Hark orange waste peel biomass asphalt hard carbon, negative electrode, battery and preparation method

Abstract

The invention discloses a harrow orange waste peel biomass asphalt hard carbon, a negative electrode, a battery and a preparation method. Belongs to the technical field of biomass hard carbon materials for sodium ion batteries. The preparation method of the asphalt hard carbon comprises the following steps: by taking waste citrus reticulata peel and asphalt as raw materials, respectively activating the raw materials through lauryl sodium sulfate and naphthalene, respectively carrying out pre-carbonization and pre-oxidation, and then carrying out mixing, acidification and carbonization treatment to obtain the biomass asphalt hard carbon. According to the present invention, the waste citrus chachiensis peel with characteristics of wide source and large peel-to-scurf ratio is efficiently recycled so as to turn waste into treasure, the biomass asphalt hard carbon with characteristics of large interlayer spacing, small specific surface area and rich closed pore volume is obtained by using the green, simple and convenient preparation method, and the carbon yield is substantially improved.

Description

Technical Field

[0001] The invention relates to the technical field of biomass pitch hard carbon, and in particular to biomass pitch hard carbon obtained by utilizing waste fruit peels. Background Art

[0002] Sodium-ion battery is a secondary battery (rechargeable battery) that mainly relies on the movement of sodium ions between the positive and negative electrodes to work. Its working principle is similar to that of lithium-ion batteries, but the electrode materials used in sodium-ion batteries are mainly sodium salts. Compared with lithium salts, sodium salts have more abundant reserves and are cheaper.

[0003] There are many types of negative electrode materials for sodium ion batteries, such as carbon materials, alloy materials, organic matter, metal compounds, etc. Among them, hard carbon materials are mainly obtained by pre-carbonization and high-temperature carbonization of resin materials or biomass materials. The preparation process is simple and the cost is low, which has attracted widespread attention. However, the hard carbon materials prepared by the existing technology have low coulombic efficiency and short platform capacity. After being assembled into soft-pack batteries, sodium precipitation and deposition are very likely to occur, resulting in poor battery cycle performance.

[0004] On the other hand, the pomelo is a very popular fruit, but its peel is thick, and a pungent smell will be produced after the peel rots. Throwing it away directly will cause great environmental pollution and harm to the human body. The asphalt raw material itself is a precursor of soft carbon. If it is not treated and carbonized, soft carbon will be generated, so the asphalt will often be pre-oxidized. For example, in patent CN 116789102 A, reeds are used as biomass raw materials, and the hard carbon prepared by pre-oxidizing asphalt in the air as a coating material has good performance. However, the asphalt after high-temperature pre-oxidation no longer has the melting property, and it is difficult to achieve uniform coating and immersion in the internal voids of the biomass in the subsequent coating process. The prepared hard carbon has inconsistent performance. In addition, the use of a strong alkaline solution to treat the biomass will dissolve the hemicellulose and part of the cellulose in the biomass, resulting in a decrease in the carbon yield. Therefore, how to reuse the discarded peels of pomelo and low-cost asphalt in an efficient and environmentally friendly manner is a problem to be solved in the prior art. Summary of the invention

[0005] In order to solve the problems of the prior art, the present invention proposes biomass asphalt hard carbon, a negative electrode, a battery and a preparation method prepared using discarded pomelo peels. The preparation method of biomass asphalt hard carbon can use discarded pomelo peels as raw materials to obtain a hard carbon material with rich closed-pore volume, high tap density, appropriate specific surface area and interlayer spacing. The sodium ion battery assembled with the hard carbon material as the negative electrode has high first-cycle coulomb efficiency and excellent specific capacity.

[0006] The technical solution of the present invention is as follows:

[0007] The method for preparing asphalt hard carbon from waste peel of citrus aurantium comprises the following steps:

[0008] (1) soaking the washed discarded tangerine peel in an aqueous solution of sodium dodecyl sulfate, and then performing a first drying to obtain a peel precursor; soaking the crushed asphalt block in an organic solution of naphthalene, and then performing a second drying to obtain an asphalt precursor;

[0009] (2) pre-carbonizing the peel precursor in air or an inert atmosphere to obtain a pre-carbonized precursor, and pre-oxidizing the asphalt precursor in air to obtain a pre-oxidized precursor;

[0010] (3) mixing the pre-carbonized precursor and the pre-oxidized precursor to obtain an intermediate mixture, and acidifying the intermediate mixture to obtain an acidified mixture;

[0011] (4) The acidified mixture is carbonized to obtain biomass pitch hard carbon.

