Oxygen-Vacancy-Assisted Dual Functional Surface Coatings Suppressing Irreversible Phase Transition of Li-Rich Layered Oxide Cathodes

Abstract

Both lattice oxygen release and the migration of transition metal (TM) ions challenge the cyclability of Li-rich Mn-based layered oxide (LMO) cathodes by inducing irreversible phase transitions. In this work, the oxygen-vacancy-assisted dual functional surface coatings of Li-rich layered oxide cathodes, including a spinel-over-phase and a Li₃PO₄ layer are fabricated for lithium-ion batteries (LIBs). The functional role of the optimized interface is mainly focused. Specifically, during the process of reorganized surface structure, the oxygen vacancies function as active sites for migrating TM ions to form the spinel over-phase and deliver the decreased binding energy of PO₄³⁻ on the LMO surface. It is found that the Li₃PO₄ layer increases the migration energy barrier of TM ions to 13.38 eV (7.62 eV for LMO). As a result, both the spinel over-phase and the Li₃PO₄ layer synergistically inhibited the irreversible phase transitions of LMO upon cycling to boost lithium storage of the cathodes. The optimized cathode maintained higher capacity retention of 95% at 0.2 C after 200 cycles in comparison to 67% for the pristine LMO. This study provides some understanding of the functional roles of the optimized dual surface coatings in suppressing the irreversible phase transition of LMO for LIBs.