Negative electrode composite materials, their preparation methods, and batteries

Abstract

This invention relates to the field of new energy batteries, specifically to a negative electrode composite material, its preparation method, and a battery. The negative electrode composite material comprises a porous carbon sphere framework and metal carbide nanoparticles; wherein at least a portion of the metal carbide nanoparticles are distributed within the pores of the porous carbon sphere framework; the metal element in the metal carbide nanoparticles includes at least one element from Group VB. The negative electrode composite material of this invention exhibits excellent uniformity and a solid structure, which is beneficial for the bulk density of the electrode material and maintaining the structural integrity of the electrode during repeated charge-discharge cycles, significantly improving the capacity and cycle stability of sodium-ion batteries.

Description

Technical Field

[0001] This invention relates to the field of new energy batteries, specifically to a negative electrode composite material, its preparation method, and a battery. Background Technology

[0002] Sodium-ion batteries are considered the most promising alternative to lithium-ion batteries due to their low cost, abundant natural sodium resources, and similar rocking-chair operating mechanism, enabling large-scale energy storage system applications. Significant progress has been made in the practical application of sodium-ion battery cathodes over the past decade, including polyanionic compounds, layered oxides, and Prussian analogs. On the anode side, various materials, such as carbonaceous materials, alloy metals, and metal chalcogenides, have been extensively explored. However, due to their complex fabrication processes and inherent electrochemical defects, most candidate materials exhibit serious limitations in large-scale applications. Carbonaceous materials are considered the most promising anode materials due to their low cost, ease of fabrication, and good reproducibility. Unlike the successful application of graphite in traditional lithium-ion batteries, the narrow interlayer spacing (0.335 nm) and thermodynamic instability of graphite intercalation compounds hinder sodium ion intercalation. Currently, it is generally accepted that graphite cannot be directly used as an anode material for sodium-ion batteries. Hard carbon consists of interlaced graphite microcrystalline layers, abundant micropores, and defects. It has a relatively large interlayer spacing, can store large amounts of sodium ions, and exhibits a large reversible capacity. Furthermore, due to the ever-increasing demands on batteries, and in order to meet the requirements of full batteries in practical applications, there is an urgent need for hard carbon anodes with high reversible capacity and appropriate low potential plateau capacity. Summary of the Invention

[0003] In view of this, the present invention aims to provide a negative electrode composite material, its preparation method and battery, to solve the problems of insufficient reversible capacity and low potential plateau capacity of hard carbon anodes in the prior art.

[0004] To solve the above-mentioned technical problems, the present invention is implemented as follows:

[0005] The present invention provides a negative electrode composite material, the negative electrode composite material comprising a porous carbon sphere framework and metal carbide nanoparticles; wherein at least a portion of the metal carbide nanoparticles are distributed within the pores of the porous carbon sphere framework;

[0006] The metal elements in the metal carbide nanoparticles include at least one element from Group VB.

[0007] Optionally, the metal carbide nanoparticles are vanadium carbide nanoparticles; optionally, based on the total mass of the negative electrode composite material, the content of the metal carbide nanoparticles is 10-30 wt%, preferably 10-15 wt%; optionally, the particle size of the metal carbide nanoparticles is 10-50 nm, preferably 20-30 nm.

[0008] Optionally, the particle size of the negative electrode composite material is 50–500 nm, preferably 100–200 nm; optionally, the specific surface area of ​​the porous carbon sphere skeleton is 5–10 m². 2 / g, preferably 5-7m 2 / g; Optionally, the pore size of the porous carbon sphere framework is ≤50nm.

[0009] A second aspect of the present invention provides a method for preparing a negative electrode composite material, the method comprising the following steps:

[0010] S1. A first solution is obtained by first mixing the metal source, modifier, and first solvent; a second solution is obtained by second mixing the carbon source precursor and the second solvent; and a third solution is obtained by third mixing the first solution and the second solution.

[0011] S2. The mixture is subjected to hydrothermal carbonization to obtain carbonized material; the carbonized material is centrifuged, washed, and then subjected to a first drying process to obtain a first material;

[0012] S3. The first material and the pore-forming agent solution are mixed and then freeze-dried to obtain the second material; the second material is subjected to a first calcination treatment and a second calcination treatment in an inert atmosphere to obtain the negative electrode composite material.

[0013] The metal element in the metal source includes at least one element from Group VB.

[0014] Optionally, the metal source is a vanadium source; preferably, the vanadium source includes at least one of sodium metavanadate, vanadium pentoxide, vanadium dioxide, vanadium chloride, and vanadium sulfate; and / or, the carbon source precursor includes at least one of xylose, fructose, sucrose, and starch; and / or, the modifier includes at least one of oxalic acid, citric acid, and acetic acid, preferably oxalic acid; and / or, the pore-forming agent in the pore-forming agent solution includes at least one of oxalic acid, salicylic acid, ammonium bioxate, and ammonium bicarbonate, preferably oxalic acid; the solvent used in the pore-forming agent solution is water; and / or, the first solvent is water; and / or, the second solvent is water.

