Exploiting high-efficiency catalysts toward hydrogen evolution reaction (HER) is a significant assignment nowadays. We find a quick and straightforward means to produce large-scale g-C3N4, which does not use template and easily obtains uniform nanostructures. And, we fabricate one-step preparation of a non-noble-metal catalyst, consisting of carbon material and transition metal only, by coupling graphitic carbon nitride (g-C3N4) with Ni. The results show that Ni/C3N4 composite catalyst possesses coral-like structure and its unique morphology is in favor of electrochemical activity for HER. Simultaneously, the Ni/C3N4 composite catalyst presented prominent activity on HER with a high exchange current density of 1.91 × 10–4 A cm–2, a low Tafel slope of 128 mV dec–1 and small overpotentials of 356 and 222 mV to reach current densities of 100 and 10 mA cm–2, which are superior to those of the state-of-the-art HER-active Ni-based compositions, as well as majority other metal-free catalysts, and even rivaled the electrocatalytic property of commercial Pt/C catalyst.Keywords: Graphitic carbon nitride; Hydrogen evolution reaction; Nanostructure; Non-noble-metal catalyst; Supergravity electrodeposition;

The synthesis of nickel cobalt sulfide is well-established because of its good electrical conductivity and great structural flexibility with low cost. It is extremely challenging to fabricate a unique structure with high tap density to improve its volumetric energy density and practical application. Here, we report a simple one-step hydrothermal method to synthesize micron-sized Ni–Co mixed sulfide solid spheres (1–2 μm in diameter). Because of the high tap density of more than 1.0 g cm–3 and the unique structure, the Ni–Co mixed sulfides demonstrate exceptional energy-storage performance. When acting as an electrode material for supercapacitors, these Ni–Co solid spheres can deliver a specific capacitance of 1492 F g–1 at a current density of 1.0 A g–1, and a retention of 76% at 10 A g–1 after 10 000 cycles. An asymmetric supercapacitor based on these solid spheres exhibits a high energy density of 48.4 W h kg–1 at a power density of 371.2 W kg–1 with excellent long-term cycling performance (91% retention of the initial specific capacitance at 5 A g–1 after 20 000 cycles). All the experiment results illustrate that the micron-sized solid-sphere Ni–Co mixed sulfides will be a promising electrode material for high-performance supercapacitors.Keywords: Long-term cycling performance; Micron-sized; NiCo2S4 solid sphere; Supercapacitors; Tap density;

The ultrathin porous carbon shell with the thickness of about 10 nm has been fabricated by a facile method using sodium citrate as carbon precursor without any activation. The electric conductivity of the material is as high as 7.12 S/cm, which contributes to a good rate performance for supercapacitor electrode without any conductive additive. When tested in 6 M KOH by three-electrode system, the C-700 sample exhibits specific capacitance of 251 F g−1 at 1 A g−1, high rate capability with the specific capacitance of 228 F g−1 at 20 A g−1, only a loss of 3% after 10000 cycles at a current density of 3 A g−1. Non aqueous performance was tested in 1 M TEA-BF4/acetonitrile, the material can deliver an energy density of 12–17 Wh kg−1 in a two-electrode system. Apparently, the porous carbon with ultrathin structure can provide low-resistant pathways and short ion diffusion channels for energy storage. Therefore, the ultrathin porous carbon shell would be a promising material particularly for applications where high power output performances are required.

•The Ni-based carbon composite catalysts show superior stability under large current density.•The crystal plane of Ni (111) plays an important role in enhancing the electrochemical activity.•Ni particles grow on carbon materials more uniformly under supergravity electrodeposition.•Graphene exhibits more specific surface than CNT and biomass carbon.In this work, preparing three nickel-based carbon composite catalysts (Ni-OCNT, Ni-ONC and Ni-rGO) by supergravity field electrodeposition for hydrogen evolution reaction (HER) from nickel sulfamate bath containing suspended nano-sized carbon materials. The crystal structure, morphology and chemical compositions of the composite catalysts were characterized by XRD and SEM measurements. The electrochemical activity of composite coatings for HER was determined by polarization measurement and electrochemical impedance spectroscopy in 1.0 M NaOH solution. The prepared nickel-based carbon composite catalysts exhibit a significant enhancement in electrocatalytic activity for HER compared with pure Ni electrode. In addition, the Ni-rGO, Ni-ONC, Ni-OCNT catalysts prepared under supergravity field demand overpotentials of 245, 177, 91 mV and 286, 224, 154 mV and 330, 286, 222 mV to drive current densities of 80, 30, 10 mA cm−2, respectively. Ni-rGO cathode presents excellent HER activity with lowest overpotentials.

Lithium cathode materials have been considered as promising candidates for energy storage applications because of their high power/energy densities, low cost, and low toxicity. However, the Li/Ni cation mixing limits their application as practical electrode materials. The cation mixing of lithium transition-metal oxides, which was first considered only as the origin of performance degeneration, has recently been reconsidered as a way to stabilize the structure of active materials. Here we find that as the duration of the post-synthesis thermal treatment (at 500 °C) of LiNi1/3Co1/3Mn1/3O2 (NCM) was increased, the Li/Ni molar ratio in the final product was found to decrease, and this was attributed to the reduction in nickel occupying lithium sites; the cation mixing subtly changed; and those subtle variations remarkably influence their cycling performance. The cathode material with appropriate cation mixing exhibits a much slower voltage decay and capacity fade during long-term cycling. Combining X-ray diffraction, Rietveld analysis, the Fourier transform infrared technique, field-emission scanning electron microscopy, and electrochemical measurements, we demonstrate that an optimal degree of Ni2+ occupancy in the lithium layer enhances the electrochemical performance of layered NMC materials and that this occurs through a “pillaring” effect. The results provide new insights into “cation mixing” as a new concept for material design utilization of layered cathodes for lithium-ion batteries, thereby promoting their further application in lithium-ion batteries with new functions and properties.

