context: The lithium-ion battery, which can convert chemical energy to electric energy, has been widely used in portable devices, such as the laptops and mobile phones. However, the pressing demand for high capacity and stability is yet to be solved, especially the cathode, which has been the bottleneck of battery capacity. The Li-rich layered oxide has gained much attention due to the extremely high capacity of over 280 mA h g−1. Recent research has revealed that the extra capacity in the Li-rich oxide comes from the participation in oxygen redox. The complex chemical and structural evolution of the Li-rich cathode has attracted extensive efforts, however, the critical problem of voltage decay remains unsolved with its elusive mechanism.
answer:  Li-rich 