Guanjie Li with the aqueous zinc batteries and the decoupled dual-salt electrolyte. Credit: University of Adelaide
Chemical engineers in Australia have designed a new kind of electrolyte which combines 2 different salts to improve the performance of safe and affordable, rechargeable aqueous zinc batteries (AZBs).
According to a new study in the journal Nature Sustainability, pouch cells made with the electrolyte retained 93% of their capacity after 900 charge-discharge cycles at 25 °C, and functioned over a temperature range of -40 to 40°C.
AZBs are a promising alternative to lithium-ion batteries, which are widely used but suffer from lithium supply limitations and safety issues due to flammable electrolytes.
“An AZB will use water-based liquid, usually water with dissolved zinc salts as the electrolyte and zinc metal as the anode,” explains Professor Zaiping Guo from the University of Adelaide’s School of Chemical Engineering, who led the research.
“The liquid is water-based so it is not flammable which makes it much safer than other batteries. They are also a promising alternative because of the abundance of zinc as a resource, its low environmental impact and the battery’s high volumetric capacity.”
Guo’s team developed the new Decoupled Dual-Salt Electrolyte (DDSE) to address key problems associated with AZBs. Commercialisation is hindered by short lifecycles due to a narrow working temperature range and uncontrollable reactions between zinc and electrolytes, which releases flammable hydrogen gas and corrodes the battery.
“One type of salt helps the battery work well in different temperatures and improves how fast the battery can charge, while the other type helps protect the zinc metal inside the battery, so it lasts much longer, ” says first author Guanjie Li.
“Together, they give the battery very good performance. It can charge quickly and work for many cycles, over a wide range of temperatures, and with very little energy loss when sitting unused.
“In our DDSE, the first salt – like zinc perchlorate Zn(ClO4)2 – stays mostly in the liquid and controls how the battery handles freezing and how fast ions move.
“The second salt – like zinc sulfate, ZnSO4 – sticks to the zinc metal surface and protects it from damage. Because each salt stays in its own area and does its own job, the battery works much better overall. We used lots of advanced tools to see this special distribution and to understand the deeper science behind how it works.”
The pouch batteries retained 100% capacity over 3,000 cycles when kept at -40°C and 91% capacity after 300 cycles at 40°C.
“This is the first time such a well-balanced performance has been achieved in our field,” says co-author Dr Shilin Zhang.
“Unlike conventional ‘lean-water’ designs by high-concentration or organic-aqueous hybrid electrolytes, our decoupling strategy results in a non-flammable, affordable, and sustainable electrolyte formula, retaining the intrinsic merits of aqueous systems.
“This approach provides a clear path toward the practical deployment of AZBs in smart grids and electric vehicles, which in turn, offers nations safer and more sustainable energy.
“Our next step is to try this electrolyte in more practical battery systems. We want to fine-tune the recipe and also improve other battery parts, so we can build a real battery prototype that has a long-life, high-energy density, and low cost.”