Graphene and quasi-2D graphene-like materials with an ultrathin thickness have been investigated as a new class of nanoscale materials due to their distinctive properties. A novel “molecular tools-assistances” strategy is developed to fabricate two kinds of graphene-based electrodes, ultrathin Fe-doped MnO₂ network coverage–graphene composites (G-MFO) and ultrathin MoS₂ network coverage–graphene composites (G-MoS₂) with special hierarchical structures. Such structures enable a large contact interface between the active materials and graphene and thus fully exploit the synergistic effect from both the high specific capacitance of MFO or MoS₂ and the superb conductivity of graphene. Benefiting from their unique structural features, G-MFO and G-MoS₂ films directly use as free-standing electrodes for flexible asymmetric supercapacitors with a nonaqueous gel electrolyte. The device achieves a high energy/power density, superior flexibility, good rate capability as well as outstanding performance stability even at a high temperature. This work represents a promising prototype to design new generation of hybrid supercapacitors for future energy storage devices.

A novel dioxaborinane-contained solid state polymer electrolyte poly((2-phenyl-1, 3, 2-dioxaborolane-4-yl) methyl methacrylate) (P(GMMA-PBA)) for symmetrical capacitors (SCs) is prepared through solution casting technique. Due to the effect of electron withdrawing of dioxaborinane groups and irregular distributed porous microstructures, the solid polymer electrolyte (SPE) exhibits an optimal ionic conductivity of 0.5 mS cm⁻¹ at ambient conditions. The electronic properties of dioxaborinane groups and their interaction with anions of electrolyte salts are further studied with density functional theory calculations. SCs fabricated with this polymer film as electrolyte and reduced graphene oxide as electrodes provide a broad potential window of 2.5 V. The energy density of this capacitor ups to 22.49 Wh kg⁻¹ with a power density of 6.34 kW kg⁻¹ at 5 A g⁻¹. After 3000 charge–discharge cycles, the capacitance of the symmetrical SPE capacitor maintains 90% of its initial values.

The electrochemical properties and overcharge protection mechanism of xylene as a new polymerizable electrolyte additive for overcharge protection of lithium ion batteries were studied by cyclic voltammetry tests, charge- discharge performance and battery power capacity measurements. It was found that when the battery was overcharged, xylene could electrochemically polymerize at the overcharge potential of 4.3–4.7 V (vs. Li/Li⁺) to form a thin polymer film on the surface of the cathode, thus preventing voltage runaway. On the other hand, the use of xylene as an overcharge protection electrolyte additive did not influence the normal performance of lithium ion batteries.