A high-capacity sodium-ion battery hard carbon negative electrode material and a preparation method thereof

Abstract

The application belongs to the technical field of negative electrode materials of sodium ion batteries, and provides a high-capacity sodium ion battery hard carbon negative electrode material and a preparation method thereof, the preparation method comprising the following steps: S1, dissolving aldehyde, benzene acid containing hydroxyl and carboxylic acid and alkali in water to obtain a mixed solution; S2, heating the mixed solution in step S1 to obtain a suspension, and drying and pre-calcining the filter cake after filtering the suspension to obtain a pre-carbonized material; S3, washing the pre-carbonized material obtained in step S2 for multiple times; S4, drying and calcining the washed pre-carbonized material to obtain the high-capacity sodium ion battery hard carbon negative electrode material. The application makes the nanoscale templates uniformly distributed in the precursor, greatly improves the sodium storage capacity and the first coulomb efficiency of the hard carbon, and obtains the high-capacity sodium ion battery hard carbon negative electrode material.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of negative electrode materials of sodium ion batteries, and particularly relates to a high-capacity sodium ion battery hard carbon negative electrode material and a preparation method thereof. BACKGROUND

[0002] Sodium ion batteries are a very promising secondary battery due to the wide range of raw material sources and low price, and are expected to be widely used in the field of energy storage. Because the diameter of sodium ions is larger than that of lithium ions, the graphite negative electrode used in lithium ion batteries cannot be applied to sodium ion batteries due to the low carbon layer spacing. Hard carbon material is amorphous carbon with a larger carbon layer spacing, and is the most mature and most promising negative electrode material at present. Generally, hard carbon is prepared by high-temperature calcination of organic precursors. The precursors mainly include biomass, resin, coal and the like. The sodium storage capacity of the directly calcined precursors is generally less than 340 mAh / g.

[0003] How to prepare a high-capacity sodium ion battery hard carbon negative electrode material has become a technical problem to be solved in the technical field of sodium ion batteries. SUMMARY

[0004] In order to solve the technical problem of low sodium storage capacity of the precursor existing in the prior art technical field of sodium ion batteries, the application provides a high-capacity sodium ion battery hard carbon negative electrode material and a preparation method thereof.

[0005] The preparation method of the high-capacity sodium ion battery hard carbon negative electrode material comprises the following steps:

[0006] S1, dissolving aldehyde, phenolic acid containing hydroxyl and carboxylic acid and alkali in water to obtain a mixed solution;

[0007] S2, heating the mixed solution in step S1 to obtain a suspension, and drying and pre-calcining the filter cake after filtering the suspension to obtain a pre-carbonized material;

[0008] S3, washing the pre-carbonized material obtained in step S2 for multiple times;

[0009] S4, drying and calcining the washed pre-carbonized material to obtain a high-capacity sodium ion battery hard carbon negative electrode material.

[0010] Further, the aldehyde in step S1 is one or more of formaldehyde, acetaldehyde, propyl aldehyde, glyoxal and malondialdehyde, which can be pure or an aqueous solution; the phenolic acid is one or more of monohydroxybenzoic acid, dihydroxybenzoic acid, monohydroxyphenylacetic acid and dihydroxyphenylacetic acid; and the alkali is one or more of lithium hydroxide, sodium hydroxide, potassium hydroxide, magnesium hydroxide, calcium hydroxide, lithium carbonate, sodium carbonate, potassium carbonate, magnesium carbonate and calcium carbonate.

[0011] Further, the molar ratio of the aldehyde group contained in the aldehyde to the benzoic acid substance in step S1 is 0.8-1.2, and the molar ratio of the base to the carboxyl group contained in the benzoic acid is 0.4-0.6 for the carbonates or the bases containing two hydroxyl groups, and the molar ratio of the base to the carboxyl group contained in the benzoic acid is 0.8-1.2 for the bases containing only one hydroxyl group.

[0012] Further, the molar concentration of the benzoic acid substance in the mixed solution in step S1 is 0.3-3 mol / L.

[0013] Further, the heating temperature in step S2 is 50-95 DEG C, and the heating time is 3-10 h.

