Hard carbon negative electrode material, and preparation method and use thereof

Abstract

The application provides a hard carbon negative electrode material and a preparation method and use thereof, and the preparation method comprises the following steps: performing acid washing and ash removal on a carbon source precursor, and then sequentially performing oxidation solidification and deep oxidation in an oxygen-containing atmosphere, the temperature of the oxidation solidification is lower than that of the deep oxidation, to obtain an oxidation precursor; sequentially performing pyrolysis and high-temperature carbonization on the oxidation precursor in an inert atmosphere, to obtain the hard carbon negative electrode material. Through the oxidation solidification and deep oxidation on the carbon source precursor, the former can increase the molecular weight of the raw material, improve the softening temperature, avoid the problem of slow mass transfer rate and uneven oxidation when directly using high-temperature oxidation, and crosslinking is achieved through deep oxidation, so that the oxidation precursor with high oxidation degree and complex crosslinking structure is obtained, and then pyrolysis and high-temperature carbonization are performed, the disorder degree and the interplanar spacing of the carbon layer are improved, so that the sodium storage performance of the negative electrode material is improved, and the capacity and the rate performance are excellent; the method is simple to operate, the raw material and process cost are low, and the application range is wide.

Description

TECHNICAL FIELD

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

[0002] At present, lithium ion batteries are widely used in mobile electronic devices, new energy vehicles, electric tools and other fields due to their high energy density and excellent safety performance. However, due to the limited lithium resources and high price, the application of lithium ion batteries in large-scale energy storage systems is limited. Compared with lithium, sodium resources are abundant in the earth's crust and low in price, and sodium ion batteries have a wide application prospect in large-scale energy storage systems and are expected to be applied to the next generation of large-scale energy storage devices.

[0003] Due to the larger radius of sodium ions than lithium ions, it is difficult for sodium ions to be embedded in the interlayer spacing of graphite negative electrodes, and graphite negative electrodes are not suitable as negative electrode materials of sodium ion batteries, so that the negative electrode material has become one of the main problems restricting the development of lithium ion batteries. Amorphous carbon materials have high sodium storage capacity due to their low graphitization degree, high disorder degree and large carbon layer spacing, and have a wide application prospect as negative electrode materials of sodium ion batteries.

[0004] Hard carbon is a kind of amorphous carbon material with disordered and curved carbon layers, which can realize intercalation, adsorption and pore filling for sodium storage, and has high capacity. The raw materials of hard carbon mainly include various carbon sources, including high molecular compounds, biomass, organic matter and the like. The commonly used organic matter includes pitch, coal and the like. However, direct carbonization of pitch and other raw materials usually forms soft carbon material with high order degree, small interlayer spacing and low sodium storage capacity. Therefore, the organic matter carbon source needs to be modified to form a cross-linked structure to improve the disorder degree and interlayer spacing of the carbon layer. However, due to the difference in types of carbon source precursors, the conventional modification method is difficult to be universal.

[0005] CN 115991467A discloses an oxidized pitch-based hard carbon negative material for sodium ion battery and a preparation method thereof, the method comprising: crushing pitch, adjusting temperature using a fluidized bed, oxidizing the crushed pitch to obtain an oxidation precursor, and then performing high-temperature carbonization treatment after screening to obtain the oxidized pitch-based hard carbon negative material. CN 109148883A discloses a pitch-based sodium ion battery negative material, a preparation method and application thereof, the method comprising: pre-oxidizing pitch precursor at 200-350℃ for 2-6h, then placing it in a high-temperature carbonization furnace, heating to 1300-1600℃ at a heating rate of 0.5-5℃ / min, and heat treating in an inert atmosphere for 1-10h to make the pre-oxidized pitch undergo carbonization and cracking reaction, and cooling to room temperature to obtain irregular fast-shaped amorphous carbon material. In the above patents, the pitch is modified by oxidation to deepen the oxidation degree of the pitch, break the ordered structure of the pitch, and improve the crosslinking degree, but there are still problems of slow mass transfer rate after melting and uneven oxidation, and the amorphous carbon formed still contains a large amount of long-range and ordered carbon layer structure and low interlayer spacing, thereby causing limited capacity after carbonization.

[0006] CN 116553512A discloses a preparation method of a hard carbon material for sodium ion battery, the preparation method comprising: uniformly mixing pitch-like substances and sulfur-containing compounds to obtain a first mixed precursor, pressing into a sheet, heat treating in an oxidizing atmosphere, cooling, obtaining crosslinked modified pitch, uniformly mixing the crosslinked modified pitch with pore-forming agents and pore-modifying agents to obtain a second mixed precursor, calcining in an inert atmosphere or a hydrocarbon atmosphere, cooling, grinding, acid washing, washing, and drying to obtain an amorphous sodium ion battery negative material. Although this method also uses pitch-like substances as raw materials and performs oxidation treatment and calcination carbonization on the pitch, it still has problems of uneven oxidation and slow mass transfer rate after melting, and also uses multiple components, which makes the operation steps more complex and increases the cost.

[0007] In summary, for the preparation process of hard carbon negative materials, the oxidation uniformity needs to be improved by selecting appropriate pre-oxidation processes according to the selection of raw precursor, to obtain ideal crosslinking structure and improve the sodium storage capacity and rate performance of the negative material. SUMMARY

[0008] In view of the problems in the prior art, the purpose of the present application is to provide a hard carbon negative material and a preparation method and use thereof, the method improves the oxidation degree and crosslinking degree of the precursor by respectively performing oxidation solidification and deep oxidation on the carbon source precursor, and then combines pyrolysis and high-temperature carbonization to improve the disorder degree and interplanar spacing of the carbon layer, thereby obtaining a hard carbon negative material, effectively improving the sodium storage capacity and improving the rate performance.

[0009] To achieve the above object, the present application adopts the following technical solutions.

[0010] In a first aspect, the present application provides a preparation method of hard carbon negative electrode material, which comprises the following steps:

[0011] (1) performing acid washing and ash removal on a carbon source precursor, and then performing oxidation solidification and deep oxidation successively in an oxygen-containing atmosphere, the temperature of the oxidation solidification being lower than that of the deep oxidation, to obtain an oxidized precursor;

[0012] (2) performing pyrolysis and high-temperature carbonization successively on the oxidized precursor obtained in step (1) in an inert atmosphere, to obtain the hard carbon negative electrode material.

