Integrated optimization design with inherent element behaviors for bulk and surface stability towards 4.7 V LiCoO2 cathode

Abstract

LiCoO₂ (LCO) cathode with higher energy density can be harvested through raising its upper cut-off voltage to 4.7 V (vs. Li⁺/Li). However, such high-voltage operation exacerbates the bulk and surface instability of LCO, which is responsible for its rapid capacity decay at high voltages. Consequently, to address these issues, an integrated optimization design is reasonably proposed, which involves Mg/F/PO₄^3- cooperative modulation for LCO (LCO-MFP) based on the inherent behaviors of these elements. Specifically, our theoretical calculations reveal the distinct distribution of Mg/F/PO₄^3- (Mg pillaring, F doping and PO₄^3- coating), which is rooted in their innate occupancy propensity. Consistent with our theoretical results, it is experimentally discerned that Mg and F atoms prefer to enter Li layer and O framework of LCO, respectively, whereas PO₄^3- gravitates towards enrichment on the surface, thereby stabilizing bulk structure, hampering the lattice O/Co evolution and enhancing surface stability. The resulting integrated optimized LCO-MFP cathode can achieve an excellent capacity retention of 81.0 % at 4.7 V after 200 cycles. This integrated optimization design is anticipated to pave the way for selecting appropriate modification elements with their intrinsic properties for high-voltage LCO cathode.