Hard carbon negative electrode material and preparation method and application thereof

Abstract

The invention relates to the technical field of sodium ion battery negative electrode materials, in particular to a hard carbon negative electrode material as well as a preparation method and application of the hard carbon negative electrode material. And the compaction density, the first efficiency and the capacity of the hard carbon negative electrode material are obviously improved. In addition, the technological process is simple, the usage amount of highly corrosive reagents (such as HF and NaOH) is reduced, low-rank coal (such as lignite and bituminous coal) can be compatible, and the raw material cost is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of sodium ion battery negative electrode materials, and particularly relates to a hard carbon negative electrode material and a preparation method and application thereof. BACKGROUND

[0002] Sodium ion batteries are considered as a substitute for lithium ion batteries due to abundant sodium resources and low cost, but the development of negative electrode materials thereof faces core challenges. Graphite, as a mature negative electrode of lithium batteries, has a too small interlayer spacing (about 0.335 nm) and is difficult to efficiently embed and extract sodium ions (the radius is 34% larger than that of lithium ions), resulting in low sodium storage capacity (usually <100 mAh / g) and poor initial efficiency. Therefore, it is urgent to develop new carbon materials suitable for sodium ion storage.

[0003] Coal, as a natural carbon-rich precursor, has the characteristics of low cost (the raw material price is only 1 / 5 of that of biomass), high carbon content (>60%) and adjustable structure, and is an ideal negative electrode candidate. However, the coal-based hard carbon directly carbonized has the following problems: (1) limited capacity: the sodium storage capacity of anthracite after one-step carbonization is only about 220 mAh / g, which is far lower than the theoretical value (>300 mAh / g); (2) low initial efficiency: surface defects and side reactions lead to an initial coulombic efficiency generally <80%, reducing the energy density of the battery; (3) low compaction density: although traditional doping (such as N and O) can improve the capacity, it increases the defect degree of the material and reduces the compaction density (affecting the volume energy density).

[0004] Researchers have optimized the performance through doping, structure regulation and other means, but there are still obstacles to industrial application: (1) complex doping process: P element doping can significantly improve the capacity, but red phosphorus is flammable and white phosphorus is highly toxic; (2) low efficiency of structure regulation: pre-oxidation or molten salt method can expand the interlayer spacing (such as the introduction of Na2CO3 additive by molten salt method), but the residual sodium salt reduces the specific capacity; (3) difficulty in balancing compaction density and capacity: nitrogen doping improves the electrical conductivity but increases the porosity, which reduces the compaction density and restricts the improvement of the volume energy density of the battery.

[0005] Therefore, there is an urgent need for a hard carbon negative electrode material that balances high capacity, high initial efficiency and high compaction. SUMMARY

[0006] Therefore, the technical problem to be solved by the present application is to overcome the defects of the prior art hard carbon negative electrode material that cannot balance high capacity, high initial efficiency and high compaction, so as to provide a hard carbon negative electrode material and a preparation method and application thereof.

[0007] To this end, in a first aspect, the application provides a preparation method of a hard carbon negative electrode material, comprising the following steps: S1, sequentially performing flotation treatment on raw coal, and then performing acid washing treatment to obtain a coal product; wherein, according to weight parts, the flotation reagent used in the flotation treatment comprises 90-98 parts of a solvent, 0.5-5 parts of Span, and 0.5-5 parts of Triton X-100; The acid washing treatment comprises first-stage acid washing, second-stage acid washing, and third-stage acid washing; The first-stage acid washing is chloridizing roasting under a mixed gas atmosphere containing hydrogen chloride and a first protective gas, at a temperature of 1000-1500 ℃; the volume percentage of hydrogen chloride in the mixed gas atmosphere is 2-10%; The second-stage acid washing is acidification using a first acid solution with a mass concentration of 10-30 wt%; the first acid solution comprises hydrofluoric acid, and also comprises hydrochloric acid or nitric acid; The third-stage acid washing is acid washing using a second acid solution with a mass percentage concentration of 5-20%; the second acid solution comprises sulfuric acid and / or nitric acid; S2, after the coal product after the acid washing treatment is subjected to mixed gas activation treatment, carbonization treatment is performed to obtain a hard carbon negative electrode material; wherein, the mixed gas used in the mixed gas activation treatment contains 1-5 vol% of hydrogen sulfide gas, 5-15 vol% of carbon dioxide, 10-30 vol% of air, and the rest is a second protective gas.

