Zinc-ion energy storage devices are inexpensive and safe, benefitting from the abundance of Zn metal and high chemical stability. However, their electrochemical performance is poor, owing to the ...unstable Zn stripping/plating process of the Zn metal anode and the occurrence of side reactions. In this study, 3D porous reduced graphene oxide-coated Zn (rGO@Zn) was prepared via electrostatic spray deposition (ESD) and used as an anode for aqueous hybrid Zn-ion capacitors (ZICs). ESD is a cost-effective one-step technique that affords excellent control over the deposition morphology. Coating 3D porous rGO with a large surface area on Zn foil, resulted in a low charge transfer resistance and small voltage hysteresis (44.5 mV) with a long cycle life of over 3000 h. Moreover, the energy density improved at high rates (25 Wh kg−1 at 10,882 W kg−1) in aqueous hybrid ZICs. In-situ synchrotron transmission X-ray microscopy and optical microscopy analyses revealed that the formation of dendrites was inhibited in the as-fabricated ZICs. Furthermore, the conductive rGO on the surface of the Zn anode stabilized the electric field during the Zn stripping/plating process, and the functional groups guided the Zn2+ deposition sites, resulting in uniform Zn deposition during cycling and improved electrochemical performance.
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Recently, owing to the increasing demand for wearable electronics, it is necessary to investigate flexible and highly safe energy storage devices. Commonly used energy storage devices, such as ...lithium-ion batteries and supercapacitors with organic electrolytes, may suffer from fire and explosion. Therefore, zinc-ion capacitors (ZICs) with nontoxic and nonflammable aqueous electrolytes have recently attracted considerable attention. In this study, high-surface-area nanoporous core-shell-structured multiwalled carbon nanotube@graphene oxide nanoribbon (NP-MWCNT@GONR) is used as the cathode material in aqueous ZICs for the first time. These ZICs exhibit a high energy density of 90 Wh kg−1 at 95 W kg−1 and a high power density of 19 kW kg−1 at 31 Wh kg−1. The cycling retention is 86.5% after 200 cycles; however, the device fails after 200 cycles owing to the formation of zinc dendrites on the anode. To suppress dendrite formation, NP-MWCNT@GONR-coated zinc anode and freeze-dried gel electrolyte are used, and the cycle life is extended beyond 2000 cycles. In-situ synchrotron transmission X-ray microscopy is performed during charging and discharging, which demonstrates that the gel electrolyte and the NP-MWCNT@GONR-coated zinc anode can effectively inhibit dendrite formation. This study reveals that ZICs with NP-MWCNT@GONR cathodes, NP-MWCNT@GONR-coated zinc anode, and gel electrolytes are highly safe energy storage devices for use in flexible and wearable electronics.
•Nanoporous MWCNT@GONR is used as cathode and protection layer in Zn-ion capacitors.•These ZICs exhibit a high energy density of 90 Wh kg−1 at 95 W kg−1.•In-situ TXM shows that protection layer and gel electrolyte can inhibit dendrites.•ZICs with NP-MWCNT@GONR cathodes are promising flexible and wearable electronics.
Prussian blue analogue (PBA)/metal–organic frameworks (MOFs) are multifunctional precursors for the synthesis of metal/metal compounds, carbon, and their derived composites (P/MDCs) in chemical, ...medical, energy, and other applications. P/MDCs combine the advantages of both the high specific surface area of PBA/MOF and the electronic conductivity of metal compound/carbon. Although the calcination under different atmospheres has been extensively studied, the transformation mechanism of PBA/MOF under hydrothermal conditions remains unclear. The qualitative preparation of P/MDCs in hydrothermal conditions remains a challenge. Here, we select PBA to construct a machine-learning model and measure its hydrothermal phase diagram. The architecture–activity relationship of substances among nine parameters was analyzed for the hydrothermal phase transformation of PBA. Excitingly, we established a universal qualitative model to accurately fabricate 31 PBA derivates. Additionally, we performed three-dimensional reconstructed transmission electron microscopy, X-ray absorption fine structure spectroscopy, ultraviolet photoelectron spectroscopy, in situ X-ray powder diffraction, and theoretical calculation to analyze the advantages of hydrothermal derivatives in the oxygen evolution reaction and clarify their reaction mechanisms. We uncover the unified principles of the hydrothermal phase transformation of PBA, and we expect to guide the design for a wide range of composites.
