An unexpected large capacity of ultrafine manganese oxide as a sodium-ion battery anode

Abstract

MnO2 is shown for the first time to be electrochemically active as a conversion anode for Na-ion batteries (NIBs). Space-confined ultrafine (UF)-MnO2, with an average crystal size of 4 nm, synthesized using a porous silicon dioxide templated hydrothermal process exhibits a high reversible sodiation capacity of 567 mA h g(-1), in contrast to the negligible activity shown by the aggregates of larger (14 nm) MnO2 nanocrystallites. The remarkably enhanced sodiation activity of the UF-MnO2 is attributable to its greatly reduced crystal size, which facilitates diffusion of Na ions, along with high surface energy arising from extensive heterogeneous interfacial bonding with the SiO2 surrounding. The UF-MnO2 anode exhibits an exceptional rate and cycle performance, exhibiting >70% capacity retention after 500 cycles. In operando synchrotron X-ray absorption near-edge structural analysis reveals combined charge-storage mechanisms involving conversion reaction between Mn(III) and Mn(II) oxides, Mn(III)-O1.5 + Na(+) + e(-)- ↔ 1/2Na2O + Mn(II)-O, and non-Mn-centered redox reactions. The finding suggests a new strategy for "activating" the potential electrochemical electrode materials that appear inactive in the bulk form.

Facile Synthesis of Nanostructured MnO2 as Anode Materials for Sodium‐Ion Batteries

“…There are several peaks at 12.7° (110), 18.1° (200), 25.7° (220), 28.8° (310), 37.5° (211), 41.9° (301), 49.8° (411), 56.3° (600), 60.2° (521), 65.2° (002), and 69.5° (541), which can be indexed to a pure phase of MnO 2 (JCPDS 44‐0141). In the case of MnO 2 nanoflowers, the broad peak features with four obvious peaks at 12.7°, 25.7°, 37.5° and 65.2° reveal the nanocrystalline nature of MnO 2 owing to the ultrathin nanopetals with a thickness of about 10 nm, which is similar to previous studies . Figure b displays the nitrogen adsorption/desorption isotherm of MnO 2 nanorods and nanoflowers.…”

“…Two charge potential plateaus at around 1.2 V and 2.4 V correspond to the formation of MnO 2 , which is consistent with the results of cyclic voltammetry (Figure c). The discharge plateau at close to 0.01 V may be ascribed to non‐Mn‐centered redox reactions, such as the interfacial sodium insertion and surface space‐charge layer, which is similar with the conversion anodes in LIBs …”

“…As a transition metal oxide, manganese dioxide has been extensively investigated as supercapacitor electrode and a promising potential anode material for LIBs due to its high theoretical lithium storage capacity (1230 mA h g −1 ), low operating voltage and natural abundance . However, as a promising anode material, manganese dioxide was rarely reported for the application in SIBs to date . What is more, nanostructure engineering has attracted much attention as an effective method in promoting performance.…”

In Situ Growth of a Feather‐like MnO2 Nanostructure on Carbon Paper for High‐Performance Rechargeable Sodium‐Ion Batteries

“…Meanwhile, it was proved that nanostructured MnO 2 materials could achieve better electrochemical performance. For instance, space‐confined MnO 2 nanocrystallites exhibited an initial discharge capacity of 567 mAh g −1 . Zhang et al reported that MnO 2 nanorods and nanoflowers could deliver an initial specific capacity of 427 and 488 mAh g −1 , respectively .…”

“…The CV curves of as‐prepared MnO 2 on CP were shown in Figure . The reduction process for the 1st cycle was different with the subsequent 4 cycles, which might due to the formation of solid electrolyte interphase (SEI) film in the electrolyte surface and some irreversible structural changes in the 1st cycle . A redox peak at 0.9 V observed for the 1st cycle could be attributed to the electrochemical reaction of carbon paper, which was consistent with the CV curves of pure carbon paper in Figure S2.…”