Study of Microstructural Changes Associated with Internal Resistance of a Li-ion Battery

Tabean, Saba | 2016

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 50720 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Asgari, Sirous
  7. Abstract:
  8. As one of the main features of Li-Ion batteries, internal resistance severely affects performance and characteristics of these batteries e.g. output power and working voltage. In this study, we tried to understand role of internal resistance on microstructure development and provide a correlative relation between microstructural features and performance of lithium-ion batteries. To catch this target, four types of Li-Ion battery chose, varying cathode type. These batteries were exposed to both normal and severe cycling conditions. Regarding to the key role of current rate on the performance of Li-ion batteries, an extensive research on different types of batteries at various current rates were done at this study. As the first priority and in the first section of current study, internal resistance was studied at different current rates. Study revealed that high current rates, play a severe impact on the battery's internal resistance. In order to further elucidate the observed trend, relationship of internal resistance and response parameters of battery including voltage drop and capacity fade, were investigated.Although a rational relationship of increased internal resistance and voltage drop was established in NMC type cathode batteries, but in fact, a clear clue of same trend was not recognized for batteries with different kinds of cathodes, which may originally comes from complexity of parameters enrolling on electrochemical impedance. As a general observation enhanced current rates at discharge state, improves internal resistance. In the second part of current study, microstructural observations were correlated to the internal resistance. SEM graphs indicates formation of deposits as well as agglomerates due to aging phenomena, during charge/discharge cycles. In the case of sample with NCA cathode, deposits were easily observable on the Anode, even at low magnification of SEM graphs, explaining capacity fade of this sample.It is revealed that current rate impose a critical effect on elemental composition of deposits, indicating increased instability at higher current rates. Reactive agents available in electrolyte and current collectors as well as migration of anodic/cathodic materials could be enumbered as the source of formed deposits
  9. Keywords:
  10. Electrochemical Impedance Spectroscopy ; Scanning Electron Microscopy (SEM) ; Battery ; Lithium ; Resistance ; Ion ; Flow Rate ; Microstructure

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