Study On The Magnetic And Electrochemical Properties Of Electrode Materials For Lithium Batteries

Lithium-ion secondary battery, as a new recycling and clean energy, is a kind of important technical method to solve energy, resource and environment problems. With the strong request of social development, the research and development of new lithium-ion battery have attached much attention. New lithium-ion battery has been developed greatly based on the new thoughts, new material and new technology and tending to high energy, high power, long life and environmental protection. The electrode materials not only show good electrochemical properties, also display abundant physical phenomena and thoughts due to the special crystal structure and multi-valence sates.In this thesis, we explored some typical kinds of electrode materials and studied their synthesis processes, lattice structure, magnetic properties and electrochemical properties. We also offered our perspective on their novel and abundant magnetic phenomena.(1) Monoclinic Li0.33Mn02 has been studied as a good 3V cathode material, but the structural transition during electrochemical cycling is still uncertainty. In this chapter, we prepare Li0.33MnO2 and find the material show good capacity retention in low voltage and the surface of Li0.33MnO2 will change into a spinel layer in high voltage by study the CV, impedance, in situ XRD, XAS and Raman. Furthermore, Li0.33MnO2 shows two magnetic transitions due to dc and ac susceptibility data. The quantitative studies on relation between ac peaks and frequencies shows Li0.33MnO2 display the transition from paramagnetism into atomic-scale spin glass, then into cluster spin glass with the decreasing of temperature.(2) Cubic NiO has a high theoretical capacity of 718 mAh g-1 as a negative material and is considered a promising negative materials because of the high capacity and low price. NiO is a typical P-type semiconductor and antiferromagnetism with Neel temperature 523 K. We synthesize Lio.29Ni0.71O by molten salt method and discuss the effect of nonmagnetic Li+ ion doping on the electrochemical and magnetic properties. Dc susceptibility shows a reentrant spin glass behavior from ferrimagnetism to spin glass in Lio.29Ni0.71O. The possible reason may lie in the multi-competitive exchange interactions when Li+ ions are introduced into NiO lattice. Li0.29Ni0.71O does not show better electrochemical properties in comparison with that of NiO which may originate from the irreversible Li2O in the fist cycling.(3) In layered Li(Nix,Mnl-x-y,Coy)O2 material, the structural phase transition during the charge/discharge process will be suppresed because Mn4+ ions shows non-Jahn-Teller effect. Co3+ ions does not have electrochemical properties and Ni2+ ions will change the valence from+2 into+3 in the electrochemical cycles. One of the major problems to restrict electrochemical properties is the disordered arrangements of transitions ions in the transition-metal layers. In this chapter, we firstly synthesizes the 442 materials, and then studies and discusses the magnetic behaviors. Our research results shows 442 material shows cluster spin glass behavior, which is quite different from the atomic spin glass in Chernova's reports. Such difference may come from the scale of disordered cluster due to the different preparation process.(4) Lithium-rich Li[Li(l/3-x/3)Mn(2/3-2x/3)Nix]O2 system has attracted much attentions in recent years due to the high specific capacity and good cycling. But the magnetic studies on this materials are lack comparatively. Such type of lithium-rich materials has rhombohedral layered structure with triangle lattice in the transition-metal layers. On the other hand this material can be considered to be the solid solution of LiMnO2 and Li2MnO3. This provide us a possibility and chance to discuss the effect of geometrical frustration and disorder on the formation of spin glass. We find Li[Li0.2Mn0.4Ni0.4]O2 show a spin-glass-like behavior. Calculated spin-frustration parameter F=7.8 is far below the standard parameter 10 which geometrical frustration works. So we can conclude that the origin of spin glass in Li[Li0.2Mn0.4Ni0.4]O2 is disorder arrangements of transition metal oxides rather than geometrical frustrartion.