Bifunctional urea surface-modified high voltage LiNi0.5Mn1.5O4 cathode for enhanced electrochemical performance

Abstract

Spinel LiNi0.5Mn1.5O4 (LNMO) cathode material has high specific energy density due to its high working voltage (4.7 V vs. Li/Li+). However, high voltage inevitably brings instability of the surface and interface layer properties and ultimately electrolyte decomposition and irreversible side reactions, which incurs structural degradation, capacity decline, and poor kinetics. Herein, a simple and novel surface modification strategy is proposed to obtain a bifunctional modification cathode material with carbon–nitrogen nanocoating and surface disorder phase transition, which is prepared through gas–solid heat treatment of pristine material and urea in a closed reactor. The surface disordered phase transition introduces favorable oxygen vacancies and synchronously constructs the fast diffusion channel of lithium ions, while the carbon–nitrogen nanocoating effectively alleviates the impedance growth of the electrode/electrolyte interface. Therefore, the surface modified U-LMNO exhibits an initial discharge capacity of 130.1 mAh g−1 at 0.2 C and a capacity retention rate of 95.1% after 200 cycles at 1 C, significantly superior to pristine P-LMNO. These results highlight the essentiality of high-voltage LNMO cathode material surface interface design and facilitate the development and commercialization of high-energy-density LNMO-based lithium-ion batteries.