Preparation method of sodium ion battery porous hard carbon negative electrode material

Abstract

The application discloses a preparation method of a porous hard carbon negative material of a sodium ion battery, and comprises the following steps: S1, preparation of a precursor mixture: uniformly mixing a first carbon source and a Dur carbon source to obtain a precursor mixture; S2, pre-carbonization treatment of a porous carbon intermediate: performing pre-carbonization treatment on the precursor mixture obtained in S1 to obtain a porous carbon intermediate; S3, refinement treatment of the porous carbon intermediate: performing crushing refinement on the porous carbon intermediate obtained in S2 to obtain a refined porous carbon intermediate; and S4, high-temperature carbonization of the porous hard carbon negative material: performing high-temperature carbonization on the porous carbon intermediate obtained in S3 to obtain a porous hard carbon negative material; the first carbon source is a multi-aromatic ring carbon source with a pyrolytic residual carbon rate of greater than or equal to 30%, the second carbon source is an organic small molecule carbon source with a pyrolytic residual carbon rate of less than or equal to 20%, and the addition amount of the second carbon source is 1-20 wt% of the first carbon source. The application has the characteristics of a green and environment-friendly process, high sodium storage capacity and small specific surface area.

Description

TECHNICAL FIELD

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

[0002] Compared with lithium ion batteries, sodium ion batteries have the characteristics of low cost, high safety, good rate performance and excellent low-temperature performance, and have great development potential in the field of large-scale energy storage.

[0003] Among sodium ion battery electrode materials, hard carbon has a wider carbon layer spacing (>0.37 nm) and abundant microporous and defect structures than graphite, and is more suitable for sodium ion storage, and is the most ideal negative electrode material.

[0004] Constructing a microporous structure in the hard carbon material is an effective means to improve the sodium storage capacity. Generally, a metal pore-forming agent such as ZnCl, KOH, NaOH, Fe2O3, Zn (NO3)2, FeCl3 and the like is added during preparation for pore-forming treatment. However, the metal pore-forming agent will cause high defect degree and large specific surface area while introducing micropores, and thus exhibit high irreversible capacity and low initial coulombic efficiency, thereby affecting the long cycle performance of the sodium ion battery. In addition, the metal pore-forming agent will also cause the introduction of metal impurities, which need to be removed by acid washing subsequently. During the acid washing process, a large amount of waste gas and waste liquid will be generated, causing environmental pollution problems, and the process is complex and the cost is high. SUMMARY

[0005] The application aims to provide a preparation method of a porous hard carbon negative electrode material of a sodium ion battery, which has the characteristics of green and environmentally friendly process, high sodium storage capacity and small specific surface area.

[0006] The application can be implemented by the following technical solutions:

[0007] The application discloses a preparation method of a porous hard carbon negative electrode material of a sodium ion battery, comprising the following steps:

[0008] S1, preparation of a precursor mixture: uniformly mixing a first carbon source and a second carbon source to obtain a precursor mixture;

[0009] S2, pre-carbonization treatment of the porous carbon intermediate: pre-carbonizing the precursor mixture obtained in S1 to obtain a porous carbon intermediate;

[0010] S3, refinement treatment of the porous carbon intermediate: crushing and refining the porous carbon intermediate obtained in step S2 to obtain a refined porous carbon intermediate;

[0011] S4. High-temperature carbonization of the porous hard carbon negative electrode material: the porous carbon intermediate obtained in step S3 is subjected to high-temperature carbonization to obtain the porous hard carbon negative electrode material.

