| Solid-state lithium metal batteries?SSLBs?exhibit superior advantage than traditional lithium ion batteries with liquid electrolytes due to higher energy density,better safety,and excellent thermal stability,and solid-state electrolytes?SSEs?play the vital role in SSLBs.Among the huge group of SSEs,inorganic oxide SSEs show higher mechanical strength and better thermal stability and draw numerous attentions in the past decades.Garnet-type Li7La3Zr2O12?LLZO?with high ionic conductivity and extraordinary stability against metallic Li surpasses other competitors and becomes the most promising candidate in the lasting competition.However,LLZO suffers from limited contact with Li due to the passivation layer at the surface when exposed to air.The huge gap between Li and LLZO cut off the Li+transfer paths,leading to disappointing interfacial impedance.Moreover,the limited interfacial contact arouses inhomogeneous Li+plating/striping during the electrochemical test and accelerates lithium dendrites growth alongside grain boundaries,causing dramatic capacity failure and safety issue.Thus,proper solutions that can release the serious interfacial problem between Li and LLZO are of great importance to realize the practical application of garnet-type SSLBs.Herein,we propose several facile and effective methods to modify the Li/LLZO interface.?1?By introducing an electronic conductive Li-Na eutectic alloy layer,Li forms intimacy contact with LLZO.The interfacial impedances decrease to 54.01?·cm2 and18.98?·cm2at room temperature and 60?,respectively.Driven by the Na+concentration difference inside the anode phase,solid-solid convection occurs between Li and Na domains during the electrochemical measurement.Thus,eutectic alloy layer maintains texture and stick to LLZO surface firmly,leading to high stability and durability.The Li-Na/LLZTO/Na-Li symmetric cells cycles steadily for over 3500hours and 3000 hours at 60?with the current densities of 50?A·cm-2and 100?A·cm-2,respectively and exhibit high critical current density up to 1.1 m A·cm-2 at room temperature.Li-Na/LLZTO/Li Fe PO4 all-solid-state batteries deliver good cycling and rate performance with an initial discharge capacity of 148.3 m Ah·g-1 at 100?A·cm-2and 116.0 m Ah·g-1 when the current density increased to 400?A·cm-2.Moreover,the Li-Na/LLZTO/Fe F3full cells display excellent electrochemical performance with an initial capacity up to 377.6 m Ah·g-1 at 200?A·cm-2 and still maintains over 200 m Ah·g-1 after 100 cycles.?2?Candle soot contains carbonaceous particles as the product of incomplete combustion of candles.When annealed in the candle flame,the Li2CO3 layer covered on the LLZO surface can be reduced by candle soot with the assistant of high temperature caused by candle combustion.Afterwards,an ultrathin candle soot layer deposits on bare LLZO surface,which can be lithiated when reacts with molten Li,and switches the garnet surface from lithiophobic to lithiophilic.The lithiated candle soot layer shows dual conductivities contributing to the Li C6 domain and tunes the electrons and Li+distribution during the electrochemical test,leading to small interfacial resistance and homogeneous Li+plating/striping.The results reveal the interfacial resistance reduces to 50.04?·cm2 at 60?and the symmetric cell cycles steadily for400 hours at the current density of 200?A·cm-2.The Li-Na/LLZTO/Fe F3full cells show enhanced cycling and rate performance with an initial capacity up to 366.4 m Ah·g-1 at200?A·cm-2 and still up to 201.0 m Ah·g-1 after 700 cycles.?3?A uniform mixed conductive layer?LTO?yield on the LLZO surface when co-sintering Li2Ti O3 precursor with LLZO pellet.The LTO layer contains Li2Ti O3 and Ti O2,Li2Ti O3 exhibit high instinct ion conductivity due to its abundant inner Li+pathways and Ti O2 with higher activity can be endowed with electronic conductivity when reacts with Li.The improved interfacial contact between Li and LLZO leads to reduced interfacial impedance and enhanced electrochemical performance.The area specific resistances of the Li/LTO-LLZO interface are only 11.78?·cm2 and 7.18?·cm2 at room temperature and 60?,respectively.The Li/LTO-LLZTO/Li symmetric cells cycle steadily for over 1600 hours with a small overpotential of 18.0 m V at 100?A·cm-2 and 1500 hours with the overpotential of 30.1 m V at 200?A·cm-2.?4?Prussian blue?PB?with metal organic framework structure can be converted to Li+conductor when substitutes Na+with Li+and exhibits electronic/ionic conductivity due to the electronic conductive?C?N framework.Herein,we introduced a thin PB interfacial layer between Li and LLZO and treated the sandwich-like structure at 230?to substitute Na+with Li+.Afterwards,the Li/PB-LLZO interfacial resistance reduces to 26.15?·cm2 at 60?and the modified Li/PB-LLZTO/Li symmetric cell cycles steadily for more than 750 hours with the current density of 100?A·cm-2.Moreover,the Li/PB-LLZTO/Li Fe PO4 all-solid-state cells deliver an initial capacity up to 171.1 m Ah·g-1 with a small overpotential of 0.086 m V at 100?A·cm-2 and a specific capacity of 135.9 m Ah·g-1 at 400?A·cm-2.?5?Amorphous Fe S2 with porous network was synthesized via a solvent-thermal method.As a typical conversion-type electrode material,Fe S2 convers to Li2S and Fe after being fully lithiated,and Li2S shows high Li+conductivity while Fe forms inner conductive network.When coated on LLZO surface,Fe S2 establishes tight contact with LLZO and acts as a binder that connects Li with LLZO.It is noteworthy that molten Li diffuses into the pores in Fe S2 network which further enhances the interfacial contact.The Li2S/Fe-Li interphase significantly reduces the interfacial impedance to 15.20?·cm2 at 60?and the ionic conductivity of the lithiated Fe S2 is 6.724*10-6 S·cm-1.With the assistant of the dual conductive interphase,the symmetric cell cycles steadily for over 400 hours with an overpotential of 25 m V at 400?A·cm-2.When the current density increases to 600?A·cm-2,the overpotential remains less than 50 m V. |
PDF Full Text Request