Preparation method of modified titanium niobate and application of modified titanium niobate in lithium ion capacitor

Abstract

The invention belongs to the technical field of energy storage materials, and relates to a preparation method of modified titanium niobate and application of the modified titanium niobate in a lithium ion capacitor, and the preparation method comprises the following steps: S1) under the protection of inert atmosphere, co-dissolving niobium salt, titanium salt, vanadium salt, molybdenum salt, aluminum salt and zirconium salt in alcohol to form a mixed solution, sequentially carrying out microwave treatment, drying and calcining on the mixed solution to obtain doped titanium niobate particles; the material meets the requirement that the molar ratio of Nb to Ti is 1.95: 1 to 2.05: 1; and S2) carrying out pulse nitriding treatment on the doped titanium niobate particles by adopting NH3 / H2 mixed gas to obtain the modified titanium niobate particles. Through Mo / V / Al / Zr multi-element synergistic doping, N gradient doping and a pulse optimization process, the optimization limitation of a traditional single doping performance index is improved, and meanwhile, the high rate capability and the cycle life of the lithium ion capacitor are improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of energy storage materials, and relates to a lithium ion capacitor negative electrode material, in particular to a preparation method of modified titanium niobate and application of the modified titanium niobate in a lithium ion capacitor. BACKGROUND

[0002] In recent years, titanium niobate is considered as a promising high-power lithium ion capacitor negative electrode material due to its significant high rate performance, safety and reversible capacity. Although titanium niobate has many advantages as a lithium ion capacitor negative electrode material, the lithium ion diffusion coefficient of the titanium niobate material is small, and the structure is unstable during the doping process, which leads to poor high rate capability and poor cycle stability of the capacitor. Therefore, the high rate capability and cycle life of the titanium niobate need to be improved.

[0003] CN112357960A discloses a preparation method of a rare earth element neodymium doped titanium niobate material and application of the material in a lithium ion capacitor. The preparation method of the titanium niobate material is as follows: 1. Dissolve a titanium source compound and oxalic acid in an organic solvent, dissolve a niobium source compound and oxalic acid in distilled water by heating and stirring, and dissolve a neodymium-containing compound in dilute hydrochloric acid; 2. Mix the three solutions prepared in step 1 to prepare a rare earth element neodymium doped titanium niobate material precursor by a heating and stirring evaporation solvent method or a solvothermal method; and 3. Heat treat the precursor obtained in step 2 to obtain a rare earth element neodymium doped titanium niobate material with good electrochemical performance. The application dopes and modifies the titanium niobate material with the rare earth element neodymium, increases the unit cell size, and improves the lithium ion conduction rate, thereby further improving the electrochemical performance of the titanium niobate and promoting the application of the titanium niobate in the lithium ion capacitor.

[0004] The titanium niobate and the doped titanium niobate prepared in the past have many advantages as lithium ion capacitor negative electrode materials, but there are still problems such as poor high rate capability and poor cycle stability of the capacitor caused by the small lithium ion diffusion coefficient of the titanium niobate material and the structural instability during the doping process. Therefore, the high rate capability and cycle life of the titanium niobate need to be improved. SUMMARY

[0005] In view of the problems of poor high rate capability and poor cycle stability of the capacitor caused by the small lithium ion diffusion coefficient of the titanium niobate material in the prior art, the application provides a preparation method of modified titanium niobate and application of the modified titanium niobate in a lithium ion capacitor. The modified titanium niobate improves the high rate capability of the lithium ion capacitor and has good cycle stability, and has the effect of synergistic improvement of the high rate capability and cycle life of the lithium ion capacitor. To achieve this purpose, the following technical solutions are adopted in the application:

[0006] A preparation method of modified titanium niobate, comprising the following steps:

[0007] S1: Dissolve niobium salt, titanium salt, vanadium salt, molybdenum salt, aluminum salt and zirconium salt in alcohol to form a mixed solution under the protection of inert atmosphere, and then sequentially perform microwave treatment, drying and calcination on the mixed solution to obtain doped titanium niobate particles; and the molar ratio of Nb:Ti is 1.95:1 to 2.05:1;

[0008] S2: Pulse nitriding treatment is performed on the doped titanium niobate particles by using NH3 / H2 mixed gas to obtain modified titanium niobate.

[0009] Further, in step S1, the mass ratio of the total mass of the niobium salt and the titanium salt to the mass of the vanadium salt, the molybdenum salt, the aluminum salt and the zirconium salt is 75:(0.5-2.5):(1-4):(0.2-1):(0.2-1), and preferably 75:(0.5-1):(2-3):(0.5-1):(0.5-1).

[0010] Further, in step S1, the niobium salt, the vanadium salt, the molybdenum salt, the aluminum salt and the zirconium salt are selected from metal nitrate, halide and their hydrates, and the titanium salt is an organic salt; preferably, the niobium salt is niobium nitrate or halide, such as niobium pentachloride, the titanium salt is titanium isopropoxide or titanium n-propoxide, the vanadium salt is VCl5, the molybdenum salt is MoCl5, the aluminum salt is Al(NO3)3·9H2O, and the zirconium salt is ZrOCl2·8H2O; the alcohol is at least one of ethanol and propanol; and the volume ratio of the total mass of the niobium salt, the titanium salt, the vanadium salt, the molybdenum salt, the aluminum salt and the zirconium salt to the alcohol is (40-70) g:(300-500) mL.

