Preparation method and application of biomass-based hard carbon negative electrode material capable of regulating pore-throat ratio

Abstract

The invention provides a preparation method and application of a biomass-based hard carbon negative electrode material with an adjustable pore-throat ratio. The preparation method comprises the following steps: carrying out hydrolysis induction treatment on a biomass-based precursor through a pore throat inducer to construct a controllable V-shaped open pore structure; and performing multi-section pyrolysis treatment to promote the opening to be closed, and forming a semi-closed pore structure with a specific pore throat / pore body ratio (pore throat ratio), thereby obtaining the hard carbon negative electrode material. According to the method, by regulating and controlling hydrolysis conditions and pyrolysis paths, the pore-throat ratio can be accurately adjusted, and the high pore body-narrow pore throat structural characteristics are constructed. The obtained hard carbon material not only inhibits the occurrence of irreversible side reaction and remarkably improves the initial coulombic efficiency (ICE), but also realizes the great improvement of platform capacity by optimizing an ion desolvation path and stabilizing an SEI structure.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of new energy materials, in particular to a preparation method of a biomass-based hard carbon negative electrode material with adjustable pore throat ratio and application thereof in a sodium ion battery. BACKGROUND

[0002] With the rapid development of renewable energy and electric transportation, green, safe and efficient energy storage technology has become an important support for global energy structure transformation. Among many energy storage systems, secondary batteries are widely used in portable electronic devices, electric vehicles and large-scale energy storage systems due to their reversibility, high energy density and portability. At present, the commercial energy storage system represented by lithium ion batteries has made remarkable development, but its long-term sustainability in the field of large-scale energy storage is being challenged due to uneven distribution of lithium resources, rising costs and environmental risks. Therefore, developing a new energy storage system with abundant resources, lower material cost and broad technical potential has become a research focus. Sodium ion batteries are considered to be one of the most promising next-generation energy storage systems because of the abundant reserves, wide distribution, mature mining technology and much lower cost of sodium elements in the earth's crust than lithium resources. Although sodium ion batteries and lithium ion batteries are highly similar in electrochemical reaction mechanism, due to the larger radius, heavier mass and poorer diffusion dynamics of sodium ions, there are still many technical challenges in the selection and design of negative electrode materials, especially in improving the reversible capacity, initial coulombic efficiency (ICE) and cycle stability.

[0003] Among many candidate negative electrode materials, hard carbon has been widely concerned due to its unique structural advantages. Hard carbon is a disordered carbon material with amorphous-microcrystalline coexistence, which has a non-layered structure, moderate sodium intercalation potential, good electronic conductivity and high cycle stability. Unlike layered carbon materials such as graphite, hard carbon has a large number of pores, defects and boundary regions inside, which can provide abundant reaction space for sodium ion intercalation and deintercalation. More importantly, hard carbon usually contains two capacity contribution mechanisms: the inclined region at high potential is mainly composed of surface adsorption and defect intercalation, while the constant potential platform capacity at low potential is derived from the filling of sodium ions in closed or semi-closed pores, and the platform capacity directly determines the upper limit of the energy density. Therefore, precise regulation of the pore structure is considered to be a key path to improve the electrochemical performance of hard carbon.

[0004] Many studies have attempted to optimize the specific surface area, pore size distribution and microcrystalline structure of hard carbon by adjusting precursor types, activation atmosphere, template assistance and other methods. However, most of the work only stays in the characterization of specific surface area and pore size range, and lacks systematic understanding of the connection mode of pore body-pore throat and its influence on electrolyte infiltration, SEI film formation and sodium ion migration behavior. Especially for the semi-closed pore structure which contributes most to the platform capacity during sodium storage, its internal closure and throat micro-narrowness have natural advantages in preventing excessive electrolyte penetration, inhibiting side reactions and optimizing SEI structure, but it has been difficult to quantify and control for a long time. Traditional parameters such as average pore size or pore volume cannot effectively characterize the degree of pore closure and ion screening ability. SUMMARY

