Realizing ultra-fast ionic transport in the cost-effective chlorospinel cathode for all-solid-state lithium-ion batteries

All-solid-state batteries (ASSBs) are widely regarded as the next generation of the most potential energy storage technology due to its advantages in energy density. However, the inherently low ionic conductivity of conventional cathode materials necessitates the incorporation of ionic additives in composite cathode, leading to a low mass ratio of active materials and thereby severely restricting the energy density of ASSBs. Herein, this study reports a series of novel chlorospinel cathodes Li_2–2xFe_1+xCl₄ (x = 0–0.15) with high ionic conductivity. In this system, the phase transition from Cmmm to Fd-3 m can be achieved through precise regulation of x content, with the associated ionic conduction mechanism being comprehensively elucidated. Li_1.9Fe_1.05Cl₄ enabled by optimized lithium-ion coordination environments and conduction pathways, delivers ultra-high ionic conductivity (6.15 × 10⁻⁵ S cm⁻¹ at 30 °C) and remarkable rate capability (88 % capacity retention after 300 cycles at 3C). Notably, exceptional cycling stability is demonstrated by the composite cathode with 95 wt % active materials content, with 580 cycles being sustained at a mass loading of 6.4 mg cm⁻² without ionic additives being required. Ex situ XRD is employed to reveal the structural evolution of Li_1.9Fe_1.05Cl₄ during lithium extraction/insertion processes. This research provides a crucial reference for the development of high-ionic conductivity and low-cost all-solid-state battery cathode design strategies.