Lithium-metal batteries are receiving great attention in recent years as an anode material. It has a higher theoretical specific capacity (3860 mAh∙g^-1) compared to the graphite (372 mAh∙g^-1) used in conventional Lithium-ion batteries.¹ However, the capacity fade resulted from unexpected dead lithium, and dendrite growth is a major issue that causes shorter cycle life and possible internal short circuits during operation.

The purpose of this study is to develop a continuum model that captures the dynamics of lithium metal deposition and stripping during repeated cycling of a lithium-metal cell. The repeated deposition and stripping of Lithium accounts for the presence of a heterogeneous growth of Lithium foil (anode) in a battery electrode. One can take advantage of the simplicity of symmetric cells to understand electrodes and electrolyte in a controlled applied potential.² The symmetric cell consists of the same materials on both electrodes, so the average potential of the system is zero. This study will compare the continuum model with experimental data for a Li/Li symmetric cell.

The mathematical model used in this study is based on the concentrated solution theory models developed by Newman and coworkers.^3-5 The mass transport of the Li-ion in the electrolyte, neglecting migration, is governed by Fick’s law. A modified Ohm’s law for the liquid electrolyte phase is considered and the Butler-Volmer equation is accounted for lithium metal deposition and stripping at the electrode.

The system will be studied with one-dimensional modeling coupled with a moving boundary representation of lithium stripping and plating.⁶ Some experimental variations such as high current density cases will also be considered. The one-dimensional model will then be extended to two-dimensional modeling to understand the trend of heterogeneous plating/growth of Lithium metal.

Acknowledgements

The authors would like to thank for the financial support of this work by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies of the DOE through the Advanced Battery Material Research (BMR) Program (Battery500 consortium) and the Clean Energy Institute (CEI) at the University of Washington and the Washington Research Foundation (WRF) for their partial monetary support during this work.

References

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