Synthesis And Investigation Of Lithium Nickle Cobalt Manganese Oxide Cathode Materials For Lithium Ion Battery

The development of electric vehicle (EV) and hybrid electric vehicle (HEV) needslithium ion battery cathode materials with excellent electrochemical performance，severaltypes of cathode materials have been investigated intensively. Compared with other cathodematerials like LiCoO2, LiMn2O4, and LiFePO4,etc., lithium nickle cobalt manganese ternaryoxide is recognized to be one of the most promising cathode material for the EV and HEVapplications, due to its following characters: high energy density, good cyclic stability andthermal stability.In this thesis, layered LiNi1-x-yCoxMnyO2cathode materials with various composition ofNi, Co and Mn are synthesized successfully. Among them, LiNi0.5Co0.2Mn0.3O2material hasbeen investigated focally, due to its good electrochemical performance. We optimized someimportant parameters and conditions in the preparation process, such as calcinationtemperature, the precursors of nickel and cobalt and manganese, and the lithium precursor.The results indicated that the optimum conditions for the synthesis of the LiNi0.5Co0.2Mn0.3O2cathode material were that the calcination temperature was900℃, the optimal nickel cobaltmanganese raw material was the acetate compounds and the optimal lithium source werelithium carbonate and lithium hydroxide.The effects of the lithium source adding method on the physical electrochemicalproperties of LiNi0.5Co0.2Mn0.3O2cathode material were investigated. When lithium acetatewas adding to the nickel cobalt manganese acetate solution, the synthesizedLiNi0.5Co0.2Mn0.3O2material had the maximum initial discharge capacity, theLiNi0.5Co0.2Mn0.3O2material synthesized by mixing the lithium acetate with the nickel cobaltmanganese oxalate through grind in mortar got the preferable cycle performance, theelectrochemical performance of the LiNi0.5Co0.2Mn0.3O2material synthesized by mixing thelithium acetate with the nickel cobalt manganese oxide through grind in mortar was the worst.In the other hand, we prepared lithium rich cathode material LiLi0.2MnxNiyMnzO2through sol-gel method, when the electrodes were fabricated and some amounts of the Pt/Coxygen reduction catalyst were added. The electrochemical performance was almost the samewhen the catalyst adding amount was1%. But the adding amount increased to2%,4%and 8%, the initial discharge capacities increased15.5mAh/g,14.8mAh/g and12.1mAh/grespectively, but the cycle performance became worse. And we attempted to reveal theprinciple of this phenomenon, in my opinion, under the catalysis of the Pt/C catalyst, the H+and O2turned into H2O, this reaction accelerated the H+and Li+exchange process, thusincreased the initial charge-discharge capacities.