[0012] The above technical scheme of the present invention uses discarded pomelo peel as biomass raw material, sodium dodecyl sulfate as its active agent, and combines it with asphalt and polycyclic aromatic hydrocarbon naphthalene. After activation treatment, pre-carbonization treatment / pre-oxidation treatment, mixing and acidification treatment and sintering carbonization, a hard carbon material is obtained. There is a synergistic effect between the raw material components and the process steps, so that the obtained hard carbon material has a high degree of disorder, rich closed-pore content and a large interlayer spacing.

[0013] In the above technical scheme of the present invention, the raw material of the waste peel of the pagoda orange is widely available and has a large output. Moreover, compared with other fruit shells, the peel of the pagoda orange accounts for a larger proportion, about 10-15%, which can make up for the defect of low yield of existing biomass carbon. It is activated by sodium dodecyl sulfate, which can not only activate some organic fat-soluble substances contained in the raw material, but also can be dissolved and swollen. In the subsequent heat treatment, the temperature contacted by the material itself is more uniform, and it also has a certain decontamination effect. The raw material asphalt has low cost, is easy to obtain, and is simple to handle. It can well coat the hard carbon formed by the waste peel of the pagoda orange. Through the polycyclic aromatic hydrocarbon naphthalene (C 10 H 8 ) is used to treat it, and the oxidizing property of the polar organic substance naphthalene can be used to promote the dehydrogenation of asphalt, increase the oxygen content, and effectively improve its oxidation degree, solving the problem of its high-temperature carbonization and easy graphitization.

[0014] The above technical solution of the present invention acidifies the intermediate mixture, which can fully wash away the residual metal ions such as K, Ca, Zn and other impurity phases therein, avoiding damage to the structure of the obtained hard carbon material.

[0015] In some preferred embodiments, the inert atmosphere is a nitrogen and / or argon atmosphere.

[0016] In some preferred embodiments, the asphalt block is a block of high-temperature petroleum asphalt with a melting point of 250-270° C. and a quinoline insoluble content of less than 0.3%, and the particle size after crushing is 5-10 μm.

[0017] The asphalt raw material used in this preferred embodiment can be fully oxidized in the air, and can achieve good coating of the pre-carbonized biomass powder, thereby improving the problem of low biomass coulomb efficiency.

[0018] In some preferred embodiments, the cleaning is performed by one or more cleaning methods selected from water washing, acid washing, and alkaline washing.

[0019] More preferably, the water washing uses deionized water and / or non-deionized water such as tap water, the alkali washing uses an aqueous solution of one or more of sodium hydroxide, potassium hydroxide, and ammonia water, and the acid washing uses one or more of hydrochloric acid, sulfuric acid, hydrofluoric acid, and phosphoric acid.

[0020] In some preferred embodiments, the immersion time in the aqueous solution of sodium dodecyl sulfate is 5-7 hours.

[0021] In some preferred embodiments, the soaking time in the organic solution of naphthalene is 24-72 hours.

[0022] In some preferred embodiments, the first drying temperature is 100-120°C.

[0023] In some preferred embodiments, the second drying temperature is 40-60°C.

[0024] In some preferred embodiments, the concentration of the aqueous solution of sodium dodecyl sulfate is 0.1-0.15 mol / L.

[0025] In some preferred embodiments, the concentration of naphthalene in the organic naphthalene solution is 5-15 wt %, and the solvent is ethanol.

[0026] In some preferred embodiments, the pre-carbonization treatment includes: heating to 250-350°C at a heating rate of 4-6°C / min and keeping warm for 20-40 minutes, then heating to 400-500°C at a heating rate of 2-4°C / min and keeping warm for 0.5-1.5 hours, then heating to 500-600°C at a heating rate of 4-6°C / min and keeping warm for 0.5-1.5 hours.

[0027] In some preferred embodiments, the pre-oxidation treatment comprises: heating to 150-250°C at a heating rate of 2-4°C / min, keeping warm for 1.5-2.5h, then heating to 270-370°C at a heating rate of 4-6°C / min, keeping warm for 0.5-1.5h.

