Modified sodium ion battery negative electrode material and preparation method thereof

Abstract

The invention belongs to the technical field of sodium-ion batteries, and particularly relates to a modified sodium-ion battery negative electrode material and a preparation method thereof. The invention relates to a modified sodium ion battery negative electrode material, which is obtained by heating and evaporating a coating material, N, N-dimethylformamide and hard carbon powder to dryness, and carbonizing in an inert atmosphere, wherein the ratio of the coating material to the N, N-dimethylformamide to the hard carbon powder is (30mg-90mg): 20mL: 1g; the coating material comprises one or more of asphalt, bituminous coal, a tetrahydrofuran extract of the asphalt and tetrahydrofuran extraction residues of the asphalt; the volume of closed pores of the modified sodium ion battery negative electrode material is 0.04-0.05 cm < 2 > / g. Most pore structures in the hard carbon can be converted from open pores to closed pores, and meanwhile, the first-circle coulombic efficiency is high.

Description

TECHNICAL FIELD

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

[0002] Energy storage devices can effectively smooth the fluctuations of intermittent clean energy such as wind and solar energy, realize time shift of energy and coordinated regulation of power grids. Compared with lithium ion batteries which rely on scarce lithium resources, sodium batteries have the advantages of high abundance of sodium element in the earth's crust, raw material cost of only about 1 / 200 of lithium carbonate, and both positive and negative electrodes can use inexpensive aluminum foil current collector, thereby reducing the system cost by 30% to 40%. With the advantages of long cycle life and intrinsic safety, sodium ion batteries have fully entered the stage of large-scale engineering application from technology verification, and have become a core energy storage technology supporting new power systems.

[0003] However, the performance bottleneck of sodium ion batteries is concentrated in the hard carbon negative electrode material. Although hard carbon has the advantages of low redox potential, small volume expansion, abundant resources and the like, the theoretical capacity can reach 350-400 mAh / g, but the first coulomb efficiency is generally lower than 80%, which seriously restricts the improvement of energy density. The core problem is that sodium ions are irreversibly adsorbed in the surface defects, micropores and interlayer structures of hard carbon, and the conversion process dynamics of intercalated sodium to quasi-metallic clusters in the closed pores is slow, resulting in a large amount of active sodium ions being permanently consumed in the first cycle. This process not only reduces the reversible capacity and affects the cycle stability, but also becomes a key scientific problem restricting the performance breakthrough of sodium batteries.

[0004] Therefore, in order to develop sodium ion batteries, it is urgent to develop high-performance hard carbon negative electrode materials. The existing technology uses hard carbon as the negative electrode of sodium ion batteries, and the current research focuses on precise control of the precursor, such as biomass and resin, and optimization of the temperature gradient and holding time in the pyrolysis process, in order to improve the reversible sodium storage site density and ion transmission channel efficiency. However, hard carbon as the negative electrode of sodium ion batteries still has the problems of low first cycle coulomb efficiency and low capacity, which restricts the development of sodium ion batteries. SUMMARY

[0005] In view of the deficiencies in the prior art, the application provides a modified sodium ion battery negative electrode material and a preparation method thereof, which can solve the technical problems of low first cycle coulomb efficiency and low capacity of hard carbon.

[0006] The application is implemented by adopting the following technical solutions: A modified sodium ion battery negative electrode material is obtained by heating and evaporating dry N,N-dimethylformamide and hard carbon powder, and carbonizing under an inert atmosphere, wherein the ratio of the coating material, N,N-dimethylformamide and hard carbon powder is 30mg-90mg:20mL:1g. The coating material includes one or more of bitumen, bituminous coal, tetrahydrofuran extract of bitumen, and tetrahydrofuran extraction residue of bitumen; The closed pore volume of the modified sodium ion battery negative electrode material is 0.04-0.05 cm 2 / g.

[0007] Preferably, the preparation steps of the tetrahydrofuran extract of bitumen and the tetrahydrofuran extraction residue of bitumen include: Mixing bitumen with tetrahydrofuran solvent and performing extraction treatment, and after separation, obtaining a first part containing soluble components and a second part containing insoluble components: After removing the solvent, the first part containing soluble components obtains the tetrahydrofuran extract of bitumen; And after drying, the second part containing insoluble components obtains the tetrahydrofuran extraction residue of bitumen.

