A Si−O−C Composite Anode: High Capability and Proposed Mechanism of Lithium Storage Associated with Microstructural Characteristics

Abstract

A blend of phenyl-substituted, branched polysilane, (Ph(2)Si)(0.85)(PhSi)(0.15), and polystyrene (1:1 in weight) has been transformed into a composite material consisting of graphene layers, Si-O-C glasses, and micropores through a pyrolytic polymer-to-ceramic conversion. Several analytical techniques have been employed to characterize the Si-O-C composite material, demonstrating the presence of the three components in its host framework. The Si-O-C composite material performs well in electrochemical operations with a characteristic voltage plateau, offering a capacity of more than 600 mA h g(-1). When polystyrene is not blended, the resulting comparative material is even less porous and shows a shorter voltage plateau in electrochemical operations. A broad resonance in the (7)Li NMR spectrum recorded at low temperature can be deconvoluted into three components in the fully lithiated state of the Si-O-C composite material derived from the polymer blend. This result indicates that the Si-O-C composite material electrochemically stores lithium species in interstitial spaces or edges of the graphene layers, directly or indirectly the Si-O-C glass phase, and the micropores. However, both the Si-O-C glass phase and micropores are minor as electrochemically active sites for lithium storage, and interstitial spaces or edges of the graphene layers act as major electrochemically active sites in this composite material. Despite the excellent cyclability of the Si-O-C composite material, the voltage plateau disappeared over cycling. This phenomenon suggests that the microstructure is delicate for repetitive lithium insertion and extraction and that newly formed sites must generate the nearly equal capacity.

Lithium intercalation into SiCN/disordered carbon composite. Part 1: influence of initial carbon porosity on cycling performance/capacity

“…Within the work of Reinold et al [12], the excellent performance of carbon-rich SiCN materials with outstanding stability and capacities up to 600 mAh g −1 has been demonstrated, including the discussion of the influence of the molecular polymer structure on the resulting ceramic microstructure and in consequence on the electrochemical performance of the material. By means of solid state NMR of lithiated and delithiated SiCN carbon phase was identified as a major lithium storage site [13], this finding being in agreement with the work of Fukui et al on SiOC materials [14]. Within our previous studies, we have also shown that composite anode materials comprised of SiCN/graphite [15] and SiCN/silicon [16] exhibit enhanced electrochemical properties compared to that of pure graphite and silicon, respectively.…”

High Rate Capability of SiOC Ceramic Aerogels with Tailored Porosity as Anode Materials for Li-ion Batteries

“…Silicon oxycarbides are ceramic structures with silicon bonded to both oxygen and carbon simultaneously. The structure of SiOC beside the amorphous silicon oxycarbide network -in which Si atoms share bonds with O and C atoms simultaneously-contains an interconnected disordered free carbon phase which accounts for many of their excellent mechanical and electrochemical properties [27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44]. It came out from our previous studies on SiOC and SiCN ceramic materials [32,52] that free carbon content is an important factor determining reversible Li storage capacity and cycling stability.…”

Lithiation Behavior of High Capacity SiCO Anode Material for Lithium-ion Battery: A First Principle Study

“…Because of the unique molecular structures, polymerderived silicon oxycarbide (SiCO) has a reversible capacity of $800 mA h g À1 and is considered as a promising anode materials for Li-ion battery [5][6][7][8][9][10][11]. SiCO has been extensively studied over the past years by experiments, and its unique nano-structure is believed to make a significant contribution to the excellent properties [5][6][7]11,12].…”