An extended thiophene chain for Ni-based porphyrin derivatives enabling a high potential and long cycle life for electrochemical charge storage

Abstract

The development of traditional inorganic electrode materials has encountered a limitation due to the scarcity of transition metal elements. Inspired by the enriched resources and adjustable structural properties of organic electrode materials, here in, we designed and synthesized [5,10,15,20-tetrathienylporphinato](M)(II) (MTTP, M = 2H, Ni, Zn) and extended thiophene chain porphyrin derivatives [5,10,15,20-tetra(2,2′-bithiophen-5-yl)porphyrinato]M(II) (MT₂TP, M = 2H, Ni, Zn) as organic cathode materials in lithium/sodium batteries. By designing an extended thiophene chain, NiT₂TP shows weaker steric hindrance induced by intermolecular polymerization of a porphyrin complex compared with NiTTP. N and S are identified as multiple charge storage sites enabling high reversible capacity. The in situ polymerization occurs during the first charging process through the C_α–H of thiophene. Benefiting from the enhanced conjugated structure, NiT₂TP delivers a specific capacity of 100 mA h g⁻¹ at a current density of 1.0 A g⁻¹ and achieves an ultra-long stable cycling performance of up to 3000 cycles with a high voltage of 3.5 V (vs. Li⁺/Li) in organic lithium batteries. This cathode can also be extended in organic sodium batteries, in which NiT₂TP displays a reversible discharge capacity of 100 mA h g⁻¹ up to 1000 cycles with a high voltage of 3.0 V (vs. Na⁺/Na). This study puts forward a new avenue for the design of universal organic cathode materials with long-cycling stability and high voltage.