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Abstract The supercapacitance performance of birnessite, which is a common layered manganese oxide mineral with the general formula of (Na, K, Ca) x (Mn4+, Mn3+) 2 O 4 ·1.5H 2 O, is greatly hindered by poor electrical conductivity, especially when the areal mass loading of the active materials is high enough for practical application. Heterogeneous atom doping is an effective way for improving the supercapacitance performance of birnessite. Herein, we mainly investigate the influence of Fe doping on the crystal structure, electronic structure and capacitance performance of birnessite [(Na, K) x (Mn4+, Mn3+) 2 O 4 ·1.5H 2 O] in detail by combining the experiments and theoretical calculations/simulations. It is found that Fe atoms mainly substitute the central trivalent Mn in [MnO 6 ] octahedral after doping without changing the crystalline phase of birnessite. Meanwhile, the particle size and surface area of Fe-doped birnessite continuously increase with the increase of the content of Fe dopant. On the other hand, the electronic conductivity of the doped birnessite firstly increases and then decreases with the increase of the Fe content due to the reduced indirect band gap and the increased number of the boundary/grain interfaces. Based on these results, the influences of Fe doping on the supercapacitance performance of birnessite electrode with very high areal mass loading of ∼10–12 mg cm−2 are elaborately discussed related to morphology, structure, electrical conductivity, and ion diffusion properties. Graphical abstract Image 1 Highlights • Fe (III) mainly substituted Mn (III) in [MnO6] octahedral after Fe doping. • Particle size decreased and surface area greatly increased after Fe doping. • The indirect band gap of Fe-doped birnessite calculated from DFT reduced. • 5 mol% Fe-doped samples showed the best capacitance performance. [ABSTRACT FROM AUTHOR]

Abstract Because the commercialized graphitic carbon as an anode material is still limited by low capacities and poor long cyclic stability, new carbonaceous materials with good electrochemical performance are still needed to be sought. In the present work, a new fluorinated carbon material was obtained from natural black talc ore by HF acid-treating method. The influences of heat treatment on the composition, morphology and structure characteristics of the fluorinated carbon were investigated and possible fluorination/defluorination mechanisms were proposed. As an anode material for Li-ion battery, the electrochemical performance of the samples was greatly influenced by their surface characteristics. The fluorinated carbon showed high capacities of ∼756 mAh/g and ∼620 mAh/g at rate of 0.1 C and 0.2 C, which resulted from more active sites provided by plenty of fluoride groups on the surface of the fluorinated carbon. In contrast, the sample annealed at 800 °C exhibited relatively high capacity of ∼477 mAh/g at rate of 0.1 C with excellent rate performance due to its better electrical conductivity caused by the removal of the fluorine groups. The present work provides a new direction for the application of black talc and other similar natural minerals. Graphical abstract Image 1 Highlights • A new fluorinated carbon material was obtained from natural black talc ore. • The effect of heat treatment on the fluorinated carbon were investigated. • The electrochemical performances of these samples were studied as anode materials. • The fluorinated carbon annealed at 800 °C exhibited excellent rate performance. • The lithium storage mechanism of these samples were explored. [ABSTRACT FROM AUTHOR]

Design and preparation of nanostructured conducting polymers (CPs) is a very important research direction for high performance CPs-based supercapacitors (SCs). With hollow structure, high surface area, tunable surface properties and abundant resources, natural halloysite is a promising template agent for preparing new nanotubular-structure CPs. Here, nanotubular-structure polyaniline was successfully synthesized using natural tubular halloysite as hard template. The obtained tubular polyaniline presents high specific capacitance at various current density as electrode material for supercapacitors. After a facile carbon coating, the carbon coated tubular polyaniline shows high specific capacitance of 654 F g−1 at the current density of 1 A g−1 and excellent electrochemical stability with capacitance retentions ∼87% after 10000 cycles. This work may prove the feasibility of preparing high performance CPs-based nanostructure electrode materials for SCs application based on inexpensive natural clay minerals. [ABSTRACT FROM AUTHOR]