•Spherical SiOC material was synthesized via a special-tailored synthetic strategy.•The hollow SiO2 nanobelts can prevent the pre-ceramic spheres from sintering.•The material is composed of monodisperse nano/submicron porous SiOC spheres.•The material exhibits high capacity and good cyclability as a Li-storage anode.•The material exhibits much superior Li-storage performance over the pristine SiOC.A spherical silicon oxycarbide (SiOC) material (monodispersed nano/submicron porous SiOC spheres) is successfully synthesized via a specially designed synthetic strategy involving pyrolysis of phenyltriethoxysilane derived pre-ceramic polymer spheres at 900 °C. In order to prevent sintering of the pre-ceramic polymer spheres upon heating, a given amount of hollow porous SiO2 nanobelts which are separately prepared from tetraethyl orthosilicate with CuO nanobelts as templates are introduced into the pre-ceramic polymer spheres before pyrolysis. This material is investigated as an anode for lithium-ion batteries in comparison with the large-size bulk SiOC material synthesized under the similar conditions but without hollow SiO2 nanobelts. The maximum reversible specific capacity of ca. 900 mAh g−1 is delivered at the current density of 100 mA g−1 and ca. 98% of the initial capacity is remained after 100 cycles at 100 mA g−1 for the SiOC spheres material, which are much superior to the bulk SiOC material. The improved lithium storage performance in terms of specific capacity and cyclability is attributed to its particular morphology of monodisperse nano/submicron porous spheres as well as its modified composition and microstructure. This SiOC material has higher Li-storage activity and better stability against volume expansion during repeated lithiation and delithiation cycling.Download high-res image (159KB)Download full-size image

A Co3O4/vapor-grown carbon fiber (VGCF) hybrid material is prepared by a facile approach, namely, via liquid-phase carbonate precipitation followed by thermal decomposition of the precipitate at 380 °C for 2 h in argon gas flow. The material is characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Brunauer-Emmett-Teller specific surface area analysis, and carbon elemental analysis. The Co3O4 in the hybrid material exhibits the morphology of porous submicron secondary particles which are self assembled from enormous cubic-phase crystalline Co3O4 nanograins. The electrochemical performance of the hybrid as a high-capacity conversion-type anode material for lithium-ion batteries is investigated by cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic discharge/charge methods. The hybrid material demonstrates high specific capacity, good rate capability, and good long-term cyclability, which are far superior to those of the pristine Co3O4 material prepared under similar conditions. For example, the reversible charge capacities of the hybrid can reach 1100–1150 mAh g−1 at a lower current density of 0.1 or 0.2 A g−1 and remain 600 mAh g−1 at the high current density of 5 A g−1. After 300 cycles at 0.5 A g−1, a high charge capacity of 850 mAh g−1 is retained. The enhanced electrochemical performance is attributed to the incorporated VGCFs as well as the porous structure and the smaller nanograins of the Co3O4 active material.

A thin composite separator with polyethylene terephthalate nonwoven membrane as the structural support and polyvinylidene fluoride-hexafluoropropylene as the coating layer for lithium-ion batteries was prepared by a simple dip-coating process. The effect of different drying temperatures on the performance of the composite separator was investigated. The results indicate that 80 °C is the optimal drying temperature, preventing leakage current problems and providing a well-developed porous structure. The drying of the composite separator at 80 °C provides a superior thermal stability, better wettability with electrolyte, higher electrolyte uptake, and ionic conductivity compared to commercially available polypropylene (PP) separator. Furthermore, the electrochemical performance consisting of electrochemical stability, self-discharge, cycle performance, rate performance of the composite separator, and PP were determined. The drying of the composite separator at 80 °C shows almost the same oxidation stability and self-discharge performance, but a better cycling and rate performance than the PP separator.

