Biomass-based precursor, hard carbon material as well as preparation method and application of biomass-based precursor and hard carbon material

Abstract

The invention belongs to the technical field of battery materials, and particularly relates to a biomass-based precursor, a hard carbon material and a preparation method and application of the biomass-based precursor and the hard carbon material. In the biomass-based precursor provided by the invention, the content of volatile components is 16wt%-40wt%, the content of oxygen is 10wt%-32wt%, the content of fixed carbon is 60wt%-82wt%, the content of water is less than or equal to 5wt%, and the content of ash is less than or equal to 0.6%. The content of volatile components, fixed carbon, ash and moisture in the biomass-based precursor is within a specific range, the biomass-based precursor has high oxygen content, and the biomass-based hard carbon material with high gram volume, high initial charge-discharge efficiency and good cycle stability can be prepared by using the biomass-based precursor. In addition, the hard carbon material prepared from different biomass raw materials can show excellent electrochemical performance without repeatedly adjusting process parameters of high-temperature sintering.

Description

Technical Field

[0001] This application belongs to the technical field of battery materials, and more specifically, relates to a biomass-based precursor, a hard carbon material, and their preparation methods and applications. Background Art

[0002] Hard carbon materials mainly use biomass as raw materials, and have the advantages of wide raw material sources, low prices, and wide application directions. They have become the mainstream anode materials for current lithium-ion batteries or sodium-ion batteries, especially suitable as anode materials for sodium-ion batteries.

[0003] Hard carbon materials are formed by sintering a carbon-containing precursor in an inert atmosphere. During the large-scale preparation of high-performance hard carbon materials, the raw material source of the precursor has an important impact on its electrochemical performance. Biomass, as a natural treasure house of solid carbon resources, is considered an ideal precursor raw material. However, its types are numerous and its components are complex. Under the same sintering process, there are obvious differences in the electrochemical performance of hard carbon materials prepared from different biomass raw materials. To eliminate this difference, it is often necessary to repeatedly adjust the sintering process parameters to make the electrochemical performance of hard carbon materials prepared from precursors with different raw material sources tend to be consistent. However, there are still some precursors with certain raw material sources that cannot produce hard carbon materials with excellent electrochemical performance. This not only greatly extends the R & D cycle and increases the R & D cost, but also makes it difficult to guarantee the electrochemical performance of the finished hard carbon materials, which is not conducive to the large-scale production of hard carbon materials. Summary of the Invention

[0004] Aiming at the defects of the prior art, the purpose of this application is to provide a biomass-based precursor, a hard carbon material, and their preparation methods and applications, aiming to solve the problems that when using biomass as the precursor raw material source to prepare hard carbon materials in the prior art, due to its numerous types and complex components, the adaptability of the conventional sintering process (sintering at 800 °C to 1600 °C for 1 h to 3 h) is poor, and the electrochemical performance of the prepared hard carbon materials is unstable. It is necessary to repeatedly adjust to obtain high-performance hard carbon materials, resulting in high production costs and long production cycles.

[0005] To achieve the above purpose, in the first aspect, this application provides a biomass-based precursor, with a volatile content of 16 wt% to 40 wt%, an oxygen content of 10 wt% to 32 wt%, a fixed carbon content of 60 wt% to 82 wt%, a moisture content ≤ 5 wt%, and an ash content ≤ 0.6%.

[0006] Preferably, in the above biomass-based precursor, the oxygen content is 15 wt% to 25 wt%.

[0007] Further preferably, in the above biomass-based precursor, the content of volatile matter is 25 wt% to 35 wt%, the content of oxygen is 15 wt% to 25 wt%, the content of fixed carbon is 70 wt% to 80 wt%, the content of moisture is < 5 wt%, and the content of ash is < 0.6 wt%.

