The Study Of The λ-MnO₂ As The Cathode Material Of The Alkaline Metal Ion Battery

As pollution-free, low-cost and safe energy storage devices, aqueous capacitor batteries have attracted many people’s attention.λ-MnO2 is a kind of electrode material which has excellent electrochemical performance, compared with other manganese dioxide which has different crystal structure, the material with the structure of three-dimensional grid is much easier for insertion/desertion of external ions. In this paper, we first single out the best concentration of HNO3, then we study the electrochemical performance of ,-MnO2 in the different lithium salts、sodium salts、magnesium salts and zinc salts, respectively.After studying the electrochemical performance of λ-MnO2 prepared by different concentration HNO3 in 0.5 mol·dm-3 MgCl2, we get that the discharge specific capacity ofλ-MnO2 prepared by 0.8 mol·dm-3 HNO3 at 15 mA-g-1 in 0.5 mol·dm-3 MgCl2 can reaches 311.2 mAh-g-1 with the best electrochemical performance. By comparing the electrochemical performance of λ-MnO2 in different lithium、sodium、magnesium and zinc salts, we find out that λ-MnO2 has the best electrochemical performance in Li2SO4、Na2SO4、MgCl2 and ZnNO3.By investigating the electrochemical performance of λ-MnO2 in Li2SO4、Na2SO4 and MgCl2,we can come to the conclusion: In terms of different concentration Li2SO4, it is easier for the desertion of Li+from λ-MnO2 in 0.5 mol·dm-3 Li2SO4 when the current density was low, and the best electrochemical performance was achieved in 1 mol·dm-3 Li2SO4 solution with high current density. In terms of different concentration Na2SO4, satisfactory electrochemical performance of λ-MnO2 is achieved in the 0.5 mol·dm-3 Na2SO4 with the current density between 15～420 mA·g-1,but when the current density is between 420～1400 mA·g-1, it is 1 mol·dm-3 Na2SO4 that makes it much easier for insertion and desertion of Na+ from λ-MnO2.In terms of different concentration MgCl2, λ-MnO2 shows the better rate capability in 0.5 mol·dm-3 MgCl2 when the current density is between 15～420 mA·g-1, at the same time, when the current density is 15 mA·g-1, the discharge capacity can reach 313.2 mAh·g-1 which is biggest discharge capacity in the experiment, and if the current density is high enough,λ-MnO2 will show the best cycling stability and rate capability in 1 mol·dm-3 MgCl2.The electrochemical performance of λ-MnO2/AC capacitor cells in 1 mol·dm-3 Na2SO4 is investigated, it shows that the discharge specific capacity of the capacitor battery has reached 85.7 mAh·g-1 at 15 mA·g-1. When the current density is 420 mA·g-1, the discharge specific capacity can still remain 28.5 mAh·g-1 after 100 cycles. Also, the electrochemical performance of λ-MnO2/AC aqueous sodium-ion capacitor cells has been studied, the results indicate that the discharge specific capacity of the capacitor battery has reached 103.1 mAh·g-1 in 1 mol·dm-3 MgCl2 when the current density is 15 mA·g-1,and when the current density increases to 1400 mA·g-1, the specific capacity of the cell still remains 30.4 mAh·g-1.Comparing the electrochemical performance of λ-MnO2 prepared by HNO3 leaching method and electrochemistry method in 0.5 mol·dm-3 MgCl2, we have come to the conclusion that λ-MnO2 prepared by HNO3 leaching method has the better rate capability in 0.5 mol·dm-3 MgCl2, and the discharge capacity can reach 313.2 mAh-g-1 at 15 mA·g-1.