Abstract
The interfacial reactions in sodium‐ion batteries (SIBs) are not well understood yet. The formation of a stable solid electrolyte interphase (SEI) in SIBs is still challenging due to the higher solubility of the SEI components compared to lithium analogues. This study therefore aims to shed light on the dissolution of SEI influenced by the electrolyte chemistry. By conducting electrochemical tests with extended open circuit pauses, and using surface spectroscopy, we determine the extent of self‐discharge due to SEI dissolution. Instead of using a conventional separator, β‐alumina was used as sodium‐conductive membrane to avoid crosstalk between the working and sodium‐metal counter electrode. The relative capacity loss after a pause of 50 hours in the tested electrolyte systems ranges up to 30 %. The solubility of typical inorganic SEI species like NaF and Na2CO3 was determined. The electrolytes were then saturated by those SEI species in order to oppose ageing due to the dissolution of the SEI.
Highlights
The increasing demand for renewable energy has resulted in an increased interest in sustainable energy conversion technologies, including solar- and wind-based technologies
In conventional alkali-ion batteries the capacity losses can be explained based on a variety of ageing mechanisms and the capacity loss mechanisms are typically different for fulland half-cells.[12,27,28]
As this study only focuses on half-cells containing Na-metal electrodes, there are three major sources of the capacity loss: solid electrolyte interphase (SEI) dissolution, ion trapping and volume expansion leading to a cracking of the active material.[27,28,29]
Summary
The increasing demand for renewable energy has resulted in an increased interest in sustainable energy conversion technologies, including solar- and wind-based technologies. The latter energy sources do not produce energy continuously, which is why stationary energy storage devices connected to the electric grid are required. Lithium-ion batteries (LIBs) have been widely used in portable applications due to their high energy densities. Sodium-ion batteries (SIBs) based on all abundant elements have attracted attention as SIBs are able to provide more cost-effective and sustainable stationary energy storage systems.[1, 2]. To facilitate the implementation of SIBs in practical applications, the long-term performance of the SIBs still needs to be improved.
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