•The influence of solvent structure overwhelms the anion size factor in the intercalation process.•The inter-gallery height of a AGIC mainly depends on the steric hindrance effect of substituent group of the solvent.•Transport of BC-solvated anions inside graphite is sluggish.•A universal way is explored to compare the relative solvation ability of different anions.•Both the anion’s oxidative stability and inter-gallery height affect cycle performance.The solvation of anions with organic solvent and its electrochemical intercalation into graphite is a significant research orientation in the electrochemical energy storage. Butylene carbonate (BC), a common solvent with higher oxidation resistance compared with ethylene carbonate (EC) and propylene carbonate (PC), is profitable in studying anion-graphite intercalation compounds (AGICs). In this paper, the electrochemical intercalation behaviors of three representative anions (BF4−, ClO4− and PF6−) in BC solution were studied and the solvation states of these anions were characterized by electrochemical in situ and ex situ techniques. The interpretation of results illuminated that all three anions were able to intercalate into graphite with the similar reversibility but different solvation state, and the conclusive role that solvent played in the intercalation process was also discovered.

Silicon (Si) has been used in Li-ion batteries (LIBs), and considerable progress has been achieved in design and engineering with improved capacity and cycling. However, large-scale application of Si-based anodes is hindered owing to the wide use of toxic raw materials, high manufacturing cost, limited capacity and unpalatable tap density. Herein, we describe a low-cost and green route to solve these problems. Composite Si–carbon nanotube (CNT) spheres were synthesized using a scalable method: rotary spray drying. These spheres were interspersed by many CNTs and wrapped Si nanoparticles (SiNPs) within them. Due to slightly rigid structure of CNTs, many void spaces in spheres could be preserved during the agglomeration of spheres. These voids could accommodate the volume expansion of Si particles and promote a stable integral structure during cycling. Importantly, this micron-grade material could improve the volume density and tap density to achieve high energy density. The prepared material showed promising reversible capacity of 2500 mA h g−1 with retention of 98% during 500 cycles. Ultra-fast discharge–charge (900 mA h g−1 at 20C) was achieved owing to the crosslinking effect between CNTs and SiNPs in these spheres. Moreover, a high-performance Si material was actualized via a simple industrial method rather than a complex synthesis.

•Methyl propionate benefits PF6− intercalation into graphite at low temperature.•Higher PF6− concentrations enlarge dual-ion cell's capacity.•Solvation of PF6− by methyl propionate determines the performance.The electrochemical intercalation of hexafluorophosphate anion into a graphite positive electrode from methyl propionate (MP) has been investigated by conventional electrochemical techniques in conjunction with in situ Raman spectroscopy and ex situ X-ray diffraction. Graphite electrodes could deliver stable reversible specific capacities higher than 100 mAh g− 1 in MP-based solutions at room temperature. Furthermore, the storage/release of PF6− anion into/from graphite electrodes becomes facilitated in MP-based solutions at a very low temperature, as compared with other solvents, such as propylene carbonate (PC) and ethyl methyl carbonate (EMC). The effect of LiPF6 concentration has also been addressed. The solvation states of the anion in the MP solutions were analyzed by nuclear magnetic resonance and infrared spectroscopy.

•Quaternary alkyl ammonium (QAA) cations as charge carriers in energy storage devices.•Three small isomeric QAA cations intercalate into graphite electrode in capacitors.•Isomeric effect on QAA storage can be studied by electrochemical in situ techniques.•Slim QAA cations are kinetically favorable for insertion into graphite electrode.Quaternary alkyl ammonium(QAA) intercalated graphite compounds are promising as efficient and environmentally benign electrode materials in electric energy storage devices. The intercalation and de-intercalation processes of three isomeric QAA cations have been investigated in graphite/activated carbon (AC) asymmetric capacitors based on propylene carbonate (PC) solutions. Some fundamental electrochemical techniques in conjunction with in situ XRD and in situ Raman spectroscopy have been employed to study the differences among them. Isopropyltrimethyl ammonium (iPTMA+) gives the most sluggish interaction with graphite. By contrast, propyltrimethyl and diethyldimethyl ammonium (PTMA+, DEDMA+) demonstrate quicker kinetic behaviors and higher rate capacity in capacitors.