[0008] The preparation method of the modified sodium ion battery negative electrode material, characterized in that, specifically includes the following steps: Mixing the coating material and N,N-dimethylformamide to obtain a coating material DMF solution; Mixing the hard carbon powder with the coating material N,N-dimethylformamide solution to obtain a mixed solution; Drying the mixed solution to obtain a mixed powder; Carbonizing the mixed powder under an inert atmosphere to obtain the modified sodium ion battery negative electrode material; The carbonization treatment conditions are: temperature is 1200-1600℃, holding time is 2h, and heating rate is 2-5℃ / min.

[0009] Preferably, the mixing conditions are repeated ultrasonic cycles of 1-5min, and each ultrasonic cycle is 50-60H Z sonication for 3s and standing for 2s.

[0010] Preferably, the drying temperature is 78-82℃, and stirring is adopted during drying at a rotation speed of 200r / min.

[0011] A sodium ion battery negative electrode prepared from a modified sodium ion battery negative electrode material, and the preparation steps are as follows: Coating a slurry formed by the modified sodium ion battery negative electrode material, conductive carbon, and polyvinylidene fluoride on a current collector, and drying under vacuum conditions to obtain a sodium ion battery negative electrode; The mass ratio of the modified sodium ion battery negative electrode material, conductive carbon, and polyvinylidene fluoride is 9:0.5-0.4:0.5-0.4.

[0012] A sodium ion battery comprises a positive electrode, a negative electrode, a separator and an electrolyte, and the negative electrode is prepared by the sodium ion battery negative electrode.

[0013] Principles of the present application: By introducing bituminous coal, a typical soft carbon precursor, high-temperature carbonization will form ordered graphite layers, and these graphite segments will preferentially move to relatively active defects at high temperatures, combine with the intrinsic segments of commercial HC at the defects, and then form closed pores. This will make part of the open pore structure in commercial HC evolve into closed pore structure, effectively improving the capacity of the platform region. The number of defects is also reduced, the irreversible adsorption of sodium ions is weakened, and the first circle coulomb efficiency and capacity are effectively improved.

[0014] Compared with the prior art, the present application has the following advantages: 1. The present application provides a modified sodium ion battery negative electrode material, which is prepared according to the following steps: mixing hard carbon powder, coating material and N,N-dimethylformamide, then stirring, drying and carbonizing to obtain the modified sodium ion battery negative electrode material. The closed pore volume of the modified sodium ion battery negative electrode material is 0.04~0.05cm 2 / g, which can make most of the internal pore structure of hard carbon closed and the first circle coulomb efficiency high and the capacity large.

[0015] 2. The preparation method of the present application improves the performance of hard carbon by changing the internal structure. Bituminous coal is a typical soft carbon precursor, high-temperature carbonization will form ordered graphite layers, and these graphite segments will preferentially move to relatively active defects at high temperatures, combine with the intrinsic segments of commercial HC at the defects, and then form closed pores.

[0016] 3. The closed pore structure constructed by the preparation method of the present application reduces the diffusion efficiency of the electrolyte to promote the rate performance, and the reversible capacity is not affected.

[0017] 4. The preparation method of the present application improves the sodium storage performance of hard carbon negative electrode from multiple dimensions, multiple levels and three-dimensional design to promote the commercialization process of sodium ion battery.

[0018] 5、First circle of the promotion of coulomb efficiency, reduce the irreversible loss of active ions, can improve the actual discharge capacity of the battery; reduce the demand for pre-sodium, thereby reducing the cost of raw materials and process cost, improve the energy density of the whole battery, increase the service life, charge transport more quickly, improve the rate performance of the battery, the first efficiency will reduce the side reaction to inhibit the production of gas, improve the safety of the battery. The energy density of the battery is improved, which will reduce the mass and volume of the battery under the same storage capacity, to a certain extent, reduce the mass of the whole vehicle or increase the storage capacity of the electric vehicle to improve the endurance. Charge transport quickly, it will improve the large current charge and discharge performance of the battery, which will greatly improve the rapid charging of mobile phones and electric vehicles. Reduce the occurrence of side reactions to reduce gas production, which reduces the phenomenon of bulging and leakage of the battery during operation, which is more secure. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 TEM image of commercial hard carbon, red line represents open pore structure.

