Conversion of lignin into dielectric materials for renewable energy storage

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Human civilization, with its heavy reliance on fossil fuels over the past century, has increased the concentration of atmospheric CO2 up about 40%. High atmospheric CO2 concentration tends to trap increased amount of infrared radiation (i.e., greenhouse effect) resulting in global warming. This in turn leads to a cascade of many meteorological disasters. Therefore, over the past few decades, researchers have been actively searching for alternative energy sources, among which solar and wind energy is gaining increasing popularity. However, owing the intermittent nature of solar and wind energy generation, it is also vitally important to develop the corresponding energy storage technologies in time. ******There are two types of energy storage devices capacitors and batteries. In general, capacitors exhibit high power density but low energy density while batteries have the opposite properties. Here, power density signifies how fast a storage device can deliver energy while energy density the amount of energy stored per unit volume of the device. That is why capacitors tend to be used for short-term while batteries for long-term storages. Commercial capacitors normally use dielectric materials, such as ceramics, to increase their storage capacity. Recently, polymer-based dielectrics are gaining more attention, as they are lightweight, flexible and easy to fabricate. In addition, polymer dielectrics are also known to possess high breakdown strength, which is vital for ideal capacitor performance (i.e., the ability to maintain dielectric properties even under high electric field (voltage)). However, the drawback of polymer-based dielectrics is their low energy density.******To increase the energy density of polymer dielectrics, one needs to increase their relative permittivity (i.e., permittivity of the polymer relative to that of vacuum), also known as dielectric constant. In general, polymers containing functional groups that are easier to be polarized exhibit higher relative permittivity. Generated as a byproduct in the pulp and paper industry, lignin, the second most abundant biomass, contains the structural attributes (a rich presence of phenyl, phenol and hydroxyl groups) that are ideal to be transformed into dielectric materials. With the development of modern synthetic chemistry, more powerful tools have become available to convert lignin into cross-linked polymeric materials with specifically tuned dielectric properties. Since lignin is an industrial waste, the successful conversion of lignin to the proposed value-added materials not only benefits the environment (use of a renewable material to store renewable energy) but also offers economic incentives. The primary goal for this project is to use lignin as a precursor to prepare inexpensive, ecofriendly materials with the desired dielectric properties that can be used in high power density and high energy density capacitors.