CN113659146B - Potassium lanthanum silicon ternary co-doped vanadium sodium phosphate electrode material and its preparation method and application - Google Patents

Abstract

The invention belongs to the technical field of new energy materials, and provides a potassium-lanthanum-silicon ternary co-doped sodium vanadium phosphate electrode material and its preparation method and application in order to solve the problems of poor electrochemical stability of sodium vanadium phosphate itself. Potassium lanthanum silicon ternary co-doped sodium vanadium phosphate electrode material is Na _3.1‑x K _x V _2−x La _x (PO ₄ ) _2.9 (SiO ₄ ) _0.1 , x=0,0.01, 0.03, 0.05, 0.07 or 0.1 ; The electrode material K ⁺ ion doped Na site, La ^{3 +} ion doped V site and Si ^{4 +} ion doped P site; with ammonium metavanadate, sodium acetate and ammonium dihydrogen phosphate as raw materials, potassium dihydrogen phosphate , lanthanum nitrate and tetraethyl silicate as doping source, oxalic acid as chelating agent, potassium lanthanum silicon ternary co-doped sodium vanadium phosphate electrode material was prepared by solution gel method. It has more dazzling electrochemical performance, higher specific capacity, excellent rate and cycle ability, simple preparation, low cost, and is conducive to industrial promotion.

Description

Potassium lanthanum silicon ternary co-doped vanadium sodium phosphate electrode material and its preparation method and application

technical field

The invention belongs to the technical field of new energy materials, and in particular relates to a potassium-lanthanum-silicon ternary co-doped vanadium-sodium phosphate electrode material and a preparation method and application thereof.

Background technique

Due to the advantages of low cost and low environmental pollution, sodium-ion batteries have attracted widespread attention in recent years, and are considered to be a new next-generation electrochemical energy storage device that can replace lithium-ion batteries. Today, sodium-ion batteries have been partially industrialized and play a vital role in commercial energy vehicles and electrical energy storage devices. Among them, sodium vanadium phosphate, a polyanionic compound, has attracted much attention due to its open sodium ion superconducting structure, high voltage platform and theoretical specific capacity, which provides a strong technical guarantee for the commercialization of sodium ion batteries.

However, the stability of the three-dimensional skeleton structure is poor. In the dynamic behavior of frequent charging and discharging of sodium ions, the phosphorus-oxygen octahedron and vanadyl-oxygen tetrahedron adjacent to the sodium ion are susceptible to internal stress and cause the structure to collapse. This restricts the electrochemical stability of sodium vanadium phosphate itself.

Contents of the invention

In order to solve the current problems such as the poor electrochemical stability of sodium vanadium phosphate itself, the present invention provides a potassium-lanthanum-silicon ternary co-doped sodium vanadium phosphate electrode material and a preparation method and application thereof. Potassium-lanthanum-silicon ternary co-doping regulates the crystal structure of sodium vanadium phosphate, constructs a conductive carbon network in situ on the particle surface, stabilizes the sodium vanadium phosphate framework to prevent collapse, and provides additional conductive channels for electrons, greatly improving the electrochemical performance of the material . The surface of the prepared sodium vanadium phosphate modified material has about 4 nanometers thick amorphous carbon coated on the periphery of sodium vanadium phosphate, and the electrode material is used in the 2016 button battery, showing excellent cycle stability and large rate long cycle It can be considered as a positive electrode material for sodium ion batteries with good application prospects.

The present invention is realized by the following technical scheme: a potassium lanthanum silicon ternary co-doped vanadium sodium phosphate electrode material, the potassium lanthanum silicon ternary co-doped vanadium sodium phosphate electrode material is Na _3.1-x K _x V _{2− x} La _x (PO ₄ ) _2.9 (SiO ₄ ) _0.1 , x=0, 0.01, 0.03, 0.05, 0.07 or 0.1; the electrode material is K ⁺ ion-doped Na site, La ³⁺ ion-doped V site and Si ^{4 +} ion doping P site; using ammonium metavanadate, sodium acetate and ammonium dihydrogen phosphate as raw materials, potassium dihydrogen phosphate, lanthanum nitrate and tetraethyl silicate as doping sources, oxalic acid as chelating agent, through solution gel Potassium-lanthanum-silicon ternary co-doped sodium vanadium phosphate electrode material was prepared by this method.

