Battery researchers, including those at Stanford University, have been focusing for years on improving lithium batteries of multiple chemistries. While IBM tries to create the 500-mile battery based on lithium-air reactions, and ReVolt in Portland works on perfecting a long-lasting zinc-air cell, Stanford researcher Hongjie Dai and his team claim to have “developed an advanced zinc-air battery with higher catalytic activity and durability than similar batteries made with costly platinum and iridium catalysts.”
The resulting battery, detailed in the May 7 online edition of the journal Nature Communications, could be the forerunner of something with greater endurance and lower cost than current efforts.
Mark Schwartz, writing for Stanford, quotes Dai, a professor of chemistry at the University and lead author of the study: “There have been increasing demands for high-performance, inexpensive and safe batteries for portable electronics, electric vehicles and other energy storage applications. Metal-air batteries offer a possible low-cost solution.”
Lithium-ion batteries, despite their limited energy density (energy stored per unit volume), high cost and safety problems, have received the most attention, says Dai, but notes that “metal-air batteries have drastically higher theoretical energy density than either traditional aqueous batteries or lithium-ion batteries,” with zinc-air having the highest energy payoff for a relatively low cost.
Zinc-air batteries combine atmospheric oxygen and zinc metal in a liquid alkaline electrolyte to generate electricity with a byproduct of zinc oxide. When the process is reversed during recharging, oxygen and zinc metal are regenerated.
Metal-air batteries with aqueous electrolytes can be inherently safe, a major advantage considering the critical monitoring necessary for lithium cells.
Usually catalytic reactions during charge and discharge are “sluggish” on zinc-air batteries. Dai’s group developed a number of Active and durable electrocatalysts on the air electrode are required to catalyze the oxygen-reduction reaction during discharge and the oxygen-evolution reaction during recharge. In zinc-air batteries, both catalytic reactions are sluggish, Dai said.
Recently, his group has developed a number of “high-performance electrocatalysts made with non-precious metal oxide or nanocrystals hybridized with carbon nanotubes. These catalysts produced higher catalytic activity and durability in alkaline electrolytes than catalysts made with platinum and other precious metals.”
“’We found that similar catalysts greatly boosted the performance of zinc-air batteries,’ Dai said. ‘A combination of a cobalt-oxide hybrid air catalyst for oxygen reduction and a nickel-iron hydroxide hybrid air catalyst for oxygen evolution resulted in a record high-energy efficiency for a zinc-air battery, with a high specific energy density more than twice that of lithium-ion technology.’”
The battery shows good reversibility and stability over weeks’ long charge and discharge cycles. Despite the encouraging results, Dai notes “challenges” with the zinc electrode and the aqueous electrolytes.
Still, intrinsic safety and increased capacity are reasons to go forward.
Other authors of the Nature Communications study are Yanguang Li (lead author), Ming Gong, Yongye Liang, Ju Feng, Ji-Eun Kim, Hailiang Wang, Guosong Hong and Bo Zhang of the Stanford Department of Chemistry.
The study was supported by Intel, a Stanford Global Climate and Energy Project exploratory program and a Stinehart/Reed Award from the Stanford Precourt Institute for Energy.
While the Stanford press release avoids sharing numerical data, the abstract for the Nature Communications paper gives a few hints as to how good the zinc-air battery might be.
“Primary and rechargeable Zn-air batteries could be ideal energy storage devices with high energy and power density, high safety and economic viability. Active and durable electrocatalysts on the cathode side are required to catalyse oxygen reduction reaction during discharge and oxygen evolution reaction during charge for rechargeable batteries. Here we developed advanced primary and rechargeable Zn-air batteries with novel CoO/carbon nanotube hybrid oxygen reduction catalyst and Ni-Fe-layered double hydroxide oxygen evolution catalyst for the cathode. These catalysts exhibited higher catalytic activity and durability in concentrated alkaline electrolytes than precious metal Pt and Ir catalysts. The resulting primary Zn-air battery showed high discharge peak power density ~265 mW cm−2, current density ~200 mA cm−2 at 1 V and energy density >700 Wh kg−1. Rechargeable Zn-air batteries in a tri-electrode configuration exhibited an unprecedented small charge–discharge voltage polarization of ~0.70 V at 20 mA cm−2, high reversibility and stability over long charge and discharge cycles.”
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