Synthesis And Electrochemical Properties Of Li-And Mn-Rich Cathode Materials For Li-Ion Batteries

Power lithium ion batteries for electric vehicles have attracted increasing attention because of the gradually exhausted oil energy and growing environmental pollution. The lithium ion batteries for electric vehicles may satisfy the demands for higher power density and energy density than those applied in digital cameras, music players and mobile phones. Much attention has been paid to the layed cathode materials of Li-rich Mn oxides xLi₂MnO₃·?1-x?LiMO₂ owing to its high specific capacity, outstanding thermal stability, low cost and good environmental compatibility. However, the poor cycle performances of Li-rich Mn oxides prevent them being appied in power lithium ion batteries for electric vechiles. In this paper, the layed cathode materials of Li-rich Mn oxides xLi₂MnO₃·?1-x?LiMO₂ were selected as the research objects. The syntheses, microstructure and electrochemical properties of the 0.15Li₂MnO₃·0.85Li (Ni_0.4Co_0.25Mn_0.35)O₂ and 0.3Li₂MnO₃·0.7Li(Ni_0.4Co_0.45Mn_0.15)O₂ with Al₂O₃ or AIF₃ coating were systemically studied, which provide an experimental foundation for further developing the layed cathode materials of Li-rich Mn oxides as power lithium ion batteries.Synthesized by using coprecipitation and high temperature solid reaction method to get the layed cathode materials of Li-rich Mn oxides of 0.15Li₂MnO₃·0.85 Li(Ni_0.4 Co_0.25 Mn_0.35)O₂ and 0.3 Li₂MnO₃·0.7Li (Ni_0.4 Co_0.45 Mn_0.15) O₂. The microstructure analysis and research show that the as synthesized materials of 0.15 Li₂MnO₃·0.85Li (Ni_0.4 Co_0.25 Mn_0.35)O₂ and 0.3 Li₂MnO₃·0.7Li (Ni_0.4 Co_0.45 Mn_0.15) O₂ have alpha NaFeO₂ layered crystal structure, microstructure of homogeneously spherical structure, and without obvious phenomenon of reunion. Further study indicate, 0.15Li₂MnO₃·0.85Li (Ni_0.4Co_0.25Mn_0.35)O₂ and 0.3Li₂MnO₃·0.7Li(Ni_0.4Co_0.45Mn_0.15)O₂ with Al₂O₃ or AlF₃ coating material has coating layer on the surface, and does not affect the main crystal structure of the Li-rich Mn oxides material.The layed materials of Li-rich Mn oxides were made into model 55150210 flexible packaging power battery, the electrochemical performance is studied. The results show that the 0.15Li₂MnO₃·0.85Li(Ni_0.4Co_0.25Mn_0.35)O₂ and 0.3Li₂MnO₃·0.7Li(Ni_0.4Co_0.45Mn_0.15)O₂ with Al₂O₃ or AIF₃ coating material exhibit good charge and discharge cycle stability. AlF₃ surface coating materials at 1 C after 500 recycling, the initial discharge capacity is 75% of 177 mAh/g, Al₂O₃ surface cladding materials under 1 C to charge and discharge current density after 500 times of charging and discharging circulation, discharge, capacitance of 75% of the initial capacity of 170 mah/g. At 1C charge and 2C discharge, the 0.15Li₂MnO₃·0.85Li (Ni_0.4Co_0.25Mn_0.35)O₂ and 0.3Li₂MnO₃·0.7Li(Ni_0.4Co_0.45Mn_0.15)O₂ with Al₂O₃ or AIF₃ coating material after more than 3500 cycles remains more than 75% of the initial specific capacity?150 mah/g? through 2.7-4.24 V, after more than 2000 cycles remains more than 78% of the initial specific capacity?157 mah/g? through 2.5-4.35V.