All-solid-state batteries are a candidate for next-generation energy-storage devices due to potential improvements in energy density and safety compared to current battery technologies. Due to their high ionic conductivity and potential scalability through slurry processing routes, sulfide solid-state electrolytes are promising to replace traditional liquid electrolytes and enable All-solid-state batteries, but stability of cathode-sulfide solid-state electrolytes interfaces requires further improvement. Herein we review common issues encountered at cathode-sulfide SE interfaces and strategies to alleviate these issues.
Solvent-mediated routes have emerged as an effective, scalable, and low-temperature method to fabricate sulfide-based solid-state electrolytes. However, tuning the synthesis conditions to optimize the electrolyte's morphology, structure, and electrochemical properties is still underexplored. Here, we report a new class of composite solid electrolytes (SEs) containing amorphous Li3PS4 synthesized in situ with a poly(ethylene oxide) (PEO) binder using a one-pot, solvent-mediated route. The solvent and thermal processing conditions have a dramatic impact on the Li3PS4 structure. Conducting the synthesis in tetrahydrofuran resulted in crystalline β-Li3PS4 whereas acetonitrile led to amorphous Li3PS4. Annealing at 140 °C increased the Li+ conductivity of an amorphous composite (Li3PS4 + 1 wt % PEO) by 3 orders of magnitude (e.g., from 4.5 × 10–9 to 8.4 × 10–6 S/cm at room temperature) because of: (i) removal of coordinated solvent and (ii) rearrangement of the polyanionic network to form P2S74– and PS43– moieties. The PEO content in these composites should be limited to 1–5 wt % to ensure reasonable Li+ conductivity (e.g., up to 1.1 × 10–4 S/cm at 80 °C) while providing enough binder to facilitate scalable processing. The results of this study highlight a new strategy to suppress crystallization in sulfide-based SEs,, which has important implications for solid-state batteries.
Lithium halide-based solid electrolytes have high Li + conductivity and are mostly synthesized through mechanochemical methods.[1] However, Li 3 InCl 6 can be readily synthesized through low-temperature aqueous solution routes by mere dehydration, presumably due to stable InCl 6 3- complexation. [2-4] Replacing In for Y results in partial hydrolysis to form YOCl during dehydration because H 2 O coordinates more strongly to Y 3+ cations. We provide insight into the reaction mechanisms involved in synthesizing halide solid electrolytes, highlighting the importance of synthetic and processing conditions to optimize their performance in all-solid-state batteries. We will describe the synthesis process of Li 3 YCl 6 using three different methods and the evolution thereof using in situ neutron diffraction. Our results show that aqueous-based synthesis requires the formation of an ammonium halide complex intermediate. We found that the synthesis method affects changes in local structure within the lattice, which then affect ionic transport and Li + diffusivity, as determined through diffusion NMR measurements. We ascribe these changes to the correlative transport of Li + . Synthesis affects particle morphology at the macroscale and relates to cycle life when used in a full cell. This project was supported by the Vehicle Technologies Office (VTO) under the Office of Energy Efficiency and Renewable Energy (EERE) as part of the Battery Materials Research (BMR) program. This research used resources at the Spallation Neutron Source, a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory. [1] Park, K.-H.; Kaup, K.; Assoud, A.; Zhang, Q.; Wu, X.; Nazar, L. F. High-Voltage Superionic Halide Solid Electrolytes for All-Solid-State Li-Ion Batteries. ACS Energy Lett. 2020, 5, 2, 533–539. [2] Li, X.; Liang, J.; Luo, J.; Norouzi Banis, M.; Wang, C.; Li, W.; Deng, S.; Yu, C.; Zhao, F.; Hu, Y.; Sham, T.-K.; Zhang, L.; Zhao, S.; Lu, S.; Huang, H.; Li, R.; Adair, K. R.; Sun, X. Air-Stable Li 3 InCl 6 Electrolyte with High Voltage Compatibility for All-Solid-State Batteries. Energy Environ. Sci. 2019, 12, 2665-2671. [3] Li, W.; Liang, J.; Li, M.; Adair, K. R.; Li, X.; Hu, Y.; Xiao, Q.; Feng, R.; Li, R.; Zhang, L.; Lu, S.; Huang, H.; Zhao, S.; Sham, T.-K.; Sun, X. Unraveling the Origin of Moisture Stability of Halide Solid- State Electrolytes by In Situ and Operando Synchrotron X-Ray Analytical Techniques. Chem. Mater. 2020,32, 16, 7019–7027. [4] Sacci, R.L.; Bennett, T.H.; Drews, A.R.; Anandan, V.; Kirkham, M.J.; Daemen, L.L.; Nanda, K. Phase evolution during lithium indium halide superionic conductor dehydration. J. Mater. Chem. A , 2021,9, 990-996.