[0008] More preferably, in the above biomass-based precursor, the content of volatile matter is 30 wt% to 32 wt%, the content of oxygen is 17 wt% to 23 wt%, the content of fixed carbon is 70 wt% to 73 wt%, the content of moisture is < 3 wt%, and the content of ash is < 0.3 wt%.

[0009] Preferably, the above biomass-based precursor is prepared by one or more processes of oxidizing, pickling, washing with water, and drying the biomass carbon source.

[0010] Preferably, the above biomass carbon source includes one or more of coconut shell, straw, walnut shell, almond shell, hazelnut shell, pine nut shell, palm shell, camellia shell, bamboo, white sugar, starch, chitosan, lignin, hemicellulose, and cellulose.

[0011] Preferably, the acid solution used in the above pickling treatment is a mixture of one or more of organic acids and inorganic acids.

[0012] Preferably, the above inorganic acid is one or more of hydrochloric acid, phosphoric acid, boric acid, pyrophosphoric acid, carbonic acid, sulfuric acid, nitric acid, and hydrofluoric acid.

[0013] Preferably, the above organic acid is one or more of formic acid, acetic acid, oxalic acid, and citric acid.

[0014] Preferably, the above oxidation treatment is: performing oxidation treatment in an oxygen-containing atmosphere, and / or performing oxidation treatment using an oxidizing agent.

[0015] In a second aspect, the present application provides a biomass-based hard carbon material, which is prepared by carbonizing the above biomass-based precursor.

[0016] Preferably, the median particle size of the above biomass-based precursor is 3 μm to 15 μm.

[0017] Preferably, the above carbonization treatment is carried out in a protective atmosphere.

[0018] Preferably, the above protective atmosphere includes at least one of nitrogen, argon, neon, helium, xenon, or krypton.

[0019] Preferably, the heating rate of the above carbonization treatment is 1 °C / min to 5 °C / min, the temperature of the carbonization treatment is 800 °C to 1600 °C, and the time of the carbonization treatment is 1.5 h to 3 h.

[0020] Preferably, after the above-mentioned biomass-based precursor is subjected to the above-mentioned carbonization treatment, it further includes performing screening treatment and / or magnetic removal treatment.

[0021] In a third aspect, the present application provides a battery anode material, which includes the above-mentioned biomass-based hard carbon material.

[0022] In a fourth aspect, the present application provides a battery, which includes the above-mentioned battery anode material.

[0023] Generally speaking, compared with the prior art, the above technical solutions conceived by the present application mainly have the following technical advantages: (1) The content of volatile matter in the biomass-based precursor provided by the present application is 16wt% - 40wt%, the content of oxygen is 10wt% - 32wt%, the content of fixed carbon is 60wt% - 82wt%, the moisture content is ≤5wt%, and the ash content is ≤0.6%. The contents of volatile matter, fixed carbon, ash, and moisture in the above-mentioned biomass-based precursor are within a specific range, and it has a relatively high content of oxygen. Using this biomass-based precursor, a biomass-based hard carbon material with high specific capacity, high first charge-discharge efficiency, and good cycle stability can be prepared.

[0024] (2) Compared with the prior art, the present application does not need to repeatedly adjust the process parameters of high-temperature sintering, and the hard carbon materials prepared from different biomass raw materials can all exhibit excellent electrochemical performance. This greatly reduces the consumption of human and material resources caused by the adjustment of the sintering process, effectively shortens the R & D cycle and R & D cost of hard carbon materials, and helps to promote the large-scale production of hard carbon materials.

[0025] (3) In a preferred embodiment, the content of oxygen in the biomass-based precursor provided by the present application is 15wt% - 25wt%. The hard carbon material prepared by subjecting the biomass-based precursor to conventional high-temperature carbonization treatment can have well-developed pores, a large sodium storage space, and a stable pore structure that does not collapse. While ensuring the strength of the hard carbon material, it meets the expansion of the sodium storage space, thus greatly improving the electrochemical performance of the biomass-based hard carbon material. Detailed Embodiments

[0026] In order to make the objectives, technical solutions, and advantages of the present application clearer, the present application will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0027] In the description of this application, it should be understood that the term "and / or" describes the association relationship of associated objects and indicates that three relationships can exist. For example, A and / or B can represent three situations: A exists alone, A and B exist simultaneously, and B exists alone. In this text, the symbol " / " indicates that the associated objects are in an "or" relationship. For example, A / B means A or B.

