Boron-sodium doped hard carbon composite materials and their preparation methods, sodium-ion batteries

Abstract

This invention relates to a boron-sodium doped hard carbon composite material and its preparation method, as well as a sodium-ion battery, belonging to the field of battery technology. The preparation method of the boron-sodium doped hard carbon composite material includes the following steps: 1) adding hard carbon or hard carbon oxide together with metallic sodium into an organic solvent, dispersing evenly, and spray-drying to obtain a solid powder; 2) keeping the solid powder obtained in step 1) at 700-900℃ for 1-3 hours under an inert atmosphere to obtain a precursor material; 3) pressing the precursor material obtained in step 2) together with copper foam into a block and using it as a working electrode, performing electrochemical deposition using cyclic voltammetry; the electrolyte for electrochemical deposition is prepared by mixing boron ester and ionic liquid; 4) washing and drying the working electrode after electrochemical deposition in step 3), and then carbonizing it at 1000-1400℃ for 1-6 hours to obtain the final product. The composite material of this invention can fully utilize the synergistic effect between the high conductivity of sodium ions and the high electronic conductivity of boron atoms during preparation, thereby improving the power performance of the material.

Description

Technical Field

[0001] This invention relates to a boron-sodium doped hard carbon composite material and its preparation method, as well as a sodium-ion battery, belonging to the field of battery technology. Background Technology

[0002] Society's demands for new energy development are increasing, and lithium-ion batteries play a crucial role in both power and energy storage batteries. However, as the application of lithium-ion batteries expands, the cost requirements are also rising. With the emergence of sodium-ion batteries, people have new expectations for low-cost, high-performance rechargeable batteries.

[0003] Sodium-ion batteries use hard carbon as the negative electrode material. Hard carbon has good isotropy, a large interlayer spacing, which enables rapid ion diffusion, good compatibility with electrolytes, a high ion diffusion coefficient, and a wide lithium intercalation potential range, which is beneficial for rapid ion insertion. However, due to the disordered layer structure of hard carbon, its electronic conductivity is poor, affecting its rate performance.

[0004] The electronic conductivity of hard carbon materials can be improved by doping with non-metallic compounds such as boron, or with metals or compounds such as silver, thereby reducing electronic impedance.

[0005] Pitch carbon, a porous carbon material with low graphitization and a disordered layered structure exhibiting short-range order and long-range disorder, is widely available and of stable quality. However, its short-range ordered structure results in fewer pores, lower specific capacity, and lower initial efficiency. Therefore, doping or coating is necessary to reduce irreversible capacity and improve initial efficiency. Currently, developing a metal or non-metal with high electronic conductivity to dope pitch carbon to improve its electronic conductivity and rate performance is of great significance. Summary of the Invention

[0006] This invention provides a boron-sodium doped hard carbon composite material and its preparation method, as well as a sodium-ion battery, to solve the problem of low discharge power in existing sodium-ion batteries.

[0007] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows:

[0008] A method for preparing a boron-sodium doped hard carbon composite material includes the following steps:

[0009] 1) Add hard carbon or hard carbon oxide together with metallic sodium into an organic solvent, disperse evenly, and spray dry to obtain a solid powder;

[0010] 2) The solid powder obtained in step 1) is kept at 700-900℃ for 1-3 hours under an inert atmosphere to obtain the precursor material;

[0011] 3) The precursor material obtained in step 2) is pressed together with copper foam and used as the working electrode for electrochemical deposition using cyclic voltammetry; the electrolyte for electrochemical deposition is prepared by mixing borate ester and ionic liquid.

[0012] 4) Wash and dry the working electrode after electrochemical deposition in step 3), and then carbonize it at 1000-1400℃ for 1-6 hours to obtain the final product.

[0013] The oxidized hard carbon in step 1) is prepared by a method comprising the following steps: dissolving asphalt in toluene, then spray drying at 200-300℃ to obtain granules, carbonizing the granules at 1200-1400℃ for 1-6 hours, then adding concentrated nitric acid and reacting at 50-70℃ for 1-3 hours, filtering, washing, and drying.

