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.    

I'll be back... in 8 hours

Some of my readers have wondered why I have been off the blogosphere in the last few months. The reason is that we brought a house and the move from the apartment to our new place has been a bit of a time sink.

First we went through the four stages of home buying:

Stage 1: What the &%#@ do you mean they accepted our bid? I thought you said we were lowballing?

Stage 2: When you use words like "downpayment", does this involve us giving you a check?

Stage 3: I assume roof's are like batteries? Meaning, when you say it is at the end of its life, there is still 80% left, right?

Stage 4: Keep repeating after me: "Owning is better than renting" and, please, stop asking "why?"!

Then we realized that owning a house also meant owning things like leaf blowers and lawn mowers! So, when I saw that there was a battery-powered lawn mower, I jumped at the chance to push my favorite technology forward.

I was looking forward to using my expertise in batteries to maintain and extend the life of my lawn mower for many years to come.

I was not particularly looking forward to mowing the lawn, but owning a battery-powered mower seemed to make up for that.

Until I realized that the top-rated battery-powered mower uses lead-acid batteries.

Lead-acid!!! really! How old school can one really get.

My first thought: Start a battery company to make Li-ion batteries for lawn mowers.

Then I started thinking about this some more. There must be a catch here. So I started digging into what it was.

Let us do some math: The battery for this lawn mower cost ~$270/kWh. That is one expensive lead-acid battery. Presumably, it is a deep-discharge battery, and so it is better made than a car battery.

And there is probably a significant markup.

Did I mention that the mower was on sale for $300! More like a mark-way-way-up.

Considering a typical Northern California growing cycle, this mower will probably be used ~50 times a year (once a week). These deep-discharge batteries can probably go a few hundred cycles. So I'm thinking 4-5 years easy.

But the bigger problem is going to be the calendar life. Sulfation can kill these cells.

Having said that, the battery is probably going to be at the top-of-charge pretty much through its life (think about it: Mown for 1 hour. Keep it plugged in all week). And remember our rule for lead-acid batteries: Keep them charged. So I think we can expect to get ~3 years from these cells.

Lets do some math for a Li-ion battery. I bought one a few weeks ago. This battery will probably last me 3 years and get me ~300 cycles or so. So it has similar specs to the lead-acid battery.

The Li-ion battery, on the other hand, cost me a whooping $2300/kWh!! No... really. This is what it cost me.

Now... knowing Apple, a new word has to be coined for their level of markup. But still this is one expensive battery.

At this price, a Li-ion lawn-mower-battery would have cost me $800!

All you MBA-types are probably cringing because you all know that cost and price are very different from each other and that the price is dictated by what the market is willing to pay (my wife is an MBA and she gave me this spiel).

Granted. So let us do a cost-differential comparison. This comes out to be ~$50/kWh more expensive for a Li-ion cell. Using this, the cost of a Li-ion battery for this mower would be higher than the lead-acid battery by... the price of lunch!

Not at Chez Panisse. But at the LBNL cafeteria (same quality, but at a much lower price?)

So why not use a Li-ion instead. After all it is almost 5x the energy density.

The mower that I have been talking about in this blog is a push mower. So the battery does not need to drag itself. All it has to do is turn the cutting blade. And space is not a big constraint. The mower's size is dictated by the size of the blade anyway.

So why bother using a new type of battery when you don't really see much of a benefit?

Frankly, although I have not looked at the life-cycle, I'll take a bet that it is probably better for the environment to use a lead-acid battery considering how much of this lead is recycled. In comparison, all you recycle in a Li-ion is the high-value metals in the cathode. The rest, literally, goes down the drain.

Maybe the math will change for a self-propelled mower. Or if the weight of the mower is an issue. But I don't see any reason to jump to using a Li-ion battery for the mower I was looking at. This business plan does not appear to have much legs.

So what did I do? I got the corded version of this mower. It cost me $100 less.

I guess the price that I'm willing to pay to push my favorite technology forward is less than $100!

In my guilt I decided to do my part for the technology by buying a Roomba.

I'm not sure if you guys know about this amazing robotic vacuum. It is pretty interesting to watch. It has sensors that make it slow down when it approaches objects, detect dirt, and prevent it from falling off of stairs.

It is not particularly good at vacuuming. But it feels like it is cleaning the floors and isn't that what's important!

But here is the kicker. The one I have has a Ni-MH battery.

I suppose I should be thankful it is not a lead-acid, but Ni-MH? COME ON!

The last time I checked, the cost of Li-ion and Ni-MH batteries were pretty comparable. And the energy density of Li-ion is 2-3x greater. And remember that in this machine (unlike the mower) the vacuum has to drag its battery along. And space is a big deal. The smaller the footprint, the smaller the space it can vacuum.

