Study Of Tin-based Alloy Negative Materials For Lithium-ion Batteries

Lithium-ion battery with high voltage and energy density, good safety, light weight, small self-discharge, long cycle life, no memory effect and non-pollution has been extensively used in electric devices. Lithium-ion battery materials has also been focused on. Carbon materials has been used in commercial lithium-ion batteries, but low capacity compared to metal lithium and lithium alloys negative materials and poor safety can not satisfy the requirement of electric vehicles. Tin-based alloy materials because of its high specific capacity, good conductivity and friendship with environment have been considered a possible alternative to carbon. However, the Sn alloys present poor cycle life because of large volume expansion during charge-discharge process because of reversible Li ion insertion and desertion. In order to overcome the problem, we need to explore novel tin-based materials, at the same time, it is necessary to control the morphology of tin-based materials, structure, composition, synthesis conditions and charge-discharge conditions to restrain the volume expansion of alloy materials during cycling and improve cycle life and safety.In this paper, Sn-Cu, Sn-Ag alloys have been synthesized by mechanical alloying method, and their electrochemical properties and reaction mechanism during cycling have been discussed. XRD, SEM, CV and EIS have been used to determine the structure, morphology, electrochemical properties and cycle performance of Sn-based alloys negative materials in Lithium-ion batteries.Experimental results show that Tin-based （Sn-Cu, Sn-Ag） alloys used as the anodic materials in lithium-ion batteries have a large irreversible capacity loss at the first cycle because of the decomposition of electrolyte and incomplete desertion of CuLi₂Sn during discharge process. Sn-Cu series alloys have been studied on Charper III. It found that Cu₆Sn₅-10%Cu composite is composed of Cu₆Sn₅, Cu₃Sn and CuSn alloys. SEM results show that the particle is distributed evenly and the size of particles are 1-2μm. This composite presents excellent cycle life, its initial discharge capacity was around 300 mAh·g^-1, after 100 cycles, the discharge capacity was remained over 200 mAh·g^-1. Experimental results show that the cycling stability of alloy electrode could be improved by controlling the potential range of charge-discharge processes. Heat treatment at low temperatute could improve the electrochemical properties, but the effect is not so good.Sn-Ag alloys have been synthesized and presented on Chapter IV. Ag₂Sn₃Zn sample shows the excellent performance. Its discharge capacity remains over 500 mAh·g^-1 after 100 cycles.