A Novel Method for Judging Health/Degradation of Lithium-Ion Batteries
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A Novel Method for Judging Health/Degradation of Lithium-Ion Batteries
Futao Kaneko1, Takahiro Kawakami1, Akira Baba1, Kazunari Shinbo1, Keizo Kato1, Shigetoshi Miyazaki2, Koichi Shimizu2, Kenichi Sato3 and Osamu Hanaoka4 1
Niigata University, 2-8050 Ikarashi, Nishi-ku, Niigata, 950-2181 Japan
2
Alps Electric Instruments, 285 Takebusa, Shinsyushinmachi, Nagano, 381-2411 Japan
3
Midori Anzen, 5-27-1 Inari, Souka, 340-0003 Japan
4
Midori Electronic, 397 Togura, Chikuma, 389-0804 Japan
ABSTRACT A novel and fundamental method was reported to judge states of lithium ion batteries (LIBs) using the capacitance and the voltage of the cells that were estimated from the real-time currents and voltage characteristics of the cells. We measured the differential capacitance, that is, dQ/dV or delta Q/ delta V that is equal to the currents (I) divided by differential voltages (dV/dt) calculated from the current and the voltage characteristics of the cell during the charging/ discharging, where Q is the charge that flows through the cell, V is the voltage of the cell and t is time. It is thought that the capacitance decrease with the degradation of the cell because the effective area of the electrodes is decreasing due to formation of undesirable compounds. The differential capacitance in some specific voltage range for the LIBs was approximately directly proportional to the state of the degradation of the cell. Therefore, it is concluded that the novel method is very useful to judge the state of the LIBs.
INTRODUCTION Lithium ion batteries (LIBs) have attracted a lot of attention to the researchers and the users because of the high capacity [1, 2]. It is very important to estimate health/degradation of LIBs utilized in vehicles, airplanes, emergency power sources and so on, as the cells with some degradations cannot show the initial performance [3-6]. It is well known that the degradation is mainly caused by some undesirable composite materials formed on the electrode surfaces due to severe conditions such as over-charge/over-discharge and charge/discharge at high temperature. Many methods are reported to evaluate the health/degradation of the LIBs. The fundamental method for the evaluation is to measure the total charges through the cell in the charging or the discharging. The internal resistance has been measured for judging the degradation because the resistance increases with the degradation [3-5]. AC impedance measurements, that is, Cole-Cole or Nyquist plot [6, 7], are also used to evaluate the degradation from the complex dielectric
constants or the profiles of the plots that depend upon the degradation [8, 9]. A model was reported to determine state of health (SOH) from some parameters in a battery cell model [10]. Electrode surfaces of degraded LIB cells have been analyzed using X-ray absorption near-edge structure analysis, high-resolution transmission electron microscopy, electron energy loss spectroscopy and X-ray photoemission spectroscopy measurements to evaluate the origin of the degradation [11, 12]. We
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