Sodium-ion battery negative electrode hard carbon material, preparation method and application thereof

Abstract

The application belongs to the technical field of sodium ion battery material preparation, and particularly relates to a negative electrode hard carbon material for sodium ion batteries and a preparation method and application thereof. The application directly crushes waste cation exchange resin, and then soaks the crushed waste cation exchange resin in a 0.1M FeCl3 solution, freezes and dries the soaked waste cation exchange resin to obtain a precursor powder; then the precursor powder is heated and calcined under a specific atmosphere at a specific heating rate; the resin hard carbon powder after high-temperature calcination is used to remove residual metal compounds in the hard carbon material, and then the hard carbon material is washed to neutral with deionized water and dried to obtain the hard carbon material. The obtained hard carbon material has a high graphitization degree and good conductivity.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of sodium ion battery material preparation, and particularly relates to a negative hard carbon material for a sodium ion battery and a preparation method and application thereof. BACKGROUND

[0002] Sodium ion batteries have become a strong competitor of the next generation of energy storage batteries due to their wide sources, low cost, safety and long cycle life. Among various materials of sodium ion batteries, the negative electrode material is a key factor restricting the energy storage application. Currently, the battery material commonly used in lithium ion batteries is graphite. However, since the radius of sodium ions is larger than that of lithium ions, and the interlayer spacing of graphite is small (0.34 nm), sodium ions cannot be embedded in the layer, so it is necessary to find a new material as a sodium storage negative electrode material for sodium ion batteries. The hard carbon has a larger interlayer spacing, and the average interlayer spacing can reach 0.41 nm. The disordered porous structure can provide a large number of vacancies and defects to store sodium ions, and is an ideal negative electrode material for sodium ion batteries. At the same time, the precursor of hard carbon has a wide source, low cost and simple preparation process, and has a broad commercial prospect.

[0003] The preparation of hard carbon precursor materials mainly includes biomass-based, resin-based and pitch-based. The resin-based material has controllable structure and high consistency, and has high research value for large-scale production and application of hard carbon materials. Ion exchange resin has a network skeleton structure and high sphericity, and is widely available, which is an ideal precursor material for hard carbon. At present, a large amount of waste ion exchange resin will cause secondary pollution to the environment through landfill or incineration. The use of waste ion exchange resin to prepare negative hard carbon material for sodium ion batteries can realize resource utilization, avoid pollution to the environment, and provide a new strategy for preparing hard carbon negative electrode. Therefore, it is urgent to develop a new process for preparing sodium battery negative hard carbon material from waste ion exchange resin with simple operation. SUMMARY

[0004] The purpose of the present application is to provide a negative hard carbon material for a sodium ion battery and a preparation method and application thereof to solve the aforementioned problems.

[0005] According to one aspect of the present application, a negative hard carbon material for a sodium ion battery is provided, which is prepared from waste cation exchange resin by mechanical grinding and crushing, soaking in a FeCl3 solution and high-temperature calcination. The obtained negative hard carbon material has an average micropore size of 2-3 nm, and the surface is distributed with carbon nanofibers with a length of 100-300 nm.

[0006] According to another aspect of the present application, a preparation method of the above-mentioned negative hard carbon material for a sodium ion battery is provided, which comprises the following steps:

[0007] S1, crushing the waste cation exchange resin to obtain resin powder;

[0008] S2, soaking the resin powder in a 0.1M FeCl3 solution, rinsing, and then freeze-drying to obtain a precursor powder;

[0009] S3, heating the precursor powder obtained in S2 to 350-400°C at a heating rate of 1-5°C / min under a nitrogen or argon atmosphere, holding for 1-3h, and purging with nitrogen;

[0010] S4, after completing step S3, heating from 400°C to 500°C at a rate of 10°C / min under a nitrogen or argon atmosphere containing 1wt% oxygen;

[0011] S5, continuing to heat at a heating rate of 1-10°C / min to 700-800°C under a nitrogen or argon atmosphere, holding for 5-7h;

[0012] S6, continuing to heat at a heating rate of 1-10°C / min to 1300°C under a nitrogen or argon atmosphere, holding for 1-3h, and naturally cooling to room temperature to obtain a hard carbon material.

