An epoxy resin-modified homopolysaccharide-derived hard carbon anode material and its preparation method and application

Abstract

Preparation method of epoxy resin modified polysaccharide-derived hard carbon anode material: Mix polysaccharide with epoxy resin to prepare a precursor; then place the precursor in an inert atmosphere for pre-burning to obtain an intermediate; then grind and crush the intermediate and place it in an inert atmosphere for high-temperature calcination to obtain the epoxy resin modified polysaccharide-derived hard carbon anode material. The present invention also provides an epoxy resin modified polysaccharide-derived hard carbon anode material prepared by this preparation method and its application in sodium ion batteries. The present invention uses liquid epoxy resin as both a coating and a structure regulating material. Combining with the suitable viscosity, high cracking temperature and rich functional groups of liquid epoxy resin, the epoxy resin is coated on the surface of the polysaccharide, and then through stabilization and carbonization process treatment, it is ensured that the prepared hard carbon anode material has excellent electrochemical performance.

Description

Technical Field

[0001] The present invention belongs to the field of sodium ion batteries, and particularly relates to an epoxy resin modified polysaccharide-derived hard carbon negative electrode material, a preparation method thereof, and an application thereof. Background Art

[0002] Sodium ion batteries (SIBs) are expected to become a commercial alternative to lithium ion batteries in the near future due to their potential low cost. Although lithium ion batteries (LIBs) are relatively mature in development, lithium resources are scarce in China, the price of lithium resources is rising continuously and the reserves are limited; sodium ion batteries have rich resource reserves, better safety, excellent rate performance and low temperature performance, and are slightly inferior to lithium batteries in terms of energy density and cycle life, but have significant cost advantages compared with lithium batteries.

[0003] High-performance negative electrode materials are one of the key factors for the industrialization of sodium ion batteries. Carbon-based negative electrode materials have a wide range of sources and strong sodium storage capacity, and have become the current mainstream choice. Carbon-based materials can be divided into hard carbon and soft carbon according to whether they can be graphitized after high-temperature treatment. Hard carbon materials have many sodium storage active sites, high specific capacity, small volume expansion after sodium insertion, good safety and stable structure, and have obvious comparative advantages. Chinese patent application with publication number CN107425215A discloses a preparation method of a starch-based composite hard carbon negative electrode material. This method uses starch as a hard carbon precursor and combines the synergism of coating materials and graphite to prepare a hard carbon negative electrode material with high first-cycle charge and discharge efficiency and good cycle performance. However, this method has cumbersome steps and high equipment costs. Therefore, there is an urgent need to study a preparation method of a sodium battery negative electrode material with simple process steps, low preparation cost and excellent electrochemical performance. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the above-mentioned deficiencies and defects in the background art, and provide an epoxy resin modified polysaccharide-derived hard carbon negative electrode material, a preparation method thereof, and an application thereof.

[0005] To solve the above technical problem, the technical solution proposed by the present invention is as follows:

[0006] A preparation method of an epoxy resin modified polysaccharide-derived hard carbon negative electrode material, comprising the following steps:

[0007] (1) Mixing polysaccharide with liquid epoxy resin to prepare a precursor;

[0008] (2) Stabilization: subjecting the precursor to pre-burning in an inert atmosphere to obtain an intermediate;

[0009] (3) Carbonization: grinding and pulverizing the intermediate and then subjecting it to high-temperature calcination in an inert atmosphere to obtain an epoxy resin modified polysaccharide-derived hard carbon negative electrode material.

[0010] In the above preparation method, preferably, in step (2), the inert gas is argon, nitrogen or helium; for the pre-calcination, the temperature is first raised to 180-500 °C at a rate of 1.5-10 °C / min, and then held for 0.5-6 h. During this process, the relatively high cracking temperature of the epoxy resin cross-links and cures with the polysaccharide, avoiding the problems of polysaccharide fusion and foaming, improving the stability of the intermediate molecular structure, greatly shortening the duration of the stabilization process and reducing energy consumption.

