RESUMEN
To alleviate the depletion of lithium resources and improve battery capacity and rate capacity, the development of aqueous zinc-ion batteries (AZIBs) is crucial. The open channels monoclinic structure Li3V2(PO4)3 is conducive to the transfer and diffusion of guest ions, making it a promising cathode material for AZIBs. Therefore, in this study, nanoneedles and particles Li3V2(PO4)3 cathode materials for AZIBs were prepared by a hydrothermal assisted sol-gel method, and the effect of synthesized pH values was studied. XRD results show that all samples had the monoclinic structure, and the Li3V2(PO4)3 sample prepared at pH = 7 exhibits (LVP-pH7) the highest peak tips and narrowest peak widths. SEM images demonstrate that all samples have the morphology character of randomly oriented needles and irregular particles, with the LVP-pH7 sample having more needle-like particles that contribute to ion diffusion. EDS results show uniform distribution of P, V, and O elements in the LVP-pH7 sample, and no obvious aggregation phenomenon is observed. Electrochemical tests have shown that the LVP-pH7 sample exhibits excellent cycling performance (97.37% after 50 cycles at 200 mA g-1) and rate ability compared to other samples. The CV test results showed that compared with other samples, the LVP-pH7 sample had the most excellent ionic diffusion coefficient (2.44 × 10-12 cm2 s-1). Additionally, the Rct of LVP-pH7 is the lowest (319.83 Ω) according to the findings of EIS and Nyquist plot fitting, showing a decreased charge transfer resistance and raising the kinetics of the reaction.
RESUMEN
Layered δ-MnO2 is a promising cathode material for aqueous zinc ion batteries (AZIBs) due to its high theoretical capacity, high operating voltage and low cost. However, the dissolution of MnO2 and the disproportionation of Mn3+ will lead to irreversible reaction and serious structural degradation of the material during cycling process. In this work, the Al3+ pre-intercalated K0.27MnO2·0.54H2O was prepared by a one-step hydrothermal method with citric acid as the complexing agent and weak reducing agent. Based on the pillars of bimetallic ions K+, Al3+ and water, the framework and interlayer of δ-MnO2 is stabilized. Besides, a certain amount of Al3+ facilitates the increase of crystal water compared with the pure K0.27MnO2·0.54H2O, which is not only conducive to promote the construction of porous and loose 3D morphology, but also beneficial to improve the stability of layered structure and accelerate the migration rate of zinc ions. Contributed to the dissolution/deposition reaction mechanism combined with H+/Zn2+ co-insertion/co-extraction mechanism, it has achieved the high capacity with the maximum reversible specific capacity of 269.5 mAh g-1 at 0.5 A g-1 and excellent stability with 205.8 mAh g-1 even after 300 cycles in Zn//Al-KMO battery.
RESUMEN
For aqueous zinc ion batteries (AZIBs), birnessite MnO2 (δ-MnO2) has been intensively used as one of the most potential cathode materials due to its layered structure, which is conducive to reversible insertion/extraction of zinc ions. However, δ-MnO2 has not been attained for zinc ion storage performance because of its inferior conductivity as well as the undesirable structural degradation upon charge/discharge cycling. Herein, we have designed two kinds of cathode materials of Cu0.06MnO2·1.7H2O (CuMO) and Bi0.09MnO2·1.5H2O (BiMO) with nanoflower structure for the first time by a facile one-step hydrothermal method, which will be applied for high-performance AZIBs.The pre-intercalated metal ions and water molecules serve as pillars to sustain the layered structures, improving the stability of these materials. Particularly, the CuMO may experience a replacement reaction except the zinc ion insertion/extraction to form metallic Cu during the cycling process, which can enhance the diffusion rate of Zn2+, thus resulting in an excellent electronic conductivity and exhibiting remarkable specific capacities. Furthermore, a pseudo-capacitance that is derived from the surface-adsorbed Cu2+and Bi3+ also contributes to the improved electrochemical performances. The reversible capacity of CuMO is estimated as 350 mAh g-1 at 0.5 A g-1, which is much higher than that of pure δ-MnO2 (190 mAh g-1 at 0.5 A g-1). However, BiMO demonstrates long-term cycling stability, maintaining a capacity of 114.5 mAh g-1 even after 1100 charged-discharged cycles at 1 A g-1. The capacity retention is found to be as high as 98.6%, which is much higher than that of pure δ-MnO2 (53.8%). This can contribute to the development of high-performance AZIBs and the application of metal ion pre-intercalation methods in other areas.
RESUMEN
Bridge carbon (13)C NMR shifts of a wide set of substituted cinnamyl anilines p-XC(6)H(4)CHCHCHNC(6)H(4)Y-p (XNO(2), Cl, H, Me, MeO, or NMe(2); YNO(2), CN, CO(2)Et, Cl, F, H, Me, MeO or NMe(2)) had been used as a probe to study the change of substituent effect in the conjugated system. The goal of this work was to study the difference among the substituent effect on SCS of all bridge carbons, and find the alternating of substituent effect in this model compounds. In this study, it was found that the change of the inductive effect and the conjugative effect on different bridge carbons is related to the bond number (m) from the substituent to the corresponding carbon, and the adjusted parameters σ(F(rel))(∗) and σ(R(ver))(∗) can be suitable to scale the difference of the inductive effect and the conjugative effect on bridge carbons. Moreover, because of the difference of substituent effect on bridge carbons, the substituent cross-interaction item Δσ(2)(Δσ(2) = (σ(F(rel))(∗)(X) + σ(R(ver))(∗)(X) - σ(F(rel))(∗)(Y) - σ(R(ver))(∗)(Y))(2)) was not suitable simply to scale the interaction between substituents X and Y for all bridge carbons, so the Δσ(2) was recommended to be divided into two parts: Δσ(F(rel))(2) (Δσ(F(rel))(2) = σ(F(rel))(∗)(X) - σ(F(rel))(∗)(Y))(2)) and Δσ(R(ver))(2) (Δσ(R(ver))(2) = (σ(R(ver))(∗)(X) - σ(R(ver))(∗)(Y))(2)). With σ(F(rel))(∗), σ(R(ver))(∗), Δσ(F(rel))(2), Δσ(R(ver))(2), and δ(C,parent), the obtained correlation equation can be used to correlate with the 159 sorts of SCS of the different bridge carbon in cinnamyl aniline derivatives. The correlation coefficient is 0.9993, and the standard deviation is only 0.53 ppm. The multi-parameter correlation equation can be recommended to predict well the corresponding bridge carbons SCS of disubstituted cinnamyl anilines.
