Biomass asphalt hard carbon from waste mandarin orange peels, negative electrode, battery and preparation method

Abstract

This invention discloses a biomass asphalt hard carbon material, negative electrode, battery, and preparation method from waste peels of the citrus fruit. It belongs to the technical field of biomass hard carbon materials for sodium-ion batteries. The preparation of the asphalt hard carbon includes: using waste peels of the citrus fruit and asphalt as raw materials, activating them separately with sodium dodecyl sulfate and naphthalene, then performing pre-carbonization and pre-oxidation, followed by mixing, acidification, and carbonization treatments to obtain biomass asphalt hard carbon. This invention efficiently recycles and utilizes the widely available and high-density waste peels of the citrus fruit, turning waste into treasure. Simultaneously, it employs a green and simple preparation method to obtain biomass asphalt hard carbon with a large interlayer spacing, small specific surface area, and abundant closed-cell volume, significantly improving carbon recovery.

Description

Technical Field

[0001] This invention relates to the technical field of biomass bitumen hard carbon, and particularly to biomass bitumen hard carbon obtained from waste fruit peels. Background Technology

[0002] Sodium-ion batteries are a type of rechargeable battery that works primarily by moving sodium ions between the positive and negative electrodes. Similar to lithium-ion batteries, sodium-ion batteries use sodium salts as their electrode material. Compared to lithium salts, sodium salts are more abundant and cheaper.

[0003] Sodium-ion batteries use a variety of anode materials, such as carbon materials, alloy materials, organic materials, and metal compounds. Among them, hard carbon materials are mainly obtained through pre-carbonization and high-temperature carbonization of resin or biomass materials. Their preparation process is simple and inexpensive, attracting widespread attention. However, hard carbon materials prepared using existing technologies have low coulombic efficiency and short plateau capacity. When assembled into pouch cells, they are prone to sodium precipitation and deposition, resulting in poor cycle performance.

[0004] On the other hand, while the tangerine peel is a highly popular fruit, its thick peel produces a pungent odor when rotting, and discarding it directly causes significant environmental pollution and harms human health. Asphalt itself is a precursor to soft carbon; if left untreated, it carbonizes to form soft carbon, thus requiring pre-oxidation. For example, patent CN 116789102 A describes the use of reeds as biomass, where pre-oxidized asphalt in air is used as a coating material to prepare hard carbon with good performance. However, asphalt that has undergone high-temperature pre-oxidation loses its melting properties, making it difficult to achieve uniform coating and penetration into the internal pores of the biomass during subsequent coating processes. This results in inconsistent hard carbon performance. Furthermore, treating biomass with a strong alkaline solution dissolves hemicellulose and some cellulose, reducing carbon yield. Therefore, how to efficiently and environmentally reuse the waste peel of the tangerine peel and low-cost asphalt is a problem that urgently needs to be solved by existing technologies. Summary of the Invention

[0005] To address the problems of existing technologies, this invention proposes a method for preparing biomass asphalt hard carbon, a negative electrode, and a battery using waste peels of the citrus fruit. The method for preparing biomass asphalt hard carbon uses waste citrus peels as raw materials to obtain hard carbon materials with abundant closed-pore volume, high tap density, and appropriate specific surface area and interlayer spacing. Sodium-ion batteries assembled with this hard carbon material as the negative electrode exhibit high first-cycle coulombic efficiency and excellent specific capacity.

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

[0007] A method for preparing biomass asphalt hard carbon from waste peels of tangerine peels includes the following steps:

[0008] (1) The washed waste mandarin orange peels were soaked in an aqueous solution of sodium dodecyl sulfate and then dried to obtain the peel precursor; the crushed asphalt blocks were soaked in an organic solution of naphthalene and then dried to obtain the asphalt precursor.

[0009] (2) The fruit peel precursor is pre-carbonized in air or an inert atmosphere to obtain a pre-carbonized precursor, and the asphalt precursor is pre-oxidized in air to obtain a pre-oxidized precursor.

