Sodium ion battery and preparation method and application thereof

Abstract

The invention provides a sodium ion battery as well as a preparation method and application thereof, and belongs to the technical field of battery materials. The sodium ion battery comprises a positive electrode, a negative electrode and an electrolyte, the positive electrode is a sodium-supplemented positive plate treated by a biphenyl sodium complex solution; the electrolyte comprises a NaPF6 basic electrolyte and an additive; and the additive is selected from at least one of 3-trimethylsilyl-2-oxazolidinone and N, N-dimethyl formamide. The resistance and capacity of the positive electrode are improved by supplementing sodium to the positive electrode, and the charge-discharge cycle life of the battery is prolonged by adding a polar reagent into the electrolyte to capture PF5 and remove trace water and harmful gas HF generated in charge and discharge.

Description

Technical Field

[0001] The present invention relates to the technical field of battery materials, and more specifically, to a sodium ion battery and a preparation method and application thereof, in particular to a sodium ion positive electrode half-cell and a preparation method and application thereof. Background Art

[0002] Sodium-ion batteries (SIBs) are secondary batteries considered the most promising candidate for large-scale energy storage systems due to their abundant, uniformly distributed, and cost-effective sodium raw material. The electrochemical performance of SIBs depends largely on the intrinsic properties of the cathode material. Among the diverse cathode materials, sodium phosphate (NFPP) composites have been extensively studied due to their fast ion transport and robust structure. However, their poor electronic conductivity and low specific capacity limit the further application of NFPP cathodes in large-scale energy storage.

[0003] Commercial electrolytes for SIBs typically consist of 1 M sodium hexafluorophosphate (NaPF6) in a mixture of cyclic and linear carbonate solvents. NaPF6 has been widely used as an electrolyte salt due to its excellent ionic conductivity, good oxidation resistance, and good compatibility with the aluminum current collector in SIBs. However, LiPF6 also has inherent disadvantages, such as low thermal stability and high sensitivity to trace water, which leads to the formation of reactive acidic compounds such as PF5 and HF. These are harmful and can cause electrolyte solvent decomposition, affect the structural stability of the solid electrolyte interface (SEI) formed at the cathode, and even lead to the dissolution and failure of transition metals in the cathode material, destroying the structure of the active material and promoting battery capacity decay. Therefore, avoiding the introduction of trace water and the generation of harmful HF gas during electrolyte preparation, battery fabrication, and testing can help improve battery capacity decay during cycling, i.e., cycle life.

[0004] Adjusting a single influencing factor is difficult to solve multi-dimensional problems. Based on this, a sodium ion battery and its preparation method and application are proposed, striving to solve the problems of existing technologies through multiple improvements. Summary of the Invention

[0005] To achieve the purpose of the invention, the present invention provides a sodium ion battery and its preparation method and application. The present invention improves the resistance and capacity of the positive electrode by supplementing sodium to the positive electrode, and increases the charge and discharge cycle life of the battery by adding polar reagents to the electrolyte to capture PF5 and remove trace water and harmful gas HF generated during charging and discharging, thereby synergistically optimizing the performance of the sodium ion battery in multiple aspects.

[0006] To achieve the above object, the technical solution of the present invention is as follows: In a first aspect, the present invention provides a sodium ion battery comprising a positive electrode, a negative electrode and an electrolyte; The positive electrode is a sodium-supplemented positive electrode sheet treated with a sodium biphenyl complex solution; The electrolyte includes a NaPF6-based electrolyte and an additive; the additive is selected from at least one of 3-trimethylsilyl-2-oxazolidinone and N,N-dimethylformamide.

[0007] In some embodiments, the negative electrode is a composite sodium sheet.

[0008] In some embodiments, the concentration of the sodium biphenyl complex solution is 0.2 mol / L to 0.6 mol / L, preferably 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, and any one component in the range consisting of any two of the above values.

[0009] In some embodiments, the sodium biphenyl complex solution is prepared by dissolving sodium in a mixed solvent of biphenyl and tetrahydrofuran.

[0010] In some embodiments, the volume ratio of biphenyl to tetrahydrofuran in the mixed solvent is 1:4.

[0011] In some embodiments, the NaPF6 based electrolyte is a NaPF6 based electrolyte with a concentration of 0.1 mol / L to 1 mol / L.

[0012] In some embodiments, in the NaPF6 base electrolyte, the concentration of NaPF6 in the base electrolyte is 0.1 mol / L~1 mol / L, preferably 0.1 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L and any one component in the range composed of any two of the above values.

[0013] In some embodiments, the mixed solvent in the NaPF6 based electrolyte is a combination of ethylene carbonate, propylene carbonate, and diethyl carbonate.

[0014] In some embodiments, the volume ratio of ethylene carbonate, propylene carbonate, and diethyl carbonate is 1:1:1.

[0015] In some embodiments, the volume ratio of the additive to the NaPF6 base electrolyte is 1:10~50, preferably 1:20~40, preferably 1:10, 1:20, 1:30, 1:40, 1:50 and any component in the range of any two of the above values.

