Electrochemical performance of DVB-modified SiOC and SiCN polymer-derived negative electrodes for lithium-ion batteries

Chemical modification of commercially available polyorganosilazane (HTT1800) and polyorganosiloxane (Polyramic RD-684a) with divinylbenzene (DVB) is accomplished via hydrosilylation reaction. The incorporation of DVB leads to an increase of the free carbon amount after pyrolysis within the corresponding SiCN and SiOC ceramics. The modification is carried out with lower, equal and higher stoichiometric ratios of the SiH to CC groups present in the Si-based polymer and DVB. FTIR results indicate a complete consumption of the SiH bonds in the case of the stoichiometric amount of DVB and polymer RD-684a, while for HTT1800 neither the stoichiometric ratio nor DVB excess leads to a complete consumption of the SiH groups. For both SiCN and SiOC ceramics the carbon content is found to increase with the amount of DVB. However, the most significant increase in free carbon content is registered for SiCN samples, namely of ca. 40%. The carbon content changed from 9.9 wt.% in the pure HTT1800-derived material up to 49.3 wt.% for the SiCN ceramic obtained with the highest amount of DVB addition. Accordingly, Li-ion storage and therefore charge storage capacity are simultaneously increased, for the first cycle from 136 to 574 mAh g−1, while columbic efficiency is raised by 10% up to 60.4%.