[0013] In the present application, for the preparation of sodium ion battery negative electrode material, the disorder degree of the carbon layer needs to be improved as much as possible to facilitate the embedding of sodium ions, thus in the present application, the carbon source precursor is first subjected to acid washing to remove inorganic impurity components, and then pre-oxidation is performed in an oxygen-containing atmosphere, which is specifically divided into two-stage oxidation processes of oxidation solidification and deep oxidation, the temperature of the former being lower than that of the latter, the former is performed before the precursor is melted to increase the molecular weight of the raw material and improve the softening temperature, thereby avoiding the problem of slow mass transfer rate and uneven oxidation caused by melting when directly using high temperature for oxidation, and then deep oxidation crosslinking is performed at a higher temperature, thereby obtaining an oxidized precursor with high oxidation degree and complex crosslinking structure, which is then subjected to pyrolysis to remove volatile components and high-temperature carbonization treatment, so as to form an amorphous hard carbon material with disordered distribution, the interplanar spacing of which is increased, which is helpful for the embedding of sodium ions, thereby improving the sodium storage performance of the negative electrode material, and the capacity and rate performance are excellent; the method is simple to operate, the raw material and process cost are low, and the application range is wide.

[0014] The following are preferred technical solutions of the present application, but not as a limitation of the technical solutions provided by the present application, through the following technical solutions, the technical purpose and beneficial effects of the present application can be better achieved and realized.

[0015] As a preferred technical solution of the present application, the carbon source precursor in step (1) comprises any one or a combination of at least two of coal tar pitch, petroleum pitch, coal or heavy carbon, and typical but non-limiting examples of the combination include: a combination of coal tar pitch and coal, a combination of coal and heavy carbon, a combination of coal tar pitch, petroleum pitch and coal, etc.

[0016] In the present application, in addition to the above two pitches, in the selection of the carbon source precursor, the coal can be selected from bituminous coal, lignite, sub-bituminous coal, coking coal or anthracite, etc., and the heavy carbon can be selected from liquefaction residue, oil shale, heavy oil, oil sand, biomass or petroleum coke, etc., the above carbon source precursors can be used alone or two or more of them can be used together.

[0017] Preferably, the carbon source precursor in step (1) is first crushed and sieved to obtain raw material particles.

[0018] Preferably, the crushing comprises breaking and grinding in sequence, and the broken particles are first dried and then ground.

[0019] Preferably, the particle size of the raw material particles selected by the sieving is 3-20 μm, such as 3 μm, 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm or 20 μm, etc., but not limited to the listed values, and other values not listed in the range are also applicable. The point value of the particle size generally represents the particle size of a single particle or the average particle size of the raw material particles. For a certain amount of raw material particles, the particle size usually has a certain range, such as 3-5 μm, 4-8 μm, 5-10 μm, 3-15 μm, 3-10 μm or 8-20 μm, etc.

[0020] Preferably, the sieved raw material particles are dried and then subjected to acid pickling and ash removal.

[0021] In the present application, the carbon source precursor is first crushed and sieved to reduce the particle size, increase the specific surface area, and facilitate the subsequent oxidation and carbonization process of the oxidizing agent. The breaking is performed by a breaker, such as a jaw breaker. The dried particles are dried in a blast drying oven at a temperature of 100-120 ℃, and then ground by a grinder and sieved by a standard vibrating screen to select raw material particles with a particle size of 3-20 μm. The selected raw material particles are then dried at 100-120 ℃ for 3-5 h.

[0022] As a preferred technical solution of the present application, the acid used in the acid pickling and ash removal in step (1) comprises hydrochloric acid and / or hydrofluoric acid, and preferably the hydrochloric acid is used first, followed by the hydrofluoric acid.

[0023] In the present application, the main role of the acid pickling is to remove inorganic components from the carbon source precursor. The hydrochloric acid is used to remove metal salts, and the hydrofluoric acid is used to remove silicate and aluminate.

[0024] Preferably, the carbon source precursor is mixed with the hydrochloric acid and stirred, and then subjected to water washing, filtration and drying after standing to obtain the first acid-pickled raw material.

[0025] Preferably, the solid-liquid ratio of the carbon source precursor to the hydrochloric acid is 1 g:(2-10) mL, such as 1 g:2 mL, 1 g:3 mL, 1 g:4 mL, 1 g:5 mL, 1 g:6 mL, 1 g:7 mL, 1 g:8 mL, 1 g:9 mL or 1 g:10 mL, etc., but not limited to the listed values, and other values not listed in the range are also applicable. Preferably, the solid-liquid ratio is 1 g:(2-4) mL.

[0026] Preferably, the mass fraction of the hydrochloric acid is 10-37%, such as 10%, 15%, 20%, 25%, 30%, 35%, 37%, or the like, but not only limited to the listed values, other values not listed in the range are also applicable, preferably 30-37%.

[0027] In the present application, the carbon source precursor after crushing and screening is mixed with hydrochloric acid, stirred at a speed of 80-120 r / min for 10-15 h, then placed for 1-3 h, washed repeatedly with distilled water until no Cl - After filtration, dry in a blast drying oven at 100-120℃ for 10-15 h to obtain the demineralized raw material.

[0028] Preferably, the first pickling raw material is mixed with hydrofluoric acid and stirred and washed, then washed with water, filtered, and dried to obtain the second pickling raw material.

[0029] Preferably, the solid-liquid ratio of the first pickling raw material and hydrofluoric acid is 1g:(1-10)mL, such as 1g:1mL, 1g:2mL, 1g:3mL, 1g:4mL, 1g:5mL, 1g:6mL, 1g:7mL, 1g:8mL, 1g:9mL, or 1g:10mL, or the like, but not only limited to the listed values, other values not listed in the range are also applicable, preferably 1g:(1-3)mL.

[0030] Preferably, the mass fraction of the hydrofluoric acid is 25-40%, such as 25%, 27%, 30%, 32%, 35%, 38%, or 40%, or the like, but not only limited to the listed values, other values not listed in the range are also applicable.

[0031] In the present application, the first pickling raw material is mixed with hydrofluoric acid and stirred at a speed of 80-120 r / min for 20-28 h, then placed for 2-4 h, the filter cake is washed with distilled water after filtration, and washed multiple times until no F - , then dry in a blast drying oven at 100-120℃ for 10-15 h to obtain the pickled raw material.

