Method for improving specific discharge capacity and sodium storage performance of sodium-ion battery

Abstract

The invention relates to a method for improving specific discharge capacity and sodium storage performance of a sodium-ion battery, and belongs to the technical field of sodium-ion batteries. The ether-based electrolyte is adopted, the sodium titanium phosphate-based electrode plate is used as the cathode, the sodium vanadium phosphate is used as the anode, and the sodium ion battery is assembled, so that the specific discharge capacity and the sodium storage performance of the sodium ion battery are improved; the electrolyte of the ether-based electrolyte is NaPF6, the solvent is diethylene glycol dimethyl ether, and the concentration of the electrolyte NaPF6 is 1-1.5 mol / L. The sodium ion battery disclosed by the invention has the specific discharge capacity of 290 to 311 mAh / g and the specific discharge energy of 290 to 329 mWh / g in a voltage interval of 3 to 0.01 V; meanwhile, good rate capability is achieved at the low rate of 0.1 C (239 mAh / g) and the high rate of 10 C (238 mAh / g); the material has the stable performance of 2000 cycles under high rate (the specific capacity retention rate is still 90% under the rate of 20C).

Description

Technical Field

[0001] The invention relates to a method for improving the specific discharge capacity and sodium storage performance of a sodium ion battery, and belongs to the technical field of sodium ion batteries. Background Art

[0002] Sodium titanium phosphate is a phosphate electrode material that has been successfully used in aqueous sodium ion batteries. NaTi2(PO4)3 is a NASICON structural material. The theoretical specific capacity of the battery in the voltage range of 3V-1.5V is 132.8mAhg -1 , but there is an additional specific capacity in the low voltage range. For the insulation and stability of the material itself, if it is to be used in electrode materials, it needs to be conductive. There are three ways to improve the electronic conductivity of the conductive carbon layer, namely, using conductive carbon (or graphene, carbon nanotube) coating, nano-cutting, doping, etc. Among them, carbon coating is the most economical and feasible technology. However, traditional carbon coating can only provide a single electron path around a single particle.

[0003] Therefore, existing aqueous sodium ion batteries based on sodium titanium phosphate electrodes have the problems of low discharge specific capacity and weak sodium storage performance. Summary of the invention

[0004] In view of the problems of low discharge capacity and weak sodium storage performance of the existing aqueous sodium ion batteries based on sodium titanium phosphate electrodes, the present invention proposes a method for improving the discharge capacity and sodium storage performance of sodium ion batteries. The present invention adopts diethylene glycol dimethyl ether or ethylene carbonate:propylene carbonate (EC:PC) as an organic solvent, and sodium titanium phosphate (sodium metal sheet as anode) or sodium vanadium phosphate (sodium titanium phosphate as anode) as the cathode current collector to improve the discharge capacity and sodium storage performance of the sodium ion battery. The sodium ion half-cell has a discharge capacity of 290 to 311 mAh / g (far exceeding the estimated theoretical capacity) and a discharge energy of 290 to 329 mWh / g in the voltage range of 3 to 0.01 V. The charge and discharge curves of the first and 28th cycles of the NVP / NTP sodium ion full battery obtained after testing are compared at 0.2C (1C = 250 mAh g -1 ) after 28 cycles of charge and discharge at a rate of 142 mAh / g, the discharge specific capacity of the sodium ion full battery increased from 101.23 mAh / g to 142 mAh / g. With the increase of the number of cycles, the specific capacity of the sodium ion battery showed an obvious growth trend.

[0005] A method for improving the discharge capacity and sodium storage performance of a sodium ion battery, the specific steps are as follows:

[0006] The organic solvent is diethylene glycol dimethyl ether or ethylene carbonate:propylene carbonate (EC:PC), and the cathode current collector is sodium titanium phosphate (sodium metal sheet as anode) or sodium vanadium phosphate (sodium titanium phosphate as anode) to improve the discharge capacity and sodium storage performance of the sodium ion battery;

[0007] The electrolyte of the ether-based electrolyte is NaPF6, and the solvent is diethylene glycol dimethyl ether; preferably, the concentration of the electrolyte NaPF6 is 1 to 1.5 mol / L;

[0008] The preparation method of the sodium titanium phosphate-based electrode plate is as follows:

