Optimization of Silicon-Graphite Anode and Chitosan Binder Material for Lithium-ion Batteries

Summary:

One of the promising approaches towards designing high energy density lithium-ion batteries (LIBs) involves the use of high-capacity anode materials. A blend of silicon (Si), with a high lithiation capacity of 3590 mAh/g (Li3.75Si) at room temperature , and graphite (Gr), endowed with limited volume change during the charge/discharge process and superior electric conductivity, presents the synergistic properties of both anode materials [1]. However, the development requires the optimization of the Si to Gr ratio as well as the polymeric binder(s). In this study, the optimization and investigation of the Si to Gr ratio and the corresponding binders were carried out. For benchmarking, carboxymethyl cellulose (CMC) and lithium poly-acrylic acid (LiPAA) were used as suitable binders for Gr and Si, respectively[2]. Further investigation of the chitosan bio-polymeric binder was carried out. Chitosan is a linear polysaccharide derived from chitin, the second abundant polysaccharide on earth after cellulose. Amino groups of chitosan can form hydrogen bonds with the Si surface hydroxyl groups, leading to solid but reversible adhesions[3], [4].
In this work, chitosan with degrees of acetylation (DA) of 0, 30 and, 50 were investigated as Si-based anode binders. Firstly, slurry preparation and optimization was studied concerning the benchmarked Si/Gr blend electrodes[1]. The electrochemical performance of the anodes was investigated in half- and full-cell configurations. In both cases, anodes with DA50 binder showed higher specific capacity, longer cycle life, and higher capacity recovery after cycling at high C-rates (5C). Therefore, DA50 was chosen as an optimized binder, and further modifications, such as cross-linking of the binder and production of free-standing electrodes were performed on DA50 binder. FTIR measurements indicate that cross-linking with citric acid was successfully completed. Additional TGA/DSC measurements showed that cross-linking improved the thermal behavior of the chitosan binder. In the following steps, the electrodes were deposited on a separator (free-standing electrodes), resulting in eliminating the Cu current collector’s usage, reducing the electrode’s weight, and producing flexible electrodes. The electrochemical performance of these electrodes showed stable behavior. Further optimization of the electrodes coated on the separator and electrochemical performance of electrodes with cross-linked chitosan binder are currently under investigation.

References:
[1] G. G. Eshetu and E. Figgemeier, “Confronting the Challenges of Next‐Generation Silicon Anode ‐Based Lithium‐Ion Batteries: Role of Designer Electrolyte Additives and Polymeric Binders,” ChemSusChem.
[2] N. Hamzelui, G. Gebresilassie, and E. Figgemeier, “Customizing Active Materials and Polymeric Binders : Stern Requirements to Realize Silicon-Graphite Anode Based Lithium-Ion Batteries .,” J. Energy Storage, vol. 35, no. July 2020, p. 102098, 2021.
[3] L. Zhang, L. Chai, Q. Qu, L. Zhang, M. Shen, and H. Zheng, “Chitosan, a new and environmental benign electrode binder for use with graphite anode in lithium-ion batteries,” Electrochim. Acta, vol. 105, pp. 378–383, 2013.
[4] L. Yue, L. Zhang, and H. Zhong, “Carboxymethyl chitosan: A new water soluble binder for Si anode of Li-ion batteries,” J. Power Sources, vol. 247, pp. 327–331, 2014.