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.