Experimental And Simulation Study On Deformation Behavior Of Graphite Anode Of Li-ion Batteries

Lithium-ion batteries are widely used in aerospace,aviation,marine and rail transportation,and have become an indispensable part of human production and life in modern society.Anode materials of Lithium-ion battery will undergo large expansion and contraction deformation during the process of lithium ion intercalation and de-intercalation.Repeated cycles will cause the accumulation of damage effects,eventually leading to failure of the electrode material.Establishing an in-situ experimental test device to reveal the deformation and failure mechanism of the anode electrode is one of the key scientific and technical problems for the development of lithium-ion batteries.In this paper,the graphite anode is taken as the research object.Through the combination of in-situ scanning electron microscopy,in-situ optical experiment and numerical simulation,the deformation evolution mechanism and lithium ion diffusion law caused by lithium expansion of the anode electrode are investigated.From the electrode structure point,the lithium ion battery is used.The commercial anode application provides technical support.The main research contents and conclusions of this paper are as follows:1 ? A macroscopic in-situ optical experimental platform was designed and established independently.An in-situ cell of a real battery was designed to reflect the true electrochemical reaction inside.Based on the colorimetric method to realize the qualitative characterization of the internal concentration field distribution of the battery during the charge and discharge process,the internal ion diffusion path of the real battery was first reported,revealing the lithium ion diffusion mechanism in the real service environment.In-situ optical experiments show that: Lithium ions are inserted into the graphite negative electrode from the surface of the electrode through the separator,and are separated from the outside of the graphite electrode near the diaphragm.The electrode surface is the priority area for lithium /de-lithium;where the internal activity of the battery is high,there is concentrated lithium intercalation area,which has uneven lithiation phenomenon.2?A microscopic in-situ scanning electron microscope experimental platform was designed and established independently,and the non-contact digital image correlation method was used to quantitatively characterize the deformation field evolution of graphite anode materials during lithiation.In situ experiments show that:The anisotropic deformation evolution process of electrode section is obtained by calculating the in-plane displacement fields and strain fields.The expansion deformation is mainly concentrated in the direction of thickness.The graphite anode has irreversible expansion for the first charge and discharge cycle and reaches half of the first deformation.In the second cycle,the maximum expansion of electrode material thickness reaches 7.98%,and a stable reversible deformation cycle is formed.3?A single-layer electrode model was developed.The finite element simulation was used to calculate the electrode expansion deformation and the equivalent lithium ion diffusion evolution of the single-layer electrode in the process of lithiation.The simulation results explain the phenomenon of macroscopic in-situ optical experiments,including the basic path of graphite electrode lithiation and lithium ion diffusion from the outside to the inside,and the intercalation /de-intercalation reaction occurs preferentially on the surface of the electrode material.Secondly,the thickness direction expansion deformation and the average strain value of the simulation calculation results are similar with the in-situ SEM experimental data,and the change trend is the same.The simulation calculation results effectively analyze the deformation and mechanism of the battery,and provide important support for the electrode structure design.