A nanocomposite of ultrafine anatase nanoparticles (<5 nm) embedded N-doped carbon (TiO2-NPs/NC) with a relatively low specific surface area was successfully synthesized by in situ pyrolysis of a new and cheap single source precursor of (H2en)3[Ti4(O2)4(Hcit)2(cit)2]·12H2O (en = ethylenediamine and H4cit = citric acid) under 550 °C and an inert atmosphere. The precursor in crystalline state was isolated from an aqueous solution containing of titanium butoxide, citric acid, hydrogen peroxide, and ethylenediamine and was characterized. The crystal structure was determined by X-ray single crystal diffraction. To our surprise, the low surface area TiO2-NPs/NC exhibits a high specific capacity, superior rate capability, excellent cycle performance, and good processability as a negative material for rechargeable lithium-ion batteries (LIBs). A large reversible capacity of 360 and 125 mA h g–1 and a high Coulombic efficiency (the average value is ∼99.8%) could be kept even after 1000 cycles under a current density of 0.3 and 6 A g–1, respectively. An analysis of the voltammetric sweep data shows that the pseudocapacitive behavior occurred at the surface of the material and the lithium intercalation processes contribute to the total stored charge, resulting in the high capacity of the TiO2-NPs/NC nanocomposite. The potentiostatic intermittent titration technique used to determine the lithium ion diffusion (DLi+) suggested the TiO2-NPs/NC nanocomposite displays a high DLi+. In addition, the high electric conductivity provided by the NC substrate and the ultrafine anatase particles can mitigate the diffusion path for electrons and ions and tolerate higher strain, and thus effectively decrease pulverization and improve the rate and cycle performance. In particular, the observed superior lithium storage properties, resulting from the low surface area nanocomposite with ultrafine nanoparticles embedded NC substrate, are expected to have fundamental and practical implications for the preparation of high performance electrodes in LIBs or other cells.Keywords: cycling stability; high rate performance; Li-ion batteries; single source precursor; TiO2-based anode;

•Surface Mn4+-rich LiMn2O4 was prepared by an off-stoichiometric strategy.•The sample shows a truncated octahedral structure with Al-rich surface layer.•The sample shows superior rate capability and capacity retention and at 55 °C.A truncated octahedral structure spinel cathode material with a nominal composition of Li1.08Al0.08Mn1.85Co0.05O3.9F0.1 (LAMCOF) and an Al-rich surface layer is successfully prepared by a sol-gel route combined with a temperature-controlled heat-treatment process. Concentration gradient of Mn4+ ions is found to decrease through the surface to the interior of the as-prepared sample. As the consequence, the LAMCOF sample delivers high rate capability and excellent cycling stability at elevated temperature, showing an initial discharge capacity of 111.1 mAh g−1 and capacity retention of 70.5% over 850 cycles at 1C rate under 55 °C. Even at 5C rate under 55 °C, it also displays a high capacity of 102.5 mAh g−1 with capacity retention of 80.0% over 850 cycles. These results reveal the importance of an off-stoichiometric strategy and a temperature-controlled heat-treatment process for the preparation of LiMn2O4-based spinel cathode material with unique crystal orientation and Mn4+-rich surface layer, which both decrease the Mn dissolution and provide interfacial stability while preserving fast Li+ diffusion, resulting in improvement of cycle performance and rate capability of the as-prepared material. This proposed synthesis method does not need a supplementary coating process and is likely suitable to prepare other high performance cathode materials.

LiMnPO4 (LMP) is one of the most potential candidates for high energy density (≈700 W h kg−1) lithium ion batteries (LIBs). However, the intrinsically low electronic conductivity and lithium ion diffusion coefficient of LMP result in its low performance. To overcome these challenges, it is an effective approach to prepare nanometer-sized Fe-doping LMP (LFMP) materials through optimization of the preparation routes. Moreover, surface coating can improve the ionic and electronic conductivity, and decrease the interfacial side reactions between the nanometer particles and electrolyte. Thus, a uniform surface coating will lead to a significant enhancement of the electrochemical performance of LFMP. Currently, considerable efforts have been devoted to improving the electrochemical performance of LiFe1-yMnyPO4 (0.5 ≤ y < 1.0) and some important progresses have been achieved. Here, a general overview of the structural features, typical electrochemical behavior, delithiation/lithiation mechanisms, and thermodynamic properties of LiFe1-yMnyPO4-based materials is presented. The recent developments achieved in improvement of the electrochemical performances of LiFe1-yMnyPO4-based materials are summarized, including selecting the synthetic methods, nanostructuring, surface coating, optimizing Fe/Mn ratios and particle morphologies, cation/anion doping, and rational designing of LFMP-based full cells. Finally, the critical issues at present and future development of LiFe1-yMnyPO4-based materials are discussed.

