Phenomenologically modeling the formation and evolution of the solid electrolyte interface on the graphite electrode for lithium-ion batteries

160

118

In this study, a phase-field model is developed to simulate the microstructure morphology evolution that occurs during solid electrolyte interphase (SEI) growth. Compared with other simulation methodologies, the phase-field method has been widely applied in the solidification modeling that has great relevance to SEI formation. The developed model can simulate SEI structure and morphology evolution, and can predict SEI thickness growth rate. X-ray photoelectron spectroscopy (XPS) experiments are performed to confirm the major SEI species as LiF, Li 2 O, ROLi, and ROCO 2 Li. Transmission electron microscopy (TEM) experiment is performed to present the SEI layer structures. The experiments reduce the complexity of the model development and provide validation to some extent. Fick's law and mass balance are applied to investigate lithium-ion concentration distributions and diffusion coefficients in different types of SEI layers predicted by the phase-field simulations. Simulation results show that lithium-ion diffusion coefficients between 298 K and 318 K are 1. 340-7.328 Lithium-ion batteries (LIBs) are widely used in many applications, such as cell phones, electric vehicles (EVs), and other energy storage modules. However, LIBs suffer from severe performance degradation due to undesired chemical reactions, 1 ageing, 2,3 corrosion, 4-6 compromised structural integrity, 7,8 and thermal runaway. 9-11 The degradation occurs during both calendar and cycling lifespans, and reduces the longevity of LIBs. Recently, much attention has been focused on LIB material decomposition, 12 e.g., the formation and growth of new components [13][14][15][16][17][18][19] due to undesired side reactions. 1,20 The main degradation mechanisms in LIBs vary with different active materials, 2 however, it is well known that a carbonaceous lithium-intercalation electrode in contact with electrolyte solution becomes covered by a passivation layer called a solid electrolyte interphase (SEI). While SEI can prevent the exfoliation of graphite materials and inhibit further electrolyte decomposition.21 SEI layer growth can also cause battery capacity fade and increase cell internal resistance. 17,[22][23][24][25][26] Therefore, the study of SEI plays a key role in battery degradation and other related performance improvement research. Many studies have been published in SEI computational and experimental studies, including but not limited to. [27][28][29][30] Many researchers have investigated SEI in LIBs in terms of structure, 7,8,29,31-33 formation and composition, 20,22,27 and thickness growth prediction and measurement. 15,16,34,35 SEI is believed to have a multilayered structure: a compact layer of inorganic components (e.g., LiF, Li 2 O) close to graphite electrode followed by a porous organic layer (e.g., ROLi, ROCO 2 Li) close to the electrolyte solution phase. 22,29,[31][32][33] The composition of SEI depends on the electrode materials and electrolyte composition.27 Broussely et al. investigated the mechanism of lithium loss in LIBs during ...

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confidence: 59%

Simulation and Experiment on Solid Electrolyte Interphase (SEI) Morphology Evolution and Lithium-Ion Diffusion

Guan

Liu

Lin

2015

160

118

“…This is in accordance with the assumption that the SEI possesses two ideal properties -a maximum conductivity for lithium-ions and an insulating conductivity for electrons. 13,52 We are aware that literature [53][54][55] still debates whether new SEI is formed at the SEI/electrolyte or the graphite/SEI interface. With our approach, we assume that new SEI is formed at the SEI/electrolyte interface.…”

