Towards High-Energy and Anti-Self-Discharge Zn-Ion Hybrid Supercapacitors with New Understanding of the Electrochemistry

Abstract

Aqueous Zn-ion hybrid supercapacitors (ZHSs) are increasingly being studied as a novel electrochemical energy storage system with prominent electrochemical performance, high safety and low cost. Herein, high-energy and anti-self-discharge ZHSs are realized based on the fibrous carbon cathodes with hierarchically porous surface and O/N heteroatom functional groups. Hierarchically porous surface of the fabricated free-standing fibrous carbon cathodes not only provides abundant active sites for divalent ion storage, but also optimizes ion transport kinetics. Consequently, the cathodes show a high gravimetric capacity of 156 mAh g−1, superior rate capability (79 mAh g−1 with a very short charge/discharge time of 14 s) and exceptional cycling stability. Meanwhile, hierarchical pore structure and suitable surface functional groups of the cathodes endow ZHSs with a high energy density of 127 Wh kg−1, a high power density of 15.3 kW kg−1 and good anti-self-discharge performance. Mechanism investigation reveals that ZHS electrochemistry involves cation adsorption/desorption and Zn4SO4(OH)6·5H2O formation/dissolution at low voltage and anion adsorption/desorption at high voltage on carbon cathodes. The roles of these reactions in energy storage of ZHSs are elucidated. This work not only paves a way for high-performance cathode materials of ZHSs, but also provides a deeper understanding of ZHS electrochemistry.

Reversible Zn2+ Insertion in Tungsten Ion-Activated Titanium Dioxide Nanocrystals for Electrochromic Windows

“…The structure optimization was implemented in the Vienna ab initio simulation package (VASP) based on DFT. To study single Zn 2+ migration in anatase TiO 2 and W-doped TiO 2 , supercell structures of 1 × 2 × 1 and 2 × 2 × 1 were constructed by using the unit cell of anatase 32 . In detail, we give the calculated energy barrier of Zn 2+ diffusion on the (001) surface, which takes the initial structure (0) as the zero point, the x-axis is the length of Zn atom in the Zn atom distance (0) structure, and the y-axis is the energy of each structure minus the energy of (0) structure, that is, if it is positive, the energy of this position is higher than (0), and if it is negative, it is lower than (0).…”

“…Among various multivalent metal ions, Zn 2+ is regarded as superior to others to trigger the electrochromism due to its simplified preparation process and nontoxicity [15,20,25,27]. Furthermore, the relatively low redox potential of Zn 2+ /Zn (−0.763 V versus standard hydrogen electrode), which shows good compatibility with pH-neutral aqueous electrolytes and thus inhibiting the occurrence of hydrogen evolution reaction [28][29][30][31][32]. As a result, the pH value of the electrolyte will be stable during the device cycling.…”

Phosphorus and Oxygen Dual‐Doped Porous Carbon Spheres with Enhanced Reaction Kinetics as Anode Materials for High‐Performance Potassium‐Ion Hybrid Capacitors

“…Such excellent rate capability and energy output are superior to many reported state‐of‐the‐art hybrid capacitors, as summarized in Figure 6d. [ 52–60 ] In addition, the constructed device also shows an exceedingly high‐capacity retention of 94.5% after 30 000 cycles at 5 A g −1 with a Coulombic efficiency above 99% (Figure 6e). Meanwhile, light‐emitting diode (LED) arrays can be successfully illuminated by two lab‐assembled PIHCs connected in series (see the inset in Figure 6e).…”

“…d) Ragone plots of different hybrid capacitors according to previous works. [ 52–60 ] e) Long‐term cycle performance of the P/O‐PCS//AC device at 5 A g −1 up to 30 000 cycles. The inset displays the illuminated LED arrays powered by our fabricated P/O‐PCS//AC device.…”

Stretchable Zn‐Ion Hybrid Battery with Reconfigurable V2CTx and Ti3C2Tx MXene Electrodes as a Magnetically Actuated Soft Robot

“…As shown in Figure 4d and Figure S22 (Supporting Information), the open circuit voltage (OCV) of our stretchable Zn-ion hybrid battery only decayed from 1.1 to 1.05 V after a 72-hour rest, showing a self-discharge rate of 0.7 mV h −1 and 91.2% of capacity retention. Compared with the other works focusing on anti-self-discharge in the literature (Table S2, Supporting Information), [33,[57][58][59][60][61][62] our Zn-ion hybrid battery exhibited an ultralow self-discharge rate and superior anti-self-discharge capability, due to its asymmetric electrode configuration and coplanar device layout. It's unlikely that anchored zinc on the s-Ti-MXene microtextures will (right) of a stretchable Zn-ion hybrid battery (cathode: s-V-MXene electrode; anode: Zn@Ti-MXene electrode; electrolyte: PVA/ZnCl 2 hydrogel).…”