Tuesday, November 1, 2016

Tips on extending battery life; from a battery guru.

Probably best to get this out of the way right upfront: The battery guru referred to is yours faithfully.  Sorry to disappoint.  

Regular readers of this blog (all seven of you) know my rather famous (!) blog post titled “Battery rules”, where, inspired by Michael Pollan, I penned a poem that went,

Don’t charge them too high
Don’t swing them too wide
Keep the temperature low to extend their life.

This post was a follow on to my other tremendously popular (read:  eight total views) post titled “Pull the plug.  Your battery will thank you.”  The posts were meant to provide an understanding on why Li-ion batteries fail and how one can use this understanding to extend the life of batteries.  

Just to be clear: These rules are for Li-ion batteries; for phones, laptops, cars etc.  Not for other kinds of batteries.  And not for every Li-ion battery known either; but the most popular ones.  

The reason’s for these rules are simple.  Li-ion batteries don’t like to be at the top of charge (because of side reactions that consume lithium).  They don’t like being charged and discharged completely (because of the volume change associated with moving a lot of lithium back and forth and the associated stresses).  And higher the temperature, more the side reactions that impact battery life. 

When the blog post was written, the whole fast charging of batteries was not a big deal.  But now, we are seeing more and more emphasis on this.  Fast charging can also be bad.  More on this at the end of the post. 

The simple statement “Pull the plug” was really a way to implement the 1st rule “Don’t charge them too high” without much thought.  In other words, don’t use your laptop like a desktop and keep it plugged in.  All. The. Time.  This only makes the side reactions worse.  Stop charging.  Let the battery discharge a bit. 

Every time I walk into a meeting and see the inevitable dive under the table to find the charging plug, followed by attaching the charging cable to the Mac laptop, only to see that the charging light is green, my blood pressure increases.  I then go thru the sermon explaining why they need to pull the plug. 

They comply.  For 15 mins. After which they are back to plugging it in.  Blood pressure increases.  Cycle repeats.

And No.  No real breakthroughs have occurred since the post that makes the rules obsolete. 

Clearly, the rules are not working.  I’m sure it is not the messenger (?).  I’m sure it is not the message.  So it must be the way the message is delivered. 

So this post is battery rules redux.  I will explain how I charge and use my battery.  Hopefully, this gives folks a sense for how they can maximize their battery. 

My track record:  I have a computer that lost 4% capacity in 2 years.  I have a phone that lost 5% capacity in 2 years.

In this post, I will focus on the phone and how I baby the battery.

First some basics:  On any typical day I only discharge my battery around 30-40%. There may be an occasional day when I will discharge the battery by 70%, but those are rare.  In other words, I could use my battery for two days without needing to recharge it. 

If my usage seems rather minimal, it is not (although I never got into the pokemon revolution).  Rather it is because of two attributes that many of you probably share. 

First, I have an iPhone 6 plus (the YUGE one that does not fit in any normal size pocket).  This means that the phone has a pretty large battery.  And although the screen size is larger, the bigger battery more than compensates for the power draw of the screen.

Second, the operating system on the phone, iOS, is very battery friendly.  I moved to the 6 plus from an Android phone (with, I believe, the KitKat version).  That phone had to be charged after an eleven hour day, despite having a reasonably large battery.  It would drain 5% of the battery capacity every hour, even when the phone was, supposedly, idle.  iOS appears to lead to less battery drain, especially during rest.

Based on my usage profile and the attributes of my phone, here is what I do:

- I charge my phone in the evening close to when I’m about to go to bed.  My battery is around 40% state of charge (SOC).  I charge it to around 80-85% SOC.  Takes me ½ hour or so.  I don’t agonize over the exact SOC, I pull the plug when I remember to. 

- I sleep and when I wake, the battery has lost maybe 3% of so of its capacity (No. I don’t sleep for 1 h.  I sleep the normal 7 h).  I don’t plug it in. Rather, I go about my day, make calls, check email, listen to podcasts, etc.   I use the phone as much as the next person.  When I get back home I’m at approximately 50% SOC and a couple of hours later, when I’m ready for bed, at 40%.  I repeat the charging cycle.

In effect, I don’t let the battery charge too high.  I don’t let it swing too wide.  In other words, I follow my rules.  I don’t leave it charging all night (i.e., where the battery is fully charged a couple of hours after we hit the bed and is sitting at the top of charge for the next 5-6 hours).  I don’t discharge it all the way down each time before charging it.

- When I feel like my day may be particular long with a lot of phone use, which for me typically means I’m on travel, I charge the phone upto 100% SOC, typically in the morning before the day starts.  Meaning, it is fully charged, but is not sitting at the top of charge for hours on end. 

- Every few months, when I’m not on travel and have a predictable week, I fully charge the battery and drain it down all the way before recharging it.  This should allow the phone to calibrate the SOC by performing a discharge capacity check. 