[0016] In some embodiments, the positive electrode includes a positive electrode active material, a binder, a dispersant, and conductive carbon.

[0017] In some embodiments, the positive electrode active material is selected from at least one of positive electrode layered oxide O3, sodium iron pyrophosphate, or sodium nickel iron manganese oxide.

[0018] In some embodiments, the dispersant is KD-1 or KD-2.

[0019] In some embodiments, the binder is selected from polyvinylidene fluoride, and the polyvinylidene fluoride is at least one of PVDF5130 and PVDFHSV-900.

[0020] In some embodiments, the conductive carbon is selected from at least one of acetylene black, Ketjen black, graphite KS-6, graphite KS-15, single-walled carbon nanotubes, graphene, SP carbon black, Kappa 100, and graphene oxide (GO). Preferably, the conductive carbon is a combination of single-walled carbon nanotubes and Kappa 100, with the weight ratio of the single-walled carbon nanotubes to Kappa 100 being 1:9.

[0021] In some embodiments, the positive electrode comprises, by weight percentage, 70-95% of a positive electrode active material, 0.5-15% of a binder, 0.01-1% of a dispersant, and 0.5-20% of a conductive carbon.

[0022] In some embodiments, in the positive electrode, the dispersant accounts for 0.01%, 0.02%, 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 1% and any component in the range of any two of the above values, by weight percentage.

[0023] In some embodiments, in the positive electrode, the positive electrode active material accounts for 70%, 72%, 74%, 76%, 78%, 80%, 82%, 84%, 86%, 88%, 90%, 92%, 93%, 94% or 95% by weight, and any component in the range of any two of the above values.

[0024] In some embodiments, in the positive electrode, the binder accounts for 0.5%, 0.98%, 1%, 2%, 3%, 4%, 5%, 8%, 10%, 12%, 15% and any component in the range of any two of the above values ​​by weight.

[0025] In some embodiments, in the positive electrode, conductive carbon accounts for 0.5%, 1%, 2%, 3%, 4%, 6%, 7%, 8%, 10%, 12%, 14%, 16%, 18%, 20% and any component in the range of any two of the above values ​​by weight.

[0026] In some embodiments, in the positive electrode, by weight percentage, the positive electrode active material accounts for 70%, the dispersant accounts for 0.1%, the binder accounts for 10% and the conductive carbon accounts for 19.9%.

[0027] In a second aspect, the present invention provides a method for preparing the sodium ion battery of the present invention, wherein: (1) The preparation process of the electrolyte includes the following steps: (1) Dissolve NaPF6 in a mixed solvent to prepare a basic electrolyte; (2) Adding additives to the basic electrolyte and mixing them evenly to prepare the electrolyte; (2) The preparation process of the positive electrode includes the following steps: S1: pre-treating the binder, conductive carbon, and positive electrode active material respectively; S2: Dispersing a binder, conductive carbon, a positive electrode active material and a dispersant in N-methylpyrrolidone to prepare a positive electrode slurry; S3: coating the positive electrode slurry on aluminum foil, drying, and sheeting to obtain a basic positive electrode; S4: soaking the base cathode in a sodium biphenyl complex solution, washing, and evaporating the solvent; (3) Using the obtained electrolyte, positive electrode and negative electrode to prepare a sodium ion battery.

[0028] In some embodiments, in S1, the pretreatment refers to: vacuum baking the conductive carbon and the positive electrode active material, and vacuum drying the binder.

[0029] In some embodiments, the negative electrode is a composite sodium sheet.

[0030] In some embodiments, the concentration of the sodium biphenyl complex solution is 0.1 mol / L to 1 mol / L. In some embodiments, the concentration of the sodium biphenyl complex solution is 0.1 mol / L to 1 mol / L, preferably 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L, and any one component in the range consisting of any two of the above values. In the present invention, "0.1 mol / L" is abbreviated as "0.1 M", and the rest is analogous.

[0031] In some embodiments, the sodium biphenyl complex solution is prepared by dissolving sodium in a mixed solvent of biphenyl and tetrahydrofuran.

[0032] In some embodiments, the volume ratio of biphenyl to tetrahydrofuran in the mixed solvent is 1:4.

[0033] In some embodiments, the additive is selected from at least one of 3-trimethylsilyl-2-oxazolidinone and N,N-dimethylformamide.

[0034] In a third aspect, the present invention provides a use of the sodium ion battery of the present invention in an energy storage device.

[0035] In some embodiments, "normal temperature" refers to room temperature of 10-40°C, preferably 20-30°C or 25°C.

[0036] Beneficial effects: The present invention provides a sodium ion battery and its preparation method and application to improve the problems of positive electrode resistance and capacitance difference of sodium batteries in the prior art, thereby improving the problem of capacity decay during battery cycling, thereby enhancing the market application of sodium batteries.

[0037] The present invention treats the basic positive electrode in a sodium-biphenyl complex solution to enrich the positive electrode with sodium, thereby successfully reducing the electrode surface resistance, improving the battery's charge and discharge capacity and first coulomb efficiency, benefiting the battery's discharge rate, and enhancing the battery's cycle performance.

