Electrochemical lithium intercalation into multiwall carbon nanotubes: a micro-Raman study

doi:10.1016/S0167-2738(00)00599-3

Solid State Ionics

Volumes 136–137, 2 November 2000, Pages 1295-1299

https://doi.org/10.1016/S0167-2738(00)00599-3 Get rights and content

Abstract

The electrochemical intercalation of lithium into carbon electrodes containing multiwall carbon nanotubes produced by electric arc technique was carried out in button cells in different electrolytes. An exfoliation of graphene layers was observed with the electrolyte LiPF₆ (1M) dissolved in ethylene carbonate (EC), propylene carbonate (PC) and dimethyl carbonate (DMC) (1:1:3 by volume). Raman spectra were recorded to elucidate the lithium intercalation mechanisms of multiwall nanotubes. The spectral changes of the Raman E_2g band showed that the lithium was intercalated between graphene layers of carbon nanotubes without the formation of n-staged phases with n higher than 2 in contrast to the intercalation into graphite which proceeds via the formation of staged graphite intercalation compounds.

Introduction

In the last decade, much research efforts have been focused on the search for suitable carbon as material for the anode of secondary lithium batteries. Among the new materials studied, multiwall carbon nanotubes (MWNTs) are of special interest since they combine structural features of graphite and fullerenes and open up different ways of interaction with foreign atoms and molecules; specifically intercalation between the pseudographitic layers and/or insertion inside the central tube [1]. Although carbon nanotubes have been the subject of many investigations, the structure of multiwall nanotubes is still a subject of controversy and no experiment has been able to determine clearly whether it is based on a Russian-doll or a Scroll model. Obviously, the physical and chemical properties of the intercalated carbon nanotubes compounds should be promising and for instance, it is known that intercalation of alkali-metals [2] allows to modify the electronic properties of the nanotubes. In a previous study [3], we have reported the electrochemical intercalation of lithium into multiwall carbon nanotubes where it has been shown that lithiated MWNTs present a ‘necklace’ structure and that nanotubes could be reversibly intercalated by lithium. In this paper, we studied by using Transmission Electron Microscopy (TEM), electrochemical intercalation in two different electrolytes and their consequences on the modification of nanotubes structure. Besides, we carried out Raman spectroscopy to interpret and discuss the electrochemical intercalation process.

Section snippets

Experimental

The material used in this investigation is purchased from MER Corporation (Tucson, AZ) and is produced by electric arc technique. The sample contains multiwall carbon nanotubes, onions and amorphous carbon. Diameters vary from 5 to 20 nm with a mean value of 15 nm and lengths are greater than 1 μm. Ends of nanotubes always appear to be capped. The electrochemical intercalation of lithium is carried out in Li/Electrolyte/MWNTs button cells prepared in an argon-filled glove box by placing

Electrochemical measurements

Fig. 1 shows the first discharge (lithium intercalation) and charge (lithium extraction) curves for carbon nanotubes studied in electrolyte (EC:PC:3DMC). This curve indicates a reversible capacity of 180 Ah/kg, compared to 372 Ah/kg in graphite. In contrast to lithium intercalation into graphite, where the formation of staged graphite intercalation compounds are characterized by voltage plateaus [4], the potential vs. capacity for carbon nanotubes, in our experimental conditions, can be

Conclusion

Micro-Raman spectroscopy showed that lithium is intercalated between graphene layers of carbon nanotubes which confirms results obtained by ⁷Li NMR and TEM pictures [3]. Electrolyte composition can affect the lithium intercalation into carbon nanotubes by introducing side reactions like exfoliation of graphene layers caused by co-intercalation of solvent molecules. The low specific capacity observed may be due to the low proportion of MWNTs in the raw material. Further investigation to

Acknowledgments

This work is partially supported by the CNRS contract 42 PRG ‘Materiaux’ #98N42/0046. We wish to thank Professors J.V. Zanchetta and J.C. Giuntini for their fruitful comments.

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Electrochemical lithium intercalation into multiwall carbon nanotubes: a micro-Raman study

Abstract

Introduction

Section snippets

Experimental

Electrochemical measurements

Conclusion

Acknowledgments

Chem. Phys. Lett.

Carbon

Chem. Phys. Lett.

Chem. Phys. Lett.

Science