Solid state electrolytes could enable significant improvements in energy density, cycle life, and safety of next-generation battery chemistries. The ability to fabricate thin electrolyte films with high ionic conductivity and excellent stability on complex architectures has been a bottleneck to realizing a wide range of 3D structured thin film and bulk batteries. Recent progress in ALD for solid state electrolytes has shown great promise, and enabling even higher conductivities and stability with Li metal anodes could dramatically enhance the energy and power density of ALD-based batteries. In addition, ALD films with high conductivity and good stability could be used for interfacial engineering of bulk-type solid and liquid based batteries to improve stability and safety.

This work demonstrates a novel ALD process for glassy lithium borate-carbonate thin films with ionic conductivities above 10^-6 S/cm at 298K. This represents a 6x improvement over the previous best reported value for an ALD solid electrolyte.¹ The composition, structure, and stability of the films are characterized with X-ray photoelectron spectroscopy and a range of electrochemical measurements. These experiments are compared with those calculated with Density Functional Theory and Molecular Dynamics to elucidate the origins of the high ionic conductivity and excellent stability. The properties are studied as a function of deposition temperature showing tradeoffs between process conditions and performance, and demonstrating the precise control afforded by the ALD process.² The optimized film remains an ionic conductor when in contact with metallic Li, with no measurable changes even over several weeks, and displays stable cycling when paired with a thin-film cathode and Li metal anode.

References

(1) Pearse, A. J.; Schmitt, T. E.; Fuller, E. J.; El-Gabaly, F.; Lin, C. F.; Gerasopoulos, K.; Kozen, A. C.; Talin, A. A.; Rubloff, G.; Gregorczyk, K. E.; Chem. Mater. 2017, 29, 3740–3753.

(2) Kazyak, E.; Chen, K. H.; Davis, A. L.; Yu, S.; Sanchez, A. J.; Lasso, J.; Bielinski, A. R.; Thompson, T.; Sakamoto, J.; Siegel, D. J.; Dasgupta, N. P.; J. Mater. Chem. A 2018, 6, 19425–19437.