A porous carbon material containing an alkali metal element and a method for producing the same

Abstract

The present application relates to a kind of porous carbon material containing alkali metal element and its preparation method.The preparation method includes: (1) carbon material powder and transition metal salt solution are mixed, stirring, dry and placed in inert atmosphere high-temperature treatment, and the carbon material loaded with transition metal particles is prepared;(2) the carbon material loaded with transition metal particles obtained is mixed with alkali metal-containing basic substance, stirring, drying, with inert gas as carrier gas, and after being calcined by reaction gas, in-situ generation of alkali metal element on the surface or interlayer of the carbon material loaded with transition metal particles;(3) the carbon material obtained in step (2) is washed by water, and treated by oxidizing agent to obtain the porous carbon material containing alkali metal element.

Description

Technical Field

[0001] This invention belongs to the technical field of active materials for carbon-based batteries, specifically relating to a porous carbon material containing alkali metal elements produced by etching with oxidizing gas and alkaline substances containing alkali metals using a transition metal salt-assisted method. Background Technology

[0002] With the increasing demand for energy materials in modern times, carbon materials are widely used in various fields due to their excellent electrical conductivity, readily available raw materials, and ease of modification. Porous carbon, as a type of material with carbon as its basic framework and an interconnected or closed network of pores, is widely used in the field of energy storage and conversion.

[0003] Currently, the main methods for preparing porous carbon are activation and template methods. Activation methods primarily use KOH, H3PO4, water vapor, and carbon dioxide, which can produce porous carbon materials with large specific surface areas, but the pore size is difficult to control (Chinese Patent Publication No. CN115636413A). While template methods can control the pore structure in an orderly manner, the production cost of templates is high, making industrialization difficult (Chinese Patent Publication No. CN115285991A). Creating larger specific surface areas is no longer a difficult problem, but the above activation conditions are not universally applicable to different materials such as graphite, hard carbon, and soft carbon, thus limiting their application. Zhang Tao et al.'s "A Method for Preparing Porous Carbon Materials by Ruthenium Particle-Assisted Etching in a Strong Alkaline Environment" (Chinese Patent Publication No. CN111732102A) utilizes transition metal particles as a catalyst and alkaline substances as an etchant to modify and etch carbon materials, preparing carbon materials with easily controllable pore size and distribution. Meanwhile, "A Lithium-Rich Porous Graphite Material and Its Preparation Method and Application" (Chinese Patent Publication No. CN115483371A) developed lithium-rich graphite with abundant deep and large pore structures. However, this method is only suitable for lithium enrichment and pore formation of graphite materials, and the process cost is limited by the high price of lithium alkali compounds and the high-temperature energy consumption of chemical activation, making it unsuitable for large-scale production. Activation using only strong alkali will be limited by the alkali / carbon mixed process, making it difficult to obtain a uniformly distributed pore structure. At the same time, the large amount of alkali also causes problems in the subsequent processing. Summary of the Invention

[0004] In view of the shortcomings of the existing technology, the purpose of this invention is to provide a low-cost and easy-to-produce porous carbon material containing alkali metal elements and its preparation method.

[0005] In a first aspect, the present invention provides a method for preparing porous carbon materials containing alkali metal elements, comprising: (1) The carbon material powder and the transition metal salt solution are mixed, stirred, dried and then subjected to high temperature treatment under an inert atmosphere to obtain carbon material loaded with transition metal particles. (2) The carbon material loaded with transition metal particles is mixed with an alkaline substance containing alkali metal, stirred and dried, and an inert gas is used as a carrier gas to introduce a reaction gas. After calcination, alkali metal elements are generated in situ on the surface or between the layers of the carbon material loaded with transition metal particles. (3) The carbon material obtained in step (2) is washed with water and treated with an oxidant to obtain the porous carbon material containing alkali metal elements.

[0006] Preferably, the carbon material is at least one selected from graphite, hard carbon, and soft carbon; the particle size of the carbon material is 3–50 μm, more preferably 5–10 μm; and the specific surface area of ​​the carbon material is 2–2000 m². 2 / g.

[0007] Preferably, the alkali metal element is potassium or lithium; the alkali metal element is generated in situ on the surface or between layers of the carbon material after calcination treatment of an alkaline substance containing alkali metal and a carbon material loaded with transition metal particles.