[0009] (1) dissolving sodium carbonate, ammonium dihydrogen phosphate, and tetrabutyl titanate in an ethylene glycol solution to obtain a solution A, adjusting the pH value of the solution A to 7.0 to 9.5 with aqueous ammonia, and coprecipitating under stirring to obtain a gel;

[0010] (2) placing the gel at a temperature of 100 to 140° C. for a hydrothermal reaction for 18 to 30 hours, cooling to room temperature, separating the solid from the liquid, washing the solid with deionized water and anhydrous ethanol in turn, drying, and grinding to obtain a sodium titanium phosphate precursor powder;

[0011] (3) calcining the sodium titanium phosphate precursor powder at a temperature of 500 to 800° C. for 2 to 8 hours to obtain sodium titanium phosphate powder;

[0012] (4) sodium titanium phosphate powder is uniformly dispersed in a deionized water-ethanol mixed solution to obtain a sodium titanium phosphate dispersion, a carbon source is added to the sodium titanium phosphate dispersion and stirred for reaction for 2 to 6 hours, the solvent is evaporated, and then the mixture is calcined at a temperature of 600 to 900° C. for 2 to 6 hours to obtain NaTi2(PO4)3 / C powder;

[0013] (5) NaTi2(PO4)3 / C powder, conductive agent, adhesive and organic solvent are uniformly mixed to obtain electrode slurry, the electrode slurry is coated on the surface of cathode current collector, and vacuum dried to obtain sodium titanium phosphate-based electrode plate.

[0014] In the step (1), the molar ratio of sodium carbonate, diammonium dihydrogen phosphate and tetrabutyl titanate is (0.505-2.25):(2.8-3.2):(1.5-2.6).

[0015] The volume ratio of deionized water to ethanol in the deionized water-ethanol mixed solution of step (4) is 1:1 to 1:4, and the concentration of the sodium titanium phosphate dispersion is 0.04 to 0.08 g / mL.

[0016] The mass ratio of the carbon source to the sodium titanium phosphate powder in the step (4) is 0.04-0.15:1.

[0017] In the step (5), the amount of the conductive agent added is 15-25% of the mass of the NaTi2(PO4)3 / C powder, and the amount of the adhesive added is 5-15% of the mass of the NaTi2(PO4)3 / C powder.

[0018] In the step (5), diethylene glycol dimethyl ether or a mixed solvent of ethylene carbonate and propylene carbonate is used, preferably, the volume ratio of ethylene carbonate to propylene carbonate (EC:PC) is 1:1, and the cathode current collector is sodium vanadium phosphate.

[0019] Preferably, the thickness of the NaTi2(PO4)3 / C powder layer on the cathode current collector surface of the sodium titanium phosphate-based electrode plate in step (5) is 10 to 14 μm.

[0020] The present invention adopts a staged firing method to prepare NaTi2(PO4)3 / C, and compares the electrochemical performance of sodium ion batteries using NTP / C as electrode materials under ester-based and ether-based electrolytes. When ether-based electrolyte (the electrolyte of the ether-based electrolyte is NaPF6 and the solvent is diethylene glycol dimethyl ether) is used as the electrolyte of the sodium ion battery, NTP / C has a reversible capacity and capacity retention that exceed theoretical speculation, and has a higher sodium ion storage position.

[0021] The beneficial effects of the present invention are:

[0022] (1) The present invention adopts a special ether-based electrolyte, a sodium titanium phosphate-based electrode plate as a cathode, and a sodium vanadium phosphate as an anode to assemble a sodium ion battery to improve the discharge capacity and sodium storage performance of the sodium ion battery;

[0023] (2) The method of preparing sodium titanium phosphate-based powder in stages according to the present invention makes the carbon source coating more uniform and the charge transfer efficiency of the sodium titanium phosphate-based electrode plate more stable, thereby improving the stability of the sodium ion battery;

[0024] (3) The sodium ion half-cell of the present invention has a discharge specific capacity of 290 to 311 mAh / g and a discharge specific energy of 290 to 329 mWh / g in the voltage range of 3 to 0.01 V; at the same time, it has good rate performance at a low rate of 0.1C (239 mAh / g) and a high rate of 10C (238 mAh / g); it has stable performance of 2000 cycles at a high rate (the specific capacity retention rate is still 90% at a rate of 20C). BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is the XRD pattern of sodium titanium phosphate powder of Example 1;