[0010] (3) The pre-carbonized precursor and the pre-oxidized precursor are mixed to obtain an intermediate mixture, and the intermediate mixture is acidified to obtain an acidified mixture;

[0011] (4) Carbonize the acidified mixture to obtain biomass asphalt hard carbon.

[0012] The above technical solution of the present invention uses waste citrus peel as biomass raw material, sodium dodecyl sulfate as its activator, and combines it with asphalt and polycyclic aromatic naphthalene. After activation treatment, pre-carbonization / pre-oxidation treatment, mixing and acidification treatment and sintering carbonization, hard carbon material is obtained. There is a synergistic effect between the raw material components and process steps, which makes the obtained hard carbon material have high disorder, rich closed pore content and large interlayer spacing.

[0013] In the above technical solutions of this invention, the raw material, waste peel of the mandarin orange, is widely available and produced in large quantities. Moreover, compared to other fruit peels, the peel of the mandarin orange accounts for a larger proportion, approximately 10-15%, which can compensate for the low carbon yield of existing biomass. Activating it with sodium dodecyl sulfate not only activates some organic fat-soluble substances in the raw material but also allows for descaling and swelling. In subsequent heat treatment, the material itself experiences more uniform temperature contact and also has a certain decontamination effect. The raw material, asphalt, is low in cost, readily available, and simple to process. It can effectively coat the hard carbon formed from the waste peel of the mandarin orange, using polycyclic aromatic hydrocarbons (PAHs) such as naphthalene (C). 10 By treating it with H8, the oxidizing property of the polar organic compound naphthalene can be utilized to promote the dehydrogenation of pitch and increase the oxygen content, which can effectively improve its oxidation degree and solve the problem of easy graphitization during high-temperature carbonization.

[0014] The above technical solution of the present invention acidifies the intermediate mixture, which can fully wash away residual metal ions such as K, Ca, Zn and other impurity phases, and avoid 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 its particle size after crushing is 5-10 μm.

[0017] In this preferred embodiment, the asphalt raw material can be fully oxidized in the air, which can achieve good coating of the pre-carbonized biomass powder and improve the problem of low biomass coulombic efficiency.

[0018] In some preferred embodiments, the cleaning is performed using one or more of the following methods: 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 alkaline washing uses an aqueous solution of one or more of sodium hydroxide, potassium hydroxide, and ammonia, and the acid washing uses one or more of hydrochloric acid, sulfuric acid, hydrofluoric acid, and phosphoric acid.

[0020] In some preferred embodiments, the soaking 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 temperature of the first drying is 100-120°C.

[0023] In some preferred embodiments, the temperature of the second drying 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 solution of naphthalene 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 holding for 20-40 min, then heating to 400-500°C at a heating rate of 2-4°C / min and holding for 0.5-1.5 h, and then heating to 500-600°C at a heating rate of 4-6°C / min and holding for 0.5-1.5 h.

[0027] In some preferred embodiments, the pre-oxidation treatment includes: heating to 150-250°C at a heating rate of 2-4°C / min, holding at that temperature for 1.5-2.5 hours, and then heating to 270-370°C at a heating rate of 4-6°C / min, holding at that temperature for 0.5-1.5 hours.

[0028] In some preferred embodiments, the mass of the pre-oxidized precursor is 5-15% of the mass of the pre-carbonized 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 process 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 holding at that temperature for 1.5-2.5 hours.

[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, with a large tap density, abundant closed-cell volume, and small specific surface area, which is conducive to the formation of a shorter SEI (Solid Electrolyte Interface), consuming less sodium ions, and improving 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 and a thickness of 3-55 nm. 2 It has a specific surface area of ​​ / g, a high electrical conductivity of nearly 15S / cm, and a 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 sodium-ion battery negative electrode includes:

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

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

[0038] The above preferred embodiments can effectively ensure the quality and performance of the obtained negative electrode by controlling the ratio of 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 does not crack, shed powder or fall off; by controlling the coating thickness, it can effectively increase the areal density of the electrode and improve the electrode performance.

