Synthesis method of Ni < 2 + >-doped Na2Ti6O13 nanotube material and application of Ni < 2 + >-doped Na2Ti6O13 nanotube material in sodium ion battery

Abstract

The invention discloses a synthesis method of a Ni < 2 + >-doped Na2Ti6O13 nanotube material and application of the Ni < 2 + >-doped Na2Ti6O13 nanotube material in a sodium-ion battery, and belongs to the field of sodium-ion battery negative electrode materials. The Ni < 2 + >-doped Na2Ti6O13 nanotube material is synthesized by a hydrothermal method and an ultrasonic method, the material is applied to a sodium ion battery half-cell, the specific capacity and the rate capability of the material are obviously improved compared with those of an undoped Na2Ti6O13 nanotube, and compared with relatively small sodium ion embedding / removing voltage researched by predecessors, the material has the advantages that the specific capacity and the rate capability of the material are greatly improved, and the performance of the sodium ion battery half-cell is greatly improved. And correspondingly, the lithium ion battery has higher energy density when being applied to a total battery, and has a better market application prospect. The invention discloses a preparation method and application of the material.

Description

Technical Field

[0001] The present invention relates to Ni 2+ Doped Na2Ti6O 13 Hydrothermal / ultrasonic synthesis of nanotubes and their application in sodium-ion batteries. Specifically, the hydrothermal method was used to synthesize Na2Ti6O 13 The nanotubes were then doped with nickel ions using an ultrasonic method to obtain Ni 2+ Doped Na2Ti6O 13 , assembled into a half-cell with undoped Na2Ti6O 13 In comparison, the specific capacity and rate performance have been significantly improved. Background Art

[0002] In recent decades, lithium-ion batteries have been widely used in portable electronic products and electric vehicles, but the scarce lithium resources cannot meet the growing demand for lithium-ion batteries. Sodium-ion batteries and lithium-ion batteries have similar working principles, and the physical and chemical properties of lithium and sodium are also similar. The content of sodium in the earth's crust reaches 2.64%, which is twice that of lithium. + Relative Li + The radius is much larger (respectively and ), so the reaction kinetics are very poor, and the large relative atomic mass of sodium leads to its low specific capacity. Therefore, seeking electrode materials with high specific capacity, excellent rate performance, safety, stability and economy is an urgent problem to be solved in the development of sodium-ion batteries. Since 2010, titanium-based materials have received widespread attention in the field of sodium-ion battery negative electrodes due to their low toxicity, low cost and abundant mineral resources. Na2Ti6O 13 Due to its special three-dimensional tunnel structure, sodium ions are more easily stored and transported in it while maintaining structural stability. 13 Can only store 1 mol of Na + The theoretical specific capacity is only 45 mAh g -1 In order to improve the electrochemical performance of sodium titanate, on the one hand, nanostructures such as nanoparticles, nanosheets, nanotubes and nanorods were studied, and hydrothermal and solid-phase methods were used to synthesize Na2Ti6O with large interlayer spacing. 13 Nanorods, at 20 mAg -1 and 500mA g -1 After 100 cycles at a current density of 2.34 Å / min, the specific capacity remained at 131.1 and 96.7 mAh g -1(LM Zhu et al. Journal of Alloys and Compounds, 2022, 906); On the other hand, the ideal performance is achieved through the synergistic effect of the composite material, by preparing layered Na2Ti3O7 and tunnel-like Na2Ti6O 13 The mixed structure of sodium titanate at 20 mA g -1 At a current density of 1.34 W, the specific capacity is 122 mAh g -1 , while at 2000mA g -1 After 4000 cycles, the specific capacity is 19.5 mAh g -1 (C.Wu et.al.Advanced Science, 2018, 5); In addition, carbon doping is also a good approach. The introduction of carbon not only increases the conductivity but also provides a stable elastic buffer layer for sodium titanate materials. Supercritical methanol is used to produce layered Na2Ti3O7 and tunnel-shaped Na2Ti6O 13 (NTO) composite at 100 mAh g -1 The specific capacity is about 80 mAh g -1 , at 1000mA g -1 After 650 cycles, the specific capacity dropped to 30 mAh g -1 (J.Hwang et.al.Journal ofSupercriticalFluids,2019,148,116-129). 2+ The effect of doping sodium titanate to replace Na+ on its electrochemical performance has not been studied so far. To this end, we first synthesized Na2Ti6O 13 The Na + Ion exchange was performed to obtain different Ni 2+ When Ni 2+ When the doping amount reaches 40wt% (NNTONT-40), the charge-discharge capacity is close to the optimal value: at 1C, the charge-discharge capacity after 100 cycles is 130.4mAh g -1 (In this article, 1C = 177mA g -1 ), compared with the undoped NTONT (92.2 mAh g -1 ) and after 1000 cycles, the charge-discharge capacity increased by 76% even at a high rate (10C). Summary of the invention

