good evening and thank you very much for coming to the latest installment of the slack
public lectures this evening our talk is by johanna
nelson wecker actually a new staff member here at the laboratory
joanna did her phd at stony brook and her expertise is
x-ray microscopy how do you take a micrographic picture with x-rays
and get rid of all those lenses which are very really very difficult for x-rays and get down to the sub-micron
scale in terms of being able to visualize things she did a lot of her uh graduate work at
berkeley at the advanced synchrotron lights at birkeland yes at the advanced synchrotron light source
and i asked her did you work on batteries and she said no i worked on yeast
but it's fine this lead that leads naturally into this
as you'll see and you're going to get a whole new experience of what those batteries are
doing in your cell phones and laptops from this lecture so let's welcome johanna to hear about
the secret life of batteries
thanks how many of you have a battery on you right now
i do how many of you could explain to your neighbor how that battery works
be honest maybe iffy okay how many of you are frustrated when
your cell phone dies before the end of the day exactly so we all want better batteries
right one last question how many of you drive an electric vehicle
a few it's pricey but hopefully with this research we can make
it more affordable for everyone so today i'm going to talk to you about batteries and i'm going to talk to you
about how using x-rays we can learn more about batteries and with that knowledge we can make better batteries
so um we are going to first start with explaining how batteries work so we're
all in the same playing field and then why we need better ones and what we need to improve about them
and then we're going to get into the real science and i'm going to show you movies of batteries breathing
expanding and contraction cracking and then eventually failing and we're also going to watch the chemistry
happen and we're going to do both of those things using x-rays and then finally we're going to take it all back figure
out what we learned figure out how we can apply that to make a better battery
so what's a battery they come in all different shapes and sizes even potatoes
you can make a battery out of a potato and run a clock on it if you'd like
the two main components are two main types of batteries are
rechargeable and single-use batteries rechargeable batteries are more
expensive but you can use them again and again and so they're useful for things that are used frequently like
your cell phone your laptop power tools the lead acid battery in your car
and the car the batteries that are all in electric vehicles as well
single use batteries are much cheaper but they only work once but they're very
reliable so they're very good for a low current over a long period of time and
so they're good in batteries and flashlights when you need it instantly and you don't want to have to recharge
your batteries of your flashlight before you can use it in your smoke detectors for example also
that potato is a single-use battery you'd have to change the potato if you
and then the normal batteries you have so the two main differences are do you
recycle it after you used it once or can you plug it in and recharge it
we're going to mostly focus on rechargeable batteries because that's what we're going to use in electric vehicles
but how does a battery work and so i'm going to use the potato battery as an example
you need three things you need two electrodes of two different types of metal for the potato battery it's
usually copper and zinc so you can use a nail or penny
and then you need your electrolyte which the potato provides it's actually phosphoric acid inside the potato that's
going to be allowing the battery to work and so if you assemble your potato battery like this
you should be able if you attach the electrodes with a piece of metal get a current across it
so if we look at it schematically we still have our two electrodes zinc and copper and they're in a bath of
electrolyte that potato right now i have not connected the battery so it's open here
and there's a potential across it but if i close the battery then we'll start
discharging so i'll close the loop and we can light a light bulb for example
and there's two things that are happening one electrons which are negative charges
are going across the wire through our light bulb and lighting our light bulb and those electrons cause the
ions and remember that an ion is a positively charged atom
so basically you've taken off two electrons from our zinc and those ions go through the
electrolyte so i'm going to play that again so the ions go through the electrolyte and the electrons
go through the metal wire and they meet up again in the
other electrode what if we want to recharge this battery potato batteries don't recharge
but assuming we could recharge the battery the electrons would go back through the
metal and the ions would pass through the electrolyte again and they would go back
to the original electrode
now the way we like to plot what's going on in a battery is in a cv curve and it's a
capacity versus voltage curve here if you know anything about capacity here's a gravimetric capacity so it means
milliamps which is a current times hours which is time over grams
which is the weight of the material um so as we charge discharge the battery
you're going to see this little red dot it's going to go through the voltage so it's going to lower its voltage as
you take capacity out and then during the charge
we're going to gain voltage back as we charge up the battery so you're
going to see a lot of these cv curves and then in the next couple in the next hour
and so this is the basic way it's working so i you now have a big idea of how
batteries work why do we need better batteries now everybody needs a better battery for
their cell phone and their laptops just because it's convenient but the real
hard batteries to make are batteries for electric vehicles but why do we want to electrify vehicles
so here are three plots and this is the x-axis is time
thousands of years and present is right here and the first plot is the global
temperature second plot is the co2 concentration in the atmosphere and the third plot is the sea level and you can
see right here i've circled the co2 concentration over the last 10 years 25 years and you can
see it is skyrocketing if we zoom in and this is from 1960 to
present day you can see the co2 concentration in the atmosphere is steadily rising
and if we looked over time the global temperature is following the
co2 and same with the sea level so if we see that the co2 concentration is
skyrocketing we can pretty much expect that the global temperature is going to also increase as well as the sea level
and we see that as well if you look over in the last few years so this is 1880 to
present day and you can see that the global temperature is starting to rise and this is 1992 to present day and this
is the sea level and it's also starting to rise
and because sea level is rising we know that the ice caps are melting and so these are outlines and yellows of the
median ice cap from 1979 to 2000 and then from 2005
minimum and then 2007 minimum and if i plotted more recently it'd be even smaller
so clearly we have too much co2 in the atmosphere so we need to turn to cleaner energy
sources so instead of using fossil fuels we need to use things that do not produce any