A thin-layer-SnO2 modified LiNi0.5Mn1.5O4@SnO2 material is synthesized via a facile synthetic approach. It is physically and electrochemically characterized as a high-voltage lithium ion battery cathode and compared to the pristine LiNi0.5Mn1.5O4 material prepared under similar conditions. The two materials are proved to be crystals of a well-defined disordered spinel phase with the morphology of aggregates of micron/submicron polyhedral particles. The Mn3+ ions and the inactive NixLiyO phase in the LiNi0.5Mn1.5O4@SnO2 is less than those in the LiNi0.5Mn1.5O4 due to incorporation of a very small amount of Sn2+ into the spinel structure upon high-temperature calcination of the precursor. Besides, the mean particle size of the LiNi0.5Mn1.5O4@SnO2 is obviously smaller than that of the LiNi0.5Mn1.5O4. The LiNi0.5Mn1.5O4@SnO2 demonstrates much superior electrochemical performance over the LiNi0.5Mn1.5O4 in terms of specific capacity, rate capability and cyclability. For example, the discharge capacities at current rates of 0.2C, 2C and 20C are 145.4, 139.9 and 112.2 mA h g−1, respectively. A capacity retention rate of ca. 75% is obtained after 500 cycles at 2C rate. The improved electrochemical performance is attributed to the positive effect of the surface protective SnO2 coating layer as well as the structural and morphological modifications of the spinel.

•A VGCF@ZnMnO3 nanocomposite material is synthesized by hydrothermal reaction.•The composite has the features of coaxial structure and improved electric conduction.•The composite exhibits high performance of Li-storage as a high-capacity anode.•The synthetic method has the advantages of cost saving and environmental benignity.•A dissolution–recrystallization mechanism is proposed for the hydrothermal reaction.Transition metal oxides are considered promising high-capacity anode materials for lithium ion batteries (LIBs). However, their intrinsic low electric conductivity and large volumetric expansion/contraction during lithiation/delithiation can cause fast capacity degradation. Hence, modification of the electrode materials by appropriate structural design is important to their applications. Here, we present study on design, synthesis and Li-storage performance of a vapor grown carbon fiber (VGCF) enhanced VGCF@ZnMnO3 coaxial-cable nanocomposite anode material for LIBs. This material is synthesized via a novel two-step strategy involving a crucial hydrothermal reaction between ZnO and prefabricated VGCF@δ-MnO2 composite in pure water at 180 °C for 12 h. This composite material exhibits high specific capacity, good rate performance and excellent cycling performance. The exhibited high performance should be attributed to the improved electric conductance due to the incorporation of VGCFs and the particular architecture of one-dimensional nanocomposite. Additionally, the hydrothermal reaction mechanism is specially focused and preliminarily studied. A dissolution–recrystallization mechanism is proposed for the hydrothermal reaction.

Separators have garnered substantial attention from researchers and developers in regard to their crucial role in the safety of lithium-ion batteries. In this study, a composite separator was prepared by coating cubic Al2O3 nanoparticles on non-woven poly(ethylene terephthalate) (PET) via a simple dip-coating process. The basic properties of the Al2O3-coated PET non-woven composite separator were characterized by scanning electron microscopy and other specific measurements in respect to its morphology, porosity, electrolyte wettability, and thermal shrinkage as well as its application in lithium-ion batteries. We found that the composite separator has outstanding thermostability, which may improve battery safety. Additionally, by comparison against the commercial Celgard 2500 separator, the proposed composite separator exhibits higher porosity, superior electrolyte wettability, and higher ionic conductivity. More importantly, the lithium-ion battery assembled with this composite separator shows better electrochemical performance (e.g., cycling and discharge C-rate capability) compared to that with the Celgard 2500 separator. The results of this study represent a simple approach to preparing high-performance separators that can be used to enhance the safety of lithium-ion batteries.