The method for preparing the potassium lanthanum silicon ternary co-doped sodium vanadium phosphate electrode material, the specific steps are as follows:

(1) Add sodium acetate, ammonium metavanadate, ammonium dihydrogen phosphate, potassium dihydrogen phosphate, lanthanum nitrate, and tetraethyl silicate with a molar ratio of 26.19:16.68:25:0.09:0.6:0.9 to 60 mL In the ionic water solution, heated to 70°C at constant temperature to form a clear solution;

(2) Take oxalic acid and dissolve it in 20ml deionized water, and dissolve it to form an oxalic acid solution with a concentration of 2.59M;

(3) Add the prepared oxalic acid solution drop by drop to the clarified solution in step (1), the color is finally stable in blue, stir at constant temperature until the precursor solution becomes 20ml viscous colloid, freeze overnight at -21°C, and then use the freezer Dryer, run at -35°C—-40°C for 48h;

(4) Dry the freeze-dried samples at 80°C for 12 hours;

(5) The obtained precursor was pre-calcined at 450°C for 4 hours in a nitrogen atmosphere, and then final-fired at 700°C for 6 hours to obtain the final product.

The application of the potassium-lanthanum-silicon ternary co-doped vanadium-sodium phosphate electrode material in a sodium-ion battery, the potassium-lanthanum-silicon ternary co-doped vanadium-sodium phosphate electrode material is used as a positive electrode material in a sodium-ion battery.

The specific method is: Na _3.1-x K _x V _2−x La _x (PO ₄ ) _2.9 (SiO ₄ ) _0.1 material is used as the active material of the positive electrode material, sodium sheet is used as the negative electrode, assembled into a 2016 button battery, and the electrolyte is NaClO ₄ +EC/DEC+5%FEC; among them, NaClO ₄ , EC, DEC and FEC respectively represent sodium perchlorate, ethylene carbonate, diethyl carbonate and fluoroethylene carbonate; 1M NaClO ₄ is dissolved in the volume ratio In the 1:1 EC/DEC system, 5 wt% FEC was added at the same time for preparation.

The present invention uses three common elements, through a mature and concise solution-gel method, K ⁺ ion doping Na site, La ³⁺ ion doping V site and Si ⁴⁺ ion doping P site, oxalic acid as chelating agent and Part of the reducing agent participates in the reduction reaction to reduce V ^{5 +} to V ³⁺ , and the excess part forms a carbon layer to coat the surface of the material, improving the conductivity of the material. The modified doped sample exhibits better cycle life and stable large-rate performance than the undoped one.

Compared with the previously reported element doping modification, this measure has obvious advantages: (1) Potassium is rich in resources, and the abundance of surface elements is extremely high. At the same time, it has the effect of extending the specific crystal axis of the crystal. The extended c axis strengthens the sodium The stability of the ion migration channel; (2) Lanthanum and silicon have uniform size characteristics, and the larger ionic radius further stabilizes and optimizes the crystal structure on the other two scales; (3) The experimental synthesis process is easy to control and can be Large-scale preparation and experimental protocols have important guiding significance for the design and development of multi-component systems.

The potassium element in the obtained material can expand the lattice size of the sodium vanadium phosphate in the c direction and introduce more sodium ion vacancies, thereby improving the conductivity of the sodium vanadium phosphate. At the same time, lanthanum and silicon elements with larger ionic radii extend the crystal in the a and b directions on the vanadium and phosphorus positions, respectively, thus providing a more stable crystal framework for the rapid insertion and deintercalation of sodium ions in the lattice, The conductivity and cycle life of sodium vanadium phosphate are further improved. According to tests and characterizations, due to the potassium-lanthanum-silicon ternary co-doping effect, the sodium-ion battery cathode material has brighter electrochemical performance, higher specific capacity, and excellent rate and cycle capability. At the same time, the preparation of the material Simple and low cost, it is expected to be popularized in industry.

Compared with the prior art, the raw materials selected in the present invention are cheap, easy to synthesize, and suitable for large-scale commercial preparation; the surface of the product of the present invention contains a uniform carbon layer coating, which is beneficial to improve the electrical conductivity of the material; compared with the unmodified Compared with the vanadium-sodium phosphate material, the crystal structure of the positive electrode material after potassium-lanthanum-silicon ternary co-doping is more stable; the product of the present invention can exhibit good rate performance and good high-rate long-cycle stability.

