Wettability of separator toward nonaqueous electrolyte can significantly affect cell performance of lithium battery. This work systemically studied the factors that affect wettability of commonly used polyolefin separator toward nonaqueous electrolyte, including solvent components, lithium salt types and their concentrations. Various wetting additives were examined. Pluronic surfactants of polyoxyethylene and polyoxypropylene triblock copolymers are reported as wetting additives to enhance the separator wettability toward electrolyte. Moreover, water was innovatively used as a wetting additive to improve separator wettability toward electrolyte. After a trace amount of H2O (200 ppm) was added into the electrolyte of 1 M LiPF6/PC, the electrolyte uptake in the polyolefin separator was significantly improved by more than three times. Based on the cell performance of LiliFePO(4) cells, it was concluded that introduction of the wetting additive H2O was helpful to improve discharge capacities and rate capability along with excellent cycling stability. (C) 2015 Elsevier B.V. All rights reserved.