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Fig. 133: a) Radiography of the standard commercial metal current collector cell undergoing failure during nail penetration. b) Radiography showing the complete absence of thermal runaway and shear stress exerted on the electrode assembly in a cell with both Al + Cu PCC. c) Reconstructed tomogram of the entire nail-penetrated cell containing Al + Cu PCC. d) An internal X-ray CT of the cell shown in (c), where numbered arrows highlight features that can be observed across multiple locations and are not limited to the example shown, where (1) shows the negative copper PCC and (2) shows the positive aluminium current collector retreating from the penetrating nail.

The highly favourable energy-storage performance parameters offered by lithium-ion energy storage technologies have led to myriad applications. These range from medical devices and portable electronics to electric vehicles and smart grid-scale energy storage. However, high-profile and widely-reported catastrophic failures have emphasised the impetus for greater understanding of the thermal runaway process and potential mitigation methods that could be implemented to prevent them.

The use of metal-coated polymer current collectors (PCC) and their conventional pure metal collector counterparts were used in the construction of commercial cylindrical 18650-format cells to observe and compare their distinct effects during nail penetration abuse testing. Cells with the aluminium polymer current collector (Al-PCC) demonstrated 100% success in prevention of failure and thermal runaway, whereas the standard cell

designs consistently underwent thermal runaway. Direct visualisation of the function of the PCC in preventing thermal runaway during nail penetration testing was evaluated with high-speed X-ray radiography at beamline ID19, similar to previous work [1,2], which provided insight into the propagation of failure (or lack thereof) over short timescales (1-2 seconds).

The function of the PCC was to isolate the electronically conductive materials at the defect induced by nail penetration to prevent internal short-circuit. The nucleation of cell failure can originate from cell operating conditions, manufacturing defects or abusive external environments, which, in most instances, cause an internal short-circuit. Therefore, this highlights the promise of isolating the most electronically conductive components as a method to prevent failure and reduce the risk of thermal runaway propagation through the cell.