[0026] Figure 2 This is the SEM image of NaTi2(PO4)3 / C powder in Example 1;

[0027] Figure 3 This is a comparison chart of the charge and discharge cycle performance of the CR2032 stainless steel button half-cell (ether-based) and the CR2032 stainless steel button half-cell (ester-based) in Example 1;

[0028] Figure 4 This is a rate performance diagram of the CR2032 stainless steel button half-cell (ether-based) in Example 1;

[0029] Figure 5 This is a high-rate long-cycle performance diagram of the CR2032 stainless steel button half-cell (ether-based) in Example 1;

[0030] Figure 6 This is a charge and discharge cycle performance diagram of the CR2032 stainless steel button half-cell (ether-based) in Example 2;

[0031] Figure 7 is the XRD pattern of sodium titanium phosphate powder of Example 3;

[0032] Figure 8 This is a comparison chart of the charge-discharge cycle performance of different molar ratios of sodium carbonate in the precursor of Example 3;

[0033] Fig. 9 This is a comparison chart of the charge and discharge performance of the NVP / NTP sodium ion battery of Example 4. DETAILED DESCRIPTION

[0034] The present invention is further described in detail below in conjunction with specific implementation modes, but the protection scope of the present invention is not limited to the described contents.

[0035] Example 1: A method for improving the discharge capacity and sodium storage performance of a sodium ion battery, the specific steps are as follows:

[0036] Using ether-based electrolyte, sodium metal electrode as cathode, sodium titanium phosphate as anode, assembled into a sodium ion battery half-cell to observe the performance of improving the discharge capacity and sodium storage performance of sodium ion batteries;

[0037] The electrolyte of the ether-based electrolyte is NaPF6, and the solvent is diethylene glycol dimethyl ether; the concentration of electrolyte NaPF6 is 1 mol / L;

[0038] The preparation method of the sodium titanium phosphate-based electrode plate is as follows:

[0039] (1) dissolving sodium carbonate, diammonium phosphate and tetrabutyl titanate in an ethylene glycol solution to obtain solution A, adjusting the pH value of solution A to 8.0 with aqueous ammonia, and coprecipitating for 5 hours under stirring to obtain a gel; the molar ratio of sodium carbonate, diammonium phosphate and tetrabutyl titanate is 0.525:3:2; a slight excess of sodium carbonate is used to balance the loss of sodium ions in subsequent processes;

[0040] (2) placing the gel at a temperature of 120° C. for a hydrothermal reaction for 20 h, cooling to room temperature, centrifuging for solid-liquid separation, washing the solid with deionized water and anhydrous ethanol for 4 times, drying at a temperature of 60° C. for 8 h, and grinding to obtain a sodium titanium phosphate precursor powder;

[0041] (3) The sodium titanium phosphate precursor powder was calcined at 720° C. for 3 h to obtain sodium titanium phosphate powder; the XRD pattern of the sodium titanium phosphate powder in this example is shown in FIG. Figure 1 ,from Figure 1 It can be seen that the diffraction peak of the obtained phase is relatively sharp, indicating good crystallinity, and its characteristic peak is consistent with the standard XRD spectrum, and the space group is R-3c (o.167), indicating that the content of other impurities is low;

[0042] (4) Sodium titanium phosphate powder is uniformly dispersed in a deionized water-ethanol mixed solution to obtain a sodium titanium phosphate dispersion, a carbon source (dopamine hydrochloride) is added to the sodium titanium phosphate dispersion and stirred for reaction for 2 hours, the solvent is evaporated at a temperature of 60°C, and then it is placed at a temperature of 720°C for calcination for 2 hours to obtain NaTi2(PO4)3 / C powder; the volume ratio of deionized water to ethanol in the deionized water-ethanol mixed solution is 1:1, and the concentration of the sodium titanium phosphate dispersion is 0.05g / mL; the mass ratio of the carbon source (dopamine hydrochloride) to the sodium titanium phosphate powder is 0.1:1; the SEM image of the NaTi2(PO4)3 / C powder in this embodiment is shown in Figure 2 ,from Figure 2 It can be seen that NaTi2(PO4)3 / C powder has good particle size uniformity and carbon coating uniformity;

