3D Asymmetric Bilayer Garnet-Hybridized High-Energy-Density Lithium–Sulfur Batteries

Abstract

Lithium garnet Li 7 La 3 Zr 2 O 12 (LLZO), with high ionic conductivity and chemical stability against a Li metal anode, is considered one of the most promising solid electrolytes for lithium−sulfur batteries. However, an infinite charge time resulting in low capacity has been observed in Li−S cells using Ta-doped LLZO (Ta-LLZO) as a solid electrolyte. It was observed that this cell failure is correlated with lanthanum segregation to the surface of Ta-LLZO that reacts with a sulfur cathode. We demonstrated this correlation by using lanthanum excess and lanthanum deficient Ta-LLZO as the solid electrolyte in Li−S cells. To resolve this challenge, we physically separated the sulfur cathode and LLZO using a poly(ethylene oxide) (PEO)-based buffer interlayer. With a thin bilayer of LLZO and the stabilized sulfur cathode/LLZO interface, the hybridized Li−S batteries achieved a high initial discharge capacity of 1307 mA h/g corresponding to an energy density of 639 W h/L and 134 W h/kg under a high current density of 0.2 mA/cm 2 at room temperature without any indication of a polysulfide shuttle. By simply reducing the LLZO dense layer thickness to 10 μm as we have demonstrated before, a significantly higher energy density of 1308 W h/L and 257 W h/kg is achievable. X-ray diffraction and X-ray photoelectron spectroscopy indicate that the PEO-based interlayer, which physically separates the sulfur cathode and LLZO, is both chemically and electrochemically stable with LLZO. In addition, the PEO-based interlayer can adapt to the stress/strain associated with sulfur volume expansion during lithiation.

High Sulfur Loading and Capacity Retention in Bilayer Garnet Sulfurized‐Polyacrylonitrile/Lithium‐Metal Batteries with Gel Polymer Electrolytes

“…Moreover, by simply reducing the dense layer thickness to our previously demonstrated 10 µ m , [ 22 ] we can project an energy density of 296 Wh kg −1 (924 Wh L −1 ), as indicated in Figure 3c,d. The energy density calculation approach was the same as our previous results [ 24 ] and can be found in Table S2 (Supporting Information). A comparison of our work with state‐of‐the‐art results for garnet Li–S cells is shown in Table S3 (Supporting Information).…”

“…[ 39,40 ] The amount of LiF increased for the 3 m GPE (Figure 4d) to nearly double the amount in 1 m GPE (Figure 4c). A peak ≈688.3 eV is attributed to decomposed FSI [ 24 ] and a peak ≈689.4 eV is attributed to fluorinated carbons. [ 39,40 ] The amount of fluorinated carbon in F 1s is significantly higher in 3 m GPE than in 1 m GPE, which is consistent with the results from C 1s spectra.…”

“…This finding suggests the DOL was only partially polymerized in the 1 m GPE. Accordingly, we infer that the incompletely polymerized 1 m GPE still has liquid‐like behavior, which allowed the sulfur cathode to come into direct contact with the Ta‐LLZO surface and react with a lanthanum‐segregated secondary phase, [ 24 ] eventually resulting in cell degradation.…”

“…[ 19 ] The porous layer can accommodate the volume change of the Li metal side during cell cycling [ 22 ] and can also withstand high Li penetration stress and high current density. [ 23 ] On the sulfur cathode side, studies have indicated that the sulfur cathode/Ta‐doped LLZO (Ta‐LLZO) interface can be unstable, with the sulfur reacting with La‐segregation phases at the Ta‐LLZO surface [ 24 ] and significant (≈80%) volume expansion during discharge [ 25,26 ] that applies significant stress/strain to the sulfur cathode/Ta‐LLZO interface, potentially resulting in crack formation in the solid ceramic phase.…”

All-Solid-State Garnet Type Sulfurized Polyacrylonitrile/Lithium-Metal Battery Enabled by an Inorganic Lithium Conductive Salt and a Bilayer Electrolyte Architecture

“…To date, development of garnet Li-S batteries has focused on use of flammable organic liquid, gel, and polymer catholytes to achieve stable cycling. ,,,− For example our group has demonstrated stable hybridized garnet Li-S cells with ether-based liquid catholytes to provide good sulfur-cathode/LLZO interfacial contact in porous garnet trilayer (porous/dense/porous) LLZO architectures. , More recently using a bilayer (dense/porous) LLZO architecture, Shi et al demonstrated a high initial discharge capacity of 1307 mAh/g at 22 °C by using a poly­(ethylene oxide)-based interlayer on the cathode side and an ether-based catholyte. A gel polymer catholyte was later introduced to further stabilize the cell cycling performance at 22 °C, achieving 80% capacity retention over 265 cycles using sulfur in the form of sulfurized polyacrylonitrile (SPAN) . With these novel trilayer and bilayer LLZO architectures, applied pressure is not necessary for cell operation.…”