Polyimide-Derived Carbon-Coated Li4Ti5O12 as High-Rate Anode Materials for Lithium Ion Batteries.

Shih-Chieh Hsu,Tzu-Ten Huang,Huei Chu Weng,Cai-Wan Chang-Jian,Yen-Ju Wu,Cheng-Zhang Lu,Ting-Yu Liu,Jen-Hsien Huang

doi:10.3390/polym13111672

Abstract

Carbon-coated Li4Ti5O12 (LTO) has been prepared using polyimide (PI) as a carbon source via the thermal imidization of polyamic acid (PAA) followed by a carbonization process. In this study, the PI with different structures based on pyromellitic dianhydride (PMDA), 4,4′-oxydianiline (ODA), and p-phenylenediamine (p-PDA) moieties have been synthesized. The effect of the PI structure on the electrochemical performance of the carbon-coated LTO has been investigated. The results indicate that the molecular arrangement of PI can be improved when the rigid p-PDA units are introduced into the PI backbone. The carbons derived from the p-PDA-based PI show a more regular graphite structure with fewer defects and higher conductivity. As a result, the carbon-coated LTO exhibits a better rate performance with a discharge capacity of 137.5 mAh/g at 20 C, which is almost 1.5 times larger than that of bare LTO (94.4 mAh/g).

Highlights

With the continuous depletion of fossil fuels and associated increasing air pollution, it is essential to raise the proportion of renewable energy supplies
To study the effect of the p-PDA moiety on the imidization process, the enthalpy of imidization for the PO-polyamic acid (PAA) and POP-PAA was recorded by differential scanning calorimetry (DSC) measurement
The enthalpy of imidization integrated from the DSC curve was calculated to be 228.6 and 235.6 J/g for PO-PAA and POP-PAA, respectively

Summary

Introduction

With the continuous depletion of fossil fuels and associated increasing air pollution, it is essential to raise the proportion of renewable energy supplies. To address the above issue, alien ion doping [2], the building of a nanoporous structure [3,4] and surface coating [5,6,7] have proven to be effective for improving the rate performance by narrowing the band gap, shortening migration paths for Li+ ions and reduction of interfacial resistance, respectively. The soft-baked precursor films were thermally imidized (150 ◦C for 30 min, 250 ◦C for 30 min, 350 ◦C for 60 min and 400 ◦C for 30 min) under N2 atmosphere to obtain the PMDA/ODA PI and PMDA/ODA/p-PDA PI denoted as PO-PI and POP-PI, respectively. The spherical LTO precursor obtained was added to the PMDA/ODA or PMDA/ODA/p-PDA PAA solution, which was stirred for 60 min and subsequently centrifuged. For the preparation of the bare LTO sample, the spray-dried precursor was directly annealed with the same heating program

Characterization

Electrochemical Analysis

Results and Discussion

Conclusions