[0020] Figure 2 TEM image of 5% bituminous coal 1400 in Example 1, red circle represents closed pore structure.

[0021] Figure 3 is the micropore test results of the battery in application example 1 and the material in comparative example 1 Figure 4 is the first circle charge-discharge curve of the battery in application example 1 and the battery in comparative example 1.

[0022] Figure 5 is the long cycle performance test results of the battery in application example 1 Figure 6 is the rate performance test results of the battery in application example 1. DETAILED DESCRIPTION

[0023] The specific embodiments of the present application are described in detail below, but it should be understood that the protection scope of the present application is not limited by the specific embodiments. Based on the examples in the present application, all other examples obtained by those skilled in the art without creative labor are within the scope of protection of the present application. The experimental methods described in each embodiment of the present application are conventional methods unless otherwise specified.

[0024] DMF represents N,N-dimethylformamide, ICE represents first circle coulomb efficiency; PVDF represents polyvinylidene fluoride, HC represents hard carbon, THF represents tetrahydrofuran, and the chemical formula is C4H8O.

[0025] Bituminous coal particles from Jiubao Stone Powder Factory; commercial hard carbon powder is Kureha type 3 from Shenzhen Keyi Zhida Technology Co., Ltd.; conductive carbon Super P from Shenzhen Keyi Zhida Technology Co., Ltd.; polyvinylidene fluoride from Kuraray; asphalt from China Shenhua Energy Co., Ltd.

[0026] Example 1 A preparation method of a modified sodium ion battery negative electrode material, the steps are as follows: S1, 50 mg of bituminous coal particles was weighed and placed in 20 mL of DMF solution, and an ultrasonic cell disrupter was used for repeated ultrasonic cycles of 1 min, and the condition of each ultrasonic cycle was 60 Hz ultrasonic for 3 s and standing for 2 s, to obtain a mixed solution A.

[0027] S2, 1 g of commercial hard carbon powder was weighed and placed in the mixed solution A, and then an ultrasonic cell disrupter was used again for repeated ultrasonic cycles of 5 min, and the condition of each ultrasonic cycle was 50 Hz ultrasonic for 3 s and standing for 2 s, to obtain a mixed solution B; a transmission electron microscope TEM was used to observe the commercial hard carbon, and the result is shown in Figure 1 , which is a TEM pattern of the commercial hard carbon, and the intrinsic structure of the commercial HC has an incomplete fully closed pore.

[0028] S3, the mixed solution B was heated to 80°C and the DMF was evaporated dry using a heating magnetic stirrer at 200 r / min, to obtain a uniformly mixed powder.

[0029] S4, the powder was placed in a tube furnace, and nitrogen was introduced as a protective gas for carbonization treatment to obtain a hard carbon powder marked as 5% bituminous coal, wherein the carbonization treatment temperature was 1400°C, the holding time was 2 h, and the heating rate was 2°C / min, marked as 5% bituminous coal 1400, to obtain a modified sodium ion battery negative electrode material.

[0030] A transmission electron microscope TEM was used to observe the 5% bituminous coal 1400, and the result is shown in Figure 2 , which is a TEM pattern of the 5% bituminous coal 1400, and after the addition of the bituminous coal, it gradually evolved into a closed pore structure, and the red circles are obvious closed pores, which are more than the original sample. A carbon dioxide adsorption and desorption experiment was performed, and the result is shown in Figure 3 , the closed pore diameter and volume of carbon dioxide adsorption and desorption, the 5% bituminous coal 1400 sample increased the number of nostrils and the volume of the closed pores was much larger, and the pore volume increased from 0.00184 cm 2 / g to 0.0446 cm 2 / g.

[0031] Example 2 The 50mg bituminous coal in Example 1 is changed to 30mg to mark 3% bituminous coal, the 80℃ heating and steaming in S3 is changed to 78℃ heating and steaming, the heating rate of 2℃ / min in S4 is changed to 5℃ / min, and the other steps are consistent with Example 1.

[0032] Example 3 The 50mg bituminous coal in Example 1 is changed to 70mg to mark 7% bituminous coal, the 80℃ heating and steaming in S3 is changed to 82℃ heating and steaming, and the other steps are consistent with Example 1.

[0033] Example 4 The 50mg bituminous coal in Example 1 is changed to 90mg to mark 9% bituminous coal, and the other steps are consistent with Example 1.

