CN117069097A - Preparation method and application of hierarchical pore hard carbon material - Google Patents

Abstract

The invention discloses a preparation method and application of hierarchical porous hard carbon. Cellulose-rich sugarcane bagasse is used as the hard carbon precursor and metal nanoparticles are used as pore-forming agents to construct hierarchical porous hard carbon materials, which solves the problem of Sodium-ion batteries have problems such as low first-cycle Coulombic efficiency, poor cycle stability, and low sodium storage performance.

Description

Preparation method and application of hierarchical porous hard carbon material

Technical areas:

The invention relates to the technical field of negative electrode materials for sodium ion batteries, and in particular to a preparation method and application of hierarchical porous hard carbon.

Background technique:

At present, research on safe and reliable new energy storage systems has become particularly important. In new electrochemical energy storage systems, lithium-ion batteries have been widely used in smart grids, electric vehicles, mobile communications and other fields due to their advantages such as high capacity and long cycle life. However, lithium resources are low in reserves and unevenly distributed in the earth's crust. , high price and other issues have become increasingly prominent in recent years. It is particularly important to develop new electrochemical energy storage systems with low prices and abundant resource reserves.

Compared with the many problems of lithium resources, sodium resources are abundant, widely distributed, and cheap. In the periodic table of chemical elements, they are in the same main group as lithium and have similar physical and chemical properties. Therefore, sodium-ion batteries have shown great potential in energy storage systems. It provides a broad development space and application scenarios. However, compared with lithium-ion batteries, the radius of sodium ions is larger, causing sodium ions to migrate slowly and expand seriously during the deintercalation process. Therefore, finding suitable electrode materials is the key to promoting the development of sodium-ion batteries. For sodium-ion batteries, the cathode materials are mainly layered oxides and polyanionic compounds, and the cathode materials show good energy density and cyclability. The matching negative electrode materials are still in a shortcoming, and the development of high-performance negative electrode materials is the hot spot and focus of sodium-ion batteries at this stage.

Sodium-ion battery anode materials are mainly divided into carbon-based, metal alloys, metal oxides and other compounds. Compared with other materials, carbon-based materials are considered to be the most promising anode materials due to their advantages such as abundant resources, low price, and simple preparation process. At present, carbon-based materials mainly include graphite, soft carbon, and hard carbon. However, graphite-like carbon materials have a large sodium ion radius, which increases the difficulty of sodium ions being deintercalated between graphite layers, resulting in reduced performance. Soft carbon refers to amorphous carbon materials with a high degree of order and can be completely graphitized above 2800°C. Currently, the advantages of soft carbon materials are low cost and high first charge and discharge efficiency, but their gram capacity is low and the mainstream capacity is Generally, it is 220-240mA hg ^-1 ; compared with other carbon materials, hard carbon has a higher gram capacity of 300mA hg ^-1 , but its low Coulombic efficiency in the first cycle and poor long-term cycle stability seriously hinder the use of hard carbon. Applications in sodium-ion batteries.

Contents of the invention:

The purpose of the present invention is to provide a preparation method and application of hierarchical porous hard carbon. Cellulose-rich sugarcane bagasse is used as the hard carbon precursor and metal nanoparticles are used as pore-forming agents to construct hierarchical porous hard carbon materials. And apply it to sodium-ion batteries to solve the problems of low first-cycle Coulombic efficiency, poor cycle stability, and low sodium storage performance of sodium-ion batteries.

The present invention is realized through the following technical solutions:

A method for preparing hierarchical porous hard carbon, which method includes the following steps:

1) Use one of metal salts such as iron nitrate (Fe(NO ₃ ) ₃ ), cobalt nitrate (Co(NO ₃ ) ₂ ), nickel nitrate (Ni(NO ₃ ) ₂ ) as the raw material, and deionized water as the solvent , ultrasonic and stir to form a uniform solution A with a metal ion concentration of 0.5wt% to 2.0wt%;

2) Add cellulose-rich sugarcane bagasse to the uniform solution A, and stir quickly under the protection of inert gas until a uniform solution B is formed; wherein the bagasse accounts for 90-98wt% of the total mass; place it in a high-pressure reaction kettle, And place it in a programmed temperature drying oven, perform programmed temperature rise, and the solid obtained by the reaction can be centrifuged, washed, and dried to obtain solid powder; the programmed temperature rise is first heated to 120°C to 140°C at a heating rate of 5°C/min, The constant temperature time is 6 to 12 hours, and then the temperature is raised to 180°C to 200°C at a heating rate of 5°C/min, and the constant temperature time is 6 to 12 hours;

3) Place the solid powder obtained in step 2) into a tube furnace, and under the protection of inert gas, raise it to 800-1000°C at a heating rate of 5°C/min. After holding the temperature for 2-4 hours, cool it naturally to room temperature. Black powder is obtained;

4) Dip the black powder obtained in step 3) into an acid solution with a concentration of 0.5 to 2.0 mol L ^-1 for 4 to 6 hours to remove the metal catalyst and obtain a hard carbon material with a hierarchical porous structure.

