Ab initio molecular dynamics simulations of the initial stages of solid-electrolyte interphase formation on lithium ion battery graphitic anodes (original) (raw)
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The development of reliable computational methods for novel battery materials has become essential due to the recently intensified research efforts on more sustainable energy storage materials. Here, we use a recently developed framework allowing to consistently incorporate quantum-mechanical activation barriers to classical molecular dynamics simulations to study the reductive solvent decomposition and formation of the solid electrolyte interphase for a graphite/carbonate electrolyte interface. We focus on deriving condensed-phase effective rates based on the elementary gas-phase reduction and decomposition energy barriers. After a short initial transient limited by the elementary barriers, we observe that the effective rate shows a transition to a kinetically slow regime influenced by the changing coordination environment and the 1
Journal of Power Sources, 2011
We have studied the formation and growth of solid-electrolyte interphase (SEI) for the case of ethylene carbonate (EC), dimethyl carbonate (DMC) and mixtures of these electrolytes using molecular dynamics simulations. We have considered SEI growth on both Li metal surfaces and using a simulation framework that allows us to vary the Li surface density on the anode surface. Using our simulations we have obtained the detailed structure and distribution of different constituents in the SEI as a function of the distance from the anode surfaces. We find that SEI films formed in the presence of EC are rich in Li 2 CO 3 and Li 2 O, while LiOCH 3 is the primary constituent of DMC films. We find that dilithium ethylene dicarbonate, LiEDC, is formed in the presence of EC at low Li surface densities, but it quickly decomposes to inorganic salts during subsequent growth in Li rich environments. The surface films formed in our simulations have a multilayer structure with regions rich in inorganic and organic salts located near the anode surface and the electrolyte interface, respectively, in agreement with depth profiling experiments. Our computed formation potentials 1.0 V vs. Li/Li + is also in excellent accord with experimental measurements. We have also calculated the elastic stiffness of the SEI films; we find that they are significantly stiffer than Li metal, but are somewhat more compliant compared to the graphite anode.
The formation of passivation films by interfacial reactions, though critical for applications ranging from advanced alloys to electrochemical energy storage, is often poorly understood. In this work, we explore the formation of an exemplar passivation film, the solid electrolyte interphase (SEI), which is responsible for stabilizing lithium-ion batteries. Using stochastic simulations based on quantum chemical calculations and data-driven chemical reaction networks, we directly model competition between SEI products at a mechanistic level for the first time. Our results recover the Peled-like separation of the SEI into inorganic and organic domains resulting from rich reactive competition without fitting parameters to experimental inputs. By conducting accelerated simulations at elevated temperature, we track SEI evolution, confirming the postulated reduction of lithium ethylene monocarbonate to dilithium ethylene monocarbonate and H2. These findings furnish fundamental insights into...
ACS Applied Energy Materials, 2019
One of the major bottlenecks to the development of alternatives to existing Li ion battery technology, such as Li metal or multivalent ion (Mg, Ca, Zn, or Al) batteries, has to do with the layer of inorganic and organic compounds that forms at the interface between the metallic anode and electrolyte via solvent and salt decomposition (the solid− electrolyte interphase or SEI). In Li metal batteries the growth of dendrites causes continual formation of new SEI, while in multivalent ion batteries the SEI does not allow for the diffusion of the ions. Finding appropriate electrolytes for such systems and gaining an understanding of SEI formation is therefore critical to the development of secondary Li metal and multivalent ion cells. In this work, we use ab initio molecular dynamics simulations to investigate the initial stages of decomposition of organic electrolytes based on ethylene carbonate (EC) and formation of the SEI on Li, Ca, and Al metal surfaces. We first find that pure EC only decomposes to CO and C 2 H 4 O 2 2− species on each type of surface. However, when a salt molecule is introduced to form an electrolyte, a second EC decomposition route resulting in the formation of CO 3 2− and C 2 H 4 begins to occur; furthermore, a variety of different inorganic compounds, depending on the chemical composition of the salt, form on the surfaces. Finally, we find that EC breaks down more quickly on Li and Ca surfaces than on Al and show that this is because the rate of charge transfer is much faster owing to their lower electronegativity and ionization energies. The molecular level understanding of decomposition and SEI formation generated by this computational modeling can lead to the design of new electrolytes for beyond-Li ion batteries.
The transition from lithium-based energy storage to post lithium systems plays a crucial part in achieving an environmentally sustainable energy infrastructure. Prime candidates for the replacement of lithium are sodium and potassium batteries. Despite being critical to battery performance, the solid electrolyte interphase (SEI) formation process for Na and K batteries remains insufficiently understood, especially compared to the well-established lithium systems. Using ab initio molecular dynamics (AIMD) simulations based on density functional theory (DFT) calculations, we study the first steps of SEI formation upon the decomposition of typical solvent molecules on lithium, sodium and potassium metal anodes. We find that two dominant products form during the early SEI formation of cyclical carbonates on alkali metal anodes, carbon monoxide and alkali-carbonate. The carbonate-producing reaction is thermodynamically favorable for all tested metals, however, Na and K exhibit a much str...
