Carbon-Based Materials As Negative Electrodes in Sodium-Ion Batteries

Abstract

Nowadays effective energy storage, especially batteries, plays a crucial role in technology development. Due to the high abundance and low cost of sodium, sodium-ion batteries are promising substitutes for widely used Li-ion cells. Graphite-based materials are commonly used as a negative electrode in lithium systems. However, sodium ions have a larger ionic radius compared to lithium ones, and also the energy of intercalation of graphite by Na + is higher than by Li + [1]. Therefore, it is necessary to use different types of carbon- based materials with greater interlayer spacing, which can be achieved through increased structural disorder. These materials could be obtained through the thermal processing of polymers [2]. Additionally, due to their high porosity, the adsorption of sodium ions is more efficient. All these properties enhance the specific capacity of negative electrodes in sodium- ion systems. As a result of thermal processing, we obtained porous carbon-based materials. The synthesized powder's electrochemical characteristics have been examined using three-electrode Swagelok®-type cells. Slurry-coated electrodes with carbon-based materials were used as the working electrode, while sodium metal was used as the reference electrode and the counter electrode. Sodium-ion systems were investigated in a high-rate test, with a charging current of 1 C and discharge current rates varying from 1 C to 10 C. Even at the highest discharge current rate, the batteries retained a high percentage of the first-cycle specific capacity. The cycle stability of sodium-ion systems was also examined. After 50 cycles of charging/discharging at a current of 1 C, the specific capacity did not decrease significantly as compared to the specific capacity of the first cycle. Furthermore, the cyclic voltammetry behaviour of these systems was also investigated. Although the two signals were not well separated, it was evident that two electrochemical phenomena were present: diffusion of sodium cations in the carbon matrix and sodium adsorption on the carbon surface. The synthesised carbon-based porous materials demonstrated stability during the charging and discharging of sodium-ion batteries. The implementation of these products in sodium-ion technology could be helpful during the process of commercialization of such energy storage systems. Acknowledgements: This work was supported by The Polish National Centre of Science through a research grant 2021/43/D/ST5/01220 entitled “High-voltage sodium-ion batteries based on exfoliated graphite electrodes”. Literature: [1] Y. Liu et al. „Origin of low sodium capacity in graphite and generally weak substrate binding of Na and Mg among alkali and alkaline earth metals”, PNAS USA 113 2016 [2] T. Zhang et al. „Recent Advances in Carbon Anodes for Sodium-Ion Batteries”. Chem. Rec. 22 2022