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Understanding Modulus Variation of the Active Layers of silicon composite electrodes

Acta Mechanica Solida Sinica 2022年第6期35卷 987-995页

作者： Bowen Sun Yanfei Zhao Yicheng Song Junqian Zhang Bo Lu Department of Mechanics Shanghai Institute of Applied Mathematics and MechanicsSchool of Mechanics and Engineering ScienceShanghai UniversityShanghai200444China Shanghai Key Laboratory of Mechanics in Energy Engineering Shanghai UniversityShanghai200444China Department of Civil Engineering School of Mechanics and Engineering ScienceShanghai UniversityShanghai200444China Zhejiang Laboratory Hangzhou311100China

The variation of the effective modulus of silicon composite electrodes,which is a fundamental feature to analyze the coupled mechanical–electrochemical behavior of Si-based electrodes in high-capacity lithium-ion batteries,remains qualitatively controversial.To clarify the contradictory experimental results,numerical modeling of a representative volume element with silicon particles,carbon-binder domains(CBDs),and pores has been performed for the lithiation process.The key parameters for modulus variation were identified and evaluated.A mesostructure change is proposed to be a crucial mechanism that affects the modulus variation,and silicon softening is another key mechanism.silicon softening and the decreasing CBD volume fraction collectively result in a decrease in the effective modulus of the composite,whereas an increase in the silicon volume fraction along with a decrease in porosity has the opposite effect.The findings of this work provide an in-depth and fundamental understanding of the mechanical properties of silicon composite electrodes.

关键词： Modulus variation silicon composite electrode Active layer Mesostructure change silicon softening

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Experimental investigation of electrode cycle performance and electrochemical kinetic performance under stress loading

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Chinese Physics B 2021年第1期30卷 380-390页

作者：刘子涵亢一澜宋海滨张茜谢海妹 Tianjin Key Laboratory of Modern Engineering Mechanics School of Mechanical EngineeringTianjin UniversityTianjin 300350China

Lithium-ion batteries suffer from mechano–electrochemical coupling problems that directly determine the battery life. In this paper, we investigate the electrode electrochemical performance under stress conditions, where seven tensile/compressive stresses are designed and loaded on electrodes, thereby decoupling mechanics and electrochemistry through incremental stress loads. Four types of multi-group electrochemical tests under tensile/compressive stress loading and normal package loading are performed to quantitatively characterize the effects of tensile stress and compressive stress on cycle performance and the kinetic performance of a silicon composite electrode. Experiments show that a tensile stress improves the electrochemical performance of a silicon composite electrode, exhibiting increased specific capacity and capacity retention rate, reduced energy dissipation rate and impedances, enhanced reactivity, accelerated ion/electron migration and diffusion, and reduced polarization. Contrarily, a compressive stress has the opposite effect, inhibiting the electrochemical performance. The stress effect is nonlinear, and a more obvious suppression via compressive stress is observed than an enhancement via tensile stress. For example, a tensile stress of 675 k Pa increases diffusion coefficient by 32.5%, while a compressive stress reduces it by 35%. Based on the experimental results, the stress regulation mechanism is analyzed. Tensile stress loads increase the pores of the electrode material microstructure, providing more deformation spaces and ion/electron transport channels. This relieves contact compressive stress, strengthens diffusion/reaction, and reduces the degree of damage and energy dissipation. Thus, the essence of stress enhancement is that it improves and optimizes diffusion, reaction and stress in the microstructure of electrode material as well as their interactions via physical morphology.

关键词： prestress loading silicon composite electrode tensile stress enhancement compressive stress suppression

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