Amorphous carbon-coated sodium ion battery negative electrode biomass hard carbon negative electrode material and preparation method thereof

Abstract

The invention discloses an amorphous carbon-coated sodium ion battery negative electrode biomass hard carbon negative electrode material and a preparation method thereof, and the preparation method comprises the following steps: S1, biomass precursor preparation: soaking a biomass raw material in an acid solution, and carrying out centrifugal drying to obtain a biomass precursor; s2, pre-carbonization: carrying out pre-carbonization treatment on the biomass precursor obtained in the step S1, and crushing and sieving to obtain a pre-carbonized material; s3, coating treatment: carrying out coating treatment on the pre-carbonized material obtained in the step S2 to obtain a coated activated material; and S4, high-temperature carbonization: performing high-temperature carbonization treatment on the coated activated material obtained in the step S3 to obtain the sodium-ion battery hard carbon negative electrode material coated with a carbon layer on the surface. The composite material has the characteristics of excellent structural stability, good cycling stability and high compactness.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium ion batteries, and in particular to an amorphous carbon-coated sodium ion battery negative electrode biomass hard carbon negative electrode material and a preparation method thereof. Background Art

[0002] Hard carbon (HC), a negative electrode material for sodium-ion batteries, is a disordered non-graphitized carbon material. Due to its unique long-range disordered and short-range ordered structure and large interlayer spacing, it exhibits significant advantages in sodium ion storage. It is one of the most widely studied and commercially available sodium battery negative electrode materials.

[0003] Current hard carbon preparation methods primarily include biomass-based, fossil fuel-based, and resin-based materials, depending on the raw material precursor. Biomass-based hard carbon offers advantages such as being renewable, abundant, inexpensive, and environmentally friendly. Furthermore, some biomass materials possess unique structures and compositions, such as being hollow, porous, and containing nitrogen, which enhance their sodium storage properties, making them ideal materials for sodium-ion battery anodes. However, sodium-ion batteries using hard carbon as anode materials suffer from rapid initial capacity decay.

[0004] The rapid initial capacity decay of sodium-ion batteries is related to the SEI interface instability and volume expansion of hard carbon. Conventional biomass-based hard carbon has the following disadvantages in the early cycles of the battery:

[0005] For example, due to the large radius of sodium ions (1.02 Å), the volume of the negative electrode will expand when embedded in hard carbon. The expansion stress causes the SEI film to repeatedly rupture and regenerate in the early stage of the cycle, forming a thick and loose interface layer. As the SEI film thickens, a large amount of active sodium and electrolyte will be consumed, resulting in a significant decrease in discharge capacity.

[0006] For example, oxygen-containing functional groups (such as hydroxyl and carboxyl) on the surface of hard carbon react with the electrolyte (such as carbonate solvent + NaPF6) to generate side reaction products such as Na2CO3 and NaF, which further increase the interfacial impedance, deteriorate the kinetic performance, and lead to increased voltage polarization, which seriously reduces the long-cycle performance. Summary of the Invention

[0007] The purpose of the present invention is to provide an amorphous carbon-coated sodium ion battery negative electrode biomass hard carbon negative electrode material and a preparation method thereof, which has the characteristics of excellent structural stability, good cycle stability and high density.

[0008] The present invention can be achieved through the following technical solutions:

[0009] The method for preparing the amorphous carbon-coated biomass hard carbon negative electrode material for a sodium ion battery negative electrode of the present invention comprises the following steps:

[0010] S1. Preparation of biomass precursor: soaking the biomass raw material in an acid solution and centrifugally drying it to obtain a biomass precursor;

[0011] S2, pre-carbonization: pre-carbonizing the biomass precursor obtained in step S1, crushing and sieving to obtain pre-carbonized material;

[0012] S3, coating treatment: coating the pre-carbonized material obtained in step S2 to obtain a coated activated material;

[0013] S4, high-temperature carbonization: subjecting the coated activated material obtained in step S3 to a high-temperature carbonization treatment to obtain a sodium ion battery hard carbon negative electrode material with a surface coated carbon layer.