[0032] As a preferred technical solution of the present application, the concentration of oxygen in the oxygen-containing atmosphere in step (1) is 10-100%, such as 10%, 21%, 30%, 40%, 50%, 60%, 80%, or 100%, or the like, but not only limited to the listed values, other values not listed in the range are also applicable.

[0033] Preferably, the concentration of the oxygen-containing atmosphere in step (1) is independently selected, preferably the same concentration, during oxidation and curing and deep oxidation.

[0034] Preferably, the oxidation curing and the deep oxidation in step (1) are both carried out in a tube furnace, preferably in the constant temperature zone of the tube furnace.

[0035] Preferably, the oxidation curing and the deep oxidation in step (1) are carried out consecutively, and the deep oxidation is carried out after the oxidation curing is completed.

[0036] As a preferred technical solution of the present application, the temperature of the oxidation curing in step (1) is lower than the softening point temperature of the carbon source precursor or the temperature corresponding to the maximum weight in the thermogravimetric curve.

[0037] Preferably, the temperature of the oxidation curing in step (1) is 70-320℃, such as 70℃, 100℃, 150℃, 200℃, 250℃, 270℃, 300℃ or 320℃, but is not limited to the listed values, and other values in the range are also applicable; the time is 1-5h, such as 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h or 5h, but is not limited to the listed values, and other values in the range are also applicable; and the heating rate is 0.2-5℃ / min, such as 0.2℃ / min, 0.5℃ / min, 1℃ / min, 1.5℃ / min, 2℃ / min, 2.5℃ / min, 3℃ / min, 4℃ / min or 5℃ / min, but is not limited to the listed values, and other values in the range are also applicable.

[0038] In the present application, different temperatures are selected for the oxidation curing according to the type of the carbon source precursor. When the carbon source precursor is selected as pitch, the temperature of the oxidation curing is generally selected to be about 10℃ lower than the softening point temperature. When the carbon source precursor is selected as coal or heavy carbon, the temperature of the oxidation curing is generally selected to be the temperature corresponding to the maximum weight in the thermogravimetric curve, because the reactivity of the precursor is the strongest at this temperature.

[0039] Preferably, the temperature of the deep oxidation in step (1) is 120-360℃, such as 120℃, 150℃, 200℃, 250℃, 270℃, 300℃, 320℃, 350℃ or 360℃, etc., but not limited to the listed values, and other values not listed in the range are also applicable; the time is 1-5h, such as 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h or 5h, etc., but not limited to the listed values, and other values not listed in the range are also applicable; the heating rate is 0.2-5℃ / min, such as 0.2℃ / min, 0.5℃ / min, 1℃ / min, 1.5℃ / min, 2℃ / min, 2.5℃ / min, 3℃ / min, 4℃ / min or 5℃ / min, etc., but not limited to the listed values, and other values not listed in the range are also applicable.

[0040] In the present application, the oxidative curing can increase the molecular weight of the raw material, increase the softening temperature, so that the precursor is not melted during deep oxidation, and the highly cross-linked oxidized precursor is easily obtained.

[0041] As a preferred technical solution of the present application, the inert atmosphere in step (2) includes any one or a combination of at least two of helium, neon or argon, and typical but non-limiting examples of the combination include: a combination of helium and neon, a combination of neon and argon, a combination of helium, neon and argon, etc.

[0042] Preferably, the pyrolysis in step (2) is carried out in a pyrolysis furnace to remove the volatile components in the oxidized precursor.

[0043] Preferably, the temperature of the pyrolysis in step (2) is 300-900℃, such as 300℃, 400℃, 500℃, 600℃, 700℃, 800℃ or 900℃, etc., but not limited to the listed values, and other values not listed in the range are also applicable; the time is 0.5-3h, such as 0.5h, 1h, 1.5h, 2h, 2.5h or 3h, etc., but not limited to the listed values, and other values not listed in the range are also applicable.

[0044] Preferably, the heating rate of the pyrolysis in step (2) is 0.5-10℃ / min, such as 0.5℃ / min, 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 8℃ / min or 10℃ / min, etc., but not limited to the listed values, and other values not listed in the range are also applicable.

[0045] Preferably, after the pyrolysis in step (2), the product is transferred to a carbonization furnace for high-temperature carbonization, preferably in the constant-temperature zone of the carbonization furnace.

[0046] In the present application, the pyrolysis product can be directly transferred to the carbonization furnace without cooling, or can be transferred after cooling.

[0047] Preferably, the temperature of the high-temperature carbonization in step (2) is 1300-1500℃, such as 1300℃, 1320℃, 1350℃, 1380℃, 1400℃, 1420℃, 1450℃, 1480℃ or 1500℃, etc., but not only limited to the listed values, other values not listed in this range are also applicable.

[0048] Preferably, the temperature of the high-temperature carbonization in step (2) is 1300-1500℃, such as 1300℃, 1320℃, 1350℃, 1380℃, 1400℃, 1420℃, 1450℃, 1480℃ or 1500℃, etc., but not only limited to the listed values, other values not listed in this range are also applicable.

[0049] Preferably, the temperature of the high-temperature carbonization in step (2) is 1300-1500℃, such as 1300℃, 1320℃, 1350℃, 1380℃, 1400℃, 1420℃, 1450℃, 1480℃ or 1500℃, etc., but not only limited to the listed values, other values not listed in this range are also applicable.

[0050] Preferably, the high-temperature carbonization in step (2) is followed by continuous inert atmosphere furnace cooling.

