Lithium Metalanode In Secondary Lithium Metal Batteries

Lithium?Li?metal is an ideal anode material for rechargeable Li batteries due to its extremely high theoretical specific capacity(3860 mAh g^-1)and the loweest negative electrochemical potential?-3.040 V vs standard hydrogen electrode?.However,lithium metal as an anode has two problems mainly:On the one hand,the very high chemical and electrochemical reactivity of Li metal results in the corrosion of Li metal by electrolyte and hence low utilization of Li metal anode and electrolyte,hence sharply reducing Coulombic efficiency and cycling lifespan.On the other hand,inhomogeneous deposition and dissolution during each plating/stripping process leads to the generation and growth of lithium dendrites,brings security risks.Considering these two problems,therefore,two strong protective layer coating lithium,and a novel electrode design by homogenizing the distribution of Li⁺on the electrode surface were presented to inhibit the growth of lithium dendrites and reduce the reactivity of lithium and electrolyte.The main research contents and results are as follows:?1?By constructing ex-situ artificial SEI layer(PVDF-HFP and PVDF-HFP-LLZO(Li₇La₃Zr₂O₁₂)),the growth of lithium dendrites are suppressed and the cycling stability of metallic lithium are improved,all those contribute to the both physical mechanical and ionic conductivity.The two modified layers have good performance in both ether electrolytes and ester electrolytes.The electrochemical properties of the PVDF-HFP-LLZO modified layer are better.For non-Li electeode-Cu,Li/Cu cells that modified by PVDF-HFP-LLZO have a stable cycle that more than 200 cycles at 0.5 mA cm^-2,1 mAh cm^-2,which is far higher than the cells with pure lithium anode?150 cycles?.In the symmetrical battery,the blank lithium symmetrical battery can only cycle for 360 h stably,while the modified lithium are more than 500 h.The PVDF-HFP in the artificial SEI layer contributes to the elasticity of the SEI,and adapt to the volume change of electrode which due to the deposition process of lithium.Meanwhile the protection layer also prevents the direct contact between fresh lithium and electrolyte,and reduces side reactions with electrolyte effectively.LLZO increases the mechanical strength and Li⁺conductivity of artificial layers.This method would make Li and non-Li anodes a more applicable candidates for advanced lithium batteries.?2?A facile and effective method is applied to pre-passivate lithium anode,which is approached by simply reaction with CF_x,developing a uniform and porous LiF layer on Li metal anodes.The electrochemical data reveal an effect extension of the cycle life of lithium anode after the construction of such LiF layer on the surface.Li/Li₄Ti₅O₁₂?LTO?cell with modified lithium anode shows capacity retention of 93.3%after 1000 cycles at2C,which is far higher than the cells with pure lithium anode?56.8%?.What's more,enhanced cycling stability without overpotential augment for over 300 cycles were proven in symmetric cells of the modified lithium anodes.?3?An artificial protective layer-Mg film formed on the surface of lithium?M-Li?which through the in-suit electrodeposition.This excellent protective layer contributes homogenneous lithium plating/stripping and a low overpotential?15 mV?after 500 h.And the M-Li/LTO cells has a high capacity retention of 86.70%after 1000 cycles in ester electrolytes at a constant charge/discharge rate of 2C.The magnesium metal film can improve the stability of the metal lithium by reducing the active site of the metal lithium,and reduce the occurrence of side reaction between the metal lithium and the electrolyte.The heterogeneous film is also suitable for the whole battery and exhibits excellent electrochemical performance.