[0011] More preferably, the inert gas is nitrogen or argon, the pre-calcination temperature is 200-500 °C, the heating rate is 2-8 °C / min, and the holding time is 1-5 h. In the present invention, the pre-calcination temperature, heating rate and time are controlled within this range. During the stabilization process, the epoxy resin and the polysaccharide cross-link and cure, improving the stability of the intermediate molecular structure, and finally obtaining a hard carbon negative electrode material with a rich pore structure and suitable for sodium-ion batteries.

[0012] In the above preparation method, preferably, in step (3), the inert gas is argon, nitrogen or helium; for the high-temperature calcination, the temperature is first raised to 900-1600 °C at a rate of 1.5-10 °C / min, and then held for 0.5-6 h.

[0013] More preferably, the inert gas is argon or nitrogen; for the high-temperature calcination, the temperature is first raised to 1000-1500 °C at a rate of 2-10 °C / min, and then held for 2-5 h. Controlling the high-temperature calcination temperature, heating rate and time within this range is beneficial to the insertion and extraction of sodium ions, improving the reversible capacity of the polysaccharide-derived hard carbon negative electrode material for sodium-ion batteries and improving its electrochemical performance.

[0014] In the above preparation method, preferably, in step (3), the particle size of the intermediate after grinding and pulverization is 60-400 mesh. More preferably, it is 50-300 mesh. Obtaining relatively uniform-sized preliminary polysaccharide-derived hard carbon material particles is beneficial to the subsequent process.

[0015] In the above preparation method, preferably, in step (1), the specific process for preparing the precursor is: adding the polysaccharide and the epoxy resin into a solvent, stirring and mixing evenly with the assistance of the solvent, and then recovering the solvent to obtain the precursor. In this step, the recovered solvent can be recycled; mixing in the solvent can, on the one hand, make the polysaccharide and the epoxy resin mix more evenly, and the appropriate viscosity of the epoxy resin can tightly coat the surface of the polysaccharide particles. On the other hand, it can also greatly reduce the risk of dust explosion.

[0016] In the above preparation method, preferably, the mass ratio of the polysaccharide to the liquid epoxy resin is 10:(0.5-5), and the mass of the solvent is 0.5-5 times the mass of the polysaccharide.

[0017] In the above preparation method, preferably, the polysaccharide is one or more of starch, cellulose, and glycogen; the liquid epoxy resin is one or more of liquid bisphenol A epoxy resin, liquid bisphenol F epoxy resin, liquid hydrogenated bisphenol A epoxy resin, and liquid hydrogenated bisphenol F epoxy resin.

[0018] In the above preparation method, preferably, the solvent is one or more of ethanol, toluene, ethyl acetate, and methyl isobutyl ketone. The resin is dissolved by the solvent to make each component mix uniformly, improving the coating effect of the liquid epoxy resin on the polysaccharide hard carbon material.

[0019] As a general inventive concept, the present invention also provides an epoxy resin-modified polysaccharide-derived hard carbon negative electrode material, which is obtained by the above preparation method.

[0020] As a general inventive concept, the present invention also provides an application of the above epoxy resin-modified polysaccharide-derived hard carbon negative electrode material in a sodium-ion battery.

[0021] Compared with the prior art, the advantages of the present invention are as follows:

[0022] (1) The present invention uses liquid epoxy resin as both a coating and a structure-regulating material. Combining with the suitable viscosity, high cracking temperature, and rich functional groups of the liquid epoxy resin, the epoxy resin is coated on the surface of the polysaccharide, and then through stabilization and carbonization process treatment, it ensures that the prepared hard carbon negative electrode material has excellent electrochemical performance.

