CN113659146A - Potassium lanthanum silicon ternary codoped vanadium sodium phosphate electrode material and preparation method and application thereof - Google Patents

Abstract

The invention belongs to the technical field of new energy materials, and provides a potassium lanthanum silicon ternary codoped vanadium sodium phosphate electrode material, and a preparation method and application thereof, in order to solve the problems of poor electrochemical stability of vanadium sodium phosphate and the like. The potassium lanthanum silicon ternary codoped vanadium phosphate sodium electrode material is Na_3.1‑xK_xV_2−xLa_x(PO₄)_2.9(SiO₄)_0.1X =0,0.01, 0.03, 0.05, 0.07, or 0.1; the electrode material K⁺Doping Na position and La with ions³⁺Ion doping of V site and Si⁴⁺Doping P position with ions; the potassium lanthanum silicon ternary codoped vanadium phosphate is prepared by taking ammonium metavanadate, sodium acetate and ammonium dihydrogen phosphate as raw materials, potassium dihydrogen phosphate, lanthanum nitrate and tetraethyl silicate as doping sources and oxalic acid as a chelating agent through a solution gel methodA sodium electrode material. Has brighter electrochemical performance, higher specific capacity, excellent multiplying power and cycle capacity, simple preparation, low cost and contribution to industrial popularization.

Description

Potassium lanthanum silicon ternary codoped vanadium sodium phosphate electrode material and preparation method and application thereof

Technical Field

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

Background

Sodium ion batteries have attracted attention in recent years due to their advantages of low cost, low environmental pollution, etc., and are considered as next-generation novel electrochemical energy storage devices that can replace lithium ion batteries. Nowadays, sodium ion batteries have been partially industrialized and play a crucial role in commercial energy vehicles and electrical energy storage devices. Among them, vanadium sodium phosphate of polyanionic compound attracts attention due to the open sodium ion superconducting structure, higher voltage platform and theoretical specific capacity, and provides powerful technical guarantee for the commercialization process of sodium ion battery.

However, the stability of the three-dimensional framework structure is poor, and in the frequent dynamic behavior of the sodium ion charging and discharging process, phosphorus oxygen octahedrons and vanadium oxygen tetrahedrons adjacent to sodium ions are easy to be subjected to internal stress action to cause structural collapse, so that the electrochemical stability of the vanadium sodium phosphate is limited to a great extent.

Disclosure of Invention

The invention provides a potassium-lanthanum-silicon ternary co-doped vanadium sodium phosphate electrode material, and a preparation method and application thereof, aiming at solving the problems of poor electrochemical stability of the existing vanadium sodium phosphate and the like. Through the potassium lanthanum silicon ternary codoping regulation and control vanadium sodium phosphate crystal structure, a conductive carbon network is built on the particle surface in situ, a vanadium sodium phosphate framework is stabilized to prevent collapse, an additional conductive channel is provided for electrons, and the electrochemical capacity of the material is greatly improved. The surface of the prepared vanadium sodium phosphate modified material is coated with amorphous carbon with the thickness of about 4 nanometers at the periphery of the vanadium sodium phosphate, and the electrode material is applied to a 2016 type button cell, so that the electrode material has excellent cycle stability and large-rate long-cycle performance, and can be considered as a sodium ion battery anode material with good use prospect.

The invention is realized by the following technical scheme: potassium lanthanum silicon ternary codoped vanadium sodium phosphate electrode material, wherein potassium lanthanum silicon ternary codopedThe mixed vanadium sodium phosphate electrode material is Na_3.1-xK_xV_2−xLa_x(PO₄)_2.9(SiO₄)_0.1 X =0,0.01, 0.03, 0.05, 0.07, or 0.1; the electrode material K⁺Doping Na position and La with ions³⁺Ion doping of V site and Si⁴⁺Doping P position with ions; the potassium lanthanum silicon ternary co-doped sodium vanadium phosphate electrode material is prepared by taking ammonium metavanadate, sodium acetate and ammonium dihydrogen phosphate as raw materials, potassium dihydrogen phosphate, lanthanum nitrate and tetraethyl silicate as doping sources and oxalic acid as a chelating agent through a solution gel method.