[0013] In some embodiments, the method for preparing a negative electrode hard carbon material for a sodium ion battery comprises the following steps:

[0014] S1, mechanically grinding and crushing waste cation exchange resin to obtain resin powder with a particle size distribution of 5-20μm;

[0015] S2, soaking the resin powder in a 0.1M FeCl3 solution for 1-2h, rinsing quickly, and then freeze-drying to obtain a precursor powder;

[0016] S3, placing the precursor powder obtained in S2 in a tube furnace, heating to 350-400°C at a heating rate of 1-5°C / min under a nitrogen or argon atmosphere, holding for 1-3h, and purging with nitrogen at a flow rate of 0.5-3L / min;

[0017] S4, after completing step S3, heating from 400°C to 500°C at a rate of 10°C / min under a nitrogen or argon atmosphere containing 1wt% oxygen;

[0018] S5, continuing to heat at a heating rate of 1-10°C / min to 700-800°C under a nitrogen or argon atmosphere, holding for 5-7h;

[0019] S6, continuing to heat at a heating rate of 1-10°C / min to 1300°C under a nitrogen or argon atmosphere, holding for 1-3h, and naturally cooling to room temperature;

[0020] S7, the resin hard carbon material after high temperature calcination in S6 is placed in 1M HCl to remove the metal compounds remaining in the hard carbon material, and then the hard carbon material is washed to neutral with deionized water and dried at 100°C under vacuum.

[0021] In step S3, the sulfonic acid groups in the resin are converted into sulfur dioxide, and if the nitrogen purging flow is too low, the sulfur dioxide cannot be removed completely, and it is easy to form sulfate with metal ions, affecting the catalytic effect of the metal ions. If the nitrogen purging flow is too large, the temperature will drop, which is not conducive to the reaction. Therefore, the nitrogen purging flow is controlled in the range of 0.5-3 L / min to ensure that the sulfur dioxide is quickly removed and to avoid the formation of sulfate with the metal elements (Fe, etc.) adsorbed in the waste resin. The sulfate not only affects the graphitization catalysis of the metal oxides in the subsequent high-temperature carbonization process, but also increases the oxygen content in the high-temperature carbonization system, causing unnecessary carbon loss at high temperature and reducing the yield of the hard carbon product.

[0022] In step S4, 1wt% oxygen is mixed in to burn off a small amount of light component carbonaceous ingredients and adjust the pores; at the same time, the oxidation of metal elements is promoted to promote the graphitization catalysis of metal oxides at 800°C in the subsequent process. The purpose of step S5 is to catalyze the formation of graphitized microcrystals by metal oxides to increase the electrical conductivity of the hard carbon material and to play a capacity. Step S6 has two effects: one is to further adjust the pore structure and the degree of graphitization by increasing the average pore size to about 2 nm; the other is to decompose the insoluble sulfate into oxides, so that it can be washed clean in step S7.

[0023] In some embodiments, the method for preparing a negative electrode hard carbon material for sodium ion batteries comprises the following steps:

[0024] S1, the waste cation exchange resin is mechanically ground and broken to obtain a resin powder with a particle size distribution of 5-20 μm;

[0025] S2, the resin powder is soaked in a 0.1M FeCl3 solution for 1-2h, then quickly rinsed and freeze-dried to obtain a precursor powder;

[0026] S3, the precursor powder obtained in S2 is placed in a tube furnace and heated to 400°C at a heating rate of 2°C / min under a nitrogen or argon atmosphere, and the nitrogen purging flow is 0.5-3 L / min;

[0027] S4, after step S3, heat from 400°C to 500°C at a rate of 10°C / min under a nitrogen or argon atmosphere containing 1wt% oxygen;

[0028] S5, continue to heat to 700°C at a rate of 5°C / min under a nitrogen or argon atmosphere, and keep the temperature for 6h;

[0029] S6, continue heating at a temperature increasing rate of 5℃ / min to 1300℃ under nitrogen or argon atmosphere, keep for 1h, and naturally cool to room temperature;

[0030] S7, stir the resin hard carbon material after high temperature calcination in S6 in 1M HCl to remove the metal compounds remaining in the hard carbon material, then wash the hard carbon material to neutral with deionized water, and vacuum dry at 100℃.