[0014] Furthermore, in step S2, the pre-carbonization conditions are as follows: a heating rate of 1-20°C / min, a pre-carbonization temperature of 250-700°C, and a pre-carbonization time of 2-5 hours; the shielding gas is nitrogen and / or argon. A suitable heating rate minimizes the internal and external temperature gradient of the material, allowing the pyrolysis reaction to slowly release volatile products, reducing internal pressure buildup and the risk of cracking, fragmentation, or the formation of large pores, thereby facilitating a more uniform pore structure. Rapid heating may lead to a rapid release of volatile products, resulting in more mesopores or macropores. Slow heating rates may cause excessive cross-linking of the precursor, hindering the subsequent full development of pores at high temperatures, resulting in a long process cycle and high energy consumption. The pre-carbonization temperature directly affects the amount and type of volatiles released, thereby determining the number, size, and distribution of pores. Higher temperatures increase the degree of cross-linking and polycondensation, generally resulting in a harder and stronger pre-carbonized body, but may also cause micropore shrinkage or collapse. Excessively low temperatures may result in insufficient reaction, preventing the formation of a well-defined carbon skeleton structure. At an appropriate pre-carbonization temperature, appropriately extending the time is beneficial to pore development, ensuring sufficient reaction within the material and improving overall uniformity. However, excessively long pre-carbonization times will promote more complete release of volatiles and secondary cracking of tar, potentially reducing pore blockage and causing some of the already formed micropores to slowly close or graphitize at high temperatures. Too short a time may result in insufficient reaction, especially with large materials or slow heating rates. The target temperature may not be reached internally, or the reaction may be incomplete, resulting in incomplete removal of heteroatoms and unstable carbon skeleton structures.

[0015] Furthermore, in step S4, the conditions for high-temperature carbonization are: a heating rate of 1-5 ℃ / min, a carbonization temperature of 900-1600 ℃, a carbonization time of 2-10 h, and a protective gas of nitrogen and / or argon. A suitable heating rate can greatly reduce the temperature gradient inside and outside the material, avoid cracking, deformation or pulverization caused by rapid expansion / contraction, and make the structural rearrangement process of the material more synchronous and uniform, which is conducive to obtaining products with uniform performance. Too fast a heating rate may cause excessive reaction or increased structural defects in the edge area of the material, and insufficient reaction in the central area; a slow heating process has a long cycle and high energy consumption. During the high-temperature carbonization process, the degree of graphitization gradually increases. The higher the carbonization temperature and the longer the carbonization time, the higher the degree of graphitization. At the same time, the interlayer spacing will gradually decrease, which is not conducive to Na + Deintercalation; low carbonization temperature and short time may lead to excessive pore volume and specific surface area, resulting in increased irreversible capacity.

[0016] Furthermore, in step S3, the carbon coating is applied to a core of the biomass hard carbon material at a weight of 5-15 wt%, with the core diameter being 3-10 μm. The coating thickness is 30-200 nm. If the coating is too thin, impurities remaining in the core of the biomass hard carbon material will migrate to the surface during the subsequent carbonization process, defeating the purpose of coating. If the coating is too thick, the cost will increase, hindering commercial application.

[0017] Furthermore, in step S3, the surface coating method is chemical vapor deposition, liquid phase coating or molten liquid phase coating; the coating equipment is fluidized bed vapor deposition equipment, rotary kiln vapor deposition equipment and mechanical fusion coating machine.

[0018] Furthermore, in step S3, the coating carbon layer is soft carbon and / or hard carbon, and the raw materials used for the coating layer are one or more of benzene, toluene, ethanol, pyridine, graphite pitch, coal pitch, epoxy resin, and phenolic resin.

[0019] Furthermore, in step S1, the acid is one or more of sulfuric acid, phosphoric acid, and hydrochloric acid, and the acid is added at a concentration of 0.1-1 mol / L. The acid concentration is crucial to the activation effect of the precursor. Too high an acid concentration may cause excessive dissolution of the precursor, severe structural damage, an increase in macropores and mesopores, and an increase in specific surface area, resulting in reduced capacity and initial efficiency. Low concentrations may not achieve the ideal activation and pore-forming effect to increase capacity.

[0020] Furthermore, in step S1, the biomass raw material is one or more of sawdust, walnut shells, coffee shells, nut shells, straw, coconut shells, bamboo, and coffee grounds.

[0021] Another aspect of the present invention is to protect an amorphous carbon-coated sodium ion battery negative electrode biomass hard carbon negative electrode material, which is prepared using the above-mentioned preparation method.

[0022] Furthermore, the negative electrode material includes a core of a biomass hard carbon material, and the surface of the core is covered with an amorphous carbon layer.

[0023] The present invention provides an amorphous carbon-coated sodium ion battery negative electrode biomass hard carbon negative electrode material and a preparation method thereof, which has the following beneficial effects:

[0024] First, excellent structural stability: The introduction of heteroatoms such as sulfur, phosphorus, and nitrogen through acid immersion can expand the interlayer spacing. The appropriate interlayer spacing can reduce the interaction force between carbon layers during sodium insertion in the hard carbon anode, resulting in lower internal stress.

