Review—An Unpredictable Hazard in Lithium-ion Batteries from Transition Metal Ions: Dissolution from Cathodes, Deposition on Anodes and Elimination Strategies

While various techniques have been developed to address the safety issues in lithium-ion batteries, there remain unknown mechanisms that induce hazards, leaving challenges in developing reliable lithium-ion systems. In this manuscript, an unpredictable hazard originated from the dissolution of transition metal ions from cathodes and their deposition on anodes is presented. The cathodes in currently commercialized lithium-ion batteries contain transition metal ions, which might dissolve in electrolytes, transport through separators and deposit on anodes. When the deposition proceeds in the form of metals, the deposited transition metals might induce a hazard due to the lithium dendrite growth on them. Since the electrolyte decomposition usually accompanies the transition metal deposition with a possibility that the electrolyte decomposition products might cover the deposited metals, the induced hazard becomes unpredictable. The typical mechanisms involved in the dissolution and deposition of transition metal ions and the possible strategies to eliminate the unpredictable hazard resulting from transition metal ions, which have been developed recently in our laboratory, are summarized.