[0008] In some embodiments, the process of the flotation treatment satisfies at least one of the following: A, the time of the flotation is 10-30 min, preferably 13-17 min; B, in the flotation treatment, the solid-liquid mass ratio is 1:5-1:10, preferably 1:7-9; C, the Span comprises one or more of Span-85, Span-80, Span-60, Span-40, and Span-20; D, the solvent comprises kerosene.

[0009] Further, in the process of the acid washing treatment, the first acid solution further comprises 5-20 wt% of nitric acid.

[0010] In some embodiments, the first protective gas is selected from one or more of Ar, He, and N2.

[0011] In some embodiments, the time of the first-stage acid washing is 1.5-2.5 h.

[0012] In some embodiments, the temperature of the second-stage acid washing is 25 ℃-100 ℃; preferably 60-100 ℃.

[0013] In some embodiments, the temperature of the third stage acid washing is 25-100°C; preferably 60-100°C.

[0014] In some embodiments, the time of the second stage acid washing is 0.5-1h.

[0015] In some embodiments, the time of the third stage acid washing is 0.5-1h.

[0016] In some embodiments, the solid-liquid mass ratio during the second stage acid washing or the third stage acid washing is 1:3-10.

[0017] In some preferred embodiments, the first acid solution is an aqueous solution containing 5-20wt% hydrofluoric acid and 5-10wt% nitric acid or hydrochloric acid; more preferably, the first acid solution is an aqueous solution containing 15-20wt% hydrofluoric acid and 5-10wt% nitric acid.

[0018] In some preferred embodiments, during the first stage acid washing, the temperature of the chloridizing roasting is 1150-1250°C, and the volume percentage of hydrogen chloride in the mixed gas atmosphere is 4-6%.

[0019] In some preferred embodiments, the second acid solution is 7-12wt% sulfuric acid.

[0020] In some embodiments, the first acid solution comprises 5-20wt% hydrofluoric acid and 5-10wt% hydrochloric acid or nitric acid.

[0021] In some embodiments, during the mixed gas activation treatment, the second protective gas is selected from one or more of Ar, He, and N2.

[0022] In some embodiments, the mixed gas activation treatment comprises contacting the coal product with the mixed gas at 300-500°C for 4-6h.

[0023] In some embodiments, during the mixed gas activation treatment, the flow rate of the mixed gas is 10-50ml / min / g.

[0024] In some embodiments, the carbonization treatment comprises a first carbonization treatment stage and a second carbonization treatment stage; the first carbonization treatment stage comprises heating at a heating rate of 2-5°C / min to a first carbonization temperature, the carbonization temperature being 400-900°C, preferably 500-800°C, and then maintaining the temperature at the first carbonization temperature for 2-5h, preferably 3-4h; the second carbonization treatment stage comprises heating at a heating rate of 2-5°C / min to a second carbonization temperature, the second carbonization temperature being 1100-1500°C, preferably 1200-1400°C, and then maintaining the temperature at the second carbonization temperature for 2-5h, preferably 3-4h.

[0025] In some embodiments, the carbonization process is carried out under a nitrogen atmosphere. The nitrogen flow rate is 30-100 ml / min / g, preferably 50 ml / min / g.

[0026] In this application, the gas flow rate refers to the volume of gas introduced per unit mass of material per unit time.

[0027] In some embodiments, the raw coal comprises one or more of lignite, bituminous coal, and anthracite. For example, lignite, bituminous coal, or anthracite from Shanxi, Xinjiang, and Inner Mongolia, with bituminous coal from Xinjiang and Inner Mongolia being preferred.

[0028] Secondly, this application also provides a hard carbon anode material prepared by any of the methods described in the first aspect.

[0029] Thirdly, this application also provides a negative electrode sheet, comprising a negative electrode current collector and a negative electrode material layer disposed on at least one side of the negative electrode current collector, wherein the negative electrode material layer comprises the hard carbon negative electrode material.

[0030] Fourthly, this application also provides a secondary battery, including the negative electrode sheet described in the third aspect.

[0031] Fifthly, this application also provides an electrical device, including the secondary battery described in the fourth aspect.