[0012] Carbon materials are generally obtained by high-temperature heat treatment of organic precursors in an inert gas atmosphere. During pyrolysis, the organic precursors undergo a series of complex chemical reactions to form a thermodynamically more stable carbon network structure. In this process, volatile substances such as H2O, CO, CO2, NH3, CH4, etc. are released along with the volatilization of heteroatoms (H, O, N, S, Cl, etc.). Different types of organic precursors, due to their different molecular structures, have significant differences in the amount of volatile substances and the residual carbon rate during carbonization. Generally speaking, carbon sources with multiple aromatic rings have a higher residual carbon rate, which is beneficial to reducing production costs; however, the amount of volatile substances during carbonization is less, and it is not easy to form a porous structure in the carbon skeleton, resulting in limited sodium storage capacity of the hard carbon prepared. Organic carbon sources with multiple heteroatom functional groups have a higher amount of volatile substances due to the pyrolysis and volatilization of heteroatom functional groups during pyrolysis, but the chemical bonds are easily broken during carbonization, and it is not easy to form a continuous carbon skeleton structure, so it is also not easy to form a porous hard carbon structure. Moreover, the lower residual carbon rate further increases the production cost.

[0013] The first carbon source is a multi-aromatic ring carbon source with a pyrolysis residual carbon rate ≥ 30%, and the second carbon source is an organic carbon source with multiple heteroatom functional groups with a pyrolysis residual carbon rate ≤ 20%.

[0014] The first carbon source is generally a multi-aromatic ring organic polymer material. It has a high content of benzene rings, less volatile substances during pyrolysis, stable and not easily broken chemical bonds, and is easy to form a relatively continuous carbon skeleton structure. The second carbon source is generally selected from organic small molecules or high molecular polymers with multiple heteroatom functional groups, which have a high content of heteroatom functional groups and strong reactivity. During pyrolysis, volatile substances are high. In this process, volatile substances such as H2O, CO, CO2, NH3, CH4, etc. are released along with the volatilization of heteroatoms (H, O, N, S, Cl, etc.), and the gas escape will form pores in the carbon skeleton structure, resulting in a hard carbon material with high porosity.

[0015] Further, the first carbon source is selected from one or more of phenolic resin, epoxy resin, lignin, nut shell, and / or coconut shell.

[0016] Further, the second carbon source is a multi-heteroatom functional group carbon source, and the multi-heteroatom functional group is one or more of -OH, -COOH, Cl, and / or -COOR.

[0017] Further, the second carbon source is selected from one or more of cellulose, glucose, citric acid, urea, polyvinyl alcohol, polyethylene glycol, polymethyl methacrylate, and / or polyvinyl chloride.

[0018] Further, the second carbon source is added in an amount of 1-20 wt% of the first carbon source. In the present application, the amount of the second carbon source added will affect the pore structure of the hard carbon material. Specifically, too high an amount of the second carbon source added will result in too much gas escaping, and the pore size formed in the carbon skeleton structure will be too large, which cannot be effectively closed in the subsequent high-temperature carbonization process, and the larger pore size does not have activity to store sodium ions, resulting in a decrease in the initial coulombic efficiency and sodium storage capacity of the hard carbon material. Too low an amount of the second carbon source added will not form abundant microporous structures in the carbon skeleton structure, failing to achieve the purpose of improving the capacity of the hard carbon.

[0019] Further, in step S1, the mixing is liquid-phase mixing and / or solid-phase mixing. The uniform mixing method is ball milling, sand milling and / or stirring.

[0020] Further, in step S2, the pre-carbonization conditions are: a temperature rising rate of 2-10 ℃ / min, an activation temperature of 400-800 ℃, and an activation time of 0.5-5 h. In the present application, the pre-carbonization temperature will affect the pore structure of the hard carbon material. Specifically, the pre-carbonization temperature should be slightly higher than the decomposition temperature of the second carbon source. If the pre-carbonization temperature is too high, the second carbon source will decompose faster; and if the pre-carbonization temperature is too low, the second carbon source will decompose in the high-temperature carbonization process, also resulting in faster decomposition of the second carbon source, too fast gas escape speed, and failure to form sufficient microporous structures.

[0021] Further, in step S3, the pulverization and refinement method is roller crushing, mechanical grinding and / or air jet milling, and the D50 of the porous carbon intermediate after pulverization and refinement is 4-12 μm, and Dmax≤30 μm.

