Anja Henss

Thiophosphate‐based solid‐state batteries (SSBs) with high‐nickel ternary cathode materials such as LiNi 0.83 Co 0.11 Mn 0.06 O 2 (NCM) represent a promising next‐generation energy storage technology due to their expected high specific discharge capacity and improved safety. However, rapid capacity fading caused by contact loss through interphase and crack formation during cell cycling is a significant problem hindering stable SSB cycling and high‐energy‐density applications. In this work, a uniform coating of poly((4‐vinyl benzyl)trimethylammonium bis(trifluoromethanesulfonylimide)) (PVBTA‐TFSI) on NCM is obtained via a spray‐drying process. This exceptionally thin cationic polymer coating of only 2–4 nm thickness on NCM helps stabilize the interface between NCM and the Li 6 PS 5 Cl solid electrolyte (SE). Electrochemical tests confirm a significant improvement in long‐term cycling performance and active mass utilization compared to uncoated NCM. In addition, the polymer coating effectively suppresses the degradation of the NCM/SE interface, particularly the formation of oxygenated species, and reduces the extent of particle cracking. Overall, these results highlight a new approach to mitigate SSB degradation using a thin cationic polymer coating on NCM for SSBs.

Solid‐state batteries (SSBs) with high‐voltage cathode active materials (CAMs) such as LiNi 1− x − y Co x Mn y O 2 (NCM) and poly(ethylene oxide) (PEO) suffer from “noisy voltage” related cell failure. Moreover, reports on their long‐term cycling performance with high‐voltage CAMs are not consistent. In this work, we verified that the penetration of lithium dendrites through the solid polymer electrolyte (SPE) indeed causes such “noisy voltage cell failure”. This problem can be overcome by a simple modification of the SPE using higher molecular weight PEO, resulting in an improved cycling stability compared to lower molecular weight PEO. Furthermore, X‐ray photoelectron spectroscopy analysis confirms the formation of oxidative degradation products after cycling with NCM, for what Fourier transform infrared spectroscopy is not suitable as an analytical technique due to its limited surface sensitivity. Overall, our results help to critically evaluate and improve the stability of PEO‐based SSBs.