Selenium Nanowire Cathodes Coated with Conductive Polymers for Fast Electron Transfer and Suppression of Shuttle Effect of Conversion Cathodes

For a few decades, rechargeable batteries have been widely applied in a wide range of applications, from portable electronics to electric vehicles(EVs), and the energy market in developing and continues to grow. Especially, EVs are increasingly in demand, require higher energy density than conventional lithium-ion batteries. This generation of LIBs is limited to a specific energy of around 225 Wh kg–1. To expand the use of LIBs into heavy equipment and heavy vehicle and other long-range automotive applications, there is a strong motivation to develop batteries with energies over 400 Wh kg–1. For this demand, many researchers are looking for cathode electrode with improved electrochemical properties to satisfies the requirements of high-energy lithium-ion batteries (LIBs).Therefore, it is urgently needed to pursue other new battery systems with high energy density. Of the explored candidates, conversion cathode, respresentative, Lithium-sulfur (Li-S) batteries have been widely studied as one of the most promising next-generation energy storage systems due to their high theoretical capacity (1675 mAh g-1) and fairly good energy density (2600 Wh kg-1). Furthermore, abundant reserves in nature, Nickel and Cobalt free, which are unstable in supply and demand, and low cost are the competitive advantages of Li-S battery.<br/>Selenium is an element in group 16 of the periodic table like sulfur, and the Li-Se battery also exhibits a redox mechanism similar to Li-S battery. Li-Se batteries have a lower specific capacity than Li-S batteries, but the volumetric energy density is not significantly different from that of Li-S batteries. On the other hand, the conductivity, which is an important property of the cathode material, is Se , which is much higher than that of S .<br/>Based on these advantages, Li-Se batteries have been researched a lot to improve their performance. Especially, carbon base materials such as CMK-3 and activated carbon are widely used for selenium anodes. Its wide porosity makes it suitable for stored large amounts of selenium, and its high conductivity can improve the poor conductivity of selenium. Additionally, many studies have been conducted to suppress the shuttle effect through surface treatment by adding functional groups to carbon. However, many processes using carbon have the disadvantage of having to manufacture the electrode through high temperature & high pressure at the high melting temperature of selenium.<br/>To clarify these issues, We synthesized selenium nanowire through selenium dioxide(SeO2) rather than melting process to compensate for these shortcomings, to facilitate electrode manufacturing. Selenium nanowire with 1d structure has superior conductivity compared to conventional selenium, and by compounding with carbon nanotube, which was the same 1d material, selenium-carbon electrode can be manufactured without melting process. Moreover, we processd of synthesizing selenium nanowire, PEDOT:PSS coating improved the conductivity of selenium nanowire and wettability with SWCNT.<br/>Our research team increased wettability with SWCNT through PEDOT:PSS coating on self-developed 1d wire Selenium nanowire, which is proved by numerous electrochemical data. After 100 cycles, the PEDOT:PSS coated SeNW capacity was down to under 20% to 410 mAhg-1, while the Pristine SeNW cathode was 162 mAhg-1, under half. Moreover, it appeared to have higher capacity at higher rates as well. This improved electrochemical stability is because the PEDOT:PSS coating layer not only plays an excellent electron transfer role to SeNW, but also improves the binding energy with lithium polyselenide, causing a faster conversion reaction.In order to further prove this phenomenon, DFT was applied to the VASP simulation to calculate the binding energy of the electrode surface and polyselenide according to the presence or absence of the PEDOT:PSS coating layer.