[0014] Further, the pre-calcination temperature in step S2 is 250-400 DEG C, the pre-calcination atmosphere is air, and the pre-calcination time is 1.5-5 h.

[0015] Further, the PH value of the water used for the last time in step S3 is 7.0-10.5.

[0016] Further, the water content of the material after drying in step S4 is less than 2%.

[0017] Further, the calcination time in step S4 is 1000-1600 DEG C, the calcination time is 1.5-5 h, and the calcination atmosphere is nitrogen or argon.

[0018] Further, the hard carbon negative electrode material for high-capacity sodium ion batteries obtained by crushing the material in step S4 has a particle size D 50 of 3-14 mu m.

[0019] The application also provides the hard carbon negative electrode material for high-capacity sodium ion batteries prepared by the preparation method.

[0020] The working principle and advantages of the application are as follows:

[0021] The application dissolves the aldehyde, the benzoic acid substance containing hydroxyl and carboxylic acid, and the base in water to obtain a mixed solution,

[0022] The mixed solution is heated under normal pressure, and in the heating process, the aldehyde and the benzoic acid are polymerized to form a polymer, and the carboxyl group contained in the benzoic acid is neutralized with the base to uniformly distribute the alkali metal on the molecular chain to obtain a solid-containing slurry. The slurry prepared by the reaction is filtered and dried to obtain a polymer solid, and the polymer solid is pre-calcined, and in this process, the alkali metal carried by the polymer is separated and forms a nano-sized carbonate, and the hydrogen and oxygen contained in the polymer are also partially separated to form a pre-carbonized material. Subsequently, the pre-carbonized material is washed, dried, and calcined with pure water to obtain a hard carbon negative electrode material for high-capacity sodium ion batteries.

[0023] The present application adopts nanoscale template pore making, then removes the template by water washing, and finally performs secondary calcination to obtain hard carbon material rich in closed micropores. Compared with the prior art, the present application makes the nanoscale template uniformly distributed in the precursor, greatly improving the sodium storage capacity and the first coulombic efficiency of the hard carbon. The reaction principle is shown as follows (illustrated by taking formaldehyde, sodium hydroxide and 2,4-dihydroxybenzoic acid as raw materials):

[0024] (1) Polymerization reaction:

[0025]

[0026] (2) Pre-calcination: The -COONa on the polymer chain generated in the polymerization reaction (1) will fall off during pre-calcination to form Na2CO3, that is, M-COONa→M+Na2CO3+CO2+H2O, wherein M represents the polymer chain. The inorganic salt Na2CO3 produced by pre-calcination agglomerates into nanoscale particles as a pore-forming agent module.

[0027] (3) Calcination: After washing the Na2CO3 produced by pre-calcination, high-temperature calcination is performed, and the micropores produced by Na2CO3 form closed nanoscale micropores for sodium storage, which can greatly improve the sodium storage capacity of the hard carbon. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 The electron microscope graph of the high-capacity sodium ion battery hard carbon negative material prepared in Example 1 of the present application;

[0029] Figure 2 The small-angle diffraction test fitting graph of the hard carbon material prepared in Example 1 and Comparative Example 1 of the present application;

[0030] Figure 3 The comparison graph of the influence of different pre-calcination temperatures of Example 1 on the first charge capacity and the first coulombic efficiency (ICE);

[0031] Figure 4 The comparison graph of the influence of different calcination temperatures of Example 1 on the first charge capacity and the first coulombic efficiency. DETAILED DESCRIPTION

[0032] The technical solutions in the embodiments of the present application will be described clearly and completely in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application belong to the scope of protection of the present application.

