Periodic Current Relaxation Mitigates Stress and Phase Instability in Single-Crystal Ni-Rich Cathodes.

Abstract

Single-crystal nickel-rich cathodes (SC-NCM) are leading candidates for next-generation high-energy-density lithium-ion batteries (LIBs) due to their structural integrity and thermal stability. However, their practical performance remains constrained by sluggish lithium-ion diffusion, internal stress accumulation, and phase instability under conventional constant-current cycling. Existing bulk or interfacial modification strategies often increase synthesis complexity and limit scalability. Here, we demonstrate that introducing periodic relaxation intervals into constant current, forming a pulse-current (PC) protocol, provides a simple and materials-independent approach to dynamically regulate Li⁺ transport and structural evolution. Pulsed cycling homogenizes ion distribution, enhances insertion/extraction kinetics, and stabilizes critical phase transitions, resulting in a 10.6% increase in initial discharge capacity and improved capacity retention over 300 cycles. Structural characterizations reveal deeper and more reversible H1-M and H2-H3 phase transitions, suppress the formation of rock-salt phases, and reduce localized stress accumulation. Furthermore, this strategy proves robust across practical operating conditions, including low temperature (-20 °C), high voltage (4.6 V), and Ah-level pouch cells. This work uncovers the mechanistic coupling between electrochemical relaxation and structural stability, offering dynamic current modulation as a broadly applicable strategy for unlocking the intrinsic performance of nickel-rich cathodes without chemical modification.