•EC suppresses PF6− insertion into graphite.•EMC facilitates PF6− insertion into graphite.•Hydrogen bonding between species in solutions contributes to these effects.•Good cycle performance has been obtained.The electrochemical intercalation of hexafluorophosphate anion into a graphite electrode has been studied in mixed solvents of ethylene carbonate (EC) and ethylmethyl carbonate (EMC). The suppression effect of EC and the favourable effect of EMC on hexafluorophosphate insertion into graphite in these electrolyte solutions have been verified by electrochemical tests, ex situ XRD and in situ Raman. Moreover, the solvation effect on anion in solutions was analyzed by nuclear magnetic resonance. In addition, long-term cycling performance of Li/graphite cells has been obtained.

A flexible and free-collector-current of silicon-based anode is facilely prepared just by coating carbon black (CB) and silicon powders layer-by-layer. The resultant electrodes with a “sandwich” structure (CB/Si/CB) are assembled into half-cell and its electrochemical properties are tested. This type of anode exhibits excellent cycling and outstanding rate capability. The superior electrochemical performances are ascribed to both flexible CB-layers to offset the volume expansion of Si-particle. And, the CB-layer with high electric conductivity can provide efficient electron conductive pathways when Si particles react with lithium. More importantly, the CB/Si/CB electrodes without the collerctor (copper-foil) are exhibited high energy density, due to the weight proportion of copper foil is exceeded 60%. The CB/Si/CB electrode is used to assemble full-cell with the same structure as free-collector LCO/CB cathode material. It imposes the energy density of 200 Wh kg−1, and can keep stable charging-discharging capability at various deformations of shapes. And the flexible-cell of high performance is obtained to meet diverse applications in energy storage devices. Until now, many flexible batteries are put forward by researchers, but these product is faced with the complex production-process, high-cost material, low energy-density. This CB/Si/CB structure is produced with the matching current manufacturing industry and the common raw material, and to get a full-cell of the high energy density.

The electrochemical behaviour of graphite positive electrode has been tested in the electrolyte solutions of 1 mol dm−3 LiPF6 dissolved in mixed solvents of sulfolane (SL) and ethylmethyl carbonate (EMC). The suppression of PF6− anion intercalation into graphite by SL has been demonstrated. Moreover, the favourable effect of EMC on PF6− insertion into graphite in SL-based solutions has been verified by ex situ XRD, ex situ Raman, and electrochemical tests. Furthermore, improved long-term cycling performance of graphite positive electrode has been obtained in solutions with suitable ratios of SL and EMC.

Silicon is one of the most promising anode materials for lithium-ion batteries. To solve the problems associated with the great volume expansion of Si during lithium storage, nano-sized Si particles are generally employed. However, their high surface activity is likely to trigger considerable electrolyte decompositions at low potential, thus the surface of these Si nano-particles need further chemical modifications. In this paper, three kinds of functional groups were grafted onto the surface of Si particles by different chemical treatments. X-ray photoelectron spectroscopy (XPS) studies proved that the structure of solid electrolyte interface (SEI) film formed on the surface of Si nano-particles depends greatly on the surface modification strategy. Electrochemical characterizations like electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) etc., also verified the distinct effects of these functional groups on the surface of nano-sized Si electrodes. The relationship between surface functional groups and electrochemical performance of the nano-Si anode material was addressed.

•The charge–discharge curves of this positive material exhibit no plateau, which is a capacitive behavior.•The capacity of the sodium ion storage device can be 50% larger than AC/AC capacitor.•The sodium ion storage device can retain 90% of capacity after 1000 charge–discharge cycles.The need of large-scale energy storage calls for the application of environmentally benign and economic sodium storage electrode materials. At present, most of the existing positive electrode materials for Na+-storage demonstrate many small plateaus, which are a disadvantage for the practical application. We found that some inert elements like Al can straighten the charge–discharge curves and stable the structure of the positive electrode materials. Here we synthesized positive electrode material of Na0.67[Mn0.75Al0.25]O2 by the spray drying method. This positive electrode material was matched with the negative electrode material of activated carbon to assemble a Na+-capacitor. This capacitor can retain 90% of capacity after 1000 charge–discharge cycles. The advantage of the Na+-capacitor in properly assessing the cycle performance of the positive electrode material has been specially pointed out. Moreover, the Na+-capacitor possesses higher volumetric energy and power densities than electric double-layer capacitors.

