Hard carbon materials with ultra-high platform capacity, preparation methods and applications

Abstract

This invention discloses a hard carbon material with ultra-high platform capacity, its preparation method, and its applications. The hard carbon material is prepared by hydrothermal reaction and high-temperature carbonization, with a particle size of 2-4 μm, a pore size of 0.4-200 nm, and a specific surface area of ​​no more than 15 m². 2 / g, with a platform capacity ratio of not less than 40%; the preparation method of hard carbon material is as follows: S1: Add surfactant to pectin aqueous solution for hydrothermal reaction, and obtain hard carbon microspheres after filtration and drying; S2: Carbonize the hard carbon microspheres of S1 at high temperature under an inert atmosphere, and obtain hard carbon material with ultra-high platform capacity after cooling. The hard carbon material of the present invention can be used as a negative electrode material for lithium-ion batteries, which can significantly improve the platform capacity ratio.

Description

Technical Field

[0001] This invention relates to the field of hard carbon materials technology, and in particular to hard carbon materials with ultra-high platform capacity, their preparation methods, and applications. Background Technology

[0002] Lithium-ion batteries are widely used in electric vehicles and electronic devices due to their high energy density, long cycle life, and safety performance. The anode material significantly determines the performance of lithium-ion batteries. Currently, commercially available lithium-ion battery anode materials are mostly graphite. Graphite, when used as a lithium-ion battery anode material, exhibits a low voltage plateau capacity and high coulombic efficiency and cycle stability, but its theoretical specific capacity (372 mAh·g) is relatively low. -1 The limitations of hard carbon, such as lithium plating during rapid charge and discharge and a low lithium-ion diffusion coefficient, prevent it from meeting the requirements for effective battery operation under fast-charging and low-temperature conditions. Compared to graphite, the short-range ordered and long-range disordered structural characteristics of hard carbon are beneficial for the rapid transport of lithium ions. Furthermore, its larger interlayer spacing and more porosity and defect structure than graphite give hard carbon not only higher specific capacity but also excellent low-temperature charge-discharge capability and rate performance. However, hard carbon prepared by methods such as heteroatom doping and activated pore formation often has a large specific surface area, low graphitization degree, and high defect content. This type of hard carbon mainly stores lithium ions through adsorption, and its charge-discharge curve only shows a ramp capacity without a clear plateau capacity, which inevitably reduces the energy density of the entire battery.

[0003] In existing research, a precursor is obtained by mixing phenolic formaldehyde solution with polyvinyl alcohol and hexamethylenetetramine, followed by microwave-assisted heating to obtain cured resin balls, and finally high-temperature carbonization to produce hard carbon with an adjustable microporous structure. Although the above method is an effective means to improve the platform capacity, it is difficult to apply in practice due to the uncontrollable reaction temperature of microwave heating and the high cost of raw materials and equipment.

[0004] Therefore, it is necessary to develop a simple and low-cost method to reduce the specific surface area and defect content of hard carbon and increase the content of graphite microcrystals, so as to extend the capacity platform of lithium-ion batteries and improve the energy density of the whole battery. Summary of the Invention

[0005] Based on the technical problems existing in the background technology, the present invention proposes a hard carbon material with ultra-high platform capacity, a preparation method and application. When used as a negative electrode material for lithium-ion batteries, the hard carbon material can significantly increase the platform capacity ratio.

[0006] The present invention proposes a hard carbon material with ultra-high platform capacity. This hard carbon material is prepared by hydrothermal reaction and high-temperature carbonization, with a particle size of 2-4 μm, a pore size of 0.4-200 nm, and a specific surface area of ​​no more than 15 m². 2 / g, the platform capacity accounts for no less than 40%.

[0007] The preparation method of the above-mentioned hard carbon material with ultra-high platform capacity proposed in this invention includes the following steps:

[0008] S1: Add surfactant to pectin aqueous solution to carry out hydrothermal reaction, and after the reaction, filter and dry to obtain hard carbon microspheres;

[0009] S2: The hard carbon microspheres of S1 are carbonized at high temperature under an inert atmosphere, and after cooling, a hard carbon material with ultra-high platform capacity is obtained.

[0010] Preferably, the surfactant in S1 is one or more of sodium dodecylbenzenesulfonate, hexadecyltrimethylammonium bromide, and polyethylene glycol.

[0011] Preferably, the concentration of the pectin aqueous solution in S1 is 1-4 wt%.

[0012] Preferably, the mass ratio of pectin to surfactant in S1 is 100:2-10.

[0013] Preferably, the hydrothermal reaction in S1 is carried out at a temperature of 160-220°C for 6-24 hours.

[0014] Preferably, the drying temperature in S1 is 75-85℃, and the drying time is 3-12h.

[0015] Preferably, the conditions for high-temperature carbonization in S2 are as follows: first, the temperature is increased to 300℃ at a heating rate of 1-5℃ / min, and held at a constant temperature for 2-5 hours; then, the temperature is increased to 800-1200℃ at a heating rate of 1-5℃ / min, and carbonized at a constant temperature for 2-5 hours.

