Investigating Low Temperature Degradation and Its Impact on the Performance and Safety of Lithium-Ion Batteries

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Lithium-ion batteries are at the forefront of facilitating the modern-day industrial revolution: a transition from petrochemical energy storage to specialised carbon-free energy storage. Batteries hold a crucial role in storing energy generated by renewables outside of peak energy demands, whilst also enabling an extended portable energy supply for applications such as electronic devices, aerospace applications and electric vehicles. Increasing the energy densities of our batteries is one of the main avenues these technologies are taking to ensure the demands of the green transition are met. In recent years, numerous high-profile failures of lithium-ion batteries have been reported1, contributing to wider concerns about the safety of high energy density cells. Inadequate management of such systems can be costly for both human health and financial damages. To accommodate these more energy-dense cells, manufacturers need to provide better assurances in safe cell operations.Apprehensions in cell safety can mainly be attributed to a cell’s ability to enter thermal runaway, a process that is most often caused by an internal short circuit (ISC). Such an event can be triggered by three different modes of abuse: thermal, mechanical, and electrical. At the anode, metallic lithium can precipitate onto the surface via three main conditions: overcharge, high charging currents, and low charging temperatures. Each of which creates a saturation of intercalated lithium-ions in the crystallographic active sites near the anode surface. This lowers the anodes surface potential until it is sufficiently low enough for lithium plating to occur. This work investigates cell function at low temperatures and how the resulting degradation affects their response to abusive conditions.Various ageing regimes were applied to a set of commercial lithium-ion cells and, by monitoring their electrochemical behaviour, carrying out ex-situ characterisation of the aged negative electrodes, and employing X-ray computed tomography (CT), this work evaluates the decline in performance observed at low temperatures. Subsequent accelerated rate calorimetry (ARC) and operando ultra-high-speed synchrotron tomography studies highlight the diminished thermal stability these aged cells possess as the states of degradation become more advanced and reveal the mechanisms through which failure occurs. These findings demonstrate why improved cell architecture and real-time management systems are necessary to realise commercial success in future battery applications. Figure 1