Experimental Evaluation of Lithium-ion Batteries at Different Cryogenic Freezing Rates

The reverse logistic challenge of transporting damaged and waste automotive lithium ion battery (LIB) packs is an escalating concern as world-wide sales of electric vehicles (EVs) continues to rise. Damaged or defective packs must currently be transported in explosion-proof steel containers to meet international regulations, which makes transportation expensive. Freezing has been identified as a potential means to avoid these significant costs since cryogenically frozen cells are safe and therefore subject to less stringent transportation legislation. Existing literature demonstrates that flash freezing has little effect on LIB electrical performance (energy capacity and impedance), during the whole automotive life of the cells (up to 20% capacity fade). However, it is impractical to flash freeze LIB packs due to their large thermal mass. Promisingly, this study suggests slower freezing rates (0.5 to 50°C/min) have no detrimental electrical performance effects, indicating whole LIB packs could be frozen without affecting performance. In an effort to minimise the energy requirements of freezing an entire LIB pack, this research also establishes that -35°C is the minimum temperature to prevent thermal runaway of Panasonic 18650 cylindrical cells during an external short circuit. This finding will help to guide the necessary in-transport temperature monitoring systems. Overall this work makes significant steps forward in optimising cryogenic strategies to facilitate reuse and remanufacture of LIB cells from a damaged pack. Development of this approach could prolong LIB useful life leading to reduced raw material consumption and improving environmental sustainability of EV adoption.