[0051] As a preferred technical solution of the present application, the preparation method comprises the following steps:

[0052] (1) The carbon source precursor is first crushed, screened, and the carbon source precursor includes any one or a combination of at least two of coal tar pitch, petroleum pitch, coal, or heavy carbon, the crushing includes crushing and grinding in turn, the crushed product is first dried and then ground to obtain raw material particles, the particle size of the raw material particles selected by screening is 3-20 μm, and the raw material particles are dried and then subjected to acid pickling and ash removal, the acid solution used for acid pickling and ash removal includes hydrochloric acid and / or hydrofluoric acid, the carbon source precursor is mixed with hydrochloric acid with a mass fraction of 10-37% and then stirred and washed, the solid-liquid ratio of the carbon source precursor to hydrochloric acid is 1 g:(2-10) mL, and after standing, the product is washed with water, filtered, and dried to obtain a first acid-pickled raw material; the first acid-pickled raw material is mixed with hydrofluoric acid with a mass fraction of 25-40% and then stirred and washed, the solid-liquid ratio of the first acid-pickled raw material to hydrofluoric acid is 1 g:(1-10) mL, and after standing, the product is washed with water, filtered, and dried to obtain a second acid-pickled raw material;

[0053] Then, oxidation curing and deep oxidation are sequentially performed in an oxygen-containing atmosphere, the concentration of oxygen in the oxygen-containing atmosphere is 10-100%, the concentration of the oxygen-containing atmosphere is independently selected during the oxidation curing and the deep oxidation, the oxidation curing and the deep oxidation are performed consecutively, the deep oxidation is continuously performed after the completion of the oxidation curing, the temperature of the oxidation curing is lower than the softening point temperature of the carbon source precursor or the temperature corresponding to the maximum weight in the thermogravimetric analysis, the temperature of the oxidation curing is 70-320℃, the time is 1-5h, and the heating rate is 0.2-5℃ / min; the temperature of the deep oxidation is 120-360℃, the time is 1-5h, and the heating rate is 0.2-5℃ / min, to obtain an oxidation precursor;

[0054] (2) The oxidation precursor obtained in step (1) is pyrolyzed in an inert atmosphere to remove volatile matter, the inert atmosphere includes any one or a combination of at least two of helium, neon or argon, the temperature of the pyrolysis is 300-900℃, the heating rate is 0.5-10℃ / min, and the time is 0.5-3h, and then high-temperature carbonization is performed, the temperature of the high-temperature carbonization is 1300-1500℃, the heating rate is 0.5-3℃ / min, and the time is 1-5h, and the inert atmosphere is continuously introduced after the high-temperature carbonization to cool down in the furnace, to obtain a hard carbon negative electrode material.

[0055] In a second aspect, the application provides a hard carbon negative electrode material prepared by the above preparation method.

[0056] As a preferred technical solution of the application, the particle size of the hard carbon negative electrode material is 3-10μm, such as 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm or 10μm, etc., but is not limited to the listed values, and other values not listed in the range are also applicable.

[0057] Preferably, the specific surface area of the hard carbon negative electrode material is 3-8m 2 / g, such as 3m 2 / g, 4m 2 / g, 5m 2 / g, 6m 2 / g, 7m 2 / g, or 8m 2 / g, etc., but is not limited to the listed values, and other values not listed in the range are also applicable.

[0058] Preferably, the layer spacing of the (002) crystal plane of the hard carbon negative electrode material is 0.37-0.39 nm, for example, 0.37 nm, 0.372 nm, 0.375 nm, 0.377 nm, 0.38 nm, 0.382 nm, 0.385 nm, 0.388 nm or 0.39 nm, etc., but not limited to the listed values, and other values not listed in the range are also applicable.

[0059] In a third aspect, the application provides a use of the hard carbon negative electrode material as described above, which is used for the preparation of a sodium ion battery as a component of a negative electrode sheet in the sodium ion battery.

[0060] In the application, the hard carbon negative electrode material is used in a sodium ion battery, and a negative electrode sheet needs to be prepared first and then assembled into a battery; the preparation process of the negative electrode sheet includes the steps of grinding, slurry preparation and coating;

[0061] In the grinding and slurry preparation process, the negative electrode active material, the conductive agent and the binder are mixed and ground in proportion, and the slurry is prepared by bonding and stirring; the specific process parameters are as follows: the conductive agent is selected as conductive carbon black SP, the binder is selected as carboxymethyl cellulose CMC and styrene-butadiene rubber SBR, the mass ratio of the negative electrode active material, SP, CMC and SBR is 90:4:2:4, the single cup homogenizer is stirred for 27 min at a speed of 1950 r / min, and the defoaming is performed for 3 min at a speed of 2150 r / min;

[0062] In the coating process, the coating thickness is 100 μm, and the surface density is controlled at 2-3 mg / cm 2 After the electrode sheet is dried, it is rolled and cut and weighed.

[0063] Compared with the prior art, the application has the following beneficial effects:

[0064] (1) The method of the application can increase the molecular weight of the raw material, improve the melting temperature, avoid the problem of slow mass transfer rate and uneven oxidation caused by melting when directly using high temperature oxidation, and obtain an oxidized precursor with high oxidation degree and complex cross-linked structure through deep oxidation and cross-linking, thereby improving the sodium storage performance of the negative electrode material and the capacity and rate performance.

[0065] (2) The method of the application is simple to operate, has low raw material and process cost, and has wide application range. BRIEF DESCRIPTION OF DRAWINGS

[0066] Figure 1 is the XRD pattern of the hard carbon negative electrode material provided by Example 3 and Comparative Example 2 of the application;

[0067] Figure 2 is a Raman spectrum of the hard carbon negative material provided by the embodiment 3 and the comparative example 2 of the present application;

[0068] Figure 3a is a TEM image of the hard carbon negative material provided by the embodiment 3 of the present application;

[0069] Figure 3b is a TEM image of the hard carbon negative material provided by the comparative example 2 of the present application;

[0070] Figure 4 is a charge-discharge curve of the sodium ion battery assembled by the hard carbon negative material provided by the embodiment 3 of the present application;

[0071] Figure 5 is a rate curve of the sodium ion battery assembled by the hard carbon negative material provided by the embodiment 3 of the present application. DETAILED DESCRIPTION

[0072] In order to better illustrate the present application, facilitate the understanding of the technical scheme of the present application, the present application is further described in detail below. However, the following examples are only simple examples of the present application, and do not represent or limit the protection scope of the present application, and the protection scope of the present application is subject to the claims.

