Enhancing Ion Transport at Primary Interparticle Boundaries of Polycrystalline Lithium‐Rich Oxide in All‐Solid‐State Batteries

Polycrystalline lithium‐rich oxide (PLRO) is a promising high‐capacity cathode for next‐generation all‐solid‐state batteries (ASSBs). However, its full potential is hindered by sluggish Li+ transport at primary interparticle boundaries, mainly due to the limited flowability of inorganic solid‐state electrolytes (SEs). Additionally, infiltrating conventional SEs into PLRO can lead to severe interfacial side reactions because of high melting points. Herein, we report a one‐step, low‐temperature (<200 °C) co‐sintering process that simultaneously synthesizes the SE and infiltrates it into the primary interparticle boundaries of PLRO, creating an integrated composite cathode for ASSBs. This process forms a continuous Li+ transport network, enabling deep bulk activation of PLRO. Meanwhile, the co‐sintering process modulates the energy bands of the antibonding transition metal 3d‐O 2p and nonbonding O 2p at the surface, achieving greater orbital overlap to suppress oxygen release and mitigate interfacial phase transformation. As a result, the PLRO‐based ASSBs exhibit an impressive discharge capacity of 271 mAh g‐1 at 0.1C, 212 mAh g‐1 at 0.5C, and retain 80.0% capacity after 150 cycles. This study highlights the importance of enhancing ion transport to maximize the performance of PLRO‐based ASSBs, offering a practical solution for advancing energy storage technologies.