Preparation And Lithium Storage Properties Of Mesoporous Hollow Carbon Spheres @ Tin Cobalt Hydroxide And Tungsten Trioxide Nanocomposites

With the development of The Times,electric vehicles and portable electronic products have produced a huge demand for new energy,lithium-ion battery（LIBs）has the advantages of high energy density,long cycle life and low cost,can meet these needs.Due to the low theoretical specific capacity of the traditional anode material graphite,it is difficult to meet the development requirements of high-performance lithium-ion batteries.It is urgent to research and develop new high-performance anode materials to replace the traditional anode materials.Compared with traditional commercial anode materials,metal hydroxide and metal oxide have higher capacity and lower processing cost,and are environmentally friendly.They are considered as one of the excellent candidates to replace graphite anode materials.However,these materials have low electrical conductivity,serious material volume change and unstable structure.In the range of metal hydroxide and metal oxide,cobalt tin hydroxide（CoSn（OH）₆）and tungsten trioxide（WO₃）are selected as the research objects.CoSn（OH）₆ cube@mesoporous hollow carbon spheres（CoSn（OH）₆ Cube@CNC）and WO₃@mesoporous hollow carbon nanospheres（WO₃@CNC）were obtained by template method,solution soaking and filling and solid phase reaction.Through the design of nanostructure and the packaging strategy of mesoporous hollow carbon ball,the performance of lithium ion batteries of stannous cobalt hydroxide and tungsten oxide was improved.The main research contents and conclusions of this paper are as follows:（1）Mesoporous hollow carbon spheres were synthesized by TPOS polymerization and RF resin surface doping.CoSn（OH）₆ Cube@CNC composite material was synthesized by in-situ synthesis of CoSn（OH）₆ nanocube in mesoporous hollow carbon sphere by soaking in solution and filling cobalt nitrate with the solid phase reaction between cobalt nitrate and sodium stannate under the aid of vacuum and melting.The mesoporous carbon hollow sphere has a diameter of about 200 nm and a wall thickness of about 50 nm.One to two independent CoSn（OH）₆-nanometer cubes with a side length of 50 mn are encapsulated inside the mesoporous carbon hollow sphere.Thermogravimetric and energy spectrum analysis showed that CoSn（OH）₆ content was55.34%.As A negative electrode of lithium ion battery,CoSn（OH）₆ Cube@CNC composite material has excellent cyclic performance,showing a specific discharge capacity of 1021 mAh·g^-1 after 400 cycles at 1 A·g^-1 current density.At the current density of 5 A·g^-1,the discharge capacity of 511 mAh·g^-1 can still be obtained after 500cycles;The specific discharge capacity of 626 mAh·g^-1 under the current of 10 A·g^-1 is outstanding,and the specific discharge capacity of 617.3 mah·g^-1 can still be restored to the original specific capacity after returning from 10 A·g^-1 to 5,2,1,0.5,0.2,0.1 A·g^-1.;The electrochemical kinetic performance is good,the diffusion coefficient of lithium ion is between 10^-10.72-10^-7.95 cm²·s^-1,The electrochemical impedance spectroscopy test shows that the composite structure has excellent transport properties of lithium ion,and the R_ct is only 80.4Ωafter 1 charge-discharge cycle.The effect of pseudocapacitance is strong,and the capacitance contribution rate reaches 83.64%at the scanning rate of 1.0m V·s^-1.The excellent lithium storage performance is mainly attributed to the small size of the cube CoSn（OH）₆ shortening the ion transport path and improving the chemical activity.On the other hand,it is attributed to the improvement of the conductivity and structural stability of the composite materials by the mesoporous hollow carbon nanospheres.（2）Mesoporous hollow carbon nanospheres were prepared by doping RF resin polymerization on the surface of silica spheres,carbonizing and etching.Na₂WO₄ was introduced into CNC by solution soaking.WO₃@CNC composite materials were synthesized by Na₂WO₄@CNC solid phase reaction under vacuum heating.The mesoporous hollow carbon sphere is about 200-300 nm in diameter,and the inner cavity is about 150 nm in diameter.The mesoporous hollow carbon sphere is packed with WO₃nanowires clustered together,with the length of about 120 nm and the thickness of about2 nm nanowires.The ratio of WO₃ was 82.13%.As the anode material of lithium ion battery,its performance is relatively excellent.After 500 cycles of 1 A·g^-1,it can still show the specific discharge capacity of 779 mAh·g^-1,and after 2000 cycles of 5 A·g^-1,it can still show the specific discharge capacity of 344 mAh·g^-1.The ratio performance of WO₃@CNC is higher than that of pure WO₃ and mesoporous hollow carbon nanospheres.The ionic diffusion coefficient is high,about 10^-10.6-10^-8.0 cm²·s^-1.The impedance is low,and the R_ct is 26.87Ωafter one charge-discharge cycle.WO₃@CNC Excellent lithium-ion battery performance is mainly due to this unique carbon frame structure as a conductive medium,improve the conductivity,promote the contact between electrolyte and WO₃,use mesoporous hollow carbon balls as containers,prevent WO₃ aggregation,and smaller WO₃ nanowires,thus able to maintain WO₃@CNC excellent electrochemical performance.