[0011] Further, in step S1, the inert atmosphere is argon or nitrogen; the microwave treatment is performed under the condition of 2-3 GHz microwave for 20-40 hours, and preferably for 30-40 hours; the drying is performed at room temperature for 4-7 days first, and then at 30-60℃ for 2-5 hours; and the calcination is performed at 800-1200℃ in air for 3-8 hours.

[0012] Further, in step S2, the volume ratio of NH3 to H2 in the NH3 / H2 mixed gas is 9:1-1:1, and preferably 4:1-3:1.

[0013] Further, the pulse nitriding treatment in step S2 is carried out at a temperature of 300-600 DEG C, preferably 400-550 DEG C, for 10-30 min, with a pulse of 5-15 s on / 3-10 s off, preferably 7-10 s on / 3-8 s off. Nitriding is a chemical heat treatment process for making nitrogen atoms penetrate into the surface layer of an object in a certain medium at a certain temperature, and common nitriding methods include liquid nitriding, gas nitriding and ion nitriding. Pulse nitriding is a gas nitriding method, in which the furnace pressure is alternately changed within a certain range through repeated gas filling and gas extraction. This pulse change helps nitrogen atoms to more uniformly penetrate into the surface layer of the object.

[0014] The inventors have found that the use of a mixed gas of ammonia and hydrogen can successfully achieve the purpose of pulse nitriding for improving the lithium ion capacitor. Hydrogen plays a key role in the mixed gas, and hydrogen promotes the diffusion of nitrogen atoms, acting as a lubricant. In the presence of a certain proportion of hydrogen, the degree of nitriding is more uniform. The proportion of hydrogen directly affects the electrochemical performance of the final product, such as conductivity, rate performance and cycle life. The inventors speculate that the possible reason is that the presence of hydrogen affects the doping form of nitrogen, increasing the solid solubility of nitrogen in the crystal lattice. However, the proportion of hydrogen in the mixed gas needs to be controlled. Too low or too high a proportion cannot effectively improve the electrochemical performance of the lithium ion capacitor.

[0015] A second object of the present application is to provide an application of the modified titanium niobate in a lithium ion capacitor. The modified titanium niobate prepared by the aforementioned method is coated with carbon and used as a negative electrode material in a lithium ion capacitor.

[0016] Further, the process conditions for the carbon coating are as follows: under an inert atmosphere, a carbon source gas is introduced, and carbon is deposited at 600-800 DEG C for 20 min-1 h. The carbon source gas is selected from at least one of C1-4 alkane, C2-4 alkene and C2-4 alkyne.

[0017] Compared with the prior art, the present application has the following beneficial effects:

[0018] The present application provides a preparation method of modified titanium niobate. Mo / V / Al / Zr co-doped substrates are synthesized by a microwave-assisted sol-gel method. The introduced Mo doping ions can improve the crystal structure, thereby widening the diffusion channel of Li + and accelerating the transmission rate of ions. V ion doping is interstitial and substitutional doping, which expands the titanium niobate lattice and obtains a wider lithium ion transmission channel, thereby further improving the rate performance of the capacitor. Meanwhile, the "double buffer" stabilizers Al and Zr elements introduced in the present application can optimize the structural stability. The small ion radius and properties of the stabilizers compensate for the excessive expansion of the lattice caused by Mo / V doping and inhibit the collapse of the structure in the cycle, thereby solving the problems of lattice mismatch, aggravated lattice distortion and stress concentration caused by multi-element doping.

[0019] Pulse gas-phase nitriding is a transition metal-nonmetal multi-element doped synergistic system based on the introduction of N doping on the basis of Mo and V doping of titanium niobate. N induces lattice distortion through ion radius difference and changes the surface doping concentration gradient, relieving the volume expansion of titanium niobate in the cycle process. Pulse N doping forces gas molecules to "intermittent penetration" on the surface of doped particles through periodic gas on-off, reducing the local concentration caused by continuous gas flow, and improving the uniformity of doping. Pulse treatment allows nitrogen atoms to gradually embed into the titanium niobate lattice, avoiding lattice defects caused by rapid doping. Periodic gas impact may induce the formation of oxygen vacancies on the surface of titanium niobate, which synergistically optimizes the energy band structure with nitrogen doping and improves the electrical performance of the material.

[0020] In summary, the present application realizes the synergistic improvement of high rate capability and cycle life of lithium ion capacitors through multi-element synergistic doping and regulation, breaking through the optimization limitation of traditional doping on single performance index. By introducing Mo / V doping, Al / Zr stabilizer, N gradient doping and pulse optimization process, the process uncontrollable problems such as structural instability of doped titanium niobate are solved, realizing the effect of maintaining the high rate capability of lithium capacitors while improving the high temperature and low temperature cycle life to a high level, providing high-quality negative electrode materials for the development of the next generation of high-power lithium ion capacitors. DETAILED DESCRIPTION

[0021] The technical solutions of the present application will be further described below through specific embodiments.