[0032] The technical solution of this invention has the following advantages: 1. The method for preparing hard carbon anode material provided by the present invention involves sequentially flotating raw coal and then acid washing to obtain coal product; wherein, by weight, the flotation reagents used in the flotation process include 90-98 parts of solvent, 0.5-5 parts of Span, and 0.5-5 parts of Triton X-100; the acid washing process includes a first-stage acid washing, a second-stage acid washing, and a third-stage acid washing; the first-stage acid washing is carried out by chlorination roasting at a temperature of 1000-1500℃ in a mixed atmosphere containing hydrogen chloride and a first protective gas; the volume percentage of hydrogen chloride in the mixed atmosphere is 2-10%; the second-stage acid washing is carried out using a first acid solution with a mass concentration of 10-30 wt%. Acidity; the first acid solution includes hydrofluoric acid, and also hydrochloric acid or nitric acid; the third stage acid washing is carried out using a second acid solution with a mass percentage concentration of 5-20%; the second acid solution includes sulfuric acid and / or nitric acid; S2, the coal product after acid washing is activated by mixed gas and then carbonized to obtain hard carbon anode material; wherein, the mixed gas used in the mixed gas activation treatment contains 1-5 vol% hydrogen sulfide gas, 5-15 vol% carbon dioxide, 10-30 vol% air, and the remainder is a second protective gas; by precisely controlling the composition and ratio of flotation reagents, the composition and ratio of mixed gas, and the precise control of the type and concentration of acid in the three-stage acid treatment, the compaction density (>1 g / cm³) can be obtained. 3 Hard carbon anode material with significantly improved first-efficiency (>88%) and reversible capacity (>290mAh / g).

[0033] Specifically, this invention uses a specific ratio of kerosene, Span, and Triton X-100 as flotation reagents to achieve targeted removal of sulfur and ash, reducing ash content to <1% and clean coal recovery rate to >85%. After three-stage acid washing, the treatment under specific concentrations and types of acids not only effectively dissolves aluminosilicates but also greatly reduces the content of magnetic materials (Fe <100ppm) and other impurity elements (Al, Si, S).

[0034] Prior to carbonization, a mixed gas activation treatment is performed. Hydrogen sulfide gas is used to catalyze the removal of residual metal elements; carbon dioxide is used to etch and form microporous precursors; and air reaction introduces oxygen-containing functional groups (such as carbonyl, carboxyl, and hydroxyl groups) and promotes intermolecular cross-linking reactions. This cross-linking significantly improves the thermal stability of coal and prevents melting and coalescence between high-temperature particles. A specific ratio of hydrogen sulfide gas, carbon dioxide, and air is used to pre-create pores on the carbon framework; excessive growth of graphite microcrystals is suppressed (ID / IG = 1.05-1.15). Through the synergistic effect of flotation, acid washing, mixed gas activation, and carbonization under the above process conditions, the compaction density, initial efficiency, and capacity of the hard carbon anode material are significantly improved. Furthermore, the process flow of this invention is simple, reduces the use of highly corrosive reagents (such as HF and NaOH), and is compatible with low-rank coals (such as lignite and bituminous coal), thus reducing raw material costs.

[0035] 2. The method for preparing hard carbon anode material provided by the present invention includes a first carbonization stage and a second carbonization stage. The first carbonization stage includes heating to a first carbonization temperature at a heating rate of 2-5℃ / min, wherein the carbonization temperature is 400-900℃, preferably 500-800℃, and then holding at the first carbonization temperature for 2-5 hours, preferably 3-4 hours. The second carbonization stage includes heating to a second carbonization temperature at a heating rate of 2-5℃ / min, wherein the second carbonization temperature is 1100-1500℃, preferably 1200-1400℃, and then holding at the second carbonization temperature for 2-5 hours, preferably 3-4 hours. By employing the above two-stage carbonization process, especially by controlling the carbonization temperature within the preferred range, structural collapse can be avoided, facilitating coke removal and increasing production capacity. Moreover, the increased interlayer spacing is beneficial for improving Na... + The diffusion rate further enhances first-efficiency and capacity.

