A method for improving the discharge capacity and sodium storage performance of sodium ion batteries

Abstract

The present invention relates to a method for improving the specific discharge capacity and sodium storage performance of a sodium ion battery, belonging to the technical field of sodium ion batteries. The present invention utilizes an ether-based electrolyte, a sodium titanium phosphate-based electrode plate as the anode, and sodium vanadium phosphate as the cathode to assemble a sodium ion battery to improve the specific discharge capacity and sodium storage performance of the sodium ion battery. The ether-based electrolyte comprises NaPF6 as the electrolyte, diethylene glycol dimethyl ether as the solvent, and the NaPF6 concentration is 1 to 1.5 mol / L. The sodium ion battery of the present invention exhibits a specific discharge capacity of 290 to 311 mAh / g and a specific discharge energy of 290 to 329 mWh / g within a voltage range of 3 to 0.01 V. It also exhibits good rate performance at a low rate of 0.1C (239 mAh / g) and a high rate of 10C (238 mAh / g). It also exhibits stable performance at high rates for 2000 cycles (with a specific capacity retention of 90% at a rate of 20C).

Description

Technical Field

[0001] The present invention relates to a method for improving the discharge specific capacity and sodium storage performance of a sodium ion battery, belonging 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 However, there is additional specific capacity in the low voltage range. For the insulation and stability of the material itself, it needs to be conductive if it is to be used as an electrode material. Improving the electronic conductivity of the conductive carbon layer can be achieved through three methods: using conductive carbon (or graphene, carbon nanotube) coating, nano-cutting, and doping. 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 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 as the cathode in the half-cell (sodium metal sheet as the half-cell anode) or sodium vanadium phosphate as the cathode in the full cell (sodium titanium phosphate as the full cell anode) to improve the discharge capacity and sodium storage performance of the sodium ion battery. The sodium ion half-cell has a discharge capacity of 290~311mAh / g in the voltage range of 3~0.01V (far exceeding the estimated theoretical capacity) and a discharge energy of 290~329mWh / g. The charge and discharge curves of the first and 28 cycles obtained by testing the NVP / NTP sodium ion full battery are compared at 0.2C (1C=250mAh g -1 ) After 28 cycles of charge and discharge at a rate of 1.5 GHz, the discharge specific capacity of the sodium-ion full battery increased from 101.23 mAh / g to 142 mAh / g. With the increase in 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, comprising the following steps:

[0006] The organic solvent is diethylene glycol dimethyl ether or ethylene carbonate:propylene carbonate (EC:PC), and the cathode is sodium titanium phosphate (sodium metal sheet is the anode) in the half-cell or sodium vanadium phosphate (sodium titanium phosphate is the anode) in the full-cell, 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 1-1.5 mol / L;

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

[0009] (1) Sodium carbonate, ammonium dihydrogen phosphate, and tetrabutyl titanate are dissolved in ethylene glycol solution to obtain solution A, the pH value of solution A is adjusted to 7.0-9.5 with aqueous ammonia, and coprecipitation is performed under stirring to obtain a gel;

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

[0011] (3) The sodium titanium phosphate precursor powder is calcined at a temperature of 500-800°C for 2-8 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 2-6 hours. The solvent is evaporated to dryness, and then the mixture is calcined at a temperature of 600-900°C for 2-6 hours to obtain NaTi2(PO4)3 / C powder.

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

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

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

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

[0017] In 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 electrode current collector is copper foil.

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

[0020] The present invention adopts a staged firing method to prepare NaTi2(PO4)3 / C. The electrochemical performance of sodium ion batteries using NTP / C as the electrode material is compared in ester-based and ether-based electrolytes. When an 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 exceeds 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 the anode, and a sodium vanadium phosphate as the cathode 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 290~311mAh / g and a discharge specific energy of 290~329mWh / g in the voltage range of 3~0.01V; at the same time, it has good rate performance at a low rate of 0.1C (239mAh / g) and a high rate of 10C (238mAh / 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 This is the XRD pattern of sodium titanium phosphate powder in 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-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-discharge cycle performance diagram of the CR2032 stainless steel button half-cell (ether-based) of Example 2;

[0031] Figure 7 This 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] Figure 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 will be further described in detail below in conjunction with specific embodiments, but the protection scope of the present invention is not limited to the contents described above.

