Preparation method of sodium-ion battery hard carbon negative electrode material with wide carbon interlayer spacing

Abstract

The invention discloses a preparation method of a sodium-ion battery hard carbon negative electrode material with a wide carbon interlayer spacing. Comprising the following steps: S1, raw material pretreatment: crushing and sieving a carbon source to obtain a refined carbon source raw material; s2, mixing treatment: uniformly mixing the refined carbon source raw material with a layering agent to obtain a mixed carbon source; s3, pre-carbonization: performing low-temperature pyrolysis on the mixed carbon source in a protective atmosphere to obtain a pre-carbonized material; s4, crushing and refining: crushing the pre-carbonized material to obtain a refined pre-carbonized material; s5, coating treatment: uniformly mixing the refined pre-carbonized material with a coating agent to obtain a surface-coated pre-carbonized material; and S6, high-temperature heat treatment: carrying out high-temperature heat treatment on the surface-coated pre-carbonized material in a protective atmosphere to obtain the final hard carbon negative electrode material. The preparation method of the sodium-ion battery hard carbon negative electrode material with the wide carbon interlayer spacing has the characteristics of excellent rate capability, high cycling stability and good safety.

Description

TECHNICAL FIELD

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

[0002] In the technical field of sodium ion batteries, hard carbon materials are considered as one of the most promising negative electrode materials due to their abundant sodium storage sites, high specific capacity and excellent structural stability.

[0003] However, there are still key technical bottlenecks in the actual industrial application of the material: the potential curve of the material has obvious slope and platform regions, and the working potential of the platform region is relatively low (<0.1 V vs. Na + ), and the low discharge platform means that the working potential of the full battery at the end of charging (i.e. during the sodium ion insertion process) is close to the deposition potential of sodium metal, so the actual potential of the negative electrode surface is easily negatively shifted and crosses the thermodynamic critical point, thereby causing the irreversible deposition of sodium metal. The deposition of sodium on the surface of the pole piece not only consumes active sodium, but also affects the cycle life, and when the sodium is severely deposited, sodium dendrites may be formed, which may pierce the separator and cause internal short circuit of the battery cell, thereby burying serious safety hazards.

[0004] In the prior art, there are methods for improving the kinetic performance of hard carbon materials by material modification, such as surface coating and element doping, but these methods often only focus on improving the electronic conductivity of the hard carbon material, and pay less attention to the impedance of sodium ion diffusion in the hard carbon material, and the improvement of the overall electrochemical performance is still limited, and it is difficult to fundamentally solve the problem of polarization and sodium deposition under large current. SUMMARY

[0005] The purpose of the present application is to provide a preparation method of a hard carbon negative electrode material of a sodium ion battery with wide carbon layer spacing, which has excellent rate performance, high cycle stability and good safety.

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

[0007] The preparation method of the hard carbon negative electrode material of the sodium ion battery with wide carbon layer spacing comprises the following steps:

[0008] S1, raw material pretreatment: crushing and sieving the carbon source to obtain a refined carbon source raw material;

[0009] S2, mixing treatment: uniformly mixing the refined carbon source raw material and the layer-expanding agent to obtain a mixed carbon source;

[0010] S3, pre-carbonization: pyrolyzing the mixed carbon source in a protective atmosphere at a low temperature to obtain a pre-carbonized material;

[0011] S4. Crushing and refining: Crushing the pre-carbonized material to obtain refined pre-carbonized material;

[0012] S5. Coating treatment: The refined pre-carbonized material is uniformly mixed with the coating agent to obtain a surface-coated pre-carbonized material;

[0013] S6. High-temperature heat treatment: The surface-coated pre-carbonized material is heat-treated at high temperature in a protective atmosphere to obtain the final hard carbon anode material.

