Electrochemical Zinc-Ion Intercalation Properties and Crystal Structures of ZnMo₆S₈ and Zn₂Mo₆S₈ Chevrel Phases in Aqueous Electrolytes

Abstract

The crystal structures and electrochemical properties of ZnxMo6S8 Chevrel phases (x = 1, 2) prepared via electrochemical Zn(2+)-ion intercalation into the Mo6S8 host material, in an aqueous electrolyte, were characterized. Mo6S8 [trigonal, R3̅, a = 9.1910(6) Å, c = 10.8785(10) Å, Z = 3] was first prepared via the chemical extraction of Cu ions from Cu2Mo6S8, which was synthesized via a solid-state reaction for 24 h at 1000 °C. The electrochemical zinc-ion insertion into Mo6S8 occurred stepwise, and two separate potential regions were depicted in the cyclic voltammogram (CV) and galvanostatic profile. ZnMo6S8 first formed from Mo6S8 in the higher-voltage region around 0.45-0.50 V in the CV, through a pseudo two-phase reaction. The inserted zinc ions occupied the interstitial sites in cavities surrounded by sulfur atoms (Zn1 sites). A significant number of the inserted zinc ions were trapped in these Zn1 sites, giving rise to the first-cycle irreversible capacity of ∼46 mAh g(-1) out of the discharge capacity of 134 mAh g(-1) at a rate of 0.05 C. In the lower-voltage region, further insertion occurred to form Zn2Mo6S8 at around 0.35 V in the CV, also involving a two-phase reaction. The electrochemical insertion and extraction into the Zn2 sites appeared to be relatively reversible and fast. The crystal structures of Mo6S8, ZnMo6S8, and Zn2Mo6S8 were refined using X-ray Rietveld refinement techniques, while the new structure of Zn2Mo6S8 was determined for the first time in this study using the technique of structure determination from powder X-ray diffraction data. With the zinc ions inserted into Mo6S8 forming Zn2Mo6S8, the cell volume and a parameter increased by 5.3% and 5.9%, respectively, but the c parameter decreased by 6.0%. The average Mo-Mo distance in the Mo6 cluster decreased from 2.81 to 2.62 Å.

Nanostructured Polypyrrole Composite Aerogels for a Rechargeable Flexible Aqueous Zn‐Ion Battery with High Rate Capabilities

“…However, the energy density of aqueous supercapacitors is rather low, as compared with that of our Zn‐ion battery. Detailed comparisons with other aqueous batteries and supercapacitors are shown in Figure e . In addition, the Zn‐ion battery has a good long‐term lifetime.…”

“…The specific capacity at high current densities is much higher than those of other Zn‐ion batteries based on ZnMn 2 O 4 /carbon (80 mAh g −1 at 2A g −1 ), LiFePO 4 (45 mAh g −1 at 10.2 A g −1 ), and LiNi 1/3 Co 1/3 Mn 1/3 O 2 @graphene@multi‐walled carbon nanotubes (MWCNTs) (68 mAh g −1 at 0.5 A g −1 ) . More comparisons with other energy storage devices are summarized in Table S1, Supporting Information . The superior rate capability makes our Zn‐ion battery fully charged in a very short period (about 20 s) at a high current density of 16 A g −1 .…”

Recent Advances in Zn‐Ion Batteries

“…In addition to the above three families of cathode materials in ZIBs, Mo 6 S 8 was also found to have the ability to adopt Zn ions . A specific capacity of 134 mAh g −1 was achieved in the first discharge process that could be divided into two steps: the formation of ZnMo 6 S 8 from Mo 6 S 8 between 1.00–0.45 V and the transformation of Zn 2 Mo 6 S 8 from ZnMo 6 S 8 around ≈0.35 V . However, this kind of cathode material does not seem intriguing considering its low maintainable discharge plateau (≈0.35 V vs Zn/Zn 2+ , Figure a).…”

Stabilized Molybdenum Trioxide Nanowires as Novel Ultrahigh‐Capacity Cathode for Rechargeable Zinc Ion Battery

“…[16][17][18] Despite these advanced features, one of the biggest block for ZIBs developed to date is their relatively low capacity in terms of the substantially inferior capacity of cathode materials than Zn anode. [21][22][23][24] A great variety of materials including MnO 2 , [25][26][27][28] ZnMn 2 O 4 , [17] Zn x Mo 6 S 6 , [29] ZnHCF, [30] Zn 0.25 V 2 O 5 ·nH 2 O, [31] VS 2 , [20] NiOOH, [32] and Co 3 O 4 [9] have been reported as promising cathodes with good electrochemical performance. [21][22][23][24] A great variety of materials including MnO 2 , [25][26][27][28] ZnMn 2 O 4 , [17] Zn x Mo 6 S 6 , [29] ZnHCF, [30] Zn 0.25 V 2 O 5 ·nH 2 O, [31] VS 2 , [20] NiOOH, [32] and Co 3 O 4 [9] have been reported as promising cathodes with good electrochemical performance.…”