Effects of LATP Particle Size on the Residual Moisture of Separator Coating and the Performance of NCM811 Batteries

Li1+xAlxTi2–x(PO4)3 (LATP) is a NASICON-type solid electrolyte that presents stability in aqueous media and high ion conductivity. With these advantages, it is expected to be used as a cathode and separator coating material for lithium-ion batteries to improve battery performance. However, it also displays a high level of residual moisture introduction due to its strong water absorption. Meanwhile, LATP particle size is a key influential factor for the residual moisture level and thereby produces an impact on the battery performance. In this research, we prepared three different particle sizes of LATP (100, 500, and 1000 nm) to investigate their effects as separator coatings on residual moisture and NCM811 battery performance. The results indicate that the water absorption of LATP is much higher than that of Al2O3 with the same particle size; the use of nanoscale LATP keeps the residual moisture of the LATP/PE separator rather high. When the particle size is in the range of 100–1000 nm, the battery’s cycling performance gradually deteriorates with the decrease of the particle size, among which the degradation of rate performance is more noticeable. More importantly, the research finds that LATP particles coated with polydopamine (PDA) can effectively reduce the coating’s residual moisture. After being coated with PDA, LATP particles with a particle size of 1000 nm result in the residual moisture content within the composite separator decreasing from 2136 to 408 ppm, thereby contributing to the optimal performance of NCM811||Li and NMC811||C batteries.