[0073] The following are typical but non-limiting examples of the present application:

[0074] Example 1:

[0075] The present embodiment provides a preparation method of a hard carbon negative material, which comprises the following steps:

[0076] (1) The carbon source precursor is first crushed, sieved, and the carbon source precursor is coal tar pitch, the crushing comprises crushing and grinding in sequence, the crushed material is first dried and then ground, to obtain raw material particles, the average particle size of the raw material particles selected by sieving is 10 μm, and then the acid washing and ash removal is carried out after drying, the acid washing and ash removal is first washed with hydrochloric acid and then washed with hydrofluoric acid, the carbon source precursor is first mixed with hydrochloric acid with a mass fraction of 18% and stirred at a speed of 100 r / min for 12 h, the solid-liquid ratio of the carbon source precursor and hydrochloric acid is 1 g:10 mL, and the water washing is carried out after standing for 2 h until there is no Cl - , after filtration, the first acid-washed raw material is dried at a temperature of 105°C for 12 h, the first acid-washed raw material is mixed with hydrofluoric acid with a mass fraction of 30% and stirred at a speed of 100 r / min for 24 h, the solid-liquid ratio of the first acid-washed raw material and hydrofluoric acid is 1 g:7.5 mL, and the water washing is carried out after standing for 3 h until there is no F - , after filtration, the second acid-washed raw material is dried at a temperature of 105°C for 12 h;

[0077] Then, oxidative curing and deep oxidation are sequentially performed under an air atmosphere, the oxidative curing and deep oxidation are performed consecutively, the oxidative curing is completed and then the deep oxidation is performed by continuously increasing the temperature, the temperature of the oxidative curing is 270℃, which is 10℃ lower than the softening point of coal tar pitch, the temperature increasing rate is 0.5℃ / min, and the time is 5h, the temperature of the deep oxidation is 330℃, the temperature increasing rate is 0.5℃ / min, and the time is 2h, to obtain an oxidation precursor;

[0078] (2) The oxidation precursor obtained in step (1) is pyrolyzed to remove volatile matter in an argon atmosphere, the temperature of the pyrolysis is 700℃, the temperature increasing rate is 2℃ / min, and the time is 3h, and then high-temperature carbonization is performed, the temperature of the high-temperature carbonization is 1400℃, the temperature increasing rate is 1℃ / min, and the time is 5h, and then argon is continuously introduced to cool down in the furnace to obtain a hard carbon negative electrode material.

[0079] Example 2:

[0080] The embodiment provides a preparation method of a hard carbon negative electrode material, and the preparation method comprises the following steps:

[0081] (1) The carbon source precursor is first crushed and sieved, the carbon source precursor is petroleum pitch, the crushing comprises crushing and grinding in sequence, the crushed product is first dried and then ground, to obtain raw material particles, the average particle size of the raw material particles selected by sieving is 5μm, and then the raw material particles are dried and subjected to acid washing and ash removal, the acid washing and ash removal comprises washing with hydrochloric acid and then washing with hydrofluoric acid, the carbon source precursor is first mixed with hydrochloric acid with a mass fraction of 10% and then stirred and washed at a rotating speed of 90r / min for 14h, the solid-liquid ratio of the carbon source precursor to the hydrochloric acid is 1g:8mL, and the carbon source precursor is water-washed for 1h until no Cl - is present, the carbon source precursor is filtered and dried at a temperature of 100℃ for 15h to obtain first acid-washed raw material, the first acid-washed raw material is mixed with hydrofluoric acid with a mass fraction of 25% and then stirred and washed at a rotating speed of 90r / min for 26h, the solid-liquid ratio of the first acid-washed raw material to the hydrofluoric acid is 1g:10mL, and the first acid-washed raw material is water-washed for 2h until no F - is present, the first acid-washed raw material is filtered and dried at a temperature of 100℃ for 15h to obtain second acid-washed raw material;

[0082] Then, oxidative curing and deep oxidation are sequentially performed under an air atmosphere, the oxidative curing and deep oxidation are performed consecutively, the oxidative curing is completed and then the deep oxidation is performed by continuously increasing the temperature, the temperature of the oxidative curing is 270℃, which is 10℃ lower than the softening point of coal tar pitch, the temperature increasing rate is 0.5℃ / min, and the time is 5h, the temperature of the deep oxidation is 330℃, the temperature increasing rate is 0.5℃ / min, and the time is 2h, to obtain an oxidation precursor;

[0083] (2) The oxidative precursor obtained in step (1) is pyrolyzed in an argon atmosphere to remove volatile matter, the pyrolysis temperature is 400℃, the heating rate is 0.5℃ / min, and the time is 2h, and then high-temperature carbonization is carried out, the high-temperature carbonization temperature is 1300℃, the heating rate is 0.5℃ / min, and the time is 4h, and after high-temperature carbonization, argon is continuously introduced to cool down in the furnace to obtain a hard carbon negative electrode material.

[0084] Example 3:

[0085] The embodiment provides a preparation method of a hard carbon negative electrode material, and the preparation method comprises the following steps:

[0086] (1) The carbon source precursor is first crushed and sieved, the carbon source precursor is bituminous coal, the crushing comprises crushing and grinding in sequence, the crushed material is first dried and then ground, to obtain raw material particles, the average particle size of the raw material particles selected by sieving is 15μm, and after drying, acid washing and ash removal are performed, the acid washing and ash removal are first washed with hydrochloric acid and then washed with hydrofluoric acid, the carbon source precursor is first mixed with hydrochloric acid with a mass fraction of 37% and then stirred and washed at a rotating speed of 110r / min for 10h, the solid-liquid ratio of the carbon source precursor and the hydrochloric acid is 1g:2mL, and after standing for 3h, water washing is performed until there is no Cl - , after filtration, drying is performed at a temperature of 120℃ for 10h to obtain first acid-washed raw material; the first acid-washed raw material is mixed with hydrofluoric acid with a mass fraction of 40% and then stirred and washed at a rotating speed of 110r / min for 22h, the solid-liquid ratio of the first acid-washed raw material and the hydrofluoric acid is 1g:2mL, and after standing for 4h, water washing is performed until there is no F - , after filtration, drying is performed at a temperature of 120℃ for 10h to obtain second acid-washed raw material;

[0087] Then, oxidation curing and deep oxidation are sequentially performed under an air atmosphere, the oxidation curing and the deep oxidation are performed consecutively, after the oxidation curing is completed, the temperature is continuously increased to perform the deep oxidation, the oxidation curing temperature is 310℃, the heating rate is 1.5℃ / min, and the time is 5h, the deep oxidation temperature is 355℃, the time is 5h, and the heating rate is 1.5℃ / min, to obtain an oxidative precursor;

[0088] (2) The oxidative precursor obtained in step (1) is pyrolyzed in an argon atmosphere to remove volatile matter, the pyrolysis temperature is 400℃, the heating rate is 0.5℃ / min, and the time is 2h, and then high-temperature carbonization is carried out, the high-temperature carbonization temperature is 1300℃, the heating rate is 0.5℃ / min, and the time is 4h, and after high-temperature carbonization, argon is continuously introduced to cool down in the furnace to obtain a hard carbon negative electrode material.