[0028] In some preferred embodiments, the mass of the pre-oxidation precursor is 5-15% of the mass of the pre-carbonization precursor.

[0029] In some preferred embodiments, the acidification uses hydrochloric acid with a concentration of 2-4 mol / L.

[0030] In some preferred embodiments, the carbonization treatment comprises: heating to 500-600°C at a heating rate of 6-8°C / min, then heating to 1200-1300°C at a heating rate of 2-4°C / min, and keeping the temperature for 1.5-2.5h.

[0031] The present invention further provides biomass pitch hard carbon prepared according to the above preparation method.

[0032] The biomass pitch hard carbon has a highly amorphous morphology, a large tap density, abundant closed-pore volume and a small specific surface area, which is conducive to the formation of a shorter SEI (Solid Electrolyte Interface), consumes less sodium ions, and improves the battery's sodium storage capacity and energy density.

[0033] In some specific embodiments, the biomass pitch hard carbon of the present invention has an interlayer spacing of 0.38 nm, a 2 / g specific surface area, high conductivity close to 15S / cm, and tap density of 0.8.

[0034] The present invention further provides a sodium ion battery negative electrode made from the biomass pitch hard carbon.

[0035] In some preferred embodiments, the preparation of the negative electrode of the sodium ion battery comprises:

[0036] The biomass pitch hard carbon is mixed with a conductive agent Super-P, a dispersant PAA and a binder SBR to obtain a mixed slurry, and the mixed slurry is coated and then dried to obtain a negative electrode sheet.

[0037] Among them, the mass content ratio of the biomass asphalt hard carbon to the conductive agent Super-P, the dispersant PAA and the binder SBR is preferably 94.5%:2.5%:1%:2%; the coating thickness is preferably 200μm; the drying preferably includes: drying at 70°C for 2h, followed by vacuum drying at 100°C for 10h.

[0038] The above preferred implementation scheme can effectively guarantee the quality and performance of the obtained negative electrode by controlling the ratio of the electrode raw materials, thereby improving the overall electrochemical performance of the assembled battery; by controlling the drying process, it can effectively ensure that the electrode piece does not crack, shed powder or fall off; by controlling the coating thickness, the surface density of the electrode piece can be effectively increased and the electrode performance can be improved.

[0039] The present invention further provides a sodium ion battery comprising the above sodium ion battery negative electrode.

[0040] In some specific embodiments, the sodium ion battery exhibits excellent electrochemical performance during charge and discharge tests, with a slope capacity of less than 105 mAh / g, a platform capacity of greater than 200 mAh / g, and an initial coulombic efficiency ICE of greater than 90% during discharge.

[0041] The biomass asphalt hard carbon of the present invention has a dense structure and a high pore content, so the discharge platform voltage of the obtained sodium ion battery is improved to about 1mV as a whole compared with similar products, reaching about 0.0058V, which is 0.0063V higher than the precipitation position of metallic sodium (-0.0015V), and can effectively inhibit the deposition of metallic sodium on the negative electrode side and the formation of sodium dendrites, thereby significantly improving the safety performance of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 is a process flow chart of the preparation of biomass pitch hard carbon in the embodiment;

[0043] Figure 2 This is the FESEM image of the biomass pitch hard carbon obtained in Example 1;

[0044] Figure 3 is the XRD pattern of the biomass pitch hard carbon obtained in Example 1;

[0045] Figure 4 This is the Capacity-Voltage diagram of the first cycle of the sodium ion battery assembled using the biomass pitch hard carbon obtained in Example 1;

[0046] Figure 5 This is a long cycle diagram of a sodium ion battery assembled using the biomass pitch hard carbon obtained in Example 1;

[0047] Figure 6 This is a high-rate long-cycle capacity diagram of a sodium-ion battery assembled using the biomass pitch hard carbon obtained in Example 1;

[0048] Figure 7 This is the first cycle cyclic voltammogram of the sodium ion battery assembled using the biomass pitch hard carbon obtained in Example 1. DETAILED DESCRIPTION

[0049] The technical scheme of the present invention will be further described below in conjunction with the embodiments and drawings of the present invention. The embodiments described below are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0050] Example 1

