CN113659146B - Potassium-lanthanum-silicon ternary co-doped sodium vanadium phosphate electrode material, and preparation method and application thereof - Google Patents
Potassium-lanthanum-silicon ternary co-doped sodium vanadium phosphate electrode material, and preparation method and application thereof Download PDFInfo
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Abstract
The invention belongs to new energy materialsThe technical field provides a potassium lanthanum silicon ternary co-doped sodium vanadium phosphate electrode material, a preparation method and application thereof, and aims to solve the problems of poor electrochemical stability and the like of sodium vanadium phosphate. Na is used as the potassium-lanthanum-silicon triple co-doped sodium vanadium phosphate electrode material 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 position, la 3+ Ion doped V-bit and Si 4+ Ion doping P site; 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 through a solution gel method. Has better electrochemical performance, higher specific capacity, excellent multiplying power and circulation capacity, simple preparation and low cost, and is beneficial to industrial popularization.
Description
Technical Field
The invention belongs to the technical field of new energy materials, and particularly relates to a potassium-lanthanum-silicon triple co-doped sodium vanadium phosphate electrode material, a preparation method and application thereof.
Background
Sodium ion batteries have been widely focused in recent years due to advantages of low cost, small environmental pollution, etc., and are considered as a next-generation novel electrochemical energy storage device that can replace lithium ion batteries. Today, sodium ion batteries have partially moved to industry and play a vital role in both commercial energy automobiles and electrical energy storage devices. Among them, sodium vanadium phosphate of polyanion compound is attracting attention because of open sodium ion superconducting structure, higher voltage platform and theoretical specific capacity, and provides powerful technical guarantee for commercialization process of sodium ion battery.
However, the three-dimensional skeleton structure has poor stability, and in the frequent dynamic behaviors of sodium ion charge and discharge, adjacent phosphorus-oxygen octahedrons and vanadium-oxygen tetrahedrons of sodium ions are easy to receive the action of internal stress to cause structural collapse, so that the electrochemical stability of the sodium vanadium phosphate is greatly restricted.
Disclosure of Invention
The invention provides a potassium lanthanum silicon ternary co-doped sodium vanadium phosphate electrode material, a preparation method and application thereof, and aims to solve the problems of poor electrochemical stability and the like of the existing sodium vanadium phosphate. The potassium lanthanum silicon triple co-doping is used for regulating and controlling the crystal structure of the sodium vanadium phosphate, a conductive carbon network is built on the surface of the particles in situ, the sodium vanadium phosphate skeleton is stabilized against collapse, and meanwhile, an extra conductive channel is provided for electrons, so that the electrochemical capacity of the material is greatly improved. The surface of the prepared sodium vanadium phosphate modified material is coated with amorphous carbon with the thickness of about 4 nanometers, and the electrode material is applied to 2016-type button cells, so that the cathode material has excellent cycle stability and high-rate long-cycle performance, and can be regarded as a sodium ion battery cathode material with good application prospect.
The invention is realized by the following technical scheme: potassium lanthanum silicon ternary co-doped sodium vanadium phosphate electrode material, wherein 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, 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; 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 through a solution gel method.
The method for preparing the potassium-lanthanum-silicon ternary co-doped sodium vanadium phosphate electrode material 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, stirring at constant temperature until the precursor solution becomes 20ml of viscous colloid, freezing overnight at-21 ℃, and then operating for 48 hours at-35-40 ℃ 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.
The potassium lanthanum silicon ternary co-doped sodium vanadium phosphate electrode material is applied to sodium ion batteries, and the potassium lanthanum silicon ternary co-doped sodium vanadium phosphate electrode material is used as a positive electrode material to be applied to sodium ion batteries.
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.
The invention uses three common elements, K through a mature and simple solution gel method + Ion doped Na position, la 3+ Ion doped V-bit and Si 4+ Ion doping P position, oxalic acid as chelating agent and reducing agent, and part of oxalic acid participating in reduction reaction to make V 5 + Reduction to V 3+ The excessive part forms a carbon layer to cover the surface of the material, so that the conductivity of the material is improved. The modified doped sample shows better cycle life and stable high-rate performance than the doped sample before being doped.