[0028] In the description of the embodiments of this application, words such as "exemplary" or "for example" are used to give examples, illustrations, or explanations. Any embodiment or design solution described as "exemplary" or "for example" in the embodiments of this application should not be construed as being more preferred or having more advantages than other embodiments or design solutions. Rather, the use of words such as "exemplary" or "for example" is intended to present relevant concepts in a specific manner.

[0029] In the description of the embodiments of this application, unless otherwise specified, "a plurality of" means two or more.

[0030] The term "fixed carbon" in this application refers to the residue after removing volatile matter, moisture, and ash from the biomass-based precursor.

[0031] This application provides a biomass-based precursor. In this biomass-based precursor, the content of volatile matter is 16 wt% - 40 wt%, the content of oxygen is 10 wt% - 32 wt%, the content of fixed carbon is 60 wt% - 82 wt%, the moisture content ≤ 5 wt%, and the ash content ≤ 0.6%.

[0032] By controlling the content of each component within a specific range, the biomass-based precursor provided by this application can enable the hard carbon material prepared from this biomass-based precursor to have advantages such as high specific capacity, high first-cycle charge-discharge efficiency, and good cycle stability without repeatedly adjusting the sintering process. In addition, the hard carbon materials prepared from different biomass raw materials all exhibit excellent electrochemical performance, which can effectively shorten the R & D cycle and R & D cost of hard carbon materials in actual production and manufacturing, and contribute to promoting the large-scale production of hard carbon materials.

[0033] In the biomass-based precursor provided by the present application, the volatile content is 16 wt% to 40 wt%, for example, it can be 16 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%; the oxygen content is 10 wt% to 32 wt%, for example, it can be 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 32 wt%; the fixed carbon content is 60 wt% to 82 wt%, for example, it can be 60 wt%, 65 wt%, 70 wt%, 75 wt%, 80 wt%, 82 wt%; the moisture content is ≤ 5 wt%, for example, it can be 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%; the ash content is ≤ 0.5%, for example, it can be 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%.

[0034] In some embodiments, in the above biomass-based precursor, the oxygen content is 15 wt% to 25 wt%.

[0035] In a preferred embodiment, in the above biomass-based precursor, the volatile content is 25 wt% to 35 wt%, the oxygen content is 15 wt% to 25 wt%, the fixed carbon content is 70 wt% to 80 wt%, the moisture content is < 5 wt%, and the ash content is < 0.6 wt%.

[0036] In a more preferred embodiment, in the above biomass-based precursor, the volatile content is 30 wt% to 32 wt%, the oxygen content is 17 wt% to 23 wt%, the fixed carbon content is 70 wt% to 73 wt%, the moisture content is < 3 wt%, and the ash content is < 0.3 wt%.

[0037] It can be understood that the present application does not specifically limit the preparation process of the above biomass-based precursor, and it can be prepared by conventional methods in the art, which are all within the protection scope of the present application.

[0038] In some embodiments, the above biomass-based precursor is prepared by one or more processes of oxidizing, pickling, washing with water, and drying the biomass carbon source. The present application does not limit the processing sequence of the above processes, and those skilled in the art can adjust it according to the selection of the biomass carbon source.

[0039] In some embodiments, according to the selection of the biomass carbon source, by adding pickling, and / or washing with water, and / or oxidation and other processes, or adjusting the corresponding process parameters, the adjustment of the volatile content, and / or fixed carbon content, and / or oxygen content, and / or moisture content, and / or ash content of the biomass-based precursor is achieved.

