Ordering Heterogeneity of [MnO6] Octahedra in Tunnel-Structured MnO2 and Its Influence on Ion Storage

Abstract

Correctly establishing a structure-property relationship is necessary to rationally develop energy materials for performance optimization. Bulk characterizations fall short of deciphering localized structural features at nanoscale and atomic scale. This work atomically resolves structural heterogeneity existing in single MnO 2 nanoparticles and demonstrates its significant effect on energy storage property, which was neglected by traditional bulk characterizations. Attention should thus be paid to controllable synthesis toward structural homogeneity with predictable/ tunable energy storage property and the proper choice of structural characterization tools. SUMMARY[MnO 6 ] octahedra are the structural units for a large family of manganese dioxides (MnO 2 ) possessing one-dimensional tunnel structures with extensive applications in catalysis and energy storage. Despite the long-range [MnO 6 ] ordering confirmed by conventional diffraction tools, surprisingly, the functional properties of a specific MnO 2 tunnel phase still vary significantly in literature with unclear structural origins. Here, we demonstrate the existence of tunnel heterogeneity featuring localized tunnel intergrowths within single MnO 2 nanoparticles via atomically resolved imaging. The degree of tunnel heterogeneity increases with the size increase of tunnels from b-MnO 2 (1 3 1 tunnel) to a-MnO 2 (2 3 2 tunnel), and to todorokite MnO 2 (3 3 3 tunnel). Furthermore, the tunnel heterogeneity within one MnO 2 nanoparticle significantly affects the energy storage kinetics even down to sub-nanometer scale. These findings are expected to call for renewed attention to the controlled synthesis of homogeneous tunnel-specific phases with predictable properties and to yield a more precise structure-property relationship in polymorphic materials.

Highly Reversible Lithium Storage of Nitrogen‐Doped Carbon@MnO Hierarchical Hollow Spheres as Advanced Anode Materials

“…Figure c and e present the TEM image and corresponding SAED pattern of NC@MnO HHSs after 200 cycles. In the SAED pattern (Figure e), the diffraction rings can be identified as the composite of MnO 2 and Li 2 O . In addition, during the initial 10 cycles in the CV curves of NC@MnO HHSs, with the cycle number increased, a weak peak at ca.…”

“…In the SAED pattern (Figure 8e), the diffraction rings can be identified as the composite of MnO 2 and Li 2 O. [49][50][51] In addition, during the initial 10 cycles in the CV curves of NC@MnO HHSs, with the cycle number increased, a weak peak at ca. 2.1 V appears and gradually enhances (Figure 5a and Figure S10a-b), which can originate from the further oxidization of Mn(II) to Mn (IV) with higher oxidation states, introducing the increasing capacity in the subsequent cyclic process.…”

Accommodation of Silicon in an Interconnected Copper Network for Robust Li‐Ion Storage

“…As shown in Figure a,b, lattice fringes with spacing of ≈0.18 nm are observed in C‐SCP, which is assigned to the (200) of Cu,19 taking into consideration that the interlayer spacing of graphite and Si is 0.34 and 0.31 nm (111), respectively. The enormous defects and grain boundaries in the Cu layer is beneficial for achieving fast transfer during cycling in LIBs 20. To better understand the fine structure of Cu layer, we removed the Si inner core in C‐SCP with HF and the product is denoted as C‐CP (see details in the Experimental Section).…”

Controllable Fabrication and Li Storage Kinetics of 1 D Spinel LiMn2O4 Positive Materials for Li‐ion Batteries: An Exploration of Critical Diameter

“…The different forms of MnO 2 possessing 1 D tunnel structures are determined by the arrangement mode of the [MnO 6 ] octahedral basic units . The K + concentration can be an important factor in controllable fabrication of α‐MnO 2 as it can serve as a template (corresponding to the chemical formula of K x MnO 2 ) in the formation of [2×2] tunnel, as can be seen in Figure a.…”

“…The different forms of MnO 2 possessing 1D tunnels tructures are determined by the arrangement mode of the [MnO 6 ]o ctahedral basic units. [29] The K + concentration can be an important factor in controllable fabrication of a-MnO 2 as it can serve as at emplate (corresponding to the chemical formula of K x MnO 2 )i nt he formation of [2 2] tunnel,a s can be seen in Figure2a. Furthermore, as eries of 1D a-MnO 2 nanorods with large diameters can be easily formed by self-assembled growth of numerous [2 2] tunnel arrays under conditions of ah igh K + concentration and more [MnO 6 ]o ctahedrons.…”