Rechargeable lithium ion batteries help to enable sustainable energy systems by storing electricity generated by intermittent renewable resources such as wind and solar energy, or by powering zero-emission electric vehicles charged by electricity from renewable resources. The two key performance measures of lithium ion batteries are capacity and recharge rate, which determine how much energy a battery can store and how long it takes to fully recharge. One approach to significantly improve capacity is to replace conventional graphite anodes with alloy-type anode materials that include the elements silicon (Si), germanium (Ge), and tin (Sn). However, these alloy materials swell up after charging, which promotes mechanical failure. This project will address this issue by adding the element selenium (Se) to alloy-type anodes made from micrometer sized particles. The resulting Se-doped microparticles may be able to reduce swelling of the anode. Advanced imaging and computational studies will gain a fundamental scientific understanding of these processes, with the long-term goal of developing commercially affordable, high-performance anode materials for better batteries. The research will be a collaborative effort between researchers at three universities - Indiana University, Mississippi State University, and the University of Texas at Austin. Furthermore, the educational activities associated with this project will be coordinated between these three institutions, and will include integration of the research into undergraduate and graduate course lectures, involvement of undergraduate students and K-12 teachers in research, and outreach to pre-college students through development of short, energy-related animated videos.
The overall goal of the research is to develop a fundamental understanding of the electrochemical, material phase, and morphological dynamics of Se-doped Ge and Sn microparticles during lithiation and de-lithiation reactions with lithium ion battery alloy-type anodes. The research plan has two objectives. The first objective is to investigate the dynamics of Se-doped materials during lithiation and de-lithiation, focusing on in situ measurement of phase and morphology change via in situ X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and transmission X-ray microscopy (TXM). Concurrently, the composition of the Se-containing inactive phase will be identified and its ionic conductivity will be determined. Furthermore, the effect of the active/inactive mixed phases on cycling performance for both Ge- and Sn-based electrodes will be studied. The second objective is to develop correlations between lithium ion battery cell performance and changes in Se-Ge and Se-Sn electrode microstructure through the afore-mentioned experiments and theoretical modeling. A phase field model that integrates the processes of electrochemical reaction, species diffusion, interfacial effects, as well as large elastoplastic deformation will be developed to simulate the concurrent evolution of phases, morphologies and stress within a Ge-Se or Sn-Se particle during lithiation and de-lithiation. Since it is likely that future high-capacity electrode materials will have large volume changes, the outcomes from the research may enable development of these new battery systems.