The method for preparing the kalium-lanthanum-silicon ternary codoped vanadium sodium phosphate electrode material comprises the following specific steps:

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

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

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

(4) drying the freeze-dried sample at 80 ℃ for 12 h;

(5) presintering the obtained precursor at 450 ℃ for 4h in the atmosphere of nitrogen, and then finally calcining at 700 ℃ for 6h to obtain a final product.

The potassium lanthanum silicon ternary codoped vanadium sodium phosphate electrode material is applied to a sodium ion battery, and the potassium lanthanum silicon ternary codoped vanadium sodium phosphate electrode material is applied to the sodium ion battery as an anode material.

The specific method comprises the following steps: na (Na)_3.1-xK_xV_2−xLa_x(PO₄)_2.9(SiO₄)_0.1The material is used as an active substance of a positive electrode material, a sodium sheet is used as a negative electrode, the material is assembled into a 2016 type button cell, and the electrolyte isNaClO₄+ EC/DEC +5% FEC; wherein, NaClO₄EC, DEC and FEC denote sodium perchlorate, ethylene carbonate, diethyl carbonate and fluoroethylene carbonate, respectively; 1M NaClO₄Dissolved in an EC/DEC system in a volume ratio of 1:1, with 5 wt% FEC being added.

The invention uses three common elements, by a mature and concise solution gel method, K⁺Doping Na position and La with ions³⁺Ion doping of V site and Si⁴⁺Doping P site with ion, using oxalic acid as chelating agent and reducing agent, and making part participate in reduction reaction to make V^{5 +}Reduction to V³⁺And the excessive part forms a carbon layer to coat the surface of the material, so that the conductivity of the material is improved. The modified doped sample exhibits better cycle life and stable high rate performance than before doping.

Compared with the doping modification by using elements reported previously, the method has the following obvious advantages: (1) the potassium resource is rich, the abundance of surface elements is extremely high, the specific crystal axis of the crystal can be extended, and the stability of a sodium ion migration channel is reinforced by the extended c axis; (2) lanthanum and silicon have uniform size characteristics, and larger ionic radius further stabilizes and optimizes the crystal structure on the other two scales; (3) the experimental synthesis process is simple to regulate and control, large-scale preparation can be realized, and the experimental scheme has important guiding significance for the design and research of a multi-element system.

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 conductive capability of the sodium vanadium phosphate. Meanwhile, lanthanum and silicon elements with larger ionic radius extend the crystal along the directions of a and b at the positions of vanadium and phosphorus respectively, so that a more stable crystal framework is provided for the rapid insertion and de-intercalation of sodium ions in crystal lattices, the conductive capability of the vanadium sodium phosphate is further improved, and the cycle life of the vanadium sodium phosphate is further prolonged. The test shows that the sodium ion battery anode material with the potassium-lanthanum-silicon ternary co-doping effect has bright electrochemical performance, higher specific capacity, excellent multiplying power and cycle capacity, is simple to prepare and low in cost, and is expected to be popularized in industry.

Compared with the prior art, the raw materials selected in the invention have low cost and simple synthesis, and are suitable for commercial large-scale preparation; the surface of the product contains uniform carbon layer coating, which is beneficial to improving the conductivity of the material; compared with the unmodified sodium vanadium phosphate material, the crystal structure of the anode material after the potassium lanthanum silicon ternary codoping is more stable; the product of the invention can show good rate performance and good high-rate long-cycle stability.

Drawings

FIG. 1 shows Na prepared in example 4_3.03K_0.07V_1.93La_0.07(PO₄)_2.9(SiO₄)_0.1The photo shows that the particle size is lower, the particles are uniformly dispersed, and the electronic conduction among the particles is favorably improved;

FIG. 2 shows Na prepared in example 4_3.03K_0.07V_1.93La_0.07(PO₄)_2.9(SiO₄)_0.1The XRD of sample occupies the space and refines the result, occupy the space and refine the result to show: k⁺Doping into Na site, La³⁺Doping into V-site while Si⁴⁺Doping into the P site and matching the designed doping amount. Doping the three-dimensional structure of the unchanged sodium vanadium phosphate;