[0051] Refer to the attached Figure 1 , biomass pitch hard carbon was prepared by the following steps:

[0052] (1) Precursor preparation, including:

[0053] The discarded tangerine peels were cleaned with deionized water, soaked in a 0.1M sodium dodecyl sulfate aqueous solution for 6 hours, and then dried in a forced air oven at 110°C for 10 hours to remove water, thereby obtaining a peel precursor;

[0054] The asphalt block was crushed into a particle size of 200 mesh by a crusher, and then ethanol and 10wt% naphthalene solvent were added, wherein the volume ratio of ethanol to asphalt powder was 2:1, and the mixture was allowed to stand and soak for 2 days, and then dried at 50°C to remove ethanol, thereby obtaining an asphalt precursor;

[0055] (2) Precursor pretreatment, including:

[0056] Pre-carbonization of the peel precursor: In a nitrogen atmosphere, the peel precursor was heated to 300°C at a heating rate of 5°C / min and kept warm for 30 minutes, then heated to 450°C at a heating rate of 3°C / min and kept warm for 1 hour, and then heated to 550°C at a heating rate of 5°C / min and kept warm for 1 hour;

[0057] Pre-oxidation of asphalt precursor: Place the asphalt precursor in a muffle furnace for air oxidation. The oxidation is divided into two stages. The temperature of the first stage is 200°C, the heating rate is 3°C / min, and the holding time is 2h. The temperature of the second stage is 320°C, the heating rate is 5°C / min, and the holding time is 1h.

[0058] (3) mixing and acidifying, comprising: mixing the pre-carbonized and pre-oxidized precursors using a planetary gravity mixer with a rotation ratio of 30% to obtain a mixture, wherein the mass of the pre-oxidized asphalt precursor is 10% of the mass of the pre-carbonized peel precursor, soaking the obtained mixture in 3M hydrochloric acid for 10 hours, and then drying at 110° C. to obtain an acidified mixture;

[0059] (4) High-temperature carbonization: The acidified mixture was placed in a tubular furnace and heated to 550 °C at a heating rate of 7 °C / min in a nitrogen atmosphere. The temperature was then raised to 1250 °C at a heating rate of 3 °C / min and kept at this temperature for 2 h. The temperature was then lowered to 50 °C and the material was taken out to obtain biomass asphalt hard carbon.

[0060] The obtained biomass pitch hard carbon was characterized by FESEM and XRD, and the results are shown in the attached Figure 2 , 3 As shown. Figure 2 It can be seen that the obtained biomass pitch hard carbon is a block with an amorphous morphology and an average size of about 4.5μm. Small particles of hard carbon remain on the surface due to uneven crushing. The material can be fully revealed at 2000 times without gold or platinum spraying, proving its good conductivity. Figure 3 Among them, ~23.2° is the (002) plane of the obtained biomass asphalt hard carbon, which is smaller than the amorphous carbon (23.8°) prepared by the conventional process, indicating that the hard carbon material has a larger interplanar spacing (0.38nm) and is easier for sodium ion transmission. ~42.5° is its (100) plane. The larger half-peak width shows that the hard carbon material exhibits a highly amorphous or disordered state, indicating that the degree of graphitization of the material is low.

[0061] Furthermore, the obtained biomass asphalt hard carbon is prepared as a negative electrode for a sodium ion battery through the following steps: the obtained biomass asphalt hard carbon, Super-P, PAA and SBR are mixed in a mass content ratio of 94.5%:2.5%:1%:2% at a speed of 500, 800, 1000 and 1500 r / min for 20 minutes for homogenization, and the obtained slurry is coated with a coating thickness of 200 μm, followed by drying at 70°C for 2 hours and vacuum drying at 100°C for 10 hours to obtain a negative electrode sheet.

[0062] The obtained negative electrode sheets were used to assemble sodium-ion batteries and their performance was tested. The first discharge used in the test was 0.1C to 0.01V, 0.05C to 0.005V; the first charge was 0.1C to 2.5V, the voltage window was 0.005-2.5V, and the electrolyte was NaPF 6 EC and DMC mixed solvent solution.