[0008] Preferably, in step (1), the transition metal salt solution is an organic or / or inorganic salt of a transition metal element, wherein the organic salt is at least one of the following: formate, acetate, ethoxide, citrate, and acetylacetone of the transition metal element; the inorganic salt is at least one of the following: hydrochloride, sulfate, nitrate, phosphate, gold hypophosphite, chlorate, perchlorate, and aminosulfonate of the transition metal element; the transition metal element is at least one of Ni, Cu, Fe, Co, Mn, Mo, Ru, Au, and Pt; the solvent of the transition metal salt solution is at least one of water, ethanol, and acetone; and the molar ratio of the transition metal salt to the carbon material is 1:(10-100), preferably 1:(30-50).

[0009] Preferably, in step (1), the drying temperature is 60-90°C and the time is 1-20 hours; the inert atmosphere is at least one of argon, nitrogen, helium, carbon monoxide, and hydrogen; the high-temperature treatment temperature is 400-800°C and the time is 1-10 hours; the heating rate is 1-20°C / min; preferably, the high-temperature treatment temperature is 500-700°C, the holding time is 1-4 hours, and the heating rate is 5-10°C / min.

[0010] Preferably, in step (2), the alkaline substance containing alkali metal is at least one of lithium hydroxide, potassium hydroxide, potassium carbonate, and lithium carbonate; the concentration of the alkaline substance containing alkali metal is 1 to 6 mol / L; and the molar ratio of the alkaline substance containing alkali metal to carbon in the carbon material loaded with transition metal particles is 1:10 to 10:1.

[0011] Preferably, in step (2), the drying temperature is 80-120°C and the time is 1-4 hours.

[0012] Preferably, in step (2), the parameters of the calcination treatment are as follows: calcination temperature is 400-1000℃, time is 2-16 hours, heating rate is 1-20℃ / min, carrier gas is at least one of argon, nitrogen, and helium, and flow rate is 100-500 ml / min / g; reaction gas is at least one of water vapor, carbon dioxide, and oxygen, gas intake is 10-200 ml / min / g, and the volume ratio of reaction gas to total gas is 10-100%; preferably, the calcination temperature is 450-850℃, time is 2-8 hours, heating rate is 5-10℃ / min, carrier gas flow rate is 100-200 ml / min / g, gas intake is 50-200 ml / min / g, and the volume ratio of reaction gas to total gas is 20-50%.

[0013] Preferably, in step (3), the oxidant is at least one of ferric chloride, potassium dichromate, hydrogen peroxide, sulfuric acid, and nitric acid; the oxidant is dissolved in water or ethanol to form an oxidizing solution; and the concentration of the oxidizing solution is 0.1 to 5 mol / L.

[0014] Preferably, in step (3), the oxidant treatment specifically involves dispersing the washed carbon material in the oxidant solution at 40–80°C for 4–20 hours.

[0015] In a second aspect, the present invention provides a porous carbon material containing alkali metal, the porous carbon material comprising macropores, micropores, and alkali metal elements distributed on the surface or between layers of the porous carbon material; the diameter of the macropores is 100 nm to 2 μm, and the diameter of the micropores is 1 to 5 nm.

[0016] Beneficial effects:

[0017] (1) The etching agent used in this invention contains alkali metal elements. Under the catalytic action of transition metal particles, the alkaline substances containing alkali metals are highly reactive with carbon materials, which can generate defects in the carbon materials that can accommodate the reversible insertion and extraction of alkali metal ions. During the physicochemical etching process, the alkali metal elements will combine with the broken bonds on the surface of the active material used in carbon-based batteries, passivate the surface defects, reduce the irreversible capacity loss in the first cycle of the battery, and improve the coulombic efficiency in the first cycle.

