Hard carbon negative electrode material and preparation method and application thereof

Abstract

This invention relates to a hard carbon anode material, its preparation method, and its application. The preparation method includes the following steps: S1. Mixing starch and sugars to obtain a precursor powder; the sugars are monosaccharides or disaccharides; S2. Pre-carbonizing the precursor powder under an inert atmosphere for 2-6 hours; S3. Ball milling the pre-carbonized hard carbon precursor to obtain pre-carbonized precursor powder with an average particle size of 5-8 μm; S4. Carbonizing the pre-carbonized precursor powder under an inert atmosphere to obtain the hard carbon anode material. This method adds monosaccharides or disaccharides to starch as a carbon source, utilizing small-molecule monosaccharides or disaccharides to optimize and modify the pore size distribution of the carbon material, shortening the starch stabilization time. The preparation process is simple, time-saving, and energy-efficient. The resulting hard carbon anode material, when paired with a specific battery system, exhibits excellent initial coulombic efficiency, good rate performance, and long cycle performance.

Description

Technical Field

[0001] This invention belongs to the technical field of sodium-ion battery anode materials, specifically relating to a hard carbon anode material, its preparation method, and its application. Background Technology

[0002] In recent years, the development and utilization of renewable and clean energy has been a continuous research hotspot in response to the depletion of traditional fossil fuels and environmental pollution. Lithium-ion batteries, as energy storage devices, are widely used in various fields due to their advantages such as high energy density, high voltage, low self-discharge, and excellent cycle performance. However, the limited reserves, uneven distribution, and high cost of lithium resources will make it difficult to provide sufficient lithium sources for the rapidly developing lithium-ion battery industry, thus limiting its future development. Sodium-ion batteries (SIBs), on the other hand, have a similar working mechanism to lithium-ion batteries. As energy storage devices, they offer high safety and stability, and sodium is abundant, widely available, and inexpensive, making them a promising candidate for future development and application.

[0003] Similar to lithium-ion batteries, the electrochemical performance of sodium-ion batteries also largely depends on the properties of the positive and negative electrode materials. Among the many sodium storage negative electrode materials, biomass-derived hard carbon has become a research hotspot due to its wide availability, green renewable nature, and high economic value. However, biomass materials have complex structures and compositions. During carbonization, different components exhibit different pyrolysis pathways, and each component interacts with reaction intermediates, making the reaction process extremely complex. Therefore, it is difficult to controllably adjust the morphology, specific surface area, pore structure, and other properties of biomass-derived carbon. In contrast, carbohydrate compounds have a single component, containing a large number of functional groups such as hydroxyl, aldehyde, and ketone. They have high chemical activity and strong modifiability, and can be modified and regulated through various reactions to achieve targeted design of the structure of their derived carbon materials. Starch, as a polysaccharide compound, is a good precursor for the preparation of hard carbon materials due to its low price, wide availability, and green renewable nature. However, direct high-temperature sintering of starch can lead to the ineffective removal of moisture and small molecules, resulting in the expansion and fusion of starch granules. To avoid this phenomenon, a long and time-consuming stabilization process is always required when preparing starch-based hard carbon materials.

[0004] Chinese patent CN116768190A discloses a method for preparing a starch-based hard carbon anode material, the anode material itself, and a sodium-ion battery. This patent involves esterifying starch with an esterifying agent, mixing it with pulverized coal, and then pre-carbonizing and high-temperature carbonizing to obtain the hard carbon material. The addition of pulverized coal in this method creates good gas venting channels within the starch, facilitating the timely removal of water vapor during heating and inhibiting foaming and coalescence of the starch while maintaining its original particle morphology. However, while the addition of pulverized coal increases the compaction density of the hard carbon material, it reduces the porosity and specific surface area, leading to a decrease in the reversible capacity and initial coulombic efficiency of the hard carbon anode material.

