The Forming Mechanisms Of The Blanking Burrs Of The Lithium-Ion Battery Electrodes And The Burr's Influence On The Battery's Failure Behavior

Safety issue of the lithium-ion battery is always of much concern to the public,and it is also a main focus of the related research.Electrodes occupy the main parts of lithium-ion battery.During the manufacturing processes,the current collectors of electrodes may be imposed with defects of overlong burrs,which could possibly hazard the safety of lithiumion batteries.But there is no detailed research discussing the mechanism in behind.In this thesis,the blanking process of electrodes and the influence of their blanking burrs are investigated,by combining experiments and finite elements analysis,to try to offer some analytical models and instructions for producing electrodes.The main works are listed as below:(1)Conducting mechanical tests on electrodes,current collectors and separators.Some conclusions were made: anode current collector(cooper foil)has higher ultimate stress and ultimate strain than cathode current collector(aluminum foil);active material layers have very weak stretching property,and significant compressing behavior;strong stretching anisotropy could be observed on separator.The mechanical models of electrodes were built using finite element software ABAQUS.The model had a ‘sandwich' multi-layer structure: crushable foam-metal-crushable foam,with bonding constraint set between layers.(2)Simulating the blanking processes of electrodes in ABAQUS,and comparing the results with that from blanking experiments.It was observed that during blanking process,weak active material layers tend to serve as ‘buffers' to the imposed blanking force,which resulted in the obviously bending and stretching phenomena of middle-layer current collectors.So long burrs could be observed.The influences of clearance and corner radius of blanking tools on the length of burrs were also studied.It could be found that both clearance and corner radius have positive effects on the length of blanking burrs,while clearance seems to have a stronger impact.(3)Probing the influence of overlong burr on the failure behavior of li-ion battery.By conducting indenting experiments and finite element analysis,a conclusion that overlong burr could cause inner short circuit before the destroy of battery's macro structure could be made.(4)Investigating the feasibility of the usage of artificial neural network,to try to unveil the relationship between the intrinsic properties of electrodes and the length of blanking burrs.A three-layer neural network was successfully built.With Monte-Carlo simulation and sensitivity analysis,it could be concluded that the length of blanking burr is most sensible to the size of active material particles,and the cohesive force between active material layers and current collectors.So they should be carefully considered when to design and test electrodes.