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Graphene paper is a promising electrode material for use in flexible supercapacitors due to its good electronic conductivity and excellent mechanical characteristics. However, layers of graphene paper have a strong tendency to restack, resulting in a seriously reduced specific surface area and limited electrochemical performance. In this paper, restacked layers of graphene paper are reopened by a vacuum-assisted method, and carbon nanotubes (CNTs) are directly deposited on the enlarged space between the opened graphene layers. Consequently, an ordered carbon composite structure with alternately arranged graphene sheets and CNTs is constructed and exhibits increased specific surface area and a 3D conductive network. The structure and morphology of the samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy and N2 adsorption/desorption measurements. The electrochemical performance was tested by galvanostatic charge-discharge test (GDC), electrochemical impedance spectroscopy (EIS) and cyclic voltammograms (CV). The obtained graphene/CNT paper exhibits a remarkably improved capacity of 170.8 F g−1, which is nearly two times higher than that obtained for a regular graphene paper.

Hybrid Sn–Co binary oxide with different Sn/Co feeding molar ratios on carbon paper are successfully obtained using a facile hydrothermal method followed by a post-annealing procedure. The results of electrochemical tests show that the electrode with a feeding molar ratio of 1:4 (named as Sn1Co4) has better electrochemical performance than that of the others. The specific capacitance can achieve 937.4 F g−1at 5 mV s−1 (580.8 F g−1 at 1 A g−1), as well as the capacitance retention is 97.5% after the galvanostatic charge-discharge for 20000 cycles at 30 A g−1. These results demonstrate that the Sn1Co4 can be considered as a potential electrode material for the next generation supercapacitor.

A novel and one-pot calcination method is applied for the fabrication of SnS nanoparticles coated by ultrathin carbon layer on carbon paper, resulting in a SnS/C-carbon paper free-standing electrode for lithium ion batteries. In this hierarchical structure, the carbon layer has dual function of buffering the volume change of SnS and anchoring SnS nanoparticles on the substrate compactly. Besides, it also can boost charge transfer kinetic in the electrode. Meanwhile, the carbon paper with three-dimensional structure allows for fully absorption of electrolyte and provides efficient transport pathways for electrons. Benefiting from these structure features, the binder-free SnS/C-carbon paper electrode exhibits excellent cyclability and delivers a reversible capacity of 696.2 mAh g−1 at a current density of 0.5 A g−1 after 200 cycles. Besides, SnS/C-carbon paper free-standing electrode achieves a reversible capacity of 562.3 mAh g−1 at a current density of 2.0 A g−1, demonstrating a promising rate ability which is significant for high power applicants. Such one-pot and novel route to synthesize SnS/C-carbon paper free-standing electrode with excellent electrochemical performance can pave the way for the development of low-cost and time-saving fabrication of free-standing anode for high-performance lithium ion batteries.

Mn3O4 nanoparticles were anchored on the surface of oxidised graphite paper via template-free hydrothermal method. Synthesized samples were characterized using different techniques such as X-ray diffraction (XRD), Raman spectroscopy, Field Emission Scanning Electron Microscopy (FE-SEM), High Resolution Transmission Electron Microscopy (HRTEM) and X-ray Photoelectron Spectroscopy (XPS). Electrochemical capacitor behaviour was evaluated using cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and electrochemical impedance spectroscopy (EIS). The binder free material was found to exhibit a specific capacitance of 471 F g−1 at a current density of 1 mA cm−2 in 1 M Na2SO4. Conductive additive free, Mn3O4 anchored electrode was used as positive electrode in the asymmetric cell fabrication; the asymmetric cell was tested at a potential window of 1.6 V and its performance characteristics were evaluated. The asymmetric cell delivered a maximum specific energy of 47 Wh kg−1 at a power density of 202.5 W kg−1 which evidenced the superior performance of the synthesized electrode material. Here in the present work, the surface oxidised graphite paper was used as an excellent current collector and active sites for anchoring Mn3O4 due to its desirable properties.

α-Fe2O3 nanoparticles/multi-wall carbon nanotubes (MWCNTs) hybrids were successfully prepared via a facile one-step hydrothermal method. The MWCNTs enhances the conductivity and provides space for stress and strain during volume expansion of α-Fe2O3 semiconductor as the anode for LIBs. The composite shows impressive electrochemical performance when it was used as the electrodes of coin cells. The α-Fe2O3 electrode with 50 wt% MWCNTs retains its capacity of 816.8 mAh g−1 after 50 cycles at the current density of 200 mA g−1, which is superior to those of contrast samples (bare α-Fe2O3, pure MWCNTs, 10 wt%, 30 wt%, 70 wt% MWCNT/α-Fe2O3 hybrids). Furthermore, the flexible carbon nanofiber paper (CNP) has also been investigated as a novel current collector with lithium storage for application in LIBs, and the capacity of free-standing α-Fe2O3/50 wt%MWCNTs/CNP hybrids electrode can retain 467.2 mAh g−1 after 50 cycles under the current density of changes from 2500 mA g−1 to 200 mA g−1. The MWCNTs improved cycle performance, enhanced reversible capacities and rate capability of MWCNTs/α-Fe2O3 anodes can attribute to the inherent conducting network, shorten electron pathway and faster reaction kinetics.