[0015] Optionally, in the first solution, the concentration of the metal element is 0.1–0.2 mol / L, and the concentration of the modifier is 0.2–0.6 mol / L; in the second solution, the concentration of the carbon source precursor, calculated as a monosaccharide, is 0.3–0.5 mol / L; the volume ratio of the first solution to the second solution is (1–2):(1–2); the concentration of the pore-forming agent solution is 0.5–1.5 mol / L; and the mass-volume ratio of the first material to the pore-forming agent solution is 1 g:(20–50) mL.

[0016] Optionally, the hydrothermal carbonization treatment is carried out in a closed, high-pressure environment; and / or, the temperature of the second calcination treatment is higher than the temperature of the first calcination treatment.

[0017] Optionally, in step S1, the conditions for the first mixing treatment include: a temperature of 60–90°C, a time of 5–10 hours, and a rotation speed of 300–500 rpm; the conditions for the second mixing treatment include: a temperature of room temperature, a time of 1–2 hours, and a rotation speed of 300–500 rpm; the conditions for the third mixing treatment include: a temperature of room temperature, a time of 1–2 hours, and a rotation speed of 300–500 rpm; and / or, in step S2, the conditions for the hydrothermal carbonization treatment include: a temperature of 180–200°C. The time is 12-24 hours; the conditions for the first drying treatment include: a temperature of 60-90°C and a time of 6-18 hours; and / or, in step S3, the conditions for the freeze-drying treatment include: a temperature of -60 to -40°C and a time of 24-48 hours; the inert atmosphere includes at least one of nitrogen, argon, and helium; the conditions for the first calcination treatment include: a temperature of 450-550°C and a time of 1-2 hours; the conditions for the second calcination treatment include: a temperature of 1000-1400°C and a time of 1-2 hours.

[0018] Optionally, the preparation method further includes cooling the material obtained from the second calcination treatment, followed by washing and a second drying treatment.

[0019] A third aspect of the present invention provides a battery comprising a negative electrode active material, wherein the negative electrode active material comprises the above-described negative electrode composite material and / or a negative electrode composite material prepared according to the above-described preparation method.

[0020] The beneficial technical effects of the present invention through the above technical solution are as follows:

[0021] (1) The negative electrode composite material of the present invention includes a porous carbon sphere skeleton and metal carbide nanoparticles. The material has excellent uniformity and solid structure, which is beneficial to the bulk density of the electrode material and the maintenance of the structural integrity of the electrode during repeated charge and discharge cycles, and can significantly improve the capacity and cycle stability of sodium-ion batteries.

[0022] (2) The method for preparing the negative electrode composite material of the present invention involves preparing porous carbon spheres modified with metal carbide nanoparticles through hydrothermal carbonization and high-temperature pyrolysis of a carbon source precursor. During the heating and decomposition process, the CO2 decomposed by the modifier can effectively etch amorphous carbon to generate an open-pore structure. During the secondary calcination process, the carbon layer rearranges at high temperature and transforms into a closed-pore structure, effectively improving the sodium storage platform capacity. At the same time, the porous carbon spheres modified with metal carbide nanoparticles have sufficient pseudo-graphite domains, which can significantly improve the low-voltage platform capacity of sodium-ion batteries. The negative electrode composite material synthesized by this method has a stable interface, forming a tight and thin SEI layer, realizing rapid charge transport kinetics at the electrode / electrolyte interface.

[0023] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0024] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the following detailed description to explain the invention, but do not constitute a limitation thereof.

[0025] Figure 1 The image shown is a SEM image of the negative electrode composite material prepared in Example 1.

[0026] Figure 2 The image shown is an HRTEM image of the negative electrode composite material prepared in Example 1. Detailed Implementation

[0027] This invention discloses a negative electrode composite material, its preparation method, and a battery. Those skilled in the art can refer to the content of this document and appropriately modify the process parameters to achieve the desired result. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included in this invention. The methods and applications of this invention have been described through preferred embodiments. Those skilled in the art can clearly modify or appropriately change and combine the methods and applications described herein without departing from the content, spirit, and scope of this invention to realize and apply the technology of this invention.

[0028] In the description of this invention, the list of items connected by the term "at least one of" or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single element or multiple elements. Item B may contain a single element or multiple elements. Item C may contain a single element or multiple elements.

[0029] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges or individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0030] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0031] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0032] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0033] To address the insufficient reversible capacity and low-potential plateau capacity of existing hard carbon anodes, this invention employs the following technical solution:

[0034] The present invention provides a negative electrode composite material, the negative electrode composite material comprising a porous carbon sphere framework and metal carbide nanoparticles; wherein at least a portion of the metal carbide nanoparticles are distributed within the pores of the porous carbon sphere framework;

[0035] The metal elements in the metal carbide nanoparticles include at least one element from Group VB.

