Hard carbon, its preparation method, and its applications

Abstract

This invention belongs to the field of battery material preparation technology, and discloses a hard carbon, its preparation method, and its applications. The preparation method includes the following steps: mixing biomass with an organic acid and esterifying it at 200-420°C to obtain an esterified material; washing the esterified material with water and then performing sintering pre-carbonization to obtain a pre-carbonized material; crushing the pre-carbonized material, then washing it with water, and then performing sintering carbonization again to obtain low-impurity, low-pH hard carbon. This invention, through esterification, water washing, pre-carbonization, water washing, and carbonization treatments, and with the esterification process carried out at a specific temperature (200-420°C), results in hard carbon with low impurity content and low pH. The preparation method of this invention uses two water washing processes instead of acid washing, saving production costs and being environmentally friendly.

Description

Technical Field

[0001] This invention belongs to the field of battery material preparation technology, and specifically relates to a hard carbon, its preparation method, and its application. Background Technology

[0002] The preparation of hard carbon anodes uses biomass as raw material. Biomass is widely available and inexpensive. However, biomass contains a large number of impurity elements. These impurities not only lead to increased ash content, resulting in poor consistency of hard carbon materials, but also cause an increase in pH, which in turn reduces the electrochemical performance of hard carbon materials.

[0003] Analyzing the content and forms of impurity elements is of great significance for their removal. Carbon, hydrogen, and oxygen are the main elements in biomass, which also contain inorganic elements such as Na, K, P, Al, S, Ca, Si, and Cl. Taking K as an example, K in a certain biomass raw material exists in three forms: water-soluble K, organic matter-bound K, and hydrochloric acid-soluble K, accounting for 73%, 22%, and 5%, respectively.

[0004] The conventional method for reducing impurities in hard carbon involves acid washing of the biomass raw materials to remove impurities, followed by water washing to remove residual acid, and then drying. However, this method is expensive, and only a few institutions are qualified to perform acid washing. Currently, acid washing of hard carbon is concentrated before sintering. Therefore, the acid washing effect is closely related to the particle size of the raw materials. However, for biomass raw materials, particle size control is generally not strict, resulting in the presence of large-particle biomass raw materials, which in turn leads to insufficient acid washing. Even with increased costs, the ash content remains high after acid washing.

[0005] Using biomass as a raw material for hard carbon results in high impurity content and high pH in the finished product. Acid washing to remove impurities from biomass is not only costly but also requires strict qualifications from acid washing units, which is not conducive to hard carbon production. Moreover, existing hard carbon prepared using acid washing methods also has a high ash content.

[0006] Therefore, there is an urgent need to provide a new method for preparing hard carbon that can obtain hard carbon with low impurity content and low pH without the use of acid washing. Summary of the Invention

[0007] This invention aims to solve at least one of the technical problems existing in the prior art. To this end, this invention proposes a hard carbon, its preparation method, and its applications. The preparation method of this invention can obtain hard carbon with low impurity content and low pH without the use of acid washing.

[0008] The inventive concept of this invention is as follows: The preparation method of this invention uses biomass as raw material, and processes it through esterification, water washing, pre-carbonization, and water washing. The esterification process is carried out at a specific temperature, which allows the biomass to complete the release and combustion of volatiles. Therefore, the organic matter in the biomass raw material can be destroyed during the esterification process, releasing impurity elements bound by the organic matter. At this time, water washing of the esterified material can not only remove most of the soluble impurities and some slightly soluble impurities, but also lower the pH of the esterified material, improve the processability of the esterified material, and at the same time save costs and eliminate the need for acid washing.

[0009] Because the esterified material has a complex structure and meandering channels after esterification, a second washing is performed after pre-carbonization. At this stage, the interlayer spacing and channels of the pre-carbonized material are larger, and the second washing can further remove soluble impurities that were not completely removed after esterification. After complete carbonization, the interlayer spacing of the material decreases and the channels become longer. Even if washing is performed after carbonization, the effect is not as good as washing again after pre-carbonization. Moreover, washing after pre-carbonization may cause material inhomogeneity due to the removal of impurities, but subsequent carbonization can ensure material consistency. If washing is performed after carbonization, the material inhomogeneity will be more pronounced.

