Hard carbon negative electrode material and preparation method and application thereof

Abstract

The application discloses a kind of hard carbon negative electrode material and its preparation method and application.The hard carbon negative electrode material has hierarchical porous structure, wherein 0.35-0.85nm micropore accounts for 40-50% of total pore volume, 2-25nm mesopore accounts for 30-50% of total pore volume;The average closed pore diameter of material is 1.7-2.2nm, and the closed pore volume is 0.091-0.117cm 3 ·g ‑1 ;The hard carbon negative electrode material has short-range pseudo-graphite microcrystalline structure, and the average lateral size is 3.81-4.18nm, and the average longitudinal size is 0.91-1.11nm.The application adopts high-concentration acid etching process, and the nanoscale impurity phase in the primary carbonization product of industrial lignin is accurately removed, and the target hard carbon negative electrode material is prepared by secondary carbonization.The hard carbon negative electrode material has high reversible sodium storage capacity, excellent initial coulombic efficiency and long cycle stability, and the preparation process is simple and easy to operate, and the production cost is low.

Description

TECHNICAL FIELD

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

[0002] Sodium resources are abundant, evenly distributed globally, and low in price. Sodium-ion batteries have similar working principles to lithium-ion batteries and excellent performance, and show broad application prospects in large-scale energy storage systems, low-speed electric vehicles, 5G base stations, and other fields. Therefore, it is of great significance to develop sodium-ion batteries. Hard carbon is an optimal choice for sodium-ion battery negative electrode materials due to its low cost, wide availability, high theoretical specific capacity, and low operating voltage. It has attracted widespread attention and research interest from the global academic and industrial communities, and has great commercial potential. However, hard carbon negative electrodes still face challenges such as low first coulombic efficiency, insufficient sodium storage capacity, poor cycle and rate performance, and other issues, which seriously hinder the commercialization process of sodium-ion batteries.

[0003] Hard carbon is composed of curved and wrinkled graphene micro-regions, defects, and pores, and has a complex structure and abundant sodium storage sites. The typical constant current charge-discharge curve of the sodium storage process can be divided into a high-potential slope region (> 0.1 V) and a low-potential platform region (< 0.1 V). A large number of studies have shown that the platform region capacity is mainly related to the deposition of sodium ions in closed pores and ultramicropores (< 1 nm). Therefore, improving the sodium storage capacity in the low-potential platform region and reducing the irreversible loss of sodium ions in the slope region are effective strategies to improve the energy density of the full battery. Therefore, designing and constructing closed nanopores and ultramicropores with appropriate sizes in the hard carbon bulk phase is the key to improving the sodium storage capacity in the low-potential platform region. At the same time, the rational construction of ultramicropores and the reduction of defect content can help improve the first coulombic efficiency of hard carbon. In summary, it is urgent to develop a simple, efficient, and controllable method to simultaneously control the nano-closed pores, ultramicropores, pseudo-graphite structure, and surface defects of hard carbon, thereby improving its first coulombic efficiency, platform capacity, rate performance, and cycle stability.

[0004] Lignin is a rich renewable biomass resource on earth, mainly derived from papermaking industrial by-products. This material has a high carbon content (about 45%), low cost, wide availability, and good consistency, making it an optimal precursor for preparing hard carbon negative electrode materials. However, due to its high aromaticity, the direct pyrolysis product of lignin is usually hard carbon with a dense structure, lacking nanoporous structure and suitable carbon framework, resulting in poor sodium storage capacity, rate performance, and low first coulombic efficiency of the obtained hard carbon. Tests have shown that the hard carbon negative electrode material prepared by direct pyrolysis of lignin has a sodium storage capacity of nearly 320 mAh·g⁻¹ and a first coulombic efficiency of nearly 85%.

[0005] In order to further improve the sodium storage capacity, rate performance and the first coulombic efficiency of the lignin-based hard carbon, the present application is directed to the cooking waste liquid (black liquor) produced by the alkali pulping in the papermaking industry, which is first subjected to evaporation concentration treatment, then deliberately added with an impurity phase, and finally subjected to acidification treatment to obtain a lignin raw material containing a high content of uniformly dispersed nanoscale impurity phase; the impurity phase can reserve space for the pore growth of the hard carbon in the subsequent carbonization process, which is beneficial to the synthesis of the hard carbon negative electrode material with developed pores. SUMMARY

[0006] The purpose of the present application is to provide a high initial efficiency and high capacity industrial lignin-based hard carbon negative electrode material with excellent rate performance and cycle stability, which can avoid or improve the related defects mentioned in the above-mentioned prior art.

