Systematic Modification of MoO₃‐Based Cathode by the Intercalation Engineering for High‐Performance Aqueous Zinc‐Ion Batteries

Abstract

Aqueous Zn-ion batteries are attracting extensive attention, but their largescale application is prevented by the poor electrochemical kinetics and terrible lifespan. Herein, a strategy of introducing the conductive poly(3,4ethylenedioxythiophene) (PEDOT) into the interlayers of α-MoO 3 is reported to systematically overcome the above shortcomings. Through data analyses of the cyclic coltammetry, electrochemical impedance spectroscopy, and galvanostatic intermittent titration technique, the electrochemical kinetics of the PEDOT-intercalated MoO 3 (PEDOT-MoO 3 ) is proved to be significantly improved. The first-principles calculations microscopically disclose that the changed energy band and the lowered binding energy between Zn 2+ and host O 2− boost electrochemical kinetics of PEDOT-MoO 3 . Meanwhile, its decreased hydrophilicity and the suppressed dissolution of molybdenum stabilizes the repeated cycling processes. Interestingly, it is found that excellent electrochemical kinetics of cathode electrode can restrain the growth of zinc dendrite on the Zn anode, prolonging the lifespan of aqueous Zn-ion batteries. As a result, the PEDOT-MoO 3 exhibits the enhanced specific capacity (341.5 vs 146.7 mAh g −1 at 0.1 A g −1 ), high rate capacity (178.2 vs 19.4 mAh g −1 at 30 A g −1 ) and prolonged cycling stability (77.6% capacity retention over 500 cycles vs 2.3% capacity retention over 100 cycles at 30 A g −1 ) compared with pristine MoO 3 . Moreover, the PEDOT-MoO 3 as cathode of quasi-solidstate ZIBs also delivers an impressive electrochemical performance.

Monitoring the Cation Coordination Sphere Using Hydrated Eutectic Electrolyte for Better Cyclic Stability and High Energy Density Zn-Ion Battery

“…The CV curves of the Zn//MoO 3 @Mn 3 O 4 ZiB coin cell were recorded based on the SNZN 2 optimized electrolyte at different scan rates in between a 0.4 and 2.3 V (Zn 2+ /Zn) working potential (Figure a). Three pairs of redox peaks arise at different scan rates due to the multiple redox conversion of Mo and Mn oxides accompanied by the insertion/extraction of Zn 2+ cations (Mo 6+ ↔ Mo 5+ ↔ Mo 4+ and Mn 4+ ↔ Mn 3+ ↔ Mn 2+ ). ,,,,,, The redox peaks were almost restraining their position with increasing from a 0.2 to 1 mV s –1 scan rate, indicating the reversible coinsertion/extraction of H + /Zn 2+ ions from the cathode material in a hydrated eutectic electrolyte. ,,, The logarithmic relationship between scan rate (v) and peak current (i) was linearly fitted to obtain the diffusive and capacitive controlled current using the power law equation (i = av b ) where a and b are the adjustable parameters. The slopes (b values) of the anodic and cathodic peaks were found to be 0.74 (P1), 0.53 (P2), 0.69 (P3), 0.68 (P4), 0.69 (P5), and 0.73 (P6), signifying the insertion/extraction of H + /Zn 2+ ions into/from the MoO 3 @Mn 3 O 4 cathode was a diffusion-controlled process (Figure b). ,, …”

“…The Raman vibrational modes were centered at 129, 160, 247, 291, 340, 382, 670, 823, and 995 cm –1 corresponding to the α-MoO 3 phase. The 315, 361, and 646 cm –1 Raman vibrational modes were ascribed to the Mn 3 O 4 phase. , …”

“…The CV curves were recorded at a 1 mV s –1 scan rate in the 0.4–2.3 V potential range for all the devices (Figure S10b). All the CV curves displayed distinguished redox peaks which were ascribed to the multivalence redox conversion of Mn and Mo oxides. ,− The 1 M ZnCl 2 electrolyte-based ZiB exhibited two broad redox peaks at ∼2.1 and 1.25 V with a narrow area covered by the CV curves. Interestingly, with the SN molecules introduction at low salt concentration, the area covered by the CV curves was improved with relatively prominent redox peaks due to the high ionic conductivity.…”

“…Three pairs of redox peaks arise at different scan rates due to the multiple redox conversion of Mo and Mn oxides accompanied by the insertion/extraction of Zn 2+ cations (Mo 6+ ↔ Mo 5+ ↔ Mo 4+ and Mn 4+ ↔ Mn 3+ ↔ Mn 2+ ). 29,30,32,34,35,37,39 The redox peaks were almost restraining their position with increasing from a 0.2 to 1 mV s −1 scan rate, indicating the reversible coinsertion/extraction of H + /Zn 2+ ions from the cathode material in a hydrated eutectic electrolyte. 34,35,37,39 The logarithmic relationship between scan rate (v) and peak current (i) was linearly fitted to obtain the diffusive and capacitive controlled current using the power law equation (i = av b ) where a and b are the adjustable parameters.…”

“…The 315, 361, and 646 cm −1 Raman vibrational modes were ascribed to the Mn 3 O 4 phase. 32,33 The morphological investigation of the MoO 3 @Mn 3 O 4 heterostructure was carried out with the FE-SEM image analysis (Figure 1b, c and Figure S2). The surface morphology of the MoO 3 @Mn 3 O 4 heterostructure was found to be a highly porous nanoflower structure, and each nanoflower was composed of an ultrathin nanosheet.…”