Performance enhanced in zinc-ion batteries
Up until now, zinc-ion batteries have been severely hampered by their rapid degradation during use. The good news is that researchers from the King Abdullah University of Science and Technology (KAUST) have developed a new electrolyte and electrode combination that improves several aspects of zinc-ion battery performance, particularly the stability over multiple charge and discharge cycles.
Stationary banks of batteries connected to renewable energy sources, such as solar installations or wind farms, will be important to the transition from the current fossil-fuel-powered electricity grid. Unlike batteries for mobile applications, such as laptops or electric cars where battery size and weight are key, stationary batteries can be relatively large and heavy, raising the possibility that alternative rechargeable battery technologies to lithium-ion could be deployed.
Batteries centred on a water-based solution of zinc ions have shown great potential for stationary storage in terms of their high capacity, low cost and lack of toxicity. But according to KAUST research scientist Yunpei Zhu, “issues including low cycling stability and fast self-discharge have prohibited practical applications of aqueous zinc-ion batteries”.
“Both of these issues are related to the design of electrolytes and electrode materials,” Zhu said. The water-based electrolyte caused problems at both electrodes of the battery, causing damaging side reactions at the anode and rapid dissolution of the cathode.
To combat these issues, Zhu and colleagues developed a water electrolyte with a very high salt concentration. The more salt ions present in the solution to bind surrounding water molecules, the fewer free water molecules are available to damage the electrodes.
As zinc salts typically show limited solubility in water, the team added sodium to produce a highly concentrated electrolyte of zinc perchlorate and sodium perchlorate. “We found this combination delivers very high solubility to suppress water activity without lowering the key attributes of zinc-ion batteries, including their high ionic conductivity, safety or environmental friendliness,” Zhu said.
In addition to the novel electrolyte, the team developed a new nanofibre-based cathode material for batteries. As explained by group leader Husam Alshareef, “The nanofibre morphology enhances ion diffusion, which ensures faster charge and discharge rates of the aqueous Zn-ion batteries.”
As published in the journal Energy & Environmental Science, the team saw almost no capacity decay over 2000 charge cycles. The new combination of electrode and electrolyte thus “potentially solves the shortcomings of conventional aqueous Zn-ion batteries”, Alshareef said, and should enable station energy storage that is cheaper, safer and more environmentally friendly than lithium-ion batteries.
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