This may sound counter intuitive:  I have a battery that should last 2 days.  But, I choose to charge it every day.  In effect I’m racking in cycles, twice as fast as I need to.  Is that not bad? 

I would posit that it is not.  The number of times the battery is cycled has to be put in context of the SOC that the battery swings, and how much time it spends at places where side reactions can dominate.  We know that batteries can cycle 300,000 times (yes.  Three hundred thousand!) when the SOC swing is kept rather small (say 3%, like what occurs in a hybrid electric vehicle).  In these situations, the calendar life of the battery (i.e., how many years it lasts) is more critical than the number of cycles.

As we widen the SOC swing, the battery life decreases.  The worst is fully charging and discharging the battery.  Even worse is going to the top of charge where we have side reactions.  My scheme minimizes the time spent at the top of charge, without overly swinging the battery. 

And it keeps me on a reasonably manageable daily schedule for charging without having to think too deeply about it.

Frankly, it would be better for me to charge the battery upto say 50-60% SOC and let us drain down to 10-20% each day.  But, that, to me, is living dangerously.  Having that extra 20%-30%  of buffer capacity gives me peace of mind (What if I get lured into Pokemon Go on my way home?).

Irrespective of what phone you have, and how you use it, the two rules (don’t charge them too high and don’t swing the too wide) will help you.

As far as the rule to keep the temperature low, I don’t keep my phone on my car dash where it is hot. My phone happens to be sitting somewhere in front of the air vents, which helps during summer.  I don’t keep my phone on hot metal tables in summer. 
I have been known to go so far as to contemplate living in frigid conditions just to avoid the high temperatures in some parts of the world.  Talk about taking ones job seriously… 

Now for the whole fast charge issue. 

In my blog post titled “The Hero with four faces: Part 1” I explored the question of fast charge and the issues surrounding it.

Short summary:  Lithium can plate (which makes the battery go boom).   If you swing the SOC too much and too fast, you can break the particles (although this may not be as big a deal as folks think it is).  And the battery tends to get hot when charged fast , violating the rule to keep temperatures low. 

Turns out that one does not want to go too low in temperature either.  We know that lithium plating is much more of a problem at low temperatures; i.e., Golidlocks effect. 

Of these, lithium plating is the one to avoid at all cost; the rest only degrade the battery and are not dangerous (unless the battery really starts to cook).  All it does it kill the battery capacity rapidly, which, for a device that one changes every 2 years, is not really a big consideration.

Having said all this, the phone maker meters in the charge from the charger.  Meaning, just because you get yourself a beefier charger does not mean that your phone is going to accept the charge.  The phone maker is supposed to watch out for the battery. 

But there is a push to use fast charge as a differentiator in consumer electronic devices.  This means is that unless the company is performing some sort of smart charging to avoid the problems above, the battery is probably not going to do well. 

So, unless you hear it from this blog, best to avoid fast charging your phone. Assuming your phone maker gives you such an option. 

In the meantime, assuming poems are not your thing, can I remind you all that that friends don’t let friends keep their batteries plugged in.  So, be a nice buddy, and ask your neighbor to pull the plug. 


Sunday, October 23, 2016

Cobalt blues: The Li-ion supply chain and the shackles it creates.

In recent weeks, two articles in the Washington Post laid bare the sorry state of the supply chain for Li-ion batteries; batteries that have made our phones into a device we use for everything (except calling people!); is changing the way we drive; and promises to change the way we generate and use energy. 

The first one on cobalt mining in Congo describes dangerous conditions, child labor, and exposure to toxic metals.  Cobalt is essential for cathodes for Li-ion batteries.  The second article on graphite, used as an anode in Li-ion batteries, digs into the pollution, environmental destruction, and health effects from mines in China.  Both stories are very well researched; connecting the dots from the mines, to the supply chain, all the way to the companies that use them in smart phones and electric cars.  The articles are also depressing.  They reveal a side of these devices none of us want to see.  It is like watching Food Inc.

One question that I have gotten since these articles came out is:  Can we move away from cobalt and natural graphite for Li-ion batteries?  This blog post delves into this topic. 

Why did we start using cobalt anyway?

Marca Doeff’s blog post does a fantastic job of walking us through the history of Li-ion cathode materials.  Lithium cobalt oxide, which John Goodenough discovered, started the whole Li-ion revolution.  Cobalt oxide was (and is) expensive, so variations have been found that have no cobalt in them. 

Lithium manganese oxide came along soon after, was eventually commercialized, and reached the market for power tools and in plug-in electric cars. Manganese oxide is significantly safer than cobalt oxide, but it also has far less energy density.  And consumer electronics and electric cars need highly energy dense materials, so manganese oxide is not that useful for these applications. 

