Effect of Different Carbon Precursors on SiO2/C Anodes for Li-Ion Batteries
Authors: Blanco Maria Valeria , Renman Viktor , Vullum-Bruer Fride 
Published: February 2020

Lithium ion batteries (LIBs) are widely used as a power source for different portable electronic devices and are considered as potential power sources for future electric vehicles and large-scale grid energy storage. However, in order to meet the demands of large-scale applications, higher energies and power densities need to be reached. In the case of commercial negative electrodes, a benchmark of a stable capacity of 1000 mAhg-1 has been established for next-generation high capacity LIBs [1].

Current LIBs use graphite as anode material, which reacts with lithium ions via intercalation inside its host structure. This kind of interaction causes minor structural changes in the host material and provides high stability and long durability to the anode. However, as the number of lithium ions that can be retained by the host structure is limited, its reversible capacity of 372 mAhg-1 cannot be enhanced. Therefore, in order to use LIBs for large-scale applications, different materials are being currently explored to replace low-capacity graphite anodes.

Among different materials, Silicon has been pinpointed as a very promising anode for next-generation high capacity LIBs, since it presents a maximum theoretical capacity of 4200 mAhg-1. However, as its interaction with lithium is via alloying/dealloying reactions, the material suffers from large volume changes during lithiation and delithiation, which causes strain and stress on the silicon lattice, leading to mechanical instabilities and fast degradation in the electrochemical performance of the anode. Another possible candidate is silica, which presents a compromise solution between the two former materials. It has a maximum theoretical capacity of 1695mAhg-1 and exhibits much less volume variation during lithiation/delithiation compared with silicon. Besides, silica is one of the most abundant materials on earth [2-4], which is of key importance from the point of view of large-scale applications.

Given that silica is an insulator, carbon-coating treatments are essential in order to decrease the electronic resistance of the electrode. In this work, we perform a systematic study to evaluate the effect of three different carbon precursors on the carbon coating of amorphous SiO2 nanoparticles to be used as anode material in LIBs. SiO2 particles were carbon coated with different amounts (20%, 40%, 60% and 80%) of glucose, sucrose and cornstarch and heat treated at high temperature under inert atmosphere. Structural, microstructural and textural properties of SiO2/C samples were analyzed in order to select the most suitable carbon precursor and to determine which amount leads to better properties. Results of thermogravimetric analysis showed a non-linear dependence between the effective carbon content on carbon coated samples and the amount of carbon precursor used. Raman spectroscopy results revealed the presence of D and G bands, which are characteristic of carbonaceous materials. Results of EDX mapping showed that carbon was homogeneously distributed on SiO2 particles and TEM bright field micrographs revealed the porous nature of the carbon layer that surrounded SiO2 particles. Gas absorption measurements indicated, in most of the cases, an increase in the total area with increasing carbon precursor content. X-ray diffraction measurements showed that SiO2 was still amorphous after the high temperature heat treatment. Finally, the electrochemical performance of the anode was evaluated and related to microstructural and textural properties.

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