Lithium ion intercalation mechanism for LiCoPO4 electrode

Hua Ju,Yanhui Xu,Jun Wu

doi:10.1186/2251-6832-4-22

Hua Ju, Yanhui Xu + Show 1 more

Open Access

https://doi.org/10.1186/2251-6832-4-22

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Abstract

Abstract Recently, there exists a discrepancy on the lithium ion de-intercalation mechanism for LiCoPO4 electrode. In the present work, the study was focused upon exploring the origin of this discrepancy by studying the dependence of the impedance spectrum on the state of charge and the carbon content. For the pure LiCoPO4 electrode, the two plateaus in the charge curve are at 4.82 and 4.92 V. We have also studied the variation of electrochemical impedance spectroscopies (EISs) with the state of charge. The EIS measurement has shown that the total interfacial resistance increases as the state of charge increases for the pure LiCoPO4 electrode. If higher content of sucrose was added in the precursor (this implies higher carbon content in the synthesized sample), only one potential plateau can be found in the charge curve. For this electrode, the total interfacial resistance decreases with the state of charge. Especially, the total interfacial resistance has a dramatic decrease when the state of charge increases from 20% to 40%. It is believed that the influence of carbon impurity on the variation tendency of the EIS pattern may reflect the change of the fine structure. For the pure LiCoPO4 electrode, the intermediate phase is Li0.20~0.45CoPO4.

Highlights

The growing crisis in energy and resource encourages scientists to search for various solutions [1,2,3,4], and in the past decades, much more attention has been paid on the research and development of lithium-ion batteries, especially the cathode and anode materials [5,6,7,8]
The shape of the charge curve depends on the carbon content
For the pure LiCoPO4 and the LiCoPO4 sample synthesized in N2 atmosphere with lower content of sucrose added in the precursor, there exist two potential plateaus in the charge curve

Summary

Introduction

The growing crisis in energy and resource encourages scientists to search for various solutions [1,2,3,4], and in the past decades, much more attention has been paid on the research and development of lithium-ion batteries, especially the cathode and anode materials [5,6,7,8]. The olivine-type LiCoPO4 cathode has been extensively studied due to its highly reversible Li-intercalation potential of 4.7 to 4.8 V [9,10,11,12,13]. Due to the expensive cost of Co sources, LiCoPO4 is not suitable for large-scale applications, but it has a potential in lithium-ion microbattery and all-solid-state lithium-ion battery. The understanding of the electrochemical behavior of LiCoPO4 is useful to improve the electrode properties of LiFePO4 and LiMnPO4 cathodes. The density of cubic olivine LiCoPO4 is reported to be 3.76 g cm−3. Its structure can transit from the olivine-type to the spine-type structure as the atmosphere pressure

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