Integrated design of covalent organic frameworks-based solid-state electrolytes and cathode materials for constructing high-performance lithium metal batteries

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Solid-state lithium metal batteries (SSLMBs) are regarded as the next-generation energy storage systems, offering enhanced safety and higher energy density. Polyethylene oxide-based solid-state electrolytes (SSEs) have garnered significant attention due to their advantages, including superior safety, straightforward fabrication processes, and high energy density. However, their low ionic conductivity has hindered the commercialization of SSLMBs. In this study, we developed a modified grafting PEG onto modified material COF-5-6 SSE slurry, which was coated onto the surface of a LiFePO4 cathode to construct an integrated SSE for SSLMBs. The B atoms in COF-5-6-PEG serve as Lewis acid sites, adsorbing and anchoring anions from lithium salts, thereby promoting the dissociation of lithium salts and releasing more Li+. Additionally, the S and O polar atoms complex with Li+, facilitating the solvation of Li+ within flexible segments and enabling rapid Li+ transport through the interconnected channels. As a result, the COF-5-6-PEG SSE membrane demonstrates a high ionic conductivity of 1.41 × 10−3 S cm−1 and a Li+ transference number of 0.47, along with stable polarization behavior for over 400 h with Li metal electrodes at 80 °C. Moreover, the Li||COF-5-6-PEG SSE||LiFePO4 cells exhibit a dendrite-free lithium metal surface, promising rate capability, and cycling performance, delivering an initial discharge capacity of 122.8 mA h g−1 at 2 C and retaining 65.5% of its capacity after 200 cycles. These results highlight that the synergistic regulation of material structure and fabrication processes is an effective strategy for designing high-performance SSEs.