A Brief History of Cathodes or, Thinking Positively about Li-ion Batteries

Guest post by Marca Doeff

While Venkat is off trekking the Himalayas, fighting space aliens, solving world hunger, fixing his Roomba, on a well-deserved vacation, he has asked me, (moi, Marca Doeff, world famous battery scientist, lowly lab rat), to whip up a light and fluffy something to feed the blog. “Fine”, I said, “should I talk about my cats or the movie I saw last week?” Judging from his response, that’s not what he had in mind (wow, I didn’t know there were so many cuss words in Tamil!). Instead I concocted this little history of cathodes for lithium-ion batteries, complete with pictures (if you want cat stories, you’re going to have to look elsewhere on the internets).

            It all started around the mid 70’s or so, when Stan Whittingham at Exxon announced his newly discovered phenomenon of lithium ion intercalation into TiS₂, in a letter to the journal Science. It turns out that TiS₂, which has the layered structure shown below, could be reduced electrochemically while simultaneously inserting lithium ions between the layers. Better yet, this process was entirely reversible! Everyone in those days was interested in making a secondary battery with a lithium metal anode work. That announcement set off a race in research labs everywhere to look for other intercalation compounds.

The layered structure of TiS₂.

In 1980, John Goodenough, who was then at Oxford, wrote a paper in the Materials Research Bulletin describing another layered compound, LiCoO₂ or LCO. This one was made with lithium already in the structure, so it had to be charged up before you could use it in a battery. The battery companies at the time didn’t like this, so they said “Goodenough, it’s not good enough!” (haha, be kind to me, it’s lonely in the lab.) LCO also was pretty oxidizing once you started taking the lithium ions out, and the electrolytes of the day just couldn’t handle it. The last laugh was on the battery companies that dissed John Goodenough, though, because just a few years later, someone figured out how to make a graphite anode work, and the lithium-ion battery was born, and then commercialized by Sony in 1991. Having lithium in the cathode structure for that configuration turned out to be just what was needed, so that you could assemble the cell in the discharged state and then charge it up. Moreover, by that time, there were better electrolytes that didn’t fall apart so readily. The higher potential at which LCO operated compared to TiS₂ was an asset, not a liability, since it meant higher energy densities in cells. Batteries with TiS₂ and the problematic lithium anode were out, and Li-ion batteries with LiCoO₂ cathodes and graphite anodes were in!

             The layered structure of LCO.  The yellow spheres represent lithium ions.

            End of story? No, that was really just the beginning. Cobalt is awfully expensive and somewhat scarce. Everyone wanted a cathode that was cheaper with more abundant elements in it, like iron or manganese or nickel. People like Jeff Dahn in Canada, Claude Delmas in France, and Tom Ohzuku in Japan started looking at other layered compounds with various combinations of nickel and cobalt and manganese in them and sometimes a soupçon of aluminum or magnesium. They and many other scientists around the world fiddled around with the formulas to get the best energy density, safety, and performance. These layered compounds are often called by their initials, like NCA (nickel cobalt aluminum) and NMC (nickel manganese cobalt) and are among the most technologically important cathodes we have today.

But let’s backtrack a bit. A few years after LiCoO₂ was discovered, Mike Thackeray, who was living in South Africa at the time, visited John Goodenough’s lab and started fooling around with manganese oxides. Only problem was that the compounds he was looking at weren’t layered but had spinel structures instead. Strictly speaking, they weren’t intercalation compounds, because “intercalation” really refers to the insertion of ions between layers, like leaves of a calendar (“inter”=between and “calation” is related to the word “calendar” from the Latin word “calends” for the first day of the month). Nevertheless, lithium ions could be removed from lithium manganese oxide (LiMn₂O₄, LMO) and inserted back in again through three-dimensional diffusional pathways in the structure. Nowadays, the use of the term “intercalation” has expanded to mean insertion of ions not only into layered structures (the original meaning) but other types of structures as well. I guess if you are a grammar prescriptivist, this shift of the language is an offense against all that is good and holy, but if you are a grammar descriptivist like I am, it’s simply a useful word to use to describe the general phenomenon of ion insertion into all kinds of structures.

 Another surprise was the olivine-structured LiFePO₄ or LFP (Goodenough, again). It wasn’t even electronically conducting! Most intercalation compounds are mixed conductors; that is, both ions and electrons can move through the structure, which is necessary for them to function. A few of them start out nearly electronically insulating, but become more conductive as they undergo redox (notably, the spinel anode material Li₄Ti₅O₁₂). All you have to do is get the reaction started (say, on particle surfaces) and then it can propagate. In contrast, what you get when you oxidize LiFePO₄ is another nearly insulating compound, FePO₄. To this day, it is somewhat of a mystery of how and why it works, and scientists spend lots of time dreaming up exotic experiments to explain its behavior and arguing over what is really happening. Hey, we have to remain employed somehow!

