Monolithic Titanium Alkoxide Networks for Lithium-Ion Conductive All-Solid-State Electrolytes

Abstract

Reticular chemistry provides opportunities to design solid-state electrolytes (SSEs) with modular tunability. However, SSEs based on modularly designed crystalline metal− organic frameworks (MOFs) often require liquid electrolytes for interfacial contact. Monolithic glassy MOFs can have liquid processability and uniform lithium conduction, which is promising for the reticular design of SSE without liquid electrolytes. Here, we develop a generalizable strategy for the modular design of noncrystalline SSEs based on a bottom-up synthesis of glassy MOFs. We demonstrate such a strategy by linking polyethylene glycol (PEG) struts and nanosized titanium-oxo clusters into network structures termed titanium alkoxide networks (TANs). The modular design allows the incorporation of PEG linkers with different molecular weights, which give optimal chain flexibility for high ionic conductivity, and the reticular coordinative network provides a controlled degree of cross-linking that gives adequate mechanical strength. This research shows the power of reticular design in noncrystalline molecular framework materials for SSEs.

Polyoxometalate-based reticular materials for proton conduction: from rigid frameworks to flexible networks

“…These materials can serve as ideal matrices for lithium-ion conductive electrolytes, as their modular design allows incorporating PEG linkers with different molecular weights to select the optimal chain flexibility for balancing their processability with ionic conductivity. 57,58…”

“…These materials can serve as ideal matrices for lithium-ion conductive electrolytes, as their modular design allows incorporating PEG linkers with different molecular weights to select the optimal chain flexibility for balancing their processability with ionic conductivity. 57,58 Similar concepts have also been extended to design POMbased flexible supramolecular networks for developing processible proton conductors. The Li group reported a supramolecular ionic network electrolyte using POMs as electrostatic crosslinkers to solidify bola-type zwitterionic liquids containing…”

Strategies to improve the ionic conductivity of quasi-solid-state electrolytes based on metal-organic frameworks

“…Consequently, the grain boundary becomes the mechanical weakest point of MOFs-QSSEs, allowing lithium dendrites to easily penetrate this region. On the other hand, the band structure at the grain boundary differs from other locations, and various factors, including grain boundary diffusion, bulk diffusion competition, and charge accumulation, contribute to the slow transmission speed of Li ions [58].…”

“…Generally, entangling and cross-linking polymer chains enhance mechanical strength, but this can decrease the flexibility of polymer chains and ion conductivity. Zhang et al devised a modular strategy to construct a polymer network with metal cluster nodes derived from amorphous MOFs and polymer struts [58]. They transformed MIL-125 into an amorphous state to obtain titanium-oxo clusters that can be randomly connected.…”

Vitrified Metal–Organic Framework Composite Electrolyte Enabling Dendrite-Free and Long-Lifespan Solid-State Lithium Metal Batteries

“…To improve the situation above, the as-synthesized polymers are widely appreciated by many researchers owing to their high ionic conductivity and flexibility. For instance, glassy titanium alkoxide networks (TANs) were incorporated with poly­(ethylene oxide) (PEO) and delivered a capacity of 128.7 mAh g –1 at 0.5C. , Despite a certain enhancement of their rate performance, there is still large room to boost due to the presence of insufficient interior interface contact generated by the worse infiltrability of viscous polymers ahead of the battery assembly. Hence, rationally optimizing interior and exterior interfaces simultaneously is one of the top priorities to enhance the comprehensive electrochemical performance of solid-state LMBs.…”