Studies On Preparation And The Electrochemical Properties Of The Cathod Material LiMnO₂ Of Lithium-ion Battery

With the increasing pressure from population, natural resources and environment since 21st century, the construction of a resource-conserving, environment-friendly society has become the primary issue of this era. In the field of energy, particularly in world market of battery, owing to its high density of both energy and volume and its good performance in safety and discharge, lithium ion battery has been now widely applied in mobile phones, mobile power as well as space technology. With the reduction of battery cost and the comprehensive improvement in battery performance, it is predictable that lithium ion battery will be used in more and more fields. cathod material of a battery determines its capacity and accounts for one third of the battery cost. However, the cathod materials of lithium ion battery respectively have their drawbacks: LiCoO₂ costs a lot due to the scarcity of cobalt, spinel LiMn2O4 makes poor cycle performance especially under high temperature, LiNiO₂ is difficult to prepare. Therefore, it is urgent to develop a low-cost and high-performance cathod materials used in lithium ion battery.The present study firstly introduces the development and the composition of lithium ion battery, explain the way lithium ion battery works, and reviews relevant previous studies. Then it focuses on how to prepare layered LiMnO₂ and explores its structure, shape and electrochemical properties. The research procedure is as follows:when the raw materials areLiOH.H₂O and Mn₂O₃,what we obtain in the muffle furnace is the pure Li₄Mn₅O₁₂ sample. It is indicated by the XRD and SEM test that the calcining time has much effect to the Micro-structure and morphology of the sample and the sample prepared under 750℃has better Micro-structure and morphology.The charge-discharge test demonstrates that the initial discharge capacity of the sample becomes small with the improvement of temperature in the experiment, while the cycle performance becomes better.The comprehensive electrochemical character of the sample prepared under 750℃is best and its initial discharge capacity is 90.62mAh/g,but its cycle performance remaines to be improved because its capacity-keeping rate is only 50% after 20 times cycle.The capacity and the cycle performance of Li₄Mn₅O₁₂ are sensitive to the amount of current. when the charge-discharge current increases from 0.15mA to 0.5mA,the discharge capacity of the sample prepared under 750℃increases gradually from 71.7mAh/g to 89.2mAh/g, showing good cycle performance.It is indicated by XRD test that when the raw material is LiaCO3 and Mn₂O₃,what we can obtain under atmosphere of indifferent gas is the pure layered LiMnO₂ sample,while if we change Li2CO3 to LiOH.H₂O,the end material is the mixture of Mn₂O₃, MnO and LiMnO₂.The SEM test demonstrates that the layer structure of the sample prepatede under 750℃is more noticeable than the sample prepatede under 600℃. It is indicated by the charge-discharge test that the LiMnO₂'s initial irreversible capacity loss is large and there is an activation process in the cyclic process. Its maximum capacity appears after 9 times cycle,increasing from the initial 109.2mAh/g to 118.2mAh/g and then the discharge capacity decreases.So the future work is to increase the initial charge-discharge efficiency and improve its cycle performance by doping other elements.It is indicated by XRD test that when the raw materials LiOH.H₂O and Mn₂O₃ offer the same quantities of Lithe and Mn, the hydrothermal preparation of LiMnO₂ produces a mixture of Mn₂O₃ and LiMnO₂, and that with the ratio of Lithe/Mn being 10:1, the product is pure layered LiMnO₂, which becomes Li₄Mn₅O₁₂ if Mn₂O₃ is replaced by MnO₂. As for the structure of LiMnO₂, the result of SEM test shows that LiMnO₂ produced at 150℃has a better layered structure than that produced at 195℃. The performance of LiMnO₂ is demonstrated by charge-discharge testing in the following two aspects. Firstly, with the improvement of temperature in the experiment, the initial charge voltage of LiMnO₂ increases while its capacity becomes small. LiMnO₂ prepared at 220℃has a much smaller capacity but a higher capacity-keeping rate compared with that produced at lower temperatures. Secondly, when the charge-discharge current increases from 0.15mA to 1mA, the discharge capacity of the electrode of LiMnO₂ decreases greatly while the cycle performance of the electrode of LiMnO₂ enhances in terms of the fast augmentation of its discharge capacity in the cycle.