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

22 June 2022, Version 1
This content is a preprint and has not undergone peer review at the time of posting.

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.

Keywords

LNMO
Lithium ion battery
Binder
Polyacrylonitrile
oxidative decomposition
Ageing

Supplementary materials

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Title
Understanding the capacity fade in polyacrylonitrile binder-based LiNi0.5Mn1.5O4 cells
Description
The electrochemical performance of a battery can be tailored via these inactive materials like binders 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 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 intermittent current interruption (ICI) technique. Through a combination of on-line electrochemical mass spectrometry (OEMS) and X-ray photoelectron spectroscopy (XPS) characterisation techniques, the degradation products can be identified as solid on the LNMO electrode surface, and no excessive gas formation 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.
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