Negative electrode hard carbon material for sodium ion battery as well as preparation method and application of negative electrode hard carbon material

Abstract

The invention belongs to the technical field of sodium-ion battery material preparation, and particularly relates to a negative electrode hard carbon material for a sodium-ion battery and a preparation method and application of the negative electrode hard carbon material. The method comprises the following steps: directly crushing the waste cation exchange resin, soaking the crushed cation exchange resin in a 0.1 M FeCl3 solution, and freeze-drying the soaked cation exchange resin to obtain precursor powder; heating and calcining the precursor powder in a specific atmosphere at a specific heating rate; residual metal compounds in the hard carbon material are removed from the resin hard carbon powder subjected to high-temperature calcination, then the hard carbon material is washed to be neutral with deionized water and then dried, and the resin hard carbon material is obtained. The obtained hard carbon material is high in graphitization degree and good in conductivity.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium ion battery material preparation, and in particular relates to a negative electrode hard carbon material for a sodium ion battery and a preparation method and application thereof. Background Art

[0002] Sodium-ion batteries have become a strong competitor for the next generation of energy storage batteries due to their wide availability, low cost, safety and high cycle life. Among the various battery materials of sodium-ion batteries, the negative electrode material is the key factor restricting its energy storage application. At present, the commonly used battery material 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 (0.34nm), sodium ions cannot be embedded in the layers. Therefore, sodium-ion batteries need to find a new material as their sodium storage negative electrode material. Hard carbon has a large interlayer spacing, with an average interlayer spacing of up to 0.41nm. It has a disordered porous structure that can provide a large number of vacancies and defects to store sodium ions well, and is an ideal negative electrode material for sodium-ion batteries. At the same time, the precursor of hard carbon is widely available, low in cost, and simple in preparation process, and has broad commercial prospects.

[0003] The main materials for preparing hard carbon precursors are biomass-based, resin-based, and asphalt-based. The resin-based materials have controllable structures and high consistency, and have high research value for large-scale production and application of hard carbon materials. Ion exchange resins have a network skeleton structure, high sphericity, and a wide range of sources, making them ideal precursor materials for hard carbon. At present, a large amount of waste ion exchange resins will cause secondary pollution to the environment through landfill or incineration. The use of waste ion exchange resins to prepare hard carbon materials for the negative electrode of sodium ion batteries can not only realize resource utilization, but also avoid pollution to the environment, and at the same time provide a new strategy for preparing hard carbon negative electrodes. Therefore, it is urgent to develop a new process for preparing hard carbon materials for the negative electrode of sodium batteries using waste ion exchange resins that is simple to operate. Summary of the invention

[0004] The object of the present invention is to provide a negative electrode hard carbon material for a sodium ion battery and a preparation method and application thereof, so as to solve the above-mentioned problems.

[0005] According to one aspect of the present invention, a negative electrode hard carbon material for a sodium ion battery is provided. The negative electrode hard carbon material is made of waste cation exchange resin as raw material, and is obtained by mechanical grinding and crushing, soaking in a FeCl3 solution and then calcining at a high temperature. The obtained negative electrode hard carbon material has an average micropore diameter of 2 to 3 nm, and carbon nanofibers with a length of 100-300 nm are distributed on the surface.

[0006] According to another aspect of the present invention, there is provided a method for preparing the above-mentioned negative electrode hard carbon material for sodium ion battery, comprising the following steps:

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

[0008] S2, soaking the resin powder in a 0.1M FeCl3 solution, rinsing, and 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, keeping the temperature 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 in a nitrogen or argon atmosphere containing 1 wt % oxygen;

[0011] S5. Continue heating to 700-800°C at a heating rate of 1-10°C / min under nitrogen or argon atmosphere, and keep warm for 5-7h;

[0012] S6. Continue heating to 1300° C. at a heating rate of 1 to 10° C. / min in a nitrogen or argon atmosphere, keep warm for 1 to 3 hours, and naturally cool to room temperature to obtain a hard carbon material.

