Electrolytes play pivotal roles in the stabilization of Li metal surface and operation at high voltages. In particular, localized high concentration electrolytes have outperformed state of the art electrolytes due to the unique solvation structures. However, a direct correlation between solvation structure in LHCEs, in particular for weakly coordinated diluents, and SEI composition is not well-understood, yet highly critical to realize high CEs beyond 99.5%. Here, a class of electrolyte based on bis(2,2,2-trifluoroethoxy)methane and 1,2-dimethoxyethane was introduced to regulate anion decomposition to achieve ultra-high Li2O content of 63% in the SEI along with a highly uniform phase distribution. These unique features enabled a record-high Columbic efficiency of 99.72% and proved the impact of homogeneously distributed high Li2O SEI. The related Li|LiNi0.8Co0.1Mn0.1O2 full cell with the negative/positive capacity ratio of 2.5 achieved 90% capacity retention after 200 cycles at 1 C and 80% retention after 596 cycles at 3 C.