Piperazine axially coordinated cobalt polyphthalocyanine polymers for high-performance lithium-ion battery anodes

Bridging-ligand modulation regulates stacking in metal-coordinated polymers. • Partially 3D cobalt polyphthalocyanine polymers via green ultrasonics. • Interlayer Co-N bridges stabilize framework for long cycling. : Metal-modified covalent organic polymers with planar π-conjugated structures are prone to aggregation due to strong interlayer π-π interactions, forming densely packed architectures that hinder electrolyte penetration and limit the accessibility of redox-active sites, thereby compromising their electrochemical performance as lithium-ion battery anodes. To address this issue, a bridging-ligand-driven strategy is proposed to regulate the aggregation behavior of such polymers. A cobalt polyphthalocyanine polymer (Co-TCNB) was synthesized and subsequently modified via an ultrasonic-assisted approach by introducing piperazine (PIP) as a bridging ligand. The axial coordination between PIP and cobalt centers constructs interlayer Co-N coordination bridges, which effectively weaken π-π interactions and alleviate dense stacking, while providing efficient pathways for charge transport and improving structural stability during repeated cycling. As a result, the cobalt polyphthalocyanine polymer bridged with piperazine (Co-TCNB-PIP) exhibits a significantly increased specific surface area and enhanced electrochemical performance. It delivers a reversible capacity of 850 mA·h·g −1 after 100 cycles at 200 mA·g −1 and maintains 640 mA·h·g −1 at 1000 mA·g −1 over prolonged cycling, demonstrating excellent rate capability and cycling stability, outperforming the majority of reported polymer-based anodes for lithium-ion batteries. Download: Download high-res image (341KB) Download: Download full-size image