[0034] Example 5 The carbonization treatment temperature of S4 step in Example 1 is changed to 1000 to mark 5% bituminous coal 1000, and the other steps are consistent with Example 1.

[0035] Example 6 The carbonization treatment temperature of S4 step in Example 1 is changed to 1200 to mark 5% bituminous coal 1200, and the other steps are consistent with Example 1.

[0036] Example 7 The carbonization treatment temperature of S4 step in Example 1 is changed to 1600 to mark 5% bituminous coal 1600, and the other steps are consistent with Example 1.

[0037] Example 8 The bituminous coal particles in Example 1 are changed to pitch, and a 5% pitch negative electrode material is obtained.

[0038] Example 9 THF is used to extract pitch, and small molecular structures inside are extracted out, named as THF-L, and the residue is named as THF-S. Then HC is coated, named as 5% THF-L, and the remaining steps are consistent with Example 1.

[0039] Example 10 The coating material is changed to the residue of THF-extracted pitch, named as 5% THF-S, and the remaining steps are consistent with Example 1.

[0040] Example 11 The 50mg bituminous coal in Example 1 is changed to 70mg THF-L to mark 7% THF-L, and the other steps are consistent with Example 1.

[0041] Example 12 Change 50 mg bituminous coal in Example 1 to 90 mg THF-L to make 9% THF-L, other steps are the same as Example 1.

[0042] Comparative Example 1 The method for preparing a battery using the modified sodium-ion battery anode material is as follows: The Kure Type 3 in Example 1 was made into CR2025 button cells with positive shell, negative shell, PP separator, sodium sheet, and electrolyte in an argon-filled glove box. The electrolyte was 1M NaPF6 in diethylene glycol dimethyl ether. Then, after standing for 10h, the charge-discharge test was performed in a Neware test cabinet at a constant temperature of 28°C.

[0043] Comparative Example 2 How is the porosity of other coating materials, how is the conductivity Application Example 1 The method for preparing a sodium-ion battery anode is as follows: 0.24g of 5% bituminous coal 1400 in Example 1, 0.0133g SuperC, and 0.0133g PVDF were mixed into a slurry, which was coated onto an aluminum foil current collector and dried in a vacuum oven at 80°C overnight to obtain a sodium-ion battery anode.

[0044] The results are shown in Figure 4 The first circle coulombic efficiency was improved from 75.98% to 85.44%, and the reversible capacity was also improved from 308mAh / g to 348mAh / g. The first circle coulombic efficiency of the 5% bituminous coal 1400 was greater than that of the original sample, and the platform capacity was also much higher than that of the original sample.

[0045] Application Example 2 The method for preparing a battery using the modified sodium-ion battery anode material is as follows: The modified sodium-ion battery anode material obtained in Example 1 was made into CR2025 button cells with positive shell, negative shell, PP separator, sodium sheet, and electrolyte in an argon-filled glove box. The electrolyte was 1M NaPF6 in diethylene glycol dimethyl ether. Then, after standing for 10h, the charge-discharge test was performed in a Neware test cabinet at a constant temperature of 28°C.

[0046] The results are shown in Figure 4 The introduction of bituminous coal increased the first circle coulombic efficiency, as shown in Figure 5 The long cycle of 5% bituminous coal 1400 had a capacity retention rate of 80% after 800 cycles, as shown in Figure 6 The rate performance of the two samples, 5% bituminous coal, was better than that of the original sample, as shown in

[0047] Application Example 3 The negative electrode materials of Examples 2-7 were made into CR2025 button cells in an argon-filled glove box with positive electrode shell, negative electrode shell, PP separator, sodium sheet, and electrolyte. The electrolyte was 1M NaPF6 in diethylene glycol dimethyl ether. After standing for 10h, the cells were then tested for charge-discharge performance in a Neware test chamber at a constant temperature of 28°C.

[0048] Application Example 4 The negative electrode materials of Examples 8-12 were made into CR2025 button cells in an argon-filled glove box with positive electrode shell, negative electrode shell, PP separator, sodium sheet, and electrolyte. The electrolyte was 1M NaPF6 in diethylene glycol dimethyl ether. After standing for 10h, the cells were then tested for charge-discharge performance in a Neware test chamber at a constant temperature of 28°C.

