Flexible Supercapacitors Based on Graphene/Boron Nitride Nanosheets Electrodes and PVA/PEI Gel Electrolytes

Abstract

All-solid-state supercapacitors have gained increasing attention as wearable energy storage devices, partially due to their flexible, safe, and lightweight natures. However, their electrochemical performances are largely hampered by the low flexibility and durability of current polyvinyl alcohol (PVA) based electrolytes. Herein, a novel polyvinyl alcohol-polyethyleneimine (PVA-PEI) based, conductive and elastic hydrogel was devised as an all-in-one electrolyte platform for wearable supercapacitor (WSC). For proof-of-concept, we assembled all-solid-state supercapacitors based on boron nitride nanosheets (BNNS) intercalated graphene electrodes and PVA-PEI based gel electrolyte. Furthermore, by varying the electrolyte ions, we observed synergistic effects between the hydrogel and the electrode materials when KOH was used as electrolyte ions, as the Graphene/BNNS@PVA-PEI-KOH WSCs exhibited a significantly improved areal capacitance of 0.35 F/cm2 and a smaller ESR of 6.02 ohm/cm2. Moreover, due to the high flexibility and durability of the PVA-PEI hydrogel electrolyte, the developed WSCs behave excellent flexibility and cycling stability under different bending states and after 5000 cycles. Therefore, the conductive, yet elastic, PVA-PEI hydrogel represents an attractive electrolyte platform for WSC, and the Graphene/BNNS@PVA-PEI-KOH WSCs shows broad potentials in powering wearable electronic devices.

Towards Integration of Two-Dimensional Hexagonal Boron Nitride (2D h-BN) in Energy Conversion and Storage Devices

“…Supercapacitors have recently been in high demand for energy storage due to their peculiar characteristics of high-power density, swift charge/discharge capability, and better safety records and a long-life cycle in comparison to batteries [106,109]. Over the last decade, 2D h-BN nanostructures (i.e., functionalized and/or doped ones) and their heterostructures have been introduced as promising inorganic materials to improve the performance of supercapacitors [35,[110][111][112]. The 2D h-BN modifications can generate available free electrons or enhance the mobility of the charge carriers in order to improve the electrochemical behavior [113][114][115][116].…”

Layer-by-Layer Self-Assembled TEMPO-Oxidized Cellulose Nanofiber/Reduced Graphene Oxide/Polypyrrole Films for Self-Supporting Flexible Supercapacitor Electrodes

“…With the rapid development of wearable electronics, energy-storage devices have gained much attention because of their high flexibility, light weight, and good electrochemical properties. − Among them, a lot of researchers have paid close attention to the flexible supercapacitors because of their higher energy density, long life cycle, and an extensive applicable temperature range. , Accordingly, many efforts recently have been focused on endowing flexible supercapacitors with higher efficiency, better cycling stability, and lower cost in order to achieve fully self-supporting flexible electronics. − As a kind of natural, renewable biomass nanomaterial, cellulose nanofibers (CNFs) show great potential for fabricating electrode materials as an ideal binder and building blocks derived from its high hydrophilicity, large specific surface area, excellent mechanical properties, and charged surface with a lot of carboxyl groups. , As a matter of fact, a lot of research proved that it is an outstanding material for preparing flexible supercapacitors. , Polypyrrole (PPy) has been frequently employed on energy-storage devices such as electrode materials because of its large specific capacitance (>600 F g –1 ), good electrical conductivity, and environmental stability. − However, it displays unsatisfactory cycling stability during electrochemical processes because of the sustained volume expansion and contraction of PPy during continuous redox processes. Therefore, graphene, carbon nanotubes (CNTs), and their derivatives are frequently used to enhance the capacitance properties of PPy as an electrode for supercapacitors. − One of them, graphene oxide (GO) displayed an effective improvement for the capacitance stability because of its excellent ductility and mechanical properties. − For these reasons, in order to fabricate supercapacitors with flexible, tensile, and high capacitance properties, CNF, graphene, and PPy are integrated regularly to prepare self-supporting flexible electrodes with a two-dimensional thin film or porous materials by different structure design and various fabrication processes. , …”

Improving thermal conductivities of textile materials by nanohybrid approaches

“…Graphene- and boron-based textiles have potential for wearable technologies, as they are able to enhance wear resistance, tearing, flexibility, piezoresistivity, and thermal and electrical conductivities ( Wang et al., 2021 ; Abu-Thabit et al., 2016 ). Such unique properties propose their use in smart textiles, wearable electronics, strain sensor, health monitoring, stretchable solar cells, supercapacitors, and field emission devices.…”