Investigation On The Effect Of Calendering Process On Microstructure Evolution And Performance Control Of Lithium-Ion Battery Electrode

In the context of striving to achieve the dual-carbon strategy goal of "carbon peak and carbon neutrality," battery energy storage technology has become an important direction for China’s automotive industry transformation and sustainable economic growth.As the core component of the battery,the electrode determines the energy density and service safety of the battery,and the calendering process is a key factor in ensuring the required compaction density of the electrode and improving the comprehensive performance of the battery.However,due to the typical layered composite structure of the electrode,which consists of a coating-collector-coating structure with porous and compressible properties,and involves the interaction between active particles and particle-current collector.The deformation mechanism during the calendering process is extremely complex,and controlling the thickness is difficult,which significantly affects subsequent performance.To deeply study and understand the microstructure evolution mechanism and its influence on the final performance of the electrode in the calendering process,this paper uses a combined approach of discrete method(DEM)element simulation,theoretical modeling,and experimental analysis to focus on the microstructure evolution mechanisms,structural anisotropy and their impact on thermal conductivity,porosity and rolling force prediction modeling,and structure and mechanical properties from the perspective of the microstructure-calendering process-mechanical properties correlation,providing theoretical guidance and basis for process formulation and rolling equipment design.DEM were employed to investigate the mechanical properties and calendering process of electrode at the microscale level.By using the Edinburgh Elasto-Plastic Adhesion(EEPA)model,we captured the interaction behavior between active particles and carbon black to obtain the macroscopic response.The simulation results were calibrated and verified by nanoindentation experimentsto to analyze the mechanical properties of the electrodes.Results showed that larger particles and NMC cathodes exhibit stronger compressive strength.By reasonably simplifying the calendering process of the electrode and analyzing the evolution of the morphology of the deformation zone,we quantitatively studied the evolution of pressure,elastic recovery,particle interaction,and coordination number between active particles and current collector.To reveal the influence mechanism of calendering on the mechanical and thermal properties of the electrode,the size and evolution of the contact force network of NMC cathode under incremental calendering conditions were calculated.By calculating the inter-particle forces and stress tensor,the impact of structural anisotropy on thermal anisotropy under a complex contact force network was revealed,and a prediction model for the thermal conductivity of the electrode was established.The correlation between the process,structure and performance was characterized.While the size and proportion of carbon black lead to a lower thermal flux,its existence increases the effective thermal conduction path at low compaction density.Furthermore,the evolution mechanism of the interfacial thermal resistance was explained,which is mainly affected by the combined effect of the number and area of contacts.To further elucidate the microscopic structural evolution and macroscopic deformation mechanics of the electrodes during calendering process,the microstructural evolution rules and mechanisms were summarized through calendering experiments.The deformation mechanisms of the electrode during calendering process include particle breakage,fusion into secondary particles,compression of PVDF network,and surface deformation of the current collector.The increase in electronic conductivity after calendering is related to the improvement of the conductive path inside the electrode and the tightening of the contact between the coating and the current collector.A model for predicting the compaction density and porosity based on the Heckel equation was derived.A theoretical model for the pressure distribution and rolling force in the deformation zone was also established by simplifying the compression of the active coating into a plane deformation problem.To understand the correlation between the structure and mechanical performance of calendered electrode,the types of macroscopic defects that easily occur during the calendering process and their impact on subsequent production and use were introduced.The surface deformation of the current collector was regarded as a micro-defect,and the interaction between particles and the current collector was analyzed based on experimental and DEM-FEM coupling simulation.The tensile test results of anode and cathode showed that the compacted coating after calendering is conducive to improving the tensile performance.The graphite anode electrode does not have isotropic characteristics,while the NMC cathode electrode shows significant tensile anisotropy.In addition,the internal adhesion of the coating after calendering was analyzed through micro-scratch experiments,and a new test method was developed to study the mechanism of the effect of the calendering process on the bonding strength between the coating and the current collector under different tensile and shear stress states.