This measure has significant advantages over the previously reported modifications using elemental doping: (1) The potassium element resource is rich, the earth surface element abundance is extremely high, the effect of extending the specific crystal axis of the crystal is achieved, and the extended c axis strengthens the stability of a sodium ion migration channel; (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, can be prepared on a large scale, and the experimental scheme has important guiding significance for the design and research and development of a multi-element system.
The potassium element in the obtained material can expand the lattice size of the sodium vanadium phosphate in the direction of c, and more sodium ion vacancies are introduced, so that the conductivity of the sodium vanadium phosphate is improved. Meanwhile, lanthanum and silicon elements with larger ionic radius extend crystals along a and b directions on vanadium and phosphorus positions respectively, so that a more stable crystal skeleton is provided for rapid intercalation and deintercalation of sodium ions in crystal lattices, and the conductivity and the cycle life of sodium vanadium phosphate are further improved. The test shows that the sodium ion battery anode material with the ternary co-doping effect of potassium, lanthanum and silicon has the electrochemical performance of brightening eyes, higher specific capacity and excellent multiplying power and circulation capacity, and meanwhile, the material is simple to prepare and low in cost, and is expected to be popularized in industry.
Compared with the prior art, the method has the advantages that the selected raw materials are low in cost, simple in synthesis and suitable for commercial large-scale preparation; the surface of the product contains a uniform carbon layer coating, which is beneficial to improving the conductivity of the material; compared with an unmodified vanadium sodium phosphate material, the crystal structure of the positive electrode material after ternary co-doping of potassium, lanthanum and silicon is more stable; the product of the invention can show good multiplying power performance and good large multiplying power long-cycle stability.
Drawings
FIG. 1 is a Na prepared in example 4 3.03 K 0.07 V 1.93 La 0.07 (PO 4 ) 2.9 (SiO 4 ) 0.1 The photo, can be seen from the figure, the particle size is lower and the dispersion is even, which is beneficial to improving the electron conduction among the particles;
FIG. 2 is a Na prepared in example 4 3.03 K 0.07 V 1.93 La 0.07 (PO 4 ) 2.9 (SiO 4 ) 0.1 XRD occupation finishing result of sample, occupation finishing result shows that：K + Doped into Na position, la 3+ Doping into V-bit while Si 4+ The doping enters the P-bit and matches the designed doping amount. Doping the three-dimensional structure of unchanged sodium vanadium phosphate;
FIG. 3 is a Na prepared in example 4 3.03 K 0.07 V 1.93 La 0.07 (PO 4 ) 2.9 (SiO 4 ) 0.1 XPS results of the samples, XPS test results indicate K in the samples + ，La 3+ And Si (Si) 4+ The method shows obvious characteristic peaks which are matched with the experimental design;
fig. 4 is a constant current charge-discharge curve measured in the case of the example 4, the comparative example 1, the example 2, the example 3, the example 5, and the example 6 when they are assembled into 2016 type coin cells, and the current density is 0.1C;
FIG. 5 is a graph of CV test comparisons at a scan rate of 0.1mVs-1 for example 4, comparative example 1, example 2, example 3, example 5, example 6 when assembled as a 2016-type button cell;
fig. 6 is a graph of the ratio performance versus time measured at different current densities for example 4, comparative example 1, example 2, example 3, example 5, and example 6 when assembled as a 2016-type button cell;
FIG. 7 is a Na prepared in example 4 3.03 K 0.07 V 1.93 La 0.07 (PO 4 ) 2.9 (SiO 4 ) 0.1 500 cycle plots of samples at 10C and 50C current densities.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments; all other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Example 1: na (Na) 3.09 K 0.01 V 1.99 La 0.01 (PO 4 ) 2.9 (SiO 4 ) 0.1 Preparation of electrode materials:
2.1380g of sodium acetate, 1.9422 g ammonium metavanadate, 2.8002 g ammonium dihydrogen phosphate, 00119 g potassium dihydrogen phosphate, 0.0378g of lanthanum nitrate and 0.816 tetraethyl silicate are added into 60 mL deionized water solution, and the mixture is heated to 70 ℃ at constant temperature to form clear solution; 6.5946g of oxalic acid was dissolved in 20ml of deionized water. The prepared oxalic acid solution is dropwise added into the clear solution, the color is finally stabilized in blue, and the mixture is stirred at constant temperature until the precursor solution becomes 20ml of viscous colloid. Transfer to vessel and freeze overnight, put into freeze dryer for 48h. 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 burned for six hours at 700 ℃ to obtain the final product.