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

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

[0015] S2, soaking the resin powder in a 0.1M FeCl3 solution for 1 to 2 hours, quickly rinsing, and 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, keeping the temperature for 1-3h, and nitrogen purge 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 in a nitrogen or argon atmosphere containing 1 wt % oxygen;

[0018] S5. Continue heating to 700-800°C at a heating rate of 1-10°C / min under nitrogen or argon atmosphere, and keep warm for 5-7h;

[0019] S6. Continue heating to 1300° C. at a heating rate of 1 to 10° C. / min under a nitrogen or argon atmosphere, keep warm for 1 to 3 hours, and cool naturally to room temperature;

[0020] S7. Place the resin hard carbon material calcined at high temperature in S6 in 1M HCl to remove the residual metal compounds in the hard carbon material, then wash the hard carbon material with deionized water until it is neutral, and dry it in vacuum at 100°C.

[0021] Among them, step S3 is the process of converting the sulfonic acid groups in the resin into sulfur dioxide. In this process, if the nitrogen purge flow rate is too low, the sulfur dioxide cannot be removed completely, and it is easy to form sulfates with metal ions, affecting the catalytic effect of metal ions; if the nitrogen purge flow rate is too large, it will cause the temperature to drop, which is not conducive to the reaction. Therefore, the nitrogen purge flow rate is controlled within the range of 0.5 to 3L / min to ensure that sulfur dioxide is quickly extracted and avoid the formation of sulfates with metal elements (Fe, etc.) adsorbed in the waste resin (sulfates not only affect the graphitization catalytic effect of metal oxides in the subsequent high-temperature carbonization process, but also cause an increase in the oxygen content in the high-temperature carbonization system, which will cause unnecessary carbon loss at high temperatures and reduce the yield of hard carbon products).

[0022] 1wt% oxygen is mixed into step S4 to burn off a small amount of light carbonaceous components and adjust the pores; at the same time, the oxidation of metal elements is promoted to promote the subsequent graphitization catalysis of metal oxides at 800°C. The role of step S5 is that metal oxides catalyze the generation of graphitized microcrystals, increase the conductivity of hard carbon materials, and exert capacity. Step S6 has two functions: one is to further increase the temperature to adjust the pore structure and graphitization degree, and adjust the average micropore size to about 2nm; the other is to decompose possible insoluble sulfates into oxides so that they can be washed clean in step S7.

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

[0024] S1, crushing the waste cation exchange resin by mechanical grinding to obtain a resin powder with a particle size distribution of 5 to 20 μm;

[0025] S2, soaking the resin powder in a 0.1M FeCl3 solution for 1 to 2 hours, quickly rinsing, and freeze-drying to obtain a precursor powder;

[0026] S3, placing the precursor powder obtained in S2 in a tube furnace, heating to 400°C at a heating rate of 2°C / min under a nitrogen or argon atmosphere, keeping the temperature for 1 to 3 hours, and a nitrogen purge flow rate of 0.5 to 3 L / min;

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

[0028] S5. Continue heating to 700°C at a heating rate of 5°C / min under nitrogen or argon atmosphere and keep warm for 6 hours;

[0029] S6. Continue heating to 1300°C at a heating rate of 5°C / min under nitrogen or argon atmosphere, keep warm for 1 hour, and cool naturally to room temperature;

[0030] S7. Stir the resin hard carbon material calcined at high temperature in S6 in 1M HCl to remove the residual metal compounds in the hard carbon material, then wash the hard carbon material with deionized water until it is neutral, and dry it at 100° C. in vacuum.

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

[0032] The beneficial effects of the present invention are:

[0033] 1. The discarded cation exchange resin is not pre-cleaned to remove possible residual mixed metal ions. As a result, the retained metal ions catalyze the generation of a certain amount of graphite crystallites during the high-temperature carbonization process to enhance conductivity.