[0025] Second, good cycle stability: The amorphous carbon layer is coated on the surface of the biomass hard carbon. The coating layer can effectively reduce the specific surface area of the material, inhibit the irreversible decomposition of the electrolyte, and improve the coulombic efficiency. At the same time, it can effectively isolate the electrolyte from the internal hard carbon material and improve the interface stability.

[0026] Third, the density is high. The acid can react with the cellulose / hemicellulose / lignin in the biomass precursor, remove the moisture in the biomass precursor, and build a rigid skeleton, thereby improving the density of the material. The high density enables the hard carbon particles to form a tight surface-to-surface contact network, enhancing electronic conductivity and reducing the side reactions of the electrolyte in the pores. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Graphs showing long cycle tests of the full batteries of Example 1, Comparative Example 1, and Comparative Example 2 at a current density of 1 C and a voltage range of 3.4-1.5 V. DETAILED DESCRIPTION

[0028] In order to enable those skilled in the art to better understand the technical solution of the present invention, the product of the present invention is further described in detail below with reference to embodiments.

[0029] The method for preparing the amorphous carbon-coated biomass hard carbon negative electrode material for a sodium ion battery negative electrode of the present invention comprises the following steps:

[0030] S1. Preparation of biomass precursor: soaking the biomass raw material in an acid solution and centrifugally drying it to obtain a biomass precursor;

[0031] S2, pre-carbonization: pre-carbonizing the biomass precursor obtained in step S1, crushing and sieving to obtain pre-carbonized material;

[0032] S3, coating treatment: coating the pre-carbonized material obtained in step S2 to obtain a coated activated material;

[0033] S4, high-temperature carbonization: subjecting the coated activated material obtained in step S3 to a high-temperature carbonization treatment to obtain a sodium ion battery hard carbon negative electrode material with a surface coated carbon layer.

[0034] Furthermore, in step S2, the pre-carbonization conditions are: a heating rate of 1-20°C / min, a pre-carbonization temperature of 250-700°C, a pre-carbonization time of 2-5 h; and the protective gas is nitrogen and / or argon.

[0035] Furthermore, in step S4, the conditions for high-temperature carbonization are: a heating rate of 1-5°C / min, a carbonization temperature of 900-1600°C, a carbonization time of 2-10 h, and a protective gas of nitrogen and / or argon.

[0036] Furthermore, in step S3, the coating amount of the carbon layer is 5-15 wt% of the core of the biomass hard carbon material, the diameter of the core is 3-10 μm, and the thickness of the coating layer is 30-200 nm.

[0037] Furthermore, in step S3, the surface coating method is chemical vapor deposition, liquid phase coating or molten liquid phase coating; the coating equipment is fluidized bed vapor deposition equipment, rotary kiln vapor deposition equipment and mechanical fusion coating machine.

[0038] Furthermore, in step S3, the coating carbon layer is soft carbon and / or hard carbon, and the raw materials used for the coating layer are one or more of benzene, toluene, ethanol, pyridine, graphite pitch, coal pitch, epoxy resin, and phenolic resin.

[0039] Furthermore, in step S1, the acid is one or more of sulfuric acid, phosphoric acid, and hydrochloric acid, and the concentration of the added acid is 0.1-1 mol / L.

[0040] Furthermore, in step S1, the biomass raw material is one or more of sawdust, walnut shells, coffee shells, nut shells, straw, coconut shells, bamboo, and coffee grounds.

[0041] Another aspect of the present invention is to protect an amorphous carbon-coated sodium ion battery negative electrode biomass hard carbon negative electrode material, which is prepared using the above-mentioned preparation method.

[0042] Furthermore, the negative electrode material includes a core of a biomass hard carbon material, and the surface of the core is covered with an amorphous carbon layer.

[0043] Example 1

[0044] This embodiment relates to an amorphous carbon-coated sodium ion battery negative electrode biomass hard carbon negative electrode material, and its preparation method includes the following steps:

[0045] S1. Preparation of biomass precursor: The biomass raw material is soaked in an acid solution and centrifuged to dry to obtain the biomass precursor. Specifically, the acid is sulfuric acid, phosphoric acid, or hydrochloric acid, and the acid concentration is 0.1-1 mol / L. The biomass raw material is sawdust, walnut shells, coffee shells, nut shells, straw, coconut shells, bamboo, or coffee grounds.

