A method for altering the mechanical properties and transport properties of conductive polymers

Conductive polymers, synthetic materials with large molecules that can conduct electricity, could have a wide range of valuable applications. For example, they were used to create sensors, photodiodes, photocells and many other devices.

In recent years, these conductive materials proved particularly promising for the creation of energy conversion and storage devices, including batteries. However, methods for adding these functions are not always reliable, which greatly limits the widespread implementation of batteries based on these materials.

Researchers at Lawrence Berkeley National Laboratory and the University of California, Berkeley recently presented a strategy that could reliably aid the development of hierarchically ordered structures (HOS) with well-defined shapes in conductive polymers. This strategy was presented in a research paper published in nature energycould open up new possibilities for creating high-performance battery technologies, in particular Lithium-ion batteries.

“In the traditional design of conductive polymers, organic functionalities are introduced via bottom-up synthetic approaches to enhance specific properties by modifying individual polymers,” Tianyu Zhu and colleagues write in their paper. “Unfortunately, the addition of functional groups leads to conflicting effects, limiting its expanded synthesis and broad applications. We show a conductive polymer with simple elementary building blocks that can be heat treated to develop hierarchically ordered structures (HOS) with well-defined nanocrystalline shapes.”

Rather than altering the initial structures of conductive polymers, as has been done in previous work, Zhu and colleagues explored the possibility of forming well-ordered 3D structures on the materials. These structures can enable desired functionalities without the need to increase the initial structural complexity of the polymer.

The approach proposed by the researchers to form these structures relies on a controlled thermal process. As part of their study, they used it specifically to improve the mechanical and transport properties of a conductive polymer called poly(9,9-dioctylfluorene-co-fluorenoneco-methylbenzoic ester), or PFM.

“Our approach to constructing permanent HOS in conductive polymers leads to significant enhancement of charge transfer properties and mechanical toughness, which are critical for practical lithium-ion batteries,” Zhou and colleagues explain in their paper. “Finally, we show that conductive polymers with HOS enable exceptional whole-cell spin performance with micron-sized highly loaded SiO._xAnodes with an areal capacity of more than 3.0 mA cm^-2 More than 300 cycles and average coulomb efficiency >99.95%. ”

Initial evaluations by this team of researchers yielded very promising results, highlighting the promise of their approach to enhancing the functionality of conductive polymers. Zhou and colleagues then showed that these reinforcing polymers enable the creation of high-performance lithium-ion batteries.

While researchers have so far applied their method primarily to polymer PFM, can be used to alter the transport properties of a wide range of others conductive polymers. This means that it could help develop many technologies and devices, including biological sensors, monitors and photovoltaics, for example helping to increase their stability, transmission efficiency and robustness.

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