Rechargeable halide-ion batteries (HIBs) are good candidates for large-scale due to their appealing energy density, low cost, and dendrite-free features. However, state-of-the-art electrolytes limit the HIBs’ performance and cycle life. Here, via experimental measurements and modelling approach, we demonstrate that the dissolutions in the electrolyte of transition metal and elemental halogen from the positive electrode and discharge products from the negative electrode cause the HIBs failure. To circumvent these issues, we propose the combination of fluorinated low-polarity solvents with a gelation treatment to prevent dissolutions at the interphase, thus, improving the HIBs’ performance. Using this approach, we develop a quasi-solid-state Cl-ion-conducting gel polymer electrolyte. This electrolyte is tested in a single-layer pouch cell configuration with an iron oxychloride-based positive electrode and a lithium metal negative electrode at 25 °C and 125 mA g–1. The pouch delivers an initial discharge capacity of 210 mAh g–1 and a discharge capacity retention of almost 80% after 100 cycles. We also report assembly and testing of fluoride-ion and bromide-ion cells using quasi-solid-state halide-ion-conducting gel polymer electrolyte.

One main challenge of realizing high-energy-density lithium−sulfur batteries is low active materials utilization, excessive use of inert components, high electrolyte intake, and mechanical instability of high-mass-loading sulfur cathodes. Herein, chunky sulfur/graphene particle electrodes were designed, where active sulfur was confined in vertically aligned nanochannels (width ∼12 nm) of chunky graphenebased particles (∼70 μm) with N, O-containing groups. The short charge transport distance and low tortuosity enabled high utilization of active materials for high-mass-loading chunky sulfur/graphene particle electrodes. The intermediate polysulfide trapping effect by capillary effect and heteroatoms-containing groups, and a mechanically robust graphene framework, helped to realize stable electrode cycling. The as-designed electrode showed high areal capacity (10.9 mAh cm −2 ) and high sulfur utilization (72.4%) under the rigorous conditions of low electrolyte/active material ratio (∼2.5 μL mg −1 ) and high sulfur loading (9.0 mg cm −2 ), realizing high energy densities (520 Wh kg −1 , 1635 Wh L −1 ).

Non–aqueous rechargeable multivalent metal (Ca, Mg, Al, etc.) batteries are promising for large–scale energy storage due to their low cost. However, their practical applications face formidable challenges owing to low electrochemical reversibility and dendrite growth of multivalent metal anodes, sluggish kinetics of multivalent ion in metal oxide cathodes, and poor electrode compatibility of flammable organic electrolytes. To overcome these intrinsic hurdles, we develop aqueous multivalent ion batteries to replace the prevailing non–aqueous multivalent metal batteries by using wide–window super–concentrated aqueous gel electrolytes, the versatile high–capacity sulfur anodes, and high–voltage metal oxide cathodes. This rationally designed aqueous battery chemistry enables the long–lasting multivalent ion batteries featured with increased high energy density, reversibility and safety. As a demonstration model, a calcium ion−sulfur||metal oxide full cell exhibited a high energy density of 110 Wh kg–1 with outstanding cycling stability. Molecular dynamics modelling and experimental investigations revealed that the side reactions could be significantly restrained through the suppressed water activity and formation of protective inorganic solid electrolyte interphase in the aqueous gel electrolyte. The unique redox chemistry has also been successfully extended to aqueous magnesium ion and aluminum ion−sulfur||metal oxide batteries. This work will boost aqueous multivalent ion batteries for low−cost large–scale energy storage.