[0043] (5) NaTi2(PO4)3 / C powder, conductive agent (Super P), adhesive (polyvinylidene fluoride PVDF), and organic solvent (N-methyl-2-pyrrolidone NMP) are uniformly mixed to obtain an electrode slurry, the electrode slurry is coated on the surface of the cathode current collector (Cu foil), and vacuum dried at a temperature of 80°C for 18 hours to obtain a sodium titanium phosphate-based electrode plate; the amount of the conductive agent (Super P) added is 20% of the total mass, and the amount of the adhesive (polyvinylidene fluoride PVDF) added is 10% of the total mass; the thickness of the NaTi2(PO4)3 / C powder layer on the cathode current collector surface of the sodium titanium phosphate-based electrode plate is 14 μm;

[0044] The charge and discharge performance test of the sodium titanium phosphate-based electrode plate in this embodiment:

[0045] The ether-based electrolyte of this embodiment (the electrolyte of the ether-based electrolyte is NaPF6, the solvent is diethylene glycol dimethyl ether; the electrolyte NaPF6 concentration is 1 mol / L) and the conventional ester-based electrolyte 1M NaClO4 in ethylene carbonate:propylene carbonate (EC:PC) = 1:1, with a metal sodium sheet as the negative electrode and reference electrode, and a glass fiber diaphragm as the diaphragm, are respectively assembled into CR2032 stainless steel button half-cells (ether-based) and CR2032 stainless steel button half-cells (ester-based) in a glove box filled with argon and with a moisture content of less than 1 ppm; after standing for 8 h, the electrochemical charge and discharge performance of the sodium titanium phosphate-based electrode sheet is tested (see Figure 3 );The charge and discharge performance of CR2032 stainless steel button half-cell (ester-based) is at 0.2C rate, and the reversible discharge capacity of the battery is from 230mAhg -1 After 100 cycles, the battery capacity decreased to 177.4 mAh g -1 The charge and discharge performance of the CR2032 stainless steel button half-cell (ether-based) in this embodiment is 0.2C, and the specific capacity after the first discharge is 240mAh g -1 After 100 cycles, the capacity is increased to 311 mAh g -1 ; Organic sodium-ion batteries using ether-based electrolytes and sodium titanium phosphate-based electrode plates as cathodes have excellent sodium storage performance;

[0046] The charge and discharge cycle performance diagram of the CR2032 stainless steel button half-cell (ether-based) in this embodiment and the cycle performance comparison diagram in ether-based and ester-based electrolytes and the rate performance are shown in Figure 3 , Figure 4 ,Depend on Figure 3 , Figure 4 It can be seen that in the cycle performance test of 0.2C rate and 0.1C~10C different rate performance tests, the cycle performance shows that the first discharge specific capacity of the electrode in ether-based and ester-based electrolytes at 0.2C is 337.27mAh g -1 and 427.67mAh g -1 , and after 100 cycles, they can reach 311.31 mAh g -1 and 177.55mAh g -1 The discharge specific capacity of the ether-based electrolyte is shown to increase gradually compared with the cycle performance of the ester-based electrolyte and the reversible specific capacity Figure 3 The growth of has exceeded the value of the theoretical specific capacity, which indicates that the formation of inorganic SEI on the surface of the material in the ether-based electrolyte has new sodium ion storage sites, and the rate of cycling the battery at different current densities Figure 4 When the current rate increases from 0.1C to 10C, the discharge capacity of the NTP / C electrode gradually decreases from 256.5 (5th cycle) to 239.3 mAh g-1 (31st cycle), which shows that its rate performance is excellent; and the charge capacity at 0.1C is lower than that at other rates, which may be due to the process of surface activation of the material and the formation of SEI film. Most importantly, even after long-term cycling at different rates, when the rate is restored to 0.1C, it can be observed that the discharge capacity of the battery is the same as the discharge capacity of the first five cycles, and this sodium ion battery has excellent rate stability;

[0047] The long cycle performance test of the CR2032 stainless steel button half-cell (ether-based) at high rate is shown in Figure 2. Figure 5 , Figure 5 It can be seen that at 20C (1C = 250mAh g -1 ) after 500 cycles of charge and discharge at a rate of 1.5 N·m3 / s, except for the first discharge cycle, the sodium ion battery still has a discharge specific capacity of 238 mAh / g after 500 cycles of charge and discharge, which proves that the battery has a good cycle retention rate.

