review on modeling of the anode solid electrolyte interphase (sei) for lithium-ion batteries - li ion battery cell

An interface layer called solid electrolyte (SEI)
It is formed on the surface of the electrode by the decomposition product of the electrolyte.
In order to prevent further electrolyte decomposition and ensure a continuous electro-chemical reaction, xi allows Li to transmit and block electrons.
Due to the complexity of the nano-thick SEI membrane structure and the lack of reliable in-situ experimental techniques, its formation and growth mechanism have not yet been fully understood.
Significant advances in computational methods make it predictable to simulate the basic principles of SEI.
This review is intended to outline the country-of-the-
Progress in artistic modeling of SEI film studies on anode, from electronic structure calculation to mid-scale modeling, covering thermodynamics and dynamics of electrolyte reduction reactions, formation of SEI, modification through electrolyte design, the correlation between battery performance and battery performance, as well as the design of artificial batteries. Multi-
The scale simulation has been summarized and compared with the experiment.
Computational details of the basic properties, such as electronic tunnels, Li-
Ion transport, chemical/mechanical stability of bulk ei and electrodes /(SEI/)
The electrolyte interface is discussed.
This review demonstrates the potential of computational methods in terms of de-convolution ei properties and artificial ei design.
We believe that computational modeling can be combined with experiments to complement each other in order to better understand the complex SEI in order to develop efficient batteries in the future.
Rechargeable lithium
Battery-based batteries have achieved a revolution from small electronics to aerospace, gradually replacing alkaline, Ni-Cd, and lead-
Acid battery due to its higher energy density.
This is the first one in more than 20 years-ion battery (LIB)
It was commercialized by Sony in 1991.
In the past few decades, the energy density has gradually increased by about 5 watts per kilogram per year, and now it is about a watt per kilogram.
However, the current energy density still cannot meet the needs of vehicle electrified (500–700u2009Whu2009kg).
One of the main obstacles to limiting lithium improvement --
The electrode/electrolyte interface based on the performance of the battery is the key to understanding the electrochemistry of the battery, as it is electronic and Li-
Ion bonding is then stored in the electrode by inserting, alloy, or simply as a Li metal.
This interface is often complicated by a layer of passive layer on the electrode.
Starting from observing the lithium metal immersed on a non-lithium metal, the understanding of this passive layer on the negative electrode
Water electrolyte of Dey.
Peled introduced the concept of solid electrolyte interface in 1979 as an electronic insulation and ion conductive passivation layer formed between the electrode and electrolyte as a solid electrolyte;
So it was named SEI.
Peled et al. summarized the component information observed over the past 20 years, further enriching this model.
1997 and Aubach and others. in 1999.
On the one hand, dense and complete ei can limit the electron tunnel, thus prohibiting the further reduction of electrolyte, which is crucial for the chemical and electro-chemical stability of the battery.
On the other hand, the formation and growth consume active lithium and electrolyte materials, resulting in capacity attenuation, increased battery resistance, and poor power density.
Until today, it is still considered "the most important but least understood "(component)
In charge Li-
Ion Batteries ", which can be attributed to the complexity of the chemical and chemical reactions that form it, and the lack of direct measurement of its physical properties.
When the redox potential of the electrode used in the battery is located outside the electrolytic window of the electrolyte, an SEI layer is formed, which is shown by Goodenough and Kim exemplary (Fig. ).
When the lowest molecular orbital is not occupied (LUMO)
The Fermi energy of the electrolyte in the battery is higher than that of the anode, and the electrolyte in the battery is stable;
Otherwise, the electrolyte can be reduced.
Similarly, if the highest molecular orbital is occupied (HOMO)
Electrolyte lower than the cathode fermilion level.
Density functional theory (DFT)
In the past, the computational electrolysis window of common electrolyte components has been summarized. However, Fig.
For an electrolyte that usually contains salt dissolved in a solvent and mixed with various additives, it is too simplified.
As shown in the figure, these details can significantly change the reduction potential.
Specifically,
Transfer reactions in the process of reduction reactions occur at potential, and LUMO calculations show that they should be stable for many anion. Similarly, H-
The transfer reaction is often coupled with electrolyte oxidation, so the oxidation potential is lower than the calculated HOMO.
Nevertheless, the LUMO of most electrolyte components is higher than that of lithium graphite (~0. 1u2009eV)
Lithium metal (0u2009eV)
Voltage, so the electrolyte on the anode is reduced.
Compared with the ei on the cathode, The ei on the anode is less stable due to the obvious reduction reaction and the larger volume expansion of the anode material.
Due to its importance to battery performance and durability, extensive research has been carried out on the anode SEI film.
Due to the unique lithium/lithium removal properties, the failure mechanism of SEI on different anode varies greatly.
Therefore, this review will focus on SEI formed on anode materials.
