Understanding the Evolution of Cathode Material in Electrochemical Process at Multi-Scale

Abstract

Nowadays it’s well recognized that developing renewable energy resources and energy conservation are key technique for us to meet with a sustainable future. Lithium ion batteries (LIBs) stood out as promising candidates for energy storage devices. Further increasing energy density and reducing cost are the major goals of researchers. Though for now, on increasing energy density more progress seems to be made with anode rather than cathode, there are still several kinds of cathode material with great expectations such as high-voltage LiCoO2, Li-rich material and Nickel-rich layered material. However, they all suffer from surface degradation, transition metal reduction and structure instability accompanied by oxygen release to some extent during the electrochemical process. Therefore, understanding the chemical compositional change and local structure transformation inside the cathode material is essential for us to contain these hazardous deteriorations from the beginning. Transmission X-ray microscope (TXM) has been proven to be a powerful experimental method for investigation on material systems at particle level especially when energy resolution is feasible and combined with data-mining technique. With this technique, we can monitor chemical compound evolution and their spatial distribution in cathode material during the electrochemical process. More excitingly it shows the possibility to see the emergence of unexpected minor phase which isn’t anticipated in the first place. Furthermore, with the aid of atomic DFT calculation and mesoscale mechanical simulation we could relate the practical performance of material in real cell with the subtle changes inside a particle. In this report by combining these methods at different length scale we offer our own insights on transition metal dissolution and precipitation, variation of chemical composition in different region of a single particle and the behavior of transition metal at different charge voltage. In general, we hope these findings could benefit our understanding on the material evolution in actual electrochemical process. Acknowledgment The work done at Brookhaven National Laboratory were supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies of the U.S. Department of Energy through the Advanced Battery Materials Research (BMR) Program, including Battery500 Consortium under contract DE-SC0012704. Research conducted at ORNL's Spallation Neutron Source was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy.