The Research on the Lithium Manganese Oxide as a Cathode Material for Lithium Secondary Battery

用尖晶石代替Li_xMn_2O_4作为可充电锂电池的正极材料。在Li_xMn_2O_4中，锂离子在萃取和插入过程中容易扩散，且Li_xMn_2O_4充放电平稳。在4V（Li/Li^+）平台上，观察到晶格参数连续变化的Li_xMn_2O_4尖晶石在1> × >0.5区域的均相反应和在0.5> × >0.13区域的两个立方相反应。在后一区域，Li_xMn_2O_4分解，作为可充电阴极循环效率较差。因此，用阳离子取代锰可以有效地提高循环效率。选择Co和Ni作为取代阳离子。在4.5 ~ 3.5V（vs Li/Li^+）范围内，Co^<3+>和Ni^<2+>是稳定的，而Li^+在充电状态下并未完全从晶格中提取出来。然而，由于在大于4.5V（vs Li/Li^+）的电势下，Co^<3+>被氧化为Co^<4+>, Ni^<2+>被氧化为Ni^<4+>，在5.0 ~ 3.5V（vs Li/Li^+）的充放电过程中，由于结构降解导致循环效率较差。然后，选择非过渡金属Li、Mg和Al。Li， Mg和Al在单相尖晶石中取代了锰的位置。然而，这种替代减少了产能。容量损失随取代物浓度的增加而增大，并依次为Al、Mg、Li。LiMn_<1.9>Al_<0.1>O_4，能量为4V（vs Li/Li^+）和0.11Ahg^<-1>（约占LiCoO_2的70%）是较好的阴极候选材料，充放电循环稳定。

In the place of Li_xCoO_2 utilized as a cathode in a practical rechargeable lithium batteries, Li_xMn_2O_4 spinel, was investigated. In Li_xMn_2O_4, lithium ion diffuses easily and Li_xMn_2O_4 was charged and discharged smoothly during lithium extraction and insersion processes. The homogeneous phase reaction of Li_xMn_2O_4 spinel with a continuous lattice parameter change in the region 1>x>0.5 and then two cubic phases of it in the region 0.5>x>0.13 were observed on the 4V(Li/Li^+) plateau. In the latter region, Li_xMn_2O_4 decomposed and its cycling efficiency as a rechargeable cathode was poor.Thus, the chemical substitution of cation for manganese was effective in the improvement of the cycling efficiency. Co and Ni were chosen as the substituion cations. Co^<3+> and Ni^<2+> were stable during charge and discharge between 4.5 to 3.5V(vs Li/Li^+) and Li^+ was not extracted perfectly from crystal lattice at the charge state. However, since Co^<3+> was oxidized to Co^<4+> and Ni^<2+> was oxidized to Ni^<4+> at the potential more than 4.5V(vs Li/Li^+), the cycling efficiencies during charge and discharge between 5.0 to 3.5V( vs Li/Li^+) were poor by the structural degradation.Then, Li, Mg and Al, which were non-transition metals, were chosen. Li, Mg and Al more than were substituted for manganese sites in a single-phase spinel. However the capacity was reduced by such substitution. Such capacity loss was increased with the increase of concentration of the substitutes and in order of Al, Mg and Li. LiMn_<1.9>Al_<0.1>O_4 with energy of 4V(vs Li/Li^+) and 0.11Ahg^<-1>(about 70% of LiCoO_2) was a better cathode condidate and cycled stably during charge and discharge.