Thermodynamic and Quantum Chemical Investigation and its Material Design of Highly Functional Oxide

本文研究了<2-x>锂二次电池正极材料LiMn_ M_xO_4（M=Al，Ni，Co，Cr，Zn，Mg）的热力学稳定性、晶体结构、电子状态与电极性能的关系。用M取代Mn可改善其循环性能。用溶液量热法测定了这些样品的溶解热，由溶解热计算了生成反应的焓变Δ HR。结果表明，随着M的含量增加，LiMn_M_xO_4的循环性能提高。当M的含量增加时，LiMn_xO_4的循环性能下降，而LiMn_xO_4的循环性能下降。当M的含量增加时，LiMn_xO_4的循环性能下降|ΔH_R| LiMn_ M_xO_4的电子密度图表明，LiMn_<2-x>M_xO_4的Mn-O共价键比LiMn_2O_4强。另一方面，LiMn_M_xO_4的Mn-O共价键<2-x>比LiMn_2O_4强。用DV-Xα方法计算了LiMn_ M_ O_4中各原子的净电荷、Li-O、Mn-O、M-O的键重叠布居数、态密度和电子密度，结果表明：LiMn_<1.75>M_<0.25>O_4中Li *y始终保持较高的值，八面体中Mn-O的共价键<1.75><0.25>比LiMn_2O_4中的强。用DV-Xα方法计算了Li_yMn_ M_xO_4的电子<2-x>态，计算了Li_yMn_<1.75>M_xO_4<0.25>中各原子的净电荷，Mn-O和M-O的键重叠布居，发现Li缺陷模型和Li_yMn_M_xO_4中Mn与O之间存在较强的共价性，Mn与O<2-x>之间的键变化较小，在充放电过程中Mn被M取代后仍保持尖晶石结构。主体结构的稳定性对于循环性能是重要的。

We investigated the relation between thermodynamic stability, crystal structures, electronic states and electrode performance of LiMn_<2-x>M_xO_4(M=Al, Ni, Co, Cr, Zn, Mg)as cathode materials for lithium secondary batteries.The cycle performance is improved by substitution of Mn with M.The heat of dissolution of these samples was measured by the solution calorimetry method.The enthalpy change per mole of atoms for the formation reaction, ΔH_R, were calculated from the heat of dissolution.The larger |ΔH_R| means a thermodynamically more stable sample.A more thermodynamically stable sample makes a stable crystal structure and leads to a good cycle performance.The crystal structure was determined by Rietveld analysis using powder neutron diffraction.The electron density distribution was obtained by XRD using MEM/Rietveld method and DV-Xα method.The electronic density maps of LiMn_<2-x>M_xO_4 shows the covalent bonding of Mn-O of LiMn_<2-x>M_xO_4 is stronger than that of LiMn2O4.On the other hands, we calculated that the net charge of each atom, the bond overlap population of Li-O, Mn-O, M-O, the density of states, and the electron density of LiMn_<1.75>M_<0.25>O_4 using first principles calculation by DV-Xα method.Li ****y always keeps high and the covalent bonding of Mn-O in the octahedron of each LiMn_<1.75>M_<0.25>O_4 is stronger than that of LiMn_2O_4.****ver, we investigated the electronic states of Li_yMn_<2-x>M_xO_4 dependence of Li content.We calculated the electronic states of Li_yMn_<1.75>M_<0.25>O_4 by DV-Xα method.The net charge of each atom, and the bond overlap populations of Mn-O and M-O were calculated.The strong covalency between Mn and 0 existed in the Li defect model and Li_yMn_<2-x>M_xO_4.The bonding change in Mn-O is small and maintained the spinel structure during the charge-discharge process by substitution of Mn with M.From these results, the stability of the host structure is important for cycle performance.