Description of drawings

Fig. 1 is the photo of Na _3.03 K _0.07 V _1.93 La _0.07 (PO ₄ ) _2.9 (SiO ₄ ) _0.1 prepared in Example 4, as can be seen from the figure, the particle size is low and uniformly dispersed, which is beneficial to improve the electrons between the particles conduction;

Figure 2 shows the XRD occupancy refinement results of the Na _3.03 K _0.07 V _1.93 La _0.07 (PO ₄ ) _2.9 (SiO ₄ ) _0.1 sample prepared in Example 4. The occupancy refinement results show that K ⁺ doping enters the Na site , La ³⁺ doped into the V site while Si ⁴⁺ doped into the P site and coincided with the designed doping amount. Doping did not change the three-dimensional structure of sodium vanadium phosphate;

Fig. 3 is the XPS result of the Na _3.03 K _0.07 V _1.93 La _0.07 (PO ₄ ) _2.9 (SiO ₄ ) _0.1 sample prepared in Example 4. The XPS test results show that K ⁺ , La ³⁺ and Si ⁴⁺ in the sample all show Obvious characteristic peaks, consistent with the experimental design;

Fig. 4 is embodiment 4, comparative example 1, embodiment 2, embodiment 3, embodiment 5, when embodiment 6 is assembled into 2016 type button battery, the constant current charge and discharge curve that measures, and current density is 0.1 C;

Fig. 5 is embodiment 4, comparative example 1, embodiment 2, embodiment 3, embodiment 5, embodiment 6 when being assembled into 2016 type button battery, at the scan rate of 0.1mVs-1 CV test contrast chart;

Fig. 6 is embodiment 4, comparative example 1, embodiment 2, embodiment 3, embodiment 5, embodiment 6 when being assembled into 2016 type button cell, the rate performance comparison curve that measures at different current densities;

Fig. 7 is the 500-cycle cycle curves of the Na _3.03 K _0.07 V _1.93 La _0.07 (PO ₄ ) _2.9 (SiO ₄ ) _0.1 sample prepared in Example 4 at current densities of 10 C and 50 C.

Detailed ways

In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present invention, rather than All the embodiments; based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts all belong to the protection scope of the present invention.

Example 1: Preparation of Na _3.09 K _0.01 V _1.99 La _0.01 (PO ₄ ) _2.9 (SiO ₄ ) _0.1 electrode material:

Take 2.1380 g sodium acetate, 1.9422 g ammonium metavanadate, 2.8002 g ammonium dihydrogen phosphate, 00119 g potassium dihydrogen phosphate, 0.0378 g lanthanum nitrate, 0.816 tetraethyl silicate, add them to 60 mL deionized aqueous solution, and heat at constant temperature At 70°C, a clear solution was formed; 6.5946g of oxalic acid was hot-dissolved in 20ml of deionized water. Add the prepared oxalic acid solution drop by drop to the clear solution, the color finally stabilizes in blue, and stir at constant temperature until the precursor solution becomes 20ml viscous colloid. Transfer to a container to freeze overnight, and place in a freeze dryer for 48 hours. The sample was taken out and placed in an oven, and dried at 80°C for 12 hours; the obtained precursor was pre-calcined at 450°C for four hours in a nitrogen atmosphere, and then finally fired at 700°C for six hours to obtain the final product.

The cathode material prepared in this example was mixed with acetylene black and polyvinylidene fluoride (PVDF) in 1.4 mL of N-methylpyrrolidone (NMP) solvent at a ratio of 7:2:1. The above mixture was ball milled for four hours to obtain a homogeneous slurry and coated on clean charcoal coated aluminum foil. After air drying at 45°C for four hours, vacuum drying was carried out overnight at 120°C, and finally an electrode sheet loaded with various materials was obtained. The assembled CR2016 button battery uses metal sodium as the negative electrode, the diaphragm is ceramic Celgard diaphragm, and the electrolyte is NaClO ₄ +EC/DEC+5%FEC; where NaClO ₄ , EC, DEC and FEC represent perchloric acid respectively Sodium, ethylene carbonate, diethyl carbonate, and fluoroethylene carbonate; 1M NaClO ₄ was dissolved in an EC/DEC system with a volume ratio of 1:1, and 5 wt% FEC was added at the same time. Assemble in a vacuum glove box.

