Innovative Approaches to Li-Argyrodite Solid Electrolytes for All-Solid-State Lithium Batteries

Abstract

Metrics & MoreArticle Recommendations CONSPECTUS: As the world transitions away from fossil energy to green and renewable energy, electrochemical energy storage increasingly becomes a vital component of the mix to conduct this transition.The central goal in developing next-generation batteries is to maximize the gravimetric and volumetric energy density and battery cycle life and improve safety. All solid-state batteries using a solid electrolyte and a lithium metal anode represent one of the most promising technologies that can achieve this goal. Highly conductive solid electrolytes (>10 mS•cm −1 ) are the key component to remove the safety concerns inherent with flammable organic liquid electrolytes and achieve high energy density by enabling high active material loading. Considering a range of inorganic solid electrolytes that have been developed to date, sulfide solid electrolytes exhibit the highest ionic conductivities, which even surpass those of conventional organic liquid electrolytes. Argyrodite-structured sulfide solid electrolytes are among the most promising materials in this class and are currently the dominantly used solid electrolytes for all-solid-state battery fabrication. Argyrodite solid electrolytes are particularly appealing because of their ultrahigh Li-ion conductivity, quasi-stable solid−electrolyte interphase (SEI) formed with Li metal, and ability to be prepared via scalable solution-assisted synthesis approaches. These factors are all vital for commercial applications.In this Account, we afford an overview of our recent development of several argyrodite superionic conductors, including Li 6.6 Si 0.6 Sb 0.5 S 5 I (24 mS•cm −1 ), Li 6.6 Ge 0.6 P 0.4 S 5 I (18 mS•cm −1 ), and Li 5.5 PS 4.5 Cl 1.5 (12 mS•cm −1 ), and a comprehensive understanding of the origin of the underlying high conductivity, namely, sulfide/halide anion site disorder and Li cation site disorder. A high degree of sulfide/halide anion site disorder (changes in anion distribution) modifies the anionic charge, which in turn strongly influences the lithium distribution. A more inhomogeneous charge distribution in anion-disordered systems generates a spatially diffuse and delocalized lithium density, resulting in faster ionic transport. Lithium cation site disorder generated by increasing Li carrier concentration through aliovalent substitution creates high-energy interstitial sites for Li ion diffusion, which activate concerted ion migration and flatten the energy landscape for Li ion diffusion. This enables high conductivity in Li-rich argyrodite superionic conductors. These concepts are also expected to promote the design of rational new solid electrolytes and fundamental understanding of the structure−ion transport relationships in inorganic ionic conductors.Collectively, a comprehensive and deep understanding of the interphase formation between argyrodite solid electrolytes and cathode active materials/Li metal and the failure mechanism of all-solid-state batteries with argyrodite solid electrolytes will lead to the bo...

Fuzzy logic: about the origins of fast ion dynamics in crystalline solids

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Figure 2 Selected classes of materials and corresponding examples of solid electrolytes with ion conductivities ranging from very poor values to values in the regime, adapted from [ 1 ]. This short overview does raise no claim to completeness as, especially in recent years, further materials were characterized such as ( ; ) [ 6 – 12 ] and variants of the Li-containing argyrodites [ 13 ]. (Online version in colour.)

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Cation Disorder and Large Tetragonal Supercell Ordering in the Li-Rich Argyrodite Li7Zn0.5SiS6

“… 1 The degree of structural disorder, which can be controlled through cationic or anionic substitution, determines the properties of argyrodite materials, so reliable characterization of such crystal structures is critical to expanding our knowledge of these systems. 5 The crystal structures of argyrodites such as Li 6 PS 5 X (X = Cl, Br) have tetrahedral close packed topologies related to that of the Laves phases (e.g., MgCu 2 ) with high symmetry aristotype argyrodite polymorphs adopting cubic F 3 m symmetry. 1 Recently, we demonstrated that the argyrodite structure can also be considered equivalent to that of antiperovskite through anion and vacancy ordering within a cubic stacking of two close-packed layers that enabled the discovery of a hexagonal argyrodite Li 6 SiO 4 Cl 2 .…”

Controlling Defects to Achieve Reproducibly High Ionic Conductivity in Na3SbS4 Solid Electrolyte

“…2,3 Chemically and electrochemically stable lithium-ion conducting oxides (e.g., lithium garnets, [4][5][6] Li-NASICONs, 7,8 and perovskites 9 ) often form a stable interface with the active materials. More polarizable, ion-conducting sulfides (e.g., Liargyrodites, [10][11][12][13] thio-LISICONs, [14][15][16] , and LGPS family [17][18][19][20] ) tend to exhibit faster ion transport despite their limited electrochemical stability window. 21,22 New classes of materials, e.g., halides and complex borates, [23][24][25][26] have also emerged as promising solid electrolytes, and the list of candidate materials continues to grow.…”