•Co partial replacement of Ir in Ti/IrO2-Sb2O5-SnO2 enhances its OER activity.•The good charge transfer and increase of OH species cause high OER activity.•The Ti/Ir0.05Co0.05Sb0.1Sn0.8Ox electrode shows good stability in basic solution.Preparation of highly efficient and inexpensive electrodes for oxygen evolution reaction (OER) is of significant importance in the development of water splitting for hydrogen production. Ternary IrO2-Sb2O5-SnO2 and cobalt-based oxides have been suggested to be high stability and low cost electrocatalysts for OER in acid and basic aqueous solution, respectively. Herein, we develop a serial of Ti/CoOx-IrO2-Sb2O5-SnO2 anodes by a simple thermal treatment of mixed metal chlorides on Ti substrate. It is found that the partial-substitution iridium by cobalt in Ti/Ir0.1Sb0.1Sn0.8Ox (Ti/C0ISS) anode shows an improved OER activity in acid and basic solution. For a Ti/Ir0.05Co0.05Sb0.1Sn0.8Ox (Ti/C5ISS) anode, small overpotentials of 0.438 and 0.498 V are needed under the current densities of 10 and 100 mA cm−2 in 0.5 M KOH, respectively. These values are remarkably lower than those of Ti/C0ISS electrode and comparable to other nanometer metal oxides catalysts. Additionally, it exhibits a low Tafel slope of 55 mV dec−1 and displays excellent electrocatalytic durability for OER in alkaline solution under a high current density. These advantages indicate Ti/C5ISS is a promising anode for water oxidation under high current densities.Cobalt partial-substitution iridium in a Ti/Ir0.1Sb0.1Sn0.8Ox anode shows a significantly improved OER activity.Download high-res image (148KB)Download full-size image

•A truncated Al, Co-co-substituted Li-rich oxyfluoride spinel was prepared.•The spinel shows high specific capacity and superior cyclability at 55 °C.•The unique morphology and composition explain its superior rate and cycle performance.Spinel LiMn2O4 cathode material has been successfully commercialized for various lithium ion batteries (LIBs) and is a very promising candidate for emerging large-scale applications in pure electric vehicles (EVs). Despite its advantages, LiMn2O4 suffers from fast capacity fading at elevated temperature stemming from Mn dissolution and structural distortion. Herein, an investigation on the structure and electrochemical performance of single/double/triple-ion substituted Li1.05Mn1.95O4, which was synthesized by a Sol-gel method combined with heat treatment at 750 °C, was firstly carried out. Enhancements of the tap density, rate capability, and cycling performance at high temperature were achieved without sacrificing its specific capacity via unique morphology control and triple-substitution (Al3+, Co3+, and F− ions) strategy. The as-prepared Li1.05Al0.05Mn1.85Co0.05O3.9F0.1 (LAMCOF) sample exhibits a high specific capacity, a superior rate capability, and an excellent long-term cyclability at the high temperature (55 °C), with the specific discharge capacities of 115 and 110 mAh g−1 and the corresponding capacity retention of 72.3% and 73.0% for up to 800 cycles at 2 and 5 C rates, respectively. The high specific capacity, an excellent cyclability, and a superior rate performance are believed to be caused by the three main reasons: (1) improvement of the specific capacity by the substitution of O2− by F−, (2) stabilization of the crystal structure derived from the synergistic roles of triple substitution by Al3+, Co3+, and F− ions, which decreases the Jahn-Teller distortions and Mn dissolution; and (3) formation of a stable interface of the active material/electrolyte resulting from the high content of Mn4+ at the surface and its unique morphology, which reduces the charge transfer resistances and favors fast Li+ intercalation/deintercalation kinetics. The as-prepared LAMCOF sample may offer a promising cathode material for the high-power LIBs with extended cycle life and superior rate capability at elevated temperature.

