Charge-transfer process at graphite/electrolyte interface and the solvation sheath structure of Li+ in nonaqueous electrolytes

The temperature- and electrolyte-dependences of the so-called charge-transfer process at graphite/electrolyte interface were investigated with impedance analyses at lithiation potential (0.15 V vs Li), and characteristic correlations between the activation energies of the process and the electrolyte compositions (such as solvent ratio and salt concentration) were established. It was found that the solvation sheath structure of Li+ is dependent on the ratios of cyclic (such as EC) to linear carbonates (such as DMC), which in turn results in different chemistries of graphite/ electrolyte interfaces and dictates the Li+-transport across such interfaces. The interdependences thus revealed could serve as useful guidelines to tailoring electrolytes of Li-ion batteries for sub-zero temperature applications. (c) 2007 The Electrochemical Society.