Electrochemical Performances Of Surface-modified ZnO, And Doped ZnO As Anodic Materials For Zinc-nickel Batteries

Zinc-nickel battery has the advantages of high energy density,high power density,high working voltage,wide working temperature,abundant materials,non-memory effect,and is an environment-friendly battery.However,due to the Zn electrode shape change,Zn dendrite formation,etc.the development of zinc-nickel battery has been limited.In this paper,the electrochemical performances of Al-doped ZnO and Ag-modified ZnO,and the size effect on ZnO are investigated.The Al-doped ZnO is prepared by a sol-gel method and calcination at 450℃.N-type doped ZnO has the better conductivity than the conventional ZnO.And Al can also affect the Zn deposition,slow down the growth of Zn crystal,and then improve the performance of Zn electrode.In the Al:Zn molar ratio range of 1%-6%,Al-doped ZnO gets the better performance than the conventional ZnO.But the Al-doped ZnO performes poorly as the doping quantity increases,because the excess Al becomes the impurity and contaminates the batteries.Though the initial capacity of Al-doped ZnO is lower than the conventional one,it is going stable and exceedes the capacity of conventional ZnO after 25 cycles.The fading rate of the Al-doped ZnO is lower than conventional ZnO.At the 60th cycle the capacity of conventional ZnO got only 160 mAh g^-1,but the Al-doped ZnO(1%,2%,3%and 6%) still has 332 mAh g^-1,436 mAh g^-1,510 mAh g^-1,266 mAh g^-1,respectively.Apparently,the Al doping can improve the cycle stability of the zinc-nickel battery.The ZnO with sizes of 100 nm and 2μm are prepared through a sol-gel method and a precipitation method,respectively.Compared with conventional ZnO(300 nm in size),the smaller ZnO particles have the better electrochemical performance and cycle stability.After 20 cycles,the biggest ZnO is coming into extroversive growth which means the dendrite formation;however,the smaller one's growth direction is irregular.It can be concluded that the smaller has the better electrochemical performance.The Ag-modification ZnO prepared by silver mirror reaction is investigated further in the paper.Ag particles are uniformly modified on the surface of ZnO particles and still exist as the metal silver in the electrode.The Ag particles improve the conductivity of Zn electrode and inhibit the dendrite formation.Through the research on the cyclic voltammetry curves and the impedance spectrum,it is found that the Ag modification little restrains the electrochemical reaction.The cyclic voltammetry curves show that the anode peak moves toward the positive slightly,and the cathode peak becames sharper,indicating that Ag-modification can make the charge process more efficient,and little affect the discharge process.The impedance spectrum farther shows that the Ag modification can decrease the charge-transfer resistance and facilitate the electrochemical reaction.