Voltage instability of battery materials has hindered the realization of high-voltage all-solid-state batteries (ASSBs). Now, 5 V-class ASSBs are enabled by a fluoride-based shielding layer, LiCl–4Li2TiF6, that combines high oxidative stability and Li+ conductivity. Applied to high-voltage cathodes, the shielding layer mitigates interfacial degradation and enables stable cycling at >5 V, including under high-capacity conditions.