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

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

[0041] The biomass pitch hard carbon of this invention has a dense structure and high porosity, thus the discharge plateau voltage of the resulting sodium-ion battery is increased by about 1mV compared to similar products, reaching about 0.0058V, which is 0.0063V higher than the sodium deposition site (-0.0015V). This effectively suppresses the deposition of sodium metal on the negative electrode side and the formation of sodium dendrites, significantly improving the battery's safety performance. Attached Figure Description

[0042] Figure 1 This is a flowchart illustrating the preparation process of biomass bitumen hard carbon in the embodiments;

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

[0044] Figure 3 The image shows the XRD pattern of the biomass bitumen hard carbon obtained in Example 1.

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

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

[0047] Figure 6 A graph showing the high-rate, long-cycle capacity of a sodium-ion battery assembled using the biomass pitch hard carbon obtained in Example 1.

[0048] Figure 7 The first cycle voltammogram is shown for a sodium-ion battery assembled using the biomass pitch hard carbon obtained in Example 1. Detailed Implementation

[0049] The technical solutions of the present invention will be further described below with reference to the embodiments and accompanying drawings. The embodiments described below are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0050] Example 1

[0051] See attached document Figure 1 Biomass bitumen hard carbon is prepared through the following steps:

[0052] (1) Precursor preparation, including:

[0053] The waste peels of the mandarin orange 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℃ for 10 hours to remove water, thus obtaining the peel precursor.

[0054] The asphalt blocks were crushed into particles with a diameter of 200 mesh using a pulverizer. Then, ethanol and 10 wt% naphthalene solvent were added, with the volume ratio of ethanol to asphalt powder being 2:1. The mixture was left to stand and soak for 2 days, and then dried at 50°C to remove the ethanol, thus obtaining the asphalt precursor.

[0055] (2) Precursor pretreatment, including:

[0056] Pre-carbonization of pericarp precursor: Under nitrogen atmosphere, the pericarp precursor was heated to 300℃ at a heating rate of 5℃ / min and held for 30min, then heated to 450℃ at a heating rate of 3℃ / min and held for 1h, and then heated to 550℃ at a heating rate of 5℃ / min and held for 1h.

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

[0058] (3) Mixing and acidification, including: 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 pericarp precursor, soaking the obtained mixture in 3M hydrochloric acid for 10 hours, and then drying it at 110°C to obtain an acidified mixture.

[0059] (4) High-temperature carbonization: The acidified mixture is placed in a tube furnace and heated to 550°C at a heating rate of 7°C / min in a nitrogen atmosphere. Then, it is heated to 1250°C at a heating rate of 3°C / min and held for 2 hours. After that, it is cooled to 50°C and the material is taken out to obtain biomass pitch hard carbon.

[0060] The obtained biomass pitch hard carbon was characterized by FESEM and XRD, and the results are attached. Figure 2 , 3 As shown. From Figure 2 It can be seen that the obtained biomass bitumen hard carbon is a block with an amorphous morphology and an average size of about 4.5 μm. Small hard carbon particles remain on the surface due to uneven crushing. The material can be fully displayed at 2000x magnification without gold or platinum spraying, which proves that it has good electrical conductivity. Figure 3 In the figure, ~23.2° is the (002) plane of the obtained biomass pitch hard carbon. This angle is smaller than that of amorphous carbon prepared by conventional process (23.8°), indicating that the hard carbon material has a larger interplanar spacing (0.38nm) and is more conducive to sodium ion transport. ~42.5° is its (100) plane. The large half-width indicates that the hard carbon material exhibits a highly amorphous or disordered state, indicating that the graphitization degree of the material is low.

