Search

Herein, the synthesis of MnO 2 nanowires decorated with transition metal-doped carbon quantum dots (MCQDs) is described for use as binder-free flexible solid-state supercapacitors. In particular, the water-soluble Fe and N co-doped MCQDs prepared by amidation reaction with ferric ammonium citrate and urea had ultrafine particle morphologies and showed super-hydrophilicity in aqueous solution, which greatly improved the contact probability between the electrode and the electrolyte. In addition, the co-doped MCQDs increased both the electrical conductivity and specific capacitance of the MnO 2 /carbon-based nanocomposites and limited the collapse and exfoliation of the MnO 2 structure during extended cycling. Compared with pristine MnO 2 electrode, the MCQDs/MnO 2 composite electrode exhibited faster charge-discharge rate and improved cycle stability with increased specific capacitance. The flexible symmetric supercapacitor constructed from the MCQDs/MnO 2 composite had a capacitance retention of 85.6 % after 10,000 charge/discharge cycles at a current density of 2 mA cm−2. In addition, the device showed a maximum power density of 4.8 W cm−2 at an energy density of 2.3 mW h cm−2, and a maximum energy density of 11.16 mW h cm−2 at a power density of 311.6 mW cm−2. The data that support the findings of this study are available from the corresponding author upon reasonable request. • A metal carbon quantum dots (MCQDs)/MnO 2 nanowire composite is described. • The MCQDs/MnO 2 composite was used to construct flexible solid-state supercapacitors. • Super-hydrophilic MCQDs improved the contact probability of the interface. • MCQDs improved the conductivity, specific capacitance and cycling stability of MnO 2. • The flexible symmetric supercapacitor exhibited good electrochemical performance. [ABSTRACT FROM AUTHOR]

MnO 2 /biomass-derived porous carbon (BPC) composites have been prepared by a hydrothermal method, in which the BPC 3D porous carbon structure was based on a banana peel. The banana peel, after freeze drying, can maintain its hierarchical natural porous structure, which provides enough growth space for MnO 2 and reduces the agglomeration of MnO 2 particles. The MnO 2 /BPC composites were characterized by XRD, FT-IR, XPS, TGA, SEM, TEM, BET. The electrochemical performance of the composites was tested in three-electrode supercapacitors using 1 M Na 2 SO 4 aqueous solution as an electrolyte. Due to the large amounts of hierarchical pores and large pore volume, the as-prepared composites exhibited good electrochemical performance. Electrochemical measurements indicated that the MnO 2 /BPC composites applied in supercapacitors had a specific capacitance of 139.6 F g −1 at 300 mA g −1 , and exhibited a good cycling stability with a capacitance retention ratio of 92.3% after 1000 cycles (at 1 A g −1 ). The MnO 2 /BPC composites with 3D porous structure are promising materials in the application of supercapacitors. [ABSTRACT FROM AUTHOR]

Nanoflower-like NiCo 2 O 4 is grown directly on a three-dimensional gelatin-based carbon–nickel foam (GCNF), which is prepared by a facile hydrothermal strategy with annealing treatment. The as-synthesized binder-free NiCo 2 O 4 /GCNF composites are used for high-performance supercapacitors. The binder-free design can avoid the "dead surface" caused by binders and additives in traditional electrodes, thus achieving more efficient charge and mass exchange, leading to improved conductivity of electrodes. Furthermore, the proposed design provides a wider interface area and abundant active sites, which significantly improve the electrochemical capacitance performance. The electrode has a high specific capacitance of 1416 F g−1 at a current density of 1 A g−1, and excellent cycling performance. An asymmetric supercapacitor (ASC) was assembled with the structure NiCo 2 O 4 /GCNF//activated carbon and a maximum voltage of 1.5 V delivers a high energy density of 48.6 W h kg−1 at a power density of 749.3 W kg−1. Moreover, the ASC shows good cycling performance with 88.5% capacitance retention after 10,000 cycles at a high rate of 5 A g−1. Image 1 • Nanoflower-like NiCo 2 O 4 was grown on a 3D gelatin-based carbon–nickel foam. • Edible gelatin as a carbon source and contributes to the capacitance of electrode. • The NiCo 2 O 4 /GCNF composites were used as binder-free electrodes for supercapacitors. • The assembled asymmetric supercapacitor exhibits good electrochemical performance. [ABSTRACT FROM AUTHOR]

Lithium titanate (Li 4 Ti 5 O 12 , LTO) has several disadvantages as active material for Li-ion batteries (LIBs) such as low conductivity and poor capacity. To overcome these drawbacks and specifically to improve electrical performance of LTO, we used solvothermal method to synthesis LTO and to dope it simultaneously with Al and Mn. Doped LTO was then incorporated into composites containing graphene (G), carbon nanotube (CNT) or carbon quantum dots (CQDs) to enhance specific capacity and conductivity of LIB anodes containing these composites as active materials. To have a further study of different carbon materials composite with doped LTO, these materials we obtained were thoroughly characterized. LTO doping and incorporation into composites not only increased its specific capacity and also decreased its impedance. Al3+ and Mn4+ substituted Ti4+ located at 16 d sites. First cycle specific capacity values and impedance values of anodes consisting of composites containing doped LTO and G, CNT or CQDs were 261.7, 286.2 and 296.5 mA h/g (at C/10 rate) and 13.99, 8.28, 18.79 Ω, respectively. Capacity retention after 100 cycles for these anodes was 84.6, 90.67 and 83.4%. LTO doping by Al3+ and Mn4+ and combining it with G, CNT or CQDs effectively improved its electrochemical performance. The best performance was obtained for anodes containing composites consisting of a combination of doped LTO and CNT. • Used carbon quantum dots to form a composite with Al3+ and Mn4+ co-doped LTO as anode material for the first time. • Compared the influence of composites with different nano-structure carbon materials. • The specific capacity of LTO-Al/Mn-CQDs increased to 296.5 mA⋅h⋅g−1 at 0.1 C. [ABSTRACT FROM AUTHOR]