[0038] The present invention adds one or two additives to the electrolyte, which not only reduces the active substances that affect the long charge and discharge cycle of the sodium battery, but also improves the occurrence of electrolyte side reactions and the corrosion of electrode materials.

[0039] The sodium ion battery provided by the present invention achieves synergistically improved battery cycle life performance by pre-treating the positive electrode sheet and adding additives to improve the electrolyte, thereby enabling the battery to have excellent long-cycle performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 Schematic diagram of the electrolyte design for sodium-ion batteries. (a) The decomposition and hydrolysis of NaPF6; (b) the removal of water and HF by 3-trimethylsilyl-2-oxazolidinone; and (c) the capture of PF5 by N,N-dimethylformamide.

[0041] Figure 2 Comparison of charge and discharge performance of different cathode half-cells at a rate of 0.1C in Example 1. (a) Comparison of gram capacity-voltage curves of different cathode half-cells at a rate of 0.1C; (b) Comparison of gram capacity and first coulombic efficiency of different cathode half-cells at a rate of 0.1C.

[0042] Figure 3 This is a comparison chart of the discharge gram capacity of the positive electrode half-cells of different positive electrode half-cells at different rates in Example 1.

[0043] Figure 4 This is a comparison chart of the surface temperature of the positive electrode half-cells of different positive electrode half-cells at different rates in Example 1.

[0044] Figure 5 1 is the Nyquist plot of different positive electrode half-cells in Example 1.

[0045] Figure 6 1C charge-discharge cycle curves of different positive electrode half-cells in Example 1.

[0046] Figure 7 This is the dQ / dV curve of the NFPP-4 positive electrode half-cell in Example 2 at different numbers of charge and discharge cycles.

[0047] The present invention will be further described below with reference to specific examples. These examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention. DETAILED DESCRIPTION

[0048] The present invention will be further described below with reference to specific examples. These examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention.

[0049] 1. Chemicals and Instruments Sodium hexafluorophosphate (NaPF6, 99.9%) was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; Ethylene carbonate (EC, 99%) and propylene carbonate (PC, 99.5%) were purchased from Shanghai Yien Chemical Technology Co., Ltd.; Diethyl carbonate (DEC, 99.9%) was purchased from Sigma-Aldrich (Shanghai) Trading Co., Ltd.; Tetrahydrofuran (99.0%) and N,N-dimethylformamide (DMF, 99.0%) were purchased from Shanghai MacLean Biochemical Technology Co., Ltd.; 3-Trimethylsilyl-2-oxazolidinone (TMS-ON, 98%) and biphenyl (>99.5%) were purchased from Shanghai Linen Technology Development Co., Ltd.; N-Methylpyrrolidone (NMP, 99.5%) was provided by Chongqing Zhongrun New Materials Co., Ltd.; Dispersant KD-1 cationic polymer dispersant (Hypremer KD1, 99%) was purchased from Guangzhou Daixun Trading Co., Ltd.; Glass fiber separator (GF / D, Whatman), a complete set of CR#2032 button battery accessories, and composite sodium sheet (0.45 mm × 15.6 mm) were purchased from Dongguan Kelude New Energy Technology Co., Ltd. The positive electrode material sodium ferric pyrophosphate NFPP (NFPP-100) and the negative electrode hard carbon (type-2) were provided by Shenzhen Kejing Zhida Technology Co., Ltd.

[0050] The battery tester (CT-4008-5VA-SI) was purchased from Shenzhen Xinwei Electronics Co., Ltd.; the electrochemical workstation (CHI660E) was purchased from Shanghai Chenhua Instrument Technology Co., Ltd.; the electrode punching machine (JK20140311) was purchased from Hefei Kejing Material Technology Co., Ltd.; the vacuum oven (DZF-6020BZ) was purchased from Shanghai Yixin Scientific Instrument Co., Ltd.; the thermocouple temperature sensor (INCOMEL600) was purchased from Yancheng Dickwei Measurement and Control System Co., Ltd.; the super clean glove box Super (1220 / 750 / 900) was purchased from Shanghai Mikaelona Electromechanical Technology Co., Ltd.; the SZQ four-sided wet film coater (50-75-100-150) was purchased from Guangdong Huaguo Precision Testing Equipment Co., Ltd.; the button battery hydraulic sealing machine (PX-HS-20) was purchased from Shenzhen Pengxiang Yunda Co., Ltd.

[0051] 2. Battery component design principles (1) Design principle and preparation of positive electrode A. Design principle: Due to the strong electron affinity of the benzene ring Bp in biphenyl, electrons spontaneously transfer from sodium metal to the conjugated benzene ring to form Bp − Free radical anions and Na + ions. Because Bp / Bp − The reduction potential (≈0.12 V vs Na / Na + ) is much lower than the open circuit potential (≈3.4 V vs Na / Na + ) and the Na insertion potential of the cathode material NFPP (≈1.65 V vs Na / Na + ), NFPP electrode from Bp − ions to accommodate sodium ions, thereby promoting the sodium enrichment of the positive electrode.