At room temperature, the assembled button cell can be subjected to a constant current charge and discharge test in the voltage range of 2.3-4.1V and a cyclic voltammetry measurement at a scan rate of 0.1mVs ^-1 . Specifically, the charge-discharge curve of the first cycle is shown in Figure 4, the CV redox peak at low scan rate is shown in Figure 5, and the cycle curve of the battery rate from 0.3 to 10c is shown in Figure 6.

After testing, the material is used as the positive electrode material of the sodium ion battery. Electrochemical tests show that the specific discharge capacity of the material can reach 100mAh g ^-1 at 0.1 C. The battery cycle rate shows that the specific discharge capacity of this material can still be maintained at 82 mAh g ^-1 at a large rate of 10C, and when the discharge rate is increased to 1C, the specific discharge capacity of this material can still quickly rise to 105 mAh g ^-1 . At the same time, the CV test was carried out at a scan rate of 0.1 V s ^-1 , and the results showed that there was an obvious split peak at around 3.2 V, which proved that two Na sites with different chemical environments were retained in the crystal.

Example 2: Preparation of Na _3.07 K _0.03 V _1.97 La _0.03 (PO ₄ ) _2.9 (SiO ₄ ) _0.1 electrode material:

Take 2.1858g sodium acetate, 2.0004 g ammonium metavanadate, 2.8655 g ammonium dihydrogen phosphate, 0.0354 g potassium dihydrogen phosphate, 0.1128 g lanthanum nitrate, 0.1808 tetraethyl silicate, add to 60 mL deionized aqueous solution, and heat at constant temperature At 70°C, a clear solution was formed; 6.5648g of oxalic acid was hot-dissolved in 20ml of deionized water. Add the prepared oxalic acid solution drop by drop to the clear solution, the color finally stabilizes in blue, and stir at constant temperature until the precursor solution becomes 20ml viscous colloid. Transfer to a container to freeze overnight, and place in a freeze dryer for 48 hours. The sample was taken out and placed in an oven, and dried at 80°C for 12 hours; the obtained precursor was pre-calcined at 450°C for four hours in a nitrogen atmosphere, and then finally fired at 700°C for six hours to obtain the final product.

The cathode material prepared in this example was mixed with acetylene black and polyvinylidene fluoride (PVDF) in 1.4 mL of N-methylpyrrolidone (NMP) solvent at a ratio of 7:2:1. The above mixture was ball milled for four hours to obtain a homogeneous slurry and coated on clean charcoal coated aluminum foil. After air drying at 45°C for four hours, vacuum drying was carried out overnight at 120°C, and finally an electrode sheet loaded with various materials was obtained. The assembled CR2016 button battery uses metallic sodium as the negative electrode, the ceramic diaphragm Celgard as the diaphragm, and the electrolyte is NaClO ₄ +EC/DEC+5%FEC; where NaClO ₄ , EC, DEC and FEC represent perchloric acid respectively Sodium, ethylene carbonate, diethyl carbonate, and fluoroethylene carbonate; 1M NaClO ₄ was dissolved in an EC/DEC system with a volume ratio of 1:1, and 5 wt% FEC was added at the same time. Assemble in a vacuum glove box.

At room temperature, the assembled button cell can be subjected to a constant current charge and discharge test in the voltage range of 2.3-4.1V and a cyclic voltammetry measurement at a scan rate of 0.1mVs ^-1 . Specifically, the charge-discharge curve of the first cycle is shown in Figure 4, the CV redox peak at low scan rate is shown in Figure 5, and the cycle curve of the battery rate from 0.3 C to 10 C is shown in Figure 6.

After testing, the material is used as the positive electrode material of the sodium ion battery. Electrochemical tests show that the specific discharge capacity of the material can reach 102mAh g ^-1 at 0.1 C. The battery cycle rate shows that the specific discharge capacity of the material can still be maintained at 81.5 mAh g ^-1 at a large rate of 10C, and when the discharge rate rises to 1C, the specific discharge capacity of the material can still quickly rise to 95 mAh g ^-1 . At the same time, the CV test was carried out at a scan rate of 0.1 V s ^-1 , and the results showed that there was an obvious split peak at around 3.2 V, which proved that two Na sites with different chemical environments were retained in the crystal.

