Preparation and electrochemical properties of V<Subscript>2</Subscript>O<Subscript>5</Subscript> submicron-belts synthesized by a sol–gel H<Subscript>2</Subscript>O<Subscript>2</Subscript> route

One-dimensional (1D) submicron-belts of V₂O₅ have been prepared by a sol–gel route using V₂O_5, H₂O₂ and aniline as starting materials. Thermogravimetric and differential thermal analysis, X-ray diffraction, Fourier transform infrared spectroscopy and scanning electron microscopy were employed to characterize the samples. Electrochemical behaviors as cathode material in rechargeable lithium-ion batteries were investigated by galvanostatic charge–discharge measurement and cyclic voltammeter. The results showed that the synthesized V₂O₅ appeared to be submicron-belts and orthorhombic structure. The V₂O₅ submicron-belts exhibited a high initial discharge capacity of 346 mAh/g and stayed 240 mAh/g after 20 cycles at 0.1 C discharge rate in the potential region 1.8–4.0 V.     

Structural and electrochemical characterization of LiFePO4/C prepared by a sol–gel route with long- and short-chain carbon sources

A fast and convenient sol–gel route was developed to synthesize LiFePO₄/C composite cathode material, and the sol–gel process can be finished in less than an hour. Polyethyleneglycol (PEG), d-fructose, 1-hexadecanol, and cinnamic acid were firstly introduced to non-aqueous sol–gel system as structure modifiers and carbon sources. The samples were characterized by X-ray powder diffraction, field emission scanning electron microscopy, and elemental analysis measurements. Electrochemical performances of LiFePO₄/C composite cathode materials were characterized by galvanostatic charge/discharge and AC impedance measurements. The material obtained using compound additives of PEG and d-fructose presented good electrochemical performance with a specific capacity of 157.7 mAh g⁻¹ at discharge rate 0.2 C, and the discharge capacity remained about 153.6 mAh g⁻¹ after 50 cycles. The results indicated that the improved electrochemical performance originated mainly from the microporous network structure, well crystalline particles, and the increased electronic conductivity by proper carbon coating (3.11%).     

In situ chemical synthesis of SnO2–graphene nanocomposite as anode materials for lithium-ion batteries

An in situ chemical synthesis approach has been developed to prepare SnO₂–graphene nanocomposite. Field emission scanning electron microscopy and transmission electron microscopy observation revealed the homogeneous distribution of SnO₂ nanoparticles (4–6 nm in size) on graphene matrix. The electrochemical reactivities of the SnO₂–graphene nanocomposite as anode material were measured by cyclic voltammetry and galvanostatic charge/discharge cycling. The as-synthesized SnO₂–graphene nanocomposite exhibited a reversible lithium storage capacity of 765 mAh/g in the first cycle and an enhanced cyclability, which can be ascribed to 3D architecture of the SnO₂–graphene nanocomposite.     

Preparation and performance characterization of polymer Li-ion batteries using gel poly(diacrylate) electrolyte prepared by in situ thermal polymerization

A gel polymer electrolyte (GPE) was prepared by in-situ thermal polymerization of 1,3-butanediol diacrylate (BDDA) in a EC/EMC/DMC electrolyte solution at 100 °C. The GPE with 15 wt.% polymer content appears as apparently dry polymer with sufficient mechanical strength and shows a high ionic conductivity of 3.2×10^–3 S cm^–1 at 20 °C. The MCMB–LiCoO₂ type polymer Li-ion batteries (PLIB) prepared using this in-situ internal polymerization method exhibit a very high initial charge–discharge efficiency of 92.1%, and can deliver 94.4% of its nominal capacity at 1.0 C rate and 70.7% of its room temperature capacity at –20 °C. Also, the PLIB cells show very good cycling ability with >85% capacity retention after 300 cycles. The excellent charge–discharge properties of the PLIB cells are attributed to the integrated structure in which the polymer matrix spreads over entire region of the cell acting as a strong binder and electrolyte carrier to produce a stabilized electrode–electrolyte interface. In addition, the fabricating process of the polymer cell is quite simple and convenient for practical applications.     

