It remains controversial over whether preferential solvation occurs when lithium salts are dissolved in typical binary electrolytes. While the role of Li+-solvation sheath in directing interphasial chemistry on graphitic anode surface has become recognized, it is imperative to understand the quantitative structure of such sheaths. Employing a soft ionization mass spectrum technique, statistic distribution of cyclic and acyclic carbonate molecules within the Li+-solvation sheath was successfully established. The quantitative mapping of sheath structure against bulk electrolyte composition reveals unambiguous preference of cyclic over acyclic carbonate molecules by Li+. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3615828] All rights reserved.