Mechanical strength is crucial to flexible supercapacitors during their practical usage. In this work, polybenzimidazole with a high tensile strength of ∼100 MPa, an anion (or proton) conducting polymer electrolyte when doped with KOH (or H 3 PO 4 ), was employed to fabricate highly robust and flexible supercapacitors. The polybenzimidazole film was integrated with activated carbon electrodes coated on graphite paper. These flexible supercapacitors exhibited low equivalent series resistance and good cycling stability of capacitance retention above 90% after 10000 cycles. Under mechanical deformations of bending, twisting, and rolling as well as a repeated bending test, the electrochemical performance of the flexible supercapacitors was well maintained, demonstrating good flexibility. The integration design showed better reliability against mechanical damage. It is an advantage for flexible supercapacitors with high energy density in mass production especially for devices based on KOH doped polybenzimidazole. This work suggests that polybenzimidazole based ion conducting polymer electrolytes are very promising for developing highly robust flexible supercapacitors in future practical applications.

In this work, Al-doped MnO (Al-MO) nanoparticles have been synthesized by a simple chemical method with the aim to enhance cycling stability. At room temperature and 50 °C, the specific capacitances of Al-MO are well-maintained after 10 000 cycles. Compared with pure MnO nanospheres (180.6 F g at 1 A g), Al-MO also delivers an enhanced specific capacitance of 264.6 F g at 1 A g. During the cycling test, Al-MO exhibited relatively stable structure initially and transformed to needlelike structures finally both at room temperature and high temperature. In order to reveal the morphology evolution process, in situ NMR under high magnetic field has been carried out to probe the dynamics of structural properties. The Na spectra and the SEM observation suggest that the morphology evolution may follow pulverization/reassembling process. The Na intercalation/deintercalation induced pulverization, leading to the formation of tiny MnO nanoparticles. After that, the pulverized tiny nanoparticles reassembled into new structures. In Al-MO electrodes, doping of Al could slow down this structure evolution process, resulting in a better electrochemical stability. This work deepens the understanding on the structural changes in faradic reaction of pseudocapacitive materials. It is also important for the practical applications of MnO-based supercapacitors.

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