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

2000 Fiscal Year Final Research Report Summary

• Project/Area Number: 10650819
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: 工業物理化学
• Research Institution: Kansai University
• Principal Investigator: TAKEHARA Zenichiro KANSAI UNIVERSITY, FACULTY OF ENGINEERING, PROFESSOR, 工学部, 教授 (00025892)
• Co-Investigator(Kenkyū-buntansha): SANO Makoto KANSAI UNIVERSITY, FACULTY OF ENGINEERING, ASSISTANT, 工学部, 助手 (00170811)
• Project Period (FY): 1998 – 2000
• Keywords: Lithium Battery / Cathode Material / Lithium Manganese Oxide Spinel / Metal Doped Material / Structural Change / Charge-Discharge Cycle / Co, Ni Doped / Al, Mg, Li Doped

Research Abstract

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.