Enhancing Li-ion diffusivity of Li1.3Al0.3Ti1.7(PO4)3 through liquid-electrolytes-induced secondary crystallization

Solid electrolytes (SEs) offer promising avenues for improving both the energy density and safety of lithium-ion batteries (LIBs). However, the grain boundary resistance remains a significant hurdle that impact the performance of LIBs, particularly when utilizing SEs in powder form. In this study, we introduce a novel approach to reduce grain boundary resistance in Li_1.3Al_0.3Ti_1.7(PO₄)₃ (LATP) via secondary crystallization induced by liquid electrolytes (LEs). By immersing nano-sized LATP powders in LiPF₆/carbonates LEs, rapid aggregation and recrystallization into bulk micrometer-sized particles occur within minutes under ambient conditions. This secondary crystallization process alters the Li distribution within LATP bulk phase, substantially reducing the grain boundary resistance and enhancing Li-ion diffusivity. Consequently, the assembled LATP-modified commercial LiNi_0.89Co_0.07Mn_0.04O₂ cathode using LiPF₆ electrolyte delivers a remarkable discharge capacity of 105.4 mAh g⁻¹ at 4C, significantly superior to the bare electrode (44.7 mAh g⁻¹). The recrystallized LATP enhances the transport properties and pathways of Li⁺ ions within the cathode material, especially at high current densities. Multinuclear and multi-dimensional solid-state NMR analysis reveal that active F⁻ ions released from the hydrolysis of LiPF₆ electrolytes act as mineralizing agent, facilitating rapid agglomeration and secondary growth of LATP grains. Our findings underscore the efficacy of secondary crystallization using LEs as a promising strategy for eliminating grain boundary resistance and facilitating fast Li-ion conduction of SEs, thereby advancing LIB performance.