[0046] S2. Pre-carbonization: The biomass precursor obtained in step S1 is pre-carbonized, crushed, and sieved to obtain a pre-carbonized material. Specifically, the pre-carbonization conditions are as follows: a heating rate of 1-20°C / min, a pre-carbonization temperature of 250-700°C, and a pre-carbonization time of 2-5 hours; nitrogen and / or argon as the protective gas; and surface coating methods such as chemical vapor deposition, liquid phase coating, or melt-liquid phase coating. Coating equipment includes fluidized bed vapor deposition equipment, rotary kiln vapor deposition equipment, and mechanical fusion coating equipment.

[0047] S3. Coating: The pre-carbonized material obtained in step S2 is subjected to coating to obtain a coated activated material. Specifically, the carbon layer coating is 5-15 wt% of the biomass hard carbon core, the core diameter is 3-10 μm, and the coating layer thickness is 30-200 nm. The coated carbon layer is soft carbon and / or hard carbon, and the raw materials used for the coating layer are benzene, toluene, ethanol, pyridine, graphite pitch, coal tar pitch, epoxy resin, or phenolic resin.

[0048] S4. High-temperature carbonization: The coated activated material obtained in step S3 is subjected to high-temperature carbonization to obtain a hard carbon anode material for a sodium ion battery with a surface-coated carbon layer. Specifically, the high-temperature carbonization conditions are: a heating rate of 1-5°C / min, a carbonization temperature of 900-1600°C, a carbonization time of 2-10 hours, and a protective gas of nitrogen and / or argon.

[0049] Example 1

[0050] This embodiment relates to an amorphous carbon-coated sodium ion battery negative electrode biomass hard carbon negative electrode material, and its preparation method includes the following steps:

[0051] S1. Preparation of biomass precursor: The biomass raw material is soaked in an acid solution and centrifuged to dry to obtain the biomass precursor. Specifically, the acid is sulfuric acid, phosphoric acid, or hydrochloric acid, and the acid concentration is 0.1-1 mol / L. The biomass raw material is sawdust, walnut shells, coffee shells, nut shells, straw, coconut shells, bamboo, or coffee grounds.

[0052] S2. Pre-carbonization: The biomass precursor obtained in step S1 is pre-carbonized, crushed, and sieved to obtain a pre-carbonized material. Specifically, the pre-carbonization conditions are as follows: a heating rate of 1-20°C / min, a pre-carbonization temperature of 250-700°C, and a pre-carbonization time of 2-5 hours; nitrogen and / or argon as the protective gas; and surface coating methods such as chemical vapor deposition, liquid phase coating, or melt-liquid phase coating. Coating equipment includes fluidized bed vapor deposition equipment, rotary kiln vapor deposition equipment, and mechanical fusion coating equipment.

[0053] S3. Coating: The pre-carbonized material obtained in step S2 is subjected to coating to obtain a coated activated material. Specifically, the carbon layer coating is 5-15 wt% of the biomass hard carbon core, the core diameter is 3-10 μm, and the coating layer thickness is 30-200 nm. The coated carbon layer is soft carbon and / or hard carbon, and the raw materials used for the coating layer are benzene, toluene, ethanol, pyridine, graphite pitch, coal tar pitch, epoxy resin, or phenolic resin.

[0054] S4. High-temperature carbonization: The coated activated material obtained in step S3 is subjected to high-temperature carbonization to obtain a hard carbon anode material for a sodium ion battery with a surface-coated carbon layer. Specifically, the high-temperature carbonization conditions are: a heating rate of 1-5°C / min, a carbonization temperature of 900-1600°C, a carbonization time of 2-10 hours, and a protective gas of nitrogen and / or argon.

[0055] Example 1

[0056] This embodiment relates to an amorphous carbon-coated sodium ion battery negative electrode biomass hard carbon negative electrode material, and its preparation method includes the following steps:

[0057] S1. Preparation of biomass precursor: The biomass raw materials are soaked in an acid solution and centrifuged to dry to obtain the biomass precursor. Specifically, the acid is sulfuric acid at a concentration of 1 mol / L; the biomass raw materials are sawdust, walnut shells, coffee shells, nut shells, and straw.

[0058] S2. Pre-carbonization: The biomass precursor obtained in step S1 is pre-carbonized, crushed, and sieved to obtain a pre-carbonized material. Specifically, the pre-carbonization conditions are: a heating rate of 20°C / min, a pre-carbonization temperature of 450°C, and a pre-carbonization time of 2 hours; nitrogen and argon as protective gases; and a fluidized bed vapor deposition apparatus for coating.

