Cu-Enhanced Bottlebrush Composite Polymer Electrolytes for Superior Mechanical and Electrochemical Performance

The development of safe and high-performance electrolytes is essential to realize the full potential of lithium metal batteries (LMBs) for next-generation energy storage. In this study, we report the design and synthesis of composite polymer electrolytes (CPEs) based on polyoxanorbornene bottlebrush polymers (BPs) with poly-(ethylene oxide) (PEO) side chains. These unique bottlebrush architectures, synthesized via ring-opening metathesis polymerization, enable precise control over mechanical properties while maintaining a high ionic conductivity. The incorporation of copper bis-(trifluoromethanesulfonyl)-imide (Cu-(TFSI)₂) into the polymer matrix enhances ionic conductivity by disrupting PEO crystallinity and modifying the local lithium coordination environment. Electrochemical impedance spectroscopy revealed that the optimized CPE with 2 wt % Cu-(TFSI)₂ exhibited a 3-fold increase in ionic conductivity compared to BPs without Cu salt incorporation. Symmetric Li|Li cells demonstrated stable cycling with low overpotential for over 500 h, highlighting the electrolyte's excellent lithium metal compatibility and dendrite suppression capabilities. Full-cell tests with LiFePO₄ (LFP) and perylenetetracarboxylic dianhydride (PTCDA) cathodes further confirmed the electrolyte's versatility, delivering high capacities, superior rate performance, and extended cycle life compared to conventional polymer electrolytes. This work demonstrates that Cu-modified bottlebrush polymer electrolytes are a promising platform for enabling high-performance, solid-state LMBs, with broad applicability to both inorganic and organic cathodes.