obtained by continuous stirring. The dispersion is then spray-dried to obtain SnCl2-hard carbon or SnCl4-hard carbon composite particles.

[0047] S4. Deposition of tin-hard carbon composite material: Under ice-water bath conditions and stirring, the composite particles are added to a sodium borohydride hydrogen evolution reaction inhibition solution. The Sn produced by the reaction is uniformly deposited on the outer surface and internal pores of the hard carbon to obtain a Sn-hard carbon composite suspension. After filtration, the tin-hard carbon composite material is obtained.

[0048] Further, the preparation method of the sodium borohydride hydrogen evolution reaction inhibition solution is as follows: under the condition of ice water bath, a sodium hydroxide water-ethanol solution is configured, sodium borohydride is added into the above solution, the mass fraction of sodium borohydride in the solution is controlled to be 0.1-1%, and the sodium borohydride hydrogen evolution reaction inhibition solution is obtained by stirring.

[0049] Further, in step S1, the concentration of the dopamine hydrochloride solution is 1-5 mg / mL.

[0050] Further, in step S2, the concentration of the sodium hydroxide solution is 0.05-0.5 mol / L.

[0051] Further, in step 3, the mass ratio of the hard carbon to the tin element is 0.01-0.3; and the concentration of the tin salt is 0.01-1 mol / L.

[0052] Further, in step S3, the sand milling time is 30-60 min, and the rotating speed is 1000-1500 r / min.

[0053] Further, in the sodium borohydride hydrogen evolution reaction inhibition solution, the molar ratio of sodium borohydride to the tin salt is 1-3, and the volume ratio of water to ethanol is 0.2-0.5.

[0054] Further, in step S3, the spray drying conditions are as follows: the inlet air temperature is 100-200 ℃, and the outlet air temperature is 50-90 ℃.

[0055] Further, in step S1, the mixing mode is one or two or more of stirring, ultrasonic, ball milling and oscillation.

[0056] Further, in steps S1 and S2, the filtering mode is one or two or more of centrifugation, suction filtration and filtration.

[0057] Embodiment 1

[0058] Step 1: 0.1319 g of porous hard carbon material is selected, 10 mL of dopamine hydrochloride solution with a concentration of 2 mg / mL is added, ultrasonic mixing is performed for 30 min, and then the pretreated hard carbon A is obtained by centrifugation.

[0059] Step 2: the pretreated hard carbon A is added into 0.1 mol / L sodium hydroxide solution, stirring is performed for 2 h, in-situ polymerization of dopamine hydrochloride on the surface of the pretreated hard carbon is realized, the polymerization layer is completely covered on the surface of the hard carbon by sufficient stirring, and then the hydrophilic hard carbon B is obtained by suction filtration.

[0060] Step 3: 100 mL of 0.1M SnCl2 solution is prepared, the hydrophilic hard carbon B is added and sand milling (1200 r / min, 45 min) is performed to make Sn 2+The suspension dispersion liquid C is obtained by fully infiltrating the interlayer or open pores of the hard carbon and continuously stirring. Then, the dispersion liquid is spray dried at an air inlet temperature of 150°C to obtain SnCl2-hard carbon composite particles D.

[0061] Step 4, under the condition of continuously ice water bath, 3.6g sodium hydroxide is dissolved in 91.2g water-ethanol (volume ratio 1:3) to form a uniform solution E, 4.8g sodium borohydride is added to the solution E, and stirring is performed to obtain a uniform solution F, which can inhibit the hydrogen evolution reaction of sodium borohydride in water.

[0062] Step 5, under the condition of ice water bath, the composite particles D are slowly added to the solution F while continuously stirring, a uniform deposition reaction of Sn in the outer surface and internal pores of the hard carbon is generated, and a Sn-hard carbon composite suspension is obtained. After filtration, the filter is repeatedly washed with deionized water to remove residual solvents and tin salts, and finally dried at 80°C to obtain a tin-hard carbon composite material G.

[0063] Example 2:

[0064] Step 1, 0.4451 g of porous hard carbon material is selected, 30 mL of 5 mg / mL dopamine hydrochloride solution is added, ball milling is performed for 2 hours, and then filtration is performed to obtain pretreated hard carbon A.

