Unraveling the impact of CNT on electrode expansion in silicon-based lithium-ion batteries

Abstract

A high-capacity silicon-based anode has been used in commercial lithium-ion batteries as a form of an addition to an existing graphite electrode for the realization of high energy density. However, under industrial conditions using high-density electrodes (>1.6 g cc(-1), low electrode porosity), the electrode expansion becomes more severe, which engenders the decrease in energy density and safety issues. Carbon nanotubes (CNTs) have emerged as promising additives due to their outstanding electrical conductivity and mechanical strength. Despite their potential, the chemo-mechanical and electrochemical roles of CNTs in silicon-based anodes are not fully understood. Herein, we identify the mechanisms by which CNTs enhance silicon-based anodes with constructive comparison of commercial conductive agents. Our results show that CNTs alleviate strain-induced interfacial reactions and control the growth of the solid electrolyte interphase (SEI) layer during cycling. CNTs provide mechanical reinforcement, reducing particle-level cracking and enhancing electron pathways, which lowers surface tension and decelerates crack propagation. This significantly diminishes electrode pulverization and swelling. As a result, we observe a stable cycling stability (Cycle life: 94.6% for 100 cycles) of silicon-graphite composite (SGC) in 1 Ah pouch-type full cell. Remarkably, the SGC blended with graphite showed better electrochemical performance at low temperature cycling, fast-charging cycling and rate capability compared to the conventional graphite.