[0010] This invention uses esterification, washing, pre-carbonization, washing, and carbonization to obtain hard carbon with low impurity content and low pH.

[0011] A first aspect of the present invention provides a method for preparing hard carbon.

[0012] A method for preparing hard carbon includes the following steps:

[0013] Biomass is mixed with organic acids and esterified at 200-420℃ to obtain esterified materials.

[0014] The esterified material is washed with water and then sintered and pre-carbonized to obtain a pre-carbonized material.

[0015] The pre-carbonized material is crushed, then washed with water, and then sintered and carbonized to obtain the hard carbon.

[0016] In some embodiments of the present invention, before mixing the biomass with the organic acid, the method further includes: pulverizing the biomass.

[0017] In some embodiments of the present invention, the organic acid includes at least one selected from maleic anhydride, citric acid, malic acid, and tartaric acid.

[0018] In some embodiments of the present invention, the mass ratio of biomass to organic acid is (85-95):(5-15), specifically 85:15, 90:10, 95:5, etc.

[0019] In some embodiments of the present invention, the biomass is selected from at least one of coconut shell, lotus leaf stalk, peanut shell, lignin, rice husk, corn cob, wheat straw, soybean straw, and cotton straw.

[0020] In some embodiments of the present invention, biomass is mixed with organic acid and esterified at 280-350°C to obtain esterified material; for example, the temperature can be heated to 280°C, 290°C, 300°C, 320°C, or 350°C. Different esterification temperatures and times result in different degrees of organic matter release, which in turn leads to different degrees of water washing for impurity removal and pH reduction. Therefore, a temperature of 280-350°C and a holding time of 2-4 hours are selected as the optimal esterification conditions.

[0021] In some embodiments of the present invention, biomass is mixed with organic acid and esterified at 200-420°C for 1.8-4 hours to obtain esterified material; for example, the holding time can be 2-4 hours, specifically 2 hours, 3 hours, or 4 hours.

[0022] In some embodiments of the present invention, after obtaining the esterified material, it is further crushed.

[0023] In some embodiments of the present invention, after obtaining the esterified material, it is further crushed to a D0.05 of the esterified material. 50 The particle size is 2-8 μm, and further 3-6 μm. For example, 3 μm, 4 μm, 5 μm, and 6 μm. This crushing facilitates the removal of impurities when the esterified material is washed with water.

[0024] In some embodiments of the present invention, the crushing method includes at least one of jaw crusher, roller crusher, or air crusher.

[0025] In some embodiments of the present invention, the water washing process involves mixing the esterified material with water at a mass ratio of 1:(3-10), soaking and washing for at least 2 hours at a water temperature of 20-60°C, followed by pressure filtration and drying. It is understood that soaking and washing can include methods such as static soaking, soaking with stirring, soaking with ultrasonic cleaning, and soaking with circulating spray. Water at this temperature provides thorough cleaning and is cost-effective. If the water temperature is too high, the cost is higher; if the water temperature is too low, the cleaning effect is weakened.

[0026] In some embodiments of the present invention, the water washing process involves mixing the esterified material with water at a mass ratio of 1:(4-8), soaking and washing for 2-4 hours at a water temperature of 25-50°C, and then performing pressure filtration and drying.

[0027] In some embodiments of the present invention, the sintering pre-carbonization temperature is 650-800°C, and the sintering pre-carbonization time is 1.5-2.5 hours.

[0028] In some embodiments of the present invention, the sintering pre-carbonization temperature is 650-800°C, and the sintering pre-carbonization time is 1.5-2 hours.

[0029] In some embodiments of the present invention, the sintering pre-carbonization is carried out under a protective atmosphere. The protective atmosphere is, for example, one or more of nitrogen or rare gases (e.g., helium, argon, krypton).

[0030] In some embodiments of the present invention, the pre-carbonized material is crushed to D... 50 The range is 1-8 μm, and further to 3-6 μm. For example, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, and 6 μm.

[0031] In some embodiments of the present invention, the pre-carbonized material is crushed and then washed with water. The washing process involves mixing the pre-carbonized material with water at a mass ratio of 1:(3-10), soaking and washing for more than 2 hours at a water temperature of 20-60°C, and then pressing and drying.

[0032] In some embodiments of the present invention, the sintering and carbonization temperature is 1100-1300℃ and the time is 1.5-2.5 hours.

