In this paper, a series of Ce-doped Li3V2(PO4)3/C composite cathode materials for Li-ion batteries were synthesized by a facile and fast microwave assisted sol–gel route. The investigation of the ...influence of Ce doping on the structural and electrochemical characteristics of Li3V2(PO4)3/C shows that the resulting composite exhibits smaller particle size, lower electron-transfer resistance, and faster lithium ion migration, which are attributed to improved lithium ion transfer by the Ce doping. At low charge/discharge rates, the Ce-doped Li3V1.98Ce0.02(PO4)3/C composite delivers a stable specific capacity of ∼170 mAh g−1 for over 100 cycles. At high rates (e.g. 10C), the Ce-doped composite is still able to deliver stable capacities of up to ∼120 mAh g−1 which is ∼60% greater than its un-doped counterpart.
•Synthesis of Ce-doped Li3V2(PO4)3/C cathode by microwave sol–gel route.•At 1C, the Ce-doped cathode delivers a stable capacity of ∼170 mAh g−1.•At 10C, the Ce-doped cathode delivers a stable capacity of ∼120 mAh g−1.
We report a novel far-infrared (FIR) thermal reduction process to effectively reduce graphene oxide films for supercapacitor electrode applications. The binder-free graphene oxide films used in this ...study were produced by electro-spray deposition of a graphene oxide colloidal solution onto stainless steel current collectors. The reduction of graphene oxide was performed using a commercial FIR convection oven that is ubiquitous in homes for cooking and heating food. The reduction process incorporated a simple, one-step FIR irradiation carried out in ambient air. Further, the FIR irradiation process was completed in ∼3min, wherein neither special atmosphere nor high temperature was employed, resulting in an economic, efficient and simplified processing technique. The as-produced FIR graphene electrode gave a specific capacitance of ∼320F/g at a current density of ∼0.2A/g with less than 94% loss in specific capacitance over 10,000 charge/discharge cycles. This is one of the best specific capacitances reported for all-carbon electrodes without any additives. Even at ultrafast charge/discharge rates (current densities as high as ∼100A/g), the FIR graphene electrode still delivered specific capacitances in excess of 90F/g. The measured energy and power densities of the FIR supercapacitors were found to be ∼3–6 times higher than commercial (activated carbon) supercapacitor devices. This excellent electrochemical performance of the FIR graphene coupled with its ease of production (in air at low temperatures) using a commercial home-use FIR convection oven indicates the significant potential of this concept for large-scale commercial electrochemical supercapacitor applications.
Mesoporous manganese oxides (MnO
2
) were synthesized via a facile chemical deposition strategy. Three kinds of basic precipitants including sodium carbonate (Na
2
CO
3
), sodium bicarbonate (NaHCO
3
...), and sodium hydroxide (NaOH) were employed to adjust the microstructures and surface morphologies of MnO
2
materials. The obtained MnO
2
materials display different microstructures. Great differences are observed in their specific surface area and porosity properties. The microstructures and surface morphologies characteristics of MnO
2
materials largely determine their pseudocapacitive behavior for supercapacitors. The MnO
2
prepared with Na
2
CO
3
precipitant exhibits the optimal microstructures and surface morphologies compared with the other two samples, contributing to their best electrochemical performances for supercapacitors when conducted either in the single electrode tests or in the capacitor measurements. The optimal MnO
2
electrode exhibits a high specific capacitance (173 F g
–1
at 0.25 A g
−1
), high-rate capability (123 F g
−1
at 4 A g
−1
), and excellent cyclic stability (no capacitance loss after 5,000 cycles at 1 A g
−1
). The optimal activated carbon//MnO
2
hybrid capacitor exhibits a wide working voltage (1.8 V), high-power and high-energy densities (1,734 W kg
−1
and 20.9 Wh kg
−1
), and excellent cycling behavior (93.8 % capacitance retention after 10,000 cycles at 1 A g
−1
), indicating the promising applications of the easily fabricated mesoporous MnO
2
for supercapacitors.
The effects of plasticizer ethylene carbonate (EC) on the AC impedance spectra and the ionic conductivity are reported. With increasing of EC concentration the semicircle in high frequency ...disappears, and the slope of the straight line in low frequency decreases. The data obtained from impedance experiments can be explained using an equivalent circuit proposed. On the other hand, the room temperature conductivity increases with EC concentration because of the increase of the segmental flexibility of PEO. For lower EC concentration samples, the temperature dependence of conductivity in low temperature range follows Arrhenius type, but when EC concentration is larger than 20%, the temperature dependence of conductivity obeys the Vogel–Tamman–Fulcher (VTF) equation in all temperature ranges.
