Preparation method and application of high-capacity starch-based sodium ion hard carbon negative electrode material

Abstract

The invention discloses a preparation method and application of a high-capacity starch-based sodium ion hard carbon negative electrode material. The preparation method comprises the following steps: adding maleic anhydride and zinc chloride into starch, uniformly mixing, putting into a crucible, putting into a drying oven of 50-100 DEG C for esterification treatment, then heating to 240-280 DEG C for pre-carbonization treatment, and collecting a precursor solid; crushing the precursor solid, putting the crushed precursor solid into a ball milling tank, and carrying out ball milling to obtain intermediate powder; and putting the intermediate powder into a graphite boat, putting the graphite boat into a tubular furnace, and performing high-temperature carbonization in an argon atmosphere to obtain the starch-based sodium ion hard carbon negative electrode material. According to the starch-based sodium ion hard carbon prepared through joint modification of maleic anhydride and zinc chloride, the interlayer spacing is remarkably increased, the oxygen content of the material is reduced, and the disorder degree, the number of closed pores and the volume are increased. The method is simple and convenient in operation steps and has the potential of large-scale production.

Description

Technical Field

[0001] The present invention belongs to the field of battery materials, and in particular relates to a preparation method and application of a high-capacity starch-based sodium ion hard carbon negative electrode material. Background Art

[0002] Electrochemical energy storage plays a vital role in the new energy technologies of the 21st century. Although lithium-ion batteries have been highly commercialized, the scarcity of lithium resources has led to a sharp increase in costs, which has limited their further development. Therefore, sodium-ion batteries, as an alternative technology, have attracted attention due to their cost-effectiveness and resource abundance. However, the development of sodium-ion batteries is limited by the compatibility of negative electrode materials. The graphite negative electrode used in traditional lithium-ion batteries is not suitable for sodium ions, because the radius of sodium ions is larger than that of lithium ions, which makes it impossible for them to be effectively deintercalated in the graphite structure. In view of this, starch-based hard carbon materials have become an ideal choice for negative electrode materials for sodium-ion batteries due to their low cost and large interlayer spacing. The defect sites of starch-based hard carbon materials provide slope capacity for the adsorption of sodium ions, while graphite domains and closed pores provide platform capacity for the intercalation storage of sodium ions. Therefore, its reversible capacity mainly comes from the low-voltage platform area. By increasing the capacity of this area, the overall energy density of the battery can be significantly improved, and then the sodium storage capacity of hard carbon can be further optimized under the joint action of multiple factors. Summary of the invention

[0003] The object of the present invention is to provide a preparation method and application of a high-capacity starch-based sodium ion hard carbon negative electrode material.

[0004] In order to achieve the above object, the present invention adopts the following technical solution:

[0005] A method for preparing a high-capacity starch-based sodium ion hard carbon negative electrode material comprises the following steps:

[0006] 1) Add maleic anhydride and zinc chloride to starch, mix well and put into a crucible, place in a 50-100° C. oven for esterification for 4-8 hours, then heat to 240-280° C., keep warm for 4-8 hours for pre-carbonization treatment, and collect the precursor solid;

[0007] 2) The precursor solid is crushed and placed in a ball mill, and the intermediate powder is obtained after ball milling;

[0008] 3) The intermediate powder is placed in a graphite boat and then placed in a tubular furnace, and carbonized at 1000-1500° C. for 1-5 hours under an argon atmosphere to obtain a starch-based sodium ion hard carbon negative electrode material with a carbon yield of 18-23%.

[0009] Furthermore, the starch is corn starch, potato starch, rice starch and the like.

[0010] Furthermore, the mass ratio of the starch, maleic anhydride and zinc chloride is 6 to 8: 1 to 2: 1. Firstly, the larger blocks of maleic anhydride and zinc chloride are crushed together and then starch is added and mixed until the powder forms flocs.

[0011] Furthermore, the ball milling speed is 1800 to 2500 rpm, the ball milling time is 8 to 15 min, and the particle size D of the intermediate powder is 50 =10~40μm.

