This book reviews the impact of water content in lithium-ion batteries (LIBs) as well as the reactivity of anodes, cathodes and electrolytes with water and processes that provide water-resistance to materials in LIBs. Water in LIBs which were constructed with anode, cathode and organic electrolyte containing lithium salts can degrade the cell performance and seriously damage the materials present. However, because a small amount of water in cells contributes to the formation of the solid electrolyte interphase, complete removal of water from cells lowers the battery performance and increases costs due to removal of water from the battery materials. This book presents the optimal concentration of water for each battery material along with appropriate removal methods and water-scavengers which were developed recently to establish both high performance and lower costs. Moreover this book describes the development of anodes and cathodes prepared by aqueous process and aqueous LIBs in which aqueous electrolytes containing lithium salts are used as an electrolyte. This book will be useful not only for academic researchers but also for company researchers who deal with LIBs.