Multifunctional Organic Electrode Materials for Sustainable and Fast-Charging Batteries

Abstract

Due to the ever-increasing energy consumption and environmental pollution by the fossil fuel-based motor vehicles, the development and application of electric vehicles attract considerable research interests from academia and industry. A key challenge for the state-of-the-art electric vehicles is the slow charge rate, which requires several hours to fully recharge the batteries in electric vehicles. Further increasing the charge rate for electric vehicle can reduce the recharge time, but it results in the failure of batteries in electric vehicles because of the limited electron/ion conductivity and slow electrochemical reaction rate of the battery materials. Therefore, exploiting new battery materials and electrode structures becomes a critical and urgent task for the development of electric vehicles. Organic materials and polymers with the advantages of low cost, abundance, high sustainability and high structural tunability are promising electrode materials for fast-charging batteries. Several novel conjugated organic materials and porous polymers based on azo group, imine group and carbonyl group are designed and synthesized for alkali-ion batteries. These multifunctional organic electrode materials demonstrate exceptional electrochemical performance in terms of long cycle life and fast-charging capability. High specific capacity and long cycle life have been achieved at both low and high current densities. At the high current density of up to 25C and 10 A/g, these new materials can still retain a reversible capacity above 100 mA/g for thousands of cycles in Li-ion and Na-ion batteries, representing one of the best performances in rechargeable batteries. To gain fundamental insights into the reaction mechanisms and fast kinetics of these new materials, X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, cyclic voltammetry, electrochemical impedance spectroscopy (EIS), and galvanostatic intermittent titration technique (GITT) are used to study the interaction between functional groups (C=O/C=N/N=N) and cations (Li+/Na+), as well as ion diffusivity and interfacial impedance. The results indicate that the fast-charging capability of multifunctional organic electrode materials is attributed to the extended conjugation structure, large surface area and high porosity. Developing conjugated and porous structures is critical for the fast reaction kinetics of organic electrode materials. Therefore, our study provides guidance for the rational structure design and performance optimization for sustainable and fast-charging organic batteries.