[0018] (2) Under the catalysis of transition metal particles, the reaction temperature of oxidizing gas and alkali-containing alkaline substances with carbon materials is further reduced. Compared with other methods that use a single alkali-containing alkaline substance to activate carbon materials, introducing oxidizing gas reduces the amount of alkaline etchant used in the chemical activation process, thus reducing production costs. Furthermore, compared to the solid-solid contact of alkali-containing alkaline substances during the reaction, the oxidizing gas produces a gas-solid contact, resulting in more uniform activation. This invention achieves the same or similar effects while reducing the activation temperature or activation time, thereby reducing production energy consumption. Attached Figure Description

[0019] Figure 1 This is a scanning electron microscope image of the lithium-containing porous graphite material in Embodiment 1 of the present invention; Figure 2 The pore size distribution curve of the lithium-containing porous graphite material in Example 1 of this invention; Figure 3 This is a graph showing the elemental content of the lithium-containing porous graphite material in Example 1 of the present invention; Figure 4 The constant current charge-discharge curve of the lithium-ion battery assembled with lithium-containing porous graphite material in Example 1 of this invention; Figure 5 This is a scanning electron microscope image (without removing nickel) of the potassium-containing porous hard carbon material in Example 4 of the present invention; Figure 6 The pore size distribution curve of the potassium-containing porous hard carbon material in Example 4 of this invention; Figure 7 This is a graph showing the elemental content of the potassium-containing porous hard carbon material in Example 4 of the present invention; Figure 8 The constant current charge-discharge curve of the sodium-ion battery assembled with potassium-containing porous hard carbon material in Example 4 of this invention; Figure 9 This is a scanning electron microscope image of the porous graphite material in Comparative Example 1 of the present invention after activation without reactive gas. Figure 10 The constant current charge-discharge curve of the lithium-ion battery assembled from porous graphite material without reactive gas activation in Comparative Example 1 of this invention. Detailed Implementation

[0020] To further illustrate the invention's content, features, and practical effects, the invention will be described in detail below with reference to embodiments. It should be noted that the modification methods of the invention are not limited to these specific implementation methods. Equivalent substitutions and modifications made by those skilled in the art based on their reading of the invention's content, without departing from the spirit and essence of the invention, are also within the scope of protection claimed by this invention.

[0021] In this invention, alkali-containing porous carbon materials with macropores and mesopores are etched by alkaline substances containing alkali metals under the catalysis of transition metal particles and reactive gases. The pore diameters range from 1 nm to 2 μm, with macropores having diameters of 100 nm to 2 μm and mesopores having diameters of 1 nm to 5 nm. The alkali metal is generated in situ on the surface or between layers of the carbon material after the alkaline substance containing the alkali metal reacts with carbon. During the chemical etching process, the alkaline substance containing the alkali metal increases the alkali metal element within the carbon material; the specific alkali metal element and the carbon material are related to the selection of the battery system.

[0022] The following is an exemplary description of the preparation method of porous carbon materials containing alkali metal elements provided by the present invention.

[0023] Preparation of carbon materials loaded with transition metal particles. (1) Mix carbon material powder and transition metal salt solution, stir and dry at 60-90℃ for 1-20h to obtain precursor A; (2) Transfer precursor A to crucible, place it under an inert atmosphere for high-temperature treatment, and after natural cooling, obtain carbon material loaded with transition metal particles. The purpose of step (1) is to achieve uniform coating of carbon material powder with metal salt by liquid phase method, so as to achieve uniform distribution of metal particles during pyrolysis.

[0024] In an optional embodiment, the carbon material is at least one of graphite, hard carbon, and soft carbon; the particle size of the carbon material can be 3 to 50 μm, preferably 5 to 10 μm.

[0025] In optional embodiments, the transition metal salt solution is an organic or / and inorganic salt of a transition metal element. The organic salt is at least one of the following: formate, acetate, ethoxide, citrate, and acetylacetonate of the transition metal element. The inorganic salt is at least one of the following: hydrochloride, sulfate, nitrate, phosphate, gold hypophosphite, chlorate, perchlorate, and aminosulfonate of the transition metal element. The transition metal element is at least one of Ni, Cu, Fe, Co, Mn, Mo, Ru, Au, and Pt. The solvent for the transition metal salt solution is at least one of water, ethanol, and acetone. Preferably, the volume ratio of water to ethanol in the solvent of the transition metal salt solution is 9:1. The reason for using a mixed solution of water and ethanol as the solvent in this invention is that ethanol can effectively improve the wettability of the aqueous solution with the carbon material, which is more conducive to the loading of the metal. The molar ratio of the transition metal salt to the carbon material can be 1:(10-100), preferably 1:40.