[0052] B. Preparation before the experiment: The positive electrode active material and conductive carbon are vacuum-baked at 105-125°C for 6-8 hours to remove the surface moisture of the solid materials; the polymer binder is vacuum-dried at 70-100°C for 3-5 hours.

[0053] C. Basic positive electrode sheet preparation process: The mass ratio of positive electrode active material: dispersant: conductive carbon: polymer binder is 7:0.01:1.99:1. The positive electrode active material is sodium ferric pyrophosphate (NFPP); the dispersant is KD-1 or KD-2; the conductive carbon is a mixture of one or more of Ketjen black, acetylene black, SP, KAPPA100, graphite KS-6, graphite KS-15, single-walled carbon nanotubes, and graphene; and the polymer binder is one or more of polyvinylidene fluoride (PVDF), polyamideimide (PAI), polyimide (PI), and polyacrylonitrile (PAN). The positive electrode active material, dispersant, conductive carbon, and polymer binder are dispersed in N-methylpyrrolidone (NMP) to form a suspension. This suspension is then evenly coated onto aluminum foil using a coating blade with a coating size of 100-250 µm and an aluminum foil thickness of 10-16 µm. The leveled coating is then exposed to hot air to evaporate the solvent, drying at 80-100°C for 2-4 hours. Finally, the base positive electrode sheet is cut into discs for later use, with a diameter of 12-16 mm.

[0054] D. Preparation of Sodium-Supplemented Cathode Sheets: Prepare a mixed solvent (biphenyl-tetrahydrofuran) by mixing biphenyl solution and tetrahydrofuran at a volume ratio of 1:4 at room temperature with stirring. In a glove box, dissolve sodium metal in the mixed solvent to prepare sodium biphenyl complex solutions at concentrations of 0.1 M, 0.2 M, 0.3 M, 0.4 M, 0.5 M, and 0.6 M. Soak the base cathode sheet in the 0.1 M, 0.2 M, 0.3 M, 0.4 M, 0.5 M, and 0.6 M sodium biphenyl complex solutions for 10-50 seconds. Wash the cathode sheet 4-6 times with tetrahydrofuran to remove residual salt. Evaporate the tetrahydrofuran in the glove box for 1-3 hours to obtain the sodium-supplemented cathode sheet.

[0055] (2) Electrolyte design principle and preparation A. Design principle: Figure 1As shown in Figure a, NaPF6 readily hydrolyzes into Na3PO4, NaF, and HF in the presence of trace water. It also has low thermal stability and is easily decomposed into PF5 and HF upon heating. If trace water in the electrolyte is not controlled, in addition to the continued decomposition of NaPF6, the resulting byproducts will continue to hydrolyze into POF3, POF2(OH), POF(OH)2, PO(OH)3, and the harmful gas HF. The byproducts PF5 and HF are detrimental to the battery's charge and discharge cycles, leading to electrolyte solvent decomposition and affecting the structural stability of the solid electrolyte interface (SEI) formed on the cathode. They can even cause the transition metal in the cathode material to dissolve and become ineffective, destroying the structure of the active material and contributing to battery capacity decay. To address these issues, the present invention designs a new electrolyte. By adding two additives, 3-trimethylsilyl-2-oxazolidinone (TMSON) and N,N-dimethylformamide (DMF), the additives jointly reduce the levels of trace water, HF, and PF5 in the electrolyte.

[0056] The removal of active species such as PF5 and HF is considered to be a key factor in achieving long charge-discharge cycles in SIBs.

[0057] like Figure 1 As shown in Figure b, the compound with trimethylsilyl (TMS) group in the additive 3-trimethylsilyl-2-oxazolidinone (TMS-ON) can effectively capture F from HF. − ions and hydroxyl groups (-OH) in water to generate alkyl ketone groups with polar carbonyl bonds, which can increase the conductivity of the electrolyte.

[0058] like Figure 1 As shown in Figure c, the polar characteristics of the amide group in the structure of the additive N,N-dimethylformamide (DMF) itself (containing C=O and NH2) cause the positively charged NH2 end of the molecule to be surrounded by methyl groups, forming a spatial barrier that prevents negative ions from approaching, and thus only associates with positive ions at the NH2 end; the lone pair of electrons on the O at the C=O end of the molecule can capture P in PF5, which can further prevent the occurrence of electrolyte side reactions and corrosion of electrode materials.

[0059] Herein, we propose TMS-ON and DMF as electrolyte additives for long-cycle SIBs.

[0060] B. Electrolyte preparation: In a glove box, weigh 0.5-1M NaPF6 (0.67-1.34 g) and place it in a 20-30 mL glass bottle. Then, place a magnetic bar in the bottle. Use a pipette with a range of 1-5 mL to pipette equal volumes of 2-10 mL of solvent (the solvents include ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC)). Then mix the solvent with the sodium salt and stir for 6-10 h until the salt is completely dissolved and the solution is clear and transparent to obtain an ester-based electrolyte.

