Urchin-like α-MnO2 formed by nanoneedles for high-performance lithium batteries

Nanostructured MnO2 as Electrode Materials for Energy Storage

“…The synthetic methods for nanostructured MnO 2 include simple reduction, coprecipitation, sol-gel, thermal decomposition, and the hydrothermal synthesis molten-salt method (see [31] for a review). Various nano-structured objects investigated over the years include nanowires [32,33,34], nanorods [35,36], nanoflowers [37], nanosheets [38], nanoflakes [39,40], nanotubes [41,42], nanourchins [43,44], nanospheres [45], nanobelts [46], nanodisks [47], and nanofibers [48]. The various morphologies of nanostructure MnO 2 materials are illustrated by the SEM images in Figure 4.…”

“…All nano-samples have a similar formation of layered δ -MnO 2 . β - and γ -MnO 2 grown as nanowires/nanorods (Figure 7), while α -MnO 2 and todorokite-type MnO 2 have fiber or needle morphologies [43]. Well-crystallized nanorods of α -MnO 2 (12 nm diameter) were prepared by the hydrothermal route in the presence of poly(sodium 4-styrene-sulfonate) using KMnO 4 and MnSO 4 mixed in a solution of water and ethanol (4:1 in volume) [65].…”

“…MnO 2 nanowires and nanorods were formed with the assistance of cetyltrimethyl ammonium bromide and polyvinyl pyrrolidone, respectively [81]. Figure 8 shows the typical X-ray diffraction pattern of the α -K x MnO 2 structure synthesized by the sol-gel route [43]. …”

Nanotechnology of Positive Electrodes for Li-Ion Batteries

“…Using ascorbic acid (vitamin C) as a single chelator, the product crystallizes in the tetragonal structure of the α-MnO2 cryptomelane (space group I4/m) with a 2 × 2 tunnels. The mean crystallite size of the α-MnO2 nanoneedles is Lc = 14 nm [13]. The same material prepared by a green technique using a mixed chelator composed by bio-reagents such as those that exhibit a smaller crystallite size of 6.4 nm, which results in primary nanorods of ~17 nm in diameter and 84 nm in length.…”

“…The same material prepared by a green technique using a mixed chelator composed by bio-reagents such as those that exhibit a smaller crystallite size of 6.4 nm, which results in primary nanorods of ~17 nm in diameter and 84 nm in length. Slight modifications of the synthesis recipe induce different morphologies of nanostructured α-MnO2; for instance, sea-urchin-like shape, with a diameter of ~3 μm, were prepared in acidic conditions [13], while a neutral medium provided a caddice-clew-like MnO2 showing lower electrochemical performance [14]. The use of mixed chelator has been successful for the growth of Li-riche layered compounds.…”