[0033] In some embodiments of the present invention, the sintering and carbonization are carried out under a protective atmosphere.

[0034] In some embodiments of the present invention, the impurity element content of the hard carbon is reduced by more than 70% (mass fraction) relative to the biomass, for example, by 75-95%. The impurity elements include K, Na, S, Ca, Al, and Si.

[0035] In some embodiments of the present invention, the pH of the hard carbon is 7.0-8.1, for example 7.0-8.0 or 7.5-7.82.

[0036] A second aspect of the present invention provides a hard carbon.

[0037] A type of hard carbon, prepared by the above method.

[0038] A third aspect of the present invention provides the application of the hard carbon obtained by the above-described preparation method.

[0039] Application of hard carbon prepared by the above method in batteries.

[0040] The battery includes a sodium-ion battery. Applying the hard carbon of the present invention as the negative electrode in a sodium-ion battery helps maintain the electrochemical performance of the sodium-ion battery due to the low impurity content and low pH of the hard carbon.

[0041] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0042] (1) The present invention uses esterification, water washing, pre-carbonization, water washing and carbonization treatment, and the esterification process is carried out at a specific temperature (200-420℃) so that the final hard carbon has low impurity content and low pH.

[0043] (2) The preparation method described in this invention uses two water washings instead of acid washing, which saves production costs and is environmentally friendly.

[0044] (3) Two crushing processes after esterification and pre-carbonization can result in a uniform particle size distribution of the material, which is beneficial for water washing to fully remove impurities and reduce ash content. However, direct acid washing of biomass results in high ash content in the final hard carbon due to the lack of strict control over biomass particle size.

[0045] (4) When testing pH, the pH of hard carbon that has not undergone impurity removal treatment will rise because impurity elements such as Na and K dissolve in water. After washing, impurity elements such as Na and K are removed, so the pH of hard carbon will decrease significantly and the processing performance of hard carbon will be improved.

[0046] (5) After pre-carbonization, water washing removes impurity elements. The material inhomogeneity caused by these elements can be ensured by subsequent carbonization and sintering. Attached Figure Description

[0047] Figure 1 This is a schematic flowchart of the preparation method in Example 1 of the present invention. Detailed Implementation

[0048] To enable those skilled in the art to more clearly understand the technical solutions described in this invention, the following embodiments are provided for illustration. It should be noted that the following embodiments do not constitute a limitation on the scope of protection claimed by this invention.

[0049] Unless otherwise specified, the raw materials, reagents or devices used in the following examples are available from conventional commercial sources or can be obtained by existing known methods.

[0050] In the following examples and comparative examples, the heating or sintering process is carried out in air unless otherwise specified.

[0051] Example 1

[0052] A method for preparing low-impurity, low-pH hard carbon includes the following steps:

[0053] After mixing the crushed coconut shell with maleic anhydride at a mass ratio of 9:1, the mixture was placed in a muffle furnace and heated at 250°C for 3 hours under air conditions to esterify the material.

[0054] The esterified material is subjected to jaw crusher, roller crusher, and air crusher to control the D of the esterified material. 50 3-6μm;

[0055] The crushed esterified material was mixed with water at a mass ratio of 1:5 and washed for 4 hours with the water temperature controlled at 28±2℃. After pressure filtration, it was dried.

[0056] The dried esterified material was placed in a tube furnace and pre-carbonized by sintering at 800°C for 2 hours under a nitrogen atmosphere to obtain the pre-carbonized material.

[0057] The pre-carbonized material is subjected to jaw crusher, roller crusher, and air crusher to control the D of the pre-carbonized material. 50 It is 3-5μm.

[0058] The crushed pre-carbonized material was mixed with water at a mass ratio of 1:5 and washed for 4 hours with the water temperature controlled at 35±2℃. After filtration, it was dried.

[0059] The dried pre-carbonized material was placed in a tube furnace and carbonized at 1300℃ for 2 hours under a nitrogen atmosphere to obtain hard carbon.

[0060] Figure 1 This is a schematic flowchart of the preparation method in Example 1 of the present invention.

[0061] Example 2

[0062] Compared with Example 1, the only difference in Example 2 is that the coconut shell and maleic anhydride are heated and kept at 280°C for 3 hours, while the rest of the process is the same as in Example 1.

