Preparation Of Modified Polypropylene Separator And Its Application For Lithium-sulfur Batteries

The polypropylene separator?PP?is one of the important component in lithium-ion batteries,which can transfer lithium-ion,separate the cathode and anode,and avoid short circuit.But the PP separator shows strong hydrophobic nature owing to its high surface energy.It is not only unfavorable to absorb the electrolyte,but also not conducive to maintain the electrolyte.Moreover,the micropores on the PP separator will be closed when temperature rises to 165 ?.Many researches focus on how to enhance the hydrophilia and thermostability of the PP separator.When the PP separator is assembled to the Li-S batteries,there is a new problem called shuttle effect.So it becomes difficult to modify the separator and alleviate the shuttle effect.To deal with these problems,we have done some researches on modification of the PP separator in this paper.When the modified PP separators are applied to Li-S batteries,the electrochemical performance are improved.?1?The PP separator coated with Al₂O₃ and CNT has been successfully prepared?CAF?.The thermal stability and the wettability of the modified separator are obviously improved due to the inorganic Al₂O₃ and porous structure of the coating layer.The coating could alleviate the shuttle effect by steric effect and chemical interaction between Al₂O₃ and polysulfides.What's more,the CNT coating layer acts as the second electrode,provides more reaction points and improves the utilization of active material due to the superior conductivity.The discharge capacity and the rate capacity of Li-S batteries assembled with CAF separator are greatly improved.The first discharge capacity is 1096 mAh g^-1,and the dstill remains 760.4 mAh g^-1 at 0.2 C after 200 cycles.?2?The hydrophobic groups of surfactant?Tween,Triton X and PEG?are strongly attached to the surface of the PP separator.It may be because the hydrophilic groups react with hydroxyl of the cross-linked silica networks.So the SiO₂ nanoparticles are decorated on the PP separator tightly with assistance of surfactant.The thermal stability and wettability of the modified separator are also improved.The first discharge capacity of the battery using the modified separator is 937 mAh g^-1.And the specific capacity still performs 603.5 mAh g^-1 with the decay rate of only 0.05% per cycle at 0.2 C after 200 cycles.?3?The polyaniline decorated PP separator has been successfully prepared by the polymerization and deposition of aniline.The wettability and the thermal stability of the modified separator are obviously improved owing to the inorganic polyaniline layer and its loose structure.The electrochemical performance of the Li-S battery with the modified separator is also improved.It is ascribed to that the polyaniline layer with conductivity could provide more reaction points and alleviate the shuttle effect.The first discharge capacity is 925.4 mAh g^-1,and remains 429.9 mAh g^-1 at 0.2 C after 200 cycles.?4?The modified separator is prepared by the copolymerization and deposition of dopamine?PD?and poly?ethylene imine??PEI?.The surface of the modified separator contains many polar functional groups?-COOH and-NH2?,which reduce the surface energy and improve the wettability of the separator.Moreover,the electrostatic interactions between PEI and polysulfides could alleviate the shuttle effect and enhance the electrochemical performance of the Li-S battery.The first discharge capacity of the Li-S batteries with the modified separator is 1033.4 mAh g^-1,and remains 411.1 mAh g^-1 at 0.2 C after 200 cycles.