Scalable conversion of residual lithium into conformal artificial cathode electrolyte interphase via a single-step wet-chemical process for high-voltage Ni-rich cathode operation

Abstract

Ni-rich layered oxide has become an indispensable cathode for incumbent lithium-ion batteries due to their high energy density and low cost. Despite these advantages, the Ni-rich cathode suffers from surface residual lithium, which causes gas evolution and gelation issue during the electrode fabrication process. Here, we demonstrate a simple wet-chemical and mass-production compatible process that converts undesirable residual lithium into an artificial cathode electrolyte interface (CEI) layer. A scalable wet chemical route effective even in bulk scale is firstly developed, where LiOH and Li2CO3 residual lithium species convert into LiF crystal through NH4F dissolved in ethanol. Pre-existing residual lithium on LiNi0.8Mn0.1Co0.1O2 (NMC811) powder surface reacts with a fluorine source NH4F saturated in ethanol, reincarnating into an artificial LiF CEI layer. A conformally formed CEI layer improves high voltage cycling up to 4.6 V vs. Li/Li+ with ∼ 10 % increase of the initial capacity retention at the 500th cycle compared to that of the control electrode. Suppression of transition metal dissolution along with thermal oxygen evolution from the Ni-rich cathode by the artificial CEI are also demonstrated. Based on validation at 10 g level, a continuous reactor with high-throughput processibility was devised. This study provides a scalable, single-step, recyclable, and inexpensive process to achieve artificial CEI layer on Ni-rich cathode by replacing residual lithium without further post-processes.