Alternant P-Type/N-Type Conjugated Bipolar Copolymer Cathodes for Advanced Aqueous Zinc-Ion Batteries

Area of Science:

• Materials Science
• Electrochemistry
• Polymer Chemistry

Background:

• Bipolar organic materials combine high capacity (n-type) and high voltage (p-type) for aqueous zinc-ion batteries (AZIBs).
• Small molecular structures in these materials often lead to dissolution and poor cycling stability.
• Phenolthiazine-based cathodes with p-type/n-type structures are being explored to overcome these limitations.

Purpose of the Study:

• To synthesize a stable bipolar polymer cathode for AZIBs.
• To investigate the dual-ion storage mechanism of the synthesized material.
• To evaluate the electrochemical performance and stability of the material in AZIBs.

Main Methods:

• Synthesis of bipolar poly(phenothiazine iodide-3,3'-diaminobenzidine) (P(PTD-DAB)).
• Spectroscopic analyses to elucidate the ion storage mechanism.
• Electrochemical testing including galvanostatic cycling, rate capability, and long-term cycling stability at various current densities and mass loadings.
• Fabrication and testing of flexible belt-shaped cells.

Main Results:

• P(PTD-DAB) exhibits a cooperative p-type/n-type dual-ion storage mechanism involving Zn²⁺/H⁺ and OTF^- ions.
• The material delivers an average operating voltage of 1 V and a specific capacity of 211.8 mAh g^-1 at 0.1 A g^-1.
• It demonstrates 90% capacity retention over 3600 cycles at 3 A g^-1 with robust stability at high mass loading (10 mg cm^-2).
• Flexible cells retain 88% capacity over 550 cycles at 3 A g^-1 under bending conditions.

Conclusions:

• The synthesized P(PTD-DAB) effectively addresses the dissolution issue of small molecular bipolar materials.
• The bipolar polymer enables high-performance AZIBs through a dual-ion storage mechanism.
• This work advances the development of bipolar polymers for high-performance and flexible energy storage devices.