[0065] Step 2, the pretreated hard carbon A is added to a 0.2 mol / L sodium hydroxide solution, stirring is performed for 1 hour, in-situ polymerization of dopamine hydrochloride on the surface of the pretreated hard carbon is achieved, the polymerization layer is fully covered on the surface of the hard carbon by fully stirring, and then centrifugation is performed to filter out the hydrophilic hard carbon B.

[0066] Step 3, 20 mL of 0.5M SnCl4 solution is prepared, the hydrophilic hard carbon B is added and sand milling (1500r / min, 30 minutes) is performed to make Sn 4+ The suspension dispersion liquid C is obtained by fully infiltrating the interlayer or open pores of the hard carbon and continuously stirring. Then, the dispersion liquid is spray dried at an air inlet temperature of 150°C to obtain SnCl2-hard carbon composite particles D.

[0067] Step 4, under the condition of continuously ice water bath, 3.6g sodium hydroxide is dissolved in 91.2g water-ethanol (volume ratio 1:3) to form a uniform solution E, 4.8g sodium borohydride is added to the solution E, and stirring is performed to obtain a uniform solution F, which can inhibit the hydrogen evolution reaction of sodium borohydride in water.

[0068] Step 5, under ice water bath condition, slowly add the composite particles D into solution F with continuous stirring, to generate uniform deposition reaction of Sn in the outer surface and internal pores of hard carbon, to obtain Sn-hard carbon composite suspension, after filtration, repeatedly wash the filter with deionized water to remove residual solvent and tin salt, finally dry at 100°C to obtain tin-hard carbon composite material G.

[0069] Case 3:

[0070] Step 1, select 29.68 mg of porous hard carbon material, add 3 mL of dopamine hydrochloride solution with a concentration of 3 mg / mL, shake and mix for 2 hours, then filter out by suction filtration to obtain pretreated hard carbon A.

[0071] Step 2, add pretreated hard carbon A to 0.05 mol / L sodium hydroxide solution, stir for 3 hours to achieve in-situ polymerization of dopamine hydrochloride on the surface of pretreated hard carbon, fully stir to make the polymerization layer completely cover the surface of hard carbon, then filter out by filtration to obtain hydrophilic hard carbon B.

[0072] Step 3, prepare 75 mL of 0.2M SnCl4 solution, add hydrophilic hard carbon B and sand mill (1400 r / min, 45 minutes) to make Sn 4+ fully penetrate into the interlayer or open pores of hard carbon, continuously stir to obtain suspension dispersion C. Then spray dry the dispersion at an inlet air temperature of 150°C to obtain SnCl4-hard carbon composite particles D.

[0073] Step 4, under continuous ice water bath condition, dissolve 0.7 mg of sodium hydroxide in 14.1 g of water-ethanol (volume ratio 1:2) to form a uniform solution E, add 0.114 g of sodium borohydride to solution E, stir to obtain a uniform solution F, which can inhibit the hydrogen evolution reaction of sodium borohydride in water.

[0074] Step 5, under ice water bath condition, slowly add the composite particles D into solution F with continuous stirring, to generate uniform deposition reaction of Sn in the outer surface and internal pores of hard carbon, to obtain Sn-hard carbon composite suspension, after filtration, repeatedly wash the filter with deionized water to remove residual solvent and tin salt, finally dry at 100°C to obtain tin-hard carbon composite material G.

[0075] Case 4

[0076] Step 1, select 101.74 mg of porous hard carbon material, add 0.8 mL of dopamine hydrochloride solution with a concentration of 2.5 mg / mL, ultrasonic mix for 45 min, then filter out by centrifugation to obtain pretreated hard carbon A.

[0077] Step 2, the pretreated hard carbon A is added into 0.3 mol / L sodium hydroxide solution, stirred for 1.5 hours to realize in-situ polymerization of dopamine hydrochloride on the surface of the pretreated hard carbon, and fully stirred to make the polymerization layer completely cover the surface of the hard carbon. Then, the hard carbon is filtered out by suction filtration to obtain hydrophilic hard carbon B.

[0078] Step 3, 67 mL of 0.3 M SnCl2 solution is prepared, and the hydrophilic hard carbon B is added and sand-milled (1300 r / min, 45 minutes) to make Sn 2+ fully infiltrate the interlayer or open pores of the hard carbon, and continuous stirring obtains a suspension dispersion C. Then, the dispersion is spray-dried at an air inlet temperature of 160°C to obtain SnCl2-hard carbon composite particles D.

