Biomass-based hard carbon material, preparation method and application thereof, and sodium / potassium ion battery

Abstract

The application relates to the technical field of batteries, and discloses a biomass-based hard carbon material, a preparation method and application thereof, and a sodium / potassium ion battery. The preparation method of the biomass-based hard carbon material comprises the following steps: (1) pre-carbonizing biomass, and then sequentially performing crushing, acid pickling, water washing and drying on the carbonized material after cooling; (2) soaking the carbonized material obtained after the treatment in step (1) in a metal salt solution, and then performing drying and carbonization; wherein the pre-carbonization temperature is lower than the carbonization temperature. According to the biomass-based hard carbon material, the electronic conductivity of the material is improved, the interlayer spacing is not reduced, the electronic transmission resistance is reduced, the sodium ion embedding resistance is not increased, the impedance of the material is reduced, and the rate performance and the cycle performance of the battery are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a biomass-based hard carbon material, a preparation method and application thereof, and a sodium / potassium ion battery. BACKGROUND

[0002] Biomass-based hard carbon materials have become the most cost-effective negative electrode material for sodium batteries due to their wide range of precursor sources, low preparation cost, and simple preparation process. However, as a negative electrode material for sodium ion batteries, biomass-based hard carbon materials face the same problem as all hard carbon materials: the presence of a large amount of sp 3 The presence of carbon increases the interlayer spacing while reducing the electronic conductivity of the material, resulting in excessively high impedance during the cycle process, and sodium ions are prone to form uneven deposition on the negative electrode surface, leading to the growth of dendrites, which ultimately pierces the separator and causes short circuits, resulting in safety problems. Therefore, there is a great need to improve the cycle performance of sodium ion batteries.

[0003] To improve the electronic conductivity of carbon materials, the general method is to increase the carbonization temperature of preparation, but this method will cause the overall decrease of the interlayer spacing of the carbon material, increase the difficulty of sodium ion insertion, and increase the impedance; heteroatom doping can effectively improve the electronic conductivity of hard carbon materials, but biomass as a solid precursor can only perform heteroatom doping on the surface of the material, only improving the electronic transmission capacity of the particle surface, and cannot improve the electronic transmission path inside the particle, ultimately resulting in minimal improvement in the performance of the negative electrode. Patent application CN114639809A discloses a composite hard carbon negative electrode material, a preparation method and application, the preparation method comprising the following steps: grinding the biomass raw material, then performing temperature calcination under a protective gas atmosphere, heat preservation, and natural cooling to room temperature to obtain biomass carbon; performing temperature calcination again on the obtained biomass carbon and a transition metal catalyst under a protective gas atmosphere, heat preservation, and natural cooling to room temperature to obtain a catalytic pyrolysis product, which is subjected to acid etching, washing to neutral, drying, and then a purified composite hard carbon negative electrode material is obtained. The present application improves the electronic conductivity of the material, but reduces the interlayer spacing, increases the resistance of sodium ion insertion, and has a high raw material cost, making it difficult to apply in industrialization.

[0004] Therefore, it is urgent to develop a hard carbon negative electrode material that improves the electronic conductivity of the material without increasing the resistance of sodium ion insertion, enhances the rate performance and cycle performance of the battery. SUMMARY

[0005] The present application aims to overcome the problem that the existing hard carbon negative material reduces the interlayer spacing while improving the electronic conductivity, increases the embedding resistance of sodium ions, and thus increases the overall impedance, resulting in reduced rate performance and cycle performance of the battery, and provides a biomass-based hard carbon material, a preparation method and application thereof, and a sodium / potassium ion battery.

[0006] To achieve the above-mentioned purpose, the present application provides a preparation method of a biomass-based hard carbon material, which comprises the following steps:

[0007] (1) pre-carbonizing the biomass, and then sequentially performing crushing, acid washing, water washing and drying on the carbonized material after cooling;

[0008] (2) soaking the carbonized material obtained after step (1) in a metal salt solution, and then performing drying and carbonization;

[0009] Preferably, the difference between the pre-carbonization temperature and the carbonization temperature is 500-1000℃.

