Harmonious Dual-Riveting Interface Induced from Niobium Oxides Coating Toward Superior Stability of Li-Rich Mn-Based...

Ni²⁺/Ni⁴⁺ and O^2-/O^2- redoxs endow the Li-rich layered oxide of Li_1.2Mn_0.6Ni_0.2O₂ (LMNO) with a considerable specific capacity and higher voltage. However, during the repeated de-/lithiation, the constant structure degradation initiated from transition metal ion dissolvement and oxygen escape leads to rapid capacity decay, which severely hinders the commercial application of LMNO. Herein, Nb₂O₅ and LiNbO₃ are fabricated on the outside of the LMNO substrate. With the appropriate ion radius, a small amount of Nb⁵⁺ enters the substrate, which could enlarge the crystal spacing and facilitate the fast Li⁺ transfer and, more importantly, change the valence state of Mn and induce the formation a Fd3̅m transition phase on the interface between the coating layer and the interior LMNO. Density functional theory (DFT) calculation has proven that the transition phase could build double-way chemical bonds both inside and outside, and the LiNbO₃ coated LMNO composite (LMNO@LNO) possesses a more stable and harmonious interface due to the higher bonding strength between LiNbO₃ and the transition phase. Therefore, LMNO@LNO demonstrates the most outstanding rate capability and long-tern cycling stability (decay rate of 0.041% per cycle during 1000 cycling at 5 C). This work provides a new inspiration for the coating materials selection and the interface stability research for the LMNO cathodes.