Towards low-cost, high energy density Li2MnO3 cathode materials

The extremely sluggish Li-ion diffusion rate at the activation plateau (similar to 4.5 V) in the initial charging is an activation bottleneck of Li2MnO3, which seriously restricts its discharge capacity (energy density) and rate performance. Herein, a targeted strategy is proposed where a few fluorines are substituted for oxygen (Li2MnO3-xFx, x = 0.00, 0.015, 0.03, 0.045). F-substitution reduces the deintercalation barrier of Li+ from the crystal structure by weakening the Li-O bond, and improves the electronic transmission performance by inducing more Mn3+ and oxygen vacancies. Therefore, a major breakthrough is made for the activation bottleneck as the lithium-ion diffusion coefficient at 4.5 V is increased by more than two orders of magnitude. Meanwhile, F-ions inhibit the grain growth along the (001) direction and decrease the primary particle sizes. In the narrow electrochemical window of 2.0-4.6 V, a first discharge capacity of 299 mA h g(-1) with a high energy density of 934 W h kg(-1) at 0.05 C, and a capacity of 200 mA h g(-1) at 1 C with a retention ratio of 92% after 100 cycles are achieved.