Enhanced structural stability of Si electrode employing TiNi/Si pillars with <100> oriented Li diffusion pathway

Abstract

As the anode materials of Li-ion batteries, pillar-shaped TiNi/Si particles fabricated by employing electrochemical etching of (100) Si wafers and TiNi alloy coating, were investigated for their structural and electrochemical properties. The most suitable porous wafer for producing Si pillars was obtained at a current density of 2.5 mA/cm2 during etching. The deposited TiNi alloy film consisted of a crystallized austenitic (B2) phase capable of inducing phase transformation through annealing at 500°C. Particularly, by coating with the inactive materials, only the (100) plane of single crystalline Si was exposed during the initial charging process to restrict Li ion movement exclusively along the <100>Si direction. The TiNi/Si electrode exhibited a lower capacity compared to the Si electrode but demonstrated improved cycling performance. It showed a charge capacity of 1110 mAh/g at 0.1 C with an initial efficiency of 77 % and maintained a capacity retention of 49 % (543 mAh/g) up to 100 cycles. After the initial cycle, Si electrodes exposed to various lithium insertion directions exhibited severe structural damage such as cracking and particle pulverization, whereas TiNi/Si electrodes demonstrated enhanced structural stability due to surface coating and restricted reaction pathway. © 2024 Elsevier B.V.