Realizing high energy-density lithium-ion batteries: High Ni-content or high cut-off voltage of single-crystal layered cathodes?

Improving Ni-content or upper cut-off voltage is usually utilized to boost the specific capacity of cathodes and the energy-density of lithium-ion batteries (LIBs). However, the performance comparison and structural evolutions between the aforementioned strategies have not been reported yet, especially under the same state of charge (SOC) of single-crystal layered ternary cathodes. Herein, the properties of single-crystal LiNi0.6Co0.1Mn0.3O2 (SC-NCM613) and LiNi0.8Co0.1Mn0.1O2 (SC-NCM811) are systematically studied under the similar Li+ deintercalation/intercalation. Both single-crystal cathodes deliver a specific capacity of about 200 mAh g−1 with a median-voltage of 3.8 V. The SC-NCM613 under the cut-off of 4.5 V shows improved cycling life than that of SC-NCM811 under 4.3 V. Both single-crystal cathodes exhibit a similar rate property at 25 °C while SC-NCM613 has enhanced high-rate capacities as testing temperature drops to 0 °C. XRD results demonstrate that the enhanced stability of SC-NCM613 is ascribed to the reduced structural distortion at high SOC. Besides, SC-NCM613 has a decreased content of Ni3+ ions, suggesting the improved air and storage stability. And Ni substituted by Mn in SC-NCM613 will reduce the cost of cathode. These results suggest that increasing the upper cut-off voltage of layered cathodes with relatively low Ni-content is a better choice for designing high-energy and low-cost LIBs.