Poly(carbazole) Coated Selenium@Conical Carbon Nanofibers Hybrid for Lithium-Selenium Batteries with Enhanced Lifespan

Mukkabla, Radha and Kuldeep, Kuldeep and M, Deepa (2018) Poly(carbazole) Coated Selenium@Conical Carbon Nanofibers Hybrid for Lithium-Selenium Batteries with Enhanced Lifespan. ACS Applied Energy Materials. ISSN 2574-0962

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Abstract

A scalable protocol enabling Selenium (Se) cathodes in Lithium (Li)-Se batteries to retain a high reversible capacity with repeated cycling is demonstrated. A hybrid of Se powder with conical carbon nanofibers (CCNFs) labeled as Se@CCNFs-20, is prepared in a non-inert atmosphere at room temperature and is used as cathode in a Li-Se cell. Reversible capacity of ~990 mAh gSe-1 is achieved at 0.1 current (C)-rate for the Li-Se@CCNFs-20 cell, which reduces to ~531 mAh gSe-1 after 100 cycles. CCNFs are composed of elongated fibers with a graphitic crystalline structure; they maximize Se uptake by the virtue of their effective surface area, promote electron conduction between the Se particles by serving as conductive interconnects and accommodate the volume expansion of Se during discharge, thus manifesting in the above described performance. This performance is bettered by coating the Se@CCNFs-20 hybrid cathode with a conducting polymer (poly(carbazole) or PCZ) layer. The PCZ coating acts a barrier that not only restricts the dissolution and cross-over of polyselenides thus improving the capacity retention of the cell, but it also amplifies the rate performance by providing interfacial properties conducive for fast Li-ion reaction with the active Se content at the cathode. This results in a significant enhancement in the electrochemical charge storage properties of the Li-Se@CCNFs-20-PCZ cell compared to the Se@CCNFs-20 based cell. The PCZ coating minimizes the capacity fade, for the cell experiences a very slow capacity decay rate of 0.0051% per cycle from 10th cycle, finally preserving a reversible capacity of ~640 mAh gSe-1 at the end of 100 cycles at 0.1 C-rate, which is the highest reversible capacity ever reported for a Li-Se cell cycled under the said conditions. High Se utilization, low polarization, and durability with an ultra-high Se loading are imparted to the Se cathode by the PCZ overlayer, thus opening up the possibilities for scale-up for practical applications.

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