Bubbles And The Future Of Electric Cars

With about three times the energy capacity by weight of today’s lithium-ion batteries, lithium-air batteries could one day enable electric cars to drive farther on a single charge. But the technology has several holdups, including losing energy as it stores and releases its charge. If researchers could better understand the basic reactions that occur as the battery charges and discharges electricity, the battery’s performance could be improved. One reaction that hasn’t been fully explained is how oxygen blows bubbles inside a lithium-air battery when it discharges. The bubbles expand the battery and create wear and tear that can cause it to fail.

A paper in Nature Nanotechnology provides the first step-by-step explanation of how lithium-air batteries form bubbles. The research was aided by a first-of-a-kind video that shows bubbles inflating and later deflating inside a nanobattery. Researchers had previously only seen the bubbles, but not how they were created.

If we fully understand the bubble formation process, we could build better lithium-air batteries that create fewer bubbles,” noted the paper’s corresponding author, Chongmin Wang, of the Department of Energy’s Pacific Northwest National Laboratory (PNNL). “The result could be more compact and stable batteries that hold onto their charge longer.”

Wang works out of EMSL, the Environmental Molecular Sciences Laboratory, a DOE Office of Science user facility located at PNNL. His co-authors include other PNNL staff and a researcher from Tianjin Polytechnic University in China.

The team’s unique video may be a silent black-and-white film, but it provides plenty of action. Popping out from the battery’s flat surface is a grey bubble that grows bigger and bigger. Later, the bubble deflates, the top turning inside of itself until only a scrunched-up shell is left behind.

The popcorn-worthy flick was captured with an in-situ environmental transmission electron microscope at EMSL. Wang and his colleagues built their tiny battery inside the microscope’s column. This enabled them to watch as the battery charged and discharged inside.

Video evidence led the team to propose that as the battery discharges, a sphere of lithium superoxide jets out from the battery’s positive electrode and becomes coated with lithium oxide. The sphere’s superoxide interior then goes through a chemical reaction that forms lithium peroxide and oxygen. Oxygen gas is released and inflates the bubble. When the battery charges, lithium peroxide decomposes, and leaves the former bubble to look like a deflated balloon.

Source: http://www.pnnl.gov/

 

Friendly Alternative To Li-Ion Battery

An unexpected discovery has led to a rechargeable battery that’s as inexpensive as conventional car batteries, but has a much higher energy density. The new battery could become a cost-effective, environmentally friendly alternative for storing renewable energy and supporting the power grid.

A team based at the Department of Energy’s Pacific Northwest National Laboratory (PNNL) identified this energy storage gem after realizing the new battery works in a different way than they had assumed. The journal Nature Energy published a paper today that describes the battery.

PNNL batteryPNNL’s improved aqueous zinc-manganese oxide battery offers a cost-effective, environmentally friendly alternative for storing renewable energy and supporting the power grid.

“The idea of a rechargeable zinc-manganese battery isn’t new; researchers have been studying them as an inexpensive, safe alternative to lithium-ion batteries since the late 1990s,” said PNNL Laboratory Fellow Jun Liu, the paper’s corresponding author. “But these batteries usually stop working after just a few charges. Our research suggests these failures could have occurred because we failed to control chemical equilibrium in rechargeable zinc-manganese energy storage systems.”

After years of focusing on rechargeable lithium-ion batteries, researchers are used to thinking about the back-and-forth shuttle of lithium ions. Lithium-ion batteries store and release energy through a process called intercalation, which involves lithium ions entering and exiting microscopic spaces in between the atoms of a battery’s two electrodes.

This concept is so engrained in energy storage research that when PNNL scientists, collaborating with the University of Washington, started considering a low-cost, safe alternative to lithium-ion batteries − a rechargeable zinc-manganese oxide battery − they assumed zinc would similarly move in and out of that battery’s electrodes. After a battery of tests, the team was surprised to realize their device was undergoing an entirely different process. Instead of simply moving the zinc ions around, their zinc-manganese oxide battery was undergoing a reversible chemical reaction that converted its active materials into entirely new ones.

Source: http://www.pnnl.gov/

Catalyst Converts Hydrogen Directly To Electricity

A research team at the Center for Molecular Electrocatalysis – Pacific Northwest National Laboratory (PNNL) has been developing catalysts that use cheaper metals such as nickel and iron to make fuel cells more economical. The one they report here can split hydrogen as fast as two molecules per second with an efficiency approaching those of commercial catalysts. The center is one of 46 Energy Frontier Research Centers established by the DOE Office of Science across USA to accelerate basic research in energy.
hydrogen electric carHyundai ix35 FCEV (Fuel Cell Electric Vehicle)

A drawback with today’s fuel cells is that the platinum they use is more than a thousand times more expensive than iron,” said chemist R. Morris Bullock, who leads the research at the Department of Energy’s Pacific Northwest National Laboratory
such a catalyst is the first iron-based catalyst that converts hydrogen directly to electricity. The result moves chemists and engineers one step closer to widely affordable fuel cells.
Source: http://www.pnnl.gov