Multiphysics Modeling for Energy Storage Materials
Open Access
- Author:
- Chen, Tianwu
- Graduate Program:
- Engineering Science and Mechanics
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- October 02, 2020
- Committee Members:
- Sulin Zhang, Dissertation Advisor/Co-Advisor
Sulin Zhang, Committee Chair/Co-Chair
Charles E Bakis, Committee Member
Francesco Costanzo, Committee Member
Donghai Wang, Outside Member
Judith Todd Copley, Program Head/Chair - Keywords:
- Continuum multi-physical model
Lithium ion batteries
Sodium ion batteries
Thermo-chemo-mechanical couplings - Abstract:
- Enabled by the small and light battery package technologies, the rechargeable or secondary batteries are nowadays worldwide used. Lithium ion batteries (LIBs) dominate the market of secondary battery systems because of their high energy density, high operating voltage, limited self-discharging and lower maintenance requirements. Typically, in a LIB cell, the cathode is a lithium compound and the graphite is the most commonly used anode material, where lithium is incorporated into both the cathode and anode by an intercalation mechanism. The intercalated materials are usually limited by the available sites, leading to relatively low capacity. To meet the rapid growth of the demand for higher energy density, many candidates of electrode materials have been proposed, where lithium reacts with them by the conversion mechanism. Meanwhile, rechargeable batteries with other charge-carriers, like sodium ion batteries (NIBs), were also proposed. However, these large high-capacity materials always have huge volumetric changes during the insertion and extraction of the ions. These volumetric changes during the charging/discharging cycle usually causes large strain mismatch between the lithiated/sodiated part and the unlithiated/unsodiated one, leading to large stress inside electrode, and further result the dislocation accumulation, fatigue, fracture and eventually pulverization of the electrodes. Although various experimental techniques have been developed to study the degradation of the electrode materials at different stage during the charging/discharging cycles, a general model to deal with stress-thermal-chemical coupling for different electrode materials is still limited. In this thesis, a continuum multi-physics model is developed, which is able to present the morphological evolution, stress generation, and mechanical failure for both cathode and anode materials in lithium or sodium ion batteries. The finite deformation kinematics and kinetics are first introduced, where the total deformation is assumed to be decomposed into the elastic, the thermo and chemical induced, and the plastic deformation. The charging/discharging process features strong coupling between the transport kinetics and mechanical stress generation. To examine whether it can capture the diffusive kinetics regulated stress generation in the electrode materials, the developed model was used to analyze the two-fold anisotropy in sodiated black phosphorous for sodium ion batteries. Then, for the stress mediates diffusive kinetics, an electrochemical driven mechanical energy harvester was analyzed by the model. The studies of degradation mechanism in rechargeable batteries have provided novel insights for the strategies to mitigate the degradation of the electrodes. Here, two examples of the applications of the developed model is presented in the structural designs for degradation mitigation for LIBs. The model explained the phenomena inside these structural designs and shed light on the further improvements of the electrode performance. Moreover, the thermo-chemo-mechanical coupling effects is not only found in the charging/discharging cycles of the secondary batteries, but also in other chemical processes. In the end, we use this multi-physical model to explain the mass distribution and shape evolution for certain catalysts during the manufacturing.