Balancing Structural Ordering and Electrochemical Performance in LiNi0.94Co0.06O2 Cathodes via PVA-Assisted Synthesis

Abstract

Ni-rich layered oxide cathodes are promising candidates for high-energy-density lithium-ion batteries; however, their electrochemical performance is strongly influenced by structural evolution, lithium stoichiometry, interfacial properties, and particle characteristics. In this study, LiNi0.94Co0.06O2 (LNCO) cathodes were synthesized through a poly(vinyl alcohol) (PVA)-assisted solution route to investigate the coupled effects of PVA molecular weight and calcination temperature on structural development and electrochemical behavior. Four LNCO samples, denoted LMW-650, HMW-650, LMW-750, and HMW-750, were systematically compared in terms of phase formation, layered structural characteristics, elemental composition, morphology, specific surface area, interfacial resistance, and electrochemical performance. The influence of calcination temperature was strongly dependent on the PVA molecular weight. Increasing the calcination temperature improved the layered-ordering indicator and reduced the interfacial resistance of the LMW-derived sample; however, this improvement did not result in a comparable enhancement in long-term cycling stability. In contrast, the HMW-derived sample calcined at 650 °C exhibited a favorable combination of layered structural characteristics, lithium stoichiometry, interfacial resistance, and electrochemical performance. These results indicate that layered ordering or surface area alone is insufficient to determine the long-term stability of ultrahigh-Ni LNCO cathodes. Instead, electrochemical behavior is governed by the combined effects of precursor characteristics and calcination-induced structural evolution. This study demonstrates that simultaneous control of PVA molecular weight and calcination temperature provides an effective strategy for tuning the structure–property relationship of low-Co, ultrahigh-Ni LNCO cathodes.