Studies on Structures and Anode Behaviors of Lithium Storage Intermetallic Compounds

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1. The local structure of Li_xMg_2Ge, which is a candidate for anode materials of lithium secondary batteries, was investigated using both X-ray diffraction and neutron diffraction. It was found that the nearest interatomic distance of the Ge-Mg increases slightly in electrochemically lithiated Mg_2Ge lattice to form a solid solution.2. To obtain a new anode material of lithium battery, electrochemical properties were investigated on Mg_2Sn synthesized by mechanical alloying (MA) method. As a result, we found that the reversible insertion-extraction of a large amount of lithium can electrochemically occur in the Mg_2Sn. The Mg_2Sn changed its crystal structure from cubic to orthorhombic with increasing MA time. The compound exhibiting good performances as an anode had an orthorhombic phase. The discharge capacity of the Mg_2Sn electrode was still maintained at 250-300 mA h g^<-1> ever after the 20 times charge-discharge cycling.3. A1Sb was synthesized using MA. Electrochemical performa … More nce was examined on the electrodes of A1Sb synthesized with different MA time. The first charge (lithium-insertion) capacity of the A1Sb electrodes decreased with increasing MA time. The discharge capacity on repeating charge-discharge cycle, however, did not show the same dependence. The electrode consisting of the 20 h MA sample exhibited the longest charge-discharge cycle life, suggesting that there is the optimum degree of internal energy, derived from the strain and/or the amorphization due to MA. These results were evaluated using X-ray diffraction and differential scanning calorimetry.4. Electrochemical tests demonstrated that the initial charge and discharge capacities of the Mg_2Sb_2 electrode were ca. 850 and 600 mA h g^<-1> which were superior to those of the conventional graphite electrode. XRD of the Mg_2Sb_2 electrodes showed that several lithium-containing compounds such as LiMgSb and Li_3Sb were successively formed during the insertion of lithium into Mg_3Sb_2. The cycle life performance of mechanically lithiated (LiMgSb) electrode was significantly enhanced in comparison with that of the Mg_3Sb_2 electrode. Less