Studying The Effect Of The Electric Field In The Formation Of Lithium Dendrites By Multi-physics Coupling Method

From the 1970 s,M.S.Whittingham proposed and began to study lithium ion battery.With the development of science and technology,lithium ion battery has become one of the mainstream energy storage devices.Lithium ion batteries have been widely used in portable electric appliances,electric vehicles,aerospace and other fields due to their unique performance advantages.However,there are still many problems in the practical application of lithium ion battery,among which the growth of lithium dendrites is one of the fundamental problems affecting the safety and stability of lithium ion battery.During the growth of lithium dendrites,electrolyte will be continuously consumed and the irreversible deposition of lithium metal will be caused.The formation of dead lithium will reduce the coulombic efficiency.The formation of lithium dendrites can even Pierce the membrane and cause the internal connection of lithium ion batteries to become short,causing the batteries to heat out of control and cause combustion and explosion.Therefore,how to effectively and safely inhibit the growth of lithium dendrites has important research value.At present,among many schemes to inhibit the growth of lithium dendrites,the following schemes have been widely recognized: 1.Control the roughness of negative electrode surface,such as coating raised surface with additives,2.Make the size of the negative particle smaller than the dynamic radius of curvature facing the street,3.The selection of electroplating potential is lower than the critical value,and the charge-discharge mechanism is improved,such as the use of pulse mode,4.Regulation of electrodeposition wettability,etc.In this paper,the relationship between electric field,lithium ion concentration and electrode surface in the process of lithium dendrite formation is simulated by multi-physical field coupling method.A simplified two-dimensional lithium ion battery model was established,and the Bulter-Volmer equation was used to describe the electrochemical reaction of the electrode,and the Nernst-Planck equation wasused to calculate the ion flux.During the simulated charging process,the rough anode surface causes uneven distribution of electric field,strong electric field at the protrudent tip,and uneven distribution of lithium ion concentration inside the battery.Due to oxidation reaction of cathode and reduction reaction of anode,the concentration of lithium ion in cathode is obviously higher than that in anode.On electrode surface size,charging voltage,current density,temperature,and concentration of electrolyte,and other research and analysis the influence factors of lithium electrode surface dendritic deposition thickness,the results show that the smaller the contact Angle and the contact radius and the anode surface is rough,lithium sedimentary thickness gets larger,the charging voltage,the increase of current density and electrolyte concentration will make sedimentary thickness increases,and protuberant location sedimentary thickness decreases with the increase of working temperature,the experiment results with others.Based on the study of the factors affecting the formation of lithium dendrites,we propose an idea of anode mesh shielding structure.Due to the existence of the shield network,the electric field between the shield network and the anode is shielded,forming a field free space.The concentration of lithium ions near the electrode surface tends to be uniform,thus inhibiting the formation of lithium dendrites.The results of the study on the surface of anode and the thickness of lithium deposition at the smooth position prove that this assumption is effective in theoretical simulation.In addition,the effects of mesh number and distance from anode on the inhibition effect were studied.The results show that the field shielding effect can be improved by increasing the mesh number and the distance between the screen and the anode surface.The shielding area of electric field is set as a space 30 μm away from the surface of electrode.The shielding effect is best when the mesh number of shielding mesh is 400 and the distance with anode is 300 μm.