Li6−xFe1−xAlxCl8 Solid Electrolytes for Cost-Effective All-Solid-State LiFePO4 Batteries

Abstract

Bulk-type all-solid-Li batteries based on inorganic solid electrolytes (SEs) are considered promising candidates for next-generation energy storage systems for their potential to overcome the limitations of current lithium-ion batteries, such as safety concerns, narrow operating temperature. Following the intensive efforts to search for affordable sulfide SEs, recently, chloride SEs are in the spotlight for their better high-voltage stability and potentially lower cost than the sulfide counterparts. However, many chloride SEs exhibiting appreciable ionic conductivity adopt rare-earth metals, which arises the motivation to search for new chloride SEs based on earth-abundant minerals. Herein, Li6−xFe1−xAlxCl8 (0 ≤ × ≤ 0.8) SEs exhibiting significantly improved ionic conductivity of 3.9 × 10−5 S cm−1 at 25°C for Li5.5Fe0.5Al0.5Cl8 compared to Li6FeCl8 (3.1 × 10−6 S cm−1) are reported. The formation of a metastable spinel-like phase was observed for Li5.5Fe0.5Al0.5Cl8 prepared by mechanical ball-milling. Furthermore, its electrochemical properties as a catholyte were examined, coupled with a LiFePO4 cathode active material.