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Molten chloride salts are promising advanced high-temperature (400-800°C) thermal energy storage (TES) and heat transfer fluid (HTF) materials in next generation concentrated solar power (CSP) plants for higher energy conversion efficiencies. However, severe corrosion of structural materials in contact with molten chloride salts is one of the most critical challenges limiting their applications at elevated temperatures. In this work, two corrosion mitigation strategies are investigated to alleviate the hot corrosion of structural materials in molten chloride salts: (1) adding corrosion inhibitor and (2) using a Fe-Cr-Al alloy with a protective alumina layer on the surface after pre-oxidation. Three commercial high temperature Fe-Cr-Ni alloys (SS 310, Incoloy ® 800 H and Hastelloy ® C-276) were exposed to molten MgCl 2 -NaCl-KCl (60-20-20 mole.-%) mixed salts with 1 wt.-% Mg as corrosion inhibitor, for 500h at 700°C under inert atmosphere. By addition of the Mg inhibitor, the corrosion rates of the studied alloys were found to be significantly reduced, more precisely by ~83 % for SS 310, ~70 % for In 800 H and ~94 % for Ha C-276 compared with the exposure tests without Mg addition. To assess the second mitigation strategy two pre-oxidized alumina forming Fe-Cr-Al alloys were exposed to the same molten chloride salts without Mg corrosion inhibitor under the same conditions. It is observed that the adherent alumina scales can effectively inhibit the dissolution of Cr and Fe and the bulk penetration of corrosive impurities. Overall, both strategies offer enormous potential for enhancing the expected lifetime of commercial alloys in molten chloride salts. Highlights  By Mg-addition the corrosion rates of alloy SS 310, In 800 H and Ha C-276 are significantly reduced. 2  Adding Mg inhibitor not only mitigates the corrosion caused by impurities, but also promotes the formation of protective MgO layer on metal surfaces.  The corrosion mitigation mechanism of Fe-Cr-Ni based alloys in molten chloride salts by adding Mg is discussed. Pre-oxidized alumina forming Fe-Cr-Al alloys show promising corrosion resistance and stability in molten chloride salts at 700°C for 500h exposure.

Simple magnesium salts with high electrochemical and chemical stability and adequate ionic conductivity represent a new-generation electrolyte for magnesium (Mg) batteries. Similar to other Mg electrolytes, the simple-salt electrolyte also suffers from high charge-transfer resistance on the Mg surface due to the adsorbed species in the solution. In the current study, we built a model Mg cell system with the Mg[B(hfip) 4 ] 2 /DME electrolyte and Chevrel phase Mo 6 S 8 cathode, to demonstrate the effect of such anode−electrolyte interfacial properties on the full-cell performance. It was found that the cell required additional activation cycles to achieve its maximal capacity. The activation process is mainly attributed to the conditioning of the anode−electrolyte interface, which could be boosted by introducing an additive amount of Mg(BH 4 ) 2 to the Mg[B(hfip) 4 ] 2 /DME electrolyte. Electrochemical and spectroscopic analyses revealed that the Mg(BH 4 ) 2 additive helps to remove the native oxide layer and promotes the formation of a solid electrolyte interphase layer on Mg. As a result, the full cell with the additive-containing electrolyte delivered a stable capacity from the second cycle onward. Further battery tests showed a reversible cycling for 600 cycles and an excellent rate capability, indicating good compatibility of the Mg(BH 4 ) 2 additive. The current study not only provides fundamental insights into the interfacial phenomena in Mg batteries but also highlights the facile tunability of the simple-salt Mg electrolytes.

Rechargeable calcium batteries possess attractive features for sustainable energy-storage solutions owing to their high theoretical energy densities, safety aspects and abundant natural resources. However, divalent Ca-ions and reactive Ca metal strongly interact with cathode materials and non-aqueous electrolyte solutions, leading to high charge-transfer barriers at the electrode-electrolyte interface and consequently low electrochemical performance. Here, we demonstrate the feasibility and elucidate the electrochemical properties of calcium-tin (Ca–Sn) alloy anodes for Ca-ion chemistries. Crystallographic and microstructural characterizations reveal that Sn formed from electrochemically dealloying the Ca–Sn alloy possesses unique properties, and that this in-situ formed Sn undergoes subsequent reversible calciation/decalciation as CaSn3. As demonstration of the suitability of Ca–Sn alloys as anodes for Ca-ion batteries, we assemble coin cells with an organic cathode (1,4-polyanthraquinone) in an electrolyte of 0.25 M calcium tetrakis(hexafluoroisopropyloxy)borate in dimethoxyethane. These electrochemical cells are charged/discharged for 5000 cycles at 260 mA g−1, retaining a capacity of 78 mAh g−1 with respect to the organic cathode. The discovery of new class of Ca–Sn alloy anodes opens a promising avenue towards viable high-performance Ca-ion batteries.

The magnesium-sulfur (Mg-S) battery has attracted considerable attention as a candidate of post-lithium battery systems owing to its high volumetric energy density, safety, and cost effectiveness. However, the known shuttle effect of the soluble polysulfides during charge and discharge leads to a rapid capacity fade and hinders the realization of sulfur-based battery technology. Along with the approaches for cathode design and electrolyte formulation, functionalization of separators can be employed to suppress the polysulfide shuttle. In this study, a glass fiber separator coated with decavanadate-based polyoxometalate (POM) clusters/carbon composite is fabricated by electrospinning technique and its impacts on battery performance and suppression of polysulfide shuttling are investigated. Mg-S batteries with such coated separators and non-corrosive Mg[B(hfip) 4 ] 2 electrolyte show significantly enhanced reversible capacity and cycling stability. Functional modification of separator provides a promising approach for improving metal-sulfur batteries.

Multivalent batteries show promising prospects for next‐generation sustainable energy storage applications. Herein, we report a polytriphenylamine (PTPAn) composite cathode capable of highly reversible storage of tetrakis(hexafluoroisopropyloxy) borate [B(hfip)4] anions in both Magnesium (Mg) and calcium (Ca) battery systems. Spectroscopic and computational studies reveal the redox reaction mechanism of the PTPAn cathode material. The Mg and Ca cells exhibit a cell voltage >3 V, a high‐power density of ∼∼3000 W kg−1 and a high‐energy density of ∼∼300 Wh kg−1, respectively. Moreover, the combination of the PTPAn cathode with a calcium‐tin (Ca−Sn) alloy anode could enable a long battery‐life of 3000 cycles with a capacity retention of 60 %. The anion storage chemistry associated with dual‐ion electrochemical concept demonstrates a new feasible pathway towards high‐performance divalent ion batteries.

Rechargeable magnesium batteries are gaining attention as promising candidates for large-scale energy storage applications because of their potentially high energy, safety and sustainability. However, the development of Mg batteries is impeded by the lack of efficient cathode materials and compatible electrode-electrolyte combinations. Herein, we demonstrate a new poly(1,4-anthraquinone)/Ketjenblack composite (14PAQ@KB) in combination with non-corrosive magne-sium tetrakis(hexafluoroisopropyloxy) borate Mg[B(hfip) 4 ] 2 (hfip = OC(H)(CF 3 ) 2 ) electrolyte towards high-energy and longlifespan Mg batteries. This combination exhibits prominent electrochemical performance including a maximum discharge capacity of 242 mA h g À 1 (approximately 93 % of the theoretical capacity), superior cycling stability (81 mA h g À 1 after 1000 cycles), and excellent rate capability (120 mA h g À 1 at 5 C).

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