Alleviating self-discharge in sodium-ion batteries via functional dual-salt electrolytes

Abstract

Sodium-ion batteries (SIBs) are regarded as the most viable alternative to lithium-ion batteries due to their low cost, excellent reversible capacity, and high resource abundance. However, SIBs exhibit severe self-discharge issue when using hard carbon as anode material, which largely restricts their practical application. In this study, dual-salt electrolytes are developed to relieve the self-discharge in SIBs for the first time. The prepared functional electrolytes can help to form a compact solid-electrolyte interphase with anion-derived compositions on the hard carbon anode, resulting in a robust structure to alleviate self-discharge. Specifically, the optimal NaFSI-0.2 electrolyte, 0.8 M sodium hexafluorophosphate (NaPF₆) and 0.2 M sodium bis(fluorosulfonyl)imide (NaFSI) in diethylene glycol dimethyl ether (G₂), enhances the capacity retention rate at 60°C after 3 days and 6 days from 62.4 % and 49.6 % to 77.2 % and 68.8 %, respectively. Experimental characterizations and DFT calculations reveal the underlying reasons for the improved high-temperature stability. This work provides a facile strategy on the electrolyte regulation to alleviate the self-discharge in SIBs and could shed light on the promotion of practical application of SIBs.