Simultaneously Modulating Li⁺ Transport Kinetics and Structural Stability in Li-Rich Mn-Based All-Solid-State...

Li-rich Mn-based oxides (LRMOs) are promising cathodes for all-solid-state lithium batteries (ASSLBs) due to their high theoretical capacity. However, their practical application is hindered by sluggish Li⁺ transport and interfacial instability. Herein, it is demonstrated that primary and secondary particle sizes of LRMOs play crucial roles in influencing Li⁺ transport kinetics and interfacial stability. With a fixed primary particle size (0.1 μm), large secondary particles (≈10 μm) impede Li⁺ transport by creating tortuous transport paths and inducing stress-induced cracks. Reducing the secondary particle size enhances Li⁺ transport kinetics; however, excessively small secondary particles (≈1 μm) lead to poor point-contact geometry at the LRMO/solid-state electrolyte (SSE) interface and increased oxygen release, triggering phase transformation and SSE oxidation, which further obstructs Li⁺ transport. An optimal secondary particle size of ≈5 μm provides a balance between Li⁺ transport efficiency and interfacial structural integrity. Furthermore, increasing the primary particle size to ≈0.46 μm reduces grain boundary resistance, enhancing Li⁺ transport and minimizing side reactions. This dual-scale optimization results in a high capacity of 200.2 mAh g^-1 at 0.05 C and excellent cycling stability with 67.4% capacity retention after 500 cycles at 0.3 C, highlighting the importance of dual-scale particle engineering for LRMO-based ASSLBs.