Interface‐Engineered All‐Solid‐State Li‐Ion Batteries Based on Garnet‐Type Fast Li⁺ Conductors

Abstract

with solid electrolytes. [ 3 ] Solid electrolytes offer many advantages and could enable the use of new high capacity electrode materials such as sulfur, [ 4 ] manganese, [5][6][7] and vanadate [ 8,9 ] -based cathodes which may not be stable and safe in the current Li-ion battery technology based on liquid electrolytes. [ 10 ] Furthermore, solid electrolytes have the promise to use directly metallic lithium anodes, i.e., preventing dendritic lithium growth, which enables even higher energy densities. From a practical point of view, one may also highlight that solid electrolytes have much-improved thermal operation windows resulting in a higher chemical and thermal stability, benefi ting the long-term operation and safety when compared to their liquid counterparts. This allows for safe packaging of the cell geometries and enables miniaturized cell architectures while simultaneously reducing the battery weight. [ 11,12 ] Among the oxide solid Li-ionic electrolytes, Li 7 La 3 Zr 2 O 12 (LLZO) garnets and their doped variants show one of the highest Li-ion conductivities in the range of ≈10 −4 S cm −1 at room temperature. [ 13 ] LLZO was fi rst synthesized and characterized in 2007 by Murugan et al. [ 14 ] Not until a few years later Geiger et al. [ 15 ] showed that LLZO appears in two different crystal structures, a cubic and a tetragonal one, with the cubic phase showing a Li-ion conductivity two orders of magnitude higher than the tetragonal phase. Using doping strategies, i.e., by introducing Al 3+ , Ga 3+ , Ta 5+ , Nb 5+ , etc., the high conductive cubic phase can be stabilized at room temperature by introducing vacancies into the Li sublattice of the structures. [16][17][18][19] One of the most commonly used dopants is Al 3+ , which stabilizes the cubic phase by substituting for three Li + , thereby creating two Li vacancies and resulting in the stoichiometry of Li 7−3 x Al x La 3 Zr 2 O 12 for the cubic phase.[ 20 ] Despite the promises, all-solid-state Li-ion batteries based on cubic LLZO solid electrolytes have still challenges in realizing high practical performances due to their high electrode-electrolyte interfacial resistances. For the investigations on all-solid-state batteries based on garnet-type cubic LLZO, most of the current research efforts are concentrated on the cathode material, most prominently on LiCoO 2 . [21][22][23][24][25][26][27] Reasonable electrochemical activities are so far only achieved by vacuum deposition of the cathode as thin fi lms, i.e., by pulsed laser deposition (PLD), because of the resulting good electrolyte-electrode contact. [ 25,26 ] Here, the exact chemical composition of the electrolyte-electrode interface also greatly determines the contact properties, the interfacial

Rechargeable Solid‐State Li–Air and Li–S Batteries: Materials, Construction, and Challenges

“…Figure 12 depicts the cross-sectional SEM images and Nyquist plots of classic electrode-electrolyte and porous electrolyte interfaces. [118] Figure 12a illustrates the classic electrode-electrolyte interface with an obvious dividing line that is similar to what we mentioned above, while the composite electrode in Figure 12b intimately embeds in the porous electrolyte surface with no clear boundary. Comparison of impedance results in Figure 12c demonstrates the lower cathode-solid electrolyte interface resistance of the surfaceengineered sample, indicating the promising availability of interface-engineered methods in SSLSB and SSLAB designs.…”

Toward garnet electrolyte–based Li metal batteries: An ultrathin, highly effective, artificial solid-state electrolyte/metallic Li interface

“…Recently, an interface-engineered all–solid-state battery was developed to adopt a porous garnet electrolyte structure to enhance Li-ion transfer at the electrode-electrolyte interface with improved capacities and cycling performance ( 51 ). We envision that garnet structure with interface engineering can be designed into interconnected ion and electron networks for Li-S and Li-O 2 batteries to host dissolved sulfur/polysulfides or active catalysts with high surface areas.…”

Hybrid Polymer/Garnet Electrolyte with a Small Interfacial Resistance for Lithium‐Ion Batteries

“…The all-solidstate ceramic batteries with garnet electrolyte usually have larger internal resistances and only work at small current densities; for example, one interface-engineered all-solidstate ceramic battery based on garnet electrolyte has a large resistance of 10 000 W and has a capacity of 20 Ah kg À1 at a current of 2 A kg À1 at 95 8C. [14] To demonstrate further the advantages of the LiF modification that decreases the interfacial resistance, Li-S cells with a LLZT and a LLZT-2LiF solid electrolyte were assembled. The solid electrolyte can efficiently block the polysulfide shuttle, which is a severe problem in Li-S batteries.…”