[0036] 3. The method for preparing hard carbon anode material provided by the present invention, by controlling the temperature of the second-stage acid washing or the third-stage acid washing to 25℃~100℃; especially 60~100℃; and / or controlling the first acid solution to be an aqueous solution containing 15~20wt% hydrofluoric acid and 5~10wt% nitric acid, and / or controlling the chlorination roasting temperature during the first-stage acid washing process to be 1150-1250℃, the volume percentage of hydrogen chloride in the mixed atmosphere to be 4~6%, and / or controlling the second acid solution to be 7-12wt% sulfuric acid, can further reduce the ash content in coal and improve the initial efficiency and capacity of the battery. Detailed Implementation

[0037] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0038] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0039] The bituminous coal used is pulverized coal from Xinjiang Jilangde Coal Mine or Shengli Coal Mine of Inner Mongolia Wujiu Coal Group. Hydrochloric acid, nitric acid, hydrofluoric acid, and sulfuric acid are all Inokai analytical grade chemicals; The oil bath used a ZNCL-GS173 intelligent thermostatic magnetic stirrer manufactured by Tianjin Yuhua Instrument Technology Co., Ltd. The rotary kiln, model OTF-1200X, was provided by Hefei Kejing Materials Technology Co., Ltd. The carbonization furnace, model GSL-1700X, was provided by Hefei Kejing Materials Technology Co., Ltd.

[0040] Example 1 This embodiment provides a method for preparing a hard carbon anode material, including the following steps: (1) Flotation treatment: 20g of bituminous coal from Jilangde Coal Mine in Xinjiang with a particle size D50 of 50μm was selected and mixed with 160g of flotation reagent. Then, flotation separation was carried out using a flotation machine for 15min, followed by drying. The flotation reagent was prepared by mixing kerosene, Span-80, and Triton X-100 in a mass ratio of 98:1:1.

[0041] (2) Acid washing treatment: The bituminous coal treated in step (1) is roasted at 1200℃ for 2 hours in a mixed atmosphere of hydrogen chloride (HCl) and nitrogen (N2) with a volume ratio of 5:95 (first stage acid washing). Then the coal is placed in a first acid solution heated in an oil bath at 100℃ and stirred for 1 hour (rotation speed of 200 rpm). The first acid solution is an aqueous solution containing 20 wt% HF and 5 wt% HNO3 (second stage acid washing). Finally, it is stirred in a second acid solution heated in an oil bath at 80℃ for 0.5 hours (rotation speed of 200 rpm). The second acid solution is an aqueous solution containing 10 wt% H2SO4 (third stage acid washing) to obtain the coal product. During the second stage acid washing or the third stage acid washing process, the solid-liquid mass ratio is 1:5.

[0042] (3) Activation treatment of mixed gas: The acid-washed coal product is placed in a rotary kiln, and mixed gas is introduced to contact the coal product. The temperature of the mixed gas is increased to 400℃ at a heating rate of 5℃ / min, and then held at a constant temperature for 5h. The flow rate of the mixed gas is 15ml / min / g. Based on a total volume of 100vol%, the composition of the mixed gas is as follows: 5vol% hydrogen sulfide gas, 10vol% carbon dioxide, 25vol% air, and the remainder is nitrogen.

[0043] (4) Carbonization treatment: The coal product after activation treatment with mixed gas is added to the carbonization furnace and carbonized under a nitrogen atmosphere with a nitrogen flow rate of 50 ml / min / g. During the carbonization treatment, the temperature is first increased to 700℃ at a heating rate of 2.5℃ / min, and then held at this temperature for 3 hours (first carbonization treatment stage). Then the temperature is increased to 1200℃ at a heating rate of 2.5℃ / min, and then held at this temperature for 3 hours (second carbonization treatment stage).

[0044] Example 2 The process is basically the same as in Example 1, except that the acid washing steps are different. The acid washing process in this example is as follows: The bituminous coal treated in step (1) is roasted at 1500℃ for 2 hours in a mixed atmosphere of hydrogen chloride (HCl) and nitrogen (N2) with a volume ratio of 2:98 (first stage acid washing). Then, the coal is placed in a first acid solution heated in an oil bath at 100℃ and stirred for 1 hour (rotation speed of 200 rpm). The first acid solution is an aqueous solution containing 5 wt% HF and 5 wt% HNO3 (second stage acid washing). Finally, the coal is stirred in a second acid solution heated in an oil bath at 80℃ for 0.5 hours (rotation speed of 200 rpm). The second acid solution is an aqueous solution containing 5 wt% H2SO4 (third stage acid washing) to obtain the coal product. In the second stage acid washing or the third stage acid washing process, the solid-liquid mass ratio is 1:6.

