Characterization and Electrochemical Properties of Graphene / Silicon Grafted Composite Materials for Applications in Lithium-Ion Battery

Density and energy performance of Li -ion batteries are highly dependent on the physical and chemical properties of the electrode materials. The negative electrode materials still offer a large area to explore to improve both capacity and reversibility for lithium storage. In this context, the development of negative electrodes based on silicon has led to numerous researches (1). The high specific capacitance of silicon (3850 mAh.g^-1) is the main asset for the use of this material. However, silicon has major drawbacks (volume expansion, irreversible formation of LixSiy alloys,... ) that cause early degradation of the electrodes.
The approach developed in our laboratory is to link the two components by a chemical bond (covalent) between the two materials. This covalent bond, resulting from a chemical grafting of a diazonium salt (4-aminoaniline) allows linking the carbon particles to silicon nanoparticles via a phenyl bridge.

This technique has been used to bond silicon nanoparticles to carbon nanotubes (2) which helped to improve the stability of the electrodes during galvanostatic cycling. The work presented here focuses on a coupling between silicon nanoparticles and graphene sheets.
Graphene is potentially interesting for Li-ion batteries applications, it has good electronic conductivity and its layered structure could promote an increase in the strength of the electrodes. The sheets can act as a buffer when the silicon particles volume increases, thereby helping to maintain the cohesion of the electrode during different cycles of charge and discharge (3). The graphene synthesis was performed according to the Hummers method and leads to particles whose specific surface area is about 200 m² /g (Figure 1).

Electrode materials were characterized by different techniques (TGA-MS, BET, SEM, IR / Raman spectroscopy, cyclic voltammetry, galvanostatic cycles ...) at different stages (graphene modification, graphene / silicon coupling) to show the presence of molecular bridges and determine their influence on the electrochemical behavior of a Li-ion battery. Performance measured 0.16A.g^-1 (Figure 2) clearly show a significant improvement in grafted materials compared to a simple mixture of graphene / Silicon materials.

Acknowledgments: The authors thank the French National Research Agency (Graf'N'Stock project) for financial support.

References

(1) M. N. Obrovac, L. Christensen, Electrochem. Solid-State Lett. 7 (2004) A93

(2) C. Martin., O. Crosnier, R. Retoux, D. Bélanger, D. M. Schleich, T. Brousse, Advanced Functional Material 21 (2011) 3524

(3) B. Nguyen, N. Kumar, J. Gaubicher, F. Duclairoir, T. Brousse, O. Crosnier, L. Dubos, G. Bidan, D. Guyomard, B. Lestriez, Adv. Energy, Materials, (2013) 3, 1351