[0007] In the first aspect, the present application provides a hard carbon negative electrode material, which has a hierarchical porous structure with micropores with a pore size of 0.35-0.85 nm and mesopores with a pore size of 2-25 nm, the micropore volume accounts for 40-50% of the total pore volume, and the mesopore volume accounts for 30-50% of the total pore volume.

[0008] The average closed pore diameter of the hard carbon negative electrode material is 1.7-2.2 nm, and the closed pore volume is 0.091-0.117 cm 3 ·g -1 ;

[0009] The hard carbon negative electrode material has a short-range pseudo-graphite crystallite structure, the average lateral size of the pseudo-graphite crystallite is 3.81-4.18 nm, the average longitudinal size is 0.91-1.11 nm, and the interlayer spacing is 0.373-0.380 nm.

[0010] According to the hard carbon negative electrode material of the present application, at least the following beneficial effects are achieved:

[0011] (1) The hard carbon negative electrode material of the present application has more suitable average interlayer spacing of 0.373-0.380 nm, which is beneficial to improve the sodium storage capacity in the slope region and the platform region.

[0012] (2) The hard carbon negative electrode material of the present application has a hierarchical porous structure and a short-range ordered pseudo-graphite structure, and the sodium ions can be quickly transported, diffused and stored, which is beneficial to improve the sodium storage capacity and rate performance of the hard carbon material.

[0013] (3) The hard carbon negative electrode material of the present application, as a negative electrode material for sodium ion batteries, has a first charge specific capacity of more than 401 mAh·g -1 at a current density of 0.1 C, and a first coulombic efficiency of ≥90%.

[0014] (4) The hard carbon negative electrode material of the present application, as a negative electrode material of a sodium ion battery, still has a specific capacity greater than 290 mAh·g -1 at a current density of 2C.

[0015] (5) The hard carbon negative electrode material of the present application, as a negative electrode material of a sodium ion battery, still has a capacity retention rate greater than 85% after 150 cycles at 2C.

[0016] In a second aspect, the present application provides a preparation method of the above hard carbon negative electrode material, comprising the following steps:

[0017] S1, adding Na2SO4 in the black liquor obtained in the papermaking process, filtering and drying after precipitating lignin by adjusting pH<3 with sulfuric acid after uniform mixing, and further mechanically crushing to obtain industrial lignin powder;

[0018] S2, performing one-time low-temperature carbonization on the industrial lignin powder obtained in step S1 under a protective atmosphere to obtain a one-time carbonized material;

[0019] S3, mechanically crushing the one-time carbonized material obtained in step S2 to obtain carbon powder, adding the carbon powder into an acid solution, and heating to react to obtain the carbon powder after reaction;

[0020] S4, washing, filtering and drying the carbon powder after reaction obtained in step S3 to obtain dry carbon powder;

[0021] S5, performing high-temperature carbonization on the dry carbon powder obtained in step S4 under a protective atmosphere to obtain a hard carbon negative electrode material.

[0022] The present application introduces a uniformly dispersed nanoscale impurity phase in the industrial lignin, which can occupy the reserved space in the low-temperature carbonization stage, not only being conducive to the formation of the target hierarchical porous structure, but also inhibiting the growth of long-range pseudo-graphite structure and promoting the formation of short-range ordered pseudo-graphite structure. The nanoscale dispersed impurity phase is mainly Na2SO4 and metal compounds containing iron and potassium.

[0023] Further, the present application uses an acid solution to heat etch and remove the impurity phase in the carbon powder obtained from the one-time carbonized material; subsequent high-temperature treatment can promote the growth of the internal structure of the carbon material to form rich closed pores, ultramicro-pores and mesoporous structures. In addition, the removal of the impurity phase can also optimize the defect structure and oxygen-containing functional group structure of the hard carbon in the secondary high-temperature carbonization process.

[0024] The short-range ordered pseudo-graphitic structure can promote the storage and transmission of sodium ions; the rich closed pores and ultramicro-pores are beneficial to the formation of sodium clusters, thereby improving the sodium storage capacity in the platform region; meanwhile, the ultramicro-pore structure and the optimized defect and oxygen-containing functional group structure can reduce the irreversible loss of sodium ions and improve the initial coulombic efficiency; and the hierarchical mesoporous structure can shorten the diffusion path of sodium ions, promote the diffusion and transmission of sodium ions, and finally improve the rate performance of the material.

