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Spinel cathode materials have great application prospects in lithium batteries (LIBs) due to their characteristics of abundant raw materials, simple preparation processes, and cobalt-free nature. During the electrochemical cycles, the specific capacity of the electrodes decreases significantly due to the dissolution of excess metal ions and mechanical degradation, which hinder their further application and development. Here, a bending curvature measurement system (BCMS) was designed to simultaneously measure the mechanical properties of the spinel cathodes during the electrochemical reaction. Three types of cathodes were chosen as the working cathode, and the coupled mechanical and electrochemical properties were analyzed to understand their degradation mechanism. During cycling, a hysteresis loop is observed for the curvature, modulus, plain strain, and stress, where LiMn2O4 (LMO) has the largest loop for the mechanical response while the LiNi0.5Mn1.5O4@Al2O3 (LNMO@Al) one has the smallest loop. Besides, the changing trend of LNMO@Al is the smallest in multiple cycles and it shows the more stable mechanical properties. This study shows from in situ mechanical measurements that the mechanical properties can greatly affect the electrochemical performance of the cathodes. These findings could offer new insights into the understanding of the electrochemical performance degradation in the spinel cathodes and can help develop strategies to enhance the performance of LIBs. [ABSTRACT FROM AUTHOR]

The cycling lifespan and coulombic efficiency of lithium-ion batteries are crucial to high C-rate applications. The Li-ion concentration is crucial in determining the mechanical integrity and structural stability of electrodes. In this work, graphite is selected as the working electrode due to its widespread use in the electric vehicle industry. The experimental data have shown that the electrodes with a mass loading of 6.54 mg cm−2 exhibited poor cycling performance and high charge transfer resistance at high charge rates. To explain this phenomenon, an in situ stress measurement system and a C-rate-dependent stress model are established to study the mechanical properties of the composite graphite electrode during the electrochemical process at various C-rates. Moreover, the effect of the Li-ion concentration-dependent modulus and C-rate-dependent partial molar volume is taken into account in the mathematical model. The computational curvature data fit well with the corresponding experimental data, highlighting the importance of considering lithium-ion concentration in mechanical stress. It has been found that stresses along the thickness of the active layer switch between compressive and tensile stresses due to the competition between bending stress and diffusion-induced stress. The stress at the outer surface of the composite graphite electrodes reaches a maximum magnitude of 27.5 MPa at a 1.5C-rate. In contrast, the stress at the interface of the active layer is maximum at a 0.5C-rate due to the existence of more lithium ions. Our study provides a direct insight into the quantitative analysis of electrode stresses at different C-rates. [ABSTRACT FROM AUTHOR]