Genesis,structural, and transport properties of La<Subscript>2</Subscript>Mo<Subscript>2-x</Subscript>W<Subscript>x</Subscript>O<Subscript>9</Subscript> prepared via mechanochemical activation

Fast oxide-ion conductors La₂Mo_2-xW_xO₉ (x = 0–1) have been prepared using mechanochemical activation (MA) of starting oxides in a high-power planetary ball mill. Studies of La₂Mo_2-xW_xO₉ genesis and structural properties using thermal analysis, XRD, SEM, IR, and Raman spectroscopy have revealed that MA results in the formation of an amorphous precursor, while the cubic β-phase is formed after calcination at 700–900 °C. Due to a high dispersion of powders, high-density pellets of W-LAMOX ceramics have been obtained already after sintering at 950 °C. Their electrical conductivity measured by the impedance spectroscopy depends on the W concentration being sufficiently high (up to 5.6?10^?3 S/cm at 630 °C) at temperatures below 650 °C.     

Highly enhanced low-temperature performances of LiFePO<Subscript>4</Subscript>/C cathode materials prepared by polyol route for lithium-ion batteries

Although LiFePO₄/C has been successfully put into practical use in lithium-ion batteries equipped on new energy vehicles, its unsatisfactory low temperature results in poor low performance of lithium-ion batteries, leading to a much smaller continue voyage course at extreme environments with low temperature for electric vehicles. In this paper, the electrochemical performance of the LiFePO₄/C prepared by polyol route was investigated at a temperature range from 25 to ?20 °C. Compared to commercial ones, as-prepared LiFePO₄/C shows a much better low-temperature performance with a reversible capacity of 30 mA h g^?1 even at 5 C under ?20 °C and a capacity retention of 91.1 % after 100 cycles at 0.1 C under 0 °C. Moreover, high-resolution transmission electron microscopy (HRTEM) revealed that this outstanding performance at low temperatures could be assigned to uniform carbon coating and the nano-sized particles with a highly crystalline structure.     

Propylene oxide-assisted fast sol–gel synthesis of mesoporous and nano-structured LiFePO4/C cathode materials

LiFePO₄/C nanocomposites are synthesized by a propylene oxide-assisted fast sol–gel method using FeCl₃, LiNO₃, NH₄H₂PO₄, and sucrose as the starting materials. It was found that after adding propylene oxide into the solution containing the starting materials, a monolithic jelly-like FePO₄ gel containing lithium and carbon source is generated in a few minutes without controlling the pH value of the solution and a time-consuming heating process. Propylene oxide plays a key role in the fast generation of the precursor gel. The final products of LiFePO₄/C are obtained by sintering the dry precursor gel. The structures, micro-morphologies, and electrochemical properties of the LiFePO₄/C composites are investigated using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, nitrogen adsorption–desorption analysis, electrochemical impedance spectrum, and charge–discharge cycling tests. The results indicate that the LiFePO₄/C composite prepared by sintering the precursor gel at 680 °C for 5 h is about 30 nm in size with a meso-porous structure (the main pore size distribution is around 3.4 nm). It delivers 166.7 and 105.8 mAh g^?1 at 0.2 and 30 C, respectively. The discharge specific capacity is 97.8 mAh g^?1 even at 40 C. The cycling performance of the prepared LiFePO₄/C composite is stable. The excellent electrochemical performance of the LiFePO₄/C composite is attributed to the nano-sized and mesoporous structure of LiFePO₄/C and the in-situ surface coating of the carbon. It was also found that propylene oxide is crucial for the generation of mesoporous and nano-structured LiFePO₄/C.     

KOH activated carbon fabrics as supercapacitor material

Carbon fabrics from viscose fibers activated with KOH have been investigated as possible electrode materials for electrochemical capacitors. The fibers were first pyrolysed at 400 or 600 °C, then saturated with KOH at C/KOH ratios from 1:3.5 to 1:5 and treated in the temperature range from 700 to 800 °C. The carbon fibers saturated with KOH were analysed by thermogravimetric and differential thermal analysis in order to get information on the temperature dependence of the KOH reaction with carbon. The electrochemical properties of the activated carbons were determined using three-electrode Swagelok^® type capacitors both in 4 M H₂SO₄ and 7 M KOH aqueous electrolytes. Specific capacities of ca. 340 and 270 F/g were determined in acidic and alkaline medium, respectively. We demonstrate that the electrical capacity for both negative and positive electrodes depends on the treatment method. The capacitance values are discussed taking into account the porous texture, the elemental composition and the surface functionality of the activated carbon fibers.     

