Effect of imidazolium-based porous polymer binder on the electrochemical performance of lithium sulfur batteries

초록

Severe polysulfide shuttle and poor conversion kinetics remain as barriers to make Li-S batteries practically viable. Polymer binders are an important component of a battery electrode although its dosage is very small. Traditionally employed PVDF binder in Li-S batteries has no significant impact in either suppressing the polysulfide shuttle or on their conversion kinetics. Ideally, the binder for a Li-S battery should suppress the polysulfide shuttle, promote the polysulfide conversion and buffer the volume expansion during charge-discharge process. Towards this direction, herein we present a new octyl imidazolium-TFSI based porous polymeric binder (PImz) in combination with CNT/S/Nickel(II) phthalocyanine tetrasulfonic acid tetrasodium salt (Na-NPT) composite. The binder offers strong polysulfide immobilizing capabilities through electrostatic interaction with the imidazolium nitrogen and pore confinement through its porous network, while a small amount of Ni-phthalocyanine could enhance the polysulfide conversion kinetics. Li-S batteries with PImz binder delivered a high specific capacity of 805 mA h/g (0.5 C) with stable performance over 300 cycles. Furthermore, the batteries with high sulfur loading similar to 3 mg/cm(2) delivered a capacity of 820 mA h/g. This newly designed porous polymeric binder is a promising and efficient alternative to the traditionally employed PVDF in terms of synthesis, cost, performance and safety.

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