Efficient microwave hydrothermal synthesis of nanocrystalline orthorhombic LiMnO2 cathodes for lithium batteries

Rod-like orthorhombic LiMnO₂ nanocrystals were successfully synthesized using temperature-controlled microwave hydrothermal route (TCMH) in a short time (30 min) at a temperature as low as 160 °C. o-LiMnO₂ obtained by two different methods was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemistry test. SEM revealed that the product obtained in case of TCMH was rod-like with a diameter of 40 nm, while the nanoparticles with 200 nm diameter were obtained by traditional hydrothermal route (TH). The dramatic formation of o-LiMnO₂ in the microwave hydrothermal field influenced the morphology and crystal structure of the final products. The formation and preferred growth orientation mechanism of o-LiMnO₂ in the microwave irradiation process was discussed. Electrochemistry performance exhibited that the as-synthesized o-LiMnO₂ nanorods reached the maximum discharge capacity of 194.2 mAh g⁻¹ at 0.1 C rate after several cycles between 2.2 and 4.4 V vs. Li⁺/Li at room temperature, which was higher than the electrochemical performance of o-LiMnO₂ obtained by TH. The experimental results showed that the TCMH method provided an effective way for preparing o-LiMnO₂ cathode material in lithium-ion batteries.     

Synthesis and electrochemical properties of LiAl0.05Mn1.95O4 by the ultrasonic assisted rheological phase method

Pure-phase and well-crystallized spinel LiAl_0.05Mn_1.95O₄ powders were successfully synthesized by a simple ultrasonic assisted rheological phase (UARP) method. The structure and morphology properties of this as-prepared powder compared with the pristine LiMn₂O₄ and LiAl_0.05Mn_1.95O₄ obtained from the solid-state reaction (SSR) method were investigated by powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). The electrochemical properties focused on the LiAl_0.05Mn_1.95O₄ by this new method have also been investigated in detail. According to these tests results, it is obviously to see that the newly prepared sample delivers a relatively high initial discharge capacity of 111.6 mAh g⁻¹, presents excellent rate capability and reversibility, and shows good cycling stability with capacity retention of 90.6% after 70 cycles. Meanwhile, the electrochemical impedance spectroscopy (EIS) investigations were employed to study the electrochemical process of Li⁺ ions with the synthesized LiAl_0.05Mn_1.95O₄ electrode in detail.     

Investigation on electrochemical properties of cerium doped lead dioxide anode and application for elimination of nitrophenol

The present work focused on the investigation of electrochemical properties of cerium doped lead dioxide anode, i.e. Ti/Ce–PbO₂. SEM, AFM, XRD and XPS were used to characterize the morphology, crystal structure and elemental states of the modified anode. Electrochemical impedance spectroscopy (EIS) was also utilized to study the electrochemical property of Ti/Ce–PbO₂. The electrochemical activity of the Ti/Ce–PbO₂ anode was investigated by means of bulk electrolysis and compared with that of a PbO₂ anode. The accelerated life test and oxidants determination were also conducted. The results indicated that the incorporation of cerium improved the electrocatalytic activity and stability of PbO₂ anode. The service life of Ti/Ce–PbO₂ electrode was much longer than that of traditional lead dioxide electrode. The electrochemical activity obtained from degradation of o-nitrophenol (o-NP) outperformed the traditional lead dioxide electrode as well. The Ti/Ce–PbO₂ electrode is considered a promising anode for the treatment of organic pollutants.     

Effects of the starting materials and mechanochemical activation on the properties of solid-state reacted Li4Ti5O12 for lithium ion batteries

Li₄Ti₅O₁₂ was synthesized by a solid-state reaction between Li₂CO₃ and TiO₂ for applications in lithium ion batteries. The effects of the TiO₂ phase and mechanochemical activation on the Li₄Ti₅O₁₂ particles as well as the corresponding electrochemical properties were investigated. Rutile TiO₂ was more desirable in acquiring high purity Li₄Ti₅O₁₂ than anatase due to the anatase to rutile phase transformation, which was found to be more rigid in the solid-state reaction than the intact rutile phase. Mechanochemical activation of the starting materials was effective in decreasing the reaction temperature and particle size as well as increasing the Li₄Ti₅O₁₂ content. The specific capacity depended significantly on the Li₄Ti₅O₁₂ content, whereas the rate capability improved with decreasing particle size due to the enhanced contact area and reduced diffusion path. Overall, a 200 nm-sized Li₄Ti₅O₁₂ powder with a specific capacity of 165 mAh/g could be synthesized by optimizing the milling method and starting materials.     