FIG. 3 shows Na prepared in example 4_3.03K_0.07V_1.93La_0.07(PO₄)_2.9(SiO₄)_0.1XPS results of the sample, the XPS test results show that K is in the sample⁺，La³⁺And Si⁴⁺All show obvious characteristic peaks, which are consistent with the experimental design;

FIG. 4 is a graph of constant current charge and discharge curves measured for example 4, comparative example 1, example 2, example 3, example 5, and example 6 in a 2016 type coin cell configuration, with a current density of 0.1C;

FIG. 5 is a comparative graph of CV testing at a scan rate of 0.1mVs-1 for example 4, comparative example 1, example 2, example 3, example 5, and example 6 when assembled as a 2016 type coin cell;

FIG. 6 is a graph comparing rate performance of example 4, comparative example 1, example 2, example 3, example 5, and example 6 when assembled into 2016 type coin cells, measured at different current densities;

FIG. 7 shows Na prepared in example 4_3.03K_0.07V_1.93La_0.07(PO₄)_2.9(SiO₄)_0.1The 500 cycle plot of the samples at 10C and 50C current densities.

Detailed Description

In order to make the objects, 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, and it is obvious that the described embodiments are some embodiments of the present invention, but not all embodiments; all other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Example 1: na (Na)_3.09K_0.01V_1.99La_0.01(PO₄)_2.9(SiO₄)_0.1Preparing an electrode material:

adding 2.1380g of sodium acetate, 1.9422 g of ammonium metavanadate, 2.8002 g of ammonium dihydrogen phosphate, 00119 g of potassium dihydrogen phosphate, 0.0378g of lanthanum nitrate and 0.816 of tetraethyl silicate into 60 mL of deionized water solution, and heating to 70 ℃ at constant temperature to form a clear solution; 6.5946g of oxalic acid were taken and hot-dissolved in 20ml of deionized water. The prepared oxalic acid solution is dropwise added into the clear solution, the color is finally stabilized at blue, and the solution is stirred at constant temperature until the precursor solution becomes 20ml of viscous colloid. Transferring to a vessel for freezing overnight, and putting into a freeze dryer for 48 h. Taking out the sample, placing the sample in an oven, and drying the sample at 80 ℃ for 12 hours; the obtained precursor is presintered for four hours at 450 ℃ in the nitrogen atmosphere, and then is finally calcined for six hours at 700 ℃ to obtain the final product.

Using the positive electrode material prepared in this example, the following 7: 2: 1 was mixed with acetylene black and polyvinylidene fluoride (PVDF) in 1.4 mL of N-methylpyrrolidone (NMP) solvent. Ball milling the mixture for four hours to obtain a mixtureCoating the slurry on clean carbon-coated aluminum foil. After blowing and drying for four hours at the temperature of 45 ℃, vacuum drying is carried out at the temperature of 120 ℃ overnight, and finally the electrode plate loaded with the materials is obtained. The assembled CR2016 type button cell uses metal sodium as a negative electrode, a diaphragm is a ceramic Celgard diaphragm, and electrolyte is NaClO₄+ EC/DEC +5% FEC; wherein, NaClO₄EC, DEC and FEC denote sodium perchlorate, ethylene carbonate, diethyl carbonate and fluoroethylene carbonate, respectively; 1M NaClO₄Dissolved in an EC/DEC system in a volume ratio of 1:1, with 5 wt% FEC being added. Assembling in a vacuum glove box.

The button cell assembled by the battery can be subjected to constant current charge and discharge test in a voltage range of 2.3-4.1V at room temperature and is 0.1mVs^-1The measurement of cyclic voltammetry was performed at a scanning rate of (1). Specifically, the first-turn charge-discharge curve is shown in fig. 4, the CV oxidation-reduction peak at low sweep speed is shown in fig. 5, and the battery rate cycle curve from 0.3 to 10c is shown in fig. 6.

The material is detected to be used as the positive electrode material of the sodium-ion battery. Electrochemical tests show that the specific discharge capacity of the material under 0.1C can reach 100mAh g^-1. The battery cycle rate shows that under the condition of 10C high rate, the specific discharge capacity of the material can still be kept at 82 mAh g^-1And when the discharge rate is increased to 1C, the material can still be quickly increased to 105mAh g^-1Specific discharge capacity of (2). At the same time 0.1V s^-1The CV test is carried out at the sweep rate of (3.2V), and the result shows that a remarkable splitting peak appears at about 3.2V, which proves that two Na sites with different chemical environments are reserved in the crystal.