[0026] In an optional embodiment, the inert atmosphere is at least one of argon, nitrogen, helium, carbon monoxide, and hydrogen; the high-temperature treatment temperature can be 400–800°C, the time can be 1–10 hours, and the heating rate can be 1–20°C / min; preferably, the high-temperature treatment temperature is 500–700°C, the holding time is 1–4 hours, and the heating rate is 5–10°C / min.

[0027] Alkali metal elements are generated in situ on the surface or between layers of carbon materials loaded with transition metal particles. The resulting carbon material loaded with transition metal particles is mixed with a small amount of alkaline substance containing alkali metals, stirred, dried, and then transferred to a crucible. The crucible is placed in a vacuum tube furnace, and an inert gas is used as the carrier gas. A reaction gas is introduced, and after calcination, alkali metal elements are generated in situ on the surface or between layers of the carbon material. Specifically, under the catalysis of the transition metal, the alkaline substance containing alkali metals and the reaction gas can construct deep pores and through-pores in the carbon material, whereas without the transition metal, no corresponding deep pore and through-pore structures are formed. Simultaneously, the transition metal catalysis lowers the reaction temperature between the alkaline substance containing alkali metals and the reaction gas with carbon, and increases the residual amount of alkali metal ions.

[0028] In optional embodiments, the alkaline substance containing alkali metal is at least one of lithium hydroxide, potassium hydroxide, potassium carbonate, and lithium carbonate; the concentration of the aqueous solution of the alkaline substance containing alkali metal can be 1–6 mol / L; the molar ratio of the alkaline substance containing alkali metal to carbon in the carbon material loaded with transition metal particles can be 1:10–10:1, preferably 1:10–1:5. The function of the alkaline substance containing alkali metal in this invention is as follows: the alkaline substance containing alkali metal acts as an oxidant, reacting with carbon at high temperature to form carbonates and gases such as carbon monoxide and carbon dioxide, thereby etching the carbon material.

[0029] In an optional embodiment, the linear velocity of the stirring can be 0.5 to 3 m / s; the drying temperature can be 80 to 120°C, and the time can be 1 to 4 hours.

[0030] In an optional embodiment, the crucible used is at least one of corundum crucible, magnesium oxide crucible, nickel crucible, and platinum crucible; preferably a nickel crucible. The reason for using a nickel crucible in this invention is that it can effectively resist alkali corrosion and can be reused in the production process without being severely damaged.

[0031] In an optional embodiment, the parameters of the calcination treatment may be as follows: calcination temperature of 400–1000°C, time of 2–16 hours, and heating rate of 1–20°C / min; the carrier gas is at least one of argon, nitrogen, and helium, with a flow rate of 100–500 ml / min / g; the reactant gas is at least one of water vapor, carbon dioxide, and oxygen, with an intake flow rate of 10–200 ml / min / g, and the volume ratio of the reactant gas to the total gas is 10–100%. Preferably, the calcination temperature is 450–850°C, time of 2–8 hours, heating rate of 5–10°C / min, carrier gas flow rate of 100–200 ml / min / g, intake flow rate of 50–200 ml / min / g, and the volume ratio of the reactant gas to the total gas is 20–50%. Introducing a reaction gas makes the oxidation of carbon materials more uniform during the reaction process and lowers the reaction temperature. Gas activation is inexpensive and more economical in industrial production. At the same time, physicochemical etching can preserve the properties that are beneficial to electrochemical devices.

[0032] Porous carbon materials containing alkali metal elements were prepared. The carbon material containing alkali metal elements and loaded with transition metal particles was washed with deionized water, then etched in an oxidizing solution. Finally, the material was washed a second time with deionized water and dried to obtain the porous carbon material containing alkali metal elements.

[0033] In an optional embodiment, the oxidizing solution may be at least one of ferric chloride, potassium dichromate, hydrogen peroxide, sulfuric acid, nitric acid in ethanol or aqueous solution, and the concentration of the oxidizing solution is 0.1–5 mol / L. The etching temperature may be 40–80°C, and the etching time may be 4–20 h.