[0012] The present invention adopts the above technical scheme, and the starch-based sodium ion hard carbon prepared by co-modification of maleic anhydride and zinc chloride has significantly improved interlayer spacing, reduced oxygen content of the material, and increased disorder and closed pore quantity and volume. The present invention has simple and convenient operation steps and has the potential for large-scale production.

[0013] The present invention has the following beneficial effects:

[0014] 1. By comparing with ordinary starch, it was found that zinc chloride can generate zinc oxide and be reduced to gaseous metallic zinc during high-temperature carbonization, which escapes from the sample, causing the continuous development of graphite domains and the contraction of some open pores to drive the open pores to gradually transform into closed pores; while maleic anhydride esterifies starch to replace the free hydroxyl groups on the starch molecular chain, reducing the hydrogen bonding force between starch molecules, reducing the crystallinity and stabilizing the closed-pore structure.

[0015] 2. Pre-carbonization can increase the degree of cross-linking of the precursor, thereby limiting the directional growth of graphite domains during high-temperature carbonization. Through the combined action of maleic anhydride and zinc chloride at high temperature, the interlayer spacing of starch-based hard carbon is significantly increased, the disorder and number of closed pores of the material are increased, and the oxygen content is reduced.

[0016] 3. Zinc chloride decomposes and escapes during the high-temperature carbonization process, eliminating the step of pickling to remove metal ions and further improving the preparation efficiency. This treatment not only simplifies the operation steps, but also has the potential for large-scale production.

[0017] 4. Compared with ordinary starch-based hard carbon, the modified hard carbon of the present invention exhibits higher reversible capacity and better rate performance in electrochemical performance.

[0018] 5. The method of the present invention is applicable to a variety of starch-based hard carbon materials, such as corn starch, potato starch and rice starch, and can significantly improve their sodium storage performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic diagram of the preparation process of the present invention.

[0020] Figure 2It is the XRD pattern of Z-CMHC, CMHC, Z-CHC and CHC.

[0021] Figure 3 are HRTEM images of CHC and Z-CMHC.

[0022] Figure 4 (a) is the comparison of the charge and discharge curves of Z-CMHC, CMHC, Z-CHC and CHC at 0.1C, and (b) is the cycle performance of Z-CMHC at 1C rate for 1000 cycles. DETAILED DESCRIPTION

[0023] Example 1 Preparation of Z-CMHC:

[0024] Maleic anhydride and zinc chloride were added to corn starch in a mass ratio of 7:1:1. The larger blocks of maleic anhydride and zinc chloride were first crushed together and then added to the starch and mixed until the powder formed flocs. The mixed materials were placed in a crucible and placed in a 75°C oven for esterification for 6 hours. The temperature was then raised to 260°C and kept for 6 hours for pre-carbonization treatment. The precursor solid was collected. The precursor solid was initially crushed and placed in a ball mill jar. It was ball milled in a high-speed ball mill at a speed of 2000 rpm for 12 minutes to obtain an intermediate powder. The particle size D of the intermediate powder was 2.34 mm. 50 =10-40 μm. Finally, the intermediate powder was placed in a graphite boat and then put into a tube furnace for high temperature carbonization at 1250° C. for 3 h in an argon atmosphere to obtain starch-based hard carbon Z-CMHC, with a final carbon yield of 18-23%.

[0025] Comparative Example 1 Preparation of CMHC:

[0026] Maleic anhydride was added to corn starch and mixed thoroughly at a mass ratio of 7:1. The mixed materials were placed in a crucible and placed in a 75°C oven for esterification for 6 hours. The temperature was then raised to 260°C and kept for 6 hours for pre-carbonization. The precursor solid was collected. The precursor solid was initially crushed and placed in a ball mill. The precursor solid was milled in a high-speed ball mill at a speed of 2000 rad min -1 Ball milling for 12 minutes to obtain an intermediate powder with a particle size of D 50 =10-40 μm. Finally, the intermediate powder is placed in a graphite boat and then put into a tube furnace for high temperature carbonization at 1200° C. for 3 h in an argon atmosphere to obtain hard carbon CMHC, with a final carbon yield of 20-25%.

