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Analysis of Ratcheting in Elastic-plastic Behavior of Li-ion Battery Electrodes

Hashemi, Mohammad Ali | 2020

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 52980 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Naghdabadi, Reza
  7. Abstract:
  8. Among the various materials, silicon anodes have the highest lithium absorption in lithium-ion batteries. But this high lithium absorption capacity can cause 300 percent volume expansion and large stresses. Experimental observations show that charge and discharge cycles may cause plastic deformation in some parts of the electrode particle. On the other hand, there is a possibility of a ratcheting phenomenon due to changing in elastic properties of the electrode material during the charging and discharging processes. However, this phenomenon has not been reported for silicon spherical electrode particles yet.This study aims to model the elastic-plastic behavior of silicon spherical electrode particles in the charge and discharge cycles and to investigate the amount of ratcheting developed in these cycles. In this model, elastic properties variations of the material by changing the concentration of lithium in the electrode are considered. The equations resulting from the electrode behavior modeling were solved by the finite difference method in the Matlab software. Numerical results indicate the existence of a ratcheting in cycles of charge and discharge. Amount of ratcheting developed in the initial cycles is large, and gradually after 14 cycles, a constant value of per cycle is reached for the element adjacent to the surface. Also, the amount of ratcheting was investigated in different parts of the electrode particle and at different charging times. As the charging time increases, the plastic deformation of each cycle decreases, but the amount of ratcheting does not change much. Also, the ratcheting developed in the stress-strain diagram is such that the amount of plastic deformation in each cycle is greater than in the previous cycle. Increasing the plastic deformation in each cycle causes the elements of the host particles more volume changing from charge to discharge. As this volume change for the adjacent element to the surface of the particle, for the fourteenth cycle (after reaching the steady-state) is equal to 1.27, but for the cycle number 800, the value of 1.85 is predicted. This volume change can cause the SEI layer to crack and reduce battery capacity
  9. Keywords:
  10. Lithium Ion Batteries ; Large Elastic-Plastic Deformations ; Diffusion Induced Deformation ; Silicon Anodes Cyclic Behavior ; Ratcheting Phenomenon

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