| Nowadays,the actual energy density of commercial lithium-ion batteries is close to its theoretical value,but it is still difficult to meet the demand for high-performance batteries in social development.Lithium(Li)metal is considered to be the lower due to its extremely high theoretical specific capacity(3860 mAh/g),lower density(0.59g/cm~3),and lowest reduction potential(-3.040 V vs.standard hydrogen electrode).A generation of ideal anode materials.However,lithium dendrite caused by uneven deposition of lithium ions during charging and discharging leads to low efficiency and short cycle life of lithium metal batteries,and brings serious safety problems,which limits the development of lithium metal anodes.From the perspective of magnetoelectrochemical deposition,this paper explores the magnetohydrodynamic effect(MHD)to inhibit the growth of lithium dendrites,that is,the magnetic field changes the motion trajectory of the moving lithium ions and improves the uneven deposition of lithium ions,thereby increasing the cycle life of the lithium metal battery.In the chapter 3,Comsol Multiphysics software simulation was used to study the lithium ion trajectory and dendrite growth mechanism during the electrodeposition process of lithium metal anode.The numerical characterization results show that under the applied magnetic field,the lithium ion is driven by the high electric field strength to cut the magnetic induction line when it is close to the bulge,and is subjected to the Lorentz force,which causes the original motion trajectory to change,and it is around the bulge.Spiral motion,evenly scattered around the bumps.It can be seen that under the MHD effect,the physical field significantly reduces the concentration polarization,promotes the liquid phase mass transfer process,effectively inhibits the growth of dendrites and obtains a dense lithium deposition layer.In the chapter 4,the in-situ observation device was designed and assembled to directly characterize the lithium deposition process and the morphology of the deposited layer.The in-situ observation results show that the thickness of the lithium deposit layer increases slowly with the increase of deposition time under the magnetic field.The macroscopically maintains a dense and uniform morphology without dendritic growth.Under the action of no magnetic field,the lithium deposit begins to change around 4 h.It is rough and dendrites appear,and the dendrites continue to grow in the subsequent 4-10 h,and the volume of the lithium deposits rapidly increases.The battery cycle performance test under different magnetic fields shows that the application of magnetic field effectively improves the cycle performance of the battery.The larger the magnetic field is,the more obvious the improvement effect is:2 T magnetic field strength is cycled at a current density of 1 mA/cm~2,and the battery can be stably cycled to 280 h.The cycle life is increased by 250%compared to the non-magnetic condition.And the nucleation overpotential and hysteresis voltage under the magnetic field are lower than the non-magnetic field condition,indicating that the application of the magnetic field promotes the uniform distribution of lithium ions in the electrolyte,reduces the concentration polarization and enhances the liquid phase mass transfer process,and promotes the lithium Uniform nucleation.In the chapter 5,the high-purity graphite felt is used as the base,and the CoNiMnP permanent magnet film is loaded on the carbon fiber by electrodeposition,and then the battery separator is formed into a"sandwich"structure with the PP separator to assemble the battery.In this experiment,the stable magnetic field generated by CoNiMnP affects the trajectory of lithium ions and achieves the purpose of uniform deposition of lithium ions.The magnetic properties test results show that the CoNiMnP film coating uniformly coated on the surface of the graphite felt is a permanent magnet material,and the cycle stability of the battery is obviously improved.At a current density of 0.5 mAh/cm~2 and a current density of 0.5 mAh/cm~2,the negative electrode microstructure of the magnetized battery is flatter and denser than that of the unmagnetized battery negative electrode.The magnetization stabilizes the cycle for 250h,and the polarization voltage is always smaller than that of the unmagnetized condition.Under the condition of 100 h,the polarization voltage began to increase sharply,and the battery was completely ineffective after being cycled to 150 h.At a small current density of 0.25 mA/cm~2,the magnetized battery is stably cycled for more than 500 h,and the polarization voltage begins to increase after 300 h of battery cycling under unmagnetized conditions.The battery is completely ineffective when cycled to 380 h.In the chapter 6,a magnetic anode current collector was prepared by magnetron sputtering method.The surface of the copper was used as the base,and the NiPt alloy permanent magnet film was magnetron sputtered on the surface to magnetize it to become a magnetic current collector.When the NiPt/Cu current collector is magnetized,the assembled lithium metal symmetrical battery cycle stability is improved.Tested at a current density of 0.5 mAh/cm~2 at a current density of 1 mA/cm~2,the microstructure of the negative electrode of the magnetized battery is significantly flatter and denser than that of the unmagnetized battery negative electrode.Under the condition of magnetization,the cycle is stable for 140 h,and the polarization voltage is always smaller than that under the unmagnetized condition.The polarization voltage starts to increase sharply after 80 h of unmagnetized conditions,and the battery is completely ineffective after being cycled to 107 h.At a current density of 0.5 mA/cm~2,the battery was stabilized for 0.5 h at a cyclic capacity of 0.5 mAh/cm~2,and the polarization voltage began to rise after 250 h of battery cycling under unmagnetized conditions.The battery completely failed when cycled to 300 h. |
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