Lithium Ytterbium-Based Halide Solid Electrolytes for High Voltage All-Solid-State Batteries

Abstract

All-solid-state Li-ion batteries that utilize nonflammable solid electrolytes are considered potential candidates for sustainable energy storage systems. Although sulfide solid electrolytes have been widely explored, their lack of electrochemical stability above 2.7 V requires the application of protective coating layer on 4 V-class cathode materials, whereas the superior oxidative stability of chloride solid electrolytes enables their direct use with such high voltage cathodes. Here, we report a metastable trigonal phase of Li3YbCl6 with an ionic conductivity of 1.0 × 10–4 S·cm–1 and mixed-metal halide solid electrolytes, Li3–x Yb1–x Zr x Cl6, with conductivities up to 1.1 mS·cm–1 at room temperature. Combined neutron, single-crystal, and powder X-ray diffraction methods reveal that Zr-substitution for Yb in Li3YbCl6 triggers a trigonal-to-orthorhombic phase transition and forms new, lower energy pathways for Li-ion migration. All-solid-state cell cycling with uncoated >4 V-class cathodes is enabled by the high electrochemical oxidation stability of the mixed-metal halide solid electrolyte.

Perspectives on Improving the Safety and Sustainability of High Voltage Lithium‐Ion Batteries Through the Electrolyte and Separator Region

“…On the other hand, thermodynamic calculations of HSEs for stable HV materials suggest the electronegativity difference between M and X (Li 3 MX 6 ) affect the structural properties and stability of these materials. [ 323 ] This study [ 324 ] also found that chlorides have the highest oxidation potential (≈4.3 V vs Li/Li + ), larger bandgap, and higher elastic moduli, making them suitable HSEs for HV cathodes. Along with high ionic conductivity, the excellent electrochemical stability of HSEs in a 2.8–4.3 V window suggests the feasibility of 4 V‐class cathode materials, without any additional coatings for SSBs.…”

“…c,d) Charge/discharge profiles for SSBs consist of cathode materials NMC 622 and Li 6.7 Si 0.7 Sb 0.3 I 5 S separator, Li-In alloy as an anode, the initial two cycles at 0.2 C rate and Coulombic efficiency, discharge capacity, and the number of cycles. Reproduced with permission [324]. Copyright 2021, American Chemical Society.…”

Highly Stable Halide‐Electrolyte‐Based All‐Solid‐State Li–Se Batteries

“…Recently, halide-based SSEs have gained continuous research interest due to their high ionic conductivity, feasible synthesis methods, and wide electrochemical windows. By optimizing the synthesis method (Li 3 YCl 6 , [17] Li 3 InCl 6 , [18] Li 2 ZrCl 6 [19] ), tuning the composition or structure (Li 3 ScCl 6 , [20,21] Zr doped Li 3 MCl 6 [M = Y, Er], [22] Li 2.25 Zr 0.75 Fe 0.25 Cl 6 , [23] Li 2.6 Yb 0.6 Hf 0.4 Cl 6 , [24] and Li 2.7 Yb 0.7 Zr 0.3 Cl 6 [25] ), and reducing the grain boundary resistance (Li 3 Y(Br 3 Cl 3 )), the room-temperature conductivity of halide SSEs can be as high as 7.2 × 10 −3 S cm −1 until now. [26] Halide SSEs can even be synthesized by a facile wet-chemistry method using water as a solvent.…”

“…Until now, all the solid-state batteries in the halide SSEs system are still focused on traditional oxide cathodes. [17,19,25,31,32] While there have been predictions that halide SSEs can be used to explore the reversible storage of Li + into new compounds other than oxide cathodes.…”

A Series of Ternary Metal Chloride Superionic Conductors for High‐Performance All‐Solid‐State Lithium Batteries

“…Recently, due to the development of superionic conductor such as Li 3 YCl 6 [14] and Li 3 InCl 6 , [19,20] metal halide SSEs have received renewed attention. [21][22][23][24][25][26][27][28][29][30][31][32][33][34] Until now, only a few metal chloride SSEs have achieved high room-temperature (RT) ionic conductivities over 10 −3 S cm −1 , including Li 3 InCl 6 , [19,20] Zr-doped Li 3 MCl 6 (M = Y, Er, Yb, In), [21,26,27,33] Li 3 Y 1−x In x Cl 6 , [22] Li x Sc Cl 3+x , [23] Li 2 Sc 2/3 Cl 4 , [24] etc. In the search for new metal chloride SSEs, a better understanding of the relationship between structure and ionic conductivity is highly demanded.…”