The intrinsic behavior of lithium fluoride in solid electrolyte interphases on lithium

Abstract

Lithium is the most attractive anode material for high-energy density rechargeable batteries, but its cycling is plagued by morphological irreversibility and dendrite growth that arise in part from its heterogeneous “native” solid electrolyte interphase (SEI). Enriching the SEI with lithium fluoride (LiF) has recently gained popularity to improve Li cyclability. However, the intrinsic function of LiF—whether chemical, mechanical, or kinetic in nature—remains unknown. Herein, we investigated the stability of LiF in model LiF-enriched SEIs that are either artificially preformed or derived from fluorinated electrolytes, and thus, the effect of the LiF source on Li electrode behavior. We discovered that the mechanical integrity of LiF is easily compromised during plating, making it intrinsically unable to protect Li. The ensuing in situ repair of the interface by electrolyte, either regenerating LiF or forming an extra elastomeric “outer layer,” is identified as the more critical determinant of Li electrode performance. Our findings present an updated and dynamic picture of the LiF-enriched SEI and demonstrate the need to carefully consider the combined role of ionic and electrolyte-derived layers in future design strategies.

Effects of Film Formation on the Electrodeposition of Lithium

“…The film repair process is kinetically faster in a fluorinated electrolyte than in an unfluorinated electrolyte. [45] HF and fluorophosphoric acid were formed in the electrolyte with 100 ppm of water, [26] thus the rapid formation of the surface film containing these compounds likely enabled the deposition of columnar metallic lithium. The morphology of the deposited lithium was heavily dependent on the type of electrolyte, the concentration of electrolyte salt, and the substrate.…”

Fluorinated Aromatic Diluent for High‐Performance Lithium Metal Batteries

“…[5b, 9] In addition, He et al discovered that LiF surrounded by an organic outer layer, which is formed as ar esult of the electrochemical decomposition of the electrolyte,isable to more effectively suppress dendritic growth than ac hemically formed LiF-containing surface layer, which easily ruptures during the growth of dendrites. [10] It was also reported that the spatial distributions of LiF and lithium oxide (Li 2 O) in the SEI layer play acrucial role for Li dendrite suppression. [11] Conventional carbonate-based electrolytes tend to generate af ragile mosaic SEI layer rich in Li 2 Oa nd lithium carbonate (Li 2 CO 3 ), which are distributed in an amorphous organic polymer matrix.…”

Wetting Phenomena and their Effect on the Electrochemical Performance of Surface‐Tailored Lithium Metal Electrodes in Contact with Cross‐linked Polymeric Electrolytes

“…In spite of that, Li metal electrodes have a high chemical reactivity which leads to (spontaneous) formation of surface layers and nontrivial interphases . During electrodeposition/electrodissolution, such interphases and surface topographies are further altered and partially rebuilt, resulting in complex and dynamic surface conditions . Li electrodeposition is also accompanied by the formation of so‐called high‐surface‐area Li (HSAL) which in turn is being formed as a result of uncontrolled accumulation of Li deposits .…”