The Preparation And Performance Research Of All-solid-state Supercapacitors Based On Polybenzimidazole Electrolyte

Supercapacitors are important energy storage devices.They have been widely used in automobiles,military weapons,instrument communication and other fields due to their significant advantages such as high power density,fast charge and discharge and excellent cycle ability.Electrolyte is the core component of supercapacitors which can be divided into liquid and solid.The solid-state electrolyte can act as the separator and the conductive medium in the supercapacitor that its performance affects the working voltage and long-term stability of the supercapacitors.Supercapacitors usually encounter severe conditions such as high temperature,strong acid/alkali and other harsh environment during the practical applications.Therefore,the electrolyte material should have high thermal stability,corrosion resistance and other properties.Due to the good ion conductivity,high thermal stability and mechanical strength of polybenzimidazole,it can be used not only as the proton exchange film and anion exchange film material,but also as the electrolyte for supercapacitors.In this paper,we prepared a porous polybenzimidazole?pPBI-IL-x%?electrolyte,x represents the content of the functional ionic liquid.The porous structure allows the film material to absorb more phosphoric acid,and its functional groups can be hydrolyzed to form the Si-O-Si cross-linked network under acidic conditions which ensure the film material has better thermal stability and mechanical strength.The conductivity of pPBI-IL-15%composite film reached 0.103 S cm^-1 at 170°C.And the supercapacitor based on pPBI-IL-15%composite film has a specific capacitance up to 85.50 F g^-1 at120°C.After 10,000 galvanostatic charge-discharge cycles,the capacitance retention rate was still 91.00%.Polybenzimidazole-based film materials exhibit excellent performance in all-solid-state supercapacitors,but the mechanical strength of the film materials will be seriously damaged by doping with phosphoric acid.Meanwhile,polybenzimidazole-based membranes can also be used as anion exchange films,due to the imidazole rings in polybenzimidazole have amphoteric properties.In order to further study the application of anion exchange film in supercapacitors.We first prepared the hydroxy polybenzimidazole?PBIOH?,and introduced the ionic liquid containing quaternary ammonium group into the system.We obtained the cross-linked film?PBIOH-IL-X?by chemical cross-linking and doping with the alkali.The introduction of ionic liquid can improve the ion conductivity and alkali resistance stability of the film material.The highest conductivity of PBIOH-IL-20 film was 0.078 S cm^-1 at 90°C which was nearly 7 times higher than that at room temperature.The ASCs-20 with PBIOH-IL-20 film as the electrolyte,and the prepared supercapacitor has 87.00%capacitance retention rate of and 92.30%coulomb efficiency after 6000 galvanostatic charge-discharge cycles.The highest power density reached 82.32 kW kg^-1.