Surface coating engineering of Li-excess cathode additive of lithium-ion batteries for initial charge compensation

Abstract

Silicon based anodes are known to have a high specific capacity and low operating voltage (less than 0.5 V vs. Li/Li+). Even so, the solid electrolyte interphase (SEI) formation induces the severe capacity loss at the first cycle, known as a critical factor in reducing the energy density of lithium-ion batteries (LIBs). To improve the energy density by compensating the initial Li+ loss, the utilization of Li-excess cathode additives has been considered as the most practical strategy for supplying surplus Li+ during the initial charge. Li2NiO2 is an ideal cathode additive thanks to its large charge capacity (≥320 mAh g−1) and low Coulombic efficiency (∼35%) at the first cycle. Surface protection of Li2NiO2 is still required, however, due to its vulnerability to moisture (H2O) and carbon dioxide (CO2) in the ambient atmosphere. In addition, Li2NiO2 becomes more structurally unstable due to oxygen (O2) gas evolution, leading to the formation of microcracks. Herein, we introduce a functional LiTaO3 coating layer onto the surface of Li2NiO2 for structural stabilization. The LiTaO3 coating layer can effectively suppress the formation of impurities (i.e., LiOH and Li2CO3) after air exposure. Furthermore, the gas evolution and mechanical cracking can be minimized by enhancing the structural integrity of Li2NiO2 during cycling.