Potential use of lithium metal anode is a primary factor behind the high-energy density promise of solid-state batteries. However, large anodic loads lead to void formation and contact loss at the lithium/solid electrolyte interface which, in turn, lead to much higher effective local current densities during the subsequent lithium plating, causing dendrite formation and cell shorting. 1, 2 This is due to the slow self-diffusion of Li atoms/vacancies, which is an inherent limitation of lithium metal. 3 Modifying the bulk physiochemical properties of lithium metal via doping/alloying (<10 at% dopant) is an attractive approach, as such a small concentration of dopants can alter lithium metal’s bulk properties, without lowering its energy density. As an example, pore formation was effectively eliminated by alloying Li with 10 at% Mg, although chemical diffusion of Li within the alloy still restricted its rate performance. 4 In this work, we report the effects of Ag as a dopant on the morphological stability and rate capability of Li-Ag alloy anodes during electrochemical cycling, as its concentration is varied in Li from 0-10 at.%. The alloy samples are prepared as 10 μm thick films, a practical form factor for solid-state batteries, via a combination of sputtering and thermal evaporation. Comparison of performance as a function of Ag content will be presented for both polymeric and inorganic solid-state electrolytes. Structural characterization of the alloy anodes via complementary techniques will also be presented. This research was sponsored by the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory (ORNL). This abstract has been authored by UT-Battelle, LLC, under contract DE-AC05-00OR22725 with the US Department of Energy (DOE). The US government retains and the publisher, by accepting the article for publication, acknowledges that the US government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for US government purposes. DOE will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http://energy.gov/downloads/doe-public-access-plan). References Kasemchainan, J.; Zekoll, S.; Spencer Jolly, D.; Ning, Z.; Hartley, G. O.; Marrow, J.; Bruce, P. G., Critical stripping current leads to dendrite formation on plating in lithium anode solid electrolyte cells. Nature Materials 2019, 18 (10), 1105-1111. Krauskopf, T.; Hartmann, H.; Zeier, W. G.; Janek, J., Toward a Fundamental Understanding of the Lithium Metal Anode in Solid-State Batteries—An Electrochemo-Mechanical Study on the Garnet-Type Solid Electrolyte Li6.25Al0.25La3Zr2O12. ACS Applied Materials & Interfaces 2019, 11 (15), 14463-14477. Jow, T. R.; Liang, C. C., Interface Between Solid Electrode and Solid Electrolyte—A Study of the Li / LiI ( Al2 O 3 ) Solid‐Electrolyte System. Journal of The Electrochemical Society 1983, 130 (4), 737-740. Krauskopf, T.; Mogwitz, B.; Rosenbach, C.; Zeier, W. G.; Janek, J., Diffusion Limitation of Lithium Metal and Li–Mg Alloy Anodes on LLZO Type Solid Electrolytes as a Function of Temperature and Pressure. Advanced Energy Materials 2019, 9 (44), 1902568.
Advances in solid electrolytes (SEs) with superionic conductivity and stabilized electrode-electrolyte interfaces are key enablers for all solid-state batteries (SSBs) to meet the energy density and cost targets for next generation batteries for electric vehicles. Compared to their ceramic counterparts, sulfide- and thiophosphate-based electrolytes offer several key advantages, including (i) exceptionally high ionic conductivities up to 10 -2 S/cm (comparable to non-aqueous liquid electrolytes) as reported for Li 10 GeP 2 S 12 and Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 , (ii) availability of low temperature and inexpensive synthesis routes to produce glass, glass-ceramic, and crystalline structures, and (iii) soft mechanical properties, which facilitates material processing. Among the drawbacks, sulfides have a narrow electrochemical window, hence limited electrochemical stability against Li-metal and cathodes and poor chemical stability including high sensitivity to moisture. Despite an intrinsic narrow thermodynamic range, most SEs rely on kinetic stability based on slow growth of the interfacial layer that has reasonable ionic conductivity and very low electronic conductivity. In addition to the thermodynamical instability, significant mechanical stresses develop in SE due to (i) volume changes of the electrode material during repeated lithiation (delithiation) and (ii) interface roughening from side reactions upon extended cycling. This effect often termed as “chemo-mechanical effect” results in poor interfacial contact between the SE and cathode. The talk will highlight a few material based approaches towards addressing the interfacial stabilities (as mentioned above) between Li 3 PS 4 SE and lithium-ion cathodes such as NMC. The area specific resistance (ASR) between SE-Cathode interfaces were optimized by coating cathode particles, varying stack pressure and doping the SE compositions. Acknowledgment - This research was conducted at Oak Ridge National Laboratory, managed by UT Battelle, LLC, for the U.S. Department of Energy (DOE) and is supported by Asst. Secretary, Energy Efficiency and Renewable Energy (EERE), Vehicle Technologies Office (VTO) through the Advanced Battery Materials Research (BMR) Program
