Spontaneous In Situ Surface Alloying of Li-Zn Derived from a Novel Zn2+-Containing Solid Polymer Electrolyte for Steady Cycling of Li Metal Battery

Solid polymer electrolytes (SPEs) are preferable in the pursuit for developing high-energy Li metal batteries due to their inherent flexibility and intimate contact with electrodes. However, continuous interfacial parasitic reactions and undesired Li dendrite growth caused by inhomogeneous plating/stripping of Li+ result in rapid deterioration of an SPE/Li interface. Herein, a novel Zn2+-containing SPE (SPE-xZn) with anionic groups partially tethered on the polymer chains is developed to meet these challenges. During cycling, Zn2+ cations inside the SPE-xZn will gradually migrate to the surface of a Li electrode and then evolve to a Li-Zn alloy layer, where Li+ can diffuse more efficiently. Meanwhile, owing to the electrostatic interaction, the immobilized anionic groups within SPE-xZn can alleviate local concentrated Li+ flux. The synergistic effects of an in situ formed alloy layer and unique macromolecular structure can promote uniform plating/stripping of Li, thus yielding a more stable SPE-xZn/Li interface. Therefore, steady cycling over 300 h at 0.2 mA cm–2 is achieved by Li/SPE-5Zn/Li, and an impressive capacity retention of 87.3% at 0.5 C after 800 cycles is realized by LFP/SPE-5Zn/Li with an average Coulombic efficiency of 99.90%.