[0003] The object of the present invention is to provide Ni 2+ Doped Na2Ti6O13 Hydrothermal / ultrasonic synthesis method of nanotubes and their application in sodium ion batteries. The technical solution of the present invention is:

[0004] (1) A method for synthesizing Na2Ti6O 13 Hydrothermal method for nanotubes: TiO2 was added to NaOH solution, stirred thoroughly and transferred to an autoclave, heated in an oven for 24 hours, centrifuged, washed and dried, and then placed in a tube furnace for annealing under argon atmosphere to obtain Na2Ti6O 13 Nanotubes (NTONT);

[0005] (2) A synthetic Ni 2+ Doped Na2Ti6O 13 Ultrasonic method for nanotubes: Based on step (1), the product NTONT of step (1) is used to perform ion exchange in a metal salt solution with different nickel contents using an ultrasonic method, followed by centrifugation and drying, and then annealing at the same temperature and time in an argon atmosphere to obtain fully dried NTONT doped with different nickel contents.

[0006] (3) Electrochemical performance test: The assembled batteries were subjected to cyclic voltammetry (CV) measurements on a CHI 760E electrochemical workstation (Shanghai Chenhua Instrument Co., Ltd.). The charge and discharge cycle performance at different rates was tested on a Xinwei battery test system (Shenzhen, China). The voltage range of this study was 0.01-2.5V.

[0007] NTONT and Ni of the present invention 2+ The doped NNTONT series was determined by XRD, Ni 2+ The doping of Ni 2+ As the doping amount increases, the TiO2 anatase phase is gradually formed ( Figure 1 ). TEM images show that these materials are tubular structures with a pore size of about 5nm, a wall thickness of about 2-3nm, and a length of 2-5um ( Figure 2 (ac)), this tubular structure has a larger specific surface area and can also shorten the transmission distance of sodium ions, thereby improving its electrochemical performance. The EDX mapping shows the uniform distribution of Na, Ti, O, and Ni elements, confirming the successful doping of Ni elements ( Figure 2 (dj)).

[0008] Figure 3 XPS shows Ni 2+ Successfully doped into NTONT, Na in NNTONT-40 + 、Ti 4+ , O 2-The valence band increase of NTONT is basically consistent, indicating that Ni 2+ The doping does not affect the valence change of NTONT elements.

