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Abstract Iron is a promising candidate for a cost‐effective anode for large‐scale energy storage systems due to its natural abundance and well‐established mass production. Recently, Fe‐ion batteries (FeIBs) that use ferrous ions as the charge carrier have emerged as a potential storage solution. The electrolytes in FeIBs are necessarily acidic to render the ferrous ions more anodically stable, allowing a wide operation voltage window. However, the iron anode suffers severe hydrogen evolution reaction with a low Coulombic efficiency (CE) in an acidic environment, shortening the battery cycle life. Herein, a hybrid aqueous electrolyte that forms a solid‐electrolyte interphase (SEI) layer on the Fe anode surface is introduced. The electrolyte mainly comprises FeCl₂and ZnCl₂as cosalts, where the Zn‐Cl anionic complex species of the concentrated ZnCl₂allows dimethyl carbonate (DMC) to be miscible with the aqueous ferrous electrolyte. SEI derived from DMC's decomposition passivates the iron surface, which leads to an average CE of 98.3% and much‐improved cycling stability. This advancement shows the promise of efficient and durable FeIBs. 

Amidst the rapid expansion of the electric vehicle industry, the need for alternative battery technologies that balance economic viability with sustainability has never been more critical. Here, we report that common lithium salts of Li2CO3 and Li2SO4 are transformed into cathode active mass in Li-ion batteries by ball milling to form a composite with Cu2S. The optimal composite cathode comprising Li2CO3, Li2SO4, and Cu2S, with a practical active mass loading of 12.5-13.0 mg/cm2, demonstrates a reversible capacity of 247 mAh/g based on the total mass of Cu2S and the lithium salts, a specific energy of 716 Wh/kg, and a stable cycle life. This cathode chemistry rivals layered oxide cathodes of Li-ion batteries in energy density but at substantially reduced cost and ecological footprint. Mechanistic investigations reveal that in the composite Li2CO3 serves as the primary active mass, Li2SO4 enhances kinetic properties and reversibility, and Cu2S stabilizes the resulting anionic radicals for reversibility as a binding agent. Our findings pave the way for directly using precursor lithium salts as cathodes for Li-ion batteries to meet the ever-increasing market demands sustainably. 

Abstract The narrow electrochemical stability window of water poses a challenge to the development of aqueous electrolytes. In contrast to non‐aqueous electrolytes, the products of water electrolysis do not contribute to the formation of a passivation layer on electrodes. As a result, aqueous electrolytes require the reactions of additional components, such as additives and co‐solvents, to facilitate the formation of the desired solid electrolyte interphase (SEI) on the anode and cathode electrolyte interphase (CEI) on the cathode. This review highlights the fundamental principles and recent advancements in generating electrolyte interphases in aqueous batteries. 

In the Mn₃O₄electrode, chloride ions are reversibly converted into atomic chlorine species. Trapped Zn²⁺cations aid in stabilizing these chlorine atoms in polychloride species.