Safety and performance implications of lithium plating induced by sub-zero temperature cycling of lithium-ion batteries

The operation of lithium-ion cells at sub-zero temperatures can result in the deposition of metallic lithium onto the surface of the negative electrode. The resulting lithium deposits have substantial ramifications for the performance and safety of the cell, with rapid capacity fade and reduced thermal stability both exhibited in cells aged under these conditions. In this study, it is found that extending the cycling temperatures of these cells to sub-zero temperatures results in a change in plating behaviour, with cells cycled at −10 °C exhibiting reversible plating behaviour and cells cycled at −20 °C plating irreversibly instead. Additionally, the nature of the plating is observed to transition from reversible to irreversible with progressive ageing in the cells cycled at −10 °C. Using operando electrochemical analysis such as voltage relaxation and Coulombic efficiency (CE) measurement, characteristics of the degradation are revealed. Electrochemical impedance spectroscopy (EIS) is also employed between cycles to provide information on the changes in internal cell processes due to plating. Ex-situ investigations complement the analysis allowing images of electrode condition to be collected. In-situ X-ray computed tomography further highlights how lithium plating compromises the structural integrity of the internal cell architecture, leading to increased safety concerns. Testing the aged cells with accelerated rate calorimetry also shows that the presence of more strongly reductive metallic lithium within a cell results in lower onset temperatures for self-heating and thermal runaway, plus an increased potential for projectiles during failure. • Degradation and safety of Li-ion cells at low temperatures examined. • Influence of temperature on Li plating on safety explored. • Jelly roll collapse due to Li-plating observed. • Multi-technique characterisation details increased safety risk at low temperatures.