Anomalous stable 4.6 V LiCoO2 in all-solid-state lithium batteries

Abstract

The commercialization of high-voltage LiCoO₂ (LCO) which possesses ultrahigh volumetric energy density is largely limited by a rapid capacity degradation. Although much progress has been made in optimizing high-voltage LCO, the long-cycled irreversible structure transformation and capacity loss is not practically solved, meaning that there are still scientific questions to be answered. Here, we report an anomalous stable 4.6 V (vs. Li/Li⁺) LCO with a record long-cycle capacity retention (94 % after 200 cycles at 2 C) in an all-solid-state lithium battery (ASSLB) system, which rarely achieved in the liquid one. The stable 4.6 V LCO originates from the unique ionic diffusion environment in the ASSLB, unlike in the liquid one, where there is a similar Li-ion diffusion velocity between the LCO’s bulk and surface structure. Such a homogenous bulk-to-surface Li concentration distribution upon cycling can well retard the irreversible phase transitions, as directly revealed by transmission electron microscopy. More broadly, this work unlocks the role of cycled Li distribution, a previously un-answered scientific question, in optimizing high-voltage Li-storage lattice and also sheds light on the design of high-voltage ASSLBs.