The development of a small-molecule organophosphorus gel polymer electrolyte additive for use in rechargeable lithium batteries is described. This organophosphorus additive is less volatile and more resistant to ignition than propylene carbonate, a well known component of gel polymer electrolytes. Moreover, the ionic conductivities of gels containing the organophosphorus additive at low molar concentrations (11-21%) exceed the ionic conductivities of gels containing equimolar amounts of propylene carbonate (5.3 x 10(-5) versus 4.8 x 10(-5) S/cm). At higher molar concentrations (31-52%) there is evidence of phase separation, but conductivities remain comparable to propylene carbonate systems.