Today we are witnessing gigantic expectations on the impact of electrochemical energy conversion and storage on the future benefit of society, which is well reflected by the prominent role that mainly batteries, but also fuel cells and supercapacitors, play in megatrends such as clean mobility (including robotics) and storage of renewable energies. Negative and positive electrodes together with the electrolyte are the major ingredients of any electrochemical system. From the very early findings of Galvani, Volta and Ritter until today, the electrolyte has always been the enabler of novel electrochemical technologies.

There are not many good things to say about Covid, but the unavoidable lockdown period during the pandemic gave Kang Xu the time to realize one of his many dreams. With this book, Kang has most successfully shaped a comprehensive up-to-date treatise targeting at marrying the enormous knowledge of the electrochemical basics of electrolytes with modern electrochemical technology and applications.

In this easy-to-read textbook, batteries, the major playground of the author for many decades, play a major role among the various electrochemical technologies that rely on the capabilities of the electrolyte used. The key role of the electrolyte in batteries is very often reflected in the name of the particular technology. A lead–acid battery contains a sulfuric acid electrolyte and alkaline aqueous and non-aqueous battery chemistries use electrolytes of the same type.

We can even go so far as to say that without looking for and eventually finding proper electrolytes, commercial applications as well as R&D of contemporary and future battery technologies such as lithium-ion batteries, lithium-metal batteries and solid-state batteries would not be possible. Because this is very often not well recognized either in academia or in industry, electrolytes may be considered as the “hidden champion” material class of advanced and future batteries.

The electrolyte is without doubt a true system component of any battery type. Hence understanding electrolytes is key for developing better batteries. This understanding includes bulk electrolyte properties, such as viscosity, ion solvation, ion–ion interactions and, of course, ion transport, which among other good reads are discussed in the first chapters of the book.

As the electrolyte is an inevitable and essential part of both electrode/electrolyte interfaces, it is concomitantly married to the 3D interphases [the solid/electrolyte interphase (SEI) and cathode/electrolyte interphase (CEI) are interphases, not interfaces] that originate from the high reactivity of the electrodes and the intrinsic instability of electrolyte components. In almost all cases, electrolyte formulations and their ad hoc interfacial/interphasial chemistries dictate and govern the fate of each battery chemistry and its performance, which is discussed in later chapters of the book.

Electrolytes are a complex and also complicated topic. Not everybody in the battery community is able to make distinguished contributions to the progress of this subject and even fewer of us are as competent to write a book on this topic as Kang Xu.

I have had the honor to know Kang Xu for many years and have spent a considerable amount of time with him on scientific and less scientific occasions. While Kang may not be able to distinguish any difference between Cabernet Sauvignon, Merlot and Shiraz, he is the one who knows everything about the enormously broad and multifaceted field of liquid electrolytes – he is a walking encyclopedia! We are privileged that he now shares his incomparable knowledge with us through this wonderful book.

Martin Winter

Münster Electrochemical Energy Technology, University of Münster, Münster, Germany