Breaking electrode symmetry: lithium redistribution-induced degradation polarity in high-energy Li-ion batteries

Abstract

Balancing lithium-ion transport between electrodes is essential to ensuring the long-term stability of lithium-ion batteries (LIBs). However, the dynamic evolution of electrode imbalance under realistic operational conditions remains poorly understood. This study investigates degradation pathways across a wide range of negative-to-positive (NP) capacity ratios (0.8–1.4) in pouch-type full cells employing high-nickel layered oxide cathodes and graphite anodes. Cathode-limited configurations (NP < 1.0) exhibit interfacial instability associated with lithium plating and unstable solid electrolyte interphase (SEI) growth, whereas anode-excess conditions (NP > 1.2) trigger irreversible cathode phase transitions and structural degradation. Electrochemical measurements, differential capacity analysis, X-ray diffraction, and depth-resolved X-ray photoelectron spectroscopy reveal distinct spatial and mechanistic degradation features as a function of NP ratio. Results indicate that asymmetric lithium transport not only governs capacity fade but also dictates divergent failure modes in electrodes. These findings emphasize the importance of designing electrode architectures that tolerate transient lithium imbalance and extend practical lithium storage limits. Such strategies offer a pathway toward more durable, energy-dense, and intrinsically safer LIB systems for next-generation energy storage applications.