Regulating surface base of LiCoO₂ to inhibit side reactions between LiCoO₂ and sulfide electrolyte

The interface instability between layered oxide cathode and sulfide electrolyte is a key point affecting the performance of sulfide-based all-solid-state lithium batteries. Coating with fast-ionic conductor and constructing core–shell structure can effectively alleviate the interfacial side reactions and improve the interfacial stability between layered oxide and sulfide electrolyte. However, what have been neglected is the surface base (including Li₂CO₃ and LiOH) of layered oxide can also affect the interfacial stability. To clarify this point clearly and improve the interfacial stability, the surface base of LiCoO₂ (LCO) is regulated and investigated in this work. First, LCO with surface base Li₂CO₃ (LCO@Li₂CO₃) is prepared by the reaction of Co₃O₄ and excess Li₂CO₃. Then, the bare LCO is obtained after LCO@Li₂CO₃ is washed with deionized water and calcined again. Besides, LCO with surface base Li₂O (LCO@Li₂O) is also prepared with the bare LCO and LiOH. As a result, the electrochemical performances of LCO@Li₂O are significantly improved and much higher than those of LCO@Li₂CO₃ and the bare LCO electrodes. In particular, LCO@Li₂O-2 cathode display the most outstanding electrochemical performances (discharge capacity 138.4 mAh·g⁻¹ at 0.2C, 105 mAh·g⁻¹ at 2C and a capacity retention of 95.4% after 150 cycles at 0.5C). The high discharge capacity and excellent cycle stability of LCO@Li₂O electrode confirm the effectiveness of regulating the surface base of layered oxide from Li₂CO₃ to Li₂O. The surface base regulating is expected to be a simple but effective strategy to construct the stable interface between the cathode and the sulfide electrolyte of the all-solid-state lithium batteries. Graphical abstract: [Figure not available: see fulltext.].