[0005] Invention objectives

[0006] To solve the existing structure recognition and control bottleneck, the present application first proposes the concept of "pore throat ratio" as a structural parameter for representing the ratio of the minimum throat diameter to the pore body diameter in the semi-closed pore structure of hard carbon materials. This parameter can more accurately reflect the relationship between closure, selectivity and structure control potential, and has good structure-performance correlation. On this basis, the present application constructs a preparation strategy based on "directed hydrolysis induction + multi-stage pyrolysis shrinkage" of biomass precursors, which realizes controllable adjustment of the pore throat ratio by controlling the hydrolysis degree of the pore throat inducer, the proportion of the pre-generated pore and the pore sealing behavior at high temperature carbonization, significantly improving the initial coulomb efficiency and platform capacity ratio of the material. The proposed pore throat ratio control technology not only provides a new path for scalable, low-cost and environmentally friendly structure optimization of hard carbon, but also provides a new dimension for understanding and improving the performance of sodium ion battery anodes.

[0007] The present application aims to provide a preparation method of a biomass-based hard carbon anode material with controllable pore throat ratio. The anode material has a first cycle coulomb efficiency of 88%-90% and a pore throat ratio of 0.10-0.22. The preparation method solves the problems of existing sodium ion battery hard carbon anode materials in terms of low initial coulomb efficiency, insufficient platform capacity and other key performance aspects.

[0008] Technical solutions

[0009] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0010] In a first aspect, the present application provides a preparation method of a biomass-based hard carbon anode material with controllable pore throat ratio, which comprises the following steps:

[0011] The biomass precursor is placed in a pore throat inducer solution for induced hydrolysis treatment to directionally control its open pore structure and form a pre-set pore morphology.

[0012] The precursor after the induction treatment is subjected to multi-stage pyrolysis treatment, the partial opening and closing of the pores are induced by gradually increasing the temperature, the degree of throat contraction is controlled, and thus a semi-closed pore hard carbon material with a specific pore throat ratio structure is obtained.

[0013] In the present application, the preparation method realizes the regulation of the predetermined "open-pore-closed-pore" conversion path of the precursor structure through acid-catalyzed hydrolysis, and further realizes the controllable construction of the semi-closed pore structure in the hard carbon by inducing the pore throat closure through pyrolysis. The high-pore-body-small-pore-throat structure formed can effectively limit the electrolyte from entering the inside of the pore body, inhibit the generation of invalid SEI, while retaining the accessible channel for sodium ions, thereby improving the initial cycle efficiency (ICE) and platform capacity.

[0014] Among them, the crushed biomass-based hard carbon precursor (such as walnut shell, coconut shell, bamboo powder, etc.) is first placed in a pore throat inducer solution and hydrolyzed under mild conditions for a certain period of time to induce the formation of a V-shaped open-pore structure; then, multi-stage pyrolysis is carried out, the first stage forms a primary carbon skeleton in the medium temperature zone (1000℃), and the second stage promotes the closure of the pore throat in the high temperature zone (1400℃) to complete the semi-closed pore configuration conversion. Finally, a closed pore system with large pore body diameter, narrow throat, and stable structure is formed.

[0015] The "pore throat ratio" defined in the present application is the ratio of the minimum throat diameter to the pore diameter of a single pore body, which is a key structural parameter reflecting the closure of the pore body and the ion sieving performance. By regulating the acid concentration, hydrolysis time, pyrolysis rate and temperature platform, the continuous adjustment of the pore throat ratio can be accurately realized to match the desolvation insertion requirements of sodium ions.

[0016] Preferably, the biomass-based hard carbon precursor includes any one or a combination of at least two of bamboo powder, walnut shell powder, coconut shell powder, bark powder, rice husk powder or straw powder.

[0017] It should be noted that the preparation method of the biomass-based hard carbon negative electrode material with regulated pore throat ratio in the present application is suitable for the modification of a wide range of biomass-based materials, including but not limited to the above-mentioned optional biomass-based hard carbon precursors, which can effectively improve the reversible capacity of the hard carbon negative electrode material after pyrolysis.

[0018] Preferably, the biomass-based hard carbon precursor is a crushed biomass-based hard carbon precursor.

