Research On Electrochemical Properties And Synthesis Of Rich Lithium Layered Li_1.2Cr_0.4Mn_0.4O₂ Material

The rapid development of electronics and technology , and the serious problems in the aspect of power sources, environment require that the lithium-ion batteries has the higher performance and better cycle life. In order to improve the performance and descend the cost, the research about positive materials is the key.Recently, LiCoO₂ is being used as cathode material in the majority of commercial lithium-ion batteries with good capacity, reversibility and rate capability, but suffers from the high cost and relative toxicity of cobalt. The resource of nickel is richer than cobalt, the price of LiNiO₂ is cheap, its specific charging-discharging capacity is high and it has no environmental pollution, but it is difficult to be synthesized . Structure of LiNiO₂ is unstable, which will cause the decrease of specific charging-discharging capacity. The thermal stability of LiNiO₂ is bad. So people take aim at lithium manganese oxides.The price of LiMn₂O₄ is cheap and easy to be systhesised. The resource of manganese is rich and it is safe to environment, but the specific charging-discharging capacity is lower and the cyclic performance of LiMn₂O₄ is worse, especially at high temperature.According to the above conditions, much effort has been made to develop possible alternatives as a positive electrode. So a lot of people has focused on another kind of manganese oxide, LiMnO₂ as a promising material for lithium-ion batteries, because it has high theoretical capacity of 285mAh/g, and low cost relative to LiCoO₂. Although there has been a lot of progress, they remained various problems for practical applications. Orthorhombic LiMnO₂ has an ordered rock sait structure of space Pmnm group. It transforms irreversibly to another material with spinel-like ordering during electrochelnical cycling., Another phase of interest in this system is monoclinic LiMnO₂ which is analogous to LiCoO₂.In this work, Layered Li₁.2Cr₀.4Mn₀.4O₂ was successfully synthesized by a sol-gel method. We choice this material because it can well solve practical problems. This material will be good to solve second problems by rich lithium and without Mn³+. At first it can prevent the conversion to anti-stability phase from layered structure.Secondly it also avoid the Jahn-Teller effect without the substance of Mn3+.Properties of structure, morphology, valence changes during charging and discharging are deeply and systematically explored by the means of XRD, SEM, XPS and so ono Effects on the structure and properities of samples were studied from different calcining condition, the best synthesis techniques are optimized0The results got from the experiments showed that good morphology was got from the sol-gel method and the effects of different calcining temperatures on structure and electrochemical property were studied. It was shown that Li1.2Cro.4Mno.4O2 treated at 850D exhibited excellently layered structure and electrochemical property? it exhibited a discharge capacity of 190mAh/g in the voltage range of 2.5⁴.4V at a specific current of 25mA/g, also keeping capacity of 140 mAh/g after 40thcycleso In order to deeply understand mechanism of charging-discharging processes, we made use of XPS method o We found that part of chromium was changing reversibly between 6+ and 3+ during charging-discharging process , but Manganese remains 4+0We synthesis the doped Li[Lio2Cro4Mno.4]o.95Coo.os02° With the doping of Co ion, the initial discharge capacity and irreversible capacity decreaseo It improved the stability of the structure. It exhibited a discharge capacity of 180mAh/g in the voltage range of 2.5 ⁴.4V at a specific current of 25mA/g, reversible capacity was maintained at a specific current of 160mAh/g after 40 cycles -At last, in order to improve the electrochemical performance of Lii 2Cro.4Mno.4O2 at large current, this material dealed with Ag can exhibit good capacity of lOOmAh/g at a specific current of 80mA/go...