[0025] In some embodiments of the present application, the content of Na2SO4 in step S1 is 5-10% of the black liquor, the drying temperature is 50-80 DEG C, and the diameter of the mechanically pulverized powder is 50-70 mu m.

[0026] In some embodiments of the present application, the one-time low-temperature carbonization temperature in step S2 is 300-1000 DEG C, and the holding time is 1-10 h.

[0027] In some embodiments of the present application, the particle size of the powder particles in step S3 is 10-100 mu m.

[0028] The suitable particle size is beneficial to the etching of the acid solution, the manufacture of more reserved spaces, and the subsequent growth of more pore structures in the secondary carbonization.

[0029] In some embodiments of the present application, the acid solution in step S3 is one or more of sulfuric acid, hydrochloric acid, nitric acid and phosphoric acid, the concentration of the acid solution is 4-10 M, if it is a mixed acid, the concentration refers to the sum of the concentrations of the components, and the liquid-solid ratio of the acid solution to the carbon powder is 20-40:1 (mL / g).

[0030] The use of high-concentration acid and heating is beneficial to etching a large number of nanoscale reserved pore spaces, and provides favorable conditions for the subsequent growth of hierarchical porous, ultramicro-porous, mesoporous and closed pores in the secondary high-temperature carbonization. When the liquid-solid ratio is lower than 20:1, the acid solution is insufficient, and the impurity phase etching is incomplete; when it is higher than 40:1, the cost is increased, and the benefit is affected. The total concentration of the mixed acid needs to meet 4-10 M, so as to ensure that the etching strength is sufficient to remove the nanoscale impurity phase.

[0031] In some embodiments of the present application, the heating temperature in step S3 is 40-95 DEG C, and the reaction time is 1-10 h.

[0032] In some embodiments of the present application, the drying temperature in step S4 is 50-70 DEG C, and the drying time is 24-48 h.

[0033] In some embodiments of the present application, the carbonization temperature in step S5 is 1100 DEG C-1600 DEG C, the carbonization time is 1-10 h, and the carbonization heating rate is 2-10 DEG C / min.

[0034] In some embodiments of the present application, the protective atmosphere in steps S2 and S5 is an inert gas, specifically argon or nitrogen, and the flow rate of the protective atmosphere is 100-400 sccm.

[0035] The present application provides a preparation method of a hard carbon negative electrode material, which has at least the following beneficial effects:

[0036] (1) The present application uses black liquor in the paper industry as raw material, introduces Na2SO4 impurity phase, and obtains lignin by acid precipitation, which has a large amount of uniformly dispersed Na2SO4, iron-containing, potassium-containing metal compounds and other impurity phases in the bulk phase; a primary carbonized material is obtained by one carbonization, and the uniformly dispersed impurity phase in the primary carbonized material is etched away in the reaction process; further high-temperature carbonization is carried out to obtain a hard carbon material with a large number of micropores, mesopores and nanometer closed pores; the hard carbon material has super large sodium storage capacity, high first coulomb efficiency, excellent rate and cycle performance. The present application etches the impurity phase of low-temperature carbon by adjusting the concentration of acid, reaction heating and time, and further high-temperature carbonization optimizes the internal pore structure, surface oxygen-containing functional groups and defect structure of the material.

[0037] (2) The hard carbon negative electrode material prepared by the present application not only has good performance, but also has high efficiency and low cost, and has good industrialization prospect.

[0038] In a third aspect, the present application provides the use of the hard carbon negative electrode material in a secondary battery.

[0039] In some embodiments of the present application, the secondary battery includes one of a sodium ion battery and a lithium ion battery.

[0040] In some embodiments of the present application, the hard carbon negative electrode material described above is used as an active material of an electrode, stirred and uniformly mixed with conductive carbon black and a PVDF binder in a ratio of 95:2.5:2.5 to form a slurry, and then scraped and coated on an aluminum foil current collector, dried in a 80℃ vacuum drying oven for 24h to obtain an electrode sheet, cut into a certain size of a round sheet, and assembled into a button cell with a sodium sheet as a counter electrode and an electrolyte selected from sodium salts of NaBF4, NaPF6, NaClO4, NaFSI and NaTFSI, and organic solvents selected from dimethyl carbonate, diethyl carbonate, propylene carbonate, ethylene carbonate, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether.

