Electro-chemo-mechanical failure in cobalt-free high-nickel cathodes: common degradation of polycrystalline and single-crystal morphologies in halide-based all-solid-state batteries

Abstract

All-solid-state batteries (ASSBs) with high-nickel cathodes face significant interfacial challenges. While single-crystalline (SC) cathodes are known to mitigate issues in liquid electrolytes, their advantage in solid-state systems is debatable. Herein, we compare cobalt-free polycrystalline (PC) and SC LiNi_0.9Mn_0.1O₂ (NM91) in a halide-based ASSB featuring a highly stable Li₃InCl₆ interface, which effectively isolates electro-chemo-mechanical effects from chemical degradation. We observe a convergent failure mode for both PC and SC NM91, which originates from the abrupt lattice contraction during the H2–H3 phase transition. This contraction induces physical detachment and void formation at the rigid cathode–electrolyte interface, severing ionic pathways and increasing the charge transfer resistance within the composite cathode. This mechanism, confirmed by re-pressurization experiments, overshadows the morphological benefits of the SC design. Our findings reveal that managing electro-chemo-mechanical stress and stabilizing the H2–H3 transition are paramount for the viability of high-nickel ASSBs.