This paper reviews approaches to the design of advanced electrolyte solutions for Li and Li-ion batteries. Important challenges are wide electrochemical windows, a wide temperature range of operation, acceptable safety features, and most important, appropriate surface reactions on the electrodes that induce efficient passivation, but not on the account of low impedance. We describe research tools, quick tests, and discuss some selected examples and strategies for R&D of solutions of improved performance. (C) 2004 Elsevier Ltd. All rights reserved.