[0014] Further, in step S2, the topcoat agent is a non-alkaline potassium and / or calcium salt, and the electrode potentials of potassium and calcium are lower than those of sodium (E°(Na⁺ / Na) = -2.71V, E°(K⁺ / K) = -2.931V, E°(Ca) = -2.931V, E°(Na⁺ / Na) = -2.71V, E°(Ca) = -2.93 ... 2 (⁺ / Ca) = -2.868V), the oxidizing power of potassium / calcium ions is weaker than that of sodium ions. Therefore, when the negative electrode material is in a sodium-poor state, during charging (sodium intercalation), electrons migrate from the external circuit to the negative electrode and react with sodium ions that migrate from the internal circuit to the negative electrode interface. After being oxidized, sodium ions form a metal-like sodium cluster inside the hard carbon material. Potassium / calcium ions have weak reactivity and do not participate in the reaction, thus maintaining good stability. In addition, potassium and calcium are non-transition metal elements with no catalytic activity, and do not catalyze the irreversible decomposition of the electrolyte at the electrode interface, avoiding any adverse effects on the cell performance after introduction. The amount of this topcoat agent added is 0.5~3wt.% of the amount of carbon source material added. If the amount of topcoat agent added is too small, the support of metal ions inside the hard carbon material will be insufficient, and the carbon layer spacing cannot be fully expanded. If the amount of topcoat agent added is too large, the excessive metal ions will destroy the carbon layer structure and affect the integrity of the carbon layer structure.

[0015] Further, in step S2, the topcoat agent is an organic salt and / or an inorganic salt. The topcoat agent is one or more of the following: CaCl2, Ca(NO3)2, CaBr2, CaSO4, Ca(H2PO4)2, CaCO3, CaHPO4, calcium acetate, calcium formate, calcium oxalate, calcium gluconate, calcium lactate, calcium citrate, calcium ascorbate, KCl, KNO3, K2SO4, KH2PO4, potassium citrate, potassium gluconate, potassium malate, potassium oxalate, and potassium acetate. In this invention, alkaline substances such as Ca(OH)2, KOH2, and K2CO3 are highly corrosive and can activate the carbon material to form micropores and destroy the carbon layer structure during the carbonization process, therefore they cannot be used.

[0016] Further, in step S6, the conditions for high-temperature heat treatment are: a protective atmosphere of nitrogen and / or argon; a heat treatment temperature of 1000-1600℃; and a holding time of 2-6 hours. In this step, the low-temperature pre-carbonized material gradually graphitizes during the high-temperature heat treatment: on the one hand, the degree of defects (single-vacancy defects, double-vacancy defects, etc.) between carbon layers decreases and the lateral dimensions of the carbon layers elongate; on the other hand, the carbon layers gradually stack to form stacked graphite-like microcrystals, and the interlayer spacing gradually narrows. The decrease in the degree of carbon layer defects and the increase in size will significantly improve the electronic conductivity of the hard carbon material and form a complete sodium ion diffusion path; however, the narrowing of the interlayer spacing will hinder the interlayer diffusion of sodium ions, affecting the solid-phase diffusion of sodium ions inside the hard carbon material, leading to severe polarization. In this invention, potassium and / or calcium microcrystals exist inside the pre-carbonized material. During the graphitization process, complete carbon layers gradually form, but the metal microcrystals support the stacked carbon layers, hindering the shrinkage of the carbon layer interlayer spacing and achieving the purpose of widening the carbon layer interlayer spacing. Therefore, this invention utilizes potassium / calcium as a layering agent to effectively widen the interlayer spacing of carbon layers while ensuring the degree of graphitization of the carbon layers. Simultaneously, during the high-temperature heat treatment process, the organic coating layer on the surface of the hard carbon material carbonizes to form a surface-coated carbon layer. This surface carbon coating layer increases the electronic conductivity of the material surface, reduces the specific surface area, and blocks the contact between calcium / magnesium ions in the hard carbon material and the electrolyte, thus inhibiting the occurrence of side reactions on the surface of the hard carbon material.

[0017] Further, in step S3, the pre-carbonization conditions are: a protective atmosphere of nitrogen and / or argon; a pre-carbonization temperature of 350-700℃; and a pre-carbonization time of 2-8 h. After pre-carbonization, the carbon source gradually pyrolyzes into carbon, while the layering agent decomposes at high temperature to form metal nanoclusters, which are distributed within the carbonaceous framework. If the pre-carbonization temperature is too low, the anions of potassium / sodium metal salts cannot be fully decomposed to form metal oxides; if the pre-carbonization temperature is too high, the size of the metal clusters will be too large, damaging the carbon layer structure.

[0018] Further, in step S5, the coating agent is one or more of asphalt, glucose, sucrose, phenolic resin, and epoxy resin, and the amount of coating agent added is 0.1-2.0 wt.% of the amount of pre-carbonized material added. The coating agent is uniformly coated on the surface of the pre-carbonized micron particles by mixing.

[0019] Furthermore, in step S4, the pulverization method is one or more of mechanical milling, air jet milling, honeycomb milling, roller milling, double roller milling, and jaw crushing, and the pulverization is to a D50 of 4-12μm.

