Engineering the Future: Unveiling the Mysteries of Solid Electrolyte Ionic Conductivity

All-solid-state batteries (SSBs) use solid materials for both the electrolyte and electrodes. This is a significant shift from traditional batteries, which typically use liquid or gel electrolytes. For example, in SSBs, the liquid or polymer gel electrolytes found in conventional lithium-ion batteries are replaced with solid electrolytes. These solid electrolytes can be made from ceramics, glass, or sulfides. The electrodes in SSBs are also solid (lithium, nickel, cobalt, and manganese) and are similar to those in regular batteries. Like in traditional batteries, lithium ions move from the negative electrode (anode) to the positive electrode (cathode) during discharge and back when charging. The solid electrolyte facilitates this ion transport without the need for a liquid medium. SSBs are considered much safer with reduced risk of fires and explosions because it does not contain flammable liquid electrolytes. Solid electrolytes can potentially allow for closer packing of materials, leading to higher energy densities. Moreover, SSBs are expected to have a longer life due to less degradation of materials compared to liquid electrolyte batteries. They can also operate effectively across a broader range of temperatures and are more stable over time. Furthermore, SSBs could enable faster charging times due to better ion conductivity of some solid materials.

SSBs are considered an important technological advancement because SSBs could significantly improve the range and safety of EVs, addressing one of the major barriers to their adoption. They are also seen as key to efficient storage solutions for solar and wind energy, facilitating a transition to renewable energy sources. They also may offer more sustainable and environmentally friendly options compared to traditional batteries. However, creating solid materials that can transport ions as effectively as liquids is challenging. Additionally, producing these batteries with consistent quality and performance is currently more complex and costly than traditional batteries. There is also the limitation of lithium dendrites which can still form and penetrate solid electrolytes, potentially causing short circuits. Solid electrolytes, while offering increased mechanical strength and reduced flammability, pose their own unique challenges. The core issue lies in their relatively low Li-ion conductivity, a factor critical to the performance of SSBs. This conductivity is influenced by two primary mechanisms: lattice diffusion within the solid phase and the limited contact area between electrolyte particles. There is extensive research to overcoming current technical and manufacturing challenges.

To address some of these challenges, a collaborative effort between NASA Langley and NASA Glenn Research Centers provided a new study published in the journal ACS Applied Materials & Interfaces led by Dr. Vesselin Yamakov explored the impact of pressure on the ionic conductivity of solid electrolytes in SSBs, crucial for safe, reliable, and high-capacity energy storage. His co-authors include April Rains, Jin Ho Kang, Lopamudra Das, Rehan Rashid, Ji Su, Rocco Viggiano, John Connell, and Yi Lin. The article investigates the interaction between particle dynamics and ionic conductivity, particularly focusing on the influence of pressurization on lithium-ion (Li-ion) conductivity. The study contrasts low and high grain boundary conductivity scenarios, providing insights into the mechanical and structural challenges posed by solid electrolytes. The research employs both theoretical modeling and experimental approaches to analyze these dynamics, aiming to enhance the performance of SSBs.

The authors employed both theoretical modeling and experimental methods to investigate the pressure dependence of ionic conductivity in solid electrolytes. The theoretical model was based on linear elastic theory and particle dynamics, predicting a power-law dependence of conductivity on pressure, differing for bulk-dominant and grain boundary-dominant conductivity. Particle dynamics simulations were used to test these predictions, modeling solid electrolyte particles under various pressure conditions. Experimentally, they measured ionic conductivity of lithium phosphorus sulfide chloride (LPSC) solid electrolyte under different fabrication pressures. These measurements were conducted using electrochemical impedance spectroscopy (EIS), with LPSC sandwiched between holey graphene layers. The experimental results qualitatively agreed with the theoretical predictions, demonstrating increased ionic conductivity with higher fabrication pressures and confirming the power-law dependence of conductivity on pressure. This work provides insights into optimizing solid electrolyte properties for improved performance in solid-state batteries.

Dr. Vesselin Yamakov and colleagues advanced our understanding of how pressure affects SE ionic conductivity. By exploring scenarios with varying grain boundary conductivities, the research unveils the scaling dependence of conductivity on pressure. This dependence is not linear; different regimes of conductivity behavior emerge based on the relationship between bulk and grain boundary conductivity. The authors’ findings suggest that electrolytes with specific particle sizes and shapes, subjected to controlled pressurization during fabrication of SSBs, could exhibit significantly enhanced ionic conductivities and enhanced performance. This insight is invaluable for engineers and researchers striving to overcome the conductivity limitations that have long hampered the broader adoption of SSBs. In conclusion, the exploration of pressure dependence in solid electrolyte ionic conductivity paves the way for the next generation of battery technologies.