In Situ Synthesis of MOF-74 Family for High Areal Energy Density of Aqueous Nickel-Zinc Batteries

Limited by single metal active sites and low electrical conductivity, designing nickel-based metal-organic framework (MOF) materials with high capacity and high energy density remains a challenge. Herein, a series of bi/multimetallic MOF-74 family materials in situ grown on carbon cloth (CC) by doping Mx+ ions in Ni-MOF-74 is fabricated: NiM-MOF@CC (M = Mn2+, Co2+, Cu2+, Zn2+, Al3+, Fe3+), and NiCoM-MOF@CC (M = Mn2+, Zn2+, Al3+, Fe3+). The type and ratio of doping metal ions can be adjusted while the original topology is preserved. Different metal ions are confirmed by X-ray absorption fine structure (XAFS). Furthermore, these Ni-based MOF electrodes are directly utilized as cathodes for aqueous nickel-zinc batteries (NZBs). Among all the as-prepared electrodes, NiCo-MOF@CC-3 (NCM@CC-3), with an optimized Co/Ni ratio of 1:1, exhibits the best electrical conductivity, which is according to the density functional theory (DFT) theoretical calculations. The NCM@CC-3//Zn@CC battery achieves a high specific capacity of 1.77 mAh cm(-2), a high areal energy density of 2.97 mWh cm(-2), and high cycling stability of 83% capacity retention rate after 6000 cycles. The synthetic strategy based on the coordination effect of metal ions and the concept of binder-free electrodes provide a new direction for the synthesis of high-performance materials in the energy-storage field.