[0048] Example 2: A method for improving the discharge capacity and sodium storage performance of a sodium ion battery, the specific steps are as follows:

[0049] Using ether-based electrolyte, sodium metal sheet as cathode, sodium titanium phosphate as anode, assembled into sodium ion half-cell, in order to improve the discharge capacity and sodium storage performance of sodium ion battery;

[0050] The electrolyte of the ether-based electrolyte is NaPF6, and the solvent is diethylene glycol dimethyl ether; the concentration of electrolyte NaPF6 is 1 mol / L;

[0051] The preparation method of the sodium titanium phosphate-based electrode plate is as follows:

[0052] (1) dissolving sodium carbonate, diammonium phosphate and tetrabutyl titanate in an ethylene glycol solution to obtain solution A, adjusting the pH value of solution A to 7.5 with aqueous ammonia, and coprecipitating for 6 hours under stirring to obtain a gel; the molar ratio of sodium carbonate, diammonium phosphate and tetrabutyl titanate is 0.515:3:2, and a slight excess of sodium carbonate is used to balance the loss of sodium ions in subsequent processes;

[0053] (2) placing the gel at a temperature of 110° C. for a hydrothermal reaction for 28 hours, cooling to room temperature, centrifuging for solid-liquid separation, washing the solid with deionized water and anhydrous ethanol for 4 times, drying at a temperature of 70° C. for 8 hours, and grinding to obtain sodium titanium phosphate precursor powder;

[0054] (3) calcining the sodium titanium phosphate precursor powder at 550° C. for 8 h to obtain sodium titanium phosphate powder;

[0055] (4) sodium titanium phosphate powder is uniformly dispersed in a deionized water-ethanol mixed solution to obtain a sodium titanium phosphate dispersion, a carbon source (rhodamine) is added to the sodium titanium phosphate dispersion and stirred for reaction for 3 hours, the solvent is evaporated at a temperature of 80°C, and then calcined at a temperature of 650°C for 6 hours to obtain NaTi2(PO4)3 / C powder; the volume ratio of deionized water to ethanol in the deionized water-ethanol mixed solution is 1:1.2, and the concentration of the sodium titanium phosphate dispersion is 0.05 g / mL; the mass ratio of the carbon source (rhodamine) to the sodium titanium phosphate powder is 0.12:1;

[0056] (5) NaTi2(PO4)3 / C powder, conductive agent (Super P), adhesive (polyvinylidene fluoride PVDF), and organic solvent (N-methyl-2-pyrrolidone NMP) are uniformly mixed to obtain an electrode slurry, the electrode slurry is coated on the surface of the cathode current collector (Cu foil), and vacuum dried at a temperature of 90°C for 16 hours to obtain a sodium titanium phosphate-based electrode plate; the amount of the conductive agent (Super P) added is 20% of the total mass, and the amount of the adhesive (polyvinylidene fluoride PVDF) added is 10% of the total mass; the thickness of the NaTi2(PO4)3 / C powder layer on the cathode current collector surface of the sodium titanium phosphate-based electrode plate is 14 μm;

[0057] The charge and discharge performance test of the sodium titanium phosphate-based electrode plate in this embodiment:

[0058] The ether-based electrolyte of this embodiment was used, a metal sodium sheet was used as the negative electrode and the reference electrode, and a glass fiber diaphragm was used as the diaphragm. CR2032 stainless steel button half-cells (ether-based) were assembled in a glove box filled with argon gas and with a moisture content of less than 1 ppm. After standing for 8 hours, the electrochemical charge and discharge performance of the sodium titanium phosphate-based electrode sheet was tested.

[0059] In this embodiment, the CR2032 stainless steel button half-cell (ether-based) adopts a high rate 20C (1C = 250 mAh g -1 ) for long cycle performance test. Figure 6 , Figure 6 It can be seen that at 20C (1C = 250mAh g -1 ) after 80 cycles of charge and discharge at a rate of 242 mAh / g, except for the first discharge cycle, the discharge specific capacity of the sodium ion battery increased from 242 mAh / g to 247 mAh / g after 500 cycles of charge and discharge. Compared with the coating of dopamine hydrochloride carbon source, the coating of rhodamine carbon source has better tolerance and makes the battery more stable.

