Silicon-Rich Amorphous SiC_x for the Lithium-Ion Batteries: How Does Strong Carbon Doping Affect the Lithiation...

Amorphous, substoichiometric silicon carbide (a-SiC_x) is explored as an anode material for lithium-ion batteries. Silicon-rich a-SiC_x nanopowders with different carbon concentrations yet otherwise comparable properties are produced and processed into electrodes. By electrochemical testing, performance data for the different materials are obtained, and in a second step, correlated with further information from detailed analysis of the lithiation and delithiation behavior as well as electrode morphology evolution dependent on the carbon concentration. An increased lithium loss in the first cycle can be linked to the carbon content in the sample, suggesting a matrix-phase-like behavior. In the first cycles, roughly 1 atom of lithium is lost per atom of carbon in the sample, and additionally, each carbon atom inertises up to 2 Si atoms. Cycling stability, on the other hand, is highest for 25.9 at.% C, with no capacity fade after 200 cycles and excellent rate capability. With a lower anode potential and reduced voltage hysteresis, especially during fast-charging, the carbon-rich samples show further benefits. Data from fast-charging and impedance analysis indicate that the solid electrolyte interphase (SEI) remains stable over long-term cycling for the carbon-rich materials. Postmortem analysis confirms the assumption that the material is operating around a rather high lithiation state.