Method for improving stability of sodium ferric pyrophosphate positive electrode material through sol-gel method doping
The Na2Fe1-xAxP2O7 composite formed by doping other elements through the sol-gel method solves the electronic conductivity and cyclic stability of the sodium ferric pyrophosphate positive electrode material, and achieves high capacity retention and good conductivity under high current density.
Patent Information
- Application Number
- CN202510393608.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-03-31
- Publication Date
- 2025-07-04
AI Technical Summary
The electron conductivity of sodium ferric pyrophosphate cathode material is poor, which affects its charge and discharge performance and cycle stability. It is especially poor in charge and discharge at high rate, and cannot meet the needs of fast charging and discharge.
Doping other elements such as Cu, Mg, Mn, Ti by the sol-gel method, Na2Fe1-xAxP2O7 composite material is formed, and a carbon cladding layer is used to improve its electronic conductivity and cyclic stability.
Under high current density, the capacity retention rate of the material is significantly improved, and the discharge specific capacity of 80.76% is still maintained after 5,000 cycles, improving the conductivity and cycle stability of the material.
Smart Images
Figure CN120261532A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of electrode materials, and more specifically, to improving the stability of sodium iron pyrophosphate cathode materials by doping through the sol-gel method. Background Art
[0002] With the continuous growth of global energy demand, the application of traditional lithium-ion batteries in fields such as large-scale energy storage faces challenges of limited lithium resources and high costs. The uneven distribution of lithium resources and the complexity of mining and refining make it crucial to find alternative energy storage technologies. Sodium-ion batteries have the potential to become a large-scale energy storage solution due to the abundance and wide distribution of sodium resources, and the research and development of sodium-ion cathode materials is one of the key links in the development of sodium-ion battery technology. Sodium ions have similar chemical properties to lithium ions, making electrochemical energy storage based on sodium ions feasible. Sodium-ion batteries have advantages in terms of cost, and the abundance of sodium resources makes the raw material cost relatively low. In addition, sodium-ion batteries also have certain characteristics in terms of safety and stability. The structural changes of their electrode materials during charge and discharge are relatively stable, reducing safety risks such as battery short circuits and thermal runaway. In some specific application scenarios, such as large-scale energy storage power stations and smart grids.
[0003] There are high requirements for the cost and safety of the battery, and the development of sodium-ion batteries and corresponding cathode materials can meet these needs. Sodium iron pyrophosphate (Na2FeP2O7) has a high specific capacity, which enables it to store more electricity when used as a battery cathode material and is a relatively safe material suitable for battery application scenarios. However, due to the polyanion structural unit isolating the valence electrons of transition metal ions, its electronic conductivity is poor, which will affect the charge and discharge performance and efficiency of the battery. And when it is charged and discharged at high rates, its performance is not good and cannot meet the requirements of fast charging and discharging. However, currently, by carbon coating sodium iron pyrophosphate, although the low electronic conductivity of the material is solved and the crystal structure stability of the material is improved to a certain extent. But it still affects its high-rate charge and discharge efficiency and cycle stability, hindering its electrochemical performance and practical application. Summary of the Invention
[0004] Object of the Invention: The object of the present invention is to improve the electronic conductivity and cycle stability of sodium iron pyrophosphate cathode materials by doping through the sol-gel method.
[0005] Technical Solution: The present invention is about the influence of doping sodium iron pyrophosphate cathode materials through the sol-gel method. The present invention improves sodium iron pyrophosphate by doping through the sol-gel method, Na2Fe 0.8 Ti 0.2At a high current density of 4 A / g of P2O7, the material still has a capacity retention rate of 80.76% after 5000 cycles.
[0006] To achieve the above object, the technical solution of the present invention is as follows:
[0007] Sodium iron pyrophosphate cathode material doped with other elements by sol-gel method, the composite material includes Na2Fe 1-x A x P2O7, where A is at least one of Cu, Mg, Mn, and Ti. The coating layer is a carbon coating layer. According to the sodium iron pyrophosphate cathode material doped with other elements described in claim 1, the doping amount is X≤0.5.
[0008] The present invention also provides a preparation method for synthesizing sodium iron pyrophosphate cathode material by sol-gel method, which includes the following steps:
[0009] (1) First, dissolve the sodium source, iron source, phosphorus source, carbon source and metal source in deionized water and stir for half an hour.