[0022] Example 1

[0023] S1: Dissolve 49 grams of niobium pentachloride in 400 mL of ethanol under nitrogen protection, add 26 grams of titanium isopropoxide, 1 gram of VCl5, 3 grams of MoCl5, 0.8 grams of Al(NO3)3·9H2O and 0.6 grams of ZrOCl2·8H2O to form a mixed solution, stir the mixed solution and keep it under 2.45 GHz microwave condition for 24 hours; then dry it at room temperature for 5 days, keep it at 50℃ for 3 hours to remove ethanol; finally, calcine it in air at 1000℃ for 5 hours to obtain doped titanium niobate particles;

[0024] S2: The doped titanium niobate particles were evenly laid out (thickness ≤ 2 mm to ensure gas permeation) in a high-temperature tube furnace quartz boat, the reaction tube was closed, N2 was filled to 0.2 MPa, and the pressure was maintained for 10 minutes to confirm that there was no leakage; NH3 and H2 gas cylinders were connected to the mixing chamber, and the flow ratio was set by the mass flow controller MFC (NH3 80 sccm, H2 20 sccm); the mixed gas outlet was connected to a pulse solenoid valve, and the on-off cycle was controlled by the controller PLC (10 s on / 5 s off); vacuum was drawn to 10-2mbar, N2 was slowly introduced to normal pressure, and the process was repeated 3 times to exclude oxygen; the temperature was raised to 500℃ at a rate of 5℃ / min, and N2 (50 sccm) was passed through the whole process for protection; after reaching 500℃, it was stabilized for 30 minutes, N2 was turned off, and NH3 / H2 mixed gas was introduced in pulse mode, with pulse parameters as follows: each time the gas was introduced for 10 seconds (flow rate 100 sccm), and then closed for 5 seconds, 30 minutes of cycle for 120 times; after the treatment was completed, the pulse gas supply was stopped, N2 protection (100 sccm) was switched, the temperature was lowered to 100℃ at a rate of 5℃ / min, and the modified titanium niobate was obtained.

[0025] Example 2

[0026] The other conditions and example 1 were the same, except that the amount of MoCl5 in step S1 was increased to 4 grams, and the specific conditions were as follows:

[0027] S1: 49 grams of niobium pentachloride were dissolved in 400 mL of ethanol under nitrogen protection, 26 grams of titanium isopropoxide, 1 gram of VCl5, 4 grams of MoCl5, 0.8 grams of Al(NO3)3·9H2O and 0.6 grams of ZrOCl2·8H2O were added to form a mixed solution, the mixed solution was stirred and kept under 2.45 GHz microwave conditions for 24 hours; then it was dried at room temperature for 5 days, and kept at 50℃ for 3 hours to remove ethanol; finally, it was calcined in air at 1000℃ for 5 hours to obtain doped titanium niobate particles;

[0028] S2: The doped titanium niobate particles were evenly laid out (thickness ≤ 2 mm to ensure gas permeation) in a high-temperature tube furnace quartz boat, the reaction tube was closed, N2was filled to 0.2 MPa, and the pressure was maintained for 10 minutes to confirm that there was no leakage; NH3and H2gas cylinders were connected to the mixing chamber, and the flow ratio was set by the mass flow controller MFC (NH380 sccm, H220 sccm); the mixed gas outlet was connected to a pulse solenoid valve, and the on-off cycle was controlled by the controller PLC (10 s on / 5 s off); vacuum was drawn to 10-2mbar, N2was slowly introduced to normal pressure, and the process was repeated 3 times to exclude oxygen; the temperature was raised to 500°C at a rate of 5°C / min, and N2(50 sccm) was passed through the whole process for protection; after reaching 500°C, it was stabilized for 30 minutes, N2was turned off, and NH3 / H2mixed gas was introduced in pulse mode, pulse parameters: each time 10 seconds (flow rate 100 sccm), 5 seconds off, 30 minutes cycle 120 times; after the treatment was completed, the pulse supply was stopped, and N2protection (100 sccm) was switched, the temperature was lowered to 100°C at a rate of 5°C / min, and modified titanium niobate was obtained.

[0029] Example 3

[0030] The other conditions and example 1 were the same, except that the doping ratio of Al and Zr in step S1 was increased, specifically:

[0031] S1: 24 grams of niobium pentachloride was dissolved in 400 mL of ethanol under nitrogen protection, after the solution was clear, 26 grams of titanium isopropoxide, 1 gram of VCl5, 3 grams of MoCl5, 0.9 grams of Al(NO3)3·9H2O and 0.7 grams of ZrOCl2·8H2O were added to form a mixed solution, the mixed solution was stirred and kept under 2.45 GHz microwave conditions for 24 hours; then it was dried at room temperature for 5 days, kept at 50°C for 3 hours to remove ethanol; finally, it was calcined in air at 1000°C for 5 hours to obtain doped titanium niobate particles;

[0032] S2: The doped titanium niobate particles were evenly laid (thickness ≤ 2 mm to ensure gas permeation) in a high-temperature tube furnace quartz boat, the reaction tube was closed, N2 was filled to 0.2 MPa, and the pressure was maintained for 10 minutes to confirm that there was no leakage; NH3 and H2 gas cylinders were connected to the mixing chamber, and the flow ratio (NH3 80 sccm, H2 20 sccm) was set by the mass flow controller MFC; the mixed gas outlet was connected to the pulse solenoid valve, and the on-off cycle (10 s on / 5 s off) was controlled by the controller PLC; vacuum was drawn to 10-2mbar, N2 was slowly introduced to normal pressure, and the process was repeated 3 times to exclude oxygen; the temperature was raised to 500℃ at a rate of 5℃ / min, and N2 (50 sccm) was passed through the whole process for protection; after reaching 500℃, it was stabilized for 30 minutes, N2 was turned off, and NH3 / H2 mixed gas was introduced in pulse mode. Pulse parameters: 10 seconds (flow rate 100 sccm) per time, 5 seconds off, 30 minutes cycle 120 times; after the treatment was completed, the pulse supply was stopped, and N2 protection (100 sccm) was switched to, the temperature was lowered to 100℃ at a rate of 5℃ / min, and the modified titanium niobate was obtained.

