Heterocyclic Conjugated Polymer Nanoarchitectonics with Synergistic Redox-Active Sites for High-Performance Aluminium Organic Batteries

Abstract

The development of cost-effective and long-life rechargeable aluminium ion batteries (AIBs) shows promising prospects for sustainable energy storage applications. Here, we report a heteroatom π-conjugated polymer featuring synergistic C=O and C=N active centres as a new cathode material in AIBs using a low-cost AlCl₃ /urea electrolyte. Density functional theory (DFT) calculations reveal the fused C=N sites in the polymer not only benefit good π-conjugation but also enhance the redox reactivity of C=O sites, which enables the polymer to accommodate four AlCl₂ (urea)₂ ⁺ per repeating unit. By integrating the polymer with carbon nanotubes, the hybrid cathode exhibits a high discharge capacity and a long cycle life (295 mAh g^-1 at 0.1 A g^-1 and 85 mAh g^-1 at 1 A g^-1 over 4000 cycles). The achieved specific energy density of 413 Wh kg^-1 outperforms most Al-organic batteries reported to date. The synergistic redox-active sites strategy sheds light on the rational design of organic electrode materials.

Keywords: AlCl3/Urea Electrolyte; Aluminium Batteries; Heterocycles; Polymer Electrodes; Redox Chemistry.

Scheme 1

Illustration of a conjugated polymer with synergistic C=O and C=N redox centres for low‐cost Al–organic battery in an AlCl₃/urea electrolyte.

Figure 1

a) Structure of isolated building block of pure PYTQ polymer. b) The optimised structure of PYTQ polymer with one AlCl₂(urea)₂ ⁺. The numbers in the structures show the calculated Bader charge values for the N and O atoms of the polymer before and after interaction with AlCl₂(urea)₂ ⁺. c) Charge density difference for the optimised structure with one AlCl₂(urea)₂ ⁺. d) Modified configuration when N are replaced with C−H. e) Configuration revolution of PYTQ polymer upon multi‐step AlCl₂(urea)₂ ⁺ accommodation. VESTA is used to produce the figures.

Figure 2

a) CV profiles. b) Galvanostatic discharge/charge profiles of PYTQ‐CNT, PYTQ, and CNT electrodes at the current density of 0.2 A g⁻¹. c) Rate capability at different current densities. d) Cycling stability of PYTQ‐CNT and PYTQ electrodes at the current density of 1 A g⁻¹. e) Ragone plots of electrode materials in AIBs.[ ⁵ , ⁸ , ¹⁹ , ²⁰ , ²¹ , ²⁵ , ³¹ ] The specific energy/power values are calculated based on the performances of cathode materials.

Figure 3

a) Different states in the charge‐discharge curve for ex situ characterizations. b) Ex situ FTIR spectra. c) Ex situ XPS survey spectra, and d) high‐resolution XPS spectra Al 2p, Cl 2p, C 1s, N 1s regions of pristine, discharged and charged states. e) The proposed redox mechanism of PYTQ polymer as cathode material in an aluminium battery with AlCl₃/urea electrolyte.

Figure 4

Electrochemical kinetic analysis of the PYTQ‐CNT electrodes. a) CV profiles at different scan rates. b) The corresponding plots of log (peak current, i) vs. log (scan rate, v) and the slop b of the redox peaks. c) The capacitive contributions in PYTQ‐CNT electrodes at different scan rates. d) The CV profile with the pseudocapacitive contribution of PYTQ‐CNT electrodes at a scan rate of 1.0 mV s⁻¹.