An all-electrochem-active silicon anode enabled by spontaneous Li–Si alloying for ultra-high performance solid-state batteries

Abstract

Li–Si alloys are considered as key anode materials for advanced silicon-based solid-state batteries (Si-ASSBs) due to their high ionic/electronic conductivity. However, the high content of Li in Li–Si alloys increases the risk of Li dendrite growth and soft short circuits during battery charging. Herein, an all-electrochem-active Si/Li₂₁Si₅ composite anode is developed with the rational architecture and optimized ratio of Li₂₁Si₅ and pure Si. By utilizing defects in the oxide layer of micron Si, the Li₂₁Si₅ alloy is first synthesized separately by a quick and spontaneous Li–Si alloying reaction, followed by its mixing with Si particles by cold-pressing. In this composite anode, the Li₂₁Si₅ grains are uniformly distributed among the Si particles, and serve as a soft buffer for Si. Due to the limited self-discharge between Li₂₁Si₅ grains and Si particles, the Li₂₁Si₅ alloy maintains a lithium-saturated state and functions as a lithium supplement. Meanwhile, it constructs a conductive network in the anode, which can facilitate the transport of lithium ions and induce their storage in Si particles, thus avoiding dendrite formation. Consequently, the Si/Li₂₁Si₅-ASSB can achieve an ultra-high initial Coulombic efficiency (ICE) of 97.8% at 25 °C, as well as a low expansion rate of 18.9% at a surprisingly large areal capacity of 17.9 mA h cm⁻². This work provides a new method and valuable insight into Li–Si alloy synthesis, and the obtained Si-based anode shows great promise for application in ASSBs.