Size effect on the thermal and mechanical performance of cylindrical lithium-ion batteries

Increasing the size of cylindrical lithium-ion batteries (LIBs) to achieve higher energy densities and faster charging represents one effective tactics in nowadays battery society. A systematic understanding on the size effect of energy density, thermal and mechanical performance of cylindrical LIBs is of compelling need. Taking the diameter D and height H of cylindrical LIBs as variables, we shed light on the energy densities, thermal and mechanical performance of cylindrical LIBs. The volumetric energy density increases with D, while the gravimetric energy density first increases with D, peaks at a certain diameter before dropping with further increasing D. The thermal performance of cylindrical LIBs could be better characterized by the diameter-to-height ratio: cells of identical capacity but with greater D/H show lower temperature rise and lower thermal gradient at high cycling rates. Mechanically, LIBs of greater D are prone to buckling on the jellyroll close to core, and may fracture under tension on outer jellyroll near the cell case. Those findings suggest the necessity to optimize D and H of cylindrical LIBs insomuch as the trade-offs between the thermal and mechanical performance.