Preparation Of Nanostructured Manganese Dioxide Films And Their Applications To Electrochemical Energy Storage

Due to the high theoretical capacity,low price,abundant reserves and environmental friendliness,manganese dioxide has been widely studied in the field of energy storage.In supercapacitors,manganese dioxide can exhibit high theoretical capacity by means of psuedocapacitive energy storage mechanism,which is much higher than carbon materials based on electric double layer capacitive mechanism,making it perfect candidate for supercapacitors with small-size and specific structure.Yet when fabricating supercapacitor as a flexible transparent device,manganese dioxide is difficult to use therein because manganese dioxide has almost no light transmittance and flexibility after being prepared into a film structure.In lithium-sulfur batteries,the strong polar manganese-oxygen bond of manganese dioxide can make a good chemisorption effect on the lithium polysulfide dissolved in the electrolyte,and as a result the shuttle effect can be inhibited.However,the poor conductivity of manganese dioxide makes it difficult to reuse the adsorbed lithium polysulfide,which limits the performances of lithium-sulfur batteries.In this paper,manganese dioxide is prepared into engineered films with special micro or nano structure,which greatly improves the performances of manganese dioxide in light transmittance,flexibility conductivity.The prepared manganese dioxide films are successfully applied to flexible and transparent supercapacitors and lithium-sulfur battery separators.The specific research results are described as follows:?1?Ordered porous polymer film templates were prepared on substrates by breath figure methods,then manganese dioxides were electrodeposited into the holes of the templates to form island-like array films.After removing the polymer template,the manganese dioxide island array electrodes and gel electrolyte were assembled into all-solid-state sandwich-like flexible transparent supercapacitors.The thickness and gap distance of the manganese dioxide island array can be controlled by adjusting the deposition time.In the island array,the blank area where was originally covered by the polymer template,can greatly improve the transmittance of the electrode.At the same time,the island-like array structure can effectively eliminate the internal stress in the film and avoid cracks during the bending operation.As a result,the assembled flexible transparent supercapacitor can achieve 44%transmittance at 550 nm,90.2%capacity retention when bent to 180°,specific area capacitance of4.73 mF cm^-2 at current density of 50?A cm^-2,and great cycling stability.?2?The ultralong manganese dioxide nanowires were prepared by hydrothermal method,then they were uniformly mixed with carbon nanotubes and vacuum-filtered onto a polypropylene separator to form a modification layer film.Such modified separators were applied to lithium-sulfur batteries,aiming to effectively suppress the shuttle effect and to improve battery performances.In the modified layer film,manganese dioxide can effectively capture dissolved lithium polysulfides by chemical adsorption,and the conductive network formed by carbon nanotubes can realize rapid transfer of electrons to accelerate the redox reaction of lithium polysulfides.At the same time,the porous structure formed by one-dimensional nanomaterials such as nanowires and nanotubes has no side effect on the normal migration of lithium ions.Applying the separators modified by the mixed film of manganese dioxide and carbon nanotubes to the lithium-sulfur batteries can significantly inhibit the shuttle effect of lithium polysulfides,and the performances and stability of the lithium-sulfur batteries can be greatly optimized.As a result,the initial capacity can reach 843.7 mAh g^-1 at current density of 1 C,and the capacity can still maintain 68.03%of the initial capacity after 500cycles,with a decay rate of only 0.136%per cycle.