[0063] Example 3

[0064] Compared with Example 1, the only difference in Example 3 is that the coconut shell and maleic anhydride are heated and kept at 350°C for 3 hours, while the rest of the process is the same as in Example 1.

[0065] Example 4

[0066] Compared with Example 1, the only difference in Example 4 is that the coconut shell and maleic anhydride are heated and kept at 300°C for 3 hours, while the rest of the process is the same as in Example 1.

[0067] Example 5

[0068] Compared with Example 1, the only difference in Example 5 is that the coconut shell and maleic anhydride are heated and kept at 420°C for 3 hours, while the rest of the process is the same as in Example 1.

[0069] Example 6

[0070] Compared with Example 1, the only difference in Example 6 is that the coconut shell and maleic anhydride are heated and kept at 200°C for 3 hours, while the rest of the process is the same as in Example 1.

[0071] Example 7

[0072] Compared with Example 1, the only difference in Example 7 is that wheat straw is used instead of coconut shells; the rest of the process is the same as in Example 1.

[0073] Example 8

[0074] A method for preparing low-impurity, low-pH hard carbon includes the following steps:

[0075] The crushed coconut shells and citric acid were mixed at a mass ratio of 95:5 and then placed in a muffle furnace. The mixture was heated at 290°C for 2 hours under air conditions to esterify the material.

[0076] The esterified material is subjected to jaw crusher, roller crusher, and air crusher to control the D of the esterified material. 50 3-6μm;

[0077] The crushed esterified material was mixed with water at a mass ratio of 1:8 and washed for 3 hours with the water temperature controlled at 40±2℃. After filtration, it was dried.

[0078] The dried esterified material was placed in a tube furnace and pre-carbonized by sintering at 650°C for 3 hours under a nitrogen atmosphere to obtain the pre-carbonized material.

[0079] The pre-carbonized material is subjected to jaw crusher, roller crusher, and air crusher to control the D of the pre-carbonized material. 50 It is 3-5μm.

[0080] The crushed pre-carbonized material was mixed with water at a mass ratio of 1:4 and washed for 5 hours with the water temperature controlled at 40±2℃. After filtration, it was dried.

[0081] The dried pre-carbonized material was placed in a tube furnace and carbonized at 1250℃ for 2.5 hours under a nitrogen atmosphere to obtain hard carbon.

[0082] Comparative Example 1

[0083] Compared with Example 1, the only difference in Comparative Example 1 is that the coconut shell and maleic anhydride are heated and kept at 180°C for 3 hours, while the rest of the process is the same as in Example 1.

[0084] Comparative Example 2

[0085] Compared with Example 1, the only difference in Comparative Example 2 is that the coconut shell and maleic anhydride are heated and kept at 450°C for 3 hours, while the rest of the process is the same as in Example 1.

[0086] Comparative Example 3

[0087] Compared with Example 1, the only difference in Comparative Example 3 is that the esterified material was not washed with water, while the rest of the process was the same as in Example 1.

[0088] Comparative Example 4

[0089] Compared with Example 1, the only difference in Comparative Example 4 is that the esterified material was not washed with water, and it was not washed with water after pre-carbonization. The rest of the process is the same as in Example 1.

[0090] Comparative Example 5

[0091] Compared with Comparative Example 4, the only difference in Comparative Example 5 is that wheat straw is used instead of coconut shells; the rest of the process is the same as that in Comparative Example 4.

[0092] Comparative Example 6

[0093] A method for preparing hard carbon includes the following steps:

[0094] (1) The crushed coconut shells were mixed and stirred in 0.5 mol / L hydrochloric acid for 2 hours for acid washing, then washed with water for 2 hours and dried.

[0095] (2) The dried coconut shell and maleic anhydride were mixed and placed in a muffle furnace and sintered at 250°C for 3 hours under air conditions to obtain esterified material.

[0096] (3) The esterified material is subjected to jaw crusher, roller crusher and gas crusher, and then placed in a tube furnace and sintered at 800°C for 2 hours under nitrogen atmosphere to obtain pre-carbonized material.

[0097] (4) The pre-carbonized material is subjected to jaw crusher, roller crusher and air crusher to control the D of the pre-carbonized material. 50 It is 3-6μm.

