Atomic Horizons Interpretation on Enhancing Electrochemical Performance of Ni-Rich NCM Cathode via W Doping: Dual Improvements in Electronic and Ionic Conductivities from DFT Calculations and Experimental Confirmation.

Abstract

The rapid capacity degradation and poor rate capability hinder the application of Rich-Ni layered LiNix Coy Mnz O2 (NCM) as cathode materials for high-energy lithium-ion batteries. In this study, density functional theory (DFT) calculations, combined with conventional electrochemical measurements, reveal from the atomic view that the dual improvements in electronic and ionic conductivities are the main facts for the property enhancement. The bandgap of the cathode material is reduced to 1.1623eV due to the increased number of electrons near the Fermi level after W intercalation. Such improved electronic conductivity subsequently leads to a suppressed polarization and reduced resistance, enabling an improved cycle life of up to 93.97% after 100 cycles at 0.5 C. Furthermore, the doping with W6+ also introduced a strong WO bond into the layered structure so that the thickness of the Li slab is expanded to 2.6476 Å, which reduces the energy barrier from 0.355 to 0.308eV for the migration of Li+ within the Li slab, as confirmed by the DFT calculation. Consequently, the rate performance is greatly improved due to the reduced diffusion energy, with a specific capacity of 159.11 mAg-1 even at 5 C rate, indicating high potential for future applications.