Study On Preparation And Properties Of Lithium Manganate As Cathode Materials Of High Power Lithium-Ion Batteries

The battery which is used to provide power to the popularity of electric bicycles,hybrid buses,electric cars and other products,become a new focus of attention.Lithium-ion power batteries has lots of advantages of light weight,small volume,large capacity,high-performance security,a single high voltage and so on.It is one of the best and the most widely used secondary battery applied to the power tool.The performance of the cathode material plays an important role in the performance of the battery.In that case,researchers work on how to select and product the cathode material.There are some candidates for the cathode material.lithium nickel oxides materials are hard to be synthesised.Lithium cobalt oxide-based material has been widely used in nowadays.However,with the reduction of cobalt resources and the protection of the environment,it will be replaced by other new materials in the future.As excellent performance new materials,lithium iron phosphate material and lithium manganese oxide material,that has been widespread concern,are most likely to replace the lithium cobalt oxide-based materials.Lithium iron phosphate material is not good at electric conductivity and low temperature resistance which hinder the research of this kind of material.Layered LiMnO2 has attracted researchers'attention because of its high theoretical specific capacity.Taking into account the above-mentioned status quo,this paper will talk about the high temperature solid-state synthesis of layered LiMnO2 material and its performance.Meanwhile,the doping of the monoclinic layered LiMnO2 will be researched by first-principles calculation in this paper.First of all,the raw materials of high temperature solid-state synthesis of layered LiMnO2 material and the performance in different external conditions will be introduced.Lithium carbonate and manganese dioxide are considered as a raw material which can be made spinel-type lithium manganese oxide in the air condition and pure orthorhombic layered lithium manganese oxide in the argon condition.According to the XRD patterns of the material,we got the best conditions of the high temperature solid-state synthesis of layered lithium manganese oxide.The best conditions in this paper are that lithium and manganese molar ratio is 1.03:1 with the synthesis temperature of 800? and time of constant temperature is 10h.The SEM photos of products are layered structure.The second part of this paper talks about the experimental synthesis of LiMnO2 material which is used as the positive electrode active material.We use this material to assemble the battery and test its electrical properties.The experimental results show that the initial charge capacity of the battery use the material of 720 ? is 227.6mAh·g-1.The specific discharge capacity can be up to 135.1mAh·g-1.The material has a good cycling stability in the case of each rate,the specific discharge capacity of lower rate(0.1C and 0.2C)is higher than 120mAh·g-1,the discharge plateau in 3V of the material is wide in the first cycle,as the charging and discharging process carried,the discharge plateau in 4V is wider.However,the capacity under high rate(1.OC and 2.0C)is poor,the degree of capacity attenuation is a little large.At a temperature of 800 ? under synthetic materials electrochemical properties.The electrical properties of material when 800? is better.Finally,because the initial discharge of the pure layered lithium manganese oxide actual has a lower capacity and a bad cycling performance under the high rate condition,we use the generalized gradient approximation(GGA)in the PW91 method based on density functional theory(DFT),do calculation of m-LiMnO2 and doping with 25%Cr and Co with first-principles.The results showed that doping Cr and Co does not changing the basic structure and electrical properties of the m-LiMnO2 material,doping with a transition metal atom can reduce Mn3+ concentration in the crystal,and reduce the John Teller effect of the material.Doping can also improve the material stability during the charging and discharging cycle,the material band lacunae can be reduced,the band intensity can be increased,thereby enhancing the conductivity of the material.We find out that m-LiMnO2 by doping with 25%Co band lacunae can be decreased a lot,it is suggested that Co-doped can improve the electrical performance of the m-LiMnO2 material,which is consistent with the conclusions of the experiment.Theoretical calculations for future material doped researches open up ideas and indicate a new direction.