Example 3: Preparation of Na _3.05 K _0.05 V _1.95 La _0.05 (PO ₄ ) _2.9 (SiO ₄ ) _0.1 electrode material:

Take 2.1618g sodium acetate, 1.9712 g ammonium metavanadate, 2.8327 g ammonium dihydrogen phosphate, 0.0432 g potassium dihydrogen phosphate, 0.1871 g lanthanum nitrate, 0.1800 tetraethyl silicate, add to 60 mL deionized aqueous solution, and heat at constant temperature At 70°C, a clear solution was formed; 6.5353g of oxalic acid was dissolved in 20ml of deionized water. Add the prepared oxalic acid solution drop by drop to the clear solution, the color finally stabilizes in blue, and stir at constant temperature until the precursor solution becomes 20ml viscous colloid. Transfer to a container to freeze overnight, and place in a freeze dryer for 48 hours. The sample was taken out and placed in an oven, and dried at 80°C for 12 hours; the obtained precursor was pre-calcined at 450°C for four hours in a nitrogen atmosphere, and then finally fired at 700°C for six hours to obtain the final product.

The cathode material prepared in this example was mixed with acetylene black and polyvinylidene fluoride (PVDF) in 1.4 mL of N-methylpyrrolidone (NMP) solvent at a ratio of 7:2:1. The above mixture was ball milled for four hours to obtain a homogeneous slurry and spread on clean charcoal coated aluminum foil. After air drying at 45°C for four hours, vacuum drying was carried out overnight at 120°C, and finally an electrode sheet loaded with various materials was obtained. The assembled CR2016 button battery uses metallic sodium as the negative electrode, the ceramic diaphragm Celgard as the diaphragm, and the electrolyte is NaClO ₄ +EC/DEC+5%FEC; where NaClO ₄ , EC, DEC and FEC represent perchloric acid respectively Sodium, ethylene carbonate, diethyl carbonate, and fluoroethylene carbonate; 1M NaClO ₄ was dissolved in an EC/DEC system with a volume ratio of 1:1, and 5 wt% FEC was added at the same time. Assemble in a vacuum glove box.

At room temperature, the assembled button cell can be subjected to a constant current charge and discharge test in the voltage range of 2.3-4.1V and a cyclic voltammetry measurement at a scan rate of 0.1mVs ^-1 . Specifically, the charge-discharge curve of the first cycle is shown in Figure 4, the CV redox peak at low scan rate is shown in Figure 5, and the cycle curve of the battery rate from 0.3 C to 10 C is shown in Figure 6.

After testing, the material is used as the positive electrode material of the sodium ion battery. Electrochemical tests show that the specific discharge capacity of the material can reach 105mAh g ^-1 at 0.1 C. The battery cycle rate shows that the specific discharge capacity of the material can still be maintained at 85 mAh g ^-1 at a large rate of 10C, and when the discharge rate rises to 1C, the specific discharge capacity of the material can still quickly rise to 103 mAh g ^-1 . At the same time, the CV test was carried out at a scan rate of 0.1 V s ^-1 , and the results showed that there was an obvious split peak at around 3.2 V, which proved that two Na sites with different chemical environments were retained in the crystal.

Example 4: Preparation of Na _3.03 K _0.07 V _1.93 La _0.07 (PO ₄ ) _2.9 (SiO ₄ ) _0.1 electrode material:

Take 2.1380 g of sodium acetate, 1.9422 g of ammonium metavanadate, 2.8002 g of ammonium dihydrogen phosphate, 0.0819 g of potassium dihydrogen phosphate, 0.2607 g of lanthanum nitrate, and 0.1792 g of tetraethyl silicate, add them to 60 mL of deionized aqueous solution, and heat at constant temperature At 70°C, a clear solution is formed; take 6.5060g of oxalic acid and dissolve it in 20ml of deionized water. Add the prepared oxalic acid solution drop by drop to the clear solution, the color finally stabilizes in blue, and stir at constant temperature until the precursor solution becomes 20ml viscous colloid. Transfer to a container to freeze overnight, and place in a freeze dryer for 48 hours. The sample was taken out and placed in an oven, and dried at 80°C for 12 hours; the obtained precursor was pre-calcined at 450°C for four hours in a nitrogen atmosphere, and then finally fired at 700°C for six hours to obtain the final product.