[0036] The negative electrode composite material of the present invention comprises a porous carbon sphere framework and metal carbide nanoparticles. This material has excellent uniformity and solid structure, which is beneficial to the bulk density of the electrode material and maintaining the structural integrity of the electrode during repeated charge-discharge cycles, and can significantly improve the capacity and cycle stability of sodium-ion batteries.

[0037] In a preferred embodiment of the present invention, the metal carbide nanoparticles are vanadium carbide nanoparticles. Vanadium carbide nanoparticles help to increase the content of pseudo-graphite domains in porous carbon spheres, thereby significantly improving the low-voltage plateau capacity of sodium-ion batteries.

[0038] According to the present invention, the content of the metal carbide nanoparticles can be 10-30 wt%, based on the total mass of the negative electrode composite material. In this invention, a suitable content of metal carbide nanoparticles is beneficial for maximizing specific capacity, increasing specific capacity, and simultaneously constructing a stable interface, forming a dense and thin SEI layer, and achieving rapid charge transport dynamics at the electrode / electrolyte interface. Exemplarily, based on the total mass of the negative electrode composite material, the content of the metal carbide nanoparticles can be any value from 10 wt%, 15 wt%, 20 wt%, 25 wt%, and 30 wt%, or any value within the range of any two of the above values. In this invention, if the content of the metal carbide nanoparticles is too high, it may lead to a large volume change in the negative electrode composite material during charge and discharge, and also increase side reactions, affecting long cycle life; if the content of the metal carbide nanoparticles is too low, it may not achieve the effect of increasing specific capacity. Preferably, based on the total mass of the negative electrode composite material, the content of the metal carbide nanoparticles can be 10-15 wt%.

[0039] According to the present invention, the particle size of the metal carbide nanoparticles can be 10–50 nm. In this invention, a suitable particle size of the metal carbide nanoparticles has the effect of mitigating volume changes, shortening ion transport paths, and enhancing the material's cycling performance. Exemplarily, the particle size of the metal carbide nanoparticles can be any value selected from 10 nm, 20 nm, 30 nm, 40 nm, and 50 nm, or any value within the range formed by any two of the above values. In this invention, if the particle size of the metal carbide nanoparticles is too large, it may lead to a prolonged transport path, a decreased ion transport rate, and poorer cycling performance; if the particle size of the metal carbide nanoparticles is too small, it may lead to an increase in side reactions in the negative electrode composite material and a decrease in coulombic efficiency. Preferably, the particle size of the metal carbide nanoparticles can be 20–30 nm.

[0040] According to the present invention, the particle size of the negative electrode composite material is 50–500 nm. In this invention, a suitable particle size of the negative electrode composite material can effectively reduce the ion transport path, accelerate the ion transport rate, and improve cycle performance. Exemplarily, the particle size of the negative electrode composite material can be any value selected from 50 nm, 100 nm, 200 nm, 300 nm, 400 nm, and 500 nm, or any value within the range formed by any two of the above values. In this invention, if the particle size of the negative electrode composite material is too large, it may lead to a prolonged transport path, a decreased ion transport rate, and poorer cycle performance; if the particle size of the negative electrode composite material is too small, it may lead to an increase in side reactions and a decrease in coulombic efficiency. Preferably, the particle size of the negative electrode composite material can be 100–200 nm.

[0041] The porous carbon sphere framework in this invention can provide a continuous conductive framework, while its good mechanical properties can shorten the transmission distance during ion and electron transport. The stable interface helps to form a dense SEI layer, which enables the battery to have good cycle stability and improves the overall electrochemical performance of the electrode.

[0042] According to the present invention, the specific surface area of ​​the porous carbon sphere framework is 5-10 m². 2 / g. For example, the specific surface area of ​​the porous carbon sphere framework can be 5m². 2 / g、6m 2 / g、7m 2 / g、8m 2 / g、9m 2 / g and 10m 2 Any value in / g or any value within the range formed by any two of the above values. In this invention, if the specific surface area of ​​the porous carbon sphere framework is too large, it may lead to an increase in the contact area with the electrolyte, resulting in increased side reactions and a decrease in coulombic efficiency and cycle life; if the specific surface area of ​​the porous carbon sphere framework is too small, it may lead to a smaller contact area with the electrolyte, a reduction in ion pathways, increased material polarization, and a decrease in cycle performance. Preferably, the specific surface area of ​​the porous carbon sphere framework can be 5-7 m² / g. 2 / g.

[0043] In this invention, to avoid contact between the electrolyte and the inner surface of the pores, an SEI is produced. The pore size of the porous carbon sphere framework is ≤50nm. Exemplarily, the pore size of the porous carbon sphere framework can be any value selected from 1nm, 10nm, 20nm, 30nm, 40nm, and 50nm, or any value within a range formed by any two of the above values.

[0044] A second aspect of the present invention provides a method for preparing a negative electrode composite material, the method comprising the following steps:

[0045] S1. A first solution is obtained by first mixing the metal source, modifier, and first solvent; a second solution is obtained by second mixing the carbon source precursor and the second solvent; and a third solution is obtained by third mixing the first solution and the second solution.