The electrode materials with large surface area and high porosity are predominant to enable the energy storage properties of electrochemical supercapacitors. Herein, lab-waste tissue paper templated trimanganese tetroxide hollow microtubes (Mn3O4 HMTs) with high porosity on their walls were synthesized via a facile biomorphic method. Initially, aqueous manganese precursor was impregnated onto the surface of cellulose fibers by means of evaporation of water molecules. After thermal treatment under ambient atmosphere, the cellulose fibers were removed, which led to the formation of Mn3O4 HMTs. The morphology, crystallinity and surface area of the prepared Mn3O4 HMTs were examined by FE-SEM, XRD and BET analyses. When tested in aqueous alkaline electrolyte, the as-prepared Mn3O4 HMTs delivered a maximum specific capacitance of 51.7 F g−1 at the current density of 1 mA cm−2 with good rate capability of 64.6% at high current density of 10 mA cm−2, which is due to the high porosity that enables an effective penetration of electrolyte ions. After 2000 cycles, the porous Mn3O4 HMTs demonstrated good cycling stability of 57.1% at a current density of 5 mA cm−2. This facile method for the preparation of hollow structured materials could provide a deep insight into novel pseudocapacitive materials.

A facile one-step solid-phase synthesis strategy is developed for synthesizing a binder-free molybdenum disulfide/carbon fibers paper (MoS2/CFP) anode. The microstructure, composition, morphology and electrochemical performances were investigated. It is found that the thin MoS2 layers are well anchored on the interlaced carbon fibers to form MoS2/CFP, which has mesoporous structure and large specific surface area of ∼18.8 m2g-1. As a result, the obtained MoS2/CFP anode exhibits a reversible capacity of 261 mAh·g−1 with 31.2% loading ratio of MoS2. After subtracting the capacity of CFP, the MoS2 in the composite anode delivers a reversible capacity of 539 mAh·g−1 and shows better cycle stability than commercial MoS2 after 100 cycles at 100 mA g−1. The remarkable electrochemical performances could be attributed to the buffer space among carbon fibers for the volume changes of MoS2 as well as the highly conductive carbon fibers network, suggesting that the MoS2/CFP is a promising binder-free anode for lithium-ion batteries.

My comments concern the significant error in the crystallographic part of the commented paper. It was discovered that the studied crystals are of sillenite type and the correct formula should be Bi25FeO39:Ni,Ti instead of BiFeO3. Moreover, the type of unit cell is not correct. Due to the doping the new type of unit cell, previously unknown, was proposed for such crystals. It was found that the studied sample contains two slightly different phases of the sillenite type. The actual chemical composition of the studied crystals is not known.

My comments concern the sever error in the crystallographic part of the commented paper. It was found that the studied crystal is of the sillenite type and the correct formula should be Bi25FeO39:Cd,Ti instead of some kind of solid solution based on BiFeO3. Moreover, the type of unit cell is not correct. Due to the double doping the new type of unit cell, previously unknown, was proposed for such crystals. The actual chemical composition of the studied crystals is not known.

Lithium sulfur batteries have been regarded as next-generation battery technology due to its high energy density, environmental benignity and abundance. However, the poor electric/ionic conductivity of sulfur limits the practical use of sulfur in an electrode. The main problem is the high solubility of long-chain polysulfides, which are the intermediates of the electrochemical processes in the liquid electrolyte. The dissolved polysulfide ions shuttle between the cathode and anode, thus causing precipitation of insulating Li 2 S 2 /Li 2 S on the surface of the electrode. The unavoidable phenomenon results in loss of active materials and fast capacity fading. In this regard, we show one simple method to prepare free-standing paper electrode used as cathode material for lithium sulfur batteries. Binder-free graphene-polypyrrole (PPy)/S-graphene (G-PPy/S-G) paper-like sandwich structural electrode was prepared by using the vacuum filtration method. In this structure, the unique graphene layers of sandwich-like framework not only serve as a conductive film, but also effectively block the diffusion of polysulfides, leading to suppression of the shuttle effect and low self-discharge behaviour. In addition, the middle layer, the PPy nanofibers can limit the diffusion of dissolved polysulfides due to the special bond with sulfur, and furthermore maintain the structural stability of the paper electrode because the nanofibers can serve as elastic springs to accommodate the huge volume changes in charging-discharging processes. When tested as cathode for Li-S batteries, the as-prepared sample G-PPy/S-G exhibits excellent electrochemical performance. We believe that our strategy could provide a useful pathway towards commercial utilizing of sulfur.