Synthesis and characterization of α-MnO2 nanowires: Self-assembly and phase transformation to β-MnO2 microcrystals

Zhang, Xiong; Yang, Wensheng; Yang, Junjiao; Evans, David G.

doi:10.1016/j.jcrysgro.2007.11.113

Cited by 80 publications

(44 citation statements)

References 33 publications

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“…And it also can be seen from the insert in Fig. 2(a) that the microrods are not in the cylindrical shape, but in the shape of pyramids, which is in accordance with that reported in the literature [18]. It is clear that the microrods are single-crystal ␤-MnO 2 from Fig.…”

Section: Resultssupporting

confidence: 90%

Temperature dependent dielectric characterization of manganese dioxide nanostructures with different morphologies at low frequency

Guan

Chen

Zhu

et al. 2010

Journal of Alloys and Compounds

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Section: Resultssupporting

confidence: 90%

Temperature dependent dielectric characterization of manganese dioxide nanostructures with different morphologies at low frequency

Guan

Chen

Zhu

et al. 2010

Journal of Alloys and Compounds

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“…5f, the attached belts tended to recrystallized to form a smooth surface. Similar oriented aggregation and recrystallization process is also discovered for a-MnO 2 [20,21].…”

Section: Growth Mechanismsupporting

confidence: 73%

Flux synthesis and growth mechanism of Na0.5MnO2 whiskers

Chu

Jiang

et al. 2011

Journal of Crystal Growth

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“…57 The simulated morphology is consistent with the macroscopic shape of β-MnO 2 determined by scanning electron microscopy (SEM). 18,58,59 Figure 2a shows an oblique view, while Figure 2b shows a view along c-axis and demonstrates that access to the route of facile c-axis migration is only available at the (101) and symmetry equivalent surfaces. The prominence of the (101) surface is consistent with previous ab intitio work on rutile MnO 2 60 and TiO 2 .…”

Section: Chemistry Of Materialsmentioning

confidence: 99%

Nanostructuring of β-MnO₂: The Important Role of Surface to Bulk Ion Migration

et al. 2013

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Manganese oxide materials are attracting considerable interest for clean energy storage applications such as rechargeable Li ion and Li−air batteries and electrochemical capacitors. The electrochemical behavior of nanostructured mesoporous β-MnO 2 is in sharp constrast to the bulk crystalline system, which can intercalate little or no lithium; this is not fully understood on the atomic scale. Here, the electrochemical properties of β-MnO 2 are investigated using density functional theory with Hubbard U corrections (DFT+U). We find good agreement between the measured experimental voltage, 3.0 V, and our calculated value of 3.2 V. We consider the pathways for lithium migration and find a small barrier of 0.17 eV for bulk β-MnO 2 , which is likely to contribute to its good performance as a lithium intercalation cathode in the mesoporous form. However, by explicit calculation of surface to bulk ion migration, we find a higher barrier of >0.6 eV for lithium insertion at the (101) surface that dominates the equilibrium morphology. This is likely to limit the practical use of bulk samples, and demonstrates the quantitative importance of surface to bulk ion migration in Li ion cathodes and supercapacitors. On the basis of the calculation of the electrostatic potential near the surface, we propose an efficient method to screen systems for the importance of surface migration effects. Such insight is valuable for the future optimization of manganese oxide nanomaterials for energy storage devices. KEYWORDS: lithium battery, surface, supercapacitor, DFT, cathode, manganese oxides ■ INTRODUCTIONEnergy storage for hybrid electric vehicles and renewable energy sources is a pressing technological challenge for which Li ion batteries and supercapacitors are key candidate systems. Due to rising future needs, there has been an intensive research effort to search for an alternative to the layered LiCoO 2 system conventionally used in rechargeable Li ion batteries. 1−4 Cobased materials pose problems due to high cost and environmental hazards upon disposal. Therefore, manganesebased oxides have been a promising class of materials for electrochemical energy storage. 5−10 β-MnO 2 has been extensively investigated as a cathode for rechargeable Li ion cells, but early work showed that bulk samples did not permit significant Li ion intercalation. 7,10,11 Initial work on β-MnO 2 supercapacitors 12 also indicated lower capacitance than for other polymorphs such as hollandite MnO 2 . Yet recent investigations have reinvigorated interest in the material. Mesoporous 10,13,14 and needle-like nanostructured 15,16 β-MnO 2 have been shown to allow good intercalation of Li ions. Both pore size and wall thickness of the mesoporous structures have been demonstrated to affect the rate capability. 9 The mesoporous β-MnO 2 cell has a capacity 10 of 284 mAh/g and good cycling stability. Recent studies of kinetics using ac impedance measurements 17 have demonstrated increased Li ion diffusion in nanosized materials. Additionally, β-MnO 2 has sho...

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Synthesis and characterization of α-MnO2 nanowires: Self-assembly and phase transformation to β-MnO2 microcrystals

Cited by 80 publications

References 33 publications

Temperature dependent dielectric characterization of manganese dioxide nanostructures with different morphologies at low frequency

Temperature dependent dielectric characterization of manganese dioxide nanostructures with different morphologies at low frequency

Flux synthesis and growth mechanism of Na0.5MnO2 whiskers

Nanostructuring of β-MnO₂: The Important Role of Surface to Bulk Ion Migration

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Synthesis and characterization of α-MnO2 nanowires: Self-assembly and phase transformation to β-MnO2 microcrystals

Cited by 80 publications

References 33 publications

Temperature dependent dielectric characterization of manganese dioxide nanostructures with different morphologies at low frequency

Temperature dependent dielectric characterization of manganese dioxide nanostructures with different morphologies at low frequency

Flux synthesis and growth mechanism of Na0.5MnO2 whiskers

Nanostructuring of β-MnO2: The Important Role of Surface to Bulk Ion Migration

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Nanostructuring of β-MnO₂: The Important Role of Surface to Bulk Ion Migration