[0059] S3. Coating: The pre-carbonized material obtained in step S2 is subjected to coating to obtain a coated activated material. Specifically, the carbon layer covers 15 wt% of the biomass hard carbon core, the core has a diameter of 3-10 μm, and the coating layer has a thickness of 30-200 nm. The raw materials used for the coating layer are benzene and toluene.

[0060] S4. High-temperature carbonization: The coated activated material obtained in step S3 is subjected to high-temperature carbonization to obtain a hard carbon anode material for a sodium ion battery with a surface-coated carbon layer. Specifically, the high-temperature carbonization conditions are: a heating rate of 5°C / min, a carbonization temperature of 1300°C, a carbonization time of 2 hours, and a protective gas of nitrogen and argon.

[0061] Example 2

[0062] This embodiment relates to an amorphous carbon-coated sodium ion battery negative electrode biomass hard carbon negative electrode material, and its preparation method includes the following steps:

[0063] S1. Biomass Precursor Preparation: The biomass raw materials are soaked in an acid solution and centrifugally dried to obtain a biomass precursor. Specifically, the acid is hydrochloric acid at a concentration of 0.5 mol / L; the biomass raw materials are sawdust, walnut shells, coconut shells, bamboo, and coffee grounds.

[0064] S2. Pre-carbonization: The biomass precursor obtained in step S1 is pre-carbonized, crushed, and sieved to obtain a pre-carbonized material. Specifically, the pre-carbonization conditions are: a heating rate of 10°C / min, a pre-carbonization temperature of 250°C, and a pre-carbonization time of 5 hours; nitrogen and argon are used as protective gases; and the coating equipment is a mechanical fusion coating machine.

[0065] S3. Coating: The pre-carbonized material obtained in step S2 is subjected to coating to obtain a coated activated material. Specifically, the carbon layer covers 10 wt% of the biomass hard carbon material core, the core has a diameter of 3-10 μm, and the coating layer has a thickness of 30-200 nm. The raw materials used for the coating layer are benzene, toluene, and phenolic resin.

[0066] S4. High-temperature carbonization: The coated activated material obtained in step S3 is subjected to high-temperature carbonization to obtain a hard carbon anode material for a sodium ion battery with a surface-coated carbon layer. Specifically, the high-temperature carbonization conditions are: a heating rate of 3°C / min, a carbonization temperature of 900°C, a carbonization time of 10 hours, and a nitrogen shielding gas.

[0067] Example 3

[0068] This embodiment relates to an amorphous carbon-coated sodium ion battery negative electrode biomass hard carbon negative electrode material, and its preparation method includes the following steps:

[0069] S1. Biomass Precursor Preparation: The biomass raw materials are soaked in an acid solution and centrifugally dried to obtain a biomass precursor. Specifically, the acid is sulfuric acid or hydrochloric acid, and the acid concentration is 0.1 mol / L. The biomass raw materials are coffee husks, nut shells, straw, coconut shells, bamboo, and coffee grounds.

[0070] S2. Pre-carbonization: The biomass precursor obtained in step S1 is pre-carbonized, crushed, and sieved to obtain a pre-carbonized material. Specifically, the pre-carbonization conditions are: a heating rate of 3°C / min, a pre-carbonization temperature of 700°C, and a pre-carbonization time of 3 hours; argon is used as the shielding gas; and the coating equipment is a rotary kiln vapor deposition device.

[0071] S3. Coating: The pre-carbonized material obtained in step S2 is subjected to coating to obtain a coated activated material. Specifically, the carbon layer covers 5 wt% of the biomass hard carbon core, the core diameter is 3-10 μm, and the coating thickness is 30-200 nm. The coating materials used are graphite pitch, coal tar pitch, epoxy resin, or phenolic resin.

[0072] S4. High-temperature carbonization: The coated activated material obtained in step S3 is subjected to high-temperature carbonization to obtain a hard carbon anode material for a sodium ion battery with a surface-coated carbon layer. Specifically, the high-temperature carbonization conditions are: a heating rate of 1°C / min, a carbonization temperature of 1600°C, a carbonization time of 6 hours, and a protective gas of argon or argon.

[0073] Example 4

[0074] This embodiment relates to an amorphous carbon-coated sodium ion battery negative electrode biomass hard carbon negative electrode material, and its preparation method includes the following steps:

[0075] S1. Biomass Precursor Preparation: The biomass raw materials are soaked in an acid solution and centrifuged to dry to obtain the biomass precursor. Specifically, the acid is phosphoric acid or hydrochloric acid, and the acid concentration is 0.4 mol / L. The biomass raw materials are sawdust, walnut shells, coffee hulls, and coffee grounds.

