A method for preparing a hard carbon anode material for sodium-ion batteries and the hard carbon anode material itself.

Abstract

This invention discloses a method for preparing hard carbon anode material for sodium-ion batteries and the hard carbon anode material itself, belonging to the field of new energy materials. It solves the problem of low plateau capacity in hard carbon anode materials during the manufacturing process. The technical solution mainly uses glucose as a precursor, which is uniformly mixed with a salt template, and then rapidly pre-carbonized in contact with a heated conductive substrate under an inert atmosphere. After washing and drying, it undergoes rapid secondary carbonization to close the pore structure, resulting in hard carbon with a long plateau capacity. The raw materials used in this invention are inexpensive, the preparation process is simple, significantly reducing time costs, and enabling high-throughput preparation. This invention is mainly used to improve the plateau capacity of hard carbon anode materials through rapid temperature control.

Description

[Technical Field]

[0001] This invention demonstrates a method for preparing a hard carbon anode material for sodium-ion batteries and the hard carbon anode material itself, belonging to the field of new energy materials technology. [Background Technology]

[0002] Since their commercialization 30 years ago, lithium-ion batteries have achieved mature industrial scale and have demonstrated excellent performance in energy storage fields such as portable electronic devices and power batteries for electric vehicles. However, in the field of large-scale energy storage, the development and promotion of lithium-ion batteries are severely hindered by factors such as high cost, resource scarcity, poor safety, and poor rate performance. Sodium-ion batteries, on the other hand, benefit from abundant and inexpensive sodium resources; sodium has a higher electrode potential, resulting in higher safety performance; sodium ions have a smaller Stokes radius, leading to faster transport efficiency and better rate performance; sodium-ion batteries also exhibit excellent low-temperature performance; and their working principle is similar to that of lithium-ion batteries, making industrialization relatively easy. Therefore, they are considered an ideal alternative for large-scale energy storage.

[0003] Hard carbon is the most promising anode material for sodium-ion batteries, exhibiting a long plateau capacity at approximately 0.1V (vs. Na+ / Na), equivalent to graphite in lithium-ion batteries. However, the plateau capacity of currently commercially available hard carbon is significantly lower than the 372 mAh / g of graphite in lithium-ion batteries, requiring further research to improve the plateau capacity of hard carbon anode materials. Previous studies on sodium storage mechanisms have shown that the closed-pore structure in hard carbon, which only allows sodium ions to enter and exit, can serve as active sites for electrochemically reversible sodium storage and is one of the ways to store sodium in the plateau region. Therefore, the key to preparing high-plateau-capacity hard carbon lies in designing as many micropores of suitable size as possible in hard carbon through pore-forming processes, and then creating abundant closed-pore structures capable of storing sodium through pore-sealing methods.

[0004] In existing processes, the precursor is carbonized to obtain hard carbon through annealing for several hours or more. However, due to the influence of thermal driving force, the carbon layer structure inside the hard carbon is severely graphitized, which leads to the deformation or collapse of the pore structure due to the pressure of carbon layer graphitization. Many sodium storage sites in the closed pore structure are lost during the carbonization process, which reduces the plateau capacity. The reduction in plateau capacity reduces the output capacity of sodium batteries at high voltage, limits the energy density of sodium batteries, and seriously restricts the development of sodium batteries. [Summary of the Invention]

[0005] The purpose of this invention is to solve the problem of low plateau capacity of hard carbon anode materials in existing processes. To this end, a method for preparing hard carbon anode materials for sodium-ion batteries and a hard carbon anode material are provided. By controlling the rapid heating and cooling, the plateau capacity of the hard carbon anode material is improved.

[0006] To solve the above-mentioned technical problems, the invention adopts the following technical solution:

[0007] A method for preparing a hard carbon anode material for sodium-ion batteries, the method comprising the following steps:

[0008] S1. Glucose is mixed with a metal salt and then compressed into tablets to obtain mixture A;

[0009] S2. The mixture A is pre-carbonized in an inert gas atmosphere by heating a conductive substrate. The temperature of the conductive substrate is controlled by adjusting the current to reach 400-1000℃ and maintained for 60-3600s. After the mixture A is cooled, it is washed and dried to obtain intermediate product B.

[0010] S3. The intermediate product B is carbonized again in an inert gas atmosphere by heating the conductive substrate. The temperature of the heated conductive substrate is controlled by adjusting the current to reach 1200-2600℃ and maintained for 30-600s to obtain the hard carbon anode material.

