Small Functional Molecules As Slurry Additives for Si-Alloy Coatings with CMC/SBR Binder

Abstract

Si-alloy based anodes are attractive for use in Li-ion batteries because of their high volumetric capacity. Polyacrylic acid (PAA) [1] binder is often used in such anodes, which contains carboxyl groups that bind to alloy surfaces, maintaining electrode integrity and forming an artificial SEI layer [2]. Aromatic binders like PI can decompose during lithiation, forming a conductive carbon network [3]. However, these binders have disadvantageous for their practical use, including superhydrophilicity, in the case of PAA; and high irreversible capacity and the cost and use of NMP solvent, in the case of PI. Sodium carboxymethyl cellulose/styrene-butadiene rubber (CMC/SBR) is currently the binder system of choice for Li-ion cell makers. Enabling the use of CMC/SBR binders with alloys could enable wider implementation of alloy electrodes. In this work, several small molecule compounds containing carboxyl groups were evaluated as slurry additives. It was found that some slurry additives could significantly improve alloy cycle life in CMC/SBR coatings. Figure 1 shows the capacity retention versus cycle number for each slurry additive. Tremendous variations in capacity retention are observed for different additives. In particular, the addition of 5% sodium mellitate and sodium citrate resulted in a large increase in cycling performance of the CMC/SBR coating beyond even that of a coating with PAA binder. This work shows that the cycle life of alloy coatings using CMC/SBR binder can be improved by the use of small molecule slurry additives. This could help enable the use of alloy based electrodes in Li-ion batteries using practical binder systems. Reference s : [1] Magasinski, Alexandre, et al. "Toward efficient binders for Li-ion battery Si-based anodes: polyacrylic acid." ACS applied materials & interfaces 2.11 (2010): 3004-3010. [2] Chen, Hao, et al. "Exploring chemical, mechanical, and electrical functionalities of binders for advanced energy-storage devices." Chemical reviews 118.18 (2018): 8936-8982. [3] Wilkes, B. N., et al. "The electrochemical behavior of polyimide binders in Li and Na cells." Journal of The Electrochemical Society 163.3 (2016): A364-A372. Figure 1