Quantum Chemical Study On The Doping Of Anode Material For Lithium-ion Battery And On The Reaction Mechanism Of The Isomerization: HNC→HCN

The investigation and development of lithium ion batteries have attracted worldwide attention due to their excellent properties such as high voltage and specific capacity. The research of cathode materials is hotspot, the layered LiCoO2, LiNiO2 and the spinel LiMn2O4 are common cathode materials for lithium ion batteries. LiMn2O4 is focused on because of its low cost, abundant material resource and easy preparation and so on. However, large capacity fade on cycling makes it difficult to commercialize. Hence, considerable efforts are made to study the doping of LiMn2O4. The rule of electronic structure changes had been studied after intercalation and substitution in the spinel LiMn2O4 and the doping of LiMn2O4 with quantum chemical Ab initio and DV- Xα.The calculation results showed that Ab initio had its advantages in the calculating of atom cluster, especially in the aspect of precision and total energy calculation. Lithium existed as ionic state in lithium-manganese oxides after losing partial electrons. The weakenning in the electrovalent bond and the strengthening in the covalent bond between manganese and oxygen due to static effect and polarization effect made the spinel structure more stable. DV- Xαwas adapted to big molecules, especially for heavy metal atom and atom cluster. The positive charge of manganese ion increased with Co3+, Al3+, V inserted and the Jahn-Teller effect was restrained. The increasing in the strength of the Mn-O bond improved the stability of spinel structure and restrained the structural transformation in the process of charge-discharge cycle and suppressed the fading of capacity. The average voltages for LiMn2O4 was calculated by total energy change between non-intercalated and intercalated models. There were two steps during the lithium insertion of Mn16O32→Li2Mn16O32→Li4Mn16O32 with 3.176V and 4.032V.Secondly, the other work of this paper was the reaction mechanism of the isomerization: HNC→HCN was studied by means of density functional theory (DFT) at the level of B3LYP/6-311++G (3df,2pd). There might exist two types: One was that the HNC molecule itself proceeded via a three-centred transition state to transform by its interior hydrogen-bonded; The other was that two HNC molecules associated at first and then proceeded via a six-centred transition state to transform by its exterior hydrogen-bond. Hydrocyanic acid and water proceeded via a five-centred transition state to transform by its exterior hydrogen-bonded. The results showed that, the...