[0011] The beneficial effects of adopting the invention are:

[0012] In this invention, glucose is used as a carbon source and metal salt is added as a template. Through rapid pre-carbonization on a heated conductive substrate, oxygen atoms in the glucose precursor and metal salt are rapidly combined in a high-energy environment, which effectively prevents oxygen atoms from combining with carbon atoms to generate volatile gases and escape, thus avoiding damage to the carbon layer. At the same time, fine metal oxide particles can be formed as sacrificial templates, so that the carbon coating on the surface of the metal oxide forms the cavity walls of the porous structure. During the subsequent cleaning process, an intermediate product B with rich microporous structure and uniform pore size is formed. Then, a closed pore structure is formed through secondary carbonization, thereby increasing the plateau capacity of the hard carbon anode material.

[0013] Furthermore, in this invention, the secondary carbonization time is controlled within 30 to 600 seconds. By controlling the secondary carbonization time at the second level, the carbon layer of intermediate product B can self-repair internal crystal defects and grow. At the same time, it twists around the open micropores to form a dense closed-pore structure. Meanwhile, it does not significantly reduce the closed-pore structure due to the formation of excessively graphitized long parallel carbon layers caused by excessive thermal driving force. Through second-level temperature control, this invention can make the hard carbon anode material have a dense closed-pore structure, thereby improving the plateau capacity of the hard carbon anode material, and further improving the output capacity and energy density of the hard carbon anode material at high voltage.

[0014] Preferably, the mass ratio of glucose to metal salt in step S1 is 0.5-10:1, and more preferably 2:1.

[0015] Preferably, the metal salt in step S1 is at least one of zinc chloride, magnesium chloride, sodium chloride, calcium chloride, ferric chloride, and copper chloride.

[0016] Preferably, the mixing process of glucose and metal salt in step S1 is carried out by one of hand milling, ball milling, dissolution drying, and dissolution freeze drying.

[0017] Preferably, the heating rate of the conductive substrate in steps S2 and S3 is 20-700℃ / s.

[0018] Preferably, the conductive substrate heated in step S2 is one of carbon cloth, carbon paper, nickel foil, tungsten boat, molybdenum boat, and graphite boat.

[0019] Preferably, the inert gas in steps S2 and S3 is either argon or nitrogen.

[0020] Preferably, in step S2, the cooled mixture A is washed with one of deionized water, hydrochloric acid solution, sulfuric acid solution and hydrofluoric acid solution, and the washing is performed at least 3 times.

[0021] The present invention also discloses a hard carbon anode material, which is prepared by the preparation method of sodium-ion battery hard carbon anode material as described in any one of the above.

[0022] Other features and advantages of the invention will be disclosed in detail in the following detailed description and accompanying drawings. [Attached Image Description]

[0023] The invention will be further described below with reference to the accompanying drawings:

[0024] Figure 1 This is a time-temperature diagram of the pre-carbonization annealing process in Example 1;

[0025] Figure 2 This is a time-temperature diagram of the secondary carbonization annealing process in Example 1;

[0026] Figure 3 The charge-discharge curve of the hard carbon material in Example 1 at a current density of 40 mA / g is shown in the first cycle.

[0027] Figure 4 The time-temperature graph for the secondary carbonization annealing process in Comparative Example 2 is shown.

[0028] Figure 5 The cumulative pore volume and pore size distribution diagrams for Example 1 and Comparative Example 1 are shown.

[0029] Figure 6 The XRD patterns of Example 1 and Comparative Example 2 are shown below.

[0030] Figure 7 A comparison chart of the charging capacity of various embodiments.

Detailed Implementation Methods

[0031] The technical solutions of the embodiments of the invention will be explained and described below with reference to the accompanying drawings. However, the following embodiments are only preferred embodiments of the invention and not all of them. Other embodiments obtained by those skilled in the art based on the embodiments in the implementation methods without creative effort are all within the protection scope of the invention.