[0010] (2) Add the carbon source and stir until milky white, stirring for half an hour.
[0011] (3) Add ethylene glycol to the above (2), stir evenly; and adjust the PH value to neutral for the material
[0012] (4) Heat and stir the material in (3) at high temperature until it is evaporated to dryness to obtain a wet gel
[0013] (5) The wet gel obtained after evaporation is first dried overnight in a vacuum environment, and then pre-calcined under an inert gas to obtain a precursor; finally, the precursor is calcined under an inert gas to obtain the sodium ion battery cathode material.
[0014] In some embodiments, the sodium source includes at least one of disodium dihydrogen pyrophosphate, trisodium hydrogen pyrophosphate, sodium pyrophosphate, sodium carbonate, sodium bicarbonate, sodium acetate, sodium oxalate, sodium nitrate, and sodium dihydrogen phosphate.
[0015] In some embodiments, the iron source includes at least one of iron nitrate, iron sulfate, iron acetate, and iron chloride.
[0016] In some embodiments, the phosphorus source includes at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, triammonium phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, pyrophosphoric acid, and sodium pyrophosphate. In some embodiments, the compound of element A includes but is not limited to oxides, chlorides, sulfates, nitrates, oxalates, and acetates of A.
[0017] In some embodiments, the molar ratio of A:Fe is 0:1, 0.05:0.95, 0.10:0.90, 0.20:0.80, 0.50:0.50.
[0018] In some embodiments, the carbon source includes at least one of citric acid, glucose, sucrose, and ascorbic acid.
[0019] In some embodiments, the drying is one of freeze-drying, spray-drying, and vacuum-drying.
[0020] Further, in step (4), the heating temperature is 80°C and the stirring speed is 500 r / min.
[0021] Further, in step (5), the heating rate is 3 - 5°C / min.
[0022] Further, in step (5), the pre-burning time is 5 - 8 h and the temperature is 200 - 400°C.
[0023] Further, in step (5), the calcination time is 10 - 12 h and the temperature is 500 - 700°C. Compared with the prior art, the beneficial effects of the present invention are that the cathode material of the present invention has good electrochemical performance. The initial discharge specific capacity of the present invention at a current density of 100 mA / g is 91.34 mAh / g; the discharge specific capacity retention rate after 5000 cycles at a voltage of 1.5 - 4.2 V and a current density of 4 A / g is 80.76%, and it has good conductivity and a simple preparation method. Description of the Drawings
[0024] Figure 1 SEM image of the iron-based pyrophosphate composite material obtained in Example 1 of the present invention;
[0025] Figure 2 SEM image of the iron-based pyrophosphate composite material obtained in Comparative Example 1;
[0026] Figure 3 XRD pattern of the iron-based pyrophosphate composite material obtained in Example 1;
[0027] Figure 4 XRD pattern of the iron-based pyrophosphate composite material obtained in Comparative Example 1;
[0028] Figure 5 Charge-discharge comparison curves of the iron-based pyrophosphate composite materials obtained in Example 1 and Comparative Example 1 at a current density of 100 mA / g;
[0029] Figure 6 Discharge specific capacity comparison of the iron-based pyrophosphate composite materials obtained in Example 1 and Comparative Example 1 at a current density of 100 mA / g;
[0030] Figure 7 For the discharge specific capacity and charge-discharge efficiency of the iron-based pyrophosphate composite material in Example 1 at a high current density of 4 A / g. Specific implementation mode
[0031] Example 1:
[0032] The preparation method provided in this example for doping titanium atoms by the sol-gel method to improve the electronic conductivity and cycle stability of the sodium iron pyrophosphate Na2Fe 0.80 Ti 0.20 P2O7 cathode material includes the following steps:
[0033] Step 1: Preparation of the precursor solution: Add 0.600 g of sodium dihydrogen phosphate, 0.808 g of iron nitrate and 0.040 g of titanium dioxide to a beaker containing 10 ml of deionized water according to the stoichiometric ratio, and stir for 0.5 h.
[0034] Step 2: Add 0.430 g of sucrose and 0.025 g of ascorbic acid to the above (1), stir for 0.5 h, and stir until it becomes milky white.
