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Strategies of mitigating dissolution of solid electrolyte interphases in sodium‐ion batteries

DOI: 10.1002/anie.202013803 DOI Help

Authors: Le Anh Ma (Uppsala University) , Andrew J. Naylor (Uppsala University) , Leif Nyholm (Uppsala University) , Reza Younesi (Uppsala University)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Angewandte Chemie International Edition

State: Published (Approved)
Published: November 2020
Diamond Proposal Number(s): 23159

Open Access Open Access

Abstract: With emerging interest in sodium‐ion battery (SIB) technology due to its cost effectiveness and high earth abundance of sodium, the search for an optimised SIB system becomes more and more crucial. It is well known that the formation of a stable solid electrolyte interphase (SEI) at the anode in Na‐based systems is a challenge due to the higher solubility of the SEI components compared to in the lithium‐ion battery case. Our knowledge about the formation and dissolution of the SEI in SIBs is so far based on limited experimental data. The aim of the present research is therefore to enhance the understanding of the behaviour of the SEI in SIBs and shed more light on the influence of the electrolyte chemistry on the dissolution of the SEI. By conducting electrochemical tests including extended open circuit pauses, we study the SEI dissolution in different time domains. With this, it is possible to determine the extent of self‐discharge due to SEI dissolution during a specific time. Instead of using a conventional separator, β‐alumina is employed as a Na‐conductive membrane to avoid crosstalk between the working electrode and Na‐metal counter electrode. The SEI composition is monitored using synchrotron‐based soft X‐ray photoelectron spectroscopy (SOXPES). The electrochemical and XPS results show that the SEIs formed in the studied electrolyte systems have different stabilities. The relative capacity loss after a 50‐hour pause in the tested electrolyte systems can be up to 30%. Among three carbonate‐based solvent systems, NaPF 6 in ethylene carbonate: diethyl carbonate exhibits the most stable SEI. The addition of electrolyte additives improves the SEI stability in PC. The electrolyte is saturated with typical SEI species, NaF and Na 2 CO 3 , in order to oppose the dissolution of the SEI. Furthermore, the solubilities of the latter additives in the different solvent systems are determined by inductively coupled plasma – optical emission spectrometry.

Journal Keywords: ageing; capacity loss; SEI dissolution; solubility; Additive

Subject Areas: Chemistry, Energy

Instruments: I09-Surface and Interface Structural Analysis