It is of great interest to develop new carbon-based materials as electrodes for supercapacitors because the conventional electrodes of activated carbons in supercapacitors cannot meet the ever-increasing demands for high energy and power densities for electronic devices. Due to their high electronic conductivity and improved hydrophilic properties, together with their easy syntheses and functionalization, N-doped carbons have shown a great potential in energy storage and conversion applications. In this review, after a brief introduction of electrochemical capacitors, we summarize the advances, in the recent six years, in the preparation methods of N-doped carbons for applications in supercapacitors. We also discuss and predict futuristic research trends towards the design and syntheses of N-doped carbons with unique properties for electrochemical energy storage.

•The advances of SnO2/graphene composites as anode materials for LIBs are reviewed.•Preparation methods and structural modifications of SnO2/graphene are presented.•Relationships of Li storage property, nanostructures and composition are discussed.•Opportunities for future work are identified.With the increasing energy demands for electronic devices and electrical vehicles, anode materials for lithium ion batteries (LIBs) with high specific capacity, good cyclic and rate performances become one of the focal areas of research. Among the various anode materials, SnO2/graphene nanocomposites have drawn extensive attentions due to their high theoretical specific capacities, low charge potential vs. Li/Li+ and environmental benignity. In this review, the advances, including the synthetic methods and structural optimizations, of the SnO2/graphene nanocomposites as anode materials for LIBs have been reviewed in detail. By providing an in-depth discussion of SnO2/graphene nanocomposites, we aim to demonstrate that the electrochemical performances of SnO2/graphene nanocomposites could be significantly enhanced by rational modifications of morphology and crystal structures, chemical compositions and surface features. Though only focusing on SnO2/graphene-based composites, the concepts and strategies should be referential to other metal oxide/graphene composites.

It has long been demonstrated that KOH and ZnCl2 can be used as efficient chemical activation agents to prepare porous carbons. Herein, we develop a green activation method, that is, one-step calcium chloride (CaCl2) activation sugar cane bagasse with urea, for the preparation of nitrogen-rich porous carbons (NPCs). The nitrogen contents, specific surface areas, pore sizes, and specific capacitances of the obtained NPCs can be effectively tuned by adjusting the ratio of carbon precursor (sugar cane bagasse), nitrogen source (urea), and activation agent (CaCl2). The synthesized three-dimensional oriented and interlinked porous nitrogen-rich carbons (3D-NPCs) contain not only abundant porosities which can impose an advantage for ion buffering and accommodation, but also high nitrogen content in the carbons which can obviously increase the pseudocapacitance. Therefore, for the typical sample, obtained from pyrolysis of the mixture of sugar cane bagasse, urea, and CaCl2 in a mass ratio of 1:2:2 at 800 °C for 2 h under N2 atmosphere, shows a high specific capacitance, excellent rate capability (with 323 and 213 F g–1 at the discharge/charge current densities of 1 and 30 A g–1, respectively), and outstanding cycle performance (a negligible capacitance loss after 10 000 cycles at 5 A g–1).Keywords: Biomass waste; CaCl2 activation; Nitrogen-rich porous carbons; Porous structure; Supercapacitors

The rate performance of LiMnPO4-based materials is further improved via synergistic strategies including a surfactant-assisted solid state method, Fe-substitution and carbon-coating. The surfactant-assisted solid state strategy effectively decreases the primary particle size of the cathode material, which can greatly shorten the diffusion distance of lithium ions. The Fe-substitution improves the effectiveness of Li+ insertion/extraction reactions in the solid phase. The uniform carbon coating layer and the conductive networks provided by the carbon between the nanoparticles ensure the continuous conductivity by the nanoparticles. As a consequence of the synergistic effects, the as prepared LiFe0.5Mn0.5PO4 sample with 6.10 wt% carbon exhibits high specific capacities and superior rate performance with discharge capacities of 155.0, 140.9 and 121 mA h g−1 at 0.1, 1 and 5 C (1 C = 170 mA g−1), respectively. Meanwhile, it shows stable cycling stability at both room temperature (25 °C, 94.8% and 90.8% capacity retention after 500 cycles at 1 and 5 C rates, respectively) and elevated temperature (55 °C, 89.2% capacity retention after 300 cycles at 5 C rate). This material may have great potential application in advanced Li-ion batteries.

Confinement of ultra-small MgTi2O5 nanoparticles in carbon is demonstrated to be an efficient method for fabricating long cycle-life anode material for sodium ion batteries. Superior rate and excellent cyclic capabilities as well as high Coulombic efficiency of the MgTi2O5–C nanocomposite, obtained from pyrolysis of a single molecule precursor, are shown.

