Microscopic Segregation Dominated Nano‐Interlayer Boosts 4.5 V Cyclability and Rate Performance for Sulfide‐Based All‐Solid‐State Lithium Batteries

To implement the growing requirement for higher energy density all‐solid‐state lithium batteries (ASSLBs), further increasing the working voltage of LiCoO2 (LCO) is a key to breaking through the bottleneck. However, LiCoO2 severe structural degradation and side reactions at the cathode interface obstruct the development of high‐voltage sulfide‐based ASSLBs (≥4.5 V). Herein, a nano‐metric Li1.175Nb0.645Ti0.4O3 (LNTO) coated LCO cathode where microscopic Ti and Nb segregation at the interface during cycling potentially stabilizes the cathode lattice, and minimizes side reactions, simultaneously, is designed. Advanced transmission electron microscopy reveals that the stable spinel phase minimizes the micro stress at the cathode interface, avoids structure fragmentation, and hence significantly enhances the long‐term cyclic stability of LNTO@LCO @ 4.5 V. Moreover, the differential phase contrast scanning transmission electron microscopy (DPC‐STEM) visualizes the nano‐interlayer LNTO to boost Li+ migration at the cathode interface. Electrochemical impedance spectroscopy (EIS) reveals that sulfide‐based cells with the LNTO nano‐layer effectively reduce the interfacial resistance to 140 Ω compared to LiNbO3 (235 Ω) over 100 cycles. Therefore, 4.5 V sulfide‐based ASSLBs offer gratifying long‐cycle stability (0.5 C for 1000 cycles, 88.6%), better specific capacity, and rate performance (179.8 mAh g–1 at 0.1 C, 97 mAh g–1 at 2 C). A nanoscale Li+ conductive interlayer Li1.175Nb0.645Ti0.4O3 is coated at the LiCoO2 surface and used in sulfide‐based all solid‐state lithium batteries (ASSLBs). With better σLi+ and microscopic segregation of Ti and Nb during the cycling process, the interlayer stabilizes the cathode lattice and simultaneously mitigates the side reactions. Therefore, ASSLBs can cycle under 4.5 V and show excellent cyclability and rate performance.