Resorcinol-Formaldehyde Carbon Xerogels as Anode Material for Lithium-Ion Battery: Synthesis, Grinding and Coating on Current Collector

Rechargeable lithium-ion batteries show great advantages over traditional batteries and are extensively used for consumer electronic devices due to their high energy density and long cycle life. However, the improvement of performance of current lithium-ion batteries requires the optimization of the materials used (electrolyte and electrodes). Therefore, tremendous efforts have been dedicated to exploring new materials with high capacity, excellent cycling performance, low cost and high safety features [1-3]. As an example, carbon xerogels are promising candidates in the development of new high performance C-based anode materials for Li-ion batteries, since such carbonaceous materials show very small changes of volume during the charge/discharge process, providing a long cycle life. Nevertheless, hard carbons also exhibit quite high irreversible capacity losses due to their intrinsic high microporosity [4]. To overcome these disadvantages, the structural and textural characteristics need to be carefully controlled. Also, due to the different morphology of these materials compared to graphite, the deposition of carbon xerogels on current collectors needs to be studied in detail.

In this work, porous carbon xerogels have been synthesized from Resorcinol-Formaldehyde mixtures by adjusting the pH of the solution in order to obtain different mesopore sizes. Monoliths of carbon xerogels are obtained after drying of the polymer gel and pyrolysis [5].
These monoliths have been ground by two different methods and particle size distributions were measured by granulometry. Mercury intrusion porosimetry and nitrogen adsorption techniques (BET) have been used to characterize the pore texture of the monolithic and the powder materials. Different conditions have been used for the mixing of carbon xerogels with a binder and a solvent to form slurries. The latter have been cast on a copper foil using bar coating with different openings. After evaporation of the solvent, the resulting coatings were analyzed using scanning electron microscopy (SEM) for the morphology and their thickness was monitored by profilometry.

First results indicate that the method of grinding has no influence on the final particle size distribution of the powder. The structural features of the carbon xerogels is well preserved for particles down to one micrometer. Nevertheless, a study of grinding duration shows that additional particles with sizes close to that of the porosity of the carbon appear. As a consequence, the grinding conditions were chosen so as to obtain a compromise between particles small enough to realize a coating on a current collector and particles large enough to maintain the carbon gel structural characteristics.

References

1) Goodenough J.B., Kim Y. J. Power Sources 2011; 196(16): 6688-6694.
2) Bruce P.G. Solid State Ionics 2008; 179: 752-760.
3) Cairns A. J., Albertus P. Ann. Rev. Chem. Biomol. Eng. 2010; 1: 299-320.
4) Tran T., Yebka B., Song X., Nazri G., Kinoshita K., Curtis D. J. Power Sources 2000; 85: 269-278.
5) Job N., Théry A., Pirard R., Marien J., Kocon L., Rouzaud J., Béguin F., Pirard J. Carbon 2005; 43: 2481-2494.