Facile preparation and electrochemical properties of large-scale Li<Subscript>1+<Emphasis Type="Italic">x</Emphasis></Subscript>V<Subscript>3</Subscript>O<Subscript>8</Subscript> nanobelts

Large-scale Li_1+x V₃O₈ nanobelts were successfully fabricated using filter paper as deposition substrate through a simple surface sol–gel method. The nanobelts were as long as tens of micrometers with widths of 0.4–1.0 μm and thickness of 50–100 nm. The nanobelts were characterized by X-ray diffration (XRD), Fourier infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM). The formation mechanism of the nanobelts was investigated, showing that the morphology of the nanobelts is mainly determined by the calcination temperature. Electrochemical properties of the Li_1+x V₃O₈ nanobelts were characterized by charge–discharge experiments, and the results demonstrate that the Li_1+x V₃O₈ nanobelts exhibit a high discharge capacity (278 mAh g⁻¹) and excellent cycling stability.     

Synthesis and characterization of core–shell F-doped LiFePO<Subscript>4</Subscript>/C composite for lithium-ion batteries

Core–shell LiFePO₄/C composite was synthesized via a sol–gel method and doped by fluorine to improve its electrochemical performance. Structural characterization shows that F⁻ ions were successfully introduced into the LiFePO₄ matrix. Transmission electron microscopy verifies that F-doped LiFePO₄/C composite was composed of nanosized particles with a ~3 nm thick carbon shell coating on the surface. As a cathode material for lithium-ion batteries, the F-doped LiFePO₄/C nanocomposite delivers a discharge capacity of 162 mAh/g at 0.1 C rate. Moreover, the material also shows good high-rate capability, with discharge capacities reaching 113 and 78 mAh/g at 10 and 40 C current rates, respectively. When cycled at 20 C, the cell retains 86% of its initial discharge capacity after 400 cycles, demonstrating excellent high-rate cycling performance.     

High-rate cathode based on Li3V2(PO4)3/C composite material prepared via a glycine-assisted sol–gel method

Carbon-coated monoclinic Li₃V₂(PO₄)₃ (LVP/C) cathode material has been successfully prepared by a novel glycine-assisted sol–gel method. The product is investigated by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM) and electrochemical method. In the range of 3.0–4.3 V, the LVP/C electrode presents excellent rate capability. It is 125.4 mAh g^{− 1} that can be delivered at 1 C charge–discharge rate and 99.5 mAh g^{− 1} is still obtained at 20 C charge–discharge rate. These results demonstrate that the carbon-coated LVP/C composite material prepared via a glycine-assisted sol–gel method has great potential for use in high-power lithium ion batteries.     

Comparison of different soft chemical routes synthesis of submicro-LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> and their influence on its electrochemical properties

A comparative study of submicro-crystalline spinel LiMn₂O₄ powders prepared by two different soft chemical routes such as hydrothermal and sol–gel methods is made. The dependence of the physicochemical properties of the spinel LiMn₂O₄ powder has been extensively investigated by using X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscope, cyclic voltammogram, charge–discharge test, and electrochemical impedance spectroscopy (EIS). The results show that the electrochemical performances of spinel LiMn₂O₄ depend strongly upon the synthesis method. The LiMn₂O₄ powder prepared by hydrothermal route has higher specific capacity and better cycling performance than the one synthesized from sol–gel method. The former has the max discharge capacity of 114.36 and 99.78 mAh g⁻¹ at the 100th cycle, while the latter has the max discharge capacity of 98.67 and 60.25 mAh g⁻¹ at the 100th cycle. The selected equivalent circuit can fit well the EIS results of synthesized LiMn₂O₄. For spinel LiMn₂O₄ from sol–gel method and hydrothermal route in the first charge process R _SEI remain almost invariable, R _e and R _ct first decreasing and then increasing with the increase of polarization potential.     

Preparation and electrochemical study of a new magnesium intercalation material Mg1.03Mn0.97SiO4

Orthorhombic magnesium manganese silicate (Mg_1.03Mn_0.97SiO₄) was prepared and evaluated as a new cathode material for rechargeable magnesium batteries. Although the electrochemical activity of the Mg_1.03Mn_0.97SiO₄ synthesized by high-temperature solid-state reaction is low, the magnesium storage capacity of nanosized Mg_1.03Mn_0.97SiO₄ prepared by modified sol–gel route and in situ carbon coating reaches 244 mAh g⁻¹. The capacity increase mechanism during charge/discharge cycling was also preliminary studied.     

