Phosphazene based LATP precursor for a CEI coating layer on high voltage LiNi0.5Mn1.5O4 cathode with improved cycling durability

Abstract

Extensive research has been conducted on NASICON type Li1+xAlxTi2-x(PO4)3 (LATP) with high Li+ ion conductivity as an artificial cathode electrolyte interphase (CEI) layer on the electrode surface to improve the cycling stability of rechargeable Li-ion batteries. Although highly soluble LATP precursor is crucial for facile and scalable coating of the CEI layer on the Li-ion battery electrode, the conventional LATP precursor suffers from poor solubility of the phosphorus source and poor Li+ ion conductivity. In this study, we present the highly soluble hexachlorophosphazene (HCP) as a novel phosphorus source of the soluble LATP precursor. Furthermore, we demonstrate that the LATP film can be optimized through the simultaneous control of the Al source and Li:Ti ratio. The optimized LATP film with an Li:Ti molar ratio of 1.5:0.8 presents the highest Li+ ion conductivity of 1.15 x 10−5 S cm−1 and the lowest activation energy of 0.26 eV. The HCP-based LATP precursor is implemented for artificial CEI layer formation. Consequently, the LATP 1 wt% coated LNMO half-cell exhibits a superior discharge capacity retention of 84.92% over the 70.97% retention of a bare LNMO half-cell at 1 C after 300 cycles. The LATP-based CEI layer presents a more effective pathway for Li+ diffusion, while preventing Mn2+ elution and side reactions during the charging/discharging process.