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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.

A phosphorus/silicon flame retardant, MVC-DOPO, was synthesized from 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and 2,4,6,4,6, via addition reaction. Its flame-retardant effect on polycarbonate (PC) was investigated. The phosphorus/silicon flame retardant increased the limited oxygen index and UL-94 rating and reduced the heat release rate and total heat release of DOPO-MVC/PC composites during combustion, indicating the excellent flame-retardant effect of MVC-DOPO on PC. MVC-DOPO inhibited the burning intensity of PC material in the gaseous phase and promoted the formation of a more viscous residue in the condensed phase. Through releasing phosphorus-containing pieces and phenoxy radicals from the phosphaphenanthrene group, MVC-DOPO quenched the combustion chain reaction in the gaseous phase; through promoting formation of a more viscous residue and a dense char layer from the main actions of the cyclotetrasiloxane group, MVC-DOPO reduced fuel release and generated a barrier effect in the condensed phase. Hence, MVC-DOPO effectively exerted a flame-retardant effect on PC material in both the gaseous and condensed phases during combustion. V C 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45815.