Another variant is lithium iron phosphate, which has a complicated IP history.  Many of you probably heard of this chemistry when A123 first commercialized this for power tools.  It has since become pretty popular in Asia for transportation applications.  The chemistry is very safe and has fantastic cycle life.  So there is hope that we can use it as the stationary storage market evolves.  But the wonderful safety and cycle life comes at the expensive of energy density, which is pretty low compared to cobalt oxide.  Ergo, limited use for high-energy applications.

In the late 90’s the nickel variant of cobalt oxide, lithium nickel oxide appeared to be gaining traction in the consumer electronics battery world.  But nickel oxide has some safety issues and this was a cause for concern.  Instead, what became more successful were a class of cathodes where the cobalt content was lowered instead of being eliminated.  These include nickel-cobalt-aluminum (NCA) and nickel-manganese-cobalt (NMC).  There was a period in the early/mid-2000’s when these variants seemed poised to displace cobalt oxide completely, partially driven by, what at that time appeared to be, the limit of cobalt oxide. 

And then, cobalt oxide got better. 

It was long thought that cobalt-based cathodes could not be used beyond a cell voltage of 4.2 V because of reactions between the cathode and the electrolyte that lead to degradation.  Today, with surface coatings to isolate the cathode from the electrolyte, combined with larger particles, cells charge to 4.4 V or more.  Coupled with the ability to achieve high tap densities (defining tap density is a blog post in itself!), cobalt oxide has again become the highest energy density battery available.  For smartphones, laptops etc., where the battery cost is relatively small, the energy density advantage is key.  So cobalt has come back to rule the Li-ion world.

But cobalt is still expensive.  So for larger batteries such as in electric cars and for stationary storage, the lower cobalt content materials such as NCA and NMC are used.  And it is not obvious to me that the high-voltage cobalt oxide cells (operating at 4.4 V) are going to be long-life batteries.  These are probably great for the 2-year change cycle for phones; not the 10-year change cycle for cars.

Although, to digress, I have a 2 year old phone that has only lost 7% of its capacity.  How, you ask?  Because I follow these wonderful battery rules.

I summarize all this in the figure below, including the options for the anode and the electrolyte (well... there really aren't many options for electrolytes!)

 Can we move away from cobalt altogether?

Not clear.  As I said before, we do have options that have no cobalt, but these options are not very high in energy density, except for the nickel oxide material.  The nickel oxide material works well, although the synthesis requires some care.  However the safety of the material is questionable.  And as the recent incidents with the Note 7 have highlighted, one should be designing safety into every component in the battery. 

In the meantime, lowering the cobalt content is probably the logical pathway.  There is a trend in the research stage to minimize the cobalt content, in some cases to as much as 10% of the transition metal content; without scarifying energy density. Some of these materials, referred to as the lithium-rich, manganese-rich materials, show enormous promise.  And they offer the hope of eliminating cobalt.  But they also appear to have some fundamental issues that need to be solved. Work continues, at universities, national labs, and in companies to bring these to market.

In addition, one can also imagine playing the same tricks on the NMC formulation that helped cobalt oxide operate at higher voltages.  This will help increase the energy density of this material, beyond what is possible with cobalt oxide.  But these are all still in the research stage. 

In batteries, the time from lab breakthrough (real ones, not the ones that are alluded to here) to market impact takes a decade or more.  So, we may be stuck with cobalt oxide for a while.  But there is hope that we can move away from it with less cobalt and maybe, one day, with no cobalt.

But, something tells me that even if that happens, we will find out that children can still be exploited and the environment destroyed in the search for the raw materials.  The issue here is probably not cobalt.  It is something far beyond what this blog was meant to address.  

Case in point is the graphite part of the Washington Post story.  Next week I will list our options for moving away from graphite anodes. 


Sunday, October 16, 2016

Finally, we know why the Note 7 exploded.

The answer, according to the New York Times:  Samsung seems to have packed it with so much innovation it became uncontrollable”.  Apparently phone components are like 4-year olds; put 3-4 of them in a room and they are ok, but pack 10 of them in a small place they will destroy the room with all the energy feeding off of each other.  Of all the theories, this one takes the cake. 

As much as I think the community should not be speculating on the underlying case of the explosion, I think we can’t help ourselves.  For battery types, this is the most interesting event that happened since the-last-time-there-was-a-fire, so we are all salivating.  What can I say: we don’t get out much. 

For non-battery types, I can see their need to know if more phones are going to be exploding.  Only way to know is to understand what happened with the Note 7. 

I have been getting this question steadily the past few weeks, so I thought I would collect all the speculation in one single place.  I also provide my views on this.  So here goes:

1. The battery was overcharged (BMS failure, too high an upper cut off voltage, aliens, whatever) and hence the fire.  I think the eager ones among us, who do not believe in waiting for more information, speculatively stated this.  I think Samsung’s revelation that there was a manufacturing flaw negates this theory.

