KAlF4 surface modification enhances high-voltage high-rate cyclability and thermal stability of 5 V-class LiNi0.5Mn1.5O4 cathode

Spinel LiNi 0 . 5 Mn 1 . 5 O 4 (LNMO) is a highly promising cathode material for next-generation lithium-ion batteries due to its high voltage platform (∼4.7 V vs. Li + /Li) and superior energy density. However, severe interfacial side reactions, electrolyte decomposition, and transition metal dissolution at high voltages severely hinder its commercial application. In this work, a ternary fluoride KAlF 4 (KAF) is innovatively introduced to construct a largely uniform, robust protective overlayer on LNMO particle surfaces. The KAF coating induces the formation of a stable organic-inorganic composite cathode electrolyte interphase (CEI) rich in Li x PO y F z . The robust CEI layer effectively mitigates HF corrosion and electrolyte decomposition, accelerates interfacial Li + reaction kinetics, and significantly improves the thermal stability of the cathode. As a result, the optimized KAF/LNMO-2% exhibits a significantly enhanced capacity retention of 84.44% after 300 cycles at 2C within 3.5–5.0 V (compared to 40.19% for bare LNMO), and delivers an excellent rate capability of 64.43 mAh g −1 at 4C. Furthermore, the assembled KAF/LNMO-2%||graphite soft-pack full battery retains 73.49% of its capacity after 100 cycles. This ternary fluoride surface modification strategy substantially improves the structural and interfacial stability of 5 V-class high-voltage cathodes, offering a practical approach for designing high-energy-density lithium-ion batteries.