[0046] S2. The mixture is subjected to hydrothermal carbonization to obtain carbonized material; the carbonized material is centrifuged, washed, and then subjected to a first drying process to obtain a first material;

[0047] S3. The first material and the pore-forming agent solution are mixed and then freeze-dried to obtain the second material; the second material is subjected to a first calcination treatment and a second calcination treatment in an inert atmosphere to obtain the negative electrode composite material.

[0048] The metal element in the metal source includes at least one element from Group VB.

[0049] The method for preparing the negative electrode composite material of this invention involves hydrothermal carbonization and high-temperature pyrolysis of a carbon source precursor to prepare porous carbon spheres modified with metal carbide nanoparticles. During the heating and decomposition process, the CO2 decomposed from the modifier can effectively etch amorphous carbon to generate an open-pore structure. During the secondary calcination process, the carbon layer rearranges at high temperature, transforming the material into a closed-pore structure, effectively improving the sodium storage plateau capacity. Simultaneously, the porous carbon spheres modified with metal carbide nanoparticles possess sufficient pseudo-graphite domains, which can significantly improve the low-voltage plateau capacity of sodium-ion batteries. The negative electrode composite material synthesized by this method has a stable interface, forming a dense and thin SEI layer, achieving rapid charge transport dynamics at the electrode / electrolyte interface.

[0050] In a preferred embodiment of the present invention, the metal source is a vanadium source; preferably, the vanadium source includes at least one selected from sodium metavanadate, vanadium pentoxide, vanadium dioxide, vanadium chloride, and vanadium sulfate.

[0051] For example, the carbon source precursor includes at least one of xylose, fructose, sucrose, and starch.

[0052] For example, the modifier includes at least one of oxalic acid, citric acid and acetic acid, preferably oxalic acid.

[0053] Exemplarily, the pore-forming agent in the pore-forming agent solution includes at least one of oxalic acid, salicylic acid, ammonium hydrogen oxalate, and ammonium bicarbonate, preferably oxalic acid; the solvent used in the pore-forming agent solution is water. In this invention, the pore-forming agent (e.g., oxalic acid) simultaneously creates pores and generates a closed-cell structure at high temperatures, resulting in high specific capacity. Simultaneously, the metal-oxygen-carbon bond (e.g., VOC bond) material interface structure generates a compact SEI layer, thereby effectively improving the first-cycle coulombic efficiency.

[0054] For example, the first solvent is water.

[0055] For example, the second solvent is water.

[0056] According to the present invention, in the first solution, the concentration of the metal element can be 0.1–0.2 mol / L. Exemplarily, the concentration of the metal element can be any value selected from 0.1 mol / L, 0.12 mol / L, 0.14 mol / L, 0.16 mol / L, 0.18 mol / L, and 0.2 mol / L, or any value within the range formed by any pair of the aforementioned values. In the present invention, the concentration of the modifier can be 0.2–0.6 mol / L. Exemplarily, the concentration of the modifier can be any value selected from 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, and 0.6 mol / L, or any value within the range formed by any pair of the aforementioned values.

[0057] According to the present invention, in the second solution, the concentration of the carbon source precursor, calculated as a monosaccharide, can be 0.3 to 0.5 mol / L. Exemplarily, in the second solution, the concentration of the carbon source precursor, calculated as a monosaccharide, can be any value selected from 0.3 mol / L, 0.35 mol / L, 0.4 mol / L, 0.45 mol / L, and 0.5 mol / L, or any value within the range formed by any pair of the above values.

[0058] According to the present invention, the volume ratio of the first solution and the second solution can be (1-2):(1-2). For example, the volume ratio of the first solution and the second solution can be any value among 1:2, 1:1, and 2:1, or any value within the range of any two of the above values.

[0059] According to the present invention, the concentration of the pore-forming agent solution can be 0.5 to 1.5 mol / L. Exemplarily, the concentration of the pore-forming agent solution can be any value selected from 0.5 mol / L, 0.75 mol / L, 1 mol / L, 1.25 mol / L, and 1.5 mol / L, or any value within the range formed by any pair of the above values.

[0060] According to the present invention, the mass-to-volume ratio of the first material to the pore-forming agent solution can be 1 g:(20-50) mL. Exemplarily, the mass-to-volume ratio of the first material to the pore-forming agent solution can be any value selected from 1 g:20 mL, 1 g:30 mL, 1 g:40 mL, and 1 g:50 mL, or any value within the range formed by any two of the above values.

[0061] According to the present invention, the hydrothermal carbonization treatment is carried out in a closed high-pressure environment. In the present invention, the hydrothermal carbonization treatment can be carried out in an autoclave. For example, the autoclave can be a 100mL polytetrafluoroethylene sealed autoclave.

[0062] In this invention, the temperature of the second calcination treatment is higher than that of the first calcination treatment. In this invention, the second material undergoes two calcination treatments. The first calcination treatment helps form a six-membered carbon ring plane, preparing for the subsequent growth of pseudo-graphite domains; the second calcination treatment helps create pores, enabling the six-membered carbon rings generated in the first calcination to develop into pseudo-graphite domains, thereby improving material properties.

