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Research Papers

# Computational Studies of Interfacial Reactions at Anode Materials: Initial Stages of the Solid-Electrolyte-Interphase Layer Formation

[+] Author and Article Information
G. Ramos-Sanchez

Departamento de Quimica,
Iztapalapa 09340, CDMX, Mexico

F. A. Soto, J. M. Seminario

Department of Chemical Engineering,
Texas A&M University,
College Station, TX 77843

J. M. Martinez de la Hoz

The Dow Chemical Company,
2301 N. Brazosport Boulevard,
Freeport, TX 77541

Z. Liu, P. P. Mukherjee

Department of Mechanical Engineering,
Texas A&M University,
College Station, TX 77843

F. El-Mellouhi

Qatar Environment and Energy Research Institute,
Doha, Qatar

P. B. Balbuena

Department of Chemical Engineering,
Texas A&M University,
College Station, TX 77843
e-mail: balbuena@tamu.edu

1Corresponding author.

Manuscript received April 14, 2016; final manuscript received July 13, 2016; published online October 20, 2016. Assoc. Editor: George Nelson.

J. Electrochem. En. Conv. Stor. 13(3), 031002 (Oct 20, 2016) (10 pages) Paper No: JEECS-16-1049; doi: 10.1115/1.4034412 History: Received April 14, 2016; Revised July 13, 2016

## Abstract

Understanding interfacial phenomena such as ion and electron transport at dynamic interfaces is crucial for revolutionizing the development of materials and devices for energy-related applications. Moreover, advances in this field would enhance the progress of related electrochemical interfacial problems in biology, medicine, electronics, and photonics, among others. Although significant progress is taking place through in situ experimentation, modeling has emerged as the ideal complement to investigate details at the electronic and atomistic levels, which are more difficult or impossible to be captured with current experimental techniques. Among the most important interfacial phenomena, side reactions occurring at the surface of the negative electrodes of Li-ion batteries, due to the electrochemical instability of the electrolyte, result in the formation of a solid-electrolyte interphase layer (SEI). In this work, we briefly review the main mechanisms associated with SEI reduction reactions of aprotic organic solvents studied by quantum mechanical methods. We then report the results of a Kinetic Monte Carlo method to understand the initial stages of SEI growth.

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## Figures

Fig. 1

Schematic figure of an electrochemical cell illustrating the chemical potentials at the anode (μa) and cathode (μc), the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO), and associated energy gap (Eg). The condition for electrochemical stability of the electrolyte is that Eg > eVoc, where eVoc is the energy associated with the open circuit voltage (Voc) and e is the electron charge.

Fig. 2

Schematic mosaic picture of the SEI layer as proposed by earlier work [1517]

Fig. 3

Schematic representation of solvent reduction proposed mechanisms during first stages of SEI formation. EC molecule is used as an example; any other cyclic carbonate molecule could follow the same mechanism. Red, gray, white and purple spheres represent oxygen, carbon, hydrogen, and lithium respectively. (See on line article for full color representation.)

Fig. 4

Schematic representation of the processes described in the KMC simulations by Methekar and co-workers (Adapted from Ref. [45])

Fig. 5

(a) Effect of the electrochemical reduction rate k2 and the EDC formation rate k4 on the growth rate of the EDC film. Both k2 and k4 vary from 10−8 site−1 s−1 to 108 site−1 s−1 and (b) SEI growth rate versus SEI formation rate k4 with different electrochemical reduction rates. The units of the growth rate (d δ /dt) are Å s−1.

Fig. 6

(a) SEI thickness variation versus time with different thickness-dependent reduction rate and (b) species fraction at the SEI/electrolyte interface with α=107. Here the reduction rate at clean anode surface is set to k2(0) = 108 site−1 s−1. Snapshots demonstrate the top view of SEI film in the coarse-grained model with α=107 and various thicknesses. Black: EC*, red: c-EC, blue: o-EC site, cyan: Li2EDC. (See on line article for full color representation.)

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