We present a new method for specific detection of oxytetracycline (OTC) at nanomolar concentrations based on a microfabricated cantilever array. The sensing cantilevers in the array are ...functionalized with self-assembled monolayers (SAMs) of OTC-specific aptamer, which acts as a recognition molecule for OTC. While the reference cantilevers in the array are functionalized with 6-mercapto-1-hexanol SAMs to eliminate the influence of environmental disturbances. The cantilever sensor shows a good linear relationship between the deflection amplitude and the OTC concentration in the range of 1.0–100 nM. The detection limit of the cantilever array sensor is as low as 0.2 nM, which is comparable to some traditional methods. Other antibiotics such as doxycycline and tetracycline do not cause significant deflection of the cantilevers. It is demonstrated that the cantilever array sensors can be used as a powerful tool to detect drugs with high sensitivity and selectivity.
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•Low-temperature electrochemical behavior of MnO2 with 4 different crystal structures was investigated.•The δ-MnO2 exhibits the best electrochemical performances at low ...temperature.•The operation temperature has more effect on the charge transfer resistance than diffusion resistance.
This paper involves preparation of four different crystal phases (δ, γ, α and λ) of MnO2 by redox, solid reaction, hydrothermal routes and delithiation of LiMn2O4, respectively. The obtained MnO2 samples have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and the Brunauer–Emmett–Teller (BET) method for micro-structural, morphological and porosity studies. Cyclic voltammetric and galvanostatic tests were carried out to evaluate their capacitive properties in an anti-freezing aqueous electrolyte at different operating temperatures ranging from 25 to −35°C. The δ-MnO2 prepared by a redox method exhibits the best electrochemical performances when conducted either in the single electrode tests (from 174.7 to 148.6Fg−1) or in the capacitor measurements (from 47.4 to 42Fg−1) as the operating temperature decreased from 25°C down to the low temperature of −35°C. Moreover, electrochemical impedance spectroscopy has been investigated and the activation energy values of different impedance components have been analyzed. It has been discovered that the operation temperature has more effect on the charge transfer resistance than diffusion resistance. To some degrees, these results have guiding significance for the low-temperature applications of manganese oxides-based electrochemical capacitors.
A series of La-doped Li
3
V
2
(PO
4
)
3
/C cathode materials for Li-ion batteries are synthesized by a sol-gel-assisted, low-temperature sintering process. La(NO
3
)
3
acts not only as the La source, ...but also, together with the intermediate product LiNO
3
, promotes combustion, the ultrahigh exothermic energy that is advantageous for the nucleation process. The subsequent sintering process at 600 °C for 4 h is sufficient to produce highly crystalline La-doped Li
3
V
2
(PO
4
)
3
/C composites. The as-prepared cathode materials display smaller particle size, lower electron-transfer resistance and faster Li ion migration, which is ascribed to enhanced Li-ion transfer because of the La doping. The resulting Li
3
V
1.96
La
0.04
(PO
4
)
3
/C cathode has a stable specific capacity of 160 mA h g
−1
at low charge-discharge rates over 100 cycles, and retained a stable capacity of up to 116 mA h g
−1
at a rate of 5 C, which is 40% higher than the undoped pristine cathode.
La-doped Li
3
V
2
(PO
4
)
3
/C cathode materials are synthesized by a sol-gel-assisted, low-temperature sintering process. The resulting cathode has a stable specific capacity of 160 mA h g
−1
at 0.2 C, and retained a stable capacity of up to 116 mA h g
−1
at 5 C.
The solubility data of lithium bis(oxalate)borate (LiBOB) were measured in six different solvents using the synthetic method and laser monitoring technique at temperatures ranging from (293.15 to ...363.15) K under atmospheric pressure. The experimental solubilities of LiBOB in different solvents were correlated by the modified Apelblat equations. It is found the calculated solubility data show good consistency with the experimental values. On this basis, some thermodynamic parameters of LiBOB in different solvents, such as dissolution enthalpy, dissolution entropy, and dissolution Gibbs free energy, are also calculated. These results concerning the solubility of LiBOB in different solvents will provide fundamental data in the commercial application of LiBOB.