2. Samsung used a 6 um separator in the battery and this lead to defects when assembling with a thin separator. This in turn led to shorts and the explosions.  As I explain below, this may be part of the story.

3. The battery had a manufacturing defect where the anode and cathode did not line up correctly, leading to edge effects, lithium plating and shorting.  This seemed very likely until the New York Times article came out. 

While these three issues are obvious ones that most battery types would guess, the New York Times articles makes the point that after initially concluding that it was the battery, Samsung realized that it was not that simple.  The article claims that Samsung could not pinpoint the reason!  Hence the wacky statement about “uncontrolled innovation”.

Let us be clear: Samsung makes great batteries. ATL makes great batteries.  If this were an obvious issue, they would have caught it after the first few weeks.  There is something to be said about the argument that this is a more complicated problem.

Since the Times article came out, we have had three more, system level, theories that have popped up.

4. The battery was being fast charged due to a chip design flaw.  Faster than it was rated for. This lead to overheating, thermal runaway, ending with you-know-what.  I’m not so sure about this.  The Note 7 phones were exploding even when not fast charged so…

5. There was so much being packed in a small volume that the battery was getting squeezed and the edges pinched, unintentionally, leading to shorts.  This theory does seem possible, but I like the theory below (which is a variant) the most. 

6. Samsung used higher content of silicon in the graphite-silicon blended anode.  The silicon expands on charge and swells the pouch.  Because the pouch was unable to swell in the phone due to the lack of space, it shorted and exploded.  I really like this theory.  There have been problems with battery swelling even before silicon came to the scene, but this has only gotten worse with silicon-graphite anodes.  Many consumer electronics companies have been worried about this and have a spec. for how much the battery can expand.  According to Mashable, the Note 7 had a 750 Wh/l battery; which is PRETTY energy dense.  Much more so than previous generations of batteries, suggesting higher silicon content than before. 

It is possible that higher silicon content combined with a thinner separator and less space in the phone for volume expansion all came together to lead to shorts and fires. 

I’m sure I’ve missed a few other theories (aliens?), but I think I got the majority of the ones I have heard.  

Now that we have that out of the way, let us talk a bit about what this all means. 

I think the initial speculation that this was a battery-level issue appears too simplistic.  Clearly, there is more to the story.  Batteries all over are safe, have been safe, and will continue to be safe.  Assuming you know what you are doing.

But what if you have “uncontrolled innovation” happen again? What is a poor battery to do if the overall system does not want to treat it kindly?  Li-ion batteries are energy storage devices.  Meaning, if you release the energy very very fast it is not going to be pretty.  So, some TLC is in order. 

But even if the system screws up how it handles the battery, shouldn’t the storage device itself be made to withstand any abuse?  As we move toward wearable technology with things attached to every part of our body, we need to ensure that the battery remains robust even if there is a system-level failure.

There has been a narrative going around that Li-ion batteries today are similar to where crystalline silicon solar cells where a decade ago: meaning, the prices are dropping and one can get installers and system integrators to come in and start to make them ubiquitous.  The Note 7 incident shows the perils of this thinking. 

Batteries are not plug and play devices where Jane-solarinstaller is going to buy something off of Alibaba and dump it in your garage and get you city permit folks to sign off as if they are inspecting your plumbing.  We better be buying from someone who knows how to make them well.  And we better know how to design the system correctly, install them well, and control them through the life of the device.

But to get the world where we do treat our batteries like we treat our microwave (bang on it to try to get it working?), we need the batteries to be robust inside out.  This requires a separate blog post, hopefully, in the near future.  

In the meantime, with the Note 7 off the streets, time for the battery folks to crawl back to the cave and focus on achieving a few breakthroughs.  Until the next incident… 


Sunday, September 11, 2016

Why are Note 7 batteries exploding?

Samsung Galaxy Note 7’s are exploding when they are charged.  The tech media is, rightly, trying to get to the bottom of this. 

Much has been said about how this can happen and the focus appears to be on overcharging Li-ion batteries and the resulting heat generation.  The only party that actually knows something about this is Samsung and they have said that there was a “minor flaw in the battery manufacturing process”. 

This does NOT sound like an overcharging problem.  This could be either misalignment of electrodes leading to lithium plating and shorting.  Or something like copper dissolution and subsequent deposition leading to shorts. 

Or something else. 

But more importantly, except for Samsung, we are all guessing.  As long as Samsung does not tell us (and I’ll go on a limb and say that they will not), we can make up anything we want.  But guess what: we are making stuff up!  We should probably stop. 

But where is the fun in that.  So let the speculation continue. 

Interestingly, the Chinese made batteries by ATL are not exploding.  Only the Samsung made ones are. So much for "low quality Chinese manufacturing"…