[0033] Example 1

[0034] A preparation method of a high-capacity sodium ion battery hard carbon negative electrode material, the preparation method comprising the following steps:

[0035] S1, dissolving formaldehyde solution, sodium hydroxide and 2,4-dihydroxybenzoic acid in water to obtain a mixed solution; wherein the molar concentration of 2,4-dihydroxybenzoic acid in the mixed solution is 1.5 mol / L, the molar ratio of formaldehyde to 2,4-dihydroxybenzoic acid is 1, and the molar ratio of sodium hydroxide to 2,4-dihydroxybenzoic acid is 1;

[0036] S2, heating the mixed solution in step S1 at 75℃ for 6.5h to obtain a suspension, drying the filter cake after filtering the suspension at 120℃ for 2h, and pre-calcining the filter cake at 300℃ for 2.5h to obtain a pre-carbonized material;

[0037] S3, washing the pre-carbonized material obtained in step S2 for multiple times, and adjusting the pH value of the last washing water to 8.2;

[0038] S4, drying the washed pre-carbonized material until the moisture content of the material is less than 2%, calcining the dried material at 1400℃ for 3h under a nitrogen atmosphere, and crushing the calcined material to obtain a high-capacity sodium ion battery hard carbon negative electrode material with a particle size D 50 of 5.7μm. Characterization tests show that the specific surface area of the prepared hard carbon material is 6.0m 2 / g.

[0039] Example 2

[0040] A preparation method of a high-capacity sodium ion battery hard carbon negative electrode material, the preparation method comprising the following steps:

[0041] S1, dissolving acetaldehyde solution, potassium hydroxide and hydroxybenzoic acid in water to obtain a mixed solution; wherein the molar concentration of hydroxybenzoic acid in the mixed solution is 0.3 mol / L, the molar ratio of acetaldehyde to hydroxybenzoic acid is 1.2, and the molar ratio of sodium hydroxide to hydroxybenzoic acid is 1.1;

[0042] S2, heating the mixed solution in step S1 at 50℃ for 10h to obtain a suspension, drying the filter cake after filtering the suspension at 120℃ for 2h, and pre-calcining the filter cake at 280℃ for 5h to obtain a pre-carbonized material;

[0043] S3, washing the pre-carbonized material obtained in step S2 for multiple times, and adjusting the pH value of the last washing water to 7.9;

[0044] S4, drying the washed pre-carbonized material until the moisture content of the material is less than 2%, calcining the dried material at 1400℃ for 3h under an argon atmosphere, and crushing the calcined material to obtain a high-capacity sodium ion battery hard carbon negative electrode material with a particle size D 50A high-capacity hard carbon anode material for sodium-ion batteries with a capacity of 13.2 mAh / g. Characterization tests show that the specific surface area of the prepared hard carbon material is 8.3 m 2 / g.

[0045] Example 3

[0046] A preparation method of a high-capacity hard carbon anode material for sodium-ion batteries, comprising the following steps:

[0047] S1, dissolving propionaldehyde solution, lithium hydroxide and hydroxyphenylacetic acid in water to obtain a mixed solution; wherein the molar concentration of hydroxyphenylacetic acid in the mixed solution is 3 mol / L, the molar ratio of propionaldehyde to hydroxyphenylacetic acid is 0.8, and the molar ratio of lithium hydroxide to hydroxyphenylacetic acid is 0.95;

[0048] S2, heating the mixed solution in step S1 at 95°C for 3h to obtain a suspension, filtering the suspension to obtain a filter cake, drying the filter cake at 120°C for 2h, pre-calcining the filter cake at 330°C for 1.5h to obtain a pre-carbonized material;

[0049] S3, washing the pre-carbonized material obtained in step S2 for multiple times, and the pH value of the last washing water is 9.3;

[0050] S4, drying the washed pre-carbonized material until the moisture content of the material is less than 2%, calcining the dried material at 1500°C for 1.5h under an argon atmosphere, and crushing the calcined material to obtain a hard carbon anode material for sodium-ion batteries with a particle size D 50 A high-capacity hard carbon anode material for sodium-ion batteries with a capacity of 13.2 mAh / g. Characterization tests show that the specific surface area of the prepared hard carbon material is 8.3 m 2 / g.

