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 Li 2 CO 3 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 LiCoO 2 (LCO) is regulated and investigated in this work. First, LCO with surface base Li 2 CO 3 (LCO@Li 2 CO 3 ) is prepared by the reaction of Co 3 O 4 and excess Li 2 CO 3 . Then, the bare LCO is obtained after LCO@Li 2 CO 3 is washed with deionized water and calcined again. Besides, LCO with surface base Li 2 O (LCO@Li 2 O) is also prepared with the bare LCO and LiOH. As a result, the electrochemical performances of LCO@Li 2 O are significantly improved and much higher than those of LCO@Li 2 CO 3 and the bare LCO electrodes. In particular, LCO@Li 2 O-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@Li 2 O electrode confirm the effectiveness of regulating the surface base of layered oxide from Li 2 CO 3 to Li 2 O. 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