Synthesis of Lithium Storage Intermetallic Compounds for Rechargeable Battery and their Structural Analysis using X-ray and Neutron

近年来，由于下一代可充电锂电池对更高容量负极的需求不断增加，储锂金属间化合物已被广泛研究。为了提高阳极的体积充放电容量，我们将重点放在稀土元素上，因为它们的密度大，并提出了新材料，如CeSn_3和LaSn_3。CeSn_3和LaSn_3电极的体积容量比实际使用的石墨电极的体积容量大约3倍，是一种有吸引力的替代电极。但是，该电极的首次充放电可逆性和循环性能与其它合金电极一样差，通过机械合金化方法在CeSn_3和LaSn_3中添加锂，克服了上述缺点。为了探讨机械锂化CeSn_3（Li_xCeSn_3）电极性能的改善，采用电化学测试和X射线、中子实验研究了机械锂化CeSn_3电极的充放电机理。结果表明，Li_xCeSn_3由CeSn_3和未知Li-Ce-Sn相组成。活性材料中的CeSn_3相在Li-Ce-Sn相中分散均匀，起到惰性基体的作用。因此，认为小晶粒尺寸的CeSn_3有利于嵌入晶粒较深的锂的逸出，Li-Ce-Sn基体释放了嵌锂时产生的应力。

Recently, lithium storage intermetallic compounds have been extensively investigated because of an increasing demand for higher capacity anode for next generation's rechargeable lithium batteries. To enhance volumetric charge and discharge capacities of the anode, we focused on rare-earth elements due to their large densities, and proposed new materials, such as CeSn_3 and LaSn_3. The volumetric capacities of CeSn_3 and LaSn_3 electrodes were about three times larger than those of graphite one practically used, suggesting an attractive alternative electrode. The electrode, however, exhibited poor reversibility at the first charge-discharge cycle and cyclability as well as other alloy electrodes previously reported.The drawbacks have been overcome by adding lithium to CeSn_3 and LaSn_3 using mechanical alloying. To discuss the improvement of electrode performance for mechanically lithiated CeSn_3 (Li_xCeSn_3) electrodes, the charge-discharge mechanism was investigated by electrochemical measurements and some experiments using X-ray and neutron. As a result, it was found that the Li_xCeSn_3 consists of CeSn_3 and unknown Li-Ce-Sn phases. The CeSn_3 phase of active material appears to be finely dispersed in the Li-Ce-Sn phase which plays a role as an inactive matrix. Therefore, it is considered that the CeSn_3 of small grain size facilitated the escape of lithium which had deeply inserted in the grain and the Li-Ce-Sn matrix released the stress generated at lithium insertion.