[0051] Example 4

[0052] A preparation method of a high-capacity hard carbon anode material for sodium-ion batteries, comprising the following steps:

[0053] S1, dissolving glyoxal solution, magnesium hydroxide and dihydroxyphenylacetic acid in water to obtain a mixed solution; wherein the molar concentration of dihydroxyphenylacetic acid in the mixed solution is 1 mol / L, the molar ratio of glyoxal to dihydroxyphenylacetic acid is 0.4, and the molar ratio of magnesium hydroxide to hydroxyphenylacetic acid is 0.5;

[0054] S2, heating the mixed solution in step S1 at 80°C for 5h to obtain a suspension, filtering the suspension to obtain a filter cake, drying the filter cake at 120°C for 2h, pre-calcining the filter cake at 250°C for 4h to obtain a pre-carbonized material;

[0055] S3, washing the pre-carbonized material obtained in step S2 for multiple times, and the pH value of the last washing water is 7.5;

[0056] S4, drying the pre-carbonized material after washing to a moisture content of the material <2%, calcining at 1100 DEG C for 4h under argon atmosphere, and crushing the calcined material to obtain a particle size D 50 A high-capacity hard carbon anode material for sodium-ion batteries with a particle size of 10.2 pm. Characterization tests show that the specific surface area of the prepared hard carbon material is 7.8 m 2 / g.

[0057] Example 5

[0058] A preparation method of a high-capacity hard carbon anode material for sodium-ion batteries, comprising the following steps:

[0059] S1, dissolving a malondialdehyde solution, calcium hydroxide and dihydroxybenzoic acid in water to obtain a mixed solution; wherein the molar concentration of dihydroxybenzoic acid in the mixed solution is 1 mol / L, the molar ratio of malondialdehyde to dihydroxybenzoic acid is 0.6, and the molar ratio of calcium hydroxide to dihydroxybenzoic acid is 0.55;

[0060] S2, heating the mixed solution in step S1 at 85 DEG C for 8h to obtain a suspension, filtering the suspension to obtain a filter cake, drying the filter cake at 120 DEG C for 2h, and pre-calcining the filter cake at 300 DEG C for 2h to obtain a pre-carbonized material;

[0061] S3, washing the pre-carbonized material obtained in step S2 for multiple times, and the pH value of the water used for the last washing is 8.5;

[0062] S4, drying the pre-carbonized material after washing to a moisture content of the material <2%, calcining at 1300 DEG C for 4.5h under argon atmosphere, and crushing the calcined material to obtain a particle size D 50 A high-capacity hard carbon anode material for sodium-ion batteries with a particle size of 8.5 pm. Characterization tests show that the specific surface area of the prepared hard carbon material is 8.5 m 2 / g.

[0063] Example 6

[0064] A preparation method of a high-capacity hard carbon anode material for sodium-ion batteries, comprising the following steps:

[0065] S1, dissolving an acetaldehyde solution, lithium carbonate and 3-hydroxybenzoic acid in water to obtain a mixed solution; wherein the molar concentration of 3-hydroxybenzoic acid in the mixed solution is 0.8 mol / L, the molar ratio of acetaldehyde to 3-hydroxybenzoic acid is 0.9, and the molar ratio of lithium carbonate to 3-hydroxybenzoic acid is 0.4;

[0066] S2, heating the mixed solution in step S1 at 70 DEG C for 7h to obtain a suspension, filtering the suspension to obtain a filter cake, drying the filter cake at 120 DEG C for 2h, and pre-calcining the filter cake at 320 DEG C for 2h to obtain a pre-carbonized material;

[0067] S3, the pre-carbonized material obtained in step S2 is washed multiple times, and the pH value of the water used in the last washing is 7;

[0068] S4, the pre-carbonized material after washing is dried to a moisture content <2%, calcined at 1000°C for 4h under an argon atmosphere, and the calcined material is crushed to obtain a high-capacity sodium-ion battery hard carbon negative electrode material with a particle size D 50 of 3μm. Characterization tests show that the specific surface area of the prepared hard carbon material is 9.2m 2 / g.