[0061] Furthermore, the obtained biomass pitch hard carbon is prepared as a sodium-ion battery negative electrode through the following steps: the obtained biomass pitch hard carbon, Super-P, PAA and SBR are mixed sequentially at a mass content ratio of 94.5%:2.5%:1%:2% at speeds of 500, 800, 1000 and 1500 r / min for 20 min to form a homogenate. The resulting slurry is then coated with a coating thickness of 200 μm, dried at 70℃ for 2 h, and then vacuum dried at 100℃ for 10 h to obtain the negative electrode sheet.

[0062] Sodium-ion batteries were assembled using the obtained negative electrode sheets, and their performance was tested. The initial discharge was from 0.1C to 0.01V and from 0.05C to 0.005V; the initial charge was from 0.1C to 2.5V, with a voltage window of 0.005-2.5V. The electrolyte was a mixed solvent solution of NaPF6 EC and DMC.

[0063] The results are attached. Figure 4-7 As shown, where, Figure 4The first-cycle performance of the sodium-ion battery shows a ramp capacity of 102 mAh / g, a plateau capacity of 217 mAh / g, and a first-cycle discharge capacity of 319.72 mAh / g. The first-cycle coulombic efficiency (ICE) is 92.01%, which is significantly better than existing hard carbon materials. This is related to the different types and structures of precursors used in this invention, the different pretreatment of precursors, the different active agents selected, and the different structures of the resulting products. At the same time, this invention selects petroleum asphalt with a higher softening point and increases its density by soaking it in naphthalene solvent, thereby increasing the hybridization density of SP2 carbon and enabling it to coat biomass carbon, resulting in a dense hard carbon material with a high porosity.

[0064] Figure 5 The long-cycle performance of the sodium-ion battery was tested. It can be seen that after 28 cycles at a current density of 0.1C, the capacity still reaches 286mAh / g, and the corresponding efficiency is still close to 100%, which shows excellent electrochemical performance. This is directly related to the closed-pore structure, surface morphology, and interlayer structure of the obtained hard carbon material. At the same time, the use of waste peels of tangerine peels as precursor materials also contributes to the excellent performance of the battery.

[0065] Figure 6 This is a graph showing the high-rate performance of a sodium-ion battery. It can be seen that at the current density of 1C (C = 300 mAh / g) in the first two cycles, the battery has a capacity of 269.42 mAh / g and an efficiency of 86.49%. In the second cycle, it has a capacity of 237.67 mAh / g. Even after increasing the current density to 2C, the battery still has a capacity of 241.43 mAh / g. This slightly higher capacity increase indicates that the battery has been continuously activated. The excellent high-rate electrochemical performance demonstrates that the hard carbon anode has excellent conductivity and can withstand continuous charging and discharging at high currents.

[0066] Figure 7 This is the cyclic voltammogram for sodium-ion battery testing. According to the test results, at a scan rate of 0.1 mV / s and a voltage range of 0.001–3.0 V, the battery perfectly exhibited a low sodium storage potential and did not show any other impurity peaks, proving that the material was free of impurities after post-processing. The relatively sharp redox peaks also demonstrate that the material possesses good conductivity and can perfectly match changes in battery voltage.

[0067] Meanwhile, the carbon material obtained in Example 1 was assembled into a CR2032 coin cell using conventional methods, and multiple related performance tests were conducted. The results are shown in Tables 1-4 below: Table 1 is the tap density test calculation table; Table 2 is the specific surface area test calculation table; Table 3 is the hard carbon powder conductivity test calculation table; and Table 4 is the theoretical calculation table of 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 shows the tap density calculation table for hard carbon powder. The test conditions were to weigh samples three times, each weighing more than 10g, to ensure that the sample packing volume was greater than 10cm³. 3 The sample was placed in a vibrating graduated cylinder, occupying approximately 70% of its volume, and vibrated continuously for 3000 cycles at a speed of 300 cycles / min. The results showed that the average tap density of the hard carbon in Example 1 was 0.846 g / cm³. 3 It has a density superior to existing pure biomass carbon, which is 0.6-0.7 g / cm³. 3 .

