Intrinsic Planar Defects Govern Durability in Single-Crystal Ni-Rich Cathodes

Single-crystal Ni-rich layered oxides are promising cathodes for high energy-density lithium-ion batteries, yet their electrochemical stability remains unexpectedly difficult to reconcile with the anticipated benefits of a grain-boundary-free architecture. Here, we reveal intrinsic planar defects as a hidden structural origin of this discrepancy in single-crystalline LiNi0.83Co0.12Mn0.05O2. Using compositionally matched cathodes with distinct defect landscapes, we identify disordered layered phase boundaries (DLPBs) as dominant defect motifs that broaden the local electrochemical state distribution and weaken intraparticle reaction coherence during Li extraction and insertion. As a result, a crystallographically single-crystal particle behaves electrochemically as a non-single-domain system, leading to diminished redox and structural reversibility. We further suggest that multistep lithiation serves as a defect-healing strategy to suppress intrinsic planar disorder, yielding single-crystal cathodes with an initial Coulombic efficiency above 90% and a capacity retention of 93% after 200 cycles at 1 C and 4.5 V. This work provides a new defect-chemistry-guided perspective for unlocking the full potential of single-crystal Ni-rich cathodes.