Sword/scabbard-shaped asymmetric all-solid-state supercapacitors based on PPy-MWCNTs-silk and hollow graphene tube for wearable applications

[Display omitted] •An innovative all-encapsulated core-sheath asymmetrical structure is proposed.•The state-of-the-art design learns from the ancient ‘sword-scabbard’ structure.•Ultrahigh length/area specific capacitance and energy density are achieved.•Remarkable electrochemical and mechanical stabilities are demonstrated. Fiber-shaped supercapacitors (FSSCs) have attracted increasing attention for wearable electronics. Herein, an asymmetrical fiber-shaped supercapacitor, AFSSCs-ICS, with an innovative encapsulated core-sheath architecture has been successfully constructed for the first time. The sword-scabbard inspired AFSSCs-ICS was fabricated by simply inserting a ‘sword’ positive electrode, PPy-MWCNTs-silk, into one tubular graphene ‘scabbard’ negative electrode with H2SO4/PVA gel as electrolyte. Notably, our newly designed PPy-MWCNTs-silk electrode had an ultrahigh length specific capacitance of 15.3 mF cm−1 (corresponding to high areal or volumetric capacitance of 676.9 mF cm−2 or 376.3 F cm−3), representing one of the highest levels among the fabric yarn derived electrodes, while the hollow graphene tube depicted a superior linear capacitance of 19.1 mF cm−1, which could match well with that of the PPy-MWCNTs-silk electrode. Benefiting from the innovative yet rational structure, and ideally balanced charges, the AFSSCs-ICS had an extended operating potential of 1.6 V, and an outstanding length specific capacitance of 2.3 mF cm−1 with a very admirable energy density of 0.8 μWh cm−1, dramatically surpassing numerous reported FSSCs. Moreover, the AFSSCs-ICS device also afforded superb electrochemical and mechanical stabilities with retentions of 81% after 3000 charging-discharging cycles and 95–105% under bending degrees from 0 to 150°. This study may pave a new way for constructing coaxial fiber-shaped energy source unit for next-generation wearable and portable miniaturized electronics.