The inert gas is one of nitrogen or argon.

Step 4) The acid solution is one of sulfuric acid, hydrochloric acid, and nitric acid.

The raw material uses cellulose-rich sugarcane bagasse as the hard carbon precursor, which is both biomass and waste, so it is cheap and easy to obtain. The addition of metal particles not only contributes to the construction of multi-level pores, but also promotes the carbonization of sugarcane bagasse. The obtained hierarchical porous hard carbon material has hierarchical pore structures such as micropores, mesopores, and macropores. Due to its rich pore structure and adjustable pore size distribution, it greatly improves the overall performance of sodium-ion batteries.

The present invention also protects the hierarchical porous hard carbon obtained by the preparation method and its application, which is mainly used as anode material for sodium ion batteries.

The invention also protects a sodium ion battery, in which the hierarchical porous hard carbon obtained by the preparation method is used as the negative electrode and the sodium flake is used as the positive electrode.

The beneficial effects of the present invention are as follows:

1) The present invention uses cellulose-rich sugarcane bagasse as the hard carbon precursor. Due to the unique macromolecular polysaccharide structure of cellulose, it is helpful to increase the yield of hard carbon and control the pore size, and metal nanoparticles are used as pore-forming agents. , constructing hierarchical porous hard carbon materials, using programmed temperature pretreatment to effectively regulate the size of metal nanoparticles to promote the generation of hierarchical porous hard carbon materials, effectively solving the low Coulombic efficiency of the first cycle of sodium-ion batteries , poor cycle stability, and low sodium storage performance, which will help promote the commercialization of sodium-ion batteries.

2) The addition of metal particles not only helps to construct multi-level pores, but also promotes the carbonization of sugarcane bagasse.

3) The hierarchical porous hard carbon material obtained by the present invention has hierarchical pore structures such as micropores, mesopores, and macropores. Due to its rich pore structure and adjustable pore size distribution, the overall performance of sodium-ion batteries has been greatly improved.

Picture description:

Figure 1 is a pore size distribution diagram of hard carbon produced in a system without added metal salt obtained in Comparative Example 1;

Figure 2 is a pore size distribution diagram of hard carbon using iron nitrate (Fe(NO ₃ ) ₃ ) salt as a pore-forming agent obtained in Example 1;

Figure 3 is a performance chart of a sodium-ion battery constructed of hard carbon using iron nitrate (Fe(NO ₃ ) ₃ ) salt as a pore-forming agent.

Detailed ways:

The following is a further description of the present invention, rather than a limitation of the present invention.

Example 1: Preparation of hierarchical porous hard carbon materials

It is completed according to the following process:

(1) Use iron nitrate (Fe(NO ₃ ) ₃ ) as the metal salt and deionized water as the solvent, sonicate and stir until a uniform solution A is formed, in which the concentration of Fe ³⁺ is 0.5wt%.

(2) Add a certain amount of cellulose-rich bagasse to the uniformly dispersed solution A, and stir rapidly under the protection of inert gas nitrogen at a stirring speed of 400 rpm until a uniform solution B is formed, in which bagasse accounts for 90wt% of the total mass. ; Place solution B in a high-pressure reaction kettle and place it in a programmed temperature drying oven. First, heat it up to 120°C at a heating rate of 5°C/min, hold the temperature for 6 hours, and then heat it up to 120°C at a heating rate of 5°C/min. 180°C, constant temperature for 6 hours, the solid obtained was centrifuged, washed, and dried to obtain solid powder, in which the washing liquid was deionized water.

(3) Place the solid powder obtained in step (2) into a tube furnace, and under the protection of inert gas nitrogen, raise it to 1000°C at a heating rate of 5°C/min. After holding the temperature for 2 hours, cool it naturally to room temperature, that is Black powder is available.

(4) Dip the black powder obtained in step (3) into 0.5 mol L ^-1 sulfuric acid solution for 6 hours at room temperature to remove the metal catalyst. Finally, a hard carbon material with a hierarchical pore structure can be obtained. The pore size distribution diagram is shown in Figure 2.