[0060] Example 3: A method for improving the discharge capacity and sodium storage performance of a sodium ion battery, the specific steps are as follows:

[0061] Using ether-based electrolyte, sodium metal sheet as cathode, sodium titanium phosphate as anode, assemble into sodium ion battery to improve the discharge capacity and sodium storage performance of sodium ion battery;

[0062] The electrolyte of the ether-based electrolyte is NaPF6, and the solvent is diethylene glycol dimethyl ether; the concentration of electrolyte NaPF6 is 1 mol / L;

[0063] The preparation method of the sodium titanium phosphate-based electrode plate is as follows:

[0064] (1) dissolving sodium carbonate, ammonium dihydrogen phosphate, and tetrabutyl titanate in an ethylene glycol solution to obtain a solution A, adjusting the pH value of the solution A to 9.0 with aqueous ammonia, and coprecipitating for 5.5 hours under stirring to obtain a gel; the molar ratios of sodium carbonate, ammonium dihydrogen phosphate, and tetrabutyl titanate are 0.515:3:2, 0.675:3:2, and 2.25:3:2, respectively; and a slight excess of sodium carbonate is used to balance the loss of sodium ions in subsequent processes;

[0065] (2) placing the gel at a temperature of 130° C. for a hydrothermal reaction for 20 h, cooling to room temperature, centrifuging for solid-liquid separation, washing the solid with deionized water and anhydrous ethanol for 4 times, drying at a temperature of 80° C. for 6 h, and grinding to obtain sodium titanium phosphate precursor powder;

[0066] (3) The sodium titanium phosphate precursor powder was calcined at 800°C for 3.5 hours to obtain sodium titanium phosphate powder; the XRD pattern of the sodium titanium phosphate powder with a molar ratio of sodium carbonate, diammonium phosphate and tetrabutyl titanate of 2.25:3:2 was shown in Table 1. Figure 7 ,from Figure 7 It can be seen that in addition to the standard peak position of sodium titanium phosphate, an additional diffraction peak with high intensity appears below the diffraction angle of 20°, which is due to the mesoporous structure formed by the new arrangement of Na ion clusters;

[0067] (4) sodium titanium phosphate powder is uniformly dispersed in a deionized water-ethanol mixed solution to obtain a sodium titanium phosphate dispersion, a carbon source (rhodamine) is added to the sodium titanium phosphate dispersion and stirred for reaction for 4 hours, the solvent is evaporated at a temperature of 70°C, and then calcined at a temperature of 800°C for 3 hours to obtain NaTi2(PO4)3 / C powder; the volume ratio of deionized water to ethanol in the deionized water-ethanol mixed solution is 1:1.1, and the concentration of the sodium titanium phosphate dispersion is 0.05 g / mL; the mass ratio of the carbon source (rhodamine) to the sodium titanium phosphate powder is 0.12:1;

[0068] (5) NaTi2(PO4)3 / C powder, conductive agent (Super P), adhesive (polyvinylidene fluoride PVDF), and organic solvent (N-methyl-2-pyrrolidone NMP) are uniformly mixed to obtain an electrode slurry, the electrode slurry is coated on the surface of the cathode current collector (Cu foil), and vacuum dried at a temperature of 100°C for 12 hours to obtain a sodium titanium phosphate-based electrode plate; the amount of the conductive agent (Super P) added is 20% of the total mass, and the amount of the adhesive (polyvinylidene fluoride PVDF) added is 10% of the total mass; the thickness of the NaTi2(PO4)3 / C powder layer on the cathode current collector surface of the sodium titanium phosphate-based electrode plate is 14 μm;

[0069] The charge and discharge performance test of the sodium titanium phosphate-based electrode plate in this embodiment:

[0070] Using the ether-based electrolyte of this embodiment, a metal sodium sheet was used as the negative electrode and the reference electrode, and a glass fiber diaphragm was used as the diaphragm. In a glove box filled with argon gas and with a moisture content of less than 1 ppm, CR2032 stainless steel button half-cells (ether-based) were assembled, respectively, and recorded as half-cell (0.515), half-cell (0.675) and half-cell (2.25); after standing for 8 hours, the electrochemical charge and discharge performance of the sodium titanium phosphate-based electrode sheet was tested;

[0071] The charge and discharge cycle tests of the half-cell (0.515), half-cell (0.675), and half-cell (2.25) of this embodiment are shown in Figure 8 ,Depend on Figure 8 It can be seen that with the increase of the molar ratio of sodium carbonate, the growth trend of the discharge specific capacity of the sodium ion battery with sodium titanium phosphate as the electrode material increases accordingly; when the addition amount is too high, the battery's cycle specific capacity performance will be greatly reduced.

