Original Design Of Aquous Energy Storage Materials And Devices And Their Performance Investigation

Employing low-cost and reliable electricity generated from renewable and clean energy sources is imperative for the sustainable development of human beings.To realize this goal,electrical energy storage（EES）is crucial to the reliability of power grid since renewable energy sources,such as wind,solar,tidal,and geothermal sources,are all inherently intermittent and spatially dispersed.Additionally,EES is also in urgent need because of the fast-growing energy demand in the areas of electric vehicles,mobile electronics,etc.Li-ion batteries（LIBs）are currently the most ccommonly used commercial EES devices.However,the scarcity of resources and the environmental impact related to the production of LIBs,as well as the safety issues during their use,severely hinder their wide deployment.Comparing with LIBs,aqueous energy storage devices like supercapacitors and batteries that based on alkaline cations,for example Li⁺,Na⁺,K⁺,Mg²⁺,Ca²⁺,Al³⁺ and Zn²⁺,as charge carriers have been reported recently due to their low cost,friendly environment and high safety.Supercapacitors are promising energy storage devices with higher power densities,shorter charging times,and longer cycle lives compared to LIBs.However,the low energy density limites their application.Hererin,firstly,we designed a 3D-nanostructured TiO₂ nanotube arrays@MnO₂nanosheets@polypyrrole（TMP）supercapacitor material,which can work in acidic solution to realize much higher capacity than that in neutral solution.To further solve the energy density and voltage problems for supercapacitor,we proposed a new view of supercapacitor called the "integrated supercapacitor".The integrated supercapacitor shows higher energy density and voltage than traditional supercapacitor.It is worth noting that the progess of aqueous batteries were continually reported recently.Their energy density is much higher than the supercapacitor and the charge rate is usually higher than LIBs.Typically,Zn-based batteries have been explored as one of the most compelling substitutes because of their intrinsic safety,low cost,and fairly higher capacity than the other aquous batteries.For capacity issue of Zn batteries,we successively proposed VS₄ with a chain crystal structure used as an intercalation cathode and a rechargeable Cu-Zn battery.Typically,a high specific capacity of 718 mAh g-1 is obtained because of the two-electron transfer reaction of Cu.However,more comprehensive problems like capacity,voltage,cost,charge rate and stability etc.should be considered for pracitcal application in the future.Thus,we further proposed a high potential deposition stratege to realize a series of ultrafast charge Zn based batteries.Additionaly,they also show multipul advantages like high capacity,high voltage and low cost etc.The work having been done in this thesis is as following.（1）Design of a unique 3D-nanostructure to make MnO₂ work as supercapacitor material in acid environment.Novel 3D-nanostructured TiO₂ nanotube arrays@MnO₂ nanosheets@polypyrrole（TMP）supercapacitor material has been designed with the capability to work in acidic condition efficiently.In this structure,TiO₂ nanotube arrays（TNAs）served as the scaffold to support MnO₂ nanosheets and polypyrrole（PPy）as a barrier to limit the dissolution of MnO₂ during discharge process.The synergistic effect of the three components in this structure significantly enhanced the cycling stability.It is found that the capacitance of TMP in 1 M H₂SO₄ solution was even 2-fold of that in traditional neutral solution（1 M Na₂SO₄ solution）due to the superior conductivity of acid solution.Finally,a full flexible solid-state asymmetric supercapacitor device composed of TMP and carbon nanotubes（TMP//CNTs）was fabricated and the voltage reached 2.2 V.The device showed excellent electrochemical performance with a high specific energy of 2.12 mWh cm-3 at a power density of 0.04 W cm-3 and remarkable cycling stability with 80.3% specific capacitance retention even after 20000 cycles.（2）A new view of supercapacitors:integrated supercapacitors.High energy density and voltage still remain a bottleneck for supercapacitors.Herein,a new view of a supercapacitor called the "integrated supercapacitor" is proposed.The electrode of the integrated supercapacitor consists of certain positive and negative materials.With this design,a single integrated electrode can work in both the positive and negative potential windows simultaneously.Additionally,the integrated full supercapacitor device shows a much higher capacitance and wider potential window than traditional single symmetric and asymmetric supercapacitors,which results from its multiple mechanisms,including the traditional positive//positive symmetric,positive//negative asymmetric,and negative//negative symmetric full supercapacitor mechanisms.（3）VS₄ with a chain crystal structure used as an intercalation cathode for aqueous Zn-ion batteries.Rechargeable aqueous zinc-ion batteries are promising energy storage devices due to their high energy density,safety,environmental friendliness,and low cost.However,their development for commercial applications remains in the beginning stages because of the limited options among positive electrodes exhibiting adequate capacity and cycle life.Furthermore,their energy-storage mechanisms are not yet well established.Here,vanadium tetrasulfide（VS₄）with a beneficial one-dimensional atomic chain structure is reported to be able to serve as a favorable intercalation cathode material for high-performance Zn-ion batteries.The energy-storage mechanism was investigated both theoretically and experimentally.The maximum capacity of this material reaches3 10 mA h g-1 and 85% of this capacity remains even after 500 cycles.（4）Realizing a rechargeable high-performance Cu-Zn battery by adjusting the solubility of Cu²⁺.The capacity of the most studied Mn-,V-,and Prussian blue analog-based cathodes of Zn-ion batteries does not exceed 400 mAh g-1.Cu is a promising cathode with a high theoretical capacity of 844 mAh g-1 based on its unique two-electron transfer process(Cu0■Cu²⁺),but Cu-Zn batteries have been impractical to recharge since they were invented by Daniell in 1836.By adjusting the solubility of Cu²⁺in an alkaline solution,a rechargeable high-performance Cu-Zn battery is achieved.A high specific capacity of 718 mAh g-1 is obtained for the prepared Cu clusters.Moreover,commercial Cu foil is explored for direct use as the cathode material and shows high capacity and stability through a simple self-activation process.（5）Realizing ultrafast charge in Zn based batteries through high potential deposition.Fast charge,extremely important in practical application,is another typical characteristic in aqueous batteries compared to LIBs with organic electrolyte,but little attention has been paid to it thus far in Zn based batteries.In this work,ultrafast charge and high capacity of the cathodes for Zn batteries are realized through the rapid conversion of low valence transition metal ions to their high valence solid oxides using a simple high potential deposition strategy.Especially for Mn based cathode,nearly 40 times of charge time is reduced compared with the traditional constant current charge method,while a high capacity is acquired simultaneously due to the multivalent conversion.