[0063] As an exemplary embodiment of the present invention, in step S1, the conditions for the first mixing treatment may include: a temperature of 60-90°C, a time of 5-10 hours, and a rotation speed of 300-500 rpm; the conditions for the second mixing treatment may include: a temperature of room temperature, a time of 1-2 hours, and a rotation speed of 300-500 rpm; the conditions for the third mixing treatment may include: a temperature of room temperature, a time of 1-2 hours, and a rotation speed of 300-500 rpm.

[0064] As an exemplary embodiment of the present invention, in step S2, the conditions for the hydrothermal carbonization treatment may include: a temperature of 180-200°C and a time of 12-24 hours; the conditions for the first drying treatment may include: a temperature of 60-90°C and a time of 6-18 hours.

[0065] As an exemplary embodiment of the present invention, in step S3, the conditions for the freeze-drying treatment may include: a temperature of -60 to -40°C and a time of 24 to 48 hours; the inert atmosphere may include at least one of nitrogen, argon, and helium; the conditions for the first calcination treatment may include: a temperature of 450 to 550°C and a time of 1 to 2 hours; the conditions for the second calcination treatment may include: a temperature of 1000 to 1400°C and a time of 1 to 2 hours.

[0066] According to the present invention, the preparation method may further include cooling the material obtained from the second calcination treatment, followed by washing and a second drying treatment. The washing solution for the washing treatment may be water, and the conditions for the second drying treatment may include a temperature of 60–90°C and a time of 6–18 hours.

[0067] A third aspect of the present invention provides a battery comprising a negative electrode active material, wherein the negative electrode active material comprises the above-described negative electrode composite material and / or a negative electrode composite material prepared according to the above-described preparation method.

[0068] The present invention will be further described in detail below through examples. All raw materials used in the examples are commercially available.

[0069] Example 1

[0070] (1) Weigh 1.2g of sodium metavanadate and 2.5g of oxalic acid and dissolve them in 50mL of deionized water. Stir magnetically at 80℃ for 8 hours to obtain the first solution. Dissolve 3g of xylose in 50mL of distilled water and stir for 30 minutes to obtain the second solution. Mix the first and second solutions and stir for 2 hours to obtain a mixed solution.

[0071] (2) The mixed solution was placed in a 200 mL polytetrafluoroethylene sealed high-temperature reactor and kept at 180 °C for 12 hours. The black product was separated by centrifugation, and then washed three times by centrifugation / washing / redispersion in water and alcohol, and dried in an oven at 80 °C for 10 hours to obtain the first material.

[0072] (3) Stir 100 mL of 1 M oxalic acid solution and 3 g of the first material for one hour, then freeze in liquid nitrogen for 30 minutes, and then freeze dry for 24 hours to obtain the sponge-like second material.

[0073] (4) Take 3g of the second material and place it in a ceramic boat. Under a nitrogen atmosphere, the heating rate is 5℃ / min, the calcination temperature is 500℃ (high-temperature decomposition of oxalic acid), and the holding time is 2 hours. Then, the temperature is increased to 1300℃ at a heating rate of 5℃ / min for a second calcination (carbon atom rearrangement to form closed pores). Finally, the temperature is cooled to 500℃ at a cooling rate of 5℃, and then naturally cooled to room temperature. The cooled material is washed three times with deionized water and dried to obtain the negative electrode composite material of this embodiment. The SEM image of the negative electrode composite material in this embodiment is shown below. Figure 1 As shown, the HRTEM image is as follows Figure 2 As shown.

[0074] Example 2

[0075] (1) Weigh 1.6g of vanadium chloride and 2.5g of oxalic acid and dissolve them in 50mL of deionized water. Stir magnetically at 80℃ for 8 hours to obtain the first solution. Dissolve 3.15g of fructose in 50mL of distilled water and stir for 30 minutes to obtain the second solution. Mix the first and second solutions and stir for 2 hours to obtain a mixed solution.

[0076] (2) The mixed solution was placed in a 200 mL polytetrafluoroethylene sealed high-temperature reactor and kept at 180 °C for 12 hours. The black product was separated by centrifugation, and then washed three times by centrifugation / washing / redispersion in water and alcohol, and dried in an oven at 80 °C for 10 hours to obtain the first material.

[0077] (3) Stir 100 mL of 1 M oxalic acid solution and 3 g of the first material for one hour, then freeze in liquid nitrogen for 30 minutes, and then freeze dry for 24 hours to obtain the sponge-like second material.

[0078] (4) Take 3g of the second material and place it in a ceramic boat. Under a nitrogen atmosphere, the heating rate is 2℃ / min, the calcination temperature is 500℃ (oxalic acid decomposes at high temperature), and the holding time is 2 hours. Then, the temperature is raised to 1300℃ at a heating rate of 5℃ / min for a second calcination (carbon atoms rearrange to form closed pores). Finally, the temperature is cooled to 500℃ at a cooling rate of 5℃, and then naturally cooled to room temperature. The cooled material is washed three times with deionized water and dried to obtain the negative electrode composite material of this embodiment.