[0010] Preferably, the difference between the pre-carbonization temperature and the carbonization temperature is 500-1000℃.

[0011] Preferably, in step (1), the pre-carbonization is performed under the protection of an inert atmosphere, and the pre-carbonization conditions include a temperature of 200-700℃, a time of 10-200min, and a temperature rising rate of 10-20℃ / min.

[0012] Preferably, in step (1), the biomass is at least one of coconut shell, fruit core, nut shell, straw and bamboo.

[0013] Preferably, in step (2), the metal salt in the metal salt solution is at least one of water-soluble calcium salt, water-soluble iron salt, water-soluble cobalt salt, water-soluble chromium salt, water-soluble nickel salt, water-soluble magnesium salt and water-soluble zinc salt.

[0014] Preferably, in step (2), the concentration of the metal salt solution is 1-6wt%.

[0015] Preferably, in step (2), the soaking time is 8-24h.

[0016] Preferably, in step (2), the carbonization is performed under the protection of an inert atmosphere, and the carbonization conditions include a temperature of 800-1500℃, a time of 10-300min, and a temperature rising rate of 10-20℃ / min.

[0017] Preferably, in step (2), boric acid and / or thiourea are also added during the soaking process.

[0018] Preferably, the method further comprises: washing, filtering and drying the material obtained in step (2) with an acidic solution and water.

[0019] Preferably, the acid in the acidic solution is at least one of hydrochloric acid, sulfuric acid, phosphoric acid and nitric acid.

[0020] The second aspect of the present application provides the biomass-based hard carbon material prepared by the above method.

[0021] The third aspect of the present application provides the use of the above biomass-based hard carbon material as a negative electrode material of a battery.

[0022] The fourth aspect of the present application provides a sodium / potassium ion battery, the negative electrode of which contains the above biomass-based hard carbon material.

[0023] Through the above technical solution, the amorphous carbon near a small part of the catalyst is catalytically graphitized by the metal catalyst, which improves the electrical conductivity without reducing the interlayer spacing, which means that the electronic transmission resistance can be reduced without increasing the sodium ion embedding resistance, and finally the overall impedance is reduced, thereby improving the cycle capacity and rate performance of the battery. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 is the XRD pattern of biomass-based hard carbon materials with different graphitization degrees;

[0025] Figure 2 is the EIS pattern of biomass-based hard carbon materials with different graphitization degrees. DETAILED DESCRIPTION

[0026] The specific embodiments of the present application are described in detail below. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present application, and are not used to limit the present application.

[0027] The endpoints of the ranges and any values disclosed herein are not limited to the precise values stated. The endpoints of the ranges and any values should be understood to be approximate. For numeric values, the endpoints of each range, the endpoints of each range and individual point values, and individual point values can be combined with each other to form one or more new numeric ranges, which should be considered to be specifically disclosed herein.

[0028] The preparation method of the biomass-based hard carbon material described in the present application comprises the following steps:

[0029] (1) pre-carbonizing the biomass, and then sequentially crushing, acid washing, water washing and drying the carbonized material after cooling;

[0030] (2) soaking the carbonized material obtained in step (1) in a metal salt solution, and then drying and carbonizing;

[0031] According to the method, the biomass still retains hydrophilic groups and water transport channels after the pre-carbonization, so that the soluble metal ions are uniformly dispersed in the material, and the catalyst exists in the form of carbide at a low carbonization temperature, cannot move, and can only catalyze the graphitization of amorphous carbon near the catalyst. The biomass is converted into graphite with strong electronic conductivity by the metal catalyst, the graphite crystallites exist as electronic transport channels and are uniformly dispersed in the hard carbon particles, the overall electronic transport capacity of the hard carbon particles is enhanced, the electronic conductivity of the material is improved, the impedance of the material is reduced, and thus the cycle capacity and rate performance of the battery are improved.

[0032] In the method, the difference between the pre-carbonization temperature and the carbonization temperature is preferably 500-1000℃, and more preferably 600-900℃, in order to graphitize part of the amorphous carbon.