The positive electrode material prepared in this example was used in accordance with 7:2:1 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 coated on a clean carbon coated aluminum foil. And (3) drying by blowing at 45 ℃ for four hours, and then carrying out vacuum drying at 120 ℃ overnight to finally obtain the electrode slice loaded with possible materials. The assembled CR2016 type button cell takes metal sodium as a cathode, a diaphragm is a ceramic Celgard diaphragm, and 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. Assembled in a vacuum glove box.
The button cell assembled with the button cell at room temperature can be subjected to constant-current charge and discharge test in the voltage range of 2.3-4.1V and can be subjected to constant-current charge and discharge test in the voltage range of 0.1mVs -1 Cyclic voltammetry measurements were performed at the scan rate of (c). Specifically, the first charge-discharge curve is shown in fig. 4, the CV redox peaks at low scan rate are shown in fig. 5,0.3 to 10c, and the battery rate cycle curve is shown in fig. 6.
The material is detected to be used as the positive electrode material of the sodium ion battery. Electrochemical tests showed thatThe specific discharge capacity of the material under 0.1C can reach 100mAh g -1 . The battery cycle rate shows that the specific discharge capacity of the material can still be kept at 82 mAh g under the condition of 10C high rate -1 And when the discharge rate is raised to 1C, the material can be quickly raised to 105mAh g -1 Is a specific discharge capacity of (a). At the same time at 0.1V s -1 The CV test is carried out at the sweeping speed, and the result shows that obvious splitting peaks appear at about 3.2 and V, thereby proving that two Na sites in different chemical environments are reserved in the crystal.
Example 2: na (Na) 3.07 K 0.03 V 1.97 La 0.03 (PO 4 ) 2.9 (SiO 4 ) 0.1 Preparation of electrode materials:
2.1858g of sodium acetate, 2.0004 g ammonium metavanadate, 2.8655 g ammonium dihydrogen phosphate, 0.0354 g potassium dihydrogen phosphate, 0.1128g of lanthanum nitrate and 0.1808 tetraethyl silicate are added into 60 mL deionized water solution, and the mixture is heated to 70 ℃ at constant temperature to form clear solution; 6.5648g of oxalic acid was dissolved in 20ml of deionized water. The prepared oxalic acid solution is dropwise added into the clear solution, the color is finally stabilized in blue, and the mixture is stirred at constant temperature until the precursor solution becomes 20ml of viscous colloid. Transfer to vessel and freeze overnight, put into freeze dryer for 48h. 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 burned for six hours at 700 ℃ to obtain the final product.
The positive electrode material prepared in this example was used in accordance with 7:2:1 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 coated on a clean carbon coated aluminum foil. And (3) drying by blowing at 45 ℃ for four hours, and then carrying out vacuum drying at 120 ℃ overnight to finally obtain the electrode slice loaded with possible materials. The assembled CR2016 type button cell takes metal sodium as a cathode, ceramic diaphragm Celgard as a diaphragm, and electrolyte as 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. Assembled in a vacuum glove box.
The button cell assembled with the button cell at room temperature can be subjected to constant-current charge and discharge test in the voltage range of 2.3-4.1V and can be subjected to constant-current charge and discharge test in the voltage range of 0.1mVs -1 Cyclic voltammetry measurements were performed at the scan rate of (c). Specifically, the first charge-discharge curve is shown in fig. 4, the CV redox peaks at low scan rate are shown in fig. 5, and the 0.3C to 10C battery rate cycle curve 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 the specific discharge capacity of the material can still be kept at 81.5 mAh g under the condition of 10C high rate -1 And when the discharge rate is raised to 1C, the material can be quickly raised to 95mAh g -1 Is a specific discharge capacity of (a). At the same time at 0.1V s -1 The CV test is carried out at the sweeping speed, and the result shows that obvious splitting peaks appear at about 3.2 and V, thereby proving that two Na sites in different chemical environments are reserved in the crystal.