[0035] Step 3: Add 0.75 ml of ethylene glycol to the mixed solution in (2), stir evenly, and then add ammonia water to make the pH neutral.
[0036] Step 4: Stir the solution in Step 3 in an oil bath at a temperature of 80 °C until the solution is evaporated to dryness to obtain a wet gel.
[0037] Step 5: Place the obtained wet gel after evaporation in a vacuum oven at 120 °C and dry it overnight. Grind the obtained dry gel and put it into a crucible. Heat it in an inert gas of high-purity argon at a heating rate of 5 °C / min to 300 °C, keep it warm for 5 h for preheating to obtain a precursor; finally, heat it at a heating rate of 5 °C / min to 550 °C for calcination and keep it warm for 10 h; to obtain the sodium-ion battery Na2Fe 0.8 Ti 0.2 P2O7 cathode material.
[0038] Step 6: Assemble the material into a coin cell for testing. The electrolyte is 1.0 M NaClO4 and the solvent is EC + DEC + 5% FEC.
[0039] After testing, the composite material obtained in this example has a discharge specific capacity of 91.34 mAh / g at a voltage of 1.5 - 4.2 V and a current density of 100 mA / g; the discharge specific capacity retention rate after 300 cycles is 94.60% at a voltage of 1.5 - 4.2 V and a current density of 100 mA / g.
[0040] The cathode material prepared by the above method greatly improves the cycle stability under high-rate charge and discharge conditions, as shown in Figure 7 , Figure 7 Figure Figure 7 shows the discharge specific capacity cycle and charge-discharge efficiency of the iron-based pyrophosphate composite material of Example 1 at a high current density of 4 A / g, and the capacity retention rate is 80.76%.
[0041] Comparative Example 1:
[0042] The preparation method provided in this example for doping titanium atoms by the sol-gel method to improve the electronic conductivity and cycle stability of sodium iron pyrophosphate Na2FeP2O7 cathode material includes the following steps:
[0043] Step 1: Preparation of precursor solution: Add 0.600 g of sodium dihydrogen phosphate and 1.010 g of iron nitrate to a beaker containing 10 ml of deionized water according to the stoichiometric ratio, and stir for 0.5 h.
[0044] Step 2: Add 0.430 g of sucrose and 0.025 g of ascorbic acid to the above (1), stir for 0.5 h until it becomes milky white.
[0045] Step 3: Add 0.75 ml of ethylene glycol to the mixed solution of (2), stir evenly and then add ammonia water to make the pH neutral.
[0046] Step 4: Stir the solution in Step 3 in an oil bath at 80 °C until the solution is evaporated to dryness to obtain a wet gel.
[0047] Step 5: Place the obtained wet gel after evaporation in a vacuum oven at 120 °C and dry it overnight. Grind the obtained dry gel and put it into a crucible. Heat it to 300 °C at a heating rate of 5 °C / min in an inert gas of high-purity argon, keep it warm for 5 h for preheating to obtain a precursor; finally, heat it to 550 °C at a heating rate of 5 °C / min and calcine it for 10 h; to obtain the sodium-ion battery Na2FeP2O7 cathode material.
[0048] Step 6: Assemble the material into a coin cell for testing, and the electrolyte is 1.0 M NaClO4 with the solvent being EC + DEC + 5% FEC.
[0049] After testing, the composite material obtained in this example has a discharge specific capacity of 87.52 mAh / g at a voltage of 1.5 - 4.2 V and a current density of 100 mA / g; at a voltage of 1.5 - 4.2 V and a current density of 100 mA / g, the discharge specific capacity retention rate after 300 cycles is 80.43%.
[0050] Example 2:
[0051] The preparation method for improving the electronic conductivity and cycling stability of sodium iron pyrophosphate Na2Fe 0.95 Ti 0.05 P2O7 cathode material by doping titanium atoms through the sol-gel method includes the following steps:
[0052] Step 1: Preparation of the precursor solution: Add 0.600 g of sodium dihydrogen phosphate, 0.960 g of iron nitrate, and 0.010 g of titanium dioxide to a beaker containing 10 ml of deionized water according to the stoichiometric ratio, and stir for 0.5 h.
