Mechanical Properties of Cathode-Electrolyte Interphase Layers in High-Voltage Lithium-Ion Batteries

We applied an amplitude-modulated/frequency-modulated scanning force microscopy method enabling quantitative mechanical characterization of thin CEI layer on rough composite electrodes surfaces. We systematically varied the number of battery cycles and monitored the morphology and elastic modulus of the interphase layers on LNMO cathodes. The pristine crystalline LNMO surface exhibited an elastic modulus of approximately 126±20 GPa, whereas the carbon-binder regions had a modulus of 1.9±0.1 GPa. Already after 5 cycles the elastic modulus on LNMO decreased to 3.2±1.2 GPa, indicating the LNMO passivation by CEI growth. After 60 cycles, the elastic modulus became homogeneous at 4.0 ± 0.7 GPa, regardless of whether it was measured on the LNMO or on the carbon-binder region. Thus, a compositionally similar interphase formed on LNMO and on the carbon-binder surfaces. This work provides insights into interfacial stability and establishes a robust and reproducible framework for quantifying the elastic modulus of interphase layers within composite electrodes.