•DFOB− considerably inserts into graphite at room temperature.•EC retards DFOB− de-intercalation from graphite at room temperature.•Transport of EC-solvated DFOB− can be accelerated at elevated temperatures.•Charge–discharge of EC-solvated DFOB− are irreversible at room temperature.Anion-graphite intercalation compounds are a promising candidate for high-potential positive electrode materials. However, electrochemical anion intercalation into graphite always suffered from the interference of organic solvent in practice. Ethylene carbonate (EC) could suppress the intercalation of some symmetrical anions into graphite like BF4−, ClO4− and PF6−. Herein, the electrochemical intercalation behavior of an anisotropic anion, difluoro(oxalato)borate (DFOB−) into graphite from pure EC solvent has been studied in activated carbon (AC)/graphite capacitors. Some fundamental electrochemical techniques in conjunction with in situ Raman spectroscopy and ex situ XRD have been applied to probe the charge storage of EC-solvated anion within graphite electrode. The influence of ambient temperature has been addressed as well. From the comparative studies on the intercalation and de-intercalation processes of EC-solvated DFOB− and BF4− into and from graphite electrodes, the extraction of EC-solvated DFOB− anion from graphite electrode has been confirmed to be a crucial step dependent on the ambient temperature.

Correction for ‘Facile synthesis of mesoporous spinel NiCo2O4 nanostructures as highly efficient electrocatalysts for urea electro-oxidation’ by Rui Ding et al., Nanoscale, 2014, 6, 1369–1376.

•GBL suppresses PF6− insertion into graphite.•This retardant effect of GBL is weaker than EC.•Transport of EC-solvated PF6− inside graphite is sluggish.•Intercalation of PF6− from GBL shares a similar pattern with that of BF4− from EC.In our recent work, the solvent of ethylene carbonate (EC) has been found to retard the intercalation of anions into graphite electrodes. Here we demonstrate that gamma-butyrolactone (GBL) also exhibits suppressive effect on the intercalation of PF6− into the interlayer space between the graphene planes. The intercalation process of PF6− into graphite electrode from GBL has been investigated by in situ XRD, in situ Raman and EQCM. Furthermore, the effect of GBL has been compared with those of EC and propylene carbonate (PC).

•EC suppresses ClO4− insertion into graphite.•ex situ XRD results indicate co-intercalation of GBL with anion.•Elevating temperatures enlarge storage capacity of EC-solvated ClO4−.•Transport of EC-solvated anion inside graphite is sluggish.Anion graphite intercalation compounds are an excellent candidate for high-potential positive electrode materials. Solvents play an important role during the intercalation processes of anions into graphite. In this contribution, the intercalation behaviors of perchlorate (ClO4−) from propylene carbonate (PC), γ-butyrolactone (GBL) and ethylene carbonate (EC) were studied with activated carbon (AC)/graphite capacitors. Both in situ Raman spectroscopy and ex situ X-ray diffraction were employed to detect the structure change of graphite electrodes caused by the electrochemical intercalation of ClO4−. Influence of solvents on the insertion of ClO4− was discussed. Besides, temperature effect was also explored.

Correction for ‘A facile hard-templating synthesis of mesoporous spinel CoFe2O4 nanostructures as promising electrocatalysts for the H2O2 reduction reaction’ by Rui Ding et al., RSC Adv., 2014, 4, 1754–1760.

Mesoporous spinel nickel cobaltite (NiCo2O4) nanostructures were synthesized via a facile chemical deposition method coupled with a simple post-annealing process. The physicochemical properties were characterized via X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectra (XPS) and nitrogen sorption measurements. The electrocatalytic performances were investigated by cyclic voltammetry (CV), chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS) tests. The obtained NiCo2O4 materials exhibit typical agglomerate mesoporous nanostructures with a large surface area (190.1 m2 g−1) and high mesopore volume (0.943 cm3 g−1). Remarkably, the NiCo2O4 shows much higher catalytic activity, lower overpotential, better stability and greater tolerance towards urea electro-oxidation compared to those of cobalt oxide (Co3O4) synthesized by the same procedure. The NiCo2O4 electrode delivers a current density of 136 mA cm−2 mg−1 at 0.7 V (vs. Hg/HgO) in 1 M KOH and 0.33 M urea electrolytes accompanied with a desirable stability. The impressive electrocatalytic activity is largely ascribed to the high intrinsic electronic conductivity, superior mesoporous nanostructures and rich surface Ni active species of the NiCo2O4 materials, which can largely boost the interfacial electroactive sites and charge transfer rates for urea electro-oxidation, indicating promising applications in future wastewater remediation, hydrogen production and fuel cells.