[0041] In some embodiments of the present application, the hard carbon negative electrode material described above is provided as an active material of an electrode, stirred and mixed with conductive carbon black and a PVDF binder in a ratio of 95:2.5:2.5 to form a slurry, and then coated on an aluminum foil current collector, dried in a vacuum drying oven at 80°C for 24h to obtain an electrode sheet, cut into a certain size of a round sheet, and assembled into a coin cell with a lithium sheet as a counter electrode, and an electrolyte selected from lithium salts of LiBF4, LiPF6, LiFSI, LiTFSI and organic solvents selected from dimethyl carbonate, diethyl carbonate, propylene carbonate, ethylene carbonate, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether. BRIEF DESCRIPTION OF DRAWINGS

[0042] In order to more clearly illustrate the technical solutions of the present application, the following will briefly introduce the drawings needed to be used in the embodiments. Obviously, the drawings described below are only some embodiments of the present application, and other drawings can also be obtained according to these drawings without creative labor for those skilled in the art.

[0043] Figure 1 The first constant current charge-discharge curve of the hard carbon negative electrode material prepared according to Example 1.

[0044] Figure 2 The first constant current charge-discharge curve of the hard carbon negative electrode material prepared according to Example 2.

[0045] Figure 3 The transmission electron microscope image of the hard carbon negative electrode material prepared according to Example 1.

[0046] Figure 4 The high-resolution image of the hard carbon negative electrode material prepared according to Example 1.

[0047] Figure 5 The X-ray diffraction pattern of the primary carbonized material prepared according to Example 1.

[0048] Figure 6 The micropore size distribution curve of the hard carbon negative electrode material prepared according to Example 1.

[0049] Figure 7 The mesopore size distribution curve of the hard carbon negative electrode material prepared according to Example 1.

[0050] Figure 8 The small-angle scattering curve of the hard carbon negative electrode material prepared according to Example 1. DETAILED DESCRIPTION

[0051] The present application will be described in detail below with reference to the drawings and specific examples.

[0052] Example 1

[0053] The embodiment provides a preparation method of a lignin-based hard carbon negative electrode material, and specific steps are as follows:

[0054] (1) 5% of Na2SO4 is added to black liquor containing lignin generated in a papermaking process, the black liquor is uniformly stirred, and a sulfuric acid solution is added to adjust pH to less than 3 to precipitate lignin, and then the lignin is filtered and dried at 70 DEG C for 24 hours, and then mechanically crushed to obtain lignin powder with a particle size of 60 μm; 20 g of the lignin powder is carbonized in a furnace in an argon atmosphere, the heating speed is 2 DEG C / minute, the holding temperature is 700 DEG C, the holding time is 1 hour, and natural cooling is performed to obtain primary carbonized material, and the primary carbonized material is mechanically crushed to a particle size of 50-55 μm;

[0055] (2) 5 g of the primary carbonized material is added to 150 mL of a 6M H2SO4 solution, heated to 85 DEG C, and stirred for 5 hours;

[0056] (3) Filtration is performed, and the material is washed with deionized water until neutral, and then placed in an oven at 70 DEG C for 24 hours to obtain dry powder;

[0057] (4) The dry powder is carbonized in an argon atmosphere, the heating speed is 2 DEG C / minute, the holding temperature is 1500 DEG C, the holding time is 2 hours, and natural cooling is performed, and then airflow crushing is performed to a particle size of about 20 μm to obtain hard carbon negative electrode material;

[0058] (5) The hard carbon negative electrode material is used as an active substance of an electrode, and is stirred and uniformly mixed with conductive carbon black and a PVDF binder at a ratio of 95:2.5:2.5 to form slurry, and then scraped and coated on an aluminum foil current collector, and dried in a vacuum drying box at 80 DEG C for 24 hours to obtain an electrode sheet, the electrode sheet is cut into a circular sheet with a certain size, a sodium sheet is used as a counter electrode, 1M NaPF6 ether is used as an electrolyte, and a button cell is assembled. The sodium storage performance is shown in Tables 1 and 2, the capacity is tested once every 10 cycles under a 2C current density, and the final capacity retention rate is 86%.

