Composite polymer electrolytes incorporating two-dimensional metal–organic frameworks for ultralong cycling in solid-state lithium batteries

Abstract

Solid polymer electrolytes (SPEs) present substantial potential for use in solid-state lithium batteries; however, their authentic usability is presently curbed by their inadequate ionic conductivity and restricted lithium-ion mobility. Herein, a strategy to enhance the performance of poly(vinylidene fluoride) (PVDF) composite polymer electrolytes (CPEs) using two-dimensional cobalt-based ultrathin metal–organic framework nanosheet (CMS) with a high aspect ratio is proposed. At a CMS loading of 8 wt%, the obtained CPEs displayed a high ionic conductivity of 6.26 × 10⁻⁴ S cm⁻¹ (28 °C). In addition, the Li⁺ transfer number and electrochemical window were significantly improved. At 28 °C and 0.1 mA cm⁻², the Li symmetric cells exhibited a long lifespan and stable cycling for over 750 h. An assembled all-solid-state Li/LiFePO₄ cell displayed an ultrahigh capacity retention of 99.92% after 650 cycles at 0.5C and also demonstrated stable cycling performance at 1C. Moreover, the cycle performance of the Li/NCM811 cells was improved. The working mechanism of the CMS in CPEs was elucidated by density functional theory (DFT) calculations. These results emphasize that this novel electrolyte has unique characteristics and offers the potential for high-performance use in practical solid-state batteries.