High‑Capacity Si/Graphene Composite Anode Fabricated via Magnesium‑Thermal Reduction for Li‑Ion Batteries

Abstract

We report a novel, scalable route to synthesize a silicon/graphene (Si/G) composite anode through in‑situ generation of SiO₂ nanoparticles on graphene sheets followed by magnesium‑thermal reduction. The resulting MR‑Si/G material combines a uniform distribution of nanoscale Si particles within a conductive graphene matrix, mitigating the 400‑% volume expansion of silicon and enhancing electronic conductivity. Electrochemical testing in 2032 coin cells shows a reversible capacity of 950 mAh g⁻¹ at 50 mA g⁻¹ after 60 cycles, demonstrating superior cycling stability and high energy density for next‑generation Li‑ion batteries.

Background

Silicon offers a theoretical capacity (~4200 mAh g⁻¹) an order of magnitude higher than commercial graphite, but its practical use is limited by large volume changes and rapid capacity fade. Recent strategies—nanostructuring silicon, embedding it in carbon matrices, and employing graphene—have improved performance, yet challenges remain. In this work we combine a hydrothermal SiO₂/graphene precursor with magnesium‑thermal reduction to produce a robust, high‑capacity Si/graphene composite.

Experimental

Materials synthesis. Graphene oxide (GO) was prepared from flake graphite via the modified Hummers method. GO (1 mg mL⁻¹) was mixed with ethanol, CTAB, and TEOS, followed by ammonia‑adjusted pH 10 and hydrothermal treatment at 180 °C for 10 h. The resulting SiO₂/GO composite was dried and subjected to magnesium‑thermal reduction: a 1:1 weight ratio of composite to Mg powder was ground, heated at 800 °C for 4 h under Ar, then washed with 1 M HCl to remove MgO by‑products. The final MR‑Si/G composite contains ~70 wt % Si.

Characterization. Phase composition was assessed by XRD (D/max 2500PC); morphology by FE‑SEM (SUPRA55) and TEM (JEM‑2100). Raman and FTIR spectra were recorded on a Renishaw RM2000 and NICOLET 560, respectively. Si content was quantified by TGA (NETZSCH TG 209F1 Libra) from 25 °C to 800 °C under air. Electrochemical performance was evaluated in 2032 coin cells (80 % MR‑Si/G, 10 % Super‑P, 10 % CMC) on Cu foil, with Li metal counter electrode and 1 M LiPF₆ in EC/DMC/EMC (1:1:1) electrolyte. Cycling tests were conducted between 0.01–3 V at 50 mA g⁻¹.

Results and Discussion

Synthesis mechanism. The schematic (Figure 1) illustrates the formation of SiO₂ nanoparticles on GO, followed by Mg‑assisted reduction to metallic Si embedded within the graphene lattice. XRD patterns (Figure 2) confirm the disappearance of GO peaks and the presence of crystalline Si, while acid washing removes residual MgO. Raman spectra (Figure 3) reveal a Si peak at ~516 cm⁻¹ and an increased I_D/I_G ratio (from 0.93 to 1.19), indicating successful Si integration and slight defect introduction. FTIR (Figure 4) shows characteristic Si–O vibrations, confirming the transformation from SiO₂ to Si.

Microstructure. SEM/TEM images (Figure 5) display uniformly dispersed ~500 nm Si nanoparticles on corrugated graphene sheets, providing mechanical buffer and continuous conductive pathways. TGA (Figure 6) indicates 70 wt % Si content.

Electrochemical performance. The first three charge/discharge curves (Figure 7) reveal an initial discharge capacity of 1570 mAh g⁻¹ (MR‑Si/G) versus 3279 mAh g⁻¹ for pure Si, with Coulombic efficiency of 75.5 % due to SEI formation. After 60 cycles at 50 mA g⁻¹, MR‑Si/G retains ~950 mAh g⁻¹, whereas pure Si drops to ~125 mAh g⁻¹ (Figure 7 c). Rate capability tests (Figure 7 d) show capacities of 1087, 915, 753, and 671 mAh g⁻¹ at 50, 100, 200, and 500 mA g⁻¹, respectively, and recover 950 mAh g⁻¹ when returning to 50 mA g⁻¹.

CV (Figure 8) confirms reversible Li/Si alloying reactions with characteristic peaks at 0.16 V (lithiation) and 0.31/0.50 V (delithiation). EIS (Figure 9) shows lower SEI resistance for MR‑Si/G compared to pure Si, underscoring the role of graphene in enhancing conductivity and stabilizing the electrode interface.

Conclusions

We have developed an efficient, low‑cost method to produce a Si/graphene composite anode via hydrothermal synthesis and Mg‑thermal reduction. The embedded Si nanoparticles within the graphene matrix effectively accommodate volume changes, resulting in a reversible capacity of 950 mAh g⁻¹ after 60 cycles at 50 mA g⁻¹. This material offers a promising platform for high‑energy Li‑ion batteries.