Architecting robust full concentration gradient NCM712 cathodes for high-energy Li-Ion batteries

Abstract

Full concentration gradient ternary oxide cathodes, with a Ni-rich core and a Mn-rich surface, have been identified to effectively enhance their interfacial and structural stability for long-life Li-ion batteries. Nevertheless, a big challenge is to address the degradient effect during high-temperature lithiation. Herein, we demonstrate the synthesis of gradient LiNi0.70Co0.10Mn0.20O2 cathodes by F-doping and intergranular LixWyOz coating. The coating layer served as a physical barrier to mitigate the interdiffusion of transition metal ions during grain boundary merging. Meanwhile, the doped F ions, occupying the O sites, can further restrict ion transfer to inner primary particles by the formation of extremely strong M-F bonds. Accordingly, the resultant gradient cathodes deliver a high reversible capacity of 211.2 mAh g-1 at 0.1C in coin-type half-cells. A superior cycling stability is achieved with a high capacity retention of 93.0% at 1C after 500 cycles within 2.7-4.5 V in pouch-type full cells. This work provides a reliable technical route to obtain high-energy Li-ion batteries by the design of high-voltage concentration gradient Ni-rich cathodes.