[0053] Step 2: Add 0.430 g of sucrose and 0.025 g of ascorbic acid to the above (1), stir for 0.5 h until it becomes milky white.
[0054] Step 3: Add 0.75 ml of ethylene glycol to the mixed solution in (2), stir evenly, and then add ammonia water to make the pH neutral.
[0055] Step 4: Stir the solution in Step 3 at a temperature of 80 °C in an oil bath until the solution is evaporated to dryness to obtain a wet gel.
[0056] Step 5: Place the obtained wet gel after evaporation in a vacuum oven at 120 °C and dry it overnight. Grind the obtained dry gel and put it into a crucible. Heat it to 300 °C at a heating rate of 5 °C / min in an inert gas of high-purity argon and hold for 5 h for preheating to obtain a precursor; finally, heat it to 550 °C at a heating rate of 5 °C / min and calcine for 10 h; to obtain the sodium-ion battery Na2Fe 0.95 Ti 0.05 P2O7 cathode material.
[0057] Step 6: Assemble the material into a coin cell for testing. The electrolyte is 1.0 M NaClO4 and the solvent is EC + DEC + 5% FEC.
[0058] After testing, the discharge specific capacity of the composite material obtained in this example is 90.79 mAh / g at a voltage of 1.5 - 4.2 V and a current density of 100 mA / g; the retention rate of the discharge specific capacity after 300 cycles is 95.69% at a voltage of 1.5 - 4.2 V and a current density of 100 mA / g.
[0059] Example 3:
[0060] The preparation method for improving the electronic conductivity and cycling stability of sodium iron pyrophosphate Na2Fe 0.90 Ti 0.10 P2O7 cathode material by doping titanium atoms through the sol-gel method includes the following steps:
[0061] Step 1: Preparation of precursor solution: Add 0.600 g of sodium dihydrogen phosphate, 0.909 g of iron nitrate, and 0.020 g of titanium dioxide into a beaker containing 10 ml of deionized water according to the stoichiometric ratio, and stir for 0.5 h.
[0062] Step 2: Add 0.430 g of sucrose and 0.025 g of ascorbic acid to the above (1), stir for 0.5 h until it becomes milky white.
[0063] Step 3: Add 0.75 ml of ethylene glycol to the mixed solution of (2), stir evenly, and then add ammonia water to make the pH neutral.
[0064] Step 4: Stir the solution in Step 3 above in an oil bath at 80 °C until the solution is evaporated to dryness to obtain a wet gel.
[0065] Step 5: Place the obtained wet gel after evaporation in a vacuum oven at 120 °C and dry it overnight. Grind the obtained dry gel and put it into a crucible. Heat it to 300 °C at a heating rate of 5 °C / min in an inert gas of high-purity argon and keep it warm for 5 h for preheating to obtain a precursor; finally, heat it to 550 °C at a heating rate of 5 °C / min and calcine it for 10 h; to obtain the Na2Fe 0.90 Ti 0.10 P2O7 cathode material.
[0066] Step 6: Assemble the material into a coin cell for testing. The electrolyte is 1.0 M NaClO4 and the solvent is EC + DEC + 5% FEC.
[0067] After testing, the discharge specific capacity of the composite material obtained in this example is 75.09 mAh / g at a voltage of 1.5 - 4.2 V and a current density of 100 mA / g; the discharge specific capacity retention rate after 300 cycles is 89.97% at a voltage of 1.5 - 4.2 V and a current density of 100 mA / g.
[0068] Example 4:
[0069] The preparation method provided in this example for improving the electronic conductivity and cycling stability of sodium iron pyrophosphate Na2Fe 0.50 Ti 0.50 P2O7 cathode material by sol-gel method doping titanium atoms includes the following steps:
[0070] Step 1: Preparation of precursor solution: Add 0.600 g of sodium dihydrogen phosphate, 0.505 g of iron nitrate, and 0.100 g of titanium dioxide into a beaker containing 10 ml of deionized water according to the stoichiometric ratio, and stir for 0.5 h.
[0071] Step 2: Add 0.430 g of sucrose and 0.025 g of ascorbic acid to the above (1), stir for 0.5 h until it becomes milky white.
