| As the critical new energy storage systems,lithium secondary batteries(LSBs)have been widely used in many fields,such as portable electronic equipment,hybrid electric vehicles,pure electric vehicles,aviation,and aerospace applications.However,its capacity and service life are still challenging to satisfy the urgent needs of engineering.Therefore,it is actively essential not only to research and develop new cathode and anode materials but also to study the effect of the electrode manufacturing process on the battery service behavior and improve the production process.Based on the continuum mechanics framework,the thesis focuses on the gradient distribution properties of the inactive components(ICs)along the coating thickness caused by the drying process of electrode slurries,explores the mechanical integrity,structural stability,and electrochemical performance of electrode composites,and develops the optimization design and rapid manufacturing method of the high-performance electrode system.The main research contents and conclusions are as follows:(1)Considering the migration of ICs and the variation in electrode material porosity during the solidification process,the evolution of its distribution,modulus,and internal stress of electrode slurries with drying time have been analyzed.Combined with the tensile properties test,the effects of drying rate,binder types,and contents on the material integrity of electrode coatings have also been studied in detail.The results show that a high drying rate can increase not only the gradient distributed effect of ICs and the drying stress but also decrease the tensile strength of electrode composites.Moreover,increasing the binder concentration in electrode slurries could decrease composites' modulus and reduce the drying stress of electrode composites.The aqueous sodium alginate adhesives are more suitable for the rapid solidification of high-energydensity electrode composites.(2)In view of the heterogeneous properties of the cured electrode composites and the lithium concentration-dependent modulus during the charging and discharging process,we have discussed the influence of drying conditions on its mechanical behavior and interface stability and proposed the method of optimizing for electrode drying.Meanwhile,it is found that the higher drying rate increases the lithium diffusion-induced stress on the surface of the electrode coating and weakens the adhesive property of the electrode interface.Notably,a non-linear decrease drying protocol(initially fast,followed by slow evaporation of solvent),NDDR is found to be greatly beneficial to boosting the resistance to cohesion failure and surface damage of the composite electrode,and the optimized processing parameters are proposed to obtain a robust production with high efficiency.(3)According to the drying-dependent interfacial properties and the two-way coupling mechanism between ion transport and hydrostatic stress,the buckling behavior of the composite electrode structure under axial load has been exhibited.The effects of drying rate,thickness ratio,current rate,and interfacial bonding strength on the critical buckling load have been clarified.It is also found that the electrode interfacial failure will occur before the buckling instability at the high rate drying condition.(4)Based on the peel strength test and the coupled mechanical-electrochemical model,the drying dependent-electrode interface impedance and the LSBs electrochemical performance tests have been carried out to compare the effects of different drying conditions and charge/discharge rates on the polarization voltage and cycle life of the battery.The results indicate that the interfacial bond strength and conductivity,charge/discharge capacity and cycle life of composite electrodes decrease with increasing drying rates.Furthermore,NDDR can improve the physical properties of the composite electrode interface and ensure a higher cycle time of the graphite halfcells.The calculated electrochemical capacity curve by interface electric contact theory is consistent with the experimental electrochemical results.(5)Using the contact mechanics method,nanoindentation,and electrical impedance spectroscopy experiments,the effects of external pressure and electrolyte materials on the performance of batteries prepared at different drying rates have been explored.The results reveal that the external pressure can reduce the resistance of the electrode interface but also decrease the ionic conductivity of the separator.With increasing external force,the relative capacity of the battery first increases and then drops,and the optimal pressure is about 1.6MPa.Moreover,the battery with ionic liquid and Celgard 2400 separator has better electrochemical performance. |
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