Design principles for solid-state lithium superionic conductors

Abstract

Lithium solid electrolytes can potentially address two key limitations of the organic electrolytes used in today's lithium-ion batteries, namely, their flammability and limited electrochemical stability. However, achieving a Li(+) conductivity in the solid state comparable to existing liquid electrolytes (>1 mS cm(-1)) is particularly challenging. In this work, we reveal a fundamental relationship between anion packing and ionic transport in fast Li-conducting materials and expose the desirable structural attributes of good Li-ion conductors. We find that an underlying body-centred cubic-like anion framework, which allows direct Li hops between adjacent tetrahedral sites, is most desirable for achieving high ionic conductivity, and that indeed this anion arrangement is present in several known fast Li-conducting materials and other fast ion conductors. These findings provide important insight towards the understanding of ionic transport in Li-ion conductors and serve as design principles for future discovery and design of improved electrolytes for Li-ion batteries.

Vacancy‐Contained Tetragonal Na3SbS4 Superionic Conductor

“…It is notable that the sulphur sublattices (inset of middle panel to Figure 1b) demonstrate an intensely distorted cubic lattice. This anion framework may benefit Na + diffusion followed the mechanism similar to the bcc‐sublattice‐contained superionic conductors described in previous study 10. Different coordinations are observed for these two types of Na + , i.e., Na at Na1 and Na2 sites bound to six and eight sulphur atoms, respectively, as shown in the right panel to Figure 1b.…”

Li+ Ion Conductors with Adamantane‐Type Nitridophosphate Anions β‐Li10P4N10 and Li13P4N10X3 with X=Cl, Br

“…[24] Trends in knownL i + ion conductors show that a bcc anion framework allows the lowest activation barrier and highest ionic conductivity,b ecause it allows direct Li hops between tetrahedral sites. [30] However,i th as recently been shown in the case of the lithium argyrodites Li 6 PS 5 X (X = Cl, Br,I )t hat the prefactor and the activation energy of ionic conduction are closely linked, and that al ow activation energy alone may not be sufficient to achieve high ion conductivity. [31] In this contribution,w er eport ar e-investigation of cubic aLi 10 P 4 N 10 .B yl owering the synthesis temperature,w eh aves ucceeded in synthesizingt he new polymorph b-Li 10 P 4 N 10 ,a nd have elucidated the phase transition between the a-a nd bpolymorphs.…”

Computational studies of solid-state alkali conduction in rechargeable alkali-ion batteries

“…Many proposed design 'rules of thumb' for fast alkali conductivity, for example, 3D interstitial networks with bottlenecks of sufficient size, 23 the presence of alkali ion disorder, 24 having a polarizable anion framework, 25 body-centered cubic system close-packed anion frameworks, 26 and so on, are limited to specific chemistries or structure types and are not readily generalizable. There has also been limited success in identifying new frameworks that share these features.…”

“…Recently, Wang et al 26 made an interesting observation that both the LGPS and Li 7 P 3 S 11 superionic conductors, which currently have the highest known Li + conductivities of any crystal, possess a bodycentered cubic system-like sulfur framework. Using NEB calculations, Wang et al 26 showed that the direct transition between tetrahedral sites leads to the lowest activation barrier compared with other transitions in close-packed anion frameworks, such as hcp and fcc ( Figure 12).…”

“…Using NEB calculations, Wang et al 26 showed that the direct transition between tetrahedral sites leads to the lowest activation barrier compared with other transitions in close-packed anion frameworks, such as hcp and fcc ( Figure 12). Though this structural feature is rarely observed in known materials, it can serve as a design guideline in developing novel fast superionic conductors.…”