Contact between Garnet-Type Solid Electrolyte and Lithium Metal Anode: Influence on Charge Transfer Resistance and Short Circuit Prevention

Abstract

Interface structure between Li and garnet-type Li6.5La3Zr1.5Ta0.5O12 (LLZT) solid electrolyte was investigated by means of electrochemical impedance spectroscopy (EIS) on symmetric cells of Li | LLZT | Li. Charge transfer resistance (RCT) between Li and LLZT was investigated using LLZT pellets with various roughness. RCT and activation energy (Ea) obtained on the flat interface is as high as 746 Ω cm2 and 0.51 eV at 25°C, respectively, indicating that the charge transfer reaction at Li | LLZT (grit number: #8000) interface is a kinetically slow process, which may suppress rate capability of all solid-state batteries. Although the lowest RCT of 363 Ω cm2 was obtained by heating up to the melting point of Li for the LLZT pellet polished with an emery paper (#400), it is supposed that electrochemically effective contact area was saturated for rougher surfaces of LLZT. To prepare interfaces with large effective contact area, Li electrodes were deposited on a LLZT pellet by vacuum-evaporation, which exhibited further low RCT of 69 Ω cm2. The interface with large effective contact area is also a key to prevention of short circuit, and a high critical current density of 0.4 mA cm−2 was demonstrated.

Formation and Stability of Interface between Garnet-Type Ta-doped Li7La3Zr2O12 Solid Electrolyte and Lithium Metal Electrode

“…In both cells, Ohmic behavior was observed at low current densities followed by deviation from Ohmic behavior at high current densities. Similar behavior has been confirmed in the literature [33,34,[40][41][42][43][44][45][46]. Furthermore, the polarization was not symmetric against the current direction, which could have been caused by an irreversibility in Li deposition and dissolution reaction at each interface between LLZT and Li in a symmetric cell [43,46].…”

“…We believe that this could be achieved by reducing the interfacial charge-transfer resistance further and by structural improvement of the garnet-type SE by decreasing the porosity [34,47,48], controlling grain size [41,44], and modifying the grain boundary [45,50].…”

“…Together with further examination of the propagation mechanism of Li dendrite into garnet-type SE, both the critical current density at which the short circuit occurs and the threshold in the capacity for Li deposition for stable cycling must be enhanced further to realize a solid-state battery with a garnet-type oxide SE and Li metal anode. We believe that this could be achieved by reducing the interfacial charge-transfer resistance further and by structural improvement of the garnet-type SE by decreasing the porosity [34,47,48], controlling grain size [41,44], and modifying the grain boundary [45,50].…”

“…The use of Li metal with extremely large gravimetric specific capacity (3860 mAh g −1 ) with the lowest redox potential as an anode leads to the high energy density of a battery, but the formation of a solid-solid interface among garnet-type SE and Li metal electrodes is another challenging issue in achieving better electrochemical performance in solid-state batteries [32][33][34]. Many approaches have been introduced to reduce the interfacial charge-transfer resistance between garnet-type SE and Li, including the introduction of thin film layers of Au [35], Si [36], Ge [37], Al 2 O 3 [38], and ZnO [39], or eliminating the secondary phases, such as LiOH and Li 2 CO 3 , by polishing the surface of SE and using multiple thermal treatments at specific temperatures before and after contact with Li [40][41][42].…”

Review—Promises and Challenges of In Situ Transmission Electron Microscopy Electrochemical Techniques in the Studies of Lithium Ion Batteries

“…10,11 LIBs are widely used in present-day portable electronic gadgets such as mobile phones, laptops, tablet computers, and video camcorders, and the medical and aerospace industries for storing photovoltaic-generated dc electricity. 12,13 Although possessing many advantages and in high demand, radical progress of such devices like LIBs has not been attained as yet because of their intrinsic complexity. 14,15 There are many concurrent electrochemical, physical, and mechanical processes during their operation, 14,16 therefore, to enhance the overall properties of LIBs with high energy-density and long cycle-life, these aforementioned processes should operate in a predictable way across multiple environments.…”