[0098] (5) The crushed pre-carbonized material is placed in a tube furnace and carbonized at 1300℃ for 2 hours under a nitrogen atmosphere to obtain hard carbon.

[0099] Comparative Example 7

[0100] Compared with Example 1, the only difference in Comparative Example 7 is that the pre-carbonized material was not washed with water; the rest of the process is the same as in Example 1.

[0101] Comparative Example 8

[0102] Compared with Comparative Example 7, the only difference in Comparative Example 8 is that the coconut shell and maleic anhydride were heated and kept at 400℃ for 1 hour, while the rest of the process was the same as that of Comparative Example 7.

[0103] Product effectiveness test

[0104] The hard carbon prepared in the above examples and comparative examples was tested for impurity element content, pH, and ash content in accordance with GB / T 41330-2022, GB 6920-1986, and GB / T2295-2008. The results are shown in Table 1.

[0105] Table 1

[0106]

[0107]

[0108] As shown in Table 1, the temperature for preparing the esterified material, the water washing of the esterified material, and the water washing of the pre-carbonized material all significantly affect the content of impurity elements in the hard carbon, as well as the pH value of the hard carbon, and also have a certain impact on the ash content. Therefore, to obtain hard carbon with low impurity content and low pH value, it is necessary to follow the preparation method of this invention. Furthermore, the preparation method of this invention uses two water washing processes instead of traditional acid washing, greatly reducing production costs and improving environmental friendliness.

Claims

1. A method for preparing hard carbon, characterized in that, Includes the following steps: The biomass is pulverized, then mixed with organic acid and esterified at 200-420℃ for 1.8-4 hours to obtain esterified material. The esterified material is washed with water and then sintered and pre-carbonized to obtain a pre-carbonized material. The pre-carbonized material is crushed, then washed with water, and then sintered and carbonized to obtain the hard carbon. The organic acid includes at least one of maleic anhydride, citric acid, malic acid, and tartaric acid. The biomass is selected from at least one of coconut shell, lotus leaf stalk, peanut shell, lignin, rice husk, corn cob, wheat straw, soybean straw, and cotton straw; The mass ratio of biomass to organic acid is (85-95):(5-15).

2. The preparation method according to claim 1, characterized in that, The esterification temperature is 280-350℃, and the holding time is 2-4h.

3. The preparation method according to claim 1, characterized in that, After obtaining the esterified material, it is further crushed, and the crushing method includes at least one of jaw crusher, roller crusher or air crusher.

4. The preparation method according to claim 1, characterized in that, After obtaining the esterified material, it is further crushed until the D50 of the esterified material is 2-8 μm; And / or, the water washing process involves mixing the esterified material with water at a mass ratio of 1:(3-10), soaking and washing for more than 2 hours at a water temperature of 20-60℃, and then performing pressure filtration and drying.

5. The preparation method according to claim 4, characterized in that, The washing process involves mixing the esterified material with water at a mass ratio of 1:(4-8), soaking and washing for 2-4 hours at a water temperature of 25-50℃, followed by pressure filtration and drying.

6. The preparation method according to claim 1, characterized in that, The sintering pre-carbonization temperature is 650-800℃, and the sintering pre-carbonization time is 1.5-2.5 hours; And / or, the sintering pre-carbonization is carried out under a protective atmosphere, which is one or more of nitrogen or rare gases; And / or, crush the pre-carbonized material to D 50 1-8μm; And / or, the pre-carbonized material is crushed and then washed with water. The washing process involves mixing the pre-carbonized material with water at a mass ratio of 1:(3-10), soaking and washing for more than 2 hours at a water temperature of 20-60℃, and then pressing and drying.

7. The preparation method according to claim 1, characterized in that, The sintering and carbonization temperature is 1100-1300℃, and the time is 1.5-2.5 hours; And / or, the sintering and carbonization are carried out under a protective atmosphere; And / or, the impurity element content of the hard carbon, relative to the biomass, is reduced by more than 70% by mass fraction; And / or, the pH of the hard carbon is 7.0-8.

1.

8. A type of hard carbon, characterized in that, It is prepared by the preparation method according to any one of claims 1-7.

9. The application of the hard carbon as described in claim 8 in a battery.

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