Tellurium Surface Doping to Enhance the Structural Stability and Electrochemical Performance of Layered Ni-Rich Cathodes

The Ni-rich layered oxides are considered as a candidate of next-generation cathode materials for high energy density lithium-ion batteries; however, the finite cyclic life and poor thermostability impede their practical applications. There is often a tradeoff between structure stability and high capacity because the intrinsical instability of oxygen framework will lead to the structural transformation of Ni-rich materials. Because of the strong binding energy between the Te atom and O atom, herein a new technology of surface tellurium (Te) doping in the Ni-rich layered oxide (LiNi0.88Co0.09Al0.03O2) is proposed to settle the above predicament. Based on density function theory calculations and experiment analysis, it has been confirmed that the doped Te6+ ions are positioned in the TM layer near the oxide surface, which can constrain the TM–O slabs by strong Te–O bonds and prevent oxygen release from the surface, thus enhancing the stability of the lattice framework in deep delithium (>4.3 V). Especially, 1 wt % Te doping (Te 1%-NCA) shows the superiority in performance improvement. Furthermore, the reversibility of H2–H3 phase transition is also improved to relieve effectively the capacity decline and the structural transformations at extended cycling, which can facilitate the fast Li+ diffusion kinetic. Consequently, Te 1%-NCA cathode exhibits the improved cycling stability even at high voltages (4.5 and 4.7 V), good rate capability (159.2 mA h g–1 at 10 C), and high thermal stability (the peak temperature of 258 °C). Therefore, the appropriate Te surface doping provides a significant exploration for industrial development of the high-performance Ni-rich cathode materials with high capacity and structural stability.