An over-current protection device comprises two metal foils and a positive temperature coefficient (PTC) material layer. The PTC material layer is sandwiched between the two metal foils and has a volume resistivity below 0.1 Ω-cm. The PTC material layer includes (i) plural crystalline polymers having at least one crystalline polymer of a melting point less than 115° C.; (ii) an electrically conductive nickel filler having a volume resistivity less than 500 μΩ-cm; and (iii) a non-conductive metal nitride filler. The electrically conductive nickel filler and non-conductive metal nitride filler are dispersed in the crystalline polymer.