Understanding the capacity fade in polyacrylonitrile binder-based LiNi0.5Mn1.5O4 cells

Abstract

Binders are electrochemically inactive components that have a crucial impact on battery aging although being present in only small amounts, typically 1-3% w/w in commercial products. The electrochemical performance of a battery can be tailored via these inactive materials by optimizing the electrode integrity and surface chemistry. Polyacrylonitrile (PAN) for LiNi0.5Mn1.5O4 (LNMO) half-cells is here investigated as a binder material to enable a stable electrode-electrolyte interface. Despite being previously described in the literature as an oxidatively stable polymer, it is shown that PAN degrades and develops resistive layers within the LNMO cathode. We demonstrate continuous internal resistance increase in LNMO-based cells during battery operation using the intermittent current interruption (ICI) technique. Through a combination of on-line electrochemical mass spectrometry (OEMS) and X-ray photoelectron spectroscopy (XPS) characterization techniques, the degradation products can be identified as solid on the LNMO electrode surface, and no excessive gas formation is seen. The increased resistance and parasitic processes are correlated to side-reactions of the PAN, possibly intramolecular cyclization, which can be identified as the main cause of the comparatively fast capacity fade.

Revealing interfacial parasitic reactions of nitrile rubber binders in all-solid-state lithium batteries

“…2c), interestingly, a new peak at 398.5 eV assigned to C]N-C was found as a shoulder peak of the main peak of C^N located at 399.5 eV, suggesting that the chemical structure of the NBR binder was presumably transformed consisting of C]N-C substituents while measuring battery performance at 60 °C. [45][46][47] As evidenced by the results above, this may indicate that the parasitic reaction was negatively affecting the interfacial properties by forming passivation layers in the NBR containing electrode, and this built up a huge interfacial resistance in the cell, resulting in a signicantly negative impact on the battery performance (Fig. 2f).…”