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

研究了替代Li_xCoO_2作为锂电池正极材料的尖晶石Li_xMn2O_4。在Li_xMn_2O_4中，锂离子易于扩散，Li_xMn_2O_4在锂的提取和插入过程中顺利充放电。在4V(Li/Li^+)平台上观察到LixMn2O4尖晶石在1&gt；x&gt；0.5区有连续晶格参数变化的均相反应，然后在0.5&gt；x&gt；0.13区有两个立方相。在后一段，LixMn2O4分解，作为可充电正极的循环效率较低，因此，用阳离子取代锰是提高循环效率的有效方法。选择Co和Ni作为取代阳离子。在4.5~3.5V(vs Li/Li^+)的充放电过程中，Co^&lt；3+&gt；和Ni^&lt；2+&gt；；然而，由于Co^&lt；3+&gt；被氧化为Co^&lt；4+&gt；，而Ni^&lt；2+&gt；在4.5V(vs Li/Li^+)以上的电位下被氧化为Ni^&lt；4+&gt；；因此，由于结构退化，在5.0~3.5V(vs Li/Li^+)的充放电过程中循环效率较低。锂、镁和铝取代了单相尖晶石中的锰位。然而，这种替代降低了容量。容量损失随取代物浓度的增加而增加，其大小顺序为Al、Mg、Li。能量为4V(vs Li/Li^+)和0.11Ahg^&lt；-1&gt；(约占LiCoO_2的70%)的LiMn_&lt；1.9&gt；Al_&lt；0.1&gt；O_4是较好的正极材料，在充放电过程中循环稳定。

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.