Lithium metal batteries (LMBs) have been considered as one of the highly attractive candidates for next-generation energy-storage devices. Ether electrolytes are compatible with lithium metal anode, however, they are excluded from being used in 4 V class batteries due to their limited oxidative stability, which highly limits the specific energy density of batteries. Herein, we demonstrate a facile and effective strategy to stabilize ether-based electrolyte with high voltage cathode LiCoO2 (LCO). The LCO is modified by Li1.5Al0.5Ge1.5(PO4)3 (LAGP) via ball milling and sintering, accompanied with salts passivation during cycling, attaining a capacity retention of 80.7% over 500 cycles with a charge cut-off voltage of 4.3 V. This study offers a viable method to improve the stability between ether-based electrolytes and high voltage cathode, and open up new possibilities for practical application in high performance lithium batteries.