Graphene oxide/polydopamine-coated Si nanocomposite (GO/PDA-Si) was synthesized by a novel facile solution-based chemical method at room temperature. The nanocomposite with a PDA coating layer of ∼1.5 nm exhibits a high reversible specific capacity and excellent cycling stability (1074 mAh g–1 after 300 cycles at 2100 mA g–1) as an anode material for lithium ion batteries. The synergistic effect of the PDA coating layer and GO plays an important role in improving the electrochemical lithium storage performances. Both of them can serve as a cushion to buffer the volume change of Si nanoparticles (NPs) during the charge/discharge process and prevent Si NPs from direct contact with a liquid electrolyte. The surface property of Si NPs was also modified by introducing secondary amine groups, which can form amide groups with carboxyl groups and hydrogen bonds with hydroxyl/carboxyl groups on GO. These chemical interactions firmly anchor Si NPs to GO so that aggregation of Si NPs can be mostly prevented. Moreover, the good lithium ion conductivity of PDA is beneficial for rate performance. The experimental results should be very useful in guiding the preparation of long-cycle-life Si-based anode materials with good rate performance using a simple surface-modification process.

A novel composite of sulfur immobilized into porous N-doped carbon microspheres (NCMSs–S) was synthesized. This composite cathode for lithium–sulfur batteries delivers a high specific capacity and superior rate capability and cycle stability, with a reversible capacity of ∼605 mA h g−1 at 2 C and 85% capacity retention after 500 cycles.

There is a great interest in the utilization of silicon-based anodes for lithium-ion batteries. However, its poor cycling stability, which is caused by a dramatic volume change during lithium-ion intercalation, and intrinsic low electric conductivity hamper its industrial applications. A facile strategy is reported here to fabricate graphene oxide-immobilized NH2-terminated silicon nanoparticles (NPs) negative electrode (Si@NH2/GO) directed by hydrogen bonding and cross-linked interactions to enhance the capacity retention of the anode. The NH2-modified Si NPs first form strong hydrogen bonds and covalent bonds with GO. The Si@NH2/GO composite further forms hydrogen bonds and covalent bonds with sodium alginate, which acts as a binder, to yield a stable composite negative electrode. These two chemical cross-linked/hydrogen bonding interactions—one between NH2-modified Si NPs and GO, and another between the GO and sodium alginate—along with highly mechanically flexible graphene oxide, produced a robust network in the negative electrode system to stabilize the electrode during discharge and charge cycles. The as-prepared Si@NH2/GO electrode exhibits an outstanding capacity retention capability and good rate performance, delivering a reversible capacity of 1000 mAh g–1 after 400 cycles at a current of 420 mA g–1 with almost 100% capacity retention. The results indicated the importance of system-level strategy for fabricating stable electrodes with improved electrochemical performance.Keywords: cross-linking; cycling stability; graphene oxide; Li-ion batteries; Si-based anode

•LiFe0.15Mn0.85PO4/C composite is prepared by a surfactant-assisted milling route.•The LiFe0.15Mn0.85PO4/C composite exhibits excellent rate and cycle capability.•Stable cycle properties are ascribed to uniform carbon-coated nanostructures.A uniform carbon coated LiFe0.15Mn0.85PO4 (LFMP/C) cathode material is synthesized by a surfactant-assisted, highly reproducible and energy-saving solid state method using a bimetallic oxalate (Fe0.15Mn0.85C2O4) precursor. The obtained LiFe0.15Mn0.85PO4/C composite is characterized by X-ray diffraction (XRD), Raman spectrum, elemental analysis (EA), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The experimental results demonstrate that the oleic acid as a surfactant, for the scale preparation of LFMP, plays a critical role in controlling size of the obtained composite. The LiFe0.15Mn0.85PO4/C exhibits high specific capacity and good rate performance. It delivers initial discharge capacities of 156.5, 142.5, 129.0 and 103.0 mAh g−1 at 0.05, 0.1, 0.5 and 1C, respectively. Moreover, it shows good cycle stability at both room temperature (25 °C, 89% and 88% capacity retention after 250 and 500 cycles at 0.5 and 1C rates, respectively) and elevated temperature (55 °C, 80% capacity retention after 200 cycles at 0.5C rate). The significantly improved rate and cycling capability of the LiFe0.15Mn0.85PO4/C is attributed to the uniform carbon coating layer on the primary particles, the conductive network provided by the carbon between the LiMn0.15Fe0.85PO4/C particles and the sufficient pores formed in the LiFe0.15Mn0.85PO4/C aggregates.