[0072] Example 4: A method for improving the discharge capacity and sodium storage performance of a sodium ion battery, the specific steps are as follows:

[0073] Using ether-based electrolyte, sodium titanium phosphate-based electrode plates as cathodes, sodium vanadium phosphate as anodes, and assembling sodium ion batteries to improve the discharge capacity and sodium storage performance of sodium ion batteries;

[0074] The electrolyte of the ether-based electrolyte is NaPF6, and the solvent is diethylene glycol dimethyl ether; the concentration of electrolyte NaPF6 is 1 mol / L;

[0075] The preparation method of the sodium titanium phosphate-based electrode plate is as follows:

[0076] (1) dissolving sodium carbonate, diammonium phosphate and tetrabutyl titanate in an ethylene glycol solution to obtain solution A, adjusting the pH value of solution A to 9.5 with aqueous ammonia, and coprecipitating for 5 hours under stirring to obtain a gel; the molar ratio of sodium carbonate, diammonium phosphate and tetrabutyl titanate is 0.675:3:2; a slight excess of sodium carbonate is used to balance the loss of sodium ions in subsequent processes;

[0077] (2) placing the gel at a temperature of 140° C. for a hydrothermal reaction for 18 h, cooling to room temperature, centrifuging for solid-liquid separation, washing the solid with deionized water and anhydrous ethanol for 4 times, drying at a temperature of 65° C. for 10 h, and grinding to obtain sodium titanium phosphate precursor powder;

[0078] (3) the sodium titanium phosphate precursor powder is calcined at 800° C. for 2 h to obtain sodium titanium phosphate powder;

[0079] (4) sodium titanium phosphate powder is uniformly dispersed in a deionized water-ethanol mixed solution to obtain a sodium titanium phosphate dispersion, a carbon source (rhodamine) is added to the sodium titanium phosphate dispersion and stirred for reaction for 5 hours, the solvent is evaporated at a temperature of 80°C, and then calcined at a temperature of 900°C for 2 hours to obtain NaTi2(PO4)3 / C powder; the volume ratio of deionized water to ethanol in the deionized water-ethanol mixed solution is 1:1.2, and the concentration of the sodium titanium phosphate dispersion is 0.05 g / mL; the mass ratio of the carbon source (rhodamine) to the sodium titanium phosphate powder is 0.12:1;

[0080] (5) NaTi2(PO4)3 / C powder, conductive agent (Super P), adhesive (polyvinylidene fluoride PVDF), and organic solvent (N-methyl-2-pyrrolidone NMP) are uniformly mixed to obtain an electrode slurry, the electrode slurry is coated on the surface of the cathode current collector (Cu foil), and vacuum dried at a temperature of 80°C for 18 hours to obtain a sodium titanium phosphate-based electrode plate; the amount of the conductive agent (Super P) added is 20% of the total mass, and the amount of the adhesive (polyvinylidene fluoride PVDF) added is 10% of the total mass; the thickness of the NaTi2(PO4)3 / C powder layer on the cathode current collector surface of the sodium titanium phosphate-based electrode plate is 14 μm;

[0081] The charge and discharge performance test of the sodium titanium phosphate-based electrode plate in this embodiment:

[0082] The ether-based electrolyte of this embodiment, the sodium titanium phosphate electrode plate as the negative electrode, the sodium vanadium phosphate electrode plate as the positive electrode, and the glass fiber diaphragm as the diaphragm are used to assemble the NVP / NTP sodium ion battery in a glove box filled with argon gas and with a moisture content of less than 1ppm; after standing for 8 hours, the electrochemical charge and discharge performance of the sodium titanium phosphate-based electrode plate is tested;

[0083] The comparison of the charge and discharge curves of the 1st and 28th cycles of the NVP / NTP sodium ion battery in this embodiment is shown in FIG. Fig. 9 ,Depend on Fig. 9 It can be seen that at 0.2C (1C = 250mAh g -1 ) after 28 cycles of charge and discharge at a rate of 142 mAh / g, the discharge specific capacity of the sodium-ion full battery increased from 101.23 mAh / g to 142 mAh / g. With the increase of the number of cycles, the specific capacity of the sodium-ion battery showed an obvious growth trend, indicating that more sodium-ion storage sites appeared in the reaction process, resulting in more electron transfer positions.

