成果報告書詳細
管理番号20150000000223
タイトル*平成26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2015/5/26
報告書年度2014 - 2014
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 simplified modelling method of Lithium-ion battery during its operation was developed using a time series method. The internal impedance of the battery was estimated only from the terminal voltage after a charging or discharging. There was no effect of internal (open-circuited) voltage vs. SOC characteristic. The measurement of the SOC dependency of the internal voltage, which was difficult to measure for a large-scale battery, was not required. The internal impedance of the battery was expressed by a simple circuit of a series connection of a resistor and some RC parallel circuits. The circuit parameters obtained by the simplified method agreed well with those by the accurate z-domain method, which has developed in this project. The simple calculation algorithm can be easily installed into a micro-processor used in Battery Management System. It was observed that the resistances of the equivalent circuit and time constants of the RC parallel circuits increased with the increase of the number of cycles of the charging and discharging.
 A prototype of a diagnosis circuit was developed using a micro-computer. The circuit integrated the difference between terminal voltage and the internal voltage after a charging or discharging. The voltage difference corresponds to the voltage across the internal impedance. The increase in the resistances of the equivalent circuit and that in the time constants of the RC parallel circuits increased the integrated voltage. Because the effect of SOC on the integrated voltage was small, a temperature correction was only required. The prototype rates the number of cycles on a scale of one to six. Although minor fluctuations are observed due to the SOC dependency, the accuracy of the estimation was satisfactory for a practical deterioration diagnosis.
 Impedance changes of NCA cathode at initial cycles were investigated in detail using a half-cell. As was observed for NMC cathode in FY2013, two semicircles were observed in the frequency ranges of > 100 Hz, and of 100 Hz to 0.1 Hz. The semicircle in the lower frequency range, which are assigned to the impedance of the charge-transfer reaction, increased significantly upon cycling.
 The propriety of the proposed transient method was investigated using a LMO/graphite full cell. When the sampling rate was increased to 5 msec, the semicircle in the lower frequency range of 100 to 0.1 Hz was reproduced well after noise removal on the software. Laboratory-size (3 x 3 cm) LMO/graphite full cells equipped with a lithium reference electrode was fabricated, and long-term cycling tests were started.
 In addition, long-term cycling tests were started using commercially available full cells (5 Ah). The impedance of the commercially available cells was measured at the initial state and after 1500 cycles, and the data agreed well with those measured at Waseda University.
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