A Comparative Study of Tin Anodes in Carbonate and Glyme Electrolytes
Authors: Khirwadkar Ameya , Amai Joseah , Nelson George J. 
Published: December 2024

Sodium-ion batteries (SIBs) are a focus of novel battery research as they present a potentially more sustainable alternative to lithium-ion batteries (LIBs) due to the abundance of sodium as well as other anode and cathode active materials. One key focus of sodium-ion battery research has been cost-effective components which exhibit high energy density and long-term cyclability. These capabilities can enable SIBs as a viable alternative to LIBs. Tin is a promising option for high-capacity anode manufacturing in SIBs because of its ability to be used independently or in other metal alloys in conjunction with suitable additives and binders. However, tin-based anodes still suffer from degradation related to excessive volume change during cycling.

The degradation of tin anodes in SIBs can be mitigated in part through application of appropriate binders and the proper formulation of the electrolyte. The advantage of using styrene butadiene rubber (SBR) in tin anodes as a complement to other binders provides a route for improving the shelf life of anodes and reducing the subsequent degradation from charging-discharging of the battery. The application of glyme-based electrolytes compared to widely used carbonate-based electrolytes can potentially improve cycling life and the overall performance of the battery as well. Copper current collectors are the default when it comes to LIB anodes but with the low reactivity of sodium and good thermal stability aluminum is a cost-effective SIB anode current collector.

Tin-based anodes are casted based on the combination of variables in current collector material, electrolyte, and addition of SBR to the binder. A mixture ratio of 70:20:10 of active material, additive and binder are considered for the slurry preparation. However, a ratio of 70:15:10:5 ratio is considered for the SBR experiments, which is 5% of the total slurry at the expense of the carbon black additive. A solvent of 70:30 mixture of deionized water and ethanol are found to be the best option which dissolved the binder and reduce agglomeration of components and delamination of the anode. An X-Ray diffraction test is run on all samples to ensure the retention of tin structure. Test cells are assembled in a half-cell configuration with a combination of current collectors, SBR and electrolytes and subjected to electrochemical characterization tests (Galvanostatic Cycling with Potential Limitation, Electrochemical Impedance Spectroscopy, and Cyclic Voltammetry) to focus on the tin anode and understand of the performance differences between these variables. The electrochemical tests are conducted on pristine cells and on the lower end of the potential window (0.01V-0.8V) at an initial C-rate of C/10 because of the ability of tin to form alloys with sodium at lower potentials.

For short-term cycling results, the aluminum current collector exhibited better performance in terms of specific capacities (~34% higher) during discharge when compared to copper current collectors in carbonate electrolytes. The lower reactivity of sodium with aluminum is likely to have provided the advantage over copper in specific capacity, which can be further explored with pre-treatment of aluminum oxides, potentially exhibiting better performance. A smaller improvement is observed in the glyme electrolyte for the aluminum current collector. The glyme electrolyte however showed a significant increase (~30%) in discharging specific capacity compared to the carbonate electrolyte. The increase in performance with glyme electrolytes is evident because of the selection of the diglyme and 1M NaClO4 sodium salt formulation, which was found to be the most viable option, and exhibited lower ionic association compared to monoglyme and lower viscosity than tetraglyme that led to higher ionic conductivity. An interchangeability between the formulations of electrolytes leaves the other half of the test matrix to be explored for future work, along with a variation in C-rate capabilities of the battery, which would present a holistic understanding of the proposed materials for this set of experiments.