[0076] S2. Pre-carbonization: The biomass precursor obtained in step S1 is pre-carbonized, crushed, and sieved to obtain a pre-carbonized material. Specifically, the pre-carbonization conditions are: a heating rate of 7°C / min, a pre-carbonization temperature of 550°C, and a pre-carbonization time of 3 hours; argon as the shielding gas; and a fluidized bed vapor deposition apparatus.

[0077] S3. Coating: The pre-carbonized material obtained in step S2 is subjected to coating to obtain a coated activated material. Specifically, the carbon layer coating is 7 wt% of the biomass hard carbon core, with the core diameter being 3-10 μm. The coating layer thickness is 30-200 nm. The raw materials used for the coating layer are benzene, toluene, ethanol, pyridine, graphite pitch, and phenolic resin.

[0078] S4. High-temperature carbonization: The coated activated material obtained in step S3 is subjected to high-temperature carbonization to obtain a hard carbon anode material for a sodium ion battery with a surface-coated carbon layer. Specifically, the high-temperature carbonization conditions are: a heating rate of 2°C / min, a carbonization temperature of 1400°C, a carbonization time of 4 hours, and an argon shielding gas.

[0079] Example 5

[0080] This embodiment relates to an amorphous carbon-coated sodium ion battery negative electrode biomass hard carbon negative electrode material, and its preparation method includes the following steps:

[0081] S1. Preparation of biomass precursor: The biomass raw materials are soaked in an acid solution and centrifuged to dry to obtain a biomass precursor. Specifically, the acid is phosphoric acid at a concentration of 0.6 mol / L; the biomass raw materials are sawdust, walnut shells, or coffee husks.

[0082] S2. Pre-carbonization: The biomass precursor obtained in step S1 is pre-carbonized, crushed, and sieved to obtain a pre-carbonized material. Specifically, the pre-carbonization conditions are: a heating rate of 12°C / min, a pre-carbonization temperature of 400°C, and a pre-carbonization time of 4 hours; argon is used as the shielding gas; and the coating equipment is a mechanical fusion coating machine.

[0083] S3. Coating: The pre-carbonized material obtained in step S2 is subjected to coating to obtain a coated activated material. Specifically, the carbon layer covers 12 wt% of the biomass hard carbon material core, the core diameter is 3-10 μm, and the coating layer thickness is 30-200 nm. The raw materials used for the coating layer are benzene, toluene, coal tar, epoxy resin, or phenolic resin.

[0084] S4. High-temperature carbonization: The coated activated material obtained in step S3 is subjected to high-temperature carbonization to obtain a hard carbon anode material for a sodium ion battery with a surface-coated carbon layer. Specifically, the high-temperature carbonization conditions are: a heating rate of 2°C / min, a carbonization temperature of 1100°C, a carbonization time of 5 hours, and a protective gas of nitrogen and argon.

[0085] Application Example 1

[0086] This embodiment relates to an amorphous carbon-coated sodium ion battery negative electrode biomass hard carbon negative electrode material, and its preparation method includes the following steps:

[0087] S1: Biomass Precursor Preparation: The fruit shells were soaked in an acid solution and then centrifuged and dried to obtain the biomass precursor. Specifically, sulfuric acid was added at a concentration of 0.5 mol / L and the soaking time was 12 hours.

[0088] S2. Pre-carbonization: The biomass precursor obtained in step S1 is pre-carbonized, and then crushed and sieved to obtain a pre-carbonized material. Specifically, the pre-carbonization temperature is 500°C, the heating rate is 5°C / min, the holding time is 2 hours, and the protective gas is nitrogen.

[0089] S3. Coating treatment: The dried pre-carbonized material is mixed with petroleum asphalt, and coated using a fusion coating machine to obtain a coated activated material, wherein the addition amount of petroleum asphalt is 6 wt%.

[0090] S4. High-temperature carbonization: The coated activated material is subjected to high-temperature carbonization at a predetermined temperature to obtain a biomass hard carbon material with a surface carbon layer. Specifically, the heating rate is 5°C / min, the high-temperature carbonization temperature is 1300°C, the carbonization time is 2 hours, and the shielding gas is nitrogen.

[0091] The resulting material was used to test the electrochemical performance of soft-pack batteries using the following method: A slurry of hard carbon material, Super P, CMC, and SBR was prepared in a ratio of 94.5:1.5:1.5:2.5. The slurry was then evenly coated onto a high-density aluminum foil using a coater. A polyanion (NFPP) cathode material and a biomass hard carbon anode were used as the negative electrode material. The electrolyte was 1 mol / L NaClO₄ in EC+DEC (1:1 vol%), and the separator was a PP / PE / PP three-layer membrane. Constant current and constant voltage charge-discharge tests were performed on the full battery at a current density of 1 C and a voltage range of 3.4-1.5 V.