[0033] Example 4

[0034] The other conditions and example 1 were the same, except that the volume ratio of NH3 in the NH3 / H2 mixed gas was increased, i.e. the volume ratio of NH3 to H2 was 3:1, which was realized by adjusting the flow rates of NH3 and H2 (the flow rate of NH3 was 75 sccm, and the flow rate of H2 was 25 sccm), and the specific process was as follows:

[0035] S1: 24 grams of niobium pentachloride was dissolved in 400 mL of ethanol under nitrogen protection, 26 grams of titanium isopropoxide, 1 gram of VCl5, 3 grams of MoCl5, 0.8 grams of Al(NO3)3·9H2O and 0.6 grams of ZrOCl2·8H2O were added to form a mixed solution, the mixed solution was stirred and kept under 2.45 GHz microwave conditions for 24 hours; then it was dried at room temperature for 5 days, and kept at 50℃ for 3 hours to remove ethanol; finally, it was calcined in air at 1000℃ for 5 hours to obtain doped titanium niobate particles;

[0036] S2: Evenly spread the doped titanium niobate particles (thickness ≤ 2 mm to ensure gas permeability) in a high-temperature tube furnace quartz boat, close the reaction tube, fill it with N2 to 0.2 MPa, and maintain the pressure for 10 minutes to confirm that there is no leakage; connect NH3 and H2 gas cylinders to the mixing chamber, and set the flow ratio (NH3 75 sccm, H2 25sccm); the mixed gas outlet is connected to a pulse solenoid valve, and the on-off cycle is controlled by a controller PLC (10s on / 5s off); vacuum is evacuated to 10-2mbar, and N2 is slowly introduced to normal pressure, and repeated 3 times to exclude oxygen; the temperature is raised to 500°C at a rate of 5°C / min, and N2 (50sccm) is passed through for protection throughout the process; after reaching 500°C, it is stabilized for 30 minutes, N2 is turned off, and a pulse mode is started to introduce NH3 / H2 mixed gas, and the pulse parameters are: ventilation for 10 seconds each time (flow rate 100sccm), off for 5 seconds, and 120 cycles in 30 minutes; after the treatment is completed, the pulse gas supply is stopped, switched to N2 protection (100sccm), and the temperature is lowered to 100°C at a rate of 5°C / min to obtain modified titanium niobate.

[0037] Example 5

[0038] Other conditions are the same as those in Example 1, except that the doping ratios of Mo, V, Al, and Zr in step S1 are reduced, specifically:

[0039] S1: 49 g of niobium pentachloride was dissolved in 400 mL of ethanol under nitrogen protection. After the solution was clarified, 26 g of titanium isopropoxide, 0.7 g of VCl5, 2.5 g of MoCl5, 0.6 g of Al(NO3)3·9H2O and 0.5 g of ZrOCl2·8H2O were added to form a mixed solution. The mixed solution was stirred and kept under 2.45 GHz microwave conditions for 24 hours; then dried at room temperature for 5 days and kept at 50°C for 3 hours to remove ethanol; finally, calcined in air at 1000°C for 5 hours to obtain doped titanium niobate particles;

[0040] S2: The doped titanium niobate particles were evenly laid (thickness ≤ 2 mm to ensure gas permeation) in a high-temperature tube furnace quartz boat, the reaction tube was closed, N2 was filled to 0.2 MPa, and the pressure was maintained for 10 minutes to confirm that there was no leakage; NH3 and H2 gas cylinders were connected to the mixing chamber, and the flow ratio (NH3 80 sccm, H2 20 sccm) was set by the mass flow controller MFC; the mixed gas outlet was connected to the pulse solenoid valve, and the on-off cycle (10 s on / 5 s off) was controlled by the controller PLC; vacuum was drawn to 10-2mbar, N2 was slowly introduced to normal pressure, and the process was repeated 3 times to exclude oxygen; the temperature was raised to 500℃ at a rate of 5℃ / min, and N2 (50 sccm) was passed through the whole process for protection; after reaching 500℃, it was stabilized for 30 minutes, N2 was turned off, and NH3 / H2 mixed gas was introduced in pulse mode, with pulse parameters as follows: 10 seconds (flow rate 100 sccm) for each time, 5 seconds for closing, 30 minutes for 120 times of circulation; after the treatment was completed, the pulse gas supply was stopped, N2 protection (100 sccm) was switched, the temperature was lowered to 100℃ at a rate of 5℃ / min, and the modified titanium niobate was obtained.