[0069] Example 7

[0070] A preparation method of a high-capacity sodium-ion battery hard carbon negative electrode material, comprising the following steps:

[0071] S1, dissolve propionaldehyde solution, sodium carbonate, and 2,4-dihydroxyphenylacetic acid in water to obtain a mixed solution; wherein the molar concentration of 2,4-dihydroxyphenylacetic acid in the mixed solution is 2.5mol / L, the molar ratio of propionaldehyde to 2,4-dihydroxyphenylacetic acid is 1.1, and the molar ratio of sodium carbonate to 2,4-dihydroxyphenylacetic acid is 0.5;

[0072] S2, heat the mixed solution in step S1 at 90°C for 4h to obtain a suspension, filter the suspension to obtain a filter cake, dry the filter cake at 120°C for 2h, and pre-calcine the filter cake at 280°C for 3h to obtain a pre-carbonized material;

[0073] S3, the pre-carbonized material obtained in step S2 is washed multiple times, and the pH value of the water used in the last washing is 9;

[0074] S4, the pre-carbonized material after washing is dried to a moisture content <2%, calcined at 1500°C for 2h under a nitrogen atmosphere, and the calcined material is crushed to obtain a high-capacity sodium-ion battery hard carbon negative electrode material with a particle size D 50 of 7.0μm. Characterization tests show that the specific surface area of the prepared hard carbon material is 6.8m 2 / g.

[0075] Example 8

[0076] A preparation method of a high-capacity sodium-ion battery hard carbon negative electrode material, comprising the following steps:

[0077] S1, dissolve formaldehyde solution, potassium carbonate, and 4-hydroxybenzoic acid in water to obtain a mixed solution; wherein the molar concentration of 4-hydroxybenzoic acid in the mixed solution is 1.2mol / L, the molar ratio of formaldehyde to 4-hydroxybenzoic acid is 0.9, and the molar ratio of potassium carbonate to 4-hydroxybenzoic acid is 0.5;

[0078] S2, the mixed solution in step S1 is heated at 97℃ for 9h to obtain a suspension, the filter cake after the suspension is filtered is dried at 120℃ for 2h, and the filter cake is precalcined at 350℃ for 2h to obtain a pre-carbonized material;

[0079] S3, the pre-carbonized material obtained in step S2 is washed multiple times, and the pH value of the water used in the last washing is 10;

[0080] S4, the pre-carbonized material after washing is dried until the moisture content of the material is less than 2%, the material is calcined at 1400℃ for 2.5h under a nitrogen atmosphere, and the calcined material is crushed to obtain a high-capacity sodium-ion battery hard carbon negative electrode material with a particle size D 50 of 6.5μm. Characterization tests show that the specific surface area of the prepared hard carbon material is 7.0m 2 / g.

[0081] Example 9

[0082] A preparation method of a high-capacity sodium-ion battery hard carbon negative electrode material, the preparation method comprising the following steps:

[0083] S1, dissolving a glyoxal solution, magnesium carbonate, and 3,5-dihydroxybenzoic acid in water to obtain a mixed solution; wherein the molar concentration of 3,5-dihydroxybenzoic acid in the mixed solution is 2.5mol / L, the molar ratio of glyoxal to 3,5-dihydroxybenzoic acid is 0.5, and the molar ratio of magnesium carbonate to 3,5-dihydroxybenzoic acid is 0.55;

[0084] S2, the mixed solution in step S1 is heated at 55℃ for 9h to obtain a suspension, the filter cake after the suspension is filtered is dried at 120℃ for 2h, and the filter cake is precalcined at 400℃ for 2.5h to obtain a pre-carbonized material;

[0085] S3, the pre-carbonized material obtained in step S2 is washed multiple times, and the pH value of the water used in the last washing is 10.5;

[0086] S4, the pre-carbonized material after washing is dried until the moisture content of the material is less than 2%, the material is calcined at 1600℃ for 5h under a nitrogen atmosphere, and the calcined material is crushed to obtain a high-capacity sodium-ion battery hard carbon negative electrode material with a particle size D 50 of 14μm. Characterization tests show that the specific surface area of the prepared hard carbon material is 8.2m 2 / g.

