An electrolyte system based on a sulfone solvent will be presented, outlining a newly discovered synergy between solvent and salt that simultaneously addresses the interfacial requirements of coupling a graphitic anode with a high voltage spinel cathode (LNMO). At the anode, a LiF-rich interphase generated by early-onset reduction of the salt anion effectively suppresses solvent co-intercalation and subsequent graphite exfoliation, enabling unprecedented and highly reversible graphite cycling in a pure sulfone system. Under aggressively oxidative conditions, QC calculations predict that high salt concentration promotes formation of complexes/aggregates which slow the decomposition of the solvent and leads to polymerizable rather than gaseous byproducts--a fundamental improvement over conventional electrolytes. These predictions are corroborated by an in-depth analysis of these functional interphases, as well as stable, long term operation of high voltage (4.85V) LNMO-graphite full cells.