Rapid determination of lithium-ion battery degradation: High C-rate LAM and calculated limiting LLI

Herein, incremental capacity-differential voltage (IC-DV) at a high C-rate (HC) is used as a non-invasive diagnostic tool in lithium-ion batteries, which inevitably exhibit capacity fading caused by multiple mechanisms during charge/discharge cycling. Because battery degradation modes are complex, the simple output of capacity fading does not yield any useful data in that respect. Although IC and DV curves obtained under restricted conditions (<0.1C, 25 °C) were applied in non-invasive analysis for accurate observation of degradation symptoms, a facile, rapid diagnostic approach without intricate, complex calculations is critical in on-board applications. Herein, LiNi0.5Mn0.3Co0.2O2 (NMC532)/graphite pouch cells were cycled at 4 and 6C and the degradation characteristics, i.e., loss of active materials (LAM) and loss of lithium inventory (LLI), were parameterized using the IC-DV curves. During the incremental current cycling, the initial steep LAM and LLI slopes underwent gradual transitions to gentle states and revealed the gap between low- and high-current measurements. A quantitative comparison of LAM at high and low C-rate showed that a ICHC revealed the relative amount of available reaction region limited by cell polarization. However, this did not provide a direct relationship for estimating the LAM at a low C-rate. Conversely, the limiting LLI, which is calculated at a C-rate approaching 0, was obtained by extrapolating the LLI through more than two points measured at high C-rate, and therefore, the LLI at 0.1C was accurately determined using rapid cycling.