Ni–reduced graphene oxide (rGO) composite cathodes were successfully prepared by composite electrodeposition under supergravity fields. The synthesized composite cathodes exhibit unique hierarchical structure with large numbers of Ni nanoparticles anchoring on the rGO surface. Specifically, the sample prepared from the electrolyte containing 0.7 g L−1 GO at rotational speed 3000 rpm displays a favorable activity toward the hydrogen evolution reaction (HER) in 1 M NaOH solution with a high exchange current density of 741.3 μA cm−2 and a low Tafel slope of 120 mV dec−1. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetric (CV) tests demonstrate that the superior catalytic activity should be ascribed to the enhanced active surface area and the improved intrinsic activity. Furthermore, the morphology and microstructure properties of Ni–rGO cathodes synthesized from various GO concentrations and supergravity fields are systematically investigated.

•3D hierarchical nanostructures Ni-(MoS2/GO) is prepared.•Depositing under supergravity fields has been applied.•The activity of Ni-(MoS2/GO) is better than that of Ni-GO and Ni-MoS2.•Low overpotential, small Tafel slope, and superior durability are achieved.We report a novel and simple approach to synthesis highly efficient and stable electrochemical catalyst of Ni-(MoS2/GO) composite coatings by electrodeposition from aqueous solution with the nickel sulphamate precursor. Depositing under supergravity fields has been applied to scatter more MoS2/GO hybrids in the coatings and decrease the size of nickel particles as far as possible and increase large amount of exposed active sites. In 1.0 M NaOH solution, Ni-(MoS2/GO) only needs overpotentials as low as −33 mV and −132 mV at a current density of −10 mA cm−2 and −100 mA cm−2, respectively. The behavior of Ni-(MoS2/GO) exceeds most of the same reported HER catalysts in previously literature. In addition, we also synthesized Ni-MoS2, Ni-GO and pure Ni catalysts use the same method. The results show that Ni-(MoS2/GO) exhibited better HER activity at a current density of −100 mA cm−2 than these catalysts. In the future research field of HER catalysis materials, the development of this material may be not limited to nickel based materials, also will be used in Fe, Co and other non noble metal based materials, outlining a general approach for the synthesis of nanostructured M-(MoS2/GO) as a class of new catalyst with efficient HER activity.

•3D hierarchical network nanostructures NiCo2S4-NF is prepared.•Bifunctional electrocatalysts for both HER and OER in alkaline solution.•Low overpotential, small Tafel slope, and superior durability are achieved.The development of cost-effective and high-efficiency electrocatalysts for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) still remains highly challenging. Exposing as many active sites as possible is the key method to improve activity of HER and OER performance. In this communication, we demonstrate a novel 3D hierarchical network NiCo2S4 nanoflake grown on Ni foam (NiCo2S4-NF) as a highly efficient and stable electrochemical catalyst. The NiCo2S4-NF exhibits overpotentials as low as 289 and 409 mV at 100 mA cm−2, superior long-term durability during a 20 h measurement, and a low Tafel slope of 89 and 91 mV dec−1 for HER and OER in 1.0 M NaOH solution. The outstanding performance is owe to the inherent activity of ultrathin NiCo2S4 nanoflakes and the special structure of NiCo2S4-NF that can provide a huge number of exposed active sites, accelerate the transfer of electrons, and facilitate the diffusion of electrolyte simultaneously.Download high-res image (193KB)Download full-size image

•Ni–MoS2 composite coating is synthesized under supergravity fields.•Synergistic effect exists of Ni and MoS2 enhance the catalytic activity of HER.•Low overpotential, small Tafel slope, and superior durability are achieved.It remains an important project for the development of water splitting electrolyze to design and synthesis of more efficient non-noble metal catalyst. In this work, a structured Ni–MoS2 composite coating has been synthesized under supergravity fields with nickel sulphamate bath containing suspended MoS2 submicro-flakes. X-ray diffraction patterns indicate that the MoS2 submicro-flakes have been successfully incorporated into the Ni matrix. Additionally, SEM shows that the prepared Ni–MoS2 composite coatings display finer grain size than the pure Ni coatings, which can increase the electrochemistry surface area and the active site of hydrogen evolution reaction. Therefore, due to the synergistic effect of molybdenum disulfide and nickel, the Ni–MoS2 composite coatings are directly used as binder-free electrode, which exhibits outstanding electrocatalytic activity for HER in 1.0 M NaOH solution at room temperature. The Ni–MoS2 composite coatings demonstrated an outstanding performance toward the electrocatalytic hydrogen production with low overpotential (100 mA cm−2 at η = 207 mV), a Tafel slope as small as 65 mV dec−1, and stable cycling performance (1200 cycles). The preeminent HER performance of this catalyst suggests that it may hold great promise for practical applications.