A high-performance α-MoO3/multiwalled carbon nanotube (MWCNT) nanocomposite material is synthesized via a novel surfactant-assisted solvothermal process followed by low-temperature calcination. Its structure, composition, and morphology are characterized by X-ray diffraction, X-ray photoelectron spectroscopy, energy-dispersive X-ray spectroscopy, carbon element analysis, nitrogen adsorption–desorption determination, scanning electron microscopy, and transmission electron microscopy techniques. Its electrochemical performance as a high-capacity lithium-ion-battery anode material is investigated by cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic discharge/recharge methods. This composite material exhibits not only high capacity but also excellent rate capability and cyclability. For example, when the discharge/charge current density is increased from 0.1 to 2 A g–1, the reversible charge capacity is only decreased from 1138.3 to 941.4 mAh g–1, giving a capacity retention of 82.7%. Even if it is cycled at a high current density of 20 A g–1, a reversible charge capacity of 490.2 mAh g–1 is still retained, showing a capacity retention of 43.1%. When it is repeatedly cycled at a current of 0.5 A g–1, the initial reversible charge capacity is 1041.1 mAh g–1. A maximum charge capacity of 1392.2 mAh g–1 is achieved at the 292th cycle. After 300 cycles, a high charge capacity of 1350.3 mAh g–1 is maintained. Enhancement of the electrical conduction contributed by the MWCNT composite component as well as the loose and porous texture of the MoO3/MWCNT composite is suggested to be responsible for the excellent performance.Keywords: composite; conversion-type anode; crystalline α-MoO3 nanoparticles; lithium-ion battery; multiwalled carbon nanotubes;

•A novel two-step approach for synthesis of LiMn2O4/multiwalled carbon nanotube (MWCNT) composite Li-ion cathode materials is reported.•The synthetic approach possesses the merits of adjustable Li/Mn ratios for Li-Mn spinel, is time- and cost-saving as well as environmentally benign.•The LiMn2O4/MWCNT composite material has the features of high crystallinity of LiMn2O4 active material and low content of carbon nanotubes.•The LiMn2O4/MWCNT composite material exhibits very high specific capacity and excellent high-rate capability and long-term cyclability.Facile synthesis of highly crystalline spinel-type LiMn2O4/multiwalled carbon nanotube (MWCNT) composite by a novel two-step approach is achieved. This approach involves an acetone-assisted hydrothermal reaction in LiOH solution using previously prepared birnessite MnO2/MWCNT composite as a manganese containing precursor. The lithium manganate spinel Li0.81Mn2O4/MWCNT composite delivers a high specific capacity of 145.4 mAh g−1 at 0.1 C-rate, which is close to the theoretic capacity of LiMn2O4 (148 mAh g−1). Besides, it exhibits excellent high-rate capability and cyclability. For example, a discharge capacity of 114.8 mAh g−1 is retained even at a high charge/discharge current rate of 20C. When it is repeatedly cycled at 1C rate for 1000 cycles, the specific capacity is decreased from the initial value of 140.4 mAh g−1 to an end value of 98.7 mAh g−1, giving 70.3% capacity retention.

In this work, highly conductive vapor grown carbon fiber (VGCF) was applied as an electrically conductive agent for facile synthesis of a nanoparticulate Mn3O4/VGCF composite material. This material exhibits super high specific capacity and excellent rate capability as a conversion-anode for lithium ion batteries. Rate performance test result demonstrates that at the discharge/charge current density of 0.2 A g–1 a reversible capacity of ca. 950 mAh g–1 is delivered, and when the current rate is increased to a high current density of 5 A g–1, a reversible capacity of ca. 390 mAh g–1 is retained. Cyclic performance examination conducted at the current density of 0.5 A g–1 reveals that in the initial 20 cycles the reversible capacity decreases gradually from 855 to 747 mAh g–1. However, since then, it increases gradually with cycle number increasing, and after 200 cycles an extraordinarily high reversible capacity of 1391 mAh g–1 is achieved.Keywords: anode; composite; lithium ion battery; nano-Mn3O4; vapor grown carbon fiber

