A high initial efficiency hard carbon material and its preparation method and application

Abstract

The present invention relates to the technical field of anode materials for sodium-ion batteries, and specifically discloses a high-first-efficiency hard carbon material, a preparation method thereof, and an application thereof. The high-first-efficiency hard carbon material comprises a hard carbon matrix and sodium-ion functionalized carbon quantum dots coated on the surface of the hard carbon matrix. The sodium-ion functionalized carbon quantum dots contain -COONa, avoiding the consumption of Na + in the electrolyte; the -OH of the sodium-ion functionalized carbon quantum dots can undergo a dehydration condensation reaction with the -COOH on the surface of the hard carbon matrix to stably wrap the sodium-ion functionalized carbon quantum dots on the surface of the hard carbon matrix without changing its interlayer distance and pore structure; the small molecule polymer chain of the sodium-ion functionalized carbon quantum dots can promote the preferential aggregation and decomposition of PF6 ‑ to form a uniform, stable and inorganic-rich SEI layer, further improving the electrochemical performance of the battery; the sodium-ion functionalized carbon quantum dots have high conductivity, avoiding the use of conductive agents.

Description

Technical Field

[0001] The present invention relates to the technical field of negative electrode materials for sodium ion batteries, and in particular to a high initial efficiency hard carbon material and a preparation method and application thereof. Background Art

[0002] Hard carbon materials have suitable interlayer distances, abundant pores, and low cost, and are widely used as the main negative electrode materials for sodium-ion batteries. The large number of -COOH functional groups on the surface of hard carbon can adsorb a large number of sodium ions by breaking the -C=O- bond, showing a high slope capacity and helping to achieve high power density. However, the reversibility of -COOH on the surface of hard carbon for sodium ion storage is poor. After the first discharge, most of the sodium ions will become dead sodium and cannot participate in subsequent reactions; and -COOH has a strong affinity for ester-based electrolyte solvents, especially ethylene carbonate (EC) and diethyl carbonate (DEC), which will cause a large number of solvent molecules to aggregate and preferentially decompose on the surface of hard carbon, thereby forming a thick, uneven, and unstable solid electrolyte (SEI) layer. The above two reasons will cause the first coulomb efficiency (referred to as the first efficiency) of hard carbon to be lower than 70%, which cannot meet the requirements of industrial use (first efficiency ≥ 90%).

[0003] At present, the content of -COOH on the surface of hard carbon can be significantly reduced by increasing the carbonization temperature, but at the same time it will cause a decrease in the interlayer distance and the disappearance of pores, which is not conducive to the storage of sodium ions. Therefore, it is necessary to design a reasonable structure and composition of hard carbon materials on the basis of retaining appropriate interlayer distance and developed pores to avoid the adverse effects of -COOH on sodium ion storage, thereby achieving high initial efficiency. Summary of the invention

[0004] In view of the above problems, the present invention provides a high initial efficiency hard carbon material and its preparation method and application, by coating the surface of the hard carbon matrix with sodium ion functionalized carbon quantum dots, thus avoiding the effect of -COOH on Na in the electrolyte. + It reduces the consumption of organic matter and helps to form a uniform, stable and inorganic-rich SEI layer, thereby improving the electrochemical performance of the battery.

[0005] In order to achieve the above-mentioned object of the invention, the embodiment of the present invention adopts the following technical solution:

[0006] In a first aspect, the present invention provides a high first-efficiency hard carbon material, comprising a hard carbon substrate and sodium ion functionalized carbon quantum dots coated on the surface of the hard carbon substrate;

[0007] The sodium ion functionalized carbon quantum dots are prepared by melting and decomposing biomass with acid and then immersing the biomass in a sodium ion solution.

[0008] Compared with the prior art, the high-efficiency hard carbon material provided by the present invention breaks the organic bonds and hydrogen bonds in the molecules during the melting decomposition of biomass acid, releasing gas molecules (such as water and carbon dioxide), leaving carbon atoms for nucleation reaction, forming small nucleation clusters, and gradually growing into nanoscale carbon particles (i.e., small molecule polymer chains). At the same time, the functional groups such as -COOH and -OH of the raw material biomass acid are anchored on the surface to form carbon quantum dots with small molecule polymer chains as the main body and a large number of functional groups such as -COOH and -OH on the surface. After the carbon quantum dots are immersed in a sodium ion solution, the sodium ion solution will ionize Na + , positively charged Na + The negatively charged -COOH will spontaneously undergo electrostatic adsorption to form -COONa groups, resulting in sodium ion functionalized carbon quantum dots.

