A MOF covalently linked by polymer chains is prepared and used as an all-solid-state polymer electrolyte for LIBs, which shows superior performance.

No abstract

Almost all the traditional ionic liquids lack liquid crystal properties.

The original poly­(ethylene oxide)-based polymer electrolytes normally show low ionic conductivity and inferior mechanical property, which greatly restrict their practical application in all-solid-state lithium-ion batteries (LIBs). In this work, a hyperbranched star polymer with poly­(ethylene glycol) methyl ether methacrylate flexible chain segments is embedded into a three-dimensional (3D) interpenetrating cross-linking network created by the rapid one-step UV-derived photopolymerization of the cross-linker (ethoxylated trimethylolpropane triacrylate) in the presence of lithium salt. The rigid 3D network framework provides the polymer electrolyte with not only enhanced mechanical behavior, including film-forming and dendrite-inhibiting capabilities, but also nanoconfinement effects, which can speed up polymer chain segmental dynamics and reduce the crystallinity of the polymer. Depending on this unique rigid–flexible coupling network, the prepared solid polymer electrolyte shows enhanced ionic conductivity (6.8 × 10–5 S cm–1 at 50 °C), widened electrochemical stability window (5.1 V vs Li/Li+), and enough mechanical stability to suppress the growth of uneven Li dendrite (the Li symmetrical cells can operate steadily at both current densities of 0.05 and 0.1 mA cm–2 for 1000 h). Moreover, the assembled LiFePO4//Li cell also exhibited good cycle performance at 50 °C, making the hyperbranched star polymer electrolyte with a nanoconfined cross-linking structure to have potential application in high-safety and high-performance LIBs.

Lignin is an eco-friendly, low-cost, and abundant natural biopolymer. However, few studies have explored the potential application of lignin as electrolyte matrix for lithium-ion batteries or obtained excellent cell performance using lignin-based electrolyte. In this paper, lignin and poly­(N-vinylimidazole)-co-poly­(poly­(ethylene glycol) methyl ether methacrylate) are mixed thoroughly in water, then a free-standing lignin-based film is obtained by casting and drying. The resulting film shows obviously higher mechanical strength (over 10 times) than that of the pure lignin film due to the construction of internal physical cross-linking network. Through activation of the prepared film by organic electrolyte, the membrane exhibits superior electrochemical performances (such as outstanding lithium-ion transfer number (0.63) and the ability to inhibit the growth of lithium dendrites). As a result, the LiFePO4/lignin-based electrolyte/Li cell presents excellent long cycle performance (∼150 mAh g–1 at 1 C more than 450 cycles) and rate capacity (110 mAh g–1 at 10 C) at room temperature (RT), which is better than that of the cells using a commercial separator. Moreover, the LiCoO2/lignin-based electrolyte/Li cell also shows superior cell performance at RT. Thus, the lignin-based electrolyte with the outstanding comprehensive property has the potential to replace separator and to be widely applied in high-performance and high-safety LIBs.