Li7La3Zr2O12 Interface Modification for Li Dendrite Prevention

The development of electrochemical energy storage devices is toward to higher energy density as well as safety. The use of metallic Li as anode for rechargeable batteries could increase as much as tenfold in the anode storage capacity when compared to nowadays carbon based anode due to its lowest native electrochemical potential ( -3.4 V vs. H2), extremely high specific capacity (3860 mA h/g) and low density (0.59 g/cm3). However, the use of metallic Li in a rechargeable battery is not successful until now due to the difficulty of suppressing the growth of Li dendrite which could cause hazard of a battery. Theoretical calculations suggest that if a shear modulus of used electrolyte is more than twice that of metallic Li, ~109 Pa, or a Li-ion transfer number tLi+ approaching 1, then the dendrite growth can be suppressed. Therefore, the garnet structured Li7La3Zr2O12 (LLZ) solid state Li-ion conductor is an ideal material for using as electrolyte in rechargeable batteries because of its unity ionic transfer number, high mechanical strength and chemical stability to metallic Li.However, Li dendrite formation was reported by Ishiguro et al [1,2] for their Nb- and Ta-substituted LLZ with unclear reason. In this research, samples which are Al-contaminated and Al-free Ta-substituted LLZ were fabricated by hot pressing as well as regular sintered process. Both samples fabricated by hot press synthesis have relative densities >99% and total conductivities ~1 mS/cm at room temperature. During the dendrite studies, impedance measurements show rapid decrease in total resistances within a couple of hundred seconds which indicates the dendrite can be formed in such a highly dense ceramic in a short time as well as in regular sintered samples. Solid-State NMR demonstrates the presence of metallic Li inside the dense pellet which is also supported by TEM-EELS result [3]. The dendrite test results, reasons for the formation of the Li-dendrite and pathways to prevent the formation of Li-dendrite by interface modification will be discussed in this presentation