Solid-solid interfaces are ubiquitous in lithium ion and other high energy density batteries. Even batteries based on organic liquid electrolytes exhibit interfacial ("solid electrolyte interphace" or "SEI") films. The atomic structure, function, and evolution of such solid-solid interfaces are challenging to elucidate using imaging and other experimental methods. Electronic structure calculation techniques provide a complementary approach. In particular, a comparative study of liquid- and solid-electrolyte batteries permits cross-polination of methods, perspectives, and paradigms. Applying solid state thermodyamic perspectives, we show that organic electrolyte molecules, and even most components of the SEI, are profoundly metastable. Under certain conditions, SEI components will evolve and decompose chemically or electrochemically. Lithium metal, silicon anode, and high voltage oxide surfaces will be used as example. Applying liquid state kinetic perspectives and LiPON as example, we show that the speciation at the interfaces in all-solid batteries are not necessarily governed by thermodynamics alone; the degradation barrier may be sufficiently high to permit the existence of metastable components. Our comparative study therefore yields an unified perspective on interfaces in solid- and liquid- based batteries.
This work was supported by Nanostructures for Electrical Energy Storage (NEES), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DESC0001160. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.