This paper reports a spinel-type LiMn2O4/carbon nanotube (CNT) composite cathode material with high electrochemical performance for energy storage applications. The composite material is prepared by hydrothermal reaction between birnessite MnO2/multiwalled carbon nanotube (MWCNT) composite and LiOH solution, followed by heat treatment at 700 °C in air atmosphere, where the MnO2/MWCNT precursor is obtained by in situ redox reaction between KMnO4 solution and MWCNTs. The heat treated LiMn2O4/CNT composite material consists of well-crystallized spinel LiMn2O4 with small amount of enwrapped segmented carbon nanotubes, which is confirmed by X-ray diffraction and transmission electron microscopy. Electrochemical experimental results demonstrate that the LiMn2O4/CNT composite material heat treated for 8 h exhibits high specific capacity and excellent high-rate capability in 5 M LiNO3 aqueous electrolyte. The (LiMn2O4/CNT)/5 M LiNO3/activated carbon hybrid supercapacitor with this LiMn2O4-based composite material as the cathode presents excellent high-power capability and good charge/discharge cyclability.Graphical abstractHighlights► LiMn2O4 with a small amount of enwrapped carbon nanotube (CNT) segments is obtained. ► This is the first report on LiMn2O4/CNT composite cathode material with this unique architecture. ► The composite material exhibits excellent high-rate capability in an aqueous electrolyte. ► Post heat treatment markedly improves the electrochemical performance of the composite.

In this paper, LiCrxFexMn2−2xO4 (x = 0, 0.05, 0.1) electrode materials were prepared by sol–gel technique and characterized by X-ray diffraction (XRD) and transmission electron microscopy or high-resolution transmission electron microscopy techniques. XRD results reveal that the Cr–Fe-co-doped LiCrxFexMn2−2xO4 materials are phase-pure spinels. The electrochemical properties of the LiMn2O4, LiCr0.05Fe0.05Mn1.9O4, and LiCr0.1Fe0.1Mn1.8O4 electrodes in 5 M LiNO3 aqueous electrolyte were investigated using cyclic voltammetry, AC impedance, and galvanostatic charge/discharge methods. In the current range of 0.5–2 A g−1, the specific capacity of the LiCr0.05Fe0.05Mn1.9O4 electrode is close to that of the LiMn2O4 electrode, but the specific capacity of the LiCr0.1Fe0.1Mn1.8O4 electrode is obviously lower than that of the LiMn2O4 electrode. When the electrodes are charge/discharge-cycled at the high current rate of 2 A g−1, the LiCr0.05Fe0.05Mn1.9O4 electrode exhibits an initial specific capacity close to that of the LiMn2O4 electrode, but its cycling stability is obviously prior to that of the LiMn2O4 electrode.

Olivine-type pristine LiMnPO4 and nickel-substituted LiNi0.05Mn0.95PO4 electrode materials were synthesized via a sol–gel route, and characterized by X-ray diffraction (XRD), transmission electron microscopy, and X-ray fluorescence analysis techniques. Their electrochemical properties in 2 M Li2SO4 aqueous solution were investigated by cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge/discharge methods. Furthermore, X-ray absorption near edge structure analysis and XRD technique were employed to study the structural change of the pristine LiMnPO4 during the first charge/discharge cycle and the first-stage repeated charge/discharge activation cycles (increase in discharge capacity with increasing cycle number). The LiMnPO4-based electrodes were found to undergo a first-stage activation process with gradual increase in discharge capacity prior to capacity degradation in the experimental condition. Partial nickel substitution for manganese in LiMnPO4 can enhance the charge transfer reaction kinetics, and thereby increase the specific capacity of the LiMnPO4-based electrode.

Spinel-type Cr-doped LiCryMn2 − yO4 (y = 0, 0.1, 0.2) electrode materials were prepared via a sol–gel route starting with lithium acetate, manganese acetate and chromium nitrate as raw materials and citric acid as chelating agent. The phase structure and morphology of the materials were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM) and scanning electron microscope (SEM) techniques. Electrochemical performances of the LiCryMn2 − yO4 electrodes in 5 M LiNO3 aqueous electrolyte were investigated using cyclic voltammetry, ac impedance and galvanostatic charge/discharge methods. Electrochemical results showed that Cr-doping could markedly improve the high-rate charge/discharge cyclability of the LiMn2O4 electrode in 5 M LiNO3 aqueous solution.