[0061] Then, use a 500 μL pipette to pipette 200-500 μL of TMS-ON and DMF additive respectively, add them to the above solution, and stir for 2-6 h until completely mixed to obtain the final electrolyte.

[0062] (3) Battery preparation and related testing A. Electrochemical testing: In a glove box, a composite sodium sheet was used as the negative electrode. A Whatman glass fiber separator (GF / D) was used, along with 30-50 µL of electrolyte and a sodium-supplemented positive electrode sheet. The cells were assembled into a CR#2032 coin cell using a gasket and spring.

[0063] B. Reversible capacity and room temperature cycle test of positive electrode half-cell: at a rate of 0.1 C (1 C = 95 mAhg -1 ), the test voltage window is 1.5 ~ 3.6 V vs Na / Na + .

[0064] The discharge rate test of the positive electrode half-cell was carried out at 0.1C, 0.5C, 1C, 2C, 3C, 5C, and 10C, and the test voltage window was 1.5 ~ 3.6 V vs Na / Na + C. Impedance measurement of the positive half-cell: This was performed on an electrochemical workstation with the initial voltage being the cell's open-circuit voltage. The high-frequency range was set to 100 kHz, and the low-frequency range was set to 10 mHz. The perturbation amplitude was set to an appropriate sine wave amplitude of 10 mV, with both the integration time and AC stabilization time being 2 s.

[0065] Example 1: Battery Preparation (1) Cathode preparation: Preparation before the experiment: The positive electrode active materials sodium iron pyrophosphate, conductive carbon KAPPA100 and single-walled carbon nanotubes were vacuum-baked at 110 °C for 6.5 h respectively; the polymer binder PVDF was vacuum-dried at 75 °C for 3.5 h.

[0066] Basic cathode sheet preparation: A suspension of 14 g of sodium ferric pyrophosphate (NFPP), 0.02 g of dispersant, 3.582 g of conductive carbon (KAPPA100), 0.398 g of single-walled carbon nanotubes, and 2 g of polymer binder was dispersed in 24.5 g of NMP in a mass ratio of 7:0.01:1.791:0.199:1. The suspension was then evenly coated onto aluminum foil using a 16-µm thick aluminum foil and a 100 µm coating blade. The leveled coating was then exposed to hot air to evaporate the solvent. The drying temperature was 100°C for 3 hours. Finally, the base cathode sheet was cut into 14 mm diameter discs for later use.

[0067] Preparation of sodium-supplemented cathode sheets: Biphenyl solution and tetrahydrofuran (THF) were stirred at room temperature in a 1:4 volume ratio to prepare a mixed solvent. In a glove box, sodium metal was dissolved in the mixed solvent to prepare sodium biphenyl complex solutions with concentrations of 0.1 M, 0.2 M, 0.3 M, 0.4 M, 0.5 M, and 0.6 M. The base cathode sheet was immersed in the 0.1 M, 0.2 M, 0.3 M, 0.4 M, 0.5 M, and 0.6 M sodium biphenyl complex solutions for 15 seconds. The cathode electrode was then washed six times with THF to remove residual salt. The resulting cathode sheet was evaporated in the glove box for 2 hours to remove the THF, resulting in sodium-supplemented cathode sheets, which were designated as sodium-supplemented cathode sheet 1, sodium-supplemented cathode sheet 2, sodium-supplemented cathode sheet 3, sodium-supplemented cathode sheet 4, and sodium-supplemented cathode sheet 5. The unimmersed cathode sheet is designated as cathode sheet 0.

[0068] (2) Preparation of electrolyte Electrolyte preparation: In a glove box, weigh 1.34 g of NaPF6 and place it in a 20 mL glass vial. A magnetic rod was then placed in the vial. Using a 5 mL pipette, 3.35 mL of equal volumes of ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) were pipetted separately to create a mixed solvent. This mixed solvent was then mixed with NaPF6 and stirred for 8 hours until the sodium salt was completely dissolved and the solution was clear and transparent, yielding an ester-based electrolyte.

[0069] Then, using a 500 μL pipette, 250 μL of TMS-ON and DMF were respectively transferred to the above solution and stirred for another 4 h until completely mixed to obtain the final electrolyte.

[0070] (3) Battery assembly: In a glove box, a composite sodium sheet was used as the negative electrode, and a Whatman glass fiber separator (GF / D) was used. 50µL of electrolyte was taken and assembled with the positive electrode sheet, gasket and spring to form a CR#2032 coin cell (positive electrode half-cell).

[0071] The positive electrode half-cells assembled using sodium-supplemented positive electrode sheet 1, sodium-supplemented positive electrode sheet 2, sodium-supplemented positive electrode sheet 3, sodium-supplemented positive electrode sheet 4, and sodium-supplemented positive electrode sheet 5 are named NFPP-1, NFPP-2, NFPP-3, NFPP-4, and NFPP-5, respectively. The positive electrode half-cell assembled using positive electrode sheet 0 is named NFPP.

