Understanding Electrode Microstructural Influence on Lithium-Sulfur Battery
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The lithium ion battery is the center of attention for many electronic devices. However, its energy and power still cannot fully satisfy demand for transport vehicles and grid storage applications as its theoretical limit approaches. Additionally, its cathode materials can be costly and heavy. In response to this problem, lithium sulfur chemistry has arisen as a promising solution with its significantly higher capacity and energy density. Theoretically, a sulfur molecule S8 accepts 16 electrons and reduces to S^2- ions, leading to a theoretical capacity of 1675.12 mAh/g of sulfur. Although the Li-S cell exhibits a good theoretical capacity, the experimental performance of Li-S cells is quite poor compared to this thermodynamic limit. The Li-S cells are assembled with solid sulfur impregnated in a background carbon matrix. This sulfur dissolves during discharge and converts to insoluble lithium sulfide (Li2S). During typical charging, the opposite process takes place, i.e., Li2S dissolves and eventually forms solid sulfur. This in turn gives rise to electrode structure being evolved in time, thus leading to transport limitations and corresponding loss of performance. A mathematical model is developed to simulate the electrochemical operation of Li-S cell. The cathode microstructure evolution is accounted for from microstructural characterizations using pore scale simulations. Different initial microstructural configurations are assigned based on different mean pore size and porosity. For a given number of solid products, the time evolution is a strong function of this initial configuration. The performance simulations explore the effects of different sulfur loading, charge-discharge rates and electrochemical operation windows for different cathode architectures. The results reveal the bottlenecks stemming out of pore blockage due to uneven precipitation. They further highlight the relative importance of electrochemical reaction rates and precipitation-dissolution kinetics.
Law, Darren (2017). Understanding Electrode Microstructural Influence on Lithium-Sulfur Battery. Master's thesis, Texas A & M University. Available electronically from