Sulfide-based all-solid-state lithium-ion batteries (ASSLIBs) are promising candidates in the next generation of energy storage technology; the voltage mismatch and the resulting side reactions at the interface between the cathode and the solid electrolyte, however, dramatically deteriorate their cycling performance. Herein, for the first time, we report that the chemical interaction between LiCoO2 (LCO) and TiO2 can be regulated by two additives, carbon and Li2CO3, which in situ form a continuous ultrathin pure-phase Li2CoTi3O8 (LCTO) layer with a stable 3D network of spinel structures, relatively low electronic conductivity (2.5 × 10−8 S cm−1) and high lithium diffusion coefficient (DLi+ = 8.22 × 10−7 cm2 s−1) on the surface of LCO. When assembled in ASSLIBs, such an LCTO layer functions as an interlayer between the LCO and the Li10GeP2S12 solid electrolyte (LGPS). As a consequence, the original interface LCO/LGPS is substituted by two new interfaces LCO/LCTO and LCTO/LGPS. DFT calculations indicate that, compared with the LCO/LGPS, the new interfaces are not only thermodynamically and electrochemically more compatible, but also have higher interfacial affinity. Therefore, the relevant ASSLIB exhibits evidently reduced interfacial impedance, and it also displays a high initial capacity of 140 mA h g−1 and a reversible discharge specific capacity of 116 mA h g−1 after 200 cycles at room temperature (0.1C). In comparison, the ASSLIB assembled without the LCTO interlayer delivers an initial capacity of 98 mA h g−1 and only retains 22.4% capacity after 100 cycles (0.1C). Even at a high cutoff voltage (4.5 V vs. Li/Li+), the ASSLIB with the LCTO interlayer could also exhibit a high initial capacity of 180 mA h g−1 and a remarkable retention of 132 mA h g−1 after 100 cycles.
