Constructing a robust integrated surface structure for enhancing the performance of Li-rich Mn-based oxides cathodes

Li-rich Mn-based oxides (LRMO) have emerged as the next-generation cathode materials for the advanced lithium-ion batteries due to its high capacity and low cost. However, its practical application has been impeded by the irreversible oxygen loss and structural deterioration of LRMO surface, resulting in low initial coulombic efficiency (ICE), capacity, and voltage degradation as well as sluggish kinetic reaction. Herein, we present a surface engineering strategy that uses NH4BF4 treatment to simultaneously integrate spinel phase, oxygen vacancies, and dual-element (B and F) doping on the LRMO surface. As a consequence, the treated LRMO, namely NHBF-2, shows much higher ICE of 89.41% with an increased capacity retention of 88.9% at 1 C after 100 cycles than the untreated LRMO (76.87% and 79.6% for ICE and capacity retention, respectively). Such improved performance of LRMO can be attributed to the robust integrated surface, where oxygen vacancies remove surface labile oxygen and suppress irreversible oxygen releasing, spinel phase promotes the Li+ diffusion kinetic, and B and F doping aids in stabilizing the surface structure. This study provides guidance for designing high-energy cathode materials with a stable surface by using surface modification on LRMO.