Synthesis of LiFePO4 material with improved cycling performance under harsh conditions

LiFePO₄ material was synthesized at 670 °C in an Ar atmosphere using a sol–gel method. This material showed a well developed XRD pattern (orthorhombic structure, Pnma) without any peaks at 2θ = 41°, indicating the absence of FeP or metallic Fe₂P impurities. The Li/LiFePO₄ cell showed a high initial discharge capacity of more than 150 mA h/g and no capacity decrease until the 70th cycle (>99.9%). This cell also exhibits excellent cycle performance at high current densities of over 30C, without any surface treatment or carbon coating onto the LiFePO₄ particles.     

Comparison of structure and electrochemical properties for 5 V LiNi0.5Mn1.5O4 and LiNi0.4Cr0.2Mn1.4O4 cathode materials

Spinel LiNi_0.5Mn_1.5O₄ and LiMn_1.4Cr_0.2Ni_0.4O₄ cathode materials have been successfully synthesized by the sol–gel method using citric acid as a chelating agent. The structure and electrochemical performance of these as-prepared powders have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and the galvanostatic charge–discharge test in detail. XRD results show that there is a small Li _y Ni_1-y O impurity peak placed close to the (4 0 0) line of the spinel LiNi_0.5Mn_1.5O₄, and LiMn_1.4Cr_0.2Ni_0.4O₄ has high phase purity, and the powders are well crystallized. SEM indicates that LiMn_1.4Cr_0.2Ni_0.4O₄ has a slightly smaller particle size and a more regular morphological structure with narrow size distribution than those of LiNi_0.5Mn_1.5O₄. Galvanostatic charge–discharge testing indicates that the initial discharge capacities of LiMn_1.4Cr_0.2Ni_0.4O₄ and LiNi_0.5Mn_1.5O₄ cycled at 0.15 C are 129.6 and 130.2 mAh g⁻¹, respectively, and the capacity losses compared to the initial value, after 50 cycles, are 2.09% and 5.68%, respectively. LiMn_1.4Cr_0.2Ni_0.4O₄ cathode has a higher electrode coulombic efficiency than that of the LiNi_0.5Mn_1.5O₄ cathode, implying that Ni and Cr dual substitution is beneficial to the reversible intercalation and de-intercalation of Li⁺.     

Improvement of high-voltage cycling behavior of Li(Ni1/3Co1/3Mn1/3)O2 cathodes by Mg, Cr, and Al substitution

To improve the electrochemical properties of Li[Ni_1/3Co_1/3Mn_1/3]O₂ at high charge end voltage (4.6 V), a series of the mixed transition metal compounds, Li(Ni_1/3Co_{1/3 − x} Mn_1/3M _x )O₂ (M = Mg, Cr, Al; x = 0.05), were synthesized via hydroxide coprecipitation method. The effects of doping Mg, Cr, and Al on the structure and the electrochemical performances of Li[Ni_1/3Co_1/3Mn_1/3]O₂ were compared by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), galvanostatic charge–discharge tests, and electrochemical impedance spectroscopy. The XRD results show that all the samples keep layered structures with R3m space group as the Li[Ni_1/3Co_1/3Mn_1/3]O₂. SEM images show that all the compounds have spherical shapes and the Cr-doped sample has the largest particle size. Furthermore, galvanostatic charge–discharge tests confirm that the Cr-doped electrode shows improved cycling performance than the undoped material. The capacity retention of Li(Ni_1/3Co_{1/3 − 0.05}Mn_1/3Cr_0.05)O₂ is 97% during 50 cycles at 2.8∼4.6 V. The improved cycling performance at high voltage can be attributed to the larger particle size and the prevention of charge transfer resistance (R _ct) increase during cycling.     

LiMn2O4 nanorods as a super-fast cathode material for aqueous rechargeable lithium batteries

LiMn₂O₄ nanorods were prepared by a facile hydrothermal method in combination with traditional solid-state reactions and characterized by X-ray diffraction analysis. Their electrochemical behavior was tested by cyclic voltammetry and repeated charge/discharge cycling. Results show that the reversible intercalation/deintercalation of Li-ions into/from LiMn₂O₄ cathode can yield up to 110 mAh/g at 4.5 C, and still retains 88% at the very large charge rate of 90 C with well-defined charge and discharge plateaus. It presents very high power density, up to 14.5 kW/kg, and very excellent cycling behavior, 94% capacity retention after 1200 cycles. It is thus a competitor for LiFePO₄.     

