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a) Si based anode tomography cell construction and X-ray direction, b) 3D reconstruction after lithiation with delamination and, c) radiography during lithiation and delamination with voltage response.
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Silicon-Lithium based rechargeable batteries offer high gravimetric capacity. However cycle life and electrode microstructure failure mechanisms remain poorly understood. Here we present an X-ray tomography method to investigate in-operando lithiation induced stress cracking leading to the delamination of a composite Si based electrode. Simultaneou...
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... customized Si-Li half-cell was assembled in an argon filled glove box (Fig. 1a). A lithium metal anode and a silicon-carbon composite cathode were used. The copper current collector rod was machined into a conical tip on the silicon side for X-ray imaging pur- poses. The final cathode composition was 70 wt% carbon-coated Si, * Electrochemical Society Active ...
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... 70 kV. Electrical wires were attached to the cell to lithiate the silicon anode and current control was main- tained through an Ivium VERTEX (Ivium, Eindhoven, Netherlands) potentiostat. A galvanostatic charge current of 100 μA was applied to the cell for 1 hour whilst monitoring voltage and simultaneously imaging the battery anode using X-rays (Fig. 1a). After 1 hour the electrode was partially lithiated and delamination was observed; then the current was stopped, electrical connectors removed and an X-ray tomography scan performed by rotating the sample. The 3D structure of the electrode, electrolyte and current collector was reconstructed using 602 projections captured over a 360 • ...
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... results show a clear difference between two regions of the sil- icon electrode. The electrode region in contact with an argon bubble (white in Fig. 1c and supplementary material) showed neither lithi- ation nor delamination, whereas the region in contact with the elec- trolyte upon lithiation lifted off and delaminated in a concave 'bow shape' away from the current collector. The inert bubble was present from battery manufacture. However, from these results it is evident that lithiation results in anode ...
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... was present from battery manufacture. However, from these results it is evident that lithiation results in anode expansion, that causes severe delami- nation. Upon volumetric expansion, stresses are generated which are accommodated through the creation of new surfaces and this results in the bowing of the anode away from the current collector (Fig. 1c- Fig. 2). Interestingly, in a few locations the anode maintains good adhesion with the current collector allowing the anode to continue to function; however, in-operando imaging also shows that, during lithiation, delamination eventually results in areas of crack propaga- tion through the electrode thickness that reach the electrolyte. This is ...
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... the anode maintains good adhesion with the current collector allowing the anode to continue to function; however, in-operando imaging also shows that, during lithiation, delamination eventually results in areas of crack propaga- tion through the electrode thickness that reach the electrolyte. This is evident through the 3D reconstruction (Fig. 1b) where it is possible to see delamination leading to regions where cracks propagate from the electrode-current collector interface through to the surface of the electrode. The local electrode-current collector adhesion would influ- ence this behavior. Over an operational lifetime, coalescence of cracks would therefore result in loss of ...
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... images during lithiation, at 100 μA (current density of 2.4 mA/cm 2 ) show the delamination of the silicon electrode from the copper current collector (Fig. 1c-Fig. 2a). The height of the delami- nation continues to increase with charging time, as does the width but at a reducing rate. From the measured voltage data a rapid decrease in the cell potential is observed, suggesting that the electrode-current collector contact resistance is increasing due to the volumetric expan- sion caused by ...
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... cell slightly decreases until reaching 1500 s. An increase in the available active sur- face area caused by delamination may be responsible for this. Though 3D data analysis the electrode-current collector contact area decreases as a result of delamination by 1.84 mm 2 from an original 4.17 mm 2 which is equivalent to a 44.1% loss of contact area (Fig. 1c). Con- currently, the interfacial area between the delamination induced void and silicon anode increases to 2.13 mm 2 , which corresponds to 21.2% of the total silicon anode area following lithiation. Consequently, the ability to track this is significant for cells since this fresh surface would result in capacity degradation through ...
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Citations
... Moreover, it is well known that the volume variation of alloy anodes could lead to interfacial delamination of active composite layer from current collector, which could result in a rapid capacity fading. [22,23] For instance, synchrotron X-ray (nano-)tomography [24,25] has been employed, and has successfully enabled the visualization of the gradual delamination of Si composite-based electrodes from the current collector in 3D. However, due to a lack of suitable characterization tools, it is still poorly understood how the volume change of active materials induces the delamination of the electrode. ...