[0034] The porous carbon material containing alkali metal elements prepared by this invention is free of impurities, and the final product is porous carbon particles with abundant macropores, micropores and mesopores and good pore size distribution.

[0035] In the method for preparing porous carbon materials containing alkali metal elements provided by the present invention, the reactions that occur in step (1) are: for example: NiCl2 + H2O + C = Ni + 2HCl + CO

[0036] The reactions that occur in step (2) are: C+H2O=CO+H2; 6LiOH+2C=2Li2CO3+3H2+2Li; 2Li+2H2O=H2+2LiOH

[0037] Step (3) involves oxidation and water washing to remove the metal, for example: acid washing (M is the loaded metal) M + xH + =M x+ +H2

[0038] The following examples further illustrate the present invention in detail. It should also be understood that the following examples are only for further explanation of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention are within the scope of protection of the present invention. The specific process parameters, etc., in the following examples are merely examples within a suitable range; that is, those skilled in the art can make appropriate selections within the appropriate range based on the description herein, and are not intended to be limited to the specific values ​​in the examples below.

[0039] Example 1

[0040] (1) Dissolve 0.311 g nickel acetate tetrahydrate (0.00125 mol) in a mixture of 4 ml water and 1 ml ethanol, add 0.6 g graphite powder (0.05 mol), stir and dry at 80 °C for 1 h, then place in a covered corundum crucible and place in a vacuum tube furnace for high-temperature treatment under an argon atmosphere. The heating program is set as follows: heating rate 5 °C / min, heating to 600 °C in 2 h, holding for 2 h and then cooling naturally to obtain precursor A1.

[0041] (2) The precursor A1 obtained in step (1) was mixed with 10 mL of 1 mol / L lithium hydroxide aqueous solution (0.01 mol), and 2 mL of anhydrous ethanol was added. The mixture was stirred and dried at 100 °C for 1 h (stirring speed was 0.5 m / s). The resulting material was then transferred to a nickel crucible and placed in a vacuum tube furnace. Argon was used as the carrier gas at a flow rate of 120 mL / min / g, and water vapor was used as the reaction gas at an inlet flow rate of 50 mL / min / g. The calcination treatment was carried out. The heating program was set as follows: heating rate 5 °C / min, heating to 700 °C in 140 min, holding at 700 °C for 3 h, and then naturally cooled to obtain precursor B1.

[0042] (3) The alkaline substances remaining in the precursor B1 were washed away with deionized water, and then placed in 20 mL of 0.1 mol / L nitric acid ethanol solution and heated to 60 °C for 4 h. After the acid washing was completed, the mixture was filtered to separate the acid solution, and then the graphite material was washed three times with deionized water and dried to obtain lithium-containing porous graphite material.

[0043] Performance testing was conducted on a coin-type lithium-ion battery. The battery assembly method was as follows: a lithium sheet was used as the positive electrode, lithium-containing porous graphite material (as in Example 1) was used as the negative electrode, Celgard 2300 was used as the separator, and the electrolyte was a DOL solution containing 0.4M LiNO3 and 0.6M LiTFSI. LiNO3 is lithium nitrate, LiTFSI is lithium bis(trifluoromethanesulfonate)imide, and DOL is 1,3-dioxolane. During testing, the temperature was room temperature, constant current charge-discharge was used, the test current was 0.1C, and the rate test was 6C.

[0044] Figure 1 The image shows a SEM image of the lithium-containing porous graphite material prepared in Example 1. As can be seen from the image, obvious pores appear on the surface and inside of the graphite material.

[0045] Figure 2 The figure shows the pore size distribution curve of the lithium-containing porous graphite material prepared in Example 1. As can be seen from the figure, the specific surface area of ​​the porous graphite material after lithium hydroxide and water vapor treatment is 2-3 m². 2 / g, and hierarchical pore sizes below 5nm can be observed.

[0046] Figure 3 The graph shows the elemental content of the lithium-containing porous graphite material in Example 1. After integrating the elemental content, the molar percentage of Li was 3.3%, confirming the presence of lithium and reducing irreversible losses caused by excessive defects during lithium-ion battery cycling.