On the left, the spinel structure of LMO and on the right, that of the olivine LFP. The yellow spheres represent Li ions in the structures.

It turns out that lots of structures with transition metals in them can insert lithium ions, even some that are completely disordered. Of course, the majority of these materials fail on some metric or other; some of them don’t have high enough capacity or energy density, some have rare or toxic metals in them, or they do something weird like dissolve or change their voltage characteristics when they are cycled. Of the hundreds of compounds that have been studied over the past forty years, only a few have passed muster. A modified version of LCO is used in consumer electronic batteries, and, depending on manufacturer, hybrid electric, plug-in hybrid, and electric vehicle batteries contain LFP, NCA, NMC, LMO, or mixtures of the last two.

Will something better come along? It’s hard to beat what we have now, but researchers are still trying. To quote the immortal Yogi Berra, it’s tough to make predictions, especially about the future!

Marca Doeff

Introducing Marca Doeff

As I contemplate the solution to the hype problem in batteries, we have a new blogger who wants to talk about a few real breakthroughs.

Marca Doeff is a Staff Scientist and a colleague at Berkeley Lab.  She taught me everything I know about cathode materials and is the person I call when I need to understand something about materials in general.  Her own research is focussed on materials for Li-ion batteries, sodium ion batteries, and solid state batteries.

She has done some really groundbreaking work in all three areas, including coming with a cathode material that has higher capacity than traditional layered materials, and decreasing the interfacial impedance between ceramic Li-ion conductors and lithium metal.  And No! She does not follow my guide to breakthroughs!

But she is also someone who has been in the thick of cathode development for Li-ion batteries for a long time and has a rich perspective on how we came to where we are today.  She is going to condense a 40 year history into a blog post.  So, for the first time on TWiB, something useful.

The researchers she writes about did not follow my guide either when they came up with their breakthroughs!

So... enjoy

Venkat 

Waiting for a breakthrough… to solve the breakthrough culture in batteries.

After my post on the hype in batteries, I had promised my seven readers that there would be a follow-on post with solutions.  But, I got to say, this has been a bit of a problem.  I have been toying with this question over the Thanksgiving break and don’t have anything profound to say… yet.    

I was toying with writing another blog post lampooning the hype culture! But I kind of regret the last post already (one does not make fun on one's own, and all that sentimental stuff) so that did not seem like a good idea. 

On top of that I’m off on vacation the coming week to India and will be gone till the end of the month.  So postings will have to wait till the New Year (although I may post something about batteries in the Indian context.  Let us see). 

But, TWiB will continue in my absence.  I have a guest blogger whose post will come up in the next 2 days.  I have couple of others who are also looking at guest blogging.  So you may actually learn something useful for a change! 

In the meantime, as I sit on the plane for 24 or 36 or whatever god-awful number of hours I have to sit on a plane, I shall be contemplating how we can get all the battery folks to tell us what is really going on.  I typically have one profound thought in a year, and have not had one yet.  So there is still hope. 

Venkat

A step-by-step guide to battery breakthroughs

It’s often said that breakthroughs cannot be scheduled.  I’m here to tell you that this is 20^th century thinking.  The statement assumes that the word “breakthrough” is unambiguously defined.   This blog post questions that assumption and provides a step-by-step guide to achieving a breakthrough.  My focus is on batteries, but with a few tweaks, one could adapt this for other areas also. 

Let me begin by saying that in the last century there was a feeling that a breakthrough was thought to be when, for example, you discover a new material for a battery that has, say, higher energy or is safer or something.  Those sorts of breakthroughs then go through the traditional rigmarole of publications, licensing, technology transfer, peer appreciation, awards, products and the rest of the boring stuff that takes 20 years to get settled.  In the age of Twitter, Facebook, Uber, and, Snapchat, this kind of time frame is for the folks unwilling to look to new ways of achieving breakthroughs.  If you belong to this “old” club, I suggest you move on.  This guide will be of no use to you.  

But what is a breakthrough anyway?  As far as I know there is no body that proclaims something a breakthrough (a Pope for science?).  And is there really such a thing as an eureka moment?  Even if you have one, it will be a year before you can reproduce the experiment and get all the techniques in place to prove it.  And if the breakthrough is supposed to be a product, it will take you 10 more years to scale it and make it.

But what if there were a reputable publication that actually called something a breakthrough.  And then this was validated and verified by other publications saying the same thing?  That appears to be in line with the scientific method, does it not?