[0032] Example 1:

[0033] In this embodiment, 2g of glucose and 1g of zinc chloride were weighed at a mass ratio of 2:1 and mixed evenly in a mortar by hand grinding. The mixture was then compressed into tablets under appropriate pressure to obtain disc-shaped mixture A. The resulting discs of mixture A were placed on carbon cloth, and under an argon atmosphere, a voltage was applied to both ends of the carbon cloth for rapid heating to perform pre-carbonization. Figure 1 Adjust the energizing current and raise the temperature to 600℃ at a rate of 70℃ / s. Hold at this temperature for 120s, then allow it to cool naturally to room temperature. Wash the pre-carbonized mixture A with 0.5M dilute hydrochloric acid solution at room temperature for 12 hours. After filtration and washing until the solution is neutral, dry to obtain intermediate product B. Place intermediate product B in a graphite boat for secondary carbonization, combining... Figure 2 The temperature was increased to 2000℃ at a rate of 45℃ / s, held for 120s, and then allowed to cool naturally to room temperature to obtain a hard carbon anode material.

[0034] The hard carbon anode material in this example was prepared into a slurry, coated on the surface of aluminum foil, vacuum dried, and then assembled into a half-cell in a glove box. The cycle performance was tested at a current density of 40 mA / g. The coulombic efficiency of the first charge-discharge curve was 85.58%, the first charge capacity was 382.9 mAh / g, and the plateau capacity was 351.1 mAh / g.

[0035] Example 2:

[0036] In this embodiment, 2g of glucose and 1g of zinc chloride were weighed at a mass ratio of 2:1 and mixed evenly in a mortar by hand grinding. The mixture was then pressed into tablets under appropriate pressure to obtain a disc-shaped mixture A. The discs of mixture A were placed on carbon cloth and pre-carbonized by applying voltage to both ends of the carbon cloth under an argon atmosphere. The current was adjusted to raise the temperature to 800°C at a rate of 160°C / s, held for 120s, and then allowed to cool naturally to room temperature. The pre-carbonized mixture A was then acid-washed with 0.5M dilute hydrochloric acid solution at room temperature for 12 hours. After filtration and washing until the solution was neutral, the mixture was dried to obtain intermediate product B. Intermediate product B was placed in a graphite boat for secondary carbonization, raised to 2000°C at a rate of 45°C / s, held for 120s, and then allowed to cool naturally to room temperature to obtain a hard carbon anode material.

[0037] The hard carbon anode material in this example was prepared into a slurry, coated on the surface of aluminum foil, vacuum dried, and then assembled into a half-cell in a glove box. The cycle performance was tested at a current density of 40 mA / g, with an initial efficiency of 83.45% and a first charge capacity of 365.8 mAh / g, of which the plateau capacity was 325.7 mAh / g.

[0038] Example 3:

[0039] In this embodiment, 2g of glucose and 1g of zinc chloride were weighed at a mass ratio of 2:1 and mixed evenly in a mortar by hand grinding. The mixture was then pressed into tablets under appropriate pressure to obtain a disc-shaped mixture A. The discs of mixture A were placed on carbon cloth and pre-carbonized by applying voltage to both ends of the carbon cloth under an argon atmosphere. The current was adjusted to raise the temperature to 1000℃ at a rate of 200℃ / s, held for 60s, and then allowed to cool naturally to room temperature. The pre-carbonized mixture A was then acid-washed with 0.5M dilute hydrochloric acid solution at room temperature for 12 hours. After filtration and washing until the solution was neutral, it was dried to obtain intermediate product B. Intermediate product B was placed in a graphite boat for secondary carbonization, raised to 2600℃ at a rate of 700℃ / s, held for 30s, and then allowed to cool naturally to room temperature to obtain a hard carbon anode material.

[0040] The hard carbon anode material in this example was prepared into a slurry, coated on the surface of aluminum foil, vacuum dried, and then assembled into a half-cell in a glove box. The cycle performance was tested at a current density of 40 mA / g, with an initial efficiency of 85.19% and a first charge capacity of 346.6 mAh / g, of which the plateau capacity was 319.0 mAh / g.

[0041] Example 4:

[0042] In this embodiment, 5g of glucose and 1g of zinc chloride were weighed at a mass ratio of 5:1 and mixed evenly in a mortar by hand grinding. The mixture was then pressed into tablets under appropriate pressure to obtain a disc-shaped mixture A. The discs of mixture A were placed on carbon cloth and pre-carbonized by applying voltage to both ends of the carbon cloth under an argon atmosphere. The current was adjusted to raise the temperature to 600°C at a rate of 70°C / s, held for 120s, and then allowed to cool naturally to room temperature. The pre-carbonized mixture A was then acid-washed with 0.5M dilute hydrochloric acid solution at room temperature for 12 hours. After filtration and washing until the solution was neutral, it was dried to obtain intermediate product B. Intermediate product B was placed in a graphite boat for secondary carbonization, raised to 2000°C at a rate of 45°C / s, held for 120s, and then allowed to cool naturally to room temperature to obtain a hard carbon anode material.