As can be seen from Figure 2, in the system using iron nitrate (Fe(NO ₃ ) ₃ ) salt as the pore-forming agent, hard carbon has abundant micropores, mesopores and macropores, and the pore size is large. This developed pore channel facilitates the rapid transfer of sodium ions in the electrolyte and also facilitates the rapid deintercalation of sodium ions. Using the hard carbon obtained in Example 1 as the negative electrode and the sodium flake as the positive electrode, a sodium ion battery was constructed. Its specific capacity is shown in Figure 3. From the figure, it can be seen that the voltage window of the battery is 0 to 3.0V, and the specific capacity It is 305mA hg ^-1 and has a high battery specific capacity.

Comparative example 1:

Referring to Example 1, the difference is that iron nitrate (Fe(NO ₃ ) ₃ ) is not added in step (1).

Disperse the cellulose-rich bagasse in deionized water and stir rapidly under the protection of inert gas nitrogen at a stirring speed of 400 rpm until a uniform solution B is formed, in which bagasse accounts for 90wt% of the total mass; solution B is placed under high pressure Reaction kettle, and placed in a programmed temperature drying oven, first raise the temperature to 120°C at a heating rate of 5°C/min, and hold the temperature for 6 hours, then raise the temperature to 180°C at a heating rate of 5°C/min, and hold the temperature for 6 hours. The obtained solid is centrifuged, washed, and dried to obtain solid powder, in which the washing liquid is deionized water.

(3) Place the solid powder obtained in step (2) into a tube furnace, and under the protection of inert gas nitrogen, raise it to 1000°C at a heating rate of 5°C/min. After holding the temperature for 2 hours, cool it naturally to room temperature, that is Black powder is available.

The final pore size distribution diagram of the hard carbon material is shown in Figure 1.

As can be seen from Figure 1, the hard carbon produced in the system without added metal salts has micropores, mesopores and macropores, and the volumes of micropores and mesopores are relatively small.

Comparing Example 1 and Comparative Example 1, it can be seen that the addition of metal particles not only contributes to the construction of multi-level pores, but also promotes the carbonization of sugarcane bagasse.

Example 2:

Referring to Example 1, the difference is that in step (1), iron nitrate (Fe(NO ₃ ) ₃ ) is replaced by cobalt nitrate (Co(NO ₃ ) ₂ ).

Example 3:

Referring to Example 1, the difference is that the programmed temperature rise program of step (2) is to first raise the temperature to 140°C at a heating rate of 5°C/min, hold the temperature for 6 hours, and then raise the temperature to 200°C at a heating rate of 5°C/min. ℃, constant temperature time 6h.

Example 4:

Referring to Example 1, the difference is that step (3) is: the solid powder obtained in step (2) is placed in a tube furnace, and under the protection of inert gas nitrogen, the temperature is raised to 5°C/min at a heating rate of 5°C/min. 800℃, constant temperature for 2 hours, then naturally cooled to room temperature, black powder can be obtained.

Claims (6)

1. A method for preparing hierarchical porous hard carbon, characterized in that the method includes the following steps: 1) Using one of iron nitrate, cobalt nitrate, and nickel nitrate as raw material, deionized water as solvent, ultrasonic and stirring to form a uniform solution A with a metal ion concentration of 0.5wt% to 2.0wt%; 2) Add cellulose-rich sugarcane bagasse to the uniform solution A, and stir quickly under the protection of inert gas until a uniform solution B is formed; wherein the bagasse accounts for 90-98wt% of the total mass; place it in a high-pressure reaction kettle, And place it in a programmed temperature drying oven, perform programmed temperature rise, and the solid obtained by the reaction can be centrifuged, washed, and dried to obtain solid powder; the programmed temperature rise is first heated to 120°C to 140°C at a heating rate of 5°C/min, The constant temperature time is 6 to 12 hours, and then the temperature is raised to 180°C to 200°C at a heating rate of 5°C/min, and the constant temperature time is 6 to 12 hours; 3) Place the solid powder obtained in step 2) into a tube furnace, and under the protection of inert gas, raise it to 800-1000°C at a heating rate of 5°C/min. After holding the temperature for 2-4 hours, cool it naturally to room temperature. Black powder is obtained; 4) Dip the black powder obtained in step 3) into an acid solution with a concentration of 0.5 to 2.0 mol L ^-1 , and immerse for 4 to 6 hours to obtain a hard carbon material with a hierarchical pore structure. 2. The preparation method according to claim 1, characterized in that the inert gas is one of nitrogen or argon. 3. The preparation method according to claim 1, characterized in that the acid liquid in step 4) is one of sulfuric acid, hydrochloric acid and nitric acid. 4. The hierarchical porous hard carbon obtained by the preparation method according to claim 1. 5. Application of the hierarchical porous hard carbon obtained by the preparation method according to claim 1, characterized in that it is used as a negative electrode material for sodium ion batteries. 6. A sodium ion battery, using the hierarchical porous hard carbon obtained by the preparation method of claim 1 as the negative electrode, and the sodium sheet as the positive electrode.