Ti3C2T MXene in-situ transformed Li2TiO3 interface layer enabling 4.5 V-LiCoO2/sulfide all-solid-state lithium batteries with superior rate capability and cyclability

All-solid-state lithium batteries (ASSLBs) based on sulfide electrolytes promise next-generation energy storage with high energy density and safety. However, the sulfide electrolytes suffer from phase instability and sluggish interfacial charge transport when pairing with layered oxide cathodes at high voltages. Herein, a simple and efficient strategy is proposed using two-dimensional Ti3C2Tx MXene as starting material to in-situ construct a 15 nm Li2TiO3 layer on a typical oxide cathode, LiCoO2. The in-situ transformation of Ti3C2Tx into Li2TiO3 layer occurs at a low temperature of 500 °C, avoiding the phase deterioration of LiCoO2. The thin Li2TiO3 layer is Li+ conducting and electrochemically stable, thereby preventing the interfacial decomposition of sulfide electrolytes induced by LiCoO2 at high voltages and facilitating Li+ transport at the interface. Moreover, Li2TiO3 can stabilize the layer structure of LiCoO2 at high voltages. Consequently, the sulfide-based ASSLB using LiCoO2@Li2TiO3 cathode can operate stably at a high voltage of up to 4.5 V (vs. Li+/Li), delivering an outstanding initial specific discharge capacity of 138.8 mAh/g with a high capacity retention of 86.2% after 100 cycles at 0.2 C. The in-situ transformation strategy may also apply to other MXenes, offering a general approach for constructing other advanced lithiated coatings for oxide cathodes.