The Study of Composite Artificial-SEI for Lithium Metal Anodes
Authors: Menkin Svetlana , Gunnarsdóttir Anna B , Jin Yanting , Grey Clare P. 
Published: February 2020

The strive for higher energy density for rechargeable lithium batteries has created a renaissance of interest in lithium-metal anodes. Yet, lithium metal secondary batteries are disadvantaged by multiple safety issues rendering this class of batteries potentially unsafe and impractical owing to the risk of thermal runaway.

The Solid-Electrolyte-Interphase (SEI) is the key factor which determines the performance and safety of lithium metal battery. The layer, formed instantaneously upon contact of the metal with the electrolyte, consists of reduction products of electrolyte components. It serves as an interphase between the metal and the electrolyte and has the properties of a solid electrolyte. It was found that ionic migration through the SEI is the rate-determining step for many battery systems, including the lithium metal batteries. [1]

It has been widely demonstrated in the literature that non-homogeneous SEI composition and morphology initiate uneven plating and stripping of lithium metal anode, resulting in dendritic short circuits. Moreover, the volume and morphology changes of the metal create stress in the SEI which increases the risk of capacity loss and safety issues due to formation of preferential sites for dendrite formation. The main goal of the formation of an artificial-SEI on the lithium-metal anode, is to overcome these risks.

So far, most of the research on an artificial SEI was focused on preventing of the natural SEI formation and has used either single-component coating or sacrificial SEI-forming additive to the electrolyte. [1,2], Here we present an alternative approach – the formation of pre-designed composite artificial SEI to facilitate improved natural SEI. The increase of the homogeneity of the current distribution on the anode surface is expected to hinder the formation of dendrites.

The study includes the effect of the chemical composition of the artificial SEI on the structure, composition and performance of the natural SEI, morphology of the plated lithium metal, faradaic efficiency, lithium ion conduction mechanisms and the performance of the modified lithium metal anode.

The study is conducted via two major routes: Solid state Nuclear Magnetic Resonance (ssNMR) spectroscopy and electrochemical characterization. A combined investigation of 1H, 7Li, 19F, and 13C ssNMR is used for the study of the composition, formation and lithium conduction mechanisms of the SEI. [3,4] The combination of impedance spectroscopy, cyclic voltammetry, chronopotentiometry and battery cycling techniques facilitates the study of SEI formation, lithium metal cycling and the development artificial SEI for practical lithium metal batteries.

The successful development of an artificial SEI on lithium metal will promote the safe operation of high energy and power lithium-anode batteries and facilitate the use of cleaner energy for transportation, grid leveling and mobile devices.

[1] E. Peled and S. Menkin, SEI- Past, Present and Future, J. Electrochem. Soc. 2017 volume 164, issue 7, A1703-A1719

[2] S.Menkin, D.Golodnitsky, E.Peled, Artificial solid-electrolyte interphase (SEI) for improved cycleability and safety of lithium-ion cells for EV applications, Electrochemistry Communications, 2009 11, 9, 1789-1791

[3] R.Bhattacharyya, B.Key, H.Chen, A.S. Best, A. F. Hollenkamp, and C.P. Grey, In situ NMR Observation of the Formation of Metallic Lithium Microstructures in Lithium Batteries, NATURE MATERIALS VOL 9 JUNE 2010

[4] O.Pecher, J.Carretero-González, K.J. Griffith, and Clare P. Grey, Materials’ Methods: NMR in Battery Research, Chem. Mater. 2017, 29, 213−242