[0078] Table 2 shows the specific surface area of ​​the samples. More than 150 mg of hard carbon powder was weighed, degassed at 300°C for 6 hours, and then weighed again after degassed to eliminate the influence of moisture and air on the values. Three tests were then conducted under a nitrogen atmosphere, yielding an average specific surface area of ​​5.84 m² for the hard carbon in Example 1. 2 / g can effectively control the capacity of the corresponding slope segment of the hard carbon sodium storage curve, indirectly improving the first-efficiency.

[0079] Table 3 shows the powder conductivity test results for the samples. The test method used was a four-probe method, where four probes were simultaneously inserted into the powder to collect data. Comparison of the data shows that the powder resistivity of the hard carbon in Example 1 is close to 15 S / cm.

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

[0081] Example 2

[0082] Biomass bitumen hard carbon was prepared using the same steps as in Example 1, except that the mass of the pre-oxidized bitumen precursor was 5% of the mass of the pre-carbonized fruit peel precursor.

[0083] Example 3

[0084] Biomass bitumen hard carbon was prepared using the same steps as in Example 1, except that the mass of the pre-oxidized bitumen precursor was 15% of the mass of the pre-carbonized fruit peel precursor.

[0085] The biomass pitch hard carbon obtained in Examples 1-3 was assembled into sodium-ion batteries according to the method in Example 1, and its electrical performance was tested. 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 asphalt varies. Because the conductivity of asphalt-derived hard carbon is not as good as that of biomass, excessive coating will reduce the initial release capacity. On the other hand, the porosity of the surface of biomass hard carbon limits the performance of the initial release. Therefore, coating with 10% asphalt is the optimal solution.

[0090] Comparative Example 1

[0091] Biomass pitch hard carbon was prepared using the same steps as in Example 1, except that the precursor used was only pure pitch and did not contain fruit peel precursor.

[0092] The results showed that Comparative Example 1 could not obtain hard carbon materials, but only soft carbon. This may be because the density of oxygen-containing functional groups was not high enough, causing graphitization to occur in the pure phase pitch during sintering at temperatures above 900℃. The obtained soft carbon material exhibited an ordered structure with only 0.35 nm between carbon layers, close to the 0.34 nm of graphite.

[0093] In terms of electrochemical performance, the battery assembled from the materials obtained in Comparative Example 1 had an initial charge capacity of 200.8 mAh g. -1 The capacity is around 1000 m / s, but no plateau appears. The capacity is mostly sloped, indicating that sodium ions cannot be effectively inserted or extracted. Sodium storage can only rely on the adsorption of surface functional groups, defects and impurity atoms.

[0094] Comparative Example 2

[0095] Biomass pitch hard carbon was prepared using the same steps as in Example 1, the only difference being that the waste fruit peel used was grapefruit waste fruit peel.

[0096] The results show that comparative example 2 can produce hard carbon material, but the specific surface area of ​​the material reaches 10⁸ m². 2 The yield was low, possibly because the single biomass carbon formed by the peel has a high volatile content, containing moisture, gas, and tar, which cannot effectively cross-link with mineral carbon sources, resulting in the loss of a large amount of carbon-containing substances.

[0097] In terms of electrochemical performance, the battery assembled from the materials obtained in Comparative Example 2 had an initial charge capacity of 289 mAh g. -1 The slope capacity is around 186mAh / g, but the first-efficiency is only 75%.

[0098] Comparative Example 3

[0099] Biomass bitumen hard carbon was prepared using the same steps as in Example 1, the only difference being that the bitumen used was pre-oxidized bitumen in the air.

[0100] The results showed that comparative example 3 could produce hard carbon materials, but the specific surface area of ​​the materials was only 5-50 m². 2 The yield was between / g and low, possibly because the pre-oxidation of asphalt in the air would burn off some of the carbon; it was also difficult to achieve uniform mixing and coating when pre-oxidized asphalt carbon powder was coated with biomass pre-carbonized powder.

