Niobium‐Based Surface Engineering Enables High Rate and Cycling Stability of High‐Voltage LiNi 0.5 Mn 1.5 O 4 Cathode

LiNi 0.5 Mn 1.5 O 4 (LNMO) is a promising high‐voltage cathode for next‐generation lithium‐ion batteries (LIBs) due to its high operating potential, low cost, and cobalt‐free composition. However, severe interfacial degradation and structural instability at 4.9 V hinder its practical application. In this work, a uniform niobium‐based coating was constructed on LNMO via a scalable sol–gel‐assisted solution process. The Nb surface layer provides the mechanical stabilization to maintain the cathode structure and suppress interfacial side reactions. In addition, it enhances Li + diffusion kinetics and is beneficial for the formation of a robust, inorganic‐rich cathode–electrolyte interphase. The optimized Nb‐LNMO electrode exhibits superior rate capability and cycling stability, retaining 98.3% capacity retention after 200 cycles at 0.3 C in LNMO|Li cells between 3.5–4.9 V, compared to 83.5% for pristine LNMO. This work highlights an effective Nb‐based interfacial engineering strategy that reinforces both structural and chemical stability, providing a general approach for designing durable high‐voltage cathodes for advanced LIBs.