The development of processes for recycling spent lithium-ion batteries requires having a good knowledge of the battery components, skills in electrochemistry and physicochemistry applied to lithium-ion batteries, and obviously, thorough backgrounds in separation science and chemical engineering. On the other hand, the engineers involved in the development of the next generations of lithium-ion batteries should integrate very early special considerations to make recycling easier and economic as well as to minimize the environmental impacts of the batteries during its whole lifecycle (eco-design). Therefore, engineers must have a very good view of the recycling processes and the corresponding physicochemistry. This chapter provides fundamental skills in electrochemistry and physicochemistry to help the engineers to develop lithium-ion batteries and processes for recycling spent lithium-ion batteries. This chapter gives prerequisites to the reader on physicochemistry and electrochemistry applied to lithium-ion batteries. After giving a short view of the battery components in the first part of this chapter, the second part brings the backgrounds to understand the physicochemical and electrochemical phenomena taking place in lithium-ion batteries. In the third part of this chapter, each unit operations of hydrometallurgical processes implemented to produce raw materials for lithium-ion batteries and to recycle spent lithium-ion batteries are presented.