The Li-ion battery market is growing fast due to its ever increasing number of applications, from electric vehicles to portable devices. These devices are in demand due to safety reasons, energy efficiency, high power density and long life duration, which drive the need for more efficient electrochemical energy storage systems. The aim of this book is to provide the challenges and perspectives for Li-ion batteries (chapters 1 and 2), at the negative electrode as well as at the positive electrode, and for technologies beyond the Li-ion with the emerging Na-ion batteries and multivalent (Mg, Al, Ca, etc) systems (chapters 4 and 5). The aim is also to alert on the necessity to develop the recycling methods of the millions of produced batteries which are going to further flood our societies (chapter 3), and also to continuously increase the safety of the energy storage systems. For the latter challenge, it is interesting to seriously consider polymer electrolytes and batteries as an alternative (chapter 6).This book will take readers inside recent breakthroughs made in the electrochemical energy systems. It is a collaborative work of experts from the most known teams in the batteries field in Europe and beyond, from academics as well as from manufacturers.