The LiNi0.5Mn1.5O4 (LNMO) spinel is an attractive cathode candidate for next generation lithium-ion batteries as it offers high power and energy density. In this paper, the effects of extra amounts of lithium addition and postannealing process on the physicochemical and electrochemical properties of the spherical LNMO material were investigated. The experimental results show that the amount of lithium and the postannealing process have significant impacts on the Mn3+ content, phase impurity (rock-salt phase) and phase structures (Fd3m and P4332) of the spherical LNMO cathode materials, so as their electrochemical performance. In particular, the phase transition from Fd3m to P4332 and the Mn3+ content of the LNMO spinels were found to be adjusted by lithium additions and the postannealing process. With the presence of Mn3+, the absence of the impurity phase (rock-salt phase) and the cation ordering in the spinels, the electrochemical rate performance and capacity retention of the products could be significantly improved. In a half cell test, LNMO cathode material with 5% of lithium excess (based on theoretical formula calculation) displays a high specific discharge capacity of 123 mAh g–1 at 2 C rate with excellent capacity retention of 84% after 500 cycles at 55 °C. All these findings show the important roles of the synergic effects of Mn3+ content, phase impurity (rock-salt phase) and phase structures (Fd3m and P4332) on the electrochemical performance improvement of LNMO-based cathode materials, which will guide the preparation of LNMO-based cathode material with excellent electrochemical performance.

Porous LiMn2O4 microspheres, which are constructed with nanometer-sized primary particles, have been synthesized by a facile method using porous MnCO3 microspheres as a self-supporting template. The LiMn2O4 microspheres were characterized by XRD, SEM and HR-TEM. The as-synthesized porous LiMn2O4 microspheres exhibit high rate capability and long-term cyclability as cathode materials for lithium ion batteries, with the specific discharge capacity of 119, 107 and 98 mA h g−1 and the corresponding capacity retention of 82, 91 and 80% for up to 500 cycles at 2, 10 and 20 C, respectively. The high rate performance and good cyclability are believed to result from the porous structure, reasonable primary particle size and high crystallinity of the obtained material, which favor fast Li intercalation/deintercalation kinetics by allowing electrolyte insertion through the nanoparticles and high structural stability during the reversible electrochemical process. The high level of Mn4+ concentration on the surface of the sample can alleviate the Jahn–Teller transition, which was triggered normally by the equal amounts of Mn4+/Mn3+ concentration on the surface of the LiMn2O4 cathode material. This good example offering extended cycle life at 20 C rate for the LiMn2O4 microspheres indicates their promising application as cathode materials for high performance LIBs.

Relatively uniform sized graphene-encapsulated sulphur (GES) composites with a core (S)–shell (graphene) structure were synthesized in one pot based on a solution-chemical reaction–deposition method. These novel GES particles were characterized by XRD, Raman spectrometry, SEM, TGA, EDS and TEM. The electrochemical tests showed that the present GES composites exhibit high specific capacity, good discharge capacity retention and superior rate capability when they were employed as cathodes in rechargeable Li–S cells. A high sulphur content (83.3 wt%) was obtained in the GES composites. Stable discharge capacities of about 900, 650, 540 and 480 mA h g−1 were achieved at 0.75, 2.0, 3.0 and 6.0 C, respectively. The good electrochemical performance is attributed to the high electrical conductivity of the graphene, the reasonable particle size of sulphur particles, and the core–shell structures that have synergistic effects on facilitating good transport of electrons from the poorly conducting sulphur, preserving fast transport of lithium ions to the encapsulated sulphur particles, and alleviating the polysulfide shuttle phenomenon. The present finding may provide a significant contribution to the enhancement of cathodes for the lithium–sulphur battery technology.

