NOVELTY - The demineralizer (100) has a housing (110) comprising an inlet port (114) and an outlet port (115), where liquid coolant is introduced into and/or discharged from an interior space of the housing through the inlet port and the outlet port, respectively. A hollow filter element (140) is filled with ion resin (141) for removing ions from the coolant and arranged between the inlet port and the outlet port. The filter element exhibits a plate-shape such that the coolant introduced through the inlet port passes through the filter element in a direction perpendicular to the filter element.    USE - Large-area coolant demineralizer for removing ions from a liquid coolant in coolant loop of a fuel cell system of a vehicle i.e. fuel cell vehicle. Uses include but are not limited to a motor vehicle e.g. passenger car, sports utility vehicle (SUV) and bus, commercial vehicle i.e. lorry, a watercraft e.g. boat and ship, an aircraft, a hybrid vehicle, an electric vehicle, a plug-in hybrid electric vehicle and a hydrogen-powered vehicle.    ADVANTAGE - The filter element exhibits the plate-shape such that the coolant introduced through the inlet port passes through the filter element in the direction perpendicular to the filter element, so that differential pressure in the demineralizer and a thickness of a layer of the ion resin are reduced to enable smooth flow of the coolant through the demineralizer, thus increasing filtering efficiency of the filter element to reduce electrical conductivity of the coolant, and hence preventing current leakage from the fuel cell stack to improve electrical safety of a driver of the vehicle while reducing manufacturing and maintenance costs of the demineralizer.    DESCRIPTION OF DRAWING(S) - The drawing shows a cross-sectional view of a large-area coolant demineralizer.'(Drawing includes non-English language text)'    Large-area coolant demineralizer (100)    Housing (110)    Inlet port of housing (114)    Outlet port of housing (115)    Filter element (140)    Ion resin (141)