So why use a 20th century battery for a 21st century machine? Strange.

A web search revealed that Li-ion Roomba's have apparently died prematurely. If this is the case, then iRobot (the company that makes the Roomba) needs to change battery suppliers.

The vacuum I got goes through 2 rooms and then runs out of juice. It could have finished my house in one charge if it had a Li-ion of the same size. Or you could have a better vacuum on it so that it actually picks up dirt instead of moving it around and still only vacuum 2 rooms. You get the point.

When I first saw this machine, I thought that all the things on Terminator (the movie) were coming true. Jokes apart, it really is a pretty decent robotic cleaner which does indeed find its way around. You can, pretty much, set it and forget it.

But then I realized that we had nothing to worry from the machines as long as battery technology evolves the way it has been in the past.

When Arnold Schwarzenegger's character said "I'll be back" on T2, he (it) actually meant "I'm running out of battery and I need to go find an outlet and charge for 8 h. I will then come back to look for you for the 1/2 hour my battery lasts. Wish me luck".

So much for the machines taking over.

If you constantly complain about how batteries are not evolving fast, did you ever consider for the second that maybe we are out to save the world in our own way?

Venkat

A Brief History of Batteries- Part 2

Last week I posted on the need to understand the history of battery development and how this will influence the future of batteries.  We conclude today with Part 2 of this series. 

Chapter 3:  If it is sparingly soluble, then lets talk. 

The lead acid battery is the first rechargeable battery ever made.  Its endurance over 150 years is a testimony to its robustness (or to the fact that battery researchers can’t seem to find anything better even after 150 years.  It is all a point of view!). 

The lead acid battery undergoes what is called dissolution-precipitation.  This is the mechanism by which charge/discharge occurs in the battery.  Basically, you dissolve the compound in solution and then it precipitates out.

The behavior of the lead-acid battery is remarkably similar to that of the zinc electrode in a Zn-manganese oxide alkaline battery or for that matter to the lithium thionyl chloride battery.

But if the lithium thionyl chloride is not a rechargeable battery and the zinc-manganese oxide is not a rechargeable battery, then why is the lead acid a rechargeable battery? 

This is because the lead sulfate is soluble in sulfuric acid (which is the electrolyte) unlike the lithium chloride.  But it’s not as soluble as the zinc oxide in potassium hydroxide.  

Its solubility is not too much, nor too little.  It’s just right!  It’s referred to as a sparingly soluble salt. 

This feature of having sparing solubility is critical in making a battery that undergoes dissolution-precipitation recharge. 

This occurs because the reactants and the products are right next to each other.  This means that when you go in reverse, there is a high probability that things go back to the same place where they came from.  Not having something move around is a great way to prevent shape change.

Once you understand that solubility is key you begin to understand the decades that were spent on trying to change the solubility of zinc oxide in electrolyte using various techniques.  And you begin to start thinking about ways to encapsulate the zinc.  And you begin to wonder if you should never let the zinc precipitate as zinc oxide and if you should just keep it as zincate by, say, flowing it. 

All these perfectly valid ideas start to make a lot of sense.  What you can’t answer is if these ideas will succeed in solving the fundamental problem with the zinc electrode. 

But we should remember that in general, the lead-acid is not the greatest battery in the world when it comes to recharging.  Think sulfation.   Remember the blog post on battery rules where I Haiku-ed my way to better battery life?  Remember that sulfation occurs in the discharged state. 

The reason for this is also fundamentally connected to this dissolution-precipitation mechanism.  On the one hand, this mechanism allows you to make a good rechargeable battery, on the other hand, it also causes it to die in time. 

Moral of this story:   If you want good rechargebility, dissolution-precipitation is not a good idea, although we may be able to live with it.    

Chapter 4:  And you thought electroplating was easy.

Electroplating has been a gift that has been giving for decades.  Probably the last big development was the via-hole plating of copper for making semiconductor chip interconnects. 

In general, plating something uniformly is not easy, but it’s not an unsolvable problem either.  We do have a lot of smoothly plated stuff all over the place. 

This is until you try plating lithium (and a few other metals, including zinc).   Plating lithium is sort of important because this would be the charging reaction if you want to make your watch battery a rechargeable battery or if you want to make a Li-sulfur or Li-air battery rechargeable. 

People spent much of the 2-3 decades of the last century trying to make a rechargeable lithium (watch) battery.  The last time I check, I was asked to buy a new watch battery and not try to recharge it. 

This is because, in the case of lithium, the plating results in dendrites and lead to shorting of the battery. 

The reason for this starts with surface inhomogeneities that lead to nucleation of the deposition process in one spot, after which ohmic and transport effects lead to further amplification of this inhomogeneity.