[0014] The mass ratio of asphalt to toluene is 10-50:500. The concentration of concentrated nitric acid is 60-65%. The mass ratio of carbonized particles to concentrated nitric acid is 1-10:500.

[0015] In step 1), the mass ratio of hard carbon or oxidized hard carbon to metallic sodium is 1-10:100. The mass ratio of organic solvent to metallic sodium is 100-500:100.

[0016] The organic solvent in step 1) is toluene.

[0017] In step 3), when the precursor material is pressed together with the copper foam, the precursor material is filled into the pores of the copper foam and then pressed.

[0018] In step 3), the mass ratio of the precursor material to the borate ester is 100:1-5.

[0019] The mass ratio of borate ester to ionic liquid is 1-5:100-500.

[0020] The borate ester is one of 4-trifluoromethylphenylboronic acid, 3,4-dimethoxyphenylboronic acid, 2,5-dimethylphenylboronic acid, 2,6-dimethylphenylboronic acid, naphthalenephenylboronic acid, or phenylboronic acid.

[0021] The ionic liquid is one of 1-ethylpyridine tetrafluoroborate, 1-ethyl-3-methylimidazolium chloride, 1-ethyl-3-methylimidazolium iodide, 1-ethyl-2,3-dimethylimidazolium trifluoromethanesulfonate, and 1,2-diethyl-3-methylimidazolium trifluoromethanesulfonate.

[0022] In step 4), the counter electrode during electrochemical deposition is a calomel electrode.

[0023] In step 4), the voltage during electrochemical deposition is -2V to 2V. The scan rate is 0.5-5mV / s. The number of scan cycles is 10-100 cycles.

[0024] A boron-sodium doped hard carbon composite material prepared by the method described above.

[0025] A sodium-ion battery includes a battery casing and a positive electrode, a negative electrode, a separator, and an electrolyte disposed within the battery casing. The negative electrode includes a negative electrode current collector and a negative electrode material layer disposed on the surface of the negative electrode current collector. The negative electrode material layer includes a negative electrode active material. The negative electrode active material is characterized in that the negative electrode active material is the aforementioned boron-sodium doped hard carbon composite material.

[0026] Beneficial effects:

[0027] In the preparation of the composite material of the present invention, sodium carbonate formed on the surface of the hard carbon core is used to enhance the lithium-ion transport rate, reduce the irreversible capacity during the charge and discharge process, and improve the initial efficiency and the sodium-ion transport rate. At the same time, the isotropic and electronic conductivity of the boron-doped amorphous carbon in the outer shell is utilized to improve the rate performance, and the synergistic effect between the high sodium-ion conductivity and the high electronic conductivity of boron atoms is brought into play to improve the power performance of the material.

[0028] Electrochemical deposition of boron salts on sodium-doped hard carbon precursor materials offers advantages over solid-phase or liquid-phase methods, including higher deposition density, stronger stability, and better uniformity. Additionally, the residual ionic liquid solvent on the material surface reduces surface defects after carbonization, thus improving initial efficiency. Attached Figure Description

[0029] Figure 1 This is a SEM image of the boron-sodium doped hard carbon composite material in Example 1. Detailed Implementation

[0030] To make the technical problems, technical solutions, and beneficial effects of this invention easier to understand, the invention will be described in detail below with reference to specific embodiments.

[0031] Preparation Example

[0032] The preparation method of oxidized hard carbon in this example includes the following steps:

[0033] Dissolve 30g of asphalt in 500g of toluene and spray granulate at 250℃. Then transfer the resulting granules to a tube furnace and carbonize at 1300℃ for 3h. Add the carbonized solid to 500g of 65% concentrated nitric acid and heat at 60℃ for 2h. Filter, wash with deionized water, and vacuum dry at 80℃ for 24h to obtain the final product.

[0034] Example 1

[0035] The method for preparing boron-sodium doped hard carbon composite material in this embodiment includes the following steps:

[0036] 1) Add 5g of metallic sodium to 300g of toluene and disperse evenly to obtain a dispersion. Then add 100g of hard carbon oxide powder to the dispersion and disperse evenly again. Then spray dry to obtain a solid powder.

