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The interfacial debonding between the active layer and the current collector has been recognized as a critical mechanism for battery fading, and thus has attracted great efforts focused on the related analyses. However, much still remains to be studied regarding practical methods for suppressing electrode debonding, especially from the perspective of mechanics. In this paper, a pre-strain strategy of current collectors to alleviate electrode debonding is proposed. An analytical model for a symmetric electrode with a deformable and limited-thickness current collector is developed to analyze the debonding behavior involving both a pre-strain of the current collector and an eigen-strain of the active layers. The results reveal that the well-designed pre-strain can significantly delay the debonding onset (by up to 100%) and considerably reduce the debonding size. The critical values of the pre-strain are identified, and the pre-strain design principles are also provided. Based on these findings, this work sheds light on the mechanical design to suppress electrode degradation. [ABSTRACT FROM AUTHOR]

Due to the complex mesostructure and components of composite active layers in lithium-ion battery (LIB) electrodes, coupled with the concentration-dependent material properties and eigenstrains, efficiently estimating the effective modulus of the active layers remains a great challenge. In this work, the classic Mori–Tanaka method is found to be unable to estimate the modulus of the active layer. By realizing the importance of the mesostructure feature, a rod-rod model is proposed. The resulting modulus is expressed analytically. It is shown that the rod-rod model can accurately estimate the modulus evolution of the active layer if the material properties of the components and the evolution of volume fractions are known in advance. Moreover, a simplified rod-rod model is also developed to reduce the complexity of the proposed method. By knowing the volume fractions at two arbitrary states of charge and subsequently determining two constants, the simplified model can estimate the modulus efficiently. Considering both its accuracy and its simplicity, the simplified rod-rod model is the most suitable for the estimation. Thus, the methods developed in this work provide a new perspective for analyzing the material properties of composite active layers in LIB electrodes. [ABSTRACT FROM AUTHOR]

Prelithiation has been intensively investigated in high-capacity lithium-ion batteries (LIBs). However, the optimization of prelithiation degrees for long service life of LIBs still remains a challenge. The positive efffect of prelithiation on suppressing degradation of LIBs, besides directly pursuing the high first Coulomb efficiency which has been widely reported in the literature, is revealed and discussed based on an analytical model focusing on the interfacial delamination in electrodes. For full charge-discharge cycling, well-designed prelithiation can effectively suppress the delamination and reduce the debonding size by approximately 25%, compared with the case without prelithiation. For the strategy combining partial charge-discharge cycling and prelithiation, the largest reversible capacity without debonding can be significantly improved by approximately 100% with well-designed prelithiation. This work is expected to provide a prelithiation design principle and further improve the mechanical stability of LIB electrodes. [ABSTRACT FROM AUTHOR]

A fully coupling model for the diffusion induced finite elastoplastic bending of bilayer electrodes in lithium-ion batteries is proposed. The effect of the mechanical stress on the lithium diffusion is accounted for by the mechanical part of the chemical potential derived from the Gibbs free energy along with the logarithmic stress and strain. Eight dimensionless parameters, governing the stress-assisted diffusion and the diffusion induced elastoplastic bending, are identified. It is found that the finite plasticity starting from the interface of the bilayer increases the chemical potential gradient and thereby facilitates the lithium diffusion. The full plastic flow makes the abnormal lithium concentration distribution possible, i.e., the concentration at the lithium inlet can be lower than the concentration at the interface (downstream). The increase in the thickness of the active layer during charging is much larger than the eigen-stretch due to lithiation, and this excess thickening is found to be caused by the lithiation induced plastic yield. [ABSTRACT FROM AUTHOR]

The state of charge (SOC) or the depth of discharge (DOD) to and the time to delamination onset and the critical size for delamination, which are potentially important in lithium ion battery design for preventing the patterned thin film electrodes from delamination, are investigated. A theoretical approach based on the cohesive model is proposed to formulate the time to and the SOC (or DOD) to delamination onset, as well as the critical size for patterned disk-like electrodes. It is found that for negative electrode the delamination initiation is dominated by mode-II during cell charging and by mode-I during cell discharging. For positive electrode both delamination modes are theoretically possible during cell charging. When the electrochemical load factor i ¯ is very high, the mode-I delamination is possible and an optimal size of electrodes exists for a given maximum i ¯ . The SOC to mode-II delamination onset decreases significantly with increasing dimensionless radius, being independent of i ¯ . When the mode-II is the dominated mode the critical size for delamination exists, and a formula for the critical size for delamination has been deduced, which is proportional to interface ductility and inversely proportional to maximum volumetric strain. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, structural configuration of layered Li-ion battery electrode plates is evaluated by analytically formulating the diffusion induced stress. Both symmetric electrode and asymmetric bilayer electrode are discussed. The thickness ratio and the modulus ratio of current collector to active plate are analytically identified to be the important influence parameters on the stress. Applying a material with smaller elastic modulus for current collector could reduce the peak stresses in both current collector and active plate. Increasing the thickness of current collector would reduce the stress in itself while promote the stress in active plate. Therefore, from mechanical viewpoint on designing an electrode, the material for current collector should be as soft and flexible as possible. And the thickness of current collector should be in an appropriate range. Basically, it should be as small as possible on the precondition that the mechanical strength is satisfied. Finally, effects of three charging conditions, i.e. uniform, galvanostatic, and potentiostatic, on the diffusion induced stress is discussed. It is found the maximum stresses for three cases are linear to the total amount of intercalated lithium ions. Based on the stresses, an optimized charging operation, i.e. first galvanostatic followed by potentiostatic, is suggested. [Copyright &y& Elsevier]