[0041] Example 6

[0042] The other conditions and example 1 were the same, except that the doping ratio of V in step (S1) was increased, and the doping ratio of Mo, Al and Zr was reduced, specifically:

[0043] S1: 49 grams of niobium pentachloride was dissolved in 400 mL of ethanol under nitrogen protection, after the solution was clear, 26 grams of titanium isopropoxide, 1.25 grams of VCl5, 1.25 grams of MoCl5, 0.4 grams of Al(NO3)3·9H2O and 0.25 grams of ZrOCl2·8H2O were added to form a mixed solution, the mixed solution was stirred and kept under 2.45 GHz microwave conditions for 24 hours; then it was dried at room temperature for 5 days, and kept at 50℃ for 3 hours to remove ethanol; finally, it was calcined in air at 1000℃ for 5 hours to obtain doped titanium niobate particles;

[0044] S2: The doped titanium niobate particles were evenly laid out (thickness ≤ 2 mm to ensure gas permeation) in a high-temperature tube furnace quartz boat, the reaction tube was closed, N2 was filled to 0.2 MPa, and the pressure was maintained for 10 minutes to confirm that there was no leakage; NH3 and H2 gas cylinders were connected to the mixing chamber, and the flow ratio was set by the mass flow controller MFC (NH3 80 sccm, H2 20 sccm); the mixed gas outlet was connected to a pulse solenoid valve, and the on-off cycle was controlled by the controller PLC (10 s on / 5 s off); vacuum was drawn to 10-2mbar, N2 was slowly introduced to normal pressure, and the process was repeated three times to exclude oxygen; the temperature was raised to 500℃ at a rate of 5℃ / min, and N2 (50 sccm) was passed through the whole process for protection; after reaching 500℃, it was stabilized for 30 minutes, N2 was turned off, and NH3 / H2 mixed gas was introduced in pulse mode, with pulse parameters as follows: each time the gas was introduced for 10 seconds (flow rate 100 sccm), and then closed for 5 seconds, 30 minutes of cycle for 120 times; after the treatment was completed, the pulse gas supply was stopped, N2 protection (100 sccm) was switched, the temperature was lowered to 100℃ at a rate of 5℃ / min, and the modified titanium niobate was obtained.

[0045] Example 7

[0046] The other conditions and Example 1 were the same, except that the doping ratio of Mo / V / Al / Zr in step (S1) was increased, specifically: the amount of MoCl5 was increased to 5 grams, the amount of VCl5 was increased to 3 grams, the amount of Al(NO3)3·9H2O was increased to 2 grams, and the amount of ZrOCl2·8H2O was increased to 2 grams.

[0047] S1: 49 grams of niobium pentachloride was dissolved in 400 mL of ethanol under nitrogen protection, and after the solution was clear, 26 grams of titanium isopropoxide, 2.5 grams of VCl5, 4 grams of MoCl5, 1 gram of Al(NO3)3·9H2O and 1 gram of ZrOCl2·8H2O were added to form a mixed solution, the mixed solution was stirred and kept under 2.45 GHz microwave conditions for 24 hours; then it was dried at room temperature for 5 days, and kept at 50℃ for 3 hours to remove ethanol; finally, it was calcined in air at 1000℃ for 5 hours to obtain doped titanium niobate particles;

[0048] S2: The doped titanium niobate particles were evenly laid out (thickness ≤ 2 mm to ensure gas permeation) in a high-temperature tube furnace quartz boat, the reaction tube was closed, and N2 was filled to 0.2 MPa, and the pressure was maintained for 10 minutes to confirm that there was no leakage; the NH3 and H2 gas cylinders were connected to the mixing chamber, and the flow ratio (NH3 80 sccm, H2 20 sccm) was set by the mass flow controller MFC; the mixed gas outlet was connected to the pulse solenoid valve, and the on-off cycle (10 s on / 5 s off) was controlled by the controller PLC; vacuum was drawn to 10-2mbar, N2 was slowly introduced to normal pressure, and the process was repeated 3 times to exclude oxygen; the temperature was raised to 500℃ at a rate of 5℃ / min, and N2 (50 sccm) was passed through the whole process for protection; after reaching 500℃, it was stabilized for 30 minutes, N2 was turned off, and NH3 / H2 mixed gas was introduced in pulse mode, with pulse parameters as follows: 10 seconds (flow rate 100 sccm) for each gas supply, 5 seconds for closing, 30 minutes for 120 cycles; after the treatment was completed, the pulse gas supply was stopped, and N2 protection (100 sccm) was switched on, the temperature was lowered to 100℃ at a rate of 5℃ / min, and the modified titanium niobate was obtained.

[0049] Example 8

[0050] The other conditions were the same as in Example 1, except that the MFC was set to a flow ratio of NH3 50 sccm and H2 50 sccm, i.e. the volume ratio of NH3 and H2 was 1:1.

[0051] Example 9

[0052] The other conditions were the same as in Example 1, except that the MFC was set to a flow ratio of NH3 90 sccm and H2 10 sccm, i.e. the volume ratio of NH3 and H2 was 9:1.

[0053] Comparative Example 1

[0054] The other conditions were the same as in Example 1, except that no Al / Zr stabilizer was added in step S1, i.e. no Al(NO3)3·9H2O and 0.6 grams of ZrOCl2·8H2O were added, and the specific operation was as follows:

[0055] S1: 49 grams of niobium pentachloride were dissolved in 400 mL of ethanol under nitrogen protection, 26 grams of titanium isopropoxide, 1 gram of VCl5, and 3 grams of MoCl5 were added after the solution was clear, a mixed solution was formed, the mixed solution was stirred and kept under 2.45 GHz microwave conditions for 24 hours; then it was dried at room temperature for 5 days, and kept at 50℃ for 3 hours to remove ethanol; finally, it was calcined in air at 1000℃ for 5 hours to obtain doped titanium niobate particles;

