Joule heating activation-assisted full-depth doping enabling fast-kinetic and stable micro silicon anodes in solid-state batteries

Abstract

Micro silicon (mSi) is a promising anode candidate for all-solid-state batteries due to its high specific capacity, low side reactions, and high tap density. However, silicon suffers from its poor electronic and ionic conductivity, which is particularly severe on a micro scale and in solid-state systems, leading to increased polarization and inferior electrochemical performance. Doping can broaden the transmission pathways and reduce the diffusion energy barrier for electrons and lithium ions. However, achieving effective, uniform doping in mSi is challenging due to its longer diffusion paths and higher energy barriers. Therefore, current doping research is primarily limited to nanosilicon. In this study, we successfully used a Joule-heating activated staged thermal treatment to achieve full-depth doping of germanium (Ge) in the mSi substrate. The Joule-heating process activated the mSi substrate, resulting in abundant vacancy defects that reduced the diffusion barrier of Ge into the silicon lattice and facilitated full-depth Ge doping. Surprisingly, the resulting Si-Ge anode exhibited significantly enhanced electrical conductivity (70 times). Meanwhile, the improved Li-ion conductivity in mSi and the reduced Young’s modulus enhance the electrode reaction kinetics and integrity after cycling. Ge-doped silicon anodes demonstrate excellent electrochemical performance when applied in sulfide solid-state half-cells and full-cells. This work provides substantial insights into the rational structural design of mSi alloyed anode materials, paving the way for the development of high-performance solid-state Li-ion batteries.