[0079] Example 3

[0080] (1) Weigh 4.1g of vanadium sulfate and 2.5g of oxalic acid and dissolve them in 50mL of deionized water. Stir magnetically at 80℃ for 8 hours to obtain the first solution. Dissolve 3.15g of starch in 50mL of distilled water and stir for 30 minutes to obtain the second solution. Mix the first and second solutions and stir for 2 hours to obtain a mixed solution.

[0081] (2) The mixed solution was placed in a 200 mL polytetrafluoroethylene sealed high-temperature reactor and kept at 180 °C for 12 hours. The black product was separated by centrifugation, and then washed three times by centrifugation / washing / redispersion in water and alcohol, and dried in an oven at 80 °C for 10 hours to obtain the first material.

[0082] (3) After stirring the mixture of 100 mL of 1 M oxalic acid solution and 3 g of the first material for one hour, it was placed in liquid nitrogen and frozen for 30 minutes, and then freeze-dried for 24 hours to obtain the sponge-like second material.

[0083] (4) Take 3g of the second material and place it in a ceramic boat. Under a nitrogen atmosphere, the heating rate is 5℃ / min, the calcination temperature is 500℃ (oxalic acid decomposes at high temperature), and the holding time is 2 hours. Then, the temperature is raised to 1300℃ at a heating rate of 5℃ / min for a second calcination (carbon atoms rearrange to form closed pores). Finally, the temperature is cooled to 500℃ at a cooling rate of 5℃, and then naturally cooled to room temperature. The material is washed three times with deionized water and dried to obtain the negative electrode composite material of this embodiment.

[0084] Example 4

[0085] (1) Weigh 4.1g of vanadium sulfate and 2.5g of oxalic acid and dissolve them in 50mL of deionized water. Stir magnetically at 80℃ for 8 hours to obtain the first solution. Dissolve 3.15g of glucose in 50mL of distilled water and stir for 30 minutes to obtain the second solution. Mix the first and second solutions and stir for 2 hours to obtain a mixed solution.

[0086] (2) The mixed solution was placed in a 200 mL polytetrafluoroethylene sealed high-temperature reactor and kept at 180 °C for 12 hours. The black product was separated by centrifugation, and then washed three times by centrifugation / washing / redispersion in water and alcohol, and dried in an oven at 80 °C for 10 hours to obtain the first material.

[0087] (3) After stirring the mixture of 100 mL of 1 M oxalic acid solution and 3 g of the first material for one hour, it was placed in liquid nitrogen and frozen for 30 minutes, and then freeze-dried for 24 hours to obtain the sponge-like second material.

[0088] (4) Take 3g of the second material and place it in a ceramic boat. Under a nitrogen atmosphere, the heating rate is 2℃ / min, the calcination temperature is 500℃ (oxalic acid decomposes at high temperature), and the holding time is 2 hours. Then, the temperature is raised to 1300℃ at a heating rate of 2℃ / min for a second calcination (carbon atoms rearrange to form closed pores). Finally, the temperature is cooled to 500℃ at a cooling rate of 5℃, and then naturally cooled to room temperature. The material is washed three times with deionized water and dried to obtain the negative electrode composite material of this embodiment.

[0089] Comparative Example 1

[0090] (1) Dissolve 3.15 g of glucose in 50 mL of distilled water and stir for 30 minutes. Place the solution in a 100 mL polytetrafluoroethylene sealed high-temperature reactor and maintain it at 180 °C for 12 hours. The product is separated by centrifugation, washed three times by centrifugation / washing / redispersion in water and alcohol, and dried in an oven at 80 °C for 10 hours to obtain carbon spheres.

[0091] (2) 1.5g of carbon ball material was placed in a ceramic boat and calcined in a nitrogen atmosphere at a temperature of 1300℃, with a heating rate of 5℃ / min. The temperature was held for two hours and then cooled to 500℃ at a cooling rate of 5℃. The material was then naturally cooled to room temperature to obtain the negative electrode composite material of this comparative example.

[0092] Comparative Example 2

[0093] (1) Dissolve 3.15 g of glucose in 50 mL of distilled water and stir for 30 minutes. Place the solution in a 100 mL polytetrafluoroethylene sealed high-temperature reactor and maintain it at 180 °C for 12 hours. The product is separated by centrifugation, and then washed three times by centrifugation / washing / redispersion in water and alcohol, and dried in an oven at 80 °C for 10 hours to obtain the first material.

[0094] (2) After stirring 100 mL of 1 M oxalic acid solution and 3 g of the first material for one hour, the mixture was placed in liquid nitrogen and frozen for 30 minutes, and then freeze-dried for 24 hours to obtain sponge-like material No. 2.