[0101] In terms of electrochemical performance, the battery assembled from the materials obtained in Comparative Example 3 had an initial charge capacity of 280-320 mAh g. -1 Around 70-85% of them are effective initially.

[0102] Comparative Example 4

[0103] Biomass pitch hard carbon was prepared using the same steps as in Example 1, except that the raked citrus peel was treated with NaOH solution for 6 hours.

[0104] The results show that comparative example 4 can produce hard carbon materials, but the specific surface area of ​​the materials will be less than 10 m². 2 The yield is around 0.5g, and the low yield is likely due to the strong alkaline solution dissolving hemicellulose and some cellulose in the biomass, reducing the yield of porous char. Furthermore, biomass itself is porous; even after washing to neutrality during post-processing and allowing it to stand for several hours, it will still be alkaline because the alkali adsorbed in the capillaries of the biomass is released. This alkali will erode the char layer during subsequent high-temperature carbonization, resulting in a low yield and an uneven, porous surface, increasing the specific surface area of ​​the material. The release of strong alkali also causes corrosion damage to high-temperature equipment, reducing its service life.

[0105] In terms of electrochemical performance, the battery assembled from the materials obtained in Comparative Example 4 had an initial charge capacity of 305 mAh g. -1 Around 78% of them were effective initially.

[0106] It should be noted that the above descriptions are merely preferred embodiments of the present invention and should not limit the scope of protection of the technical solutions of the present invention. Any modifications made to the technical solutions described in the foregoing embodiments, or equivalent substitutions of technical features, by those skilled in the art within the spirit and principles of the present invention, should be included within the scope of protection of the present invention.

Claims

1. A method for preparing biomass bitumen hard carbon from waste mandarin orange peels, characterized in that, It includes the following steps: (1) The washed waste mandarin orange peels were soaked in an aqueous solution of sodium dodecyl sulfate and then dried to obtain the peel precursor; the crushed asphalt blocks were soaked in an organic solution of naphthalene and then dried to obtain the asphalt precursor. (2) The fruit peel precursor is pre-carbonized in air or an inert atmosphere to obtain a pre-carbonized precursor, and the asphalt precursor is pre-oxidized in air to obtain a pre-oxidized precursor. (3) The pre-carbonized precursor and the pre-oxidized precursor are mixed to obtain an intermediate mixture, and the intermediate mixture is acidified to obtain an acidified mixture; (4) Carbonize the acidified mixture to obtain biomass asphalt hard carbon.

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

3. The preparation method according to claim 1, characterized in that, In step (1), the cleaning is performed by one or more of the following methods: water washing, acid washing, and alkali washing; and / or, the soaking time in the aqueous solution of sodium dodecyl sulfate is 5-7 h; and / or, the soaking time in the organic solution of naphthalene is 24-72 h; and / or, the temperature of the first drying is 100-120 °C; and / or, the temperature of the second drying 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℃ at a heating rate of 4-6℃ / min and holding for 20-40 min, then heating to 400-500℃ at a heating rate of 2-4℃ / min and holding for 0.5-1.5 h, then heating to 500-600℃ at a heating rate of 4-6℃ / min and holding for 0.5-1.5 h; and / or, the pre-oxidation treatment includes: heating to 150-250℃ at a heating rate of 2-4℃ / min and holding for 1.5-2.5 h, then heating to 270-370℃ at a heating rate of 4-6℃ / min and holding for 0.5-1.5 h.

6. The preparation method according to claim 1, characterized in that, In step (3), the mass of the pre-oxidized precursor is 5-15% of the mass of the pre-carbonized 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 process includes: heating to 500-600℃ at a heating rate of 6-8℃ / min, then heating to 1200-1300℃ at a heating rate of 2-4℃ / min, and holding at that temperature for 1.5-2.5h.

8. 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 biomass pitch hard carbon as described in claim 8.

10. A sodium-ion battery comprising the sodium-ion battery negative electrode as described in claim 9.

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