Lithium insertion in ultra-thin nanobelts of Ag2V4O11/Ag

In this study, ultra-thin nanobelts of Ag₂V₄O₁₁/Ag were successfully synthesized. The synthesized ultra-thin nanobelts of Ag₂V₄O₁₁/Ag are highly crystalline and the thickness is found to be about 5 nm. A lithium battery using ultra-thin nanobelts of Ag₂V₄O₁₁/Ag as the active materials of the positive electrode exhibits a high initial discharge capacity of 276 mAh g⁻¹, corresponding to the formation of Li_xAg₂V₄O₁₁ (x = 6). With increased cycling, the electrode made of ultra-thin nanobelts of Ag₂V₄O₁₁/Ag tends to loose electrochemical activity due to Ag⁺ ions in the ultra-thin nanobelts of Ag₂V₄O₁₁ were reduced and new phase was formed.     

Core–shell Ni0.5TiOPO4/C composites as anode materials in Li ion batteries

Pristine Ni_0.5TiOPO₄ was prepared via a traditional solid-state reaction, and then Ni_0.5TiOPO₄/C composites with core–shell nanostructures were synthesized by hydrothermally treating Ni_0.5TiOPO₄ in glucose solution. X-ray diffraction patterns indicate that Ni_0.5TiOPO₄/C crystallizes in monoclinic P2₁/c space group. Scanning electron microscopy and transmission electron microscopy show that the small particles with different sizes are coated with uniform carbon film of ∼3 nm in thickness. Raman spectroscopy also confirms the presence of carbon in the composites. Ni_0.5TiOPO₄/C composites presented a capacity of 276 mAh g⁻¹ after 30 cycles at the current density of 42.7 mA g⁻¹, much higher than that of pristine Ni_0.5TiOPO₄ (155 mAh g⁻¹). The improved electrochemical performances can be attributed to the existence of carbon shell.     

CO2 attraction by specifically adsorbed anions and subsequent accelerated electrochemical reduction

The electrochemical reduction of CO₂ was studied on a copper mesh electrode in aqueous solutions containing 3 M solutions of KCl, KBr and KI as the electrolytes in a two and three phase configurations. Electrochemical experiments were carried out in a laboratory-made, divided H-type cell. The working electrode was a copper mesh, while the counter and reference electrodes were Pt wire and Ag/AgCl electrode, respectively. Results of our work suggest a reaction mechanism for the electrochemical reduction of CO₂ in the two phase configuration where the presence of Cu-X as the catalytic layer facilitates the electron transfer from the electrode to CO₂. Electron-transfer to CO₂ may occur via the X_ad⁻(Br⁻, Cl⁻, I⁻)-C bond, which is formed by the electron flow from the specifically adsorbed halide anion to the vacant orbital of CO₂. The stronger the adsorption of the halide anion to the electrode, the more strongly CO₂ is restrained, resulting in higher CO₂ reduction current. Furthermore, it is suggested that specifically adsorbed halide anions could suppress the adsorption of protons, leading to a higher hydrogen overvoltage. These effects may synergistically mitigate the overpotential necessary for CO₂ reduction, and thus increase the rate of electrochemical CO₂ reduction.     

