We employed 2D/3D X-ray computed tomography in conjunction with microzone analysis to study the failure mechanisms of lithium-ion battery packs at low temperatures. A nondestructive X-ray computed tomography strategy confers the direct and comprehensive observation of the hard-swelling of lithium-ion battery packs at low temperatures. X-ray computed tomographic images indicate that severe wrinkles occur in the electrode components, thus shedding light on the evolution of the failure process, which provides a valid secondary analysis of the failure mechanisms without damaging the battery pack. Combined with the results of the microzone analysis, swelling failure can be attributed to the generation of Li dendrites, volume expansion and delamination of the active materials. These processes can be caused by the slow electrochemical kinetics of the active materials at low temperatures.