[0089] Example 4:

[0090] The embodiment provides a preparation method of a hard carbon negative electrode material, and the preparation method comprises the following steps:

[0091] (1) The carbon source precursor is first crushed, screened, and the carbon source precursor is coal liquefaction residue, the crushing comprises crushing and grinding in sequence, the crushed product is first dried and then ground, to obtain raw material particles, the average particle size of the raw material particles selected by the screening is 12 μm, and then the acid washing and ash removal are performed after drying, the acid washing and ash removal are first performed by using hydrochloric acid washing and then performed by using hydrofluoric acid washing, the carbon source precursor is mixed with 30% hydrochloric acid by mass fraction, stirred and washed at a rotating speed of 120 r / min for 12 h, the solid-liquid ratio of the carbon source precursor and the hydrochloric acid is 1 g:4 mL, and water washing is performed for 2 h until no Cl - is present; after filtration, drying is performed at a temperature of 110 ℃ for 12 h to obtain first acid-washed raw material; the first acid-washed raw material is mixed with 35% hydrofluoric acid by mass fraction, stirred and washed at a rotating speed of 120 r / min for 20 h, the solid-liquid ratio of the first acid-washed raw material and the hydrofluoric acid is 1 g:5 mL, and water washing is performed for 3 h until no F - is present; after filtration, drying is performed at a temperature of 110 ℃ for 12 h to obtain second acid-washed raw material;

[0092] Then, oxidation curing and deep oxidation are sequentially performed under an air atmosphere, the oxidation curing and the deep oxidation are continuously performed, after the oxidation curing is completed, the temperature is continuously increased to perform the deep oxidation, the temperature of the oxidation curing is 270 ℃, the temperature increasing rate is 4 ℃ / min, and the time is 4 h, the temperature of the deep oxidation is 340 ℃, the temperature increasing rate is 2.5 ℃ / min, and the time is 5 h, to obtain an oxidation precursor;

[0093] (2) The oxidation precursor obtained in the step (1) is pyrolyzed to remove volatile components in a neon atmosphere, the temperature of the pyrolysis is 900 ℃, the temperature increasing rate is 8 ℃ / min, and the time is 1 h, and then high-temperature carbonization is performed, the temperature of the high-temperature carbonization is 1350 ℃, the temperature increasing rate is 1.5 ℃ / min, and the time is 3 h, after the high-temperature carbonization, neon gas is continuously introduced to cool down in the furnace, to obtain a hard carbon negative electrode material.

[0094] Embodiment 5:

[0095] The embodiment provides a preparation method of a hard carbon negative electrode material, and the preparation method refers to the method in the embodiment 3, and the difference lies in that the atmosphere conditions of the oxidation curing and the deep oxidation in the step (1) are a mixed gas of oxygen and argon, the oxygen concentration is 40%, the temperature of the oxidation curing is 292 ℃, and the temperature of the deep oxidation is 320 ℃.

[0096] Embodiment 6:

[0097] The embodiment provides a preparation method of a hard carbon negative electrode material, which refers to the method in the embodiment 3, and the difference is that the atmosphere condition of the oxidation curing and the deep oxidation in the step (1) is a mixed gas of oxygen and argon, and the oxygen concentration is 80%; the temperature of the oxidation curing is 273 DEG C, and the temperature of the deep oxidation is 320 DEG C.

[0098] Embodiment 7:

[0099] The embodiment provides a preparation method of a hard carbon negative electrode material, which refers to the method in the embodiment 3, and the difference is that the temperature of the high-temperature carbonization in the step (2) is 1500 DEG C, and the temperature rising rate is 3 DEG C / min.

[0100] Embodiment 8:

[0101] The embodiment provides a preparation method of a hard carbon negative electrode material, which refers to the method in the embodiment 3, and the difference is that the temperature of the pyrolysis in the step (2) is 600 DEG C, the temperature rising rate is 3 DEG C / min, and the time is 3h.

[0102] Comparative example 1:

[0103] The comparative example provides a preparation method of a hard carbon negative electrode material, which refers to the method in the embodiment 1, and the difference is that the oxidation curing in the step (1) is not carried out, and the deep oxidation is directly carried out, and the time is the total time of the original oxidation curing and deep oxidation, that is, 7h.

[0104] Comparative example 2:

[0105] The comparative example provides a preparation method of a hard carbon negative electrode material, which refers to the method in the embodiment 3, and the difference is that the oxidation curing in the step (1) is not carried out, and the deep oxidation is directly carried out, and the time is the total time of the original oxidation curing and deep oxidation, that is, 10h.

[0106] Comparative example 3:

[0107] The comparative example provides a preparation method of a hard carbon negative electrode material, which refers to the method in the embodiment 3, and the difference is that the temperature rising rate of the high-temperature carbonization in the step (2) is 5 DEG C / min.

[0108] The structural parameters of the hard carbon negative electrode materials prepared in the above embodiment 1-8 and comparative examples 1-3 are shown in Table 1, wherein the XRD graph of the hard carbon negative electrode material in the embodiment 3 and the comparative example 2 is shown in Figure 1 , the Raman spectrum graph is shown in Figure 2 , the TEM graph of the hard carbon negative electrode material in the embodiment 3 is shown in Figure 3a , and the TEM graph of the hard carbon negative electrode material in the comparative example 2 is shown in Figure 3b .

[0109] Table 1

[0110]

[0111]

[0112] d in Table 1 002 is the interlayer spacing of the (002) crystal plane of the hard carbon negative electrode material, Lc is the thickness of the radial carbon microcrystal, La is the length of the carbon microcrystal, I D / I G is the ratio of amorphous carbon and graphitized carbon in the microcrystal, and describes the defect degree of the carbon microcrystal.

[0113] From Table 1, the interlayer spacing of the (002) crystal plane in the examples is all above 0.37 nm, and I D / I G are all above 2.0, which are significantly higher than the data in the comparative examples; from the XRD pattern in Figure 1 , it can be seen that the characteristic peak intensity corresponding to the (002) crystal plane in Example 3 is smaller, and the graphitization degree is low; from the Raman spectrum in Figure 2 , it can be seen that the ratio of the peak area representing amorphous carbon and graphitized carbon is higher in Example 3; from the TEM pattern in Figure 3a and Figure 3b , it can be seen that the interlayer spacing of the (002) crystal plane, and it can be concluded that the interlayer spacing in Example 3 is greater than that in Comparative Example 2; it can be seen that the interlayer spacing of the hard carbon negative electrode material prepared in the examples is wide, the amorphous degree is high, which is helpful to improve the performance of the battery.