[0031] According to another aspect of the present application, the use of the above-mentioned negative hard carbon material in the preparation of a sodium ion battery negative electrode is provided. Specifically, the above-mentioned negative hard carbon material is mixed with a conductive agent Super P and a binder PVDF in a mass ratio of 8:1:1, a proper amount of N-methyl pyrrolidone is added to form a slurry, which is then coated and cut into electrode sheets for use in the preparation of a sodium ion battery negative electrode.

[0032] The present application has the following advantages:

[0033] 1. The discarded cation exchange resin is not pre-cleaned to remove possible residual mixed metal ions, so that the remaining metal ions play a role in catalyzing the generation of a certain amount of graphite crystallites during high-temperature carbonization to enhance the electrical conductivity.

[0034] 2. Since the source of the discarded ion exchange resin is complex, the resin powder is soaked in a FeCl3 solution to ensure that at least Fe compounds are contained during high-temperature carbonization to promote the catalytic synthesis of graphitized phases in the hard carbon material.

[0035] 3. Pre-soaking the resin powder to adsorb metal ions (Fe 3+ ) with larger diameters can promote the maximum expansion of the internal cross-linked structure, and the use of freeze-drying to maintain the expanded structure of the resin is beneficial to the large pore structure of the hard carbon material after carbonization.

[0036] 4. In the process of preparing the negative hard carbon material for sodium ion batteries, the use of stepwise heating has the advantage of catalyzing the generation of graphitized crystallites at a lower temperature of 700-800℃ compared to direct heating to 1300℃, which reduces the holding time at high temperature of 1300℃ (generally more than 6 hours). BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 XRD spectra of the hard carbon materials obtained in the examples and comparative examples.

[0038] Figure 2 Charge-discharge curves of the hard carbon materials obtained in the examples and comparative examples.

[0039] Figure 3 Rate performance of the hard carbon materials obtained in the examples and comparative examples.

[0040] Figures 4-6 SEM image of the hard carbon material of Example 1.

[0041] Figure 7 Cycle life graph of the hard carbon material of Example 1. DETAILED DESCRIPTION

[0042] The application will be further described in conjunction with specific embodiments. Unless otherwise specified, the following raw materials are commercially available.

[0043] Example 1

[0044] The preparation method of the negative electrode hard carbon material for sodium ion battery comprises the following steps:

[0045] 1. The waste cation exchange resin is mechanically ground and broken to obtain resin powder with a particle size distribution of 5-20 μm;

[0046] 2. 5 g of the above resin powder is soaked in a 0.1 M FeCl3 solution for 2 h, quickly rinsed with deionized water, and then freeze-dried to obtain a precursor powder;

[0047] 3. The above precursor powder is placed in a tube furnace, heated to 400°C at a rate of 2°C / min under a nitrogen atmosphere, and kept for 2 h with a nitrogen purge flow of 0.8 L / min; then the atmosphere is adjusted to 1 wt% oxygen-containing nitrogen, and heated from 400°C to 480°C at a rate of 10°C / min; continue to heat at a rate of 5°C / min under a nitrogen atmosphere to 700°C, and keep for 6 h; finally, heat at a rate of 5°C / min under a nitrogen atmosphere to 1300°C, keep for 3 h, and naturally cool to room temperature;

[0048] 4. The high-temperature calcined resin hard carbon powder is stirred in 1 M HCl to remove the metal compounds remaining in the hard carbon material, washed with deionized water until neutral, and dried to obtain 1.589 g of hard carbon material, which is denoted as HC.

[0049] Comparative Example 1

[0050] The preparation method of the negative electrode hard carbon material for sodium ion battery of Comparative Example 1 is based on Example 1, and the nitrogen purge flow is reduced from 0.8 L / min to 0.2 L / min, and the specific steps are as follows:

[0051] 1. The waste cation exchange resin is mechanically ground and broken to obtain resin powder with a particle size distribution of 5-20 μm;

[0052] 2. 5 g of the above resin powder is soaked in a 0.1 M FeCl3 solution for 2 h, quickly rinsed, and then freeze-dried to obtain a precursor powder;

[0053] 3. The precursor was placed in a tube furnace and heated to 400°C at a rate of 2°C / min under a nitrogen atmosphere, with a nitrogen purge flow of 0.2 L / min for 2 h. The subsequent carbonization steps and process parameters were consistent with Example 1, and 1.502 g of hard carbon material was obtained, denoted as HC-D1.

