Unveiling the Role of Cooling Rate Modulation in Tailoring Cation Ordering and Spherical Morphology of LiNi0.5Mn1.5O4 Cathodes of Li-Ion Batteries

The electrochemical performance of LiNi0.5Mn1.5O4 (LNMO) is strongly influenced by the interplay between crystal structure and particle morphology, both of which are determined by thermal regulation. This study systematically investigates the influence of the cooling-rate regulation on hierarchical morphology, ordered-to-disordered phase formation, and electrochemical behavior of spherical LNMO synthesized via coprecipitation. The results reveal that the cooling-rate strategy balances the thermodynamic tendency toward crystal and morphological evolution. Slower cooling promotes the transformation from a highly disordered Fd3̅m spinel to a more ordered P4332 phase, thereby reducing Mn3+ formation and rock-salt impurities. In terms of morphology, rapid cooling produces small polyhedral grains and highly porous microspheres, whereas slow cooling yields larger, well-defined primary particles with smoother surfaces. Owing to this structural-morphological trade-off, neither rapid nor slow cooling provided optimal electrochemical performance. Instead, the LNMO sample synthesized at a moderate cooling rate (LNMO C5) achieved the optimal balance among partial cation disorder, controlled Mn3+ content, and a well-defined hierarchical spherical morphology, resulting in the lowest charge-transfer resistance and polarization. Consequently, LNMO C5 delivered a high discharge capacity of 96.36 mAh g–1 at 5C and excellent cycling stability with 97.90% capacity retention after 400 cycles at 0.5C. These findings highlight that cooling-rate regulation is a simple yet effective strategy for tailoring the thermodynamic and kinetics balance of LNMO, providing a reference for the future development and optimization of high-voltage LNMO cathode materials.