[0072] (4) Battery test 1 At a rate of 0.1 C (1 C = 95 mAh g -1 ), the test voltage window is 1.5 ~ 3.6 V vs Na / Na + , the positive electrode half-cells NFPP-1, NFPP-2, NFPP-3, NFPP-4, NFPP-5 and NFPP were charged and discharged, and the results in Table 1 and Figure 2 .

[0073]

[0074] from Figure 2 From the first charge-discharge curves of each positive electrode half-cell in a, it can be seen that with the increase in the concentration of the sodium biphenyl complex (Na-Bp complex) solution, the capacity of the positive electrode half-cell first increases and then decreases, with the NFPP-4 positive electrode half-cell having the largest capacity. + As the concentration of the pretreatment solution increases, the inflection point of the discharge curve of the corresponding positive half-cell appears increasingly earlier, possibly due to premature reduction of the active material. The voltage drop inflection point of NFPP is the later, indicating that the compatibility between the pretreated positive electrode and the electrolyte has changed, possibly due to changes in the internal structure of the positive half-cell, leading to premature reduction. Furthermore, among the tested positive half-cells, NFPP-1, NFPP-2, NFPP-3, NFPP-4, and NFPP-5 all exhibited greater charge and discharge capacity per gram than the positive half-cell NFPP, indicating that immersion of the positive electrode in the Na-Bp complex solution is beneficial in increasing the battery's charge and discharge capacity per gram.

[0075] from Figure 2As can be seen from b, the blue column represents the battery's charge capacity in grams, and the orange column represents the battery's discharge capacity in grams. It is easy to notice that the battery with an orange column higher than the blue column is NFPP-4, and the battery with a blue column significantly higher than the orange column is NFPP. This indicates that the NFPP-4 positive electrode half-cell has the largest discharge capacity in grams and first coulombic efficiency, which are 110.15 mAh g -1 , 101.36%; the battery with the smallest discharge capacity and first coulombic efficiency is NFPP, with values ​​of 95.86 mAh g -1 , 95.49%. It can be seen that after the positive electrode sheet is immersed in a Na-Bp complex solution of appropriate concentration, the charge and discharge capacity and the first coulombic efficiency of the positive electrode half-cell can be effectively improved.

[0076] (5) Battery Test 2 In order to further explore the effect of cathode pretreatment on the discharge performance of the battery, the cathode half-cell was discharged at 0.1 C, 0.5 C, 1 C, 2 C, 3 C, 5 C, and 10 C, and the test voltage window was 1.5 ~ 3.6 V vs Na / Na + , and tracked its surface temperature at the same time. The battery test environment temperature was 25 ℃. Figure 3-Figure 4 and as shown in Table 2.

[0077]

[0078] from Figure 3 It can be seen that at different discharge rates, the discharge capacity of the NFPP-4 half-cell is the largest, and at the same rate, the discharge capacity of the battery prepared after the positive electrode sheet is treated with different concentrations of sodium biphenyl complex solution shows a trend of first increasing and then decreasing, indicating that the pretreatment of the positive electrode sheet with Na-Bp complex solution is beneficial, and the positive electrode sheet is beneficial to the discharge rate of the battery after being soaked in a sodium biphenyl complex solution of appropriate concentration.

[0079] It can be seen from Table 2 that the capacity retention rate of the NFPP-4 half-cell is 92.83% under 10 C high rate discharge.

[0080] from Figure 4Table 2 shows that the battery surface temperature increases with increasing discharge rate. At the same rate, the temperature initially increases and then decreases, with the NFPP-4 showing the lowest temperature. For the same battery at different rates, the NFPP-4 half-cell exhibits the smallest temperature difference / temperature rise during rate discharge. Table 2 shows that at a high-rate discharge of 10°C, the surface temperature of the NFPP-4 half-cell is 65.82°C, resulting in a temperature rise of 40.82°C. During high-rate discharge, while the current increases, the heat generated by the ohmic internal resistance increases the battery temperature. Furthermore, during rapid charge and discharge, the electrolyte and electrode materials experience increased polarization, generating additional heat and contributing to a slight increase in the battery surface temperature. The minimal temperature and temperature rise indicate that the NFPP-4 half-cell has relatively low internal resistance or polarization.

[0081] (6) Battery Test 3 Next, we continued to explore the effect of cathode pretreatment on battery resistance. + After 300 cycles at a rate of 1C in the voltage window, the impedance test was performed. Figure 5 shown.

[0082] Figure 5 The real impedance Z' and the imaginary impedance -Z'' on the horizontal axis generally correspond to a Faradaic process, which typically reflects the kinetics of the electrode / solution interface. The diameter of the semicircle represents the charge transfer resistance Rct. A larger Rct indicates a more difficult redox reaction at the electrode. It is not difficult to see that the semicircle of the NFPP half-cell is the largest, while that of the NFPP-4 half-cell is the smallest. The semicircles of the positive electrode half-cells NFPP, NFPP-1, NFPP-2, NFPP-3, NFPP-4, and NFPP-5 show a pattern of first decreasing and then increasing. This indicates that the NFPP-4 half-cell has the highest mass-to-charge transfer rate (mass and charge transfer) at the electrode surface, resulting in the fastest chemical reaction. Therefore, pretreatment of the positive electrode with the sodium biphenyl complex solution successfully reduced the electrode surface resistance.