Example 3: na (Na) 3.05 K 0.05 V 1.95 La 0.05 (PO 4 ) 2.9 (SiO 4 ) 0.1 Preparation of electrode materials:
2.1618g of sodium acetate, 1.9712 g ammonium metavanadate, 2.8327 g ammonium dihydrogen phosphate, 0.0432 g potassium dihydrogen phosphate, 0.1871g of lanthanum nitrate and 0.1800 tetraethyl silicate are added into 60 mL deionized water solution, and the mixture is heated to 70 ℃ at constant temperature to form clear solution; 6.5353g of oxalic acid was dissolved in 20ml of deionized water. The prepared oxalic acid solution is dropwise added into the clear solution, the color is finally stabilized in blue, and the mixture is stirred at constant temperature until the precursor solution becomes 20ml of viscous colloid. Transfer to vessel and freeze overnight, put into freeze dryer for 48h. 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 burned for six hours at 700 ℃ to obtain the final product.
The positive electrode material prepared in this example was used in accordance with 7:2:1 ratio to acetylene black and polyvinylideneVinyl fluoride (PVDF) was mixed in 1.4 mL of N-methylpyrrolidone (NMP) solvent. The mixture was ball milled for four hours to give a uniform slurry and was butchered on a clean carbon coated aluminum foil. And (3) drying by blowing at 45 ℃ for four hours, and then carrying out vacuum drying at 120 ℃ overnight to finally obtain the electrode slice loaded with possible materials. The assembled CR2016 type button cell takes metal sodium as a cathode, ceramic diaphragm Celgard as a diaphragm, and electrolyte as 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. Assembled in a vacuum glove box.
The button cell assembled with the button cell at room temperature can be subjected to constant-current charge and discharge test in the voltage range of 2.3-4.1V and can be subjected to constant-current charge and discharge test in the voltage range of 0.1mVs -1 Cyclic voltammetry measurements were performed at the scan rate of (c). Specifically, the first charge-discharge curve is shown in fig. 4, the CV redox peaks at low scan rate are shown in fig. 5, and the 0.3C to 10C battery rate cycle curve is shown in fig. 6.
The material is detected to be used as the positive electrode material of the sodium ion battery. Electrochemical test shows 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 still be kept at 85 mAh g under the condition of 10C high rate -1 And when the discharge rate is raised to 1C, the material can be quickly raised to 103 mAh g -1 Is a specific discharge capacity of (a). At the same time at 0.1V s -1 The CV test is carried out at the sweeping speed, and the result shows that obvious splitting peaks appear at about 3.2 and V, thereby proving that two Na sites in different chemical environments are reserved in the crystal.
Example 4: na (Na) 3.03 K 0.07 V 1.93 La 0.07 (PO 4 ) 2.9 (SiO 4 ) 0.1 Preparation of electrode materials:
2.1380g of sodium acetate, 1.9422 g ammonium metavanadate, 2.8002 g ammonium dihydrogen phosphate, 0.0819 g potassium dihydrogen phosphate, 0.2607g of lanthanum nitrate and 0.1792 tetraethyl silicate are added into 60 mL deionized water solution, and the mixture is heated to 70 ℃ at constant temperature to form clear solution; 6.5060g of oxalic acid was dissolved in 20ml of deionized water. The prepared oxalic acid solution is dropwise added into the clear solution, the color is finally stabilized in blue, and the mixture is stirred at constant temperature until the precursor solution becomes 20ml of viscous colloid. Transfer to vessel and freeze overnight, put into freeze dryer for 48h. 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 burned for six hours at 700 ℃ to obtain the final product.
