Light-weighting of battery casing for lithium-ion device energy density improvement

Abstract

Battery casings are essential components in all types of lithium and lithium-ion batteries (LIBs) and typically consist of nickel-coated steel hard casings for 18650 and 21700 cell formats. These steel casings comprise over one quarter of total battery cell mass and do not actively contribute to battery capacity. It is therefore possible to achieve considerable battery performance improvements, in terms of device energy density, by reducing the mass of the battery casing. Following successful completion of an industry-academic technology programme of light-weighting battery casings, this paper reports our research activities to understand the practical performance of aluminium hard casings which are 63 % lighter than a state-of-the-art steel casing. A popular exemplary battery chemistry, Lithium Titanate anode / Lithium Iron Phosphate cathode, which is well-known for high power and good safety, was employed. Research investigations include (a) the optimisation of standard commercial LIB manufacturing process for aluminium casings, (b) the production of 18650 LIBs using aluminium casings, (c) electrochemical analysis and safety testing of the cells, comparing with those assembled with steel. The aluminium casings could readily be incorporated into standard commercial LIB manufacturing process with minimal process changes and provided a > 25 % boost to energy density. Crucially, stress testing of the cells revealed no added safety challenges associated with the material change. Lightweight Al hard casings have presented a possible solution to help address weight sensitive applications of lithium-ion batteries that require high power (or high energy). The approaches herein are battery materials agnostic and can be applied to different cell geometries to help fast-track battery performance improvements.