| Lithium-ion batteries are widely used in various products with a significant advantage of high energy density, high voltage and less pollution. However, lithium-ion battery can produce different stress states because of different service conditions in the process of electrochemical cycle, which may lead to serious influence to the electrochemical performance and safety performance of the battery. Therefore, it is of great significance to measure the deformation evolution of lithium ion battery for its design and reliability analysis in the process of electrochemical cycle. In this paper, the mechanical behavior of electrode material and current collector that may occur was studied through the view of mechanical. The mechanism of electrochemical properties of lithium-ion battery leading to failure and mechanical safety problem were discussed. The main conclusions are summarized as follows:Firstly, the surface field test system is designed based on 3D-DIC to observe charging and discharging cycles of lithium-ion battery. It can record the displacement and strain evolution of lithium-ion battery during the previous five charge and discharge cycles at 1 C and 0.8 C charge-discharge rates in real-time. Experimental results show that, since the lithium-ion intercalation and deintercalation processes in graphite at different state of charge and discharge, the surface of lithium-ion batteries in the X direction, Y direction and Z direction will change. When the state of charge is 0 and 100%, the displacement of the surface of the battery is respectively minimum and maximum. Displacement in the Z direction than in the X direction and Y direction changes significantly larger, the maximum is up to 249.6 ?m.Secondly, variation of adhesive strength between electrode material and current collector is tested after 0 cycles,50 cycles,100 cycles,150 cycles and 200 cycles. The results show that, regardless of the positive electrode material or negative electrode material, adhesive strength between electrode material and current collector is reduced with the increase in the number of charging and discharging cycles. The adhesive strength between the cathode material and the current collector is respectively 839.66 kPa,401.65 kPa,230.42 kPa,184.57 kPa and 132.62 kPa at the above-mentioned charge and discharge cycles; the adhesive strength between the anode material and the current collector is respectively 284.58 kPa, 183.16 kPa,173.67 kPa,129.11 kPa and 55.92 kPa at the above-mentioned charge and discharge cycles. The adhesive strength between the cathode material and the collector is higher than the adhesive strength of the anode electrode material and the current collector under the same charge and discharge cycles. The microstructure evolution of fracture between the electrode material and the current collector is observed using the self-developed mechanical testing system.Thirdly, Raman spectroscopy for different cycles (0 cycles,50 cycles,100 cycles,150 cycles and 200 cycles) of the stress characteristics of graphite anodes and LiCoO2 cathodes are tested and analyzed. We also studied the variation of the positive and negative material on the surface morphology at 1 C charge-discharge rate under different state of charging and discharging cycles. It indicates that the graphite anode always produces compressive stress after charging and discharging cycles and compressive stress increases with the charge-discharge cycles, its influence leads to not only change of the graphite anode volume, but also cracking and fracture of graphite particles. However, the residual stress of LiCoO2 cathode is very small a charge-discharge cycles. As the charge-discharge cycles, cracks begin to appear between the graphite particles and gradually increase, the original smooth surface of compact LiCoO2 particles appear uneven surface and the distribution is more loose. |
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