Application Of PVDF-HFP/NiO Composite Membrane And Structural Surface Modification In Lithium Electrode Protection

Lithium battery is a widely used secondary energy storage device.How to improve the performance of the battery has been the direction of many researchers for a long time.In terms of battery anode material selection,lithium metal is regarded as an ideal anode material for lithium secondary battery due to its extremely high theoretical specific capacity（3860 mAh/g）and extremely negative potential（-3.040V vs SHE）.However,there are still many unsolved problems when lithium metal is directly used as anode material in lithium battery,among which the most prominent one is the dendrite growth of lithium anode in the charge cycle of battery.The appearance of lithium dendrites will lead to battery capacity decline,volume expansion,and even cause battery short circuit,explosion and other serious safety accidents.Based on the above reasons,this work from a different perspective,through the lithium cathode surface of artificial composite membrane,and with functional groups of the modified metal skeleton to structured processing methods of lithium electrode,hope can optimize the structure of battery cathode,lithium ion deposition uniformity degree,improve the cathode surface to inhibit the uncontrollability of lithium dendrite growth,protect the cathode surface morphology,and thus to improve the performance of cell cycle experiment.（1）Firstly,nanometer NiO powder was prepared in this work.Then,PVDF-HFP was used as film forming agent.According to the different mass ratios of NiO and PVDF-HFP,PVDF-HFP artificial composite membrane was prepared and applied in Li/Li symmetric battery.After the application of the composite film in Li/Cu cells,the battery can maintain a coulombic efficiency of more than 98%after 250 cycles.In the constant current charge-discharge and multiplier tests of Li/NCM battery,the performance of the battery with composite film was also significantly improved.By means of XRD,SEM,XPS,EIS,LSV,nano indentation and other tests before and after the cycle,it is proved that the composite film not only contributes to the reduction of battery interface resistance,but also forms the internal structure conducive to the uniform deposition of lithium ions in the cycle process,so as to inhibit the growth of dendrites and improve the life of lithium metal.（2）with the idea of metal skeleton surface modification as the starting point,the polyacrylonitrile solution was treated with thioamidation,and then the foam copper skeleton treated by dilute nitric acid was infiltrated and chelated,so that large amounts of nitrogen containing functional groups were formed on the surface of foam copper,such as-NH₂,-NH and-C≡N.Using reactive copper foam as a lithium metal skeleton,the surface modified three-dimensional porous lithium electrode was obtained by electrodeposition of lithium metal.The Li/Li symmetrical battery assembled with the above lithium electrodes can circulate for 335 hours at a current density of 3mA/cm²,which is much longer than that of ordinary bare lithium sheets for 50 hours.The number of stable cycles of Li/Cu battery can be increased from 140cycles to 550 cycles by replacing ordinary lithium electrodes with experimental lithium electrodes.In Li/NCM batteries,the performances of Li/NCM batteries were also optimized by surface porous lithium anodes.The experimental mechanism was tested and analyzed in terms of physical structure and chemical reaction principle by means of measurement and calculation of surface bonding energy.（3）Based on the experimental idea of surface modification of porous copper collector,this work continues to use foam copper as a metal framework,and then vulcanizing it to form a dense and uniform CuS layer on its surface,and then put it in acetonitrile solution to heat and supersonic reaction.The-C≡N and amide nitrogen functional groups are successfully generated on the surface of the copper sheet,and also reach the grafting content on the surface of the copper skeleton.The prepared foam copper skeleton is used to finish lithium plating on the surface,and is used as a lithium electrode in Li/Li symmetric battery,Li/Cu half cell and Li/NCM battery.The experimental results show that the Li/Li symmetrical battery assembled with the above lithium electrodes can circulate stably for 400 hours at a current density of3mA/cm².In Li/Cu batteries,98.5%higher coulomb efficiency can be maintained after 550 cycles.In Li/NCM batteries,the specific capacity retention rate is 78.90%after 300 cycles,and the specific capacity of the NCM electrode can still reach 122mAh/g at 0.5C after experiencing the rate test at different current densities of 0.1-4C.This fully shows that the lithium electrode treated by the experiment has a good cycle stability.