The electrocatalytic oxidative polymerization of o-phenylenediamine by reduced graphene oxide and properties of poly(o-phenylenediamine)

The electrocatalytic oxidative polymerization of o-phenylenediamine (o-PD) was performed on a reduced graphene oxide (RGO)/glassy carbon (GC) electrode. The electrolysis of o-PD was carried out using cyclic voltammetry and potentiostatic and galvanostatic methods. The experimental results demonstrated that the reduced graphene oxide (RGO) has a pronounced catalytic ability for the electrochemical oxidative polymerization of o-PD in a 0.60 M H₂SO₄ solution compared to the bare GC electrode; however, graphene oxide has only a slight catalytic ability for the electrochemical oxidative polymerization of o-PD. The above three electrochemical techniques confirmed that there is a considerable discrepancy between the characteristics of the electrocatalytic oxidation of a species and the characteristics of the electrocatalytic oxidative polymerization of o-PD. This effect occurs because the charges passed during the electrolysis of o-PD on the bare GC electrode were mainly consumed for the formation of the soluble oligomer; however, RGO plays an important role in suppressing the formation of the soluble oligomer. An unexpected result was obtained: two or three pairs of the redox peaks of poly(o-phenylenediamine) (PoPD), synthesized using RGO as a catalyst, occur on the cyclic voltammogram in a wider potential range, depending on the polymerization conditions; however, only one pair of redox peaks occurs on the cyclic voltammogram of the conventional PoPD in a narrow potential range under exactly the same experimental conditions. The NMR and ESR spectra of the PoPD polymerized on the RGO/GC electrode are presented in this paper.     

Electrochemical performance of LiV3−xNixO8 cathode materials synthesized by a novel low-temperature solid-state method

A series of cathode materials for lithium ion batteries with the formula LiV_3−xNi_xO₈ (x = 0.000, 0.025, 0.050 and 0.100) have been synthesized by a novel low-temperature solid-state method. The synthesized cathode materials have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), discharge-charge test, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). These results indicate that LiV_2.95Ni_0.050O₈ shows much better electrochemical performances than LiV₃O₈. This is due to better electrochemical reversibility and lower particle-to-particle resistance after Ni²⁺ doping.     

Antimonides (FeSb2, CrSb2) with orthorhombic structure and their nanocomposites for rechargeable Li-ion batteries

Intermetallic FeSb₂ and CrSb₂ and their nanocomposites (FeSb₂/C and Sb/Cr₃C₂/C) were prepared using solid-state routes, such as heat-treatment and high-energy mechanical milling, in order to enhance the electrochemical properties of Sb. These electrodes were tested as anode materials for rechargeable Li-ion batteries. The reaction mechanism of intermetallic FeSb₂ and CrSb₂ was investigated using ex situ X-ray diffraction and high resolution transmission electron microscopy. The FeSb₂/C and Sb/Cr₃C₂/C nanocomposite electrodes exhibited greatly enhanced electrochemical behaviors compared to the FeSb₂ and CrSb₂ electrodes. Additionally, the Sb/Cr₃C₂/C nanocomposite electrode showed a better electrochemical performance than the FeSb₂/C nanocomposite electrode.     

On the LiCo2/3Ni1/6Mn1/6O2 positive electrode material

LiCo_2/3Ni_1/6Mn_1/6O₂ layered oxide was synthesized by the combustion method that led to a crystalline phase with good homogeneity and low particles size. The structural properties of the prepared positive electrode material were investigated by performing XRD Rietveld refinement. Practically no Li/Ni mixing was detected evidencing that the studied compound adopts almost an ideal α-NaFeO₂ type structure. The Li||LiCo_2/3Ni_1/6Mn_1/6O₂ cell showed a discharge capacity of 199 mAh g⁻¹ when cycled in the 2.7–4.6 V potential range while the best cycling performances were recorded when the upper cut off is fixed at 4.5 V. Structural changes in Li_xCo_2/3Ni_1/6Mn_1/6O₂ with lithium electrochemical de-intercalation were studied using X-ray diffraction. This study clearly shows the existence of a solid solution domain in the 0.1 < x < 1.0 composition range while for x = 0.1, a new phase appears explaining the decrease of the electrochemical performance when the cell is cycled at high upper cut off voltage.     

Interfacial reactions at electrode/electrolyte boundary in all solid-state lithium battery using inorganic solid electrolyte, thio-LISICON

Electrode/electrolyte interface was studied for all solid-state batteries using inorganic solid electrolyte with the crystalline thio-LISICON and glassy Li-Si-P-S-O systems. The formation of the interfacial phase depends on the electrolyte. The thio-LISICON (Li_3.25Ge_0.25P_0.75S₄) and the Li-Al negative electrode provided the best electrode/electrolyte interface for fast charge-discharge characteristics, while the SEI phase formed at the Li-Al/Li₃PO₄-Li₂S-SiS₂ glass boundary caused high interfacial resistance. The formation of the SEI phase is general behavior at the electrode/electrolyte interface of solid-state batteries, and the fast electrochemical reaction is attained as a result of optimization of the electrode/electrolyte combination.     