[0092] Comparative Example 1

[0093] This embodiment relates to an amorphous carbon-coated sodium ion battery negative electrode biomass hard carbon negative electrode material, and its preparation method includes the following steps:

[0094] S1. Pre-carbonization: The biomass precursor is pre-carbonized and then crushed and sieved to obtain a pre-carbonized material. Specifically, the pre-carbonization temperature is 500°C, the heating rate is 5°C / min, the holding time is 2 hours, and the protective gas is nitrogen.

[0095] S2. Coating treatment: The dried pre-carbonized material is mixed with petroleum asphalt, and coated using a fusion coating machine to obtain a coated activated material, wherein the addition amount of petroleum asphalt is 6 wt%.

[0096] S3. High-temperature carbonization: The coated activated material is subjected to high-temperature carbonization at a specific temperature to obtain a biomass hard carbon material with a surface carbon layer. Specifically, the heating rate is 5°C / min, the high-temperature carbonization temperature is 1300°C, the carbonization time is 2 hours, and the protective gas is nitrogen.

[0097] The resulting material was used to test the electrochemical performance of soft-pack batteries using the following method: A slurry of hard carbon material, Super P, CMC, and SBR was prepared in a ratio of 94.5:1.5:1.5:2.5. The slurry was then evenly coated onto a high-density aluminum foil using a coater. A polyanion (NFPP) cathode material and a biomass hard carbon anode were used as the negative electrode material. The electrolyte was 1 mol / L NaClO₄ in EC+DEC (1:1 vol%), and the separator was a PP / PE / PP three-layer membrane. Constant current and constant voltage charge-discharge tests were performed on the full battery at a current density of 1 C and a voltage range of 3.4-1.5 V.

[0098] Comparative Example 2

[0099] This embodiment relates to an amorphous carbon-coated sodium ion battery negative electrode biomass hard carbon negative electrode material, and its preparation method includes the following steps:

[0100] S1. Preparation of biomass precursor: The fruit shell raw material was soaked in an acid solution and then centrifuged and dried to obtain the biomass precursor. Specifically, the added acid was sulfuric acid at a concentration of 0.5 mol / L, and the soaking time was 12 hours.

[0101] S2. Pre-carbonization: The biomass precursor obtained in step S1 is pre-carbonized, and then crushed and sieved to obtain a pre-carbonized material. Specifically, the pre-carbonization temperature is 500°C, the heating rate is 5°C / min, the holding time is 2 hours, and the protective gas is nitrogen.

[0102] S3. High-temperature carbonization: The pre-carbonized material is subjected to high-temperature carbonization to obtain a biomass hard carbon material. Specifically, the heating rate is 5°C / min, the high-temperature carbonization temperature is 1300°C, the carbonization time is 2 hours, and the protective gas is nitrogen.

[0103] The resulting material was used to test the electrochemical performance of soft-pack batteries using the following method: A slurry of hard carbon material, Super P, CMC, and SBR was prepared in a ratio of 94.5:1.5:1.5:2.5. The slurry was then evenly coated onto a high-density aluminum foil using a coater. A polyanion (NFPP) cathode material and a biomass hard carbon anode were used as the negative electrode material. The electrolyte was 1 mol / L NaClO₄ in EC+DEC (1:1 vol%), and the separator was a PP / PE / PP three-layer membrane. Constant current and constant voltage charge-discharge tests were performed on the full battery at a current density of 1 C and a voltage range of 3.4-1.5 V.

[0104] The interlayer spacing of the hard carbon negative electrode in Application Example 1 is 0.413 nm, the interlayer spacing in Comparative Example 1 is 0.372 nm, and the interlayer spacing in Comparative Example 2 is 0.408 nm. The large interlayer spacing can alleviate the lattice strain and volume expansion of sodium ion embedding, significantly reduce the internal stress, and thus improve the cycle stability.

[0105] The compacted density of the hard carbon negative electrode in Application Example 1 is 1.02 g / cm 3 The acid can react with the cellulose / hemicellulose / lignin in the biomass precursor, remove the moisture in the biomass precursor, and build a rigid skeleton, thereby increasing the compaction density of the material. High compaction allows the hard carbon particles to form a tight surface-to-surface contact network, enhancing electronic conductivity while reducing side reactions of the electrolyte in the pores.