Spinel LiMn1.5Ni0.5O4 (LMNO) sub-micrometer-sized spheres were prepared in one step using porous MnCO3 microspheres as a self-supporting template. The LMNO spheres were characterized by XRD, SEM and TEM. The obtained LMNO was in a well-crystallized cubic phase with little impurity. It showed high rate capability and excellent cycling stability as a cathode material for lithium ion batteries. Initial discharge capacities of 122.0, 120.3, 119.5 and 112.1 mAh g− 1 were found at 2, 3, 5 and 10C respectively with 1C being 146.7 mA g− 1. Their capacity retentions are 92, 91, 82 and 79% respectively after 500 cycles. The as-prepared LMNO is a promising cathode material for high power and long-life lithium ion batteries.Highlights► Facile synthesis route for LiMn1.5Ni0.5O4 sub-micrometer-sized spheres with high crystallinity ► Outstanding capacity retention (76%) even after 1500 charge/discharge cycles at 2C rate ► Good rate performance and high energy density (112 mAh g− 1 at 10C rate with 4.6 V discharge voltage plateau)

Unique hollow Fe3O4/C spheres are prepared by a simple one-pot solvothermal method, with spinel structure and 750 nm in diameter identified by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. The hollow Fe3O4/C spheres exhibit excellent cycling and rate performance as anode material for lithium ion batteries, delivering reversible specific capacities of 984 mAh g−1 even after 70 cycles at 0.2 C, 620 mAh g−1 at 2 C, and 460 mAh g−1 at 5 C, respectively. Lithium insertion mechanisms are also proposed in terms of the ex situ XRD analysis of the electrodes after discharged and charged to certain voltages together with cyclic voltammetry (CV) and voltage profile.Graphical abstractHighlights► The self-assembled hollow Fe3O4/C spheres favor a fast kinetic with facilitating the electron transportation, the lithium ions insertion/deinsertion and less volume expansion during cycling. ► Hollow Fe3O4/C spheres was first reported as anode material with excellent cycling and rate performance. ► Lithium insertion mechanisms are also proposed systematically based on the ex situ XRD analysis. ► This simple, inexpensive synthesis approach can be scale-up easily and used for producing of other hollow spherical materials for high power LIBs.

Monodispersed hollow Fe3O4 spheres with different diameters and shell thickness were synthesized by a simple solvothermal process and were investigated as anode materials for lithium ion batteries (LIBs). The shell of the hollow spheres exhibited porous structure composed of aggregated Fe3O4 nanoparticles. The composition and morphology of the obtained samples were characterized by X-ray powder diffraction (XRD), Raman spectra, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). A novel formation mechanism was proposed based on the results of time-dependent reactions. The electrochemical tests of the hollow Fe3O4 spheres were performed to determine the reversible capacity, rate and cycling performance as anode materials for LIBs. The Fe3O4 obtained from the reaction at 200 °C for 48 h exhibited the best specific capacity and capacity retention and superior rate performance compared to other Fe3O4 spheres, which is ascribed to their reasonable particle size, high crystallinity and hollow spherical structures. Different conductive additive were used to investigate the electrochemical performance of Fe3O4 hollow spheres. The binary conductive additives containing acetylene black (AB) and carbon nanobutes (CNTs) improved the electrochemical performance of the Fe3O4 hollow spheres obviously. The results reveal that there is a synergistic effect of the particle size, crystallinity and conductive agents on the electrochemical properties of the hollow Fe3O4 spheres.Highlights► Hollow Fe3O4 spheres with different diameters were obtained from solvothermal route. ► Hollow Fe3O4 spheres have excellent electrochemical performance as an anode material. ► The crystallinity and conductive agents have synergies on the discharge capacity.

Three isostructural heterobimetallic nitrilotriacetatoperoxotitanate complexes of general formula [M(H2O)5]2[Ti2(O2)2O(nta)2]·7H2O [M = Co (1), Ni (2) and Zn (3)] have been isolated in pure crystals directly from the quaternary system of M2+–Ti(OC4H9)4–H2O2–H3nta (H3nta = nitrilotriacetic acid) at pH = 4.0 and have been characterized by elemental analyses, IR, thermal analysis (TGA), and single-crystal X-ray diffraction. Single crystal X-ray analysis reveals that the titanium atom in these complexes features seven-fold-coordination, each surrounded by six oxygen atoms and one nitrogen atom. The divalent transition metal ions in these compounds are hexa coordinated, surrounded by five water molecules and one bridged carboxylato oxygen atom. The TGA and XRD results prove that complexes 1–3 undergo facile thermal decomposition to form pure CoTiO3, NiTiO3 and ZnTiO3 at 700 °C respectively. The morphologies, microstructures, and crystallinity of the residues obtained after pyrolysis were characterized by transmission electron microscopy and powder X-ray diffraction.