[0037] 2) Place the solid powder obtained in step 1) in a tube furnace, continuously introduce argon gas to maintain the argon atmosphere, then heat to 700℃, hold for 3 hours, and cool to room temperature to obtain the precursor material.

[0038] 3) Take 100g of the precursor material obtained in step 2) and continuously add it to the surface of the foamed copper plate. Use a plastic plate to scrape it back and forth to make the precursor material completely penetrate into the foamed copper. Then press it to obtain a composite foamed copper plate with the precursor material incorporated.

[0039] The composite foam copper plate was used as the working electrode, the saturated calomel electrode was used as the counter electrode, and 3g of 4-trifluoromethylphenylboronic acid was added to 100g of 1-ethylpyridine tetrafluoroboronic acid ester and dispersed evenly as a solvent.

[0040] Electrochemical deposition was performed using cyclic voltammetry. The scan rate was 1 mV / s within the voltage range of -2 V to 2 V, and the scan was performed for 50 cycles. The cells were then washed with deionized water and dried under vacuum at 80 °C for 24 h.

[0041] 4) Carbonize the electrode after drying in step 3) at 1200℃ for 3 hours to obtain the final product.

[0042] The sodium-ion battery of this embodiment is a coin cell, comprising a battery casing, within which are disposed a positive electrode, a negative electrode, a separator, and an electrolyte. The negative electrode includes a negative current collector and a negative electrode material layer disposed on the surface of the current collector. The negative electrode material layer is obtained by mixing a negative electrode active material with a conductive agent SP, a binder LA132, and water through a process of slurry preparation, coating, drying, and rolling. The negative electrode active material is the aforementioned boron-sodium doped hard carbon composite material. The positive electrode is a sodium sheet. The electrolyte is a NaPF6 solution, and the solvent is a mixed solvent obtained by mixing EC and DEC in a volume ratio of 1:1, wherein the NaPF6 concentration is 1.1 mol / L. The separator is a polyethylene propylene (PEP) composite membrane.

[0043] Example 2

[0044] The method for preparing boron-sodium doped hard carbon composite material in this embodiment includes the following steps:

[0045] 1) Add 1g of metallic sodium to 100g of toluene and disperse evenly to obtain a dispersion. Then add 100g of hard carbon oxide powder to the dispersion and disperse evenly again. After that, spray dry to obtain a solid powder.

[0046] 2) Place the solid powder obtained in step 1) in a tube furnace, continuously introduce argon gas to maintain the argon atmosphere, then heat to 700℃, hold for 3 hours, and cool to room temperature to obtain the precursor material.

[0047] 3) Take 100g of the precursor material obtained in step 2) and continuously add it to the surface of the foamed copper plate. Use a plastic plate to scrape it back and forth to make the precursor material completely penetrate into the foamed copper. Then press it to obtain a composite foamed copper plate with the precursor material incorporated.

[0048] The composite foam copper plate was used as the working electrode, and the saturated calomel electrode was used as the counter electrode. 1 g of 3,4-dimethoxyphenylboronic acid was added to 100 g of 1-ethyl-3-methylimidazolium chloride ionic liquid and dispersed evenly as a solvent.

[0049] Electrochemical deposition was performed using cyclic voltammetry at a scan rate of 0.5 mV / s within a voltage range of -2 V to 2 V for 10 cycles. The cells were then washed with deionized water and dried under vacuum at 80 °C for 24 h.

[0050] 4) Carbonize the electrode after drying in step 3) at 1000℃ for 6 hours to obtain the final product.

[0051] The sodium-ion battery in this embodiment is a coin cell, and the negative electrode active material uses the boron-sodium doped hard carbon composite material of this embodiment. The rest is the same as in Embodiment 1.

[0052] Example 3

[0053] The method for preparing boron-sodium doped hard carbon composite material in this embodiment includes the following steps:

[0054] 1) Add 10g of metallic sodium to 500g of toluene and disperse evenly to obtain a dispersion. Then add 100g of hard carbon oxide powder to the dispersion and disperse evenly again. After that, spray dry to obtain a solid powder.

[0055] 2) Place the solid powder obtained in step 1) in a tube furnace, continuously introduce argon gas to maintain the argon atmosphere, then heat to 700℃, hold for 3 hours, and cool to room temperature to obtain the precursor material.

