Development Of Electrode And Electrolyte Materials For Rechargeable Aqueous Zinc Ion Batteries

The reviving aqueous zinc-ion batteries（AZIBs）has recently attracted a lot of attention because of their inexpensive cost and safety.They are good candidates for large-scale energy storage applications owing to their high abundance and high capacity of zinc metal anode,as well as cheap and highly safe aqueous electrolytes.However,the accessible inorganic metal oxides as electrode materials reap instability and other issues,including dissolution into the electrolyte,weak conductivity,poor phase structures,static repulsion,and structure lattice collapse.Up to now,the electrode materials of AZIBs could be enhanced via interfacial modification,structural engineering,and molecular functionalization.The development of metal ion-intercalated active materials for excellent electrochemical performance in AZIBs is challenging.The structure instability and intrinsic electrostatic repulsion of the lattice framework cause structural breakdown and low-rate performance.In response to these problems,we report yttrium vanadium oxide-poly（3,4-ethylenedioxythiophene）（PEDOT@YVO）composite as stable cathode material for AZIBs.The introduction of PEDOT in YVO nanorods improves the crystalline structure with an enlarged interplanar lattice spacing of3.4?.The PEDOT@YVO composite electrode demonstrates effective electric conductivity and a higher initial specific capacity of 308.5 m Ah g^-1 than that(125.5 m Ah g^-1)of the pure YVO at 0.2C rate.It also features a long-term stable discharge-charge cycle performance of 4,000 cycles with a capacity retention of 79.2%at 1C rate,better than YVO(29.4 m Ah g^-1).The oxygen vacancies and improved electrical conductivity of the composite account for the invigorated electrochemical performance.Consequently,this work reveals another avenue for constructing unique electrodes to enhance the electrochemical properties of AZIBs.Next,although the layered structures of the inorganic materials demonstrate broad ion migration channels and potential promise,but they are not fully environmentally friendly and usually show structure distortions and interstitial repulsion.Hence,organic molecular materials are used as green cathodes for batteries due to their inherent soft crystalline structures.However,conventional organic batteries suffer from rapid capacity fading.Organic compounds are inclined to dissolve in the electrolyte,which limits the long-term cycling performance of lithium-organic batteries.Carbon skeletons show efficacy in confining the organic cathodes.Herein we investigate the electrochemical performance of aqueous zinc-ion batteries with binder-free composite cathode consisting of carbon nanotubes（CNTs）and naphthoquinone（NQ）-based organics.The quinones are trapped in the nanoporous structure of the CNT framework,and thus the dissolution is minimized.The composite cathodes show stable and high rate cyclability owing to the high electrical conductivity and confinement of the CNT network.The NQ composite cathode exhibits an initial capacity of 333.5 m Ah g^-1,which is close to the theoretical capacity of 339.0 m Ah g^-1.Furthermore,it is uncovered that modifying NQ with functional groups significantly impacts the electrochemical behavior,including the redox potential and capacity retention.With the electron-withdrawing or electron-donating groups,dichlone and 2-（（4-Hydroxyphenyl）amino）naphthalene-1,4-dione（APh-NQ）show better performance than that of NQ with improved capacity retention from 41.0%to 70.9%and 68.3%,respectively,after 1000 cycles.The work promotes the development of binder-free organic cathodes for the aqueous Zn-ion battery and sheds light on designing high-performance electrodes for low-cost energy storage systems.Finally,though the resurgence of water-based ZIBs is promising for large-scale storagesystems owing to their high safety,the challenges of ZIBs still exist for the electrochemical process at low temperatures where the electrolyte is of low ionic conductivity and suffers from freezing.Therefore,we report decayed networks of hydrogen bond in dimethyl sulfoxide（DMSO）-water mixed solution by morphing the water-based electrolyte with a dosage of DMSO additive.A suitable aqueous DMSO hybrid electrolyte（H₂O:DMSO=2:1,molar ratio）maintains a high ionic conductivity of 0.12 m S cm^-1 at-50℃,suppressing the freezing of free-water and alleviating the phase transition temperature of the binary DMSO-water electrolyte to-125℃.Furthermore,the"fast ion conductor"KSn₂（PO₄）₃（KSn P）coated on Zn anode renders issue-free cycling performance of the DMSO-based AZIBs at low temperatures with freezing-free property.The KSn P@Zn|DMSO-H₂O|KSn P@Zn symmetric cell maintains a steady polarization and shows remarkable stripping/plating behavior over 2000 h（1000 cycles）at-20°C,which is better than the bare Zn that retires and surceases cycling after 1300 h.The KSn P@Zn/PEDOT@YVO batteries performed at ultra-low temperatures have long-term performance,retain an impressive specific capacity of 135.8 m Ah g^-1（89.9%of the original capacity）after 1000 cycles at 0.2 C and-20°C conditions.This research marks a significant step toward the development of aqueous batteries,which may be used in very low-temperature environments.