For the S3E-CP measurements, LCO symmetric cells at 50% SOC were subjected to galvanostatic pulses with current density ranging from 5 -100 mA cm -2 . Each pulse was terminated at a capacity limit of 15 μAh cm -2 , which is ~ 10% of the cyclable capacity of the symmetric cell. Immediately after each pulse, the cell was held at an applied voltage of 0 V. This resulted in a peak current comparable to the galvanostatic pulse, and the current decayed to less than a C/100 rate within 3 min. The length of the rest step at 0 V was varied as a function of current (from 3 to 30 min) to reduce measurement time while mitigating resistive heating. After each rest step, a PEIS measurement was taken to ensure stability. The maximum current density was limited to 100 mA cm -2 to reduce the total measurement time. Before and after collecting the S3E-CP dataset, which took ~ 4 h, the impedance measured with PEIS increased by only 0.3% (Fig. ).