The positive electrode material prepared in this example was used in accordance with 7:2:1 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 butchered on a clean carbon coated aluminum foil. And (3) drying by blowing at 45 ℃ for four hours, and then carrying out vacuum drying at 120 ℃ overnight to finally obtain the electrode slice loaded with possible materials. The assembled CR2016 type button cell takes metal sodium as a cathode, ceramic diaphragm Celgard as a diaphragm, and electrolyte as 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. Assembled in a vacuum glove box.
The button cell assembled with the button cell at room temperature can be subjected to constant-current charge and discharge test in the voltage range of 2.3-4.1V and can be subjected to constant-current charge and discharge test in the voltage range of 0.1mVs -1 Cyclic voltammetry measurements were performed at the scan rate of (c). Specifically, the first charge-discharge curve is shown in fig. 4, the CV redox peaks at low scan rate are shown in fig. 5, and the 0.3C to 10C battery rate cycle curve is shown in fig. 6. The SEM image of the particles is shown in fig. 1, the XRD finishing result is shown in fig. 2, and the energy spectrum of the main doping element is shown in fig. 3. 10 The long cycle results at C and 50C super-magnification are shown in fig. 7.
Through detection, the material is used as the positive electrode material of the sodium ion battery, the particle size of the particles is only about 100nm, and the particles are uniformly dispersed, so that the electrolyte is fully infiltrated. Electrochemical tests showed that the material was at 0The specific discharge capacity under 1, C can reach 110h g -1 . The battery cycle rate shows that the specific discharge capacity of the material can still be kept at 96mAh g under the condition of 10C high rate -1 And when the discharge rate is raised to 1C, the material can be quickly raised to 112 mAh g -1 Is a specific discharge capacity of (a). At the same time at 0.1V s -1 The CV test is carried out at the sweeping speed, and the result shows that obvious splitting peaks appear at about 3.2 and V, thereby proving that two Na sites in different chemical environments are reserved in the crystal. Meanwhile, XRD results show that all characteristic peaks show R-3C space groups and composite NVP characteristic structures, and the introduction of three elements can be considered to not damage the crystal composition. XPS tests show that all peaks can well correspond to element energy levels, and the doping source successfully enters the system. Meanwhile, under the discharge multiplying power of 10C, the material can still keep 60 mAh g after 500 circles of circulation -1 Even in the extreme case of 50C, there is 40 mAh g -1 Is available.
Example 5: na (Na) 3 K 0.1 V 1.9 La 0.1 (PO 4 ) 2.9 (SiO 4 ) 0.1 Preparation of electrode materials:
2.1027g of sodium acetate, 1.8993 g ammonium metavanadate, 2.7521 g ammonium dihydrogen phosphate, 0.1163 g potassium dihydrogen phosphate, 0.3700g of lanthanum nitrate and 0.1780 tetraethyl silicate are added into 60 mL deionized water solution, and the mixture is heated to 70 ℃ at constant temperature to form clear solution; 6.4626g of oxalic acid was dissolved in 20ml of deionized water. The prepared oxalic acid solution is dropwise added into the clear solution, the color is finally stabilized in blue, and the mixture is stirred at constant temperature until the precursor solution becomes 20ml of viscous colloid. Transfer to vessel and freeze overnight, put into freeze dryer for 48h. 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 burned for six hours at 700 ℃ to obtain the final product.
The positive electrode material prepared in this example was used in accordance with 7:2:1 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 uniformityIs deposited on a clean carbon-coated aluminum foil. And (3) drying by blowing at 45 ℃ for four hours, and then carrying out vacuum drying at 120 ℃ overnight to finally obtain the electrode slice loaded with possible materials. The assembled CR2016 type button cell takes metal sodium as a cathode, ceramic diaphragm Celgard as a diaphragm, and electrolyte as 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. Assembled in a vacuum glove box.
The button cell assembled with the button cell at room temperature can be subjected to constant-current charge and discharge test in the voltage range of 2.3-4.1V and can be subjected to constant-current charge and discharge test in the voltage range of 0.1mVs -1 Cyclic voltammetry measurements were performed at the scan rate of (c). Specifically, the first charge-discharge curve is shown in fig. 4, the CV redox peaks at low scan rate are shown in fig. 5, and the 0.3C to 10C battery rate cycle curve is shown in fig. 6.