Example 2: na (Na)_3.07K_0.03V_1.97La_0.03(PO₄)_2.9(SiO₄)_0.1Preparing an electrode material:

adding 2.1858g of sodium acetate, 2.0004 g of ammonium metavanadate, 2.8655 g of ammonium dihydrogen phosphate, 0.0354 g of potassium dihydrogen phosphate, 0.1128g of lanthanum nitrate and 0.1808 g of tetraethyl silicate into 60 mL of deionized water solution, and heating to 70 ℃ at constant temperature to form a clear solution; 6.5648g of oxalic acid were taken and hot-dissolved in 20ml of deionized water. The prepared oxalic acid solution is dropwise added into the clear solution, the color is finally stabilized at blue, and the solution is stirred at constant temperature until the precursor solution becomes 20ml of viscous colloid. Transferring to a vessel for freezing overnight, and putting into a freeze dryer for 48 h. Taking out the sample, placing the sample in an oven, and drying the sample at 80 ℃ for 12 hours; the obtained precursor is presintered for four hours at 450 ℃ in the nitrogen atmosphere, and then is finally calcined for six hours at 700 ℃ to obtain the final product.

Using the positive electrode material prepared in this example, the following 7: 2: 1 was mixed with acetylene black and polyvinylidene fluoride (PVDF) in 1.4 mL of N-methylpyrrolidone (NMP) solvent. The mixture was ball milled for four hours to obtain a uniform slurry and coated on clean aluminum foil coated with carbon. After blowing and drying for four hours at the temperature of 45 ℃, vacuum drying is carried out at the temperature of 120 ℃ overnight, and finally the electrode plate loaded with the materials is obtained. The assembled CR2016 type button cell uses metal sodium as a negative electrode, a ceramic diaphragm Celgard as a diaphragm and NaClO as electrolyte₄+ EC/DEC +5% FEC; wherein, NaClO₄EC, DEC and FEC denote sodium perchlorate, ethylene carbonate, diethyl carbonate and fluoroethylene carbonate, respectively; 1M NaClO₄Dissolved in an EC/DEC system in a volume ratio of 1:1, with 5 wt% FEC being added. Assembling in a vacuum glove box.

The button cell assembled by the battery can be subjected to constant current charge and discharge test in a voltage range of 2.3-4.1V at room temperature and is 0.1mVs^-1The measurement of cyclic voltammetry was performed at a scanning rate of (1). Specifically, the first-turn charge-discharge curve is shown in fig. 4, the CV oxidation-reduction peak at low sweep rate is shown in fig. 5, and the rate cycle curve of the battery from 0.3C to 10C is shown in fig. 6.

The material is detected to be used as the positive electrode material of the sodium-ion battery. Electrochemical tests show that the specific discharge capacity of the material under 0.1C can reach 102mAh g^-1. The battery cycle rate shows that under the condition of 10C high rate, the specific discharge capacity of the material can still be maintained at 81.5 mAh g^-1And when the discharge rate is increased to 1C, the material can still be quickly increased to 95mAh g^-1Specific discharge capacity of (2). At the same time 0.1V s^-1The result of CV test at the sweep rate of (3) shows that obvious splitting peak appears at about 3.2V, which proves that different chemical environments are reserved in the crystalTwo Na sites.

Example 3: na (Na)_3.05K_0.05V_1.95La_0.05(PO₄)_2.9(SiO₄)_0.1Preparing an electrode material:

adding 2.1618g of sodium acetate, 1.9712 g of ammonium metavanadate, 2.8327 g of ammonium dihydrogen phosphate, 0.0432 g of potassium dihydrogen phosphate, 0.1871g of lanthanum nitrate and 0.1800 g of tetraethyl silicate into 60 mL of deionized water solution, and heating to 70 ℃ at constant temperature to form a clear solution; 6.5353g of oxalic acid were taken and hot-dissolved in 20ml of deionized water. The prepared oxalic acid solution is dropwise added into the clear solution, the color is finally stabilized at blue, and the solution is stirred at constant temperature until the precursor solution becomes 20ml of viscous colloid. Transferring to a vessel for freezing overnight, and putting into a freeze dryer for 48 h. Taking out the sample, placing the sample in an oven, and drying the sample at 80 ℃ for 12 hours; the obtained precursor is presintered for four hours at 450 ℃ in the nitrogen atmosphere, and then is finally calcined for six hours at 700 ℃ to obtain the final product.

