Those lithium-ion batteries we’ve come to appreciate in cell phones and other small portable electronics don’t last as long as one would like – the full charge shrinks a little with each recharge.

Stanford researchers have developed part of a new dream battery with a new electrode that employs crystalline nanoparticles of a copper compound.  During the laboratory tests, the electrode survived 40,000 cycles of charging and discharging, after which it could still be charged to more than 80 percent of its original charge capacity.  That’s over a 100 years of daily charges.

The Stanford researchers use nanoparticles of a copper compound in developing a high-power battery electrode that is so inexpensive to make, so efficient and so durable that it could be used to build batteries big enough for economical large-scale energy storage on the electrical grid.

Copper Crystal Electrode Graphic. Click image for more info.

Colin Wessells, a graduate student in materials science and engineering who is the lead author of a paper describing the research, published this week in Nature Communications said, “At a rate of several cycles per day, this electrode would have a good 30 years of useful life on the electrical grid.”

Yi Cui, an associate professor of materials science and engineering, who is Wessell’s adviser and a coauthor of the paper adds, “That is a breakthrough performance — a battery that will keep running for tens of thousands of cycles and never fail.”

That’s a pair of pretty cheery guys with a big claim in hand.

It’s because the electrode’s durability derives from the atomic structure of the crystalline copper hexacyanoferrate used to make it. The crystals have an open framework that allows ions — electrically charged particles whose movements en masse either charge or discharge a battery — to easily go in and out without damaging the electrode. Most batteries fail because of accumulated damage to an electrode’s crystal structure.

Now add because the ions can move so freely, the electrode’s cycle of charging and discharging is extremely fast, which is important because the power you get out of a battery is proportional to how fast you can discharge the electrode.

Fast and very very long lifetime at low cost.

To maximize the benefit of the open structure, the Stanford scientists needed to use the right size ions. Too big and the ions would tend to get stuck and could damage the crystal structure when they moved in and out of the electrode. Too small and they might end up sticking to one side of the open spaces between atoms, instead of easily passing through. The right-sized ion turned out to be hydrated potassium, a much better fit compared with other hydrated ions such as sodium and lithium.

Wessells explains, “We decided we needed to develop a ‘new chemistry’ if we were going to make low-cost batteries and battery electrodes for the power grid.”  So they chose to use a water-based electrolyte, which Wessells described as “basically free compared to the cost of an organic electrolyte” such as is used in lithium ion batteries. They made the battery’s electrical materials from readily available precursors such as iron, copper, carbon and nitrogen — all of which are extremely inexpensive compared with lithium.

That means Stanford team’s new electrode is for working in a potassium battery.  “It fits perfectly – really, really nicely,” said Cui. “Potassium will just zoom in and zoom out, so you can have an extremely high-power battery.”  Potassium is much less expensive than lithium.

The speed of the electrode is further enhanced because the particles of electrode material that Wessell synthesized are tiny even by nanoparticle standards — a mere 100 atoms across.  Those modest dimensions mean the ions don’t have to travel very far into the electrode to react with active sites in a particle to charge the electrode to its maximum capacity, or to get back out during discharge.

Cui’s research group has a lot of recent research effort on batteries including lithium with the focus on high energy density, a lot of power in a small size.  For portable electronics that’s a primary concern.  But as the power need increases the size can be larger.  For grid storage size and portability hardly matter.  It’s the cost and the cycle times to replacement that matter.

Here’s the known catch – the sole significant limitation to the new electrode for potassium electrolyte is that its chemical properties cause it to be usable only as a high voltage electrode. But every battery needs two electrodes – a high voltage cathode and a low voltage anode — in order to create the voltage difference that produces the  electricity to flow. The researchers need to find another material to use for the anode before they can build an actual battery.

But Cui said they have already been investigating various materials for an anode and have some promising candidates.
Cui and Wessells point out that other electrode materials have been developed that show tremendous promise in laboratory testing but would be difficult to produce commercially. That should not be a problem with their electrode.

Wessells has been able to readily synthesize the new electrode material in gram quantities in the lab. He said the process should easily be scaled up to commercial levels of production. “We put chemicals in a flask and you get this electrode material. You can do that on any scale,” he said.  “There are no technical challenges to producing this on a big-enough scale to actually build a real battery.”

Even though they haven’t constructed a full battery yet, the performance of the new electrode is so superior to any other existing battery electrode that Robert Huggins, an emeritus professor of materials science and engineering who worked on the project, said the electrode “leads to a promising electrochemical solution to the extremely important problem of the large number of sharp drop-offs in the output of wind and solar systems” that result from events as simple and commonplace as a cloud passing over a solar farm.

The Stanford group is on to something more basic with the crystalline copper hexacyanoferrate structure. It’s a clue to finding other crystalline constructions to answer the low volt electrode question.  There is sure to be someone realizing the science could yield low cost electrodes for even denser lithium-ion electrolytes.

It would be quite something if the major electrolyte chemistries were to have electrode pairs with recharge cycles in the tens of thousands at very fast charge rates.  The effect would change the economics in more than just cost per watt hours, but the need for watt hour capacity.

Imagine – trading up the cell phone and keeping the battery, the major cost component, for several models.  Manufactures and consumers have to love that idea.

Go Stanford.


4 Comments so far

  1. Matt Musson on November 25, 2011 8:27 AM

    One firm near Charlotte is restarting a lithium processing plant. Although they bring their raw material up from Argentina, they will turn our finished lithium metal.

    Strategically, it will be good to have a home grown source of lithium if battery manufacture takes off with these new electrodes.

  2. | CleanTechnica on November 29, 2011 12:12 PM

    […] water-based electrolyte, which Wessells says is “basically free.”However, according to New Energy and Fuel, more development work needs to be undertaken on this project. As it turns out, the new […]

  3. Stanford Researchers Explore Large-Scale Renewable Energy Storage | Volumatrix Group on December 1, 2011 10:36 PM

    […] according to New Energy and Fuel, more development work needs to be undertaken on this project. As it turns out, the new […]

  4. Lucy on January 18, 2012 9:55 PM

    well. water-based electrolyte may limit the operation voltage, isn’t it?

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