Solid-State Batteries Get a Boost From Semiconductor Manufacturing Techniques
Researchers turn to methods used in the semiconductor industry to solve long-standing challenges facing solid-state electrolytes.
Solid-state batteries (SSBs) are hailed as a technology pivotal to advancing energy storage solutions. Viewed as the next evolutionary step in battery technology, SSBs promise enhanced safety, higher energy density, and longer life cycles, making them especially attractive for applications like electric vehicles and large-scale energy storage.
Automakers like Toyota are considering using solid-state batteries in their electric vehicles. Image used courtesy of Toyota
However, the development of SSBs has been hindered by many challenges, especially those surrounding electrolyte design. Recently, researchers from the Argonne National Laboratory addressed these challenges by employing techniques borrowed from the semiconductor industry.
Solid-State Electrolyte Challenges
A key component of SSBs is the solid-state electrolyte (SSE), which facilitates ion transport between the electrodes. Sulfide-based SSEs, such as argyrodites, are particularly promising because of their high ionic conductivity and favorable mechanical properties. However, these materials face critical challenges that hinder their widespread adoption and practical application.
One major challenge is the intrinsic instability of sulfide-based SSEs under ambient conditions. These materials are highly sensitive to atmospheric moisture and oxygen, leading to rapid degradation and loss of performance. This instability makes them difficult to process at scale and limits their viability in real-world applications.
There are many tradeoffs in the design of lithium argyrodite SSEs. Image used courtesy of Li et al.
Additionally, the interfaces between the SSE and the electrodes (cathode and anode) are problematic. Instability at these interfaces can significantly limit the overall cell performance and lifetime, as unwanted chemical reactions can occur, forming resistive layers and degrading the electrolyte material.
Finally, these materials have extremely high reactivity with lithium metal, often used as an anode in SSBs. This reactivity can form dendrites—needle-like structures that grow through the electrolyte, potentially causing short circuits and posing significant safety risks.
Solving the Solid-State Electrolyte
To tackle these problems, the Argonne team employed atomic layer deposition (ALD), a method long used in semiconductor manufacturing.
ALD involves the application of thin film coatings, layer by layer, at the atomic level. This precision allows for exceptional control over the material properties. The researchers adapted ALD to apply thin coatings of aluminum oxide (Al2O3) on argyrodite powders, a class of sulfide-based SSEs.
The ALD Al2O3 coatings markedly enhanced the stability of argyrodites under ambient conditions. These coatings significantly lowered the reactivity of argyrodites with air, reducing the degradation typically observed when these materials encounter atmospheric oxygen and moisture. Remarkably, argyrodite powders coated with ten cycles of ALD Al2O3 exhibited negligible (≤1%) weight changes following 240 minutes of dry O2 exposure and only about a 17% weight gain under humid O2 exposure. This contrasted sharply with uncoated argyrodites, which showed approximately 19% and 100% weight gains under similar conditions. This improvement indicates that the electrolytes could be more easily and safely handled during manufacturing, a vital step toward commercial application.
Cell performance before and after the ALD application. Image used courtesy of Hood et al.
Furthermore, the ALD method positively impacted the electrochemical properties of the electrolytes. The coatings resulted in an up to two-fold increase in ionic conductivity. Specifically, pellets pressed from powders coated with 1 and 10 ALD Al2O3 cycles exhibited ionic conductivity values of 1.2 ± 0.05 × 10^-3 S cm^-1 and 1.7 ± 0.05 × 10^-3 S cm^-1 at 25°C, respectively. This enhancement in ionic conductivity implies faster charging rates, a critical aspect for electric vehicle applications.
Additionally, the coatings altered the interface between the electrolytes and the electrodes, reducing harmful reactions that degrade performance and battery life. Through atomic-level surface structure control, the researchers successfully optimized the electrolyte-electrode interactions, thereby boosting the overall efficiency and battery lifespan.
A Better Battery Future
Through the innovative application of a semiconductor production technique, the Argonne researchers demonstrated a significant advancement in the field of battery technology. Their work solved some pressing challenges facing SSBs and paved the way for the practical implementation of these high-performance, safer batteries in various applications, including electric vehicles.