Quasi-solid polymer electrolytes (QPE) composed of Li salts, polymer matrix, and solvent, are beneficial for improving the security and energy density of batteries. However, the ionic conduction mechanism, existential form of solvent molecules, and interactions between different components of QPE remain unclear. Here we develop a multispectral characterization strategy combined with first-principles calculations to unravel aforesaid mysteries. The results indicate that the existential state of solvent in QPE is quite different from that in liquid electrolyte. The Li cations in gel polymer electrolyte are fully solvated by partial solvent molecules to form a local high concentration of Li+ , while the other solvent molecules are fastened by polymer matrix in QPE. As a result, the solvation structure and conduction mechanism of Li+ are similar to those in high-concentrated liquid electrolyte. This work provides a new insight into the ionic conduction mechanism of QPE and will promote its application for safe and high-energy batteries.

Insights into the Ionic Conduction Mechanism of Quasi-Solid Polymer Electrolytes through Multispectral Characterization.

By introducing lithiophilic groups and electrochemically stable quinolyl aromatic ring linkages, we prepared covalent organic frameworks (COFs) exhibiting a large band gap with an ultralow HOMO value (-6.2 eV under vacuum) and oxidative stability up to 5.6 V (versus Li+ /Li) as solid-state electrolytes (SSEs). The obtained flexible COF SSE thin films showed a holistically oriented arrangement along the (001) facet with remarkable ionic conductivity up to 1.5×10-4  S cm-1 at 60 °C and excellent mechanical strength with a high Young's modulus of 10.5 GPa. Molecular dynamic simulations showed that lithium ions are transmitted in this COF SSE by directional hopping paths with fast drift velocity. The COF SSE film was used to assemble all-solid-state lithium metal batteries with nickel-rich cathodes (NMC811). The batteries demonstrated stable cycling performance over 400 cycles, high coulombic efficiency (>99 %), and could also withstand abuse tests, such as folding.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/anie.202184762

High-Voltage-Tolerant Covalent Organic Framework Electrolyte with Holistically Oriented Channels for Solid-State Lithium Metal Batteries with Nickel-Rich Cathodes.

The development of ionic conductors with extreme stretchability, superior ionic conductivity, and harsh‐environment resistance is urgent while challenging because the tailoring of these performances is mutually exclusive. Herein, a hydrophobicity‐constrained association strategy is presented for fabricating a liquid‐free ion‐conducting fluorinated elastomer (ICFE) with microphase‐separated structures. Hydrophilic nanodomains with long‐range ordering and selectively enriched Li ions provided high‐efficient conductive pathways, yielding impressive room‐temperature ionic conductivity of 3.5 × 10–3 S m–1. Hydrophobic nanodomains with abundant and reversible hydrogen bonds endow the ICFE with superior damage‐tolerant performances including ultrastretchability (>6000%), large toughness (17.1 MJ m–3) with notch insensitivity, antifatigue ability, and high‐efficiency self‐healability. Due to its liquid‐free characteristic and surface‐enriched hydrophobic nanodomains, the ICFE demonstrates an extreme temperature tolerance (−20 to 300 °C) and unique underwater resistance. The resultant ICFE is assembled into a proof‐of‐concept skin‐inspired sensor, showing impressive capacitive sensing performance with high sensitivity and wide‐strain‐range linearity (gauge factor to 1.0 in a strain range of 0–350%), excellent durability (>1000 cycles), and unique waterproofness in monitoring of complex human motions. It is believed that the hydrophobicity‐constrained association method boosts the fabrication of stretchable ionic conductors holding a great promise in skin‐inspired ionotronics with harsh‐environment tolerance.

A Waterproof Ion‐Conducting Fluorinated Elastomer with 6000% Stretchability, Superior Ionic Conductivity, and Harsh Environment Tolerance

The use of solid electrolytes can fundamentally change energy storage systems due to higher security and energy density. Herein, we design a hydrogen-bonded polyethylene oxide (PEO) composite solid electrolytes (CSEs),...

Hydrogen bonding enhanced SiO2/PEO composite electrolytes for solid-state lithium batteries

Recent advances of composite electrolytes for solid-state Li batteries

Solid-state lithium metal batteries built with composite polymer electrolytes using cubic garnets as active fillers are particularly attractive owing to their high energy density, easy manufacturing and inherent safety. However, the uncontrollable formation of intractable contaminant on garnet surface usually aggravates poor interfacial contact with polymer matrix and deteriorates Li + pathways. Here we report a rational designed intermolecular interaction in composite electrolytes that utilizing contaminants as reaction initiator to generate Li + conducting ether oligomers, which further emerge as molecular cross-linkers between inorganic fillers and polymer matrix, creating dense and homogeneous interfacial Li + immigration channels in the composite electrolytes. The delicate design results in a remarkable ionic conductivity of 1.43×10 -3 S cm -1 and an unprecedented 1000 cycles with 90% capacity retention at room temperature is achieved for the assembled solid-state batteries.

Jun He

Papers

In-situ intermolecular interaction in composite polymer electrolyte for ultralong life quasi-solid-state lithium metal batteries.