[0033] In the method, the pre-carbonization in step (1) can be carried out in a primary carbonization device.

[0034] In the method, in order for the biomass to still retain hydrophilic groups and water transport channels after the pre-carbonization, the pre-carbonization in step (1) is preferably carried out under the protection of an inert atmosphere, and the pre-carbonization conditions include: the heating rate is preferably 10-20℃ / min, and more preferably 10-15℃ / min; the temperature is preferably 200-700℃, and more preferably 300-500℃; and the time is preferably 10-200min, and more preferably 20-60min.

[0035] In the method, the inert atmosphere in step (1) can be a conventional inert atmosphere in the art. In a preferred case, the inert atmosphere used is at least one of nitrogen, argon and helium, and in order to improve the electronic conductivity of the material, nitrogen is most preferred, and in a preferred case, the purity of the nitrogen is 99.0-99.9wt%.

[0036] In the method, the crushing in step (1) can be carried out by a crusher.

[0037] In the present invention, in step (1), the particle size of the pulverized particles can be 1-20 μm, and the particle size of the pulverized particles is preferably 2-8 μm in order to enhance the electronic conductivity of the material.

[0038] In the present invention, in step (1), in order to enhance the electronic conductivity of the material, the acid in the acid washing is preferably at least one of hydrochloric acid, sulfuric acid, phosphoric acid, and nitric acid, and in a more preferred case, the acid in the acid washing is hydrochloric acid.

[0039] In the present invention, in step (1), the concentration of the acid in the acid washing can be 1-14 mol / L, and the concentration of the acid in the acid washing is preferably 1-6 mol / L in order to enhance the electronic transportability of the material.

[0040] In the present invention, in step (1), the acid washing and the water washing can be performed by filtration or centrifugation. In order to reduce the impedance of the material, the water washing is preferably repeated multiple times until it is neutral.

[0041] In the present invention, in step (1), the temperature of the drying can be 90-130 °C, and the temperature of the drying is preferably 100-120 °C in order to enhance the cycle ability of the material.

[0042] In the method of the present invention, in step (1), the biomass can be at least one of coconut shell, fruit core, nut skin, straw, and bamboo. In order to enhance the electronic conductivity of the material, the biomass is preferably coconut shell and / or bamboo.

[0043] In the method of the present invention, in step (2), the metal salt in the metal salt solution can be at least one of water-soluble calcium salt, water-soluble iron salt, water-soluble cobalt salt, water-soluble chromium salt, water-soluble nickel salt, water-soluble magnesium salt, and water-soluble zinc salt. In order to enhance the electronic transportability of the material, in a preferred case, the metal salt in the metal salt solution is water-soluble iron salt, and in a more preferred case, the metal salt in the metal salt solution is ferric nitrate.

[0044] In the method of the present invention, in step (2), the concentration of the metal salt solution can be 1-6 wt%. In order to graphitize the amorphous carbon, in a preferred case, the concentration of the metal salt solution is 1-5 wt%.

[0045] In the method of the present invention, in step (2), the soaking time can be 8-24 h, and the soaking time is preferably 8-15 h in order for the metal salt to be completely deposited.

[0046] In the method of the present invention, in step (2), after the soaking, the solid phase can be separated by filtration.

[0047] In the method of the present application, in step (2), in order to ensure complete removal of moisture, the drying is preferably vacuum drying, and the conditions of the drying are preferably: temperature 90-120°C, time 24-48h, and vacuum degree 20-40Pa. The conditions of the drying are more preferably: temperature 100-120°C, time 24-36h, and vacuum degree 25-35Pa. In this context, the vacuum degree refers to the atmospheric pressure minus the absolute pressure.

[0048] In the method of the present application, in step (2), in order to ensure that the metal salt is reduced to the metal element, the carbonization is preferably carried out in a roller kiln.

[0049] In the method of the present application, in step (2), the carbonization is carried out under the protection of an inert atmosphere, and the conditions of the carbonization can include: heating rate 10-20°C / min, temperature 800-1500°C, and time 10-300min. In order to ensure that the metal salt is reduced to the metal element, the conditions of the carbonization preferably include: heating rate 10-15°C / min; temperature 1000-1400°C; and time 80-120min.

