Effect of K-doping on the Electrochemical Performance of Ca_3Co_4O_9 Anode for Li-ion Batteries

Ca3CO4O9 （CCO） and Ca2.95K0.05Co4O9 （CKCO） powders have been prepared by the polyacrylamide gel method. CKCO shows increased capacity and better cycling stability compared with CCO. After cycled for 50 cycles at 0.5 C, CKCO retains a capacity of 223 mAh.g-1, almost twice than CCO. The electrochemical impedance spectroscopy （EIS） tests shows the CKCO sample has a lower initial charge transfer resistance （Rot） and undergoes smaller Rot change during cycling than the CCO sample, indicating improved electrochemical performance by K-doping.

Highly efficient K-doped Mn-Ce catalysts with strong K-Mn-Ce interaction for toluene oxidation

In this study,K_(x)-Mn-Ce catalysts prepared by sol-gel method were investigated for toluene oxidation.Compared with Mn-Ce,the catalytic performance of K_(x)-Mn-Ce was further improved.X-ray diffraction(XRD),high resolution transmission electron microscopy(HRTEM)and Raman analyses demonstrate that K ions enter the lattice of CeO_(2) and disperse uniformly.The results of X-ray photoelectron spectroscopy(XPS),H_(2)-temperature programmed reduction(H_(2)-TPR).and O_(2)-temperature programmed desorption(O_(2)-TPD)analyses indicate that there is a strong interaction between K,Mn and Ce;the charge co mpensation effect would be induced when K ions enter the lattice of CeO_(2),which leads to more oxygen vacancies due to the generation of more Ce^(3+).Toluene-TPD shows that K-doping enhances the activation ability of toluene.Among all catalysts,K0.1-Mn-Ce shows the highest concentration of Mn^(4+),Ce^(3+),Osur,and redox ability,resulting in higher low-temperature catalytic activity.Additionally,the results of stability and water resistance also prove that K0.1-Mn-Ce catalyst possesses excellent stability and water resistance.

Improvement of dielectric （Ba,Sr）TiO3 thin tunability and loss tangent of films with K doping

Ba0.6Sr0.4TiO3 thin films doped with K were deposited on Pt/Ti/SiO2/Si substrates by the chemical solution deposition method. The structure, surface morphology and the dielectric and tunable properties of Bao.6Sro.4TiO3 thin films have been studied in detail. The K content in Ba0.6Sro.4TiO3 thin films has a strong influence on the material＇s properties including surface morphology and the dielectric and tunable properties. It was found that the Curie temperature of K-doped Bao.6Sr0.4TiO3 films shifts to a higher value compared with that of undoped Ba0.6Sr0.4TiO3 thin films, which leads to a dielectric enhancement of K-doped Ba0.6Sr0.4TiO3 films at room temperature. At the optimized content of 0.02 mol, the dielectric loss tangent is reduced significantly from 0.057 to 0.020. Meanwhile, the tunability is enhanced obviously from 26% to 48% at the measured frequency of 1 MHz and the maximum value of the figure of merit is 23.8. This suggests that such films have potential applications for tunable devices.

Improving rate performances of Li-rich layered oxide by the co-doping of Sn and K ions

The specific capacities and power performances of conventional cathode materials are still needed to improve in order to meet the demand for electrical vehicles.Li-rich layered oxide delivers a high specific capacity,but poor rate performances.Chemical doping is an effective way to address this challenge due to the expanded crystal lattice.Unlike a single ion substitution in the literature,here Li-rich layered oxides were doped by Sn and K to achieve the favorite rate performance,where Sn and K were assumed to replace transition metal ion and Li ion,respectively.Results indicate the co-doped samples result in an increasing capacity retention by more than 40%from 107.9(contrast sample)to 151.5 mAh g^(-1)(co-doped sample)at 10 C-rate.Electrochemical impedance spectroscopy(EIS)and calculated diffusion coefficient of Li^(+) also confirmed the favorite rate performances for co-doped sample.Combining results of Rietveld structure refinement,we proposed that the reason for rate performances comes from the enlarged crystal lattices,which provides a smooth diffusion tunnel for Lithium ions during the charge/discharge processes.The as-adopted method provides a possibility to achieve the improved rate performances by co-doping big-size ions at the different crystal sites.

Comparison study on strategies to prepare nanocrystalline Li2ZrO3-based absorbents for CO2 capture at high temperatures

A comparison study has been conducted on the strategies for synthesizing nanocrystalline Li2ZrO3 and K- doped Li2ZrO3 absorbents for CO2 capture at high temperatures, including solid-state and liquid-phase meth- ods, citrate route, and starch-assisted sol-gel method combined with freeze-drying technique. The absorption properties, including uptake rate and absorption capacity, of synthesized absorbents were investigated by thermo- gravimetric analysis （TGA） at different CO2 partial pressures. The nanosized Li2ZrO3 crystals synthesized by the citrate route exhibit a faster uptake and a higher, nearly stoichiometric absorption capacity than those synthesized by the solid-state and liquid-phase methods. The doping of K into Li2ZrO3 can significantly improve the uptake rate of CO2, especially at low CO2 partial pressures. For the synthesis of K-doped Li2ZrO3, the citrate route has poor reproducibility and scalability, whereas the starch-assisted sol-gel method combined with freeze-drying technique is reproducible and easily scaled up, and the thus synthesized absorbents possess excellent CO2 capture properties.