Advances in solid electrolytes (SEs) with superionic conductivity and stabilized electrode-electrolyte interfaces are key enablers for all-solid-state batteries (SSBs) to meet the energy density and cost targets for next-generation batteries for electric vehicles. Argyrodite sulfide-based electrolytes with the nominal composition Li 6 PS 5 X; where X= Cl and/or Br, I provide several key advantages over other types of SE counterparts, including (i) exceptionally high ionic conductivities up to 10 -2 S/cm at room temperature (comparable to nonaqueous liquid electrolytes), (ii) availability of low temperature and inexpensive synthesis routes to produce glass, glass-ceramic, and crystalline structures, and (iii) soft mechanical properties facilitating material processing and solid-state battery (SSB) fabrication. Several key challenges exist for the practical use of the argyrodite sulfide-based electrolyte in an SSB: (i) scale-up synthesis to produce phase-pure materials, (ii) rationale processing method development to produce free-standing thin film SSEs, and (iii) identifying buried interfacial side-reaction products at the electrode/electrolyte interfaces using advanced characterization tools. In this talk, we will present our recent achievements focusing on tackling each of these challenges, including (i) solution-based synthesis of Li 6 PS 5 X; (ii) optimizing binder, slurry composition, and processing method to make Li 6 PS 5 X thin film (<50 µm) SSEs, and (iii) combining in-situ Raman spectroscopy and microscopy with complementary electrochemical impedance spectroscopy (EIS) to explore electrode/ Li 6 PS 5 X interfacial stability. Acknowledgment This research conducted at Oak Ridge National Laboratory, managed by UT Battelle, LLC, for the U.S. Department of Energy (DOE) is sponsored by the Office of Energy Efficiency and Renewable Energy (EERE) in the Vehicle Technologies Office (VTO) through the Advanced Battery Materials Research (BMR) Program.
Synthesis of Li 3 YCl 6 is facilitated by the addition of NH 4 Cl. Synthesis method affects local ordering and Li + dynamics as determined by neutron diffraction, impedance and NMR spectroscopy.
All-solid-state lithium metal batteries promise a specific energy >500 Wh/kg. A solid-state electrolyte (SSE) plays an irreplaceable role in reaching such an energy density goal. Among different SSE types, the sulfide and thiophosphate-based SSE has emerged as a prominent class of soft ionic conductors. Compared to their ceramic and oxide SSE counterparts, sulfide SSEs provide several favorable advantages, including a) high room temperature ionic conductivity up to 10 mS/cm that is comparable to liquid-based electrolytes; b) ductile and mechanically soft SSE that enables better processible and intimate contact with electrodes; and c) scalability with solution-based low-temperature synthesis route. However, when paring with a high voltage cathode, such as lithium nickel manganese cobalt oxide (NMC), the (electro)chemical instability of the sulfide SSE at the electrode/SSE interfaces becomes a major challenge to tackle with. The interfacial instability can result in up to 50% initial capacity loss in a Li/sulfide SSE/NMC battery, thereby keeping the sulfide SSEs from commercialization. Herein, by using neutron computed tomography, we trace in situ lithium displacement in an all-solid-state battery composed of a 7 Li anode, nat Li 3 PS 4 (LPS) electrolyte, and a nat LiNi 0.8 Mn 0.1 Co 0.1 O 2 (NMC811) cathode. We show that after the first galvanostatic charge/discharge cycle, lithium accumulates at the LPS/NMC811 interface and preferably fills in the pre-formed cracks in the cold-pressed LPS SSE pellet. Such irreversible lithium displacement contributes to the initial capacity loss of the Li/LPS/NMC battery. Our findings suggest that to achieve high-capacity retention of an all-solid-state sulfide-based battery using an NMC cathode, the cathode/sulfide interface should be better engineered and the defects of the LPS pellet should be suppressed. Acknowledgment This research was conducted at Oak Ridge National Laboratory, managed by UT Battelle, LLC, for the U.S. Department of Energy (DOE) and is supported by Asst. Secretary, Energy Efficiency and Renewable Energy (EERE), Vehicle Technologies Office (VTO) through the Advanced Battery Materials Research (BMR) Program. This research used resources at High Flux Isotope Reactor, a DOE Office of Science User Facilities operated by the Oak Ridge National Laboratory.
