Preparation And Application Of Mesoporous Polypyrrole In Lithium-sulfur Batteries

The commericial development of lithium-sulfur batteries is hindered by the inherent electron/ion insulation of element sulfur,the huge volume expansion during the cycling,and the"shuttle effect"caused by soluble lithium polysulfide intermediates(Li₂S_n,4?n?8).Polypyrrole materials with high electro/ion conductivity,good chemical stability can effectively inhibit the diffusion of polysulfides in the discharge/charge processes.Therefore,there is a great potential for application of polypyrrole in the field of lithium-sulfur batteries.In order to improve the electrochemical performance of the sulfur-polypyrrole(S-PPy)cathode,a three-dimensional mesoporous PPy material(3DMPPy)was prepared by hard-template method,and a one-dimensional mesoporous PPy material(1DMPPy)was prepared by dual templates method.The mesoporous PPy materials were mixed with element sulfur to prepare S-PPy composite.Then,the effects of morphologies and sulfur contents on the electrochemical performance were studied using different S-PPy electrodes.The main research contents are as following:(1)3DMPPy and S-3DMPPy composite were prepared by hard-template of silica nanospheres.The influences of different silica templates on the morphology and electrochemical properties of the composite were investigated.The results show that3DOMPPy is obtained by using silica nanospheres with uniform particle size,and a three-dimensional mesoporous PPy material with ordinary morphology(3DPPy)is obtained by using silica nanospheres with non-uniform particle size as templates.The two PPy with different morphologies were mixed with element sulfur to obtain S-PPy composite.The lithium-sulfur batteries with S-3DOMPPy cathode exhibit excellent electrochemical performance:the discharge specific capacity can reach 936 m Ah g^-1 after 100 cycles at 0.1C.(2)The effect of sulfur content on the electrochemical performance of lithium-sulfur batteries with S-3DOMPPy cathode was investigated.Studies have shown that the cycling capacity of S-3DOMPPy electrode gradually decrease with the increase of element sulfur content in S-3DOMPPy composite.The L-S-3DOMPPy electrode maintains the highest discharge capacity after 100 cycles(936 m Ah g^-1).(3)1DMPPy and S-1DMPPy composite were prepared by using dual templates synthesized by self-assembling silica nanospheres in porous anodic aluminum oxide(AAO)membrane channels.The influences of different concentrations of silica nanospheres sol on the morphology and electrochemical properties of lithium-sulfur batteries were investigated.The results show that one-dimensional ordered mesoporous PPy nanowire material(1DOMPPy)is obtained by using high concentration silica nanospheres,and one-dimensional mesoporous PPy nanotube material(1DPPy)is obtained by using low concentration silica nanospheres.The cathodes of lithium-sulfur batteries were prepared by mixing polypyrrole with element sulfur.Lithium-sulfur batteries with S-1DOMPPy cathode exhibit excellent electrochemical performance:the specific discharge capacity is maintained at 1014 m Ah g^-1 after 100 cycles at 0.1C.