The lithium ion battery is widely used in electric vehicles (EV). The battery degradation is the key scientific problem in battery research. The battery aging limits its energy storage and power output capability, as well as the performance of the EV including the cost and life span. Therefore, a comprehensive review on the key issues of the battery degradation among the whole life cycle is provided in this paper. Firstly, the battery internal aging mechanisms are reviewed considering different anode and cathode materials for better understanding the battery fade characteristic. Then, to get better life performance, the influence factors affecting battery life are discussed in detail from the perspectives of design, production and application. Finally, considering the difference between the cell and system, the battery system degradation mechanism is discussed.