Rechargeable zinc-air batteries have gradually attracted much attention worldwide due to their high capacity, high energy density and low price. Oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) correspond to the charging and discharging processes in rechargeable zinc-air battery, respectively. At present, commercial Pt/C and IrO₂ catalysts hinder the large-scale application of zinc-air batteries due to low reserves, high prices and poor stability. Therefore, exploring high performance, low cost and high stability with dual functional catalysts is important for the development of rechargeable zinc-Air batteries. The metal-organic frameworks (MOFs) have high specific surface area, structural stability, good catalytic activity and application prospects. Transition metals have high catalytic activity, but they are easily corroded in alkaline solutions. Non-metallic materials are inexpensive and have catalytic activity under a specific structure. Taking the advantages of the above-mentioned materials, ZIF-67 was used as the precursor, along with heteroatom doping and high temperature heat treatment to prepare a porous carbon material FeNi-CoP/NC containing multiple transition metals and non-metal particles as a zinc-air battery catalyst. Physical and chemical characterizations, and catalytic performance testing of the catalyst were carried out by SEM, XRD, XPS and electrochemical methods, and finally assembled into a full battery for charge and discharge performance experiments. The results showed that the prepared FeNi-CoP/NC catalyst had rhombohedral dodecahedron structure and specific surface area of 402 m²·g^-1. The half-wave potential went up to 0.83 V when used as an electrocatalyst for oxygen reduction reaction in zinc-air batteries. After 5000 cycles, the current density only lost 5.06% and the half-wave potential changed little, revealing a good stability; the overpotential of OER was 290 mV at the current density of 10 mA·cm^-2. And the catalyst could be kept stable for 12 h at 100 mA·cm^-2. The performance test of the full battery demonstrated that the peak power density was as high as 150 mW·cm^-2, and a narrow potential gap of 0.6 V was maintained at the current density of 3 mA·cm^-2. The good catalytic activity might be mainly attributable to the fact that doping with multiple metal elements can provide rich valences to accelerate the four-step coordinated proton/electron transfer step, and the good conductivity of CoP also effectively improves the catalytic activity of FeNi-CoP/NC. This work provides useful guidance for improving the electrocatalytic performance of the catalyst through simple doping and heat treatment strategies.

With the rapid development of electric vehicles, enormous demands are made for higher energy density, better cycling performance and lower cost of lithium-ion batteries (LIBs). As an important high capacity cathode material for LIBs, the high nickel layered oxide material LiNi_0.8Co_0.1Mn_0.1O₂(NCM811) can reach an energy density of 760 Wh·kg^-1. The ultra-high nickel ternary positive electrode material (LiNi_1-x-yCo_xMn_yO₂, x ≥ 0.90) has a specific capacity of more than 210 mAh·g^-1, and can realize higher energy density. Besides, an ultra-high nickel material uses lower cobalt content, and reduces material cost. Tungsten oxide coating has been reported to effectively improve the electrochemical performance of ternary materials, but no reports can be found for tungsten oxide coating modified ultra-high nickel cathode materials. On the other hand, phosphate coating has been widely used in surface coating modification of high nickel cathode materials to improve their electrochemical performance, but it is difficult to achieve uniform coating. Phosphotungstic acid (PTA) can function as a double coating with tungsten oxide (WO₃) and phosphate at the same time, which is expected to achieve better electrochemical performance than single coating. In this work, LiNi_0.96Co_0.02Mn_0.02O₂ (NCM96) was selected. The NCM96 precursor and PTA/WO₃ were dispersed in ethanol for mixing. After drying, the product was mixed with lithium source and sintered, so as to achieve tungsten oxide and phosphotungstic acid coating. The structures, morphologies and electrochemical performances of the PTA modified and WO₃ modified NCM96 materials are compared. The results showed that, in the process of either PTA or WO₃ coating modification, W and P elements were not doped into the lattice of NCM96 material, forming a relatively uniform coating structure, in which the WO₃ coating modification led to single element coating structure, while the PTA coating modification led to P/W double elements coating structure. Electrochemical test and analysis revealed that the two types of the surface modification methods had no effects on the first cycle discharge capacity of the NCM96 material, while had effectively improved the long-term cycling performances. By comparing the high temperature electrochemical performance of the WO₃ and PTA coated samples, the PTA coated sample NCM96@1wt%PTA material exhibited superior cycling stability at 60 °C indicating that the P/W double elemental surface modification with PTA is superior to the W single elemental modification with WO₃.

This paper systematically summarizes the research progress of hard carbon anode materials in sodium ion batteries(SIBs) and the development of the corresponding sodium storage mechanism in recent years, and reviews the performance improvement strategies of hard carbon materials from the aspects of structural design and electrolyte regulation. The effects of the selection of precursors, carbonization temperature, pretreatment, pore formers, heteroatom doping, material compounding, electrolyte regulation and pre-sodiumization on the sodium storage performance of hard carbon anode materials are briefly described. This paper provides new insights into the design, synthesis and electrolyte matching of high-performance and low-cost hard carbon materials, and looks forward to the direction of further research and development of SIBs hard carbon anode materials in the future.

Behaviors of electrified interface under different applied potentials/charges play the central role in electroplating process and electrochemical corrosion. The mechanism, however, is unclear yet for a surface atom dissolving/depositing from/on an electrode surface under an applied potential. The energy barrier along the reaction path is the key variable. The present work conductes hybrid first-principle/hybrid calculations to study the direct and indirect dissolution/deposition of a Cu atom on perfect/stepped Cu(111) planar electrodes in an electrolyte under different excess charges. Energy profiles present a linear relationship between the energies of the initial/final state and the activation state of different reaction paths under different applied charges, obeying the Brønsted-Evans-Polanyi relation. The activation energy is also a linear or quadratic function of charge density per unit surface area during direct and indirect dissolution/deposition. These simple relations provide a simple way to deduce the activation energy from the energy of stable states under different charge levels. Analytical formula indicates the occurrence of automatic dissolution from step sites at the applied surface charge density larger than 0.135 |e|/Ų. When the applied charge density is between 0.086 |e|/Ų and 0.105 |e|/Ų, the energy barrier for electrodeposition to the planar surface becomes smaller than zero, while there is a small barrier for surface diffusion, indicating indirect deposition with surface diffusion as the rate determining step. When the applied surface charge density further decreases to lower than 0.086 |e|/Ų, the concentration effects of the available deposition sites on steps and planar surface are ignored, becoming mainly the direct deposition because of the energy barrier of surface diffusion.