Effects of surface morphological and micro-structural change on the electrochemical properties of Sn-based anode for lithium-ion battery

Abstract

Sn has received much attention as an alternative anode material for lithium ion batteries due primarily to its high theoretical capacity (994 mAh g-1). Sn anodes, however, have exhibited poor cyclability due to the crumbling by severe volume expansion (up to about 260%) that occurs during alloying of $Li^{+}$ with Sn. In this study, Sn based anodes have been designed to improve their charge/discharge performances by adopting the two strategies; i) Synthesis of porous Sn anode with a multi-layered structure by electrodeposition, The electrochemical performance of a Sn electrode synthesized on Cu foil by electrodeposition in a pyrophosphate-based bath was examined by modifying its morphology by controlling the cathodic current density. As the cathode current density increased, the morphology of the electrodeposit changed from a smooth-compact structure to a microscopically multi-layered structure with open spaces between adjacent layers. The porosity of the multi-layered Sn electrode was measured to be more than 60% of its volume. The cycle performance and coulombic efficiency of the multi-layered Sn electrode were higher than those of the smooth Sn electrode, due primarily to the buffering effects of the open spaces between the layers against the volume expansion of the Sn anode during cycling. ii) Synthesis of Sn anode by electrodepositing Sn on a porous Cu foam substrate, The effects of Cu substrate morphology and post electrodeposition on the porosity, adhesion as well as the mechanical strength of Cu foam electrodeposits are examined. The porosity of Cu foam is enhanced by changing the morphology of the Cu substrate from smooth to nodular because $H_2$ bubbles are split into small bubbles by the nodules. In addition, the adhesive properties of Cu foam deposited on the nodular Cu foil are improved by the mechanical interlocking effects of the nodules. As a result of post electrodeposition treatment, the mechanical strength of the Cu foam is significa...