•NSO-HPC was simply prepared by chemical polymerization and carbonization.•Hierarchical pore structure and heteroatom doping make good electrochemical property.•NSO-HPC show high capacitance, good rate performance and cycle stability in 6 M KOH.•NSO-HPC based supercapacitor shows specific energy of 35.3 Wh kg−1 in 1 M TEABF4/AN.This work report the synthesis of porous carbon with hierarchical pore structure and uniform nitrogen-sulfur-oxygen doping. The favorable pore structure (micro-, meso-, and macro-pores) is beneficial to ion adsorption and transportation, and the doping heteroatoms can introduce electrochemical active sites which contribute to additional pseudocapacitance. Therefore, the carbon material shows good electrochemical performance when employed as supercapacitor electrode. High specific capacitance (367 F g−1 at 0.3 A g−1), good rate performance and stable cycling characteristics are obtained in 6 M KOH. In addition, when tested in 1 M H2SO4, a higher specific capacitance (382 F g−1 at 0.3 A g−1) is delivered. Furthermore, the assembled symmetric cell yields a maximum specific energy of 35.3 W h kg−1 in 1 M TEABF4/AN, significantly improving the specific energy of carbon-based supercapacitors.

Low lithium ion diffusivity and poor electronic conductivity are two major drawbacks for the wide application of LiFePO4 in high-power lithium ion batteries. In this work, we report a facile and efficient carbon-coating method to prepare LiFePO4/graphitic carbon composites by in situ carbonization of perylene-3,4,9,10-tetracarboxylic dianhydride during calcination. Perylene-3,4,9,10-tetracarboxylic dianhydride containing naphthalene rings can be easily converted to highly graphitic carbon during thermal treatment. The ultrathin layer of highly graphitic carbon coating drastically increased the electronic conductivity of LiFePO4. The short pathway along the [010] direction of LiFePO4 nanoplates could decrease the Li+ ion diffusion path. In favor of the high electronic conductivity and short lithium ion diffusion distance, the LiFePO4/graphitic carbon composites exhibit an excellent cycling stability at high current rates at room temperature and superior performance at low temperature (−20 °C).

Lithium–sulfur batteries have attracted increasing attention as one of the most promising candidates for next-generation energy storage systems. However, the poor cycling performance and the low utilization of sulfur greatly hinder its practical applications. Here we report the improved performance of lithium–sulfur batteries by coating Ti3C2Tx MXene nanosheets (where T stands for the surface termination, such as -O, -OH, and/or -F) on commercial “Celgard” membrane. In favor of the ultrathin two-dimensional structure, the Ti3C2Tx MXene can form a uniform coating layer with a minimum mass loading of 0.1 mg cm–2 and a thickness of only 522 nm. Owing to the improved electric conductivity and the effective trapping of polysulfides, the lithium–sulfur batteries with MXene-functionalized separators exhibit superior performance including high specific capacities and cycling stability.Keywords: lithium−sulfur batteries; MXene; polysulfides; separator; Ti3C2Tx

Poor electrical conductivity and mechanical instability are two major obstacles to realizing high performance of MnO2 as pseudocapacitor material. The construction of unique hierarchical core–shell nanostructures, therefore, plays an important role in the efficient enhancement of the rate capacity and the stability of this material. We herein report the fabrication of a hierarchical α-MnO2 nanowires@ultrathin δ-MnO2 nanosheets core–shell nanostructure by adopting a facile and practical solution-phase technique. The novel hierarchical nanostructures are composed of ultrathin δ-MnO2 nanosheets with a few atomic layers growing well on the surface of the ultralong α-MnO2 nanowires. The first specific capacitance of hierarchical core–shell nanostructure reached 153.8 F g–1 at the discharge current density of as high as 20 A g–1, and the cycling stability is retained at 98.1% after 10 000 charge–discharge cycles, higher than those in the literature. The excellent rate capacity and stability of the hierarchical core–shell nanostructures can be attributed to the structural features of the two MnO2 crystals, in which a 1D α-MnO2 nanowire core provides a stable structural backbone and the ultrathin 2D δ-MnO2 nanosheet shell creates more reactive active sites. The synergistic effects of different dimensions also contribute to the superior rate capability.Keywords: core−shell nanostructures; cycling stability; manganese dioxide; nanosheets; nanowires; supercapacitors;

•Wool-ball-like Ni-CNTs cathodes were synthesized by a one-step electrodeposition.•Supergravity field was utilized to prepare non-noble metal cathode for HER.•The composite cathodes with significantly enhanced HER activity were reported.•Cathodes with finer grain size and homogeneous distribution of CNTs were obtained.In this work, supergravity fields are performed to prepare Ni-CNTs composite cathodes with wool-ball-like morphology from the Watts bath containing well-distributed functionalized CNTs. The prepared Ni-CNTs composite cathodes are used as noble metal-free electrocatalyst with favorable electrocatalytic activity for hydrogen evolution reaction (HER) in alkaline solutions. The crystal structure and morphology of the composite cathodes are characterized by XRD and SEM measurements. The electrochemical activities of the cathodes are characterized through Tafel polarization measurement, electrochemical impedance spectroscopy and cyclic voltammetric study in 1.0 M NaOH solution. The results indicate that catalytic activities of the Ni-CNTs cathodes prepared under supergravity fields are enhanced significantly, and the sample prepared at rotating speed 3000 rpm from the bath containing 1 g dm−3 CNTs exhibits the highest HER activity with smallest Tafel slope and largest exchange current density of 823.9 μA cm−2. Furthermore, the effects of both the CNTs concentrations and the intensities of supergravity fields on the properties of the Ni-CNTs cathodes are investigated.