In this study, we investigated the effects of ligand substitution in Prussian blue analog (PBA) cathode materials on the performance of aqueous sodium-ion batteries. NaCuFe(CN)6 (NaCuHCF) and ...ligand-modified PBAs, NaxCuFe(CN)5(C6H4N2) (NaxCuCNPFe), and NaxCuFe(CN)5(CH3C6H4NH2) (NaxCuTolFe) were tested in different electrolytes. The NaxCuCNPFe and NaxCuTolFe cathodes exhibited the best capacity retention of ∼50% after 2000 cycles in 1 M Na2SO4, which is much higher than that of the NaCuHCF cathode (0% capacity remained after 2000 cycles). To understand the charge–discharge mechanism of PBA cathodes, in situ synchrotron X-ray absorption spectroscopy and X-ray diffraction were performed. To demonstrate practical energy storage applications, PBAs were tested in full-cell configurations with an anode made of sodium titanium phosphate (NTP) coated with reduced graphene oxide and carbon (NTP@C@RGO). The NaxCuCNPFe//NTP@C@RGO and NaxCuTolFe//NTP@C@RGO full cells in 17 m NaClO4 aqueous electrolyte exhibited high power densities of up to 4338 W kg−1 (with an energy density of 18.11 Wh kg−1) and 4742 W kg−1 (with an energy density of 11.87 Wh kg−1), respectively. Our study demonstrates the potential of optimizing organic ligands in PBAs and electrolytes for the improvement of the cycling stability of high-power aqueous sodium-ion batteries.
Aqueous zinc‐based energy storage devices possess superior safety, cost‐effectiveness, and high energy density; however, dendritic growth and side reactions on the zinc electrode curtail their ...widespread applications. In this study, these issues are mitigated by introducing a polyimide (PI) nanofabric interfacial layer onto the zinc substrate. Simulations reveal that the PI nanofabric promotes a pre‐desolvation process, effectively desolvating hydrated zinc ions from Zn(H2O)62+ to Zn(H2O)42+ before approaching the zinc surface. The exposed zinc ion in Zn(H2O)42+ provides an accelerated charge transfer process and reduces the activation energy for zinc deposition from 40 to 21 kJ mol−1. The PI nanofabric also acts as a protective barrier, reducing side reactions at the electrode. As a result, the PI‐Zn symmetric cell exhibits remarkable cycling stability over 1200 h, maintaining a dendrite‐free morphology and minimal byproduct formation. Moreover, the cell exhibits high stability and low voltage hysteresis even under high current densities (20 mA cm−2, 10 mAh cm−2) thanks to the 3D porous structure of PI nanofabric. When integrated into full cells, the PI‐Zn||AC hybrid zinc‐ion capacitor and PI‐Zn||MnVOH@SWCNT zinc‐ion battery achieve impressive lifespans of 15000 and 600 cycles with outstanding capacitance retention. This approach paves a novel avenue for high‐performance zinc metal electrodes.
A 3D polyimide (PI) nanofabric interface is applied to a zinc substrate, effectively enhancing the uniformity of zinc plating and mitigating the side reactions. The PI nanofabric plays a pivotal role in promoting a “pre‐desolvation” process (Zn(H2O)62+→Zn(H2O)42+) before zincion reduction. The exposed zinc ion in Zn(H2O)42+ provides more accessible space for the charge transfer process compared to Zn(H2O)62+, contributing to substantially improved zinc plating uniformity.
