Rare Earth Elements Doped Lithium Magnate Spinels Cathode For Lithium-ion Batteries

Lithium-ion batteries are green and rechargeable secondary power, they are widely used in mobile phones, computers and other equipments, due to high working-voltage, large energy density. The emphases on lithium-ion batteries are further to improve their performances and reduce their costs. Normal spinel lithium manganese oxides, LiMn2O4 is considered as a promising cathode material for lithium-ion batteries, for its advantages such as low cost, low toxicity, and relatively high energy density.The recent developments in normal spinel LiMn2O4 were reviewed on its crystal structure and properties. The lithium magnate spinels doped rare earth elements, used as the cathode for Li-ion batteries, were synthesized from Li2CO3 and EMD by solid state reaction, and were characterized by XRD, FESEM, ICP as well as electrochemical performance testing. The structure, electrochemical performance and the correlations between them were all discussed in detail for these doped spinels.It was found that the isotropically cubic-structured lithium magnate spinels, prepared at 750℃ for 20h in air, have a standard spinel structure, excellent electrochemical reversibility, a high specific capacity, and good cycle performance.The effects of the rare-earth elements on electrochemical performance and spinel structure of LiMn2O4.has been investigated. XRD analysis showed that the cathode materials modified by doping rare earth elements have a standard spinel structure. The results of electrochemical testing indicated that doping rare earth elements can improve the cycle performance of the material. LiMn1.95La0.05O4, LiMn1.98Sm0.02O4 and LiMn1 .98Y0.02O4 (vs. Li) showed better capacity retention than LiMn2O4, even though the first discharge capacity (96mAh/g, 100mAh/g, 106mAh/g) was lower than that (116 mAh/g) of LiMn2O4, at 0.5C charge and discharge rate. The capacity retention of LiMn1.98Sm0.02O4 over 100 cycles was about 86.3%, and the capacity retention of LiMn1.95La0.05O4 and LiMn1.98Y0.02O4 over 50 cycles was about 87% and 85.5%. The research showed that the material doped with rare earth elements have expanded the diffusing tunnel of lithium ion and stabilized sample's framework. The mechanism of rare earth elements for the improvement of the cycle performance of LiMn2O4has also discussed using the principle of crystal field..Al and F co-doped LiMn2O4(LiMn1.98Al0.0203.98F0.02 (vs Li) ) has a rather good electrochemical peformance. Al and F co-doping not only increases the first specific discharge capacity but also meliorate cycle performance of LiMn2O4 The discharge capacity of Al/Fco-doped LiMn2O4 reachs 120mAh/g in the first cycle and remains over 100 mAh/g after 100th cycles. Plastic Li-ion batteries (PPLIB) using LiMn1.98Al0.02O3.98F0.02 and CMS as the cathode and anode materials showed a high initial capacity of 105 mAh/g and good retentivity of 85% after 70 cycles using a 0.5C charge and discharge rate.