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@ARTICLE{Kwiecien:866896,
      author       = {Kwiecien, Monika and Huck, Moritz and Badeda, Julia and
                      Zorer, Caner and Komut, Kuebra and Yu, Qianru and Sauer,
                      Dirk},
      title        = {{V}ariation of {I}mpedance in {L}ead-{A}cid {B}atteries in
                      the {P}resence of {A}cid {S}tratification},
      journal      = {Applied Sciences},
      volume       = {8},
      number       = {7},
      issn         = {2076-3417},
      address      = {Basel},
      publisher    = {MDPI},
      reportid     = {FZJ-2019-05956},
      pages        = {1018 -},
      year         = {2018},
      abstract     = {Acid stratification is a common issue in lead-acid
                      batteries. The density of the electrolyte rises from the top
                      to the bottom and causes inhomogeneous current distribution
                      over the electrodes. The consequences are unequal aging
                      processes provoking earlier battery failure. In stationary
                      applications electrolyte circulation pumps are sporadical
                      installed in the battery to mix the acid. For automotive
                      applications passive mixing systems are implemented by some
                      battery manufacturers against stratification. Stratification
                      does not show any distinct voltage-current profile to be
                      recognizable online. However, it increases the voltage and
                      affects the impedance, which both are essential information
                      for diagnostic purpose. Impedance spectra were performed
                      here on lead-acid test cells with adjusted stratification
                      levels to analyze the influence on the impedance in details.
                      It is observed, that the high-frequency impedance is
                      decreased in the stratified cell and that in contrast to
                      this the charge-transfer resistance is increased. Based on
                      simulations with a spatially-resolved equivalent electrical
                      circuit the increased charge-transfer resistance could be
                      explained with an inhomogeneous State-of-Charge resulting in
                      an accumulation of sulfate crystals in the bottom part of
                      the electrodes. These sulfate crystals further affected
                      recorded impedance spectra after the electrolyte was
                      homogenized.},
      cin          = {IEK-12},
      ddc          = {600},
      cid          = {I:(DE-Juel1)IEK-12-20141217},
      pnm          = {131 - Electrochemical Storage (POF3-131)},
      pid          = {G:(DE-HGF)POF3-131},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000441814300008},
      doi          = {10.3390/app8071018},
      url          = {https://juser.fz-juelich.de/record/866896},
}