The positive electrode material prepared in this example was mixed with acetylene black and polyvinylidene fluoride (PVDF) in a ratio of 7:2:1 in 1.4 mL of N-methylpyrrolidone (NMP) solvent. The above mixture was ball milled for four hours to obtain a homogeneous slurry and spread on clean charcoal coated aluminum foil. After air drying at 45°C for four hours, vacuum drying was carried out overnight at 120°C, and finally an electrode sheet loaded with various materials was obtained. The assembled CR2016 button battery uses metallic sodium as the negative electrode, the ceramic diaphragm Celgard as the diaphragm, and the electrolyte is NaClO ₄ +EC/DEC+5%FEC; where NaClO ₄ , EC, DEC and FEC represent perchloric acid respectively Sodium, ethylene carbonate, diethyl carbonate, and fluoroethylene carbonate; 1M NaClO ₄ was dissolved in an EC/DEC system with a volume ratio of 1:1, and 5 wt% FEC was added at the same time. Assemble in a vacuum glove box.

At room temperature, the assembled button cell can be subjected to a constant current charge and discharge test in the voltage range of 2.3-4.1V and a cyclic voltammetry measurement at a scan rate of 0.1mVs ^-1 . Specifically, the charge-discharge curve of the first cycle is shown in Figure 4, the CV redox peak at low scan rate is shown in Figure 5, and the battery rate cycle curve from 0.3 C to 10 C is shown in Figure 6. In order to better represent its characteristics, it is further analyzed detection. The SEM image of the particles is shown in Figure 1, the XRD refinement result is shown in Figure 2, and the energy spectrum of the main doping elements is shown in Figure 3. The long cycle results are shown in Fig. 7 at super large magnifications of 10 C and 50 C.

After testing, the material is used as the positive electrode material of the sodium ion battery, and the particle size is only about 100nm, and the dispersion is uniform, which is conducive to the full infiltration of the electrolyte. Electrochemical tests show that the specific discharge capacity of the material can reach 110h g ^-1 at 0.1 C. The battery cycle rate shows that the specific discharge capacity of this material can still be maintained at 96mAh g ^-1 at a high rate of 10C, and when the discharge rate is increased to 1C, the specific discharge capacity of this material can still quickly rise to 112 mAh g ^-1 . At the same time, the CV test was carried out at a scan rate of 0.1 Vs ^-1 , and the results showed that there was an obvious split peak at about 3.2 V, which proved that two Na sites with different chemical environments remained in the crystal. At the same time, the XRD results show that all the characteristic peaks indicate the R-3C space group, compound NVP characteristic structure, it can be considered that the introduction of three elements will not destroy its crystal composition. The XPS test shows that all peaks can well correspond to the energy levels of the elements, indicating that the dopant source has successfully entered the system. At the same time, at a discharge rate of 10C, the material can still maintain a discharge specific capacity of 60 mAh g ^-1 after 500 cycles, and even in the extreme case of 50C, there is still a discharge specific capacity of 40 mAh g ^-1 available. use.

Example 5: Preparation of Na ₃ K _0.1 V _1.9 La _0.1 (PO ₄ ) _2.9 (SiO ₄ ) _0.1 electrode material:

Take 2.1027g sodium acetate, 1.8993 g ammonium metavanadate, 2.7521 g ammonium dihydrogen phosphate, 0.1163 g potassium dihydrogen phosphate, 0.3700 g lanthanum nitrate, 0.1780 tetraethyl silicate, add to 60 mL deionized aqueous solution, and heat at constant temperature At 70°C, a clear solution was formed; 6.4626g of oxalic acid was hot-dissolved in 20ml of deionized water. Add the prepared oxalic acid solution drop by drop to the clear solution, the color finally stabilizes in blue, and stir at constant temperature until the precursor solution becomes 20ml viscous colloid. Transfer to a container to freeze overnight, and place in a freeze dryer for 48 hours. The sample was taken out and placed in an oven, and dried at 80°C for 12 hours; the obtained precursor was pre-calcined at 450°C for four hours in a nitrogen atmosphere, and then finally fired at 700°C for six hours to obtain the final product.