[0009] In the constant current charge and discharge curve (GCD) curve ( Figure 4 (a) Among the various nickel-doped materials, after 100 cycles at a current density of 1C, the discharge capacity is improved to varying degrees compared with that of the undoped NTONT. In particular, NNTONT-40 is as high as 130.4 mAh g -1 , than NTONT (92.2mAh g -1 ) increased by 41%, and the Coulombic efficiency reached almost 100%. Figure 4 (b) is the corresponding initial charge and discharge curve at 1C. Figure 4 As shown in (c), NNTONT-40 provides 245 (0.2C), 172 (0.4C), 158 (0.6C), 148 (0.8C), 134 (1C), 120 (2C), 96 (5C), 77 (10C), 67 (15C), and 61.6 (20C) mAh g at different rates. -1 Whether at low rate (0.2C) or high rate (20C, about 3500mA g -1 ) all demonstrate its superior electrochemical performance over NTONT. Figure 4 (d) is a long-term test at 10C. After 1000 cycles, the specific capacity of NNTONT-40 is 90 mAh g -1 , compared with NTONT (51mAh g -1 ) increased by 75%, and the Coulomb efficiency was close to 100%. It can be considered that under high current density, NNTONT-40 still has a great advantage in long cycle.

[0010] The preparation method of the invention is simple, the raw materials are readily available, the performance is excellent and it is suitable for industrial application. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 It is the XRD (X-ray diffraction) diagram of the NTONT, NNTONT-20, NNTONT-40 and NNTONT-60 materials of the present invention.

[0012] Figure 2 Morphological characterization: (a) TEM (transmission electron microscopy) image of NNTONT-40; (bc) HRTEM (high-resolution transmission electron microscopy) image and selected NNTONT-40 FFT (fast Fourier transform) pattern; (d) SEM image of local NNTONT-40 particles; (ej) elemental mapping images.

[0013] Figure 3 XPS (X-ray photoelectron spectroscopy) analysis: (a) full spectra of NTONT and NNTONT-40; (be) high-resolution spectra of Ni 2p, Na 1s, O 1s and Ti 2p (NNTONT-40); (fh) high-resolution spectra of Na 1s, O 1s and Ti 2p (NTONT).

[0014] Figure 4 Electrochemical properties of NTONT, NNTONT-20, NNTONT-40, and NNTONT-60: (a) 1C cycle performance; (b) initial charge and discharge curves at 1C; (c) rate performance from 0.2C to 20C; (d) long cycle performance at 10C. DETAILED DESCRIPTION

[0015] Implementation case 1.Na2Ti6O 13 Synthesis and preparation of nanotubes (NTONT)

[0016] (1) Preparation steps: 0.8 g TiO2 was added to 40 ml 10 M NaOH solution, stirred for about 3 h, and transferred to a 50 ml Teflon-lined stainless steel autoclave. After the autoclave was kept in an oven at 130 ° C for 24 h, the white precipitate was extracted, centrifuged, and washed with ethanol and deionized water for about 5 times to make its pH value between 8 and 9. The obtained white solid was dried in an oven at 120 ° C overnight to remove the moisture. Finally, it was ground into powder and heated at 500 ° C in argon in a tubular furnace for 5 h to obtain Na2Ti6O 13 Nanotubes (NTONT).

[0017] (2) Assemble the battery and test the battery performance: A mixture of active material: acetylene black: CMC = 7:2:1 by mass ratio was fully ground with deionized water as solvent, coated on copper foil and vacuum dried to obtain a working electrode. The counter electrode was a sodium sheet, and the electrolyte was a 1.0M NaClO4 solution dissolved in EC (ethylene carbonate) : PC (propylene carbonate) = 1:1 (volume ratio), and 5wt% FEC (fluoroethylene carbonate) was added as an additive. Glass fiber (GF / F) was used as a separator in a glove box to assemble a 2032 button battery.

[0018] Implementation case 2. 20% Ni 2+ Doped Na2Ti6O 13 Synthesis and preparation of nanotubes (NNTONT-20)

[0019] (1) Preparation steps: First prepare 10 mg ml -1Ni(NO3)2·6H2O solution: Weigh 500 mg Ni(NO3)2·6H2O solid, add it into a beaker containing 50 ml deionized water, and sonicate for ten minutes to fully dissolve it for later use; take the NTONT of Case 1 and dry it at 120°C, take 50 mg into a centrifuge tube, add 1 ml Ni(NO3)2·6H2O (10 mg ml -1 ) solution. Ultrasonic treatment for 40 minutes, centrifugal separation, deionized water washing several times, the product was placed in a 60 ° C vacuum drying oven overnight. The product was ground into powder, placed in a tube furnace, and kept warm in argon at 500 ° C for 5 hours to finally obtain NNTONT-20 (20 is m Ni(NO3)2·6H2O / m NTO mass percentage);

[0020] (2) Assembling batteries and testing battery performance: as in implementation case 1-(2).