•One step method.•Bulk production.•High j0.•High catalytic activity of HER.Ni–S/CeO2 composite materials for hydrogen evolution reaction (HER) have been prepared by an electrodeposition method under supergravity field from nickel sulfamate. With the different mass concentrations of CeO2, the morphology and X-ray diffraction patterns of Ni–S/CeO2 are diverse. Apparently, the CeO2 contents of Ni–S/CeO2 composite electrodes under supergravity fields are higher than that under normal gravity field. In addition, the HER catalytic activity of Ni–S/CeO2 composite electrodes can be measured in 1.0 M NaOH at 298 K. The results show that overpotential of Ni–S/CeO2 electrode of 7 g/L CeO2 under 3000 rpm is the least, suggesting perhaps too much content of CeO2 hinder the desorption of Hads, or too little CeO2 can not play palpable roles in improving the catalytic activity and increasing oxygen vacancies. And the exchange current density j0 value of Ni–S/CeO2 composite electrode prepared under the speed of 3000 rpm, which is 1.16 times larger than the Ni–S/CeO2 of 0 g/L CeO2, is 1.9 times higher than that under normal gravity field. EIS results suggest that there exists a synergetic effect on HER between CeO2 and Ni–S alloy matrix.

Three-dimensional (3D) interconnected N-enriched hierarchical porous lamellar carbon (NPLC) with a multilevel pore structure has been fabricated by a wet impregnation method using waste nitrogen-containing mantis shrimp shell as a carbon precursor and KOH as an impregnation solution. The synthesized NPLC-2 shows a large surface area of 1222.961 m2 g−1 calculated by the BET method, a hierarchical porous structure analyzed by the density functional theory (DFT) model, and a high nitrogen content of 1.78% quantified by X-ray photoelectron spectroscopy (XPS). Moreover, the NPLC-2 sample exhibits an ultra-high specific capacitance of 312.62 F g−1 at 0.3 A g−1, excellent rate capability with a specific capacitance of 272.56 F g−1 at 20.0 A g−1 and outstanding cycling stability with around 96.26% capacitance retention after 10000 cycles at a high current density of 20.0 A g−1. In addition, NPLC-2 presents a high energy density of 15.05 W h kg−1 at 270 W kg−1, and up to 10.12 W h kg−1 even at a large power density of 14580 W kg−1. Therefore, the prepared material can be applied in high energy density and high power density demanding fields.

The low electronic conductivity and one-dimensional diffusion channel along the b axis for Li ions are two major obstacles to achieving high power density of LiFePO4 material. Coating carbon with excellent conductivity on the tailored LiFePO4 nanoparticles therefore plays an important role for efficient charge and mass transport within this material. We report here the in situ catalytic synthesis of high-graphitized carbon-coated LiFePO4 nanoplates with highly oriented (010) facets by introducing ferrocene as a catalyst during thermal treatment. The as-obtained material exhibits superior performances for Li-ion batteries at high rate (100 C) and low temperature (−20 °C), mainly because of fast electron transport through the graphitic carbon layer and efficient Li+-ion diffusion through the thin nanoplates.Keywords: carbon coating; graphitization; high rate; lithium−iron phosphate; low temperature

•LiFePO4@CNT core–shell nanowire was synthesized using low-energy-consumption method.•The method can be easily scaled up for mass production.•The high rate and low temperature performances are enhanced via modifying with CNT.A high-energy efficient method is developed for the synthesis of LiFePO4@CNT core–shell nanowire structures. The method consists of two steps: liquid deposition approach to prepare FePO4@CNT core–shell nanowires and solvothermal lithiation to obtain the LiFePO4@CNT core–shell nanowires at a low temperature. The solution phase method can be easily scaled up for commercial application. The performance of the materials produced by this method is evaluated in Li ion batteries. The one-dimensional LiFePO4@CNT nanowires offer a stable and efficient backbone for electron transport. The LiFePO4@CNT core–shell nanowires exhibit a high capacity of 132.8 mAh g−1 at a rate of 0.2C, as well as high rate capability (64.4 mAh g−1 at 20C) for Li ion storage.

A novel lanthanum phosphate and carbon co-coated LiFePO4 cathode material successfully prepared via liquid-phase precipitation reaction combined with carbothermal reduction method has been studied in Li+ ion batteries. The LiFePO4 electrode modified by carbon layer deposited with appropriate amount of lanthanum phosphate shows higher reversible capacity and stable cycle performance compared with the LiFePO4/C electrode. These superior performances are owing to the good conductivity and stability of the hybrid coating layer which enhances the electron and Li+ ion transport on the surface of the LiFePO4 material, thus elevates the transfer kinetics of the electrode. The LiFePO4/C-LaPO4 (4.0 mol%) electrode showed a stable cyclability and the highest capacity among all the LiFePO4/C-xLaPO4 samples. The initial discharge capacity of the LiFePO4/C-LaPO4 (4.0 mol%) electrode was 150.7, 142.3, 116.6 and 80.3 mA h g−1 at 1, 2, 5 and 10 C rates, respectively.