[0043] The hard carbon anode material in this example was prepared into a slurry, coated on the surface of aluminum foil, vacuum dried, and then assembled into a half-cell in a glove box. The cycle performance was tested at a current density of 40 mA / g, with an initial efficiency of 84.67% and a first charge capacity of 331.4 mAh / g, of which the plateau capacity was 301.1 mAh / g.

[0044] Example 5:

[0045] In this embodiment, 2g of glucose and 1g of magnesium chloride were weighed at a mass ratio of 2:1 and mixed evenly in a mortar by hand grinding. The mixture was then pressed into tablets under appropriate pressure to obtain a disc-shaped mixture A. The discs of mixture A were placed on carbon cloth and pre-carbonized by applying voltage to both ends of the carbon cloth under an argon atmosphere. The current was adjusted to raise the temperature to 400°C at a rate of 20°C / s, held for 3600s, and then allowed to cool naturally to room temperature. The pre-carbonized mixture A was then acid-washed with 0.5M dilute hydrochloric acid solution at room temperature for 12 hours. After filtration and washing until the solution was neutral, it was dried to obtain intermediate product B. Intermediate product B was placed in a graphite boat for secondary carbonization, raised to 2600°C at a rate of 20°C / s, held for 30s, and then allowed to cool naturally to room temperature to obtain a hard carbon anode material.

[0046] The hard carbon anode material in this example was prepared into a slurry, coated on the surface of aluminum foil, vacuum dried, and then assembled into a half-cell in a glove box. The cycle performance was tested at a current density of 40 mA / g, with an initial efficiency of 81.59% and a first charge capacity of 308.4 mAh / g, of which the plateau capacity was 280.5 mAh / g.

[0047] Comparative Example 1:

[0048] The method in this embodiment is the same as that in embodiment 1. The main difference is that the pre-carbonization of glucose and metal salt in this embodiment is carried out in a tube furnace, with a slow heating rate of 10°C / min to 600°C, and after holding at that temperature for 60 minutes, it is naturally cooled to room temperature.

[0049] The hard carbon anode material in this example was prepared into a slurry, coated on the surface of aluminum foil, vacuum dried, and then assembled into a half-cell in a glove box. The cycle performance was tested at a current density of 40 mA / g, with an initial efficiency of 80.97% and a first charge capacity of 303.5 mAh / g, of which the plateau capacity was 272.1 mAh / g.

[0050] The specific surface area of ​​intermediate product B obtained by slow heating in this comparative example, as determined by nitrogen adsorption-desorption test, was 1203 m². 2 / g, micropore volume is 0.437cm³ 3 / g; while the intermediate product B obtained by rapid heating and cooling in Example 1 has a specific surface area of ​​1666m². 2 / g, micropore volume is 0.602cm³ 3 / g; combination Figure 5 Test results show that the present invention can effectively produce a more abundant and uniform microporous structure; after secondary carbonization, the volume of the hard carbon micropores in both the comparative example and Example 1 is less than 0.050 cm³. 3 / g indicates that it has been converted into a closed pore structure that is undetectable by nitrogen. Example 1 has more micropores available for conversion than this comparative example, and therefore has more closed pores, which can also be confirmed by the difference in platform capacity between the two.

[0051] Comparative Example 2:

[0052] The method in this embodiment is the same as that in embodiment 1. The main difference is that in this embodiment, the secondary carbonization is carried out at a slow heating rate of 10℃ / min to 2000℃, and after holding at that temperature for 60 minutes, it is naturally cooled to room temperature.

[0053] The hard carbon anode material in this example was prepared into a slurry, coated on the surface of aluminum foil, vacuum dried, and then assembled into a half-cell in a glove box. The cycle performance was tested at a current density of 40 mA / g, with an initial efficiency of 80.06% and a first charge capacity of 304.9 mAh / g, of which the plateau capacity was 277.8 mAh / g.