Calcium titanate (CaTiO3) was conveniently synthesized by thermal decomposition of a single-source precursor [Ca(H2O)3]2[Ti2(O2)2O(NC6H6O6)2]·2H2O at low temperature. This single-source precursor was characterized by elemental analysis, IR spectrum, thermal gravimetric analysis and X-ray single crystal diffraction. The calcined products at different temperature were further characterized by powder X-ray diffractions and IR spectra. The morphology, microstructure, and crystallinity of the resulting CaTiO3 materials have been characterized by SEM and TEM. The BET measurement revealed that the CaTiO3 powders had a surface area of 14.0 m2/g. In addition, the microwave dielectric properties of the resulting CaTiO3 material have been measured.

Pure nanocrystallite magnesium titanate (MgTiO3) was conveniently synthesized by thermal decomposition of a cheap and water-soluble heterobimetallic single source precursor [Mg(H2O)5]2[Ti2(O2)2O(NC6H6O6)2]·7H2O at low temperature. This single source precursor was obtained in high yield and in a crystalline form from the quaternary system of MgO–Ti(OC4H9)4–H2O2–H3nta (H3nta = nitrilotriacetic acid) at pH 4.0. It was characterized by elemental analysis, IR spectrum, NMR, thermal gravimetric analysis and X-ray single-crystal diffraction. The morphology, microstructure, and crystallinity of the resulting MgTiO3 materials have been characterized by transmission electron microscopy and X-ray diffraction. The TEM image of the resulting MgTiO3 powders only consists of the nano-scale crystallites with the crystalline size of 30–100 nm.Nanocrystallite magnesium titanate (MgTiO3) was conveniently synthesized by thermal decomposition of a water-soluble and cheap single molecule precursor.

Two pure spinel ZnFe2O4 nanocrystals have been synthesized by hydrothermal approach with/without an organic carboxylic acid-assisted reaction. The effects of synthetic parameters on morphologies, phase-purity and particle sizes of the obtained samples were investigated. The as-prepared samples were characterized by XRD, EDS, UV–vis, FT-IR, XPS, nitrogen adsorption–desorption and TEM. The photocatalytic properties of the obtained ZnFe2O4 samples were investigated to determine their visible-light induced degradation of rhodamine B (RhB). The results show that the as-synthesized ZnFe2O4 nanoplates using succinic acid-assisted hydrothermal approach has good photocatalytic activity, which is probably attributed to the multiple synergetic factors that stem from their low band gap, regular plate morphology, high crystallinity, reasonable pores sizes. The results from current study suggest that the ZnFe2O4 with particle morphology, suitable specific surface areas and high crystallinity will have potentially application for treatment of the organic dyes (RhB) in the polluted water.

It is of great interest to develop new carbon-based materials as electrodes for supercapacitors because the conventional electrodes of activated carbons in supercapacitors cannot meet the ever-increasing demands for high energy and power densities for electronic devices. Due to their high electronic conductivity and improved hydrophilic properties, together with their easy syntheses and functionalization, N-doped carbons have shown a great potential in energy storage and conversion applications. In this review, after a brief introduction of electrochemical capacitors, we summarize the advances, in the recent six years, in the preparation methods of N-doped carbons for applications in supercapacitors. We also discuss and predict futuristic research trends towards the design and syntheses of N-doped carbons with unique properties for electrochemical energy storage.

Porous LiMn2O4 microspheres, which are constructed with nanometer-sized primary particles, have been synthesized by a facile method using porous MnCO3 microspheres as a self-supporting template. The LiMn2O4 microspheres were characterized by XRD, SEM and HR-TEM. The as-synthesized porous LiMn2O4 microspheres exhibit high rate capability and long-term cyclability as cathode materials for lithium ion batteries, with the specific discharge capacity of 119, 107 and 98 mA h g−1 and the corresponding capacity retention of 82, 91 and 80% for up to 500 cycles at 2, 10 and 20 C, respectively. The high rate performance and good cyclability are believed to result from the porous structure, reasonable primary particle size and high crystallinity of the obtained material, which favor fast Li intercalation/deintercalation kinetics by allowing electrolyte insertion through the nanoparticles and high structural stability during the reversible electrochemical process. The high level of Mn4+ concentration on the surface of the sample can alleviate the Jahn–Teller transition, which was triggered normally by the equal amounts of Mn4+/Mn3+ concentration on the surface of the LiMn2O4 cathode material. This good example offering extended cycle life at 20 C rate for the LiMn2O4 microspheres indicates their promising application as cathode materials for high performance LIBs.