While there are many review articles in the literature, this article will focus on computational studies related to SEI formation, growth, properties, functions, and electrolyte and artificial SEI Design.
Anode ei is usually composed of the reduction products of the electrolyte, which are formed by the reaction between the electrode and the electrolyte due to the electronic leakage of the anode.
Research over the past 40 years has helped to gain a broad understanding of the formation and composition of SEI, an understanding that has been summarized in other reviews.
To put it simply, SEI is a submembrane with complex and heterogeneousstructure.
A movie can be seen as more than one
Layered structure-
Inorganic inner layer near the electrode/SEI interface (
Rick, leukemia and LiO)
Let Li transport;
Organic (
Diethylene glycol dilithium (LiEDC)
And ROLi, where R depends on the solvent)
The outer layer, near the SEI/electrolyte interface, is heterogeneous, porous and permeable to Li and electrolyte solvent molecules. The in-
Recently, the plane structure and component heterogeneity of SEI were solved.
The formation of SEI structure was observed by in situ electrolytic atomic force microscope (AFM)
On the graphite electrodeThe three-
Multi-dimensional
The layer SEI structure and its mechanical properties were measured by scanning force spectrum of Si electrode.
From a more comprehensive perspective, SEI is more than one
Multi-layer film, each of which has a mosaic structure whose composition, structure and performance change over time.
Different components, and their nature, influence their performance in a coordinated and complex manner.
Over the past 50 years, a gradual understanding of safety and the environment has been summarized in the picture. .
Two major unknowns have been holding back the current lithium-based battery.
First, the electrolyte reduction reaction that causes this complex structure near the surface of the electrode is not clear.
Secondly, for such a complex structure, the relationship between structure and nature is largely unknown.
Because there are these two unknowns, it has always been an attempt in design --and-error process.
Due to the importance of ei, the battery field has been constantly looking for new ways to modify Li-
Ion batteries during circulation (
Called "in vivo" design, analogy with living cells)
Or by depositing an artificial SEI coating on the electrode in front of the batteryassembly (
Called "in vitro" design).
The ultimate goal is to reduce irreversible loss of capacity and reduce interface resistance to improve battery performance.
Ei is usually obtained in vivo through different additives.
In contrast, due to complex parasitic reactions at the anode/electrolyte interface, in vitro SEI design is expected to be more controllable than in vivo modification.
Although SEI was first observed on a non-lithium electrode
Water electrolyte, metal lithium anode is replaced by graphite anode due to safety reasons.
Achieve high energy density in LIBs, high
Capacity electrodes such as Si, Sn, Sb and their alloys are introduced, and lithium metals have gained new interest due to their high specific capacity, low density and lowest oxidation-reduction potential.
Ei on graphite can provide acceptable life in commercial Li
Ion batteries, despite a loss of more than 50% capacity in a well
The LIB of the design can be attributed to the growth of SEI.
In contrast, the development of high-tech also faces more challenges.
Capacity anode material.
For example, for anode materials like Si, the SEI is unstable after repeated cycles due to its large capacity accompanied by a large volume change.
Large volume changes can cause ei damage, resulting in low Cullen efficiency (As shown in the figure. ). Nano-
Structural Si can avoid Si fracture, but it must be optimized with chemical and mechanical stable ei due to high surface area to avoid ei mechanical-electro-chemical degradation and achieve high Cullen efficiency.
As far as the lithium metal anode is concerned, it is still an outstanding issue that may cause short circuit and electronic disconnection of lithium.
The origin of this problem is the very active surface of the Li metal, because xi must be formed on the surface of the Li.
As the surface of the Li metal becomes rough, Moss and branch-like, continuous parasitic ei growth occurs, resulting in low Cullen efficiency.
Therefore, the ideal SEI film should inhibit the growth of shoot crystals, roughness of the surface, and reduce the accidental side reaction that occurs at the SEI/electrolyte interface.
These new design challenges require coupling and system design methods.
The current experimental methods are still difficult to characterize SEI properties (
Other than chemical composition)
In particular, the properties of thermodynamics and dynamics.
Fortunately, predictive modeling can make up for the limitations of experimental research and play an important role in understanding battery science at length scales from electronics to complete battery systems.
This review will focus on the modeling work of SEI film on the anode.
Not only do we comment on the existing statusof-the-
At the same time, art research is also devoted to revealing the future research needs of this topic.
We will first discuss the modeling of SEI formation in the "Modeling of electrolyte reduction mechanism" section, especially the initial reduction mechanism of electrolyte.
How these insights lead to the computational design of electrolyte additives will be discussed in the section "modification and design in vivo of xi.
In the section "starting with known components, the correlation between xi performance and battery performance", we review the computational studies based on the prediction of ion/electronic transport and mechanical performance of known xi components, andbriefly)
Associate these SEI properties with battery performance, degradation, and aging.
Then, in the section "in vitro design of new forces", the opportunity for artificial New Forces design will be reviewed.