UBC Theses and Dissertations
Development of a conductive lignin-based current collector for wearable batteries Eghtesad, Mahdieh
The continuing demand for wearable electronics requires the development of lightweight and low-volume energy storage systems as the source of power. We consider the integration of a solar cell and a battery as a continuous power source for wearables. This thesis focuses only on the battery. The current collector of batteries currently used in wearables are heavy and bulky; thus, a metalized nanofibrous network is proposed to retain functionality (high electrical conductivity and support) of the current collector, while possessing lower weight and volume. Furthermore, compared to state-of-the-art lithium-ion batteries, zinc – manganese dioxide (Zn-MnO₂) batteries are of interest due to their lower cost, environmentally-friendliness, and abundance of materials. To fabricate the metalized nanofibrous network, lignin, a natural polymer, is used as the precursor for electrospinning. The produced fibers are thermally stabilized and electroless plated with copper to meet the conductivity requirements. Finally, a layer of MnO₂ paste is brush-coated on the copper plated fibers and the electrochemical performance of the assembled Zn-MnO₂ battery is analyzed. This work harnesses the optimization of the electrospinning solution, thermal stabilization, and electroless copper plating solution. The electrospinning solution is optimized by varying its viscosity. In general, higher viscosity results in larger diameters and fewer beads. Thermal stabilization optimization involves changing the final temperature of the process. Higher final temperature allows for more cross-linking and cleavage of bonds; however, above thermal degradation, fiber fusion is observed. These two optimizations allow for achievement of smallest fiber diameter for lightweight and low-volume applications. The plating solution is optimized for attainment of highest conductivity, by adjusting the reducing agent amount, sonication time, and plating time. Generally, conductivity increases by increasing these parameters. However, above a certain threshold, higher formaldehyde amount reduces the reaction rate and longer sonication can break down the sample. This lignin current collector is assessed with respect to the currently used carbon paper current collector. It is evident that lignin current collector has a higher conductivity and longer cycle life, while possessing smaller initial capacity. For wearable batteries, lifespan (cycle life) is a significant factor. Hence, the lignin current collector shows promise for wearable batteries.
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