Synergistic Dual‐Additive Electrolyte for Interphase Modification to Boost Cyclability of Layered Cathode for Sodium Ion Batteries

Abstract

The electrolyte additive plays an important role in determining the crucial properties of batteries such as cycling stability and safety. Compared to material development, research on electrolyte and interphase is still in the early stage for sodium ion batteries (SIBs). Herein, for the first time, succinic anhydride (SA) is investigated as a synergistic filming additive to fluoroethylene carbonate (FEC), and the lifespan of the dual‐additive Na/Na0.6Li0.15Ni0.15Mn0.55Cu0.15O2 (NLNMC) cell is significantly improved, maintaining capacity retention of 87.2% over 400 cycles at 1 C rate. For comparison, the batteries with only one of the two additives or without any additive show much inferior electrochemical performance. After the addition of SA, the interphase layer on the surface of cycled NLNMC material becomes uniform and stable, which contains more oxygen‐rich organic species and less NaF. Additionally, the addition of SA also has an impact on the interphase layer in the sodium anode part as indicated by electrochemical impedance spectroscopy (EIS) and energy dispersive spectrometer (EDS) results. Moreover, the online differential electrochemical mass spectrometry (OEMS) tests show the dual‐additive cell has less CO2 generation during the initial two cycles compared to that with only FECs which demonstrates another advantage of SA for practical application.

Emerging Era of Electrolyte Solvation Structure and Interfacial Model in Batteries

“…Recently, more and more researchers are realizing that the Li + solvation structure and desolvation process can affect an electrode’s performance significantly. − However, it remains a challenge to illustrate the process, because the molecular behaviors in the bulk electrolyte and at the electrolyte–electrode interface are abstractive, dynamic, and non-quantitative . Despite the findings on the effect of solvation structure in electrolytes, the battery performance has been ascribed to the solvation-structure-derived SEI that has a specific composition, thickness, and/or morphology, − which is an endless loop that fails to involve the specific solvation structure-derived interfacial model (i.e., Li + desolvation process) in the liquid since the battery performance is ascribed to the SEI again. − Thus, different viewpoints need to be clarified and emphasized to set direct scientific relationships between molecular interactions of electrolyte species and electrode performance, so as to make a breakthrough in this field and beyond.…”

Ether-based electrolytes for sodium ion batteries

“…11a). 31 To form a stable and protective interfacial layer, many film-forming additives were developed in sodium-ion batteries, including FEC, 141 VC, 142 succinic anhydride (SA), 143 and sodium difluorophosphates (NaDFP). 144 However, the majority of studies focused on the modification of carbonate-based electrolytes.…”

Metallic Sodium Anodes for Advanced Sodium Metal Batteries: Progress, Challenges and Perspective

“…The interface oxidation and reduction processes can produce a powerful SEI film to stabilize Na anodes and promote the uniform plating of Na. According to the above principles, various additives have been devised, like FEC, [161,162] acetamide, [163] Diamondoids, [164] Nitrofullerene, [165] IL, [166] potassium bis(trifluoromethylsulfonyl)imide (KTFSI), [167] Na polysulfide, [168] SiCl 4 , [169] SnCl 2 [170] and tetramethylthiuram disulfide. [109] Among all these additives, fluorides are the most commonly used because it can form highly stable NaF-rich SEI films.…”