Renewable energy sources like solar and wind power generate electricity that fluctuates significantly depending on weather conditions and time of day. Energy storage technology that can serve as a massive "dam"—storing this surplus power and releasing it when needed—represents one of the biggest bottlenecks on the path to a decarbonized society.
Currently widely used lithium-ion batteries offer high performance, but because they use flammable organic solvents, challenges remain in terms of safety and cost when deploying them in grid-scale massive systems. This is why researchers around the world have turned their attention to "aqueous zinc batteries"—which use abundant, inexpensive resources and aqueous electrolytes, eliminating fire risk.
However, this promising technology has long been hindered by one decisive weakness. A research team including Wenyong Chen and Fei Wang of Fudan University, along with Changkun Zhang of the Dalian Institute of Chemical Physics, tackled this problem with a counterintuitive approach: eliminating the fixed electrode entirely. They reported their findings in the June 24, 2026 issue of the journal Nature Energy.
The Limits of Solid Electrodes and the Shift to a "Flowing" Slurry
Charging and discharging a battery is fundamentally a repeated cycle in which metal ions receive electrons at the electrode surface and deposit as metal, followed by the reverse dissolution process. In conventional metal batteries, this reaction takes place on a fixed, solid electrode surface.
In the case of zinc batteries, zinc ions (Zn²⁺) deposit as metallic zinc on the electrode with every charge cycle, but this deposition never proceeds uniformly. Electric current concentrates at microscopic protrusions, from which tree-like crystalline structures called "dendrites" grow. If these crystals grow too large, they eventually pierce through the insulating layer and cause a short circuit. Furthermore, as charge-discharge cycles repeat, the electrode itself undergoes repeated expansion and contraction in volume, causing physical cracking and delamination. This mechanical degradation combined with interfacial instability has been the root cause of the short lifespan of aqueous zinc batteries.
For half a century, the conventional wisdom and central research challenge for extending battery life has been "controlling the solid surface"—suppressing dendrite formation and keeping the electrode surface as smooth as possible. Researchers have tried every conceivable method to prevent solid electrode degradation, from coating protective films on electrode surfaces to fine-tuning electrolyte compositions. But as long as the fundamental structure remains fixed, the effectiveness of these approaches is limited. As charge-discharge cycles continue, the gradual erosion of the solid electrode by internal stress and non-uniform reactions can be considered an almost physically unavoidable fate.
The research team drew their inspiration from a visit to a zinc smelting plant. There, zinc ions in solution are continuously reduced to metallic zinc. They wondered whether this dynamic electron transfer process could be used directly for energy storage within a flowing system, rather than a fixed electrode.
What they developed is a battery using a "Flowing Zinc Slurry (FZS)." A slurry refers to a mud-like mixture of solid particles suspended in a liquid.
Their design completely eliminates the conventional fixed zinc electrode. Instead, nanoscale zinc particles are dispersed in a conductive liquid medium, which is pumped and circulated between an external tank and an electrochemical cell. During charging, zinc ions in the liquid transform into metallic zinc; during discharging, they revert back to zinc ions. This transforms the electrode from a "static plate" into a "dynamic carrier."
The greatest advantage of using a slurry is the absence of a "fixed scaffold" on which dendrites can grow. Because the particles are constantly flowing and continuously redispersed, there is no opportunity for localized protrusions to grow and cause a short circuit. The flexible liquid medium also absorbs the stress from physical expansion and contraction.
Interfacial Chemistry to Contain Dendrites and Proof of Durability
However, a battery cannot function simply by mixing zinc particles into a liquid and letting it flow. During charge-discharge cycles, particles can aggregate with one another, or unwanted side reactions (such as hydrogen gas generation) can occur upon reacting with the aqueous electrolyte.
Here, the research team combined the flow design with a chemical technique they call "ligand-based surface control." A ligand is a molecule that binds to metal ions and alters their properties.
The research team added ligands to the slurry that specifically bind to the surface of the zinc nanoparticles. These ligands precisely control the growth rate of the particles during charge-discharge cycles, preventing excessive dendrite growth and parasitic side reactions. As a result, monodisperse zinc nanocrystals of uniform size exist stably within the slurry.
To ensure a pathway for electrons, the team also incorporated a hollow carbon network. Even with particles in a dispersed state, electricity flows smoothly throughout the entire system. Chemical surface control and physical flow design function in a mutually complementary manner.
The completed slurry battery demonstrated figures at the laboratory level that surpass conventional limits.
"Coulombic efficiency"—which indicates how much electricity can be extracted relative to the amount put in during charge-discharge—is a critical metric for measuring the reversibility of a metal battery. In the research team's measurements, they recorded an extremely high Coulombic efficiency of 99.94% at a high current density of 8 mA cm⁻². This means that virtually no energy loss occurred due to irreversible zinc deposition.
| Metric | Test Conditions | Recorded Value |
|---|---|---|
| Coulombic efficiency | Current density 8 mA cm⁻² | 99.94% |
| Continuous operation of symmetric cell | Current density 22.5 mA cm⁻², capacity 135 mAh cm⁻² | 5,128 hours |
| Capacity retention of FZS || MnO₂ full cell | After 5,500 cycles at rate of 10 A g⁻¹ | 81.1% of initial capacity |
| Sustained performance of FZS || O₂ full cell | Current density 1.35 mA cm⁻² | 100 hours (maintaining 1.65 Ah) |
Durability tests were also conducted under harsher conditions. In experiments using a symmetric cell, the researchers succeeded in achieving continuous operation for 5,128 hours (approximately 213 days by simple calculation, dividing by 24) at an even higher current density of 22.5 mA cm⁻².
With practical applications in mind, tests on a full cell using manganese dioxide (MnO₂) as the positive electrode (FZS || MnO₂) showed that even after 5,500 cycles of rapid charging and discharging (10 A g⁻¹), the battery maintained 81.1% of its initial capacity. Achieving this level of longevity in conventional aqueous metal-ion batteries is extremely rare.
The team also verified sustained performance in a zinc-air battery configuration using an air cathode (FZS || O₂ full cell). At a current density of 1.35 mA cm⁻², the battery was confirmed to maintain a capacity of 1.65 Ah over 100 hours. This demonstrates that the slurry electrode functions stably even when the positive electrode configuration is changed to suit different applications.
Technical Challenges Toward Scale-Up
The zinc slurry battery is a system that combines the best features of conventional redox flow batteries and metal batteries. Like a redox flow battery, it offers the scalability to easily increase energy storage capacity simply by enlarging tank capacity, while also boasting high energy density because it uses metal itself—rather than a solution of dissolved ions—as the energy carrier. Furthermore, because it uses zinc, an inexpensive and safe material, it is ideally suited for large-scale energy storage facilities at grid scale.
However, this technology will not be socially implemented overnight. The current results remain, ultimately, a laboratory-level demonstration.
The greatest focus going forward is whether the system can be scaled up to practical dimensions. As equipment grows larger, advanced engineering will be required for pumping technology to circulate the mud-like slurry uniformly through piping over extended periods without clogging, as well as for thermal management. Stability under irregular charge-discharge cycles when actually connected to highly variable renewable energy grids also remains unverified.
Even so, this research—which broke through the limitations of solid electrodes with the reverse approach of "fluidization"—has opened up new possibilities for energy storage. If this concept expands beyond zinc to flowable energy carriers using other metals, the massive batteries supporting a decarbonized society may take on a form entirely different from what we currently imagine.