成果報告書詳細
管理番号20140000000201
タイトル*平成25年度中間年報 革新型蓄電池先端科学基礎研究事業 革新型蓄電池先端科学基礎研究開発 (6)
公開日2014/5/17
報告書年度2013 - 2013
委託先名学校法人早稲田大学
プロジェクト番号P09012
部署名スマートコミュニティ部
和文要約
英文要約 This research aims at the R & D Initiative for Scientific Innovation of Next Generation Battery / Durability Analysis of Li-Ion Batteries (LIB) using in-situ Impedance Method. Using ac impedance analysis for LIB, we research an analysis of the status of the LIB. Moreover, we evaluate the trend of the change in the condition of the electrode, electrolyte, and separator during the degradation of the LIB. Our research is establishment of method for the analysis method of status of degradation of the LIB by Ac impedance analysis.
 The purposes of the research in FY2013 were to evaluate impedance response of additive containing LIBs, which are composed of ionic resistance of electrolyte and solid electrolyte interphase (SEI), and charge transfer resistance, combining comparison with state variation of each anode and cathode due to LIB degradation. For further understanding, the impedance response was analyzed by using proper equivalent circuit. The parameter variation calculated by the analysis was discussed from the standpoint of physical variation in the LIB. Also, novel anode of Si-O-C composite, which is expected to be an electrode for next generation LIB, was evaluated by means of ac impedance measurement.
(1) A LIB was evaluated by means of ac impedance under low temperature circumstance. As the results, each impedance response was clearly separated. Thus, the method to divide whole impedance response into each impedance response could be established. At the same time, a LIB was evaluated by means of ac impedance under high temperature circumstance. As the results, rise of plots to vertical line which can be considered the Warburg impedance of finite length type was observed between 10 mHz and 1 mHz over 40 oC. These responses were caused by temperature characteristics of ion diffusion in both anode and cathode. Therefore, the non-destructive evaluation method for commercial LIB, which does not have a reference electrode, was demonstrated.
(2) A LIB made in our laboratory was evaluated by LC-QTOF/MS to detect the degradation in the LIB in detail. As the results, many phosphate ester and carbonate based compounds were detected. These compounds would affect the degradation of the LIB. Thus, the effectiveness of LC-QTOF/MS for detection of the LIB degradation was indicated.
(3) A fabrication process of LIB was optimized to improve the charge-discharge property of the LIB. A middle LIB, which can deliver the capacity of 1.5 Ah, was successfully fabricated by multi-layering.
(4) A LIB contains vinylene carbonate (VC) as an additive was evaluated by means of ac impedance. The addition of VC in LIB was enable to evaluate the graphite anode even after degradation; the anode of the LIB without additive was hard to be evaluated after degradation because of large inductive response. The impedance analysis on the LIB with VC revealed that the charge transfer resistance of the cathode was ca. 10 times higher than that of the anode. Thus, the charge transfer resistance of the cathode revealed to be one of the limitations on the LIB operation. The change in LIB by the addition of VC that enabled to be detected was the suppression of LiF formation on the anode. On the other hand, the change on the cathode was not detected by XPS even though the resistance increase in higher frequency region was observed. The result implies the active material might be changed, not the surface film, which can be detectable by XPS.
(5) Si-O-C composite anode, which was developed in our laboratory, was evaluated by means of ac impedance. With increasing cycles, the impedances of charge transfer, SEI and ionic diffusion increased. Among them, the charge transfer resistance was highest through the cycles. The impedance due to SEI drastically increased in the initial cycles. This result corresponded with the low charge-discharge efficiency in the initial cycles. Thus, the impedance analysis can be applicable even for a novel anode system.
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