Novel triphenylamine-based polyimides as promising organic cathode for lithium/sodium-ion batteries

Abstract

Organic carbonyl cathode materials are expected to be excellent candidates for widespread application in next-generation lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs) owing to their high theoretical specific capacity, low cost, sustainability, environmental friendliness, and structural diversity. However, organic carbonyl cathode materials face some key challenges, including high solubility in organic electrolytes and low discharge platform, which hinder their practical applications. Herein, a novel poly(4-aminotriphenylamine-3,3′,4,4′-benzophenone tetramide) (PTNBI) electrode has been synthesized through the polymerization of 4-aminotriphenylamine with 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA), addressing the two crucial issues of solubility and low discharge platform. As a cathode material for LIBs, the PTNBI electrode exhibits a high discharge platform of 3.5 V, and a good initial specific discharge capacity of ∼135 mA h g⁻¹ at 50 mA g⁻¹, whilst retaining good cycling stability after 100 cycles. The CV curves show that the redox potentials (∼3.5 V/∼4.0 V) correspond to the process of de-doping/doping of the PF₆⁻ anions at the triphenylamine unit, whilst the redox potentials (∼2.26 V/∼2.41 V) correspond to the insertion/extraction of lithium ions at the carbonyl group of the anhydride. Meanwhile, as a cathode material for SIBs, the PTNBI electrode delivers a discharge platform of 3.0 V, and an initial specific discharge capacity of ∼106 mA h g⁻¹ at 50 mA g⁻¹ with remarkable cycling performance. The PTNBI material incorporates a triphenylamine unit with a high discharge voltage and a carbonyl anhydride with high theoretical capacity, which effectively addresses the issues of low discharge platform and high solubility, thereby enhancing the specific capacity. This approach provides guidance for other organic electrode materials by tackling high solubility and low discharge platform challenges.