Radially oriented Ni₃(HITP)₂ microspheres as high-performance anode materials for Li-ion capacitors with exceptional energy density and cycling stability

Developing of high-energy, high-power-density energy storage devices is challenging. Despite being promising electrode materials for these devices, metal–organic frameworks (MOFs) have poor electrical conductivity and weak ligand–metal coordination. Here, the highly conductive MOF, Ni₃(HITP)₂, which comprises radially oriented microspheres, is adopted as the anode for Li-ion capacitors (LICs). The half-cell demonstrates high reversible capacity (834 mAh g⁻¹) at 50 mA g⁻¹ with minimal capacity reduction, attributable to the participation of C and N functional groups of the ligand and Ni²⁺ in the redox reactions during charge/discharge. Especially, density functional theory calculations show that, apart from the inner rings, participation of the outer rings of Ni₃(HITP)₂ in the redox reactions is responsible for the high Li ⁺ storage capacity. An LIC with a Ni₃(HITP)₂ anode and commercial activated-carbon cathode demonstrates high specific energy (120.7 Wh kg⁻¹) at 89.2 W kg⁻¹, nearly twice as high as that of graphite-based LICs, and maintains specific energy of 25.8 Wh kg⁻¹ even at high specific power (7.16 kW kg⁻¹), over the range 1–4.4 V, along with high cycling stability (76% capacity retention over 10000 cycles). The proposed radially oriented Ni₃(HITP)₂ microspheres have potential for application as the anode in high-performance energy storage devices.