•Three-dimensional inter-connected porous networks of manganese oxide/carbon composites were successfully developed.•The powdery composite possesses good conductivity and favorable porosity.•The composite electrode delivers an outstanding specific capacitance of 807 F g−1 at 1 A g−1.Manganese oxide/carbon (MnOx/C) composites have been successfully prepared via a high temperature heat treatment method followed by the electrochemical oxidation. The presence of carbon not only enhances the electronic conductivity of manganese oxides (MnOx), but also provides more active sites for the transformation of manganese monoxide (MnO) during the galvanostatic charge–discharge process. Simultaneity, the interconnected porous structures of MnOx/C samples are believed to provide a continuous channel for the diffusion of electrolyte ion and shorten the diffusion length of ions involved in the charge/discharge cycling processes. Consequently, these advantages endow the MnOx/C electrode a better capacitance performance, a superior long-term cyclic stability and outstanding rate capability compared with pristine MnOx. More importantly, the composites show a fascinating capacitance of 807 F g−1 at 1 A g−1, which is much higher than the reported hydrous RuO2 electrodes. It can be easily speculated that MnOx/C composites will act as a promising electrode materials for designing high-performance supercapacitors.

•Nitrogen-doped hierarchically porous coralloid carbon/sulfur composites were prepared•Nitrogen atoms were introduced to improve electrochemical properties•The intriguing structural features benefited discharge capacity and cycling stabilityNitrogen-doped hierarchically porous coralloid carbon/sulfur composites (N-HPCC/S) served as attractive cathode materials for lithium–sulfur (Li–S) batteries were fabricated for the first time. The nitrogen-doped hierarchically porous coralloid carbon (N-HPCC) with an appropriate nitrogen content (1.29 wt%) was synthesized via a facile hydrothermal approach, combined with subsequent carbonization–activation. The N-HPCC/S composites prepared by a simple melt–diffusion method displayed an excellent electrochemical performance. With a high sulfur content (58 wt%) in the total electrode weight, the N-HPCC/S cathode delivered a high initial discharge capacity of 1626.8 mA h g−1 and remained high up to 1086.3 mA h g−1 after 50 cycles at 100 mA g−1, which is about 1.86 times as that of activated carbon. Particularly, the reversible discharge capacity still maintained 607.2 mA h g−1 after 200 cycles even at a higher rate of 800 mA g−1. The enhanced electrochemical performance was attributed to the synergetic effect between the intriguing hierarchically porous coralloid structure and appropriate nitrogen doping, which could effectively trap polysulfides, alleviate the volume expansion, enhance the electronic conductivity and improve the surface interaction between the carbon matrix and polysulfides.

The low electronic conductivity and Li ion diffusion ability are two major obstacles to realize its wide application for LiFePO4 materials. The material with hierarchical conductive structure and lower antisite defects concentration can effectively enhance the electronic conductivity and Li ion diffusion ability. We firstly report here a modified solvothemal process for the fabrication of hierarchical conductive C/LiFePO4/CNTs composite with less antisite defects. It is found that the modified solvothemal process is facilitated to decrease FeLi antisite defects and enhance the electronic continuity between LFP and CNTs. In favor of its unique properties, the C/LFP/CNTs composites can deliver superior rate capability and cycling stability. Remarkably, even at a high rate of 20C (3400 mA g−1), a high initial discharge capacity of 91.6 mAh g−1 and good cycle retention of 95% with almost 100% coulombic efficiency are still obtained after 100 cycles.The hierarchical conductive C/LiFePO4/CNTs composite with less antisite defects is synthesized by a modified solvothemal process and delivers superior electrochemical performance with high rate capability and good capacity retention.

Three-dimensional (3D) interconnected N-doped porous carbons (NPCs) with different levels of pore structure are synthesized by a template method using MnOx as template and N-enriched pyrrole as carbon source. The fabricated materials show favorable pore size distribution in the range about 3–4 nm and moderate nitrogen content changing from 0.94 to 1.63 at%. Used as electrode material, the NPC originated from the optimum pyrolysis temperature of 750 °C demonstrates the best capacitance performance with a high specific capacitance of about 239.30 F g−1 at 0.5 A g−1. Moreover, it reveals an outstanding rate capability and the specific capacitance reaches 212.90 F g−1 at 10.0 A g−1 (up to 88.97% capacitance retention), as well as excellent cycling stability (∼10% capacitance loss after 5000 cycles) tested in 6 M KOH aqueous solution. Such exquisite performance may be ascribed to a unique combination of high specific surface area, suitable pore size distribution and introduction of nitrogen atoms.

The olivine-type LiFe1-xYxPO4/C (x = 0, 0.01, 0.02, 0.03, 0.04, 0.05) products were prepared through liquid-phase precipitation reaction combined with the high-temperature solid-state method. The structure, morphology, and electrochemical performance of the samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), energy-dispersive spectroscopy (EDS), galvanostatic charge-discharge, cyclic voltammetry, and electrochemical impedance spectroscopy (EIS). We found that the small amount of Y3+ ion-doped can keep the microstructure of LiFePO4, modify the particle morphology, decrease charge transfer resistance, and enhance exchange current density, thus enhance the electrochemical performance of the LiFePO4/C. However, the large doping content of Y3+ ion cannot be completely doped into LiFePO4 lattice, but existing partly in the form of YPO4. The electrochemical performance of LiFePO4/C was restricted owing to YPO4. Among all the doped samples, LiFe0.98Y0.02PO4/C showed the best electrochemical performance. The LiFe0.98Y0.02PO4/C sample exhibited the initial discharge capacity of 166.7, 155.8, 148.2, 139.8, and 121.1 mAh g−1 at a rate of 0.2, 0.5, 1, 2, and 5 C, respectively. And, the discharge capacity of the material was 119.6 mAh g−1 after 100 cycles at 5 C rates.

