High Performance Anodes For Sodium-ion Batteries

As the increase of population and the improvement of life quality, so as the amount of energy we need increase. We have entered the mobile internet era, thus more and more recharge batteries are in demand. The launch of Tesla pure electric vehicle detonated electric vehicle industry which drew many car companies` attention to fabricate pure electric vehicles. Moreover, the worsening environment pushes us to optimize our energy resource mix. Lithium-ion batteries are most used as secondary batteries nowadays. Because of its high voltage, energy density and good cycle performance, it is considered to be the power of pure electric vehicle. However, the quantity of lithium resource is quite low which cannot meet the requirement of the market. The chemical properties of lithium and sodium are similar since they both belong to the first main group. If proper cathodes and anodes of sodium-ion batteries are found, sodium-ion batteries can serve as chemical energy storage type since sodium resource are abundant. In this paper, we focused on fabrication of high performance anodes for sodium-ion batteries.Antimony is considered to be a promising anode for sodium-ion batteries because of its high specific capacity(660mAh g-1). During charge and discharge cycles, it suffers large volume effect which will cause the loss of capacity. By decreasing the particle-size and carbon-coating, the capacity loss of antimony can be prevented. In this paper, we use chitosan as carbon source and particle-size control agent to fabricate the carbon-coating Sb composite. Due to these organic groups(-OH,-C=O,-N-H etc.), chitosan has strong interaction with positive ions. During the process, chitosan will self-wrap on the surface of antimony oxide particles preventing them grow. The obtained Sb/CCHI composite exhibited high capacity, good cycle performance and excellent rate performance. At the current of 500 mA g-1, it shows reversible capacity of 402 mAh g-1 at first cycle and maintains 94% capacity after 100 cycles. Even at current of 32 A g-1, it still shows reversible capacity of 138 mAh g-1.Phosphorus has highest capacity among anodes for sodium-ion batteries. However, its disadvantages(such as low electric conductivity, enormous volume effect and hard to process) make it hard to use. Since the phosphorus source is abundant, the cost will decease if proper phosphides are found suitable as anodes for sodium-ion batteries. By researching literature and studious trials, we succeed in synthesis CuP2/C composite and test it as anode for sodium-ion batteries for the first time. CuP2/C composite maintains reversible capacity of 600.2mAh g-1 after 10 cycles at the current of 150 mA g-1, showing it a promising low cost anode material.