Regulating Mechano-Electrochemical Process for Uniform Lithium-Ion Extraction in Ni-Rich Single-Crystal Cathodes

Both mechanical and electrochemical processes critically govern the performance of single-crystal Ni-rich cathodes of lithium-ion batteries. Although electrochemically induced lattice defects are widely regarded as detrimental to cycling stability, mechanically introduced defects during electrode fabrication are commonly assumed to be similarly harmful. Contrary to this prevailing assumption, we demonstrate that although mechanical compression does introduce various structural defects, transmission electron microscopy reveals that these pre-existed defects are self-passivated during cycling and contribute negligibly to degradation. Instead, densification process unexpectedly enhances both cycling stability and rate capability, primarily due to reduced porosity and improved electronic connectivity. We further identify that capacity degradation is dominated by lattice distortions arising from rapid c-axis contraction during the H2-H3 phase transition, which triggers strain accumulation, planar gliding, and crack propagation - all of which are significantly alleviated in densified electrodes. Molecular dynamics simulations corroborate these findings, showing compact electrode structure promotes more uniform lithium-ion extraction and mitigates stress concentration, thereby preserving the cathode's layered structure. These findings reveal the mechano-electrochemical coupling from electrode to lattice level, providing a multiscale perspective to optimize electrode manufacturing for durable high-energy batteries.