Hydrothermal synthesis and characterization of Co2.85Si0.15O4 solid solutions and its carbon composite as negative electrodes for Li-ion batteries

• Facile hydrothermal method was used to synthesise Co2.85Si0.15O4 solid solution.
• The structural analysis of Co2.85Si0.15O4 was carried out using Rietveld refinement.
• FE-SEM images reveals that the formation of uniform cube shape Co2.85Si0.15O4 particles.
• The Co2.85Si0.15O4@C composite delivered the enhanced capacity and better cycling stability.

Co2.85Si0.15O4 solid solution was successfully synthesized using a facile hydrothermal method for the first time. The structural and morphological features of prepared powders were thoroughly investigated by different techniques. The Rietveld refinement assured the formation of spinel structured Co2.85Si0.15O4 without any impurity phases. The FT-IR and Raman spectrums revealed the presence of SiO2, and carbon with the Co2.85Si0.15O4 solid solution. The X-ray photoelectron spectroscopy inferred that the Co exists in +2 and +3 oxidation state and Si exists in multivalence state. Surface morphological analysis demonstrated that the formation of cube shape Co2.85Si0.15O4 microparticles are embedded in to amorphous SiO2 matrix, which was confirmed using SAED pattern. The inactive nature of amorphous SiO2 in Co2.85Si0.15O4 was confirmed by CV studies. Consequently, it was electrochemically active while making composite with carbon, since it reduces SiO2 into SiOx. The cycling stability of Co2.85Si0.15O4@C composite provided superior electrochemical performance than the pristine Co2.85Si0.15O4. The composite delivers the specific capacity of 444 mAh g−1 at 75 mA g−1 after 50 cycles with feeble capacity fading. The EIS spectra corroborates the composite exhibit the lower charge transfer resistance (Rct) and solid electrolyte interphase resistance (RSEI) compared to pristine Co2.85Si0.15O4. This further confirmed that carbon composite enhanced the inherent conductive nature and rate capability of pristine Co2.85Si0.15O4 electrode.