Abstract: Layered Mn-based series LiLi_x(MnM)_1-xO₂ (M=Ni, Co, Cr, …) due to its much higher capacity is one of the very promising candidates of cathodes, which has become a research hotspot recently and attracted more and more attention. Especially, with the aid of advanced characterization techniques including in-situ analysis, studies on the complex structure and high-capacity delivering mechanism of the series have achieved significant progress. In the paper, the structural characterization and charge-discharge behavior of the high-energy density layered cathode were briefly introduced. Study progresses on the voltage degradation, interface/surface variation during cycling and performance improvements of LiLi_x(MnM)_1-xO₂ were reviewed in detail particularly in view of its exiting issues. Furthermore, the challenges and prospects in the high-energy density layered cathode materials were also discussed herein.