Manganese‐Oxide‐Based Electrode Materials for Energy Storage Applications: How Close Are We to the Theoretical Capacitance?

Abstract

Of the transition metals, Mn has the greatest number of different oxides, most of which have a special tunnel structure that enables bulk redox reactions. The high theoretical capacitance and capacity results from a greater number of accessible oxidation states than other transition metals, wide potential window, and the high natural abundance make MnO species promising electrode materials for energy storage applications. Although MnO electrode materials have been intensely studied over the past decade, their electrochemical performance is still insufficient for practical applications. Currently, there is a trade-off between specific capacitance and loading mass. MnO species have intrinsically poor electrical conductivity, and current structural designs are not sophisticated enough to accommodate enough redox-active sites. Recent studies have certainly made progress in increasing capacitance through making use of electrically conductive components and controlling the morphology of the MnO species to expose more surface area. To increase the capacitance of MnO electrodes to the largest extent without limiting loading mass, further structural design at the nanoscale and manipulation of the electrically conductive component are required. An ideal nanostructure is proposed to guide future research toward closing the gap between achieved and theoretical capacitance, without limiting the loading mass.

MnO2/Carbon Composites for Supercapacitor: Synthesis and Electrochemical Performance

“…Therefore, the improvement of active materials mainly involves high reversible capacitance, structural stability, and rapid cation diffusion at high charge/discharge rates. A useful and direct approach is to uniformly modify MnO 2 materials onto layered porous conductive functional carbon materials to construct electrodes (Hu et al, 2018). The carbon materials can be served as a highly conductive and stable current collector, and its interconnection holes are beneficial for ion diffusion, whereas MnO 2 can shorten the transmission distance of ions to prepare a high-performance electrode material.…”

Self-assembled α-MnO2 urchin-like microspheres as a high-performance cathode for aqueous Zn-ion batteries

“…Typically, AZIBs consist of an intercalation-type cathode, a zinc metal anode and a Zn 2+ -based aqueous electrolyte, which demonstrate attractive features of large theoretical capacity (820 mA h g −1 and 5855 mA h cm −3 ), wide working potential window (0-2 V), reversible plating/stripping of Zn, high safety, environmental friendliness, low cost and facile manufacturing process [1][2][3][4]. Since Kang's group [5] [6][7][8][9]. Among them, the α-MnO 2 -based AZIBs exhibit the highest specific capacity of more than 380 mA h g −1 , long-term reversibility and extraordinary rate capability, which benefit from their 2×2 tunnel structure with corner-sharing double MnO 6 octahedra chains [10].…”

“…The bigger AUMs were urchin-like microspheres with hollow cavity, while the smaller AUMs were radiating agglomerates of the α-MnO 2 nanofibers. The assembled AUM-based ZIBs achieved high initial capacity of 308.0 mA h g −and maintained at 243 6. mA h g −1 after 200 cycles.…”

MOF-derived manganese oxide/carbon nanocomposites with raised capacitance for stable asymmetric supercapacitor

“…However, like other TMO materials, their performance is affected by poor electrical conductivity and low surface area, when derived from the conventional solution processing routes. [28][29][30][31] To improve the capacitance of manganese oxides, especially upon high loading mass, an apparent strategy is to develop MOF-derived manganese oxide/carbon nanocomposites, as mentioned above. 29 According to Das and et al, it is feasible to transform Mn-MOFs into manganese oxide/carbon nanocomposites by calcination in an inert atmosphere.…”

“…[28][29][30][31] To improve the capacitance of manganese oxides, especially upon high loading mass, an apparent strategy is to develop MOF-derived manganese oxide/carbon nanocomposites, as mentioned above. 29 According to Das and et al, it is feasible to transform Mn-MOFs into manganese oxide/carbon nanocomposites by calcination in an inert atmosphere. 32 Nevertheless, MnO x is one of the rather complicated oxides with variable valences, phases and structures.…”