[0056] S2: The doped titanium niobate particles were evenly laid (thickness ≤ 2 mm to ensure gas permeation) in a high-temperature tube furnace quartz boat, the reaction tube was closed, and the pressure was maintained at 0.2 MPa for 10 minutes to confirm that there was no leakage; the NH3 and H2 gas cylinders were connected to the mixing chamber, and the flow ratio (NH3 80 sccm, H2 20 sccm) was set by the mass flow controller MFC; the mixed gas outlet was connected to the pulse solenoid valve, and the on-off cycle (10 s on / 5 s off) was controlled by the controller PLC; vacuum was drawn to 10-2mbar, and N2 was slowly introduced to atmospheric pressure, which was repeated three times to exclude oxygen; the temperature was raised to 500°C at a rate of 5°C / min, and N2 (50 sccm) was passed through the whole process for protection; after reaching 500°C, it was stabilized for 30 minutes, N2 was turned off, and NH3 / H2 mixed gas was introduced in pulse mode, with pulse parameters of: 10 seconds (flow rate 100 sccm) for each gas supply, 5 seconds off, 30 minutes cycle 120 times; after the treatment was completed, the pulse gas supply was stopped, and N2 protection (100 sccm) was switched to, the temperature was lowered to 100°C at a rate of 5°C / min, and modified titanium niobate was obtained.

[0057] Comparative Example 2

[0058] The other conditions and Example 1 were the same, except that N doping was not performed in step S2, specifically:

[0059] S1: 49 grams of niobium pentachloride was dissolved in 400 mL of ethanol under nitrogen protection, 26 grams of titanium isopropoxide, 1 gram of VCl5, 3 grams of MoCl5, 0.8 grams of Al(NO3)3·9H2O and 0.6 grams of ZrOCl2·8H2O were added to form a mixed solution, the mixed solution was stirred and kept under 2.45 GHz microwave conditions for 24 hours; then dried at room temperature for 5 days, 50°C for 3 hours to remove ethanol; finally calcined at 1000°C in air for 5 hours, doped titanium niobate particles were obtained;

[0060] S2: The doped titanium niobate particles were evenly laid (thickness ≤ 2 mm to ensure gas permeation) in a high-temperature tube furnace quartz boat, the reaction tube was closed, and the pressure was maintained at 0.2 MPa for 10 minutes to confirm that there was no leakage; the NH3 and H2 gas cylinders were connected to the mixing chamber, and the flow ratio (NH3 80 sccm, H2 20 sccm) was set by the mass flow controller MFC; the mixed gas outlet was connected to the pulse solenoid valve, and the on-off cycle (10 s on / 5 s off) was controlled by the controller PLC; vacuum was drawn to 10-2mbar, and N2 was slowly introduced to atmospheric pressure, which was repeated three times to exclude oxygen; the temperature was raised to 500°C at a rate of 5°C / min, and N2 (50 sccm) was passed through the whole process for protection; after reaching 500°C, it was stabilized for 30 minutes, N2 was turned off, and NH3 / H2 mixed gas was introduced in pulse mode, with pulse parameters of: 10 seconds (flow rate 100 sccm) for each gas supply, 5 seconds off, 30 minutes cycle 120 times; after the treatment was completed, the pulse gas supply was stopped, and N2 protection (100 sccm) was switched to, the temperature was lowered to 100°C at a rate of 5°C / min, and modified titanium niobate was obtained.

[0061] Comparative Example 3

[0062] The other conditions and Example 1 were the same, except that N doping was not performed in step S2, specifically:

[0063] S1: 24 grams of niobium pentachloride was dissolved in 400 mL of ethanol under nitrogen protection, after the solution was clear, 26 grams of titanium isopropoxide, 1 gram of VCl5, 3 grams of MoCl5, 0.8 grams of Al(NO3)3·9H2O and 0.6 grams of ZrOCl2·8H2O were added to form a mixed solution, the mixed solution was stirred and kept under 2.45 GHz microwave condition for 24 hours; then it was dried at room temperature for 5 days, kept at 50°C for 3 hours to remove ethanol; finally, it was calcined in air at 1000°C for 5 hours to obtain titanium niobate particles doped with niobium;

[0064] S2: The titanium niobate particles doped with niobium were evenly laid (thickness ≤2 mm to ensure gas penetration) in a high-temperature tube furnace quartz boat, the reaction tube was closed, filled with N2 to 0.2 MPa, and kept for 10 minutes to confirm no leakage; heated to 500°C at a rate of 5°C / min, protected by N2 (50 sccm) throughout the process; after reaching 500°C, it was stabilized for 30 minutes, N2 was turned off, and NH3 / H2 mixed gas (volume ratio 4:1) was introduced, with a flow rate of 100 sccm, for 30 minutes, then switched to N2 protection, with a flow rate of 100 sccm, and cooled to 100°C at a rate of 5°C / min to obtain modified titanium niobate.