Using the positive electrode material prepared in this example, the following 7: 2: 1 was mixed with acetylene black and polyvinylidene fluoride (PVDF) in 1.4 mL of N-methylpyrrolidone (NMP) solvent. The mixture was ball milled for four hours to give a uniform slurry and was slaughtered on clean carbon coated aluminum foil. After blowing and drying for four hours at the temperature of 45 ℃, vacuum drying is carried out at the temperature of 120 ℃ overnight, and finally the electrode plate loaded with the materials is obtained. The assembled CR2016 type button cell uses metal sodium as a negative electrode, a ceramic diaphragm Celgard as a diaphragm and NaClO as electrolyte₄+ EC/DEC +5% FEC; wherein, NaClO₄EC, DEC and FEC denote sodium perchlorate, ethylene carbonate, diethyl carbonate and fluoroethylene carbonate, respectively; 1M NaClO₄Dissolved in an EC/DEC system in a volume ratio of 1:1, with 5 wt% FEC being added. Assembling in a vacuum glove box.

The button cell assembled by the battery can be subjected to constant current charge and discharge test in a voltage range of 2.3-4.1V at room temperature and is 0.1mVs^-1The measurement of cyclic voltammetry was performed at a scanning rate of (1). Specifically, the first-turn charge-discharge curve is shown in fig. 4, the CV oxidation-reduction peak at low sweep rate is shown in fig. 5, and the rate cycle curve of the battery from 0.3C to 10C is shown in fig. 6.

The material is detected to be used as the positive electrode material of the sodium-ion battery. Electrochemical tests show that the specific discharge capacity of the material under 0.1C can reach 105mAh g^-1. The battery cycle rate shows that the specific discharge capacity of the material can be kept at 85 mAh g under the condition of 10C high rate^-1And when the discharge rate is increased to 1C, the material can still be rapidly increased to 103 mAh g^-1Specific discharge capacity of (2). At the same time 0.1V s^-1The CV test is carried out at the sweep rate of (3.2V), and the result shows that a remarkable splitting peak appears at about 3.2V, which proves that two Na sites with different chemical environments are reserved in the crystal.

Example 4: na (Na)_3.03K_0.07V_1.93La_0.07(PO₄)_2.9(SiO₄)_0.1Preparing an electrode material:

adding 2.1380g of sodium acetate, 1.9422 g of ammonium metavanadate, 2.8002 g of ammonium dihydrogen phosphate, 0.0819 g of potassium dihydrogen phosphate, 0.2607g of lanthanum nitrate and 0.1792 of tetraethyl silicate into 60 mL of deionized water solution, and heating to 70 ℃ at constant temperature to form a clear solution; 6.5060g of oxalic acid were taken and hot-dissolved in 20ml of deionized water. The prepared oxalic acid solution is dropwise added into the clear solution, the color is finally stabilized at blue, and the solution is stirred at constant temperature until the precursor solution becomes 20ml of viscous colloid. Transferring to a vessel for freezing overnight, and putting into a freeze dryer for 48 h. Taking out the sample, placing the sample in an oven, and drying the sample at 80 ℃ for 12 hours; the obtained precursor is presintered for four hours at 450 ℃ in the nitrogen atmosphere, and then is finally calcined for six hours at 700 ℃ to obtain the final product.