[0087] Example 10

[0088] A preparation method of a high-capacity sodium-ion battery hard carbon negative electrode material, the preparation method comprising the following steps:

[0089] S1, dissolving a malondialdehyde solution, calcium carbonate and 3,4-dihydroxyphenylacetic acid in water to obtain a mixed solution; wherein the molar concentration of 3,4-dihydroxyphenylacetic acid in the mixed solution is 1.8 mol / L, the molar ratio of malondialdehyde to 3,4-dihydroxyphenylacetic acid is 0.45, and the molar ratio of calcium carbonate to 3,4-dihydroxyphenylacetic acid is 0.51;

[0090] S2, heating the mixed solution in step S1 at 80℃ for 5.5h to obtain a suspension, drying the filter cake after filtering the suspension at 120℃ for 2h, and pre-calcining the filter cake at 300℃ for 3h to obtain a pre-carbonized material;

[0091] S3, washing the pre-carbonized material obtained in step S2 for multiple times, and adjusting the pH value of the water used in the last washing to 8.5;

[0092] S4, drying the washed pre-carbonized material until the moisture content of the material is less than 2%, calcining the dried material at 1200℃ for 3.5h under a nitrogen atmosphere, and crushing the calcined material to obtain a high-capacity sodium-ion battery hard carbon negative electrode material with a particle size D 50 of 7.6μm. Characterization tests show that the specific surface area of the prepared hard carbon material is 7.7m 2 / g.

[0093] Comparative Example 1

[0094] A preparation method of a sodium-ion battery hard carbon negative electrode material, the preparation method comprising the following steps:

[0095] S1, dissolving a formaldehyde solution and 2,4-dihydroxybenzoic acid in water to obtain a mixed solution; wherein the molar concentration of 2,4-dihydroxybenzoic acid in the mixed solution is 1.5 mol / L, and the molar ratio of formaldehyde to 2,4-dihydroxybenzoic acid is 1;

[0096] S2, heating the mixed solution in step S1 at 75℃ for 6.5h to obtain a suspension, drying the filter cake after filtering the suspension at 120℃ for 2h, and pre-calcining the filter cake at 300℃ for 2.5h to obtain a pre-carbonized material;

[0097] S3, washing the pre-carbonized material obtained in step S2 for multiple times, and adjusting the pH value of the water used in the last washing to 8.2;

[0098] S4, drying the washed pre-carbonized material until the moisture content of the material is less than 2%, calcining the dried material at 1400℃ for 3h under a nitrogen atmosphere, and crushing the calcined material to obtain a sodium-ion battery hard carbon negative electrode material with a particle size D 50 of 6.5μm. Characterization tests show that the specific surface area of the prepared hard carbon material is 7.5m 2 / g.

[0099] Comparative Example 2

[0100] A preparation method of a sodium ion battery hard carbon negative electrode material, the preparation method comprising the following steps:

[0101] S1, dissolving formaldehyde solution, sodium hydroxide and 2,4-dihydroxybenzoic acid in water to obtain a mixed solution; wherein the molar concentration of 2,4-dihydroxybenzoic acid in the mixed solution is 1.5 mol / L, the molar ratio of formaldehyde to 2,4-dihydroxybenzoic acid is 1, and the molar ratio of sodium hydroxide to 2,4-dihydroxybenzoic acid is 1.0;

[0102] S2, heating the mixed solution in step S1 at 75°C for 6.5h to obtain a suspension, and drying the filter cake after filtering the suspension at 120°C for 2h, and pre-calcining at 600°C for 2.5h to obtain a pre-carbonized material;

[0103] S3, washing the pre-carbonized material obtained in step S2 multiple times, and adjusting the pH value of the last washing water to 8.2;

[0104] S4, drying the washed pre-carbonized material to a moisture content of <2%, calcining at 1400°C for 3h under a nitrogen atmosphere, and crushing the calcined material to obtain a sodium ion battery hard carbon negative electrode material with a particle size D 50 of 7.9μm. Characterization tests show that the specific surface area of the prepared hard carbon material is 13.2m 2 / g.

[0105] Comparative Example 3

[0106] A preparation method of a high-capacity sodium ion battery hard carbon negative electrode material, the preparation method comprising the following steps:

[0107] S1, dissolving formaldehyde solution, sodium hydroxide and 2,4-dihydroxybenzoic acid in water to obtain a mixed solution; wherein the molar concentration of 2,4-dihydroxybenzoic acid in the mixed solution is 1.5 mol / L, the molar ratio of formaldehyde to 2,4-dihydroxybenzoic acid is 1, and the molar ratio of sodium hydroxide to 2,4-dihydroxybenzoic acid is 1.0;