[0065] Comparative Example 4

[0066] The other conditions and Example 1 were the same, except that Mo / Al / Zr was co-doped (i.e. without V doping), specifically:

[0067] S1: 24 grams of niobium pentachloride was dissolved in 400 mL of ethanol under nitrogen protection, after the solution was clear, 26 grams of titanium isopropoxide, 1 gram of VCl5, 3 grams of MoCl5, 0.8 grams of Al(NO3)3·9H2O and 0.6 grams of ZrOCl2·8H2O were added to form a mixed solution, the mixed solution was stirred and kept under 2.45 GHz microwave condition for 24 hours; then it was dried at room temperature for 5 days, kept at 50°C for 3 hours to remove ethanol; finally, it was calcined in air at 1000°C for 5 hours to obtain titanium niobate particles doped with niobium;

[0068] S2: The doped titanium niobate particles were evenly laid out (thickness ≤ 2 mm to ensure gas permeation) in a high-temperature tube furnace quartz boat, the reaction tube was closed, N2was filled to 0.2 MPa, and the pressure was maintained for 10 minutes to confirm that there was no leakage; NH3and H2gas cylinders were connected to the mixing chamber, and the flow ratio (NH380 sccm, H220 sccm) was set by the mass flow controller MFC; the mixed gas outlet was connected to the pulse solenoid valve, and the on-off cycle (10 s on / 5 s off) was controlled by the controller PLC; vacuum was drawn to 10-2mbar, N2was slowly introduced to normal pressure, and the process was repeated 3 times to exclude oxygen; the temperature was raised to 500°C at a rate of 5°C / min, and N2(50 sccm) was passed through the whole process for protection; after reaching 500°C, it was stabilized for 30 minutes, N2was turned off, and NH3 / H2mixed gas was introduced in pulse mode, with pulse parameters as follows: each time the gas was introduced for 10 seconds (flow rate 100 sccm), and then turned off for 5 seconds, 30 minutes of cycle for 120 times; after the treatment was completed, the pulse gas supply was stopped, and N2protection (100 sccm) was switched on, the temperature was lowered to 100°C at a rate of 5°C / min, and modified titanium niobate was obtained.

[0069] Comparative Example 5

[0070] The other conditions and Example 1 were the same, except that V / Al / Zr co-doping (i.e., without Mo doping) was used, and the specific conditions were as follows:

[0071] S1: 49 grams of niobium pentachloride was dissolved in 400 mL of ethanol under nitrogen protection, 26 grams of titanium isopropoxide, 1 gram of VCl5, 0.8 grams of Al(NO3)3·9H2O and 0.6 grams of ZrOCl2·8H2O were added to form a mixed solution, the mixed solution was stirred and kept under 2.45 GHz microwave conditions for 24 hours; then it was dried at room temperature for 5 days, and kept at 50°C for 3 hours to remove ethanol; finally, it was calcined in air at 1000°C for 5 hours to obtain doped titanium niobate particles;

[0072] S2: Evenly spread the doped titanium niobate particles (thickness ≤ 2 mm to ensure gas permeability) in a high-temperature tube furnace quartz boat, close the reaction tube, fill it with N2 to 0.2 MPa, and maintain the pressure for 10 minutes to confirm that there is no leakage; connect NH3 and H2 gas cylinders to the mixing chamber, and set the flow ratio (NH3 80 sccm, H2 20sccm); the mixed gas outlet is connected to a pulse solenoid valve, and the on-off cycle is controlled by a controller PLC (10s on / 5s off); vacuum is evacuated to 10-2mbar, and N2 is slowly introduced to normal pressure, and repeated 3 times to exclude oxygen; the temperature is raised to 500°C at a rate of 5°C / min, and N2 (50sccm) is passed through for protection throughout the process; after reaching 500°C, it is stabilized for 30 minutes, N2 is turned off, and a pulse mode is started to introduce NH3 / H2 mixed gas, and the pulse parameters are: ventilation for 10 seconds each time (flow rate 100sccm), off for 5 seconds, and 120 cycles in 30 minutes; after the treatment is completed, the pulse gas supply is stopped, switched to N2 protection (100sccm), and the temperature is lowered to 100°C at a rate of 5°C / min to obtain modified titanium niobate.

[0073] Application Example 1

[0074] The modified titanium niobate prepared in Example 1 was carbon-coated. The specific process was as follows: acetylene gas was introduced at a flow rate of 20 sccm under Ar atmosphere, and deposition was carried out at 700°C for 30 minutes to obtain a negative electrode material with a carbon layer thickness of about 5 nm; the negative electrode material (92 wt%), Super P (5 wt%), and CMC / SBR (3 wt%, CMC:SBR = 1:2) were dispersed in deionized water and coated on a copper foil (coating amount ~3 mg / cm 2 ), vacuum dried at 120℃ and rolled to an electrode density of 1.8g / cm 3 , and obtain titanium niobate pole piece; titanium niobate pole piece is used as negative electrode, and activated carbon is (specific surface area 2200m 2 / g) as the positive electrode, 1 M LiPF6in EC / EMC / FEC (3:5:2, v / v / v) as the electrolyte, and Al2O3-coated PE film as the separator, and they were assembled into 2032-type button capacitors in an argon glove box.

[0075] Application Example 2-9

[0076] The rest is the same as Application Example 1, except that the modified titanium niobate prepared in Examples 2-9 is used respectively.

[0077] Comparative Example Application Examples 1-5

[0078] The rest is the same as that of Application Example 1, except that the modified titanium niobate prepared in Comparative Examples 1-5 is used respectively.

[0079] The high rate capability, high temperature and low temperature cycle life of the capacitors of the above application examples and the comparative application examples were evaluated, and the results are shown in Tables 1-2 below.