Electrochemical properties of LiCoyMn2−yO4 synthesized using a combustion method in a voltage range of 3.5–5.0 V

LiCo_yMn_2−yO₄ (y = 0.00, 0.04 and 0.08) were synthesized using a combustion method, and the electrochemical properties were examined in the voltage range of 3.5–5.0 V. The XRD patterns of the synthesized samples were similar, and the samples had a spinel phase structure. The first charge capacity curves exhibited an inflection in the voltage range of 4.2–5.0 V, where it is believed that additional, previously unreported phase transition occurs. The voltage vs. x curves for the first to fifth cycle exhibited two distinct voltage plateaus, corresponding well to a two-phase reaction and a one-phase reaction, respectively, as reported previously. For the voltage range of 3.5–5.0 V, the first discharge capacity increased and the cycling performance improved as y increased. Among these samples, LiCo_0.08Mn_1.92O₄ had the largest first discharge capacity of 132.5 mA h/g at 600 μA/cm², and its cycling efficiency was 91.1% at the 15th cycle in the voltage range of 3.5–5.0 V.     

The investigation on electrochemical reaction mechanism of CuF2 thin film with lithium

Crystalline CuF₂ thin films were prepared by pulsed laser deposition under room temperature. The physical and electrochemical properties of the as-deposited thin films have been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), galvanostatic cycling and cyclic voltammetry (CV). Reversible capacity of 544 mAh g⁻¹ was achieved in the potential range of 1.0–4.0 V. A reversible couple of redox peaks at 3.0 V and 3.7 V was firstly observed. By using ex situ XRD and TEM techniques, an insertion process followed by a fully conversion reaction to Cu and LiF was revealed in the lithium electrochemical reaction of CuF₂ thin film electrode. The reversible insertion reaction above 2.8 V could provide a capacity of about 125 mAh g⁻¹, which makes CuF₂ a potential cathode material for rechargeable lithium batteries.     

Agar-assisted sol-gel synthesis and electrochemical characterization of TiNb2O7 anode materials for lithium-ion batteries

TiNb₂O₇ powders are synthesized via a newly developed agar-assisted sol-gel process for the first time. Phase-pure TiNb₂O₇ powders are obtained upon calcination at 800 °C. On contrast, TiNb₂O₇ powders synthesized via the conventional solid-state method require high calcination temperature at 1100 °C for the complete compound formation. The samples synthesized with agar improve the morphology with submicron-sized particles. The formed porous structure is favorable for enhancing the electrochemical kinetics due to the large contact area between the electrode and the electrolyte. Based on the electrochemical active surface area analysis, the electrical double-layer capacitance of TiNb₂O₇ powders synthesized via both the agar-assisted and the solid-state method is 145 mF cm^?2 and 22 mF cm^?2, respectively. The electrochemical active surface area of the sample prepared via the agar-assisted method is higher than that of the sample prepared via the solid-state method. The TiNb₂O₇ sample synthesized via the agar-assisted process yields 284 mAh g^?1 at 0.1 C, whereas the sample synthesized via the conventional solid-state method yields only 265 mAh g^?1 at 0.1 C. The discharge capacities of the agar-assisted synthesized sample are 205 mAh g^?1 and 174 mAh g^?1 at 5 C and 10 C, respectively. Moreover, the sample exhibits high capacity retention of 91% after 100 discharge-charge cycles at 5 C. Based on the obtained results, the agar-assisted sol-gel process is inferred as one of the facile methods for preparing high performance anode materials for lithium-ion batteries.     