[0019] Preferably, the particle size of the biomass-based hard carbon precursor is 225-325 mesh, for example, it can be 225 mesh, 275 mesh, 325 mesh, etc.

[0020] Preferably, the pore throat inducer is ZnCl2, AlCl3, MgCl2, with a concentration of 0.5-2 mol / L, for example, it can be 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, etc., preferably 1 mol / L.

[0021] Preferably, the mass ratio of the biomass-based hard carbon precursor and the pore throat inducer is 3:(50-200), for example, it can be 3:50, 3:100, 3:150, 3:200, etc., preferably 3:150.

[0022] Preferably, the pore throat directional reconstruction process treatment includes ultrasonic dispersion and heating stirring in sequence.

[0023] Preferably, in the pore throat directional reconstruction process treatment, the temperature of ultrasonic dispersion is 40°C.

[0024] Preferably, in the pore throat directional reconstruction process treatment, the power of ultrasonic dispersion is 100W.

[0025] Preferably, in the pore throat directional reconstruction process treatment, the time of ultrasonic dispersion is 10 min.

[0026] Preferably, in the pore throat directional reconstruction process treatment, the rotation speed of heating stirring is 500 rpm.

[0027] Preferably, in the pore throat directional reconstruction process treatment, the temperature of heating stirring is 60-100°C, for example, it can be 60°C, 70°C, 80°C, 90°C, 100°C, etc., preferably 80°C.

[0028] Preferably, in the pore throat directional reconstruction process treatment, the time of heating stirring is 6-24h, for example, it can be 6h, 12h, 16h, 24h, etc., preferably 16h.

[0029] Preferably, the pore throat directional reconstruction process treatment further includes washing and drying in sequence.

[0030] Preferably, the washing liquid used in the washing is deionized water, and the washing is performed at least 3 times until the washing liquid is neutral.

[0031] Preferably, the drying is vacuum drying.

[0032] Preferably, the temperature of the vacuum drying is 80-100°C, for example, it can be 80°C, 90°C, 100°C, etc., preferably 90°C.

[0033] Preferably, the time of the vacuum drying is 6-24h, for example, it can be 6h, 12h, 18h, 24h, etc., preferably 18h.

[0034] Preferably, the multi-stage pyrolysis treatment is a two-step pyrolysis, the temperature of the first step pyrolysis is 600-1000℃, for example, it can be 600℃, 700℃, 800℃, 900℃, 1000℃, etc., preferably 900℃; the temperature of the second step pyrolysis is 1200-1600℃, for example, it can be 1200℃, 1300℃, 1400℃, 1500℃, 1600℃, etc., preferably 1500℃.

[0035] Preferably, the time of the pyrolysis treatment is 1-12h, for example, it can be 1h, 3h, 6h, 9h, 12h, etc., preferably 6h.

[0036] Preferably, the heating rate of the pyrolysis treatment is 3-8℃ / min, preferably 5℃ / min.

[0037] Preferably, the pyrolysis treatment is carried out under a protective gas atmosphere.

[0038] Preferably, the protective gas includes any one of nitrogen or argon.

[0039] In a second aspect, the present application provides a biomass-based hard carbon negative electrode material for regulating pore throat ratio, which is prepared by the preparation method for regulating pore throat ratio as described in the first aspect, has a high semi-closed pore ratio and an optimized pore throat structure, and can effectively improve the sodium ion intercalation capacity and initial coulombic efficiency.

[0040] In a third aspect, the present application provides an application of the biomass-based hard carbon negative electrode material for regulating pore throat ratio as described in the second aspect in the preparation of a sodium ion battery negative electrode sheet, which is suitable for the construction of a negative electrode current collector in a high-energy density and long-life sodium ion energy storage system.

[0041] In a fourth aspect, the present application provides a sodium ion battery negative electrode sheet material, which includes the biomass-based hard carbon material for regulating pore throat ratio as described in the second aspect, and can have excellent ion storage performance and platform capacity proportion while maintaining structural stability.

[0042] Preferably, the raw materials for preparing the sodium ion battery negative electrode sheet material include: a battery negative electrode slurry and a metal foil.

