Atomic force nanorheology for in-situ exploration of nanoscale SEI layers in real-life rechargeable batteries electrodes.

Abstract

Solid electrolyte interphase (SEI) is a nanoscale thin layer with complex nanomechanical properties that separates batteries negative electrode and the electrolyte to allow free flow of active ions (Li or Na), while precluding electron flow. Robust and high performance SEI is critical for batteries performance, cyclability and safety, and the ability to study SEI properties in real-space and real-time (operando) holds the key for development of efficient and safe batteries. Here we report an efficient approach allowing to probe the nanoscale mechanical homogeneity of SEI layers with the nanoscale depth resolution via scanning nanorheology microscopy (NRM). In NRM the shear forces acting on the atomic force microscopy (AFM) nanoscale tip measured as tip penetrates the SEI layer from the electrolyte to the solid electrode surface provide a 1D quantitative measure of local storage and loss elastic moduli of the SEI along the path of the tip. A key feature of a new 1D-NRM is ability to probe nanoscale SEI dynamics operando in real-life battery electrodes that have micrometre scale roughness while providing nanometre scale depth resolution. Significantly, we show that due to the nature of shear-force measurements, NRM effectively eliminates the dependence of the measurements on the diameter of the AFM tip, a parameter that otherwise the hardest to quantify in AFM nanomechanical measurements. We successfully apply a new approach to quantify details of SEI formation process on the hard carbon negative electrodes in Na-ion batteries.