[0079] Step 4, 0.113 g of sodium hydroxide is dissolved in 18.8 g of water-ethanol (volume ratio 1:3.5) to form a uniform solution E, and 0.19 g of sodium borohydride is added to the solution E to obtain a uniform solution F. The solution F system can inhibit the hydrogen evolution reaction of sodium borohydride in water.

[0080] Step 5, under the condition of ice water bath, the composite particles D are slowly added to the solution F while continuously stirring, to generate a uniform deposition reaction of Sn in the outer surface and internal pores of the hard carbon, to obtain a Sn-hard carbon composite suspension. After filtration, the filter is repeatedly washed with deionized water to remove residual solvents and tin salts, and finally dried at 70°C to obtain a tin-hard carbon composite material G.

[0081] Example 5:

[0082] Step 1, 7.418 g of porous hard carbon material is selected, and 1000 mL of dopamine hydrochloride solution with a concentration of 4 mg / mL is added, and the mixture is ultrasonic ball-milled for 3 hours. Then, the pretreated hard carbon A is filtered out by filtration.

[0083] Step 2, the pretreated hard carbon A is added into 0.25 mol / L sodium hydroxide solution, stirred for 2.5 hours to realize in-situ polymerization of dopamine hydrochloride on the surface of the pretreated hard carbon, and fully stirred to make the polymerization layer completely cover the surface of the hard carbon. Then, the hard carbon is filtered out by suction filtration to obtain hydrophilic hard carbon B.

[0084] Step 3, 25 mL of 0.4 M SnCl4 solution is prepared, and the hydrophilic hard carbon B is added and sand-milled (1500 r / min, 60 minutes) to make Sn 4+ fully infiltrate the interlayer or open pores of the hard carbon, and continuous stirring obtains a suspension dispersion C. Then, the dispersion is spray-dried at an air inlet temperature of 190°C to obtain SnCl4-hard carbon composite particles D.

[0085] Step 4, under the condition of continuous ice-water bath, 0.273g sodium hydroxide was dissolved in 34.2g water-ethanol (volume ratio 1:3.5) to form a uniform solution E, 3.8g sodium borohydride was added into solution E, and a uniform solution F was obtained by stirring. The solution F system can inhibit the hydrogen evolution reaction of sodium borohydride in water.

[0086] Step 5, under the condition of ice-water bath, composite particles D were slowly added into solution F under continuous stirring, a uniform deposition reaction of Sn in the outer surface and internal pores of hard carbon was generated, and a Sn-hard carbon composite suspension was obtained. After filtration, the filter was repeatedly washed with deionized water to remove residual solvents and tin salts, and finally dried at 90°C to obtain tin-hard carbon composite material G.

[0087] Example 6

[0088] Step 1, 0.8903g porous hard carbon material was selected and added into 50mL dopamine hydrochloride solution with a concentration of 1.5 mg / mL, and then ultrasonic oscillation mixing was carried out for 1 hour, followed by filtration to obtain pretreated hard carbon A.

[0089] Step 2, the pretreated hard carbon A was added into 0.1 mol / L sodium hydroxide solution and stirred for 2 hours to realize in-situ polymerization of dopamine hydrochloride on the surface of pretreated hard carbon. After sufficient stirring, the polymerization layer completely covered the surface of hard carbon, and then the filter was obtained by filtration to obtain hydrophilic hard carbon B.

[0090] Step 3, 200mL of 0.05M SnCl2 solution was prepared, and hydrophilic hard carbon B was added and sand ground (1000r / min, 30 minutes) to make Sn 2+ fully penetrate into the interlayer or open pores of hard carbon, and a suspension dispersion C was obtained by continuous stirring. Then the dispersion was spray dried at an inlet air temperature of 150°C to obtain SnCl2-hard carbon composite particles D.

[0091] Step 4, under the condition of continuous ice-water bath, 3.96g sodium hydroxide was dissolved in 1238g water-ethanol (volume ratio 1:2.5) to form a uniform solution E, 3.8g sodium borohydride was added into solution E, and a uniform solution F was obtained by stirring. The solution F system can inhibit the hydrogen evolution reaction of sodium borohydride in water.