Activated carbon aerogel as electrode material for coin-type EDLC cell in organic electrolyte

Carbon aerogel (CA) was prepared by a carbonization of resorcinol–formaldehyde (RF) polymer gels, and it was chemically activated with KOH to obtain activated carbon aerogel (ACA) for electrode material for EDLC in organic electrolyte. Coin-type EDLC cells with two symmetrical carbon electrode were assembled using the prepared carbon materials. Electrochemical performance of the carbon electrodes was measured by galvanostatic charge/discharge and cyclic voltammetry methods. Activated carbon aerogel (20.9 F/g) showed much higher specific capacitance than carbon aerogel (7.9 F/g) and commercial activated carbon (8.5 F/g) at a scan rate of 100 mV/s. This indicates that chemical activation with KOH served as an efficient method to improve electrochemical performance of carbon aerogel for EDLC electrode in organic electrolyte. The enhanced electrochemical performance of activated carbon aerogel was attributed to the high effective surface area and the well-developed pore structure with appropriate pore size obtained from activation with KOH.     

Physical,electrochemical and supercapacitive properties of activated carbon pellets from pre-carbonized rubber wood sawdust by CO2 activation

The physical and electrochemical properties of the activated carbon pellet electrodes have been investigated. Activated carbon pellets were prepared from single step carbonization process of pre-carbonized rubber wood sawdust at a temperature of 800 °C that followed with a CO₂ activation process at temperature in the range of 700–1000 °C. The BET characterization on the sample found that the surface area of the carbon pellet increased with the increasing of the activation temperature. The optimum value was as high as 683.63 m² g⁻¹. The electrical conductivity was also found to increase linearly with the increasing of the activation temperature, namely from 0.0075 S cm⁻¹ to 0.0687 S cm⁻¹ for the activation temperature in the range of 700–1000 °C. The cyclic voltammetry characterization of the samples in aqueous solution of 1 M H₂SO₄ also found that the specific capacitance increased with the increasing of the activation temperature. Typical optimum value was shown by the sample activated at 900 °C with the specific capacitance was as high as 33.74 F g⁻¹ (scan rate 1 mV s⁻¹). The retained ratio was as high as 32.72%. The activated carbon pellet prepared from the rubber wood sawdust may found used in supercapacitor applications.     

Influence of co-precipitation temperature on microstructure and electrochemical properties of Li[Li<Subscript>0.2</Subscript>Mn<Subscript>0.54</Subscript>Ni<Subscript>0.13</Subscript>Co<Subscript>0.13</Subscript>]O<Subscript>2</Subscript> cathode materials for lithium ion batteries

The layered Li-rich Mn-based cathode materials Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂ were prepared by using co-precipitation technique at different temperatures, and their crystal microstructure and particle morphology were observed and analyzed by XRD and SEM. The electrochemical properties of these samples were investigated by using charge-discharge tests, electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV), respectively. The results indicated that all samples are of high purity. When the precursors were co-precipitated at 50 °C, their cathode materials have the most uniform and full particles and exhibit the highest initial discharge capacity (289.4 mAh/g at 0.1C), the best cycle stability (capacity retention rate of 91.2 % after 100 cycles at 0.5C), and the best rate performance. The EIS results show that the lower charge transfer resistance of 50 °C sample is responsible for its superior discharge capacity and rate performance.     

Microstructural and electrochemical properties of rf-sputtered LiFePO4 thin films

LiFePO₄ has been synthesized by hydrothermal synthesis. A 2-in. sputtering target has been prepared using synthesized powder and employed for the deposition of LiFePO₄ films by radio frequency magnetron sputtering. Microstructural properties have been studied by using X-ray diffraction, Raman spectroscopy, and atomic force microscope. The films deposited at 350 °C with subsequent annealing at 600 °C for 4 h exhibited well-crystallized peaks along with (101) predominant orientation which corresponds to orthorhombic olivine-type structure with Pnma space group. The electrochemical properties have been studied for films in aqueous as well as in non-aqueous media. Both the electrochemical cells at same current density of 20 μA/cm² delivered the same initial discharge capacity around 38 μAh/cm² μm. The Li//LiFePO₄ cell exhibited good cycling stability for the first 20 cycles.     