[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 an ether-based electrolyte, a sodium metal electrode plate as the anode and sodium titanium phosphate as the cathode, a sodium ion battery half-cell was assembled to observe the performance of improving the sodium ion battery's discharge capacity and sodium storage performance;

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

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

[0039] (1) Sodium carbonate, ammonium dihydrogen phosphate, and tetrabutyl titanate were dissolved in ethylene glycol solution to obtain solution A, and the pH value of solution A was adjusted to 8.0 with aqueous ammonia. The solution was coprecipitated for 5 hours under stirring to obtain a gel. The molar ratio of sodium carbonate, ammonium dihydrogen phosphate, and tetrabutyl titanate was 0.525:3:2. A slight excess of sodium carbonate was used to balance the loss of sodium ions in the subsequent process.

[0040] (2) The gel was subjected to hydrothermal reaction at 120°C for 20 h, cooled to room temperature, centrifuged for solid-liquid separation, and the solid was washed four times with deionized water and anhydrous ethanol, dried at 60°C for 8 h, and ground to obtain sodium titanium phosphate precursor powder;

[0041] (3) The sodium titanium phosphate precursor powder was calcined at 720°C for 3 hours to obtain sodium titanium phosphate powder; the XRD pattern of the sodium titanium phosphate powder in this embodiment 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 pattern. 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 h. The solvent is evaporated at a temperature of 60°C, and then the mixture is calcined at a temperature of 720°C for 2 h 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 0.05 g / 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 FIG. 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) were mixed evenly to obtain an electrode slurry, which was coated on the surface of the cathode current collector (Cu foil) and vacuum dried at 80°C for 18 hours to obtain a sodium titanium phosphate-based electrode plate; the amount of the conductive agent (Super P) added was 20% of the total mass, and the amount of the adhesive (polyvinylidene fluoride PVDF) added was 10% of the total mass; the thickness of the NaTi2(PO4)3 / C powder layer on the surface of the electrode collector of the sodium titanium phosphate-based electrode plate was 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 NaClO4in ethylene carbonate:propylene carbonate (EC:PC) = 1:1, with a metal sodium sheet as the negative electrode and reference electrode, and a glass fiber separator as the separator, were assembled into CR2032 stainless steel button half-cells (ether-based) and CR2032 stainless steel button half-cells (ester-based) in an argon-filled glove box 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 (see Figure 3 ); The charge and discharge performance of CR2032 stainless steel button half-cell (ester-based) is at a rate of 0.2C, and the reversible discharge capacity of the battery is from 230mAhg -1 After 100 cycles, the 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 electrodes 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 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 different rate performance tests of 0.1C~10C, the cycle performance shows that the first discharge specific capacity of the electrode at 0.2C in ether-based and ester-based electrolytes is 337.27mAh g -1 and 427.67mAh g -1 , and after 100 cycles, they can reach 311.31mAh g -1 and 177.55mAh g -1 The discharge specific capacity is 2.34V. Compared with the cycle performance of ester-based electrolyte, the cycle performance of ether-based electrolyte shows a gradual increase and the reversible specific capacity is 2.34V. Figure 3 The growth has exceeded the theoretical specific capacity, which indicates that the formation of inorganic SEI on the surface of the material in the ether-based electrolyte has led to the emergence of new sodium ion storage sites. 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; the charge capacity at 0.1C is lower than that at other rates, which may be due to the surface activation of the material and the formation of the 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, indicating that 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 was performed. 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 GHz, except for the first cycle of discharge, 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 anode, sodium titanium phosphate as cathode, assembled into a sodium ion half-cell to improve the discharge capacity and sodium storage performance of the sodium ion battery;

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

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

[0052] (1) Sodium carbonate, ammonium dihydrogen phosphate, and tetrabutyl titanate were dissolved in ethylene glycol solution to obtain solution A, and the pH value of solution A was adjusted to 7.5 with aqueous ammonia. The solution was coprecipitated for 6 hours under stirring to obtain a gel. The molar ratio of sodium carbonate, ammonium dihydrogen phosphate, and tetrabutyl titanate was 0.515:3:2, and a slight excess of sodium carbonate was used to balance the loss of sodium ions in the subsequent process.

