A self-healing hydrogel improves zinc battery stability, limits corrosion and dendrites, and supports flexible cells that recover performance after cuts, advancing safer water-based energy storage.
(Nanowerk Spotlight) Lithium-ion batteries power most portable electronics, but they rely on flammable organic liquids and materials that can be costly to secure. They also demand strict control systems to operate safely. These limits motivate efforts to design safer batteries built from abundant elements and water-based electrolytes.
Zinc metal stands out as a strong candidate. It is inexpensive, widely available, and stable in handling. A water-based electrolyte also removes the fire risk of organic solvents. Zinc can store a large amount of charge at useful voltages. Yet pairing zinc with water creates persistent chemical problems. Water breaks down at the zinc surface and produces hydrogen gas. Corrosion sets in, and thin needle like zinc filaments called dendrites can grow during charging. These structures can puncture internal layers and cause the cell to fail. Past stabilizing approaches, such as additives, coatings, or solid barriers, improve one issue but often introduce new weaknesses like brittleness or reduced ion movement.
Hydrogel electrolytes offer a promising balance. They are soft polymer networks filled with water that conduct ions well and resist mechanical failure. But earlier hydrogels showed tradeoffs. Some healed quickly after cuts but were too weak for real devices. Others were stronger but slow to repair or allowed zinc corrosion because they held too much free water. A hydrogel that combines fast healing, strength, and a stable chemical environment would be a significant step.
The hydrogel, called PHBC-4, is a self-healing polymer electrolyte designed specifically for rechargeable zinc metal batteries. It is built to move zinc ions efficiently, suppress harmful reactions at the metal surface, and recover after mechanical damage. The researchers test it in several formats, including a flexible pouch cell that can be cut during operation and then restored.
The schematic representation showing the preparation of a self-healing hydrogel polymer electrolyte and the flexible quasi-solid state zinc metal battery fabrication. (Image: Reproduced with permission from Wiley-VCH Verlag) (click on image to enlarge)
PHBC-4 is made from two water absorbing polymers that form its network. Boric acid, a zinc salt, and an ionic liquid are added to create a dense set of reversible bonds. These include strong but reconnecting boron–oxygen bonds, many small hydrogen bonds, and temporary links involving zinc ions. Together, these interactions give the gel both mechanical strength and rapid healing.
Water in PHBC-4 is not free flowing. It is mostly bound to the polymer framework, which reduces the amount available to react at the zinc surface. This helps suppress hydrogen gas formation and corrosion and creates a more stable environment during charging.
The hydrogel conducts ions at a level similar to good aqueous electrolytes, reaching 4.6 × 10⁻² S cm⁻¹. It also behaves as a soft solid that stretches to many times its length before breaking. When cut, the pieces seal within seconds and recover most of their strength within minutes. Control hydrogels without boric acid or with altered water composition heal far less effectively.
These structural features influence zinc behavior strongly. In a direct comparison, a cell using a simple aqueous electrolyte remains stable for 383 hours before deterioration. A matching cell using PHBC-4 remains stable for 1032 hours under the same operating conditions. The zinc surface stays smooth rather than developing dendrites or corrosion products. This reflects both more uniform zinc deposition and the reduced reactivity inside the hydrogel.
The team then pairs PHBC-4 with a manganese oxide-based cathode. Over extended cycling, the gel-based cell keeps 67 percent of its initial capacity after 1000 cycles, while the same cathode with a standard aqueous electrolyte keeps only 27 percent. The hydrogel reduces damaging reactions in the cathode and steadies the zinc anode.
To demonstrate practical use, the researchers build a flexible pouch cell with an active area of 3 × 3 cm². It retains stable performance over hundreds of cycles and continues working when bent or folded. Its open circuit voltage stays near 1.90 V during mechanical deformation.
They then perform the most revealing test. While the pouch cell powers a light emitting diode, they cut it with scissors. The voltage drops as the cut interrupts the ion pathway. After the edges are pressed together and the pouch is resealed, the voltage returns and the cell resumes cycling. After several cuts and repairs, the battery still delivers about 71.0 mAh g⁻¹, which equals 87 percent of its post damage capacity.
This study shows how a hydrogel electrolyte built from reversible bonds can stabilize zinc metal, reduce unwanted reactions, and recover from physical damage. PHBC-4 combines efficient ion transport with fast healing and strong mechanical integrity. It supports both long-lasting coin cells and flexible pouch cells that continue operating after being cut. These traits strengthen the case for zinc-based batteries as safer and more resilient alternatives to conventional lithium-ion systems.
For authors and communications departmentsclick to open
Lay summary
Prefilled posts
ORCID information
Sreekumar Kurungot (CSIR-National Chemical Laboratory)
, 0000-0001-5446-7923 corresponding author
Nanowerk Newsletter
Get our Nanotechnology Spotlight updates to your inbox!
Thank you!
You have successfully joined our subscriber list.
Become a Spotlight guest author! Join our large and growing group of guest contributors. Have you just published a scientific paper or have other exciting developments to share with the nanotechnology community? Here is how to publish on nanowerk.com.