[0059] Embodiment 2

[0060] The embodiment provides a preparation method of a lignin-based hard carbon negative electrode material, and specific steps are as follows:

[0061] (1) 10% of Na2SO4 is added to the black liquor containing lignin in step (1) of embodiment 1, argon in steps (1) and (4) of embodiment 1 is replaced by nitrogen, and other operation steps remain unchanged, and then hard carbon negative electrode material is obtained;

[0062] (2) The hard carbon negative electrode material obtained above is used as the active material of the electrode, and is stirred and uniformly mixed with conductive carbon black and a PVDF binder at a ratio of 95:2.5:2.5 to form a slurry, which is then scraped and coated on an aluminum foil current collector, dried in a vacuum drying oven at 80°C for 24 h to obtain an electrode sheet, cut into a circular sheet of a certain size, and assembled into a button cell with a sodium sheet as the counter electrode and 1M NaPF6 ether as the electrolyte. The electrochemical sodium storage performance is shown in Table 1.

[0063] Example 3

[0064] The present example provides a preparation method of a lignin-based hard carbon negative electrode material, and the specific steps are as follows:

[0065] (1) The holding temperature in step (1) of Example 1 is set to 300°C, and the holding time is 5h. The sulfuric acid in step (2) of Example 1 is replaced with hydrochloric acid, and the concentration of the hydrochloric acid is 4M. The other operation steps remain the same as those in Example 1 to obtain a hard carbon negative electrode material.

[0066] (2) The hard carbon negative electrode material obtained above is used as the active material of the electrode, and is stirred and uniformly mixed with conductive carbon black and a PVDF binder at a ratio of 95:2.5:2.5 to form a slurry, which is then scraped and coated on an aluminum foil current collector, dried in a vacuum drying oven at 80°C for 24 h to obtain an electrode sheet, cut into a circular sheet of a certain size, and assembled into a button cell with a sodium sheet as the counter electrode and 1M NaPF6 ether as the electrolyte. The electrochemical sodium storage performance is shown in Table 1.

[0067] Example 4

[0068] The present example provides a preparation method of a lignin-based hard carbon negative electrode material, and the specific steps are as follows:

[0069] (1) The holding temperature in step (1) of Example 1 is set to 300°C, and the holding time is 5h. The sulfuric acid in step (2) of Example 1 is replaced with hydrochloric acid, and the concentration of the hydrochloric acid is 4M. The other operation steps remain the same as those in Example 1 to obtain a hard carbon negative electrode material.

[0070] (2) The hard carbon negative electrode material obtained above is used as the active material of the electrode, and is stirred and uniformly mixed with conductive carbon black and a PVDF binder at a ratio of 95:2.5:2.5 to form a slurry, which is then scraped and coated on an aluminum foil current collector, dried in a vacuum drying oven at 80°C for 24 h to obtain an electrode sheet, cut into a circular sheet of a certain size, and assembled into a button cell with a sodium sheet as the counter electrode and 1M NaPF6 ether as the electrolyte. The electrochemical sodium storage performance is shown in Table 1.

[0071] Example 5

[0072] The present example provides a preparation method of a lignin-based hard carbon negative electrode material, and the specific steps are as follows:

[0073] (1) The temperature of the heat preservation in step (4) of Example 1 is 1600°C, the heat preservation time is 5h, the sulfuric acid in step (2) of Example 1 is replaced by phosphoric acid, the primary carbonization material in step (1) of Example 1 is mechanically pulverized to a particle size of 5-10μm, and other operation steps remain the same as in Example 1 to obtain a hard carbon negative electrode material;

[0074] (2) The hard carbon negative electrode material obtained above is used as the active material of an electrode, which is mixed with conductive carbon black and a PVDF binder in a ratio of 95:2.5:2.5 to form a slurry, which is then scraped onto an aluminum foil current collector and dried in a vacuum drying oven at 80°C for 24h to obtain an electrode sheet, which is cut into a circular sheet of a certain size, a sodium sheet is used as the counter electrode, and 1M NaPF6 ether is used as the electrolyte to assemble a button cell. The electrochemical sodium storage performance is shown in Table 1.

