成果報告書詳細
管理番号20140000000207
タイトル*平成25年度中間年報 安全・低コスト大規模蓄電システム技術開発 共通基盤研究 過渡現象を利用する大規模蓄電システムの非破壊劣化診断技術の開発
公開日2014/5/17
報告書年度2013 - 2013
委託先名学校法人同志社同志社大学
プロジェクト番号P11007
部署名スマートコミュニティ部
和文要約
英文要約A modified modelling method of Lithium-ion battery during its operation was developed. The internal impedance of the battery was estimated only from the terminal voltage and the current waveforms during its operation. The internal (open-circuited) voltage vs. SOC characteristic was removed from the modelling. The measurement of the SOC dependency of the internal voltage, which was difficult to measure for a large-scale battery, was not required. The model circuit became a simple circuit of a series connection of a constant voltage source and RC circuits expressing an internal impedance. The modification stabilized the estimation of the circuit parameters, and enlarged the application field of the dynamic circuit parameter estimation, because no extra charging/discharging circuit and no removal of the battery from the equipment were required.
 The frequency characteristic of the internal impedance was obtained from the model circuit expressed by a rational function in z-domain by the method developed in the previous year. The impedance agreed with that measured by a conventional AC superposition method. The accuracy of the proposed method was confirmed by laboratory tests and running tests of an electric bike.
 The estimation method and the equivalent circuit were applicable not only to a lifetime-estimation but also to a numerical simulation of an equipment driven by the battery, because the internal impedance obtained by the method was able to represent its frequency characteristic, which also expressed the transient response of the battery.
 Impedance spectra of NCM cathode at initial cycles were investigated in detail using a half-cell. Even at OCV (~3 V vs. Li/Li+), a semicircle was observed in the frequency range of 100kHz to 60Hz, which was assigned to the impedance of the electronic contact in the composite electrode (active material and carbon). In addition to the semicircle in the high frequency range, another semicircle appeared in the range 100 to 0.1 Hz at potentials higher than 3.7 V, which was assigned to the impedance for the charge-transfer resistance, as reported in FY2012. Durability tests of a LMO/graphite full cell at 60 degree C were carried out. Two semicircles, which have not been assigned to specific electrochemical processes, were observed in impedance spectra. The impedance of both semicircles increased after repeated cycling at 60 degree C.
 The propriety of the proposed transient method was investigated using a LMO/graphite full cell. When the sampling rate was fixed at 1 s, the data at around 0.5 Hz agree well with those obtained by the impedance method. When the sampling rate was increased to 5 msec, the semicircle in the low frequency range of 100 to 0.1 Hz was reproduced well in some cases. However, in most cases, the analysis suffered from a high noise level, and it was found that a reduction of the noise level is important to improve the reproducibility of data for the measurements in the frequency range of 100 to 0.1 Hz.
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