Polymer based multi-layer Al composite current collector improves battery safety.

• Self-breaking design of composite current collector helps improve battery safety. • Self-breaking is fulfilled by introducing oxygen when evaporating aluminum layer. • Extra oxygen forms multilayer structure containing Al oxide on the polymer core. • Short circuit path is spontaneously cut-off by the multilayer structure. • Battery will not undergo thermal runaway when being penetrated. The safety problem obstructs the large-scale application of high energy batteries. Instantaneous short circuit at millisecond triggers uncontrollable thermal runaway in high energy batteries. Herein, to shut down the short circuit at early stage, we accomplish the safety design using composite current collector that spontaneously breaks due to its heterogeneous ductility. The composite current collector has a core with high ductility (the polyethylene terephthalate base), and a skin with low ductility (multi-layer metal). Controlled oxygen is introduced when evaporating aluminum atoms onto the polyethylene terephthalate base, therefore the skin layer will be composed of aluminum and aluminum-oxide layers in staggered rows. The multi-layer skin is more susceptible to crack under the mesoscopic deformation than the plastic core, thereby preventing short circuit by cutting off the pathway of electrons. The cell assembled by the multi-layer composite current collector can pass the nail penetration test without spark, fire and explosion, while the cell with pure current collector and composite current collector with single layer skin cannot. The assembled cell has comparable electrochemical performance (88% capacity retention after 450 cycles) with the reference cell. This work affords novel ideas for the high safety structural design of high energy batteries. [ABSTRACT FROM AUTHOR]