[0075] Example 6

[0076] The present example provides a method for preparing a lignin-based hard carbon negative electrode material, and the specific steps are as follows:

[0077] (1) The primary carbonization material in step (1) of Example 1 is mechanically pulverized to a particle size of 80-100μm, the temperature of the heat preservation in step (4) of Example 1 is 1100°C, the heat preservation time is 10h, and the 6M sulfuric acid in step (2) of Example 1 is replaced by a mixed acid solution of 3M sulfuric acid and 3M hydrochloric acid, and other operation steps remain the same as in Example 1 to obtain a hard carbon negative electrode material;

[0078] (2) The hard carbon negative electrode material obtained above is used as the active material of an electrode, which is mixed with conductive carbon black and a PVDF binder in a ratio of 95:2.5:2.5 to form a slurry, which is then scraped onto an aluminum foil current collector and dried in a vacuum drying oven at 80°C for 24h to obtain an electrode sheet, which is cut into a circular sheet of a certain size, a sodium sheet is used as the counter electrode, and 1M NaPF6 ether is used as the electrolyte to assemble a button cell. The electrochemical sodium storage performance is shown in Table 1.

[0079] Example 7

[0080] The present example provides a method for preparing a lignin-based hard carbon negative electrode material, and the specific steps are the same as in Example 1, except that the performance of the material for lithium ion batteries is tested according to the following steps.

[0081] The hard carbon negative electrode material obtained in Example 1 is used as the active material of an electrode, which is mixed with conductive carbon black and a PVDF binder in a ratio of 95:2.5:2.5 to form a slurry, which is then scraped onto a copper foil current collector and dried in a vacuum drying oven at 80°C for 24h to obtain an electrode sheet, which is cut into a circular sheet of a certain size, a lithium sheet is used as the counter electrode, and 1M LiPF6 ester is used as the electrolyte to assemble a button cell. The electrochemical lithium storage performance is shown in Table 1.

[0082] Comparative Example 1

[0083] The embodiment provides a preparation method of a lignin-based hard carbon negative electrode material, and specific steps are as follows:

[0084] (1) In step (1) of the embodiment 1, no Na2SO4 is added in the papermaking black liquor, and other operation steps remain unchanged, to obtain a hard carbon negative electrode material;

[0085] (2) The hard carbon negative electrode material obtained above is used as an active substance of an electrode, and is stirred and uniformly mixed with conductive carbon black and a PVDF binder at a ratio of 95:2.5:2.5 to form a slurry, and is scraped and coated on an aluminum foil current collector, and is dried in a 80 ℃ vacuum drying box for 24 h to obtain an electrode sheet, and the electrode sheet is cut into a circular sheet of a certain size, sodium is used as a counter electrode, 1M NaPF6 ether is used as an electrolyte, and a button cell is assembled. The electrochemical sodium storage performance is shown in Table 1.

[0086] Comparative example 2

[0087] The embodiment provides a preparation method of a lignin-based hard carbon negative electrode material, and specific steps are as follows:

[0088] (1) In step (2) of the embodiment 1, 6M sulfuric acid is replaced by 2M sulfuric acid, and other operation steps remain unchanged, to obtain a hard carbon negative electrode material;

[0089] (2) The hard carbon negative electrode material obtained above is used as an active substance of an electrode, and is stirred and uniformly mixed with conductive carbon black and a PVDF binder at a ratio of 95:2.5:2.5 to form a slurry, and is scraped and coated on an aluminum foil current collector, and is dried in a 80 ℃ vacuum drying box for 24 h to obtain an electrode sheet, and the electrode sheet is cut into a circular sheet of a certain size, sodium is used as a counter electrode, 1M NaPF6 ether is used as an electrolyte, and a button cell is assembled. The electrochemical sodium storage performance is shown in Table 1.

[0090] Test example 1

[0091] The test example tests the charge-discharge performance of the examples 1-7 and the comparative examples 1-2 by using a button cell at room temperature (25 ℃), and the test results are shown in Table 1.

[0092] Table 1: Electrochemical performance of the examples 1-7 and the comparative examples 1-2

[0093] It can be found from the battery performance test results in Table 1 that the sodium ion negative electrode half-cell assembled by using the lignin-based hard carbon obtained by using the high-concentration acid etching process has a first coulomb efficiency of more than 90%, a reversible capacity of more than 400 mAh·g -1 , and a high rate performance, and the reversible capacity is more than 290 mAh·g -1 at a 2C current density.