[0023] (2) In the preparation method of the present invention, the solvent is used to mix the polysaccharide and the epoxy resin, which can ensure that the polysaccharide and the epoxy resin are mixed uniformly. The suitable viscosity of the epoxy resin can closely coat the surface of the polysaccharide dust particles, and at the same time, it can greatly reduce the risk of dust explosion; the epoxy resin has a high cracking temperature and crosslinks and cures with the polysaccharide during the stabilization process, avoiding the problems of polysaccharide fusion and foaming, improving the stability of the intermediate molecular structure, thereby greatly shortening the duration of the stabilization process and reducing the energy consumption, and finally obtaining a hard carbon negative electrode material with a rich pore structure and suitable for sodium-ion batteries.

[0024] (3) The hard carbon negative electrode material prepared by the present invention has a high charging specific capacity, high initial charge-discharge efficiency, good cycle performance, and good rate charge-discharge performance.

[0025] (4) In the preparation process of the present invention, no additional low-temperature curing is required. The process is simple, easy to operate, has high safety performance, low energy consumption, and the preparation process is green and pollution-free, and is easy to realize mass production. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1FT-IR spectra of starch, epoxy resin and precursor prepared in Example 1 of the present invention.

[0027] Figure 2 DSC curves of starch, epoxy resin and precursor prepared in Example 1 of the present invention.

[0028] Figure 3 SEM images of the hard carbon anode material prepared in Example 1 of the present invention.

[0029] Figure 4 Charge-discharge curves of the hard carbon anode material prepared in Example 1 of the present invention.

[0030] Figure 5 Physical photos of the intermediates prepared in Example 1, Example 2 and the comparative example of the present invention. Detailed Description of the Invention

[0031] To facilitate the understanding of the present invention, the present invention will be described more comprehensively and meticulously below in conjunction with the accompanying drawings of the specification and preferred embodiments, but the protection scope of the present invention is not limited to the following specific embodiments.

[0032] Unless otherwise defined, all professional terms used hereinafter have the same meaning as commonly understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the protection scope of the present invention.

[0033] Unless otherwise specifically stated, various raw materials, reagents, instruments and equipment used in the present invention can be obtained through market purchase or can be prepared by existing methods.

[0034] In the present invention, there is no special limitation on the method of solvent recovery, as long as the purpose of recovering the solvent and saving costs can be achieved.

[0035] In the following examples and comparative examples, the half-cell test method is as follows: The prepared negative electrode material samples are respectively mixed evenly with conductive agent acetylene black and binder polytetrafluoroethylene emulsion in a mass ratio of 80:10:10 in NMP, and then pressed into tablets on aluminum foil to obtain negative electrode sheets. The negative electrode sheets are placed in a vacuum drying oven at 80 °C for 8 hours for vacuum drying and standby. Using a sodium metal sheet as the positive electrode, a CR2025 type button sodium ion battery is assembled for electrochemical testing.

[0036] In the following examples and comparative examples, the liquid bisphenol A epoxy resin is selected from the E51 type of Baling Petrochemical, and the liquid bisphenol F epoxy resin is selected from the 170 type of Kunshan Nan Ya.

[0037] Example 1:

[0038] A preparation method of an epoxy resin modified homopolysaccharide-derived hard carbon anode material of the present invention includes the following steps:

[0039] (1) Take 50 g of soluble potato starch and 5 g of liquid bisphenol A epoxy resin, add them to 40 mL of ethyl acetate and mix evenly, then perform rotary evaporation to recover the solvent and obtain a precursor.

[0040] (2) Put the precursor obtained in step (1) into a tubular furnace, under the protection of argon, heat it to 500 °C at a heating rate of 5 °C / min, and keep it warm for 2 h to obtain an intermediate.

[0041] (3) Grind the obtained intermediate, pass it through a 100-mesh sieve, put it into a high-temperature furnace, under the protection of an argon atmosphere, heat it to 1400 °C at a heating rate of 10 °C / min, and keep it warm for 2 h to obtain an epoxy resin modified homopolysaccharide-derived hard carbon anode material.

