Origin of fast charging in solid-state batteries revealed by Cryo-transmission X-ray microscopy

The interface issue poses a limitation on the fast charging of solid-state batteries (SSBs), with the high-impedance non-Faraday electric field serving as a pivotal factor. However, the mechanism of fast-charging capability degradation triggered by the dynamic evolution of non-Faraday electric fields remains unclear due to the lack of particle-scale nondestructive detection techniques. Here, we dissect the generation and elimination processes of non-Faradaic electric field in segments using the developed operando cryogenic transmission X-ray microscopy (Cryo-TXM). This method accurately tracks the ion self-balancing pathways in LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) post-fast-charging, elucidating the high polarization during late charging caused by exacerbated irreversible local electric field. By intermittently applying reverse potential during fast charging to alleviate the exacerbation of non-Faradaic electric field at the cathode interface, we achieved a roughly 400% reversible capacity increase of SSBs at 10 C. This insightful dynamic imaging method effectively captures and resolves the transient, opaque signals within SSBs, significantly enhancing their fast-charging performance.