[0050] In the present application, in step (2), the inert atmosphere can be a conventional inert atmosphere in the art. In order to ensure that the metal salt can be reduced to the metal element, in the preferred case, the inert atmosphere used is at least one of nitrogen, argon and helium, and most preferably nitrogen, in order to reduce the cost of preparing the material, and preferably the purity of the nitrogen is 99.0-99.9wt%.

[0051] In the method of the present application, in step (2), boric acid and / or thiourea can also be added during the soaking. In order to graphitize the amorphous carbon, in the preferred case, boric acid or thiourea is also added during the soaking.

[0052] In the method of the present application, in order to improve the electronic conductivity of the material, the method also preferably includes: the material obtained in step (2) is washed with an acidic solution and water, filtered and dried.

[0053] In the method of the present application, the acid in the acidic solution can be at least one of hydrochloric acid, sulfuric acid, phosphoric acid and nitric acid. In order to completely wash the catalyst in the biomass-based hard carbon material, the acid in the acidic solution is preferably hydrochloric acid.

[0054] In the method of the present application, in step (2), the concentration of the acidic solution can be 1-14mol / L, and in order to ensure complete removal of the metal, the concentration of the acid in the pickling is preferably 1-6mol / L.

[0055] In the method of the present application, in step (2), in order to reduce the impedance of the material, the water washing is preferably repeated multiple times until neutral.

[0056] In the method of the present application, in step (2), in order to ensure complete washing of the material, the filtration is preferably performed by suction filtration.

[0057] In the method of the present application, in step (2), in order to ensure complete removal of moisture, the drying is preferably performed by vacuum drying, and the drying conditions are preferably as follows: temperature of 90-120°C, time of 24-48h, and vacuum degree of 20-40Pa. In order to achieve partial graphitization of the amorphous carbon, the drying conditions are more preferably as follows: temperature of 100-120°C, time of 24-36h, and vacuum degree of 25-35Pa.

[0058] In some embodiments, the method for preparing the biomass-based hard carbon material of the present application comprises the following steps:

[0059] (1) placing at least one of coconut shell, fruit pits, nut shells, straw, and bamboo in a primary carbonization device, pre-carbonizing under the protection of an inert atmosphere at a temperature of 200-700°C at a temperature increase rate of 10-20°C / min for 10-200min, cooling the obtained carbonized material, and crushing it into particles with a particle size of 10nm or less by a crusher, then performing acid washing by at least one of hydrochloric acid, sulfuric acid, phosphoric acid, and nitric acid at a concentration of 1-14mol / L, then performing water washing until the solution is neutral, then performing centrifugation or filtration on the carbonized material after the acid washing and water washing, and then drying at a temperature of 90-130°C;

[0060] (2) placing the carbonized material obtained after step (1) in a metal salt solution with a concentration of 1-6wt% for 8-24h, the metal salt in the metal salt solution being at least one of water-soluble calcium salt, water-soluble iron salt, water-soluble cobalt salt, water-soluble chromium salt, water-soluble nickel salt, water-soluble magnesium salt, and water-soluble zinc salt, then performing vacuum drying at a temperature of 90-120°C for 24-48h after separating the solid phase, then placing it in a roller hearth kiln, carbonizing under the protection of an inert atmosphere at a temperature of 800-1500°C at a temperature increase rate of 10-20°C / min for 10-300min, then performing cleaning by at least one of hydrochloric acid, sulfuric acid, phosphoric acid, and nitric acid at a concentration of 1-14mol / L, then performing water washing until neutral, and then performing filtration and vacuum drying at a temperature of 90-120°C for 24-48h.