Synthesis and electrochemical properties of graphene-SnS2 nanocomposites for lithium-ion batteries

Graphene-SnS₂ nanocomposites were prepared via a solvothermal method with different loading of SnS₂. The nanostructure and morphology of the samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The XRD patterns revealed that hexagonal SnS₂ was obtained. SEM and TEM results indicated that SnS₂ particles distributed homogeneously on graphene sheets. The electrochemical properties of the samples as active anode materials for lithium-ion batteries were examined by constant current charge–discharge cycling. The composite with weight ratio between graphene and SnS₂ of 1:4 had the highest rate capability among all the samples and its reversible capacity after 50 cycles was 351 mAh/g, which was much higher than that of the pure SnS₂ (23 mAh/g). With graphene as conductive matrix, homogeneous distribution of SnS₂ nanoparticles can be ensured and volume changes of the nanoparticles during the charge and discharge processes can be accomodated effectively, which results in good electrochemical performance of the composites.     

球磨辅助高温固相法制备Li1.0Na0.2Ni0.13Co0.13Mn0.54O2正极材料及其性能

以乙酸盐(乙酸锂、乙酸钠、乙酸钴、乙酸镍、乙酸锰等)为原材料,采用球磨辅助高温固相法制备Li_(1.0)Na_(0.2)Ni_(0.13)Co_(0.13)Mn_(0.54)O_2正极材料。借助XRD、SEM等表征材料的结构和形貌,利用循环伏安、恒流充放电、交流阻抗等方法研究材料的电化学性能。结果表明,钠的掺杂导致颗粒表面光滑度降低,形成Na_(0.77)Mn O_(2.05)新相。0.05C活化过程中,掺钠样品和未掺钠样品首次放电比容量分别为258.4 m Ah·g~(-1)和215.8 m Ah·g~(-1),库伦效率分别为75.2%和72.8%;2C放电比容量分别为116.3 m Ah·g~(-1)和106.2 m Ah·g~(-1)。研究发现,掺钠可减小首次充放电过程的不可逆容量,提高容量保持率;改善倍率性能与容量恢复特性;降低SEI膜阻抗和电荷转移阻抗;掺钠后样品首次循环就可以基本完成Li_2Mn O_3组分向稳定结构的转化,而未掺杂的样品需要两次循环才能逐步完成该过程;XPS结果表明,掺钠样品中Ni~(2+)、Co~(3+)、Mn~(4+)所占比例明显提高,改善了样品的稳定性和电化学性能;循环200次后的XRD结果表明掺钠与未掺钠材料在脱嵌锂反应中的相变化过程基本一致,良好有序的层状结构遭到破坏是循环过程中容量衰减的主要原因。     

Carbon-Coated SiO2 Composites as Promising Anode Material for Li-Ion Batteries

Porous silica-based materials are a promising alternative to graphite anodes for Li-ion batteries due to their high theoretical capacity, low discharge potential similar to pure silicon, superior cycling stability compared to silicon, abundance, and environmental friendliness. However, several challenges prevent the practical application of silica anodes, such as low coulombic efficiency and irreversible capacity losses during cycling. The main strategy to tackle the challenges of silica as an anode material has been developed to prepare carbon-coated SiO₂ composites by carbonization in argon atmosphere. A facile and eco-friendly method of preparing carbon-coated SiO₂ composites using sucrose is reported herein. The carbon-coated SiO₂ composites were characterized using X-ray diffraction, X-ray photoelectron spectroscopy, thermogravimetry, transmission and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy, cyclic voltammetry, and charge–discharge cycling. A C/SiO₂-0.085 M calendered electrode displays the best cycling stability, capacity of 714.3 mAh·g⁻¹, and coulombic efficiency as well as the lowest charge transfer resistance over 200 cycles without electrode degradation. The electrochemical performance improvement could be attributed to the positive effect of the carbon thin layer that can effectively diminish interfacial impedance.     