[0083] (7) Battery Test 4 The assembled cathode half-cell was subjected to a 1 C cycle charge-discharge test with a test voltage window of 1.5 ~ 3.6 Vvs Na / Na + The results are as follows Figure 6 shown.

[0084] Figure 6The capacity retention trends are similar to those observed for discharge retention and impedance in the rate tests described above. At room temperature and 1°C, the capacity retention of the NFPP, NFPP-1, NFPP-2, NFPP-3, NFPP-4, and NFPP-5 cathode half-cells initially increases and then decreases. The best performance was achieved by the NFPP-4 cathode half-cell, achieving a capacity retention of 99.28% after 1200 cycles.

[0085] Example 2: (1) Preparation of electrolyte The electrolyte formula is as follows: ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) are prepared into a mixed solvent in a volume ratio of 1:1:1; a 1M NaPF6-based electrolyte is prepared using the mixed solvent with a total volume of 20 mL, which is recorded as electrolyte 1.

[0086] Add 500 µL of either 3-trimethylsilyl-2-oxazolidinone (TMS-ON) or N,N-dimethylformamide (DMF) to the base electrolyte and shake thoroughly. All operations were performed in a glove box with an oxygen concentration of less than 0.1 ppm.

[0087] The specific electrolyte preparation is shown in Table 3 below:

[0088] (2) Battery preparation and performance testing (a) In a glove box, a composite sodium sheet was used as the negative electrode. A Whatman glass fiber separator (GF / D) was used, along with 50 µL of the electrolyte prepared in Table 3 and the positive electrode prepared in Example 1. A gasket and spring were used to assemble the cells into a CR#2032 coin cell.

[0089] In order to explore the effect of electrolyte additives on battery cycle, the present invention set up an experimental control under the condition of controlling a single variable, and conducted experiments at 1.5 ~ 3.6 V vs Na / Na + The capacity retention rate data obtained from the 1C cycle test for 1200 weeks in the voltage range is shown in Table 4.

[0090]

[0091] As shown in the second row of Table 4, the capacity retention of the NFPP half-cell using cathode sheet 0 and electrolyte No. 1 has deteriorated to 52.34% after 1200 cycles at 1C. The addition of additives to prepare different electrolytes effectively extended the cycle life of the NFPP half-cells. The NFPP half-cell using electrolyte No. 4 showed the best performance, at 79.34%. This demonstrates that simply changing the electrolyte composition is not enough to fully achieve excellent long-cycle performance.

[0092] Comparison of Different Electrolyte Injection: Each row in Table 4 (horizontally) shows that the capacity retention of half-cells in the NFPP-1, NFPP-2, NFPP-3, NFPP-4, and NFPP-5 series varies significantly when using the same sodium-supplemented cathode plate in combination with different electrolytes. Specifically, the capacity retention of half-cells prepared with different electrolytes, with electrolyte No. 4, containing both TMS-ON and DMF additives, achieving the highest capacity retention, while half-cells prepared with both additives exhibited better capacity retention than those prepared with either additive alone. Furthermore, half-cells prepared with either additive alone exhibited better capacity retention than those prepared with no additives. The best cycling performance was achieved with the half-cell prepared with electrolyte No. 4 and the NFPP-4 cathode using sodium-supplemented cathode plate No. 4, achieving an astonishing capacity retention of 99.28%.

[0093] Comparison of Different Positive Electrodes: Each column in Table 4 (vertical) shows that using the same electrolyte in combination with different sodium-supplemented cathodes results in significantly different capacity retention rates. It can be seen that all cathode cells injected with Electrolyte No. 1 experienced significant performance degradation (capacity retention below 80%) after 1200 cycles of 1C charge-discharge. Cycle retention initially increased and then decreased with increasing concentration of the cathode pretreatment solution. Cycle performance of half-cells injected with Electrolyte No. 2, Electrolyte No. 3, and Electrolyte No. 4 exhibited the same pattern of increasing and then decreasing performance, with the NFPP-4 series cathode half-cells exhibiting the best performance.

[0094] Table 4 shows that the NFPP series half-cells, filled with the most compatible electrolyte No. 4, achieved a cycle retention rate of only 79.34%. The NFPP-4 series half-cells, equipped with the best pretreated electrode sheets and filled with electrolyte No. 1, also achieved a capacity retention rate of only 75.56%. This indicates that electrolyte modification or cathode sheet pretreatment alone can improve battery cycle performance to a certain extent, but adjusting a single influencing factor is unlikely to address multiple issues. Electrode material properties must be optimized in tandem with electrolyte composition. Half-cells assembled with pretreated cathode sheets and filled with the additive-containing electrolytes No. 2, No. 3, and No. 4 all achieved capacity retention rates exceeding 90%, demonstrating that cathode pretreatment strategies and electrolyte modification can synergistically improve battery cycle life.