[0054] Combination Figure 6 The XRD curve of this comparative example has a sharper peak and a larger R value than the XRD curve of Example 1, indicating that the carbon structure of this comparative example sample has a smaller proportion of single layers and a larger proportion of multilayer layers, indicating that the carbon layer structure in this comparative example is thicker. At the same time, the peak position of the XRD curve of this comparative example is shifted to a higher angle compared with the XRD curve of Example 1, indicating that the carbon layer spacing of this comparative example sample is narrower. Both of these signs indicate that this comparative example sample has a higher degree of graphitization, which will affect the closed pore structure and thus reduce the plateau capacity.

[0055] Comparative Example 3:

[0056] This embodiment is a comparative example of Example 1. The main difference is that in this embodiment, the pre-carbonization of glucose and metal salt is carried out in a tube furnace, with a slow heating rate of 10℃ / min to 600℃, held for 60 min, and then naturally cooled to room temperature. The secondary carbonization is carried out with a slow heating rate of 10℃ / min to 2000℃, held for 60 min, and then naturally cooled to room temperature.

[0057] The hard carbon anode material in this example was prepared into a slurry, coated on the surface of aluminum foil, vacuum dried, and then assembled into a half-cell in a glove box. The cycle performance was tested at a current density of 40 mA / g, with an initial efficiency of 81.64% and a first charge capacity of 267.2 mAh / g, of which the plateau capacity was 241.8 mAh / g.

[0058] Comparative Example 4:

[0059] This embodiment is a comparative example of Example 1. The main difference is that in this embodiment, the obtained mixture A disc is placed in a graphite boat and heated to 2000°C at a slow heating rate of 45°C / min. After holding at this temperature for 60 minutes, it is allowed to cool naturally to room temperature.

[0060] The hard carbon anode material in this example was prepared into a slurry, coated on the surface of aluminum foil, vacuum dried, and then assembled into a half-cell in a glove box. The cycle performance was tested at a current density of 40 mA / g, with an initial efficiency of 80.83% and a first charge capacity of 261.9 mAh / g, of which the plateau capacity was 213.6 mAh / g.

[0061] The above description is merely a specific embodiment of the invention, but the scope of protection of the invention is not limited thereto. Those skilled in the art should understand that the invention includes, but is not limited to, the contents described in the accompanying drawings and the specific embodiments above. Any modifications that do not depart from the functional and structural principles of the invention will be included within the scope of the claims.

Claims

1. A method for preparing a hard carbon anode material for sodium-ion batteries, characterized in that, The preparation method includes the following steps: S1. Glucose is mixed with a metal salt and compressed into tablets to obtain mixture A; the metal salt is at least one of zinc chloride, magnesium chloride, sodium chloride, calcium chloride, ferric chloride, and copper chloride. S2. The mixture A is pre-carbonized in an inert gas atmosphere by heating a conductive substrate. The temperature of the heated conductive substrate is controlled to reach 400~1000℃ by adjusting the current and maintained for 60~3600s. After the mixture A is cooled, it is washed and dried to obtain intermediate product B. S3. The intermediate product B is carbonized in an inert gas atmosphere by heating the conductive substrate. The temperature of the heated conductive substrate is controlled to reach 1200~2600℃ by adjusting the current and maintained for 30~600s to obtain the hard carbon anode material. The heating rate of the conductive substrate in steps S2 and S3 is 20-700℃ / s.

2. The method for preparing the hard carbon anode material for sodium-ion batteries according to claim 1, characterized in that: In step S1, the mass ratio of glucose to metal salt is 0.5-10:

1.

3. The method for preparing the hard carbon anode material for sodium-ion batteries according to claim 1, characterized in that: The mixing process of glucose and metal salt in step S1 is carried out by one of the following methods: hand milling, ball milling, dissolution drying, and dissolution freeze drying.

4. The method for preparing the hard carbon anode material for sodium-ion batteries according to claim 1, characterized in that: In step S2, the heated conductive substrate is one of carbon cloth, carbon paper, nickel foil, tungsten boat, molybdenum boat, and graphite boat.

5. The method for preparing the hard carbon anode material for sodium-ion batteries according to claim 1, characterized in that: In steps S2 and S3, the inert gas is either argon or nitrogen.

6. The method for preparing the hard carbon anode material for sodium-ion batteries according to claim 1, characterized in that: In step S2, the cooled mixture A is washed with one of deionized water, hydrochloric acid solution, sulfuric acid solution and hydrofluoric acid solution, and the washing is performed at least 3 times.

7. A hard carbon anode material, characterized in that: The hard carbon anode material is prepared using the preparation method for sodium-ion battery hard carbon anode material as described in any one of claims 1 to 6.

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