Extremely inexpensive grid-scale batteries

We have a new paper out, dealing with our long-term effort to develop extremely inexpensive and safe batteries for large-scale use. The full title is “Rechargeability and economic aspects of alkaline zinc-manganese dioxide cells for electrical storage and load leveling.” The idea driving the research is that since DOE cost targets for grid-scale storage are very low ($100/kWh), battery design should begin with the cheapest and safest materials possible, instead of trying to adapt high-power lithium-ion battery designs.

Zinc and manganese dioxide fit that bill, and what the paper shows is that by reducing the depth of discharge (DOD) to some fraction of the full capacity, long cycle life can be achieved at extremely low cost. The plot below shows that at 10% DOD over 3000 cycles are typical, while at 20% DOD it is over 500. These are base designs, focusing on electrode construction, materials, porosity, etc, with no additives or specialty materials. Assuming one cycle a day, this is an 8.5 year lifespan at 10% DOD.

Zn-MnO2 cycle life

Cycling a fraction of the DOD like this allows a long lifespan, while keeping the cost low. This shallow-cycled Zn-MnO2 battery comes in very low in lifetime investment cost, 2-5 ¢/kWh/cycle. Using numbers taken from the literature, this is in or below the projected range of vanadium-redox and sodium-metal-halide (ZEBRA) batteries, while being low-temperature and generally lower complexity than these. An extra benefit is that since only a fraction of the Zn-MnO2 capacity is cycled, the reserve capacity can be used in emergencies.

Zn-MnO2 lifetime cost

Over the last few years we’ve developed these types of batteries in many shapes and sizes, supported by DOE’s ARPA-E program as well as other entities like the utility Con Edison. A couple of battery racks in the CUNY lab are shown below. A little over a year ago Urban Electric Power LLC was spun out, and in their battery labs a few blocks away on 127th Street they’ve been developing the batteries for commercialization, and refining the design for higher power and longer life.

CUNY Energy Institute battery racks

Our analysis in the paper addresses evolution of the batteries during their lifetime. If you notice above, at 10% DOD the efficiency falls from near 90% to near 80% during cycling, due to a kind of “formation” of the materials. The analysis, which was Nilesh Ingale’s doctoral thesis, is too dense to describe in full but a combined modeling+experimental effort shows that the MnO2 active particles in the cathode become coated with hetaerolite (ZnMn2O4) and this resistive film drops performance. Below you see this resistivity plotted against cycle number, showing the effect mostly occurs in the first 150 cycles. Preventing this will help efficiency, but could also impact how the batteries are made and lower cost.

Zn-MnO2 film formation


Berkshire Hathaway to buy Duracell

duracell batteries

Warren Buffett’s company will pay about $3 billion for Duracell. Duracell’s main product is single-use alkaline Zn-MnO2 batteries, although they produce other primary chemistries including a high-power lithium iron disulfide cell. In the rechargeable market they sell three different Ni-MH batteries, in the same familiar form factors as the primary cells: AA, AAA, C, D, and 9V.

In the past few years we’ve been developing rechargeable Zn-MnO2 batteries for large-scale use, such as electrical grid storage. When doing basic Zn-MnO2 research, I often use electrodes produced by our research group, but then repeat the experiments using Duracell batteries. This is to avoid any intellectual property haggles when talking about my research, but also because Duracells are so reliably made that it helps assure me any experiment will be repeatable. In other words, Duracell batteries are a gold standard for Zn-MnO2.

Although Warren Buffett tends to want companies to keep doing what they already do best, the Yahoo Finance article about the deal couldn’t help but mention larger markets Duracell could try to move into:

Still, demand remains for the single-use batteries that power TV remotes, purring animated cats and many other electronic toys. And some experts say there is plenty of opportunity for Duracell if it can find ways to sell more rechargeables and tap into the market for large batteries used in vehicles and on the power grid. With Berkshire Hathaway’s vast resources, which included $62.4 billion cash at the end of September, and its 10 percent stake in Chinese carmaker BYD, it’s tempting to think of this deal as a play on electric vehicles, said Jeff Chamberlain, who helps direct energy storage research at the Argonne National Laboratory.

Dr. Nilesh

Nilesh ESA

Nilesh Ingale got his Ph.D. yesterday here at the CUNY Energy Institute. He and I have worked closely for several years, modeling alkaline batteries, worrying about manganese dioxide. Congratulations, my man. Here’s my favorite Nilesh picture, from 2012: he’s taken Valerio’s ID to get into an event at the Electricity Storage Association conference. I don’t remember why. Maybe they had good food?

I read the news today oh boy, about an impact factor that made the grade

Today I got an email from Elsevier titled “Elsevier Publishes the Top 8 Electrochemistry Journals,” which proclaimed “including the top-ranked journal Biosensors and Bioelectronics which has an Impact Factor of 6.451!” And a helpful graphic, given below free of charge with no advertising fee to Elsevier:

electrochemistry impact factors

I don’t read much into a journal’s purpose beyond its name. What does it mean that Biosensors and Bioelectronics is the “top-ranked” electrochemistry publication? I always thought it was for biosensors. (And bioelectronics.) Does this just mean the field of biosensors is taking off like a rocket? Or does it mean that the journal is “good,” transcending the areas of study stated in the name, making it an appropriate venue for any high-profile topic, such as discovery of gravitons or life on other planets? NEW PLAN: I’m sending everything I have to Biosensors and Bioelectronics, even my grocery list.