[0043] Preferably, the battery negative electrode slurry includes the following components by weight fraction: 70-90 parts of the biomass-based hard carbon negative electrode material for regulating pore throat ratio, 0-15 parts of a conductive agent, and 5-20 parts of a binder.

[0044] In the battery negative electrode slurry, the addition amount of the biomass-based hard carbon negative electrode material for regulating pore throat ratio is 70-90 parts, for example, it can be 70 parts, 75 parts, 80 parts, 85 parts, 90 parts, etc., preferably 80 parts.

[0045] The conductive agent is added in an amount of 0-15 parts in the battery negative electrode slurry, for example, 0 parts, 5 parts, 10 parts, 15 parts, etc., preferably 10 parts.

[0046] Preferably, the conductive agent is Ketjen black.

[0047] The binder is added in an amount of 5-20 parts in the battery negative electrode slurry, for example, 5 parts, 10 parts, 15 parts, 20 parts, etc., preferably 10 parts.

[0048] Preferably, the binder is PVDF.

[0049] Preferably, the metal foil is a copper foil.

[0050] Preferably, the loading amount of the battery negative electrode slurry on the metal foil is 0.9-1.1 mg / cm 2 , for example, 0.9 mg / cm 2 , 0.95 mg / cm 2 , 1 mg / cm 2 , 1.05 mg / cm 2 , 1.1 mg / cm 2 , etc.

[0051] Preferably, the sodium-ion battery negative electrode material is prepared by the following steps:

[0052] The biomass-based hard carbon negative electrode material with regulated pore throat ratio, the conductive agent and the binder are uniformly mixed in NMP to prepare the battery negative electrode slurry.

[0053] After the battery negative electrode slurry is coated on the surface of the metal foil, drying is performed to obtain the sodium-ion battery negative electrode sheet material.

[0054] In a fifth aspect, the present application provides a sodium-ion battery, which comprises the biomass-based hard carbon negative electrode material with regulated pore throat ratio according to the second aspect, or the sodium-ion battery negative electrode sheet material according to the fourth aspect.

[0055] Preferably, the sodium-ion battery further comprises: a counter electrode, an electrolyte and a separator.

[0056] Preferably, the material of the counter electrode is metallic sodium.

[0057] Preferably, the electrolyte comprises: a sodium salt and a solvent.

[0058] Preferably, the sodium salt comprises sodium hexafluorophosphate (NaPF6).

[0059] Preferably, the solvent comprises diethylene glycol dimethyl ether (DIGLYME).

[0060] Preferably, the concentration of the sodium salt is 1 mol / L.

[0061] Preferably, the diaphragm is glass fiber (GF / A).

[0062] Beneficial effects

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

[0064] (1) The present application realizes controllable adjustment of pore size structure by carrying out pore throat directional reconstruction process on biomass-based hard carbon precursor in the material preparation process, and exposes more open pores and active sites;

[0065] (2) The present application realizes corresponding regulation of carbon layer structure by high-temperature carbonization, so as to optimize the composition and structure of biomass-based precursor to improve the reversible capacity of the material, including but not limited to optimization of crystallinity, pore size structure, etc., high initial coulombic efficiency and optimized pore throat structure; the initial coulombic efficiency is 88%-90%, the pore throat ratio is 0.10-0.22, and the final hard carbon material is obtained. BRIEF DESCRIPTION OF DRAWINGS

[0066] In order to more clearly illustrate the specific embodiments of the present application or the technical solutions in the prior art, the drawings needed in the specific embodiments or prior art description will be briefly introduced below. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0067] Figure 1 The scanning electron microscope image of the biomass-based hard carbon negative material with adjustable pore throat ratio provided by Example 1 of the present application.

[0068] Figure 2 The X-ray diffraction pattern of the biomass-based hard carbon negative material with adjustable pore throat ratio provided by Example 1 of the present application.

[0069] Figure 3 The charge-discharge curve diagram of the sodium ion battery assembled by the biomass-based hard carbon negative material with adjustable pore throat ratio provided by Example 1 of the present application at 0.05C rate.

