Understanding the Origin of the Ultrahigh Rate Performance of a SiO₂-Modified LiNi_0.5Mn_1.5O₄ Cathode for Lithium-Ion Batteries

LiNi0.5Mn1.5O4 (LNMO) is one of the most promising cathode materials for next-generation lithium-ion batteries for rapid charging–discharging applications. The surfaces of LNMO samples are coated with different amounts (0.5–2.0 wt %) of silica (SiO2) using a cost-effective and scalable ball milling process, and the surface-modified samples shows excellent electrochemical stability with conventional liquid electrolyte. The advantages of this coating are demonstrated by the improved electrochemical performances at ambient and elevated temperatures (25 and 55 °C) using half- and full-cell configurations. The solid electrolyte interface (SEI) and coating properties have been highlighted by ex situ TEM analysis, which indicates the close attachment and good wetting of the SiO2 layer with the LNMO active particles. Importantly, the 1 wt % SiO2-coated material cycled at 10, 40, and 80 C rates for 400 cycles exhibits excellent cycling stability with capacity retentions of 96.7, 87.9, and 82.4%, respectively. The 1 wt % SiO2-coated material also shows excellent cycling stability when charged at 6 C (10 min.) and discharged at C/3 for 500 cycles. The interfacial resistances of the SiO2-coated LiNi0.5Mn1.5O4 is found to be much lower compared to bare material and does not considerably increase with the amount of coating. Overall, the scalable and cost-effective strategy of SiO2 coating applied to LiNi0.5Mn1.5O4 lowers the interfacial charge transfer resistance and enables the materials to be suitable for extremely fast-charging electric vehicle battery applications.