[0034] 2. Since the sources of waste ion exchange resins are complex, the resin powder is immersed in a FeCl3 solution to ensure that at least Fe compounds are contained in the high-temperature carbonization process to promote the catalytic synthesis of the graphitized phase in the hard carbon material.

[0035] 3. Pre-soaking of resin powder to absorb metal ions with larger diameter (Fe 3+ ), which can promote the maximum expansion of the internal cross-linked structure, and freeze drying is used to keep the resin in an expanded structure, which is beneficial to the larger pore structure of the hard carbon material after carbonization.

[0036] 4. In the process of preparing the negative electrode hard carbon material for sodium ion battery of the present invention, the staged heating is adopted. Compared with directly heating to 1300°C, the main advantage is that it can catalyze the generation of graphitized microcrystals at a lower temperature of 700-800°C, thereby reducing the high temperature insulation time of 1300°C (generally more than 6 hours). BRIEF DESCRIPTION OF THE DRAWINGS

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

[0038] Figure 2 1 and 2 are charge and discharge curves of the hard carbon materials obtained in the examples and comparative examples.

[0039] Figure 3 The figure shows the rate performance of the hard carbon materials obtained in the examples and comparative examples.

[0040] Figure 4-6 The following is a SEM image of the hard carbon material of the embodiment.

[0041] Figure 7 Graph showing the cycle life of the hard carbon material of the embodiment. DETAILED DESCRIPTION

[0042] The present invention is further described in detail below in conjunction with specific embodiments. Unless otherwise specified, the following raw materials are commercially available.

[0043] Example 1

[0044] A method for preparing a negative electrode hard carbon material for a sodium ion battery comprises the following steps:

[0045] 1. The discarded cation exchange resin is crushed by mechanical grinding to obtain resin powder with a particle size distribution of 5 to 20 μm;

[0046] 2. Take 5 g of the above resin powder, soak it in 0.1 M FeCl3 solution for 2 h, rinse it quickly with deionized water and freeze-dry it to obtain a precursor powder;

[0047] 3. Place the above precursor powder in a tube furnace, heat to 400°C at a rate of 2°C / min in a nitrogen atmosphere, keep warm for 2 hours, and purge nitrogen at a flow rate of 0.8L / min; then adjust the atmosphere to nitrogen containing 1wt% oxygen, and heat from 400°C to 480°C at a rate of 10°C / min; continue to heat to 700°C at a rate of 5°C / min in a nitrogen atmosphere, and keep warm for 6 hours; finally, heat to 1300°C at a rate of 5°C / min in a nitrogen atmosphere, keep warm for 3 hours, and cool naturally to room temperature;

[0048] 4. The resin hard carbon powder after high-temperature calcination was stirred in 1M HCl to remove the residual metal compounds in the hard carbon material, washed with deionized water until neutral and then dried to obtain 1.589 g of hard carbon material, recorded 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 rate is reduced from 0.8 L / min to 0.2 L / min. The specific steps are as follows:

[0051] 1. The discarded cation exchange resin is crushed by mechanical grinding to obtain resin powder with a particle size distribution of 5-20 μm;

[0052] 2. Take 5 g of the above resin powder, soak it in 0.1 M FeCl3 solution for 2 h, rinse it quickly and then freeze-dry it to obtain a precursor powder;

[0053] 3. Place the above precursor in a tubular furnace and heat to 400°C at a rate of 2°C / min in a nitrogen atmosphere, keep warm for 2 hours, and use a nitrogen purge flow rate of 0.2L / min. The subsequent carbonization steps and process parameters are consistent with those in Example 1 to obtain 1.502g of hard carbon material, recorded as HC-D1.

