Synthesis Of Layered LiNi_0.8Co_0.1Mn_0.1O₂ Cathode Material By A Fast Co-precipitation Method And Improvement Of Its Electrochemical Performance

During the past few decades, lithium-ion batteries have been widely used as power sources for various portable electronic devices due to their high energy density, light weight, long cycle life, and environmental friendliness. More recently, they have attracted growing attention as power supplies for hybrid electronic vehicles, plug-in hybrid vehicles and electronic vehciles. However, commercialization of these batteries for the automotive industries demands further improvement in energy density and safety for batteries. At present, LiCoO2 is considered to be the more promising positive electrode material owing to its high capacity and good reversibility. Nevertheless, commecialization of LiCoO2 is greatly hindred by its high cost and non-envirnmental friendliness. By contrast, the Ni-rich layered transition metal oxides Li[Ni1-xMx]O2 (M=Co, Mn, Al ect.) are emereged as the most promising cathode materials due to their relatively low cost and high reversible capacity. Among these materials, LiNio.8Co0.1Mn0.1O2 represents a promising cathode material with a high reversible capacity of～200 mAh g-1, which is much higher than that of commercial LiCoO2.However, practical application of LiNi0.8Co0.1Mn0.1O2 to lithium ion battreis is still hampered by its poor cyclability and rate capabilily. It has been found that the electrochemical performance of LiNi0.8Co0.1Mn0.1O2 largely depends on the synthesis method employed. Because synthesis methode could, in turn, impact on the crystallinity, phase purity, grain size, and cation mixing of final product. The traditional co-precipitation method has been widely used as an effective process to attain Ni0.8Co0.1Mn0.1(OH)2 precursor with in molecular level. But the difficulties associated with the long precipitation time (12h) and complicated synthesis precedures make it hard to produce the nano-scaled materials by the traditional co-precipitation approach. It has been found that improving the cycling performance and rate capability of electrode materials is needed smaller particles since they shorten the Li+ion diffusion paths and enhance the ionic transportation in the electrode. Therefore, an alternative synthesis method to fabricate the nanoscaled LiNi0.8Co0.1Mn0.1O2 cathode materials with superior electrochemical performance remains to be a great challenge.In this work, we synthesized the uniformly distributed nanoscale Ni0.8Co0.1Mn0.1(OH)2 precursor by a fast co-precipitation method. The influence of the main important process parameters, reaction time, PH values, sintering atmosphere and sintering temperature on the crystal quality and electrochemical performance of the as-prepared LiNi0.8Co0.1Mn0.1O2 is investigated in detail and a range of structural, morphological and electrochemical techniques are conducted to give a feedback to the as-prepared LiNi0.8Co0.1Mn0.1O2 materials. We find that the optimal process parameters for the LiNi0.8Co0.1Mn0.1O2are precipitation time of 1 min, Ph value of 11.50 and sitering temperature of 760℃ under oxygen flowing.Finally, Layered LiNi0.8Co0.1Mn0.1O2-Graphene composite is synthesized by a facile chemical approach and used as the cathode material for lithium-ion batteries. The structural and morphological features of as-prepared LiNi0.8Co0.1Mn0.1O2-Grapbhene composite are investigated with a range of characterization methods. The electrochemical results revealed that the LiNi0.8Co0.1Mn0.1O2-graphene composite shows a large initial discharge capacity up to 212.9 mAh g-1 as well as good cycling performance and good rate capability. The outstanding electrochemical performance of the graphene-modified LiNi0.8Co0.1Mn0.1O2 composite can be attributed to the improved electrical conductivity and structural stability due to the highly conductive graphene matrix.