[0022] Further, in step S4, the high-temperature carbonization conditions are: a temperature rising rate of 0.5-5 ℃ / min, a carbonization temperature of 1000-1600 ℃, and a carbonization time of 1-10 h. In the present application, the above conditions will also affect the pore structure of the hard carbon material. Specifically, reducing the temperature rising rate, increasing the carbonization temperature and increasing the carbonization time will reduce the specific surface area of the hard carbon material. However, too slow a temperature rising rate, too high a carbonization temperature and too long a carbonization time will increase the time cost and reduce the economic benefit, which is not conducive to actual production. In addition, too high a carbonization temperature will result in too narrow an interlayer spacing of the carbon layer in the hard carbon material, which is not conducive to the migration of sodium ions in the hard carbon material, affecting the electrochemical performance of the hard carbon material. Therefore, the performance and cost should be considered to select the optimal preparation conditions.

[0023] The present application has the following beneficial effects:

[0024] First, the process is green and environmentally friendly. This invention does not use metal pore-forming agents, does not introduce additional metal impurities, and does not require subsequent acid washing and impurity removal steps, which can reduce production costs and reduce environmental pollution problems. The process is simple. Based on this, the pore structure of hard carbon materials, such as total pore volume and average pore diameter, can be effectively controlled by changing the type of the second carbon source and carbonization conditions.

[0025] Secondly, it boasts high sodium storage capacity, utilizing carbon-containing organic materials with high char residue (≥30%) as the carbon source. These materials have a high benzene ring content, resulting in low volatile matter release during pyrolysis, relatively stable chemical bonds that are not easily broken, and a more continuous carbon skeleton structure. Low char residue (≤20%) carbon-containing organic materials are used as the organic pore-forming agent. These materials contain numerous heteroatom functional groups, which continuously decompose during pyrolysis, releasing volatile substances such as H2O, CO, CO2, NH3, and CH4. This gas escape creates pores within the carbon skeleton structure, leading to higher porosity in the hard carbon material and thus increasing its sodium storage capacity.

[0026] Third, the material has a small specific surface area. The second carbon source decomposes during the pre-carbonization process, generating a porous structure with a larger specific surface area. In the subsequent high-temperature carbonization process, the high temperature causes the pore walls of the open pores on the material surface to collapse, transforming them into closed pores, resulting in a decrease in specific surface area. This, in turn, reduces the irreversible decomposition of the electrolyte and improves the first-cycle coulombic efficiency of the carbon material. Attached Figure Description

[0027] Figure 1 The first-week charge-discharge curve of Application Example 1;

[0028] Figure 2 The charge-discharge curves for the first week of application Example 2 are shown. Detailed Implementation

[0029] To enable those skilled in the art to better understand the technical solution of the present invention, the product of the present invention will be further described in detail below with reference to embodiments and accompanying drawings.

[0030] This invention discloses a method for preparing a porous hard carbon anode material for sodium-ion batteries, comprising the following steps:

[0031] S1. Preparation of precursor mixture: The first carbon source and the Dürr carbon source are mixed evenly to obtain a precursor mixture;

[0032] S2. Pre-carbonization treatment of porous carbon intermediate: The precursor mixture obtained in S1 is pre-carbonized to obtain porous carbon intermediate;

[0033] S3. Refining treatment of porous carbon intermediate: The porous carbon intermediate obtained in step S2 is pulverized and refined to obtain a refined porous carbon intermediate.

[0034] S4, high-temperature carbonization of the porous hard carbon negative electrode material: the porous carbon intermediate obtained in step S3 is subjected to high-temperature carbonization to obtain the porous hard carbon negative electrode material;

[0035] The first carbon source is a polyaromatic carbon source with a pyrolysis residual carbon rate of 30% or more, the second carbon source is an organic small molecule carbon source with a pyrolysis residual carbon rate of 20% or less, and the addition amount of the second carbon source is 1-20 wt% of the first carbon source.

[0036] Further, the first carbon source is selected from one or more than two of phenolic resin, epoxy resin, lignin, nut shell and / or coconut shell.

[0037] Further, the second carbon source is a multi-heteroatom functional group carbon source, and the multi-heteroatom functional group is one or more than two of -OH, -COOH, Cl and / or -COOR.