[0047] Figure 4 The figure shows the constant current charge-discharge curves of the lithium-ion battery assembled from lithium-containing porous graphite material in Example 1. As can be seen from the figure, due to the presence of lithium and the abundant pores in the graphite, the coulombic efficiency of the graphite sample after pore formation with water vapor and lithium hydroxide remained at 90.3% in the first cycle, without significant negative reactions caused by the newly formed pores. Meanwhile, at a 6C rate test, the reversible capacity was 362 mAh / g.

[0048] Example 2

[0049] The preparation process of the lithium-containing graphite material in Example 2 is the same as in Example 1, except that: in step (2), the reaction gas is oxygen, the gas inlet is 50 ml / min / g, argon is used as the carrier gas, the flow rate is 100 mL / min / g, and the heating program is set as follows: heating rate 5℃ / min, heating to 450℃ in 150 min, holding for 2 h and then naturally cooling to obtain precursor B2. The subsequent water washing and acid washing treatments are the same as in Example 1.

[0050] Example 3

[0051] The preparation process of the lithium-containing graphite material in Example 3 is the same as in Example 1, except that: in step (2), the reaction gas is carbon dioxide, the gas inlet is 50 ml / min / g, and argon is used as the carrier gas with a flow rate of 100 mL / min / g. The heating program is set as follows: heating rate 5℃ / min, heating to 850℃, holding for 3 hours and then naturally cooling to obtain precursor B3. The subsequent water washing and acid washing treatments are the same as in Example 1.

[0052] Example 4

[0053] In Example 1, the graphite was replaced with coconut shell biomass hard carbon to prepare potassium-containing porous hard carbon material. The specific steps are as follows:

[0054] (1) Dissolve 0.366 g of nickel acetylacetonate (0.00125 mol) in 5 ml of ethanol mixture, add 0.6 g of hard carbon (0.05 mol), stir and dry at 60 °C for 0.5 h, then place in a covered corundum crucible and place in a vacuum tube furnace for high-temperature treatment under an argon atmosphere. The heating program is set as follows: heating rate 5 °C / min, heating to 500 °C in 2 h, holding at 500 °C for 2 h, and then naturally cooling to obtain precursor A4.

[0055] (2) The precursor A4 obtained in step (1) was mixed with 10 mL of 1 mol / L potassium hydroxide aqueous solution (0.01 mol), and 2 mL of anhydrous ethanol was added. The mixture was stirred and dried at 100 °C for 1 h (stirring speed was 0.5 m / s). The resulting material was then transferred to a nickel crucible and placed in a vacuum tube furnace. Argon was used as the carrier gas at a flow rate of 100 mL / min / g, and water vapor was used as the reaction gas at an inlet flow rate of 50 mL / min / g. The heating program was set as follows: heating rate 5 °C / min, heating to 650 °C in 2.5 h, holding at 650 °C for 2 h, and then naturally cooled to obtain precursor B4.

[0056] (3) The alkaline substances remaining in the precursor B4 were washed away with deionized water, and then placed in 20 mL of 0.1 mol / L nitric acid ethanol solution and heated to 60 °C for 4 h. After dissolution, the mixture was filtered to separate the acid solution, and then the graphite was washed three times with deionized water and dried to obtain potassium-containing porous hard carbon material.

[0057] Performance tests were conducted on a coin-type sodium-ion battery. The battery assembly method was as follows: a sodium metal sheet was used as the positive electrode, the potassium-containing porous hard carbon material (as in Example 4) was used as the negative electrode, a Whatman glass fiber membrane was used as the separator, and a solution of diethylene glycol dimethyl ether containing 1 mol / L NaPF6 was used as the electrolyte. The battery was assembled into a CR2032 type in an argon-protected glove box. During the test, the temperature was room temperature, constant current charge and discharge was used, and the test current was 0.1C.

[0058] Figure 5 This is a SEM image of the potassium-containing porous hard carbon material prepared in Example 4. The nickel particles have not been removed from this image. It can be seen that there are obvious deep pores and large pores where transition metal particles are present. Since hard carbon is more reactive than graphite, etching results in a greater distribution of pores.

