Silicon is a cheap, abundant, material with readily modified morphology and surface chemistry and has the potential to store more than ten times the amount of lithium than graphite in a lithium ion battery. However, during cycling in a battery the massive 300% volume expansion and contraction of silicon quickly leads to cracking of the silicon as well as damage to the solid electrolyte interphase. To mitigate the damage to the silicon, coatings and mechanical restraints might be applied which allow the silicon to expand but apply a residual stress to help keep the particle intact. Here, microfabrication techniques including electron beam lithography are used to create idealized silicon structures. These structures are then assembled into a custom electrochemical cell for <i>in situ</i> analysis by an atomic force microscope (AFM). Using the AFM in both imaging and nanoindentation modes, the evolution and mechanical properties of the structures and the SEI are tracked during both lithiation and delithiation. The nanoindentation results are compared to finite element analysis models. Most notably, it is found that the mechanical properties of even nanoscale silicon materials do not recover after one cycle when the particles are unconfined. Additionally, Si structures without rigid mechanical supports experience plastic deformation prior to cracking. Finally, the challenges facing AFM-enabled nanoindenation and associated Oliver Pharr Analysis will be presented including a description of framework for software to rapidly analyze these complex results.

In situ AFM nanoindentation and morphology analysis of mechanically constrained microfabricated silicon anodes

249th National Meeting (2015)

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