UC San Diego

Recently, anionic activity, oxygen redox reaction, has been discovered in the electrochemical processes, providing extra reversible capacity for lithium-rich layered oxide cathode. However, the huge irreversible capacity loss in the first charge–discharge cycle and voltage degradation during cycling process prevent their utilization in LIBs. Herein, modified carbonate co-precipitation synthesis without addition of chelating agent is introduced to obtain meso-structure controlled Li-rich layered oxides. This unique design not only decreases surface area compared with the sample with dispersive particles, but also increases overall structure mechanical stability compared with the sample with larger secondary particles as observed by TXM. As a result, the voltage decay and capacity loss during long term cycling have been minimized to a large extent.

Gas–solid interface reaction is designed to achieve delicate control of oxygen activity through uniformly creating oxygen vacancies without affecting structural integrity of Li-rich layered oxides. Theoretical calculations and experimental characterizations demonstrate that oxygen vacancies provide a favorable ionic diffusion environment in the bulk and significantly suppress gas release from the surface. The target material is achievable in delivering a discharge capacity as high as 301 mAh g-1 with initial Coulombic efficiency of 93.2%. After 100 cycles, a reversible capacity of 300 mAh g-1 still remains without any obvious decay in voltage. We further design a path to remove the defects in the structure of Li-rich layered oxides by high temperature annealing. This treatment recovers the superstructure and average discharge voltage. The novel understanding of the structure metastability and reversibility phenomenon will provide clues for identifying more realistic pathway to fully address voltage decay issue of high-capacity Li-rich layered oxide electrodes.

On the other hand, Magnesium-ion batteries (MIBs) have twofold volumetric energy density than that of lithium without the dendritic deposition morphology associated with Li, which makes MIBs attractive options. We investigate the feasibility of using anatase-phase TiO2 as an electrode material for MIBs. Electrochemical, microscopic, and spectroscopic analyses are performed in order to probe Mg-ion insertion as well as determine the limitation of TiO2 as a viable electrode material.