Interfacial Study on Solid Electrolyte Interphase at Li Metal Anode: Implication for Li Dendrite Growth

Abstract

The Solid electrolyte interphase (SEI), either naturally formed or artificially designed, plays a critical role in the stability and durability of Li-ion batteries (LIBs). It is even more important for high energy density electrodes such as Li metal anodes, which is subjected to large volumetric and interfacial variations due to Li deposition/stripping cycles during operation. Currently, there is a lack of understanding of the role of SEI/Li interfaces and their mechanical and electrochemical properties. In this paper, we present an interfacial study to evaluate the two major SEI components, LiF and Li 2 CO 3 , based on density functional theory (DFT) calculations. The calculated interfacial energy results show that the Li 2 CO 3 /Li interface has higher interfacial mechanical strength. To achieve the practical application of reversible high energy density Li metal electrode (3860 mAh g −1 ) for future "beyond Li-ion batteries", 1-3 one of the most significant challenges is to mitigate irreversible Li-dendrite formation.4-10 Dendrite formation is also often a concern for fast charging and low temperature operation in current Li-ion battery technology. Li dendrite formation and growth can be controlled by many factors. Intrinsically, dendrite morphology is determined by material properties, such as surface energy and growth anisotropy. However, it may also be influenced by other factors such as local current distribution 11,12 (due to electrode surface roughness and compositional inhomogeneity, etc.), operation voltage and charging rate, 13,14 as well as electrolyte composition. 7,15The dendrite growth process can also be strongly affected by the properties of solid electrolyte interphase (SEI), the passivation thin layer between electrolyte and electrode. Electrolyte solvents, such as ethylene carbonate (EC) and dimethyl carbonate (DMC) will naturally reduce and decompose at the low potential Li metal surface and spontaneously form an SEI layer. 16 First proposed by Peled in 1970s, 17 SEI remains "the most important but least understood" 18,19 in rechargeable LIBs due to its complicated content that is highly dependent on numerous factors such as electrolytes and additives, 20 electrode surface 21,22 and operating conditions. 23 Many recent efforts have been focused on using different electrolytes to alter the property of SEI or developing artificial coatings on the Li surface to mitigate dendrite growth. Therefore, it is important to understand how the SEI and coating properties may impact Li dendrite formation.After decades of debates, 4,17,24,25 there are some general agreements on the role of SEI in Li dendrites formation mechanisms ( Figure 1). Since Li metal oxidizes instantly when in contact with electrolyte, the only two probable Li plating sites are inside SEI and at Li anode surface, which is further determined by two processes: electron tunneling from anode to SEI and Li ion diffusion from electrolyte to anode. In most LIBs, where the well formed SEI is insulating enough to block electron tunneling f...

Chemomechanical modeling of lithiation-induced failure in high-volume-change electrode materials for lithium ion batteries

“…For examples, SEI formation and dendrite growth of Li are regulated by the electrode-electrolyte interface; [134][135][136] stress generation and failure of the electrode materials depends on the motion and morphology of the reaction front. The correlation of the interlayer process and the degradation has motivated fundamental understanding of the interfacial processes on the one hand, and tailoring and modifying the interfaces as ways to mitigate degradation on the other.…”

Review on modeling of the anode solid electrolyte interphase (SEI) for lithium-ion batteries

“…The observation that LiF has better electron insulating property than Li 2 CO 3 is consistent with another interface model evaluating the electron potential drop at LiF/Li and Li 2 CO 3 /Li interfaces. 159 Leung and Jungjohann 160 also reported that LiF with more negative electron affinity is more effective for electron blocking than Li 2 O on Li electrode surface. Through a novel DFT/ Green's function method, Benitez et al 162,162 computed the electron transfer resistance (dV/dI) in a nano-device model consisting of an electrode and a molecule representing SEI components, such as Li 2 CO 3 , LiF, Li 2 O, or lithiated SiO 2.…”

“…189 DFT calculations showed that the Li 2 CO 3 /Li interface bears higher interfacial mechanical stability than LiF/Li interface. 159 However, even the maximum work of adhesion at the Li (001)/Li 2 CO 3 (001) interface is only 0.17 J m −2 , which is relatively low for typical metal/ceramics interfaces. With classical Monte Carlo (MC) and DFT-based methods, Soto and Balbuena 190 found that the oligomers attach/adhere firmly to the Li 13 Si 4 (010) surface with calculated adsorption energies in a range of 3-4 eV and if the coverage oligomer on the surface reaches approximately 1 oligomer per nm 2 , the surface-oligomer interaction will dominate the stabilization of the interface system.…”

A Flexible Electron-blocking Interfacial Shield for Dendrite-free Solid Lithium Metal Batteries

“…The Li 2 CO 3 (001)/Li(001) and LLZO(110)/Li(001) models were built following Ref. [56][57][58] . For structural relaxation and energy/density of states calculations, an energy cutoff of 520 eV and a 1´1´1 K-point Monkhorst-Pack grid were used.…”