Using the positive electrode material prepared in this example, the following 7: 2: 1 was mixed with acetylene black and polyvinylidene fluoride (PVDF) in 1.4 mL of N-methylpyrrolidone (NMP) solvent. The mixture was ball milled for four hours to give a uniform slurry and was slaughtered on clean carbon coated aluminum foil. After blowing and drying for four hours at the temperature of 45 ℃, vacuum drying is carried out at the temperature of 120 ℃ overnight, and finally the electrode plate loaded with the materials is obtained. The assembled CR2016 type button cell uses metal sodium as a negative electrode, a ceramic diaphragm Celgard as a diaphragm and NaClO as electrolyte₄+ EC/DEC +5% FEC; wherein, NaClO₄，EC，DEC and FEC represent sodium perchlorate, ethylene carbonate, diethyl carbonate and fluoroethylene carbonate, respectively; 1M NaClO₄Dissolved in an EC/DEC system in a volume ratio of 1:1, with 5 wt% FEC being added. Assembling in a vacuum glove box.

The button cell assembled by the battery can be subjected to constant current charge and discharge test in a voltage range of 2.3-4.1V at room temperature and is 0.1mVs^-1The measurement of cyclic voltammetry was performed at a scanning rate of (1). Specifically, the first-turn charge-discharge curve is shown in fig. 4, the CV oxidation-reduction peak at low sweep speed is shown in fig. 5, and the rate cycle curve of the battery from 0.3C to 10C is shown in fig. 6. The SEM image of the particles is shown in fig. 1, the XRD refinement result is shown in fig. 2, and the energy spectrum of the main doping element is shown in fig. 3. The results of the long cycle at the 10C and 50C super magnifications are shown in fig. 7.

The detection shows that the material is used as the anode material of the sodium-ion battery, the particle size of the particles is only about 100nm, the particles are uniformly dispersed, and the full infiltration of electrolyte is facilitated. Electrochemical tests show that the specific discharge capacity of the material under 0.1C can reach 110h g^-1. The battery cycle rate shows that under the condition of 10C high rate, the specific discharge capacity of the material can still be kept at 96mAh g^-1And when the discharge rate is increased to 1C, the material can still be rapidly increased to 112 mAh g^-1Specific discharge capacity of (2). At the same time 0.1V s^-1The CV test is carried out at the sweep rate of (3.2V), and the result shows that a remarkable splitting peak appears at about 3.2V, which proves that two Na sites with different chemical environments are reserved in the crystal. Meanwhile, XRD results show that all characteristic peaks show an R-3C space group and are combined with an NVP characteristic structure, and the introduction of the three elements can not damage the crystal composition. XPS tests show that all peak values can well correspond to element energy levels, and that the doping source successfully enters a system. Meanwhile, under the discharge rate of 10C, the material can still maintain 60 mAh g after being circulated for 500 circles^-1The specific discharge capacity of the lithium ion battery is 40 mAh g even in the extreme case of 50C^-1The discharge specific capacity of the lithium battery can be used.

Example 5: na (Na)₃K_0.1V_1.9La_0.1(PO₄)_2.9(SiO₄)_0.1Preparing an electrode material:

adding 2.1027g of sodium acetate, 1.8993 g of ammonium metavanadate, 2.7521 g of ammonium dihydrogen phosphate, 0.1163 g of potassium dihydrogen phosphate, 0.3700g of lanthanum nitrate and 0.1780 of tetraethyl silicate into 60 mL of deionized water solution, and heating to 70 ℃ at constant temperature to form a clear solution; 6.4626g of oxalic acid were taken and hot-dissolved in 20ml of deionized water. The prepared oxalic acid solution is dropwise added into the clear solution, the color is finally stabilized at blue, and the solution is stirred at constant temperature until the precursor solution becomes 20ml of viscous colloid. Transferring to a vessel for freezing overnight, and putting into a freeze dryer for 48 h. Taking out the sample, placing the sample in an oven, and drying the sample at 80 ℃ for 12 hours; the obtained precursor is presintered for four hours at 450 ℃ in the nitrogen atmosphere, and then is finally calcined for six hours at 700 ℃ to obtain the final product.

