# Conjugation-Induced Self-Selective Coordination Enables Organic Polymers with Low-Temperature Ammonium-Ion Storage

## TL;DR

A new organic polymer enables efficient ammonium-ion storage at low temperatures, improving energy storage safety and performance.

## Contribution

A self-selective coordination mechanism in a conjugated polymer enables low-temperature ammonium-ion storage with high stability.

## Key findings

- The polymer delivers 107 mAh g−1 at 20 A g−1 under 25 °C with 99% capacity retention at −50 °C.
- The material enables stable cycling for over 3,000 cycles at −50 °C.
- Symmetric carbonyl groups act as active sites for reversible NH4+ coordination.

## Abstract

Aqueous ammonium-ion (NH4+) batteries/capacitors, recognized for inherent high safety and fast diffusion kinetics, are a promising alternative for sustainable energy storage. However, the development of ammonium-ion energy storage devices has been hindered by the poor compatibility between the distinctive solvation structure of NH4+ ions and conventional organic electrode materials, especially under low-temperature conditions. Here, a redox-active conjugated polymer with self-selective coordination mechanism is designed for achieving high-rate and low-temperature performance. The electron delocalization induced by the conjugated backbone facilitates rapid electronic transport in electrodes, delivering an ultrahigh-rate capacity of 107 mAh g−1 at 20 A g−1 under 25 °C and stable cycling performance with 99% capacity retention under −50 °C. Theoretical calculations and experimental investigations reveal that the inherent structural self-selectivity renders symmetrically arranged carbonyl groups as active binding sites for NH4+ storage, leading to a reversible 4-electron coordination process. Hence, the assembled all-organic hybrid ammonium-ion capacitor enables a long cycle life for over 3,000 cycles at −50 °C, which surpasses the lowest operating temperature reported for ammonium-ion devices, thus propelling the advancement of ammonium-ion energy storage technologies at low temperatures.