To improve the cyclability of spinel LiMn2O4 in aqueous electrolyte, Al-doped LiAlxMn2−xO4 (x = 0.05, 0.1, 0.15) materials are prepared using a room-temperature solid-state grinding reaction followed by calcination at different temperatures for different durations, respectively. Their phase structures and morphologies are characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques. Electrochemical performances of the materials are investigated by cyclic voltammetry and galvanostatic charge/discharge methods. XRD results reveal that the crystallinity of the LiAl0.1Mn1.9O4 increases with increasing calcination temperature and calcination time. However, when the calcination temperature is increased to 800 °C, a small amount of Mn3O4 impurity phase is detected in the product calcined for 12 h, due to the decomposition of LiAl0.1Mn1.9O4, while the product calcined for a shorter time of 3 or 6 h is found to be LiAl0.1Mn1.9O4 single phase. TEM results confirm that the grain size of the materials increases with increasing calcination temperature. Electrochemical experiments demonstrate that the charge/discharge cyclability of the LiAl0.1Mn1.9O4 increases with increase in calcination temperature and calcination time. Compared with the pristine LiMn2O4, the Al-doped LiAlxMn1−xO4 show the obviously improved cyclability, especially for the LiAl0.1Mn1.9O4 calcined at an elevated temperature for 12 h.

A nanostructured spinel LiMn2O4 electrode material was prepared via a room-temperature solid-state grinding reaction route starting with hydrated lithium acetate (LiAc·2H2O), manganese acetate (MnAc2·4H2O) and citric acid (C6H8O7·H2O) raw materials, followed by calcination of the precursor at 500 °C. The material was characterized by X-ray diffraction (XRD) and transmission electron microscope techniques. The electrochemical performance of the LiMn2O4 electrodes in 2 M Li2SO4, 1 M LiNO3, 5 M LiNO3 and 9 M LiNO3 aqueous electrolytes was studied using cyclic voltammetry, ac impedance and galvanostatic charge/discharge methods. The LiMn2O4 electrode in 5 M LiNO3 electrolyte exhibited good electrochemical performance in terms of specific capacity, rate dischargeability and charge/discharge cyclability, as evidenced by the charge/discharge results.

Nanostructured manganese dioxide (MnO2) materials were synthesized via a novel room-temperature solid-reaction route starting with Mn(OAc)2·4H2O and (NH4)2C2O4·H2O raw materials. In brief, the various MnO2 materials were obtained by air-calcination (oxidation decomposition) of the MnC2O4 precursor at different temperatures followed by acid-treatment in 2 M H2SO4 solution. The influence of calcination temperature on the structural characteristics and capacitive properties in 1 M LiOH electrolyte of the MnO2 materials were investigated by X-ray diffraction (XRD), infrared spectrum (IR), transmission electron microscope (TEM) and Brunauer–Emmett–Teller (BET) surface area analysis, cyclic voltammetry, ac impedance and galvanostatic charge/discharge electrochemical methods. Experimental results showed that calcination temperature has a significant influence on the textural and capacitive characteristics of the products. The MnO2 material obtained at the calcination temperature of 300 °C followed by acid-treatment belongs to nano-scale column-like (or needle-like) γ,α-type MnO2 mischcrystals. While, the MnO2 materials obtained at the calcination temperatures of 400, 500, and 600 °C followed by acid-treatment, respectively, belong to γ-type MnO2 with the morphology of aggregates of crystallites. The γ,α-MnO2 derived from calcination temperature of 300 °C exhibited a initial specific capacitance lower than that of the γ-MnO2 derived from the elevated temperatures, but presented a better high-rate charge/discharge cyclability.

