成果報告書詳細
管理番号100012548
タイトル*平成19年度中間年報 次世代自動車用高性能蓄電システム技術開発 次世代技術開発 還元雰囲気通電焼結プロセスを用いた高容量含硫黄複合正極材料の研究開発
公開日2009/4/24
報告書年度2007 - 2007
委託先名独立行政法人産業技術総合研究所
プロジェクト番号P07001
部署名燃料電池・水素技術開発部
和文要約以下本編抜粋:1.研究開発の内容及び成果等次世代車載用リチウム二次電池の高エネルギー密度化のために、高容量を示す含硫黄複合正極材料を開発する。そのために、本研究では、還元雰囲気で材料の合成・複合化が可能な通電焼結プロセスを用い、金属硫化物と含硫黄有機物を複合化させ、従来の方法では得られなかった新規な硫黄系正極材料を創製する。
英文要約Research and development of high-capacity sulfur-based active material - carbon composite positive electrode using spark-plasma-sintering process under reductive conditions (National Institute of Advanced Industrial Science and Technology) FY: 2007-2008 Sulfur-based active materials are promising candidates as cathodes for high energy density lithium secondary batteries, applicable for next-generation hybrid electric vehicles, due to its high theoretical capacity. However, they have mainly two problems to be solved for their practical applications; low electrical conductivity and rapid cycle degradation. To solve these problems, we aim to prepare sulfur-based active materials - carbon composite positive electrode using spark-plasma-sintering process under reductive conditions. In addition, the electrolytes will be also explored for further improvement of the cycleability. In this year, we first developed a convenient process to prepare metal sulfides with higher sulfur contents, that is, NiS2 and FeS2, which have higher theoretical capacities among the metal sulfides. Traditionally, metal sulfides have been prepared by thermal treatment of metal with elemental sulfur. Such preparation includes complicated processes, for example, heating and vaporizing the sulfur in a sealed tube for longer time. Therefore, more simplified process is necessary for developing the sulfur-based cathode materials. Here we used porous metals (Ni, Fe) as the starting materials to enhance the sulfurization at larger surface area, and the sulfurization reaction was conducted in a graphite die by applying a pulsed DC current to it for heating (spark-plasma-sintering process). Such reductive condition is advantageous for suppressing the oxidation of both metal and sulfur. By applying this procedure, single phase NiS2 and FeS2 were finally obtained. The electrochemical discharge/charge tests for the obtained NiS2 with conventional non-aqueous electrolyte (1M LiPF6/(EC+DMC)) showed that the initial discharge capacity was ca. 820 mAh/g, which was about 94% of the theoretical value (870 mAh/g). However, the capacity retention after 10 cycles was about 20%. Such larger capacity fading would be originated from the poor reversibility of NiS2 during charging, formation of soluble polysulfides, and/or disconnection between the active material and current collector. For improving the cyclability of NiS2, several non-aqueous electrolytes were explored. As a first attempt, we examined the applicability of 1M LiTFSI/Triglyme electrolyte for the above-mentioned NiS2. The initial discharge capacity was ca. 800 mAh/g, which was comparable to the value with conventional non-aqueous electrolytes. However, the cells showed larger specific capacity (> 900 mAh/g) during charging. Although the origin of this observation is not clarified, some degradation of electrolytes might be caused during charging.
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