[0108] S2, heating the mixed solution in step S1 at 75°C for 6.5h to obtain a suspension, and drying the filter cake after filtering the suspension at 120°C for 2h, and pre-calcining at 300°C for 2.5h to obtain a pre-carbonized material;

[0109] S3, washing the pre-carbonized material obtained in step S2 multiple times, and adjusting the pH value of the last washing water to 8.2;

[0110] S4. Dry the washed pre-carbonized material until the moisture content is <2%, calcine it at 1800℃ for 3 hours under a nitrogen atmosphere, and then pulverize the calcined material to obtain particle size D. 50 A high-capacity hard carbon anode material for sodium-ion batteries with a surface area of ​​8.1 μm was prepared. Characterization tests showed that the specific surface area of ​​the prepared hard carbon material was 3.6 m². 2 / g.

[0111] The hard carbon materials prepared in Examples 1-10 and Comparative Examples 1-3 were added to N-methylpyrrolidone (NMP) in a mass ratio of 9:0.5:0.5 with sodium alginate as a binder and SuperP as a conductive agent to obtain a slurry. This slurry was then uniformly coated onto copper foil to form an electrode. The electrode was subsequently dried in a vacuum oven at 120°C for 10 hours. The electrode was then cut and assembled into a coin cell using sodium metal as the counter electrode. Charge-discharge tests were performed. The electrolyte was a mixture of NaPF6 dissolved in dimethyl carbonate (DMC) and ethylene carbonate (EC) (volume ratio 1:1), with a NaPF6 concentration of 1 mol / L. The electrochemical test results at 0.1°C are shown in Table 1.

[0112] Table 1 Test Results of Hard Carbon Materials

[0113]

[0114]

[0115] Analysis based on the attached diagram:

[0116] Figure 1 The electron microscope image of the material prepared for Example 1 shows the bulk structure of the material.

[0117] The preparation steps of the hard carbon material in Comparative Example 1 were basically the same as those in Example 1, except that sodium hydroxide, a pore-forming agent, was not added during the process. The resulting material had a specific surface area of ​​7.5 m². 2 The initial discharge and charge capacities were 342 mAh / g and 278 mAh / g, respectively, with an initial coulombic efficiency of 81.3%. Its sodium storage capacity was significantly lower than that of Comparative Example 1, which is attributed to the absence of a pore-forming agent in Comparative Example 1. Figure 2 This is a fitted graph of the small-angle diffraction test results for the hard carbon materials prepared in Example 1 and Comparative Example 1. For small-angle diffraction tests, the abscissa q is at... The diffraction intensity in the vicinity is positively correlated with the number of nanoscale micropores. From Figure 2 As can be seen, in Example 1 The diffraction intensity in the vicinity is significantly greater than that in Comparative Example 1, indicating that the hard carbon material prepared in Example 1 does indeed contain more sodium storage micropores and therefore has a higher sodium storage capacity.

[0118] Figure 3 The comparison chart of the influence of different pre-calcination temperatures of Example 1 on the first charge capacity and the first coulombic efficiency: when the pre-calcination temperature is lower than 250℃, the carboxylic acid groups on the polymer chain cannot be completely removed, and the rich nano micropores cannot be formed, and the part of the carboxylic acid groups which are not removed will be brought into the calcination process due to containing alkaline metals, resulting in that the hard carbon material is activated, that is, the internal complete structure is destroyed; when the pre-calcination temperature is higher than 400℃, the pore-forming agent is seriously agglomerated, greatly increasing the pore diameter of the micropores, and the nano-scale closed micropores for storing sodium cannot be formed, which also leads to that the specific surface area of the material is significantly increased, and the first coulombic efficiency is greatly reduced. The preparation steps of the hard carbon material of Comparative Example 2 are basically the same as those of Example 1, except that the calcination temperature in the pre-calcination process is changed to 600℃. The prepared material has a specific surface area of 13.2m 2 / g, the first discharge and charge capacities are 389mAh / g and 293mAh / g respectively, and the first coulombic efficiency is only 75.3%. The sodium storage capacity is significantly reduced compared with Example 1.