[0038] Further, the second carbon source is selected from one or more than two of cellulose, glucose, citric acid, urea, polyvinyl alcohol, polyethylene glycol, polymethyl methacrylate and / or polyvinyl chloride.

[0039] Further, in step S1, the mixing is liquid phase mixing and / or solid phase mixing. The uniform mixing mode is ball milling, sand milling and / or stirring.

[0040] Further, in step S2, the pre-carbonization conditions are: a heating rate of 2-10 ℃ / min, an activation temperature of 400-800 ℃, and an activation time of 0.5-5 h.

[0041] Further, in step S3, the pulverization and refinement mode is roller crushing, mechanical grinding and / or air jet milling, and the D50 of the pulverized and refined porous carbon intermediate is 4-12 μm and Dmax≤30 μm.

[0042] Further, in step S4, the high-temperature carbonization conditions are: a heating rate of 0.5-5 ℃ / min, a carbonization temperature of 1000-1600 ℃, and a carbonization time of 1-10 h.

[0043] Example 1

[0044] The application discloses a preparation method of a porous hard carbon negative electrode material for a sodium ion battery.

[0045] S1, preparation of a precursor mixture: uniformly mixing a first carbon source and a Dur carbon source to obtain a precursor mixture;

[0046] S2, pre-carbonization treatment of a porous carbon intermediate: pre-carbonizing the precursor mixture obtained in S1 to obtain a porous carbon intermediate;

[0047] S3, refinement treatment of the porous carbon intermediate: the porous carbon intermediate obtained in step S2 is crushed and refined to obtain a refined porous carbon intermediate;

[0048] S4, high-temperature carbonization of the porous hard carbon negative electrode material: the porous carbon intermediate obtained in step S3 is subjected to high-temperature carbonization to obtain the porous hard carbon negative electrode material.

[0049] In the present application, the first carbon source is a multi-aromatic ring carbon source with a pyrolytic residual carbon rate of ≥30%, the second carbon source is an organic small molecule carbon source with a pyrolytic residual carbon rate of ≤20%, and the addition amount of the second carbon source is 20wt% of the first carbon source.

[0050] Specifically, the first carbon source is nut shell. The second carbon source is a multi-heteroatom functional group carbon source, the multi-heteroatom functional group is selected from -OH, -COOH, Cl and / or -COOR; and the second carbon source is citric acid.

[0051] In the present application, in step S1, the mixing is solid-phase mixing. The uniform mixing method is sand milling.

[0052] In the present application, in step S2, the pre-carbonization conditions are: a heating rate of 6 ℃ / min, an activation temperature of 400℃, and an activation time of 5 h.

[0053] In the present application, in step S3, the crushing and refining method is roller mechanical milling, and the D50 of the crushed and refined porous carbon intermediate is 4-12 μm, and the Dmax is ≤30 μm.

[0054] In the present application, in step S4, the high-temperature carbonization conditions are: a heating rate of 3 ℃ / min, a carbonization temperature of 1000℃, and a carbonization time of 10 h.

[0055] Example 2

[0056] The present application discloses a preparation method of a porous hard carbon negative electrode material for sodium ion batteries, comprising the following steps:

[0057] S1, preparation of a precursor mixture: uniformly mixing a first carbon source and a Dur carbon source to obtain a precursor mixture;

[0058] S2, pre-carbonization treatment of the porous carbon intermediate: pre-carbonizing the precursor mixture obtained in S1 to obtain a porous carbon intermediate;

[0059] S3, refinement treatment of the porous carbon intermediate: the porous carbon intermediate obtained in step S2 is crushed and refined to obtain a refined porous carbon intermediate;

[0060] S4, high-temperature carbonization of the porous hard carbon negative electrode material: the porous carbon intermediate obtained in step S3 is subjected to high-temperature carbonization to obtain the porous hard carbon negative electrode material.

