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P2-Na0.67Ni0.33Mn0.67O2 is a promising cathode for sodium-ion batteries in large-scale energy storage applications due to their advantages of low cost, high energy density, superior sodium ion conductivity, and good air stability, whereas their structural rearrangement at high voltage above 4.2 V and the appearance of Na+/vacancy ordering result in fast capacity decay and poor rate capability, which lead to unsatisfactory performance that fails to meet practical demands. In this paper, we propose a dual-ion doping strategy coupling both cations and anions. Thanks to their collaborative effect, the optimized cathode material P2-Na0.67Ni0.33Mn0.57Ti0.1O1.95F0.05 exhibits greatly improved stability in the voltage range of 2.3–4.3 V at a high rate. Specifically, it retains 79.59% of its initial capacity after 500 cycles at 5C, in contrast to 19.91% of the undoped material. Experimental and theoretical investigations on working mechanisms illustrate that Ti4+ and F− dual-ion doping effectively suppresses the P2–O2 phase transition and facilitates sodium ion diffusion kinetics. Moreover, a P2-Na0.67Ni0.33Mn0.57Ti0.1O1.95F0.05//hard carbon full cell delivers a high reversible capacity of 122 mA h g−1 with a high energy density of 365 W h kg−1 based on the mass of the cathode material. This study provides an efficient strategy to promote the application of layered oxide cathodes in practical sodium-ion batteries. [ABSTRACT FROM AUTHOR]

The heavy metal ion hexavalent chromium (Cr(VI)) in wastewater significantly threatens public health. Heterojunction photocatalysts typically demonstrate high reduction efficiency in water for Cr(VI) contamination. Overcoming the drawbacks of single metal organic frameworks (MOFs) or covalent organic frameworks (COFs), MOF@COF heterostructures inherit the advantages of large porosity, high surface area, and multiple active sites of single components. Herein, we report novel hybrid UiO-66-NH2@HDU-25 heterojunctions based on a condensation reaction. The optimal ratio of UiO-66-NH2@HDU-25 presented significantly superior photocatalytic activity to most reported MOFs and COFs due to heterojunction formation, which promoted charge separation. Under identical conditions, the optimally formulated UiO-66-NH2@HDU-25 could remove over 99% of Cr(VI), approximately 1.8 and 2.6 times the original UiO-66-NH2 and HDU-25 levels. Furthermore, the UiO-66-NH2@HDU-25 (8 : 1) heterojunction demonstrated favorable reusability and stability over five reaction cycles. Various experiments and density functional theory (DFT) calculations investigated the charge carrier transport pathways and possible photocatalytic mechanisms. The Z-scheme mechanism for the photocatalytic Cr(VI) reduction by UiO-66-NH2@HDU-25 was proposed and validated. This work aims to open new horizons for preparing novel photocatalyst heterojunctions with excellent visible light responsiveness for environmental water remediation. [ABSTRACT FROM AUTHOR]

Abstract: LiFePO4/C composite was prepared at 700 ∘C for 5 h by gas-phase diffused permeation (DP) and its electrochemical properties were improved by Al3+ diffused permeation on the surface of LiFePO4/C. The structural and electrochemical properties were examined by means of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), cyclic voltammetry (CV) and charge–discharge cycling performance. XRD and SEM analysis showed that LiFePO4/C and Al3+ permeation LiFePO4/C are olivine-type phase and the average particle size was about 100–250 nm with uniform distribution. LiFePO4/C exhibits initial discharge capacity of 131.9 and 101 mAh g−1 at 0.1 C and 3 C, respectively. While the cathode material of Al3+ permeation LiFePO4/C shows a better performance and has initial discharge capacity of 152.9 and 108.3 mAh g−1 corresponding to 0.1 C and 3 C. [Copyright &y& Elsevier]