Synthesis And Electrochemical Properties Of Rare Earth Doped-LiMn₂O₄ Spinel As Cathodic Material For Rechargeable Li-battery

The spinel LiMn₂O₄ has been a potential and active one of the second generation Li-ion battery cathode materials for its good security, nontoxic, inexpensive and environmentally benign, which also has a high work voltage and high specific energy. In this paper, we reviewed the recent research programs on Li-ion battery and the cathode materials;especially, the second-generation cathode materials of LiMn₂O₄ was introduced in detail by doping or coating et al measure, which influence on their electrochemical performance. The significant drawbacks of LiMn₂O₄ are generally thought as its rapid capacity decayed with increasing cycles number. Our reaserch also studied on how to improve and modify that drawback of LiMn₂O₄, main contents are listed as follows:1. A soft chemical process was used to synthesize the title Sc-doped Li_1.05Sc_xMn_2-xO₄ spinel, which involves the combination of proper metal salts in aqueous solution and evaporation with the assistance of ethanol as additive. It was found that the spinel phase could be formed at a modest temperature as low as 400 ℃. Li_1.05Sc_0.01Mn_1.99O₄ shows good electrochemical properties, after first cycle, the specific capacity is 122.7mAh/g, 30 cycles, the specific capacity is 101.2 mAh/g. The samples were evaluated as cathodic materials for secondary Li-battery exhibiting an improved reversibility and cycleablity, which was attributed to the addition of Sc (III) by stabilizing the spinel lattice.2. The spinel phases of Li_1.05RE_xCr_yMn_2-x-yO₄ (RE=Sc, Ce, Pr, Tb;01.05Sc_0.01Cr_0.03Mn_1.96O₄, the capacity of the cell maintained 91% of the initial capacity at the 80th cycle. The rare earth elements of the variable valent metals such as Pr³⁺, Tb³⁺ with transition metal Cr³⁺ as co-substituent do not stable framework of spinel or improve the cycling performance. Cyclic voltammetry (CV) were measured to provide clues for the improved cyclingperformance of cathode electrodes. Sc-Cr co-doped Li1.05ScxCryMn2-x.yO4 spinels demonstrated substantially improved capacity retention on cycling than Li1.05ScxMn2.xO4 or Li1.05CryMn2.yO4 for lithium-ion batteries.3. Simultaneous substitution of double rare earth ions such as Sc and Eu,Gd, Y or Ce, Pr, Tb et.al. for Mn3+ in the LiMn2O4 spinel phase was attempted with the aim of developing a stable spinel framework with good capacity retention. Cathode materials of the X-ray diffraction studies showed that Sc-Y doped spinel formed phase-pure compounds in the compositional range studied. However, both co-doping of Sc and Y led to decrease in the lattice parameters. Cyclic voltammograms showed that two these co-doped spinel phases were more stable electrochemically for Li1.05Sco.01Yo.01Mn1.98O4.4. In addition, we are still going on researching electrochemical properties of Lii+xMn2-xO4 or Lii+xMyMn2-x-y04 (M=Sc, Cr). Li1.02Mn1.9gO4 shows good electrochemical properties, after first cycle,the specific capacity is 119mAh/g, 30 cycles, the specific capacity is 102 mAh/g.5. A new method for synthesizing coating Ag to the Sc doped Li1.05Sco.01Mn1.99O4. Ag-coatted Lii.o5Sco.oiMni.9904shows good electrochemical properties, after first cycle,the specific capacity is 116.6 mAh/g, 50 cycles, the specific capacity is 105.4 mAh/g.6. At the end, we report a new method with coordination to form LiMnL for synthesizing layered lithium manganese or spinel lithium manganese, this method can effective control the ratio of Li/Mn and reduce complex process of experiment. It is a new method that for synthesizing layered lithium manganese.