... Finite element modeling revealed that electrode volume expansion exerts greater stress at its contact area with the current collector than that in the bulk electrode. [24] In light of this, we can deduce that this z-direction (perpendicular to current collector) favored volume variation of the Sn/carbon/binder composite imposes a higher mechanical stress/strain at the interface area contacting the current collector compared with the stress/strain in the x-y plane within the Sn composite bulk. Therefore, the adhesive bonding between the Sn electrode and the current collector provided by the binder tends to gradually weaken and deteriorate during repetitive cycling, which eventually leads to the mechanical detachment and delamination of composite electrodes from the current collector during long-term operation. ...
Tin (Sn) holds great promise as an anode material for next-generation lithium (Li) ion batteries but suffers from massive volume change and poor cycling performance. To clarify the dynamic chemical and microstructural evolution of Sn anode during lithiation and delithiation, synchrotron X-ray energy-dispersive diffraction and X-ray tomography are simultaneously employed during Li/Sn cell operation. The intermediate Li-Sn alloy phases during de/lithiation are identified, and their dynamic phase transformation is unraveled which is further correlated with the volume variation of the Sn at particle- and electrode-level. Moreover, we find that the Sn particle expansion/shrinkage induced particle displacement is anisotropic: the displacement perpendicular to the electrode surface (z-axis) is more pronounced compared to the directions (x- and y-axis) along the electrode surface. This anisotropic particle displacement leads to an anisotropic volume variation at the electrode level and eventually generates a net electrode expansion towards the separator after cycling, which could be one of the root causes of mechanical detachment and delamination of electrodes during long-term operation. The unraveled chemical evolution of Li-Sn and deep insights into the microstructural evolution of Sn anode provided here could guide future design and engineering of Sn and other alloy anodes for high energy density Li- and Na-ion batteries.
... The repeated volume expansion and contraction during cycling cause high mechanical stress within electrode and cell that ultimately has a negative effect on cell performance and lifetime. The mechanical stress causes particle cracking [10][11][12], delamination of electrode material [13,14], and loss of active silicon due to loss of electrical contact between particles [15]. When the particles crack, fresh silicon exposed to the electrolyte reacts leading to the formation of a thicker solid electrolyte interphase (SEI) with the consequence of loss of available lithium in the cell [16]. ...
Silicon is a promising candidate to replace graphite as the anode active material for lithium-ion cells due to its high specific capacity. However, the material undergoes large volume changes upon lithiation causing mechanical stress and accelerated capacity fade when used in cells. To overcome these problems, knowledge about the expansion behaviour of silicon-based cells is vital. In this study, stacked pouch cells with a Sialloy/
graphite composite anode have been investigated by means of dilatometry. Experiments have been conducted with a specifically developed measurement set-up to determine the cell expansion under well-defined mechanical pressure. Upon full charge, the cells show a reversible thickness change of approx. 3.3% and a significant hysteresis behaviour for both the cell voltage and the thickness change. The cell expansion shows an irregularity, and the maximum cell thickness is observed at about 85% state of charge during discharge and not when the cell is fully charged. The hysteresis is further assessed by additional electrical measurements on stacked pouch cells and single-layer cells combined with operando dilatometry. The results indicate that the expansion irregularity during discharge is the result of cathode expansion, since the Si-alloy/graphite anode
does not show significant contraction in this region.
... 154,163 Similar to interfacial debonding of the active materials from the binder, the volume expansion/contraction of the composite electrode as a whole during electrochemical cycles can cause separation from the current collector. 164 The separation (often termed delamination) at the binder/current collector interface is a significant degradation mechanism occurring during the electrochemical cycles. 165 The delamination from the current collector increases the contact resistance and generates electronic limitations within the electrode. ...