[0092] Step 5, under the condition of ice-water bath, composite particles D were slowly added into solution F under continuous stirring, a uniform deposition reaction of Sn in the outer surface and internal pores of hard carbon was generated, and a Sn-hard carbon composite suspension was obtained. After filtration, the filter was repeatedly washed with deionized water to remove residual solvents and tin salts, and finally dried at 60°C to obtain tin-hard carbon composite material G.

[0093] To effectively evaluate the technical effects of the present application, the tin-carbon composite, carboxymethyl cellulose CMC and conductive carbon black Super P obtained in the above six examples are uniformly mixed in a ratio of 8:1:1, and coated to obtain an electrode sheet. The electrode sheet and a sodium sheet are assembled into a sodium ion half battery in a glove box, and the electrochemical performance of the battery is tested on a Neware.

[0094] The electrode sheet obtained in the above examples and a sodium sheet are assembled into a half battery in a glove box with a water-oxygen value of less than 0.01 ppm, and the electrochemical performance is tested on a Neware. The specific items are as follows:

[0095] Example 1 is subjected to XRD characterization to obtain an XRD spectrum.

[0096] Example 2 is subjected to charge-discharge at a current density of 100 mA / g to obtain a charge-discharge curve.

[0097] Example 3 is subjected to CV test at a scan rate of 0.05 mV / s and a voltage range of 0.01-1.5 V.

[0098] Example 4 is subjected to cycling at a current density of 1000 mA / g to obtain the cycling performance.

[0099] Example 5 is subjected to charge-discharge at a current density of 100 mA / g to obtain the charge-discharge curve of the first three cycles.

[0100] Example 6 is subjected to rate charge-discharge at a current density of 0.1 C, 0.5 C, 1 C, 2 C, 5 C and 10 C (1 C=847 mA / g) to obtain the rate performance.

[0101] Figure 1 As can be seen, the tin-carbon composite obtained in Example 1 has obvious diffraction peaks of tin, which are consistent with the standard spectrum of tin. Figure 1 Therefore, it is indicated that the tin crystal form obtained is very good.

[0102] Figure 2 As can be seen, the tin-carbon composite negative electrode obtained has super-high charge-discharge capacity, and the first charge capacity is as high as 706.3 mAh / g, and the first efficiency can reach 81.3%. The powder obtained in Example 2 has four platforms in charge-discharge, which is consistent with the charge-discharge platform of tin, and the charge-discharge capacity is very high. Because the tin particle size obtained is small, it is beneficial to the transmission of sodium ions, and the overall sodium extraction and insertion can be realized.

[0103] Figure 3 As can be seen, the tin-carbon composite negative electrode obtained has strong reaction reversibility and reaction activity, and the CV peak is obvious, which is consistent with the charge-discharge platform of tin. With the increase of the number of cycles, the current of the peak only increases but does not decrease, and there is no peak shift, indicating that the reaction polarization is small.

[0104] Figure 4The cycle diagram of the tin-carbon composite negative electrode obtained from Example 4 at 1000 mA / g was obtained, and the capacity retention rate after different cycles was calculated (capacity retention rate = capacity after a specific cycle / capacity of the first cycle at the same current density). Figure 4 It can be seen that Example 4 has better cycle stability in 200 cycles, and the capacity almost does not decay. This is because the carbon provides a buffer space for the volume expansion of tin, inhibits the crushing and pulverization of tin, and thus has good cycle performance.

[0105] Figure 5 It can be seen that the first three cycles of the tin-carbon composite negative electrode obtained from Example 5 at 100 mA / g show that the reversibility of the material reaction is very good, and the first three cycles almost coincide without obvious platform decay, and the capacity slowly increases. And the charge-discharge curve has four platforms, which is consistent with the charge-discharge platform of tin, and the charge-discharge capacity is high, because the tin particle size obtained is small, which is beneficial to the transmission of sodium ions, and the overall sodium extraction and insertion can be realized. The first three cycles of charge-discharge curve are almost consistent, indicating that the reversibility of the material reaction is very high, which indicates that the purity of the obtained tin is high.

