| The service and safety performance of lithium-ion battery are greatly affected by the cutting quality of electrode materials.Quality defects resulting from tool wear of rotary knife slitting and die cutting can be solved with laser cutting technology.However,there are delamination and obvious heat affected zone(HAZ)along the kerf edge when long-pulsed laser is applied to electrode cutting.With the characteristic of ultra-short pulse duration,ultrafast laser can effectively reduce the thermal effect in the processing,and it is expected to improve the laser cutting quality of the electrode materials.In this thesis,based on the ultrafast laser cutting experimental system,the cutting mechanism,cutting efficiency and cutting quality of ultrafast laser cutting anode material are studied.The mechanism of ultrafast laser cutting anode is analyzed according to the kerf morphology of ultrafast laser cutting graphite layer,copper foil and anode material.It can be observed by scanning electron microscope(SEM)that material melting phenomenon was absent when ultrafast laser is employed to anode cutting,and there are re-deposited granular materials on the upper surface of anode.These phenomena indicate that the ultrafast laser cutting mechanism of anode material is mainly vaporization.During the cutting process,the mechanism of ultrafast laser cutting copper foil is a combination of rapid thermal vaporization,thermal melting and phase explosion,the graphite directly exposed to the laser beam was vaporized by laser energy,while the graphite not exposed to the laser beam was gasified by laser energy transmitted from the copper foil due to the composite structure of anode material.In addition,the upper graphite layer also absorbed the energy radiated by the plasma,and was then removed by gasification and shedding.The cutting efficiency of ultrafast laser cutting anode were characterized by the volume of material removal and the maximum cutting speed.The influence of processing parameters such as laser power and pulse width on the cutting efficiency was investigated.On one hand,the removal volume of ultrafast laser cutting anode increases with the increase of laser power and decrease of pulse width,and decreases with the increase of processing times and scanning speed.The removal volume of copper is much lower than that of graphite layer,and the anode removal volume is a piecewise function of laser power,indicating that the cutting process is dominated by copper.On the other hand,the maximum cutting speed increases as the laser power increases and the pulse width decreases.With the trend,the minimum laser power required to achieve a specific cutting speed or the maximum cutting speed at a specific power can be predicted,which provide insights into the selection of laser equipment and process parameters.The cutting quality of ultrafast laser cutting anode was studied,the characteristics of cutting quality and its measurements were determined,the causes of quality defects were analyzed,and the optimal process parameters were obtained.In this thesis,the cutting quality was characterized by the delamination width and HAZ size.According to the analysis of Raman spectroscopy and the practical processing conditions,it is determined that the HAZ boundary in this thesis is the boundary of the dark region in graphite layer.Heat accumulation and transfer are the main causes of delamination and HAZ.At the same time,plasma spectroscopy shows that high temperature plasma is generated during the cutting process,so the thermal radiation of plasma may also be a cause of delamination and HAZ.For a single-scan cutting,the anode cutting quality increases with the decrease of laser power and pulse width,and increases with the cutting speed.High cutting quality was obtained with the optimal parameters,which the delamination width and HAZ are 22—28?m and 51—70?m for the upper layer,respectively.In addition,delamination was greatly reduced or even completely eliminated and HAZ size was also effectively reduced when a multi-scan cutting was applied to anode cutting,which is a great improvement for anode cutting quality. |
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