[0061] In some other embodiments, the method for preparing the biomass-based hard carbon material of the present application comprises the following steps:

[0062] (1) placing at least one of coconut shell, fruit core, nut shell, straw and bamboo in a primary carbonization device, pre-carbonizing under the protection of inert atmosphere at a temperature of 300-500℃ with a temperature rising rate of 10-15℃ / min for 20-60min, cooling the carbonized material and crushing it into particles with a particle size of 2-8μm by a pulverizer, acid washing the carbonized material by at least one of hydrochloric acid, sulfuric acid, phosphoric acid and nitric acid with a concentration of 1-6mol / L, washing with water until neutral, centrifuging or filtering the carbonized material after acid washing and water washing, and drying at a temperature of 100-120℃;

[0063] (2) placing the carbonized material obtained after step (1) in a metal salt solution with a concentration of 1-5wt% and boric acid and / or thiourea for 8-15h, the metal salt in the metal salt solution being at least one of water-soluble calcium salt, water-soluble iron salt, water-soluble cobalt salt, water-soluble chromium salt, water-soluble nickel salt, water-soluble magnesium salt and water-soluble zinc salt, vacuum drying at a temperature of 100-120℃ for 24-36h after separating the solid phase by filtration, placing the dried material in a roller hearth kiln, carbonizing under the protection of inert atmosphere at a temperature of 1000-1400℃ with a temperature rising rate of 10-15℃ / min for 80-120min, washing with at least one of hydrochloric acid, sulfuric acid, phosphoric acid and nitric acid with a concentration of 1-14mol / L, washing with water until neutral, filtering and vacuum drying at a temperature of 100-120℃ for 24-36h.

[0064] The application further provides a biomass-based hard carbon material prepared by the above method.

[0065] The application further provides application of the above biomass-based hard carbon material as a battery negative electrode material.

[0066] The application further provides a sodium / potassium ion battery, the negative electrode of which contains the above biomass-based hard carbon material.

[0067] The biomass-based hard carbon material, the preparation method and application thereof and the sodium / potassium ion battery of the application will be further described by examples. The examples are implemented on the premise of the technical scheme of the application, and detailed implementation modes and specific operation processes are given, but the protection scope of the application is not limited to the following examples.

[0068] The experimental methods in the following examples are all conventional methods in the art, unless otherwise specified. The experimental materials used in the following examples are all commercially available, unless otherwise specified.

[0069] Example 1

[0070] (1) The coconut shell was placed in a primary carbonization device, and pre-carbonized at a temperature of 400℃ for 30 min under nitrogen protection at a temperature increasing rate of 10℃ / min. The carbonized material was cooled and then ground into particles with a particle size of 1-20μm by a grinder. The particles were then washed with hydrochloric acid with a concentration of 1 mol / L by centrifugation, washed with water by centrifugation for multiple times until neutral, and then dried at a temperature of 110℃;

[0071] (2) The carbonized material obtained after step (1) was soaked in an iron nitrate solution with a concentration of 1wt% for 8h. The solid phase was separated by filtration and then vacuum dried at a temperature of 110℃ and a vacuum degree of 30Pa for 36h. After drying, the material was placed in a roller kiln and carbonized at a temperature of 1200℃ for 100 min under inert gas protection at a temperature increasing rate of 10℃ / min. The material was washed with hydrochloric acid with a concentration of 1 mol / L, washed with water for multiple times until neutral, filtered, and then vacuum dried at a temperature of 110℃ and a vacuum degree of 30Pa for 36h.

[0072] The biomass-based hard carbon material prepared according to the method of Example 1 was ground and mixed with carbon black and PVDF at a mass ratio of 8:1:1, and then coated on the surface of a copper foil. The copper foil was then vacuum dried at 90℃ for 4h. A sodium metal was used as the counter electrode, a glass fiber was used as the separator, and a NaPF6 solution with a concentration of 1 mol / L was used as the electrolyte. The coin cell was assembled in a glove box, and the type of the coin cell was CR2032. The assembled coin cell was tested on a battery test system. The specific surface area, the first coulombic efficiency, and the powder resistivity were recorded in Table 1. The XRD characterization graph was recorded in Figure 1 , and the EIS graph was recorded in Figure 2 .

