| As one of the new energy storage devices,lithium-ion batteries are recognized as a highly efficient secondary battery due to their high energy density,high power density and long cycle life.The pursuit of high stability and high capacity of lithium batteries has become the research goal today.The Si,Ge,and Sn-based anode materials of the new high-capacity lithium-ion battery are accompanied by huge volume changes during charge and discharge,which leading to the separation of the anode material from the current collector,resulting in a decrease in battery cycle performance.The use of copper foam as the negative current collector can improve the stability of the battery,thereby alleviating the volume change caused by lithium deintercalation and prolonging the cycle life of the battery.The cyclic load in charge and discharge cycle is the main reason of the failure of current collector.In this dissertation,three-dimensional model of foamed copper with different structures was established,and the compression and fatigue simulations were carried out.The stress distribution and deformation mode during the deformation process were explored.The fatigue behavior of open-cell foamed copper with different pore sizes in the electrolyte was investigated.Research and analysis of its surface microscopic morphology reveals the interaction between electrolyte and cyclic loading.The main research results are as follows:(1)The stress-strain curves of copper foam with different pore size and identical pore structures are approximately the same as in simulation.In simulation,the strut perpendicular to stress direction hardly deforms,and the strut with a 45° to the load direction undergoes large deformation.The angle between the strut and load direction is an important factor affecting the deformation degree of strut.When the stress exceeds its yield limit,cracking occurs at the joint of struts.When the compressive strain is 12.05%,the copper foam cracks and germination occurs,and fine cracks appear.The applied stress at this time was 0.9423 MPa.Using co-simulation of abaqus and fesafe software,the fatigue life of copper foam can be predicted more accurately.In general,the fatigue life obtained by the simulation is larger than the experimental result,and it is more similar to the experiment in the high cycle fatigue.(2)A simulation model with concentric ring cross-section strut is established,its whole stress-strain curve is similar to that of simulation model with triangular cross-section strut.During the whole compression process,the simulation model with triangular cross-section strut is more accurately in reflecting the deformation and local stress.(3)Through the corrosion fatigue experiment of copper foam,it is found that the fatigue life of copper foam increases with the increase of the pore diameter under the same cyclic load,which is similar to the fatigue result in air.Pitting pits on the surface of the material during corrosion fatigue can cause cracks in the joints of the strut,causing fatigue failure of material.During the fatigue process,electrolyte enters into the interior of the material through fatigue microcracks and pitting holes.When the electrolyte enters in the rib,it will corrode the layered structure,weaken the bonding force between different layers,causing a fall of surface layer of the material and an acceleration of the fatigue failure of the foamed copper. |
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