•TMADFOB dissolved in EC/PC as electrolyte for electrochemical capacitors.•Ionic conductivity rises with the addition of ethylene carbonate.•Ethylene carbonate suppresses the DFOB− intercalation into graphite.Tetramethyl ammonium difluoro(oxalato)borate (TMADFOB) dissolved in the mixed solvents of ethylene and propylene carbonates (EC/PC) instead of neat PC have been proposed as the electrolyte solutions for electrochemical capacitors. The ionic conductivity of 1 M TMADFOB-EC/PC electrolyte solutions has been measured. It climbs up monotonously as EC content increases. Accordingly, the power density of electric double-layer capacitors is enhanced with certain EC addition. The optimum EC content for the power of EDLCs is about 30 volume percentage in the mixed EC/PC solvents. This tendency has been testified by impedance study. The electrochemical behavior of activated carbon/graphite capacitors using these electrolyte solutions has also been studied by galvanostatic charge–discharge test and the charge storage mechanism at the graphite positive electrode has been investigated by in situ XRD and ex situ Raman. The effect of EC addition on DFOB− intercalation into graphite has also been addressed at both room and elevated temperatures.

•SDS enhances mesoporous structures and surface electroactive sites.•SDS-assisted NiCo2O4 electrode shows faster electrochemical kinetics.•SDS-assisted NiCo2O4 electrode exhibits enhanced electrocatalytic activity.•Surface physicochemical properties strongly affect electrocatalytic behavior.Mesoporous nickel cobaltite (NiCo2O4) nanoparticles have been synthesized via a facile hydrothermal strategy with the assistance of sodium dodecyl sulfate (SDS) soft template (ST). Their physicochemical properties have been characterized via X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectra (EDS), transmission electron microscopy (TEM), X-ray photoelectron spectra (XPS) and nitrogen sorption measurements. Their electrocatalytic performances have been examined by cyclic voltammetry (CV), linear sweep voltammetry (LSV), chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS) tests. The obtained NiCo2O4 materials exhibit a typical nanoscale crystalline hexagonal morphology with specific surface area (SSA) and mesopore volume of 88.63 m2 g−1 and 0.298 cm3 g−1. Impressively, the SDS-assisted NiCo2O4 electrode shows a catalytic current density of 125 mA cm−2 and 72% retention for consecutive 1000 s at 0.6 V in 1 M KOH and 0.5 M CH3OH electrolytes towards methanol (CH3OH) electrooxidation, which is better than the one without SDS assistance. The pronounced electrocatalytic activity is largely ascribed to their higher surface intensities of Co and Ni species and superior mesoporous nanostructures, which provide the richer electroactive sites and faster electrochemical kinetics, leading to the enhanced electrocatalytic activity.

Mesoporous spinel cobalt ferrite (CoFe2O4) nanostructures were synthesized via a facile Al2O3-assisted hard-templating (HT) strategy. Their physicochemical properties were characterized by X-ray diffraction (XRD), scanning electron microscopy-energy dispersive X-ray spectra (SEM-EDS), X-ray photoelectron spectra (XPS) and nitrogen sorption measurements. Their electrocatalytic performances towards H2O2 reduction reaction (HRR) were investigated by cyclic voltammetry (CV), chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS) tests. The obtained CoFe2O4 materials exhibit a superior mesoporous nanostructure with a particle size of around 20 nm, a specific surface area (SSA) of 140.6 m2 g−1 and a mesopore volume of 0.2410 cm3 g−1, which favor their desirable electrocatalytic activity. A current density of 123 mA cm−2 at −0.39 V (vs. Hg/HgO) in 3 M NaOH and 0.5 M H2O2 electrolytes was delivered for HRR. Moreover, the CoFe2O4 electrode exhibits a good stability for the catalytic reaction, showing the promising applications for H2O2-based alkaline fuel cells (AFCs).