[0073] Example 2

[0074] (1) The bamboo was placed in a primary carbonization device, and pre-carbonized at a temperature of 500℃ for 20 min under nitrogen protection at a temperature increasing rate of 20℃ / min. The carbonized material was cooled and then ground into particles with a particle size of 1-20μm by a grinder. The particles were then washed with hydrochloric acid with a concentration of 3 mol / L by filtration, washed with water by filtration for multiple times until neutral, and then dried at a temperature of 120℃;

[0075] (2) The carbonized material obtained after step (1) is immersed in a 1 wt% iron nitrate solution for 15 h, and the solid phase is separated by filtration and vacuum dried at a temperature of 90°C and a vacuum degree of 25 Pa for 48 h. After drying, it is placed in a roller hearth kiln and heated to a temperature of 1500°C at a heating rate of 20°C / min under the protection of an inert atmosphere for carbonization lasting 80 min. It is washed with 3 mol / L hydrochloric acid, washed with water multiple times until neutral, filtered, and vacuum dried at a temperature of 90°C and a vacuum degree of 25 Pa for 48 h.

[0076] The biomass-based hard carbon material prepared according to the method of Example 2 is mixed with carbon black and PVDF at a mass ratio of 8:1:1, and then coated on the surface of a copper foil. After vacuum drying at 90°C for 4 h, a CR2032 button cell is assembled in a glove box using sodium metal as the counter electrode, glass fiber as the separator, and a 1 mol / L NaPF6 solution as the electrolyte. The assembled button cell is tested on a battery test system, and the specific surface area, initial coulombic efficiency, and powder resistivity are recorded in Table 1.

[0077] Example 3

[0078] (1) Coconut shells are placed in a primary carbonization device and pre-carbonized at a temperature of 300°C under the protection of nitrogen at a heating rate of 15°C / min for 60 min. The carbonized material is cooled and then ground into particles with a particle size of 10 nm using a grinder. The particles are washed with 6 mol / L hydrochloric acid by centrifugation, washed with water multiple times by centrifugation until neutral, and then dried at a temperature of 100°C.

[0079] (2) The carbonized material obtained after step (1) is immersed in a 2 wt% iron nitrate solution for 10 h, and the solid phase is separated by filtration and vacuum dried at a temperature of 120°C and a vacuum degree of 35 Pa for 24 h. After drying, it is placed in a roller hearth kiln and heated to a temperature of 1000°C at a heating rate of 15°C / min under the protection of an inert atmosphere for carbonization lasting 120 min. It is washed with 6 mol / L hydrochloric acid, washed with water multiple times until neutral, filtered, and vacuum dried at a temperature of 120°C and a vacuum degree of 35 Pa for 24 h.

[0080] The biomass-based hard carbon material prepared according to the method of Example 3 was mixed with carbon black and PVDF at a mass ratio of 8:1:1, and then coated on the surface of a copper foil. Then, vacuum drying was performed at 90°C for 4h. A sodium metal was used as a counter electrode, a glass fiber was used as a separator, and a NaPF6 solution with a concentration of 1mol / L was used as an electrolyte. A CR2032 button cell was assembled in a glove box, and then tested in a battery test system. The specific surface area, the first coulombic efficiency, and the powder resistivity were recorded in Table 1. The XRD characterization graph was recorded in Figure 1 , and the EIS graph was recorded in Figure 2 .

[0081] Example 4

[0082] (1) Coconut shells were placed in a primary carbonization device, and pre-carbonization was performed under nitrogen protection at a temperature of 500°C with a temperature increase rate of 10°C / min for 30min. The carbonized material was cooled and then crushed into particles with a particle size of 10nm by a crusher. Then, the carbonized material was subjected to acid washing with hydrochloric acid with a concentration of 1mol / L by centrifugation. The carbonized material was washed with water multiple times by centrifugation until it was neutral. Then, the carbonized material was dried at a temperature of 110°C.