[0080] Constant current charge-discharge test: The button capacitors were subjected to constant current charge-discharge test at 30 or 60°C using a Wuhan Lexin LX-PCBT-138-32D type program-controlled tester. The voltage range of the charge-discharge test was 1-3V, and the test rate was 1-20C. Generally, the assembled capacitors were allowed to stand at room temperature for 12h, and then subjected to 2 cycles of activation at 0.2C rate before other charge-discharge tests. The specific test conditions were as follows: the discharge capacity and charge-discharge efficiency performance test was carried out at 3.0V, the reference capacity was set to 200mA / g, and 1C corresponded to a current density of 200mA / g.

[0081] Table 1 is the high rate capability of the lithium capacitors of the application examples and the comparative application examples; Table 2 is the analysis of the life evaluation of the lithium ion capacitors of the application examples and the comparative application examples under high temperature and low temperature cycle use, and the specific results are as follows.

[0082] Table 1: High rate capability of lithium capacitors of the examples and the comparative examples

[0083]

[0084] Table 2: Cycle life evaluation of lithium ion capacitors of the examples and the comparative examples

[0085]

[0086]

[0087] As can be seen from Tables 1-2, the lithium ion capacitors assembled from the modified titanium niobate of the embodiments of the present application have the effect of maintaining the high rate capability of the lithium capacitors while improving the high temperature and low temperature cycle life to a high level. In the comparative application example 1, the titanium niobate prepared without adding Al / Zr stabilizer in the comparative example 1 is used, and it can be seen that the rate performance of the assembled lithium ion capacitors is slightly lower than that of the application examples, but the cycle use performance is poor, indicating that the Al / Zr stabilizer has a great influence on the cycle life of the capacitors. In the comparative example 2, N is not doped, and the high rate performance and cycle use effect of the lithium ion capacitors in the comparative application example 2 are poor. In the comparative example 3, the N doping is not carried out in a pulse manner, and the lithium ion in the comparative application example 3 corresponding thereto has a satisfactory low rate capability, but poor high rate capability and cycle life. In the comparative examples 4-5, V or Mo is not doped, and the lithium ion in the comparative application examples 4-5 corresponding thereto has slightly poor low / high rate capability and cycle life. Therefore, the modified titanium niobate using multi-element doping and N pulse doping has better performance, showing great advantages.

Claims

1. A method for preparing modified titanium niobate, comprising the following steps: S1: Under an inert atmosphere, niobium salt, titanium salt, vanadium salt, molybdenum salt, aluminum salt, and zirconium salt are dissolved in alcohol to form a mixed solution, and the mixed solution is then subjected to microwave treatment, drying, and calcination to obtain doped titanium niobate particles; the materials satisfy a Nb:Ti molar ratio of 1.95:1 to 2.05:1; S2: Pulse nitriding treatment is performed on the doped titanium niobate particles using a NH3 / H2 mixed gas to obtain modified titanium niobate.

2. The method for preparing modified titanium niobate according to claim 1, wherein the mass ratio of the total mass of the niobium salt and the titanium salt to the vanadium salt, the molybdenum salt, the aluminum salt, and the zirconium salt in step S1 is 75:(0.5-2.5):(1-4):(0.2-1):(0.2-1).

3. The method for preparing modified titanium niobate according to claim 2, wherein the mass ratio of the total mass of the niobium salt and the titanium salt to the vanadium salt, the molybdenum salt, the aluminum salt, and the zirconium salt in step S1 is 75:(0.5-1):(2-3):(0.5-1):(0.5-1).

4. The method for preparing modified titanium niobate according to claim 1, wherein in step S1, the niobium salt, vanadium salt, molybdenum salt, aluminum salt, and zirconium salt are selected from metal nitrates, halide salts, and hydrates thereof, and the titanium salt is an organic salt; preferably, the niobium salt is a nitrate or halide salt of niobium, the titanium salt is titanium isopropoxide or titanium n-propoxide, the vanadium salt is VCl5, the molybdenum salt is MoCl5, the aluminum salt is Al(NO3)3·9H2O, and the zirconium salt is ZrOCl2·8H2O; the alcohol is at least one of ethanol and propanol; and the volume ratio of the total mass of the niobium salt, titanium salt, vanadium salt, molybdenum salt, aluminum salt, and zirconium salt to the alcohol is (40-70) g:(300-500) mL.

5. The method for preparing modified titanium niobate according to claim 1, wherein the inert atmosphere in step S1 is argon or nitrogen; the microwave treatment is performed at 2-3 GHz for 20-40 hours; the drying is performed at room temperature for 4-7 days, followed by drying at 30-60°C for 2-5 hours; and the calcination is performed in air at 800-1200°C for 3-8 hours.

6. The preparation method according to claim 1, wherein in the NH3 / H2 mixed gas in step S2, the volume ratio of NH3 to H2 is 9:1-1:1, preferably 4:1-3:

1.

7. The preparation method according to claim 1, wherein the conditions of the pulse nitriding in step S2 are: temperature 300-600°C, preferably 400-550°C, time 10-30 min, pulse on 5-15 s / off 3-10 s, preferably 7-10 s on / 3-8 s off.

8. Application of modified titanium niobate in lithium ion capacitors, characterized in that: The modified titanium niobate prepared by the preparation method according to any one of claims 1 to 7 is used as a negative electrode material in a lithium ion capacitor after being coated with carbon.

9. The use according to claim 8, wherein the process conditions for carbon coating are: in an inert atmosphere, a carbon source gas is introduced, and deposition is performed at 600-800°C for 20 min-1 h; the carbon source gas is selected from at least one of C1-4 alkanes, C2-4 alkenes, and C2-4 alkynes.

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