Amorphous SiCO ceramics exhibit a high Li storage capacity and are promising anode materials. The capacity per gram of SiCO material exceeds that of graphite by a factor of 2 to 3; relative to the amount of “free” carbon in SiCO materials by a factor of close to 6. Hence, in SiCO the ratio is 1 Li for every “free” C – in comparison to graphite, which reaches its limit with the composition LiC6. While Li storage of SiCO is supported by several studies, persists even after 1000 cycles of charging and discharging, the capacity and mechanisms of Li insertion are not understood –– not at least due to the difficulties in structural characterization of amorphous ceramics. To provide some light on the subject, we present combined modeling and simulation studies of Li insertion in SiCO. Atomistic models of amorphous SiCO in various forms, glasses with and without so-called “free” carbon, a variety of SiO2-C bilayer systems, and nano-structured SiCO models have been crafted and investigated within density functional theory. Random insertion of Li atoms tests for sites with high and favorable insertion energy. As shown previously, Li prefers bonding to O as cationic Li+, while the surplus electron is promoted to unoccupied states. The SiC content of the SiCO glass phase changes the chemical potential of unoccupied states and impacts the enthalpy of insertion. Furthermore, availability and locality of an electron reservoir – in the form of extended aromatic carbon units or graphene – affect favorable Li sites and distribution of the stored charge. Li reacts with this SiO2 layers creating a partially reduced LiSiO phase, which adds to the storage capacity of graphene layers. Though not yet complete, the picture we deliver provides motivation for multiple experimental studies.

Li insertion in SiCO anode materials: On the way to understand capacity and mechanisms

254th National Meeting (2017)

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