Proposition of PhD thesis

 

Silicon/carbon nanocomposites for high performance lithium/ion battery anodes

 

Nowadays, improving the energy efficiency of systems is an important objective for reducing fossil fuel consumption and CO₂ emissions. Electrochemical energy storage systems are able to take an important part in this strategy, allowing lost energy to be recovered and further delivered on demand. Among the electrochemical systems, lithium-ion batteries are one of the most promising, especially for automotive applications. However, the storage capacity of negative carbon electrodes (372 mAh/g) is not enough high for affording important energy needs. Therefore, it is necessary to develop new electrode materials.

 

Having a theoretical capacity of 3578 mAh/g (Li3,75Si), silicon seems to represent an interesting alternative to carbons. However, due to its important volumetric expansion (~300%), the electrodes based on silicon are rapidly damaged with simultaneous performance loss of the battery. In this context, strategies have been developed in order to preparing more performing materials based on silicon. It has been especially claimed that performance can be improved when using carbon/silicon nanocomposites. In our case, we have selected to preparing these composites by mechanical milling of silicon/carbon mixtures. Since our first results are very promising, this PhD thesis will be devoted to improve the preparation conditions by controlling the atmosphere, time, presence of solvent, nature of carbon and silicon precursors …Then, electrodes will be manufactured from the composites and implemented in lithium batteries. Electrochemical cycling protocols will be adjusted in order to enhance the cycle life of the accumulators. 

 

The experimental work will be performed in Research Centre on Divided Matter (Orléans) and in CEA/LITEN (Grenoble). The prepared nanocomposites will be characterized by structural and textural techniques : X ray diffraction (XRD), Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), X ray Photoelectron Spectroscopy (XPS), gas adsorption, Thermoprogrammed Desorption, …Electrochemical measurements will be essentially realized by galvanostatic charge/discharge. Other techniques, as cyclic voltammetry, impedance spectroscopy, might be also applied. In situ 7Li NMR experiments during the charge/discharge of a battery are also planned to investigate the state of lithium.

 

Grant financed by CNRS and CEA

 

Contacts:

François Béguin (beguin@cnrs-orleans.fr); ++33 (0)238255375

Encarnacion Raymundo-Pinero (raymundo@cnrs-orleans.fr); ++33(0)238255361