Experimental Corroboration of Lithium Orthothioborate Superionic Conductor by Systematic Elemental Manipulation

The Li superionic conductor Li₃BS₃ has been theoretically predicted as an ideal solid electrolyte (SE) due to its low Li⁺ migration energy barrier and high ionic conductivity. However, the experimentally synthesized Li₃BS₃ has a 10⁴ times lower ionic conductivity. Herein, we investigate the effect of a series of cation and anion substitutions in Li₃BS₃ SE on its ionic conductivity, including Li_3-xM_0.05BS₃ (M = Cu, Zn, Sn, P, W, x = 0.05, 0.1, 0.2, 0.25), Li_3-yBS_2.95X_0.05 (X = O, Cl, Br, I, y = 0.05, 0.1) and Li_2.75-xP_0.05BS_3-xCl_x (x = 0.05, 0.1, 0.15, 0.2, 0.4, 0.6). Amorphous ionic conductor Li_2.55P_0.05BS_2.8Cl_0.2 has a high ion conductivity of 0.52 mS cm^-1 at room temperature with an activation energy of 0.41 eV. The electrochemical performance of all-solid-state batteries with Li_2.55P_0.05BS_2.8Cl_0.2 SEs show stable cycling with a discharge capacity retention of >97% after 200 cycles at 1C under 55 °C.