Recently, room-temperature stationary sodium-ion batteries (SIBs) have received extensive investigations for large-scale energy storage systems (EESs) and smart grids due to the huge natural abundance and low cost of sodium. The SIBs share a similar "rocking-chair" sodium storage mechanism with lithium-ion batteries; thus, selecting appropriate electrodes with a low cost, satisfactory electrochemical performance, and high reliability is the key point for the development for SIBs. On the other hand, the carefully chosen elements in the electrodes also largely determine the cost of SIBs. Therefore, earth-abundantmetal-based compounds are ideal candidates for reducing the cost of electrodes. Among all the high-abundance and low-cost metal elements, cathodes containing iron and/or manganese are the most representative ones that have attracted numerous studies up till now. Herein, recent advances on both ironand manganese-based cathodes of various types, such as polyanionic, layered oxide, MXene, and spinel, are highlighted. The structure-function property for the iron-and manganese-based compounds is summarized and analyzed in detail. With the participation of iron and manganese in sodium-based cathode materials, real applications of room-temperature SIBs in large-scale EESs will be greatly promoted and accelerated in the near future.
It is highly desired but still remains challenging to design and develop a Co-based nanoparticle-encapsulated conductive nanoarray at room temperature for high-performance water oxidation electrocatalysis. Here, it is reported that room-temperature anodization of a Co(TCNQ) (TCNQ = tetracyanoquinodimethane) nanowire array on copper foam at alkaline pH leads to in situ electrochemcial oxidation of TCNQ into water-insoluable TCNQ nanoarray embedding Co(OH) nanoparticles. Such Co(OH) -TCNQ/CF shows superior catalytic activity for water oxidation and demands only a low overpotential of 276 mV to drive a geometrical current density of 25 mA cm in 1.0 m KOH. Notably, it also demonstrates strong long-term electrochemical durability with its activity being retrained for at least 25 h, a high turnover frequency of 0.97 s at an overpotential of 450 mV and 100% Faradic efficiency. This study provides an exciting new method for the rational design and development of a conductive TCNQ-based nanoarray as an interesting 3D material for advanced electrochemical applications.
A Mn-based NASICON-type Na 4 VMn(PO 4 ) 3 cathode is considered to be one of the most promising substitutions for Na 3 V 2 (PO 4 ) 3 due to the huge abundance and appropriate redox potential from Mn. However, the current Na 4 VMn(PO 4 ) 3 /C cathode still delivers a limited electrochemical performance due to the sluggish kinetics and negative structural degradation caused by the Mn in the structure. Herein, a selective replacement of vanadium rather than manganese in the Na 4 VMn(PO 4 ) 3 system was developed to fully utilize the manganese element and enhance the structural stability. Both experimental and calculation results affirmed that the Al-substituted Na 4 V 0.8 Al 0.2 Mn(PO 4 ) 3 cathode shows favorable Na + kinetics and structure stability. The resulting Na 4 V 0.8 Al 0.2 Mn(PO 4 ) 3 reveals a discharge capacity of ∼84 mA h g −1 at 40 C and renders a capacity retention of 92% after cycling 1000 times at 5 C. Inspired by the availability of Al dopants, we also demonstrated the Al-doped Mn-richer Na 4.2 V 0.6 Al 0.2 Mn 1.2 (PO 4 ) 3 to be a viable candidate for Mn-rich phosphate cathodes.
Capacity fading induced by unstable surface chemical properties and intrinsic structural degradation is a critical challenge for the commercial utilization of Ni-rich cathodes. Here, a highly stabilized Ni-rich cathode with enhanced rate capability and cycling life is constructed by coating the molybdenum compound on the surface of LiNi 0.815 Co 0.15 Al 0.035 O 2 secondary particles. The infused Mo ions in the boundaries not only induce the Li 2 MoO 4 layer in the outermost but also form an epitaxially grown outer surface region with a NiO-like phase and an enriched content of Mo 6+ on the bulk phase. The Li 2 MoO 4 layer is expected to reduce residential lithium species and promote the Li + transfer kinetics. The transition NiO-like phase, as a pillaring layer, could maintain the integrity of the crystal structure. With the suppressed electrolyte−cathode interfacial side reactions, structure degradation, and intergranular cracking, the modified cathode with 1% Mo exhibits a superior discharge capacity of 140 mAh g −1 at 10 C, a superior cycling performance with a capacity retention of 95.7% at 5 C after 250 cycles, and a high thermal stability.
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