Chemomechanics is an old subject, yet its importance has been revived in rechargeable batteries where the mechanical energy and damage associated with redox reactions can significantly affect both the thermodynamics and rates of key electrochemical processes. Thanks to the push for clean energy and advances in characterization capabilities, significant research efforts in the last two decades have brought about a leap forward in understanding the intricate chemomechanical interactions regulating battery performance. Going forward, it is necessary to consolidate scattered ideas in the literature into a structured framework for future efforts across multidisciplinary fields. This review sets out to distill and structure what the authors consider to be significant recent developments on the study of chemomechanics of rechargeable batteries in a concise and accessible format to the audiences of different backgrounds in electrochemistry, materials, and mechanics. Importantly, we review the significance of chemomechanics in the context of battery performance, as well as its mechanistic understanding by combining electrochemical, materials, and mechanical perspectives. We discuss the coupling between the elements of electrochemistry and mechanics, key experimental and modeling tools from the small to large scales, and design considerations. Lastly, we provide our perspective on ongoing challenges and opportunities ranging from quantifying mechanical degradation in batteries to manufacturing battery materials and developing cyclic protocols to improve the mechanical resilience.
... 21,22 Failure to sustain these stresses can cause cracking in electrodes and delamination from current collectors, leading to reductions in accessible battery energy, power density, round trip efficiency, and lifetime. [23][24][25] Sintered electrodes must satisfy the multifunctional role of meeting both electrochemical and mechanical demands of the brittle porous thin film of active material. This results in considering both the electrochemical and mechanical properties of the electrode during the earliest stages, and information is needed on relevant process-property coupling. ...
In the development of materials to meet increasing demands for energy storage, complex materials and systems will need to be investigated. One emerging area is multifunctional energy storage materials, where a battery electrode needs to satisfy other properties in addition to those associated with storing electrochemical energy. An example explored in this report is sintered electrodes for lithium‐ion batteries, where the electrode is only comprised of a porous sintered structure of the electroactive ceramic material. The sintered electrode must be multifunctional in that the porous ceramic itself must sustain the compressive mechanical stresses involved in fabricating the battery cell, as well as the stresses that result during electrochemical charge and discharge cycles. Toward meeting these multifunctional demands, anodes were fabricated using an ice‐templating technique, resulting in directionally porous materials. This study reports the microstructure and compressive mechanical properties of an ice‐templated sintered electrode material both before and after electrochemical cycling, revealing whether electrochemical cycling affects the microstructure and strength. For the specific electroactive material investigated as ice‐templated sintered anodes, the strain with electrochemical cycling was known to be minimal, and the microstructure and compressive strength were found to be retained after multiple charge and discharge cycles. These results suggest multifunctional ice‐templated lithium‐ion battery electrodes can be produced with both high strength and high cell level energy density. Ice‐templated sintered electrodes are multifunctional battery materials with desirable mechanical and electrochemical properties provided by their unique directionally aligned porous microstructure. This is the first study of these thick and high‐energy electrodes to report mechanical properties both before and after cycling. Microstructure and mechanical properties were retained after electrochemical cycling, suggesting that at least for relatively low strain materials that ice‐templated sintered electrodes are mechanically robust to strain induced by charge/discharge cycling. This study evaluated the mechanical and microstructural properties of ice‐templated lithium‐ion battery electrodes containing only sintered electroactive material. Ice‐templating resulted in aligned pores that improve ion transport properties and aligned ceramic‐rich regions which increase electrode compressive strength. For the material evaluated herein, the mechanical strength and microstructure features were retained even after charge/discharge cycling of the material which involved substantial changes in intercalation/deintercalation of lithium from the solid material phase.
... The internal impedance of the cells increases with increasing SEI layer thickness [10,11]. The repeated particle cracking leads to pulverization, electrical insulation of the silicon, and film delamination [12]. ...
... Therefore, a thick SEI layer formed on the surface of the failing electrodes, which was probably produced as a degradation product of the liquid electrolyte during cycling. The groups of Peled and Aurbach [12,39] investigated the SEI-related side reactions that occur at cyclized negative electrodes of lithium batteries. These works show that lithiumions are irreversibly trapped by oligocarbonate molecules that deposit in the electrode pores. ...
