A recrystallized organic cathode with high electrical conductivity for fast sodium-ion storage†

Organic electrode materials have attracted much attention in the field of batteries owing to their low-cost, structure diversity and environmental friendliness. However, most of them suffer from low electrical conductivity, sluggish reaction kinetics, and poor cycle life. In this work, we develop a strategy of fabricating a naphthalene diimide-based sodium salt cathode with high electrical conductivity for facilitating the charge transfer and accelerating the reaction kinetics by the dissolution/reprecipitation process. The recrystallization process of naphthalene molecules in water enhances intermolecular π–π interactions, leading to the formation of a uniform rod-like morphology and significantly increasing its electrical conductivity, which allows fast charge transfer kinetics and high ionic conductivity of organic electrodes in sodium-ion batteries. Therefore, the recrystallized organic cathode (NDI-ONa-r) exhibits a high specific capacity of 145 mA h g⁻¹ at 0.1 A g⁻¹, excellent fast charge/discharge performance (70 mA h g⁻¹ at 20 A g⁻¹, about 127C), and an ultra-long cycle life of 30 000 cycles at 10 A g⁻¹ with a capacity retention of 87%. As a result, the NDI-ONa-r//HC full cells also show a high specific capacity of 140 mA h g⁻¹ at 0.1 A g⁻¹ and good rate performance. Our work presents a potential way to fundamentally facilitate fast electron transport and ion diffusion in organic electrode materials, which would motivate their application in high-performance sodium-ion batteries.