[0063] The results are attached Figure 4-7 As shown, Figure 4The first-cycle performance of the sodium ion battery shows that the slope capacity of the battery in the first-cycle discharge is 102mAh / g, the platform capacity is 217mAh / g, the first-cycle discharge capacity reaches 319.72mAh / g, and the first-cycle coulomb efficiency ICE is 92.01%, which is significantly better than the existing hard carbon materials. This is related to the different types and structures of precursors used in the present invention, different pretreatments of the precursors, different selected active agents, and different product structures. At the same time, the present invention selects petroleum asphalt with a higher softening point, and by soaking it in naphthalene solvent, the density is increased, the hybridization density of SP2 carbon is improved, and the biomass carbon is coated thereon, so that the obtained hard carbon material has a dense structure and a high void density.

[0064] Figure 5 From the long cycle performance test of the sodium ion battery, it can be seen that the battery still has a capacity of 286mAh / g after 28 consecutive cycles at a current density of 0.1C, and the corresponding efficiency is still close to 100%, with excellent electrochemical performance, which is directly related to the closed-pore structure, surface morphology, and large interlayer of the obtained hard carbon material. At the same time, using the waste peel of the pomelo as a precursor material also enables the battery to exhibit excellent performance.

[0065] Figure 6 This is a high-rate performance diagram for sodium-ion battery testing. It can be seen that at the current density of 1C (C = 300mAh / g) in the first two cycles, the battery has a capacity of 269.42mAh / g and an efficiency of 86.49 in the first cycle, and a capacity of 237.67mAh / g in the second cycle. After increasing the current density to 2C, the battery still has a capacity of 241.43mAh / g. The slightly higher capacity growth indicates that the battery has been continuously activated, and the excellent high-rate electrochemical performance indicates that the hard carbon negative electrode has excellent conductivity and can withstand continuous charge and discharge under large currents.

[0066] Figure 7 This is a cyclic voltammogram of a sodium-ion battery test. According to the test results, at a scan rate of 0.1mV / S and a voltage range of 0.001-3.0V, the battery perfectly exhibited a low sodium storage potential and did not show other impurity peaks, proving that there were no impurities in the material after post-treatment; and the sharp redox peaks also proved that the material had good conductivity and could fully match the changes in battery voltage.

[0067] At the same time, the carbon material obtained in Example 1 was assembled into a CR2032 button battery by a conventional method, and multiple relevant performance tests were carried out. The results are shown in Tables 1-4 below: Table 1 is a tap density test calculation table, Table 2 is a specific surface area test calculation table; Table 3 is a hard carbon powder conductivity test calculation table; Table 4 is a theoretical calculation table for the microstructure.

[0068] Table 1

[0069]

[0070] Table 1

[0071] Specific surface area test 1 Specific surface area test 2 Specific surface area test 3 Mean unit 6.1 5.65 5.78 5.84 <![CDATA[m 2 / g]]>

[0072] Table 2

[0073]

[0074]

[0075] Table 3

[0076] D(002) Lc(002) La(100) Nc Dis-order (%) Graphitic(%) 0.38nm 0.69nm 0.76nm 2.81 0.48 0.52

[0077] Table 1 is the calculation table of the tap density of hard carbon powder. The test conditions are to weigh the sample three times with a mass greater than 10g to ensure that the sample filling volume is greater than 10cm 3 , placed in a vibrating measuring cylinder, accounting for about 70% by volume, and vibrated continuously for 3000 times at a speed of 300 times / min. The results showed that the average tap density of the hard carbon in Example 1 was 0.846 g / cm 3 , which is better than the existing pure biomass carbon density of 0.6-0.7g / cm 3 .

[0078] Table 2 shows the specific surface area of ​​the samples. Weigh more than 150 mg of hard carbon powder, degas at 300°C for 6 hours, and weigh the mass again after degassing to exclude the influence of moisture and air on the value. Then, three tests were carried out in a nitrogen atmosphere, and the average specific surface area of ​​the hard carbon in Example 1 was 5.84 m 2 / g, which can effectively control the capacity of the corresponding slope section of the hard carbon sodium storage curve and indirectly improve the first efficiency.

[0079] Table 3 shows the powder conductivity test of the sample, the test method is a four-probe method, during the test, four probes are simultaneously inserted into the powder to perform point sampling test. By comparing the data, it can be obtained that the powder resistivity of the hard carbon of Example 1 is close to 15S / cm.