[0061] In the present application, the first carbon source is a multi-aromatic ring carbon source with a pyrolytic residual carbon rate of 30% or more, and the second carbon source is an organic small molecule carbon source with a pyrolytic residual carbon rate of 20% or less, and the addition amount of the second carbon source is 4% by weight of the first carbon source.

[0062] Specifically, the first carbon source is phenolic resin or epoxy resin. The second carbon source is a multi-heteroatom functional group carbon source, and the multi-heteroatom functional group is one or more of -OH, -COOH, Cl and / or -COOR; the second carbon source is cellulose or glucose.

[0063] In the present application, in step S1, the mixing is liquid phase mixing. The uniform mixing method is ball milling.

[0064] In the present application, in step S2, the pre-carbonization conditions are: a heating rate of 10 ℃ / min, an activation temperature of 600 ℃, and an activation time of 0.5 h.

[0065] In the present application, in step S3, the pulverization and refinement method is roller crushing, and the D50 of the pulverized and refined porous carbon intermediate is 4-12 μm, and Dmax is ≤30 μm.

[0066] In the present application, in step S4, the high-temperature carbonization conditions are: a heating rate of 5 ℃ / min, a carbonization temperature of 1300 ℃, and a carbonization time of 1 h.

[0067] Example 3

[0068] The present application discloses a preparation method of a sodium ion battery porous hard carbon negative electrode material, comprising the following steps:

[0069] S1, preparation of a precursor mixture: uniformly mixing a first carbon source and a Dur carbon source to obtain a precursor mixture;

[0070] S2, pre-carbonization treatment of a porous carbon intermediate: pre-carbonizing the precursor mixture obtained in S1 to obtain a porous carbon intermediate;

[0071] S3, refinement treatment of the porous carbon intermediate: pulverizing and refining the porous carbon intermediate obtained in step S2 to obtain a refined porous carbon intermediate;

[0072] S4, high-temperature carbonization of the porous hard carbon negative electrode material: high-temperature carbonizing the porous carbon intermediate obtained in step S3 to obtain a porous hard carbon negative electrode material.

[0073] In the present application, the first carbon source is a multi-aromatic ring carbon source with a pyrolytic residual carbon rate of 30% or more, and the second carbon source is an organic small molecule carbon source with a pyrolytic residual carbon rate of 20% or less, and the addition amount of the second carbon source is 4% by weight of the first carbon source.

[0074] Specifically, the first carbon source is lignin, nut shell. The second carbon source is a multi-heteroatom functional group carbon source, the multi-heteroatom functional group is -OH, -COOH, Cl and / or -COOR; the second carbon source is polyethylene glycol, polymethyl methacrylate and polyvinyl chloride.

[0075] In the present application, in step S1, the mixing is liquid phase mixing and solid phase mixing. The uniform mixing mode is stirring.

[0076] In the present application, in step S2, the pre-carbonization condition is: the heating rate is 2 ℃ / min, the activation temperature is 800 ℃, and the activation time is 3 h.

[0077] In the present application, in step S3, the pulverization and refinement mode is air jet milling, and the D50 of the pulverized and refined porous carbon intermediate is 4-12 μm, and Dmax≤30 μm.

[0078] In the present application, in step S4, the high-temperature carbonization condition is: the heating rate is 0.5 ℃ / min, the carbonization temperature is 1600 ℃, and the carbonization time is 6 h.

[0079] Example 4

[0080] The application discloses a preparation method of a sodium ion battery porous hard carbon negative electrode material.

[0081] S1, preparation of a precursor mixture: uniformly mixing a first carbon source and a Dur carbon source to obtain a precursor mixture;

[0082] S2, pre-carbonization treatment of a porous carbon intermediate: performing pre-carbonization treatment on the precursor mixture obtained in S1 to obtain a porous carbon intermediate;

[0083] S3, refinement treatment of the porous carbon intermediate: performing pulverization and refinement on the porous carbon intermediate obtained in step S2 to obtain a refined porous carbon intermediate;

[0084] S4, high-temperature carbonization of the porous hard carbon negative electrode material: performing high-temperature carbonization on the porous carbon intermediate obtained in step S3 to obtain a porous hard carbon negative electrode material.

