Disodium naphthalene dicarboxylate based negative electrode engineering for organic-inorganic hybrid sodium batteries

Abstract

This article presents the engineering of disodium naphthalene dicarboxylate (Na2-NDC) based negative organic electrodes for sodium-ion batteries. Firstly, different synthesis strategies were used to modify the morphology and crystal structure of the active material particles in order to improve their electrochemical performance. The engineering of the electrodes was then carried out to maximize the composite performances, which were initially evaluated in half-cells against Na. After electrode optimization, a complete cell was assembled by coupling the Na2-NDC negative electrode with Na3V2(PO4)2F3 (NVPF) as an inorganic-based cathode, to obtain a complete so-called “hybrid” cell. A thorough electrochemical study of the complete cell was carried out to evaluate the cell stability during cycling using different electrolyte additives. Thanks to the electrode and electrolyte optimizations, the NVPF/Na2-NDC hybrid cell demonstrated remarkable electrochemical performance, in terms of reversible capacity, cycling stability and rate performance. The full cells in the present work showed an energy density between 260 and 300 Wh/kg in the first cycle at low C-rate, and an energy density of 120–155 Wh/kg after 400 cycles, superior to those previously reported in the literature for the hybrid cell.In addition, a series of post-mortem analyses were carried out, based on GC/MS analysis, UV–Vis spectroscopy and electron microscopy (SEM/EDX), to understand the evolution of the performance over time and thus guide future research in this field to design the next generation of more durable and easily recycled sodium-ion battery.