Unravelling the influence of quasi single-crystalline architecture on high-voltage and thermal stability of LiNi0.5Co0.2Mn0.3O2 cathode for lithium-ion batteries

As a common commercial lithium ion battery cathode material, the development of layered LiNi0.5Co0.2Mn0.3O2 (NCM) is restricted by the relatively unsatisfied energy density, which can be improved by elevating the operating potential range (>4.3 V). However, the conventional secondary particles of LiNi0.5Co0.2Mn0.3O2 (C-NCM) with abundant grain boundaries will suffer from the anisotropic expansion coupled with severe electrode/electrolyte interface parasitic reactions under the high-voltage and elevated-temperature conditions, inevitably resulting in the structural collapse with intergranular cracks and long-term cycling degradation. Herein, the quasi single-crystalline LiNi0.5Co0.2Mn0.3O2 (SC-NCM) with primary particles of 3–6 μm diameter is developed, which exhibits superior cycling performance as well as significantly improved structural integrity, even at elevated-temperature (45 °C) and high-voltage (4.6 V). Remarkably, the SC-NCM||graphite pouch-type full cell maintains 98.7% of its initial capacity at harsh conditions of 45 °C and charged voltage of 4.4 V after 500 cycles with only 0.0026% decay per cycle. More importantly, the fundamental understandings of the quasi single-crystalline architecture on structure stability and phase transformation are clearly unraveled. The results reveal that the SC-NCM primary particles with micron-sizes morphology can effectively prevent the generation of intergranular cracks, thereby alleviating the irreversible structural degradation. Meanwhile, the undesired side interactions are mitigated by the reduced electrode/electrolyte interfaces, thus alleviating the irreversible phase transformation. This work provides an insight into the strategy of developing single-crystalline micron-sized particles, which can maintain the structural stability and improve cycling life of NCM cathodes, even under the harsh operating condition of elevated-temperature and high-voltage.