Can Zinc-Sulfur Batteries Compete with Lithium-Ion?

Lithium-ion batteries have transformed the economy—and due to the portable electronics they enable, even society. But lithium-ion batteries can be expensive, consume rare resources, and are challenging to manufacture. Engineers have been looking to other battery chemistries to replace lithium-ion if certain drawbacks are fixed. For instance, zinc-sulfur batteries have a higher energy density than lithium-ion batteries, but zinc-anode corrosion, low conductivity, and dendrite growth have hindered their commercial viability.  

If the performance of zinc-sulfur batteries can be enhanced, they may eventually become cost-competitive with lithium-ion batteries with less impact to the environment.  

Chase Cao, professor of mechanical and aerospace engineering at Case Western Reserve University in Cleveland, has been inspired by the potential of zinc-based batteries, with their abundant materials and safety advantages, to explore their commercial viability by experimenting with the structure and chemistry of the electrolyte. The results the experiments generated surprised him. They hint at the capability for zinc-sulfur (Zn-S) batteries to outcompete lithium-ion batteries.  
 

The problem with dendrites 

One of the key challenges with Zn-S batteries include slow redox kinetics of sulfur cathode conversion and inadequate anode stability. Cao experimented with the tuning of the electrolyte structure by adding propylene glycol methyl ether (PM) as a co-solvent and ZnI₂ as an electrolyte additive. 

By adding PM and ZnI₂, the electrolyte network structure was optimized, enhancing the interfacial stability between the cathode and anode while promoting the reversibility of sulfur cathodic transitions.  

“PM reshaped the ligand structure, improving Zn²⁺ transport kinetics,” Cao said. “Additionally, PM interacted synergistically with ZnI₂ to reduce cell polarization, catalyze sulfur cathode reactions, and mitigate I_3⁻-induced zinc anode corrosion, significantly enhancing the electrochemical performance of the aqueous zinc-sulfur battery.” 

These adjustments enhanced energy capacity by 20 percent, improved conductivity, and  stabilized and inhibited the growth of zinc dendrites. 

Dendrites can be a big problem if they grow long enough to connect the positive and negative sides of the battery, which can short out and create a fire. (That problem in lithium-ion batteries has led to fatalities.) 

“These additives not only enhance battery efficiency but also address long-standing safety concerns by mitigating dendrite formation,” said co-researcher Guiyin Xu, a professor at Donghua University in Shanghai. “The result is a compact, higher-density battery that can recharge more times without significant degradation.” 
 

Three key goals 

Cao wanted to improve zinc-anode corrosion, boost low electrical conductivity, and control dendrite growth. Overcoming these challenges required a meticulous approach to material selection and electrochemical design.  

“Identifying additives that could simultaneously improve conductivity, stabilize the anode, and suppress dendrites was a complex process,” he said, “demanding extensive experimentation and collaboration with experts from institutions like Fudan University and the Hong Kong University of Science and Technology.” 

One of the most surprising outcomes was the extent to which the additives improved overall battery performance. While the team was expecting some enhancement in conductivity and stability, the 20 percent increase in energy capacity and the near-complete suppression of dendrite growth exceeded their expectations.  

“Another unexpected finding was the synergy between the additives, which not only addressed individual issues but also contributed to a more compact and efficient battery design,” Cao said. “These results underscored the potential of zinc-sulfur batteries to outperform traditional systems in ways we hadn’t fully predicted at the outset.” 

For mechanical engineers, noted Cao, the development of high-performance zinc-sulfur batteries offers several compelling aspects. First, the enhanced energy density enables the design of smaller, lighter power systems, which is critical for applications like soft swimming robotics, aerospace systems, and wearable devices. “This allows engineers to optimize mechanical designs for efficiency and portability without compromising performance,” Cao said.  

Second, the improved safety profile—achieved by mitigating dendrite formation—reduces the need for complex thermal management systems, simplifying integration into mechanical frameworks. And the durability and rechargeability of these batteries “support the development of long-lasting, autonomous systems, such as the biologically inspired swimming robots I’m exploring with my team, which require robust energy solutions to operate in challenging environments,” Cao said. 
 

Beyond affordability and safety 

Aqueous zinc-sulfur batteries have the potential to power a wide range of applications—from renewable energy systems to portable electronics—with reduced environmental impact and reliance on scarce materials. But the implications of this breakthrough extend beyond affordability and safety. Zinc-sulfur batteries have a higher energy density than lithium-ion counterparts, enabling smaller, longer-lasting designs.  

From a mechanical engineering perspective, the resulting battery design is particularly novel. Its high energy density and compact form factor enable mechanical engineers to rethink system architectures, reducing weight and volume in applications like robotics and aerospace. Additionally, Cao said, “Our focus on integrating these batteries into soft robotics required creative electrochemical and mechanical co-design, ensuring the energy system withstands the dynamic stresses of flexible, biologically inspired machines.” 

Next steps involve refining the battery’s performance through further optimization of the additive formulations and exploring scalable manufacturing techniques.  

“The team plans to conduct extensive testing in real-world applications, such as renewable energy storage and robotic systems, to validate long-term reliability,” Cao said. 

Over the next few years, he envisions their research advancing toward commercialization, with zinc-sulfur batteries becoming a viable alternative for a range of industries. “My team is particularly focused on integrating these batteries into soft robotics and space technologies, where their lightweight, high-capacity properties could enable breakthroughs in autonomy and endurance,” Cao said. “Continued collaboration with academic and industry partners will be essential to achieving these goals.” 

Mark Crawford is a technology writer in Corrales, N.M.