[0020] Furthermore, in step S1, the carbon source is one or more of the following: glucose, sucrose, starch, asphalt, anthracite, lignite, bituminous coal, coconut shell, walnut shell, apricot shell, nut shell, sawdust, bamboo powder, coffee shell, straw, wheat straw, and reed, which are organic compounds rich in carbon.

[0021] Furthermore, in step S1, the purpose of crushing and sieving is to reduce the particle size of the carbon source, so as to facilitate the thorough mixing of the subsequent layering agent and the carbon source. The aperture of the sieve is ≤2mm.

[0022] Furthermore, in step S2, the mixing method includes solid-phase mixing and liquid-phase mixing. It is not limited to a specific mixing method. Any mixing method that can achieve uniform mixing of carbon source and topcoat agent can be applied to this invention.

[0023] This invention provides a method for preparing a hard carbon anode material for sodium-ion batteries with a wide carbon interlayer spacing, which has the following beneficial effects:

[0024] First, it offers excellent rate performance. This invention utilizes potassium / calcium salts as a layering agent, effectively widening the interlayer spacing of carbon layers while ensuring the graphitization degree of the carbon layers, thus reducing the diffusion resistance of sodium ions inside the hard carbon material; simultaneously, the surface coating improves the electronic conductivity of the hard carbon material. The simultaneous improvement of ionic and electronic conductivity thus enhances the rate performance of the hard carbon material.

[0025] Secondly, it has high cycle stability. This invention improves the rate performance of hard carbon materials through topcoat agents and surface coating, alleviates sodium precipitation caused by polarization, and thus improves the cycle stability of the battery.

[0026] Third, it has good safety. The negative electrode material prepared by this invention has better kinetics and can slowly desorb sodium, avoiding the formation of sodium dendrites and improving the safety of the battery. Detailed Implementation

[0027] 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.

[0028] The present invention discloses a method for preparing a wide carbon interlayer spacing hard carbon anode material for sodium-ion batteries, comprising the following steps:

[0029] S1. Raw material pretreatment: The carbon source is crushed and sieved to obtain a refined carbon source raw material;

[0030] S2. Mixing process: The refined carbon source material and the topping agent are mixed evenly to obtain a mixed carbon source;

[0031] S3, Pre-carbonization: The mixed carbon source is pyrolyzed at low temperature in a protective atmosphere to obtain pre-carbonized material;

[0032] S4. Crushing and refining: Crushing the pre-carbonized material to obtain refined pre-carbonized material;

[0033] S5. Coating treatment: The refined pre-carbonized material is uniformly mixed with the coating agent to obtain a surface-coated pre-carbonized material;

[0034] S6. High-temperature heat treatment: The surface-coated pre-carbonized material is heat-treated at high temperature in a protective atmosphere to obtain the final hard carbon anode material.

[0035] Further, in step S2, the topping agent is a non-alkaline potassium and / or calcium salt; the amount of the topping agent added is 0.5 to 3 wt.% of the amount of carbon source material added.

[0036] Further, in step S2, the topping agent is an organic salt and / or an inorganic salt, and the topping agent is one or more of the following: CaCl2, Ca(NO3)2, CaBr2, CaSO4, Ca(H2PO4)2, CaCO3, CaHPO4, calcium acetate, calcium formate, calcium oxalate, calcium gluconate, calcium lactate, calcium citrate, calcium ascorbate, KCl, KNO3, K2SO4, KH2PO4, potassium citrate, potassium gluconate, potassium malate, potassium oxalate, and potassium acetate.

[0037] Furthermore, in step S6, the conditions for high-temperature heat treatment are: the protective atmosphere is nitrogen and / or argon; the heat treatment temperature is 1000-1600℃; and the heat treatment time is 2-6h.

[0038] Furthermore, in step S3, the pre-carbonization conditions are: the protective atmosphere is nitrogen and / or argon; the pre-carbonization temperature is 350-700℃; and the pre-carbonization time is 2-8 h.

[0039] Further, in step S5, the coating agent is one or more of asphalt, glucose, sucrose, phenolic resin, and epoxy resin, and the amount of coating agent added is 0.1-2.0 wt.% of the amount of pre-carbonized material added.

[0040] Furthermore, in step S4, the pulverization method is one or more of mechanical milling, air jet milling, honeycomb milling, roller milling, double roller milling, and jaw crushing, and the pulverization is to a D50 of 4-12μm.