Olivine LiFePO4 with nanoplate, rectangular prism nanorod and hexagonal prism nanorod morphologies with a short b-axis were successfully synthesized by a solvothermal in glycerol and water system. The influences of solvent composition on the morphological transformation and electrochemical performances of olivine LiFePO4 are systematically investigated by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and galvanostatic charge–discharge tests. It is found that with increasing water content in solvent, the LiFePO4 nanoplates gradually transform into hexagonal prism nanorods that are similar to the thermodynamic equilibrium shape of the LiFePO4 crystal. This indicates that water plays an important role in the morphology transformation of the olivine LiFePO4. The electrochemical performances vary significantly with the particle morphology. The LiFePO4 rectangular prism nanorods (formed in a glycerol-to-water ratio of 1:1) exhibit superior electrochemical properties compared with the other morphological particles because of their moderate size and shorter Li+ ion diffusion length along the [010] direction. The initial discharge capacity of the LiFePO4@C with a rectangular prism nanorod morphology reaches to 163.8 mAh g–1 at 0.2 C and over 75 mAh g–1 at the high discharging rate of 20 C, maintaining good stability at each discharging rate.Keywords: electrochemical performance; lithium ion batteries; lithium iron phosphates; shape controlled nanoparticles; solvothermal;

•Novel cerous phosphate and carbon hybrid coating LiFePO4 is successfully synthesized.•The hybrid coating layer is favorable for fast electron and Li+ ion transport.•The high rate and low temperature performances are enhanced via modifying with CePO4.Novel cerous phosphate and carbon hybrid coating LiFePO4 cathode material successfully synthesized via liquid-phase precipitation reaction combined with the high temperature solid state method have been studied in lithium ion batteries. LiFePO4 deposited an appropriate amount of cerous phosphate in carbon coating layer shows higher reversible capacity and stable cycle performance compared with the LiFePO4/C. The good conductivity and stability of the hybrid coating layer can be favorable for these properties of LiFePO4, which increase Li+ ion and electronic transport on the surface and into the bulk of LiFePO4 electrode, avoid HF dissolving LiFePO4 in electrolyte, and facilitate the transfer kinetics. LiFePO4/C–CePO4 (1.0 mol%) electrode exhibits a stable cyclability and the highest capacity among all the LiFePO4/C–xCePO4 samples. The initial discharge capacity of LiFePO4/C–CePO4 (1.0 mol%) is 166.1, 161.4, 143.7 and 120.3 mAh g−1 at 1, 2, 5 and 10 C rates, respectively. And the capacity retention remains as high as 77.5% even after 650 cycles at 10 C. In addition, the material shows a higher reversible specific capacity of 100.9 mAh g−1 under lower discharging rate at −20 °C.

Cupric ion substituted LiFePO4/C composites were successfully synthesized via a two-step solid state reaction method. The SEM mapping demonstrates that cupric is well substituted in LiFePO4. Interestingly, the XRD spectra indicate that the substituted cupric could enlarge the interplanar distance of planes that parallelled to [010] direction of LiFePO4 crystallines, which could widens the diffusion channels of Li+ along [010] direction. For further research, Lithium ion storage behavior of as-synthesized cupric ion substituted LiFePO4/C products were investigated via various electrochemical strategies, and the highest capacity of 152.4, 144.4, 126.7 and 110.5 mAh g−1 was achieved by LiFe0.985Cu0.015PO4/C at discharge rate of 1, 2, 5, and 10 C, respectively. Compared the result with that of LiFePO4/C, we can see that cupric ion substituted LiFePO4/C composites show enhanced electrochemical activity for Li+ storage with decreased overpotential and increased high rate capability for electrochemical reaction.

A novel hierarchical MnO2/carbon strip (MnO2/C) microsphere is synthesized via galvanostatic charge–discharge of a MnO@C matrix precursor where the carbon is from a low-cost citric acid. This hierarchical structure is composed of manganese oxides nanoflakes and inlaid carbon strips. The ultrathin nanoflakes assemble to form porous microspheres with a rippled surface superstructure. Due to its improved conductivity and remarkable increased phase contact area, this novel structure exhibits an excellent electrochemical performance with a specific capacitance of 485.6 F g–1 at a current density of 0.5 A g–1 and an area capacitance as high as 4.23 F cm–2 at a mass loading of 8.7 mg cm–2. It also shows an excellent cycling stability with 88.9% capacity retention after 1000 cycles. It is speculated that the present low-cost novel hierarchical porous microspheres can serve as a promising electrode material for pseudocapacitors.Keywords: Carbon sources; Galvanostatic charge−discharge; Manganese oxides; Porous; Pseudocapacitor;

