A new study suggests that solid-state lithium metal batteries may not provide the big energy boost many have hoped for.
Researchers found that using lithium lanthanum zirconium oxide (LLZO) as a solid electrolyte in these batteries results in only a small increase in energy density compared to today’s lithium-ion batteries.
The research, published in Energy Storage Materials, raises questions about the practicality of fully solid-state batteries.
Are solid-state batteries really better?
Solid-state lithium metal batteries have been seen as the future of energy storage because they promise better safety and higher energy performance.
LLZO, a popular solid electrolyte material, is known for being stable and having good ionic conductivity.
However, a team of researchers found that even under ideal conditions, an LLZO-based battery would only achieve an energy density of 272 Wh/kg. This is barely an improvement over the 250–270 Wh/kg offered by current lithium-ion batteries.
One of the biggest issues with LLZO is its density. While it provides good volumetric energy density (823 Wh/L), its weight reduces the overall energy advantage.
Additionally, LLZO is brittle, making it hard to manufacture in thin, defect-free sheets. It is also expensive to produce and has problems with lithium dendrites, which can cause battery failure.
“LLZO is a stable material, but its weight and mechanical challenges make it difficult to use in real-world batteries,” said Eric Jianfeng Cheng, the study’s lead author from Tohoku University.
Since fully solid-state LLZO batteries have major drawbacks, researchers are now looking at hybrid solutions. One promising idea is LLZO-in-polymer composite electrolytes, which combine LLZO with flexible materials to improve manufacturing and reduce weight. Another approach is quasi-solid-state batteries, which use a small amount of liquid electrolyte to improve performance and durability.
“Instead of trying to build a fully ceramic solid-state battery, we need to rethink our strategy,” said Cheng. “By combining LLZO with polymers or gel-based electrolytes, we can improve manufacturing, reduce weight, and still achieve high performance.”
This study, conducted with researchers from Tohoku University, MIT, UW Madison, Johns Hopkins University, and others, highlights the need for practical engineering solutions in battery development. While solid-state lithium metal batteries are still promising, this research suggests that hybrid designs may be the best path forward for balancing energy performance, cost, and manufacturability.
Instead of expecting a revolutionary breakthrough from solid-state batteries, we may need to focus on incremental improvements to make next-generation energy storage a reality.