Low-temperature sintering effects on NASICON-structured LiSn<Subscript>2</Subscript>P<Subscript>3</Subscript>O<Subscript>12</Subscript> solid electrolytes prepared via citric acid-assisted sol-gel method

LiSn₂P₃O₁₂ with sodium (Na) super ionic conductor (NASICON)-type rhombohedral structure was successfully obtained at low sintering temperature, 600 °C via citric acid-assisted sol-gel method. However, when the sintering temperature increased to 650 °C, triclinic structure coexisted with the rhombohedral structure as confirmed by X-ray diffraction analysis. Conductivity–temperature dependence of all samples were studied using impedance spectroscopy in the temperature range 30 to 500 °C, and bulk, grain boundary and total conductivity increased as the temperature increased. The highest bulk conductivity found was 3.64?×?10^?5 S/cm at 500 °C for LiSn₂P₃O₁₂ sample sintered at 650 °C, and the lowest bulk activation energy at low temperature was 0.008 eV, showing that sintering temperature affect the conductivity value. The voltage stability window for LiSn₂P₃O₁₂ sample sintered at 600 °C at ambient temperature was up to 4.4 V. These results indicated the suitability of the LiSn₂P₃O₁₂ to be exploiting further for potential applications as solid electrolytes in electrochemical devices.     

Effect of high-temperature crystallization on the electrochemical properties of LiNi<Subscript>0.5</Subscript>Co<Subscript>0.2</Subscript>Mn<Subscript>0.3</Subscript>O<Subscript>2</Subscript> synthesized from a lithiated transition metal oxide precursor

The lithiated transition metal oxide precursor (LNCMO) with typical α-NaFeO₂ structure and imperfect crystallinity, obtained from a hydrothermal process, was pretreated at 500 °C and then subjected to sintering at 800–920 °C to synthesize the ternary layered LiNi_0.5Co_0.2Mn_0.3O₂ (NCM523). X-ray diffraction (XRD), scanning electron microscope (SEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and charge/discharge testing were used for investigating the effect of the high-temperature crystallization on the properties of the NCM523 cathode materials. The results show that the materials heated at 880–900 °C possess superior cation ordering, perfect crystallinity, and excellent electrochemical performances, among which the material heated at 900 °C delivers better performances, with the initial discharge capacity of 152.6 mAh g^?1 at 0.5 C over 3.0 to 4.3 V and the capacity retention of 95.5% after 50 cycles. Furthermore, the effect of the high-temperature crystallization on the Li⁺ diffusion coefficient, potential polarization, and electrochemical resistance are discussed.     

Efficient electrochromic device based on sol–gel prepared WO<Subscript>3</Subscript> films

Tungsten oxide (WO₃) films were prepared on indium–tin oxide (ITO) glass by sol–gel method. The influence of annealing temperature on the structural, morphological, optical, electrochemical, and electrochromic properties has been investigated. The film annealed at 250 °C with an amorphous structure exhibits a noticeable electrochromic performance, such as the highest optical modulation of 58.5 % at 550 nm, high electrochemical stability, and excellent reversibility (Q _b/Q _c?=?96.3 %). An electrochromic (EC) device based on WO₃/NiO complementary structure shows improved performance. It exhibits high optical transmittance modulation of 62 % at 550 nm, excellent cycling stability, and relatively fast electrochromic response time (10 s for coloration and 19 s for bleaching).     

A facile hydrothermal method to prepare LiFePO4/C submicron rod with core–shell structure

Submicron rod LiFePO₄/C has been synthesized via a facile hydrothermal process. The morphology, crystal structure, and charge–discharge performance of the prepared samples were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and galvanostatic charge–discharge testing. The SEM and TEM illustrate that submicron rods with a width of about 140 nm and a length of up to 400 nm have been obtained. The TEM test also indicates a “core–shell” structure with a 1.5–2 nm carbon shell on the LiFePO₄ core. Even though the separate carbon-coated procedure is not used in this method, the electrochemical behavior results are satisfied. It displays that LiFePO₄/C has highly crystalline and a desirable core–shell structure with uniform carbon film. Galvanostatic battery testing shows that LiFePO₄/C delivers 104 mAh g^?1 at 5 C rates. The highest specific capacity of 166 mAh g^?1 is achieved at 0.1 C rate, and 99.8 % of the initial specific capacitance remained after 30 cycles.     

