Quantum Chemistry Calculation On Battery Material Of LiFePO₄ System

The constant development of the new energy is the important foundation of sustainable development of human society. With the progress of science and technology, the demands for the portable energy of people are stronger and stronger . So, people are seeking cheap, security, chemical power material of secondary lithium batteries which friendly to environment and with excellent performance. Recently , people find that LiMPO₄ is the anodal material of potential lithium ion battery with the above fine performance .It should be noted that it is an irreversible trend from molecule chemistry to materials chemistry. The interaction among molecules in composite materials has attracted much attention from chemistry and material science researcher. On the base of theoretically calculation, molecule structure and bonding model of LiFePO₄ and LiMPO₄ molecule were investigated in this thesis. Moreover, the inner information of molecule such as covalent bonds, wave function, state density were also obtained by analysis.UMPO₄ (M=Mn, Fe, Co and Ni) and FePO₄ are studied by density function and discrete variation (DFT-DVM) method. The correlation among composition, electronic structure, chemical bond and property has been studied. According to the figure of DOS, M 3d partial DOS mainly contributes to the lowest conduction band(LCB), O 2p mainly contributes to and highest valence band(HVB) near to the Fermi level, and other partial DOS are further away from the Fermi level.The ionic and covalent bonds of LiFePO₄ are both weaker than those of FePO₄, and the variations of DOS also show that the electronic conductivity of LiFePO₄ should be larger than that of FePO₄. The strengths of ionic and covalent bonds mainly decrease in UMPO₄ from Mn to Ni, and the variations of density of state(DOS) show that the electronic conductivity should be increased from Mn to Ni. The results meet with the experiment.LiFePO₄ doped by M atoms (M=Mn, Fe, Co and Ni) are studied by densityfunction and discrete variation (DFT-DVM) method. The correlation among composition, electronic structure, chemical bond and property has also been studied. The strengths of ionic and covalent bonds mainly decrease in LiFePC>4 doped by M atoms from Mn to Ni, and the variations of density of state(DOS) show that the electronic conductivity should be increased from Mn to Ni. But it hasn't proved by experiment.