The Effects of Trace Yb Doping on the Electrochemical Performance of Li‐Rich Layered Oxides

• Published in: ChemSusChem 2019-05, Vol.12 (10), p.2294-2301
• Main Authors: Bao, Liying, Yang, Zeliang, Chen, Lai, Su, Yuefeng, Lu, Yun, Li, Weikang, Yuan, Feiyu, Dong, Jinyang, Fang, Youyou, Ji, Zhe, Shi, Chen, Feng, Wu
• Format: Article
• Language: English
• Subjects: batteries; Cathodes; Charge transfer; Chemical reactions; Doping; Electrochemical analysis; Electrode materials; Flux density; Lithium; lithium-ion batteries; Manganese; Nickel; Photoelectrons; rare earth; Transition metals; ytterbium
• ISSN: 1864-5631; 1864-564X
• DOI: 10.1002/cssc.201900226

Layered lithium‐rich cathode materials are one of the most promising cathode materials owing to their higher mass energy density than the commercial counterparts. A series of trace Yb‐doped lithium‐rich cathode materials Li1.2Mn0.54Ni0.13Co0.13−xYbxO2 (0≤x≤0.050) were synthesized and the effects were investigated by XRD, X‐ray photoelectron spectroscopy, and high‐resolution TEM. The participation of Yb ions in electrochemical reactions and the larger binding energy of Yb−O than M−O (M=Mn, Ni, Co), which expands the lithium layer spacing and stabilizes the oxygen stacking, resulted in excellent performance of materials doped with a limited Yb content (x≤0.005). However, higher doping amounts (x>0.005) significantly increased the charge‐transfer impedance and led to a sharp deterioration in electrochemical performance. The reason lies in the large difference in ionic radius between the transition metals (Mn, Co, and Ni) and Yb. There is an upper limit to the amount of Yb ions in the lattice. If the amount of Yb is higher than the limit, excess Yb ions enter the Li layers instead of staying in the transition‐metal layers or even segregate on the surface and form electrochemically inert oxides. Upper limit of Yb: Because of the large difference in ionic radius between transition metals (Mn, Co and Ni) and Yb, the amount of Yb ions that exists in a lattice has an upper limit. A small amount of Yb ions can occupy transition‐metal sites along with an expanded lithium layer spacing and elevated electrochemical performance, instead of entering the Li layers.