[0045] Example 3 The process is basically the same as in Example 1, except that the acid washing steps are different. The acid washing process in this example is as follows: The bituminous coal treated in step (1) is roasted at 1000℃ for 1.5h in a mixed atmosphere of hydrogen chloride (HCl) and nitrogen (N2) with a volume ratio of 10:90 (first stage acid washing). Then the coal is placed in a first acid solution heated in an oil bath at 70℃ and stirred for 0.5h (rotation speed of 200rpm). The first acid solution is an aqueous solution containing 10wt%HF and 10wt%HNO3 (second stage acid washing). Finally, it is stirred in a second acid solution heated in an oil bath at 100℃ for 1h (rotation speed of 200rpm). The second acid solution is a solution containing 20wt% sulfuric acid (third stage acid washing) to obtain the coal product. In the second stage acid washing or the third stage acid washing process, the solid-liquid mass ratio is 1:10.

[0046] Example 4 The process is essentially the same as in Example 1, except that the activation treatment step for the mixed gas is different. In this example, the activated gas treatment is as follows: The acid-washed coal product is placed in a rotary kiln, and a mixed gas is introduced to contact the coal product. The temperature in the mixed gas is increased to 300°C at a rate of 5°C / min, and maintained at this temperature for 6 hours. The flow rate of the mixed gas is 10 ml / min / g. Based on a total volume of 100 vol%, the composition of the mixed gas is as follows: 2 vol% hydrogen sulfide gas, 5 vol% carbon dioxide, 15 vol% air, and the remainder nitrogen.

[0047] Example 5 This example is essentially the same as Example 1, except for the different flotation and carbonization steps. The flotation process in this example is as follows: 20g of bituminous coal from the Jilangde coal mine in Xinjiang, with a particle size D50 of 50μm, was mixed with 140g of flotation reagent. The mixture was then subjected to flotation separation using a flotation machine for 13 minutes, followed by drying. The flotation reagent was prepared by mixing kerosene, Span-80, and Triton X-100 in a mass ratio of 90:5:5.

[0048] The carbonization process in this embodiment is as follows: The coal product, after activation treatment with a mixed gas, is added to a carbonization furnace and carbonized under a nitrogen atmosphere at a flow rate of 60 ml / min / g. During the carbonization process, the temperature is first increased to 500°C at a rate of 5°C / min, and then held at this temperature for 4 hours (first carbonization stage). Then, the temperature is increased to 1400°C at a rate of 5°C / min, and then held at this temperature for 4 hours (second carbonization stage).

[0049] Example 6 It is basically the same as Example 1, except that Span-60 of the same quality is used instead of Span-80 in the flotation process.

[0050] Example 7 It is basically the same as Example 1, except that Span-85 of the same quality is used instead of Span-80 in the flotation process.

[0051] Example 8 The process is essentially the same as in Example 1, except for the carbonization process. In this example, the carbonization process is as follows: The coal product, after activation treatment with a mixed gas, is added to a carbonization furnace and carbonized under a nitrogen atmosphere at a flow rate of 50 ml / min / g. During carbonization, the temperature is first increased to 400°C at a rate of 2.5°C / min, and then held at this temperature for 3 hours (first carbonization stage). Then, the temperature is increased to 1500°C at a rate of 2.5°C / min, and then held at this temperature for 3 hours (second carbonization stage).

[0052] Example 9 The process is basically the same as in Example 1, except that the carbonization process is different. In this example, the carbonization process is as follows: The coal product after mixed gas activation is added to a carbonization furnace and carbonized under a nitrogen atmosphere at a flow rate of 50 ml / min / g. During the carbonization process, the temperature is first increased to 900°C at a rate of 2.5°C / min, and then held at that temperature for 3 hours (first carbonization stage). Then, the temperature is increased to 1100°C at a rate of 2.5°C / min, and then held at that temperature for 3 hours (second carbonization stage).