[0095] (3) Take 3g of the second material and place it in a ceramic boat. Calcine it in a nitrogen atmosphere at a temperature of 500°C and a heating rate of 5°C / min. Hold it at the temperature for two hours. Then heat it to 1300°C at a heating rate of 2°C / min for a second calcination (carbon atoms rearrange to form closed pores). Finally, cool it to 500°C at a cooling rate of 5°C and then let it cool naturally to room temperature to obtain the negative electrode composite material of this comparative example.

[0096] Comparative Example 3

[0097] (1) Weigh 4.1g of vanadium sulfate and 2.5g of oxalic acid and dissolve them in 50ml of deionized water. Stir magnetically at 80℃ for 8 hours to obtain the first solution. Dissolve 3.15g of glucose in 50ml of distilled water and stir for 30 minutes to obtain the second solution. Mix the first and second solutions and stir for 2 hours to obtain a mixed solution.

[0098] (2) The mixed solution was placed in a 200 mL polytetrafluoroethylene sealed high-temperature reactor and kept at 180 °C for 12 hours. The black product was separated by centrifugation, and then washed three times by centrifugation / washing / redispersion in water and alcohol, and dried in an oven at 80 °C for 10 hours to obtain the first material.

[0099] (3) Take 3g of the first material and place it in a ceramic boat. Under a nitrogen atmosphere, the heating rate is 2℃ / min. The temperature is raised to 1300℃ at a heating rate of 2℃ / min for calcination. Finally, the temperature is cooled to 500℃ at a cooling rate of 5℃ and then naturally cooled to room temperature. The material is washed three times with deionized water and dried to obtain the negative electrode composite material of this comparative example.

[0100] The negative electrode composite materials prepared in Examples 1-4 and Comparative Examples 1-3 were used as the negative electrode active material, carbon black as the conductive agent, and sodium carboxymethyl cellulose as the binder to prepare a negative electrode slurry. The mixing mass ratio of negative electrode active material: conductive agent: binder = 8:1:1. This negative electrode slurry was coated onto the surface of copper foil to obtain a negative electrode sheet. A sodium metal sheet was used as the counter electrode and a glass fiber membrane as the separator. An electrolyte was prepared by dissolving 1.0 mol / L NaPF6 in diethylene glycol dimethyl ether. The negative electrode sheet, separator, and positive electrode sheet were assembled in that order and immersed in the electrolyte. The cells were then assembled into a CR2032 button cell in an argon glove box.

[0101] The prepared CR2032 button cell was subjected to electrical performance testing using the Land battery testing system. The button cell was subjected to constant current charge-discharge tests at 25°C and current density XC, with a voltage range of 0 to 2V.

[0102] (1) Initial discharge capacity, initial charge capacity, and initial coulombic efficiency (first efficiency) tests:

[0103] The vehicle was discharged to 0V under constant current at a current density of 0.1C, and the discharge capacity at this point was recorded as the initial discharge capacity. Then, it was charged to 2V under constant current at a current density of 0.1C, and the charging capacity at this point was recorded as the initial charging capacity. The initial coulombic efficiency = initial charging capacity / initial discharge capacity * 100%. The specific test results are shown in Table 1.

[0104] Table 1

[0105]

[0106]

[0107] As can be seen from Table 1, the coin cells containing the negative electrode composite materials prepared in Examples 1 to 4 all have high initial discharge capacity (over 500 mAh / g) and initial coulombic efficiency (over 88%), while the coin cells prepared in Comparative Example 1 have an initial discharge capacity of only 261.3 mAh / g and an initial coulombic efficiency of 83.1%.

[0108] (2) Capacity retention (cycle performance) test:

[0109] Discharge to 0V under constant current at a current density of 1C, and record the discharge capacity at this point as the initial discharge capacity; then charge to 2V under constant current at a current density of 1C; repeat the above charge-discharge cycle for 500 cycles, and record the discharge capacity on the 500th cycle. The capacity retention rate = discharge capacity on the 500th cycle / initial discharge capacity * 100%. See Table 2 for specific values.

[0110] Table 2

[0111] Current density (1C) Capacity retention rate (%) Example 1 90.8 Example 2 90.2 Example 3 90.3 Example 4 90.6 Comparative Example 1 82.4 Comparative Example 2 84.7 Comparative Example 3 87.3

[0112] As can be seen from Table 2, after 500 cycles, the coin cells containing the negative electrode composite materials prepared in Examples 1 to 4 all have high capacity retention (greater than 90%), showing excellent cycle stability. However, the coin cells containing the negative electrode composite materials prepared in Comparative Examples 1 to 3 have lower capacity retention, with Comparative Example 1 having only 82.4%, and poor cycle stability.

