Safety and reliability of Li-ion batteries

Energy storage solutions based on batteries are becoming more and more popular in electric vehicles and also stationary applications. Especially lithium-ion (Li-ion) batteries are increasingly employed due to their competitive performance compared to other battery types. The increasing energy density of Li-ion cells (Wh/L) and at the same time the increasing amount of stored total energy in the various solutions accentuate the efforts on battery safety and measures to maintain a maximum on safety and reliability. Focusing on Li-ion batteries on the cell level, this review paper provides an introduction to the safety and reliability topic. First, an overview on the most common Li-ion cell chemistries with their performance and safety features is given. Then insights on cell failure mechanisms and consequences in regular and abnormal operations are provided. Both non-energetic failure modes and energetic ones, such as thermal runaway, are described, including their root causes. Mitigation solutions such as charge interruption devices and positive temperature coefficient switches are described and discussed. Regarding battery safety and reliability assessment, the most relevant design aspects, such as failure propagation suppression within modules and thermal aspects are also described. It is explained that a holistic system approach from single cells to module and pack/rack aspects up to the full system is required, when maximizing safety and reliability. A full description of all safety levels would however be beyond the scope of this paper and we focus on the first level, i.e. on the Li-ion battery cell aspects.