[0085] In the present application, the first carbon source is a multi-aromatic ring carbon source with a pyrolytic residual carbon rate of ≥30%, the second carbon source is an organic small molecule carbon source with a pyrolytic residual carbon rate of ≤20%, and the addition amount of the second carbon source is 10wt% of the first carbon source.

[0086] Specifically, the first carbon source is phenolic resin, epoxy resin, lignin, nut shell and coconut shell. The second carbon source is a multi-heteroatom functional group carbon source, the multi-heteroatom functional group is -OH, -COOH, Cl and / or -COOR; the second carbon source is cellulose, glucose, citric acid, urea, polyvinyl alcohol.

[0087] In the present application, in step S1, the mixing is liquid phase mixing. The uniform mixing method is sand milling and stirring.

[0088] In the present application, in step S2, the pre-carbonization conditions are: a temperature rising rate of 6 ℃ / min, an activation temperature of 600 ℃, and an activation time of 3 h.

[0089] In the present application, in step S3, the pulverization method is mechanical milling and air jet milling, and the D50 of the pulverized porous carbon intermediate is 4-12 μm, and Dmax≤30 μm.

[0090] In the present application, in step S4, the high-temperature carbonization conditions are: a temperature rising rate of 3 ℃ / min, a carbonization temperature of 1300 ℃, and a carbonization time of 6 h.

[0091] Application Example 1

[0092] S1, Preparation of the precursor mixture: uniformly mix the phenolic resin carbon source and the citric acid pore-forming agent by using a ball milling method, wherein the mass of the citric acid is 20% of the mass of the phenolic resin.

[0093] S2, Pre-carbonization treatment of the porous carbon intermediate: place the prepared precursor mixture in a high-temperature furnace, and heat it to 400 o C at a temperature rising rate of 10 o C / min in a nitrogen gas atmosphere, and keep it at this temperature for 1 h to obtain a porous carbon intermediate;

[0094] S3, Refining treatment of the porous carbon intermediate: air jet mill the above carbon intermediate to a D50 of 7 μm and a Dmax≤25 μm.

[0095] S4, High-temperature carbonization of the porous hard carbon negative electrode material: place the refined porous carbon intermediate obtained in step S3 in a high-temperature furnace, and heat it to 1200 o C at a temperature rising rate of 2 o C / min in a nitrogen gas atmosphere, and keep it at this temperature for 3 h to obtain a porous hard carbon material.

[0096] Nitrogen adsorption-desorption test and He gas true density test show that the specific surface area and the true density of the hard carbon material are 5.3 m 2 / g and 1.75 g / cm 3 , respectively, indicating that the material has a large porosity and a small specific surface area.

[0097] The obtained material was subjected to electrochemical performance test according to the following method: the hard carbon material, Super P, CMC, and SBR were mixed into a homogenate at a mass ratio of 94:1.5:2:2.5, then the black slurry was coated on a copper foil using a 120 um four-side preparation device, and then the film was dried in a 100 oC vacuum drying oven for 2 hours. The electrode film was punched into a circular sheet with a radius of 0.6 mm using a sheet puncher, and a CR2016 type button cell was assembled in a glove box using metal sodium as the counter electrode, 1 mol / L NaClO4EC+DEC (1:1 vol%) as the electrolyte, and a PP / PE / PP three-layer separator.

[0098] Figure 1 The first cycle charge-discharge curve of the hard carbon material electrode showed that the reversible specific capacity of the electrode was 368.4 mAh / g, and the first cycle coulombic efficiency was 91.1%, indicating a high sodium storage capacity and first efficiency, which was related to the high internal porosity and low specific surface area of the material.

[0099] Application Example 2

[0100] S1, Preparation of the precursor mixture: the phenolic resin carbon source and the pore-forming agent glucose were uniformly mixed using a ball milling method, wherein the mass of the glucose was 20% of the mass of the phenolic resin.

