[Final Blog #1] Solid-State Battery Research Abstract

Solid-state batteries are a newly emerging interest in battery research for their improvement of conventional lithium-ion batteries with liquid electrolyte. They promise a replacement of volatile and flammable liquid electrolyte as well as greater energy storage due to the removal of a separator. Multiple aspects about solid-state batteries must still be tackled: low ion conductivity of the electrolyte, low mechanical strength, and most importantly, the issue of forming a stable electrode-electrolyte interface. Unlike liquid electrolytes, SSB’s solid electrolyte is more brittle and may not form a good interface with the electrode, which would make it harder for ion conduction. In order to address these issues, I explored composite solid electrolyte – varying polymer addition methods, polymer compositions, and battery test parameters. It was important to find a balance of mechanical strength and conductivity.  

The choice of solid electrolyte was a composite solid electrolyte, by adding polymer to argyrodite (LPSCl). Various methods of creating solid electrolyte were explored and to compare, the conductivity and mechanical strength were measured. Two major observations were made or confirmed through this part. First of all, thermal annealing generally improves conductivity. Comparing among all the tested methods, an overall increase in conductivity along with an increase in temperature was repeatedly noticed. This signals that given a polymer with thermal stability (no degradation at high temperature), the composite can be annealed. Secondly, uniform addition of polymer to LPSCl is crucial in determining the optimal method for solid electrolyte. Additionally, low, medium, and high weight percent composition polymers were examined. Since larger composition of polymer would mean better mechanical strength, solution processing method was the safest method. This was confirmed by XRD and was most likely due to its ability to uniformly disperse the polymer throughout the solid electrolyte.

After the choice of composite processing method, I went on with making a full coin cell with the selected solid electrolyte to mimic the real application of the solid state batteries. Some key aspects from changing around the parameters are that increasing the pressure on the cell (by increasing the number of spacers in the coin cell) would improve the electrode-electrolyte interface and conduct better. The use of coin cells for testing allowed more tests to be conducted in a more effective manner. 

There are still some lingering questions of reproducibility, temperature dependence, and choice of polymers. Improvements on these aspects are to be tackled in the future experiments. 

 

(There are some omitted details due to the issue of confidentiality).