[0114] The hard carbon negative electrode materials prepared in Examples 1-8 and Comparative Examples 1-3 are used to prepare negative electrode sheets, which are used for the assembly of sodium ion batteries; wherein, the preparation process of the negative electrode sheet includes the steps of grinding, pulp making, and coating; specifically, the hard carbon negative electrode material, SP, CMC and SBR are ground according to the mass ratio of 90:4:2:4, and the pulp is made by bonding and magnetic stirring, and the process parameters are: single-cup homogenizer stirring for 27 min, rotation speed 1950 r / min, defoaming for 3 min, rotation speed 2150 r / min; in the coating process, the coating thickness is 100 μm, and the area density is controlled at 2-3 mg / cm 2 , and the negative electrode sheet is dried and then rolled, and then cut and weighed;

[0115] The positive electrode of the sodium ion battery is sodium, the electrolyte is 1 mol NaFP6 dissolved in ethylene carbonate EC and dimethyl carbonate DMC in a volume ratio of 1:1, the separator is glass fiber GF / D, and after assembly, electrochemical test is carried out, the conditions of the electrochemical test are: static time 7 h, discharge at 0.1 C, charge at 0.1 C, and the cut-off voltages are 5 mV and 2 V, respectively; the test environment is: temperature 25±1℃, humidity 40%RH; and the results of the electrochemical test are shown in Table 2, wherein the charge-discharge curve of the sodium ion battery assembled by the hard carbon negative electrode material in Example 3 is shown in Figure 4 , and the rate curve is shown in Figure 5 .

[0116] Table 2

[0117]

[0118]

[0119] From Table 2, it can be seen that when the sodium ion battery assembled by the hard carbon negative electrode material in the examples is subjected to electrochemical test, the first charge specific capacity at a current density of 0.1 C can reach 275 mAh g -1 , and the first coulombic efficiency can reach more than 85%; taking Example 3 as an example, it can be seen from Figure 4 and Figure 5 that in the first three charge-discharge processes, the charge specific capacity at a current density of 0.1 C is basically maintained unchanged, and with the increase of the rate, the charge specific capacity can still be maintained to be more than 200 mAh / g, indicating that the material has good rate performance and is beneficial to improve the fast charging capacity of the battery.

[0120] Comparative Examples 1 and 2 are not subjected to oxidation curing operation, and compared with the corresponding examples, the oxidation degree and crosslinking degree are low, thereby causing the reduction of sodium storage capacity and rate performance; in Comparative Example 3, the heating rate is too high during high-temperature carbonization, and after surface melting reaction, it is easy to prevent the internal reaction from continuing, so that the reaction is uneven during carbonization, and the internal carbonization is not sufficient, thereby causing the reduction of sodium storage performance.

[0121] From the above examples and comparative examples, it can be seen that the method described in the application can increase the molecular weight of the raw material, improve the melting temperature, avoid the problem of slow mass transfer rate and uneven oxidation caused by melting when directly using high temperature oxidation, and then crosslink by deep oxidation, so as to obtain an oxidation precursor with high oxidation degree and complex crosslinking structure, and after pyrolysis to remove volatile matter, combined with high-temperature carbonization treatment, the disorder degree and interplanar spacing of the carbon layer are improved, thereby improving the sodium storage performance of the negative electrode material, and the capacity and rate performance are excellent; the method is simple to operate, the raw material and process cost are low, and the application range is wide.

[0122] Applicants declare that the detailed method of the present application is illustrated by the above-mentioned examples, but the present application is not limited to the above-mentioned detailed method, i.e. it does not mean that the present application must rely on the above-mentioned detailed method to be implemented. It should be understood by those skilled in the art that any improvement of the present application, equivalent replacement of the method of the present application, addition of auxiliary steps, selection of specific modes, etc. fall within the protection scope and disclosure scope of the present application.

Claims

1. A method for preparing a hard carbon anode material, characterized in that, The preparation method includes the following steps: (1) The carbon source precursor is acid-washed and deashed, and then oxidized and cured and deep oxidized in sequence under an oxygen-containing atmosphere. The temperature of the oxidization and curing is lower than that of the deep oxidation to obtain an oxidized precursor. The carbon source precursor includes any one or a combination of at least two of coal tar pitch, petroleum pitch, coal or heavy carbon. The temperature of the oxidization and curing is 250~320℃. The temperature of the deep oxidation is 320~360℃. (2) The oxide precursor obtained in step (1) is subjected to pyrolysis and high-temperature carbonization in an inert atmosphere to obtain a hard carbon anode material; the pyrolysis temperature is 700~900℃.

2. The preparation method according to claim 1, characterized in that, In step (1), the carbon source precursor is first crushed and sieved to obtain raw material particles.

3. The preparation method according to claim 2, characterized in that, The pulverization process includes crushing and grinding in sequence. After crushing, the material is first dried and then ground.

4. The preparation method according to claim 2, characterized in that, The particle size of the raw material particles selected by the sieving is 3~20μm.

5. The preparation method according to claim 2, characterized in that, The screened raw material particles are then dried and then acid-washed to remove ash.

6. The preparation method according to claim 1, characterized in that, The acid solution used in step (1) for pickling and deashing includes hydrochloric acid and / or hydrofluoric acid.

7. The preparation method according to claim 6, characterized in that, The acid washing and deashing in step (1) involves first washing with hydrochloric acid and then washing with hydrofluoric acid.

8. The preparation method according to claim 7, characterized in that, The carbon source precursor is mixed with hydrochloric acid, stirred and washed, allowed to stand, washed with water, filtered and dried to obtain the first pickling raw material.

9. The preparation method according to claim 8, characterized in that, The solid-liquid ratio of the carbon source precursor to hydrochloric acid is 1 g:(2~10) mL.

10. The preparation method according to claim 7, characterized in that, The hydrochloric acid has a mass fraction of 10-37%.

11. The preparation method according to claim 8, characterized in that, The first pickling raw material is mixed with hydrofluoric acid, stirred and washed, allowed to stand, washed with water, filtered and dried to obtain the second pickling raw material.