[0040] In some embodiments, by adding pickling, washing with water and other processes, or adjusting the corresponding process parameters, the adjustment of the ash content of the biomass-based precursor is achieved.

[0041] In some embodiments, by adding processes such as oxidation and adjusting parameters of different oxidation processes, such as different oxidation methods, use of different oxidants, number of oxidation times, etc., the oxygen content of the biomass-based precursor is adjusted.

[0042] In some embodiments, after subjecting the biomass carbon source to various processes, the moisture content of the biomass-based precursor is adjusted by drying.

[0043] This application does not limit the source of the above-mentioned biomass carbon source. For example, the above-mentioned biomass carbon source can be a commercially available product or can be obtained by crushing biomass raw materials. In some embodiments, the above-mentioned biomass carbon source is, for example, selected from one or more of coconut shell, straw, nut shells (such as walnut shell, almond shell, hazelnut shell, chestnut shell, pine nut shell, etc.), palm shell, oil tea shell, bamboo, white sugar, biomass polymers (such as starch, chitosan, lignin, hemicellulose, cellulose, etc.). Those skilled in the art can select conventional crushing methods to crush the above-mentioned biomass carbon source, and the crushing methods include but are not limited to one or two or more combinations of mechanical ball milling, impact, shearing, and air flow impact.

[0044] In some embodiments, the acid solution used in the above pickling treatment is a mixture of one or more of organic acids and inorganic acids; the above inorganic acids are one or more of hydrochloric acid, phosphoric acid, boric acid, pyrophosphoric acid, carbonic acid, sulfuric acid, nitric acid, and hydrofluoric acid; the above organic acids are one or more of formic acid, acetic acid, oxalic acid, and citric acid.

[0045] This application does not particularly limit the concentration of the acid solution. Considering easy availability and operation safety, the concentration of the acid solution can be, for example, 0.5 mol / L to 5 mol / L.

[0046] In some embodiments, the dosage of the acid solution can be, for example, 0.1 to 50 times or more of the mass of the biomass, such as 0.1, 1, 2, 5, 10, 20 times. In some embodiments, the time of the above pickling treatment is 1 h to 10 h, and the purpose is to remove most of the ash in the biomass. In some embodiments, the above pickling treatment can be carried out at room temperature or elevated temperature. It can also be carried out with or without stirring, for example, pickling treatment is carried out by soaking. Those skilled in the art can appropriately adjust the mass ratio of the biomass or its derivatives to the acid solution according to the concentration of the acid solution, and extend or shorten the time of the pickling treatment, all within the protection scope of this application.

[0047] In some embodiments, the water washing can be carried out by using a solvent to spray-wash or soak-wash the material to be water-washed, etc., so as to remove some water-soluble substances. If the acid washing step is carried out before the water washing, the water washing can remove the acid-soluble impurities and the unreacted acid solution in the biomass, and improve the purity of the biomass material. In some embodiments, the solvent used for the above water washing can be, but is not limited to, water.

[0048] In some embodiments, the purpose of the above drying is to remove the residual moisture on the surface of the biomass material.

[0049] In some embodiments, the operation of the above oxidation treatment is: carrying out the oxidation treatment in an oxygen-containing atmosphere. In some other embodiments, the operation of the above oxidation treatment is: carrying out the oxidation treatment by using an oxidizing agent.

[0050] It can be understood that the oxidation treatment process can be carried out with a single oxidation, or multiple oxidations of two or more times. When multiple oxidations are adopted, the two oxidations can adopt the same oxidation method, or different oxidation methods. For example, oxidation in an oxygen-containing atmosphere can be carried out two or more times; oxygen-containing atmosphere oxidation and oxidant oxidation can also be carried out separately.

[0051] In some embodiments, the time of the above oxidation treatment is 1h to 3.5h.

