Preparation And Lithium Ion Batteries Performance Of CuO/a-Si Anode Materials

With the advent of the information age,the fields of portable communication devices,mobile devices,and electric vehicles have developed rapidly,and the demand for energy storage devices has increased dramatically.Since the advent of lithium ion batteries,it has rapidly developed into the most ideal energy storage and energy supply system.The negative electrode material is a important part of the lithium storage of the lithium ion battery,and the graphite negative electrode material is currently the most widely used commercial negative electrode material.,which has good cycle stability,and has huge reserves,low cost,and simple preparation,but its theoretical specific capacity is low(372 m Ah·g^-1),the current use is close to the limit value.Therefore,the development of new anode materials with high energy density,cycle stability and environmental friendly preparation methodto replace traditional graphite anode materials has become the current research focus.As a representative of metal oxidation,CuO has the advantages of high theoretical specific capacity(674 m Ah·g^-1),abundant resources,simple preparation,and low production cost,but it has the problems of volume expansion and low conductivity.The nanowire structure has large specific surface area,which can increase the insertion site of lithium ions,increase the capacity,and can effectively shorten the ion transmission path and improve the material conductivity.In addition,Si-based negative electrode material has very high theoretical specific capacity.Combining it with CuO nanowires can greatly increase the capacity and improve the cycle performance of the battery.In this paper,copper oxide nanowires are prepared by anodizing method followed with annealing,which effectively alleviates the inherent volume change of metal oxides and improves cycle stability and capacity.Then,copper oxide nanowires are coated with amorphous silicon by PECVD deposition and magnetron sputtering to prepare a CuO/a-Si core-shell structure.The structural advantages of nanowires and the high specific capacity of silicon materials are used to improve the performance of lithium ion battery.The specific work is as follows:1.Copper oxide nanowires are prepared by anodizing of copper foil and annealing at 200°C in air.The effects of anodizing time on the structure and lithium battery performance of copper oxide nanowires under constant voltage were studied.The results show that as the deposition time increases,the size and density of the nanowires increase,but too long the deposition time will cause the nanowire size to be too large,the porosity will decrease.The optimal deposition time is 1000s.The prepared copper oxide nanowires are assembled into a half-batteries.The batteries have high reversible specific capacity and stable cycle performance.After 500 cycles at 1C rate,the specific capacity is 607.6 m Ah·g^-1,and the average specific capacity for 10 cycles at 5C rate is 427.7m Ah·g^-1.It has good rate performance and can be used in fast charging.2.Two methods of PECVD and magnetron sputtering are used to coat amorphous silicon on the copper oxide nanowires.The morphology of the CuO/a-Si core-shell structure prepared by the two methods and its performance as anode materials in lithium ion batteries were studied.It is found that the amorphous silicon coated by PECVD will damage the copper oxide nanowires.A large amount of hydrogen in the experimental gas will reduce the copper oxide to metallic copper particles.The copper particles deposited on the surface of the nanowires are not conducive to the uniformity of silicon Cladding.The amorphous silicon coated by magnetron sputtering has a more uniform morphology,forming an interconnected structure,which has better structural stability and electrochemical performance.At a rate of 0.1C,the first cycle's specific discharge capacity of the battery is 2524 m Ah·g^-1,and the specific discharge capacity is 1502 m Ah·g^-1 when the cycle is 200 cycles;at the rate of 0.5C,the specific discharge capacity of the first cycle is 2176 m Ah·g^-1,the specific discharge capacity is 748 m Ah·g^-1when the cycle is 200 cycles.It shows that the magnetron sputtering deposition process has better controllability,the prepared material has a more uniform and complete morphology,and has a better adhesion with the substrate.3.Magnetron sputtering deposition method is used to add a carbon layer on the surface of the CuO nanowires and the CuO/a-Si core-shell structure to improve the electrical conductivity of them,thereby to enhance their capacity and electrochemical performance.The results show that coating the carbon layer on the copper oxide nanowires can significantly increase the specific capacity,but the cycle stability is reduced.Adding a carbon layer in the middle or outermost layer of CuO/a-Si will have different effects.The outer layer of coated carbon can steadily increase the capacity and cycle performance of the material.Adding a carbon layer in between CuO and the a-Si does not increase the capacity,but the cycle is more stable.It demonstrates the structural stabilizing effect of carbon on CuO/a-Si materials and the improvement of its performance.