Graphene oxide coated functional separators as efficient metal chloride blocking layers for chloride ion batteries

Chloride ion batteries, as attractive energy storage systems, possess the merits of abundant resources, reliable safety, and high theoretical volumetric energy density. Among the current cathode materials for chloride ion batteries, metal chlorides with high theoretical gravimetric energy density have been regarded as some of the most promising candidates as cathode materials. However, owing to the dissolution of metal chlorides into the liquid electrolyte, forming soluble complex anions (e.g. [CuCl₄]²⁻ and [NiCl₄]²⁻) that subsequently shuttle to the anode, their cycling lifespans are typically limited to just one cycle. Herein, graphene oxides with different loading contents are coated onto a commercial glass fiber separator by vacuum filtration and sandwiched between a CuCl₂ or NiCl₂ cathode and the separator. The as-prepared graphene oxide coating layers with appropriate channel size allow the selective passage of Cl⁻ while blocking the transportation of complex anions across the separator. Through the incorporation of the permselective GO coating layers, the electrochemical performance of the metal chloride cathodes is significantly enhanced. The maximum initial discharge capacities of 452 and 541 mA h g⁻¹ at 10 mA g⁻¹ can be achieved with the CuCl₂ and NiCl₂ cathodes, respectively. Reversible capacities of 144 mA h g⁻¹ and 177 mA h g⁻¹ are still retained after 30 cycles for the CuCl₂ and NiCl₂ cathodes, respectively. The corresponding energy densities of 1107 W h kg⁻¹ for CuCl₂ and 1022 W h kg⁻¹ for NiCl₂ are superior to those of previously reported cathodes.