Na0.67Ni0.33Mn0.67O2 is a prospective layered cathode material for sodium-ion batteries owing to its low cost, ease of synthesis, and high specific capacity. However, due to direct contact with electrolytes during the cycling process, the cyclic stability is not satisfied. To address this issue, magnesium oxide (MgO) surface modification was performed in this study to improve the material’s cycling properties. MgO layers of various thicknesses were successfully coated onto the cathode, and their electrochemical performances were thoroughly investigated. Among the as-prepared samples, the 2 wt% MgO-coated sample demonstrated the best rate capability and cycling stability. It had an initial reversible discharge capacity of 105 mAh g−1 in the voltage range from 2.0 to 4.5 V at 0.2 C with a high cycle retention of 81.5%. Electrochemical impedance spectroscopy (EIS) results showed that the 2 wt% MgO-coated electrode had the highest conductivity due to the smaller charge transfer resistance (Rct) value. All the test results show that the MgO modification improves the electrochemical properties of Na0.67Ni0.33Mn0.67O2 cathode material. This research could lead to the development of a promising strategy for improving the electrochemical performance of next-generation sodium-ion batteries.

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High manganese austenitic steel has attracted increasing attention for its application in liquefied natural gas storage tank materials due to its excellent ductility and low cost. This paper presents an overview of the research progress of high manganese austenitic steel in recent years. As a structural material used at a low temperature environment, high manganese steel should not only have certain strength, but also good toughness to prevent brittle fracture at a low temperature. In this work, factors affecting mechanical properties of high manganese steel are discussed, possible reasons for the deterioration of low-temperature properties are analyzed, and the strengthening and toughening mechanisms of materials are elaborated, which may be beneficial to improve properties of high manganese austenitic steel.

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The effect of Cl− concentration on stress corrosion cracking (SCC) susceptibility of high manganese steel was investigated by slow strain rate tensile (SSRT) test, electrochemical test, and immersion test in different NaCl concentration solutions. The results show that the SCC susceptibility of the test steel first increases and then decreases with the increase in Cl− concentration. When the NaCl concentration was 10.5%, the SCC susceptibility was the highest, and the fracture showed river-like transgranular quasi-cleavage morphology, obvious tearing ridge, and strong brittle fracture characteristics. The corrosion current density of the sample first increases and then decreases with the increase in Cl− concentration in the corrosive medium. The corrosion electrochemical reaction and corrosion product layer play a synergistic role in SCC in low concentration Cl− medium. The enrichment of alloying element compounds in the corrosion layer leads to the local acidification below the corrosion layer, which promotes the anodic dissolution (AD) and forms pitting corrosion on the substrate surface. When the Cl− concentration is high, the local AD and hydrogen embrittlement (HE) caused by the dissolved oxygen will be weakened, and SCC susceptibility is reduced.