[0083] (2) The carbonized material obtained in step (1) was immersed in an iron nitrate solution with a concentration of 3wt% for 8h. The solid phase was separated by filtration, and then vacuum dried at a temperature of 110°C and a vacuum degree of 30Pa for 36h. Then, the carbonized material was placed in a roller hearth kiln and carbonized at a temperature of 1000°C with a temperature increase rate of 10°C / min under inert gas protection for 100min. The carbonized material was washed with hydrochloric acid with a concentration of 1mol / L, and then washed with water multiple times until it was neutral. The carbonized material was filtered and vacuum dried at a temperature of 110°C and a vacuum degree of 30Pa for 36h.

[0084] The biomass-based hard carbon material prepared according to the method of Example 4 was mixed with carbon black and PVDF at a mass ratio of 8:1:1, and then coated on the surface of a copper foil. Then, vacuum drying was performed at 90°C for 4h. A sodium metal was used as a counter electrode, a glass fiber was used as a separator, and a NaPF6 solution with a concentration of 1mol / L was used as an electrolyte. A CR2032 button cell was assembled in a glove box, and then tested in a battery test system. The specific surface area, the first coulombic efficiency, and the powder resistivity were recorded in Table 1. The XRD characterization graph was recorded in Figure 1 , and the EIS graph was recorded in Figure 2 .

[0085] Example 5

[0086] The biomass-based hard carbon material was prepared according to the method of Example 1, except that the iron nitrate solution with a concentration of 1wt% was replaced by an iron nitrate solution with a concentration of 5wt%.

[0087] The biomass-based hard carbon material prepared according to the method of Example 5 was mixed with carbon black and PVDF at a mass ratio of 8:1:1, and then coated on the surface of a copper foil. The coated copper foil was vacuum dried at 90°C for 4h. A sodium metal was used as a counter electrode, a glass fiber was used as a separator, and a NaPF6 solution with a concentration of 1 mol / L was used as an electrolyte. A coin cell was assembled in a glove box, and the type of the coin cell was CR2032. The assembled coin cell was tested in a battery test system. The specific surface area, the first coulombic efficiency, and the powder resistivity were recorded in Table 1. The XRD characterization graph was recorded in Figure 1 , and the EIS graph was recorded in Figure 2 .

[0088] Example 6

[0089] The biomass-based hard carbon material was prepared according to the method of Example 1, except that the immersion in the 1wt% iron nitrate solution for 8h was replaced by immersion in a 1wt% iron nitrate solution and a 3wt% boric acid solution for 8h.

[0090] The biomass-based hard carbon material prepared according to the method of Example 6 was mixed with carbon black and PVDF at a mass ratio of 8:1:1, and then coated on the surface of a copper foil. The coated copper foil was vacuum dried at 90°C for 4h. A sodium metal was used as a counter electrode, a glass fiber was used as a separator, and a NaPF6 solution with a concentration of 1 mol / L was used as an electrolyte. A coin cell was assembled in a glove box, and the type of the coin cell was CR2032. The assembled coin cell was tested in a battery test system. The specific surface area, the first coulombic efficiency, and the powder resistivity were recorded in Table 1.

[0091] Example 7

[0092] The biomass-based hard carbon material was prepared according to the method of Example 1, except that the immersion in the 1wt% iron nitrate solution for 8h was replaced by immersion in a 1wt% iron nitrate solution and a 3wt% thiourea solution for 8h.

[0093] The biomass-based hard carbon material prepared according to the method of Example 7 was mixed with carbon black and PVDF at a mass ratio of 8:1:1, and then coated on the surface of a copper foil. The coated copper foil was vacuum dried at 90°C for 4h. A sodium metal was used as a counter electrode, a glass fiber was used as a separator, and a NaPF6 solution with a concentration of 1 mol / L was used as an electrolyte. A coin cell was assembled in a glove box, and the type of the coin cell was CR2032. The assembled coin cell was tested in a battery test system. The specific surface area, the first coulombic efficiency, and the powder resistivity were recorded in Table 1.

[0094] Example 8

[0095] The biomass-based hard carbon material prepared according to the method of Example 1 was mixed with carbon black and PVDF at a mass ratio of 8:1:1, and then coated on the surface of a copper foil. The mixture was vacuum dried at 90°C for 4h. A potassium metal was used as a counter electrode, a glass fiber was used as a separator, and a KPF6 solution with a concentration of 1mol / L was used as an electrolyte. A CR2032 button cell was assembled in a glove box, and the assembled button cell was tested on a battery test system. The specific surface area, the first coulombic efficiency, and the powder resistivity were recorded in Table 1.