[0042] Perform infrared spectroscopy tests on the starch, bisphenol A epoxy resin used in this example, and the precursor obtained in step (1) respectively. As Figure 1 shown, for the epoxy resin, 915 cm -1 and 828 cm -1 correspond to the bending vibration peak and deformation vibration peak of the epoxy group respectively. For the intermediate obtained after pre-burning at 500 °C after the epoxy resin and starch are mixed evenly, the intensities of the above two peaks are greatly weakened or even disappear, indicating that the starch has an opening ring effect on the epoxy resin, further cross-links into a network structure, and plays a role in stabilizing the precursor structure.

[0043] Perform DSC tests on the starch, bisphenol A epoxy resin used in this example, and the precursor obtained in step (1) respectively. As Figure 2 shown, for the starch, the endothermic peak near 120 °C corresponds to the removal of adsorbed water, and the endothermic peak near 280 °C corresponds to the crystallization melting of the starch. For the precursor after the epoxy resin and starch are mixed evenly, the crystallization melting peak almost disappears during the heating process, indicating that the addition of the epoxy resin effectively solves the problem of melting and foaming during the heating of the starch. At the same time, the exothermic peak that appears near 287.5 °C corresponds to the ring-opening polymerization of the epoxy resin and starch to form a network structure, which plays a role in stabilizing the precursor structure.

[0044] Perform SEM characterization on the epoxy resin modified homopolysaccharide-derived hard carbon anode material prepared in this example. As Figure 3 shown, from Figure 3 it can be seen that the surface of this hard carbon anode material is smooth and has a multi-level structure. Combining with the good electrochemical performance later, it shows that by modifying the homopolysaccharide precursor with epoxy resin, it can achieve a better effect of controlling the microstructure of the hard carbon.

[0045] The hard carbon anode material prepared in this example was assembled into a CR2025 button sodium-ion battery for performance testing. In the voltage range of 0.01 - 3.0 V and at a current density of 0.1C, 30 mAh g -1 , the initial charge specific capacity reached 338 mAh / g, and the first Coulombic efficiency reached 73% (see Figure 4 ). After 100 cycles at a current density of 1C, 300 mAh g -1 , the capacity retention rate was still 94.1%.

[0046] Example 2:

[0047] A preparation method of an epoxy resin-modified homopolysaccharide-derived hard carbon anode material of the present invention includes the following steps:

[0048] (1) Take 50 g of soluble potato starch and 5 g of liquid bisphenol F epoxy resin, add them to 40 mL of ethyl acetate, mix evenly, and then perform rotary evaporation to recover the solvent to obtain a precursor.

[0049] (2) Put the precursor obtained in step (1) into a tube furnace, under the protection of an argon atmosphere, heat it to 500 °C at a heating rate of 5 °C / min, and keep it at this temperature for 2 h to obtain an intermediate.

[0050] (3) Grind the obtained intermediate, pass it through a 100-mesh sieve, put it into a high-temperature furnace, under the protection of an argon atmosphere, heat it to 1400 °C at a heating rate of 10 °C / min, and keep it at this temperature for 2 h to obtain an epoxy resin-modified homopolysaccharide-derived hard carbon anode material.

[0051] The epoxy resin-modified homopolysaccharide-derived hard carbon anode material prepared in this example was assembled into a CR2025 button sodium-ion battery in the same manner as in Example 1 and subjected to performance testing. The results showed that the intermediate prepared with bisphenol F epoxy resin would not expand and foam under the regulation of the resin. During charge and discharge at a rate of 0.1C in the voltage range of 0.01 - 3V, the initial charge specific capacity reached 330 mAh / g, the first Coulombic efficiency reached 72%, and after 100 cycles at a current density of 1C (300 mA g -1 ), the capacity retention rate was still 94.6%, and the cycling performance was stable.

[0052] Example 3:

[0053] A preparation method of an epoxy resin-modified homopolysaccharide-derived hard carbon anode material of the present invention includes the following steps:

[0054] (1) Take 50 g of microcrystalline cellulose and 10 g of liquid bisphenol A epoxy resin, add them to 60 mL of ethyl acetate, mix evenly, and then perform rotary evaporation to recover the solvent to obtain a precursor.

