| Lithium-ion batteries(LIBs)have been widely employed as an important power source in a wide range of applications such as laptops,mobile phones and electric vehicles.However,with the acceleration of life in modern society,LIBs are often subjected to fast charging and discharging,resulting in lithium dendrite growth and deposition,which seriously affects the lifetime of LIBs.In LIBs,the growth of lithium dendrite is coupled with diffusion,electrochemical reactions and electric fields.It is a complex problem has yet to be comprehensively understood.Therefore,this paper studies the coupled competitive relationship between lithium dendrite growth and the lithium intercalation in electrode,using both experimental techniques and numerical simulations to understand the influence of various factors on lithium dendrite growth.The results would shed some light on the inhibition of lithium dendrite growth in LIBs.In this paper,we firstly observe the lithium intercalation and lithium dendrite growth of different shaped electrodes by experiment.It shows that lithium dendrite appears to grow at the edges of the electrode when the electrode is not saturated with lithium and more readily grow at the tip of the electrode where the curvature is greater.Three different types of lithium dendrite are observed: unstable lithium dendrite,stable lithium dendrite and dead lithium.At the same time,the growth of lithium dendrite in local area can inhibit the lithium intercalation in the nearby electrode area,and there is a competitive relationship between them.To further study this competitive relationship,quantitative electrochemical evaluation of the amount of lithium intercalation and the amount of lithium dendrite growth in the electrode are carried out separately,while the charging process of graphite electrodes with lithium dendrite is simulated numerically.It is found that the nucleation of lithium dendrite changes the electric field distribution.With the higher electric field strength attracted to the tip of the lithium dendrite,the flux of lithium-ion in the electrolyte is highly uneven and is heavily concentrated near the tip of the dendrite.Lithium-ion is hardly reaching the inner electrode region.This leads to continuous growth of dendrites,while the lithium intercalation is inhibited.This paper also studies the mechanical and electrochemical performances of microporous collector electrode.Current collectors with micro pores are employed instead of the traditional metallic foil current collectors.On one hand,employment of porous current collector increases the stacking ratio of the active material so as to improve the battery energy density.On the other hand,the porous current collector provides a coarser interface with the active layer so that the bonding strength between the collector and active layer is enhanced.The mechanical and electrochemical performances of the new electrodes are investigated.Peeling experiments are performed to study the interfacial strength.A theoretical explanation of the peeling strength is provided.The 180° peeling test shows that the interfacial bonding strength of the microporous collector electrode is twice that of the traditional electrode.The interface of the microporous collector electrode between the active layer and the collector has better mechanical performance due to less debonding during charging and discharging.The cycling performance test and the variable rate performance test are conducted on the microporous collector electrode.It is found that the microporous collector electrode has a higher energy density.Meanwhile,other electrochemical performances are basically the same as the traditional electrode.The research in this paper provides a new experimental method for the observation of lithium intercalation behavior and lithium dendrite growth,a theoretical foundation for the quantitative analysis of the amount of lithium intercalation and the amount of lithium dendrite growth,and a new idea for the structural design of LIBs. |
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