[0054] Comparative Example 2

[0055] The preparation method of the negative electrode hard carbon material for sodium ion battery of Comparative Example 2 is to pre-clean the discarded cation exchange resin on the basis of Example 1 and then perform the subsequent process. The specific steps are as follows:

[0056] 1. The discarded ion exchange resin is washed with deionized water and anhydrous ethanol for multiple times, dried, and then mechanically ground to obtain a precursor powder with a particle size distribution of 5-20 μm;

[0057] 2. Take 5 g of the above resin powder, soak it in 0.1 M FeCl3 solution for 2 h, rinse it quickly and then freeze-dry it to obtain a precursor powder;

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

[0059] Comparative Example 3

[0060] The preparation method of the negative electrode hard carbon material for sodium ion battery of Comparative Example 3 is to pre-clean the discarded cation exchange resin on the basis of Example 1 without soaking in FeCl3 solution, and the specific steps are as follows:

[0061] The discarded ion exchange resin was washed with deionized water and anhydrous ethanol for several times, 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 0.1 M FeCl3 solution) was directly placed in a tube furnace, and the subsequent carbonization steps and process parameters were consistent with those in Example 1, and 1.82 g of hard carbon material was obtained, recorded 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 in a mass ratio of 8:1:1, respectively, and an appropriate amount of N-methylpyrrolidone was added to form a slurry, which was then coated and cut into electrode sheets. With hard carbon as the negative electrode, sodium sheet as the counter electrode, glass fiber as the separator, and 1M NaClO4 (EC:DEC=1:1, with 5vol%FEC) as the electrolyte, they were assembled into CR2032 button batteries in an argon-filled glove box, and the charge and discharge tests were carried out on a blue electric tester under constant temperature and humidity conditions at 30℃. The following are the test results.

[0063] 1. XRD results

[0064] Depend on Figure 1 It can be seen from the XRD results that the hard carbon materials obtained from the comparative example and the embodiment are both typical hard carbon materials, wherein the hard carbon materials obtained from the embodiment, comparative example 1 and comparative example 2 all show a sharp graphite microcrystal diffraction peak at 2θ of 26-27°, which indicates that metal ions can promote the catalytic conversion of a portion of the hard carbon material into graphite microcrystals, thereby obtaining better overall conductivity of the material; at the same time, compared with comparative example 2, the graphite peak intensity of the embodiment 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, and the high decomposition temperature of the sulfate leads to a weakening of the graphitization catalytic performance of the metal elements, and increases the oxygen content of the system during the high-temperature carbonization process, which will further reduce the carbon yield and porosity, affecting the sodium storage performance.

[0065] 2. Electrochemical performance results

[0066] Figure 4-6 It shows that a large number of nano-carbon fibers are generated on the surface of the carbon material under the action of the catalyst, indicating that the graphitization degree of the hard carbon material HC in Example 1 is higher and the conductivity is better, so the performance of up to 337.6 mAh·g -1 The discharge capacity and the first coulombic efficiency of 91.9% at 1A·g -1 The capacity retention rate was as high as 88.7% after 400 cycles under the same conditions.

[0067] In comparative example 1, the nitrogen purge flow rate was small in the early stage of carbonization, which increased the risk of sulfur dioxide produced by the decomposition of sulfonic acid groups and the metal elements forming sulfates. The high decomposition temperature of sulfates weakened the graphitization catalytic performance of metal elements and increased the oxygen content of the system during the high-temperature carbonization process, reducing the carbon yield and porosity. The discharge specific capacity of the obtained hard carbon HC-D1 was 293.4 mAh g -1 .

[0068] In Comparative Example 2, other metal elements were eluted and only Fe element was used as the catalyst of carbonaceous material high-temperature graphite microcrystals. The discharge capacity of the obtained hard carbon HC-D2 reached 312.6 mAh·g -1 .

[0069] In Comparative Example 3, the discarded cation exchange resin was pre-cleaned. There was no metal ion catalysis to convert part of the carbonaceous material into graphite crystals. The conductivity of the obtained hard carbon HC-D3 was low, which was not conducive to the use of capacity. Therefore, the discharge specific capacity of Comparative Example 3 was relatively low.