The cathode material prepared in this example was mixed with acetylene black and polyvinylidene fluoride (PVDF) in 1.4 mL of N-methylpyrrolidone (NMP) solvent at a ratio of 7:2:1. The above mixture was ball milled for four hours to obtain a homogeneous slurry and spread on clean charcoal coated aluminum foil. After air drying at 45°C for four hours, vacuum drying was carried out overnight at 120°C, and finally an electrode sheet loaded with various materials was obtained. The assembled CR2016 button battery uses metallic sodium as the negative electrode, the ceramic diaphragm Celgard as the diaphragm, and the electrolyte is NaClO ₄ +EC/DEC+5%FEC; where NaClO ₄ , EC, DEC and FEC represent perchloric acid respectively Sodium, ethylene carbonate, diethyl carbonate, and fluoroethylene carbonate; 1M NaClO ₄ was dissolved in an EC/DEC system with a volume ratio of 1:1, and 5 wt% FEC was added at the same time. Assemble in a vacuum glove box.

At room temperature, the assembled button cell can be subjected to a constant current charge and discharge test in the voltage range of 2.3-4.1V and a cyclic voltammetry measurement at a scan rate of 0.1mVs ^-1 . Specifically, the charge-discharge curve of the first cycle is shown in Figure 4, the CV redox peak at low scan rate is shown in Figure 5, and the cycle curve of the battery rate from 0.3 C to 10 C is shown in Figure 6.

After testing, the material is used as the positive electrode material of the sodium ion battery. Electrochemical tests show that the specific discharge capacity of the material can reach 95mAh g ^-1 at 0.1 C. The battery cycle rate shows that the discharge specific capacity of the material is only 55 mAh g ^-1 at a high rate of 10C, and when the discharge rate rises to 1C, the material can still quickly recover to a discharge specific capacity of 95 mAh g ^-1 . At the same time, the CV test was carried out at a scan rate of 0.1 V s ^-1 , and the results showed that there was an obvious split peak at around 3.2 V, which proved that two Na sites with different chemical environments were retained in the crystal.

Example 6: Na ₃ V ₂ (PO ₄ ) ₃ prepared according to the method of the present invention

Add 2.3692g of sodium dihydrogen phosphate and 1.5401g of ammonium metavanadate to 60 mL of deionized aqueous solution, and heat at a constant temperature to 70°C to form a clear solution; take 4.9790g of oxalic acid and dissolve it in 20ml of deionized water. The prepared oxalic acid solution was added dropwise to the clear solution, and the color finally stabilized to blue, and 0.1957 g of carbon nanotubes were added under continuous stirring, and stirred at a constant temperature until the precursor solution became 20 ml of viscous colloid. Transfer to a container to freeze overnight, and place in a freeze dryer for 48 hours. The sample was taken out and placed in an oven, and dried at 80°C for 12 hours; the obtained precursor was pre-calcined at 450°C for four hours in a nitrogen atmosphere, and then finally fired at 700°C for six hours to obtain the final product.

The cathode material prepared in this example was mixed with acetylene black and polyvinylidene fluoride (PVDF) in 1.4 mL of N-methylpyrrolidone (NMP) solvent at a ratio of 7:2:1. The above mixture was ball milled for four hours to obtain a homogeneous slurry and spread on clean charcoal coated aluminum foil. After air drying at 45°C for four hours, vacuum drying was carried out overnight at 120°C, and finally an electrode sheet loaded with various materials was obtained. The assembled CR2016 button battery uses metallic sodium as the negative electrode, the ceramic diaphragm Celgard as the diaphragm, and the electrolyte is NaClO ₄ +EC/DEC+5%FEC; where NaClO ₄ , EC, DEC and FEC represent perchloric acid respectively Sodium, ethylene carbonate, diethyl carbonate, and fluoroethylene carbonate; 1M NaClO ₄ was dissolved in an EC/DEC system with a volume ratio of 1:1, and 5 wt% FEC was added at the same time. , assembled in a vacuum glove box.

At room temperature, the assembled button cell can be subjected to a constant current charge and discharge test in the voltage range of 2.3-4.1V and a cyclic voltammetry measurement at a scan rate of 0.1mVs ^-1 . Specifically, the charge-discharge curve of the first cycle is shown in Figure 4, the CV redox peak at low scan rate is shown in Figure 5, and the cycle curve of the battery rate from 0.3 C to 10 C is shown in Figure 6.

After testing, the material is used as the positive electrode material of the sodium ion battery. Electrochemical tests show that the specific discharge capacity of the material can reach 96mAh g ^-1 at 0.1 C. The battery cycle rate shows that the specific discharge capacity of the material can still be maintained at 82 mAh g ^-1 at a large rate of 10C, and when the discharge rate rises to 1C, the specific discharge capacity of the material can still quickly rise to 101 mAh g ^-1 . At the same time, the CV test was carried out at a sweep rate of 0.1 V s ^-1 , and the results showed that there was only a single reduction peak at around 3.2 V, proving that the crystal structure collapsed.

