Modeling Battery Performance Due to Intercalation Driven Volume Change in Porous Electrodes

Abstract

Simulations are presented that result from incorporating dimensional and porosity changes in porous electrodes caused by volume changes in the active material during intercalation into a detailed lithium-ion battery model. Porosity and dimensional changes in an electrode can significantly affect the resistance of the battery during cycling, which in turn alters the reaction distributions in the porous electrodes. In addition, volume changes generate stresses in the electrode which can lead to premature failure of the battery. Here, material conservation equations are coupled with the mechanical properties of porous electrodes to link dimensional and porosity changes to stresses and the resulting resistances that occur during the intercalation processes. Through the use of porous rock mechanics, porosity and strain gradients can be predicted based on state of discharge and discharge rate. Several different battery casings and discharge rates are examined and operating curves are predicted.

Accounting for Non-Ideal, Lithiation-Based Active Material Volume Change in Mechano-Electrochemical Pouch Cell Simulation

“…The fundamental governing equations and construction of the coupled mechano-electrochemical model used in this study has been described in previous work. [20][21][22][23] During charging and discharging, Li + ions move from the cathode to the anode and from the anode to the cathode, respectively. The lithiation and de-lithiation of the anode and cathode lead to active material volume change.…”

“…), the mechanical behavior of each individual cell component must be incorporated. Previously, the porous electrodes were assumed to follow porous rock mechanics; [20][21][22] however, a recent study measured the practical stress/strain response of an electrode saturated with incompressible electrolyte. 14 The porous components in the cell will have a unique stress/strain relationship due to the decreasing porosity (increasing mechanical contact) as well as flow of electrolyte upon compression.…”

“…19 Previously, our group developed a model which predicts the split between electrode porosity and electrode dimensional changes upon active material particle lithiation. [20][21][22] This volume change model was used to show the theoretical effect of a cell casing's compressibility on porosity as well as the formation of non-uniform reaction distributions at high C-rates. Recently, our group incorporated measured mechanical behavior for the individual cell components and cell packing to simulate realistic electrode-scale and cell-scale mechanical responses.…”

Two-Dimensional Materials to Address the Lithium Battery Challenges

“…The pulverization of electrode materials due to volume expansion and stress accumulation during cycling is a major challenge for high-capacity electrodes, especially anode materials, and limits the cycle life and performance of LIBs . Although the intercalation electrodes such as graphite and lithium-titanate spinel (LTO) introduce very stable electrochemical properties with very low-volume expansion upon de/lithiation (<7%), they have far lower theoretical capacity compared with other alloying or conversion-type active materials. , The high-specific-capacity group IV elements such as Si-, Ge-, and Sn-based electrodes are among the alloying-type anodes that have led to significant attention for their application in LIBs. , Si, Ge, and Sn can accommodate more than four Li + ions in their structure and have a theoretical capacity of 4200, 1625, and 994 mA h/g respectively . However, these anode materials usually suffer from large volumetric variations (>300%) upon de/lithiation which leads to electrode pulverization, short cycle life, and considerably low capacity retention …”

“…232 Although the intercalation electrodes such as graphite and lithium-titanate spinel (LTO) introduce very stable electrochemical properties with very low-volume expansion upon de/lithiation (<7%), they have far lower theoretical capacity compared with other alloying or conversion-type active materials. 233,234 The high-specific-capacity group IV elements such as Si-, Ge-, and Sn-based electrodes are among the alloying-type anodes that have led to significant attention for their application in LIBs. 235,236 Si, Ge, and Sn can accommodate more than four Li + ions in their structure and have a theoretical capacity of 4200, 1625, and 994 mA h/g respectively.…”