The Effect of Transition Metal(Al, Co) Ions Doping in α-MnO2 Materials As the Rechargeable Zinc Ion Battery

Abstract

Lithium-ion batteries (LIBs) have been drawn significant attention as energy storage devices with high energy density and high power. However, nowadays, the attention of many researchers has been focused on exploration of new battery systems. The promising battery systems are sodium ion battery, all-solid state battery, zinc ion battery and so on. In this study, we report a zinc ion battery system which uses MnO2 materials as the cathode, because zinc metal have advantages such as natural abundancy, safety, un-poisonous, low cost and easy handling in open air. Also, manganese dioxide (MnO2) has been widely investigated as electrode materials owing to high natural abundance, low cost and non-toxicity. This MnO2 appears in various crystallographic polymorphs such as α-, β-, γ-, δ-, and ε-MnO2. Among these materials, α-MnO2 is comprised of the basic MnO6 octahedral units which are linked through edges and/or corners to forms crystallographic structures that correspond to different type of polymorphs. However, α-MnO2/Zn ion battery has drawbacks such as the formation of by-product, poor electric conductivity and capacity retention during cycling. To improve the some properties, we conducted the doping of Al, Co ion in the α-MnO2 structure and we anticipate that the doped transition metal Al and Co ions would affect not only electrochemical property but also structural stabilization. Therefore, we report on the effect of transition metal (Al, Co) doping in α-MnO2 materials on structure and electrochemistry. The Al∙Co-α-MnO2 nanorods was synthesized via hydrothermal method and the Al and Co source was added in molar ratios (5%, 15%, and 25%) to obtain Al∙ Co-α-MnO2 with various doping levels. The crystalline phase of the synthesized products was characterized by powder XRD using Cu-Kα radiation. Using these XRD data, lattice parameters were performed to identify the variation of a-,c- axis and volume. Also, ICP-AES was carried to measure the amount of Al and Co ion in the MnO2 structure. Also, SEM and TEM were employed to observe the surface and morphology of particle. The electrochemical tests were performed in coin type zinc cell. The used electrolyte solution was 1 M ZnSO4 (pH 4.0). The coin cells were charged and discharged between 1.0 and 1.8 V at room temperature. The XRD patterns of bare α-MnO2 and doped α-MnO2 obvious appeared single phase with I4/m space group and the XRD data of the Al, Co-doped α-MnO2 exhibited peak shift. The result of lattice parameter appeared change in values of a-, c-axis and volume. According to ICP-AES results, we could identify the amount of doped Al and Co ions. The electrochemical performances of the bare and Al, Co doped MnO2 electrode were tested in the voltage range of 1.0 – 1.8 V. Details will be discussed in the conference site. Figure 1