[0009] In the present invention, the sodium ion functionalized carbon quantum dots contain -COONa, which, compared with -COOH, avoids the Na + The -OH of the sodium ion functionalized carbon quantum dots can undergo a dehydration condensation reaction with the -COOH on the surface of the hard carbon matrix, stably encapsulating the sodium ion functionalized carbon quantum dots on the surface of the hard carbon matrix without changing its interlayer distance and pore structure, thereby not reducing the demand for Na + storage; the small molecule polymer chains of sodium ion functionalized carbon quantum dots can promote PF through electrostatic adsorption 6 - (Hexafluorophosphate anions) preferentially aggregate and decompose to form a uniform, stable and inorganic-rich SEI layer, thereby further improving the electrochemical performance of the battery; and due to the nano effect, the sodium ion functionalized carbon quantum dots have high conductivity, avoiding the use of conductive agents and increasing the loading mass of active materials (ie, high first-efficiency hard carbon materials), ultimately achieving the battery's high first coulombic efficiency and excellent sodium storage capacity.

[0010] Preferably, the mass ratio of the hard carbon matrix to the sodium ion functionalized carbon quantum dots is 1:(1-3).

[0011] Preferably, the hard carbon matrix is ​​prepared by carbonizing a high molecular polymer.

[0012] Further preferably, the high molecular polymer includes at least one of phenolic resin, polyvinylidene fluoride or lignin.

[0013] Further preferably, the carbonization temperature is 800° C. to 900° C., and the carbonization time is 3 h to 4 h.

[0014] In the present invention, the high molecular polymer is carbonized at low temperature (<1000°C) to form porous hard carbon, so that the hard carbon matrix has a certain interlayer distance and pore structure, which is beneficial to Na +storage; and when the polymer is carbonized at a specific temperature, its surface will contain a large number of -COOH functional groups.

[0015] Preferably, the biomass acid includes at least one of malic acid, mucic acid, caffeic acid, benzoic acid, alginic acid or citric acid.

[0016] Further preferably, the biomass acid includes at least one of malic acid, mucic acid, caffeic acid or benzoic acid.

[0017] Through a large number of experiments, the present invention found that compared with alginic acid, citric acid or other biomass acids, malic acid, mucic acid, caffeic acid or benzoic acid have smaller molecular weights, shorter molecular chains, and are more easily broken into nuclei. The SEI layer formed by the small molecule polymer chains in the prepared sodium ion functionalized carbon quantum dots through electrostatic adsorption is more uniform and stable, thereby further improving the electrochemical performance of the battery.

[0018] Preferably, the sodium ion solution includes at least one of a sodium hydroxide solution, a sodium bicarbonate solution, a sodium carbonate solution or a sodium chloride solution.

[0019] Preferably, the concentration of the sodium ion solution is 3 mol / L to 4 mol / L.

[0020] Preferably, the mass volume ratio of the biomass acid to the sodium ion solution is (5-9) g: (30-50) mL.

[0021] The present invention has found through a large number of experiments that too low a concentration of sodium ion solution (or too little dosage) will result in the ionized Na + Very little, can not fully combine with sodium ions to functionalize the -COOH functional groups on the surface of carbon quantum dots; too high concentration (or too much dosage) will lead to a large amount of free Na + In the subsequent reaction with the hard carbon matrix, these free Na + It will react with the -COOH on the surface of the hard carbon matrix, hindering the binding between -OH and -COOH, resulting in insufficient binding between the sodium ion functionalized carbon quantum dots and the hard carbon matrix, which will adversely affect the electrochemical performance of the battery.

[0022] In a second aspect, the present invention provides a method for preparing the high initial efficiency hard carbon material, comprising the following steps:

[0023] S1, melting and decomposing the biomass acid at 180°C to 200°C to obtain carbon quantum dots;

[0024] S2, immersing the carbon quantum dots in a sodium ion solution to obtain a solution containing sodium ion functionalized carbon quantum dots;

[0025] S3, placing the hard carbon matrix into the solution containing the sodium ion functionalized carbon quantum dots, reacting at 130° C. to 150° C. to obtain a high initial efficiency hard carbon material.

