Ni2+/Ni4+ and O2-/On2- redoxs endow the Li-rich layered oxide of Li1.2Mn0.6Ni0.2O2 (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.
Keywords: Li-rich layered oxides; interfacial bonding energy; lithium ion batteries; long cycle life; nbium oxides coating.