New Insights into Understanding Irreversible and Reversible Lithium Storage within SiOC and SiCN Ceramics

Abstract

Within this work we define structural properties of the silicon carbonitride (SiCN) and silicon oxycarbide (SiOC) ceramics which determine the reversible and irreversible lithium storage capacities, long cycling stability and define the major differences in the lithium storage in SiCN and SiOC. For both ceramics, we correlate the first cycle lithiation or delithiation capacity and cycling stability with the amount of SiCN/SiOC matrix or free carbon phase, respectively. The first cycle lithiation and delithiation capacities of SiOC materials do not depend on the amount of free carbon, while for SiCN the capacity increases with the amount of carbon to reach a threshold value at ~50% of carbon phase. Replacing oxygen with nitrogen renders the mixed bond Si-tetrahedra unable to sequester lithium. Lithium is more attracted by oxygen in the SiOC network due to the more ionic character of Si-O bonds. This brings about very high initial lithiation capacities, even at low carbon content. If oxygen is replaced by nitrogen, the ceramic network becomes less attractive for lithium ions due to the more covalent character of Si-N bonds and lower electron density on the nitrogen atom. This explains the significant difference in electrochemical behavior which is observed for carbon-poor SiCN and SiOC materials.

Structural Design of Polymer‐Derived SiOC Ceramic Aerogels for High‐Rate Li Ion Storage Applications

“…Low carbon SiOC has high initial capacities but lacks cycling stability. The optimized compositions in terms of reversible capacity and cyclability have been found close to the 50/50 wt% between the free carbon and SiOC amorphous matrix …”

UV Raman spectroscopy of segregated carbon in silicon oxycarbides

“…Polymer-derived ceramics possess a variety of interesting properties like outstanding thermal stability against decomposition and crystallization, 1)3) excellent high-temperature creep resistance, 4), 5) piezoresistivity at ambient as well as high temperature, 6) high reversible capacity concerning lithium-ion uptake and release 7) and electromagnetic shielding 8) which all rely on the presence of a segregated carbon phase randomly distributed within a glassy matrix.…”

Electrochemical Li Storage Properties of Carbon-Rich B–C–N Ceramics

“…The first cycle charging capacity of BC 4 N is much higher and amounts to 1030 mAh¨g´1, while the discharge capacity amounts to 737 mAh¨g´1, with a much higher first cycle efficiency of 72%. It should also be noted that most of the capacity is recovered below 1.5 V, and the investigated materials present reduced hysteresis in comparison to other polymer-derived electrode material [18,36]. TEM micrographs for both BC2N and BC4N are presented in Figure 3.…”

“…Core-shell silicon oxycarbide-carbon nanotubes composites demonstrate extremely high capacities of~800 mAh¨g´1 and good capacity recovering at high current [33], while embedding of silicon nanoparticles in SiOC matrix lead to material stabilization with respect to prolonged cycling [34,35]. Outstanding electrochemical properties of SiOC and SiCN materials with respect to reversible lithium storage have been explained in relation to their complex amorphous nanostructure and the presence of a high amount of disordered free carbon distributed in the final ceramic matrix [28,[36][37][38]. However, initial irreversible capacity loss is still a concern for these silicon-based PDCs.…”