That complicated paragraph is tying to tell you that it plates out like a needle sticking out of the electrode.  The needle can puncture through the separator and short to the cathode.  As I keep mentioning in these blog posts, shorting a battery is not a good idea.  Really, it is not.

Same problem happens in the zinc electrode.  Zinc wants to plate out as a dendrite instead of a smooth surface.  Same reasons as above. 

Every electrochemist that learns of this issue immediately thinks of 10 things to try that could solve the problem.   Turns out all 10 ideas probably don’t work.

There have been, literarily, thousands of studies on trying to solve this issue.  The most promising appears to be using a separator that is hard and prevents the dendrite from growing. 

But as of today, we do not have a method to prevent lithium dendrites at room temperature and give us good power capability.  It’s a problem that is still around. 

The moral of this story:  If your battery requires you to plate out a metal, it is probably going to be an issue achieving good rechargebility. 

And if you want to make a rechargeable Li-air or Li-S electrode, getting the lithium to recharge is, I’m pretty confident, a pre-requisite. 

Epilogue:  Rules to live by. 

So how do we make a rechargeable Li-S and Li-air (or zinc-air) battery?

If I knew that I would not be writing blog posts!

But we need to beat three things that history has taught us: 

1.     Avoid electrodes that require a plating reaction. 

2.     If you have a product that is highly soluble, you are in trouble

3.     If you don’t have any solubility, its worse

One can avoid all this by finding systems where no structural changes happen.  Thus were born systems like Ni-MH, Li-ion, and Ni-hydrogen.  These systems have their own problems, but atleast we are starting with something that has certain inherent advantage.   I will elaborate on these problems in the very near future when I delve into the present-day developments in batteries. 

But suffice to say, if you want to make the battery of the future, then you have to beat the three issues listed above. 

Along the way, you may make the batteries of the past also work.  

Venkat

A Brief History of Batteries- Part 1

When I was around 13 years old I remember learning about primary batteries in school.   This was about the time when I had also encounter lead-acid batteries and had realized that the car starter battery is being charged periodically.  I began to wonder why some batteries could not be recharged while other could.  Thus began my fascination with batteries. 

The above story is probably not true.  But it’s etched in my memory probably because it provides me with a romanticized notion of why I work on batteries today.  In reality, I was probably contemplating something more useful like “what is the point of learning math?”.   

Nonetheless, the question posed is an interesting one in that if we want to understand how to make a rechargeable battery that lasts a long time over many cycles, we first need to understand why some batteries do not recharge.  

The development of batteries is deeply rooted in this understanding (atleast one hopes it is and that it isn’t a series of accidents!).  Many of the ideas that people are proposing today for better batteries are in some ways trying to beat the fundamental limitations that prevent recharging of these primary batteries. 

If you don’t want to make the mistakes of the past, you better understand the past.  This post is an attempt to do just that. 

The topic I’m discussing is technical.  I’ve tried my best to make it accessible.  In doing so, I lose some technical accuracy; but this is the price of making it understandable.    

This blog post is written in the style of a novel.  The story of rechargeability can be written in a very linear fashion which steps through time to illustrate the rules one after another.  But this would make it easy to understand. Where is the fun in that!

So, I’ve borrowed a page from Quentin Tarantino’s movie Pulp Fiction and scrambled the narrative.  Each storyline is distinct, and they are all interrelated.  If the stories were arranged chronologically as the systems developed we would go Chapter 3, 2, 4, 1, Prologue, Epilogue.  I personally think the scrambled version reads better. 

This week I will start with the Prologue and Chapters 1 and 2.  Next week I will finish with Chapters 3 and 4 and the Epilogue. 

Fortunately, these stories are easier to follow when compared to Pulp Fiction.

And there is no swearing or violence. 

Prologue:  Do I smell sulfur in the air?  

There has been a lot of interest over the last few years on two systems that have been around for years.  These batteries are sold as going “beyond lithium-ion”.   These systems use lithium metal as the negative electrode and air (rather, the oxygen in the air) or sulfur as the positive electrode.  Some consider these systems to the Holy Grail of battery research. 

The promise that these battery chemistries hold is enormous.  In the case of lithium-air, the gravimetric energy is an order of magnitude higher than today’s batteries.  Think cars that can drive 500+ miles, cell phones that actually last all day, laptops that can last the complete transatlantic flight...  The volumetric energy is not that great, but hey, let us focus on the positives, shall we.

But there is a hitch (there always is).

In the case of lithium-air, it turns out that recharging lithium metal is a problem.  And the oxygen in the air reacts to form a compound that is basically pretty insoluble. 

In the case of sulfur, the lithium metal continues to be a problem.  And the sulfur electrode undergoes a series of reactions giving products that are either highly soluble, or insoluble.  All the products are a real pain to deal with and history shows us that dealing with them may not be for the faint of heart. 

