Combining Superionic Conduction and Favorable Decomposition Products in the Crystalline Lithium–Boron–Sulfur System: A New Mechanism for Stabilizing Solid Li-Ion Electrolytes

Abstract

We report a solid-state Li-ion electrolyte predicted to exhibit simultaneously fast ionic conductivity, wide electrochemical stability, low cost, and low mass density. We report exceptional density functional theory (DFT)-based room-temperature single-crystal ionic conductivity values for two phases within the crystalline lithium–boron–sulfur (Li–B–S) system: 62 (+9, −2) mS cm–1 in Li5B7S13 and 80 (−56, −41) mS cm–1 in Li9B19S33. We report significant ionic conductivity values for two additional phases: between 0.0056 and 0.16 mS/cm –1 in Li2B2S5 and between 0.0031 and 9.7 mS cm–1 in Li3BS3 depending on the room-temperature extrapolation scheme used. To our knowledge, our prediction gives Li9B19S33 and Li5B7S13 the second and third highest reported DFT-computed single-crystal ionic conductivities of any crystalline material. We compute the thermodynamic electrochemical stability window widths of these materials to be 0.50 V for Li5B7S13, 0.16 V for Li2B2S5, 0.45 V for Li3BS3, and 0.60 V for Li9B19S33. Individually, these materials exhibit similar or better ionic conductivity and electrochemical stability than the best-known sulfide-based solid-state Li-ion electrolyte materials, including Li10GeP2S12 (LGPS). However, we predict that electrolyte materials synthesized from a range of compositions in the Li–B–S system may exhibit even wider thermodynamic electrochemical stability windows of 0.63 V and possibly as high as 3 V or greater. The Li–B–S system also has a low elemental cost of approximately 0.05 USD/m2 per 10 μm thickness, which is significantly lower than that of germanium-containing LGPS, and a comparable mass density below 2 g/cm3. These fast-conducting phases were initially brought to our attention by a machine learning-based approach to screen over 12,000 solid electrolyte candidates, and the evidence provided here represents an inspiring success for this model.

Computational Design of Double-Layer Cathode Coatings in All-Solid-State Batteries

“…The first three have been previously suggested in the literature as interface coatings for solid-state batteries. 61,62 In experiments, improved cycling performance was observed in Li4SnS4 (isostructural to Li4GeS4)-coated LiCoO2 compared with pristine LiCoO2 in contact with the LGPS electrolyte. 63 The identified sulfide coating materials effectively extend the electrochemical stability window with respect to phosphorous oxidation (Figure 3a).…”

Accelerated Atomistic Modeling of Solid-State Battery Materials With Machine Learning

“…The ML-based model exhibits an F1 score of 0.50, which is 3.5 times better than random search, allowing for a screening on 12,831 Licontaining crystalline solids from the MP database. Following the recommendations of the ML model, the authors investigated 21 candidate SSEs with AIMD simulations (Figure 8B) (Sendek et al, 2019) and experiments (Figure 8C) (Sendek et al, 2020a). The crystalline lithium−boron−sulfur (Li−B−S) system appears to be more conductive and twice as stable as LGPS, and is at the same time less expensive.…”

Fast Li‐Ion Conductivity in Superadamantanoid Lithium Thioborate Halides

“…Lithium thioborates, a material class with similar properties to lithium thiophosphates, have been neglected in comparison, despite having shown great promise [5] . This phase space has been revived recently with computational studies on lithium thioborate materials pointing to extremely fast ion conductivities and improved electrochemical stability over lithium thiophosphate materials [6] . Seminal work on thioborates during the 1980s‐1990s focused on Li 2 S‐B 2 S 3 and Li 2 S‐B 2 S 3 ‐LiI fast‐ion conducting glasses, [7] which we have expanded on recently by exploring a quaternary Li 2 S‐B 2 S 3 ‐LiI‐SiO 2 system [8] .…”

“…[5] This phase space has been revived recently with computational studies on lithium thioborate materials pointing to extremely fast ion conductivities and improved electrochemical stability over lithium thiophosphate materials. [6] Seminal work on thioborates during the 1980s-1990s focused on Li 2 S-B 2 S 3 and Li 2 S-B 2 S 3 -LiI fast-ion conducting glasses, [7] which we have expanded on recently by exploring a quaternary Li 2 S-B 2 S 3 -LiI-SiO 2 system. [8] Concomitant with the glasses, Li 2 S-B 2 S 3 crystalline analogues were discovered by Krebs et al [9] One such thioborate is Li 6+2x [B 10 S 18 ]S x (x % 2), [10] which exhibits a thio-borate network composed of supertetrahedral clusters (also referred to as superadamantanoid) B 10 S 20 structural units.…”