Estimation and the Material Design for Functional Oxides by Thermodynamic Measurement

与LiCoO2相比，LiMn2O4具有成本低的优点，作为充放电电位高的锂二次电池正极活性材料备受关注。从热力学的角度研究了结构与电极性能的关系。首先，合成了富Li尖晶石Li_&lt；1.33&gt；Mn_&lt；1.67&gt；O_4，缺陷尖晶石Li_&lt；0.89&gt；Mn_&lt；1.78&gt；O_4，以及用Al部分替代Mn的尖晶石LiMn_&lt；2-x&gt；Al_xO_4，研究了样品的性能、结构与正极性能的关系。根据溶解热计算了标准生成热Δ_1H^0和反应热变ΔH。用这些参数考察了体系的热力学稳定性。锰的价态和晶格参数随结构和金属含量的变化而变化。LiMn_lt；1.8&gt；Al_&lt；0.2&gt；O_4和Li_…晶体结构的中子衍射分析考察了More&lt；1.1&gt；Mn_&lt；1.7&gt；Al_&lt；0.2&gt；O_4。结果表明，随着Li、Al含量的增加，(Mn，Li，Al)-O的键距减小，晶格能绝对值(傅立叶方法)增大。此外，还研究了第一性原理计算(DV-Xα)方法。结果表明，Mn-O键的共价键比Li-O键的共价键强。此外，还用溶液量热法测定了样品的溶解热。当ΔA_fh^0和ΔH减小时，其循环性能较好。另一方面，计算了电池反应前后晶格能的变化。结果表明，当正极活性材料的热力学稳定性增加，晶格能变化减小时，其循环性能较好，相应地，主体结构的稳定性和正极活性材料中离子态Li的存在，对循环性能的改善起到了促进作用。较少

LiMn_2O_4 has an advantage of low cost compared with LiCoO_2 and it pays attention as a positive electrode active material for the Lithium secondary battery, which has high charge-discharge potential. The relation between the structure and the electrode characteristics from the viewpoint of thermodynamics was investigated. First, the samples was synthesized of the Li rich spinel, Li_<1.33>Mn_<1.67>O_4, the defect spinel, Li_<0.89>Mn_<1.78>O_4, and substitution spinel to partially replace Mn by Al, LiMn_<2-x>Al_xO_4. It was investigated the relation between property, structure, and ode performance of the samples. Furthermore, the standard enthalpy of formation, Δ_1H^0, and the enthalpy change of reaction, ΔH, were calculated form the heat of dissolution. Thermodynamic stability was examined by these parameters. The Mn valence and lattice parameter a changed with change of structure and metal contents. The crystal structure analysis by neutron diffraction of LiMn_<1.8>Al_<0.2>O_4 and Li_ … More <1.1>Mn_<1.7>Al_<0.2>O_4 was examined. As a result, the bond distance of (Mn, Li, Al)-O decreased and absolute value of the lattice energy (Fourier method) increased with increasing Li and Al. Moreover, the first principle calculation (DV-Xα) method was investigated. From the results, covalent bond of the Mn-O bond was stronger than the Li-O bond. Furthermore, the heats of dissolution of the samples were measured by the solution calorimetry method. When ΔA_fH^0 and ΔH decreased, it brought to a good cycle performance. On the other hand, a change in lattice energy before and after the cell reaction were calculated. From the results, when thermodynamic stability of a positive electrode active material increased and the change of lattice energy decreased, it brought good cycle performance.Accordingly, it is suggested that the stability of the host structure and the existence of Li, which is ionic state in the positive electrode active material, brought to improvement for the cycle performance. Less