Effect of dual improved electronic and cationic conductivity via W doping on cyclability and rate performance of LiNi0.90Co0.04Mn0.03Al0.03O2 cathode for rechargeable LiBs

Abstract

Ni-rich layered cathodes are considered to be the most suitable high-capacity electrode material for current needs since their reversible capacity of over 200 mAh·g−1 and high operating voltage. However, the conventional Ni-rich layered cathodes inevitably go through rapid capacity degradation and poor rate performance. Herein, a designed strategy is proposed that W doping can regulate the electronic structure of NCMA(LiNi0.90Co0.04Mn0.03Al0.03O2) materials, presenting upgraded cyclability and enhanced rate performance. In this study, combined with density functional theory (DFT) calculation and conventional electrochemical measurements, revealed that the dual improvements of electronic and cationic conductivity are the possible reasons for the promoted electrochemical behavior. The bandgap of W-doped cathode material is reduced from 1.3857 to 1.2479 eV, which arises from the increased amount of electrons near Fermi energy after W doping. Such enhancement in electronic conductivity subsequently diminishes the polarization of the electrodes, thus the capacity retention of W-doped material after 100 cycles at 0.5C is greatly improved from 32.3 % to 95.0 %. Meanwhile, the strong WO bond intensifies cationic conductivity, facilitating Li+ diffusion. The introduction of W cations expands the thickness of Li slab up to 2.71 Å. Such improvements thereafter lead to a specific capacity of 155 mAh·g−1 at 5C. Compared to the pristine sample, W-NCMA cathode displays high potential for EV application.