High-voltage superionic and humidity-tolerant Li2.5Sc0.5Zr0.5Cl6 conductor for lithium batteries via preferred orientation

Chloride solid electrolytes (CSEs) have good compatibility with commercial oxide cathode materials and show great potential for application in all-solid-state Li metal batteries (ASSLMBs). However, achieving simultaneously low cost, high ionic conductivity, excellent moisture tolerance, and robust electrochemical stability with >4 V-class cathodes for CSEs remains challenging. Herein, we report a facile Zr substitution strategy to increase the degree of preferred orientation and lower the Li+ diffusion barrier of the (001) plane, i.e. the ab plane, of Li3ScCl6, thus boosting the ion conduction kinetics and framework stability. As such, Li2.5Sc0.5Zr0.5Cl6 exhibits a high conductivity of 2.23 mS cm−1 and low activation energy of 0.26 eV at room temperature (RT). ASSLMBs are constructed using a LiNi0.8Co0.1Mn0.1O2cathode, Li2.5Sc0.5Zr0.5Cl6 electrolyte, and Li-In anode, and deliver an exceptional initial Coulombic efficiency of 89.6 % at RT and can run stably over 200 cycles with 90 % capacity retention at 0.2C. In-situ electrochemical impedance inspection of the battery further reveals a high interfacial stability between Li2.5Sc0.5Zr0.5Cl6 and LiNi0.8Co0.1Mn0.1O2. Moreover, Li2.5Sc0.5Zr0.5Cl6 demonstrates high wet fatness with a preserved structure stability and high ionic conductivity after exposure to atmosphere with 5 % relative humidity. Such humidity tolerance and cost-effectiveness solve two major obstacles for the application of CSEs.