Swallow-Nest Architectures with Cobalt Molybdate Particulates Fixed Constructed Carbon Nanotube Supports for Stable Sodium-Ion Battery Anode

Abstract

A swallow-nest architecture is fabricated through in situ prefabricated heating using cobalt molybdate (CoMoO4) as the subject and acid-functionalized carbon nanotubes (AF-CNTs) as the skeleton (CoMoO4/AF-CNT nest). The CoMoO4/AF-CNT nest is fixed via the C–O–Mo bond between the AF-CNT supports and CoMoO4 nanoparticles and hydrogen bonds of neighboring CNTs. The size of CoMoO4 in the CoMoO4/AF-CNT nest is confined to the nanometer level (30 nm), which will lead to negligible nanoscale volume changes during charge and discharge. The swallow-nest architecture can enhance the stability of the electrode, thus accelerating electrolyte penetration and providing fast diffusion channels for charge and Na+ ion transfer. When used as the anode of sodium-ion batteries, the CoMoO4/AF-CNT nest electrodes exhibit a reversible capacity of 151.6 mA h g−1 at the promising current densities of 2.0 A g−1 with degradation rate lower than 5.4 μA h g−1 cycle−1 after 2000 cycles.

Mesoporous Mulberry-like CoMoO4: A Highly Suitable Anode Material for Sodium Ion Batteries over Lithium Ion Batteries

“…The obtained capacity decay and lower Coulombic efficiency in the initial discharge/charge cycle are mainly due to the formation of the partially irreversible SEI layer . It can be seen that the Coulombic efficiency undoubtedly improves in the consequent cycles and rises to ∼100% in the 50th cycle.…”

“…It is also believed that the additional voltage plateaus are due to the mixed metal oxide anodes, which represent the oxidation state of different transition metals being oxidized and reduced during charge/discharge cycles . Furthermore, a broad reduction peak located at 0.16 V can be ascribed to the formation of the SEI film on the electrode surface by the decomposition of the electrolyte. , Later on, the subsequent cycles clearly show the shifting of the reduction peak from ∼0.87 to ∼1.14 V, which could be possibly due to the complete destruction of CoMoO 4 along with the breaking of the Co–O–Mo bond . At the reverse, a small anodic peak observed at ∼1.90 V relates to the oxidation of Mo 0 to Mo 4+ . , Furthermore, the other two anodic peaks displayed at ∼0.68 and ∼ 2.20 V mainly correspond to the conversion of Co to Co 2+ and Mo 4+ to Mo 6+ , respectively. − …”

“…Since the insertion of Na + ions is an irreversible process, it leads to the complete destruction of the CoMoO 4 nanostructure . Instead of CoMoO 4 , the CoO and MoO 3 may undergo reversible conversion reactions with Na + from the second cycle onward . It is also believed that the additional voltage plateaus are due to the mixed metal oxide anodes, which represent the oxidation state of different transition metals being oxidized and reduced during charge/discharge cycles .…”

“…More importantly, the clubbing of two electrochemically active metal oxides may also combine their competitive advantages such as the flexibility to alter the theoretical capacity, control of the working voltages, etc. In addition, the excellent synergistic effect between two different metal ions is another remarkable characteristic of mixed transition metal oxide anode materials. , In this continuation, cobalt molybdate (CoMoO 4 ) has come out as an attractive mixed transition metal oxide anode material for both LIBs and SIBs, which may be due to the variable oxidation states (between +2 and +6) of molybdenum (Mo) as well as the harmonized conductivity of two metals. , In addition, the high theoretical capacity of CoMoO 4 (980 mAh g –1 : CoMoO 4 + 8M → Co + Mo + 4M 2 O, where M = Li + /Na + ), which is almost three times that of graphite, is another promising characteristic to use it as an anode material. ,,− Apart from this, CoMoO 4 also shows high redox activity as well as excellent capacity retention with the formation of cobalt oxide during electrochemical reaction, leading to its notable supremacy over other molybdates such as NiMoO 4 , ZnMoO 4 , Fe 2 (MoO 4 ) 3 , etc. , However, the issue of low electronic conductivity, strong agglomeration tendency, and large volumetric expansion/contraction during insertion/de-insertion reactions limits the CoMoO 4 application. , Thus, various strategies to fabricate CoMoO 4 nanostructures such as nanoparticles, , nanosheets, − nanorods, microspheres, hollow nanostructures, etc., have been implemented to overcome these issues. In contrast, the synthesis of CoMoO 4 nanocomposites such as CoMoO 4 @C, CoMoO 4 /polypyrrole, CoMoO 4 /carbon fabric, CoMoO 4 /Co 3 O 4 , etc., has also been reported to increase the electronic conductivity of CoMoO 4 .…”

“…In addition, the excellent synergistic effect between two different metal ions is another remarkable characteristic of mixed transition metal oxide anode materials. 15,21 In this continuation, cobalt molybdate (CoMoO 4 ) has come out as an attractive mixed transition metal oxide anode material for both LIBs and SIBs, which may be due to the variable oxidation states (between +2 and +6) of molybdenum (Mo) as well as the harmonized conductivity of two metals. 15,21 In addition, the high theoretical capacity of CoMoO 4 (980 mAh g −1 : CoMoO 4 + 8M → Co + Mo + 4M 2 O, where M = Li + /Na + ), which is almost three times that of graphite, is another promising characteristic to use it as an anode material.…”