Current-Corrected Cycling for True Electrode Performance Measurement

In battery research, galvanostatic cycling is the most widely used method to evaluate electrode performance.1 By applying pre-set current throughout the test, this method often fails to accurately reflect electrode performance at the designed cycling rate (particularly for high-rate cycling) because the actual capacity can be considerably affected by polarization and electrode degradation.2 To address this issue, a current-corrected galvanostatic cycling (CCGC) method is proposed, in which the current is actively adjusted during cycling based on the measured capacity of previous cycles.3 Compared to the traditional galvanostatic cycling (TGC) method, which may result in cycling rates that are hundreds of times faster than the designed rate, the proposed cycling strategy can effectively measure rate-dependent electrode performance precisely at designated rates. As shown in Figure 1, graphite electrodes were cycled in half cells at different rates ranging from C/20 to 5C using TGC and CCGC methods. For TGC, the capacity decreases quickly at rates higher than C/5 and becomes negligeable when the rate is ≥ 2C. This is because the actual cycling rates are much higher than the designed rates when the capacity becomes lower due to polarization, as shown in Figure 1(b). For instance, at a designed 5C rate, the observed actual cycling rate for TGC is 1200 C – 3600 C, about 500 times higher than the designed rate. In addition to the low capacities at high rates, at C/2 the capacity is not stable, due to the increasing overpotential, which causes staging plateaus to be truncated by the lower potential cutoff. References J. Liu et al., Nat. Energy, 4, 180–186 (2019). C. Heubner, M. Schneider, and A. Michaelis, Adv. Energy Mater., 10, 1902523 (2020). Z. Yan, B. Scott, S. L. Glazier, and M. N. Obrovac, Batter. Supercaps (2021) doi: 10.1002/batt.202100345. Figure 1 (a) Lithiation capacity and (b) the actual cycling rate of graphite electrodes cycled at different rates using CCGC and TGC. Reproduced with permission from ref 3. Copyright 2021 Wiley-VCH GmbH. Figure 1