[0070] Figure 4 The cycle curve diagram of the sodium ion battery assembled by the biomass-based hard carbon negative material with adjustable pore throat ratio provided by Example 1 of the present application at 2C rate. DETAILED DESCRIPTION

[0071] The technical solutions of the present application will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative efforts belong to the scope of protection of the present application.

[0072] The present application will be further described below by way of examples. Unless otherwise specified, the materials in the examples are prepared according to the existing methods or directly purchased from the market.

[0073] Example 1

[0074] The present embodiment provides a preparation method of a biomass-based hard carbon negative electrode material with adjustable pore throat ratio, which specifically comprises the following steps:

[0075] S1, pore throat directional reconstruction process treatment:

[0076] 3g of walnut shell-based hard carbon precursor was placed in 100mL of 2mol / L MgCl2, ultrasonically dispersed at 40℃ and 100W for 10min, then stirred at 80℃ and 500rpm for 16h, and then washed with deionized water for multiple times. The washed solid was placed in a vacuum drying oven and vacuum dried at 90℃ for 18h to obtain a pore throat induced biomass-based hard carbon precursor.

[0077] S2, two-step pyrolysis treatment:

[0078] The pore throat induced biomass-based hard carbon precursor was placed in an argon atmosphere, heated to 900℃ at a heating rate of 5℃ / min, and pyrolyzed at 900℃ for 6h, and then cooled to 25℃ at a cooling rate of 2℃ / min to obtain a primary pyrolysis hard carbon material;

[0079] The primary pyrolysis hard carbon material was placed in an argon atmosphere, heated to 1500℃ at a heating rate of 5℃ / min, and pyrolyzed at 1500℃ for 6h, and then cooled to 25℃ at a cooling rate of 2℃ / min to obtain a biomass-based hard carbon negative electrode material with adjustable pore throat ratio. The first week coulombic efficiency thereof was 85.3%, and the pore throat ratio was 0.13.

[0080] Example 2

[0081] The present embodiment provides a preparation method of a biomass-based hard carbon negative electrode material with adjustable pore throat ratio, which specifically comprises the following steps:

[0082] S1, pore throat directional reconstruction process treatment:

[0083] Put 1 g of walnut shell-based hard carbon precursor into 50 mL of 1 mol / L FeCl3pore throat inducer, ultrasonic dispersion at 40℃, 100W for 10 min, then stir at 100℃ with a rotation speed of 300 rpm for 12 h, then wash with deionized water for several times, put the washed solid into a vacuum drying oven, vacuum drying at 100℃ for 6 h, get the pore throat induced biomass-based hard carbon precursor.

[0084] S2, two-step pyrolysis treatment:

[0085] Put the pore throat induced biomass-based hard carbon precursor into an argon atmosphere, heat to 1000℃ at a heating rate of 5℃ / min, and pyrolyze at 1000℃ for 6 h, cool to 25℃ at a cooling rate of 2℃ / min, get the primary pyrolysis hard carbon material;

[0086] Put the primary pyrolysis hard carbon material into an argon atmosphere, heat to 1300℃ at a heating rate of 5℃ / min, and pyrolyze at 1300℃ for 6 h, cool to 25℃ at a cooling rate of 2℃ / min, get the pore throat ratio regulated biomass-based hard carbon negative electrode material. The first week coulombic efficiency is 81.1%, and the pore throat ratio is 0.18.

[0087] Example 3

[0088] S1, pore throat directional reconstruction process treatment:

[0089] Put 3 g of bamboo-based hard carbon precursor into 100 mL of 2 mol / L AlCl3pore throat inducer, ultrasonic dispersion at 40℃, 100W for 10 min, then stir at 100℃ with a rotation speed of 300 rpm for 16 h, then wash with deionized water for several times, put the washed solid into a vacuum drying oven, vacuum drying at 90℃ for 6 h, get the pore throat induced biomass-based hard carbon precursor.

