SYNTHESIS AND ELECTROCHEMICAL PROPERTIES OF Sn0.35-0.5xCo0.35-0.5xZnxC0.30 COMPOSITE

A series of Sn0.35-0.5xCo0.35-0.5xZnxC0.30(x=0, 0.05, 0.10, 0.15, 0.20) composites as novel anode materials used in lithium-ion batteries were synthesized from Sn, Co, Zn element powders and carbon black using solid-state sintering and ball milling, and the influences of Zn content on the structures and the electrochemical properties of those materials were analyzed. XRD data of the sintered powders illustrated that minor amount phase CoSn2 is formed firstly in the CoSn matrix phase with increasing content of Zn. Then, a little amounts of Co3Sn2, Zn and Sn are also precipitated. Most of Zn atoms dissolve into CoSn phase and lead to lattice distortion of the matrix. As a result, the lattice parameters a, c and unit cell volume V of CoSn phase are all reduced first and then enlarged with increasing content of Zn. Electrochemical analysis showed that the initial discharge capacity and initial charge-discharge efficiency are both improved first and then tended to stablility with increasing content of Zn, and as x=0.15, reach the maximums, 343 mA-h/g and 73.8%, respectively. The reversible capacity remains above 87.6% of the initial discharge capacity after 25 charge-discharge cycles. The lattice distortion caused by Zn solution and the formation of multiphase are beneficial for accelerating the diffusion of Li+ and enhancing the stability of structure, so the electrochemical properties are improved significantly. The sintered powder Sn0.275Co0.275Zn0.15C0.30 was milled for different times (t=10, 20 and 30 h), and it is shown that the refinements of grains and particles improved discharge capacity obviously, however, charge-discharge efficiency and cycle performance changed little.