The innovation engine for new materials

Michael Toriyama

Michael Toriyama


Materials Science and Engineering


University of Illinois at Urbana-Champaign


Jonas Kaufman
Sanjeev Kolli

Faculty Sponsor(s): 

Anton Van der Ven

Faculty Sponsor's Department(s): 


Project Title: 

Theoretical Study of Phase Formations in KxCoO2

Project Description: 

Potassium (K) ion batteries offer a viable alternative to their lithium ion counterparts for large-scale energy storage applications due to lower production costs and comparably low standard redox potential. The choices of cathode and anode, the two battery components related to various parameters such as usable voltage range and capacity, are crucial for performance optimization. However, a fundamental understanding of phase formation in many cathode materials is yet to be established, which is important for realizing potential battery degradation mechanisms. By utilizing a statistical mechanics code and first principles Density Functional Theory (DFT) calculations, we systematically study ground state orderings of KxCoO2 with respect to K-ion composition x, where the cathode material is layered cobalt oxide (CoO2). Our findings show that a multitude of phases form at different compositions of K-ions, some of which are the exact orderings found in a similar system, NaxCoO2. We also report the discovery of a new phase that is stabilized by undulating CoO2 layers at high K-ion compositions, which has not been reported for smaller ions such as Li and Na in this cathode material. This is attributable to large alkali-alkali repulsions between K-ions, which suggests that synthesizing KxCoO2 at these compositions may lead to breakdown of the layered structure primarily due to strain energy effects. Accordingly, we develop a theoretical understanding of mechanical and electrical characteristics of KxCoO2 from first-principles for energy storage applications.