[0005] Therefore, in order to solve the problem of excessively long stabilization time in starch preparation, it is urgent to find a method for preparing hard carbon anode materials, and to obtain anode materials and sodium-ion batteries. Summary of the Invention

[0006] The primary objective of this invention is to overcome the aforementioned problems in the prior art and provide a method for preparing hard carbon anode materials.

[0007] A second objective of this invention is to provide a hard carbon anode material.

[0008] A third objective of this invention is to provide a sodium-ion battery negative electrode.

[0009] The fourth objective of this invention is to provide a sodium-ion battery.

[0010] The above-mentioned objective of the present invention is achieved through the following technical solution:

[0011] A method for preparing a hard carbon anode material, the method comprising the following steps:

[0012] S1. Mix starch and carbohydrates to obtain a precursor powder; the carbohydrates are monosaccharides or disaccharides;

[0013] S2. The precursor powder is pre-carbonized under an inert atmosphere for 2-6 hours.

[0014] S3. The pre-carbonized hard carbon precursor is ball-milled to obtain pre-carbonized precursor powder with an average particle size of 5-8 μm.

[0015] S4. The pre-carbonized precursor powder is carbonized under an inert atmosphere to obtain a hard carbon anode material.

[0016] When starch is used to prepare hard carbon materials, it usually requires a long stabilization time to obtain high-performance hard carbon anode materials. However, the inventors discovered that by mixing sugars with starch, during the stabilization or pre-carbonization process, small molecule monosaccharides or disaccharides are carbonized and deposited on the surface of starch-based carbon materials, forming a large number of micropores and mesopores, increasing the specific surface area, and thus improving the electrochemical performance of starch-based hard carbon anode materials. When these materials are made into batteries, the initial coulombic efficiency and other properties are significantly improved.

[0017] In this invention, the type of starch is not limited, and known starches used in the preparation of hard carbon materials can be selected.

[0018] Preferably, the starch mentioned in step S1 is either tapioca starch or corn starch.

[0019] More preferably, the sugar substance mentioned in step S1 is either glucose or sucrose.

[0020] More preferably, the mass ratio of starch to sugar is (1-3):1.

[0021] To avoid problems such as gelatinization of starch granules due to expansion during heating when preparing hard carbon materials, starch is usually pre-carbonized or stabilized. Pre-carbonization at an appropriate temperature can effectively control the quantity, size, and distribution of raw materials, thereby controlling the quantity, size, and distribution of pores in hard carbon materials. The temperature and heating rate of the pre-carbonization process can refer to existing technologies.

[0022] Preferably, the pre-carbonization temperature in step S2 is 200-400°C.

[0023] More preferably, the pre-carbonization temperature in step S2 is 300°C.

[0024] More preferably, the pre-carbonization time in step S2 is 3-4 hours.

[0025] Preferably, the heating rate of the pre-carbonization in step S2 is 1-5℃ / min.

[0026] More preferably, the heating rate of the pre-carbonization in step S2 is 1-2 °C / min.

[0027] Preferably, the inert atmosphere in step S2 is either nitrogen or helium.

[0028] In order to better adjust the pore structure of hard carbon materials and achieve sufficient carbonization during subsequent carbonization processes, ball milling is used before carbonization to obtain pre-carbonized precursor powder with small particle size. The ball milling speed, ball-to-material ratio and ball milling time can refer to existing technologies.

[0029] Preferably, in step S3, the ball mill material is abrasive: agate beads = 1:20, the ball mill speed is 500 rpm, and the ball mill is set to rotate forward and reverse for 30 minutes each, alternating 4-12 times.

[0030] Carbonization can further regulate the large number of micropores and mesopores formed in the pre-carbonization or stabilization process, increase the specific surface area of ​​the material, facilitate the insertion and extraction of sodium ions, and thus improve the electrochemical performance of hard carbon anode materials. The temperature and heating rate of the carbonization process can be referenced from existing technologies.

[0031] Preferably, the carbonization temperature in step S4 is 1200-1500℃.

[0032] More preferably, the carbonization temperature in step S4 is 1400-1500°C.

[0033] Preferably, the carbonization time in step S4 is 2-5 hours.

[0034] More preferably, the carbonization temperature in step S4 is 2-3 hours.

[0035] Preferably, the heating rate of carbonization in step S2 is 1-5℃ / min.

[0036] More preferably, the heating rate of carbonization in step S2 is 1-2 °C / min.

[0037] Preferably, the inert atmosphere in step S4 is either nitrogen or helium.

[0038] A hard carbon anode material is prepared by the above-described method for preparing hard carbon anode materials.

[0039] The above-mentioned hard carbon anode material is used in the preparation of anodes in sodium-ion batteries.

[0040] A sodium-ion battery negative electrode is obtained through the following preparation process: a conductive agent, a binder, a solvent and the above-mentioned hard carbon negative electrode material are mixed to obtain a slurry, and then the slurry is coated onto a current collector and dried to obtain the negative electrode.

[0041] The conductive agent, binder, solvent, and current collector used to prepare the sodium ion negative electrode can be referenced from existing technologies.

[0042] Preferably, the mass ratio of hard carbon anode material, conductive agent, and binder is 94:(2-5):(2-5).

[0043] More preferably, the conductive agent is acetylene black, the binder is CMC and styrene-butadiene rubber, the solvent is deionized water, and the ratio of the hard carbon negative electrode material to acetylene black to CMC to styrene-butadiene rubber is 94:2:4:2. Preferably, the current collector is aluminum foil or copper foil, and the drying method is vacuum drying.

[0044] More preferably, the current collector thickness is 0.2 mm and the drying time is 12-24 h.

[0045] A sodium-ion battery includes a positive electrode, a negative electrode, a separator, and an electrolyte; the negative electrode is the negative electrode of the aforementioned sodium-ion battery.

[0046] The positive electrode, separator, and electrolyte that make up a sodium-ion battery can refer to existing technologies.

[0047] Preferably, the diaphragm is a glass fiber membrane.

[0048] Preferably, in the electrolyte, the sodium salt is one of NaPF6, NACF3SO3, and NaClO4, and the organic solvent of the electrolyte is at least one of DME, DMC, and EC.

[0049] Compared with the prior art, the beneficial effects of the present invention are:

[0050] (1) The present invention uses starch and sugars to co-carbonize, which not only maintains the single carbon source component, but also forms a large number of micropores and mesopores during the stabilization or pre-carbonization process, optimizes the pore size distribution of carbon materials, improves the problem of long starch stabilization time in traditional methods, and improves the preparation efficiency; moreover, the method used in the present invention is simple and easy to implement, the raw materials are cheap and readily available, and the preparation conditions are mild and controllable, which has good prospects for production application.

[0051] (2) The hard carbon material prepared in this invention, when used as the negative electrode material of a sodium-ion battery and assembled with an electrolyte, significantly improves the initial coulombic efficiency of sodium-ion batteries compared to those made using starch as the carbon source alone. The initial reversible capacity of the sodium-ion battery of this invention reaches 349.34 mAh g. -1 The initial coulomb efficiency reached 96.3%, with excellent rate performance at 300 Ahg. -1 It achieves high capacity retention at high current density and stable long charge-discharge cycle performance, resulting in improvements in multiple performance aspects. Attached Figure Description

[0052] Figure 1 The first-week charge-discharge curves and first coulombic efficiency diagrams are for Example 1, Comparative Example 1, and Comparative Example 2.

[0053] Figure 2 This is a charge / discharge rate performance diagram for Example 1.

[0054] Figure 3 This is a graph showing the charge-discharge long-cycle performance of Example 1.

[0055] Figure 4 This is a graph showing the charge-discharge long-cycle performance of Example 2.

[0056] Figure 5 This is a graph showing the charge-discharge long-cycle performance of Example 3. Detailed Implementation

[0057] To more clearly and completely describe the technical solution of the present invention, the present invention will be further described in detail below through specific embodiments. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention. Various changes can be made within the scope of the claims of the present invention.