•The NiCo2O4 materials exhibit superior mesoporous nanostructures.•The NiCo2O4 electrode shows high catalytic activity toward CH3OH electro-oxidation and H2O2 electro-reduction.•The behavior of NiCo2O4, NiO and Co3O4 electrodes was compared.•The NiCo2O4 shows the potential as non-Pt electrocatalyst for AFCs.Porous nickel cobaltite (NiCo2O4) nanostructures were synthesized via a facile chemical deposition route. Their physicochemical properties were characterized via X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectra (XPS) and nitrogen sorption measurements. Their electrocatalytic performances were investigated by cyclic voltammetry (CV), chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS) tests. The obtained NiCo2O4 materials exhibit typical agglomerate porous nanostructures with the specific surface area (SSA) and pore volume of 190.1 m2 g−1 and 1.136 cm3 g−1. Remarkably, the NiCo2O4 materials exhibit higher electrocatalytic activity, lower overpotential, better stability and greater tolerance compared to those of NiO and Co3O4 materials synthesized by the same procedure. As for the NiCo2O4 electrode, a current density of 98 mA cm−2 was obtained toward CH3OH electro-oxidation at 0.6 V in 1 M KOH and 0.5 M CH3OH electrolytes, and a current density of 223 mA cm−2 was achieved toward H2O2 electro-reduction at −0.3 V in 3 M NaOH and 0.5 M H2O2 electrolytes. Moreover, the NiCo2O4 electrode shows a desirable stability for both electrocatalytic reactions. The impressive electrocatalytic activity is largely attributable to the binary electroactive sites of Co and Ni species, intrinsic high electronic conductivity and superior porous nanostructures of the NiCo2O4 electrode, which are very promising for further development of high performance non-Pt catalysts alkaline fuel cells (AFCs).

•Spinel NiCo2O4 as anode for hybrid NiCo2O4/AC Na-ion capacitors was investigated.•The designed 3.0-V-class capacitor exhibited superior performance to the theoretical 4.3-V-class capacitor.•The designed 3.0 V-class capacitor was mass-optimized.•The Na-ion insertion/extraction reactions in the NiCo2O4 anode were controlled.Sodium (Na)-ion-based energy storage devices have been regarded as a promising alternative to the traditional lithium (Li)-ion-based energy systems because of the more abundant Na reserves on the earth. This work, we have made an investigation about spinel nickel cobaltite (NiCo2O4) as an anode material for Na-ion capacitors (NICs). The NiCo2O4 materials have been fabricated via a facile and scalable chemical deposition route. The obtained NiCo2O4 materials display a typical agglomerate porous morphology with large specific surface area (190.1 m2 g−1) and high mesopore volume (0.943 cm3 g−1). The NiCo2O4 electrode was found to show non-preferable Na-ion insertion/extraction behavior under the full charge/discharge condition. The designed 3.0-V class NiCo2O4/activated carbon (AC) hybrid capacitor exhibits a much superior performance to the theoretical 4.3-V class capacitor, owing to the effective control of Na-ion insertion/extraction reactions in the NiCo2O4 electrode. The mass-optimized (1:1) 3.0-V class capacitor exhibits desirable energy and power performances (13.8 Wh kg−1, 308 W kg−1 at 0.4 A g−1), good cycling stability (61.2% energy retention after 2000 cycles at 0.15 A g−1) and excellent Coulombic efficiency (almost at 100%), indicating a potential application of spinel NiCo2O4 for NICs.

The interactions between silicon particles and polymeric binders are a key factor during the course of manufacturing high-capacity Si anodes for lithium-ion batteries. Polymeric binders usually compensate for the volumetric over-changes of silicon particles, and then prevent electrode deformation while keeping the integrity of electron and ion pathways. This work explores an efficient synthesis method to directly anchor a reliable binder tightly on the surface of Si particles by in situ polymerization of an acrylic acid monomer in the mixing process of Si-based slurry. The resultant Si composite electrode possesses a highly elastic structure, which can provide a highly extensible space accommodating volume expansion/contraction of Si particles during lithiation/delithiation. Moreover, the cross-linked acrylic acid network results in a strong cohesive force between Si particles and auxiliary materials, such as conductive agent and copper foil. Accordingly, a satisfactory electrochemical performance of the Si anode can be gained, including a high initial coulombic efficiency of ∼73% and stable cycling performance (∼82% retention over 300 cycles at a current density of 4 A g−1). Such a novel and facile fabrication process represents an appealing method for manufacturing high-performance Si-based anodes using micron-sized Si particles with low cost.