[0053] Comparative Example 1 The process is basically the same as in Example 1, except that the concentration of acid in each stage of the pickling process is different. In this comparative example, the volume ratio of HCl to N2 in the first pickling stage is 1:99, the second pickling stage uses an aqueous solution containing 2wt% HF and 3wt% HNO3, and the third pickling stage uses an aqueous solution containing 5wt% sulfuric acid.

[0054] Comparative Example 2 The process is basically the same as in Example 1, except that the concentration of acid in each stage of the pickling process is different. In this comparative example, the volume ratio of HCl to N2 in the first pickling stage is 15:85, the second pickling stage uses an aqueous solution containing 20wt% HF and 25wt% HNO3, and the third pickling stage uses an aqueous solution containing 10wt% H2SO4.

[0055] Comparative Example 3 It is basically the same as Example 1, except that the first stage of pickling is omitted in the pickling process.

[0056] Comparative Example 4 It is basically the same as Example 1, except that the roasting temperature of the first stage pickling is adjusted to 1600°C.

[0057] Comparative Example 5 It is basically the same as Example 1, except that the roasting temperature of the first stage pickling is adjusted to 900°C.

[0058] Comparative Example 6 It is basically the same as Example 1, except that Span-80 is omitted from the flotation reagent.

[0059] Comparative Example 7 It is basically the same as Example 1, except that Triton X-100 is omitted from the flotation reagent.

[0060] Comparative Example 8 The process is essentially the same as in Example 1, except that Triton X-100 is replaced with sodium dodecylbenzenesulfonate of the same mass in the flotation reagent.

[0061] Comparative Example 9 The process is basically the same as in Example 1, except that the mixed gas used in the mixed gas activation process is different. In this comparative example, the total volume of the mixed gas is 100 vol%, and the composition of the mixed gas is as follows: 10 vol% carbon dioxide, 25 vol% air, and the remainder is nitrogen.

[0062] Comparative Example 10 The process is basically the same as in Example 1, except that the mixed gas used in the mixed gas activation process is different. In this comparative example, the total volume of the mixed gas is 100 vol%, and the composition of the mixed gas is as follows: 5 vol% hydrogen sulfide gas, 35 vol% air, and the remainder is nitrogen.

[0063] Comparative Example 11 The process is basically the same as in Example 1, except that the mixed gas used in the mixed gas activation process is different. In this comparative example, the total volume of the mixed gas is 100 vol%, and the composition of the mixed gas is as follows: 5 vol% hydrogen sulfide gas, 45 vol% carbon dioxide, and the remainder is nitrogen.

[0064] Comparative Example 12 The process is basically the same as in Example 1, except that the mixed gas used in the mixed gas activation process is different. In this comparative example, the total volume of the mixed gas is 100 vol%, and the composition of the mixed gas is as follows: 10 vol% hydrogen sulfide gas, 20 vol% carbon dioxide, 5 vol% air, and the remainder is nitrogen.

[0065] Test Example 1 The ash content and impurity element content of the acid-washed coal products tested in Examples 1-3, 5-7 and Comparative Examples 1, 3-8 are as follows: The ash content of the acid-washed coal products of each embodiment and comparative example was determined in accordance with the provisions of GB / T9345.1-2008 "Determination of Ash Content in Plastics - Part 1: General Method". The elemental content of the acid-washed coal products of each embodiment and comparative example was tested in accordance with the provisions of GB / T 26050—2024 "Determination of Metallic Element Content in Hard Alloys - X-ray Fluorescence Spectrometry". The results are shown in Table 1 below.

[0066] Table 1. Test results of ash content and impurity element content

[0067] As shown in Table 1, compared with Comparative Examples 1 and 3-8, the ash content of the coal products obtained in each embodiment of this application is significantly reduced, and the content of iron and other impurity elements is also significantly reduced.

[0068] Compared with Examples 2 and 3, Example 1 can further reduce the content of ash, magnetic substances and other impurities in coal and improve product quality by limiting the pickling process conditions to a preferred range.

[0069] Compared with Examples 6 and 7, Example 1 can further reduce the content of ash, magnetic substances and other impurities in coal and improve product quality by limiting the pickling process conditions to a preferred range.