[0041] Further, in step S1, the carbon source is one or more of the following: glucose, sucrose, starch, asphalt, anthracite, lignite, bituminous coal, coconut shell, walnut shell, apricot shell, nut shell, sawdust, bamboo powder, coffee shell, straw, wheat straw, and reed.

[0042] Furthermore, in step S1, the aperture of the sieve is ≤2mm.

[0043] Furthermore, in step S2, the mixing method includes solid-phase mixing and liquid-phase mixing.

[0044] Example 1

[0045] This embodiment relates to a hard carbon anode material for sodium-ion batteries with a wide carbon interlayer spacing, and its preparation method includes the following steps:

[0046] S1. Raw material pretreatment: The carbon source is crushed and passed through a sieve with a pore size ≤2mm to obtain a refined carbon source raw material; specifically, the carbon source is glucose or sucrose.

[0047] S2. Mixing treatment: The refined carbon source material and the topping agent are uniformly mixed in a solid phase to obtain a mixed carbon source; specifically, the amount of the topping agent added is 3 wt.% of the amount of carbon source material added, and the topping agent is CaCl2, Ca(NO3)2, potassium malate, potassium oxalate, and potassium acetate;

[0048] S3. Pre-carbonization: The mixed carbon source is pyrolyzed at low temperature in a protective atmosphere to obtain pre-carbonized material; specifically, the pre-carbonization conditions are: the protective atmosphere is nitrogen; the pre-carbonization temperature is 700℃; and the pre-carbonization time is 5 h.

[0049] S4. Crushing and refining: The pre-carbonized material is crushed to obtain a refined pre-carbonized material; specifically, the crushing method is jaw crushing, and the material is crushed to a D50 of 4-12μm.

[0050] S5. Coating Treatment: The refined pre-carbonized material is uniformly mixed with a coating agent to obtain a surface-coated pre-carbonized material; specifically, the coating agent is asphalt, glucose, or sucrose, and the amount of coating agent added is 2.0 wt.% of the amount of pre-carbonized material.

[0051] S6. High-temperature heat treatment: The surface-coated pre-carbonized material is heat-treated at high temperature in a protective atmosphere to obtain the final hard carbon anode material. Specifically, the conditions for high-temperature heat treatment are: nitrogen atmosphere; heat treatment temperature: 1600℃; holding time: 4h.

[0052] Example 2

[0053] This embodiment relates to a hard carbon anode material for sodium-ion batteries with a wide carbon interlayer spacing, and its preparation method includes the following steps:

[0054] S1. Raw material pretreatment: The carbon source is crushed and passed through a sieve with a pore size ≤2mm to obtain a refined carbon source raw material; specifically, the carbon source is bamboo powder, coffee shell, straw, wheat straw, and reed;

[0055] S2. Mixing treatment: The refined carbon source material and the topping agent are uniformly mixed in the liquid phase to obtain a mixed carbon source; specifically, the amount of the topping agent added is 1 wt.% of the amount of carbon source material added, and the topping agent is calcium citrate, calcium ascorbate, KCl, KNO3, K2SO4, KH2PO4, and potassium citrate;

[0056] S3. Pre-carbonization: The mixed carbon source is pyrolyzed at low temperature in a protective atmosphere to obtain pre-carbonized material; specifically, the pre-carbonization conditions are: the protective atmosphere is argon; the pre-carbonization temperature is 550℃; and the pre-carbonization time is 2 h.

[0057] S4. Grinding and refining: Grind the pre-carbonized material to obtain a refined pre-carbonized material; specifically, the grinding method is air jet milling and honeycomb milling, grinding to a D50 of 4-12μm;

[0058] S5. Coating Treatment: The refined pre-carbonized material is uniformly mixed with a coating agent to obtain a surface-coated pre-carbonized material; specifically, the coating agent is phenolic resin or epoxy resin, and the amount of coating agent added is 1 wt.% of the amount of pre-carbonized material.

[0059] S6. High-temperature heat treatment: The surface-coated pre-carbonized material is heat-treated at high temperature in a protective atmosphere to obtain the final hard carbon anode material. Specifically, the conditions for high-temperature heat treatment are: argon as the protective atmosphere; heat treatment temperature of 1300℃; and holding time of 2 hours.

