Incorporation of redox-active polyimide binder into LiFePO4 cathode for high-rate electrochemical energy storage

Qing Zhang,Chengen He,Xianggang Wang,Yingkui Yang,Shengqiang Qiu,Xun Cui,Jinlong Zhang,Zongfeng Sha

doi:10.1515/ntrev-2020-0092

Abstract

Abstract Commercial LiFePO4 (LFP) electrode still cannot meet the demand of high energy density lithium-ion batteries as a result of its low theoretical specific capacity (170 mA h g−1). Instead of traditional electrochemical inert polyvinylidene fluoride (PVDF), the incorporation of multifunctional polymeric binder becomes a possible strategy to overcome the bottleneck of LFP cathode. Herein, a novel polyimide (PI) binder was synthesized through a facile hydrothermal polymerization route. The PI binder exhibits better connection between active particles with uniform dispersion than that of PVDF. The multifunctional PI binder not only shows well dispersion stability in the organic electrolyte, but also contributes to extra capacity because of the existence of electrochemical active carbonyl groups in the polymer chain. Besides, the high intrinsic ion conductivity of PI also results in promoted ion transfer kinetic. Consequently, the LFP cathode using PI binder (LFP–PI) shows larger capacity and better rate capability than LFP cathode with PVDF binder (LFP–PVDF). Meanwhile, the superior binding ability also endows LFP–PI with great cycling stability compared to the LFP–PVDF electrode.

Highlights

Lithium-ion batteries (LIBs) have covered most of the aspects of human civilization such as various mobile electronic devices, electric vehicles, and large-scale energy storage [1,2,3,4,5,6,7,8]
A multifunctional PI was successfully synthesized through a facile hydrothermal polymerization method and served as a binder for commercial LFP cathode
Compared to the traditional polyvinylidene fluoride (PVDF) binder, the PI binder serves as the effective bridges between active particles with stable distribution while boosting ion diffusion through the electrode

Summary

Introduction

Lithium-ion batteries (LIBs) have covered most of the aspects of human civilization such as various mobile electronic devices, electric vehicles, and large-scale energy storage [1,2,3,4,5,6,7,8]. The poor electronic conductivity and low ion mobility result in inferior rate capability for the LFP cathode [11,12]. Some other binders such as polytetrafluoroethylene, carboxyl methyl cellulose, polyacrylic acid, and styrene butadiene rubber have been used in various energy storage systems [23,28] Their differences in solubility, dispersion, adhesion strength, conductivity, and electrochemical stability make them only suitable for specific solvent, electrolyte, or voltage window [29,30,31]. The morphology, dispersion, chemical stability in organic electrolyte, and structural stability during long cycles of LFP electrodes fabricated with PVDF (LFP–PVDF) and PI (LFP–PI) binders were investigated and compared in detail.

Materials

Characterization

Electrochemical measurements

Conclusion