Above-mentioned embodiment illustrates: the present invention uses simple solution-gel method, successfully doped potassium lanthanum silicon three elements in sodium vanadium phosphate. The potassium element in the inventive product can expand the sodium vanadium phosphate crystal lattice in the c-axis direction, thereby introducing more active sodium ion sites and improving the conductivity of the sodium vanadium phosphate. At the same time, lanthanum and silicon elements with larger ionic radii extend the crystal in the a and b directions on the vanadium and phosphorus positions, respectively, thus providing a more stable crystal framework for the rapid insertion and deintercalation of sodium ions in the lattice, The conductivity and cycle life of sodium vanadium phosphate are further improved. According to the test and characterization, due to the ternary co-doping of potassium lanthanum silicon, the invented product has more dazzling electrochemical performance, high rate and long cycle stability, higher specific capacity and excellent rate and cycle ability. At the same time, The material is simple to prepare and low in cost, and is expected to be popularized in industry.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, rather than limiting them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: It is still possible to modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the technical solutions of the various embodiments of the present invention. scope.

Claims (3)

1. A potassium lanthanum silicon ternary co-doped sodium vanadium phosphate electrode material is characterized in that: the potassium-lanthanum-silicon ternary co-doped sodium vanadium phosphate electrode material is Na _3.1-x K _x V _2−x La _x (PO ₄ ) _2.9 (SiO ₄ ) _0.1 X=0.01, 0.03, 0.05, 0.07, or 0.1; the electrode material K ⁺ Ion doped Na position, la ³⁺ Ion doped V-bit and Si ⁴⁺ Ion doping P site; amorphous carbon with the surface being 4 nanometers thick is coated on the periphery of the sodium vanadium phosphate; ammonium metavanadate, sodium acetate and ammonium dihydrogen phosphate are used as raw materials, monopotassium phosphate, lanthanum nitrate and tetraethyl silicate are used as doping sources, oxalic acid is used as a chelating agent, and the potassium lanthanum silicon ternary co-doped sodium vanadium phosphate electrode material is prepared by a solution gel method and comprises the following specific steps:

(1) The molar ratio is 26.19:16.68:25:0.09:0.6: adding 0.9 of sodium acetate, ammonium metavanadate, monoammonium phosphate, monopotassium phosphate, lanthanum nitrate and tetraethyl silicate into 60 mL deionized water solution, and heating to 70 ℃ at constant temperature to form clear solution;

(2) Dissolving oxalic acid in 20ml deionized water to prepare oxalic acid solution with concentration of 2.59M;

(3) Dropwise adding the prepared oxalic acid solution into the clear solution in the step (1), stabilizing the color to be blue finally, and stirring at constant temperature until the precursor solution becomes 20ml of viscous colloid; freezing overnight at-21 ℃, and then running for 48 hours at-35 ℃ to-40 ℃ by using a freeze dryer;

(4) Drying the freeze-dried sample at 80 ℃ for 12 hours;

(5) The obtained precursor is presintered for 4 hours at 450 ℃ in the nitrogen atmosphere, and then is finally burned for 6 hours at 700 ℃ to obtain the final product.

2. The application of the potassium-lanthanum-silicon triple co-doped sodium vanadium phosphate electrode material in a sodium ion battery as claimed in claim 1, which is characterized in that: the potassium lanthanum silicon ternary co-doped sodium vanadium phosphate electrode material is used as an anode material to be applied to a sodium ion battery.

3. The use according to claim 2, characterized in that: the specific method comprises the following steps: na (Na) _3.1-x K _x V _2−x La _x (PO ₄ ) _2.9 (SiO ₄ ) _0.1 The material is used as an active substance of a positive electrode material, a sodium sheet is used as a negative electrode, the negative electrode is assembled into a 2016-type button cell, and an electrolyte is NaClO ₄ +EC/DEC+5% FEC; wherein NaClO ₄ EC, DEC and FEC represent sodium perchlorate, ethylene carbonate, diethyl carbonate and fluoroethylene carbonate, respectively; naClO of 1M ₄ Dissolved in an EC/DEC system with a volume ratio of 1:1, and added with 5. 5 wt% of FEC for preparation.

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