Safety issues caused by internal short circuits in lithium-ion batteries

Safety related incidents and accidents involving lithium-ion batteries (LIBs) are often in the news. Even though catastrophic failure is rare, the high socioeconomic risks associated with battery thermal runaway reactions cannot be overlooked, as demonstrated by recent high-profile events. Among all the known types of battery failure modes, the internal short circuit (ISC) tops the list of the major safety concerns for the lithium-ion battery. However, a clear picture of the LIB's electrochemical safety behavior in the context of the ISC remains to be fully established. Herein we show that mechanical indentation techniques are capable of producing highly repeatable and controllable ISC modes in a manner that allows the electrochemical safety behavior of LIBs to be categorized based on the state of charge (SOC), ISC resistance, and electrode area. Our results identify the fundamental mechanism(s) of various electrochemical responses to the ISC through a combination of experiment, numerical simulation, and analysis. With the understanding that complicated electrochemical phenomena occur after the triggering of an ISC, we examine the safety boundaries and create an electrochemical behavior map for LIBs after ISCs. We anticipate that this discovery will lead to new opportunities for battery safety design, manufacturing, monitoring, and utilization with beneficial consequences to a battery-intensive, mobile, and green society in terms of much reduced battery safety concerns.