Non-aqueous electrolyte liquids such as carbonate solvents have been widely employed in the commercial lithium-ion batteries and in the development of next-generation rechargeable batteries. The decomposition products of the organic electrolyte and additive molecules contribute to the formation of solid electrolyte interphases (SEIs) on the electrode surface, which have key impacts on battery's electrochemical performance. The rational engineering of electrolyte systems demands precise understanding of the electrochemical reaction pathways as well as the decomposition products of the electrolytes. Mass spectrometry (MS) is a well-established molecular analytical approach that can provide critical information for unambiguous structure assignment based on its mass-resolving power. In recent years, the application of MS for battery research has been expanding rapidly, providing valuable insights about the chemical species generated during battery operation and electrolyte evolution. This review aims to summarize the recent advances of MS technique-based analysis of electrolyte decomposition products as well as SEIs, and thus to demonstrate the high utility of MS methods for characterization of battery systems.

Imide electrolyte salts have received increasing interest in lithium-sulfur battery (LSB) research due to their oxidation capacity, thermal stability, and cycling stability. Although the ionic conductivity of imide electrolytes is moderate, a LSB with imide electrolyte salts exhibits improved charge-discharge (CD) cycling capacity and Coulombic efficiency. Here, we applied an effective strategy to suppress polysulfide dissolution by using a micelle-structured fluorinated ether-based additive (F4EO2) with lithium bis(trifluorosulfonyl)imide (LiTFSI) and lithium bis(fluorosulfonyl)imide (LiFSI) electrolyte salts. In contrast to the LiFSI electrolyte, the LiTFSI imide electrolyte with F4EO2 additive shows a superior performance in terms of its compatibility with the lithium (Li)-metal anode, electrochemical stability, cycling stability, and high specific discharge capacity of ca. 1331 mAh/g using the sulfur/carbon (S/C) composite//electrolyte//Li-metal battery configuration at 0.1C. The LSB performance is enhanced with an increase of the concentration of the F4EO2 additive in the electrolyte solution. The results demonstrate that the electrolyte solution with the F4EO2 additive and LiTFSI salt improves the LSB performance by suppressing polysulfide dissolution and forming a favorable passivation layer on the Li-metal anode, leading to a specific discharge capacity of ca. 1221 mAh/g after 20 cycles and 950 mAh/g after 100 cycles (for T5FDLiTFSI), respectively, with a Coulombic efficiency of ca. 99.98% and 99.99% after 20 and 100 CD cycles, respectively.

Lithium-ion batteries (LIBs) power virtually all modern portable devices and electric vehicles, and their ubiquity continues to grow. With increasing applications, however, come increasing challenges, especially when operating conditions deviate from room temperature. While high-temperature performance and degradation has been extensively studied in LIBs, sub-zero Celsius performance has received less attention, despite being critical for batteries in transportation roles. Although many individual processes contribute to the capacity loss commonly observed in LIBs at low temperatures, most of them are governed to some extent by the non-aqueous liquid electrolyte present throughout the cell interior. Therefore, electrolyte engineering presents an unparalleled opportunity to study and address the fundamental causes of low-temperature failure. In this review, we first briefly cover the various processes that determine lithium-ion performance below 0 °C. Then, we outline recent literature on electrolyte-based strategies to improve said performance, including various additives, solvents and lithium salts. Finally, we summarize these findings and provide some perspectives on the current state of the field, including promising new areas of investigation.

Owing to the negative impact of the extensive utilization of batteries on the environment, sustainability of the cells needs to be included in the systemic research of batteries. Herein, a dissolvable ionic crosslinked polymer (DICP) is exploited as a binder for lithium–sulfur batteries by crosslinking the polyacrylic acid and polyethyleneimine through carboxy-amino ionic interaction. This interaction is pH-controlled, and therefore, the crosslinked binder network can be readily dissociated under basic conditions, providing a facile strategy enabling valuable components recycled through a convenient washing method. The sulfur cathode prepared using the recycled carbon–sulfur composite can deliver comparable capacity as that of fresh electrode. In addition, evidence from cell performance and characterizations, such as in situ X-ray absorption spectroscopy, in situ UV–visible spectroscopy, X-ray photoelectron spectroscopy, and density functional theory calculation, confirms that DICP is a more effective binder than its commercial counterpart on suppressing polysulfide dissolution in the electrolyte. Exploiting reversible crosslinked polymer binder for recyclable Li–S batteries with ameliorated electrochemical performance, this study illuminates sustainable development for large-scale energy storage systems.

The Li-S battery is a promising next-generation technology due to its high theoretical energy density (2600 Wh kg^-1) and low active material cost. However, poor cycling stability and coulombic efficiency caused by polysulfide dissolution have proven to be major obstacles for a practical Li-S battery implementation. In this work, we develop a novel strategy to suppress polysulfide dissolution using hydrofluoroethers (HFEs) with bi-functional, amphiphlic surfactant-like design: a polar lithiophilic "head" attached to a fluorinated lithiophobic "tail." A unique solvation mechanism is proposed for these solvents whereby dissociated lithium ions are readily coordinated with lithiophilic "head" to induce self-assembly into micelle-like complex structures. Complex formation is verified experimentally by changing the additive structure and concentration using small angle X-ray scattering (SAXS). These HFE-based electrolytes are found to prevent polysulfide dissolution and to have excellent chemical compatibility with lithium metal: Li||Cu stripping/plating tests reveal high coulombic efficiency (>99.5%), modest polarization, and smooth surface morphology of the uniformly deposited lithium. Li-S cells are demonstrated with 1395 mAh g^-1 initial capacity and 71.9% retention over 100 cycles at >99.5% efficiency-evidence that the micelle structure of the amphiphilic additives in HFEs can prohibit polysulfide dissolution while enabling facile Li⁺ transport and anode passivation.