[0090] S2, two-step pyrolysis treatment:

[0091] Put the pore throat induced biomass-based hard carbon precursor into an argon atmosphere, heat to 1000℃ at a heating rate of 5℃ / min, and pyrolyze at 1000℃ for 6 h, cool to 25℃ at a cooling rate of 2℃ / min, get the primary pyrolysis hard carbon material;

[0092] Put the primary pyrolysis hard carbon material into an argon atmosphere, heat to 1500℃ at a heating rate of 5℃ / min, and pyrolyze at 1500℃ for 6 h, cool to 25℃ at a cooling rate of 2℃ / min, get the pore throat ratio regulated biomass-based hard carbon negative electrode material. The first week coulombic efficiency is 79.8%, and the pore throat ratio is 0.21.

[0093] Example 4

[0094] The embodiment provides a preparation method of a biomass-based hard carbon negative electrode material with a regulated pore-throat ratio, which is different from the embodiment 1 only in that the pore-throat inducing agent is changed into ZnCl2, and other steps are completely consistent with the embodiment 1, and the first cycle coulombic efficiency of the biomass-based hard carbon negative electrode material with the regulated pore-throat ratio obtained is 83.6%, and the pore-throat ratio is 0.15.

[0095] The embodiment 5 provides a preparation method of a biomass-based hard carbon negative electrode material with a regulated pore-throat ratio, which is different from the embodiment 1 only in that the concentration of the pore-throat inducing agent is changed into 0.5 mol / L, and other steps are completely consistent with the embodiment 1, and the first cycle coulombic efficiency of the biomass-based hard carbon negative electrode material with the regulated pore-throat ratio obtained is 81.9%, and the pore-throat ratio is 0.19.

[0096] The embodiment 6 provides a preparation method of a biomass-based hard carbon negative electrode material with a regulated pore-throat ratio, which is different from the embodiment 1 only in that the pore-throat directional reconstruction process treatment time is changed into 12 h, and other steps are completely consistent with the embodiment 1, and the first cycle coulombic efficiency of the biomass-based hard carbon negative electrode material with the regulated pore-throat ratio obtained is 82.9%, and the pore-throat ratio is 0.16.

[0097] The embodiment 7 provides a preparation method of a biomass-based hard carbon negative electrode material with a regulated pore-throat ratio, which is different from the embodiment 1 only in that the second pyrolysis temperature is changed into 1300 DEG C, and other steps are completely consistent with the embodiment 1, and the first cycle coulombic efficiency of the biomass-based hard carbon negative electrode material with the regulated pore-throat ratio obtained is 77.8%, and the pore-throat ratio is 0.21.

[0098] The embodiment 8 provides a preparation method of a biomass-based hard carbon negative electrode material with a regulated pore-throat ratio, which is different from the embodiment 2 only in that the first pyrolysis temperature is changed into 800 DEG C, and other steps are completely consistent with the embodiment 2, and the first cycle coulombic efficiency of the biomass-based hard carbon negative electrode material with the regulated pore-throat ratio obtained is 80.3%, and the pore-throat ratio is 0.18.

[0099] The comparative example 1 provides a preparation method of a biomass-based hard carbon negative electrode material with a regulated pore-throat ratio, and the preparation method specifically comprises the following steps:

[0100] S1, aqueous solution treatment:

[0101] The comparative example 1 provides a preparation method of a biomass-based hard carbon negative electrode material with a regulated pore-throat ratio, and the preparation method specifically comprises the following steps:

[0102] S1, aqueous solution treatment:

[0103] The comparative example 1 provides a preparation method of a biomass-based hard carbon negative electrode material with a regulated pore-throat ratio, and the preparation method specifically comprises the following steps:

[0104] S1, aqueous solution treatment:

[0105] The 3 g walnut shell precursor was placed in 100 mL of deionized water, ultrasonically dispersed at 40°C and 100 W for 10 min, then stirred at 80°C and 500 rpm for 16 h, and the washed solid was placed in a vacuum drying oven at 90°C and vacuum dried for 18 h to obtain a biomass-based hard carbon precursor;

[0106] S2, two-step pyrolysis treatment:

[0107] The biomass-based hard carbon precursor was placed in an argon atmosphere, heated to 900°C at a rate of 5°C / min, and pyrolyzed at 900°C for 6 h, then cooled to 25°C at a rate of 2°C / min to obtain a primary pyrolysis hard carbon material;

[0108] The primary pyrolysis hard carbon material was placed in an argon atmosphere, heated to 1500°C at a rate of 5°C / min, and pyrolyzed at 1500°C for 6 h, then cooled to 25°C at a rate of 2°C / min to obtain the biomass-based hard carbon negative material with regulated pore throat ratio, with a first cycle coulombic efficiency of 77.8% and a pore throat ratio of 0.27.

