Investigation of Capacity Degradation in Rechargeable Batteries

Project Objective: The primary objective of the project is to address two fundamental questions: (1) Where and what kind of irreversible processes occur at the electrodes? (2) How do these processes affect the capacity, energy efficiency, and cycle life of the battery? The ultimate goal of the study is to seek the possibility to minimize the irreversible phase formations by modifying the electrode structure and the electrode or electrolyte compositions, thereby improving the performance of the battery.

For ideal rechargeable Lithium (Li)-ion batteries (including Li-ion polymer batteries), the charge and discharge process (the inter-conversion of electric energy and chemical energy) should be nearly reversible, energy efficient, and have minimal physical changes. However, during charge and discharge cycling, a number of phases and large changes in structure typically occur at the electrodes in the battery cell. Some of the phases and structure changes are irreversible, thus resulting in capacity decay with cycles, low energy efficiency, and short-cycle life.

In this work we investigates the cycling characteristics and performance of Li-ion cell using electrochemical impedance spectroscopy (EIS), x-ray diffraction analysis (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Mechanisms for capacity degradation and reduce cell performance of commercial Li-ion cells are suggested. In addition, Morphological analysis will be use along with EIS to understand the formation of surface film with continuous charge-discharge cycling. In order to interpreter EIS measurement results and understand the physical and electrochemical properties changes as a function of cycle life, a physical based equivalent circuit model was developed and implement to Li-ion batteries using LixCoO2 and LixFePO4 cathode electrodes.


Fig. 1. SEM micrograph of the anode (LixC6) from (a) new cell, (b) after 30 cycles, (c) after 300 cycles, and (d) 1300 cycles.

Fig. 2. Comparison of the experimental spectra for Li-ion polymer cell for fresh and continuous cycled cell. Frequency range from 10 mHz to 20 kHz.

References

  1. P.L. Moss, R. Fu, G. Au, E.J. Plichta, Y. Xin, and J.P. Zheng, "Investigation of Cycle Life of Li-LixV2O5 Rechargeable Batteries", J. Power Sources, 124, 261 (2003).
  2. Z. Ma, P. Moss, R.Fu, G. Au, E.J. Plichta, and J.P. Zheng, "Investigation of LixV2O5 Cathode Electrodes from Li-Rechargeable Batteries at Different Charge States Using NMR Spectroscopy", J. New Materials for Electrchem. Sys. 7, 270 (2004).
  3. J.P. Zheng, P.L. Moss, R. Fu, Z. Ma, Y. Xin, G. Au and E.J. Plichta, "Capacity Degradation of Lithium Rechargeable Batteries", J. Power Sources, 146, 753 (2005).
  4. P.L. Moss, J.P. Zheng, G. Au, P.J. Cygan, and E.J. Plichta, "Transmission Line Model for Describing Power Performance of Electrochemical Capacitors", J. Electrochem. Soc. 154, A1020 (2007).
  5. P.L. Moss, J.P. Zheng, G. Au, and E.J. Plichta, "An Electrical Circuit Model for Dynamic Performance of Li-ion Polymer Batteries", J. Electrochem. Soc. 155, A986 (2008).
  6. P.L. Moss, G. Au, E.J. Plichta, and J.P. Zheng, "Investigation of solid electrolyte interfacial layer development during continuous cycling using ac impedance spectra and micro-structural analysis", J. Power Sources, 189, 66 (2009).
  7. P.L. Moss, G. Au, E.J. Plichta, and J.P. Zheng "Study of Capacity Fade of Lithium-Ion Polymer Rechargeable Batteries with Continuous Cycling", J. Electrochem. Soc. 157, A1 (2010).

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