[0016] Preferably, the inert gas in S2 is nitrogen and / or argon.

[0017] The present invention relates to the application of the aforementioned hard carbon material with ultra-high platform capacity in lithium-ion energy storage devices.

[0018] Beneficial technical effects of the present invention:

[0019] The hard carbon material prepared by this invention has a particle size in the micrometer range. The larger particle size of the hard carbon has a smaller specific surface area and a smaller contact area with the electrolyte, which can reduce the formation of solid electrolyte interfacial film and improve the reversible capacity of the battery. Furthermore, the hard carbon has abundant graphite microcrystals. The high graphite microcrystal content can promote the intercalation of lithium ions into the interlayer, enabling the hard carbon material to be used as a negative electrode material for lithium-ion batteries, which can significantly increase the proportion of platform capacity. Attached Figure Description

[0020] Figure 1 This is a SEM image of the hard carbon material of Example 1 proposed in this invention;

[0021] Figure 2 This is a TEM image of the hard carbon material of Example 1 proposed in this invention;

[0022] Figure 3 The X-ray powder diffraction pattern of the hard carbon material in Example 1 of this invention;

[0023] Figure 4 The charge-discharge curves of hard carbon materials used as negative electrode materials in lithium-ion batteries in Example 1 and Comparative Example 2 of this invention are shown.

[0024] Figure 5 The diagram shows the rate performance of the hard carbon materials in Examples 1 and 2 of this invention as negative electrode materials for lithium-ion batteries. Detailed Implementation

[0025] The present invention will be further explained below with reference to specific embodiments.

[0026] Example 1

[0027] The preparation method of the hard carbon material with ultra-high platform capacity proposed in this invention has the following steps:

[0028] (1) First, dissolve 1g of pectin in 50ml of deionized water and add 0.1g of sodium dodecylbenzenesulfonate. Stir well and put into the inner liner of a polytetrafluoroethylene hydrothermal reactor. Carry out the hydrothermal reaction in an oven at 190℃ for 12h. After the reaction, filter to obtain hard carbon microspheres and dry them in an 80℃ oven for 12h.

[0029] (2) The microspheres were placed in an argon atmosphere and heated to 300°C at a heating rate of 5°C / min and kept at a constant temperature for 2 hours. Then, the temperature was increased to 1000°C at a heating rate of 3°C / min and carbonized at a constant temperature for 2 hours. After that, the microspheres were naturally cooled to room temperature to obtain a hard carbon material with ultra-high platform capacity.

[0030] The morphology and structure of the obtained samples were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction, respectively. The results are shown in the figure. Figure 1 , Figure 2 and Figure 3 From SEM ( Figure 1 ), TEM Figure 2 ) and XRD Figure 3 It can be seen that the material obtained is a hard carbon microsphere with abundant graphite microcrystals and a particle size of about 3 μm.

[0031] Example 2

[0032] The preparation method of the hard carbon material with ultra-high platform capacity proposed in this invention has the following steps:

[0033] (1) First, dissolve 2g of pectin in 50ml of deionized water and add 50mg of cetyltrimethylammonium bromide. Stir well and put into the inner liner of a polytetrafluoroethylene hydrothermal reactor. Carry out the hydrothermal reaction in an oven at 200℃ for 24h. After the reaction, filter to obtain hard carbon microspheres and dry them in an 80℃ oven for 12h.

[0034] (2) The microspheres were placed in an argon atmosphere and heated to 300°C at a heating rate of 3°C / min and kept at a constant temperature for 4 hours. Then, the temperature was increased to 1200°C at a heating rate of 5°C / min and carbonized at a constant temperature for 2 hours. After that, the microspheres were naturally cooled to room temperature to obtain a hard carbon material with ultra-high platform capacity.

[0035] Example 3

[0036] The preparation method of the hard carbon material with ultra-high platform capacity proposed in this invention has the following steps:

[0037] (1) First, dissolve 1g of pectin in 50ml of deionized water and add 0.1g of polyethylene glycol. Stir well and put it into the inner liner of a polytetrafluoroethylene hydrothermal reactor. Carry out the hydrothermal reaction in an oven at 180℃ for 6 hours. After the reaction, filter to obtain hard carbon microspheres and dry them in an 80℃ oven for 9 hours.

[0038] (2) The microspheres were placed in an argon atmosphere and heated to 300°C at a heating rate of 3°C / min. The temperature was kept constant for 4 hours. Then the temperature was increased to 1000°C at a heating rate of 3°C / min and carbonized at constant temperature for 4 hours. After that, the microspheres were naturally cooled to room temperature to obtain a hard carbon material with ultra-high platform capacity.

[0039] Comparative Example 1

[0040] The steps for preparing hard carbon materials according to this scheme are as follows:

[0041] 1g of pectin was placed in an argon atmosphere and heated to 300℃ at a heating rate of 3℃ / min, and held at a constant temperature for 4 hours. Then, the temperature was increased to 1000℃ at a heating rate of 3℃ / min and carbonized at a constant temperature for 4 hours. After that, it was naturally cooled to room temperature to obtain hard carbon material.

