A novel NaSn intermetallic improves critical electrochemical interfaces between molten sodium and NaSICON ceramic electrolyte at low temperatures (110 °C).

soluble intermediate products during charge-discharge can result in a crossover between the two electrodes and consequent self-discharge, resulting in a reduction in cell efficiency. Furthermore, with the traditional porous-separator approach, any dendrite formed with metal-based anodes could penetrate through the separator into the cathode, causing short-circuit and safety hazards.From the electrochemical point of view, many liquid-phase or gas-phase materials exhibit both high electrochemical capacity and high operating voltages. They are promising to be used as electrodes for electrochemical energy storage systems. [3] However, as discussed above, the chemical crossover issue in batteries with the traditional porous separator strictly limits the use of liquid or gaseous electrode materials in a battery. Therefore, alternative reliable separator-strategies must be developed to make good use of liquid or gaseous electrode materials. Separating the liquid-phase or gas-phase electrodes with a solid electrolyte provides a promising strategy to not only avoid the liquid (or gaseous)-reactant crossover, but also completely circumvents the metal dendrite concerns. However, at present, cationic solid electrolytes at ambient temperatures are practically limited to alkali-metal ions (e.g., Li + and Na + ions). Although these solid electrolytes can be used with any catholyte or anolyte solutions, they have previously been used only for the development of nonaqueous (with organic anolytes or with molten electrodes) Li + -or Na +ion batteries. [4] This is because under the traditional battery operating principle, the transporting ion (Li + or Na + ion) in the solid electrolyte is directly involved in the anode reaction. Therefore, Li-based or Na-based anode has to be adopted in a battery, respectively, with a Li + -ion or a Na + -ion solid electrolyte, and neither Li nor Na can be used in aqueous environments. [5] Divalent-ion-based battery chemistries (e.g., Zn and Fe) can be used in aqueous solutions, but solid electrolytes capable of transporting divalent ions are practically unavailable due to the higher charge and heavier mass of the ions. [6] In view of the above considerations, it is, therefore, impossible or difficult to develop aqueous batteries with the currently available solidstate electrolytes (Li + -ion and Na + -ion solid electrolytes).Herein, we demonstrate a unique mediator-ion strategy for the development of aqueous batteries with a solid-electrolyte separator by properly managing the solid-state electrolyte (SSE), anolyte (the aqueous electrolyte at the anode), and catholyte This study presents a battery concept with a "mediator-ion" solid electrolyte for the development of next-generation electrochemical energy storage technologies. The active anode and cathode materials in a single cell can be in the solid, liquid, or gaseous form, which are separated by a sodium-ion solid-electrolyte separator. The uniqueness of this mediator-ion strategy is that the redox reactions at the anode and the cathode are...

Large-scale energy storage for the electric grid will require low-cost and high-energy-density solutions. We demonstrate in this letter a rechargeable zinc-aqueous polysulfide battery in which a metallic zinc anode is separated from a liquid aqueous polysulfide catholyte by an alkali-metal-ion solid-state electrolyte, wherein the alkali metal ion is Na or Li. The solid-state electrolyte effectively separates the anode from the reactive polysulfide catholyte, preventing the crossover of the polysulfide species and maintaining good electrochemical performance with a reversible discharge capacity of 822 mA h g with nearly 100% Coulombic efficiency.

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Low-temperature molten sodium batteries show remarkable promise as the kind of low-cost, large-scale, reliable energy storage technology which is key to enabling a sustainable, safe, and resilient electric grid. Here, we describe a combination of cathode chemistry and engineered interfaces needed to reduce the molten sodium battery operating temperature from ∼300 °C to near 100 °C. This approach involves the development of a fully molten, inorganic sodium battery comprising a sodium anode, a NaSICON (Na 3 Zr 2 Si 2 PO 12 ) solid electrolyte separator, and a sodium iodide/aluminum bromide liquid catholyte operated at 110 °C. Battery performance is greatly improved by the application of a Sn coating on the anode-facing side of the NaSICON electrolyte and by the activation of a carbon felt current collector, together enabling the low-temperature molten sodium battery to achieve 200 cycles at 110 °C. The advancement of the low operating temperature molten sodium battery shows promise as a low-cost, large-scale energy storage system.