[0053] (2) The gel was subjected to hydrothermal reaction at 110°C for 28 hours, cooled to room temperature, centrifuged for solid-liquid separation, and the solid was washed four times with deionized water and anhydrous ethanol, dried at 70°C for 8 hours, and ground to obtain sodium titanium phosphate precursor powder;

[0054] (3) The sodium titanium phosphate precursor powder is calcined at 550°C for 8 hours 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 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, 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) were mixed evenly to obtain an electrode slurry, which was coated on the surface of the cathode current collector (Cu foil) and vacuum dried at 90°C for 16 hours to obtain a sodium titanium phosphate-based electrode plate; the amount of the conductive agent (Super P) added was 20% of the total mass, and the amount of the adhesive (polyvinylidene fluoride PVDF) added was 10% of the total mass; the thickness of the NaTi2(PO4)3 / C powder layer on the surface of the electrode collector of the sodium titanium phosphate-based electrode plate was 14 μm;

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

[0058] Using the ether-based electrolyte of this example, sodium metal sheets were used as the negative electrode and reference electrode, and a glass fiber separator was used as the separator. CR2032 stainless steel button-type half-cells (ether-based) were assembled in a glove box filled with argon 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 = 250mAh g -1 ) for long cycle performance test. Figure 6 , Figure 6 It can be seen that at 20C (1C=250mAh g -1 ) After 80 charge and discharge cycles at a rate of 1.5 GHz, except for the first discharge cycle, the sodium ion battery has a discharge specific capacity of 247 mAh / g after 500 cycles of charge and discharge, up from 242 mAh / g. 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 anode, sodium titanium phosphate as cathode, assembled into a sodium ion battery half-cell to improve the sodium ion battery discharge capacity and sodium storage performance;

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

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

[0064] (1) Sodium carbonate, ammonium dihydrogen phosphate, and tetrabutyl titanate were dissolved in ethylene glycol solution to obtain solution A, and the pH value of solution A was adjusted to 9.0 with aqueous ammonia. The solution was coprecipitated for 5.5 hours under stirring to obtain a gel. The molar ratios of sodium carbonate, ammonium dihydrogen phosphate, and tetrabutyl titanate were 0.515:3:2, 0.675:3:2, and 2.25:3:2, respectively. Sodium carbonate was slightly excessive to balance the loss of sodium ions in the subsequent process.

[0065] (2) The gel was subjected to hydrothermal reaction at 130°C for 20 h, cooled to room temperature, centrifuged for solid-liquid separation, and the solid was washed four times with deionized water and anhydrous ethanol, dried at 80°C for 6 h, and ground to obtain sodium titanium phosphate precursor powder;

[0066] (3) The sodium titanium phosphate precursor powder was calcined at 800℃ for 3.5h to obtain sodium titanium phosphate powder; the XRD pattern of sodium titanium phosphate powder with a molar ratio of sodium carbonate, ammonium dihydrogen phosphate and tetrabutyl titanate of 2.25:3:2 was shown in Figure 2. Figure 7 ,from Figure 7 It can be seen that in addition to the standard peak position of sodium titanium phosphate, there are additional diffraction peaks with high intensity 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 4 hours, the solvent is evaporated at 70°C, and then the mixture is calcined at 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, 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) were mixed evenly to obtain an electrode slurry, which was 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 was 20% of the total mass, and the amount of the adhesive (polyvinylidene fluoride PVDF) added was 10% of the total mass; the thickness of the NaTi2(PO4)3 / C powder layer on the surface of the electrode collector of the sodium titanium phosphate-based electrode plate was 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 example, a sodium metal sheet as the negative electrode and reference electrode, and a glass fiber separator as the separator, CR2032 stainless steel button half-cells (ether-based) were assembled in a glove box filled with argon and with a moisture content of less than 1 ppm. These cells were labeled as half-cell (0.515), half-cell (0.675), and half-cell (2.25), respectively. After standing for 8 hours, the electrochemical charge and discharge performance of the sodium titanium phosphate-based electrode sheets 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 cycle specific capacity performance of the battery 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 plate as anode, sodium vanadium phosphate electrode plate as cathode, assembled into a sodium ion full battery to improve the sodium ion battery discharge capacity and sodium storage performance;

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

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

[0076] (1) Sodium carbonate, ammonium dihydrogen phosphate, and tetrabutyl titanate were dissolved in ethylene glycol solution to obtain solution A, and the pH value of solution A was adjusted to 9.5 with aqueous ammonia. The solution was coprecipitated for 5 h under stirring to obtain a gel. The molar ratio of sodium carbonate, ammonium dihydrogen phosphate, and tetrabutyl titanate was 0.675:3:2. A slight excess of sodium carbonate was used to balance the loss of sodium ions in the subsequent process.