If we are to succeed in getting these batteries to work, we first need to understand why similar concepts have failed in the past. 

Chapter 1:  A business plan that can’t fail- Take cheese; make milk.

  

You may remember my previous blog post where I alluded to the lithium thionyl chloride battery.  

This chemistry is used for missile applications.  In this battery lithium dissolves from Li metal on the negative electrode and the resulting lithium ions combine with thionly chloride (SOCl2) to form lithium chloride (LiCl) in the positive electrode. 

This is the process that occurs on discharge and it works pretty well.  If you want to recharge this battery, you will need to take the lithium chloride and convert is into thionyl chloride.   This is where the problem occurs. 

Lithium chloride is an insoluble solid.  Once you form it, it pretty much sits around and starts clogging up the whole cell.  Converting lithium chloride back to thionyl chloride is like trying to find a Quentin Tarantino movie with no violence- its not hard to find; its impossible to find!

Think of this as taking a pot full of hot milk and adding lemon juice to it.  The milk curdles and you get cheese.  There is pretty much no way to get back to milk and lemon juice from cheese (as far as I know).  Same story with lithium chloride. 

If, on the other hand, the lithium chloride were soluble in the electrolyte and dissociated in the solution, one can think of trying to recharge the system.  However, because lithium chloride is not soluble, there is no way to recharge the battery. 

Moral of the story:  If the product of your reaction leads to an insoluble product, in some batteries, recharging can be a problem.

The caveat “in some batteries”, is kind of important, but that is not for this post.    

Something similar happens in the lithium carbon monofluoride system (Li-CFx).  In this system, much like the thionly chloride system above, the lithium dissolves and reacts with the carbon monofluoride to form lithium fluoride and carbon; both solids.  Trying to go back to the starting chemicals by reacting the lithium fluoride with the carbon is pretty much impossible.  It’s the cheese to milk problem. 

So solubility is something we ought to be paying attention to when it comes to recharging. 

But what if the product of the reaction is highly soluble (think salt in water)?  This must be the best thing possible for recharging, would it not? 

Turns out that this is not true either.  This would be the story of the zinc electrode.  As in the zinc-manganese oxide alkaline battery (the Energizer-bunny battery).

Chapter 2:  If only the Dead Sea weren’t as salty. 

The alkaline battery is actually a rechargeable battery.  It’s just that it is not a very good one.  Some of you may remember that there were rechargeable alkaline batteries in the market that promised a few cycles. These all appear to be gone from the market.  I guess no one wants to carry around a charger. 

The positive electrode (MnO₂) in these batteries can recharge thousands of times if you are careful to avoid certain phases.  I personally believe that this chemistry is worth revisiting. 

It’s the zinc electrode that is the problem.  The reaction involves zinc electrochemically reacting and forming a complex called zincate.  As the concentration of zincate increases, it precipitates out as zinc oxide.   Think of this as adding salt into water.  You can only add so much salt before the solution gets saturated and any more salt you add stays as crystals. 

This is the simple version. 

The whole reaction scheme is actually pretty complicated.  Turns out that five other reactions can happen in this battery depending on various conditions.  Some years ago, I was involved in modeling of the zinc-MnO₂ battery and it is by far the most complicated battery chemistry there is.  Lithium batteries are so much easier to understand with compared to this system. 

The zinc oxide has pretty high solubility in the electrolyte (potassium hydroxide). What this means is that zinc oxide easily goes into solution to form zincate in the electrolyte.  One would think this is great for recharging and it is.  But it turns out that when you try to deposit the zinc from the zincate, it does not deposit in the same place where it dissolved. 

This leads to the structure of the zinc electrode changing continuously as you charge and discharge the battery repeatedly.  This is referred to as shape change.  Shape change leads to the zinc depositing as a solid mass in the one part of the electrode.  And this solid mass is hard to react.  Slowly, as the solid mass gets more pronounced, the zinc electrode fades. 

Reduce the solubility of zinc oxide and you can decrease the shape change and increase the cycle life. There is some wonderful data that shows that. This is like somehow making salt less soluble in water.  Turns out that in reality this approach also kills the power of the battery and so this is not a real solution. 

The reason why the shape change happens is a bit complicated, and probably not relevant at this stage.   What does matter is that, in some batteries, very high solubility can be a bad thing and can decrease the ability to recharge. 

Moral of the story:  High solubility may not necessarily be a good thing for recharging.

So we have a problem.  Neither no solubility nor high solubility appears to be a good idea.  So how do we make a rechargeable battery?

We shall look at that in the next chapter.  Next week. 

Now… isn’t that a nice tease!  Stay tuned. 

Venkat