Foreword by Jeff Dahn Free

I have been working on lithium and lithium-ion batteries for 44 years, beginning in 1978. I was trained as a materials physicist and up until about 2008 I concentrated most of my work on new positive and negative electrode materials. Only in 2008 did graduate student Aaron Smith (now at Apple) and I realize that the most important remaining frontier in lithium-ion battery research was improving lifetimes to the multi-decade scale to enable electrical energy storage (EES) and second use of EV batteries. At this point, much of the work in our laboratory started to focus on the electrolyte of lithium-ion batteries. This is because the degradation in lithium-ion cells comes about due to unwanted parasitic reactions between the charged electrode materials and the electrolyte. These are the same reactions that also provide the beneficial solid/electrolyte interphase (SEI) layers on the electrode surfaces.

In 2008, I knew virtually nothing about electrolytes and began reading papers from the US Army Research Laboratory (ARL). Kang Xu, Richard Jow, Michael Ding, Oleg Borodin, S. S. Zhang and others at ARL had done an incredible amount of world-class research on all aspects of electrolytes, including electrolyte additives, for lithium-ion cells and had elevated their laboratory to probably the world-leading center for electrolyte research. I began reading their papers. Kang Xu’s review article published in 2004 became a “Bible” for our group. In 2014, Kang Xu wrote his second review article on electrolytes for lithium-ion cells which, again, became required reading for students working on long-lifetime lithium-ion cells in our group.

This book which Kang Xu has produced is a complete treatise on electrolytes with a focus on lithium-ion batteries. I read many sections of the book in its prepublication stage and the content is exceptional. Readers of all backgrounds working on lithium-ion batteries will especially appreciate Parts B and C of this book, which focus on practical aspects of electrolytes. For a practical guy like me, Chapters 11, 12, 15 and 16 especially are standouts. Graduate students and researchers working in this space will appreciate the entire book!

Even though this book explains many aspects of electrolytes and electrolyte/electrode interfaces for lithium-ion cells, many mysteries remain. For me, most important is a truly detailed understanding of what makes the best SEI on the negative electrode and the best cathode/electrolyte interphase on the positive electrode. Detailed studies, using surface-sensitive techniques, have identified elements, functional groups, molecules and compounds that are incorporated into good SEI layers and how these can be affected by the presence of one or sometimes two electrolyte additives. However, a true understanding of why these particular species yield good interphases is lacking.

As the world moves towards the “electrification of everything”, multi-decade long lifetime and sustainability (not energy density) of lithium-ion, sodium-ion and other batteries will become of paramount importance to reduce the need for recycling and replacement. Understanding all the minute details of the electrolyte/electrode interphase will be essential to create batteries that can last a century.

This book is the best place for researchers embarking on that journey to start.

Jeff Dahn

Dalhousie University, Halifax, Nova Scotia, Canada