Two-dimensional unilamellar cation-deficient metal oxide nanosheet incorporated composite polymer electrolytes for...

Composite polymer electrolytes (CPEs) are considered among the leading contenders for next-generation all-solid-state lithium-metal batteries. However, CPEs simultaneously face multiple significant challenges, including reduced ion transference number, insufficient ionic conductivity, and poor cycling stability, which severely limit their practical applicability. Herein, we have designed a multifunctional unilamellar inorganic nanosheets (Ti_0.87O₂) additive for CPEs with cationic defects which is capable of simultaneously addressing all aforementioned challenges. The atomic Ti vacancies facilitate the direct passage of lithium ions through the nanosheets, and the monolayer structure accelerates the diffusion of lithium ions through the nanosheets. In addition, the atomic Ti vacancies can promote lithium salt dissociation while hindering anion transport. These two features of Ti_0.87O₂ nanosheet additives collectively enhance the ionic conductivity and lithium transference number. Furthermore, benefiting from the large specific surface area and defects, the Ti_0.87O₂ nanosheets can accommodate a high density of lithium ions, thereby releasing them to mitigate the polarization and elongating the Sand's time, which ultimately improves the battery's cycling stability. Finally, the ionic conductivity of CPE incorporated with this additive has improved by 42 times. Furthermore, the Li||Li symmetric cell demonstrates stable cycling for over 700 h at 0.1 mA cm^-2. This work provides a new avenue for designing novel additives to develop solid-state electrolytes that offer excellent ionic conductivity and stability.