LiClO4-doped plasticized chitosan and poly(ethylene glycol) blend as biodegradable polymer electrolyte for supercapacitors

Biodegradable polymer electrolyte comprising the blend of chitosan (CS) and poly(ethylene glycol) (PEG) plasticized with ethylene carbonate and propylene carbonate, as host polymer, and lithium perchlorate (LiClO₄), as a dopant, was prepared by solution casting technique. The ionic conductivity has been calculated using the bulk impedance obtained through impedance spectroscopy. The variation of conductivity and dielectric properties has been investigated as a function of polymer blend ratio, plasticizer content and LiClO₄ concentration at temperature range of 298–343 K. The DSC thermograms show two broad peaks for CS/PEG blend and increased with increase in the LiClO₄ content. The maximum conductivity has been found to be 1.1?×?10^?4 S cm^?1 at room temperature for 70:30 (CS/PEG) concentration. The electric modulus of the electrolyte film exhibits a long tail feature indicative of good capacitance. The activation energy of all samples was calculated using the Arrhenius plot, and it has been found to be 0.12 to 0.38 eV. A carbon–carbon supercapacitor has been fabricated using this electrolyte, and its electrochemical characteristics and performance have been studied. The supercapacitor showed a fairly good specific capacitance of 47 F?g^?1.     

The preparation and electrochemical properties of the Li-excess cathode material Li1 + x (Mn0.7Fe0.3)1 − x O2 by coprecipitation method

The Fe-substituted Li₂MnO₃ cathode materials were synthesized by the coprecipitation method. The effects of the different precipitants of Na₂CO₃ and NaOH on the structure, morphology, and electrochemical performance were investigated by X-ray diffractometry, scanning electron microscopy, dQ/dV plots, and charge–discharge tests. The results indicate that the materials prepared using both precipitants possess layered α-NaFeO₂ structure with R-3m space group. However, the material prepared using Na₂CO₃ shows smaller primary particle size as well as higher discharge capacity. The cycling test shows that the initial discharge capacity is 206 mAh g^?1 in the voltage range of 2.5–4.8 V under current density of 30 mA g^?1 at 30 °C and 231 mAh g^?1 in the voltage range of 2.0–4.8 V. Meanwhile, the discharge capacity fades to 191 mAh g^?1 after 20 cycles. The activated Mn⁴⁺ was confirmed to contribute to the high reversible capacities.     

Effects of different precipitants on LiNi<Subscript>0.5</Subscript>Mn<Subscript>1.5</Subscript>O<Subscript>4</Subscript> for lithium ion batteries prepared by modified co-precipitation method

Effects of two different precipitants of Na₂CO₃ and Na₂C₂O₄ on LiNi_0.5Mn_1.5O₄ (LNMO) cathode materials, which are prepared by a modified co-precipitation method, have been investigated. Various measurements have been applied to characterize the physical and electrochemical performances of LNMO. Compared with the LNMO prepared by the oxalate co-precipitation (LNMO2), the material synthesized by the carbonate co-precipitation (LNMO1) not only shows more uniform porosity and smaller particles but also has a better rate capability and cycling performance. In addition, the sample prepared by carbonate has a stable spherical structure, due to the fact that carbonate co-precipitation with less gas release during calcination can prevent the destruction of the as-prepared LNMO material structure and promote the formation of regular particle and aperture. Based on the electrochemical test results, LNMO1 shows greatly enhanced electrochemical performance of a high initial discharge capacity of 125.6 mAh g^?1 at 0.25 °C, as well as a preferably capacity retention of 96.5% after 100 cycles at 0.5 °C. And even at a high rate of 10 °C, the discharge capacity of LNMO1-based cell still approaches 83.1 mAh g^?1.     

Enhanced electrochemical performance of lithium vanadium phosphate as cathode by LiBOB/LiTFSI with additive in EC/EMC

A series of Li₃V₂(PO₄)₃/C (LVP/C) samples with monoclinic structure indexed to P2₁/n space group were synthesized using V₂O₃ as vanadium source by solid state reaction method by different sintering temperatures. It was found that the LVP/C sintered at 750 °C with a carbon content 3 wt.% was the optimum condition for this synthesis. The structural, morphological, superficial, and textural properties of LVP/C were characterized by XRD, SEM, TEM, and XPS. The electrochemical performance was evaluated by galvanostatic charge–discharge cycling using new high voltage electrolyte. The optimized cell delivered an initial discharge capacity of 187 mAh g^?1 in the higher cut-off voltage of 3.0–4.8 V vs. Li⁺/Li⁰ at 0.2 C rate, with a capacity retention of 88 %, 89 %, and 61 % after 50 cycles discharging at 1 C, 2 C, and 4 C, respectively. The capacity can be almost recovered at 0.5 C after long cycles. The excellent stability is contributed to the new high-voltage electrolyte.     

