A graphene@framework polymer derived from addition polymerization of phthalocyanine/dicarboxaldehyde as a negative material for lithium-ion batteries

A new grid framework polymer (β-4,4′-biphenyl dicarboxaldehyde phthalocyanine nickel (BDC-NiPc)) is synthesized by the addition polymerization of tetraamino-substituted nickel phthalocyanine with 4,4′-biphenyl dicarboxaldehyde. The obtained BDC-NiPc shows very low solubility in organic electrode solvents such as ethylene carbonate(EC), diethyl carbonate(DEC), methyl ethyl carbonate(MEC) and propene carbonate(PC), resulting in better stability in electrolyte solvents, which is highly beneficial for the cycling stability of a battery electrode. Moreover, BDC-NiPc displays a porous structure and large specific surface area, which exposes many active points and provides more lithium-ion transmission channels. As a result, lithium-ion batteries incorporating a BDC-NiPc electrode show superior electrochemical energy storage performance. The BDC-NiPc electrode presents an initial discharge capacity of 631.52 mA h g−1. In the first 30 cycles, the capacity slightly decreases and then gradually increases, and the discharge capacity increases to 1163.6 mA h g−1 after 762 cycles, which represents an increase of 84.25%. Thereafter, to verify the observed gradual improvement of the electrode performance, a graphene composite BDC-NiPc electrode (BDC-NiPc@GN) was prepared, which showed significantly improved performance compared with the pristine BDC-NiPc electrode. This graphene composite and a series of characterization analyses fully confirm that the porous organic framework structure and the dispersion and conductivity of the active substance are the crucial factors affecting the behaviors of the organic electrode material in lithium-ion batteries.