[0052] In some embodiments, the material to be oxidized is subjected to oxidation treatment in an oxygen-containing atmosphere. After the reaction ends, a biomass-based precursor is obtained. Among them, the above oxygen-containing atmosphere includes, but is not limited to, oxygen, air, etc.; the temperature of the above oxidation treatment is 200°C to 375°C, preferably 300°C to 350°C.

[0053] In some embodiments, the material to be oxidized is mixed with an oxidizing agent for oxidation treatment. Among them, the above oxidizing agent includes one or more of, but is not limited to, hydrogen peroxide, concentrated nitric acid, concentrated sulfuric acid, potassium permanganate, etc.

[0054] In some embodiments, if water washing is carried out after the oxidation treatment with an oxidizing agent, the water washing can also remove the residual oxidizing agent in the product.

[0055] Through the oxidation treatment of the present application, the content of volatile matter and the content of oxygen in the volatile matter in the biomass-based precursor can be increased, so that after the biomass-based precursor undergoes conventional high-temperature carbonization treatment, an excellent pore structure can be obtained, and the sodium storage space of the hard carbon material can be improved.

[0056] In some embodiments, the material to be oxidized is mixed with an oxidizing agent for the first oxidation treatment, and then the second oxidation treatment is carried out in an oxygen-containing atmosphere.

[0057] On the other hand, the biomass-based hard carbon material can be prepared after the biomass-based precursor provided by the present application undergoes carbonization treatment, including the following steps: Carbonize the biomass-based precursor under a protective atmosphere to obtain the biomass-based hard carbon material.

[0058] In some embodiments, the median particle size of the above-mentioned biomass-based precursor is 3 μm to 15 μm, which is conducive to the subsequent coating of the obtained hard carbon material by the homogenization process and meets the requirements of the downstream industry for the material compaction degree. In some embodiments, a conventional crushing method can be selected to crush the above-mentioned biomass-based precursor to obtain a biomass-based precursor with a suitable median particle size.

[0059] In some embodiments, the above-mentioned protective atmosphere includes at least one of nitrogen, argon, neon, helium, xenon or krypton.

[0060] In some embodiments, the heating rate of the above-mentioned carbonization treatment is 1 °C / min to 5 °C / min, the temperature is 800 °C to 1600 °C, and the time is 1.5 h to 3 h.

[0061] In some embodiments, after the above-mentioned biomass-based precursor is carbonized, a demagnetization treatment is further included, which can reduce the content of magnetic substances in the biomass-based hard carbon material and improve the cycle stability of the battery assembled with the hard carbon material. In some embodiments, the above-mentioned demagnetization treatment is performed several times, such as 1 to 5 times. In some embodiments, the magnetic field strength of the above-mentioned demagnetization treatment is ≥20000 Gs. Exemplarily, the magnetic field strength of the above-mentioned demagnetization treatment is 20000 Gs to 50000 Gs.

[0062] The biomass-based hard carbon material prepared by using the biomass-based precursor provided in this application has a high specific capacity, a high first-cycle charge-discharge efficiency, and excellent electrochemical performance.

[0063] In some embodiments, the biomass-based hard carbon material prepared in this application can be used as the hard carbon material for sodium-ion batteries. In some embodiments, the above-mentioned hard carbon material for sodium-ion batteries can be the hard carbon negative electrode material for sodium-ion batteries.

[0064] On the other hand, this application also provides a battery negative electrode material, which includes the above-mentioned biomass-based hard carbon material.

[0065] In some embodiments, the above-mentioned battery negative electrode material includes a lithium-ion battery negative electrode material and a sodium-ion battery negative electrode material.

[0066] On the other hand, this application also provides a battery, which includes the above-mentioned battery negative electrode material.

[0067] In some embodiments, the above-mentioned battery includes a lithium-ion battery and a sodium-ion battery.