[0058] Example 1

[0059] S1. Place cassava starch and glucose in a mortar at a mass ratio of 1:1 and grind by hand for 30 minutes to obtain a well-mixed powder.

[0060] S2. Place the powder from S1 in a ceramic crucible and pre-carbonize it by heating it from 25°C to 300°C at a rate of 2°C / min for 3 hours under an inert atmosphere to obtain a fluffy black solid.

[0061] S3. The dried black solid obtained in S2 is placed in a ball mill for ball milling. The ball mill material is abrasive: agate beads = 1:20. The rotation speed is 500 rpm. The ball mill is set to rotate forward and reverse for 30 minutes each, and the cycle is repeated 6 times to obtain black powder.

[0062] S4. The black powder obtained in S3 is placed in a ceramic crucible and carbonized under a nitrogen atmosphere by heating from 25°C to 1500°C at a rate of 2°C / min for 2 hours. After natural cooling to room temperature, sodium ion hard carbon material is obtained.

[0063] The conductive agent, binder, solvent and hard carbon anode material obtained in S4 are mixed to obtain a slurry. The slurry is then coated onto the current collector and dried to obtain the hard carbon anode material.

[0064] The ratio of hard carbon: acetylene black: binder CMC: styrene-butadiene rubber is 94:2:4:2, and the solvent is deionized water.

[0065] The above-obtained hard carbon material negative electrode sheet is assembled with a positive electrode, a separator, and an electrolyte to obtain a coin cell sodium-ion battery.

[0066] The diaphragm is a glass fiber membrane, and the electrolyte is 1M NaCFSO3 DME.

[0067] Figure 1 The button batteries prepared in Example 1, Comparative Example 1, and Comparative Example 2 were tested at 20 mAg. -1 First-cycle charge-discharge curves and initial coulombic efficiency plot at current density. Figure 1It can be seen that the reversible specific capacity of the hard carbon material co-carbonized from cassava starch and glucose prepared in Example 1 is 349.34 mAh g. -1 The initial coulombic efficiency was 96.3%, and the reversible specific capacity of the cassava starch hard carbon material prepared by Comparative Example 1 was 217.9 mAh g⁻¹. -1 The initial coulombic efficiency was 88%, and the reversible specific capacity of the cassava starch hard carbon material prepared by Comparative Example 2 was 303.4 mAh g⁻¹. -1 The initial Coulomb efficiency was 92.7%.

[0068] Figure 2 The button cell prepared in Example 1 was subjected to a temperature range of 20-1500 Ahg. -1 Charge-discharge rate performance at current density. (From...) Figure 2 It can be seen that the battery prepared in Example 1 has performance at 20, 30, 60, 120, 240, 300, 600, 1200, and 1500 mAg. -1 The reversible capacities obtained at different current densities were 371.28, 353.60, 325.19, 316.85, 301.05, 293.70, 272.21, 251.10, and 214.78 mAh g. -1 , at 20mAhg -1 It can still maintain a high reversible capacity after 100 cycles.

[0069] Figure 3 The button cell prepared in Example 1 was subjected to a temperature of 300 Ahg. -1 Graphs showing the long-cycle performance of charge-discharge at high current density. (From...) Figure 3 It can be seen that the hard carbon material co-carbonized from cassava starch and glucose still retains a capacity of 354.8 mAh g after 100 cycles under high current. -1 .

[0070] Based on the above data, it can be seen that adding glucose to cassava starch for co-carbonization can shorten the starch stabilization time while significantly improving the specific capacity and initial coulombic efficiency of sodium-ion batteries made with hard carbon anode materials. Furthermore, it exhibits good capacity retention and long-term cycle stability under high current.

[0071] Example 2

[0072] This embodiment provides a method for preparing a sugar-based hard carbon anode material for sodium-ion batteries. The preparation process is basically the same as that in Example 1, except that the raw materials in S1 are corn starch and glucose, with a mass ratio of 1:1.

[0073] Figure 4 The button cell prepared in Example 2 has a capacity of 300 mAh g. -1 Charging and discharging long-cycle performance diagram under high current density.