[0109] Comparative Example 2

[0110] This comparative example provides a biomass-based hard carbon negative material with regulated pore throat ratio, and the preparation method specifically comprises the following steps:

[0111] S1, pore throat directional reconstruction process:

[0112] The 3 g walnut shell-based hard carbon precursor was placed in 100 mL of 2 mol / L MgCl2, ultrasonically dispersed at 40°C and 100 W for 10 min, then stirred at 80°C and 500 rpm for 16 h, then washed with deionized water several times, and the washed solid was placed in a vacuum drying oven at 90°C and vacuum dried for 18 h to obtain a pore throat induced biomass-based hard carbon precursor.

[0113] S2, pyrolysis treatment:

[0114] The pore throat induced biomass-based hard carbon precursor was placed in an argon atmosphere, heated to 900°C at a rate of 5°C / min, and pyrolyzed at 900°C for 6 h, then cooled to 25°C at a rate of 2°C / min to obtain the biomass-based hard carbon negative material with regulated pore throat ratio, with a first cycle coulombic efficiency of 68.1% and a pore throat ratio of 0.31.

[0115] Test Example 1

[0116] Electrochemical performance test

[0117] Test sample: biomass-based hard carbon negative electrode material with regulated pore throat ratio provided by examples 1-8 and modified biomass hard carbon negative electrode material provided by comparative examples 1-2;

[0118] Test method:

[0119] (1) Preparation of sodium ion battery negative electrode sheet: 80 parts of hard carbon negative electrode material, 10 parts of Ketjen black and 10 parts of binder (specific name: PVDF) are weighed by mass fraction, and are dissolved in NMP to obtain battery negative electrode slurry; the battery negative electrode slurry is coated on the surface of copper foil, and the coating amount is 1.0 mg / cm 2 ; vacuum drying is carried out in a vacuum drying box at 80℃ for 10h, the sheet is cut with a mold to obtain the sodium ion battery negative electrode sheet.

[0120] (2) Assembly of sodium ion battery: metal sodium is used as the counter electrode, the electrolyte is 1mol / L NaPF6 (solvent is DIGLYME), and the separator is glass fiber (GF / A), and a C2032 button cell is formed in an argon-filled glove box.

[0121] (3) Charge and discharge performance test: CT-4008 battery test system of Wuhan Blue Light Electronic Co., Ltd. is used.

[0122] The test results are shown in Table 1 and Figures 3-4

[0123] Table 1

[0124]

[0125] From the test results in Table 1, it can be seen that the biomass-based hard carbon negative electrode material obtained by accurately regulating the pore throat ratio according to the present application has excellent performance in sodium ion batteries. The charge capacity of the prepared battery system can reach more than 320 mAh / g, the discharge capacity can reach up to 446 mAh / g, and the initial coulombic efficiency (ICE) is about 80%, wherein the sample with the lowest pore throat ratio (0.13) shows the best performance, the initial coulombic efficiency is as high as 85.3%, the charge capacity is as high as 381 mAh / g, and the platform capacity is significantly improved.

[0126] The results show that by introducing the pore throat ratio design concept, combined with directional structure induction and multi-stage pyrolysis strategy, the semi-closed pore structure in hard carbon can be accurately constructed. The regulated pore throat ratio structure not only effectively limits the deep infiltration of electrolyte and inhibits the excessive generation of invalid SEI film, but also retains the sodium ion insertion channel and improves the ion utilization efficiency of the platform reaction. With the increase of the pore throat ratio from 0.13 to 0.31, the initial week ICE decreases significantly, and the charge and discharge capacity also decreases, which fully proves that the pore throat structure has a dominant regulating effect on the electrochemical performance. ​

[0127] Therefore, the material preparation method of the present application builds a moderate open pore structure in the precursor treatment stage, and realizes the shrinkage and closure of the pore throat in the high-temperature carbonization stage, finally obtains a hard carbon material with low pore throat ratio, significantly improves the sodium storage capacity and initial efficiency from the pore structure level, and breaks through the performance bottleneck of traditional hard carbon materials.