[0027] Comparative Example 2 Preparation of Z-CHC

[0028] Zinc chloride was added to corn starch and mixed thoroughly at a mass ratio of 7:1. The mixed materials were placed in a crucible and placed in a 260°C oven for pre-carbonization for 6 hours. The precursor solid was collected. The precursor solid was initially crushed and placed in a ball mill jar. The precursor solid was milled in a high-speed ball mill at a speed of 2000 rad min -1 Ball milling for 12 minutes to obtain an intermediate powder with a particle size of D 50 =10-40 μm. Finally, the intermediate powder is placed in a graphite boat and then put into a tube furnace for high temperature carbonization at 1200° C. for 3 h in an argon atmosphere to obtain hard carbon Z-CHC, with a final carbon yield of 20-25%.

[0029] Comparative Example 3 Preparation of CHC

[0030] The corn starch was placed in a crucible and placed in a 260°C oven for pre-carbonization for 6 hours, and the precursor solid was collected. The precursor solid was initially crushed and placed in a ball mill jar and then milled in a high-speed ball mill at a speed of 2000 rad min -1 Ball milling for 8-15 minutes, the particle size of the intermediate powder is D 50 =10-40 μm, thereby obtaining an intermediate powder. Finally, the intermediate powder is placed in a graphite boat and then placed in a tube furnace, and carbonized at 1200°C for 3 hours under an argon atmosphere to obtain ordinary hard carbon CHC, with a final carbon yield of 23-28%.

[0031] Application example: Battery assembly test

[0032] Hard carbon, CMC and carbon black were mixed and ground in a mass ratio of 80-85:5-10:10-15 and evenly coated on copper foil as the working electrode, metallic sodium as the counter electrode, and the electrolyte was 1.0M NaPF6 DEGDME solution. The battery was assembled in a glove box under argon protection (oxygen and moisture content were both less than 0.1ppm) and tested using the Xinwei battery test system.

[0033] Figure 2 XRD patterns of corn starch-based hard carbon (Z-CMHC) samples modified by maleic anhydride and zinc chloride, corn starch-based hard carbon (CMHC) modified by maleic anhydride, corn starch-based hard carbon (Z-CHC) modified by zinc chloride, and ordinary corn starch-based hard carbon (CHC). It can be seen from the figure that the starch-based hard carbon materials are amorphous as a whole, and the interlayer spacing d is and This shows that compared with the initial phase, although the interlayer spacing of samples modified with zinc chloride and maleic anhydride has expanded to a certain extent, the expansion of the interlayer spacing of hard carbon samples modified with maleic anhydride and zinc chloride is the most obvious.

[0034] Figure 3HRTEM images of CHC and Z-CMHC are compared. As can be seen from Figure (a), the thick carbon layer of CHC has more defective openings and higher disordered crystallites, which to some extent makes Na + Embedded defects increase the slope capacity and the irreversible capacity. In Figure (b), Z-CMHC shows more obvious lattice fringes and a higher degree of graphitization. Due to the random stacking and limited rearrangement of short-range curved carbon ribbons in the typical vortex-like graphite domain microstructure, the open disordered carbon crystals and open nanopores are transformed into short-range ordered carbon structures and closed nanopores. The measured (002) crystal plane spacings of CHC and Z-CMHC are 0.379nm and 0.396nm, respectively, which is consistent with the XRD data. These can be used for Na + Storage provides more active sites.