[0106] The rate performance diagram of the electrode sheet obtained from Example 6 at 0.1C, 0.5C, 1C, 2C, 5C and 10C (1C = 847 mA / g) shows that the tin-carbon composite negative electrode obtained has excellent rate performance, even at a large current density of 10C still has a capacity of 332.7 mAh / g, which is because the material has excellent conductivity and fast ion diffusion. Figure 6

[0107] The above examples are only specific embodiments of the present application, which are described in more detail and in detail, but should not be construed as limiting the scope of the present patent. It should be noted that for those skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, and these obvious alternative forms all belong to the protection scope of the present application.​

Claims

1. A method for preparing a highly dispersed tin-hard carbon composite anode material for sodium-ion batteries, characterized in that... Includes the following steps: S1. Hard carbon material pretreatment: Porous hard carbon is used as raw material. Dopamine hydrochloride solution is added for pretreatment. After thorough mixing, the mixture is filtered out to obtain pretreated hard carbon. S2. In-situ polymerization on hard carbon surface: Pretreated hard carbon is added to sodium hydroxide solution to achieve in-situ polymerization of dopamine hydrochloride on the surface of pretreated hard carbon. Stirring makes the polymer layer completely cover the surface of hard carbon, and then filtering out to obtain hydrophilic hard carbon. S3. Preparation of composite particles: Hydrophilic hard carbon is added to SnCl2 solution or SnCl4 solution and milled to make Sn... 2+ or Sn 4+ The particles are fully penetrated into the interlayer or open pores of hard carbon, and a suspension is obtained by continuous stirring. The dispersion is then spray-dried to obtain SnCl2-hard carbon composite particles or SnCl4-hard carbon composite particles. S4. Deposition of tin-hard carbon composite material: SnCl2-hard carbon composite particles or SnCl4-hard carbon composite particles are added to sodium borohydride hydrogen evolution reaction inhibition solution under ice-water bath conditions and stirring. The Sn produced by the reaction is uniformly deposited on the outer surface and internal pores of hard carbon to obtain Sn-hard carbon composite suspension. After filtration, tin-hard carbon composite anode material is obtained.

2. The preparation method of the highly dispersed sodium-ion battery tin-hard carbon composite anode material according to claim 1, characterized in that: The preparation method of sodium borohydride hydrogen evolution reaction inhibition solution is as follows: Under ice-water bath conditions, prepare a water-ethanol solution of sodium hydroxide, add sodium borohydride to the above solution, control the mass fraction of sodium borohydride in the solution to be 0.1-1%, and stir to obtain a uniform sodium borohydride hydrogen evolution reaction inhibition solution.

3. The method for preparing the highly dispersed sodium-ion battery tin-hard carbon composite anode material according to claim 1, characterized in that: In step S1, the concentration of the dopamine hydrochloride solution is 1-5 mg / mL.

4. The method for preparing the highly dispersed sodium-ion battery tin-hard carbon composite anode material according to claim 1, characterized in that: In step S2, the concentration of the sodium hydroxide solution is 0.05-0.5 mol / L.

5. The method for preparing the highly dispersed sodium-ion battery tin-hard carbon composite anode material according to claim 1, characterized in that: In step S3, the mass ratio of hard carbon to tin in the SnCl2 solution or SnCl4 solution is 0.01-0.3; the concentration of the SnCl2 solution or SnCl4 solution is 0.01-1 mol / L.

6. The method for preparing the highly dispersed sodium-ion battery tin-hard carbon composite anode material according to claim 1, characterized in that: In step S3, the grinding time is 30-60 min and the rotation speed is 1000-1500 r / min.

7. The method for preparing the highly dispersed sodium-ion battery tin-hard carbon composite anode material according to claim 2, characterized in that: In the sodium borohydride hydrogen evolution reaction inhibition solution, the molar ratio of sodium borohydride to SnCl2 in SnCl2 solution or SnCl4 in SnCl4 solution is 1-3, and the volume ratio of water to ethanol is 0.2-0.

5.

8. The method for preparing the highly dispersed sodium-ion battery tin-hard carbon composite anode material according to claim 1, characterized in that: In step S3, the conditions for spray drying are: the inlet air temperature is 100-200℃ and the outlet air temperature is 50-90℃.

9. The method for preparing the highly dispersed sodium-ion battery tin-hard carbon composite anode material according to claim 1, characterized in that: In step S1, the mixing method is one or more of stirring, ultrasonication, ball milling, and vibration.

10. The method for preparing the highly dispersed sodium-ion battery tin-hard carbon composite anode material according to claim 1, characterized in that: In steps S1 and S2, the filtration method is one or more of centrifugation, vacuum filtration, and filtration.

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