| AVS 62nd International Symposium & Exhibition | |
| Energy Frontiers Focus Topic | Tuesday Sessions |
| Session EN+EM+NS+SE+SS+TF-TuA |
| Session: | Batteries and Supercapacitors |
| Presenter: | Manjula Nandasiri, Pacific Northwest National Laboratory |
| Authors: | M.I. Nandasiri, Pacific Northwest National Laboratory P. Bhattacharya, Pacific Northwest National Laboratory A. Schwarz, Pacific Northwest National Laboratory D. Lu, Pacific Northwest National Laboratory D.A. Tomalia, NanoSynthons LLC W.A. Henderson, Pacific Northwest National Laboratory J. Xiao, Pacific Northwest National Laboratory |
| Correspondent: | Click to Email |
Lithium-sulfur (Li-S) batteries are one of the most promising energy storage systems, offering up to five-fold increase in energy density as compared with state-of-the-art lithium-ion batteries to meet the growing demand for environmentally benign energy storage devices with high energy density, low cost, and long life time. For practical applications, high sulfur (active material) loading (> 2 mg/cm2) within the carbon cathode in Li-S batteries is essential. Most reports on engineered cathode materials for Li-S batteries are based upon low sulfur loadings (typically ~1 mg/cm2), which are impractical and often give misleading results. It is unknown how these novel engineered cathodes behave under high sulfur loading conditions. The binder is perhaps the most critical material in achieving a high sulfur loading in carbon cathodes. We have recently used dendrimers with various surface chemistries as functional binders in Li-S cells with SuperP-carbon/S as the cathode material. Even without engineering the cathode, very favorable cycling stability and electrolyte wetting were obtained with these binders. It was attributed to the high density of surface functional groups on the dendrimers, high curvature of the binder and its porosity, and the interactions between the large number of basic nitrogen and oxygen atoms on the dendrimers and lithium polysulfides.
Here, we will discuss the fundamental properties of dendrimers as aqueous binders for Li-S battery cathodes and compare their performance with other aqueous, commonly used linear polymeric binders such as styrene butadiene rubber (SBR) and sodium carboxyl methyl cellulose (CMC). Specifically, generation 4 polyamidoamine (PAMAM) dendrimers with hydroxyl (OH), 3-carbomethoxypyrrolidinone (CMP), and sodium carboxylate (COONa) surface functional groups served as good, electrochemically stable binders at high S loadings (~3-5 mg/cm2) with high initial capacities (> 1000 mAh/g). In comparison to CMC-SBR binder-based electrodes which failed at high C-rates (0.2C) after 40 cycles, dendrimer-based binders showed a capacity retention of >85% for more than 100 cycles. It was also observed that acidic groups and all-NH2 surface groups are poor binders, whereas binders with COO- and neutral surface groups (OH, CH3) show better performance. X-ray photoelectron spectroscopy was used to identify different surface functional groups in these dendrimers and understand their interactions with SuperP-carbon/S cathode. In addition, a detailed physico-chemical characterization using IR spectroscopy and XANES/EXAFS will be presented to substantiate the superior dendrimer-carbon/S interactions.