[0059] Figure 6 The figure shows the pore size distribution curve of the potassium-containing porous hard carbon material in Example 4. By controlling the reaction conditions, the specific surface area is significantly increased compared to porous graphite and raw hard carbon, reaching a maximum of 2000 m². 2 / g, in addition to macropores and deep pores, pore size distribution tests also showed that the increase in specific surface area was mainly due to the increase in micropores caused by activation.

[0060] Figure 7 The diagram shows the elemental content of the potassium-containing porous hard carbon material in Example 4. C and O are elements naturally present in hard carbon, aluminum is the aluminum foil substrate used in the test, and potassium is the potassium remaining in the hard carbon after etching.

[0061] Figure 8 The constant current charge-discharge curves of the sodium-ion battery assembled with potassium-containing porous hard carbon material in Example 4 show that the first-cycle efficiency of our hard carbon is significantly improved. This is because oxygen functional groups such as carbonyl and hydroxyl groups in hard carbon, as well as some defect sites on carbon, can serve as anchoring sites for cations. Therefore, K + Defect sites in hard carbon are passivated to reduce the impact of oxygen functional groups and other defects on Na. + Irreversible adsorption.

[0062] Example 5

[0063] The preparation process of the potassium-containing porous hard carbon material in Example 5 is the same as in Example 4, except that: in step (2), the reaction gas is oxygen, the inlet gas flow rate is 50 ml / min / g, argon is used as the carrier gas, the flow rate is 100 mL / min / g, and the heating program is set as follows: heating rate 5℃ / min, heating to 450℃ in 90 min, holding for 2 h and then naturally cooling to obtain precursor B5. The subsequent water washing and acid washing treatment methods are the same as in Example 4.

[0064] Example 6

[0065] The preparation process of the potassium-containing porous hard carbon material in Example 6 is the same as in Example 4, except that the reaction gas in step (2) is carbon dioxide, and the gas inlet is 100 mL / min / g. The heating program is set as follows: heating rate 5℃ / min, heating to 800℃ in 160 min, holding at the temperature for 2 h and then naturally cooling to obtain precursor B6. The subsequent water washing and acid washing treatments are the same as in Example 4.

[0066] Comparative Example 1

[0067] The preparation process of the lithium metal porous graphite material in Comparative Example 1 is the same as that in Example 1, except that no reaction gas is introduced in step (2).

[0068] Performance testing was conducted on a coin-type lithium-ion battery. The battery assembly method was as follows: a lithium sheet was used as the positive electrode, lithium-containing porous graphite material (as in Example 1) was used as the negative electrode, Celgard 2300 was used as the separator, and the electrolyte was a 1:1 solution of DOL containing 1M LiNO3 (lithium nitrate), LiTFSI (lithium bis(trifluoromethanesulfonate)imide), and DOL (1,3-dioxolane). During the test, the temperature was room temperature, constant current charge-discharge was used, the test current was 0.1C, and the rate test was 6C.

[0069] Figure 9 The image shows a scanning electron microscope image of the porous graphite material in Comparative Example 1 after activation without reactive gas. As can be seen from the image, without the introduction of reactive gas, a small amount of alkaline etchant cannot etch micron-sized pores on the surface of the carbon material. Only a slight reaction can be observed on the end face of the graphite, indicating an incomplete reaction.

[0070] Figure 10 The constant current charge-discharge curves of the lithium-ion battery assembled from porous graphite material without reactive gas activation in Comparative Example 1 are shown in the figure. As can be seen from the figure, without the introduction of reactive gas, the small amount of alkaline etchant caused more irreversible loss in the first cycle of the battery due to its insufficient etching reaction. The capacity of the first cycle was only 83% coulombic efficiency, and its capacity was 310 mAh / g under 6C charge-discharge conditions.

