With the growing popularity of battery-powered mobility, battery safety and performance reliability have been prioritized by battery industries. Despite advanced manufacturing processes of large-scale commercial Li-ion cells, “latent defects” that can accidentally appear due to imbalanced battery design, invisible faults, and extreme operating conditions still threaten performance degradation and battery fire. Hence, it is urgently necessary to detect such latent defects in advance and understand the impacts of cell parameters and operating conditions on the battery failure scenario. For straightforward analysis of commercial cells, real-time, non-invasive visualizing of battery inside and diagnosing battery aging have been recognized through in-operado battery imaging technology based on X-rays, neutrons, and ultrasound which can penetrate the active materials, cell components, and external packaging. Moreover, a battery imaging technique to visualize the current distribution pattern using a magnetic field induced at batteries under external current load has also been proposed. This review will comprehensively discuss the imaging techniques inside the battery from atomic and molecular levels in electrode materials and interfaces to macro-scale battery systems, and examine qualitative case studies and recently unveiled phenomena.