[0094] Test Example 2

[0095] This test example tests the micropore, mesopore, closed pore, closed pore volume of Examples 1-7 and Comparative Examples 1-2, and the test results are shown in Table 2. The closed pore volume is calculated using the true density of the hard carbon negative electrode material, and the average closed pore diameter is calculated by fitting the small-angle scattering curve of the hard carbon negative electrode material. The N2 and CO2 adsorption-desorption isotherms of the hard carbon negative electrode material are tested at 77K and 273K, respectively, using a Micromeritics 3Flex physical adsorption instrument to complete the pore structure characterization; then based on the adsorption branch of the isotherm, the non-local density functional theory (NLDFT) method is used as the main analysis means, and the specific surface area calculated by the multipoint Brunauer-Emmett-Teller (BET) method is used for auxiliary verification, and finally the pore size distribution of the hard carbon negative electrode material is obtained, and the test data are shown in Table 2.

[0096] Table 2: Micropore, mesopore distribution and proportion, and closed pore and closed pore volume of Examples 1-7 and Comparative Examples 1-2

[0097] The embodiments of the application are described in detail above with reference to the drawings, but the application is not limited to the above embodiments, and various changes can be made within the knowledge of those skilled in the art without departing from the purpose of the application. In addition, the embodiments of the application and the features in the embodiments can be combined with each other without conflict.

Claims

1. A hard carbon negative electrode material, characterized in that, The hard carbon negative electrode material has a hierarchical porous structure, the hierarchical porous structure has micropores with a pore size of 0.35-0.85 nm and mesopores with a pore size of 2-25 nm, the micropore volume accounts for 40-50% of the total pore volume, and the mesopore volume accounts for 30-50% of the total pore volume. The average closed pore diameter of the hard carbon negative electrode material is 1.7-2.2 nm, and the closed pore volume is 0.091-0.117 cm 3 ·g -1 ; The hard carbon negative electrode material has a short-range pseudo-graphite crystallite structure, the average lateral size of the pseudo-graphite crystallite is 3.81-4.18 nm, the average longitudinal size is 0.91-1.11 nm, and the interlayer spacing is 0.373-0.380 nm. 2.The hard carbon negative electrode material of claim 1, characterized in that, The preparation method of the hard carbon negative electrode material comprises the following steps: S1, adding Na2SO4 in the black liquor obtained by the papermaking process, filtering and drying after precipitating lignin by adjusting the pH to less than 3 with sulfuric acid, and further mechanically crushing to obtain industrial lignin powder; S2, performing one-time low-temperature carbonization on the industrial lignin powder obtained in step S1 under a protective atmosphere to obtain one-time carbonization material; S3, mechanically crushing the one-time carbonization material obtained in step S2 to obtain carbon powder, adding the carbon powder into an acid solution, and heating to react to obtain reacted carbon powder; S4, washing, filtering and drying the reacted carbon powder obtained in step S3 to obtain dry carbon powder; S5, performing high-temperature carbonization on the dry carbon powder obtained in step S4 under a protective atmosphere to obtain a hard carbon negative electrode material.

3. The method for preparing the hard carbon anode material according to claim 2, characterized in that, The content of Na2SO4 in step S1 is 5-10% of the black liquor, the drying temperature is 50-80℃, and the diameter of the industrial lignin powder is 50-70μm.

4. The method of claim 2, wherein the hard carbon negative electrode material is prepared by the steps of: preparing a mixture of a carbon source and a polymer; and heating the mixture to form the hard carbon negative electrode material. The carbonization temperature in step S2 is 300-1000℃, and the carbonization time is 1-10h.

5. The method for preparing the hard carbon anode material according to claim 2, characterized in that, The acid solution in step S3 is one or more of sulfuric acid, hydrochloric acid, phosphoric acid and nitric acid, the concentration of the acid solution is 4-10M, if it is a mixed acid, the concentration refers to the sum of the concentrations of the components, and the liquid-solid ratio of the acid solution to the carbon powder is 20-40:1 (mL / g).

6. The method for preparing the hard carbon anode material according to claim 2, characterized in that, The heating reaction temperature in step S3 is 40-95℃, and the heating reaction time is 1-10h.

7. The method for preparing the hard carbon anode material according to claim 2, characterized in that, The drying temperature in step S4 is 50-70℃, and the drying time is 24-48h.

8. The method for preparing the hard carbon anode material according to claim 2, characterized in that, The carbonization temperature in step S5 is 1100-1600℃, the carbonization time is 1-10h, and the carbonization heating rate is 2-10℃ / min.

9. Use of the hard carbon negative electrode material according to claim 1 in a sodium-ion secondary battery or a lithium-ion secondary battery.

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