[0080] Table 4 shows the microstructure data of the prepared hard carbon samples. Figure 3 The XRD data and the microscopic properties of the product calculated using relevant formulas include: the interlayer spacing is 0.38nm, the crystallite length is 0.69nm, the crystallite height is 0.76nm, and the number of stacking layers is 2.81, proving that the material has a highly disordered structure, among which disordered carbon accounts for approximately 48% of the entire hard carbon material.

[0081] Example 2

[0082] The biomass pitch hard carbon was prepared by the same steps as in Example 1, except that the mass of the pre-oxidized pitch precursor was 5% of the mass of the pre-carbonized peel precursor.

[0083] Example 3

[0084] The biomass pitch hard carbon was prepared by the same steps as in Example 1, except that the mass of the pre-oxidized pitch precursor was 15% of the mass of the pre-carbonized peel precursor.

[0085] The biomass pitch hard carbon obtained in Examples 1-3 was assembled into a sodium ion battery in the manner of Example 1 and the electrical performance was tested, and the results are shown in Table 5 below:

[0086] Table 5

[0087]

[0088]

[0089] It can be seen that the performance of hard carbon coated with different asphalts is different. Because the conductivity of asphalt-derived hard carbon is not as good as biomass, too much coating will reduce the first release capacity; on the other hand, the porosity of the surface of biomass hard carbon limits the first effect, so using 10% asphalt coating is the best option.

[0090] Comparative Example 1

[0091] The same steps as in Example 1 were used to prepare biomass pitch hard carbon, the only difference being that the precursor used was pure pitch only, without the peel precursor.

[0092] The results show that no hard carbon material can be obtained in Comparative Example 1, but only a soft carbon can be obtained. The reason may be that the density of oxygen-containing functional groups is not large enough, causing the pure phase pitch to graphitize when sintered at more than 900°C. The structure of the obtained soft carbon material is in an ordered state, and the carbon layer is only 0.35nm, close to the 0.34nm of graphite.

[0093] In terms of electrochemical performance, the first cycle capacity of the battery assembled from the material obtained in Comparative Example 1 is 200.8 mAh g -1 However, no platform appears and the capacity is mostly a slope, which indicates that sodium ions cannot be effectively inserted and extracted, and sodium can only be stored by relying on surface functional groups, defects and impurity atom adsorption.

[0094] Comparative Example 2

[0095] The biomass pitch hard carbon was prepared by the same steps as in Example 1, except that the waste peels used were grapefruit waste peels.

[0096] The results show that the hard carbon material can be obtained in Comparative Example 2, but the specific surface area of ​​the material is 108m 2 / g, and the yield is low. The reason may be that the single biomass carbon formed by the peel has a large volatile content, including water, gas, and tar, etc., which cannot be effectively cross-linked with the mineral carbon source, and more carbon-containing substances will be lost.

[0097] In terms of electrochemical performance, the first cycle capacity of the battery assembled from the material obtained in Comparative Example 2 is 289 mAh g -1 About, of which the slope capacity reaches 186mAh / g and the first efficiency is only 75%.

[0098] Comparative Example 3

[0099] The same steps as in Example 1 were used to prepare biomass asphalt hard carbon, the only difference being that the asphalt used was asphalt that had been pre-oxidized in air.

[0100] The results show that hard carbon material can be obtained in Comparative Example 3, but the specific surface area of ​​the material is between 5 and 50 m 2 / g, and the yield is low. The reason may be that the pre-oxidation of asphalt in air will burn away part of the carbon; it is difficult to achieve uniform mixing and coating when the pre-oxidized asphalt carbon powder is coated with the biomass pre-carbonized powder.

[0101] In terms of electrochemical performance, the first cycle capacity of the battery assembled from the material obtained in Comparative Example 3 is 280-320 mAhg -1 About, of which the initial effect is only 70-85%.

[0102] Comparative Example 4

[0103] The biomass pitch hard carbon was prepared by the same steps as in Example 1, except that the raked tangerine peels were treated with NaOH solution for 6 h.

