MIT Sequential Decomposition Synthesis process produces thin solid-state electrolytes without sintering

A team from MIT has developed a new approach to fabricating oxide-based solid-state electrolytes that are comparable in thickness to the polymer separators found in current Li-ion batteries without sintering: sequential decomposition synthesis (SDS). An open-access paper describing the approach and its application to processing Li garnets is published in the RSC journal Energy & Environmental Science.

Overview of sequential decomposition synthesis (SDS) processing. A) Schematic representation of SDS processing, B) SEM images of Li-garnet films processed via SDS (after annealing at spraying and after 750 °C under a flow of pure O₂), C) processing temperature, events, and ionic conductivity of Li garnets synthesized via powder, sol-gel, and SDS processing. D) Film thicknesses and E) drying and densification budget for processing Li garnets via SDS compared with those of other methods. Hood et al.

State-of-the-art lithium-ion batteries (LIBs), with liquid-based electrolytes, face numerous performance-related complications. For example, the Li-metal anode, having the highest electrochemical specific energy known for solids of 3860 mAh/g, cannot be used with traditional organic liquid electrolytes in LIBs because of poor performance and safety concerns. Recent progress in solid-state battery (SSB) electrolytes such as Li garnets (e.g., Li_6.25Al_0.25La₃Zr₂O₁₂, LLZO) provide a promising alternative to liquid-based electrolytes with wide electrochemical stability (0.05 to ~4.7 V), fast Li⁺ conductivity in the mS/cm range under ambient conditions, structural retention in the presence of water, non-flammability, and perhaps most importantly, compatibility with a Li-metal anode through the formation of a stable tetragonal-like interphase at the Li garnet/Li interface.

Nevertheless, two major challenges for Li-garnet electrolytes in SSBs are i) their large-scale processability as technologically viable films close in thickness to polymer separators in LIBs (below 20 μm) and ii) stabilization of the cubic, high-conductivity phase as mechanically robust films.

In a solid-state battery, the electrolyte functions as both the separator and the medium for shuttling ions between the anode and cathode, and consequently, thicker solid electrolyte separators compromise the volumetric/gravimetric energy of the full cell. Thus, the exploration of feasible chemistries and processing techniques to produce dense Li⁺-conducting solid separators between 1 and 20 μm thickness is not only missing from the literature but also deserves special attention from the field.

—Hood et al.

In addition to delivering the thickness range required, SDS offers immense opportunities to obtain the desired phase at significantly lower processing temperatures (

Due to the wider electrochemical stability window of SDS-manufactured solid electrolytes such as Li garnets and potential to integrate excess Li during the SDS process, this represents an important step to delivering cost-effective ceramic process alternatives toward established polymer battery separators,the researchers said.

Additionally, the SDS method offers new options for future battery architectures and omits high-temperature sintering to enable the synthesis of new Li-electrolyte materials for which co-bonding or sintering at lower temperatures is challenging.

Resources

• Zachary D Hood, Yuntong Zhu, Lincoln Miara, Won-seok Chang, Philipp Simons and Jennifer L. M. Rupp (2022) “A Sinter-Free Future for Solid-State Battery Designs” Energy Environ. Sci. doi: 10.1039/D2EE00279E