[0060] Example 3

[0061] This embodiment relates to a hard carbon anode material for sodium-ion batteries with a wide carbon interlayer spacing, and its preparation method includes the following steps:

[0062] S1. Raw material pretreatment: The carbon source is crushed and passed through a sieve with a pore size ≤2mm to obtain a refined carbon source raw material; specifically, the carbon source is asphalt, anthracite, lignite, bituminous coal, coconut shell, walnut shell, apricot shell, nut shell, sawdust, and bamboo powder.

[0063] S2. Mixing treatment: The refined carbon source material and the topping agent are uniformly mixed in a solid phase to obtain a mixed carbon source; specifically, the amount of the topping agent added is 0.5 wt.% of the amount of carbon source material added, and the topping agent is Ca(H2PO4)2, CaCO3, CaHPO4, KCl, KNO3, K2SO4, KH2PO4, potassium citrate, potassium gluconate, or potassium malate;

[0064] S3. Pre-carbonization: The mixed carbon source is pyrolyzed at low temperature in a protective atmosphere to obtain pre-carbonized material; specifically, the pre-carbonization conditions are: the protective atmosphere is nitrogen and argon; the pre-carbonization temperature is 350℃; and the pre-carbonization time is 8 h.

[0065] S4. Crushing and refining: The pre-carbonized material is crushed to obtain a refined pre-carbonized material; specifically, the crushing method is honeycomb mill, roller mill, or double roller mill, and the material is crushed to a D50 of 4-12μm.

[0066] S5. Coating Treatment: The refined pre-carbonized material is uniformly mixed with a coating agent to obtain a surface-coated pre-carbonized material; specifically, the coating agent is glucose, sucrose, or phenolic resin, and the amount of coating agent added is 0.3 wt.% of the amount of pre-carbonized material.

[0067] S6. High-temperature heat treatment: The surface-coated pre-carbonized material is heat-treated at high temperature in a protective atmosphere to obtain the final hard carbon anode material. Specifically, the conditions for high-temperature heat treatment are: the protective atmosphere is nitrogen and argon; the heat treatment temperature is 1000℃; and the holding time is 6 hours.

[0068] Example 4

[0069] This embodiment relates to a hard carbon anode material for sodium-ion batteries with a wide carbon interlayer spacing, and its preparation method includes the following steps:

[0070] S1. Raw material pretreatment: The carbon source is crushed and passed through a sieve with a pore size ≤2mm to obtain a refined carbon source raw material; specifically, the carbon source is glucose, sucrose, starch, asphalt, apricot shell, nut shell, sawdust, bamboo powder, and coffee shell.

[0071] S2. Mixing treatment: The refined carbon source material and the topping agent are uniformly mixed in a solid phase to obtain a mixed carbon source; specifically, the amount of the topping agent added is 0.5~3 wt.% of the amount of carbon source material added, and the topping agent is CaCl2, Ca(H2PO4)2, CaCO3, calcium gluconate, calcium lactate, calcium citrate, potassium citrate, potassium gluconate, potassium malate, potassium oxalate, or potassium acetate;

[0072] S3. Pre-carbonization: The mixed carbon source is pyrolyzed at low temperature in a protective atmosphere to obtain pre-carbonized material; specifically, the pre-carbonization conditions are: the protective atmosphere is nitrogen and argon; the pre-carbonization temperature is 600℃; and the pre-carbonization time is 5 h.

[0073] S4. Crushing and refining: The pre-carbonized material is crushed to obtain a refined pre-carbonized material; specifically, the crushing method is roller milling or double roller milling, and the material is crushed to a D50 of 4-12μm;

[0074] S5. Coating Treatment: The refined pre-carbonized material is uniformly mixed with a coating agent to obtain a surface-coated pre-carbonized material; specifically, the coating agent is asphalt, sucrose, or epoxy resin, and the amount of coating agent added is 1.5 wt.% of the amount of pre-carbonized material.

[0075] S6. High-temperature heat treatment: The surface-coated pre-carbonized material is heat-treated at high temperature in a protective atmosphere to obtain the final hard carbon anode material. Specifically, the conditions for high-temperature heat treatment are: the protective atmosphere is nitrogen and argon; the heat treatment temperature is 1200℃; and the holding time is 3 hours.

[0076] Example 5

[0077] This embodiment relates to a hard carbon anode material for sodium-ion batteries with a wide carbon interlayer spacing, and its preparation method includes the following steps:

[0078] S1. Raw material pretreatment: The carbon source is crushed and passed through a sieve with a pore size ≤2mm to obtain a refined carbon source raw material; specifically, the carbon source is glucose, sucrose, starch, asphalt, anthracite, lignite, bituminous coal, coconut shell, walnut shell, apricot shell, nut shell, sawdust, bamboo powder, and coffee shell.

