Building Dendrite-Free Zinc Batteries for Grid Storage

While Li-ion batteries are the commercial go-to battery today, there are many other battery architectures out there which have much higher theoretical energy densities. However, for one reason or another―often relating to stability and cycle longevity―these batteries have not yet become a commercially feasible option. 

When it comes to grid-scale storage applications, there is always the risk that Li-ion batteries are too flammable (due to the flammable organic electrolytes) for long-term usage. While they are the best option currently, the continuous risk of an explosion occurring is prompting new avenues to be explored. 

Zinc-based batteries have emerged as one potential option for grid-scale storage because they use an aqueous electrolyte that is much safer and unlikely to catch fire compared to an organic electrolyte. On top of this, zinc batteries have a good volumetric capacity that could rival lithium in these applications. There have been many different zinc batteries developed to date, including Zn-metal, Zn-halide, Zn-organic, static Zn-ion batteries, and Zn redox flow batteries. It’s thought that the redox flow batteries could be used for stationary grid storage, but zinc batteries have some critical issues around inhomogeneous zinc deposition and stripping that lead to dendrite formation. 

Zinc Flow Batteries: A Promising Option 

Among the different zinc batteries, zinc polyiodide flow batteries (ZIFBs) have a high energy density, reversibility, and cost-effectiveness that make them one of the more promising zinc candidates for grid-scale storage applications. This is because iodide cathodes have a high standard rate constant compared to other halides, such as bromine, which provides a better current and power density compared to the more popular zn-bromine batteries. Iodine is also a lot less toxic and corrosive than bromine batteries, making it safer, and ZIFBs have a good theoretical energy density of around 322 WhL-1 and a low electrolyte cost. 

Issues with Zinc Flow Batteries 

Zinc batteries―including zinc anodes in conventional battery architecture―have some serious issues with inhomogeneous zinc deposition and stripping that can cause dendrite formation. Like other zinc batteries, this issue is also prevalent in ZIFBs. The deposition and stripping process is further intensified by the electrode roughness, zinc ion distribution, and the electric field around the electrode, leading to dendrites forming perpendicular to the electrode. Like all dendrites, these initially small dendrites soon become large dendrites that pierce the separator and cause the battery to short-circuit. At high capacities and current density, dendrite formation evolves more rapidly, so to guarantee ZIFB stability, they are typically operated at a lower capacity and current density―which is not an ideal scenario. 

Inhibiting Dendrite Formation 

A lot of work has been done over the years in the battery space to inhibit dendrite formation, including a range of novel approaches, such as nucleation adjustment, 2D diffusion suppression, and polarisation mitigation. 

Scientists have found that they control zinc nucleation by strengthening the interactions between zinc nuclei and the electrode surface. Zinc nucleation plays a key role in suppressing dendrite formation, so a stronger interaction can reduce the chance of dendrites forming. It’s been found that by pre-positioning nucleation seed materials that possess strong zincophilic characteristics on to the electrode, a uniform electrodeposition can be achieved that lowers the chance of dendrite formation. 

It’s also been found that zinc ions that diffuse on the electrode surface try to find the most energetically favourable site to undergo charge transfer―in a process known as 2D diffusion. This diffusion can cause a localised bias in the electrodeposition on a specific area of the electrode, leading to a greater chance of dendrites forming. So, controlling the 2D diffusion is also key to suppressing dendrite formation. 

Finally, it’s been found that reducing both the electrochemical polarisation and concentration polarisation can help to suppress dendrite formation. This has been found to be possible using 3D porous materials that have a high specific area. 

Copper-Based “Electron Sponge” Removes Dendrites from Zinc Flow Batteries 

Researchers have now taken to using a copper-based “electron sponge” to try to suppress dendrite formation in ZIFBs. The researchers found that uniform zinc electrodeposition could be greatly improved by using highly zincophilic copper oxide nanoparticles in a graphite electrode. The researchers used these nanoparticles as nucleation seeds to simultaneously demonstrate nucleation adjustment and 2D suppression at the electrode interface to facilitate a better degree of control over zinc crystallinity and produce a battery that had an efficient stripping process with minimal residual zinc. 

The researchers found that this approach created a strong electronic redistribution between the zinc ions and copper oxide nanoparticles, where the zinc nucleated around the pre-distributed copper oxide sites in the electrode. This is because copper oxide has excellent electron-accepting and -donating capabilities in electron-rich and electron-deficient environments―resembling the properties and characteristics of a sponge. 

The ’electron sponge’ effect arises due to stable and strong bonding between the zinc bonding with the oxygen in the copper oxide―leading to a tight electronic connection between the copper oxide matrix and the zinc ions. This leads to a low energy barrier for nucleation, a highly negatively polarised copper oxide, a low surface diffusivity, and a directed growth of zinc ions that is lateral (along the 002 crystallographic plane) to the electrode instead of being vertically orientated away from it―suppressing dendrite growth. 

The electron sponge approach was fundamental to mitigating dendrite growth and creating dendrite-free ZIFBs. This led to an improvement over other ZIFBs, with an energy density of 180 Wh L-1, a current density of 140 mA cm-2, an areal capacity of 463 mAh cm-2, an energy efficiency of 86.9% at 20 mA cm-2, an average coulombic efficiency of 98.7, and a long cycle stability of over 2500 cycles. Going forward, a strategy has been developed that can be built upon to develop more commercially feasible ZIFBs for grid-scale storage applications and other stationary storage applications. 

Reference: 

Yang J-H. et al, Zincophilic CuO as electron sponge to facilitate dendrite-free zinc-based flow battery, Nature Communications, 16, (2025), 844.