[0077] (2) The gel was subjected to a hydrothermal reaction at 140°C for 18 hours, cooled to room temperature, centrifuged for solid-liquid separation, and the solid was washed four times with deionized water and anhydrous ethanol, dried at 65°C for 10 hours, and ground to obtain sodium titanium phosphate precursor powder;

[0078] (3) The sodium titanium phosphate precursor powder is calcined at 800°C for 2 hours 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 5 hours, the solvent is evaporated at 80°C, and then calcined at 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, 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) were mixed evenly to obtain an electrode slurry, which was coated on the surface of the cathode current collector (Cu foil) and vacuum dried at 80°C for 18 hours to obtain a sodium titanium phosphate-based electrode plate; the amount of the conductive agent (Super P) added was 20% of the total mass, and the amount of the adhesive (polyvinylidene fluoride PVDF) added was 10% of the total mass; the thickness of the NaTi2(PO4)3 / C powder layer on the surface of the electrode collector of the sodium titanium phosphate-based electrode plate was 14 μm;

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

[0082] Using the ether-based electrolyte of this embodiment, a sodium titanium phosphate electrode plate as the negative electrode, a sodium vanadium phosphate electrode plate as the positive electrode, and a glass fiber separator as the separator, an NVP / NTP sodium ion full cell was assembled in a glove box filled with argon and with a moisture content of less than 1 ppm; after standing for 8 hours, the electrochemical charge and discharge performance of the NVP / NTP sodium ion full cell was tested;

[0083] The comparison of the charge and discharge curves of the 1st and 28th cycles of the NVP / NTP sodium ion full battery in this embodiment is shown in FIG. Figure 9 ,Depend on Figure 9 It can be seen that at 0.2C (1C=250mAh g -1 ) After 28 cycles of charge and discharge at a rate of 1.5 GHz, the discharge specific capacity of the sodium-ion full battery increased from 101.23 mAh / g to 142 mAh / g. With the increase in 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 during the reaction, resulting in more electron transfer positions.

[0084] The above describes the specific embodiments of the present invention in detail, but the present invention is not limited to the above embodiments. Various changes can be made within the knowledge of ordinary technicians in this field without departing from the scope 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 anodes, and sodium vanadium phosphate as cathodes, a sodium ion battery is assembled to improve the discharge capacity and sodium storage performance of the sodium ion battery; 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) Sodium carbonate, ammonium dihydrogen phosphate, and tetrabutyl titanate are dissolved in ethylene glycol solution to obtain solution A, the pH value of solution A is adjusted to 7.0-9.5 with aqueous ammonia, and coprecipitation is performed under stirring to obtain a gel; (2) placing the gel at a temperature of 100-140°C for a hydrothermal reaction for 18-30 hours, cooling to room temperature, separating the solid and the liquid, washing the solid with deionized water and anhydrous ethanol in sequence, drying, and grinding to obtain sodium titanium phosphate precursor powder; (3) The sodium titanium phosphate precursor powder is calcined at a temperature of 500-800°C for 2-8 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 2-6 hours. The solvent is evaporated to dryness, and then the mixture is calcined at a temperature of 600-900°C for 2-6 hours to obtain NaTi2(PO4)3 / C powder. (5) NaTi2(PO4)3 / C powder, conductive agent, adhesive and organic solvent are mixed evenly to obtain electrode slurry, the electrode slurry is coated on the surface of the electrode collector, and vacuum dried to obtain sodium titanium phosphate-based electrode plates.

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

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

1.

5. The method for improving the discharge specific capacity and sodium storage performance of a sodium ion battery according to claim 1, wherein: In 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.

6. The method for improving the discharge specific capacity and sodium storage performance of a sodium ion battery according to claim 1, wherein: In step (5), the organic solvent is diethylene glycol dimethyl ether or a mixed solvent of ethylene carbonate and propylene carbonate, and the electrode current collector is copper foil.

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: In 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 10-14 μm.

Images