High-voltage, super-stable sodium–zinc hybrid batteries

Aqueous, non-lithium-based, rechargeable batteries are promising candidates for next-generation large-scale energy storage systems owing to their safety credentials and low cost. However, their commercialization is hindered by a narrow electrochemical stability window and relatively low energy density.

With the development of advanced electrolytes a precursor to improved performance, researchers from the China University of Petroleum have reported a breakthrough which represents a significant leap forward in the field of aqueous battery technologies.

The team has synthesized a novel hydrogel electrolyte that, when paired with a Prussian blue cathode, achieves outstanding energy density and cyclability in sodium-zinc hybrid ion batteries.

The newly developed hydrogel electrolyte, named Zn–SA–PSN, is built on a polymer network featuring interconnected amide chains and hydrophilic functional groups, which are key to its high performance. This design delivered an impressive ionic conductivity of 43 mS·cm⁻¹, significantly surpassing traditional electrolytes, and an expanded electrochemical stability window of 2.5 V. The broader stability window supports higher voltage operations, critical for enhancing the energy density of batteries.

When paired with a Prussian blue cathode, the sodium-zinc hybrid battery demonstrates remarkable performance, achieving over 6000 cycles with a minimal capacity decay of just 0.0096% per cycle at a high current density of 25 C. This stability is attributed to the hydrogel electrolyte’s ability to suppress side reactions and inhibit dendrite growth, which are common challenges in zinc anodes.

Additionally, the battery achieves an energy density of approximately 220 Wh/kg and outstanding rate performance, with capabilities of up to 5 C.

According to the researchers, the Zn–SA–PSN electrolyte is compatible with both aqueous sodium-zinc hybrid batteries and zinc-ion batteries.

“Our hydrogel electrolyte represents a significant advancement in the field of aqueous batteries,” said Dr. Linjie Zhi, lead researcher on the project. “Its ability to maintain high performance over thousands of cycles and at high current densities is a testament to its potential for practical applications in energy storage. This innovation addresses critical limitations in current battery technologies and opens new avenues for further development.”

Their findings are discussed in Advanced high-voltage and super-stable sodium–zinc hybrid ion batteries enabled by a hydrogel electrolyte published in the journal Energy Materials and Devices.