[Display omitted] • This work designed Ni 35 Cu 15 Zr 15 Ti 35 MG ribbon as a dealloying precursor. • Flexible porous Cu x O/NiO photo-assisted hybrid electrode was synthesized. • The photoelectrode exhibits an intriguing multi-layered porous architecture. • The photoelectrode demonstrates the enhanced energy storage with light radiation. • The mechanism of photo-assisted charging supercapacitors was investigated. With the utilization of sustainable sunlight efficiently, it is of paramount important to develop a new type of electrode for boosting photo-assisted supercapacitor performance. Herein, this work originally designs the Ni 35 Cu 15 Zr 15 Ti 35 metallic glass (MG) ribbon as dealloying precursor. Benefiting from the different oxidation behavior of Ni and Cu metals during the dealloying and anodizing processes, a new type of multi-layered porous hybrid photoelectrode (namely Cu x O/np-NiCu@NiCuO/MG, x = 1, 2) that simultaneously achieve the flexible, hierarchical porous structure as well as the NiO/Cu 2 O heterojunction, are successfully synthesized. An intriguing multi-layered structure consists of the outermost photosensitive Cu x O nanowire layer formed by the anodizing technique, the nanoporous NiCu@NiCuO layer just beneath the nanowire layer via the dealloying as well as the glass central layer offering an excellent flexibility. In particular, 3D interconnected hierarchical porous structure is benefit to the penetration and utilization of visible light efficiently. The photoelectrode demonstrates a maximum specific capacitance of 1182.2 F cm−3 with light irradiation, which is 18% higher than that without light. This photo-assisting charging for the supercapacitor is ascribed to the combination of photosensitive Cu x O and pseudocapacitive NiO components. Moreover, the photoelectrode exhibits an excellent flexibility and the photocurrent response is basically unchanged after bending for 1000 times. The aqueous supercapacitor shows a maximum energy density of 44.9 mWh cm−3 under light. This work provides new insights into the development of next generation wearable photo-assisted supercapacitor. [ABSTRACT FROM AUTHOR]

Abstract Partial lithiation strategies for silicon composite electrodes are experimentally investigated in this article. Two types of partial lithiation, i.e. voltage- and capacity-control strategies, are presented. Capacity loss and irreversibility of silicon electrodes are significantly suppressed by either partial lithiation strategy without any complicated modifications or treatments. The capacity of partially lithiated silicon electrodes is even higher than that of fully lithiated one after certain cycles. The images of scanning electron microscope suggest that the mechanical damage generated in partially lithiated electrodes is less than that in fully lithiated one. Furthermore, after dozens of cycles with partial lithiation, capacity decay also slows down in subsequent full charge-discharge cycles. The presented experimental results suggest that the partial lithiation strategy relieves the coupled mechanical-electrochemical degradation and is a promising approach for the long-term use of silicon composite electrodes. [ABSTRACT FROM AUTHOR]

This paper discovers and reveals a phenomenon of feigned death induced by partial delithiation in silicon composite electrodes. Unexpected extremely rapid capacity fading occurs in the initial dozens of the cycles with low upper cut-off voltages. By looking into the irreversibility, the crack, the elemental analysis and the thickness/weight of the electrode, it suggests that the rapid capacity fading is not induced by degradation. Additionally, by providing a reboot with full delithiation, the capacity can be recovered completely, which confirms the integrity of the electrode. This novel type of capacity fading is named by "feigned death" to distinguish it from the "true death" caused by degradation. It is further confirmed that the feigned death is caused by the asymmetric phase transformation between crystalline and amorphous phases in silicon electrodes. When the depth of lithiation is high enough to generate the c-Li 3.75 Si phase but the depth of delithiation is too low to eliminate the generated crystalline phase, the feigned death is triggered. The findings of this work provide an in-depth understanding of the electrochemical performance of Si-based electrodes. • The impact of partial delithiation on cycling performances of silicon electrodes is revealed. • Feigned death of silicon electrodes is discovered. • Feigned death is caused by the asymmetric phase transformation of lithiated silicon. [ABSTRACT FROM AUTHOR]

An analytical model of mechanical contact problems in composite electrodes of lithium-ion batteries is developed in this article. Two typical types of mechanical contact, namely contact between particles and contact between particle and current collector, are investigated. Key parameters that affect the contact problem are identified from the analytical solution. High uniformity of the particle size is found to be critical to the electrode. Furthermore, a soft current collector could significantly reduce the contact stress and hence is also suggested. It is figured out that contact stress is comparable to or even higher than the diffusion-induced stress under free-expansion state, even if the mechanical constraint in electrodes is weak. To highlight the significance of contact stress, an electrochemical cycling verification experiment which involves a charging pause is conducted. Both analytical and experimental results indicate that the mechanical contact plays a crucial role in the evaluation of mechanical stability of lithium-ion battery electrodes. • Analytical solutions of PP and PC contact are established. • The contact stress can be higher than the diffusion-induced stress. • The stress within the active particle is mainly induced by mechanical contacts. [ABSTRACT FROM AUTHOR]