報告書番号

T53

タイトル（和文）

リチウム二次電池の劣化機構と評価技術に関する研究

タイトル（英文）

A Study of Degradation Mechanism and Evaluation Methods on Lithium Secondary Batteries

概要 （図表や脚注は「報告書全文」に掲載しております）

電力の負荷平準化技術の中で、電池電力貯蔵技術が実用化に近いものと期待されている。電池電力貯蔵を実現するためには単電池の大型化、長寿命化、組電池技術に関わる問題の解決が重要である。充放電に伴う電解液の劣化は電池性能、サイクル寿命、安定性などに影響を与えることから、電極と有機電解液との反応挙動を検討した。Li/MoS2系電池の劣化は充放電に伴う正極活物質の構造変化と密接に関係し、低率放電ほど電解液の分解を加速する。一方、C/LiCoO2系リチウムイオン電池は、通常作動電圧範囲では、溶媒間の交換反応により電解液組成変化を生じるが、電解液分解は非常に少ない。しかし、過充電域では正極活物質からの酸素発生とこれによる溶媒の酸化分解反応、過放電域では溶媒の還元分解反応による電解液劣化と多量のガス発生が起こる。これは組電池運転時、電池の個別管理が必要となる。

概要 （英文）

The object of this paper is to study the application of lithium secondary batteries as energy storage systems, that is, the technological factors involved in creating large-size and large-capacity batteries, extending the cycle life of batteries, and establishing series and/or parallel connections using batteries. For this purpose,battery performance was estimated through comparison of a 1-Wh and a 70-Wh battery, and operating conditions for extending the cycle life of the batteries was proposed by clarifying the degradation mechanism. The behavior of batteries connected in systems were determined based on the effects of the voltage balance and current distribution among batteries used in a multicell. First, in examining the application of their batteries to an energy storage system, the performance of a 1-Wh and a 70-Wh battery were compared, and the possibility of scaling up the batteries was clarified. The characteristics and performance of the 1-Wh and the 70-Wh battery were found to be acceptable. Second, to prolong the cycle life of a battery,the effect of the battery voltage and current on compositional changes in the electrolyte solution and gas generation during charge/discharge cycling were examined. Structural changes in the cathode active material during cycling were found to be strongly affected by the decomposition of electrolyte solution. Furthermore, investigation and elimination of the negative factors affecting the degradation of batteries led to the establishment of operating conditions to prolong cycle life. Third, because an energy storage system requires batteries connected in series or parallel, a test method is necessary to evaluate the behavior of batteries connected in the system, particularly to clarify the cycle performance of the batteries that are overcharged and overdischarged. A float connection method allowing the behavior of a battery at a series-connected multicell to be evaluated was developed, and the cycle performance of overcharged and overdischarged batteries was assessed. The relative advantages of series-based and parallel-based connection was also evaluated, and the effects of voltage and current are discussed. Finally, the above results are summarized and the conclusions of this study are explained. This study indicated that it is possible to scale up a battery, and that prolonging cycle life is also possible with the investigation and elimination of negative factors affecting the degradation of batteries. In addition, series- and/or parallel-connected multicell operation was shown to be advantageous in terms of its charge/discharge voltage profiles. This study was carried out to provide a direction for research and development on lithium secondary batteries for application to energy storage systems.

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