Effects of ester-based electrolyte composition and salt concentration on the Na-storage stability of hard carbon anodes

• Published in: Journal of power sources Vol. 471; p. 228455
• Main Authors: Chen, Cheng, Wu, Mengqiang, Liu, Jiahao, Xu, Ziqiang, Zaghib, Karim, Wang, Yuesheng
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 30.09.2020
• Subjects: Electrochemical stability; Ester-based electrolytes; Hard carbon; NaTFSI; Sodium-ion batteries; Hard carbon; NaTFSI; Sodium-ion batteries; Electrochemical stability; Ester-based electrolytes
• ISSN: 0378-7753; 1873-2755
• DOI: 10.1016/j.jpowsour.2020.228455

Hard carbon (HC) is the most feasible anode for Na-ion batteries (NIBs). However, HC electrodes suffer from low initial coulombic efficiency (ICE), poor rate capability and cyclic instability. Here, a systematic investigation was carried out to understand the effect of Na salt, esters-based solvent and concentration on the electrochemical performance of hard carbon spheres (HCSs) electrodes. Based on the experimental results, 2 M NaTFSI/DC:DMC electrolyte delivers the best initial reversible capacities of 332 mAh·g−1, high ICE of 83.5% and excellent electrochemical stability of 90% after 100 cycles at 0.1C and 80% after 300 cycles at 1C. In addition, the drastic capacity fading phenomenon of HCSs electrode occurs in ultrahigh concentration electrolyte (5 M NaTFSI/EC:DMC) after cycles, and this drastic capacity fading mechanism is revealed by the ex-situ strategies of the Raman, SEM and capacity-recovery experiment. The proposed moderate concentrated electrolyte and failure mechanism of ultrahigh concentration electrolyte for HC electrode provide further insights in developing preferable electrolyte for NIBs. [Display omitted] •The Na+ storage properties of HC anodes using various electrolyte were tested.•Concentration of NaTFSI-based electrolytes are controlled for matching HC anodes.•The optimized electrolyte with HC anodes represents high stability for Na+ storage.•Failure mechanism of saturation-concentration electrolytes was putted forward.