Li3V2(PO4)3 modified LiFePO4/C cathode materials with improved high-rate and low-temperature properties

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.     

Effects of CO2 activation on porous structures of coconut shell-based activated carbons

In this paper, textural characterization of an activated carbon derived from carbonized coconut shell char obtained at carbonization temperature of 600 °C for 2 h by CO₂ activation was investigated. The effects of activation temperature, activation time and flow rate of CO₂ on the BET surface area, total volume, micropore volume and yield of activated carbons prepared were evaluated systematically. The results showed that: (i) enhancing activation temperature was favorable to the formation of pores, widening of pores and an increase in mesopores; (ii) increasing activation time was favorable to the formation of micropores and mesopores, and longer activation time would result in collapsing of pores; (iii) increasing flow rate of CO₂ was favorable to the reactions of all active sites and formation of pores, further increasing flow rate of CO₂ would lead carbon to burn out and was unfavorable to the formation of pores. The degree of surface roughness of activated carbon prepared was measured by the fractal dimension which was calculated by FHH (Frenkel-Halsey-Hill) theory. The fractal dimensions of activated carbons prepared were greater than 2.6, indicating the activated carbon samples prepared had very irregular structures, and agreed well with those of average micropore size.     

Electrochemical characterization of ionic liquid based gel polymer electrolyte for lithium battery application

High molecular weight polymer poly(vinylidenefluoride-co-hexafluoropropylene) (PVdF-HFP), ionic liquid 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMIMFSI), and salt lithium bis(trifluoromethanesulfonyl)imide (LiTFSI)-based free-standing and conducting ionic liquid-based gel polymer electrolytes (ILGPE) have been prepared by solution cast method. Thermal, electrical, and electrochemical properties of 80 wt% IL containing gel polymer electrolyte (GPE) are investigated by thermogravimetric (TGA), impedance spectroscopy, linear sweep voltammetry (LSV), and cyclic voltammetry (CV). The 80 wt% IL containing GPE shows good thermal stability (~?200 °C), ionic conductivity (6.42?×?10^?4 S cm^?1), lithium ion conductivity (1.40?×?10^?4 S cm^?1 at 30 °C), and wide electrochemical stability window (~?4.10 V versus Li/Li⁺ at 30 °C). Furthermore, the surface of LiFePO₄ cathode material was modified by graphene oxide, with smooth and uniform coating layer, as confirmed by scanning electron microscopy (SEM), and with element content, as confirmed by energy dispersive X-ray (EDX) spectrum. The graphene oxide-coated LiFePO₄ cathode shows improved electrochemical performance with a good charge-discharge capacity and cyclic stability up to 50 cycles at 1C rate, as compared with the without coated LiFePO₄. At 30 °C, the discharge capacity reaches a maximum value of 104.50 and 95.0 mAh g^?1 for graphene oxide-coated LiFePO₄ and without coated LiFePO₄ at 1C rate respectively. These results indicated improved electrochemical performance of pristine LiFePO₄ cathode after coating with graphene oxide.     

Studies on the removal of As(III) and As(V) through their adsorption onto granular activated carbon/MnFe2O4 composite: isotherm studies and error analysis

The granular activated carbon/MnFe₂O₄ composite with a mass ratio of 2:1 was synthesized using a simple chemical coprecipitation procedure and used for the removal of As(III) and As(V) from synthetically prepared wastewater. Physicochemical analysis of the composite was carried out through Brunauer, Emmett and Teller surface area and total pore volume, Fourier Transform Infrared Spectroscopy (FT-IR) and Scanning Electron Micrograph and Energy-Dispersive X-Ray Spectroscopy (SEM-EDX). The impact of various adsorption parameters such as the initial pH, adsorbent dose, contact time, temperature and initial arsenic concentration were systematically investigated to evaluate the optimum operating conditions. Nonlinear regression analysis was employed to identify the best-fit isotherm on the basis of three correlation coefficients and three error functions and also to predict the parameters involved in one one-parameter, six two-parameter, nineteen three-parameter, three four-parameter and one five-parameter isotherms. The maximum adsorption capacities estimated using the Langmuir model were 1253 mg/g for As(III) and 1314 mg/g for As(V) at 30 °C temperature and 70 min contact time. The results showed that As(III) and As(V) removal was strongly pH-dependent with an optimum pH value of 7.0 and 4.0, respectively. The mean adsorption energy (E) calculated from the D–R model indicated the nature of adsorption being ion exchange type.