[0054] Comparative Example 2

[0055] The preparation method of the negative electrode hard carbon material for sodium ion batteries in Comparative Example 2 was as follows: the waste cation exchange resin was pre-cleaned before the subsequent process based on Example 1.

[0056] 1. The waste cation exchange resin was cleaned multiple times with deionized water and anhydrous ethanol, and then dried and mechanically ground to obtain a precursor powder with a particle size distribution of 5-20 μm.

[0057] 2. 5 g of the above resin powder was soaked in a 0.1 M FeCl3 solution for 2 h, rinsed quickly, and then freeze-dried to obtain a precursor powder.

[0058] 3. The precursor was placed in a tube furnace, and the subsequent carbonization steps and process parameters were consistent with Example 1, and 1.536 g of hard carbon material was obtained, denoted as HC-D2.

[0059] Comparative Example 3

[0060] The preparation method of the negative electrode hard carbon material for sodium ion batteries in Comparative Example 3 was as follows: the waste cation exchange resin was pre-cleaned without soaking in a FeCl3 solution based on Example 1.

[0061] The waste cation exchange resin was cleaned multiple times with deionized water and anhydrous ethanol, and then dried and mechanically ground to obtain a precursor powder with a particle size distribution of 5-20 μm. 5 g of the ground resin powder (without soaking in a 0.1 M FeCl3 solution) was directly placed in a tube furnace, and the subsequent carbonization steps and process parameters were consistent with Example 1, and 1.82 g of hard carbon material was obtained, denoted as HC-D3.

[0062] The obtained hard carbon materials HC, HC-D1, HC-D2, and HC-D3 were mixed with the conductive agent Super P and the binder PVDF at a mass ratio of 8:1:1, and an appropriate amount of N-methyl pyrrolidone was added to form a slurry, which was then coated and cut into electrode sheets. With hard carbon as the negative electrode, a sodium sheet as the counter electrode, glass fiber as the separator, and 1 M NaClO4 (EC:DEC = 1:1, with 5 vol% FEC) as the electrolyte, a CR2032 type button cell was assembled in an argon-filled glove box, and charge-discharge tests were performed on a blue electric tester under constant temperature and humidity conditions at 30°C. The test results are as follows.

[0063] 1. XRD results

[0064] Depend on Figure 1 The XRD results show that the hard carbon materials obtained in the comparative examples and the examples are all typical hard carbon materials. Among them, the hard carbon materials obtained in the examples, comparative examples 1 and 2 all showed a sharp graphite microcrystal diffraction peak at 2θ of 26-27°. This indicates that metal ions can promote the catalytic conversion of some hard carbon materials into graphite microcrystals, thereby obtaining better overall material conductivity. At the same time, compared with comparative example 2, the graphite peak intensity of the examples is higher, indicating that multi-metal elements have a better catalytic effect on the formation of graphite microcrystals. The graphitization peak intensity of comparative example 1 is lower, indicating that sulfur dioxide produced by the decomposition of sulfonate in the early stage of carbonization forms sulfate with metal elements. The high decomposition temperature of sulfate weakens the graphitization catalytic performance of metal elements and increases the oxygen content of the system during the high-temperature carbonization process, which will further reduce carbon yield and porosity, affecting sodium storage performance.

[0065] 2. Electrochemical performance results

[0066] Figures 4-6 The results show that a large number of carbon nanofibers were generated on the surface of the carbon material under the action of a catalyst, indicating that the HC hard carbon material in Example HC has a higher degree of graphitization and better conductivity, thus achieving a high 337.6 mAh·g. -1 The discharge capacity and initial coulombic efficiency of 91.9% are achieved at 1 A·g -1 Under these conditions, the capacity retention rate is as high as 88.7% after 400 cycles.

[0067] In Comparative Example 1, the low nitrogen purging flow rate during the initial carbonization stage increased the risk of sulfur dioxide produced by sulfonate decomposition forming sulfates with metal elements. The high decomposition temperature of sulfates weakens the graphitization catalytic performance of the metal elements and increases the oxygen content of the system during high-temperature carbonization, reducing carbon yield and porosity. The resulting hard carbon HC-D1 had a discharge specific capacity of 293.4 mAh·g. -1 .