[0072] Step 3: Add 0.75 ml of ethylene glycol to the mixed solution in (2), stir evenly and then add ammonia water to make the pH neutral.
[0073] Step 4: Stir the solution in Step 3 above in an oil bath at 80 °C until the solution is evaporated to dryness to obtain a wet gel.
[0074] Step 5: Place the obtained wet gel after evaporation in a vacuum oven at 120 °C and dry it overnight. Grind the obtained dry gel and put it into a crucible. Heat it to 300 °C at a heating rate of 5 °C / min in an inert gas of high-purity argon and keep it warm for 5 h for preheating to obtain a precursor; finally, heat it to 550 °C at a heating rate of 5 °C / min and calcine it for 10 h; to obtain the Na2Fe 0.50 Ti 0.50 P2O7 cathode material.
[0075] Step 6: Assemble the material into a coin cell for testing. The electrolyte is 1.0 M NaClO4 and the solvent is EC + DEC + 5% FEC.
[0076] After testing, the discharge specific capacity of the composite material obtained in this example is 80.32 mAh / g at a voltage of 1.5 - 4.2 V and a current density of 100 mA / g; the discharge specific capacity retention rate after 300 cycles is 78.33% at a voltage of 1.5 - 4.2 V and a current density of 100 mA / g.
[0077] It is verified that the cycle stability and material conductivity of the cathode material prepared in this example have been greatly improved.
[0078] The above is only the selected embodiment of the present invention and does not impose any limitation on the present invention. Any person skilled in the art, without departing from the technical solution of the present invention, makes any form of equivalent replacement or modification and other changes to the technical solution and technical content disclosed by the present invention, all of which belong to the content of the technical solution of the present invention and still fall within the protection scope of the present invention.
Claims
1. Sodium iron pyrophosphate cathode material doped by sol-gel method, the composite material comprising Na2Fe 1-x A x P2O7, wherein, A is at least one of Cu, Mg, Mn, and Ti. The coating layer is a carbon coating layer.
2. The sodium iron pyrophosphate cathode material doped with other elements according to claim 1, wherein the doping amount is X≤0.
5.
3. The preparation method of the sodium iron pyrophosphate cathode material doped with other elements according to claim 1 or 2, characterized in that, It includes the following steps: Mix the sodium source, iron source, carbon source, and metal source, perform sol-gel, drying, grinding, and calcine at 550 °C in an inert gas atmosphere to obtain the iron-based pyrophosphate cathode material.
4. The preparation method of the sodium iron pyrophosphate cathode material doped by the sol-gel method according to claim 3, characterized in that, The molar ratio of Na, Fe, and P in the sodium source, iron source, and phosphorus source is 2:(1 - X):
2.
5. The preparation method of the sodium iron pyrophosphate cathode material doped by the sol-gel method according to claim 3, characterized in that, The sodium source includes at least one of disodium dihydrogen pyrophosphate, trisodium hydrogen pyrophosphate, sodium pyrophosphate, sodium carbonate, sodium bicarbonate, sodium acetate, sodium oxalate, sodium nitrate, and sodium dihydrogen phosphate. The iron source includes at least one of iron nitrate, iron sulfate, iron acetate, and iron chloride. The phosphorus source includes at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, ammonium phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, pyrophosphoric acid, and sodium pyrophosphate. The compound of element A includes but is not limited to the oxide, chloride, sulfate, nitrate, oxalate, and acetate of A. The carbon source includes at least one of citric acid, glucose, sucrose, and ascorbic acid. The drying is one of freeze-drying, spray-drying, and vacuum-drying.
6. According to claim 3, the heating temperature is 80 °C and the stirring speed is 500 r / min.
7. According to claim 3, the heating rate is 3 - 5 °C / min, the pre-calcination time is 5 - 8 h, the temperature is 200 - 400 °C, the calcination time is 10 - 12 h, and the temperature is 500 - 700 °C.
8. A cathode material, characterized in that, It includes the iron-based phosphate composite material described in claim 1 or 2 or the iron-based phosphate composite material obtained by the preparation method described in any one of claims 3 - 7.
9. The positive electrode is characterized in that, It includes the cathode material described in claim 7. Electrochemical energy storage device, characterized in that, It includes the cathode described in claim 8.