Study On Anode Protection Of Lithium Metal Battery Based On Electrolyte Addtives Strategy

In today’s society,the energy crisis is becoming more and more serious.The development of new energy and efficient energy storage devices is imminent.Although the current Li-ion battery(LIB)is the best in the current energy storage devices,there is a serious shortage of specific capacity when facing the urgent demand of large-scale equipment system.Rechargeable Li-metal battery(LMB)using lithium metal as anode material has a high theoretical specific capacity and energy density,thus it shows the promise to be developed into the next generation of rechargeable battery.However,during the normal electrochemical cycles,the growth of lithium dendrites of Li metal has been hindering the development of lithium metal batteries,which leads to the worse performance and great safety hazards.In order to overcome this difficult problem,an effective and practical strategy of lithium-metal anodes protection based on electrolyte additive is proposed to suppress the lithium dendrites during charge and discharge processes,thus enables the lithium metal battery highly reversible with a much improved overall electrochemical performance.Therefore,to solve the problem of dendrites growth and performance decay in LMB,in this work,a variety of suitable materials as electrolyte additives were proposed to study the electrochemical properties of electrode surface under the influence of different additives.Different electrode reaction mechanisms were revealed by XRD(X-Ray Diffraction),SEM(Scanning Electron Microscopy),EDX(Energy Dispersive X-Ray Spectroscopy),EIS(Electrochemical Impedance Spectroscopy),CV(Cycle Voltammetry)and XPS(X-Ray Photoelectron Spectroscopy).The main research contents and results include:(1)By adding Magnesium(II)Bis(trifluoromethanesulfonyl)imide(Mg(TFSI)2)as electrolyte additive,the effects of different molar concentrations on the performance of LMB have been first studied.Dissoluble Mg(TFSI)2 is employed as a degradable electrolyte additive,leading to in-situ plating of porous Mg network when contacting with reductive Li atoms.Mg adatoms with extremely low diffusion energy barrier as lithiophilic sites enable a smooth or flaky morphology of Li surface even under a high current density of 2 mA/cm2 and high capacity of 6 mAh/cm2.Mg salt additive significantly extends the cycling life of Li||Cu asymmetric cells up to 240 and 200 cycles for carbonate and ether electrolytes respectively.Under a current density as high as 5 mA/cm2,the Li||Cu cell based on ether system can still survive up to 140 cycles with a small voltage hysteresis close to 60 mV.The hysteresis can be reduced to below 25 mV for lasting 200 cycles at 1 mA/cm2.In brief,this additive strategy provides a facile solution to in-situ construction of conductive anode-electrolyte interface with low interface resistance for alleviating uneven Li nucleation.(2)Several kinds of Metal-Organic Framework(MOF)materials were synthesized and used as electrolyte additives to explore the effects of different mass fraction(wt%)concentration or different current density on the performance of LMB in the traditional carbonate electrolyte system.It has been found in experiments that,under 0.5 mA/cm2,the lifespan of Li||Li symmetric cell can achieve above 1400 h,and Li||Cu asymmetric cells can last more than 200 cycles.Through kinds of subsequent characterization tests,it is found that the low nucleation overpotential and significantly-reduced interfacial resistance contribute to the Li ions transport.Besides,corresponding increase of LiF component in SEI layer and the porous interfacial layer of the electrode play an important role in reducing the side reaction at the electrode,reducing the actual current density and promoting the smoothness of Li deposition.Thus,the inhibition of dendrite growth was realized.