Dissertation > Industrial Technology > Electrotechnical > Independent power supply technology (direct power) > Battery

First-Principle Study on the Doped Spinel LiMn2O4

Author AnYongLiang
Tutor YuZeMin
School Harbin University of Science and Technology
Course Materials Science
Keywords Spinel LiMn2O4 Doping First-principles Electronic structure
Type Master's thesis
Year 2009
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LiMn 2 O 4 as an electrode material has a resource-rich, low-price, high-potential, environmentally friendly, the safety performance advantages, the most promising replace LiCoO 2 < / sub> of a new generation of lithium-ion battery cathode material. But it exists in the process of charge-discharge cycle does not cause serious capacity decay phenomenon due to poor structural stability and high temperature stability, which also limit it to further market commercialization main factor. Over the years, many scientists through a variety of preparation approaches (such as doping, surface coating, etc.) to change its structure in order to improve the stability and electrochemical properties. For microscopic electronic structure calculations reported less paper the spinel LiMn 2 O 4 materials and the doping system of electronic structure calculation explore from theory to explain the doping mechanism and period of the LiMn 2 O 4 cathode materials synthesis and modification to provide meaningful theoretical guidance. This paper mainly of LiMn 2 O 4 doped Ni, Co doped crystal model, and based on the primacy of the density functional theory (DFT) principle pseudopotential plane wave method undoped LiMn 2 O 4 crystal doped crystal doped electronic structure of the system investigated in the band structural characteristics and the variation of the structure, electronic density of states, the calculated results show that: the LiMn 2 O 4 is a direct bandgap ionic conductor of Li-ion is relatively free and independent. Strong overlap close to the Fermi level of the Mn-3d electron orbit and O-2P electron orbit, so interaction between Mn and O strong, play the role of the structure stable. Ni, Co doped system remain single spinel structure, the decline in the total energy of the system, the unit cell volume decreases, the density of states of the valence band widens, the Mn-O bond order increases, the bond length decreases net charge of the Mn and O ions are increased, and therefore Mn, O interaction increases, the doping of Ni, Co increase the average intensity of the Mn-O bond, enhance of LiMn 2 O 4 < / sub> stability of the spinel structure, it is possible to effectively inhibit the structural changes in the charge and discharge, is also conducive to the improvement of the cycle performance of the lithium ion battery. System Li doping density of states of intensity decreased, LI ions and O ions reduce the key sequence, the bond length increases described interaction of Li and O weakened doped systems, improvement of the performance of the system conductive. Separate doping Ni Fermi level rise; alone doped Co when the Fermi level is reduced; composite doping system can reduce the gap significantly improve the conductive properties for the best. Ni is greater than the system overall electronic characteristics Co.

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