Using the positive electrode material prepared in this example, the following 7: 2: 1 was mixed with acetylene black and polyvinylidene fluoride (PVDF) in 1.4 mL of N-methylpyrrolidone (NMP) solvent. The mixture was ball milled for four hours to give a uniform slurry and was slaughtered on clean carbon coated aluminum foil. After blowing and drying for four hours at the temperature of 45 ℃, vacuum drying is carried out at the temperature of 120 ℃ overnight, and finally the electrode plate loaded with the materials is obtained. The assembled CR2016 type button cell uses metal sodium as a negative electrode, a ceramic diaphragm Celgard as a diaphragm and NaClO as electrolyte₄+ EC/DEC +5% FEC; wherein, NaClO₄EC, DEC and FEC denote sodium perchlorate, ethylene carbonate, diethyl carbonate and fluoroethylene carbonate, respectively; 1M NaClO₄Dissolved in an EC/DEC system in a volume ratio of 1:1, with 5 wt% FEC being added. Assembling in a vacuum glove box.

The button cell assembled by the battery can be subjected to constant current charge and discharge test in a voltage range of 2.3-4.1V at room temperature and is 0.1mVs^-1The measurement of cyclic voltammetry was performed at a scanning rate of (1). Specifically, the first-turn charge-discharge curve is shown in fig. 4, the CV oxidation-reduction peak at low sweep rate is shown in fig. 5, and the rate cycle curve of the battery from 0.3C to 10C is shown in fig. 6.

The material is detected to be used as the positive electrode material of the sodium-ion battery. Electrochemical tests show that the material is inThe specific discharge capacity under 0.1C can reach 95mAh g^-1. The battery cycle rate shows that under the condition of 10C high rate, the specific discharge capacity of the material is only 55 mAh g^-1And when the discharge rate is increased to 1C, the material can still be quickly increased to 95mAh g^-1Specific discharge capacity of (2). At the same time 0.1V s^-1The CV test is carried out at the sweep rate of (3.2V), and the result shows that a remarkable splitting peak appears at about 3.2V, which proves that two Na sites with different chemical environments are reserved in the crystal.

Example 6: na prepared according to the method of the invention₃V₂(PO₄)₃

2.3692g of sodium dihydrogen phosphate and 1.5401 g of ammonium metavanadate are added into 60 mL of deionized water solution, and the mixture is heated to 70 ℃ at constant temperature to form a clear solution; 4.9790g of oxalic acid were taken and hot-dissolved in 20ml of deionized water. The prepared oxalic acid solution is dropwise added into the clear solution, the color is finally stabilized at blue, 0.1957g of carbon nano tubes are added under continuous stirring, and the mixture is stirred at constant temperature until the precursor solution becomes 20ml of viscous colloid. Transferring to a vessel for freezing overnight, and putting into a freeze dryer for 48 h. Taking out the sample, placing the sample in an oven, and drying the sample at 80 ℃ for 12 hours; the obtained precursor is presintered for four hours at 450 ℃ in the nitrogen atmosphere, and then is finally calcined for six hours at 700 ℃ to obtain the final product.

Using the positive electrode material prepared in this example, the following 7: 2: 1 was mixed with acetylene black and polyvinylidene fluoride (PVDF) in 1.4 mL of N-methylpyrrolidone (NMP) solvent. The mixture was ball milled for four hours to give a uniform slurry and was slaughtered on clean carbon coated aluminum foil. After blowing and drying for four hours at the temperature of 45 ℃, vacuum drying is carried out at the temperature of 120 ℃ overnight, and finally the electrode plate loaded with the materials is obtained. The assembled CR2016 type button cell uses metal sodium as a negative electrode, a ceramic diaphragm Celgard as a diaphragm and NaClO as electrolyte₄+ EC/DEC +5% FEC; wherein, NaClO₄EC, DEC and FEC denote sodium perchlorate, ethylene carbonate, diethyl carbonate and fluoroethylene carbonate, respectively; 1M NaClO₄Dissolved in an EC/DEC system in a volume ratio of 1:1, with 5 wt% FEC being added. And assembling in a vacuum glove box.

The button cell assembled by the battery can be subjected to constant current charge and discharge test in a voltage range of 2.3-4.1V at room temperature and is 0.1mVs^-1The measurement of cyclic voltammetry was performed at a scanning rate of (1). Specifically, the first-turn charge-discharge curve is shown in fig. 4, the CV oxidation-reduction peak at low sweep rate is shown in fig. 5, and the rate cycle curve of the battery from 0.3C to 10C is shown in fig. 6.