[0021] Implementation case 3. 40% Ni 2+ Doped Na2Ti6O 13 Synthesis and preparation of nanotubes (NNTONT-40)

[0022] (1) Preparation steps: The preparation steps were the same as those in Case 2-(1), except that 10 mg / ml -1 The amount of Ni(NO3)2·6H2O is 2ml, and finally NNTONT-40 (40 is m Ni(NO3)2·6H2O / m NIO mass percentage);

[0023] (2) Assembling batteries and testing battery performance: as in implementation case 1-(2).

[0024] Example 4. 60wt%Ni 2+ Doped Na2Ti6O 13 Synthesis and Preparation of Nanotubes (NNTONT-60)

[0025] (1) Preparation steps: The steps were the same as those in Case 2-(1), except that 10 mg ml -1 The amount of Ni(NO3)2·6H2O is 3ml, and finally NNTONT-60 (60 is m Ni(NO3)2·6H2O / m NTO mass percentage).

[0026] (2) Assembling batteries and testing battery performance: as in implementation case 1-(2).

Claims

1. A Ni 2+ Doped Na2Ti6O 13 The synthesis method of nanotube (NNTONT) material is characterized by: First, a certain amount of TiO2 was added to 10M NaOH solution, stirred, and then kept in an oven at 130℃ for 24h using the hydrothermal method. After centrifugal washing, Na2Ti6O 13 After drying, 1 ml, 2 ml and 3 ml Ni(NO3)2·6H2O (10 mg ml -1 ) solution. Ultrasonic treatment for 40 minutes, centrifugal separation, deionized water washing several times, the product was placed in a 60 ° C vacuum drying oven overnight. The product was ground into powder, placed in a tube furnace, and kept warm at 500 ° C in argon for 5 hours to finally obtain NNTONT-20, NNTONT-40 and NNTONT-60 as pale yellow solids, of which 20, 40, 60 are m Ni(NO3)2·6H2O / m NTO mass percentage.

2. The synthesis method according to claim 1, characterized in that: The synthesis is divided into two steps. First, pure Na2Ti6O is synthesized by hydrothermal treatment of TiO2 in 10M NaOH and then annealing. 13 The nanotubes were then annealed after ultrasonic ion exchange in a nickel nitrate solution to obtain NNTONT.

3. The synthesis method according to claim 1 is characterized in that: The nickel source was Ni(NO3)2·6H2O, and the solution concentration was 10 mg ml -1 , just the amount added is different, the added amount is 1ml, 2ml and 3ml to get NNTONT-20, NNTONT-40 and NNTONT-60 respectively.

4. The synthesis method according to claim 1 is characterized in that: During ion exchange, the ultrasonic time was 40 min, and after centrifugation, deionized water was added and washed 5 times.

5. The synthesis method according to claim 1 is characterized in that: All samples were dried after washing and annealed at 500 °C for 5 h in a tube furnace with Ar.

6. The NNTONT-40 material according to claim 1 is characterized in that: As the negative electrode material of sodium ion battery, the charge and discharge capacity after 100 cycles at 1C condition is 130.4 mAh g -1 .

7. The NNTONT material according to claim 1 is characterized in that: All kinds of materials are flower-shaped, spherical and mesh-shaped structures woven by nanotubes with a pore diameter of about 5nm, a wall thickness of about 2-3nm and a length of 2-5um.

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