Understanding and Controlling Atomic and Nanoscale Structural Rearrangement in Nanoporous Electrode Materials for Lithium and Sodium Ion Batteries

Control of structural change at the nanoscale is key to improving functionality in many new energy materials. This talk specifically focuses on nanostructured electrode materials for lithium or sodium ion batteries. When lithium or sodium ions are inserted into a host electrode material, structural change can occur across multiple length scale. At the atomic scale, local structural change is generally required to accommodate the insertion of alkali metal atoms in the host lattice, and this change can occur in a continuous manner (solid-solution like, or second-order transition), or in a discontinuous manner (in a first-order phase transition). Those phase-transition dynamics are intimately tied to the ion ordering within the electrode material and to the speed at which ions can be inserted into and removed from the lattice. The first part of this talk, will thus focus on controlling ion ordering and phase-transition dynamics with a goal of creating fast charging electrode materials. We find that the synthesis of materials with nanoscale domain sizes and the judicious introduction of disorder together provide ideal avenues to control the dynamics of atomistic structural rearrangements, allowing for the development of fast charging electrode material.
Ion insertion can also lead to volume expansion, and this can result in dynamic cracking of electrode materials up cycling, a phenomenon that is particularly ubiquitous for high capacity anode materials like alloy anodes. While this large length scale structural change is harder to control, we have found that the use of ductile amorphous phases combined with nanoscale porosity can mitigate some of the structural degradation associated with large volume changes. To understand this process in detail, we use operando transmission X-ray microscopy (TXM) with nanometer scale spatial resolution to follow changes in both the nanoscale pores system and in the overall particle shape and size upon cycling. The results provide insight into the complex dynamics that occur within electrode materials upon cycling, and provide potential routes to better control all of these process in the quest for high performance energy materials.