Highly reversible electrochemical reaction of insoluble 3D nanoporous polyquinoneimines with stable cycle and rate performance

Carbonyl compounds have potential for use as cathode materials of secondary batteries because of their large specific capacities, stable redox active centers, high efficiencies and ability to regenerate, however their intrinsic solubilities and low electrical conductivities present challenges to hinder their practical utilization. Here, three-dimensional nanoporous polyquinoneimines (PQ) were synthesized by hydrothermal polymerization reactions, and examined as electrode materials in lithium-ion batteries to solve these problems of solubility and electronic conductivity. The large specific surface area (116.95 m² g⁻¹) and abundant pore structure (0.2428 cm³ g⁻¹) of the PQ, which were formed by the anisotropic growth of nanosized rose flakes, shortened the lithium-ion diffusion path and reduced lithium solubility. The capacities of the PQ electrodes of 1 mg cm⁻² were 228 (1st cycle; theoretical capacity of PQ with 4 electron reaction is 228 mAh g⁻¹) and 103 (1000th) mAh g⁻¹ at 50 mA g⁻¹, and the declined rate per cycle at 200 mA g⁻¹ was only 0.05% (0.077 mAh g⁻¹ per cycle) within the first 1000 cycles. The capacity of the 500th cycle with a high load of 3 mg cm⁻² was 123 mAh g⁻¹, exhibiting a coulombic efficiency of 99%. The molecular structure during lithiation was calculated with density functional theory and showed that the robust bridge bond formed and promoted the electrochemical activity of the charge/discharge process.