[0119] Figure 4 The comparison chart of the influence of different calcination temperatures of Example 1 on the first charge capacity and the first coulombic efficiency: when the calcination temperature is lower than 1000℃, the internal highly twisted hard carbon structure cannot be formed, resulting in that the sodium storage sites are less and the capacity is low; when the calcination temperature is higher than 1600℃, the nano-scale closed micropores contained are collapsed and disappear in the calcination process. The preparation steps of the hard carbon material of Comparative Example 3 are basically the same as those of Example 1, except that the calcination temperature in the calcination process is changed from 1400℃ to 1800℃. The obtained material has a specific surface area of 3.6m 2 / g, the first discharge and charge capacities are 344mAh / g and 308mAh / g respectively, and the first coulombic efficiency is 89.5%. The sodium storage capacity is significantly reduced compared with Example 1.

[0120] In summary, the hard carbon material rich in closed micropores is obtained by using nano-scale template pore-forming, then removing the template by water washing, and finally performing secondary calcination. The nano-scale template is uniformly distributed in the precursor by the present application, greatly improving the sodium storage capacity and the first coulombic efficiency of the hard carbon, and obtaining the high-capacity hard carbon negative electrode material for sodium ion batteries.

[0121] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made by those skilled in the art within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a high-capacity sodium-ion battery hard carbon anode material, the method comprising the following steps: S1.dissolving an aldehyde, a benzoic acid containing hydroxyl and carboxylic acid, and a base in water to obtain a mixed solution; S2.heating the mixed solution obtained in step S1 to obtain a suspension, filtering the suspension to obtain a filter cake, and drying and pre-calcining the filter cake to obtain a pre-carbonized material; S3.washing the pre-carbonized material obtained in step S2 for multiple times; and S4.drying and calcining the washed pre-carbonized material to obtain the high-capacity sodium-ion battery hard carbon anode material; wherein the aldehyde in step S1 is one or more of pure formaldehyde, acetaldehyde, propyl aldehyde, glyoxal, and malondialdehyde, or an aqueous solution thereof; the benzoic acid is one or more of monohydroxybenzoic acid, dihydroxybenzoic acid, monohydroxyphenylacetic acid, and dihydroxyphenylacetic acid; and the base is one or more of lithium hydroxide, sodium hydroxide, potassium hydroxide, magnesium hydroxide, calcium hydroxide, lithium carbonate, sodium carbonate, potassium carbonate, magnesium carbonate, and calcium carbonate; the pre-calcination temperature in step S2 is 250-400℃, the pre-calcination atmosphere is air, and the pre-calcination time is 1.5-5h; the calcination temperature in step S4 is 1000-1600℃, the calcination time is 1.5-5h, and the calcination atmosphere is nitrogen or argon; the molar ratio of the aldehyde group contained in the aldehyde to the benzoic acid in step S1 is 0.8-1.2, the molar ratio of the base to the carboxyl group contained in the benzoic acid is 0.4-0.6 for a carbonate or a base containing two hydroxyl groups, and the molar ratio of the base to the carboxyl group contained in the benzoic acid is 0.8-1.2 for a base containing only one hydroxyl group; the molar concentration of the benzoic acid in the mixed solution in step S1 is 0.3-3 mol / L; the heating temperature in step S2 is 50-95℃, and the heating time is 3-10h; the pH value of the water used for the last washing in step S3 is 7.0-10.5; and the water content of the material after drying in step S4 is less than 2%. ​ ​ ​ ​ ​ ​ 2. The method of claim 1, wherein the method is characterized by: ​ 3. The method of claim 1, wherein the method is characterized by: ​ 4. The method of claim 1, wherein the method is characterized by: ​ 5. The method for preparing the high-capacity sodium-ion battery hard carbon anode material according to claim 1, characterized in that, ​ 6. The method of claim 1, wherein the high-capacity sodium-ion battery hard- carbon anode material is prepared by the method comprising: ​ 7. The method of claim 1, wherein the method is characterized by: The step S4 carries out the crushing to the hard carbon negative material of high capacity sodium ion battery, obtains the particle size D 50 The hard carbon is 3-14 μm.

8. A high-capacity sodium-ion battery hard carbon anode material, characterized in that, ​

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