Performance improvement of LiMn2O4 as cathode material for lithium ion battery with bismuth modification

Spinel lithium manganese oxides (LiMn2O4) modified with and without bismuth by sol-gel method were investigated by theoretical calculation and experimental techniques, including galvanostatic charge/discharge test (CC), cyclic voltammetry (CV), chronopotentiometry (Cl?), 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 LiMn2O4 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 LiPF6) 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. (c) 2008 Elsevier B.V. All rights reserved.