So, for the purposes of moving forward, let us define a breakthrough as just that: It is proclaimed as such by more than one publication.  Also to help us move forward, publications will be broadly classified as a peer reviewed journal article, or a newspaper, or a blog, or a tweet etc.  i.e., as long as the word breakthrough and your work appear on the World Wide Web somewhere, you are golden.  This guide will help you get there.

A disclaimer:  The results are only guaranteed if you follow each and every step.

Step 1:  Before you begin the research, try not to read the literature.  The peer-reviewed literature is full of things that have been tried before.  If you read them carefully, then what you are doing will not be new.  Remember this mantra (courtesy of NBC when they were promoting reruns in the 90s):  “If you haven’t seen it before, its new to you”. 

Step 2:  As you start the research, remember that facts just get in the way.  The literature is full of facts (hence Step 1).   In 1492 everyone thought the world was flat; until Columbus took to the seas.¹  Then we all thought it was round, until Tom Friedman proved it was flat.  Until The Matrix came out, we thought gravity was forever binding us to the earth.  Breakthroughs happen when these laws are broken and it takes a bold person to go where no person has gone before.  To paraphrase Marsellus Wallace from Pulp Fiction, you may feel a slight sting every once in a while when it seems like you are violating faraday’s law.  Those are the facts f*ing with you.   f* facts.

Step 3:  Now that you have done your due diligence and ignored everything, it is time to focus.  Try to work on a newly-discovered material, or atleast one that has been forgotten for a while.  This is an important step.  As much as you can go after Steps 1 and 2, the more studied the material, the harder it is to prove to yourself that you are violating all the well-known laws because you are charting a new path rather than screwing up.  It’s so much easier to believe this if it’s a brand new material.  Graphene is good (not as a battery material, but remember Step 2). So are fullerenes  (granted they are old, but it seems like its time to revisit them).  Graphite, on the other hand, could be bad; unless you plan to use it in a new way; in which case it can be good.  Lithium metal is ALWAYS good; but if you go this route you really need to get religion on Steps 1 and 2.  

Step 4:  As you start getting data on the new invention, revisit Step 2.  Revisit it often, especially when you feel down. 

Step 5:  Time to start writing the paper.  Always state that your invention is better than Li-ion.  The only way to get anyone excited is to say that.  This may sound hard, but it is not.  There are many metrics that need to be satisfied for a battery, including, energy, power, charge time, cost, life, safety, low temperature and high temperature stability.  If you think that you have something that looks better in any one of these, you are doing better than Li-ion.  Cost is the easy one if all else fails.  You can always safely say something like “our preliminary cost estimates suggest that the battery will cost less than something-small/kWh”.  Other end of the spectrum is energy, which is the hardest.  If you go down this path you really need Step 6. 

Step 6:  Always confuse energy with power.  It’s completely appropriate to say “Our pixie dust battery can discharge a factor of 10 faster than Li-ion, therefore EVs based on pixie dust have a longer driving range comparable to Li-ion EVs”  or “our batteries can be charged in 5 minutes, providing more energy than any battery known to man or aliens. On a separate note, we only seem to get one cycle from our battery; we think this has something to do with aliens” 

Step 7:  The paper is ready and it is time to submit.  Never send the paper to a journal that specializes in publishing papers in batteries.  This will get your paper into the hands of traditional battery-types who remember past history, know what works and what does not, and have a strong scientific foundation in the field.  Such knowledge can be an impediment to your out-of-the-box thinking.  Remember Step 2.  Always choose a journal that is disconnected from the battery field. 

Step 8:  With the paper coming out, it is time to prepare for a press release.  Remember that the press wants to hear that this is a breakthrough.   So despite what the peer-reviewed paper proves, make sure you call it a breakthrough at the press release.  Remember that Steve Jobs did not really have a working iPhone when he announced it to the world, and declared that they would ship in 6 months.  If it is good enough for Steve, I’m sure it is good enough for you.  So don’t be shy in telling the press how great your battery will be.  Make sure that you give interviews to numerous publications.  Remember our definition of a breakthrough:  you need multiple publications to say it is one.  So target many outlets. 

Step 9:  The day has arrived; the publications are out; and you have spend the better part of the day googling yourself to see how far the word has spread.  This is the day when you may hear skepticism (some contained within the articles and others in emails addressed to you).  Remember Step 2.  Remind yourself that the iPhone had many critics (e.g, the proximity sensor will not work.  Who would want to surf the web on a phone anyway? Atleast they got the first problem right!).  If it worked out for Steve Jobs, then it could work out for you too.   

