Studies On The Electrochemical Performance Of The Tin-copper Alloys Negative Materials

Tin is a potential anodic material used for lithium ions batteries for its hightheoretical capacity of 990 mAh/g. However, during charge and discharge process, thevolume-expanding ratio of the tin anode is too large to produce good cycling performanceduring charge-discharge test. And the sample is to become the powdered alloy afterlong-term tested. To improve the electrochemical performance of the tin alloy, thisdissertation is planning to prepare the Cu and Sn alloys by adopting the methods of theactivity/non-activity composite alloy. The research work included the several aspectsblow.Firstly, by sintered the tin-copper films eleetroplated from the alkaline solutions atdifferent temperatures, several kinds of tin-copper alloys were prepared XRD, TG-DTA,Electrochemical impedance, AFM, SEM and charge-discharge test were employed tostudy the effect of preparation condition on the electrochemical performance of thesamples. The research results showed that the coating behavior is optimum when thesodium stannate concentration is 60 g/L. The as-prepared sample shows the bestelectrochemical properties in all samples. The tin-copper alloy sintered at 280℃with amonoclinic structure of Cu₆Sn₅ (Space group: C2/c) exhibits a large crystal and the stablestructure during charge-discharge cycles. The sample exhibits a discharge capacity of 503mAh/g in the 1st cycle and the capacity fading rate is 33 % in 40 cycles in the voltageregion from 0.03 to 2.0 V.Secondly, the tin films coated on the copper film sintered at 380℃in the mixingatmosphere of the 4:24 ratio of airflow and argon flow. The sintered product is composedof the tin-copper alloy coated with the composite oxide film. The first cycle dischargecapacity of this sample is 1451 mAh/g. After 40 cycles, its capacity is higher than 600mAh/g.Thirdly, a SnCuNiCo alloy sample was firstly prepared by sintered the as-preparedsample consisted of the tin-copper alloy coated with nickel-cobalt alloy. Thecharge-discharge results showed that the best-sintered temperature is 230℃. The firstcycle discharge capacity of the sample is 408 mAh/g and its charge-discharge efficiency at the 1st cycle is 80%, which result shows that the doping reduced the capacity loss. Theoptimization synthesis condition is the 6:1 mass ratio between tin and nickel-cobalt.