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confidence: 99%

A SEI Modeling Approach Distinguishing between Capacity and Power Fade

Kindermann

Keil

Frank

et al. 2017

In this paper we introduce a pseudo two-dimensional (P2D) model for a common lithium-nickel-cobalt-manganese-oxide versus graphite (NCM/graphite) cell with solid electrolyte interphase (SEI) growth as the dominating capacity fade mechanism on the anode and active material dissolution as the main aging mechanism on the cathode. The SEI implementation considers a growth due to non-ideal insulation properties during calendar as well as cyclic aging and a re-formation after cyclic cracking of the layer during graphite expansion. Additionally, our approach distinguishes between an electronic (σ SEI ) and an ionic (κ SEI ) conductivity of the SEI. This approach introduces the possibility to adapt the model to capacity as well as power fade. Simulation data show good agreement with an experimental aging study for NCM/graphite cells at different temperatures introduced in literature. © The Author Lithium-ion batteries are one of the most promising candidates for energy storage in future stationary storage systems and electric vehicles.1-3 Enormous research efforts have been conducted to get a thorough understanding of the system "lithium-ion cell" and to further develop it for higher energy and power density, higher safety standards as well as longer cycle life. 4 The aging behavior of lithium-ion batteries has been a focus issue of battery research since the introduction of lithium-ion cells by Sony in 1991. 5 Reviews by Agubra et al., 6,7 Arora et al., 8 Aurbach et al., 9,10 Birkl et al., 11 Broussely et al., 12 Verma et al. 13 and Vetter et al. 14 are just a few examples of the extensive literature regarding aging behavior. Commonly accepted and experimentally verified aging phenomena as mentioned in the previously cited literature are electrolyte decomposition leading to solid electrolyte interphase (SEI) and cathode electrolyte interphase (CEI) growth, solvent co-intercalation, gas evolution with subsequent cracking of particles, a decrease of accessible surface area and porosity due to SEI growth, contact loss of active material particles due to volume changes during cycling, binder decomposition, current collector corrosion, metallic lithium plating and transition-metal dissolution from the cathode. The listed aging mechanisms can be assigned to three different categories that are a loss of lithium-ions (LLI), an impedance increase and a loss of active material (LAM). 12,[15][16][17][18] The LLI is synonymous to a decrease in the amount of cyclable lithium-ions as they are trapped in a passivating film on either of the electrodes or in plated metallic lithium. Due to the growth of the passivating layers and/or the formation of rock-salt in the cathode (residue of the cathode active material after transition-metal dissolution), kinetic transport of lithium-ions through those inactive areas is limited and results in an impedance rise. An LAM can be caused by the dissolution of transition-metal-ions from the cathode bulk material, changes in the electrode composition and/or changes in crystal structure of the a...

“…Cell performance degradation due to side reactions is termed as chemical degradation, which is known to be the main cause of lithium loss in well-made LIBs. 5,6,[8][9][10] These side reactions lead to marching of the charge and discharge endpoints.11,12 Such side reactions and their effects on the cell life are relatively less explored.The solid state diffusion of lithium atoms in and out of host electrode particles results in diffusion induced stresses (DISs) and volume changes in electrode particles during charge and discharge. Depending upon the operating conditions these stresses may have various effects on the electrodes such as mechanical fatigue and fracture of the electrode particles, electrode particle isolation from the composite matrix, or SEI fracture, to name a few.…”

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confidence: 99%

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confidence: 99%

Electrode Side Reactions, Capacity Loss and Mechanical Degradation in Lithium-Ion Batteries

Deshpande

Pan

et al. 2015

188

127

For advancing lithium-ion battery (LIB) technologies, a detailed understanding of battery degradation mechanisms is important. In this article, experimental observations are provided to elucidate the relation between side reactions, mechanical degradation, and capacity loss in LIBs. Graphite/Li(Ni 1/3 Mn 1/3 Co 1/3 )O 2 cells of two very different initial anode/cathode capacity ratios (R, both R > 1) are assembled to investigate the electrochemical behavior. The initial charge capacity of the cathode is observed to be affected by the anode loading, indicating that the electrolyte reactions on the anode affect the electrolyte reactions on the cathode. Additionally, the rate of "marching" of the cathode is found to be affected by the anode loading. These findings attest to the "cross-talk" between the two electrodes. During cycling, the cell with the higher R value display a lower columbic efficiency, yet a lower capacity fade rate as compared to the cell with the smaller R. This supports the notion that columbic efficiency is not a perfect predictor of capacity fade. Capacity loss is attributed to the irreversible production of new solid electrolyte interphase (SEI) facilitated by the mechanical degradation of the SEI. The higher capacity fade in the cell with the lower R is explained with the theory of diffusion-induced stresses (DISs). Lithium-ion batteries (LIBs) are widely used in small, portable, electronic devices due to their high energy density, high voltage, low self-discharge rate, and good cycle performance.1,2 Yet, for automotive propulsion applications, LIBs need improvement in volumetric and gravimetric energy density and with performance over the life of the vehicle. This is one of the major motivations of researchers worldwide focusing on developing cheaper and more durable LIBs for applications such as hybrid vehicles, electric vehicles, and other large-scale energy storage systems. 3Capacity decay during storage and charge-discharge cycling is one of the major challenges that limit the life of LIBs. Instability of the electrolyte at the operating potentials results in side reactions on the electrode surfaces, part of which lead to the formation of solid electrolyte interphases (SEIs). [4][5][6][7] Side reactions may result in lower coulombic efficiency, loss of usable capacity of the cell, and increase of cell impedance. Cell performance degradation due to side reactions is termed as chemical degradation, which is known to be the main cause of lithium loss in well-made LIBs. 5,6,[8][9][10] These side reactions lead to marching of the charge and discharge endpoints.11,12 Such side reactions and their effects on the cell life are relatively less explored.The solid state diffusion of lithium atoms in and out of host electrode particles results in diffusion induced stresses (DISs) and volume changes in electrode particles during charge and discharge. Depending upon the operating conditions these stresses may have various effects on the electrodes such as mechanical fatigue and fracture of the electr...