As the world is moving towards more sustainable energy solutions, the emergence of next-generation batteries is a crucial and indispensable milestone. One such next-generation battery is the lithium-ion battery (LIB), which has been currently dominating the energy solutions sector. However, lithium is sparsely distributed across geographies, increasing extraction difficulties and battery production cost. Other next-generation batteries, such as sodium-ion batteries (NIBs) and potassium-ion batteries (KIBs), are promising alternatives to LIBs, offering resource-unconstrained, cost-effective, and sustainable energy storage solutions.

However, as one of the major hurdles for these batteries, the electrochemical behaviors/reactions that occur at the electrode-electrolyte interphase can be highly unstable, leading to reduced performance and shorter battery life. Until now, many aspects of these interphases were often insufficiently elucidated, limiting the potential of NIBs and KIBs for practical applications like grid-scale storage and electric vehicles.

To offer a more precise understanding of the electrode-electrolyte interphase, Assistant Professor Changhee Lee, along with Professor Shinichi Komaba, from the Department of Applied Chemistry, Tokyo University of Science, Japan, led a systematic review on the properties of the solid-electrolyte interphase (SEI) and the cathode-electrolyte interphase (CEI) of NIBs, KIBs, and LIBs. Going beyond just being a comparative review, the researchers were able to redefine the concept of the interphase layer in alkaline metal-ion batteries. Their paper was published online in the journal Advanced Energy Materials on January 30, 2026.

“We wanted to reconsider the conventional assumption about the ideal interphases and provide detailed principles on their design,” explains Dr. Lee. “The SEI and CEI layers in NIBs and KIBs should be understood from a perspective distinct from that of LIBs, based on their fundamental characteristics such as solubility of SEI/CEI, electrolyte stability, and ionic transport properties. By redefining these interphases, we can fundamentally improve the interfacial stability, which directly translates into safer, longer-lasting batteries.” To this end, the team found that previous misunderstandings about interphase behavior had limited the performance of NIBs and KIBs.

While many developers and researchers recognize that the stability of interphases plays a critical role in rapid capacity degradation and safety issues in batteries, a complete understanding of these interfacial phenomena has been hindered by fundamental limitations in analysis. By taking a unified approach to compare the SEI and CEI layers across NIBs and KIBs, the authors could identify overlooked factors that directly affect battery performance. They suggest that the SEI and CEI layers cannot be considered as static and completely solid, but instead as a dynamic, semi-solid interphase layer. Also, the intrinsic role of binders and mechanisms occurring at the interphases cannot be overlooked or generalized. These findings highlight that careful control of interphase properties through materials choice, electrolyte formulation, and binder selection can significantly extend battery life while maintaining safety and efficiency for next-generation battery systems.

“Even relatively small changes in the interphases can have a dramatic impact on cycle life,” notes Prof. Komaba. “Our work highlights how optimizing these layers for next-generation NIBs and KIBs can open up near-term opportunities to significantly improve battery stability and performance.”

The researchers also investigate the frequently overlooked aspect of self-discharge. Although NIBs and KIBs function at lower cathode potentials, the electrolyte instability and less dense formation of CEI increase the rate of self-discharge. This finding emphasizes the need to understand the chemistry behind self-discharge to improve the long-term stability and commercialization of batteries.

The practical implications of this research are significant. Safer and more durable NIBs and KIBs could be deployed in grid energy storage systems to better manage renewable energy sources such as solar and wind. They could also be used in electric vehicles, power tools, and portable electronics, offering a more sustainable and affordable alternative to LIBs.

In addition to the technical contributions, the study underscores the future perspectives and the existing challenges in this domain. According to Dr. Lee, “This field currently lacks the capability to fully resolve structure and chemistry of the interphases, often deviating from understanding realistic battery environments. By employing multimodal characterization techniques that can investigate the true electrochemical conditions, deeper insights regarding the interphase behavior can be obtained.”

In summary, this research is a significant milestone in updating the conceptual framework of interphase design. By prioritizing interphase design, scientists and engineers can produce efficient NIBs and KIBs, potentially transforming the way energy is stored and used in everyday life.

Reference

Title of original paper	:	Comparative Insights and Overlooked Factors of Interphase Chemistry in Alkali Metal-Ion Batteries
Journal	:	Advanced Energy Materials
DOI	:	10.1002/aenm.202506154