Polyacrylamide gel synthesis and sintering of Mg2SiO4:Eunanopowder

A Mg₂SiO₄:Eu³⁺ nanopowder was synthesized by a polyacrylamide gel method. In this route, the gelation of the solution is achieved by the formation of a polymer network which provides a structural framework for the growth of particles. The densification of the powders was also studied. An amorphous nanopowder was synthesized and crystallized to Mg₂SiO₄ after heat-treatment via a solid-state reaction at a relatively low temperature of about 700 °C. The powders prepared by the polyacrylamide gel method showed better sinterability than the powders synthesized by the conventional sol–gel method. The relative density of the sample was 97% at 1500 °C.     

Preparation and electrochemical characterization of TiO2 nanowires as an electrode material for lithium-ion batteries

Anatase TiO₂ nanowires containing minor TiO₂(B) phase were prepared by a hydrothermal chemical reaction followed by the post-heat treatment at 400 °C. The phase structure and morphology were analyzed by X-ray diffraction, Raman scattering, transmission electron microscope, and field-emission scanning electron microscopy. The electrochemical properties were investigated by employing constant current discharge-charge test, cyclic voltammetry, and electrochemical impedance techniques. These nanowires exhibited high rate capacity of 280 mAh g⁻¹ even after 40 cycles, and the coulombic efficiency was approximately 98%, indicating excellent cycling stability and reversibility. The electrochemical impedance spectra showed a stable kinetic process of the electrode reaction. These results indicated that the TiO₂ nanowires have promising application for high energy density lithium-ion batteries.     

Enhanced Photocatalytic Hydrogen Evolution Over CaTi1−x Zr x O3 Composites Synthesized by Polymerized Complex Method

The solid solution of CaTi_1−x Zr _x O₃ (x = 0–0.15) was successfully synthesized by the polymerized complex (PC) method. This study has exhibited the advantage of the PC method to prepare a highly active CaTiO₃ compared with the conventional solid-state reaction (SSR) method. More importantly, further improvement in phase purity and large surface area was achieved by the doping of Zr⁴⁺, leading to remarkable enhancement of photocatalytic activities compared to pure CaTiO₃. The quantum yield for H₂ evolution over the most active photocatalyst, Pt (1.0 wt%)/CaTi_0.93Zr_0.07O₃, was 1.91% and 13.3% in photoreactions from pure water and aqueous ethanol solution, respectively for 0.1 g photocatalyst, which was about 3.3 and 2.5 times compared to that of PC-derived CaTiO₃.     

Conventional- and microwave-hydrothermal synthesis of LiMn2O4: Effect of synthesis on electrochemical energy storage performances

The LiMn₂O₄ electrode materials were synthesized by the conventional-hydrothermal and microwave-hydrothermal methods. The electrochemical performances of LiMn₂O₄ were studied as supercapacitors in LiNO₃ electrolyte and lithium-ion battery cathodes. The microwave-hydrothermal method can synthesize LiMn₂O₄ electrode materials with reversible electrochemical reaction in a short reaction time and low reaction temperature than conventional-hydrothermal route. The capacitance of LiMn₂O₄ electrode increased with increasing crystallization time in conventional-hydrothermal route. The results showed that LiMn₂O₄ supercapacitors had similar discharge capacity and potential window (1.2 V) as that of ordinary lithium-ion battery cathodes. In LiNO₃ aqueous electrolyte, the reaction kinetics of LiMn₂O₄ supercapacitors was very fast. Even, at current densities of 1 A/g and 5 A/g, aqueous electrolyte gave good capacity compared with that in organic electrolyte at a current density of 0.05 A/g.     

Electropolymerization kinetics of a binary mixture of pyrrole and o‐aminobenzoic acid and characterization of the obtained polymer films

Poly (pyrrol‐co‐o‐aminobenzoic acid) has been synthesized electrochemically from an aqueous acid medium. The initial rate of electrocopolymerization reaction on platinum electrode is small and the rate law is: Rate = K₂ [D]^1.02[HCl] ^1.44[M]^2.00. The apparent activation energy (E_a) is found to be 90.11 kJ mol^?1. The polymer films obtained have been characterized by cyclic voltammetry, X‐ray diffraction, elemental analysis, thermogravimetric analysis, scanning electron microscopy, ¹H NMR, and IR‐spectroscopy. The mechanism of the electrochemical polymerization reaction has been discussed. The monomer reactivity ratios (r₁ and r₂) were calculated. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008