Modification of Battery Separators via Electrospinning to Enable Lamination in Cell Assembly

To meet the requirements of today’s fast-growing Li-ion battery market, cell production depends on cheap, fast and reliable methods. Lamination of electrodes and separators can accelerate the time-consuming stacking step in pouch cell assembly, reduce scrap rate and enhance battery performance. However, few laminable separators are available on the market so far. This study introduces electrospinning as a well-suited technique to apply thin functional polymer layers to common battery separator types, enabling lamination. The method is shown to be particularly appropriate for temperature resistant ceramic separators, for which stable interfaces between separator and electrodes were formed and capacity fading during 600 fast charging cycles was reduced by 44%. In addition, a straightforward approach to apply the method to other types of separators is presented, including separator characterization, coating polymer selection, mechanical tests on intermediates and electrochemical validation in pouch cells. The concept was successfully used for the modification of a polyethylene separator, to which a novel fluoroelastomer was applied. The stability of the electrode/separator interface depends on the polymer mass loading, lamination temperature and lamination pressure, whereas poorly selected lamination conditions may cause damage on the separator. Appropriate adhesion force of 8.3 N/m could be achieved using a polymer loading as low as 0.25 g/m 2 . In case separator properties, coating polymer, morphology of the fibrous coating and lamination conditions are well adjusted to each other, the implementation of electrospinning and lamination allows for faster, more flexible and robust pouch cell production at comparable or better electrochemical cell behaviour.