12. The preparation method according to claim 11, characterized in that, The solid-liquid ratio of the first pickling raw material to hydrofluoric acid is 1g:(1~10)mL.

13. The preparation method according to claim 7, characterized in that, The hydrofluoric acid has a mass fraction of 25-40%.

14. The preparation method according to claim 1, characterized in that, The oxygen concentration in the oxygen-containing atmosphere described in step (1) is 10~100%.

15. The preparation method according to claim 14, characterized in that, The concentration of the oxygen-containing atmosphere in step (1) is selected independently during oxidative curing and deep oxidation.

16. The preparation method according to claim 15, characterized in that, The concentration of the oxygen-containing atmosphere in step (1) is the same for both oxidative curing and deep oxidation.

17. The preparation method according to claim 1, characterized in that, The oxidation curing and deep oxidation in step (1) are both carried out in a tube furnace.

18. The preparation method according to claim 17, characterized in that, The oxidation curing and deep oxidation in step (1) are both carried out in the constant temperature zone of the tube furnace.

19. The preparation method according to claim 1, characterized in that, In step (1), the oxidation curing and deep oxidation are carried out in sequence, and after the oxidation curing is completed, the temperature is raised to carry out deep oxidation.

20. The preparation method according to claim 1, characterized in that, The oxidation curing temperature in step (1) is lower than the softening point temperature of the carbon source precursor or the temperature corresponding to the maximum weight when selecting thermogravimetric analysis.

21. The preparation method according to claim 1, characterized in that, The oxidation curing time in step (1) is 1~5h, and the heating rate is 0.2~5℃ / min.

22. The preparation method according to claim 1, characterized in that, The deep oxidation time in step (1) is 1~5h, and the heating rate is 0.2~5℃ / min.

23. The preparation method according to claim 1, characterized in that, The inert atmosphere in step (2) includes any one or a combination of at least two of helium, neon or argon.

24. The preparation method according to claim 1, characterized in that, The pyrolysis in step (2) is carried out in a pyrolysis furnace to remove volatiles from the oxidizing precursor.

25. The preparation method according to claim 1, characterized in that, The pyrolysis time in step (2) is 0.5~3h.

26. The preparation method according to claim 1, characterized in that, The heating rate of the pyrolysis in step (2) is 0.5~10℃ / min.

27. The preparation method according to claim 1, characterized in that, After pyrolysis in step (2), the product is transferred to a carbonization furnace for high-temperature carbonization.

28. The preparation method according to claim 27, characterized in that, After pyrolysis in step (2), the product is transferred to the constant temperature zone of the carbonization furnace.

29. The preparation method according to claim 1, characterized in that, The high-temperature carbonization temperature in step (2) is 1300~1500℃.

30. The preparation method according to claim 1, characterized in that, The heating rate of the high-temperature carbonization in step (2) is 0.5~3℃ / min.

31. The preparation method according to claim 1, characterized in that, The high-temperature carbonization time in step (2) is 1~5h.

32. The preparation method according to claim 1, characterized in that, After the high-temperature carbonization in step (2), an inert atmosphere is continuously introduced to cool the furnace.

33. The preparation method according to claim 1, characterized in that, The preparation method includes the following steps: (1) The carbon source precursor is first crushed and sieved. The carbon source precursor includes any one or at least two of coal tar pitch, petroleum pitch, coal or heavy carbon. The crushing includes crushing and grinding in sequence. After crushing, the raw material particles are dried and then ground to obtain raw material particles. The particle size of the raw material particles selected by sieving is 3~20μm. After drying, the raw material is acid washed and deashed. The carbon source precursor is first mixed with hydrochloric acid with a mass fraction of 10~37% and then stirred and washed. The solid-liquid ratio of the carbon source precursor to hydrochloric acid is 1g:(2~10)mL. After standing, the raw material is washed with water, filtered and dried to obtain the first acid washing raw material. The first acid washing raw material is mixed with hydrofluoric acid with a mass fraction of 25~40% and then stirred and washed. The solid-liquid ratio of the first acid washing raw material to hydrofluoric acid is 1g:(1~10)mL. After standing, the raw material is washed with water, filtered and dried to obtain the second acid washing raw material. Then, oxidation curing and deep oxidation are carried out sequentially in an oxygen-containing atmosphere, wherein the oxygen concentration in the oxygen-containing atmosphere is 10-100%, and the oxygen concentration is independently selected during oxidation curing and deep oxidation. The oxidation curing and deep oxidation are carried out consecutively. After the oxidation curing is completed, the temperature is raised to carry out deep oxidation. The temperature of the oxidation curing is lower than the softening point temperature of the carbon source precursor or the temperature corresponding to the maximum weight during thermogravimetric analysis. The temperature of the oxidation curing is 250-320℃, the time is 1-5h, and the heating rate is 0.2-5℃ / min. The temperature of the deep oxidation is 320-360℃, the time is 1-5h, and the heating rate is 0.2-5℃ / min, to obtain the oxidation precursor. (2) The oxidized precursor obtained in step (1) is pyrolyzed in an inert atmosphere to remove volatiles. The inert atmosphere includes any one or a combination of at least two of helium, neon or argon. The pyrolysis temperature is 700~900℃, the heating rate is 0.5~10℃ / min, and the time is 0.5~3h. Then, high-temperature carbonization is carried out. The high-temperature carbonization temperature is 1300~1500℃, the heating rate is 0.5~3℃ / min, and the time is 1~5h. After the high-temperature carbonization, an inert atmosphere is continuously introduced to cool down the furnace to obtain a hard carbon anode material.

34. A hard carbon anode material obtained by the preparation method according to any one of claims 1-33.

35. The hard carbon anode material according to claim 34, characterized in that, The particle size of the hard carbon anode material is 3~10μm.

36. The hard carbon anode material according to claim 34, characterized in that, The specific surface area of ​​the hard carbon anode material is 3~8m². 2 / g.

37. The hard carbon anode material according to claim 34, characterized in that, The interlayer spacing of the hard carbon anode material (002) is 0.37~0.39 nm.

38. The use of a hard carbon anode material according to any one of claims 34-37, characterized in that, The hard carbon anode material is used in the preparation of sodium-ion batteries, serving as a component of the anode sheet in sodium-ion batteries.

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