Claims

1. A method for preparing a porous carbon material containing alkali metal elements, characterized in that, include: (1) The carbon material powder and the transition metal salt solution are mixed, stirred, dried and then subjected to high temperature treatment under an inert atmosphere to obtain carbon material loaded with transition metal particles; the transition metal element in the transition metal salt solution is at least one of Ni, Cu, Fe, Co and Ru; the temperature of the high temperature treatment is 400 to 800°C and the time is 1 to 10 hours. (2) The carbon material loaded with transition metal particles is mixed with an alkaline substance containing alkali metal, stirred and dried. An inert gas is used as the carrier gas, and a reaction gas is introduced. After calcination, an alkali metal element is generated in situ on the surface or between the layers of the carbon material loaded with transition metal particles. The alkali metal element is at least one of potassium and lithium. The alkali metal element is generated in situ on the surface or between the layers of the carbon material after calcination of the alkaline substance containing alkali metal and the carbon material loaded with transition metal particles. The carbon material is at least one of graphite and hard carbon. The particle size of the carbon material is 3-50 μm. The concentration of the alkaline substance containing alkali metal is 1-6 mol / L. The molar ratio of the alkaline substance containing alkali metal to carbon in the carbon material loaded with transition metal particles is 1:10-10:

1. The reaction gas is at least one of water vapor, carbon dioxide, and oxygen. The calcination temperature is 400-1000℃ and the time is 1-16 hours. (3) The carbon material obtained in step (2) is washed with water and treated with an oxidant to obtain the porous carbon material containing alkali metal elements; the oxidant is at least one of ferric chloride, potassium dichromate, hydrogen peroxide, sulfuric acid and nitric acid.

2. The preparation method according to claim 1, characterized in that, The particle size of the carbon material is 5-10 μm; the specific surface area of the carbon material is 2-2000 m 2 / g.

3. The preparation method according to claim 1 or 2, characterized in that, In step (1), the transition metal salt solution is an organic salt or / inorganic salt of a transition metal element, wherein the organic salt is at least one of the following: formate, acetate, ethanolate, citrate, acetylacetone salt of the transition metal element; and the inorganic salt is at least one of the following: hydrochloride, sulfate, nitrate, phosphate, gold hypophosphite, chlorate, perchlorate, aminosulfonate of the transition metal element. The solvent for the transition metal salt solution is at least one of water, ethanol, and acetone; The molar ratio of the transition metal salt to the carbon material is 1:(10-100).

4. The preparation method according to claim 3, characterized in that, The molar ratio of the transition metal salt to the carbon material is 1:(30-50).

5. The preparation method according to claim 1, characterized in that, In step (1), the drying temperature is 60-90°C and the time is 1-20 hours; the inert atmosphere is at least one of argon, nitrogen, helium, carbon monoxide, and hydrogen; and the heating rate is 1-20°C / min.

6. The preparation method according to claim 5, characterized in that, The high-temperature treatment is performed at a temperature of 500–700°C, with a holding time of 1–4 hours and a heating rate of 5–10°C / min.

7. The preparation method according to claim 1, characterized in that, In step (2), the alkaline substance containing alkali metal is at least one of lithium hydroxide, potassium hydroxide, potassium carbonate and lithium carbonate.

8. The preparation method according to claim 1, characterized in that, In step (2), the drying temperature is 80-120°C and the time is 1-4 hours.

9. The preparation method according to claim 1, characterized in that, In step (2), the heating rate of the calcination treatment is 1-20℃ / min; the carrier gas is at least one of argon, nitrogen, and helium, the flow rate is 100-500ml / min / g; the gas intake is 10-200ml / min / g, and the volume ratio of the reaction gas to the total gas is 10-100%.

10. The preparation method according to claim 9, characterized in that, The parameters for the calcination treatment are as follows: calcination temperature is 450-850℃, time is 2-8 hours, heating rate is 5-10℃ / min, carrier gas flow rate is 100-200ml / min / g, gas intake is 50-200ml / min / g, and the volume ratio of reaction gas to total gas is 20-50%.

11. The preparation method according to claim 1, characterized in that, In step (3), the oxidant is dissolved in water or ethanol to form an oxidizing solution; the concentration of the oxidizing solution is 0.1 to 5 mol / L.

12. The preparation method according to claim 1, characterized in that, In step (3), the oxidant treatment specifically involves etching the water-washed carbon material by placing it in the oxidant solution at 40–80°C for 4–20 hours.

13. A porous carbon material containing alkali metal elements prepared by the preparation method according to any one of claims 1-12, characterized in that, The porous carbon material includes macropores, micropores, and alkali metal elements distributed on the surface or between layers of the porous carbon material; the diameter of the macropores is 100 to 2 μm, and the diameter of the micropores is 1 nm to 5 nm.

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