Tin-Based Composites With Graphene As Anodes For Sodium Ion Batteries

New energy, which is presented by wind power and solar energy, is attracting more and more attention because of its green and renewable properties. But its discontinuation and instability inhibits the smooth feed into the grid. Large-scale energy storage system can be a hopeful solution.Sodium-ion batteries have a lot of advantages, such as high energy density, environmently friendly nature, unlimited resources and low cost. These advantages make sodium-ion batteries potential for large-scale applications.This work focuses on the anodes. Graphite, a widely used anode for lithium-ion battery, does not work in a sodium-ion one. And other carbon materials seldom show capacities more than 300 mAh g-1. Alloy materials earn great superiority. Among these alloys, tin delivers a capacity as high as 847 mAh g-1. The nontoxicity and low potential properties make tin promising. We adopt nanosized structure and graphene as a solution to the common problem of volume expansion.This work will demonstrate solvothermal synthesis of composites of SnO2/rGO and SnS2/rGO. Furthermore, a series of characterization and electrochemical performance tests will go through. For SnO2/rGO nanohybrid, a capacity of 430 mAh g-1 and a retention rate of 47% are achieved under a low current and a large current of 1600 mA g-1 respectively. SnS2/rGO is even more superior.649 mAh g-1 is obtained at 100 mA g-1. After 300 cycles at 200 mA g-1, a charge capacity of 509 mAh g-1 is kept, corresponding to capacity retention of ～86%. The hybrid can still exhibit a charge capacity of 360 mAh g-1 after 500 cycles at 400 mA g-1. In the rate performance, SnS2/rGO exhibits 337 mAh g-1 under a rate of 28 C.Besides, EIS test is performed. The results show that the composite has smaller resistance than the bare materials. And the resistance of composite stays stable while bare materials increase with the growth of cycle number. Ex situ XPS and TEM results show that a tnin SEI layer forms after several cycles. And the SEI layer plays a significant role in the good performance of the composite.