Solid-state batteries could help create safer, higher-energy storage systems for electric vehicles, portable electronics and other emerging technologies. Muhammad Mudassar Aslam’s research explores how solid polymer electrolytes and modified metal-organic frameworks could address some of the challenges currently preventing solid-state lithium-metal batteries from becoming commercially practical.
In this Q&A, Aslam explains how solid-state batteries differ from conventional lithium-ion batteries, the limitations facing their development and how molecular-level materials design could help advance the technology.
Can you explain your research on solid-state batteries and what makes them different from conventional lithium-ion batteries?
My research is focused on solid-state lithium-metal batteries, which is really the next step beyond the lithium-ion batteries we use today in phones, laptops, and EVs.
The batteries most of us use right now rely on a liquid electrolyte, the material that carries lithium ions back and forth between the two electrodes as the battery charges and discharges. That liquid works well, but it's flammable, and over time it also allows the lithium metal on the anode side to grow into needle-like structures called dendrites. If those dendrites reach the other electrode, they can short the battery and, in the worst case, cause it to catch fire.
Solid-state batteries replace that liquid with a solid electrolyte instead. Because it's not a liquid, it's nonflammable, and it physically resists dendrite growth, which makes the whole battery inherently safer. It also opens the door to using lithium metal directly as the anode instead of graphite, which means a lot more energy packed into the same amount of space.
Specifically, I work with a type of solid electrolyte called a solid polymer electrolyte, or SPE. Unlike the ceramic or glass-based solid electrolytes some other groups study, polymer electrolytes are flexible and make good physical contact with the electrodes, which is a real problem for the rigid ceramic ones. The tradeoff is that polymer electrolytes have historically struggled to move lithium ions fast enough to be practical.
To get around that, we designed a composite electrolyte that combines a polymer matrix with a metal-organic framework (MOF), MOFs are porous crystalline materials whose chemical structure and internal pore surfaces can be tailored at the molecular level. In my work, I modified the MOF by attaching electron withdrawing groups to it, which changes how strongly it interacts with the lithium salt in the electrolyte. The goal is to use this modified MOF to create more efficient and selective pathways for lithium-ion transport through the polymer electrolyte. The MOF helps promote lithium-salt dissociation while restricting the movement of the counter anions. This allows a larger fraction of the ionic current to be carried by lithium ions and creates low-resistance pathways for their movement through the electrolyte. In this way, we are not simply adding a filler to a polymer, we are engineering the chemistry inside the electrolyte to control how lithium ions move.
What are some of the biggest challenges currently limiting solid-state battery development, and how is your work helping address them?
One of the major challenges with solid-state batteries is finding an electrolyte that can simultaneously provide high ionic conductivity, wide electrochemical stability, good chemical and interfacial compatibility with electrodes. Inorganic solid electrolytes can have high ionic conductivity, but their rigidity can lead to poor contact with the electrodes. Solid polymer electrolytes offer greater flexibility and better interfacial contact, but they generally suffer from relatively low room-temperature ionic conductivity and low lithium-ion transference numbers. These limitations can lead to concentration polarization, increased resistance and unstable battery performance. Maintaining a stable interface with lithium metal and suppressing lithium dendrite growth are also important challenges.
My research addresses these problems by engineering the internal environment of the polymer electrolyte using electron withdrawing functionalized MOF. The MOF provides an ordered porous network, while the electron-withdrawing groups alter the chemical environment of the pores. Together, these effects strengthen interactions with the TFSI⁻ anions, weaken the association between Li⁺ and TFSI⁻, and promote more selective and efficient lithium-ion transport.
The results so far are encouraging. Our functionalized MOF based composite polymer electrolyte achieved a higher room-temperature ionic conductivity and improved lithium-ion transference number compared with the polymer electrolyte without the MOF. It also demonstrated stable lithium plating and stripping in lithium symmetric cells with a low overpotential. In comparison, polymer electrolyte short-circuited much earlier.
These results show how molecular-level modification of a MOF can simultaneously influence ion transport and electrode-electrolyte interfacial stability, two issues that often have to be addressed together when developing practical solid-state electrolytes.
What potential impact could solid-state batteries have on the future of energy storage, electric vehicles, or other technologies?
Solid-state batteries have the potential to contribute to safer, higher-energy-density energy storage. Replacing flammable liquid electrolytes with solid materials could reduce some of the safety risks associated with conventional batteries, while compatibility with lithium-metal anodes could provide a pathway toward storing more energy for a given battery mass or volume. These characteristics are particularly attractive for applications such as electric vehicles, portable electronics and other technologies where energy density and safety are important.
For my research specifically, the broader goal is to understand how we can design the chemistry of a solid electrolyte at the molecular level. By modifying the pore surfaces of MOFs, we can potentially control lithium-salt dissociation, restrict anion movement and create preferential pathways for lithium-ion transport. Our results demonstrate that functionalization of MOF is a promising strategy for combining high lithium-ion conductivity, selective Li⁺ transport and improved interfacial stability within an ultrathin composite polymer electrolyte.
My advisor, Dr. Yang, has been incredibly helpful throughout this research, from putting me on the right idea to helping me solve the critical problems we faced along the way, and I am truly grateful to her for all of it. Ultimately, I hope this type of materials design can contribute to overcoming some of the electrolyte and interface limitations that currently stand between laboratory-scale solid-state batteries and practical high-energy lithium-metal batteries. Rather than solving one performance parameter in isolation, the aim is to develop electrolytes in which ionic conductivity, lithium-ion selectivity, interfacial stability and safety can be improved together.
Connect with Muhammad Mudassar Aslam on LinkedIn.