Modulation of Lithium Ion Transport and Cycling Stability Using Rigid and Flexible Urethane Moieties on the Backbone...

Area of Science:

• Materials Science
• Electrochemistry
• Polymer Chemistry

Background:

• Graphite is the standard anode material for lithium-ion batteries, but faces limitations due to volume changes and poor conductivity.
• Conjugated polymers offer tunable properties and ease of synthesis, presenting an alternative for battery applications.
• Enhancing the capacitive charge storage component is crucial for improving energy device performance.

Purpose of the Study:

• To synthesize and evaluate novel diketopyrrolopyrrole (DPP)-based conjugated polymers as potential anode materials for lithium-ion batteries.
• To investigate the impact of urethane moieties on ion transport and capacitive charge storage.
• To correlate polymer structure, including spacer type (alkyl, phenyl, biphenyl), with electrochemical performance and stability.

Main Methods:

• Synthesis of three DPP-based conjugated polymers with varying spacers and integrated urethane functionalities.
• Electrochemical characterization, including charge-discharge cycling and cyclic voltammetry, to assess capacity, stability, and ion diffusion.
• X-ray photoelectron spectroscopy (XPS) to analyze the binding of lithium ions and understand charge transport mechanisms.

Main Results:

• Polymers with alkyl and phenyl spacers demonstrated stable cycling over 4000 cycles, significantly exceeding graphite's theoretical capacity.
• The polymer with an alkyl spacer achieved a high specific capacity of 600 mAh/g, with charge storage dominated by an 81% capacitive component.
• XPS analysis confirmed lithium ion binding to carbonyl groups, highlighting the role of urethane in facilitating charge transport.

Conclusions:

• DPP-based conjugated polymers incorporating urethane moieties show great promise as high-performance anode materials for lithium-ion batteries.
• The alkyl-spaced polymer exhibited exceptional specific capacity and a dominant capacitive charge storage mechanism.
• The study highlights the importance of polymer structure and urethane functionalization for optimizing ion transport and battery performance.