Aqueous Zinc batteries get core technology

Aqueous zinc-ion batteries (AZIBs) hold a lot of promise if the right technological advancements are carried out and has the potential to even exceed the adoption of lithium-ion batteries (LIBs).

When it comes to energy storage systems (ESSs), LIBs have a lion’s share due to technology maturity; however, there are multiple risk factors including fire risk, instability in supply of lithium, disposal issues and higher price. In contrast, AZIBs use water as an electrolyte there reducing fire risk and costing is also a major advantage as price of zinc, the raw material, is only one-sixteenth of that of lithium.

Researchers in Korea have announced they have developed a technology for manufacturing “high-density zinc metal anodes,” which is key to commercializing AZIBs. This manufacturing technology is expected to act as a catalyst for the mass production of AZIBs because zinc metal anodes with high energy density and long lifespan can be produced through a simple electroplating process by using low-cost and ecofriendly solutions.

In theory, because AZIBs utilize two electrons per ion, they are advantageous in terms of volumetric energy density relative to alkali metal-ion batteries. If the capacity of the zinc metal used as the anode for making the battery does not exceed twice that of the cathode, it is possible to realize an energy density comparable to that of the LIBs commercialized today. Furthermore, even if the capacity of the zinc metal reaches five times that of the cathode, it is still competitive in that it is similar to that of sodium-ion batteries, which are attracting attention as the next generation of batteries owing to their low cost and material abundance.

However, zinc metal anodes restrict the energy density and lifespan of AZIBs because of the irregular growth of nanoparticles during battery operation. A low zinc metal particle density and a large surface area in the anode accelerate corrosion with the electrolyte, thus depleting the active zinc metal and the electrolyte. Existing studies have typically used zinc metals that were 20 times thicker than what was required to counteract the lifespan limitations; paradoxically, this led to an inevitable decline in energy density and cost competitiveness, the biggest strengths of AZIBs.

The new study at the KIST controlled the microstructure of zinc metal anodes to reduce the prevalence of the side reactions that induce the decline in energy density and lifespan of AZIBs. The team adopted a deep eutectic solvent (DES) solution, which can be easily synthesized at room temperature, was to construct the compact zinc anodes. This DES solution is composed of choline chloride and urea mixed at a mole ratio of 1:2; the mixture becomes a liquid complex with a melting point of 12 °C. The researchers confirmed that a zincophilic copper–zinc alloy layer spontaneously forms between the zinc and copper current collectors within the DES, enabling high-density zinc particles to grow. The researchers succeeded in using this discovery to develop an electroplating process that allows zinc metals to grow densely and evenly in the low-cost and ecofriendly DES solution.

Application of the manufactured zinc metal anode to an aqueous zinc battery system showed that the corrosion reactions are effectively suppressed, and the capacity is maintained at more than 70% after more than 7000 repeated charges and discharges. This result is exceptional relative to those of similar existing studies that utilized thin zinc, and the values far exceed the charging and discharging lifespans (1000–2000 times) of commercial LIBs.

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