[0068] It should be understood that materials that are the same as or similar to the types, models, qualities, properties, or functions of the reagents and instruments used in the following embodiments can be used to implement this application. Unless otherwise specified, the experimental methods used in the following embodiments are all conventional methods. Unless otherwise specified, the materials, reagents, etc. used in the following embodiments can all be obtained from commercial sources.

[0069] The following are examples and comparative examples: Example 1 The preparation method of the biomass-based precursor provided in this example includes the following steps: (1) Raw material preparation: Select coconut shell as the biomass raw material.

[0070] (2) Pickling treatment: Mix the above-mentioned biomass raw material and a nitric acid solution with a concentration of 1 mol / L in a mass ratio of 3:1 for pickling. The pickling time is 3 h to obtain a suspension; then filter, wash with water, and dry the moisture to obtain the material to be oxidized.

[0071] (3) Oxidation treatment: Place the above-mentioned material to be oxidized in air for oxidation treatment. Among them, the temperature of the oxidation treatment is 350 °C, and the time of the oxidation treatment is 2 h. After the reaction ends, a biomass-based precursor is obtained.

[0072] Example 2 Similar to Example 1, the difference is that in step (1), straw is selected as the biomass raw material.

[0073] Example 3 Similar to Example 1, the difference is that in step (2), the acid solution used for pickling treatment is a hydrochloric acid solution with a concentration of 1 mol / L; in step (3), the temperature of the oxidation treatment is 200 °C, and the time of the oxidation treatment is 2 h.

[0074] Example 4 Similar to Example 1, the difference is that in step (2), the acid solution used for pickling treatment is a nitric acid solution with a concentration of 2 mol / L; in step (3), the temperature of the oxidation treatment is 375 °C, and the time of the oxidation treatment is 2 h.

[0075] Example 5 Similar to Example 1, the difference is that in step (2), the acid solution used for pickling treatment is a hydrochloric acid solution with a concentration of 0.5 mol / L.

[0076] Example 6 Similar to Example 1, the difference is that in step (3), two oxidation treatments are carried out by using potassium permanganate as the oxidant and air oxidation. Specifically: the above-mentioned material to be oxidized and a potassium permanganate solution with a concentration of 0.5 mol / L are mixed according to a mass ratio of 3:1 for the first oxidation treatment, and the time for the first oxidation treatment is 1 h; then it is filtered, washed with water, and dried to remove moisture, and the second oxidation treatment is carried out under air, the temperature for the second oxidation treatment is 325 °C, and the time for the second oxidation treatment is 1 h.

[0077] Example 7 Similar to Example 1, the difference is that in step (2), the biomass raw material and a nitric acid solution with a concentration of 1 mol / L are mixed according to a mass ratio of 1:1 for pickling treatment.

[0078] Example 8 Similar to Example 1, the difference is that in step (2), the acid solution used for pickling treatment is a hydrochloric acid solution with a concentration of 1 mol / L; in step (3), hydrogen peroxide is used as the oxidant for oxidation treatment. Specifically, the above-mentioned material to be oxidized and a hydrogen peroxide solution with a concentration of 1 mol / L are in a mass ratio of 1:1, and then it is filtered, washed with water, and dried to remove moisture to obtain the biomass-based precursor.

[0079] Comparative Example 1 Similar to Example 1, the difference is that step (3) oxidation treatment is not carried out.

[0080] Comparative Example 2 Similar to Example 1, the difference is that the temperature of the oxidation treatment in step (3) is 400 °C.

[0081] Comparative Example 3 Similar to Example 1, the difference is that step (2) pickling treatment is not carried out.

[0082] Comparative Example 4 Similar to Example 8, the difference is that after the oxidation treatment with hydrogen peroxide in step (3), it is filtered, washed with water, and naturally air-dried to obtain the biomass-based precursor.

[0083] Comparative Example 5 Similar to Example 1, the difference is that neither step (2) pickling treatment nor step (3) oxidation treatment is carried out.

