Creating battery electrolytes – the component that carries the charged particles back and forth between a battery's two terminals – has always been a tradeoff.
Solid-state inorganic electrolytes move the particles extremely efficiently, but being solid and inorganic means they're also brittle, hard to work with and difficult to connect seamlessly with the terminals. Polymer electrolytes are a dream to work with, but just don't move the charged ions as well.
Mixing the two to create hybrid electrolytes creates, well, mixed results.
"There's a dilemma. Is a hybrid the best of both worlds in terms of higher ionic conductivity from the inorganic and good mechanical properties from the polymer, or is it a combination of their worst properties?" said Asst. Prof. Chibueze Amanchukwu of the University of Chicago Pritzker School of Molecular Engineering (UChicago PME) .
A new technique from Amanchukwu Lab builds inorganic and polymer electrolytes at the same time, in the same vessel. This "one-pot" in-situ method creates a controlled, homogenous blend, pairing the conductivity of the inorganic solids with the flexibility of the polymers.
"When you make lithium metal batteries, the in-situ method outperforms the physical mixing method quite substantially," Amanchukwu said.
Their work was published in Chemistry of Materials .
Although the study focused on battery electrolytes, the new technique will have impact in semiconductor research, electronics, industrial coatings, sealants and any other field that relies on hybrid materials.
"Let's say you want something that stretches really well and can twist and turn – like wearable electronics – what you could do is engineer the polymer such that you have the mechanical flexibility with that material," said first author Priyadarshini Mirmira, PhD'24.
Uniting the streams
Making hybrid materials currently involves two streams of synthesis. The inorganic and polymer materials are made separately even if both are synthesizing at the same time – then there's the extra time needed to mix the two materials together.
It's an annoyance in the lab, but an economic hurdle at the mass production scales industry requires.
"From an industrial standpoint, that's really difficult and expensive to try to scale up," Mirmira said. "If you can make the two of them in a one-pot approach, you've now reduced the labor that you need in order to make the hybrid material."
Mixing high-tech synthetic materials has the same problems as mixing oatmeal – lumps. A clotted, lumpy blend means inefficient batteries, clumped sealants, less utile electronics.
"I've made the powder, the ceramic, I've made the polymer, let me mix them," Amanchukwu said. "The challenge is what makes a good mix? Do you want good mixing? Do you not? Do the particles agglomerate? Do they not?"
Not only does making the materials together in one pot create a perfect physical blend, but the team also saw some materials come together chemically.
"For some combinations of the inorganic precursor and the polymer precursor, we saw evidence of cross-linking, meaning a chemical bond between the inorganic and the polymer," Amanchukwu said. "That's just new materials chemistry that got us excited."
Multiple applications
The paper focused on lithium batteries because they're the most common in EVs, grid storage and other applications. But the technique also can work with sodium batteries, which are advancing as a less-expensive, more plentiful alternative to lithium.
"It's really a matter of changing one of the reactants on the inorganic to make it applicable for a sodium battery cell as well," Mirmira said.
Scaling the one-pot process up to the levels needed for industrial manufacturing will require "a couple of different knobs to tune," Mirmira said. The process needs to be completely air-free, for starters, processed under argon or another inert gas. That's easier to maintain in the lab than on a factory floor.
Second, the pot gets hot. Getting to industrial levels will require precise tuning – the vessel has to get hot enough to synthesize the polymer, but not so hot that it goes past the materials' degradation temperature.
"When you scale up this reaction, you're going to have more material, the vessel is going to get even more hot, essentially," Mirmira said. "So you've got to worry about temperature control."
Once those obstacles are overcome, the research will lead to perfect, homogenous hybrids created in an economically and chemically efficient manner.
"That kind of control of being able to have a fully integrated inorganic polymer material was a challenge we were trying to solve, and a pretty cool thing we were able to achieve," Mirmira said.
Citation: "In Situ Inorganic and Polymer Synthesis for Conformal Hybrid Sulfide-Type Solid State Electrolytes," Mirmira et al, Chemistry of Materials, January 22, 2025. DOI: 10.1021/acs.chemmater.4c02835
