Mitigating internal shorting to enhance battery safety with gradient-conductivity cathodes

Abstract

Internal short circuits and the resulting catastrophic battery failure is difficult to detect and can occur under normal working conditions. To enable future high-energy density batteries, particularly lithium metal, an inexpensive internal short protection scheme is required. Here, we selectively remove conductive carbon from the cathode surface, creating a gradient-conductivity electrode. The process etches to a depth of only 5–10 μm and the active particles maintain electrical contact through the backside allowing for otherwise unaltered battery performance. When a lithium dendrite contacts the cathode surface, it will react with the oxide particle rather than contacting the carbon network. The active material now acts as a resistive element limiting the current. During shorting tests induced by abuse charging, cells containing conductivity-gradient cathodes saw a 2x reduction in short circuit current and accompanying temperature rise compared to cells with uniform conductivity cathodes. The reduction in short circuit current thus renders the event harmless. Postmortem analysis shows the dendrites only contact the surface oxide particles, supporting the viability of this gradient conductivity electrode design. Our approach utilizes the intrinsic resistivity of the active material to improve battery safety, is broadly applicable, and incurs no penalty in energy density. • Electrode with gradient conductivity mitigates thermal runaway due to shorting. • Electrode fabricated by selectively removing conductive carbon from the surface. • The increased short circuit resistance reduces current and temperature rise. • Battery performance remains unaltered until a shorting event.