[0055] (2) Put the precursor obtained in step (1) into a tube furnace, and under the protection of an argon atmosphere, heat it to 500 °C at a heating rate of 5 °C / min, and keep it at this temperature for 2 h to obtain an intermediate product.

[0056] (3) Grind the obtained intermediate product, sieve it through a 100-mesh sieve, put it into a high-temperature furnace, and under the protection of an argon atmosphere, heat it to 1400 °C at a heating rate of 10 °C / min, and keep it at this temperature for 2 h to obtain an epoxy resin-modified polysaccharide-derived hard carbon anode material.

[0057] Assemble the epoxy resin-modified polysaccharide-derived hard carbon anode material prepared in this example into a CR2025-type button sodium-ion battery in the same manner as in Example 1 and conduct performance tests. Perform charge-discharge tests at a voltage range of 0.01 - 3 V and a rate of 0.1C. The initial charge specific capacity can reach 328 mAh / g, and the first Coulombic efficiency is 71%. After cycling 100 times at a current density of 1C (300 mA g -1 ), the capacity retention rate is still 93.8%. Conduct scale-up processing on this batch, and the same effect can also be achieved.

[0058] Example 4:

[0059] A preparation method of an epoxy resin-modified polysaccharide-derived hard carbon anode material of the present invention includes the following steps:

[0060] (1) Take 50 g of soluble corn starch and 20 g of liquid bisphenol A epoxy resin, add them to 60 mL of ethyl acetate, mix them evenly, and then recover the solvent to obtain a precursor.

[0061] (2) Put the precursor obtained in step (1) into a tube furnace, and under the protection of an argon atmosphere, heat it to 300 °C at a heating rate of 5 °C / min, and keep it at this temperature for 2 h to obtain an intermediate product.

[0062] (3) Grind the obtained intermediate product, sieve it through a 100-mesh sieve, put it into a high-temperature furnace, and under the protection of an argon atmosphere, heat it to 1400 °C at a heating rate of 5 °C / min, and keep it at this temperature for 2 h to obtain an epoxy resin-modified polysaccharide-derived hard carbon anode material.

[0063] Assemble the epoxy resin-modified polysaccharide-derived hard carbon anode material prepared in this example into a CR2025-type button sodium-ion battery in the same manner as in Example 1 and conduct performance tests. Perform charge-discharge tests at a voltage range of 0.01 - 3 V and a rate of 0.1C. The initial charge specific capacity can reach 331 mAh / g, and the first charge-discharge efficiency is 72%. After cycling 100 times at a current density of 1C (300 mA g -1 ), the capacity retention rate is still 93.6%.

[0064] Comparative Example 1:

[0065] The preparation method of the hard carbon anode material in this comparative example includes the following steps:

[0066] (1) Take 50 g of soluble potato starch and put it into a tubular furnace. Under the protection of an argon atmosphere, heat it to 500 °C at a heating rate of 5 °C / min and hold for 2 h to obtain an intermediate product.

[0067] (2) Grind the intermediate product obtained in step (1), pass it through a 100-mesh sieve, and then put it into a high-temperature furnace. Under the protection of argon gas, heat it to 1400 °C at a heating rate of 10 °C / min and hold for 2 h to obtain the hard carbon anode material.

[0068] The photos of the intermediate products of Example 1, Example 2, and this comparative example are as Figure 5 shown. From left to right, they are the intermediate products of Example 1, Example 2, and Comparative Example 1. It can be Figure 5 seen that epoxy resin is introduced in Example 1 and Example 2. During the stabilization process, the epoxy resin can crosslink with starch, thereby improving the stability of the intermediate molecular structure and avoiding the problem of melting and foaming during the stabilization process.