Step 10: Remember “Practice makes perfect”.  So go back to Step 1 and repeat. 

All the best. 

Venkat

1.  Now, you may search Wikipedia, or read some articles that claim that the earth was known to be round since before the Common Era.  But that is because you are reading the literature.  Did we not drill into you in Step 1 that this was bad!   Now stop looking up stuff and get with the program.    

Developing a roadmap for energy storage deployment

In my post titled “A boom. Then a bust. And now, a new equilibrium?” I had argued that this was a very unique time in batteries.  My opinion is that there are two fundamental trends that we need to pay attention to:

1.   Batteries are getting increasingly deployed, both in vehicles and on the grid, despite high costs.  

2.  Costs of batteries are coming down.  Typically, costs fall at 5-6% per year.  With the present push by the big companies, costs are expected to come down by a factor of two within the next 5 years. 

Let us talk about the first trend:  We have always had batteries in phones and laptops, but in the last few years, they have come on their own in bigger applications.  And this is despite the higher costs. 

Nissan has decided to commercialize a cheaper car with less battery (and, consequently,  less range), while Tesla makes a big car with a big battery to kill range anxiety (but adding wallet anxiety?). 

Utilities all across this country are deciding to install storage on the grid to learn more about how they work and how to monetize them, while home-owners with a green thumb (and a wallet to match) are thinking about how to stick it to the big guy. 

All this means that we are learning, everyday, about how the batteries are working in the real world.  Do they cycle well?  How does the fade change with temperature?  Are we going to get our money back if we buy a battery versus building a transmission line?  And what is the actual cost of the Tesla Powerwall per kWh once you add the invertor and pay for the labor? 

This is great for everyone.  Deployment will be the key to figuring out what works and what does not.

And this trend will only increase with the second trend of decreasing costs.  Many more will decide to go for an EV and install batteries with solar panels.  We will plug the EVs on the grid to try to learn if they can help pay for the costs.  We will plug them in all at the same time and we will know how the grid will react. 

But reality is that batteries will still be expensive, maybe a factor of two more than where they need to be. They will still have less life than solar panels.  And less energy than gasoline.  And will be less safe than Niagara falls (well… I suppose that depends on how hard you want to kill yourself!).   We will need new systems to satisfy these gaps. 

But new systems will require time and money to reach the market.  Both of which become scarce commodities when big players are cutting the costs of Li-ion batteries dramatically. 

This was the context for the day when more than 200 of us met at the 2015 Bay Area Battery Summit on Nov 3 at Berkeley Lab.  It was a great day with insightful talks and panels, wonderful hallway conversations with thoughts leader from academia and National Labs, industry, and policy makers. 

The main theme was to explore the interplay between technological innovations in batteries; the changing market, and the role policy can play in accelerating deployment.

I thought I would use this blog as a way to list a few key discussion points that I heard.   These are fodder for future blog posts, so I will keep them short.

- Storage resembles the solar market in the late 2000’s.  But there are differences (and significant ones at that).  What can we learn from solar?

- What does the equivalent of the California Solar Initiative look like for storage?

-  If reality is that the battery has to do more than one thing for it to be cost effective on the grid, what are those low-hanging use cases? And how can we get policy to align with this reality?

- What is the balance between deploying what we already have versus finding new things that can solve the cost, life, energy and/or safety challenges?

- If we do find something new, the reality is that we need 10 years and $300M to get it to market.  And on Day 1, the price of that battery will be huge!  How do these technologies compete with an existing technology where depreciation is already in play?

- How do we solve the conundrum that end users want to see data on a real system, while most startups can only make a few small cells? 

- Should someone in the midst of starting a battery company attempt to stay within the Li-ion manufacturing framework (to ensure that the big players buy them out)?  How can they try to disrupt the existing players and avoid the risk not being to get to scale?

- What are the role of the Federal and State governments, and the role of Universities and National Labs in ensuring that we have a portfolio of technologies in the market?

- And, the impossible problem: How do you get battery companies (and researchers) to stop overhyping what they do?  Funny enough, I was writing a blog post about this last week, but got distracted by the event.  Will get back to that next week.

As you can see, a VERY busy day with very deep conversations.   Over the next 2 months we will be consolidating the answers to these questions and providing a roadmap for ensuring success in the battery space.

One of the speakers (who, in the interest of fairness, will not be named) felt that batteries were somewhere around the “peak of inflated expectations” in the hype cycle.  Resetting expectations and doubling down on innovation and deployment will be crucial in moving towards productivity. 

But first, we need to talk about (and address) the problem of hype in batteries.  This will be the subject of my next couple of blog posts.

Stay tuned.

Venkat