The material is detected to be used as the positive electrode material of the sodium ion battery. Electrochemical test shows that the specific discharge capacity of the material under 0.1C can reach 95mAh g -1 . The battery cycle rate shows that the specific discharge capacity of the material is only 55 mAh g under the condition of 10C high rate -1 And when the discharge rate is raised to 1C, the material can be quickly raised to 95mAh g -1 Is a specific discharge capacity of (a). At the same time at 0.1V s -1 The CV test is carried out at the sweeping speed, and the result shows that obvious splitting peaks appear at about 3.2 and V, thereby proving that two Na sites in different chemical environments are reserved in the crystal.
Example 6: na prepared according to the method of the present invention 3 V 2 (PO 4 ) 3
2.3692g of sodium dihydrogen phosphate and 1.5401 g ammonium metavanadate are added into 60 mL deionized water solution, and the solution is heated to 70 ℃ at constant temperature to form clear solution; 4.9790g of oxalic acid was dissolved in 20ml of deionized water. The prepared oxalic acid solution is dropwise added into the clear solution, the color is finally stabilized in blue, 0.1957g of carbon nano tubes are added under continuous stirring, and the constant temperature stirring is carried out until the precursor liquid becomes 20ml of viscous colloid. Transfer to vessel and freeze overnight, put into freeze dryer for 48h. 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 burned for six hours at 700 ℃ to obtain the final product.
The positive electrode material prepared in this example was used in accordance with 7:2:1 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 butchered on a clean carbon coated aluminum foil. And (3) drying by blowing at 45 ℃ for four hours, and then carrying out vacuum drying at 120 ℃ overnight to finally obtain the electrode slice loaded with possible materials. The assembled CR2016 type button cell takes metal sodium as a cathode, ceramic diaphragm Celgard as a diaphragm, and electrolyte as 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. Assembled in a vacuum glove box.
The button cell assembled with the button cell at room temperature can be subjected to constant-current charge and discharge test in the voltage range of 2.3-4.1V and can be subjected to constant-current charge and discharge test in the voltage range of 0.1mVs -1 Cyclic voltammetry measurements were performed at the scan rate of (c). Specifically, the first charge-discharge curve is shown in fig. 4, the CV redox peaks at low scan rate are shown in fig. 5, and the 0.3C to 10C battery rate cycle curve is shown in fig. 6.
The material is detected to be used as the positive electrode material of the sodium ion battery. Electrochemical test shows that the specific discharge capacity of the material under 0.1C can reach 96mAh g -1 . The battery cycle rate shows that the specific discharge capacity of the material can still be kept at 82 mAh g under the condition of 10C high rate -1 And when the discharge rate is raised to 1C, the material can be quickly raised to 101 mAh g -1 Is a specific discharge capacity of (a). At the same time at 0.1V s -1 CV test is carried out at the sweeping speed of (2), and the result shows that only a single reduction peak exists at about 3.2 and V, thus proving that the crystal structure collapses.
The above examples illustrate: the invention successfully dopes potassium lanthanum silicon ternary element into sodium vanadium phosphate by using a simple solution gel method. The potassium element in the product can expand the lattice of the sodium vanadium phosphate in the c-axis direction, so that more active sodium ion sites are introduced, and the conductivity of the sodium vanadium phosphate is improved. Meanwhile, lanthanum and silicon elements with larger ionic radius extend crystals along a and b directions on vanadium and phosphorus positions respectively, so that a more stable crystal skeleton is provided for rapid intercalation and deintercalation of sodium ions in crystal lattices, and the conductivity and the cycle life of sodium vanadium phosphate are further improved. The test shows that the product has better electrochemical performance, high-rate long-cycle stability, higher specific capacity, excellent rate and cycle capacity, simple preparation and low cost, and is expected to be popularized in industry.
Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present invention, and not for limiting the same; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some or all of the technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit of the invention.
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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