Strategies for Mitigating Dissolution of Solid Electrolyte Interphases in Sodium‐Ion Batteries

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.

Tracking Passivation and Cation Flux at Incipient Solid‐Electrolyte Interphases on Multi‐Layer Graphene using High Resolution Scanning Electrochemical Microscopy

“…We acknowledge that sample rinsing and the ex-situ nature of XPS measurements will alter the composition of the SEI to some extent and therefore impact the XPS analysis. [55] For example, dissolution of both inorganic and organic species during rinsing has been reported in Na-ion batteries, [58] along with the formation of species such as carbonates due to air exposure. [55] Therefore, we limit our analysis to a qualitative evolution of overall species (such as fluorinated phases and hydrocarbons) between SEIs formed À 1.4 V and À 3.0 V, (in Figure 5a).…”

Deep Eutectic Solvents as Nonflammable Electrolytes for Durable Sodium‐Ion Batteries

“…This is problematic for battery performance, as the SEI should ideally be strong, insoluble, and stable to ensure optimal electrochemical characteristics. [8,[11][12][13][14] The 5.86 m NaTFSI/NMA DES may offer an improved battery performance at 55 C because of the potential formation of robust surface films, as was previously observed for other concentrated electrolytes. [43] Despite the improved reductive stability caused by its high concentration, the stability of 5.86 m NaTFSI/NMA is not high enough to be used in a cell with sodium metal as the negative electrode.…”

“…This is problematic for battery performance, as the SEI should ideally be strong, insoluble, and stable to ensure optimal electrochemical characteristics. [ 8,11–14 ] The 5.86 m NaTFSI/NMA DES may offer an improved battery performance at 55 °C because of the potential formation of robust surface films, as was previously observed for other concentrated electrolytes. [ 43 ]…”

“…[9,10] A robust and passivating salt-derived solidÀelectrolyte interphase (SEI) is beneficial for battery durability, offering long-term stability of operation. [8,[11][12][13][14][15][16][17] In addition, the electrolyte's oxidative stability can be improved because of the donation of solvent lone electron pairs to the salt cation. [18] For instance, increasing the LiTFSI concentration was shown to enhance the oxidative stability from 4 V versus Li þ /Li to %5 V versus Li þ /Li for both [Li(triethylene glycol dimethyl ether)] [TFSI] and [Li(tetraethylene glycol dimethyl ether)] [TFSI].…”

Layered Oxide Cathode‐Electrolyte Interface towards Na‐Ion Batteries: Advances and Perspectives

“…For CEI components, since Na tends to form long and weak covalent bonds with other atoms, [12] the properties and species of Na-based solid electrolyte interface could differ from its identical lithium components, [13,14] such as higher solubility and inferior electrochemical stability of carbonates (e. g., Na 2 CO 3 vs. Li 2 CO 3 ). [12,15] For liquid electrolyte, when employing same salt anion and solvents, electrolyte of sodium salt system could show lower de-solvation energy than that of lithium salt. [16] Even it ensures fast Na + transfer kinetics that may enable good rate performance, higher reaction activity could also be deduced between electrolyte and formed CEI layer.…”