| AVS 57th International Symposium & Exhibition | |
| In Situ Microscopy and Spectroscopy Topical Conference | Tuesday Sessions |
| Session IS+SS-TuA |
| Session: | In Situ Microscopy/Spectroscopy – Interfacial Chemistry/Catalysis |
| Presenter: | A. Subramanian, Sandia National Laboratories |
| Authors: | A. Subramanian, Sandia National Laboratories J.P. Sullivan, Sandia National Laboratories J. Huang, Sandia National Laboratories M.J. Shaw, Sandia National Laboratories N. Hudak, Sandia National Laboratories Y. Zhan, Rice University J. Lou, Rice University |
| Correspondent: | Click to Email |
Nanoscale materials offer a number of potential advantages for Li-ion batteries: examples include low-cost LiFePO4 nanoparticle cathodes that exhibit good rate performance despite having low electrical conductivity and high-capacity conversion anodes that have high cycle life despite large volume changes per cycle, e.g. Si nanowires. However, one of the challenges with the use of nanoscale materials is their electrochemical characterization, particularly assessing structural changes in nanoscale particles, or reaction product layer interfaces, such as the solid-electrolyte-interphase (SEI). This requires tools with atomic to nanoscale spatial resolution. To meet this need, we have developed a micro-electromechanical systems (MEMS)-based platform for performing electrochemical measurements using volatile electrolytes inside a transmission electron microscope (TEM). This platform uses flip-chip assembly with special alignment features and multiple buried electrode configurations. The nanoscale materials of interest are assembled into the viewing area using dielectrophoresis (DEP). This permits the incorporation of a diverse array of nanoscale particles, including the co-assembly of anode materials in proximity to cathode materials. As an initial realization of the MEMS-based platform, we have developed an unsealed platform that permits in situ TEM electrochemistry using ionic liquid electrolytes or ex situ electrochemistry and TEM imaging using conventional battery electrolytes. We have demonstrated these approaches using β-MnO2 nanowire cathodes that were individually assembled using DEP. These wires were lithiated over a range of potentials, in ethylene carbonate-based electrolytes with lithium metal as a counter electrode, in order to produce a range of lithium content. Using TEM and solid-state electrical characterization, we observed that lithiation introduces increasing lattice disorder particularly at the nanowire surfaces; yet, the wires remain β-phase. The electrical measurements revealed a monotonic decrease in electrical conductivity with increasing lithium content, consistent with electronic localization at defects or an increased band gap. From these results, we conclude that in situ TEM characterization tools will enable important mechanistic understanding of Li-ion battery materials. This work was supported by LDRD and EFRC projects and was performed, in part, at CINT, a U.S. DOE, Office of Basic Energy Sciences user facility. Sandia is a multiprogram laboratory operated by Sandia Corp., a wholly owned subsidiary of Lockheed Martin Company, for the U.S. DOE’s NNSA under contract DE-AC04-94AL85000.