Intercalation of Lithium into Graphite: Insights from First-Principles Simulations
The Journal of Physical Chemistry C, 2020
Understanding ion intercalation at electrodeelectrolyte interfaces is key to the development of energy storage and water desalination. In this work, we investigate the Li + kinetics at a prototypical interface between graphite anodes and an organic electrolyte, and we elucidate key factors that determine the ion transport, using first-principles methodology coupling ab-initio molecular dynamics simulations with a solvation model. We show that surface chemical composition significantly influences the kinetics of ion intercalation from the liquid into the graphite. We find that this is partly related to the ion desolvation process, which varies notably for different graphite surface chemical terminations. In addition, interfacial polarization is found to play an important role in determining energy barriers for ion transfer. We also discuss the impact of electrode potentials, which is often neglected in conventional first-principles calculations despite being a key factor in device configurations. Our study provides insights into the coupling of electronic and ionic effects of interfacial chemistry on ion transport at complex electrode-electrolyte interfaces.
The Journal of Physical Chemistry C, 2016
A detailed understanding of the mechanism of the formation of the solid electrolyte interphase (SEI) is crucial for designing high-capacity and longer-lifecycle lithium-ion batteries. The anode-side SEI primarily consists of the reductive dissociation products of the electrolyte molecules. Any accurate computational method for studying the reductive decomposition mechanism of electrolyte molecules is required to include an explicit electronic degree of freedom. In this study, we employed our newly developed eReaxFF method to investigate the major reduction reaction pathways of SEI formation with ethylene carbonate (EC) based electrolytes. In the eReaxFF method, electrons are treated explicitly in a pseudoclassical manner. The method has the ability to simulate explicit electrons in a complex reactive environment. Our eReaxFF-predicted results for the EC decomposition reactions are in good agreement with the quantum chemistry data available in the literature. Our molecular dynamics (MD) simulations capture the mechanism of the reduction of the EC molecule due to electron transfer from lithium, ring opening of EC to generate EC − /Li + radicals, and subsequent radical termination reactions. Our results indicate that the eReaxFF method is a useful tool for large-scale simulations to describe redox reactions occurring at electrode−electrolyte interfaces where quantum-chemistry-based methods are not viable because of their high computational requirements.
Batteries & Supercaps
The solid electrolyte interphase (SEI) on graphite anodes is a key enabler for rechargeable lithium-ion batteries (LIBs). It ensures that only Li + ions and no damaging electrolyte components enter the anode and hinders electrolyte decomposition. Its growth should be confined to the initial SEI formation process and stop once the battery is in operation to avoid capacity/ power loss. In technical LIB cells, the SEI is formed at constant current, with the potential of the graphite anode slowly drifting from higher to lower voltages. SEI formation rate, composition, and structure depend on the potential and on the chemical properties of the anode surface. Here, we characterize SEIs formed at constant potentials on the chemically inactive basal plane of highly oriented pyrolytic graphite (HOPG). X-ray photoemission spectroscopy (XPS) detects carbonate species only at lower formation potentials. Cyclic voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS) with Fc/Fc + as an electrochemical probe demonstrate how the formation potential influences ion transport and electrochemical kinetics to and at the anode surface, respectively. Breaking the EIS data down to a Distribution of Relaxation Times (DRT) reveals distinct kinetics and transport related peaks with varying Arrhenius-type temperature dependencies. We discuss our findings in the context of previous electrochemical studies and existing SEI models and of SEI formation protocols suitable for industry. [a] B.
Journal of the American Chemical Society, 2001
Reductive decomposition mechanisms for ethylene carbonate (EC) molecule in electrolyte solutions for lithium-ion batteries are comprehensively investigated using density functional theory. In gas phase the reduction of EC is thermodynamically forbidden, whereas in bulk solvent it is likely to undergo one-as well as two-electron reduction processes. The presence of Li cation considerably stabilizes the EC reduction intermediates. The adiabatic electron affinities of the supermolecule Li + (EC) n (n ) 1-4) successively decrease with the number of EC molecules, independently of EC or Li + being reduced. Regarding the reductive decomposition mechanism, Li + (EC) n is initially reduced to an ion-pair intermediate that will undergo homolytic C-O bond cleavage via an approximately 11.0 kcal/mol barrier, bringing up a radical anion coordinated with Li + . Among the possible termination pathways of the radical anion, thermodynamically the most favorable is the formation of lithium butylene dicarbonate, (CH 2 CH 2 OCO 2 Li) 2 , followed by the formation of one O-Li bond compound containing an ester group, LiO(CH 2 ) 2 CO 2 (CH 2 ) 2 OCO 2 Li, then two very competitive reactions of the further reduction of the radical anion and the formation of lithium ethylene dicarbonate, (CH 2 OCO 2 -Li) 2 , and the least favorable is the formation of a C-Li bond compound (Li carbides), Li(CH 2 ) 2 OCO 2 Li. The products show a weak EC concentration dependence as has also been revealed for the reactions of LiCO 3with Li + (EC) n ; that is, the formation of Li 2 CO 3 is slightly more favorable at low EC concentrations, whereas (CH 2 OCO 2 Li) 2 is favored at high EC concentrations. On the basis of the results presented here, in line with some experimental findings, we find that a two-electron reduction process indeed takes place by a stepwise path. Regarding the composition of the surface films resulting from solvent reduction, for which experiments usually indicate that (CH 2 OCO 2 Li) 2 is a dominant component, we conclude that they comprise two leading lithium alkyl bicarbonates,
Journal of Electrochemical Energy Conversion and Storage, 2016
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 ...