[0095] (b) The NFPP-4 cathode half-cell was assembled with sodium-supplemented cathode sheet 4 and electrolyte No. 4, and its electrochemical behavior during 1C charge and discharge for 1200 cycles was investigated. Figure 7 shown.

[0096] Figure 7 The dQ / dV curve of the NFPP-4 positive electrode half-cell is shown in Figure 2. Figure 7 It can be seen that from the 1st to the 100th cycle, at 2.81 V vs Na / Na + Reduction peak at 2.96 V vs Na / Na + The peak intensity of the oxidation peak increases slightly. After 600 cycles, the peak intensity decreases slightly, the most obvious being at 3.05 V vs Na / Na + The reduction peak at 1000 is no longer sharp, indicating a slower electrochemical reaction at this voltage. This could be due to a small amount of active material failure in the cathode material or dynamic changes in the SEI film composition that hinder mass-charge transfer at the electrode surface. However, overall, the dQ / dV curves from 1 to 1200 cycles overlap well, demonstrating good charge-discharge cycling performance and good cycling stability for NFPP-4.

[0097] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A sodium ion battery, characterized in that including positive electrode, negative electrode and electrolyte; The positive electrode is a sodium-supplemented positive electrode sheet treated with a sodium biphenyl complex solution; The sodium biphenyl complex solution is prepared by dissolving sodium in a mixed solvent of biphenyl and tetrahydrofuran; the molar concentration of the sodium biphenyl complex solution is 0.2 mol / L to 0.6 mol / L; The electrolyte includes a NaPF6 base electrolyte and additives; the additives are 3-trimethylsilyl-2-oxazolidinone and N,N-dimethylformamide, and the mixed solvent in the NaPF6 base electrolyte is a combination of ethylene carbonate, propylene carbonate, and diethyl carbonate.

2. The sodium ion battery according to claim 1, characterized in that The volume ratio of biphenyl to tetrahydrofuran in the mixed solvent is 1:

4.

3. The sodium ion battery according to claim 1, characterized in that The NaPF6 basic electrolyte is a NaPF6 basic electrolyte with a concentration of 0.1 mol / L~1 mol / L.

4. The sodium ion battery according to claim 3, characterized in that The volume ratio of the additive to the NaPF6 basic electrolyte is 1:10~50; the volume ratio of the ethylene carbonate, propylene carbonate and diethyl carbonate is 1:1:

1.

5. The sodium ion battery according to claim 1, characterized in that The positive electrode comprises a positive electrode active material, a binder, a dispersant and conductive carbon; The positive electrode active material is selected from at least one of positive electrode layered oxide O3, sodium iron pyrophosphate or sodium nickel iron manganate; The dispersant is KD-1 or KD-1; The binder is selected from polyvinylidene fluoride, and the polyvinylidene fluoride is at least one of PVDF5130 and PVDFHSV-900; The conductive carbon is selected from at least one of acetylene black, Ketjen black, graphite KS-6, graphite KS-15, single-walled carbon nanotubes, graphene, SP carbon black, Kappa100, and graphene oxide; The negative electrode is a composite sodium sheet.

6. The sodium ion battery according to claim 5, characterized in that The positive electrode comprises, by weight percentage, 70-95% of a positive electrode active material, 0.5-15% of a binder, 0.01-1% of a dispersant, and 0.5-20% of conductive carbon.

7. A method for preparing a sodium ion battery according to any one of claims 1 to 6, characterized in that: (1) The preparation process of the electrolyte includes the following steps: (1) Dissolve NaPF6 in a mixed solvent to prepare a basic electrolyte; (2) Adding additives to the basic electrolyte and mixing them evenly to prepare the electrolyte; (2) The preparation process of the positive electrode includes the following steps: S1: pre-treating the binder, conductive carbon, and positive electrode active material respectively; S2: Dispersing the binder, conductive carbon, positive electrode active material and dispersant in NMP to prepare positive electrode slurry; S3: coating the positive electrode slurry on aluminum foil, drying, and sheeting to obtain a basic positive electrode; S4: soaking the base cathode in a sodium biphenyl complex solution, washing, and evaporating the solvent; (3) Using the obtained electrolyte, positive electrode and negative electrode to prepare a sodium ion battery.

8. The preparation method according to claim 7, characterized in that: The negative electrode is a composite sodium sheet; in S1, the pretreatment refers to: vacuum baking the conductive carbon and the positive electrode active material respectively, and vacuum drying the binder.

9. The preparation method according to claim 7, characterized in that: The molar concentration of the sodium biphenyl complex solution is 0.1 mol / L to 1 mol / L; The sodium biphenyl complex solution is prepared by dissolving sodium in a mixed solvent of biphenyl and tetrahydrofuran; The additives are 3-trimethylsilyl-2-oxazolidinone and N,N-dimethylformamide.

10. Use of the sodium ion battery according to any one of claims 1 to 6 or the sodium ion battery prepared by the method according to claim 7 in an energy storage device.

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