[0049] Application Example 5 A method for preparing a sodium-ion battery negative electrode, comprising the following steps: 0.9g of 5% bituminous coal 1400 in Example 1, 0.05g of Super P, and 0.05g of PVDF were mixed into a slurry, which was coated onto an aluminum foil current collector and dried in a vacuum oven at 80°C overnight to obtain a sodium-ion battery negative electrode.

[0050] Application Example 6 A method for preparing a sodium-ion battery negative electrode, comprising the following steps: 0.9g of 5% bituminous coal 1400 in Example 1, 0.04g of Super P, and 0.04g of PVDF were mixed into a slurry, which was coated onto an aluminum foil current collector and dried in a vacuum oven at 80°C overnight to obtain a sodium-ion battery negative electrode.

[0051] Experiment 1 The cells obtained in Application Examples 2 and 3 were tested for electrochemical performance, and the results are shown in Table 1: Table 1 Electrochemical performance of bituminous coal sodium-ion battery Experiment 2 The cells obtained in Application Example 4 were tested for electrochemical performance, and the results are shown in Table 2: Table 2 Electrochemical performance of pitch sodium-ion battery The above-mentioned are only embodiments of the present application, and common technical solutions and / or common knowledge of the scheme are not described in detail. It should be pointed out that, for those skilled in the art, without departing from the technical solutions of the present application, a number of modifications and improvements can be made, which should also be considered as the protection scope of the present application, and these will not affect the effect and practicality of the patent. The protection scope claimed in the present application should be subject to the content of its claims, and the specific implementation mode and the like recorded in the specification can be used to explain the content of the claims.

Claims

1. A modified sodium-ion battery anode material, characterized in that, The coating material, N,N-dimethylformamide and hard carbon powder are mixed, dried and carbonized under inert atmosphere to obtain the modified sodium ion battery negative electrode material; wherein the ratio of the coating material, N,N-dimethylformamide and hard carbon powder is 30mg-90mg:20mL:1g. The coating material comprises one or more of bitumen, bituminous coal, tetrahydrofuran extract of bitumen and tetrahydrofuran extraction residue of bitumen. The closed pore volume of the modified sodium ion battery negative electrode material is 0.04~0.05cm 2 / g.

2. The modified sodium-ion battery anode material of claim 1, wherein, The preparation steps of the tetrahydrofuran extract of bitumen and the tetrahydrofuran extraction residue of bitumen comprise: The bitumen is mixed with a tetrahydrofuran solvent and subjected to extraction treatment, and after separation, a first part containing soluble components and a second part containing insoluble components are obtained: After the first part containing soluble components is subjected to solvent removal, the tetrahydrofuran extract of bitumen is obtained; and after the second part containing insoluble components is dried, the tetrahydrofuran extraction residue of bitumen is obtained.

3. The method for preparing the modified sodium-ion battery anode material according to claim 1, characterized in that, Specifically, the following steps are included: The coating material and N,N-dimethylformamide are mixed to obtain a coating material DMF solution; The hard carbon powder is mixed with the coating material DMF solution to obtain a mixed solution; The mixed solution is dried to obtain a mixed powder; The mixed powder is subjected to carbonization treatment under inert atmosphere to obtain the modified sodium ion battery negative electrode material; The carbonization treatment is performed at a temperature of 1200-1600℃, a holding time of 2h and a heating rate of 2-5℃ / min.

4. The production method according to claim 3, characterized by, The mixing condition is repeated ultrasonic cycle 1~5 min, and the condition of each ultrasonic cycle is 50~60 H Z Ultrasonic 3 s, stand 2 s.

5. The preparation method according to claim 3, characterized in that, The drying temperature is 78-82℃.

6. The preparation method according to claim 3, characterized in that, The stirring speed during drying is 200r / min.

7. A sodium-ion battery anode prepared from the modified sodium-ion battery anode material of claim 1, characterized in that, The preparation steps are as follows: A slurry of the modified sodium ion battery negative electrode material, conductive carbon and polyvinylidene fluoride is applied to a current collector, which is dried under vacuum to obtain a sodium ion battery negative electrode; The mass ratio of the modified sodium ion battery negative electrode material, conductive carbon and polyvinylidene fluoride is 9:0.5-0.4:0.5-0.

4.

8. A sodium-ion battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte, characterized in that, The negative electrode is prepared from the sodium ion battery negative electrode of claim 7.

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