[0026] In the present invention, at a specific temperature, the biomass acid undergoes melting decomposition to form carbon quantum dots with small molecular polymer chains as the main body and a large number of functional groups such as -COOH and -OH on the surface; the carbon quantum dots are immersed in a sodium ion solution, and the positively charged Na + The negatively charged -COOH spontaneously undergoes electrostatic adsorption to obtain sodium ion functionalized carbon quantum dots; the hard carbon matrix is ​​placed in a solution containing the sodium ion functionalized carbon quantum dots, and the -OH in the sodium ion functionalized carbon quantum dots and the -COOH on the surface of the hard carbon matrix undergo a dehydration condensation reaction at a specific temperature, so that the sodium ion functionalized carbon quantum dots are stably coated on the surface of the hard carbon matrix to obtain a high initial efficiency hard carbon material.

[0027] The present invention has found through a large number of experiments that in S3, if the reaction temperature is too low, the dehydration condensation reaction between -COOH and -OH will be very slow, resulting in very few sodium ion functionalized carbon quantum dots coated on the surface of the hard carbon matrix and a low coating rate; if the reaction temperature is too high, the sodium ion functionalized carbon quantum dots will agglomerate with each other, resulting in uneven coating of the hard carbon matrix and a reduced coating rate.

[0028] Preferably, in S1, the melting and decomposition time is 30 min to 50 min.

[0029] Preferably, in S2, the immersion temperature is 5°C to 40°C, and the immersion time is 2h to 3h.

[0030] Preferably, in S3, the mass volume ratio of the hard carbon matrix to the solution containing sodium ion functionalized carbon quantum dots is (3~5)g:(30~50)mL.

[0031] Preferably, in S3, the reaction time is 30 min to 45 min.

[0032] For example, in S3, after the reaction is completed, the following steps are further performed: cooling, solid-liquid separation, washing and drying the solid to obtain a high-efficiency hard carbon material.

[0033] In a third aspect, the present invention provides an application of the high initial efficiency hard carbon material in a sodium ion battery.

[0034] In a fourth aspect, the present invention provides a negative electrode material for a sodium ion battery, comprising the high initial efficiency hard carbon material. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a SEM image of the high first-efficiency hard carbon material in Example 1 of the present invention; the arrows in the image represent the sodium ion functionalized carbon quantum dots;

[0036] Figure 2 This is the XPS graph of the high first-efficiency hard carbon material in Example 1 of the present invention. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0038] Unless otherwise specified, the materials used in the present invention are all commercially available products.

[0039] Example 1

[0040] This embodiment provides a high first-effect hard carbon material, which is composed of a hard carbon matrix and sodium ion functionalized carbon quantum dots in a mass ratio of 1:2, wherein the sodium ion functionalized carbon quantum dots are coated on the surface of the hard carbon matrix.

[0041] The method for preparing the high initial efficiency hard carbon material comprises the following steps:

[0042] Sa, Preparation of hard carbon matrix:

[0043] The phenolic resin was carbonized at 860°C for 3.4 hours to obtain a hard carbon matrix.

[0044] Preparation of Sb, Na ion functionalized carbon quantum dots:

[0045] Sb-1, 8 g of malic acid was melt-decomposed at 190 °C and kept warm for 40 min to obtain carbon quantum dots;

[0046] Sb-2, place the above carbon quantum dots in 42mL Na + The mixture was immersed in a sodium hydroxide solution with a concentration of 3.4 mol / L and stirred at room temperature for 2.5 h to obtain a solution containing sodium ion functionalized carbon quantum dots.

[0047] Sc, Preparation of high first-efficiency hard carbon materials:

[0048] 4 g of hard carbon matrix was placed in the above solution containing sodium ion functionalized carbon quantum dots, reacted at 140° C. for 40 min, cooled to room temperature, solid-liquid separation was performed, and the solid was washed and dried to obtain a high-efficiency hard carbon material.

[0049] It should be noted that the present invention does not limit the order of Sa and Sb.

[0050] The high first-efficiency hard carbon material prepared in this embodiment was subjected to electron microscope scanning and X-ray photoelectron spectroscopy testing. The results are as follows: Figure 1~Figure 2As shown in the figure, it can be seen that the surface of the high-efficiency hard carbon material has granular sodium ion functionalized carbon quantum dots, and the Na element is detected, indicating that -COONa is generated after immersion in sodium hydroxide solution.