The 3D battery concept applied on silicon–graphite electrodes (Si/C) has revealed a significant improvement of battery performances, including high-rate capability, cycle stability, and cell lifetime. 3D architectures provide free spaces for volume expansion as well as additional lithium diffusion pathways into the electrodes. Therefore, the cell degradation induced by the volume change of silicon as active material can be significantly reduced, and the high-rate capability can be achieved. In order to better understand the impact of 3D electrode architectures on rate capability and degradation process of the thick film silicon–graphite electrodes, we applied laser-induced breakdown spectroscopy (LIBS). A calibration curve was established that enables the quantitative determination of the elemental concentrations in the electrodes. The structured silicon–graphite electrode, which was lithiated by 1C, revealed a homogeneous lithium distribution within the entire electrode. In contrast, a lithium concentration gradient was observed on the unstructured electrode. The lithium concentration was reduced gradually from the top to the button of the electrode, which indicated an inhibited diffusion kinetic at high C-rates. In addition, the LIBS applied on a model electrode with micropillars revealed that the lithium-ions principally diffused along the contour of laser-generated structures into the electrodes at elevated C-rates. The rate capability and electrochemical degradation observed in lithium-ion cells can be correlated to lithium concentration profiles in the electrodes measured by LIBS.
... There are several factors contributing to the chemical and mechanical damage/degradation of electrode materials during electrochemical cycling, which include the formation of solid electrolyte interface associated with the loss of metal ions and the decomposition of electrolyte [3] and the increase in the resistance to the insertion and de-insertion of metal atoms [4,5], phase transition [6,7], alloying and dealloying [8][9][10][11][12], surface cracking [13][14][15][16][17], nano cavitation [18,19], delamination [20,21] and dendrite growth [22][23][24][25]. In the heart of the structural damage/degradation is the cycling-induced cracking and cavitation, which is dependent on the insertion and de-insertion of metal atoms. ...
Most analyses of the mechanical deformation of electrode materials of lithium-ion battery in the framework of continuum mechanics suggest the occurring of structural damage/degradation during the de-lithiation phase and cannot explain the lithiation-induced damage/degradation in electrode materials, as observed experimentally. In this work, we present first-principle analysis of the interaction between two adjacent silicon atoms from the Stillinger-Weber two-body potential and obtain the critical separation between the two silicon atoms for the rupture of Si-Si bonds. Simple calculation of the engineering-tensile strain for the formation of Li-Si intermetallic compounds from the lithiation of silicon reveals that cracking and cavitation in lithiated silicon can occur due to the formation of Li-Si intermetallic compounds. Assuming the proportionality between the net mass flux across the tip surface of a slit crack and the migration rate of the crack tip, we develop analytical formulas for the growth and healing of the slit crack controlled by lithiation and de-lithiation, respectively. It is the combinational effects of the state of charge, the radius of curvature of the crack tip and local electromotive force that determine the cycling-induced growth and healing of surface cracks in lithiated silicon.
... Previous experimental observation shows that 250 nm thick Si thin films coated on copper (Cu) foils exhibit near theoretical capacity for a limited number of cycles, whereas, the capacity fades drastically upon further cycling due to fracture and delamination [24]. Tariq et al. [25] presented an X-ray tomography method to investigate in-operando lithiation induced delamination of a composite Si based electrode. Simultaneous voltage measurements revealed increased cell resistance correlating with severe delamination. ...
Silicon is a promising candidate for the negative electrode in lithium-ion battery. However, silicon-based electrodes experience large volume changes during the lithiation-delithiation process, which may lead to their failure and hinder their application. Delamination of the silicon layer from the current collector substrate is one of the critical failure modes; its effects on the performance degradation of Si anode need to be better understood. In this study, a multi-physics based finite element model is established to investigate the impact of Si layer delamination, where an artificial insulating interface is introduced to simulate the delamination phenomenon. It is found that delamination could result in a large amount of residual lithium within Si phase at the end of the delithiation process, leading to the capacity degradation of the Si anode. Furthermore, depth of delamination, Si layer thickness and charging/discharging C-rate are three critical influencing factors for the performances of the Si anode. With the increase of depth of delamination and Si layer thickness, the remaining useful capacity of the Si anode will gradually reduce. In addition, under high C-rate operating conditions, the capacity loss of the anode will be largely exaggerated by the presence of the delamination.
... Hence, new challenges lay in the manner of measuring Li-ion electrode morphological changes occurring upon cycling, especially at a very small length scale and in 3D. Recently, different imaging techniques have been used to study various Si-based electrodes, like scanning transmission electron microscopy (STEM) [10,11], focused ion beam/scanning electron microscopy (FIB/SEM) tomography [12,13], and X-ray computed tomography (XRCT) [14][15][16][17][18][19][20][21][22][23][24]. The XRCT is the most versatile technique offering a large range of spatial resolution depending on the X-ray source and the setup used. ...