[0079] S2. Mixing treatment: The refined carbon source material and the topping agent are uniformly mixed in the liquid phase to obtain a mixed carbon source; specifically, the amount of the topping agent added is 1 wt.% of the amount of carbon source material added, and the topping agent is calcium acetate, calcium formate, calcium oxalate, calcium gluconate, calcium lactate, calcium citrate, calcium ascorbate, potassium gluconate, potassium malate, potassium oxalate, or potassium acetate;

[0080] S3. Pre-carbonization: The mixed carbon source is pyrolyzed at low temperature in a protective atmosphere to obtain pre-carbonized material; specifically, the pre-carbonization conditions are: the protective atmosphere is nitrogen and argon; the pre-carbonization temperature is 400℃; and the pre-carbonization time is 7 h.

[0081] S4. Crushing and refining: The pre-carbonized material is crushed to obtain a refined pre-carbonized material; specifically, the crushing method is air jet milling, and the material is crushed to a D50 of 4-12μm;

[0082] S5. Coating Treatment: The refined pre-carbonized material is uniformly mixed with a coating agent to obtain a surface-coated pre-carbonized material; specifically, the coating agent is sucrose or epoxy resin, and the amount of coating agent added is 1 wt.% of the amount of pre-carbonized material.

[0083] S6. High-temperature heat treatment: The surface-coated pre-carbonized material is heat-treated at high temperature in a protective atmosphere to obtain the final hard carbon anode material. Specifically, the conditions for high-temperature heat treatment are: the protective atmosphere is nitrogen and argon; the heat treatment temperature is 1400℃; and the holding time is 3 hours.

[0084] Application Example 1

[0085] This embodiment relates to a hard carbon anode material for sodium-ion batteries with a wide carbon interlayer spacing, and its preparation method includes the following steps:

[0086] S1. Raw material pretreatment: Crush the coconut shells and sieve them to obtain coconut shell powder raw material with a particle size ≤2mm.

[0087] S2. Mixing Treatment: Coconut shell powder and potassium gluconate are evenly dispersed in water, and then dried to obtain a mixed carbon source. The amount of potassium gluconate added is 1.2 wt.% of the coconut shell powder.

[0088] S3. Pre-carbonization: The mixed carbon source obtained in step S2 is pyrolyzed at 600℃ for 3 hours in a nitrogen atmosphere to obtain pre-carbonized material.

[0089] S4. Pulverization: The pre-carbonized material obtained in step S3 is pulverized by airflow to a D50 of 7μm.

[0090] S5. Coating Treatment: The pre-carbonized material with a D50 of 7 μm obtained in step S4 is uniformly mixed with asphalt to obtain a pre-carbonized material with an asphalt coating. The amount of asphalt added is 1.5 wt.% of the total amount of pre-carbonized material.

[0091] S6. High-temperature heat treatment: The surface-coated pre-carbonized material obtained in step S5 is treated at 1200°C for 4 hours in a nitrogen atmosphere to obtain the hard carbon anode material of Application Example 1.

[0092] Application Example 2 (Coconut Shell + CaCl2)

[0093] This embodiment relates to a hard carbon anode material for sodium-ion batteries with a wide carbon interlayer spacing, and its preparation method includes the following steps:

[0094] S1. Raw material pretreatment: Crush the coconut shells and sieve them to obtain coconut shell powder raw material with a particle size ≤2mm.

[0095] S2. Mixing Treatment: Coconut shell powder and CaCl2 are uniformly dispersed in water, then dried to obtain a mixed carbon source. The amount of CaCl2 added is 0.8 wt.% of the coconut shell powder.

[0096] S3. Pre-carbonization: The mixed carbon source obtained in step S2 is pyrolyzed at 650°C for 3 hours in a nitrogen atmosphere to obtain pre-carbonized material.

[0097] S4. Pulverization: The pre-carbonized material obtained in step S3 is pulverized by airflow to a D50 of 7μm.

[0098] S5. Coating Treatment: The pre-carbonized material with a D50 of 7 μm obtained in step S4 is uniformly mixed with asphalt to obtain a pre-carbonized material with an asphalt coating. The amount of asphalt added is 1.5 wt.% of the total amount of pre-carbonized material.