[0084] The contents of volatile matter, oxygen, fixed carbon, moisture, and ash in the biomass-based precursors prepared in each example and comparative example were tested. The specific testing method is as follows: (a) Volatile matter content: It was determined by referring to the standard method of GB / T 212-2008.

[0085] (b) Oxygen content: It was determined by referring to the elemental analyzer method.

[0086] (c) Fixed carbon content: Determined with reference to GB / T 3521-2023.

[0087] (d) Moisture content: Determined with reference to the graphite chemical analysis method of GB / T 6283-2008.

[0088] (e) Ash content: Determined with reference to the graphite chemical analysis method of GB / T 6283-2008.

[0089] The specific components of the biomass-based precursors prepared in each example and comparative example are shown in Table 1.

[0090] Table 1 Components of the biomass-based precursors prepared in examples and comparative examples

[0091] Application Examples 1-13 The preparation method of the hard carbon material provided by this application includes the following steps: S1. Crush the above-prepared biomass-based precursor to obtain a biomass-based precursor powder with a D50 of 6 μm.

[0092] S2. Place the biomass precursor powder prepared in step S1 in a tube furnace, perform high-temperature carbonization by sintering at 1300 °C for 2 h under a nitrogen atmosphere, and then perform screening and demagnetization. The mesh diameter of the sieve is 325 mesh, and the discharge port is connected to a demagnetizing rod of 20000 Gs to obtain a biomass-based hard carbon material.

[0093] Test the electrochemical performance of the biomass-based hard carbon material. The test method is as follows: Assemble the above biomass-based hard carbon material into a button cell as the anode material of a sodium-ion battery. Specifically, mix the biomass-based hard carbon material, the binder polyvinylidene fluoride, and conductive carbon black in a mass ratio of 92:4:4 to make a slurry, uniformly coat it on an aluminum foil and dry it to make an electrode. Use a sodium sheet as the counter electrode, select a glass fiber film as the separator, and use a mixed solution of 1 mol / L NaPF6 and ethylene carbonate (EC):dimethyl carbonate (DEC) = 1:1 vol.% as the electrolyte to make a button cell. Test the above button cell. The test conditions are: in a constant temperature cabinet at 25 °C, in the range of 0-2.5 V, perform a constant current charge-discharge test in the manner of a nominal gram capacity of 200 mAh / g.

[0094] The test results of the electrochemical performance of the biomass-based hard carbon material prepared with the above biomass-based precursor are shown in Table 2.

[0095] Table 2 Electrochemical performance of the biomass-based hard carbon material prepared with the biomass-based precursor

[0096] From Tables 1 and 2, by comparing Application Examples 1-8 and Application Examples 9-13, it is found that when the oxygen content in the biomass-based precursor is too low (Comparative Example 1), the oxygen content is too high (Comparative Example 2), the ash content is too high (Comparative Example 3), the moisture content is too high (Comparative Example 4), or the fixed carbon content is too high (Comparative Example 5), the electrochemical performance of the biomass-based hard carbon material prepared from the biomass precursor is poor, and the specific capacity or the first charge-discharge efficiency of the assembled battery is low. When the volatile content in the biomass-based precursor is 16 wt% - 40 wt%, the oxygen content is 10 wt% - 32 wt%, the fixed carbon content is 60 wt% - 82 wt%, the moisture content ≤ 5 wt%, and the ash content is ≤ 0.6 wt%, after the biomass-based precursor undergoes conventional high-temperature carbonization treatment, an excellent pore structure can be obtained, and at the same time, it has an appropriate degree of surface defects, thereby synergistically improving the specific capacity and the first charge-discharge efficiency of the biomass-based hard carbon material.