[0113] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a negative electrode composite material, characterized in that, The preparation method includes the following steps: S1. A first solution is obtained by first mixing the metal source, modifier, and first solvent; a second solution is obtained by second mixing the carbon source precursor and the second solvent; and a third solution is obtained by third mixing the first solution and the second solution. S2. The mixture is subjected to hydrothermal carbonization to obtain carbonized material; the carbonized material is centrifuged, washed, and then subjected to a first drying process to obtain a first material; S3. The first material and the pore-forming agent solution are mixed and then freeze-dried to obtain the second material; the second material is subjected to a first calcination treatment and a second calcination treatment in an inert atmosphere to obtain the negative electrode composite material. The metal source is a vanadium source; the modifier includes at least one of oxalic acid, citric acid, and acetic acid. The conditions for the hydrothermal carbonization treatment include: a temperature of 180~200℃ and a time of 12~24h; The conditions for the first calcination treatment include: a temperature of 450~550℃ and a time of 1~2h; the conditions for the second calcination treatment include: a temperature of 1000~1400℃ and a time of 1~2h. The negative electrode composite material comprises a porous carbon sphere framework and metal carbide nanoparticles; wherein at least a portion of the metal carbide nanoparticles are distributed within the pores of the porous carbon sphere framework; the metal carbide nanoparticles are vanadium carbide nanoparticles.

2. The preparation method according to claim 1, characterized in that, The vanadium source includes at least one of sodium metavanadate, vanadium pentoxide, vanadium dioxide, vanadium chloride, and vanadium sulfate. And / or, the carbon source precursor includes at least one of xylose, fructose, sucrose and starch; And / or, the modifier is oxalic acid; And / or, the pore-forming agent in the pore-forming agent solution includes at least one of oxalic acid, salicylic acid, ammonium hydrogen oxalate, and ammonium bicarbonate; the solvent used in the pore-forming agent solution is water; And / or, the first solvent is water; And / or, the second solvent is water.

3. The preparation method according to claim 2, characterized in that, The pore-forming agent in the pore-forming agent solution is oxalic acid.

4. The preparation method according to claim 1, characterized in that, In the first solution, the concentration of the metal element is 0.1~0.2 mol / L, and the concentration of the modifier is 0.2~0.6 mol / L; In the second solution, the concentration of the carbon source precursor, calculated as a monosaccharide, is 0.3~0.5 mol / L; The volume ratio of the first solution to the second solution is (1~2):(1~2); The concentration of the pore-forming agent solution is 0.5~1.5 mol / L; The mass-to-volume ratio of the first material to the pore-forming agent solution is 1 g: (20~50) mL.

5. The preparation method according to claim 1, characterized in that, The hydrothermal carbonization treatment is carried out in a closed, high-pressure environment; and / or, The temperature of the second calcination treatment is higher than the temperature of the first calcination treatment.

6. The preparation method according to claim 1 or 5, characterized in that, In step S1, the conditions for the first mixing treatment include: a temperature of 60~90℃, a time of 5~10h, and a rotation speed of 300~500rpm; the conditions for the second mixing treatment include: a temperature of room temperature, a time of 1~2h, and a rotation speed of 300~500rpm; the conditions for the third mixing treatment include: a temperature of room temperature, a time of 1~2h, and a rotation speed of 300~500rpm. And / or, In step S2, the conditions for the first drying process include: a temperature of 60~90℃ and a time of 6~18h; And / or, In step S3, the freeze-drying conditions include: a temperature of -60 to -40°C and a time of 24 to 48 hours; the inert atmosphere includes at least one of nitrogen, argon, and helium.

7. The preparation method according to claim 1, characterized in that, The preparation method further includes cooling the material obtained from the second calcination treatment, followed by washing and second drying treatment.

8. A negative electrode composite material, characterized in that, The negative electrode composite material is prepared by the method according to any one of claims 1 to 7; The negative electrode composite material comprises a porous carbon sphere framework and metal carbide nanoparticles; wherein at least a portion of the metal carbide nanoparticles are distributed within the pores of the porous carbon sphere framework. The metal carbide nanoparticles are vanadium carbide nanoparticles.

9. The negative electrode composite material according to claim 8, characterized in that, Based on the total mass of the negative electrode composite material, the content of the metal carbide nanoparticles is 10~30 wt%; The particle size of the metal carbide nanoparticles is 10~50 nm.

10. The negative electrode composite material according to claim 9, characterized in that, Based on the total mass of the negative electrode composite material, the content of the metal carbide nanoparticles is 10~15wt%; The particle size of the metal carbide nanoparticles is 20~30nm.

11. The negative electrode composite material according to claim 8, characterized in that, The particle size of the negative electrode composite material is 50~500nm; The specific surface area of ​​the porous carbon sphere framework is 5~10 m². 2 / g; The pore size of the porous carbon sphere framework is ≤50nm.

12. The negative electrode composite material according to claim 11, characterized in that, The particle size of the negative electrode composite material is 100~200nm; The specific surface area of ​​the porous carbon sphere framework is 5~7m². 2 / g.

13. A battery, characterized in that, The battery includes a negative electrode active material, wherein the negative electrode active material includes a negative electrode composite material prepared by the preparation method according to any one of claims 1 to 7 and / or a negative electrode composite material according to any one of claims 8 to 12.

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