[0070] Test Example 2 The hard carbon anode materials prepared in each embodiment and comparative example are used to make anode sheets and then assembled into batteries. The specific methods are as follows: Preparation of the negative electrode sheet: The negative electrode material, conductive carbon black SP, polyacrylic acid PAA, carboxymethyl cellulose CMC, and styrene-butadiene rubber SBR prepared according to the above-described embodiments and comparative examples of the present invention are mixed in a weight ratio of 95.5:1:2.3:0.6:0.6 and dispersed in water to form a uniform slurry. This slurry is coated onto a copper foil current collector, dried, and cold-pressed to obtain the negative electrode sheet.

[0071] Preparation of the positive electrode: Sodium sheets are used directly as the positive electrode. The sodium sheets should meet the following requirements: the purity of sodium is not less than 99.9% to minimize the side reactions of impurities on the electrolyte and interface; the sodium sheet has a uniform thickness of 0.45 mm to ensure an excess and stable sodium source during testing; before use, the fresh oxide layer on the surface of the sodium sheet should be scraped off with a scraper or mold in a glove box filled with inert gas (such as argon), and immediately punched into a smooth sodium sheet of the required diameter (usually slightly smaller than the inner diameter of the battery case) to ensure that a fresh and stable interface is formed between it and the electrolyte.

[0072] Electrolyte: Ethylene carbonate (EC), dimethyl carbonate (DMC), and propylene carbonate (PC) are mixed evenly in a mass ratio of 40:30:30 to obtain an organic solvent. Sodium hexafluorophosphate is dissolved in the above organic solvent and mixed evenly to obtain the electrolyte. Based on the mass of the electrolyte, the concentration of sodium hexafluorophosphate is 1.5M.

[0073] Button cell fabrication: A button cell is assembled using the negative electrode sheet, sodium sheet, separator (PE porous polymer film), gasket, spring contact, and button cell casing prepared above, and then injected with the prepared electrolyte. The following tests are performed: (1) Initial efficiency and reversible capacity: At 25°C, the battery is charged to 3.0V with a constant current of 20 mA / g, and then discharged to 0.01V with the same current. This initial discharge capacity is the reversible capacity (or initial discharge specific capacity) of the hard carbon material. The initial efficiency is calculated according to the following formula: Initial efficiency = Initial discharge capacity of the battery / Initial charge capacity of the battery × 100%.

[0074] (2) Plateau voltage: Obtain the first discharge voltage-capacity curve from the reversible capacity test described above. Differentiate the discharge curve with respect to the capacity to obtain the differential capacity curve (dQ / dV curve). The voltage value corresponding to the peak of the sodium storage platform in the hard carbon material pore on this curve is the plateau voltage.

[0075] (3) Compacted density: Weigh a certain mass (denoted as m, approximately 0.5 g) of the negative electrode powder material to be tested, place it into a standard cylindrical mold, and use a powder tablet press to hold it under a pressure of 5 t for 60 seconds to form a dense blank. After depressurization, measure the thickness (h) and diameter (d) of the blank, and calculate its volume (V = π*(d / 2)). 2 *h). The compaction density of the negative electrode powder material is calculated using the formula: Compaction density (g / cm³) 3 = mass m (g) / volume V (cm³) 3 The calculation yielded the result.

[0076] Table 2 Test results of electrical performance

[0077] As can be seen from the results in Table 2, compared with the other examples, the secondary batteries of the present application can significantly improve the reversible capacity, initial voltage, and plateau voltage while increasing the compaction density.

[0078] Comparing Example 1 with Examples 6-7, it can be seen that Example 1 can further improve the reversible capacity of the battery by using Span-80.

[0079] Compared with Examples 8-9, Example 1 shows that by limiting the carbonization temperature of the first carbonization treatment stage and the second carbonization treatment stage to a preferred range, Example 1 can further improve the battery's initial efficiency, reversible capacity and plateau voltage.

[0080] Test Example 3 Weigh the coal powder before and after flotation in Examples 1 and 5-7, and calculate the clean coal recovery rate. Clean coal recovery rate = weight of coal powder after flotation / weight of coal powder before flotation × 100%. The results are as follows: Table 3 Test results of clean coal recovery rate

[0081] As shown in Table 3, the flotation method of the present invention has a high clean coal recovery rate. In particular, the clean coal recovery rate can be further improved by using Span-80 in Examples 1 and 5.