The rate performance of LiMnPO4-based materials is further improved via synergistic strategies including a surfactant-assisted solid state method, Fe-substitution and carbon-coating. The surfactant-assisted solid state strategy effectively decreases the primary particle size of the cathode material, which can greatly shorten the diffusion distance of lithium ions. The Fe-substitution improves the effectiveness of Li+ insertion/extraction reactions in the solid phase. The uniform carbon coating layer and the conductive networks provided by the carbon between the nanoparticles ensure the continuous conductivity by the nanoparticles. As a consequence of the synergistic effects, the as prepared LiFe0.5Mn0.5PO4 sample with 6.10 wt% carbon exhibits high specific capacities and superior rate performance with discharge capacities of 155.0, 140.9 and 121 mA h g−1 at 0.1, 1 and 5 C (1 C = 170 mA g−1), respectively. Meanwhile, it shows stable cycling stability at both room temperature (25 °C, 94.8% and 90.8% capacity retention after 500 cycles at 1 and 5 C rates, respectively) and elevated temperature (55 °C, 89.2% capacity retention after 300 cycles at 5 C rate). This material may have great potential application in advanced Li-ion batteries.

Three isostructural heterobimetallic nitrilotriacetatoperoxotitanate complexes of general formula [M(H2O)5]2[Ti2(O2)2O(nta)2]·7H2O [M = Co (1), Ni (2) and Zn (3)] have been isolated in pure crystals directly from the quaternary system of M2+–Ti(OC4H9)4–H2O2–H3nta (H3nta = nitrilotriacetic acid) at pH = 4.0 and have been characterized by elemental analyses, IR, thermal analysis (TGA), and single-crystal X-ray diffraction. Single crystal X-ray analysis reveals that the titanium atom in these complexes features seven-fold-coordination, each surrounded by six oxygen atoms and one nitrogen atom. The divalent transition metal ions in these compounds are hexa coordinated, surrounded by five water molecules and one bridged carboxylato oxygen atom. The TGA and XRD results prove that complexes 1–3 undergo facile thermal decomposition to form pure CoTiO3, NiTiO3 and ZnTiO3 at 700 °C respectively. The morphologies, microstructures, and crystallinity of the residues obtained after pyrolysis were characterized by transmission electron microscopy and powder X-ray diffraction.

A novel composite of sulfur immobilized into porous N-doped carbon microspheres (NCMSs–S) was synthesized. This composite cathode for lithium–sulfur batteries delivers a high specific capacity and superior rate capability and cycle stability, with a reversible capacity of ∼605 mA h g−1 at 2 C and 85% capacity retention after 500 cycles.

Confinement of ultra-small MgTi2O5 nanoparticles in carbon is demonstrated to be an efficient method for fabricating long cycle-life anode material for sodium ion batteries. Superior rate and excellent cyclic capabilities as well as high Coulombic efficiency of the MgTi2O5–C nanocomposite, obtained from pyrolysis of a single molecule precursor, are shown.

Relatively uniform sized graphene-encapsulated sulphur (GES) composites with a core (S)–shell (graphene) structure were synthesized in one pot based on a solution-chemical reaction–deposition method. These novel GES particles were characterized by XRD, Raman spectrometry, SEM, TGA, EDS and TEM. The electrochemical tests showed that the present GES composites exhibit high specific capacity, good discharge capacity retention and superior rate capability when they were employed as cathodes in rechargeable Li–S cells. A high sulphur content (83.3 wt%) was obtained in the GES composites. Stable discharge capacities of about 900, 650, 540 and 480 mA h g−1 were achieved at 0.75, 2.0, 3.0 and 6.0 C, respectively. The good electrochemical performance is attributed to the high electrical conductivity of the graphene, the reasonable particle size of sulphur particles, and the core–shell structures that have synergistic effects on facilitating good transport of electrons from the poorly conducting sulphur, preserving fast transport of lithium ions to the encapsulated sulphur particles, and alleviating the polysulfide shuttle phenomenon. The present finding may provide a significant contribution to the enhancement of cathodes for the lithium–sulphur battery technology.