Molecular Self-Assembled Ether-Based Polyrotaxane Solid Electrolyte for Lithium Metal Batteries

Abstract

Poly(ethylene oxide) has been widely investigated as a potential separator for solid-state lithium metal batteries. However, its applications were significantly restricted by low ionic conductivity and a narrow electrochemical stability window (<4.0 V vs Li/Li+) at room temperature. Herein, a novel molecular self-assembled ether-based polyrotaxane electrolyte was designed using different functional units and prepared by threading cyclic 18-crown ether-6 (18C6) to linear poly(ethylene glycol) (PEG) via intermolecular hydrogen bond and terminating with hexamethylene diisocyanate trimer (HDIt), which was strongly confirmed by local structure-sensitive solid/liquid-state nuclear magnetic resonance (NMR) techniques. The designed electrolyte has shown an obviously increased room-temperature ionic conductivity of 3.48 × 10–4 S cm–1 compared to 1.12 × 10–5 S cm–1 without assembling polyrotaxane functional units, contributing to the enhanced cycling stability of batteries with both LiFePO4 and LiNi0.8Co0.15Al0.05O2 cathode materials. This advanced molecular self-assembled strategy provides a new paradigm in designing solid polymer electrolytes with demanded performance for lithium metal batteries.

Polymer-in-Salt Electrolyte from Poly(caprolactone)-graft-polyrotaxane for Ni-Rich Lithium Metal Batteries at Room Temperature

“…The exceptional ionic conductivity of PGPE is attributed to the high swinging motion of PCL sidechains, which greatly facilitate the motion of lithium ions between cathode and anode electrodes. The enhanced swinging motion capability of PCL sidechains is believed to be associated with the sliding and rotation of the cyclic molecules along the axial polymer chain, which creates unique segmental dynamics. , In addition, the enhanced segmental motion of the PCL sidechains is also confirmed by the disappearance of the PCL crystals of PGPE, as depicted in Figure S5. Moreover, the ionic conductivities of both the PGPE and the PEO/LiFSI-based PISE are consistent with the Arrhenius equation: σ­( T ) = A exp­(− E a / RT ), where A is the pre-exponential factor, E a and R are the activation energy and the ideal gas constant, respectively.…”

“…To overcome this, supramolecular polymers of polyrotaxane (PR), in which the cyclic molecules are threaded on an axis linear polymer chain, have attracted significant research interest . The sliding and rotation of the cyclic molecules along the axial polymer chain create unique functional nanomaterials with novel dynamic properties. , By grafting short PCL segments onto the cyclic molecules of cyclodextrin (CD), this additional kinetic freedom can be exploited to produce a solid polymer electrolyte with significantly enhanced polymer segmental motions, ultrahigh ionic conductivity, and other favorable electrochemical properties. , In addition, the solid polymer electrolyte comprising a polymer-in-salt matrix, with a lithium salt content exceeding 50 wt %, presents significant potential despite its limited research thus far. Notably, this system facilitates facile and straightforward attainment of high ionic conductivity at room temperature.…”

“…13 The sliding and rotation of the cyclic molecules along the axial polymer chain create unique functional nanomaterials with novel dynamic properties. 14,15 By grafting short PCL segments onto the cyclic molecules of cyclodextrin (CD), this additional kinetic freedom can be exploited to produce a solid polymer electrolyte with significantly enhanced polymer segmental motions, ultrahigh ionic conductivity, and other favorable electrochemical properties. 16,17 In addition, the solid polymer electrolyte comprising a polymer-in-salt matrix, with a lithium salt content exceeding 50 wt %, presents significant potential despite its limited research thus far.…”

Multiple Dynamic Bonds‐Driven Integrated Cathode/Polymer Electrolyte for Stable All‐Solid‐State Lithium Metal Batteries

“…[41] The extracted activation energies (E a ) for DSICE electrolytes were calculated to be 0.206, 0.212, 0.235, 0.244 eV, respectively, which are far lower than the ever-reported polymer electrolytes, [32,42,43] indicative of a lower energy barrier for Li + transport. [37] The transport of Li + in DSICE electrolytes is tied to the glass transition temperature (Tg) and was further studied by differential scanning calorimetry (DSC), as shown in Figure S7.…”

Multiple Dynamic Bonds‐Driven Integrated Cathode/Polymer Electrolyte for Stable All‐Solid‐State Lithium Metal Batteries

“…However, there exists a canonical tradeoff between ion transport feature and mechanical properties of current polymer electrolytes [33,34] . Sacrificial bonds including dynamic covalent bonds and supramolecular interaction have recently been introduced into polymer electrolytes to address the above conflicts, improving both the robustness and toughness properties with little regard for ionic conductivity [35–38] . Their efforts have been focused on improving the properties of the bulk electrolytes to alleviate the electrolyte‐electrodes interface issues, which is still limited to physical contact at the macroscopic scale.…”