[0056] 3) Take 100g of the precursor material obtained in step 2) and continuously add it to the surface of the foamed copper plate. Use a plastic plate to scrape it back and forth to make the precursor material completely penetrate into the foamed copper. Then press it to obtain a composite foamed copper plate with the precursor material incorporated.

[0057] The composite foam copper plate was used as the working electrode, and the saturated calomel electrode was used as the counter electrode. 5g of 2,5-dimethylphenylboronic acid was added to 100g of 1-ethyl-3-methylimidazolium iodide ionic liquid and dispersed evenly as a solvent.

[0058] Electrochemical deposition was performed using cyclic voltammetry. The scan rate was 5 mV / s within the voltage range of -2 V to 2 V, and the scan was performed for 100 cycles. The working electrode was then washed with deionized water and dried under vacuum at 80 °C for 24 h.

[0059] 4) Carbonize the electrode after drying in step 3) at 1400℃ for 1 hour to obtain the final product.

[0060] The sodium-ion battery in this embodiment is a coin cell, and the negative electrode active material uses the boron-sodium doped hard carbon composite material of this embodiment. The rest is the same as in Embodiment 1.

[0061] Example 4

[0062] The method for preparing boron-sodium doped hard carbon composite material in this embodiment includes the following steps:

[0063] 1) Add 5g of metallic sodium to 300g of toluene and disperse evenly to obtain a dispersion. Then add 100g of hard carbon oxide powder to the dispersion and disperse evenly again. After that, spray dry to obtain a solid powder.

[0064] 2) Place the solid powder obtained in step 1) in a tube furnace, continuously introduce argon gas to maintain the argon atmosphere, then heat to 800℃, hold for 2 hours, and cool to room temperature to obtain the precursor material.

[0065] 3) Take 100g of the precursor material obtained in step 2) and continuously add it to the surface of the foamed copper plate. Use a plastic plate to scrape it back and forth to make the precursor material completely penetrate into the foamed copper. Then press it to obtain a composite foamed copper plate with the precursor material incorporated.

[0066] The composite foam copper plate was used as the working electrode, and the saturated calomel electrode was used as the counter electrode. 2g of 4-trifluoromethylphenylboronic acid and 1g of naphthalenephenylboronic acid were added to 100g of 1-ethylpyridine tetrafluoroborate and dispersed evenly as a solvent.

[0067] Electrochemical deposition was performed using cyclic voltammetry at a scan rate of 0.5 mV / s within a voltage range of -2 V to 2 V for 50 cycles. The cells were then washed with deionized water and dried under vacuum at 80 °C for 24 h.

[0068] 4) Carbonize the electrode after drying in step 3) at 1400℃ for 1 hour to obtain the final product.

[0069] The sodium-ion battery in this embodiment is a coin cell, and the negative electrode active material uses the boron-sodium doped hard carbon composite material of this embodiment. The rest is the same as in Embodiment 1.

[0070] Example 5

[0071] The difference between this embodiment and Embodiment 1 is that hard carbon material is used instead of hard carbon oxide, while the rest is the same as in Embodiment 1.

[0072] Comparative Example 1

[0073] The preparation method of the composite material in this comparative example differs from that in Example 1 in that the precursor material in step 2) is replaced with oxidized asphalt, while the rest is the same as in Example 1.

[0074] Comparative Example 2

[0075] The preparation method of the composite material in this comparative example includes the following steps:

[0076] 1) Add 5g of metallic sodium to 300g of toluene and disperse evenly to obtain a dispersion. Then add 100g of hard carbon oxide powder to the dispersion and disperse evenly again. Then filter and spray dry to obtain a solid powder.

[0077] 2) Place the solid powder obtained in step 1) in a tube furnace, continuously introduce argon gas to maintain the argon atmosphere, then heat to 700℃, carbonize for 3 hours, and cool to room temperature to obtain the precursor material.