[0101] S2, pre-carbonization treatment of the porous carbon intermediate: the prepared precursor mixture was placed in a high-temperature furnace and heated to 500 oC at a heating rate of 5 oC / min in a nitrogen gas atmosphere, and held for 1 h to obtain a porous carbon intermediate; o C / min to 500 oC, and held for 1 h to obtain a porous carbon intermediate; o C / min to 500 oC, and held for 1 h to obtain a porous carbon intermediate;

[0102] S3, refinement treatment of the porous carbon intermediate: the above carbon intermediate was pulverized by air flow milling to a D50 of 7 μm and a Dmax≤25 μm.

[0103] S4, high-temperature carbonization of the porous hard carbon negative electrode material: the refined porous carbon intermediate obtained in step S3 was placed in a high-temperature furnace and heated to 1200 oC at a heating rate of 2 oC / min in a nitrogen gas atmosphere, and held for 3 h to obtain a porous hard carbon material.

[0104] Nitrogen adsorption-desorption test and He gas true density test showed that the specific surface area and true density of the hard carbon material were 4.2 m 2 / g and 1.80 g / cm 3 , indicating that the material had a large porosity and a small specific surface area.

[0105] The obtained material was subjected to electrochemical performance test according to the following method: the hard carbon material, Super P, CMC and SBR were mixed into a homogenate at a mass ratio of 94:1.5:2:2.5, then the black slurry was coated on a copper foil using a 120 um four-side preparation device, and then the film was dried in a 100℃ vacuum drying oven for 2 hours. The electrode film was punched into a round sheet with a radius of 0.6mm using a sheet punching machine, a metal sodium was used as a counter electrode, 1mol / L NaClO4 EC+DEC (1:1vol%) was used as an electrolyte, and a PP / PE / PP three-layer separator was used to assemble a CR2016 type button cell in a glove box. The above button cell was subjected to constant current charge and discharge test, the current density was 0.1C (1C=300 mAh / g), and the voltage range was 2-0.005 V.

[0106] Figure 2 The first cycle charge-discharge curve of the hard carbon material electrode was as follows: the reversible specific capacity of the electrode was 345.5 mAh / g, the first cycle coulombic efficiency was 91.4%, and the electrode showed a high sodium storage capacity and first efficiency, which was related to the high internal porosity and low specific surface area of the electrode.

[0107] The above examples are only specific embodiments of the present application, and the description is more specific and detailed, but it cannot be understood as a limitation on the scope of the patent of the present application. It should be noted that for ordinary skilled persons in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, and these obvious alternative forms all belong to the protection scope of the present application.

Claims

1. A method for preparing a porous hard carbon anode material for sodium-ion batteries, characterized in that The method comprises the following steps: S1, preparation of a precursor mixture: uniformly mixing a first carbon source and a second carbon source to obtain a precursor mixture; S2, pre-carbonization treatment of a porous carbon intermediate: performing pre-carbonization treatment on the precursor mixture obtained in S1 to obtain a porous carbon intermediate; the pre-carbonization conditions are: a heating rate of 2-10 ℃ / min, an activation temperature of 400-800 ℃, and an activation time of 0.5-5 h; S3, refinement treatment of the porous carbon intermediate: performing refinement treatment on the porous carbon intermediate obtained in step S2 to obtain a refined porous carbon intermediate; S4, high-temperature carbonization of a porous hard carbon negative electrode material: performing high-temperature carbonization on the porous carbon intermediate obtained in step S3 to obtain a porous hard carbon negative electrode material; the high-temperature carbonization conditions are: a heating rate of 0.5-5 ℃ / min, a carbonization temperature of 1000-1600 ℃, and a carbonization time of 1-10 h; The first carbon source is a multi-aromatic ring carbon source with a pyrolytic residual carbon rate of ≥30%, the second carbon source is an organic small molecule carbon source with a pyrolytic residual carbon rate of ≤20%, and the addition amount of the second carbon source is 1-20 wt% of the first carbon source; the first carbon source is selected from one or two or more of phenolic resin, epoxy resin, lignin, nut shell, and / or coconut shell.

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