[0099] S6. High-temperature heat treatment: The surface-coated pre-carbonized material obtained in step S5 is treated at 1200°C for 4 hours in a nitrogen atmosphere to obtain the hard carbon anode material of Application Example 2.

[0100] Comparative Example 1

[0101] This embodiment relates to a hard carbon anode material for sodium-ion batteries, and its preparation method includes the following steps:

[0102] S1. Raw material pretreatment: Crush the coconut shells and sieve them to obtain coconut shell powder raw material with a particle size ≤2mm.

[0103] S2. Mixing treatment: Disperse coconut shell powder in water and then dry it to obtain dried coconut shell powder carbon source.

[0104] S3. Pre-carbonization: The coconut shell powder carbon source obtained in step S2 is pyrolyzed at 600℃ for 3 hours in a nitrogen atmosphere to obtain pre-carbonized material.

[0105] S4. Pulverization: The pre-carbonized material obtained in step S3 is pulverized by airflow to a D50 of 7μm.

[0106] S5. Coating Treatment: The pre-carbonized material with a D50 of 7 μm obtained in step S4 is uniformly mixed with asphalt to obtain a pre-carbonized material with an asphalt coating. The amount of asphalt added is 1.5 wt.% of the total amount of pre-carbonized material.

[0107] S6. High-temperature heat treatment: The surface-coated pre-carbonized material obtained in step S5 is treated at 1200℃ for 4 hours in a nitrogen atmosphere to obtain the hard carbon anode material of Comparative Example 1.

[0108] Comparative Example 2

[0109] This embodiment relates to a hard carbon anode material for sodium-ion batteries, and its preparation method includes the following steps:

[0110] S1. Raw material pretreatment: Crush the coconut shells and sieve them to obtain coconut shell powder raw material with a particle size ≤2mm.

[0111] S2. Mixing Treatment: Coconut shell powder and potassium gluconate are evenly dispersed in water, and then dried to obtain a mixed carbon source. The amount of potassium gluconate added is 1.2 wt.% of the coconut shell powder.

[0112] S3. Pre-carbonization: The mixed carbon source obtained in step S2 is pyrolyzed at 600℃ for 3 hours in a nitrogen atmosphere to obtain pre-carbonized material.

[0113] S4. Pulverization: The pre-carbonized material obtained in step S3 is pulverized by airflow to a D50 of 7μm.

[0114] S5. High-temperature heat treatment: The pre-carbonized material obtained in step S4 is treated at 1200℃ for 4 hours in a nitrogen atmosphere to obtain the hard carbon anode material of Comparative Example 2.

[0115] To effectively verify the technical effects of the present invention, the following tests were conducted:

[0116] The reversible capacities in the first week of application example 1, application example 2, comparative example 1 and comparative example 2 were 302, 298, 294 and 286 mAh / g, respectively, and the ICE were 93.2%, 92.8%, 93.0% and 90.4%, respectively. This indicates that the introduction of potassium salt or calcium salt will not have an adverse effect on the capacity and ICE of the hard carbon material.

[0117] The XRD test results showed that the average carbon interlayer spacing of Application Example 1, Application Example 2, Comparative Example 1 and Comparative Example 2 were 3.92, 3.98, 3.79 and 3.82 nm, respectively, indicating that the layering agent can effectively broaden the carbon interlayer spacing.

[0118] The Raman test results were fitted to Application Example 1, Application Example 2, Comparative Example 1, and Comparative Example 2. D / I G The disorder values ​​were 1.83, 1.85, 1.84 and 1.80, respectively. The similar disorder values ​​indicate that the introduction of potassium / sodium microcrystals will not destroy the carbon layer structure or affect the integrity of the carbon layer.

[0119] The electronic conductivity of the powder was measured to be 24, 30, 26 and 3.3 S / cm under 10 MPa pressure in Application Example 1, Application Example 2, Comparative Example 1 and Comparative Example 2, respectively, indicating that surface coating can significantly improve the electronic conductivity of hard carbon materials.

[0120] Rate performance tests showed that the capacity retention rates of Example 1, Application Example 2, Comparative Example 1, and Comparative Example 2 at 5C were 87.6%, 82.0%, 72.1%, and 75.4%, respectively, indicating that the synergistic effect of the topcoat agent and the surface coating layer can effectively improve the rate performance of hard carbon materials.

