High Safety Lithium Metal Batery System And Microscopic Mechanism Research On Lithium Dendrite Growth

Among the existing battery systems,lithium ion batteries(LIBs)have been comprehensively studied.Although the energy density of LIBs is higher than those of lead-acid batteries and nickel-metal hydride batteries,the customers' demand for higher energy density still can not be satisfied.The high specific capacity of lithium metal(3860 mAh g-1)and low reduction potential(-3.04 V vs.SHE)make it one of the most promising anode materials,thus many researchers start to focus on lithium metal batteries.However,there are many problems with lithium metal anodes,such as non-uniform lithium deposition,relative infinity volume expansion,lithium dendrites induced short circuit,etc.,which have hindered the practical application of rechargeable lithium metal batteries in the past 40 years.Based on this background,this thesis presents a simple,effective and cost-effective method to promote uniform lithium deposition and reduce the volumetric expansion of lithium metal anodes through a 3D porous copper mesh current collector/lithium metal composite anode.The high specific surface area of the composite electrode facilitates the electrochemical reaction kinetics,reduces the local current density of the negative electrode,and inhibits the growth of lithium dendrites.At the same time,the porous structure of the composite electrode also provides a "cage" for the redeposited lithium,which can relieve the volume expansion of the lithium anode during cycling.In electrochemical characterization,the coulombic efficiency of this composite electrode was 93.8%after 100 cycles,whereas for ordinary lithium negative electrode only 30.9%after 70 cycles.It exhibits a stable long cycle life of at least 1280 hours at 0.5 mA cm-2 and a small electrochemical impedance(only 29 ? cm2 after 1 cycle vs.136 ? cm2 vs.conventional lithium negative).This composite anode is also successfully used in the Li/Li4Ti5O12 battery.In addition,this thesis proposes to use pulse current charging instead of constant current charging to stabilize the lithium metal anode.The results based on all-atom molecular dynamics simulations show that the migration and diffusion of Li+ and potential ion concentration gradients in the electrolyte play a key role in reducing dendrite formation and promoting stable cell cycling.The best ratio of Ton/Toff can lead to the highest diffusion coefficient of Li+,and the weak correlation between Li ion and counter ion is better.The results of electrochemical cycling also show that pulsed current can improve the deposition of lithium ions on the electrode surface,reduce the possibility of lithium dendrite growth and the volume expansion of Li electrode,and finally extend the life of lithium metal batteries.