[0070] Table 1 Discharge capacity and efficiency results of different groups

[0071] serial number <![CDATA[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 are only some embodiments of the present invention. For those skilled in the art, several modifications and improvements can be made without departing from the creative concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. A negative electrode hard carbon material for a sodium ion battery, characterized in that: The hard carbon material is obtained by using waste cation exchange resin as raw material, mechanically grinding and crushing, soaking in FeCl3 solution and then calcining at high temperature. Carbon nanofibers are distributed on the surface of the obtained hard carbon material.

2. The method for preparing the negative electrode hard carbon material for sodium ion battery according to claim 1, characterized in that: The steps include: S1, crushing the discarded cation exchange resin to obtain resin powder; S2, soaking the resin powder in a FeCl3 solution, rinsing, and freeze-drying to obtain a precursor powder; 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, keeping the temperature for 1-3h, and purging with nitrogen; S4, after completing step S3, heating from 400° C. to 500° C. at a rate of 10° C. / min in a nitrogen or argon atmosphere containing 1 wt % oxygen; S5. Continue heating to 700-800°C at a heating rate of 1-10°C / min under nitrogen or argon atmosphere, and keep warm for 5-7h; S6. Continue heating to 1300° C. at a heating rate of 1 to 10° C. / min in a nitrogen or argon atmosphere, keep warm for 1 to 3 hours, and naturally cool to room temperature to obtain hard carbon powder.

3. The method for preparing a negative electrode hard carbon material for a sodium ion battery according to claim 2, characterized in that: The waste cation exchange resin in S1 is crushed by mechanical grinding, and the particle size distribution of the crushed resin powder is 5 to 20 μm.

4. The method for preparing a negative electrode hard carbon material for a sodium ion battery according to claim 2, characterized in that: The nitrogen purge flow rate in S3 is 0.5 to 3 L / min.

5. The method for preparing the negative electrode hard carbon material for sodium ion battery according to any one of claims 2 to 4, characterized in that: The method also includes the purification of the hard carbon material, and the specific steps are: placing the hard carbon material after high-temperature calcination of S6 in 1M HCl, then washing the hard carbon material with deionized water until it is neutral, and vacuum drying at 100°C.

6. The method for preparing a negative electrode hard carbon material for a sodium ion battery according to claim 2, characterized in that: The steps include: S1, crushing the waste cation exchange resin by mechanical grinding to obtain a resin powder with a particle size distribution of 5 to 20 μm; S2, soaking the resin powder in a 0.1M FeCl3 solution for 1 to 2 hours, rinsing, and freeze-drying to obtain a precursor powder; 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, keeping the temperature for 1-3h, and nitrogen purge flow rate of 0.5-3L / min; S4, after completing step S3, heating from 400° C. to 500° C. at a rate of 10° C. / min in a nitrogen or argon atmosphere containing 1 wt % oxygen; S5. Continue heating to 700-800°C at a heating rate of 1-10°C / min under nitrogen or argon atmosphere, and keep warm for 5-7h; S6. Continue heating to 1300° C. at a heating rate of 1 to 10° C. / min under a nitrogen or argon atmosphere, keep warm for 1 to 3 hours, and cool naturally to room temperature; S7. Place the resin hard carbon material calcined at high temperature in S6 in 1M HCl to remove the residual metal compounds in the hard carbon material, then wash the hard carbon material with deionized water until it is neutral, and dry it in vacuum at 100°C.

7. Use of the negative electrode hard carbon material for sodium ion battery according to claim 1 in the preparation of sodium ion batteries.

8. A sodium ion battery negative electrode, characterized in that: The negative electrode hard carbon material according to claim 1 is mixed with a conductive agent and a binder, and then a solvent is added to form a slurry and then applied.

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