A branched dihydrophenazine-based polymer as a cathode material to achieve dual-ion batteries with high energy and power density

Abstract

Organic electrode materials have exhibited good electrochemical performance in batteries, but their voltages and rate capabilities still require improvement to meet the increasing demand for batteries with high energy and power density. Herein, we design and synthesize a branched dihydrophenazine-based polymer (p-TPPZ) as a cathode material for dual-ion batteries (DIBs) through delicate molecular design. Compared with the linear dihydrophenazine-based polymer (p-DPPZ, with a theoretical capacity of 209 mAh g–1), p-TPPZ possessed a higher theoretical capacity of 233 mAh g–1 and lower highest occupied molecular orbital energy levels,which resulted in a high actual capacity (169.3 mAh g–1 at 0.5 C), an average discharge voltage of 3.65 V (vs. Li+/Li) and a high energy density (618.2 Wh kg–1, based on the cathode materials). The branched structure of p-TPPZ led to a larger specific surface area than that of p-DPPZ, which was beneficial for the electrolyte infiltration and fast ionic transport, contributing to the high power density. Due to the fast reaction kinetics, even at a power density of 23,725 W kg–1 (40 C), the energy density still reached 474.5 Wh kg–1. We also made a detailed investigation of the p-TPPZ cathode's charge storage mechanism. This work will stimulate the further molecular design to develop organic batteries with both high energy and power density.

Keywords

• Organic dual-ion batteries
• Branched polymers
• Dihydrophenazine-based polymers
• Organic cathodes
• Conjugated porous materials