[0128] Finally, it should be pointed out that: the above embodiments are only used to illustrate the technical solutions of the present application, and not to limit it. Although the present application has been described in detail with reference to the above embodiments, those skilled in the art should understand that: without departing from the core idea of the present application - "pore throat ratio control to build semi-closed pore structure to improve sodium storage performance", the specific structure design, precursor type, pyrolysis path and other technical links can still be modified, or some or all of the technical features can be replaced equivalently; the above modifications or replacements shall not deviate from the scope of the technical solutions claimed by the present application.

Claims

1. A method for preparing a biomass-based hard carbon negative electrode material with adjustable pore-throat ratio, characterized in that: The preparation method comprises the following steps: The biomass precursor is placed in a pore throat inducer solution and subjected to a directional hydrolysis induction treatment to obtain a pretreated precursor with an open pore structure; The precursor is subjected to a two-step pyrolysis treatment to promote partial closure of the open pore structure and adjust the pore-throat ratio to 0.10-0.22, thereby obtaining the biomass-based hard carbon negative electrode material.

2. The method for preparing a biomass-based hard carbon negative electrode material with adjustable pore-throat ratio according to claim 1, characterized in that: The biomass precursor includes any one of bamboo powder, walnut shell powder, coconut shell powder, bark powder, rice husk powder or straw powder, or a combination of at least two thereof; And / or, the biomass precursor is pulverized biomass with a particle size of 270-325 mesh.

3. The method for preparing a biomass-based hard carbon negative electrode material with adjustable pore-throat ratio according to claim 2, characterized in that: The pore throat inducer solution is an aqueous solution of AlCl3, FeCl3, MgCl2 or a mixture thereof, and the mass ratio of the biomass to the pore throat inducer solution during treatment is 3:(50-200); The concentration of the pore throat inducer solution is 0.5-2 mol / L.

4. The method for preparing a biomass-based hard carbon negative electrode material with adjustable pore-throat ratio according to claim 3, characterized in that: The pore throat inducer hydrolysis treatment includes sequential heating ultrasonic dispersion and heating stirring; The ultrasonic dispersion temperature is 40°C, the power is 100W, and the ultrasonic dispersion time is 10min. The heating and stirring speed is 500 rpm, the heating and stirring temperature is 60°C-100°C, and the heating and stirring time is 6-24h; And / or, the hydrolysis treatment further includes sequential washing and drying steps.

5. The method for preparing a biomass-based hard carbon negative electrode material with a controlled pore-throat ratio according to claim 4, characterized in that: In the two-step pyrolysis, the temperature of the first step pyrolysis is 600-1000°C, and the temperature of the second step pyrolysis is 1200-1600°C; the cooling rate in the two steps is 1-5°C / min, and the temperature is reduced to 23-28°C; And / or, the pyrolysis treatment time is 1-12h; And / or, the heating rate of the pyrolysis treatment is 3-8°C / min.

6. A biomass-based hard carbon negative electrode material with adjustable pore-throat ratio, characterized in that: The biomass-based hard carbon negative electrode material is prepared by the preparation method according to any one of claims 1 to 5, and the negative electrode material has a first-cycle coulombic efficiency of 88% to 90% and a pore-throat ratio of 0.10 to 0.

22.

7. Use of the biomass-based hard carbon negative electrode material with adjustable pore-throat ratio as claimed in claim 6 in preparing a negative electrode sheet for a sodium ion battery.

8. A negative electrode plate for a sodium ion battery, characterized in that: The sodium ion battery negative electrode plate includes the biomass-based hard carbon negative electrode material according to claim 6.

9. A sodium ion battery, characterized in that: The sodium ion battery includes the biomass-based hard carbon negative electrode material with adjustable pore-throat ratio as claimed in claim 6, or the sodium ion battery negative electrode sheet as claimed in claim 8.

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