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Influence of Temperature on Microstructure and Performance of a Lithium-ion Battery

Zaker, Nafiseh | 2016

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 49340 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Asgari, Sirous
  7. Abstract:
  8. In this study, the effect of temperature on the microstructure and electrochemical properties of the NMC batteries has been studied. An extensive set of accelerated aging tests has been carried out employing a Li-ion high energy 18650 system (2.2 Ah, negative electrode: carbon, positive electrode: Li(Ni0.5Mn0.3Co0.2) O2. Different influence factors on cycle aging, such as temperature and discharge rate have been investigated. The aged 18650 cells have been inspected via scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), impedance spectroscopy, and X-ray diffraction (XRD) after disassembly to find more information about the chemical reasons of the degradation and structural changes. Higher rate of undesirable reactions, such as electrolyte oxidation or lithium salt decomposition is found to be the consequence of increasing temperature and also the composition of the precipitates transforms from carbonates to phosphates or fluorides. SEM images indicate that some kinds of cracks and isolated particles are appeared because of released gases from the electrolyte oxidation, stress from lithiated-delithiated of electrodes, and resin deposition used to make composited electrode. On the other hand, cracks and isolated particles lead to the growth of SEI layer and reduction of active material respectively, which cause capacity drop afterwards. Due to the further dissolution of the transition metals cathode structure are damaged severely by increasing temperature and discharge rate, its particles are agglomerated, and some holes are formed on its cover as well. The increase of impedance and inner resistance of the cell have been studied using EIS. The rise of the cell resistance is mainly caused by an increase of the cathode impedance and proves lack of thermal stability of the cathode. According to Ohm's law, expressing as the current increases lot of heat is generated, discharge rate increase leads to intensification of temperature gradient applied to the electrodes of the battery and heterogeneous flow distribution. Therefore, the battery is destroyed at higher rate. The results also demonstrate battery performance variation which might be consequence of non-uniform structural parameters and production problems
  9. Keywords:
  10. Microstructure ; Temperature ; Lithium Ion Batteries ; Temperature Effect ; Electrochemical Properties ; Nickel-Manganese-Cobalt (NMC) Bateries

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