The morphology of electrochemically deposited lithium (EDLi) plays critical role on the cycling stability and safety performance of Li metal batteries. However, However, formidable challenges and shortcomings of Li metal electrode are currently plaguing its practical application, and the two greatest ones are safety and cycle life. Both of which are associated with the dendritic Li deposition morphology.^1-4 Especially, the key parameters that control the morphologies remain largely obscure. Here we use cryogenic transmission electron microscopy (cryo-TEM) to probe, at atomic level, the features of solid electrolyte interphase (SEI) on Li particle and Li whisker formed in the same coin cell using carbonate electrolyte and ether electrolyte. In the carbonate-based electrolyte, the SEI layer on the Li whisker and Li particle is similarly monolithic amorphous structure, but the composition and spatial distribution of the chemical species within the SEI are distinctively different for Li particle and Li whisker. In the ether-based localized high concentration electrolyte (LHCE), the SEI layer on the Li particle leads to a mosaic structured SEI with few Li₂O nanoparticles embedded, and rich of sulfur (S) in composition, especially at the outer layer SEI (mainly from anion salt decomposition), while the SEI layer of Li whisker displays bilayer structure. The distinctive difference of SEI on Li particle and Li whisker from the same coin cell delineates insight on the direct correlation between features of SEI layer and Li morphology, leading to possible tuning of crucial structural and chemical features of SEI to regulate the morphology of Li deposit.

1      Xu, K., Electrolytes and Interphases in Li-Ion Batteries and Beyond. Chem Rev 2014, 114 (23), 11503-11618.

2      Cheng, X. B.;  Zhang, R.;  Zhao, C. Z.; Zhang, Q., Toward Safe Lithium Metal Anode in Rechargeable Batteries: A Review. Chem Rev 2017, 117 (15), 10403-10473.

3      Lin, D. C.;  Liu, Y. Y.; Cui, Y., Reviving the lithium metal anode for high-energy batteries. Nat Nanotechnol 2017, 12 (3), 194-206.

4      Zou, P.;  Sui, Y.;  Zhan, H.;  Wang, C.;  Xin, H. L.;  Cheng, H. M.;  Kang, F.; Yang, C., Polymorph Evolution Mechanisms and Regulation Strategies of Lithium Metal Anode under Multiphysical Fields. Chem Rev 2021.