Nonflammable Dual-Salt Electrolytes for Graphite/LiNi_0.8Co_0.1Mn_0.1O₂ Lithium-Ion Batteries: Li⁺ Solvation Structure and Electrode/Eelectrolyte Interphase

Trimethyl phosphate (TMP) is the most promising safe solvent for lithium-ion battery (LIB) electrolyte because of the nonflammability, oxidation stability, and low cost, but its application is hindered by incompatibility with the graphite anode. Herein, nonflammable electrolytes with ordinary concentration (1 mol L–1) are designed for graphite/LiNi0.8Co0.1Mn0.1O2 (Gr/NCM811) LIBs with TMP/2,2,2-trifluoroethyl methyl carbonate (FEMC) binary solvents. Stable cycling of the Li/Gr half cells with high capacity is achieved via modulation of the Li+ solvation structure. A dual-salt strategy of lithium hexafluorophosphate/lithium difluoro(oxalato)borate is further used to realize the high performance of the Gr/NCM811 full cells. More significantly, the functions and relationship of Li+ solvation structure and electrode/electrolyte interphase are elucidated. Li+ solvation structure and interphase are respectively the thermodynamic and kinetic factors for the side reactions of the electrolyte occurring at the electrode/electrolyte interphase, which should be considered comprehensively in the design of electrolytes for high-energy density LIBs

A Molybdenum Polysulfide <i>In-Situ</i> Generated from Ammonium Tetrathiomolybdate for High-Capacity and High-Power Rechargeable Magnesium Battery Cathodes

Rechargeable magnesium batteries (RMBs) are a promising large-scale energy-storage technology with low cost and high reliability. However, developing high-performance cathode materials remains the most prominent obstacle because of the insufficient magnesium-storage active sites and unfavorable magnesium cation transport paths, as well as the strong interaction between the cathode material and the bivalent magnesium cation. Herein, ammonium tetrathiomolybdate is demonstrated to be a high-performance RMB cathode material. Ammonium tetrathiomolybdate exhibits a high capacity of 333 mAh g–1 at 50 mA g–1 and a good rate performance of 129 mAh g–1 at 5.0 A g–1 (∼15 C). An amorphous structure with plenty of efficient magnesium-storage active sites and open magnesium transport paths is in situ formed during the first cycle via ammonium extraction. The covalent-like bond between the molybdenum and sulfur delocalizes the negative charge, weakening the interaction with the bivalent magnesium cation and accelerating the kinetics. The covalent-like molybdenum–sulfur bond also promotes the simultaneous redox of molybdenum and sulfur, leading to a high specific capacity. The present work introduces a high-capacity and high-power RMB cathode material, elucidates the origin of the high performance, and provides insights for the design and optimization of RMB cathode materials