Multistep Improvement of Pilot-Scale 21700 Cells for Increased Fast-Charging Capability: Combining Optimized Electrolyte, Cell Design and Fast-Charging Protocol

Abstract

In this publication, different cell- and charging parameters (advanced fast-charging protocol, 21700 tab design, electrolyte composition) are changed in a systematic step-by-step approach to reduce charging time while keeping the anode and cathode cell chemistry and electrodes (graphite—NMC 622 full cell) unchanged. Preliminary tests were carried out using 3-electrode full cells with a Li metal reference electrode to identify charging conditions that avoid Li metal deposition. In addition, the effects of the anode potential are investigated in 3-electrode full cells with a Li metal reference electrode. The optimized charging protocols from the 3-electrode full cells were then transferred to 2-electrode pilot-scale 21700 full cells. Two different tab designs (1 × 1 welded tabs and 120 × 125 foil tabs) were used in these cells. To improve the charging time further, an electrolyte with higher ionic conductivity was used under the best conditions from the previous tests. Cross-sectional in situ optical microscopy was used to visualize the transport effects within the anode. In the optimized 21700 cell (advanced fast-charging, 120 × 125 foil tabs, better Li+ transport in the electrolyte), the synergistic effects of the three different optimization steps reduced the charging time to 80% SOC by 46% compared to the baseline cell.