Poor Man’s Atomic Layer Deposition of LiF for Additive-Free Growth of Lithium Columns

Abstract

Lithium metal is an ideal material for high-energy, cost-effective rechargeable energy storage systems. The thermodynamically unfavorable solid−liquid interface between the lithium metal and organic electrolyte necessitates the formation of an interlayer (SEI) which is known to have significant impact on lithium morphologies. Less well understood is the impact of the current collector substrate on the morphology of electrodeposited lithium. Here we report on the morphology of electrodeposited lithium as a function of the chemical pretreatments of the working electrode. We find that a copper substrate pretreatment with acidic solutions (sulfuric, oxalic, or acetic acid) results in the deposition of close-packed lithium columns with a uniform diameter. A controlled study of the pre-electrodeposited copper surface indicates that the formation of a 5−8 nm thick LiF protective layer on copper substrate from a chemical reaction between adsorbed surface water layer in acidic solutions and LiPF 6 electrolyte is the key process in the electrochemical growth of lithium columns. We anticipate that this simple chemical approach can be generalized as a scalable, low-cost, additive-free substrate treatment method for depositing a LiF protective layer, broadly applicable in the development of uniform lithium films.

Enabling “lithium-free” manufacturing of pure lithium metal solid-state batteries through in situ plating

“…The Limetal anode is then formed electrochemically on the first charge cycle by electroplating Li contained within the cathode. In liquidbased batteries, this concept has been demonstrated, but it's feasibility is limited by the high reactivity of Li with traditional liquid electrolytes, leading to low cycling efficiency 9,10,[12][13][14] .…”

A Growing Appreciation for the Role of LiF in the Solid Electrolyte Interphase

“…The results demonstrated that the electrochemical performance of batteries with ex situ fabrication of LiF SEI on the anode is better than that of without an LiF layer. These ex situ fabrication approaches include atomic layer deposition (ALD), [ 112 ] the reaction of Li metal with fluorinated precursors, [ 113 ] decomposing LiPF 6 on copper substrate, [ 114 ] and physical vapor deposition (PVD). [ 115 ]…”

“…Reproduced with permission. [ 114b ] Copyright 2017, Wiley‐VCH. e) One‐pot solution coating of LiF layer on the Li metal anode.…”

Effects of Film Formation on the Electrodeposition of Lithium

“…LiF-rich surface films have been artificially fabricated via pretreatment of the electrode, including hydrolysis of LiPF 6 and atomic layer deposition. [18][19][20] Further, a film was formed via electrodeposition using an electrolyte containing an additive, such as HF aqueous solution, [14] CsPF 6 , [15] LiAsF 6 , [21] and a trace amount of water. [22,23] However, the role and effective amount of LiF in the film must be further investigated to improve lithium metal anodes.…”

“…These properties have led to previous investigations regarding the role of LiF with other inorganic and organic components. LiF‐rich surface films have been artificially fabricated via pretreatment of the electrode, including hydrolysis of LiPF 6 and atomic layer deposition [18–20] . Further, a film was formed via electrodeposition using an electrolyte containing an additive, such as HF aqueous solution, [14] CsPF 6 , [15] LiAsF 6 , [21] and a trace amount of water [22,23] .…”