[0051] Example 2

[0052] This embodiment provides a high first-effect hard carbon material, which is composed of a hard carbon matrix and sodium ion functionalized carbon quantum dots in a mass ratio of 1:3, wherein the sodium ion functionalized carbon quantum dots are coated on the surface of the hard carbon matrix.

[0053] The method for preparing the high initial efficiency hard carbon material comprises the following steps:

[0054] Sa, Preparation of hard carbon matrix:

[0055] The polyvinylidene fluoride was carbonized at 840°C for 3.6 hours to obtain a hard carbon matrix.

[0056] Preparation of Sb, Na ion functionalized carbon quantum dots:

[0057] Sb-1, 9 g of mucic acid was melt-decomposed at 190 °C and kept warm for 40 min to obtain carbon quantum dots;

[0058] Sb-2, place the above carbon quantum dots in 38mL Na + The solution was immersed and stirred in a sodium chloride solution with a concentration of 3.7 mol / L at room temperature for 2.5 hours to obtain a solution containing sodium ion functionalized carbon quantum dots.

[0059] Sc, Preparation of high first-efficiency hard carbon materials:

[0060] 3 g of hard carbon matrix was placed in the above solution containing sodium ion functionalized carbon quantum dots, reacted at 140° C. for 35 min, cooled to room temperature, solid-liquid separation was performed, and the solid was washed and dried to obtain a high-efficiency hard carbon material.

[0061] It should be noted that the present invention does not limit the order of Sa and Sb.

[0062] Example 3

[0063] This embodiment provides a high first-efficiency hard carbon material, which is composed of a hard carbon matrix and sodium ion functionalized carbon quantum dots in a mass ratio of 1:1, wherein the sodium ion functionalized carbon quantum dots are coated on the surface of the hard carbon matrix.

[0064] The method for preparing the high initial efficiency hard carbon material comprises the following steps:

[0065] Sa, Preparation of hard carbon matrix:

[0066] Lignin (purchased from Aladdin Reagent Network, 8068-05-1) was carbonized at 800°C for 4 hours to obtain a hard carbon matrix.

[0067] Preparation of Sb, Na ion functionalized carbon quantum dots:

[0068] Sb-1, 5 g of caffeic acid was melt-decomposed at 180 °C and kept warm for 50 min to obtain carbon quantum dots;

[0069] Sb-2, place the above carbon quantum dots in 50mL Na + The mixture was immersed in a 3 mol / L sodium bicarbonate solution and stirred at room temperature for 3 h to obtain a solution containing sodium ion functionalized carbon quantum dots.

[0070] Sc, Preparation of high first-efficiency hard carbon materials:

[0071] 5 g of hard carbon matrix was placed in the above solution containing sodium ion functionalized carbon quantum dots, reacted at 130° C. for 45 min, cooled to room temperature, solid-liquid separation was performed, and the solid was washed and dried to obtain a high-efficiency hard carbon material.

[0072] It should be noted that the present invention does not limit the order of Sa and Sb.

[0073] Example 4

[0074] This embodiment provides a high first-effect hard carbon material, which is composed of a hard carbon matrix and sodium ion functionalized carbon quantum dots in a mass ratio of 1:2, wherein the sodium ion functionalized carbon quantum dots are coated on the surface of the hard carbon matrix.

[0075] The method for preparing the high initial efficiency hard carbon material comprises the following steps:

[0076] Sa, Preparation of hard carbon matrix:

[0077] The phenolic resin was carbonized at 900°C and kept warm for 3 hours to obtain a hard carbon matrix.

[0078] Preparation of Sb, Na ion functionalized carbon quantum dots:

[0079] Sb-1, 7 g of benzoic acid was melt-decomposed at 200 °C and kept warm for 30 min to obtain carbon quantum dots;

[0080] Sb-2, place the above carbon quantum dots in 30mL Na + The mixture was immersed in a sodium carbonate solution with a concentration of 4 mol / L and stirred at room temperature for 2 hours to obtain a solution containing sodium ion functionalized carbon quantum dots.

[0081] Sc, Preparation of high first-efficiency hard carbon materials:

[0082] 3.5 g of hard carbon matrix was placed in the solution containing sodium ion functionalized carbon quantum dots, reacted at 150° C. for 30 min, cooled to room temperature, solid-liquid separation was performed, and the solid was washed and dried to obtain a high-efficiency hard carbon material.

[0083] It should be noted that the present invention does not limit the order of Sa and Sb.