[0104] The results show that comparative example 4 can obtain hard carbon material, but the specific surface area of ​​the material will be less than 10m 2 / g, and the yield is low. The reason may be that the strong alkaline solution will dissolve the hemicellulose and part of the cellulose in the biomass, reducing the yield of the pore-forming carbon. In addition, the biomass itself is porous. Even if it is washed to neutrality in the post-treatment, it will still be alkaline after standing for several hours. This is because the alkali adsorbed by the capillaries in the biomass is released. This part of the alkali will etch the carbon layer during the subsequent high-temperature carbonization, resulting in a low yield and an uneven porous shape on the surface, which increases the specific surface area of ​​the material. The release of strong alkali also causes corrosion damage to high-temperature equipment, resulting in a reduction in the service life of the equipment.

[0105] In terms of electrochemical performance, the first cycle capacity of the battery assembled from the material obtained in Comparative Example 4 is 305 mAh g -1 About, of which the first effect is only 78%.

[0106] It should be noted that the above is only a preferred embodiment of the present invention, which should not limit the protection scope of the technical solution of the present invention. Any modification of the technical solution recorded in the above embodiments and equivalent replacement of technical features by ordinary technicians in the field within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing asphalt hard carbon from waste peel of citrus fruit, characterized in that: It includes the following steps: (1) soaking the washed discarded tangerine peel in an aqueous solution of sodium dodecyl sulfate, and then performing a first drying to obtain a peel precursor; soaking the crushed asphalt block in an organic solution of naphthalene, and then performing a second drying to obtain an asphalt precursor; (2) pre-carbonizing the peel precursor in air or an inert atmosphere to obtain a pre-carbonized precursor, and pre-oxidizing the asphalt precursor in air to obtain a pre-oxidized precursor; (3) mixing the pre-carbonized precursor and the pre-oxidized precursor to obtain an intermediate mixture, and acidifying the intermediate mixture to obtain an acidified mixture; (4) The acidified mixture is carbonized to obtain biomass pitch hard carbon.

2. The preparation method according to claim 1, characterized in that: The asphalt block is a block of high-temperature petroleum asphalt with a melting point of 250-270° C. and a quinoline insoluble matter content of less than 0.3%. The particle size of the asphalt block after crushing is 5-10 μm.

3. The preparation method according to claim 1, characterized in that: In step (1), the cleaning adopts one or more cleaning methods selected from water washing, acid washing and alkali washing; and / or the soaking time in the aqueous solution of sodium dodecyl sulfate is 5-7h; and / or the soaking time in the organic solution of naphthalene is 24-72h; and / or the first drying temperature is 100-120°C; and / or the second drying temperature is 40-60°C.

4. The preparation method according to claim 1, characterized in that: In step (1), the concentration of the aqueous solution of sodium dodecyl sulfate is 0.1-0.15 mol / L; and / or the concentration of naphthalene in the organic solution of naphthalene is 5-15 wt %, and the solvent is ethanol.

5. The preparation method according to claim 1, characterized in that: In step (2), the pre-carbonization treatment includes: heating to 250-350°C at a heating rate of 4-6°C / min and keeping warm for 20-40min, then heating to 400-500°C at a heating rate of 2-4°C / min and keeping warm for 0.5-1.5h, then heating to 500-600°C at a heating rate of 4-6°C / min and keeping warm for 0.5-1.5h; and / or, the pre-oxidation treatment includes: heating to 150-250°C at a heating rate of 2-4°C / min, keeping warm for 1.5-2.5h, then heating to 270-370°C at a heating rate of 4-6°C / min, and keeping warm for 0.5-1.5h.

6. The preparation method according to claim 1, characterized in that: In step (3), the mass of the pre-oxidation precursor is 5-15% of the mass of the pre-carbonization precursor; and / or the acidification uses hydrochloric acid with a concentration of 2-4 mol / L.

7. The preparation method according to claim 1, characterized in that: In step (4), the carbonization treatment includes: heating to 500-600°C at a heating rate of 6-8°C / min, then heating to 1200-1300°C at a heating rate of 2-4°C / min, and keeping the temperature for 1.5-2.5h.

8. The biomass pitch hard carbon prepared by the preparation method according to any one of claims 1-7.

9. A sodium ion battery negative electrode made from the biomass pitch hard carbon according to claim 8.

10. A sodium ion battery comprising the sodium ion battery negative electrode according to claim 9.

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