[0042] Comparative Example 2

[0043] The hard carbon material used in this solution is commercially available Kuraray hard carbon material.

[0044] Comparative Example 3

[0045] In the preparation of the hard carbon material in this scheme, glucose is used instead of pectin, and all other conditions are the same as in Example 1.

[0046] Comparative Example 4

[0047] In the preparation of the hard carbon material in this scheme, tamarind polysaccharide gum is used instead of pectin, and all other conditions are the same as in Example 1.

[0048] The hard carbon materials prepared in Examples 1-3 and Comparative Examples 1-4 were mixed with a conductive agent and PVDF in an 8:1:1 ratio, respectively. Then, an appropriate amount of N-methylpyrrolidone was added and the mixture was stirred until homogeneous. The homogeneous slurry was uniformly coated onto copper foil and vacuum dried to serve as the negative electrode. A lithium foil was used as the counter electrode. The electrolyte was a 1M LiPF6 mixture of propylene carbonate (PC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a 1:1:1 volume ratio. A PP membrane was used as the separator. A coin cell was assembled. Charge-discharge tests were conducted using a Blue Battery testing system under the following conditions: 0.05Ag... -1 It is charged and discharged at a current density with a voltage range of 0.001-2V.

[0049] The hard carbon materials prepared in the examples and comparative examples were subjected to relevant physical and electrochemical performance tests, and the results are shown in Tables 1 and 2.

[0050] Table 1 Physical property parameters of hard carbon materials

[0051]

[0052]

[0053] Table 2 Electrochemical Performance Data of Hard Carbon Materials

[0054]

[0055] As can be seen from the experimental results in Table 1, the hard carbon material prepared by the method of the present invention has a high carbon content and a low oxygen defect content. Compared with the bulk hard carbon of Comparative Example 1, the micron-sized carbon spheres of Example 1 exhibit a lower specific surface area. Compared with the hard carbon synthesized using other sugars as raw materials in Comparative Examples 3 and 4, the hard carbon synthesized using pectin as raw material has a larger particle size and a richer content of graphite microcrystals.

[0056] As can be seen from the test results in Table 2, the hard carbon material prepared by the method of the present invention exhibits an ultra-high plateau capacity ratio, excellent charge-discharge specific capacity and better cycle stability as a negative electrode material for lithium-ion batteries.

[0057] Figure 4 and Figure 5The figures show the charge-discharge curves and rate performance of the hard carbon material with ultra-high plateau capacity prepared in Example 1 and the commercially available Kuraray hard carbon material in Comparative Example 2 as negative electrode materials for lithium-ion batteries. The figures show that the hard carbon material prepared in Example 1 exhibits a longer low voltage plateau capacity and better electrochemical rate performance compared to the Kuraray hard carbon material in Comparative Example 2.

Claims

1. A method for preparing hard carbon materials with ultra-high platform capacity, characterized in that, The hard carbon material is prepared by hydrothermal reaction and high-temperature carbonization, with a particle size of 2-4 μm, a pore size of 0.4-200 nm, and a specific surface area of ​​no more than 15 m². 2 / g, with platform capacity accounting for no less than 40%; The preparation method of hard carbon materials with ultra-high platform capacity is as follows: S1: Add surfactant to pectin aqueous solution to carry out hydrothermal reaction, and after the reaction, filter and dry to obtain hard carbon microspheres; S2: The hard carbon microspheres of S1 are carbonized at high temperature under an inert atmosphere, and after cooling, a hard carbon material with ultra-high platform capacity is obtained. The surfactant in S1 is one or more of sodium dodecylbenzenesulfonate, hexadecyltrimethylammonium bromide, and polyethylene glycol.

2. The method for preparing hard carbon material with ultra-high platform capacity according to claim 1, characterized in that, The concentration of pectin aqueous solution in S1 is 1-4 wt%.

3. The method for preparing hard carbon material with ultra-high platform capacity according to claim 1, characterized in that, The mass ratio of pectin to surfactant in S1 is 100:2-10.

4. The method for preparing hard carbon material with ultra-high platform capacity according to claim 1, characterized in that, The hydrothermal reaction in S1 takes place at a temperature of 160-220℃ for 6-24 hours.

5. The method for preparing hard carbon material with ultra-high platform capacity according to claim 1, characterized in that, The drying temperature in S1 is 75-85℃, and the time is 3-12 hours.

6. The method for preparing hard carbon material with ultra-high platform capacity according to claim 1, characterized in that, The conditions for high-temperature carbonization in S2 are as follows: first, heat to 300℃ at a heating rate of 1-5℃ / min, maintain the temperature for 2-5 hours, then heat to 800-1200℃ at a heating rate of 1-5℃ / min, and carbonize at the temperature for 2-5 hours.

7. The method for preparing hard carbon material with ultra-high platform capacity according to claim 1, characterized in that, The inert gas in S2 is nitrogen and / or argon.

8. The application of the hard carbon material with ultra-high platform capacity prepared by the preparation method described in claim 1 in lithium-ion energy storage devices.

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