[0084] Example 5

[0085] This embodiment provides a high first-efficiency hard carbon material, whose composition and preparation method are similar to those of embodiment 1, except that in Sb-1, malic acid is replaced with alginic acid of the same mass. The remaining conditions are the same as those of embodiment 1 and will not be described in detail.

[0086] Example 6

[0087] This embodiment provides a high first-efficiency hard carbon material, whose composition and preparation method are similar to those of embodiment 2, except that in Sb-1, mucic acid is replaced with citric acid of the same mass. The remaining conditions are the same as those of embodiment 2 and will not be described in detail.

[0088] Example 7

[0089] This embodiment provides a method for preparing a high first-efficiency hard carbon material, which is similar to the embodiment 1, except that the temperature of the melting decomposition in Sb-1 is replaced with 220° C. The other conditions are the same as those in the embodiment 1 and will not be described in detail.

[0090] Example 8

[0091] This embodiment provides a method for preparing a high first-efficiency hard carbon material, which is similar to the embodiment 2, except that: in Sb-2, Na + The concentration was changed to 2 mol / L. The other conditions were the same as those in Example 2 and will not be described in detail.

[0092] Example 9

[0093] This embodiment provides a method for preparing a high first-efficiency hard carbon material, which is similar to the embodiment 3, except that in Sc, the reaction temperature is replaced with 170° C. The remaining conditions are the same as those in the embodiment 1 and will not be described in detail.

[0094] Comparative Example 1

[0095] This comparative example provides a hard carbon material, which is composed of a hard carbon matrix and carbon quantum dots in a mass ratio of 1:2, wherein the carbon quantum dots are coated on the surface of the hard carbon matrix.

[0096] The preparation method of the hard carbon material is similar to that of Example 1, and specifically comprises the following steps:

[0097] Sa, Preparation of hard carbon matrix:

[0098] Same as Example 1, no further details will be given.

[0099] Preparation of Sb, carbon quantum dots:

[0100] Sb-1, same as in Example 1, no further description is given;

[0101] Sb-2, put the above carbon quantum dots in 42 mL of ethanol, immerse and stir for 2.5 h at room temperature to obtain a solution containing carbon quantum dots.

[0102] Sc, Preparation of high first-efficiency hard carbon materials:

[0103] 4 g of hard carbon matrix was placed in the above solution containing carbon quantum dots, reacted at 140° C. for 40 min, cooled to room temperature, solid-liquid separation was performed, and the solid was washed and dried to obtain a hard carbon material.

[0104] Application Example 1

[0105] This application example provides a sodium ion half-cell, and the preparation method thereof comprises the following steps:

[0106] Sd, the high first-effect hard carbon material of Example 1, the binder sodium alginate and water are ground and mixed, the mass ratio of the high first-effect hard carbon material to the sodium alginate is 95:5, and a mixed slurry with a solid content of 90% is obtained (no conductive agent needs to be added).

[0107] Se, the mixed slurry is coated on the surface of the copper foil, and the coating amount is 3.5g / cm 3 After vacuum drying at 80°C for 12 h, the resulting product was cut into small discs of Φ12 mm to obtain the negative electrode sheet.

[0108] Sf, using sodium metal sheet as the counter electrode and glass fiber as the diaphragm, with 1 mol / L NaPF 6 EC / DEC is used as the electrolyte, and the negative electrode sheets are assembled into batteries to obtain sodium ion half-cells.

[0109] Application Examples 2~9

[0110] This application example provides a sodium ion half-cell, and its preparation method is similar to that of application example 1, except that in Sd, the high first efficiency hard carbon material of embodiment 1 is replaced by high first efficiency hard carbon materials of embodiments 2 to 9 of equal mass. The remaining conditions are the same as those of application example 1 and will not be described in detail.

[0111] Application Comparative Example 1

[0112] This comparative application example provides a sodium ion half-cell, and its preparation method is similar to that of application example 1, except that in Sd, the high first efficiency hard carbon material of embodiment 1 is replaced by the hard carbon material of comparative example 1 of equal mass. The remaining conditions are the same as those of application example 1 and will not be described in detail.

[0113] Application Comparative Example 2

[0114] This comparative application example provides a sodium ion half-cell, and its preparation method is similar to that of application example 1, except that in Sd, the high first efficiency hard carbon material of embodiment 1 is replaced with a hard carbon matrix of equal mass prepared by the preparation method of embodiment 1. The remaining conditions are the same as those of application example 1 and will not be described in detail.

