The invention relates to a separator for non-aqueous-type electrochemical devices that has been coated with a polymer binder composition having polymer particles of two different sizes, one fraction of the polymer particles with a weight average particle size of less than 1.5 micron, and the other fraction of the polymer particles with a weight average particle size of greater than 1.5 microns. The bi-modal polymer particles provide an uneven coating surface that creates voids between the separator and adjoining electrodes, allowing for expansion of the battery components during the charging and discharging cycle, with little or no increase in the size of the battery itself. The bi-modal polymer coating can be used in non-aqueous-type electrochemical devices, such as batteries and electric double layer capacitors.