Effect of complexing agents on the electrochemical performance of LiFePO4/C prepared by sol-gel method

Rong Yang,Jou-Hyeon Ahn,Bailing Jiang,Erwei Kang

doi:10.1186/1556-276x-7-40

Rong Yang, Jou-Hyeon Ahn + Show 2 more

Open Access

https://doi.org/10.1186/1556-276x-7-40

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Abstract

LiFePO4/C is synthesized via sol-gel method using Fe3+ as iron sources and different complexing agents, followed by sintering at high temperature for crystallization. The amount of carbon in these composites is less than 6.8 wt.%, and the X-ray diffraction experiment confirms that all samples are pure single phase indexed with the orthorhombic Pnma space group. The particle size of the LiFePO4/C synthesized by acetic acid as a complexing agent is very fine with a size of 200 nm. The electrochemical performance of this material, including reversible capacity, cycle number, and charge-discharge characteristics, is better than those of LiFePO4/C synthesized by other complexing agents. The cell of this sample can deliver a discharge capacity of 161.1 mAh g-1 at the first cycle. After 30 cycles, the capacity decreases to 157.5 mAh g-1, and the capacity fading rate is 2.2%. The mechanism is studied to explain the effect of a complexing agent on the synthesis of LiFePO4/C by sol-gel method. The results show that the complexing agent with a low stability constant may be proper for the synthetic process of LiFePO4/C via sol-gel method.

Highlights

LiCoO2, LiNiO2, and LiMn2O4 have been widely used as cathode materials in lithium-ion batteries currently
Experiment Various LiFePO4/C cathode materials were synthesized by sol-gel method with acetic acid, ethanediol, oxalic acid, and ethylenediamine as complexing agents, and they were named as SGAc, SGEg, SGOc, and SGEn, respectively
No evidence of diffraction peaks for crystalline carbon appeared in the diffraction pattern, which indicated that the carbon generated from the complexing agent was amorphous and that its presence did not influence the structure of LiFePO4/C

Summary

Introduction

LiCoO2, LiNiO2, and LiMn2O4 have been widely used as cathode materials in lithium-ion batteries currently. Most researchers have placed much more emphasis on the processing of the sol-gel method and its effect on the structures and electrochemical performances of cathode materials, but the mechanism is hardly studied to explain the effect of complexing agents in the process of preparation.

Results

Conclusion