[0068] Comparative Example 2, by eluting other metal elements and using only Fe as the catalyst for high-temperature graphite microcrystals of carbonaceous material, yielded a hard carbon HC-D2 with a discharge specific capacity of 312.6 mAh·g. -1 .

[0069] Comparative Example 3 pre-cleaned the waste cation exchange resin. Without the catalysis of metal ions, some carbonaceous materials were converted into graphite microcrystals. The resulting hard carbon HC-D3 had low conductivity, which was not conducive to the capacity utilization. Therefore, the discharge specific capacity of Comparative Example 3 was relatively low.

[0070] Table 1. Results of discharge specific capacity and efficiency for different groups

[0071] Number Discharge specific capacity (mAh-g -1 ) Efficiency (%) Example 1 337.6 91.9％ Comparative Example 1 293.4 89.4％ Comparative Example 2 312.6 90.4％ Comparative Example 3 266.4 84.1％

[0072] The above merely describes some embodiments of the present application. For those skilled in the art, without departing from the concept of the present application, several modifications and improvements can be made, which are within the scope of the present application.

Claims

1. A method for preparing hard carbon negative electrode material for sodium-ion batteries, characterized in that, Includes the following steps: S1. The waste cation exchange resin containing sulfonic acid groups is crushed to obtain resin powder; S2. The resin powder is soaked in FeCl3 solution, rinsed, and then freeze-dried to obtain the precursor powder. S3. The precursor powder obtained in S2 is heated to 350-400℃ in a nitrogen or argon atmosphere at a heating rate of 1-5℃ / min, held for 1-3 h, and then purged with nitrogen. S4. After completing step S3, heat from 400°C to 500°C at a rate of 10°C / min in a nitrogen atmosphere containing 1wt% oxygen or an argon atmosphere containing 1wt% oxygen. S5. Continue heating in a nitrogen or argon atmosphere at a heating rate of 1~10℃ / min to 700~800℃, and hold for 5~7h. S6. Continue heating in a nitrogen or argon atmosphere at a heating rate of 1~10℃ / min to 1300℃, hold for 1~3h, and cool naturally to room temperature to obtain hard carbon powder.

2. The method for preparing the hard carbon negative electrode material for sodium-ion batteries according to claim 1, characterized in that, The waste cation exchange resin in S1 is crushed by mechanical grinding, and the particle size of the crushed resin powder is distributed in the range of 5~20μm.

3. The method for preparing the hard carbon negative electrode material for sodium-ion batteries according to claim 1, characterized in that, The nitrogen purging flow rate in S3 is 0.5~3 L / min.

4. The method for preparing the hard carbon negative electrode material for sodium-ion batteries according to any one of claims 1-3, characterized in that, It also includes the purification of hard carbon materials. The specific steps are as follows: place the hard carbon materials after high-temperature calcination of S6 in 1M HCl, then wash the hard carbon materials with deionized water until neutral, and dry them under vacuum at 100℃.

5. The method for preparing the hard carbon negative electrode material for sodium-ion batteries according to claim 1, characterized in that, Includes the following steps: S1. The waste cation exchange resin is mechanically ground and crushed to obtain resin powder with a particle size distribution of 5~20μm; S2. Soak the resin powder in 0.1M FeCl3 solution for 1-2 hours, rinse, and then freeze-dry to obtain the precursor powder. S3. Place the precursor powder obtained in S2 in a tube furnace and heat it to 350-400°C at a heating rate of 1-5°C / min under a nitrogen or argon atmosphere. Hold it at this temperature for 1-3 hours, with a nitrogen purging flow rate of 0.5-3 L / min. S4. After completing step S3, heat from 400°C to 500°C at a rate of 10°C / min in a nitrogen atmosphere containing 1wt% oxygen or an argon atmosphere containing 1wt% oxygen. S5. Continue heating in a nitrogen or argon atmosphere at a heating rate of 1~10℃ / min to 700~800℃, and hold for 5~7h. S6. Continue heating to 1300℃ in a nitrogen or argon atmosphere at a heating rate of 1~10℃ / min, hold for 1~3 hours, and then cool naturally to room temperature. S7. Place the resin hard carbon material after high-temperature calcination in 1M HCl to remove residual metal compounds in the hard carbon material, then wash the hard carbon material with deionized water until neutral, and dry it under vacuum at 100℃.

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