[0096] Comparative Example 1

[0097] The biomass-based hard carbon material was prepared according to the method of Example 1, except that the carbonized material obtained after step (1) was not soaked in a 1wt% iron nitrate solution. The results are shown in Table 1.

[0098] Comparative Example 2

[0099] The biomass-based hard carbon material was prepared according to the method of Example 2, except that the carbonized material obtained after step (1) was not soaked in a 1wt% iron nitrate solution. The results are shown in Table 1.

[0100] Table 1

[0101]

[0102] As can be seen from the results in Table 1 and Figure 2 It can be seen that the powder resistivity and the impedance of the biomass-based hard carbon material according to the embodiments of the present application are small, indicating that the sodium ion insertion resistance is small, and the cycle performance and rate performance of the battery are good. The specific surface area and the first coulombic efficiency do not change with the graphitization degree of the hard carbon material. The electronic conductivity is increased, and the impedance is reduced without affecting the first coulombic efficiency and the specific surface area, indicating that the cost of the present application is low, and the performance-price ratio is high.

[0103] As can be seen from Figure 1 It can be seen that the internal partial structure of the biomass-based hard carbon material according to the present application is catalytically graphitized, and the graphitization degree increases with the increase of the concentration of the metal salt solution.

[0104] The preferred embodiments of the present application have been described in detail above, but the present application is not limited thereto. Within the technical concept of the present application, various simple modifications can be made to the technical solutions of the present application, including the combination of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as disclosed by the present application, and fall within the protection scope of the present application.

Claims

1. A method for producing a biomass-based hard carbon material, characterized by, The method comprises the following steps: (1) pre-carbonizing the biomass, and then sequentially crushing, acid washing and water washing the obtained carbonized material after cooling; (2) soaking the carbonized material obtained after step (1) in a metal salt solution, and then drying and carbonizing; wherein the pre-carbonization temperature is lower than the carbonization temperature; in step (2), the metal salt in the metal salt solution is at least one of water-soluble calcium salt, water-soluble iron salt, water-soluble cobalt salt, water-soluble chromium salt, water-soluble magnesium salt and water-soluble zinc salt; in step (2), boric acid and / or thiourea are added during the soaking.

2. The method of claim 1, wherein, The difference between the pre-carbonization temperature and the carbonization temperature is 500-1000℃.

3. The method according to claim 1 or 2, characterized in that, In step (1), the pre-carbonization is carried out under the protection of inert atmosphere, and the pre-carbonization conditions include: the temperature rising rate is 10-20℃ / min, the temperature is 200-700℃, and the time is 10-200min.

4. The method according to claim 1 or 2, characterized in that, In step (1), the biomass is at least one of coconut shell, fruit core, nut shell, straw and bamboo.

5. The method of claim 1, wherein, In step (2), the concentration of the metal salt solution is 1-6wt%.

6. The method of claim 1 or 2, wherein, In step (2), the soaking time is 8-24h.

7. The method according to claim 1 or 2, characterized in that, In step (2), the carbonization is carried out under the protection of inert atmosphere, and the carbonization conditions include: the temperature rising rate is 10-20℃ / min, the temperature is 800-1500℃, and the time is 10-300min.

8. The method of claim 1, 2, or 5, wherein, The method further comprises: cleaning, filtering and drying the material obtained in step (2) with an acidic solution and water.

9. The method of claim 8, wherein, The acid in the acidic solution is at least one of hydrochloric acid, sulfuric acid, phosphoric acid and nitric acid.

10. A biomass-based hard carbon material prepared by the method of any one of claims 1-9.

11. Use of the biomass-based hard carbon material of claim 10 as a battery anode material.

12. A sodium / potassium-ion battery, characterized in that, The anode of the sodium / potassium ion battery contains the biomass-based hard carbon material of claim 10.

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