[0097] Among them, the specific capacity of the biomass-based hard carbon material prepared from the biomass-based precursors provided in Example 3 and Example 7 needs to be further improved. The reason may be that the oxygen content in the volatile matter of the biomass-based precursor is relatively low (less than 15 wt%), resulting in insufficient pore development of the hard carbon material and less sodium storage space, thus reducing the specific capacity of the hard carbon material. The first charge-discharge efficiency of the biomass-based hard carbon material prepared from the biomass-based precursor provided in Example 4 is relatively low. The reason may be that the oxygen content in the volatile matter of the biomass precursor is relatively high (greater than 30%), resulting in more pores generated during the carbonization process of the biomass-based precursor, the specific surface area of the hard carbon material becomes larger, and the structure of the hard carbon material is unstable or even collapses, thus resulting in a decrease in the first efficiency of the hard carbon material.

[0098] It can be seen from Examples 1-2, 5-6, and 8 that when the volatile content in the biomass-based precursor is 25 wt% - 35 wt%, the oxygen content is 15 wt% - 25 wt%, the fixed carbon content is 70 wt% - 80 wt%, the moisture content < 5 wt%, and the ash content is < 0.6 wt%, the biomass-based hard carbon material prepared from the biomass precursor has better specific capacity and first charge-discharge efficiency, and better electrochemical performance.

[0099] Further, in Examples 1 to 2 and 6, when the content of volatile matter in the biomass-based precursor is 30 wt% to 32 wt%, the content of oxygen is 17 wt% to 23 wt%, the content of fixed carbon is 70 wt% to 73 wt%, the content of moisture is < 3 wt%, and the content of ash is < 0.3 wt%, the hard carbon material prepared by subjecting the biomass-based precursor to conventional high-temperature carbonization treatment has well-developed pores, a large sodium storage space, and a stable pore structure without collapse, that is, while ensuring the strength of the hard carbon material, the expansion of the sodium storage space is satisfied, so that the biomass-based hard carbon material has the optimal specific capacity and the best electrochemical performance.

[0100] Those skilled in the art can easily understand that the above are only the preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A biomass-based precursor, characterized in that, In the biomass-based precursor, the content of volatile matter is 16 wt% to 40 wt%, the content of oxygen is 10 wt% to 32 wt%, the content of fixed carbon is 60 wt% to 82 wt%, the content of moisture is ≤ 5 wt%, and the content of ash is ≤ 0.6%.

2. The biomass-based precursor according to claim 1, wherein In the biomass-based precursor, the content of oxygen is 15 wt% to 25 wt%.

3. The biomass-based precursor according to claim 1 or 2, wherein The biomass carbon source of the biomass-based precursor is selected from one or more of coconut shell, straw, walnut shell, almond shell, hazelnut shell, pine nut shell, palm shell, oil-tea camellia shell, bamboo, white sugar, starch, chitosan, lignin, hemicellulose, and cellulose.

4. A biomass-based hard carbon material, characterized in that, The biomass-based hard carbon material is prepared by carbonizing the biomass-based precursor according to any one of claims 1 to 3.

5. The biomass-based hard carbon material according to claim 4, wherein The median particle size of the biomass-based precursor is 3 μm to 15 μm.

6. The biomass-based hard carbon material according to claim 4, wherein The carbonization treatment is carried out in a protective atmosphere, and the protective atmosphere includes at least one of nitrogen, argon, neon, helium, xenon, or krypton.

7. The biomass-based hard carbon material according to claim 4, wherein The heating rate of the carbonization treatment is 1 °C / min to 5 °C / min, the temperature of the carbonization treatment is 800 °C to 1600 °C, and the time of the carbonization treatment is 1.5 h to 3 h.

8. The biomass-based hard carbon material according to claim 4, wherein After the biomass-based precursor is subjected to the carbonization treatment, it further includes performing a screening treatment and / or a demagnetization treatment.

9. A negative electrode material for a battery, characterized in that, The battery negative electrode material includes the biomass-based hard carbon material according to any one of claims 4 to 8.

10. A battery, characterized in that, The battery includes the battery negative electrode material according to claim 9.

Images