•LiFePO4 nanoplates prepared by facile solvothermal synthesis expose large (010) plane.•The polyester network formed by the esterification reaction could entirely wrap LiFePO4.•The polyester wrapped on the surface of LiFePO4 transformed into the uniform carbon layer after calcination.•LiFePO4/C nanoplates have good high-rate and low-temperature performance.A facile solvothermal synthesis and esterification reaction combined with a high temperature calcination technique has been developed to prepare the uniform carbon coating LiFePO4 nanoplates. The carbon coating LiFePO4 nanoplates are investigated by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscope (SEM), transmission electron microscope (TEM), galvanostatic intermittent titration technique (GITT) and galvanostatic charge–discharge test. A reasonable growth mechanism of LiFePO4 nanoplates is proposed on the basis of time dependent experimental results. The results show that each nanoplate is a LiFePO4 single crystal with the large (010) plane. According to Raman spectroscopy analysis, carbon is uniformly coated on the surface of LiFePO4 nanoplates. Electrochemical test results also indicate that the carbon coating LiFePO4 nanoplates exhibit a high reversible specific capacity of 144.8 mAh g−1 at 0.5 C and 116.9 mAh g−1 under lower discharging rate at −20 °C.

•Ni(OH)2/Ni/graphene composites were prepared by a facile one-step method.•The supergravity field has positive effects on the synthesis process of composites.•The Ni(OH)2/Ni/graphene electrode exhibits a specific capacitance of 2609 F g−1.A method of electrodeposition under supergravity field is proposed to prepare Ni(OH)2/Ni/graphene composites. Particles composed of Ni(OH)2 and Ni are covered by a thin graphene coating. The Ni(OH)2/Ni/graphene composite is evaluated as electrodes for supercapacitors, which shows that the specific capacitance of Ni(OH)2/Ni/graphene is 2609 F g−1 at a current density of 0.5 A g−1 in 6 M KOH solution. In addition, it could still reach 1020 F g−1 at a current density of 4 A g−1. On the other hand, electrodeposition under supergravity field could decrease concentration polarization and promote ion diffusion, which is a promising strategy for the fabrication of nanocomposites.

•The equipment is devised based on the requirement of the experiment.•TiC powders are synthesized from inexpensive TiO2 and graphite powders.•TiC-CDC is successfully synthesized by electrolysis of TiC powder in molten CaCl2.•TiC-CDC has much higher purity, displays a superior electrocapacitive performance.A nanoporous titanium carbide derived carbon (TiC-CDC) is successfully synthesized by electrolysis of TiC powder in molten CaCl2. The electrolysis was conducted at 850 °C for 48 h in argon at an applied constant voltage of 3.1 V. The structure of the resulting carbon is characterized by X-ray diffraction, Raman spectroscopy and Transmission electron microscope techniques. Cyclic voltammetry and galvanostatic charge/discharge measurements are applied to investigate electrochemical performances of the TiC-CDC material. The results show that the obtained product is TiC-CDC, which is a mixture of amorphous carbon and ordered graphite phase with a highly degree of graphitization. Cyclic voltammetry measurements on the TiC-CDC do not show any major faradic reactions within the experimental voltage range. A specific capacitance of 160 F/g at a current density of 300 mA/g was achieved from the sample synthesized at 850 °C.

Aluminum doped MnO2 nanoparticles were synthesized by a simple liquid-phase process using potassium permanganate as oxidation agent, glycol as reducing agent. Specific capacitance of the optimal sample electrode can reach 290 F g−1 after 10 cycles. The electrode also exhibits excellent cycle stability, retaining 86.6 % after 1,000 cycles. The infrared absorption bands of aluminum doped manganese oxide shift to high wave number for the reason that aluminum ion has smaller nuclear charge. The doping of aluminum strengthens the Mn–O bond and decreases the aggregation degree, thus the electrochemical properties are enhanced.

MnC2O4/graphene composites are prepared by a facile hydrothermal reaction with KMnO4 using ascorbic acid as a reducing agent. Olive-like MnC2O4 particles are distributed uniformly on the surface of graphene sheets. The composites are evaluated as supercapacitor electrodes, which show that the specific capacitance of MnC2O4/graphene composites is 122 F g−1, more than twice as high as that of free MnC2O4 at a current density of 0.5 A g−1. In addition, this composite material exhibits an excellent cycle stability with the capacitance retention of 94.3 % after 1,000 cycles.

Cobalt-doped MnO2, as electrode material for supercapacitor, was synthesized by pulse electrodeposition method. The morphology and structure of the products were characterized by X-ray diffraction (XRD) and field-emission scanning electron microscope (FE-SEM). The results show that the crystal structure of the products is γ-type, and the samples reveals a porous texture composed of manganese oxide nanosheets. Cyclic voltammetry (CV), electrochemical impedance spectrometry (EIS), and galvanostatic charge–discharge tests indicate that doping cobalt has great effect on the electrochemical performance of manganese dioxide material. A specific capacitance of 354 F g−1 is obtained when the molar ratio of Mn to Co is 200:10. After 100 charge–discharge cycles in 6 M KOH solution, the specific capacitance stabilized at 333.6 F g−1, exhibiting excellent capacitance retention ability.

MnO2/graphite electrode material is successfully synthesized by electrodeposition under supergravity field from manganese acetate and graphite suspending solution. X-ray diffraction and field emission scanning electron microscopy show that the obtained composite is γ-MnO2/graphite. The process of depositing the MnO2/graphite was shown by the schematic illustration. Galvanostatic charge/discharge and cyclic voltammograms tests are applied to investigate electrochemical performances of the composite electrodes prepared under supergravity fields. MnO2/graphite synthesized under supergravity field exhibits good discharge capacitance and the specific capacitance is 367.77 F g−1 at current density of 0.5 A g−1. It is found that supergravity field has effects on the electrochemical performances of MnO2/graphite material.

