Thermal Runaway of Lithium-Ion Batteries without Internal Short Circuit

Context & ScaleWith the explosive growth of portable devices and electric vehicles, there is an urgent need for safer Li-ion batteries (LIBs) with even higher energy density. The most catastrophic failure mode of LIBs is thermal runaway (TR) accidents; while TR only happens occasionally, it is a serious threat for the battery user and people nearby. In this paper, the mechanism behind TR without internal short circuiting is reported for the first time. A polyethylene terephthalate ceramic separator was used in battery tests to exclude the occurrence of an internal short circuit that is inducing Joule heat. Test results indicated that chemical crosstalk between the cathode and anode is the hidden mechanism that triggers TR, during which cathode-released oxygen is consumed by the lithiated anode, with a heat release rate of 87.8 W/g. The results advance understanding of the complicated TR mechanism in high-energy-density LIBs and should help in their future design.Highlights•Thermal runaway of 25-Ah LIBs without internal short circuits is reported•Cathode-produced oxygen is consumed by the anode with heat generation•Chemical crosstalk is the hidden thermal runaway mechanism at high temperature•Cathode with inferior thermal stability may trigger the TR more intensivelySummaryWe demonstrate herein that not only internal short circuiting, but also chemical crossover, is the mechanism behind thermal runaway that can occur in lithium-ion batteries due to abuse conditions. In situ experiments showed that during thermal runaway, the cathode releases oxygen by a phase transition, and this oxygen is consumed by the lithiated anode. The released highly oxidative gas reacts with reductive LiCx with tremendous heat generation centered at 274.2°C with heat flow of 87.8 W g−1. To confirm the proposed mechanism, we froze a battery undergoing the thermal runaway process by liquid nitrogen and subjected it to detailed post-test analysis. Our results revealed the hidden thermal runaway mechanism of chemical crossover between the battery components without a severe internal short circuit. These findings provide an important insight into the rational design of automotive lithium-ion batteries as well as solid-state batteries.Graphical abstract