Triazine crosslinked polyionic liquid: An electrolyte-stable, lithiophilic and electrostatic shielding layer for uniform lithium plating/stripping

Rational design of functional layer on Cu current collector with polymer material is an effective strategy to improve electrochemical performance of batteries with Li anode. Here, a multifunctional solvent-stable layer, which contains triazine crosslinked polyionic liquid (cPIL) as the polymer matrix and in-situ formed LiF nanoparticle as filler (cPIL-LiF), is constructed on Cu foil to regulate the plating/stripping behavior of Li. The cPIL with excellent lithiophilicity and electrostatic shielding performance ensures homogeneous Li⁺ flux and promotes uniform Li deposition. The LiF nanoparticles and TFSI anions in cPIL-LiF contribute to the formation of the stable LiF- and Li₃N-rich solid electrolyte interphase (SEI). Due to these superiorities, excellent interfacial stability is achieved and, consequently, dense and dendrite-free Li deposition is well maintained during cycling. The cPIL-LiF coated Cu enables an improved cycling stability with coulombic efficiency of ∼98% for 200 cycles, much better than the bare Cu and the Cu modified with the commonly used polymers. Moreover, the full cells with Li₄Ti₅O₁₂/LiFePO₄ cathodes and cPIL-LiF-Cu@Li (limited amount of deposited Li) demonstrate apparently enhanced electrochemical performance. This work provides new perspectives to construct electrolyte-stable artificial protective layer on Cu current collector for stable Li plating/stripping and enriches the understanding on the development of high-performance Li metal-based batteries.