Influence of negative electrode coatings in all-solid-state lithium metal batteries on the electrochemical performance

The use of solid-state electrolytes offers a transformative solution to the limitations of conventional lithium ion batteries, promising higher energy density, improved safety, and longer cycle life. All-solid-state batteries are considered the leading technology of the future, as their mechanical stability enables using lithium metal electrodes, characterized by a low standard potential (0 V vs Li/Li+) and high specific capacity (3860 mAh g-1).
The thiophosphate single-ion conducting electrolyte material Li6PS5Cl is known for its high ionic conductivity, competing with state-of-the-art liquid electrolytes. However, due to a small chemical stability window, it is easily reduced in contact with lithium metal. This research investigates the potential of inorganic coatings to meet this challenge and further enhance the performance of solid-state lithium-metal batteries by improving interfacial compatibility.
To reduce electrolyte decomposition at the negative electrode surface, recent studies use Li-In alloy instead of lithium metal, hence trading in both the remarkable standard potential and the specific capacity. The introduction of thin coating layers on top of the lithium metal electrode combines the better surface conditions of the former, while keeping the high specific capacity advantages of the latter. Thus, coating layers can contribute to the application of high-performance solid-state lithium metal batteries.
The cycling behavior of solid-state lithium metal batteries is a critical factor for their widespread adoption, mainly ruled by the lithium ion diffusion on the negative electrode side. Enhanced critical current density is an important step towards high power applications, ensuring the battery can deliver high current without compromising safety and life time. The present study investigates the dependency of the critical current density for multiple coating materials and thicknesses. Electrochemical impedance spectroscopy further reveals the effect of the coating on the interfacial resistances.
Overall, this work demonstrates that the integration of thin coating layers represents a significant step toward achieving high performance solid-state lithium metal batteries.

[1] J. Janek and W. G. Zeier, Nat Energy, 2016, 1 (9), 1167.

[2] J. Kang et al., Energy Storage Materials, 2022, 52, 130–160.

[3] Y. Wang etal., ACS Appl. Mat. Int., 2020, 12 (31), 34771–34776.