[0078] 3) Take 100g of the precursor material obtained in step 2), add it together with 3g of 4-trifluoromethylphenylboronic acid to 100g of 1-ethylpyridine tetrafluoroboronic acid ester and disperse evenly. Filter, dry the solid under vacuum at 80℃ for 24h, then transfer it to a tube furnace and carbonize it at 1200℃ for 3h under an argon atmosphere to obtain the product.

[0079] Experimental Example

[0080] (1) SEM testing

[0081] The hard carbon composite material prepared in Example 1 was subjected to SEM testing, and the test results are as follows: Figure 1 As shown.

[0082] Depend on Figure 1 As can be seen, the hard carbon composite material exhibits a granular structure with uniform size and a particle size between (10 and 15) μm.

[0083] (2) Physicochemical properties

[0084] Referring to the test methods in GB / T-24533-2019 "Graphite Anode Materials for Lithium-ion Batteries", the hard carbon composite materials prepared in Examples 1-5 and Comparative Examples 1-2 were subjected to particle size, tap density, specific surface area, elemental analysis, and specific capacity tests. Simultaneously, the interlayer spacing of the materials was measured by XRD. The test results are shown in Table 1 below. According to Table 1, the hard carbon composite materials prepared in the examples have slightly smaller particle sizes, and their tap density and specific surface area are also larger than those in the comparative examples.

[0085] (3) Button cell battery test

[0086] The hard carbon composite materials obtained in Examples 1-5 and Comparative Examples 1-2 were used as negative electrode materials and assembled into coin cells A1, A2, A3, A4, A5, B1, and B2 according to the following steps:

[0087] A binder, conductive agent, and solvent are added to the negative electrode material, stirred to form a slurry, coated onto copper foil, and then dried and rolled to obtain the negative electrode sheet. The binder used is LA132, the conductive agent is SP, and the solvent is double-distilled water. The mass-to-volume ratio of the negative electrode material, SP, LA132, and double-distilled water is 94g:2g:

[0088]

[0089] 4g: 220mL; the electrolyte used is NaPF6 / EC+DEC (EC and DEC volume ratio 1:1, concentration 1.1mol / L). A sodium metal sheet is used as the counter electrode, and a polyethylene propylene (PEP) composite membrane is used as the diaphragm.

[0090] The battery assembly was conducted in an argon-filled glove box, and the electrochemical performance was tested using a Wuhan Landian CT2001A battery tester. The charge / discharge voltage range was 0.00V to 2.00V, and the charge / discharge rate was 0.1C. The rate capability (2C / 0.1C) and cycle performance (0.2C / 0.2C, 200 cycles) of the coin cells were also tested.

[0091] The test data is detailed in Table 1.

[0092] Table 1

[0093] As shown in Table 1, compared with Comparative Example 1, the boron-sodium doped hard carbon composite materials prepared in Examples 1-3 exhibit significantly improved initial discharge capacity, initial efficiency, rate performance, and cycle performance. This is because, in this invention, boron doping enhances the electronic conductivity of the material, thereby improving rate performance. Simultaneously, sodium doping reduces the irreversible capacity of the material and increases the sodium ion insertion / extraction rate during charge and discharge, thus improving rate performance.

[0094] (4) Pouch Battery Testing

[0095] Using the boron-sodium doped hard carbon composite materials from Examples 1-5 and Comparative Examples 1-2 as the negative electrode, the negative electrode sheet was prepared by slurry mixing and coating. A layered oxide (NaFe1 / 3Mn1 / 3Ni1 / 3O2) was used as the positive electrode, NaPF6 (solvent EC+DEC, volume ratio 1:1, concentration 1.3mol / L) was used as the electrolyte, and Celegard 2400 was used as the separator to prepare a 2Ah soft pack battery.

[0096] High-temperature storage performance test:

[0097] The test conditions are as follows: the battery capacity under full charge is tested at 60℃ and recorded as X1. After being placed at 60℃ for 30 days, the battery capacity is tested again and recorded as X2. The charge retention is calculated as X2 / X1*100%. Then, the battery is fully charged to its maximum capacity (100% SOC) and its capacity is tested as X3. The recovery capacity is calculated as X3 / X1*100%.

[0098] Cyclic performance: 25°C, 1°C / 1°C, 500 cycles.

[0099] The results are detailed in Table 2.

