2020 journal article

Dislocation based stresses during electrochemical cycling and phase transformation in lithium-ion batteries

COMPUTATIONAL MATERIALS SCIENCE, 171.

By: P. Dhiman n & H. Huang n

co-author countries: United States of America 🇺🇸
author keywords: Lithium-ion battery; Dislocations; Stresses; Cyclic voltammatery
Source: Web Of Science
Added: November 11, 2019

Lithium iron phosphate (LiFePO4) contains defects that play an important role in structural degradation of batteries. Linear defects called dislocations are introduced inside the lithium ion battery material during fabrication process accompanied by distortion produced stress fields around them. The present study deals with these mechanical stresses around dislocations in lithium iron phosphate and the change in stress field during phase transformation of lithium iron phosphate electrode material. A model consisting of multiple dislocations inside a lithium iron phosphate material incorporating anisotropic material properties is used to calculate stress fields using linear elastic theory and the superposition method. The stress fields around dislocations during phase transformation of lithium-iron phosphate are numerically calculated by incorporating the anisotropic properties of the material. The change in electrochemical behaviour of material due to change in stress field during phase transformation is also studied, where a modified electrochemical kinetics equation (i.e., Butler Volmer equation) is derived and used to account for dislocation induced stresses during the reversible cyclic voltammatery of the lithium iron phosphate. The results shows the stress inside material does not remain constant during phase transformation and its variations are dislocation orientation dependent. In addition, the result shows that the presence of stress fields around dislocations changes the electrochemical behaviour of the material as suggested by the shift in the cyclic voltammograms. The effect of increasing scan rate on cyclic voltammogram is also studied for lithium iron phosphate. The results show that the increase in current at peaks is independent of the orientation of dislocations studied. Moreover, the decrease in current corresponding to a particular overvoltage value before anodic peak and increase in current after the anodic peak is found to be somehow proportional to the scan rate. Increased scan rates show increased deviation of current from a cyclic voltammogram for material in which there is no phase transformation. The results provide an insight into how presence of defects and phase transformation changes the electrochemical behaviour of the material. It is concluded that the combined effect of the stresses induced around dislocations during phase transformation and high scan rate can be used for modifying battery materials for various applications by changing electrochemistry of electrodes. The present study incorporates electrochemistry, defects and phase transformation into one battery chemistry and thus is important in our understanding of the Li-ion batteries.