Parasitic-Reaction-Triggered Performance Deterioration of Long-Term Cycling Nickel-Rich Cathodes

Ni-rich LiNi1-x-yMnxCoyO2 (NMC, x+y < 0.5) materials are widely regarded as the promising cathodes for high-energy-density and cost-effective lithium-ion batteries. Cycling performance deterioration is a long-standing challenge for Ni-rich NMC, especially at high potentials (>4.3V vs. Li/Li+). The fundamental understanding of failure mechanisms is crucial for the development of long-life lithium-ion technologies. In our investigation, full cells cycled to 4.35 V for 1000 cycles lose about 49% of their initial capacity, while the counterparts cycled to 4.15V lose only 27% of their initial capacity after 1000 cycles. The relatively low capacity loss of the low voltage cells (4.15 V) is dominated by the impedance hike, while the drastically increased (more than half of) capacity loss of high voltage cells (4.35 V) is contributed from the irreversible degradation of the electrode materials. The post-mortem diagnosis suggests that parasitic reactions are the primary driving force for severe deteriorations, including the irreversible phase transformation. The generally concerned transition metal dissolution and bulk phase transformation negligibly make direct contributions to the severe capacity loss, but the loss of active cathode materials has some substantially detrimental impacts on irreversible capacity loss. Our findings emphasize that mitigating parasitic reactions is crucial for enabling long life of Ni-rich cathodes. Figure 1