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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]

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]

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]

Lithium (Li) concentration-dependent mechanical properties are crucial to the performance and durability of lithium ion batteries. Here, we report an in situ measurement of the evolution of elastic modulus and partial molar volume of commercial graphite electrodes. A bending model is developed to analyze the relationship between large curvature changes and materials properties. The curvature changes of the electrode are captured using a CCD camera during electrochemical cycling. Composite graphite electrodes with different thickness ratios are chosen as the working electrode. The modulus and partial molar volume are extracted which are both associated with the stress evolution of electrodes. The results show that the elastic modulus increases during the second lithiation process, while the partial molar volume shows a stage change corresponding to the phase change of graphite materials. These results are important for the mechanical modeling and provide basic information for the commercial graphite electrodes. Image 1 • Lithium concentration-dependent mechanical properties were measured in situ. • A mechanics model was developed to analyze the curvature deformation of electrodes. • Elastic modulus and partial molar volume of the commercial graphite electrode were reported. [ABSTRACT FROM AUTHOR]

The present study consists in the development of an analytical model and the performance of 180° peeling tests aimed at evaluating the interfacial adhesive properties of graphite electrodes of lithium–ion batteries in different charging/discharging states. In order to determine the interfacial peeling strength, uniaxial tensile tests were conducted and an analytical model was used to obtain the elastic modulus of copper foil and the graphite active layer in different charging/discharging states. Results of the application of the interfacial peeling strength analytical model indicate that the interfacial peeling strength between graphite active layer and current collector does not depend exclusively on the energy release rate but also on the strain energy stored in the collector as a consequence of the expansion of the active layer associated with the insertion within it of lithium ions. The results of the 180° peeling tests indicate that the interfacial peeling strength of the fully charged electrode is larger than the corresponding parameters measured in the fresh, soaked, and fully discharged electrodes. The predictions based on the analytical model and the experimental data collected on the interfacial peeling strength are in good agreement with each other. Image 107001 [ABSTRACT FROM AUTHOR]

• An analytical model was established to characterize the mode-II energy release rate. • A novel plasticity-assisted zero-degree peeling test was proposed to obtain a stable crack propagation stage. • The effect of dimensionless stress, indices of hardening, and load transfer length on energy release rate were analyzed. • An excellent agreement between the theoretical calculation and numerical result was demonstrated. Lithium-ion batteries integrate heterogeneous materials such as active layers and current collectors, resulting in interfaces prone to delamination during the charge/discharge process. The mode-II energy release rate is a key index to evaluate the interfacial adhesion properties and structural integrity of electrodes. In this study, an analytical model considering the energy balance principle and a nonlinear constitutive model was established to characterize the mode-II energy release rate. A novel plasticity-assisted zero-degree peeling test (PAZDPT) is proposed to obtain a stable crack propagation stage where the peeling force is determined to calculate the mode-II energy release rate. Several parameter studies were conducted to verify the approximation of the stress distributions and simplification of the analytical model. The accuracy of the analytical model was validated against finite-element calculations. The results demonstrated an excellent agreement between the theoretical calculation and numerical results. Moreover, PAZDPT is conducive to steady crack propagation because it restricts the energy accumulation around the crack tip. The analytical model and newly proposed PAZDPT can also be extended to determine the mode-II energy release rate of other types of interfaces in bilayer thin-film materials. [ABSTRACT FROM AUTHOR]

Abstract: Magnetic Fe3O4 nanoparticles (Nano-Fe3O4) were prepared by co-precipitation method and a disposable glucose biosensor was fabricated by drop coating of ferricyanide (Ferri)-Nano-Fe3O4 mixture onto the surface of screen-printed carbon electrodes (SPCEs), and then by layering-on glucose oxidase (GOD). The electrochemical characteristics of modified SPCEs were analyzed by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and chronoamperometry (CA). The glucose biosensors exhibit a relatively fast response (<15s) and high sensitivity (ca. 1.74μAmM−1) with a wide linear range up to 33.3mM (600mgdL−1) of glucose. [Copyright &y& Elsevier]