Role Of Electrode Drying Parameters On The Mechanical Integrity Of Composite Electrode For The Lithium Secondary Battery

How to properly control the drying process of the electrode and thus to improve its electrochemical performance and reduce the energy consumption during the electrode production process is an essential topic in the lithium secondary battery industries.In this paper,starting from the migration of inactive components during drying of an electrode,and combined with theoretical and experimental tests,the effect of drying on the elastic properties of the electrode is studied.Secondly,the critical physical and mechanical parameters of the electrode under different drying temperatures and binding systems are measured and analyzed.Then,the strength problems upon electrochemical usage,which affects the mechanical integrity of the electrode are studied.The corresponding correlation with the degradation of cycle performance is also discussed.Finally,the drying parameters are thereby optimized.The main research contents and conclusions are as follows:（1）By considering the drying kinetics of the slurry,the quantitative relationship between the two key parameters of drying temperature and drying air velocity and the solvent evaporation rate is given.Furthermore,the shrinkage of the electrode slurry and the migration behavior of the inactive components during the drying process were analyzed.The elastic properties of the electrode after drying were estimated by the S-mixing method of porous media.The results show that:the evaporation rate of the solvent has a positive non-linear correlation with the drying air velocity and temperature;after drying,the concentration of inactive components in the electrode presents a distribution pattern of high at the electrode free surface and low at the electrode/collector interface;Due to the differences in solvent evaporation rates,diffusion coefficients,and adsorption properties,the distribution of inactive components in each binding systems are quite different.In addition,affected by the non-uniform distribution of inactive components,the elastic modulus of the electrode after drying also shows a gradient distribution.And,the calculated average modulus for the dried electrode is in good agreement with the experimental data.（2）Carbon-coated Si O₂ composite electrodes with different drying temperatures and binding systems were prepared,and their quasi-static tensile performances,interfacial tensile-shear properties and electrochemical impedance parameters were tested.The results showed that the elastic modulus and tensile strength of the active layer for each binding system are gradually decreased as the drying temperature increases.Among them,the tensile strength of electrodes with SBR/CMC is the highest.The interface tensile-shear strength of each binding system corresponding to the composite electrode also declines with the increasing drying temperatures.And the tensile-shear strength of the electrode with SBR/CMC is relatively less affected by temperature.As for the lithium-ion transport,as the drying temperature increases,the Li⁺diffusion coefficients for the three systems all reduces.（3）Based on theoretical analysis,the analytical solutions for the peak tensile stress and the peak interface shear stress during the constant current-constant voltage cycle of an electrode are obtained.Hence,the effect of drying on the mechanical integrity of the electrode upon electrochemical service is analyzed.By comparing with the experimental data of electrode cycle performance,it is found that the strength of the electrode during service is the key to the electrode cycle performance.Therefore,based on the drying time of the electrode under different drying parameters and the internal stress during electrochemical service,the electrode drying parameters are optimized.It was found that under the precondition of meeting the service strength of the electrode,the optimal drying method would be high air temperature with low air velocity.