(Keynote) Current Density Outliers in Batteries at Rest

Abstract

The need for creating safe electrolytes for lithium batteries is significant given the continued safety problems associated with current lithium-ion batteries. On the other hand, increasing electric vehicle (EV) adoption requires lithium-ion batteries that can be charged quickly. Some EV batteries have caught on fire despite neither being charged nor discharged. While the lithium that plates on graphite during fast charging affects battery safety, so do the internal ionic currents that occur when the battery is at rest after charging. These currents are difficult to quantify due to the absence of external current. We study a graphite electrode at rest after 6C fast charging using X-ray microtomography. We quantify spatially resolved current density distributions that originate at plated lithium and end in underlithiated graphite particles. The median current density at the plated lithium phase approaches zero in about 10 minutes after the battery current is stopped. Surprisingly, however, the range of current density was independent of time, with outliers above 20 mA cm-2. The persistence of outliers provides a clue as to the origin of catastrophic failure in batteries at rest. Some suggestions on how the outliers may be modeled using 3D Newman models will be discussed.