[0035] Table 1 Composition and structure test results of various hard carbon materials

[0036]

[0037] Table 1 shows the composition and structure test results of various hard carbon materials. D / I G The values ​​were 1.02 and 1.08 respectively, while the I D / I G The carbon-oxygen ratios of Z-CMHC (26.6) and CMHC (28.5) are higher than those of CHC (17.7) and Z-CHC (23.3). This is because the sp ratios of the hard carbon and carbon-oxygen bond defect sites are higher than those of the Z-CMHC (26.6) and CMHC (28.5). 3 Due to the increase of hybrid carbon, the proportion of CO groups gradually decreases to the most appropriate equilibrium value. And the larger specific surface area means that its defect concentration is higher and there are more open pores. Z-CMHC has a smaller specific surface area and a higher C / O ratio, which also proves the transformation of the material from open pores to closed pores, and also explains the reason for the decrease in oxygen content. The above structural data show that with the intervention of maleic anhydride and zinc chloride, the appropriate reduction in oxygen content can increase the carbonization degree of carbon materials.

[0038] Figure 4Electrochemical performance test of hard carbon in sodium ion battery. (a) CHC, Z-CHC, CMHC and Z-CMHC at 0.1C (1C = 300mA g -1 ) first charge and discharge curve. Comparing the four samples, the high voltage slope area in the charge and discharge curve of CHC accounts for a large proportion of the entire charge and discharge capacity, while the proportion of the low voltage platform area outside the high voltage slope area of ​​the charge and discharge curve of other samples has increased to varying degrees, and the reversible capacity is 298.4 mAh g -1 、326.1mAh g -1 、338.3mAh g -1 and 374mAh g -1 The first coulombic efficiency (ICE) is 88.9%, 89.5%, 90.1% and 90.3% respectively, and its sodium storage performance has been greatly improved. (b) Z-CMHC cycles 1000 times at 1C. The reversible capacity is 320.3mAh g after 1000 cycles at a current density of 1C. -1 , the capacity retention rate is 87%. It can be clearly seen that the capacity of the hard carbon platform has been greatly improved after being modified by maleic anhydride and zinc chloride.

[0039] From the above, it can be seen that the effect of the closed pores of the modified starch-based hard carbon has a significant effect on the performance improvement. The common starch has a lower ICE due to the large number of open pores after high-temperature carbonization. With the addition of maleic anhydride, the oxygen content is reduced, and zinc chloride further strengthens the degree of graphitization, which reduces defects and open pores and increases closed pores, which greatly increases the platform capacity and improves ICE.

Claims

1. A method for preparing a high-capacity starch-based sodium ion hard carbon negative electrode material, characterized in that: The following steps are involved: 1) Add maleic anhydride and zinc chloride to starch, mix well and put into a crucible, place in a 50-100°C oven for esterification for 4-8 h, then heat to 240-280°C and keep warm for 4-8 h for pre-carbonization treatment, and collect the precursor solid; 2) The precursor solid is crushed and placed in a ball mill to obtain an intermediate powder after ball milling; 3) The intermediate powder is placed in a graphite boat and then placed in a tube furnace for high-temperature carbonization at 1000-1500°C for 1-5 h under an argon atmosphere to obtain a starch-based sodium ion hard carbon negative electrode material.

2. The method for preparing a high-capacity starch-based sodium ion hard carbon negative electrode material according to claim 1, characterized in that: The starch is corn starch, potato starch or rice starch.

3. The method for preparing a high-capacity starch-based sodium ion hard carbon negative electrode material according to claim 1, characterized in that: The mass ratio of the starch, maleic anhydride and zinc chloride is 6-8:1-2:

1.

4. The method for preparing a high-capacity starch-based sodium ion hard carbon negative electrode material according to claim 1, characterized in that: The ball mill has a rotation speed of 1800-2500 rpm and a ball milling time of 8-15 min.

5. The method for preparing a high-capacity starch-based sodium ion hard carbon negative electrode material according to claim 1, characterized in that: The particle size D of the intermediate powder 50 =10~40μm.

6. Application of the starch-based sodium ion hard carbon negative electrode material obtained by the preparation method according to any one of claims 1 to 5 in sodium ion batteries.

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