[0069] The hard carbon anode material prepared in this comparative example was tested and measured. The process is referred to the relevant content of Example 1. Charge-discharge tests were carried out at a voltage range of 0.01 - 3 V and a rate of 0.1C. The first charge-discharge efficiency was 68%, the charge specific capacity was 302 mAh / g. After cycling 100 times at a current density of 1C (300 mA g -1 ), the capacity retention rate was only 88%. Compared with the performance of the epoxy resin-modified polysaccharide-derived hard carbon in the present invention, it is significantly lower. This is because the starch was modified with epoxy resin, and the epoxy resin can regulate the microstructure of starch and improve the electrochemical performance of the hard carbon anode material.

[0070] In summary, the epoxy resin-modified polysaccharide-derived hard carbon anode material of the present invention has good electrochemical performance when applied in sodium-ion batteries. Its first-cycle charge capacity is above 320 mAh / g. After cycling 100 weeks at a high current density, the capacity hardly decays, indicating its excellent cycling performance.

[0071] The preparation method of the hard carbon negative electrode material provided by the present invention uses epoxy resin as both the coating and structure regulating material. By utilizing the suitable viscosity, high pyrolysis temperature, and rich functional groups of epoxy resin, the epoxy resin is coated on the surface of the polysaccharide, and a hard carbon negative electrode material derived from epoxy resin-modified polysaccharide for sodium-ion batteries with excellent sodium storage performance is prepared. Moreover, the selected process means is a low-cost, easy-to-synthesize, green and environmentally friendly synthesis process for polysaccharide hard carbon materials, which has the characteristics of simple operation, strong repeatability, scalability, and low cost. The obtained hard carbon negative electrode material derived from epoxy resin-modified polysaccharide for sodium-ion batteries has a rich pore structure and exhibits excellent electrochemical performance. It is an ideal negative electrode material for sodium-ion batteries and has good application prospects.

[0072] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A preparation method of an epoxy resin modified polysaccharide-derived hard carbon anode material, characterized in that, it comprises the following steps: (1) Mix polysaccharide with liquid epoxy resin to prepare a precursor; wherein, the mass ratio of the polysaccharide to the liquid epoxy resin is 10:(0.5~5); (2) Place the precursor in an inert atmosphere for pre-calcination to obtain an intermediate; wherein, the pre-calcination is to first heat up to 180-500 °C at a rate of 1.5-10 °C / min, and then keep it warm for 0.5-6 h; (3) Grind and crush the intermediate and then place it in an inert atmosphere for high-temperature calcination to obtain the epoxy resin modified polysaccharide-derived hard carbon anode material.

2. The preparation method according to claim 1, characterized in that, in step (2), the inert gas is argon, nitrogen or helium.

3. The preparation method according to claim 1, characterized in that, in step (3), the inert gas is argon, nitrogen or helium; the high-temperature calcination is to first heat up to 900-1600 °C at a rate of 1.5-10 °C / min, and then keep it warm for 0.5-6 h.

4. The preparation method according to claim 1, characterized in that, in step (3), the particle size of the intermediate after grinding and crushing is 60-400 mesh.

5. The preparation method according to any one of claims 1 to 4, characterized in that, in step (1), the specific process of preparing the precursor is: add polysaccharide and liquid epoxy resin to a solvent, stir evenly, and then recover the solvent to obtain the precursor.

6. The preparation method according to claim 5, characterized in that, the mass of the solvent is 0.5-5 times the mass of the polysaccharide.

7. The preparation method according to claim 5, characterized in that, the polysaccharide is one or more of starch, cellulose, glycogen; the liquid epoxy resin is one or more of liquid bisphenol A epoxy resin, liquid bisphenol F epoxy resin, liquid hydrogenated bisphenol A epoxy resin, liquid hydrogenated bisphenol F epoxy resin.

8. The preparation method according to claim 5, characterized in that, the solvent is one or more of ethanol, toluene, ethyl acetate, methyl isobutyl ketone.

9. An epoxy resin modified polysaccharide-derived hard carbon anode material, characterized in that, it is prepared by the preparation method according to any one of claims 1 to 8.

10. An application of the epoxy resin modified polysaccharide-derived hard carbon anode material according to claim 9 in a sodium ion battery.

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