Studies On LiNi_1-x-yMn_xCo_yO₂ Cathode Material For Lithium Ion Batteries

As a new generation cathode material, LiNi₁-x-yMn_xCo_yO₂ cathode material has great potential for being a new kind of cathode candidate for its excellent electrochemical performance and low cost, showing an attractive prospect at minitype-portable electric sources and large-scale power supplies. For these reasons, LiNi₁-x-yMn_xCo_yO₂ has been studied intensively as a cathode material to replace the presently used LiCoO₂. However, the electrochemical performance of LiNi₁-x-yMn_xCo_yO₂ has been greatly affected by the oxidation of Ni²+ and Mn²+, and the layered structure of the material is hard to be synthesized. Recently, LiNi₁-x-yMn_xCo_yO₂ cathode material is made by being calcined at more than 900℃ for more than 10 hours, and this technics is so complex that it makes this kind of material hard to be applying in industry. Furthermore, for this cathode material is studied for only a few years, there are not many reports on it and the discharge capacity of this kind of material, of which is made in our country, is just 140mAh/g, which makes the industrialized production of LiNi₁-x-yMn_xCo_yO₂ becoming impossible. For a solution to these problems, extensive studies have been carried out on the synthesizing of LiNi₁-x-yMn_xCo_yO₂ in this paper. The sample LiNi₁-x-yMn_xCo_yO₂, synthesized in air atmosphere and lower temperature, shows satisfactory performance. Its initial discharge capacity is 160.8mAh/g, its initial discharge efficiency is over 90.6%, and the 40th discharge capacity only deceases 4.9%, showing good electrochemical stabilities.Differed from present cathode materials research thought and method, we have brought forward the idea of emphasizing on the study of the precursor. We studies on the influence of the precursor LiNi₁-x-yMn_xCo_yO₂ on the structure and electrochemical performance. In this paper, co- precipitation method has been used to synthesized LiNi₁-x-yMn_xCo_yO₂. The relations between the performance and crystal structure of the precursor and type of Ni-salts, pH, temperature, Ni/Mn/Co ratio and ageing time have been investigated. The results indicate that the process conditions including type of Ni-salts, pH, Ni/Mn/Co ratio, temperature and ageing time are important for the preparation of the precursor. At last, we synthesized the precursor LiNi₁-x-yMn_xCo_yO₂ in the process conditions that: using nitrate as stuff, the pH is 8.50, Ni/Mn/Co ratio is 0.4:0.3:0.3(mol ratio), temperature is 50℃ and ageing time is 1.5 hours, respectively. The precursor we have got has great activity of reaction.High temperature solid state method was used to synthesis LiNi₁-x-yMn_xCo_yO₂. The relations between the electrochemical properties and crystal structure of LiNi₁-x-yMn_xCo_yO₂ and calcining temperature, calcining time, Ni/Mn/Co ratio and the...