High energy density batteries are becoming essential to satisfy the demands of fast growing portable electronic and electric vehicle markets. There are great efforts in the battery community to explore new materials with a high energy density. However, the challenge is formidable and even if potential materials can be identified, it still takes years, if not a decade, to commercialize. Therefore, it is reasonable to investigate modifications of existing materials to improve battery energy density.

LiCoO₂, the first commercialized material, is still the most used cathode material to-date due to its simple synthesis process, high energy density, and good cycle life. Conventionally, only a limited amount of its capacity was utilized due to the concern of its structural instability. However, with better understanding of this electrode material, more and more energy has been achieved by pushing its cutoff voltage to higher values without sacrificing electrochemical performance. Currently, LiCoO₂ is operated as high as 4.4V in full cells, which is equivalent to 4.45V vs. Li, and yields a specific capacity of 180mAh/g. This is close to a 20% capacity increase compared to the early 140 mAh/g capacity. In this study, we investigated the possibility of increasing the LiCoO₂ upper cutoff voltage to even higher voltages, such as 4.5V or even 4.6V, with capacities greater than 190 mAh/g.

It has been well understood that LiCoO₂ will go through a phase transition when half the lithium is removed from the structure. This phase transition will affect the stability of its structure and lead to poor cycling performance. Doping is a common method to suppress the phase transition. In order to study the doping effect, aluminum doped LiCoO₂ (LCO-A) cathode materials were prepared by ShanShan, China. The electrochemical characterization clearly indicates that the phase transition is suppressed for the doped LiCoO₂, which demonstrated excellent cycling performance. Following their electrochemical characterization, the LiCoO₂ cathode materials were further studied to examine their chemical composition, morphologies, structure, and surface properties. The results shed further light on the development of high energy LiCoO₂.

Acknowledgement

Support from David Howell and Peter Faguy of the U.S. Department of Energy’s Office of Vehicle Technologies Program is gratefully acknowledged. This work was performed, in part, at the Electron Microscopy Center for Materials Research, Center for Nanoscale Materials and Advanced Photon Source, Offices of Science, Offices of Basic Energy, and Offices of Sciences User Facility operated for U.S. Department of Energy (DOE) Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357.