[0074] Example 3

[0075] This embodiment provides a method for preparing a sugar-based hard carbon anode material for sodium-ion batteries. The preparation process is basically the same as in Example 1, except that: in S1, the raw materials are corn starch and glucose in a mass ratio of 1:1; and in S2, the pre-carbonization treatment takes 6 hours.

[0076] Figure 5 The button cell prepared in Example 3 has a capacity of 20 mAh g. -1 Charging and discharging long-cycle performance at current density.

[0077] Comparative Example 1

[0078] S1. Weigh an appropriate amount of cassava starch and place it in a ceramic crucible. Stabilize it in a muffle furnace with a temperature increase of 2℃ / min from 25℃ to 220℃ for 12 hours to obtain a yellowish-brown powder.

[0079] S2. Place the powder obtained in S1 into a ball mill for ball milling. The ball mill material is abrasive: agate beads = 1:20. The rotation speed is 500 rpm. Set the ball mill to rotate forward and reverse for 30 minutes each, and repeat the cycle 6 times to obtain a yellowish-brown powder.

[0080] S3. The powder obtained in S2 is placed in a ceramic crucible and carbonized under a nitrogen atmosphere by heating from 25°C to 1500°C at a rate of 2°C / min for 2 hours. After natural cooling to room temperature, sodium ion hard carbon material is obtained.

[0081] The conductive agent, binder, solvent and hard carbon anode material obtained in S3 are mixed to obtain a slurry. The slurry is then coated onto the current collector and dried to obtain the hard carbon anode material.

[0082] The ratio of hard carbon: acetylene black: binder CMC: styrene-butadiene rubber is 94:2:4:2, and the solvent is deionized water.

[0083] The above-obtained hard carbon material negative electrode sheet is assembled with a positive electrode, a separator, and an electrolyte to obtain a coin cell sodium-ion battery.

[0084] The diaphragm is a glass fiber membrane, and the electrolyte is 1M NaCFSO3 DME.

[0085] Comparative Example 2

[0086] This embodiment provides a method for preparing a sugar-based hard carbon anode material for sodium-ion batteries. The preparation process is basically the same as that of Comparative Example 1, except that the stabilization treatment in S1 is carried out for 24 hours.

[0087] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a hard carbon anode material, characterized in that, The method includes the following steps: S1. Mix starch and sugars in a mass ratio of (1-3):1 to obtain precursor powder, wherein the sugars are monosaccharides or disaccharides; S2. The precursor powder is pre-carbonized in an inert atmosphere for 2-6 hours and at a temperature of 200-400°C. S3. The pre-carbonized hard carbon precursor is ball-milled to obtain pre-carbonized precursor powder with an average particle size of 5~8µm. S4. The pre-carbonized precursor powder is carbonized under an inert atmosphere to obtain a hard carbon anode material.

2. The preparation method according to claim 1, characterized in that, The starch mentioned in step S1 is at least one of tapioca starch or corn starch.

3. The preparation method according to claim 1, characterized in that, The carbonization temperature in step S4 is 1200-1500℃, and the carbonization time is 2-5 hours.

4. A hard carbon anode material, characterized in that, It is prepared by the preparation method described in any one of claims 1-3.

5. The application of the hard carbon anode material according to claim 4 in the preparation of anodes in sodium-ion batteries.

6. A sodium-ion battery negative electrode, characterized in that, The anode is obtained by the following preparation process: a conductive agent, a binder, a solvent and the hard carbon anode material of claim 4 are mixed to obtain a slurry, and then the slurry is coated onto a current collector and dried to obtain the anode.

7. The sodium-ion battery negative electrode as described in claim 6, characterized in that, The mass ratio of hard carbon anode material, conductive agent, and binder is 94:(2-5):(2-5).

8. A sodium-ion battery, characterized in that, It includes a positive electrode, a negative electrode, a separator, and an electrolyte; the negative electrode is the negative electrode of the sodium-ion battery according to claim 6.

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