[0106] like Figure 1 As shown, the capacity retention rates of the full batteries of Example 1, Comparative Example 1 and Comparative Example 2 after 400 cycles are 96.61%, 93.51% and 95.78%. Compared with the uncoated biomass hard carbon negative electrode, the coated biomass hard carbon can reduce the direct contact between the active material and the electrolyte, inhibit side reactions, reduce irreversible capacity loss, and make the SEI film formed on the surface more uniform and stable, avoiding Na⁺ consumption and capacity decay caused by repeated rupture / regeneration. The coating layer can also serve as a mechanical support, effectively inhibiting the expansion and contraction of the active material and preventing the electrode from pulverizing or rupturing. Through the combined effects of the above-mentioned structural stability and side reaction inhibition, the hard carbon coating significantly inhibits the rapid early capacity decay.

[0107] The above embodiments are merely specific embodiments of the present invention, and their descriptions are relatively specific and detailed. However, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make various modifications and improvements without departing from the scope of the present invention, and such obvious alternatives are all within the scope of protection of the present invention.

Claims

1. A method for preparing an amorphous carbon-coated sodium ion battery negative electrode biomass hard carbon negative electrode material, characterized in that The following steps are involved: S1. Preparation of biomass precursor: soaking the biomass raw material in an acid solution and centrifugally drying it to obtain a biomass precursor; S2, pre-carbonization: pre-carbonizing the biomass precursor obtained in step S1, crushing and sieving to obtain pre-carbonized material; S3, coating treatment: coating the pre-carbonized material obtained in step S2 to obtain a coated activated material; S4, high-temperature carbonization: subjecting the coated activated material obtained in step S3 to a high-temperature carbonization treatment to obtain a sodium ion battery hard carbon negative electrode material with a surface coated carbon layer.

2. The method for preparing the amorphous carbon-coated biomass hard carbon negative electrode material for sodium ion battery according to claim 1, characterized in that: In step S2, the pre-carbonization conditions are: a heating rate of 1-20°C / min, a pre-carbonization temperature of 250-700°C, a pre-carbonization time of 2-5 hours; and the protective gas is nitrogen and / or argon.

3. The method for preparing the amorphous carbon-coated biomass hard carbon negative electrode material for sodium ion battery according to claim 1, characterized in that: In step S4, the high-temperature carbonization conditions are: a heating rate of 1-5°C / min, a carbonization temperature of 900-1600°C, a carbonization time of 2-10 h, and a protective gas of nitrogen and / or argon.

4. The method for preparing an amorphous carbon-coated biomass hard carbon negative electrode material for a sodium ion battery according to claim 1, characterized in that: In step S3, the coating amount of the carbon layer is 5-15 wt% of the core of the biomass hard carbon material, the diameter of the core is 3-10 μm, and the thickness of the coating layer is 30-200 nm.

5. The method for preparing an amorphous carbon-coated sodium ion battery negative electrode biomass hard carbon negative electrode material according to claim 1, characterized in that: In step S3, the surface coating method is chemical vapor deposition, liquid phase coating or molten liquid phase coating; the coating equipment is fluidized bed vapor deposition equipment, rotary furnace vapor deposition equipment and mechanical fusion coating machine.

6. The method for preparing an amorphous carbon-coated sodium ion battery negative electrode biomass hard carbon negative electrode material according to claim 1, characterized in that: In step S3, the coating carbon layer is soft carbon and / or hard carbon, and the raw materials used for the coating layer are one or more of benzene, toluene, ethanol, pyridine, graphite pitch, coal pitch, epoxy resin, and phenolic resin.

7. The method for preparing an amorphous carbon-coated biomass hard carbon negative electrode material for a sodium ion battery according to claim 1, characterized in that: In step S1, the acid is one or more of sulfuric acid, phosphoric acid, and hydrochloric acid, and the concentration of the added acid is 0.1-1 mol / L.

8. The method for preparing an amorphous carbon-coated biomass hard carbon negative electrode material for a sodium ion battery according to claim 1, characterized in that: In step S1 , the biomass raw material is one or more of sawdust, walnut shells, coffee shells, nut shells, straw, coconut shells, bamboo, and coffee grounds.

9. An amorphous carbon-coated biomass hard carbon negative electrode material for sodium ion batteries, characterized by: The method is prepared according to any one of claims 1 to 8.

10. The amorphous carbon-coated biomass hard carbon negative electrode material for sodium ion batteries according to claim 9, characterized in that: The invention comprises a core of a biomass hard carbon material, the surface of which is covered by an amorphous carbon layer.

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