Study On Synthesis And Electrochemical Characteristics Of LiNi_0.8Co_0.1Mn_0.1O₂ Cathode Material For Lithium Ion Batteries

Lithium-ion batteries (LIB) with high energy density, power capability and long cycle life are used to power portable electronic devices such as cellular phones and laptop computers and have long been considered as possible power source for electric vehicle (EV), hybrid electric vehicle (HEV) and high efficiency energy-storage systems. Layered LiCoO₂ is the most widely used cathode material in the present-day commercial Li-ion batteries. However, due to its high cost and toxicity, considerable effort has been expended over the past decade to find possible alternatives to LiCoO₂.Recently, LiNi_0.8Co_0.1Mn_0.1O₂ as a special case among the Li[Ni1-2xCoxMnx]O₂ series which x is 0.1 has attracted a great deal of interest in the investigation of cathode materials of LIB to replace the presently popular LiCoO₂ because the combination of Ni, Co, Mn can provide advantages such as high reversible capacity, stable cycling performance, good thermal stability, excellent rate capability and low cost. It is considered to be one of the best candidates of positive electrode material for hybrid electric vehicle (HEV) power source system. In this dissertation,the studies on the synthesis, morphology, structure and electrochemical performance of LiNi_0.8Co_0.1Mn_0.1O₂ as cathode materials for lithium ion batteries were carried out systemically and in detail.In this paper, the uniform spherical metal hydroxide (Ni_0.8Co_0.1Mn_0.1)(OH)₂ was prepared via hydroxide co-precipitation as precursor. This paper represents details of the optimized spherical (Ni_0.8Co_0.1Mn_0.1)(OH)₂ formation process by control reaction time, pH, amount of chelating agent, etc., during co-precipitation reaction. The results indicated that the optimum conditions for spherical (Ni_0.8Co_0.1Mn_0.1)(OH)₂ were that the pH of the aqueous solution was 11.5, the NH₃/M was 2.5 and the reaction time was 16h.Layered spherical LiNi_0.8Co_0.1Mn_0.1O₂ powders with high tap-density were successfully synthesized by mixing uniform co-precipitated spherical (Ni_0.8Co_0.1Mn_0.1)(OH)₂ with LiOH?H2O followed by heat-treatment. The mixture was pre-heated at 480℃and kept in this temperature for 5h, then kept at 650℃for 9h. The effects of calcination temperature, time and Li/(Ni+Mn+Co) ratio on electrochemical properties of the LiNi_0.8Co_0.1Mn_0.1O₂ were studied intensively. The results showed that the sample of LiNi_0.8Co_0.1Mn_0.1O₂ which were sintered for 16h at 750℃in a flowing oxygen atmosphere exhibited the best electrochemical performance.In this study, the morphology, tap-density, structure and electrochemical performance of the sample LiNi_0.8Co_0.1Mn_0.1O₂ obtained at optimal conditions have been further studied. The particle shape is still spherical, which is the same as the precursor (Ni_0.8Co_0.1Mn_0.1)(OH)₂. The SEM micrograph of LiNi_0.8Co_0.1Mn_0.1O₂ showed that a large number of spherical primary particles with an average size of about 500-800 nm pilled loosely to form quasi-spherical secondary particle. The corresponding tap-density was about 2.3-2.5 g·cm^-3, of which the value is close to that of commercialized LiCoO₂. Electrochemical measurement showed that it delivers an initial discharge capacity of 168.6 mA·h/g during the first charge and discharge cycle and the first coulombic efficiency is 90.5%, and the discharge capacity at the 20th cycle was 161.7 mA·h/g. The material will be potential cathode material for Li-ion battery.