Lithium-ion battery swelling characterisation using high-resolution optical fibre-based surface profiler and thermal imaging

Although lithium-ion battery deformation is a fundamental issue in the battery industry, characterizing and optimizing battery swelling remains inherently difficult due to shortcomings in existing methods to assess multi-aspect swelling involving chemical, thermal, electrical and mechanical factors. This leads to substantial gaps in understanding the root causes of swelling in practical battery systems where individual cells are aggregated into complete packs. This paper proposes a novel distributed optical sensor with mm level resolution to reveal the complex underlying mechanism of battery swelling in multiparameter (current, voltage, temperature, strain) and multi-dimensional (surface profiler and thermal image) monitoring. Bump-like swelling profiles are found with the spatial-resolved optical measurement, indicating an easy strain accumulation in the central area of pouch cells. Different causes of battery swelling - thermal, lithium intercalation/deintercalation and applied current are systematically classified and validated. Fast charge/discharge induced swelling predominantly drives battery expansion. Lithium deintercalation happening on the anode primarily contributes to the cell shrinkage during certain discharge process (Depth of Discharge