[0115] Application Comparative Example 3

[0116] This comparative application example provides a sodium ion half-cell, and its preparation method is similar to that of application example 1, except that in Sd, the high first efficiency hard carbon material of embodiment 1 is replaced by a hard carbon matrix of equal mass prepared by the preparation method of embodiment 2. The remaining conditions are the same as those of application example 1 and will not be described in detail.

[0117] Verification test

[0118] X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM) and N 2 The adsorption / desorption curves respectively test the percentage content, interlayer distance and specific surface area of ​​-COOH in the hard carbon substrates of Examples 1 to 2, the high first-efficiency hard carbon materials of Examples 1 to 9 and the hard carbon material of Comparative Example 1. The test results are shown in Table 1.

[0119] Table 1 Physical and chemical properties test results of hard carbon materials or hard carbon matrix

[0120]

[0121] The sodium ion half-cells of Application Examples 1 to 9 and Comparative Examples 1 to 3 were placed on a Land CT2001A battery testing system for electrochemical performance testing. The test temperature was 25°C, the test electrochemical window was 0V to 2.5V, and the test current density was 30mA / g, that is, the corresponding charge and discharge tests were carried out under constant current conditions. The starting voltage of charging was 0V and the ending voltage was 2.5V, and the starting voltage of discharging was 2.5V and the ending voltage was 0V. The test results are shown in Table 2.

[0122] Table 2 Electrochemical performance test results of sodium ion half-cell

[0123]

[0124] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modification, equivalent substitution or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A high initial efficiency hard carbon material, characterized in that: It comprises a hard carbon matrix and sodium ion functionalized carbon quantum dots coated on the surface of the hard carbon matrix; the mass ratio of the hard carbon matrix to the sodium ion functionalized carbon quantum dots is 1:(1-3); The sodium ion functionalized carbon quantum dots are prepared by melting and decomposing biomass acid and then immersing it in a sodium ion solution; the biomass acid includes at least one of malic acid, mucic acid, caffeic acid or benzoic acid.

2. The high initial efficiency hard carbon material according to claim 1, characterized in that: The sodium ion solution includes at least one of a sodium hydroxide solution, a sodium bicarbonate solution, a sodium carbonate solution or a sodium chloride solution; The concentration of the sodium ion solution is 3 mol / L to 4 mol / L; The mass volume ratio of the biomass acid and the sodium ion solution is (5-9) g: (30-50) mL.

3. The high initial efficiency hard carbon material according to claim 1, characterized in that: The hard carbon matrix is ​​prepared by carbonizing a high molecular polymer.

4. The high initial efficiency hard carbon material according to claim 3, characterized in that: The high molecular polymer includes at least one of phenolic resin, polyvinylidene fluoride or lignin; The carbonization temperature is 800° C. to 900° C., and the carbonization time is 3 h to 4 h.

5. The method for preparing a high initial efficiency hard carbon material according to any one of claims 1 to 4, characterized in that: The following steps are involved: S1, melting and decomposing the biomass acid at 180°C to 200°C to obtain carbon quantum dots; S2, immersing the carbon quantum dots in a sodium ion solution to obtain a solution containing sodium ion functionalized carbon quantum dots; S3, placing the hard carbon matrix into the solution containing the sodium ion functionalized carbon quantum dots, reacting at 130° C. to 150° C. to obtain a high initial efficiency hard carbon material.

6. The method for preparing a high initial efficiency hard carbon material according to claim 5, characterized in that: In S1, the melting and decomposition time is 30min to 50min; In S2, the immersion temperature is 5°C to 40°C, and the immersion time is 2h to 3h; In S3, the mass volume ratio of the hard carbon matrix to the solution containing sodium ion functionalized carbon quantum dots is (3-5) g: (30-50) mL; In S3, the reaction time is 30 min to 45 min.

7. Use of the high initial efficiency hard carbon material according to any one of claims 1 to 4 or the high initial efficiency hard carbon material prepared by the preparation method of the high initial efficiency hard carbon material according to any one of claims 5 to 6 in sodium ion batteries.

8. A sodium ion battery negative electrode material, characterized in that: The invention comprises the high initial efficiency hard carbon material as described in any one of claims 1 to 4 or the high initial efficiency hard carbon material prepared by the preparation method of the high initial efficiency hard carbon material as described in any one of claims 5 to 6.

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