The Electrochemical Behavior Of Spinel Manganese Oxide Electrodes For Aqueous Lithium-Ion Battery

Lithium-ion secondary battery duo to high specific energy and good cycle performance has attracted considerable attention, but its disadvantages of high cost and low safety can not been ignored by using organic electrolyte. The aqueous lithium-ion secondary battery could be possible in theory if cathode and anode materials that are all stable in aqueous solution can be found. Spinel lithium manganese complex is preferable because of low cost, good performance and environmental friendliness.The spinel LiMn2O4 is synthesized by the citrous acid method. The X-ray diffraction pattern of LiMn2O4 show that the product is a spinel phase with a=0.824nm cubic unit cell. The cyclic voltammetric measurement of LiMn2O4 is performed in aqueous solution with various pH values. It is obtained that the evolution of hydrogen and oxygen can be suppressed about pH=5, the Li+ ions intercalate into (or deintercalate from) LiMn2O4 lattice with two steps, the splitting of redox peaks is not apparent with increasing scan rate. Using test battery Li1-xMn2O4/Li+, NO3-, Zn2＋/Zn, the electrochemical behavior of LiMn2O4 as the positive electrode is studied by galvanostatic charge/discharge tests. It is found that Li1-xMn2O4→LiMn2O4 in aqueous solution involves two processes. The specific capacity of this battery can reach 112mAh/g under low current density.Treatment of the spinel LiMn2O4 with aqueous acid produces λ-MnO2. X-ray diffraction and atomic absorption spectroscopy show that λ-MnO2 with lattice constant of 0.806nm preserves the structural framework of the LiMn2O4 and the conversion of LiMn2O4 to λ-MnO2 results in some contraction of the lattice. TG and DSC measurements indicate that λ-MnO2 is a metastable form of MnO2, upon sufficient heating, reverts to the more stable β-MnO2.The comparison of the CV curves of λ-MnO2 with electrolysis MnO2 (EMD) shows that λ-MnO2 is reversible well. The galvanostatic discharge curve of λ-MnO2 in 5mol/L LiNO3 aqeous solution is similar to that in organic electrolyte, and the discharge mechanism is the homogeneous intercalation of Li+ ions. The test battery LiMn2O4/Li＋, NO3-/λ-MnO2 can hold for 5 hours under current density of 0.2mA/cm2, and give a specific capacity of 87.4mAh/g, an average voltage of 0.4V. Although the specificcapacity of this battery is much smaller than the theoretical values, it realizes aqueous lithium-ion battery by using managese compounds as electrodes.