[0121] Cyclic performance tests showed that the capacity retention rates of Application Example 1, Application Example 2, Comparative Example 1, and Comparative Example 2 after 100 cycles at a 2C rate were 97.2%, 95.6%, 84.3%, and 85.1%, respectively, indicating that the synergistic effect of the topcoat agent and the surface coating layer can effectively improve the cycling performance of hard carbon materials.

[0122] The above embodiments are merely specific examples of the present invention, and their descriptions are quite specific and detailed, but they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these obvious substitutions all fall within the protection scope of the present invention.

Claims

1. A method for preparing a hard carbon anode material for sodium-ion batteries with a wide carbon interlayer spacing, characterized in that... Includes the following steps: S1. Raw material pretreatment: The carbon source is crushed and sieved to obtain a refined carbon source raw material; S2. Mixing process: The refined carbon source material and the topping agent are mixed evenly to obtain a mixed carbon source; S3, Pre-carbonization: The mixed carbon source is pyrolyzed at low temperature in a protective atmosphere to obtain pre-carbonized material; S4. Crushing and refining: Crushing the pre-carbonized material to obtain refined pre-carbonized material; S5. Coating treatment: The refined pre-carbonized material is uniformly mixed with the coating agent to obtain a surface-coated pre-carbonized material; S6. High-temperature heat treatment: The surface-coated pre-carbonized material is heat-treated at high temperature in a protective atmosphere to obtain the final hard carbon anode material.

2. The method for preparing the wide carbon interlayer spacing sodium-ion battery hard carbon anode material according to claim 1, characterized in that: In step S2, the topping agent is a non-alkaline potassium and / or calcium salt; the amount of the topping agent added is 0.5 to 3 wt.% of the amount of carbon source material added.

3. The method for preparing the wide carbon interlayer spacing sodium-ion battery hard carbon anode material according to claim 1, characterized in that: In step S2, the topping agent is an organic salt and / or an inorganic salt, and the topping agent is one or more of the following: CaCl2, Ca(NO3)2, CaBr2, CaSO4, Ca(H2PO4)2, CaCO3, CaHPO4, calcium acetate, calcium formate, calcium oxalate, calcium gluconate, calcium lactate, calcium citrate, calcium ascorbate, KCl, KNO3, K2SO4, KH2PO4, potassium citrate, potassium gluconate, potassium malate, potassium oxalate, and potassium acetate.

4. The method for preparing the wide carbon interlayer spacing sodium-ion battery hard carbon anode material according to claim 1, characterized in that: In step S6, the conditions for high-temperature heat treatment are: the protective atmosphere is nitrogen and / or argon; the heat treatment temperature is 1000-1600℃; and the heat treatment time is 2-6h.

5. The method for preparing the wide carbon interlayer spacing sodium-ion battery hard carbon anode material according to claim 1, characterized in that: In step S3, the pre-carbonization conditions are: the protective atmosphere is nitrogen and / or argon; the pre-carbonization temperature is 350-700℃; and the pre-carbonization time is 2-8 h.

6. The method for preparing the wide carbon interlayer spacing sodium-ion battery hard carbon anode material according to claim 1, characterized in that: In step S5, the coating agent is one or more of asphalt, glucose, sucrose, phenolic resin, and epoxy resin, and the amount of coating agent added is 0.1-2.0 wt.% of the amount of pre-carbonized material added.

7. The method for preparing the wide carbon interlayer spacing sodium-ion battery hard carbon anode material according to claim 1, characterized in that: In step S4, the pulverization method is one or more of mechanical milling, air jet milling, honeycomb milling, roller milling, double roller milling, and jaw crushing, and the pulverization is to a D50 of 4-12μm.

8. The method for preparing the wide carbon interlayer spacing sodium-ion battery hard carbon anode material according to claim 1, characterized in that: In step S1, the carbon source is one or more of the following: glucose, sucrose, starch, asphalt, anthracite, lignite, bituminous coal, coconut shell, walnut shell, apricot shell, nut shell, sawdust, bamboo powder, coffee shell, straw, wheat straw, and reed.

9. The method for preparing the wide carbon interlayer spacing sodium-ion battery hard carbon anode material according to claim 1, characterized in that: In step S1, the aperture of the sieve is ≤2mm.

10. The method for preparing the wide carbon interlayer spacing sodium-ion battery hard carbon anode material according to claim 1, characterized in that: In step S2, the mixing methods include solid-phase mixing and liquid-phase mixing.