The performances and degradation mechanisms of a commercial artificial graphite/LiNi0.5Co0.2Mn0.3O2 pouch cell at different cutoff voltages and temperatures

Tremendous efforts have been made in improving the electrochemical properties of LiNi0.5Co0.2Mn0.3O2 (NCM523)-based lithium-ion batteries in lab-scale coin cells. However, two questions remain to be answered, including what is the practical performance of high-energy-density based pouch cells in all-climate and why has a charge cutoff voltage of ≥4.4 V still not been commercialized in NCM523-based cells. Herein, an ~2 Ah artificial graphite/LiNi0.5Co0.2Mn0.3O2 (AGr/NCM523) pouch cell was developed, and the cell behaviors at 4.2 and 4.4 V under cold, room and hot temperature conditions were researched in detail. When charged to 4.4 V, a specific capacity of 185.7 mAh g−1 was achieved, along with gravimetric and volumetric energy-densities of 261.9 Wh kg−1 and 640.1 Wh L−1, respectively; additionally a similar rate and low-temperature (0, −10 and −20 °C) discharge capabilities were maintained at compared with those of the cell at 4.2 V. However, the practical applications of this 4.4 V AGr/NCM523 cell are hindered by its low storage stability at 70 °C and short service life upon cycling at 0, 25 and 45 °C. Various characterizations were employed to differentiate the contributions of the cutoff voltage to the cycling degradation mechanism. Results reveal that side reactions, especially electrolyte breakdown, increased at both the cathode and anode interphases, which notably increased the impedance and became the major reason for the capacity fade of the cell at 4.4 V. Notably, the damage to the interior structure of NCM523 was similar to that of NCM523 at 4.2 V. This fundamental and comprehensive understanding of NCM523 in a full cell will pave the way for optimizing state-of-the-art NCM523 materials and high-voltage LIBs.