Researchers from Tohoku University, Shanghai Jiao Tong University, MIT, UW Madison, Johns Hopkins University, and St Andrews University collaborated on a study that highlights the need for workable engineering solutions to strike a compromise between cost, manufacturing feasibility, and energy performance by pointing out the drawbacks of completely ceramic solid-state batteries. The study was published in the journal Energy Storage Materials.
Illustration of an LLZO-based, bipolar-stacked, all-solid-state Li-metal pouch cell. The parameters of the cell components are selected to approximate the practical limits for calculating the cell's energy density. Image Credit: Eric Jianfeng Cheng et al.
According to the study, the anticipated energy density benefits of garnet-type solid electrolytes for lithium metal batteries may be exaggerated. An all-solid-state lithium metal battery (ASSLMB) employing lithium lanthanum zirconium oxide (LLZO) would only have a gravimetric energy density of 272 Wh/kg, according to the study.
This is a slight improvement above the 250–270 Wh/kg existing lithium-ion batteries provide. Given its high production costs and manufacturing difficulties, the results imply that composite or quasi-solid-state electrolytes might be more practical substitutes for LLZO.
All-solid-state lithium metal batteries have been viewed as the future of energy storage, but our study shows that LLZO-based designs may not provide the expected leap in energy density. Even under ideal conditions, the gains are limited, and the cost and manufacturing challenges are significant.
Eric Jianfeng Cheng, Study Lead Author and Researcher, WPI-AIMR, Tohoku University
The promise of enhanced safety and energy efficiency makes solid-state lithium metal batteries a viable next-generation technology. A top contender for solid electrolytes, LLZO is prized for its ionic conductivity and stability. However, detailed modeling of a workable LLZO-based pouch cell casts doubt on the claim that this material greatly increases energy density.
Even with a high-capacity cathode and an ultrathin 25 μm LLZO ceramic separator, the study indicates that the battery's performance is only marginally better than the best traditional lithium-ion cells.
The study highlights one important problem: LLZO's density raises the total cell mass and decreases the anticipated energy savings. Despite reaching a volumetric energy density of about 823 Wh/L, LLZO's additional weight and expense make it impractical. Large-scale application is further complicated by the material's brittleness, the challenge of creating thin sheets free of defects, and problems with lithium dendrites and voids at the interface.
LLZO is an excellent material from a stability standpoint, but its mechanical limitations and weight penalty create serious barriers to commercialization.
Eric Jianfeng Cheng, Study Lead Author and Researcher, WPI-AIMR, Tohoku University
Alternatively, hybrid techniques that combine LLZO with other materials are being investigated by researchers. LLZO-in-polymer composite electrolytes are a potential approach that enhances flexibility and manufacturing while maintaining good ionic conductivity.
A different strategy is the use of quasi-solid-state LLZO electrolytes, which improve ionic transport and structural integrity by incorporating a small quantity of liquid electrolytes. These hybrid designs have been shown to be more stable over the long run.
“Instead of focusing on a fully ceramic solid-state battery, we need to rethink our approach. By combining LLZO with polymer or gel-based electrolytes, we can improve manufacturability, reduce weight, and still maintain high performance,” said Cheng.
Journal Reference:
Cheng, J. E., et al. (2025) Li-stuffed garnet solid electrolytes: Current status, challenges, and perspectives for practical Li-metal batteries. Energy Storage Materials. doi.org/10.1016/j.ensm.2024.103970