Aqueous Zinc-ion Energy Storage Devices: Reaction Mechanism Of Electrode Materials And Wide-Temperature Integrated Device Design

Aqueous zinc ion(Zn²⁺)energy storage devices have attracted much attention due to their high energy density,high power density,good safety,and simple preparation process.Till now,a large number of Zn²⁺energy storage systems have been studied by scientists.However,electrode materials with high capacity,good stability and fast kinetics are still lacking.Even for the most widely studied manganese oxide,the Zn²⁺storage mechanism remains controversial.Therefore,it is necessary to understand the energy storage mechanism of Zn²⁺for the development of electrode materials.Meanwhile,gel electrolyte has the advantages of good safety,flexibility and packing convenience,which can avoid the leakage and evaporation of liquid electrolyte,and is conducive to the integrated construction of energy storage devices.Especially,the development of gel electrolytes with anti-freezing and heat-resisting abilities is necessary for the wide temperature range application of energy storage devices.In view of the above problems and requirements,novel electrode materials and the energy storage mechanisms,wide temperature range gel electrolytes,and integrated energy storage devices are studied in this dissertation.The details are as follows:1.A layered structureδ-MnO₂ cathode with an interlayer spacing of～7?is prepared directly on the current collector,which is favorable for the reversible intercalation of Zn²⁺.The binder-freeδ-MnO₂ enables a favorable“layered to layered”Zn²⁺storage mechanism without interference.Driven by H₂O,Zn²⁺and H⁺move fast and coexist stably betweenδ-MnO₂ layers,and the large spaced layered structure makes the ion intercalation more stable in kinetics and thermodynamics.Thanks to the special layered structure and reaction mechanism ofδ-MnO₂,the Zn-Mn battery exhibits a high specific capacity of 330.67 m Ah g^-1,a high energy density of 432.05Wh kg^-1,a high power density of 8.33 k W kg^-1,and ultralong stability up to 10000cycles.Based on the use of flexible substrate and gel electrolyte,the Zn-Mn battery exhibits good flexibility,and works well over a broad temperature range of 0～40°C,and can power small electronics.This work provides scientific guidance for the development of high-performance multivalent ion batteries by designing cathode materials with advanced crystal structure.2.A wide temperature range gel electrolyte based on 1 m Zn（ClO₄）₂+3.5 m Mg（ClO₄）₂ deep eutectic solvent（DES）is prepared.The synergistic effect of anion and cations on freezing point of DES is confirmed by spectral characterization.With containing four HBs acceptors,Mg²⁺displays strong electrostatic attraction with O atom of H₂O,and ClO₄^-can form a lot of hydrogen bonds（HBs）with H₂O molecules.By simultaneously adjusting the chemical environment around H and O atoms of H₂O molecules,the DES exhibits an ultra-low freezing point of-116.92^oC,and the gel electrolyte prepared from the DES also exhibits an ionic conductivity of 0.285 m S cm^-1 at-70^oC.The excellent low-temperature performance of DES-based gel electrolyte and its compatibility with Zn anode enable the constructed flexible Zn-Mn battery to exhibit good electrochemical performance at low temperatures.At-70^oC,it shows a high specific capacity of 76.83 m Ah g^-1,good rate performance,and stable cycling performance.The Zn-Mn battery can also operate stably within a wide temperature range of-70 to 80^oC.This work provides new ideas for the development of Zn-Mn battery with a wide working temperature range.3.In order to further utilize the layeredδ-MnO₂ cathode with high capacity and excellent ion-intercalation kinetics,an advanced wide-temperature range zinc hybrid supercapacitor（ZHSC）is constructed with AC anode,δ-MnO₂ cathode and novel PVA-based hydrogel electrolyte.The deposition of Zn is avoided by adjusting the voltage,and the capacitance of AC is thus fully realized.The assembled ZHSC exhibits a high energy density of 47.86 Wh kg^-1(3.94 m Wh cm^-3),a high power density of 5.81 k W kg^-1(0.48 W cm^-3),and excellent cycling stability of 30000 cycles.Glycerol（GL）additive and freezing/thawing technique are utilized together to prepare anti-freezing PVA gel electrolyte.The additive of GL not only inhibits the freezing of water,but also forms intermolecular and intramolecular hydrogen bonds with polymer and H₂O to lower the freezing point.The freezing-thawing method promotes the formation of PVA microcrystals at the crosslinking point in the gel electrolyte,which significantly improves the thermal stability and tensile property of the gel electrolyte.The integrated ZHSC device cycles well over a broad temperature range of-30～80^oC.This work highlights the great potential of our ZHSC for all-climate applications.4.The energy density of ZHSC is severely limited by the low specific capacitance of carbon materials.To further improve the capacity and energy density of ZHSC,a pseudocapacitive Mo O₂ anode with high specific capacity is designed,and a ZHSC device is integrated withδ-MnO₂ cathode and PVA-Zn Cl₂ gel electrolyte.The influence of anions on the electrochemical performance of Mo O₂ is studied by using different Zn²⁺-salt electrolytes.It is found that Cl^-can reduce the desolvation energy of hydrated Zn²⁺clusters,resulting in the full contact and reaction between Zn²⁺and Mo O₂.Spectrum characterizations reveal the energy storage mechanism of Mo O₂.The constructed ZHSC device exhibits a high specific capacity of 102.19 m Ah g^-1,a superior energy density of 97.63 Wh kg^-1,good rate performance,and ultra-long cycle stability.In addition,the ZHSC device can operate in a wide temperature range from-30^oC to 80^oC.This work provides a good example for constructing ZHSCs that simultaneously possess high capacity and wide-temperature working ability.