... Surprisingly, by comparing Fig. 3b and c, the SNR are almost equivalent with Soleil and SLS facilities despite a ten times higher flux at SLS (~10 14 for SLS compared to ~10 13 for Soleil). A CNR increase is however noticeable thanks to a lower energy (20 keV for SLS compared to 25 keV for Soleil) which increases contrast between low attenuating materials. ...
... [1,32] In other words, the in-plane crack induced by the in-plane stress (i.e., stress along the direction perpendicular to the thickness) is the major form of fracture occurred in the active layers. [28,33] Fracture in the active layer parallel to the surface was also reported [34,35] and will be discussed in Subsection 3.2. ...
... The three-dimensional morphological evolution can be visualized and quantified. For example, Tariq et al. presented this method to investigate lithia-026201-7 tion induced delamination of a composite silicon electrode, [34] as shown in Fig. 7(d). The delamination area was considerably large (44.1% of the initial interface) in this system. ...
... Note that, fracture in the active layer parallel to its surface or the interface was also reported in studies of silicon electrodes. [34,35] It is very likely to be trigged by the growth of interfacial delamination. [34] This type of electrode-level fracture is not discussed independently, as its impact on electrochemical performance is identical to that of the interfacial delamination. ...
Fracture occurred in electrodes of the lithium-ion battery compromises the integrity of the electrode structure and would exert bad influence on the cell performance and cell safety. Mechanisms of the electrode-level fracture and how this fracture would affect the electrochemical performance of the battery are of great importance for comprehending and preventing its occurrence. Fracture occurring at the electrode level is complex, since it may involve fractures in or between different components of the electrode. In this review, three typical types of electrode-level fractures are discussed: the fracture of the active layer, the interfacial delamination, and the fracture of metallic foils (including the current collector and the lithium metal electrode). The crack in the active layer can serve as an effective indicator of degradation of the electrochemical performance. Interfacial delamination usually follows the fracture of the active layer and is detrimental to the cell capacity. Fracture of the current collector impacts cell safety directly. Experimental methods and modeling results of these three types of fractures are concluded. Reasonable explanations on how these electrode-level fractures affect the electrochemical performance are sorted out. Challenges and unsettled issues of investigating these fracture problems are brought up. It is noted that the state-of-the-art studies included in this review mainly focus on experimental observations and theoretical modeling of the typical mechanical damages. However, quantitative investigations on the relationship between the electrochemical performance and the electrode-level fracture are insufficient. To further understand fractures in a multiscale and multi-physical way, advancing development of the cross discipline between mechanics and electrochemistry is badly needed.
... However, electrode materials typically suffer from large volumetric changes during cycling and subsequently large stresses. 1 Silicon, for instance, has a typical volume change of up to 300% during intercalation [2][3][4] and graphite has a volume expansion of approximately 10%. 5 The resulting stresses can cause surface and intergranular cracking, leading to pulverisation of electrode particles and creation of new surfaces for the formation and growth of the solid-electrolyte interphase (SEI) layer. [6][7][8] Consequently, this leads to capacity and power fade. ...
Whilst extensive research has been conducted on the effects of temperature in lithium-ion batteries, mechanical effects have not
received as much attention despite their importance. In this work, the stress response in electrode particles is investigated through
a pseudo-2D model with mechanically coupled diffusion physics. This model can predict the voltage, temperature and thickness
change for a lithium cobalt oxide-graphite pouch cell agreeing well with experimental results. Simulations show that the stress level
is overestimated by up to 50% using the standard pseudo-2D model (without stress enhanced diffusion), and stresses can accelerate
the diffusion in solid phases and increase the discharge cell capacity by 5.4%. The evolution of stresses inside electrode particles
and the stress inhomogeneity through the battery electrode have been illustrated. The stress level is determined by the gradients of
lithium concentration, and large stresses are generated at the electrode-separator interface when high C-rates are applied, e.g. fast
charging. The results can explain the experimental results of particle fragmentation close to the separator and provide novel insights
to understand the local aging behaviors of battery cells and to inform improved battery control algorithms for longer lifetimes.
