Tin-coated graphite electrodes as composite anodes for Li-ion batteries. Effects of tin coatings thickness toward intercalation behavior

The electrochemical behavior of graphite anodes, coated by 50-500 angstrom-thick Sn layers, is discussed in the present paper. Morphology and structure of the modified electrode surfaces are described, and the charge/discharge behavior is evaluated by galvanostatic cycles at temperatures down to -30 degrees C. The enhanced kinetics of the intercalation/deintercalation process is studied by cyclic voltammetry and electrochemical impedance spectroscopy, focusing on the role played by the Sn coatings in the intercalation/deintercalation mechanism. The results show that the metal layers modify and stabilize the electrode/electrolyte interphase and that the intercalation process is mediated by reversible Li-Sn alloys formation. Moreover, all the Sn coatings are effective in modifying the energy barriers related both to the Li(+) desolvation step and to the migration of the desolvated Li(+) ion through the modified surface layers. As a consequence, the overall polarization for the charge-transfer process is reduced, and enhanced low-temperature intercalation performances are obtained. (C) 2011 Elsevier B.V. All rights reserved.