LiFePO4/C surface modified with Li3V2(PO4)3 is prepared with a sol–gel combustion method. The structure and electrochemical behavior of the material are studied using a wide range of techniques such as X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope, galvanostatic charge–discharge, and electrochemical impedance spectroscopy. It is found that LiFePO4/C surface modified with Li3V2(PO4)3 has the better electrochemical performance. The discharge capacity of the as-prepared material can reach up to 153.1, 137.7, 113.6, and 93.3 mAh g−1 at 1, 2, 5, and 10 C, respectively. The capacitance of the LiFePO4/C modified by Li3V2(PO4)3 is higher under lower discharging rate at −20 °C, and the initial discharge capacity of 0.2 C is 131.4 mAh g−1. It is also demonstrated that the presence of Li3V2(PO4)3 in the sample can reduce the charge transfer resistance in the range of −20 to 25 °C, resulting in the enhanced electrochemical catalytic activity.

The olivine-type samarium-doped LiFe1 − xSmxPO4/C (x = 0, 0.01, 0.02, 0.03, 0.04, and 0.05) composites were synthesized via liquid-phase precipitation reaction combined with the high-temperature solid-state method. The structure, morphology, and electrochemical performance of the samples were characterized by X-ray diffraction, scanning electron microscope, transmission electron microscope, energy dispersive spectroscopy, galvanostatic charge–discharge, galvanostatic intermittent titration technique, and electrochemical impedance spectroscopy. The results showed that the small amount of Sm3+ ion-doped can keep the olivine microstructure of LiFePO4, modify the particle morphology, decrease polarization overpotential and charge transfer resistance, and enhance exchange current density, thus improve the electrochemical performance of the LiFePO4/C. However, the large doped content of Sm3+ ion can form more SmPO4, which can weaken the electrochemical performance of LiFePO4/C. Among all the doped samples, LiFe0.99Sm0.01PO4/C showed the best rate capacity, cycling stability, and low temperature performance. The LiFe0.99Sm0.01PO4/C sample exhibited the initial discharge capacity of 148.1, 133.4, 117.5, and 106.6 mAh g−1 at 1C, 2C, 5C, and 10C, respectively. In addition, the discharge capacity of the material was 94.8 mAh g−1 after 800 cycles at 10C. Moreover, the initial discharge capacity of 0.1C, 0.2C, 0.5C, and 1C were 104.4, 96.2, 53.9, and 50.8 mAh g−1 at −20 °C.

•The crystal orientations of the as-prepared LiFePO4 were discussed.•The diffusion energy barriers of Li ions for LiFe1–xCoxPO4 were calculated.•Doping Co can markedly improve the electrochemical performance of LiFePO4/C.A series of olivine LiFe1 − xCoxPO4/C (x = 0, 0.005, 0.01, 0.015, 0.02 and 0.025) nanoplates were synthesized by a facile solvothermal synthesis combined with esterification reaction. The structure, morphology and electrochemical performance of the samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), galvanostatic intermittent titration technique (GITT), galvanostatic charge/discharge tests and electrochemical impedance spectroscopy (EIS). Based on the first-principle density functional theory (DFT), the diffusion energy barriers of Li ions for LiFe1 − xCoxPO4 (x = 0–0.025) were also calculated to further investigate the influence of doping Co on LiFePO4/C cathode material. The results showed that the prepared nanoplates with a very thin thickness along b-axis grow preferentially along the [001] direction of (101) lattice planes, which can minish the distance of Li+ ion diffusion along the [010] direction. The calculated results suggested that the LiFe0.99Co0.01PO4/C had a lowest lithium ion diffusion energy barrier, accordingly possessing a highest lithium ion diffusion coefficient. The electrochemical performance was improved by doping an appropriate amount of Co, and it might be attributed to the fact that the doped Co ion can enhance exchange current density and lithium ion diffusion coefficient. Among all the doped samples, LiFe0.99Co0.01PO4/C exhibited the best rate capability and cycling stability, with the initial discharge capacity of 154.5 mAh g− 1 at 0.5 C. Remarkably, it still showed a high discharge capacity of over 96.9 mAh g− 1 and good cycle retention even at a high rate of 10 C.

•The effect of Py additive in Li-S batteries is investigated for the first time.•A surface protect layer on cathode through electrochemical oxidation polymerization.•PPy can act as a conductive/absorbing agent or barrier layer to trap polysulfides.•An appropriate amount of pyrrole additive leads to improving performance.Lithium–sulfur batteries are a promising energy storage devices beyond conventional lithium ion batteries. However, the “shuttle effect” of soluble polysulfides is a major barrier between electrodes, resulting in rapid capacity fading. To address above issue, pyrrole has been investigated as an electrolyte additive to trap polysulfides. When pyrrole is added into electrolyte, a surface protective layer of polypyrrole can be formed on the sulfur cathode, which not only acts as a conductive agent to provide an effective electron conduction path but also acts as an absorbing agent and barrier layer suppressing the diffusion of polysulfide intermediates. The results demonstrate that an appropriate amount of pyrrole added into the electrolyte leads to excellent cycling stability and rate capability. Apparently, pyrrole is an effective additive for the entrapment of polysulfides of lithium-sulfur batteries.