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<p>Birnessite-type MnO<sub>2</sub> (BM) is a promising anode material for lithium-ion batteries (LIBs) due to its high theoretical capacity and low lithiation voltage. However, its poor conductivity and structural instability limit long-term performance. In this work, we report an optimized in situ hydrothermal synthesis of BM–graphene (BM–Gr) composites, guided by thermodynamic equilibrium modeling using the HSC Chemistry software package to model phase formation. The effects of NaOH/H<sub>2</sub>O<sub>2</sub> concentration, reaction time, and graphene loading on phase stability and morphology were systematically studied and validated experimentally. Structural, morphological, and compositional analyses (XRD, FE-SEM, EDS, TEM, and XPS) confirmed that pure birnessite was successfully synthesized and uniformly anchored on graphene, without secondary phases such as Mn<sub>3</sub>O<sub>4</sub> or MnOOH. Graphene incorporation induced oxygen vacancies (V<sub>O</sub>) and Mn–O–C interfacial bonding, narrowing the bandgap from 1.7 (BM) to 1.4&#xa0;eV (BM–Gr). The optimized BM–Gr electrode delivered an initial lithiation capacity of 2097&#xa0;mAh&#xa0;g<sup>−1</sup> and maintained 758&#xa0;mAh&#xa0;g<sup>−1</sup> after 175 cycles at 450&#xa0;mA&#xa0;g<sup>−1</sup>, compared to 86&#xa0;mAh&#xa0;g<sup>−1</sup> for BM after 50 cycles. Electrochemical impedance spectroscopy revealed an ~ 18-fold increase in the Li⁺ diffusion coefficient after cycling (7.10 × 10<sup>–13</sup> to 1.27 × 10<sup>–11</sup>&#xa0;cm<sup>2</sup>&#xa0;s<sup>−1</sup>), attributed to improved ion transport pathways and enhanced structural stability from the conductive graphene framework. These results demonstrate that thermodynamically guided BM–Gr synthesis provides a viable strategy for producing structurally robust, high-capacity anodes for next-generation LIBs.</p>

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Optimization of in situ hydrothermal synthesis of birnessite MnO2/graphene composite: thermodynamic insights and enhanced electrochemical performance for Li-ion battery anodes

  • 期刊论文

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  • 发表日期：

    2025年9月23日

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  • Azadeh Abdi,
  • Rasoul Sarraf-Mamoory,
  • Michael Stich,
  • Christoph Baumer,
  • Fabian Ullmann,
  • Stefan Krischok,
  • Andreas Bund

摘要

Birnessite-type MnO2 (BM) is a promising anode material for lithium-ion batteries (LIBs) due to its high theoretical capacity and low lithiation voltage. However, its poor conductivity and structural instability limit long-term performance. In this work, we report an optimized in situ hydrothermal synthesis of BM–graphene (BM–Gr) composites, guided by thermodynamic equilibrium modeling using the HSC Chemistry software package to model phase formation. The effects of NaOH/H2O2 concentration, reaction time, and graphene loading on phase stability and morphology were systematically studied and validated experimentally. Structural, morphological, and compositional analyses (XRD, FE-SEM, EDS, TEM, and XPS) confirmed that pure birnessite was successfully synthesized and uniformly anchored on graphene, without secondary phases such as Mn3O4 or MnOOH. Graphene incorporation induced oxygen vacancies (VO) and Mn–O–C interfacial bonding, narrowing the bandgap from 1.7 (BM) to 1.4 eV (BM–Gr). The optimized BM–Gr electrode delivered an initial lithiation capacity of 2097 mAh g−1 and maintained 758 mAh g−1 after 175 cycles at 450 mA g−1, compared to 86 mAh g−1 for BM after 50 cycles. Electrochemical impedance spectroscopy revealed an ~ 18-fold increase in the Li⁺ diffusion coefficient after cycling (7.10 × 10–13 to 1.27 × 10–11 cm2 s−1), attributed to improved ion transport pathways and enhanced structural stability from the conductive graphene framework. These results demonstrate that thermodynamically guided BM–Gr synthesis provides a viable strategy for producing structurally robust, high-capacity anodes for next-generation LIBs.