It is now about 50 years since the concept of intercalation reactions for storing energy in electrochemical cells was discovered in the Corporate Research Laboratory of Esso (now ExxonMobil). Now they dominate portable energy storage and, having enabled the communications revolution, are ready to enable the electrification of transportation and intermittent renewable electric generation, such as solar and wind. The original lithium batteries used lithium-metal anodes and ether-based electrolytes, because lithium plating is much more efficient with the latter. With the advent of the higher voltage layered oxides and graphitic anodes, the electrolytes switched to organic carbonates, which are more stable at the higher potentials of the oxides. These are still the predominant electrolytes used today. However, they are not thermodynamically stable relative to the anode and often also to the cathode, so protective films must be generated. These so-called solid/electrolyte interphase (SEI) films present challenges to the operation of the cells with additional costs during the formation process at the manufacturing plant. Today’s commercial cells achieve less than 25% of their theoretical energy density, but to achieve higher levels will demand pushing all the materials to their limits. This in turn demands that we understand and then eliminate all side reactions. Many of these undesired side reactions are related to the reactivity of the electrolyte, so we must better understand the electrolyte.

This book by Kang Xu addresses this critical need, which has been neglected in most research over the last several decades addressing mostly the cathode. The author has previously published two critically acclaimed reviews in Chemical Reviews, and this book now presents the more fundamental underpinning needed for significant advances to be made. It does not restrict itself to the electrolyte alone but also covers the critical interactions with the electrodes, namely the interfaces and interphases. It concludes with a discussion of the other cell components.

It is my expectation that this book will enable researchers to discover new more stable and less costly electrolytes that will allow batteries with energy densities exceeding 500 W h kg⁻¹ and 1000 W h L⁻¹. I wish you good reading and great research. Let us move to the next level and create a greener environment for our children and their children.

M. Stanley Whittingham

2019 Nobel Laureate in Chemistry Binghamton, NY, USA