[0082] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing a hard carbon anode material, characterized in that, Includes the following steps: S1. The raw coal is subjected to flotation treatment, followed by acid washing treatment to obtain coal products; wherein, by weight, the flotation reagents used in the flotation treatment include 90-98 parts of solvent, 0.5-5 parts of Span and 0.5-5 parts of Triton X-100. The pickling process includes a first-stage pickling, a second-stage pickling, and a third-stage pickling. The first stage of pickling involves chlorination roasting at a temperature of 1000-1500°C under a mixed atmosphere containing hydrogen chloride and a first protective gas; the volume percentage of hydrogen chloride in the mixed atmosphere is 2-10%. The second stage of pickling involves acidification using a first acid solution with a mass concentration of 10-30 wt%; the first acid solution includes hydrofluoric acid, as well as hydrochloric acid or nitric acid. The third stage of pickling involves using a second acid solution with a mass percentage concentration of 5-20%; the second acid solution includes sulfuric acid and / or nitric acid. S2. After acid washing, the coal product is activated by mixed gas and then carbonized to obtain hard carbon anode material. The mixed gas used in the mixed gas activation process contains 1-5 vol% hydrogen sulfide gas, 5-15 vol% carbon dioxide, 10-30 vol% air, and the remainder is a second protective gas.

2. The method for preparing the hard carbon anode material according to claim 1, characterized in that, The flotation process satisfies at least one of the following: A. The flotation time is 10-30 minutes, preferably 13-17 minutes; B. In the flotation process, the solid-liquid mass ratio is 1:5 to 1:10, preferably 1:7-9; C. The span includes one or more of span-85, span-80, span-60, span-40, and span-20; D. The solvent includes kerosene.

3. The method for preparing the hard carbon anode material according to claim 1 or 2, characterized in that, The pickling process satisfies at least one of the following: (1) During the pickling process, the first protective gas is selected from one or more of Ar, He, and N2; (2) The pickling time for the first stage is 1.5-2.5 hours; (3) The temperature of the second or third stage pickling is 25℃~100℃; preferably 60~100℃; (4) The pickling time for the second or third stage is 0.5-1 hour; (5) During the second or third stage pickling process, the solid-liquid mass ratio is 1:3~10; (6) The first acid solution is an aqueous solution containing 5-20 wt% hydrofluoric acid and 5-10 wt% nitric acid or hydrochloric acid; preferably, the first acid solution is an aqueous solution containing 15-20 wt% hydrofluoric acid and 5-10 wt% nitric acid. (7) During the first stage of pickling, the chlorination roasting temperature is 1150-1250℃, and the volume percentage of hydrogen chloride in the mixed atmosphere is 4-6%; (8) The second acid solution is 7-12 wt% sulfuric acid.

4. The method for preparing the hard carbon anode material according to claim 1, characterized in that, In the mixed gas activation treatment, the second protective gas is selected from one or more of Ar, He, and N2; And / or, the mixed gas activation treatment includes contacting the coal product with the mixed gas at 300~500℃ for 4-6 hours; And / or, during the mixed gas activation process, the flow rate of the mixed gas is 10~50 ml / min / g.

5. The method for preparing the hard carbon anode material according to claim 1, characterized in that, The carbonization process includes a first carbonization process stage and a second carbonization process stage. The first carbonization treatment stage includes heating to a first carbonization temperature at a heating rate of 2~5℃ / min, wherein the carbonization temperature is 400~900℃, preferably 500~800℃, and then holding at the first carbonization temperature for 2~5h, preferably 3~4h. The second carbonization process includes heating to a second carbonization temperature at a heating rate of 2-5°C / min, the second carbonization temperature being 1100-1500°C, preferably 1200-1400°C, and then holding at the second carbonization temperature for 2-5 hours, preferably 3-4 hours.

6. The method for preparing the hard carbon anode material according to claim 1, characterized in that, The raw coal includes one or more of lignite, bituminous coal, and anthracite.

7. The hard carbon anode material prepared by the method of any one of claims 1-6.

8. A negative electrode sheet, characterized in that, The device includes a negative electrode current collector and a negative electrode material layer disposed on at least one side of the negative electrode current collector, the negative electrode material layer comprising the hard carbon negative electrode material as described in claim 7.

9. A secondary battery, characterized in that, Includes the negative electrode sheet as described in claim 8.

10. An electrical device, characterized in that, Includes the secondary battery as described in claim 9.

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