[0100] Table 2

[0101] Charge retention Capacity recovery Cyclic performance Example 1 94.8％ 97.5％ 95.3％ Example 2 94.7％ 97.9％ 95.0％ Example 3 93.5％ 96.6％ 95.7％ Example 4 93.3％ 96.3％ 95.3％ Example 5 93.0％ 95.8％ 95.0％ Comparative Example 1 90.8％ 92.9％ 92.4％ Comparative Example 2 91.4％ 93.1％ 92.9％

[0102] As can be seen from Table 2, the high-temperature storage performance of the materials in the examples is better than that of the comparative examples. This is because the electrochemical deposition method is used to deposit boron salts on the sodium-doped hard carbon precursor materials, which improves the compatibility between the material surface and the electrolyte, reduces the side reactions of the materials, and improves the high-temperature storage performance and cycle performance.

Claims

1. A method for preparing a boron-sodium doped hard carbon composite material, characterized in that, Includes the following steps: 1) Add hard carbon or hard carbon oxide together with metallic sodium into an organic solvent, disperse evenly, and spray dry to obtain a solid powder; 2) The solid powder obtained in step 1) is kept at 700-900℃ for 1-3 hours under an inert atmosphere to obtain the precursor material; 3) The precursor material obtained in step 2) is pressed together with copper foam and used as the working electrode for electrochemical deposition using cyclic voltammetry; the electrolyte for electrochemical deposition is prepared by mixing borate ester and ionic liquid. 4) Wash and dry the working electrode after electrochemical deposition in step 3), and then carbonize it at 1000-1400℃ for 1-6 hours to obtain the final product.

2. The method for preparing boron-sodium doped hard carbon composite material according to claim 1, characterized in that, The oxidized hard carbon in step 1) is prepared by a method comprising the following steps: dissolving asphalt in toluene, then spray drying at 200-300℃ to obtain granules, carbonizing the granules at 1200-1400℃ for 1-6 hours, then adding concentrated nitric acid and reacting at 50-70℃ for 1-3 hours, filtering, washing, and drying.

3. The method for preparing boron-sodium doped hard carbon composite material according to claim 1, characterized in that, In step 1), the mass ratio of hard carbon or hard carbon oxide to metallic sodium is 1-10:

100.

4. The method for preparing boron-sodium doped hard carbon composite material according to claim 1, characterized in that, In step 3), the mass ratio of the precursor material to the borate ester is 100:1-5.

5. The method for preparing boron-sodium doped hard carbon composite material according to claim 4, characterized in that, The mass ratio of borate ester to ionic liquid is 1-5:100-500.

6. The method for preparing boron-sodium doped hard carbon composite material according to any one of claims 1-5, characterized in that, In step 3), the borate ester is one of 4-trifluoromethylphenylboronic acid, 3,4-dimethoxyphenylboronic acid, 2,5-dimethylphenylboronic acid, 2,6-dimethylphenylboronic acid, naphthalenephenylboronic acid, or phenylboronic acid.

7. The method for preparing boron-sodium doped hard carbon composite material according to any one of claims 1-5, characterized in that, In step 3), the ionic liquid is one of 1-ethylpyridine tetrafluoroborate, 1-ethyl-3-methylimidazolium chloride, 1-ethyl-3-methylimidazolium iodide, 1-ethyl-2,3-dimethylimidazolium trifluoromethanesulfonate, and 1,2-diethyl-3-methylimidazolium trifluoromethanesulfonate.

8. The method for preparing boron-sodium doped hard carbon composite material according to claim 7, characterized in that, In step 4), the voltage during electrochemical deposition is -2V to 2V.

9. A boron-sodium doped hard carbon composite material prepared by the method of claim 1.

10. A sodium-ion battery, comprising a battery casing and a positive electrode, a negative electrode, a separator, and an electrolyte disposed within the battery casing, wherein the negative electrode comprises a negative electrode current collector and a negative electrode material layer disposed on the surface of the negative electrode current collector, the negative electrode material layer comprising a negative electrode active material, characterized in that, The negative electrode active material is the boron-sodium doped hard carbon composite material as described in claim 9.

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