Study On The Corrosion Behaviors And Fatigue Behaviors In Different Environment Of Copper Foam For Anode Current Collector In Lithium-ion Battery

Lithium-ion batteries have been widely used in mobile phones and other portable electronic devices as a clean and efficient secondary battery.The stability of active materials in the battery is crucial to the maintenance of high power and energy density of lithium-ion batteries.Besides,current collectors are important components of lithium-ions batteries which can load the active substance,collect current,minimize the internal resistance and enhance cycling stability.However,current collectors usually suffer from severe corrosion damage and fatigue damage in the electrolyte of lithium-ion batteries,which cause the separation of electrode and current collector.As a new type of negative current collector,open-cell copper foam has a broad application prospects in the lithium-ion batteries,which can alleviate the separation of anode materials and current collector effectively,further increasing the cycle life of the battery.The corrosion performance of current collector in the electrolyte of lithium-ion batteries and the fatigue behavior of open-cell copper foam in the air and electrolyte environment were investigated in this dissertation,which have an important guiding significance for the application of copper foam in lithium-ion battery.The main results as follows:(1)Electrochemical analysis method was used to compare the corrosion behavior and mechanism of copper foil and copper foam in the electrolyte of lithium-ion battery,it was found that the corrosion type of copper foil in the electrolyte of lithium-battery is pitting corrosion while the open-cell copper foam shows uniform corrosion.The corrosion process was accompanied by the formation and decomposition of copper oxide,HF stemming from the decomposition of LiPF6 in the electrolyte is the main reason which cause the corrosion of materials.With the increase of hole density in copper foam,the difficulty of ion diffusion also increased and corrosion products were easier to deposit on the surface of strut.The corrosion behavior of 40 PPI open-cell copper foam at the initial stage was influenced by diffusion,corrosion area decreased gradually due to the crystallization of the products generated by corrosion and the decomposition of electrolyte occurred on strut,which caused the disappearance of diffusion effect.(2)A bigger pore diameter related to a longer fatigue life of open-cell copper foam under low stress amplitude.At the initial stage,fatigue deformation was mainly concentrated in the center of the material area.Deformation area was perpendicular to the loading direction or exhibited a certain tilt angle,but a large horizontal deformation area will be formed in the end of fatigue.It can be concluded that the thickness of strut increases with the increasing pore size,which related to a better compressive property.The cracks generated at the joints of strut have the greatest influence on the fatigue life of the materials(3)The electrolyte environment can accelerate the fatigue failure of the open-cell foamed copper material.Under low stress amplitude,the sample immersed in the electrolyte exhibited different fatigue deformation regular compare with that in the air.The material will undergo brittle fracture in the fatigue process under the electrochemical-mechanical interaction.After corrosion fatigue failure,it can be found that the sample suffered fatigue damage such as craze and peeling of strut as well as corrosion damage which occurred as uniform corrosion.The open-cell copper foam with a larger pore size had a smaller deformation rate at the initial stage of fatigue but a greater deformation rate at the final stage.