<i>In Situ</i> Forming Asymmetric Gel Polymer\nElectrolyte Enhances the Performance of High-Voltage Lithium Metal\nBatteries

With the rapid evolution of electric vehicle technology,\nconcerns\nregarding range anxiety and safety have become increasingly pronounced.\nBattery systems with high specific energy and enhanced security, featuring\nternary cathodes paired with lithium (Li) metal anodes, are poised\nto emerge as next-generation electrochemical devices. However, the\nasymmetric configuration of the battery structure, characterized by\nthe robust oxidative behavior of the ternary cathodes juxtaposed with\nthe vigorous reductive activity of the Li metal anodes, imposes elevated\nrequisites for the electrolytes. Herein, a well-designed gel polymer\nelectrolyte with asymmetric structure was successfully prepared based\non the Ritter reaction of cyanoethyl poly(vinyl alcohol) (PVA-CN)\nand cationic ring-opening polymerization of s-Trioxane. With the aid\nof the sieving effect of separator, the <i>in situ</i> asymmetric\ngel polymer electrolyte has good compatibility with both the high-voltage\ncathodes and Li anodes. The amide groups generated by PVA-CN after\nthe Ritter reaction and additional cyano groups can tolerate high\nvoltages up to 5.1 V, matching with ternary cathodes without any challenges.\nThe functional amide and cyano groups participate in the formation\nof the cathode electrolyte interface and stabilize the cathode structure.\nMeanwhile, the <i>in situ</i> formed ether-based polyformaldehyde\nelectrolyte is beneficial for promoting uniform Li deposition on anode\nsurfaces. Li–Li symmetric cells demonstrate sustained stability\nover 2000 h of cycling at a current density of 1 mA cm<sup>–2</sup> for 1 mAh cm<sup>–2</sup>. Furthermore, the capacity retention\nrate of Li(Ni<sub>0.6</sub>Mn<sub>0.2</sub>Co<sub>0.2</sub>)O<sub>2</sub>–Li cells with 0.5 C cycling after 300 cycles is 92.2%,\ndemonstrating excellent cycle stability. The electrolyte preparation\nstrategy provides a strategy for the progress of high-performance\nelectrolytes and promotes the rapid development of high-energy-density\nLi metal batteries.