Metal–Organic Framework-Coated Fiber Network Enabling Continuous Ion Transport in Solid Lithium Metal Batteries

Abstract

Poly­(ethylene oxide) (PEO)-based solid-state polymer electrolytes (SPEs) have limited application in lithium metal batteries due to their low room-temperature ionic conductivity and high interfacial impedance with electrodes. Constructing efficient enhancers is a promising way to tackle these critical issues, but still remains a huge challenge. In this study, a continuous and hierarchical lithium-ion transport network was constructed by growing a copper-based metal–organic framework (MOF) (Cu–MOF-74) on a three-dimensional (3D) nonwoven fabric (NWF). The incorporation of the high-surface-area NWF effectively prevents MOF particle agglomeration, thereby creating a 3D interconnected network of ion transportation channels that span both vertically and laterally. Additionally, MOF nanoparticles with functional groups exhibit a high affinity toward bis­(tri-fluoromethanesulfonyl) imide anions, which is facilitated by hydrogen bonding between oxygen-containing functional groups and fluorine, as well as metal–oxygen bonds, releasing more free lithium ions. The as-prepared electrolyte exhibits a fast ionic conductivity of 1.0 × 10–4 S cm–1 at 30 °C, a high lithium-ion transference number of 0.39, and a wide electrochemical window of 4.9 V. The all-solid-state Li–LiFePO4 cells possess a high initial discharge capacity of 160.4 mAh g–1 at 0.5C, excellent rate performance (specific capacity reached 148.6 mAh g–1 at 2.0C), and good cycle stability. This approach presents a cost-effective and efficient strategy for enhancing PEO-based SPEs, providing a promising direction for overcoming the challenge of low ionic conductivity in all-solid-state lithium metal batteries.

Challenges and Solutions of Solid‐State Electrolyte Film for Large‐Scale Applications

“…Compared with 2D thin film substrates, substrates with 3D structures are more effective in solving the problems of insufficient interfacial contact and ion transport network between SSE and lithium metal. As reported, a metal‐organic skeleton (MOF)@ nonwoven fabric (NWF) substrate was constructed by growing a copper‐based MOF on a three‐dimensional (3D) NWF, and SPE (Li‐MOF@NWF/PEO) membranes (130 um) [ 188 ] with vertically and horizontally spanning ion‐transport networks were constructed by immersing this substrate into an electrolyte solution containing LiTFSI. In addition, hydrogen bonding between oxygen‐containing functional groups and fluorine as well as metal‐oxygen bonding in MOF improved the affinity of MOF nanoparticles for bis(trifluoromethanesulfonyl)imide anions, which resulted in the release of more free lithium‐ions.…”

“…Although the solution casting method has been widely used for the large‐scale preparation of polymer‐based SSEs due to the simplicity and maturity of the process, the ability to incorporate a variety of additives as needed, the ease of preparing composite solid electrolytes with oxide/sulfide SSEs, and the ease of infiltration into porous and skeletal materials, the method has been prominent in CPEs in particular due to the integration of the advantages of each of the SPEs and inorganic SSEs. [ 170–172 ] There are five main structural designs studied, namely free‐standing SSE, [ 159–169 ] skeleton supporting SSE, [ 173–194 ] SSE with low tortuosity, [ 195–198 ] electrode‐supporting SSE [ 199–201 ] and in situ polymerization. [ 182,202–208 ] However, it is worth noting that the solution casting method is mainly based on SPE for the preparation and design of CSE, and the introduction of SPE will force the ASSB to operate at high temperatures, in addition, the complete filling of pores in the skeleton is a challenge, too little will lead to the limitation of the performance of composite solid electrolyte, and too much will affect the energy density of the battery.…”