Fig 1

Schematic illustration of a two-stage SEI formation mechanism. SEICu formation proceeds via a two-stage mechanism: direct electron transfer (ET) dominates at high copper potentials (ECu > +1 V vs. Li+/Li), while lithium underpotential deposition (Li UPD) governs additional interphase growth at lower potentials (ECu < +0.5 V). Reproduced with permission from Ref. [5]. Copyright 2025, Springer Nature."

Fig 2

Bridging SEI chemistry, formation, and passivation. The electrochemical decomposition of FSI− initiates SEI formation by continuously generating key inorganic species, including Li2S, LiF, and Li2O. These species undergo a dynamic dissolution–precipitation equilibrium, resulting in their partitioning between the bulk electrolyte (blue) and the compact SEI layer on the copper surface (red). This interfacial distribution is selectively and quantitatively elucidated using non-washing and washing XPS protocols, respectively. Reproduced with permission from Ref. [5]. Copyright 2025, Springer Nature."