Performance improvement of LiMn 2O 4 as cathode material for lithium ion battery with bismuth modification
Spinel lithium manganese oxides (LiMn 2O 4) modified with and without bismuth by sol-gel method were investigated by theoretical calculation and experimental techniques, including galvanostatic charge/discharge test (GC), cyclic voltammetry (CV), chronopotentiometry (CP), electrochemical impedance spectroscopy (EIS), inductively coupled plasma (ICP), powder X-ray diffraction (XRD), BET measurement, and infrared spectroscopy (IR). It is found that the performance of LiMn 2O 4 can be improved by the bismuth modification. The modified and the unmodified samples have almost the same initial discharge capacity, 118 and 120 mAh g -1, respectively. However, the modified sample has better cyclic stability than the unmodified sample. After 100 cycles, the capacity remains 100 and 89 mAh g -1 for the modified and the unmodified samples, respectively. Moreover, the results from EIS show that the modified sample has a quicker kinetic process for Li ion intercalation/de-intercalation than the unmodified one; the charge-transfer resistance of the former is less than one-sixth of that of the latter. After immersion in electrolyte (DMC:EC:EMC = 1:1:1, 1 mol L -1 LiPF 6) for 10 h at room temperature, the modified sample has less change in open circuit potential, crystal volume, and vibration absorption of Mn-O bond, and has less dissolution of manganese into solution than the unmodified sample.