The material is detected to be used as the positive electrode material of the sodium-ion battery. Electrochemical tests show that the specific discharge capacity of the material under 0.1C can reach 96mAh g^-1. The battery cycle rate shows that under the condition of 10C high rate, the specific discharge capacity of the material can still be kept at 82 mAh g^-1And when the discharge rate is increased to 1C, the material can still be quickly increased to 101 mAh g^-1Specific discharge capacity of (2). At the same time 0.1V s^-1The CV test is carried out at the sweep rate of (3.2V), and the result shows that only a single reduction peak exists, which proves that the crystal structure collapses.

The above examples illustrate: the invention successfully dopes the kalium-lanthanum-silicon ternary element into the sodium vanadium phosphate by using a simple solution gel method. The potassium element in the product can expand the vanadium sodium phosphate crystal lattice in the c-axis direction, so that more active sodium ion sites are introduced, and the conductivity of the vanadium sodium phosphate is improved. Meanwhile, lanthanum and silicon elements with larger ionic radius extend the crystal along the directions of a and b at the positions of vanadium and phosphorus respectively, so that a more stable crystal framework is provided for the rapid insertion and de-intercalation of sodium ions in crystal lattices, the conductive capability of the vanadium sodium phosphate is further improved, and the cycle life of the vanadium sodium phosphate is further prolonged. Tests show that due to the ternary codoping effect of the kalium, lanthanum and silicon, the product has bright electrochemical performance, high rate and long cycle stability, high specific capacity, excellent rate and cycle capacity, and meanwhile, 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 solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.

Claims (4)

1. The potassium lanthanum silicon ternary co-doped vanadium sodium phosphate electrode material is characterized in that: the potassium lanthanum silicon ternary codoped vanadium phosphate sodium electrode material is Na_3.1-xK_xV_2−xLax(PO₄)_2.9(SiO₄)_0.1X =0,0.01, 0.03, 0.05, 0.07, or 0.1; the electrode material K⁺Doping Na position and La with ions³⁺Ion doping of V site and Si⁴⁺Doping P position with ions; the potassium lanthanum silicon ternary co-doped sodium vanadium phosphate electrode material is prepared by taking ammonium metavanadate, sodium acetate and ammonium dihydrogen phosphate as raw materials, potassium dihydrogen phosphate, lanthanum nitrate and tetraethyl silicate as doping sources and oxalic acid as a chelating agent through a solution gel method.

2. The method for preparing the kalium-lanthanum-silicon ternary codoped vanadium sodium phosphate electrode material of claim 1 is characterized in that: the method comprises the following specific steps:

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

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

(3) dropwise adding the prepared oxalic acid solution into the clear solution obtained in the step (1), and stirring at constant temperature until the precursor solution becomes 20ml of viscous colloid, wherein the color is finally stable at blue; freezing at-21 deg.C overnight, and performing freeze drying at-35 deg.C to-40 deg.C for 48 hr;

(4) drying the freeze-dried sample at 80 ℃ for 12 h;

(5) presintering the obtained precursor at 450 ℃ for 4h in the atmosphere of nitrogen, and then finally calcining at 700 ℃ for 6h to obtain a final product.

3. The application of the kalium lanthanum silicon ternary codoped vanadium sodium phosphate electrode material in a sodium ion battery, which is characterized in that: the potassium lanthanum silicon ternary codoped vanadium sodium phosphate electrode material is used as an anode material and applied to a sodium ion battery.

4. Use according to claim 3, characterized in that: the specific method comprises the following steps: na (Na)_3.1-xK_xV_2−xLax(PO₄)_2.9(SiO₄)_0.1The material is used as an active substance of a positive electrode material, a sodium sheet is used as a negative electrode, a 2016 type button cell is assembled, and the electrolyte is NaClO₄+ EC/DEC +5% FEC; wherein, NaClO₄EC, DEC and FEC denote sodium perchlorate, ethylene carbonate, diethyl carbonate and fluoroethylene carbonate, respectively; 1M NaClO₄Dissolved in an EC/DEC system in a volume ratio of 1:1, with 5 wt% FEC being added.

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