Excellent Polymerized Ionic-Liquid-Based Gel Polymer Electrolytes Enabled by Molecular Structure Design and Anion-Derived Interfacial Layer.

Polymerized ionic liquid (PIL)-based gel polymer electrolytes (GPEs) are well known as highly safe and stable electrolytes but with low ambient ionic conductivity. Herein, we first designed and synthesized an IL monomer with a long and flexible side chain and then mixed it with LiTFSI and MEMPTFSI to construct a PIL-based GPE (denoted as GM-GPE). The special molecular structure of the monomer greatly improves the ionic transport through the PIL chain, and the introduction of MEMPTFSI plasticizer further improves the ionic conductivity, promoting a TFSI--anion-derived SEI formation to suppress Li dendrite growth and forming an electrostatic shielding effect of MEMP+ cations to promote the uniform deposition of Li+. Consequently, the as-prepared GM-GPE exhibits high ambient ionic conductivity (4.3 × 10-4 S cm-1, 30 °C), robust electrochemical stability, excellent thermal stability, nonflammability, and superior ability to inhibit Li dendrite growth. The resultant LiFePO4|GM-GPE|Li cell exhibits a high discharge capacity of 150 mA h g-1 at 0.2 C along with a good cycling stability and rate capability. This work brings about new guidance for the development of high-quality GPEs with high ionic conductivity, high stability, and safety for long cycling and dendrite-free lithium metal batteries.

Co-Intercalation-Free Ether-Based Weakly Solvating Electrolytes Enable Fast-Charging and Wide-Temperature Lithium-Ion Batteries.

Ether-based electrolytes are competitive choices to meet the growing requirements for fast-charging and low-temperature lithium-ion batteries (LIBs) due to the low viscosity and low melting point of ether solvents. Unfortunately, the graphite (Gr) electrode is incompatible with commonly used ether solvents due to their irreversible co-intercalation into Gr interlayers. Here, we propose cyclopentyl methyl ether (CPME) as a co-intercalation-free ether solvent, which contains a cyclopentane group with large steric hindrance to obtain weakly solvating power with Li+ and a wide liquid-phase temperature range (-140 to +106 °C). A weakly solvating electrolyte (WSE) based on CPME and fluoroethylene carbonate (FEC) cosolvents can simultaneously achieve fast desolvation ability and high ionic conductivity, which also induces a LiF-rich solid electrolyte interphase (SEI) on the Gr anode. Therefore, the Gr/Li half-cell with this WSE can deliver outstanding rate capability, stable cycling performance, and high specific capacity (319 mAh g-1) at an ultralow temperature of -60 °C. Furthermore, a practical LiFePO4 (loading ≈25 mg cm-2)/Gr (loading ≈12 mg cm-2) pouch cell with this WSE also reveals outstanding rate capability and stable long-term cycling performance above 1000 cycles with a high Coulombic efficiency (≈99.9%) and achieves an impressive low-temperature application potential at -60 °C.