Spontaneous In Situ Surface Alloying of Li-Zn Derived from a Novel Zn<sup>2+</sup>-Containing Solid Polymer Electrolyte for Steady Cycling of Li Metal Battery
Zhen Zeng, Shang Wang, Jun Cheng, Guangmei Hou, Deping Li, Guifang Han, Lijie Ci
Abstract
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%.