Synthesis and characterization of submicron size particles of LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> by microemulsion route

Among the various positive electrode materials investigated for Li-ion batteries, spinel LiMn₂O₄ is one of the most important materials. Small particles of the active materials facilitate high-rate capability due to large surface to mass ratio and small diffusion path length. The present work involves the synthesis of submicron size particles of LiMn₂O₄ in a quaternary microemulsion medium. The precursor obtained from the reaction is heated at different temperatures in the range from 400 to 900 °C. The samples heated at 800 and 900 °C are found to possess pure spinel phase with particle size <200 nm, as evidenced from XRD, SEM, and TEM studies. The electrochemical characterization studies provide discharge capacity values of about 100 mAh g⁻¹ at C/5 rate, and there is a moderate decrease in capacity by increasing the rate of charge–discharge cycling. Studies also include charge–discharge cycling and ac impedance studies in temperature range from −10 to 40 °C. Impedance data are analyzed with the help of an equivalent circuit and a nonlinear least squares fitting program. From temperature dependence of charge-transfer resistance, a value of 0.62 eV is obtained for the activation energy of Mn³⁺/Mn⁴⁺ redox process, which accompanies the intercalation/deintercalation of the Li⁺ ion in LiMn₂O₄.     

Lithium electrochemistry of NiSe2: A new kind of storage energy material

NiSe₂ thin film has been successfully fabricated by reactive pulsed laser deposition and was investigated for its electrochemistry with lithium for the first time. The reversible discharge capacities of NiSe₂/Li cells cycled between 1.0 V and 3.0 V were found in the range of 314.9–467.5 mA h g⁻¹ during the first 200 cycles. By using ex situ X-ray diffraction, transmission electron microscopy, and selected-area electron diffraction measurements, the intermediates of β-NiSe, and Ni₃Se₂ were identified during the reversible conversions of NiSe₂ into metal nickel and Li₂Se. Both cation (nickel) and anion (selenium) in NiSe₂ provide the redox active centers in its electrochemical reaction with lithium, indicating one of the features of its lithium electrochemistry. The high reversible capacity and good cycle ability of NiSe₂ electrode made it become a promising cathode material for future rechargeable lithium batteries.     

Hybrid Structures of Sisal Fiber Derived Interconnected Carbon Nanosheets/MoS2/Polyaniline as Advanced Electrode Materials in Lithium-Ion Batteries

In this work, we designed and successfully synthesized an interconnected carbon nanosheet/MoS₂/polyaniline hybrid (ICN/MoS₂/PANI) by combining the hydrothermal method and in situ chemical oxidative polymerization. The as-synthesized ICNs/MoS₂/PANI hybrid showed a “caramel treat-like” architecture in which the sisal fiber derived ICNs were used as hosts to grow “follower-like” MoS₂ nanostructures, and the PANI film was controllably grown on the surface of ICNs and MoS₂. As a LIBs anode material, the ICN/MoS₂/PANI electrode possesses excellent cycling performance, superior rate capability, and high reversible capacity. The reversible capacity retains 583 mA h/g after 400 cycles at a high current density of 2 A/g. The standout electrochemical performance of the ICN/MoS₂/PANI electrode can be attributed to the synergistic effects of ICNs, MoS₂ nanostructures, and PANI. The ICN framework can buffer the volume change of MoS₂, facilitate electron transfer, and supply more lithium inset sites. The MoS₂ nanostructures provide superior rate capability and reversible capacity, and the PANI coating can further buffer the volume change and facilitate electron transfer.     

Electropolymerization of ionic liquid substituted polyphenylene as supercapacitors materials

A new type of polyphenylene, ionic liquid (IL) 1,3-methylimidazolium hexafluorophosphate substituted, has been prepared by electrodeposition on Au electrode surface via pulse galvanostatic method in 1-butyl-3-methylimidazolium hexafluorophosphate solution. The obtained polymer film had a spherulitic morphology with smallest grains of around 500 nm. Infrared spectrometry revealed that polyphenylene was deposited to a certain extent. The capacitive behavior of the IL substituted polyphenylene was investigated by cyclic voltammetry (CV) and galvanostatic charge–discharge method in 0.2 mol L⁻¹ H₂SO₄ aqueous solutions or pure IL [bmim]PF₆. The specific capacitance of the polymer at the charge–discharge current density of 1 mA cm⁻² equaled 206 F g⁻¹ in acidic aqueous solution or 164 F g⁻¹ in [bmim]PF₆. Additionally, excellent charge–discharge cycle stability (over 85% value of specific capacitance remained after 600 charge–discharge cycles) and power characteristics of the polymer electrode were observed in both electrolytes.