Stable and Unstable Diglyme-Based Electrolytes for Batteries with Sodium or Graphite as Electrode

Abstract

We study the stability of several diglyme-based electrolytes in sodium|sodium and sodium|graphite cells. The electrolyte behavior for different conductive salts [sodium trifluoromethanesulfonate (NaOTf), NaPF 6 , NaClO 4 , bis-(fluorosulfonyl)imide (NaFSI), and sodium bis-(trifluoromethanesulfonyl)imide (NaTFSI)] is compared and, in some cases, considerable differences are identified. Side reactions are studied with a variety of methods, including X-ray diffraction, scanning electron microscopy, transmission electron microscopy, online electrochemical mass spectrometry, and in situ electrochemical dilatometry. For Na|Na symmetric cells as well as for Na|graphite cells, we find that NaOTf and NaPF 6 are the preferred salts followed by NaClO 4 and NaFSI, as the latter two lead to more side reactions and increasing impedance. NaTFSI shows the worst performance leading to poor Coulombic efficiency and cycle life. In this case, excessive side reactions lead also to a strong increase in electrode thickness during cycling. In a qualitative order, the suitability of the conductive salts can be ranked as follows: NaOTf ≥ NaPF 6 > NaClO 4 > NaFSI ≫ NaTFSI. Our results also explain two recent, seemingly conflicting findings on the degree of solid electrolyte interphase formation on graphite electrodes in sodium-ion batteries [

Copper Thiophosphate (Cu3PS4) as Electrode for Sodium‐Ion Batteries with Ether Electrolyte

“…In a previous study, we found a very strong influence of the conductive salt on reactions in diglyme based electrolytes, with NaOTf and NaPF 6 being preferred for sodium and graphite electrodes. [ 31 ] Figure S6 (Supporting Information) shows that, for lithium, the best capacity retention was found for a voltage window between 1–2.5 V versus Li + /Li, with a capacity of 170 mAh g(Cu 3 PS 4 ) −1 retained after 200 cycles at 50 mA g −1 using 1 m LiTFSI in diglyme. Figure S7 (Supporting Information) shows results for various electrolyte compositions at two different current densities (50 and 120 mA g −1 ).…”

A Sodium Polysulfide Battery with Liquid/Solid Electrolyte: Improving Sulfur Utilization Using P2S5 as Additive and Tetramethylurea as Catholyte Solvent

“…For the anode compartment, sodium metal was pressed on a cylindrical stainless‐steel current collector, which was immersed in a solution of NaOTf in 2G (0.25–0.5 m ). The choice of NaOTf/2G as electrolyte solution is motivated because of its good stability and low interface resistance compared with other electrolyte solutions . Despite these advantages, it is of note that dendrite formation remains an issue, see Figure S2, Supporting Information.…”

“…The choice of NaOTf/2G as electrolyte solution is motivated because of its good stability and low interface resistance compared with other electrolyte solutions. [14] Despite these advantages, it is of note that dendrite formation remains an issue, [15] see Figure S2, Supporting Information. Galvanostatic discharging occurs at around 1.7 V (22 C), see Figure 1, though only a limited capacity was achieved at a current of 0.01 C (%500 μA).…”

Challenges of today for Na-based batteries of the future: From materials to cell metrics

“…Interestingly, ether-based electrolytes have shown excellent performances. They not only have been successfully employed to enable cointercalation of solvated Na + ions into graphite [125,191], but they also present an ability to form a very stable SEI and enhance the Na stripping/plating efficiency. While for LIBs glyme-based electrolytes have been outperformed by ester-based ones, whether glymes will be a valid alternative electrolyte system for NIBs is still an open question.…”