Nanostructured MnO2/carbon nanotubes composite electrode material was prepared using the liquid-phase deposition reaction starting with potassium permanganate (KMnO4) and manganese acetate (Mn(Ac)2·4H2O) as the reactants and carbon nanotubes (CNTs) as the substrates. The structure and morphology of the material was characterized by X-ray diffraction, infrared spectroscopy, and transmission electron microscope techniques. The electrochemical properties of the nano-MnO2/CNTs composite electrode in 1 M LiAc and 1 M MgSO4 solutions and in 1 M RAc (R = Li, Na, and K)–1 M MgSO4 mixed solutions, respectively, were studied. Experimental results demonstrated that the specific capacitance and rate discharge ability of the nano-MnO2/CNTs composite electrode in 1 M LiAc–1 M MgSO4 mixed solution is superior to that in 1 M LiAc or 1 M MgSO4 solution. For the 1 M RAc (R = Li, Na, and K)–1 M MgSO4 mixed electrolytes, the specific capacitance of the composite electrode was found to be in the following order: LiAc > NaAc > KAc.

In the present work, a nanostructured manganese dioxide material was synthesized by a sol–gel method starting with manganese acetate (MnAc2·4H2O) and citric acid (C6H8O7·H2O) raw materials, and characterized by X-ray diffraction, infrared spectroscopic and transmission electron microscope techniques. The electrochemical properties and the influence of temperature on supercapacitive behaviors of the nano-MnO2 electrode in 1 M LiOH electrolyte were investigated using electrochemical methods. Experimental results show that the MnO2 electrode can exhibit an excellent pseudocapacitive behavior in 1 M LiOH electrolyte, and a high specific capacitance of 317 F g−1 can be obtained at a charge/discharge current rate of 100 mA g−1 and at the temperature of 25 °C. We found that temperature has a crucial influence on the discharge specific capacitance of the electrode. The specific capacitance at 25 °C is higher than that at 15 or 35 °C.

Polyvinyl alcohol (PVA)-sodium polyacrylate (PAAS)-KOH-H2O alkaline polymer electrolyte film withhigh ionic conductivity was prepared by a solution-casting method. Polymer Ni(OH)2/activated carbon (AC) hybridsupercapacitors with different electrode active material mass ratios (positive to negative) were fabricated using this alkaline polymer electrolyte, nickel hydroxide positive electrodes, and AC negative electrodes. Galvanostatic charge/discharge and electrochemical impedance spectroscopy (EIS) methods were used to study the electrochemical performance of the capacitors, such as charge/discharge specific capacitance, rate charge/discharge ability, and charge/discharge cyclic stability. Experimental results showed that with the decreasing of active material mass ratio m(Ni(OH)2)/m(AC), the charge/discharge specific capacitance increases, but the rate charge/discharge ability andthe charge/discharge cyclic stability decrease.

A thin-layer-SnO2 modified LiNi0.5Mn1.5O4@SnO2 material is synthesized via a facile synthetic approach. It is physically and electrochemically characterized as a high-voltage lithium ion battery cathode and compared to the pristine LiNi0.5Mn1.5O4 material prepared under similar conditions. The two materials are proved to be crystals of a well-defined disordered spinel phase with the morphology of aggregates of micron/submicron polyhedral particles. The Mn3+ ions and the inactive NixLiyO phase in the LiNi0.5Mn1.5O4@SnO2 is less than those in the LiNi0.5Mn1.5O4 due to incorporation of a very small amount of Sn2+ into the spinel structure upon high-temperature calcination of the precursor. Besides, the mean particle size of the LiNi0.5Mn1.5O4@SnO2 is obviously smaller than that of the LiNi0.5Mn1.5O4. The LiNi0.5Mn1.5O4@SnO2 demonstrates much superior electrochemical performance over the LiNi0.5Mn1.5O4 in terms of specific capacity, rate capability and cyclability. For example, the discharge capacities at current rates of 0.2C, 2C and 20C are 145.4, 139.9 and 112.2 mA h g−1, respectively. A capacity retention rate of ca. 75% is obtained after 500 cycles at 2C rate. The improved electrochemical performance is attributed to the positive effect of the surface protective SnO2 coating layer as well as the structural and morphological modifications of the spinel.