[0084] The specific implementation modes of the present invention are described in detail above, but the present invention is not limited to the above implementation modes, and various changes can be made within the knowledge scope of ordinary technicians in this field without departing from the purpose of the present invention.

Claims

1. A method for improving the discharge capacity and sodium storage performance of a sodium ion battery, characterized in that: The specific steps are as follows: Using ether-based electrolyte, sodium titanium phosphate-based electrode plates as cathodes, sodium vanadium phosphate as anodes, and assembling sodium ion batteries to improve the discharge capacity and sodium storage performance of sodium ion batteries; The electrolyte of the ether-based electrolyte is NaPF6, and the solvent is diethylene glycol dimethyl ether; The preparation method of the sodium titanium phosphate-based electrode plate is as follows: (1) dissolving sodium carbonate, ammonium dihydrogen phosphate, and tetrabutyl titanate in an ethylene glycol solution to obtain a solution A, adjusting the pH value of the solution A to 7.0 to 9.5 with aqueous ammonia, and coprecipitating under stirring to obtain a gel; (2) placing the gel at a temperature of 100 to 140° C. for a hydrothermal reaction for 18 to 30 hours, cooling to room temperature, separating the solid from the liquid, washing the solid with deionized water and anhydrous ethanol in turn, drying, and grinding to obtain a sodium titanium phosphate precursor powder; (3) calcining the sodium titanium phosphate precursor powder at a temperature of 500 to 800° C. for 2 to 8 hours to obtain sodium titanium phosphate powder; (4) sodium titanium phosphate powder is uniformly dispersed in a deionized water-ethanol mixed solution to obtain a sodium titanium phosphate dispersion, a carbon source is added to the sodium titanium phosphate dispersion and stirred for reaction for 2 to 6 hours, the solvent is evaporated, and then the mixture is calcined at a temperature of 600 to 900° C. for 2 to 6 hours to obtain NaTi2(PO4)3 / C powder; (5) NaTi2(PO4)3 / C powder, conductive agent, adhesive and organic solvent are uniformly mixed to obtain electrode slurry, the electrode slurry is coated on the surface of cathode current collector, and vacuum dried to obtain sodium titanium phosphate-based electrode plate.

2. The method for improving the discharge specific capacity and sodium storage performance of a sodium ion battery according to claim 1, characterized in that: In step (1), the molar ratio of sodium carbonate, diammonium dihydrogen phosphate and tetrabutyl titanate is (0.505-2.25):(2.8-3.2):(1.5-2.6).

3. The method for improving the discharge specific capacity and sodium storage performance of a sodium ion battery according to claim 1, characterized in that: The volume ratio of deionized water to ethanol in the deionized water-ethanol mixed solution of step (4) is 1:1 to 1:4, and the concentration of the sodium titanium phosphate dispersion is 0.04 to 0.08 g / mL.

4. The method for improving the discharge specific capacity and sodium storage performance of a sodium ion battery according to claim 1, characterized in that: The mass ratio of the carbon source to the sodium titanium phosphate powder in step (4) is 0.04 to 0.15:

1.

5. The method for improving the discharge specific capacity and sodium storage performance of a sodium ion battery according to claim 1, characterized in that: In step (5), the amount of conductive agent added is 15-25% of the mass of NaTi2(PO4)3 / C powder, and the amount of adhesive added is 5-15% of the mass of NaTi2(PO4)3 / C powder.

6. The method for improving the discharge specific capacity and sodium storage performance of a sodium ion battery according to claim 1, characterized in that: The organic solvent in step (5) is diethylene glycol dimethyl ether or a mixed solvent of ethylene carbonate and propylene carbonate, and the cathode current collector is sodium vanadium phosphate.

7. The method for improving the discharge specific capacity and sodium storage performance of a sodium ion battery according to claim 1, characterized in that: Step (5) The thickness of the NaTi2(PO4)3 / C powder layer on the cathode current collector surface of the sodium titanium phosphate-based electrode plate is 10 to 14 μm.

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