Molecular Ionic Composite Polymer Electrolytes for High-Voltage Batteries

Area of Science:

• Materials Science
• Electrochemistry
• Polymer Chemistry

Background:

• Polymer electrolytes are key for safe, high-energy lithium batteries, but face challenges like parasitic side reactions and decomposition at electrode-electrolyte interfaces.
• Existing polymer electrolytes often require additional liquid components, complicating cell assembly and limiting performance in high-voltage systems.

Purpose of the Study:

• To develop novel free-standing polymer electrolyte membranes using molecular ionic composites (MICs) to address interfacial instability in high-voltage lithium batteries.
• To investigate the mechanical, electrochemical, and cycling performance of MICs as a potential replacement for conventional liquid electrolytes.

Main Methods:

• Synthesis of molecular ionic composites (MICs) comprising a charged rigid-rod ionic polymer (PBDT) and mobile ions from ionic liquids, lithium salts, and additives.
• Characterization of MIC electrolytes' ionic conductivity, electrochemical stability window (ESW) using linear sweep voltammetry (LSV), and mechanical properties (tensile strength, elastic modulus).
• Assembly and testing of NMC811||Li metal cells utilizing the optimized MIC electrolytes to evaluate cycling stability and capacity retention.

Main Results:

• Optimized MIC electrolytes demonstrated high ionic conductivity (3.21 mS cm⁻¹ at 60 °C) and a wide electrochemical stability window (5 V vs Li|Li⁺).
• MICs exhibited excellent mechanical properties with a tensile strength of 6.3 MPa and an elastic modulus of 450 MPa.
• NMC811||Li metal cells with MICs showed good cycling stability, delivering an initial capacity of 212 mAh g⁻¹ and retaining 93% after 100 cycles at 60 °C.

Conclusions:

• Molecular ionic composites (MICs) present a promising, stable, and mechanically robust polymer electrolyte platform for high-voltage lithium batteries.
• MICs effectively mitigate interfacial issues, enabling enhanced electrochemical stability and good cycling performance, paving the way for safer energy storage solutions.