co2 like like wind solar and other things like nuclear and
geothermal but if we turn to
using cleaner energy sources we need to think about what we use the
energy for so this is just electricity which is easy to convert well relatively easy to convert
but there's a large pie section for transportation and it's not
as clear on how you would convert clean energy to use in transportation
it's pretty inconvenient or just ridiculous
so we really need to think about storing our clean energy into a battery so we
can take our clean energy store it into large batteries and then we can put those batteries into a car and then plug
our car in when we've run out of charge and so that's why we really need to improve
these batteries
so in 1991 there was a big breakthrough in battery technology rechargeable
battery technology and that was with the lithium-ion battery and it revolutionized the portable electronics
device so we went from gigantic per sized car phones to our iphones of today
so here is a plot of different types of batteries and specific power on the y-axis and
specific energy on the x-axis so specific energy means that we can if we
go along the x-axis we can get more miles from our electric vehicle with the same
amount of weight if we go up the y-axis we can get more acceleration with the same amount of weight ideally in an
electric vehicle you want lots of miles lots of acceleration so we want to go up the diagonal
lead acid battery what you have in your car right now is down here and we've progressively
switched to nickel and that's improved our
mileage as well as our acceleration lithium ion batteries are up here lithium metal which has the potential to
work but it is currently very hazardous is even better
if we continue up this plot however we can compare it to fossil fuels and this is
really what our target is fossil fuels are way up here so we've got a long way to go
if we want to get up to fossil fuels so we basically want to force our way up
this slope so that we can make a vehicle that's electric that's going to run
like you expect a vehicle to run and since the 1990s since we invented
lithium-ion batteries there's really been only incremental improvements on rechargeable batteries so we really need
a scientific breakthrough that's going to help us go from here all the way up to here
so currently where are we standing in electric vehicles right now
the range is from 70 to 165 miles per charge which is
getting better every day unfortunately the 165 is a tesla
and really what they did is just eliminate the trunk space so you are carrying a large volume
of batteries the battery life however is actually really nice
we can run 200 000 miles on a single battery and maybe even more
um so we're really actually quite good on that um however charge times if you own an
electric vehicle you realize that you typically charge overnight or when you're at work because charge times take
from 6 to 12 hours ideally there are now fast charges charging stations which
take 15 to 30 minutes if i owned an electric vehicle i would not use them knowing what i know about
batteries um it's not a good idea i would do it in emergency but that's it
finally the cost if you compare a ford focus that's electric and that's the base model
compared to a similarly equipped non-electric ford focus the difference is twelve thousand dollars and that's
just the battery so we really need to lower the cost so that everyone can afford an electric
vehicle so these are the three things that we really need to work on the focus of this talk is trying to
improve the range and trying to improve it without reducing the battery lifetime and that's
a difficult thing to do so we want to look for a new anode
material here's a plot of the capacity the how
much range you can get from a single charge and different materials currently we use
carbon the most the best
material we can think of is pure lithium metal however it's flammable and it causes issues all of those
problems with air buses catching fire tesla's catching fire computer batteries
catching fire that's 10 times worse if you use pure lithium metal so people are working on it but it's
very tricky so the next best thing is to use alloying electrodes now an alloy is
just a mix of metals so you can have either of these three metals silicon
which has the best it's about five times higher capacity than the carbon that we use now
germanium which is about four times higher and tin which is only about two times higher now those alloys
means that these metals are mixing with lithium and forming an alloy
during the battery charging and discharging and you can also see that if you look on
the periodic table they're all right down the same column so they kind of make sense
you get worse capacity the heavier the material is so silicon would be the best material that
we want to look at
as i said they're alloying materials so if you take any of these metals silicon germanium or tin and you start inserting
lithium metal into the metal you form an alloy of lithium and that metal and it has a
large capacity it stores lots of lithium ions but there's also this large volume
change as you're putting lithium ions in your whole structure is expanding
that can cause issues it can cause cracking and fracturing in your material
so this is actually one of these metals it used to be a film that was very smooth and this is
after cycling you can see there's giant cracks in it and it's been compared to a dry lake bed
so we want to be able to reduce these cracks in fracturing because they're limiting the battery lifetime so we can
get this really nice capacity we can drive our electric vehicle really far compared to what we can right now
but your battery is only going to last 500 cycles maybe you're not gonna you're
gonna have to buy your battery about your new battery every year
so for the rest of the talk we're gonna study germanium and i said that silicon was the best
and germanium's a little heavier so it's not as good capacity but with x-rays it was easier for us to
to see germanium than it was to see silicon and so we chose that um but and it also represents all of
these materials tin silicon and germanium so if we know something about germanium we can
hypothesize about silicon as well unlike silicon it has a large lithium
ion mobility lithium ions can move very easily in germanium and also
electrons can move very easily in lithium silicon on the other hand is pretty it's
a pretty good conductor it's a pretty good insulator
so what we think is happening in germanium as we insert lithiums here's some
germanium particles we're not really sure what happens while we're considering lithium so we really
want to know what's happening right here what chemistries are happening but we know they expand
we're not exactly sure what lithium germanium alloy we have so we really want to figure that out
after we've inserted all the lithium that we can and then when we take out the lithium we're really not sure what chemistries
are going on as we're taking out the lithium but we do know that after the lithium
has been taken out germanium particles are fractured maybe pieces have fallen off
so we want to explore the chemistry and we want to explore the changes in size cracking and if the
particles break apart to do that we're going to use x-rays and
we're going to use three different techniques we're going to use x-ray imaging using a microscope
we're going to use x-ray diffraction to look at the crystal structure and we're going to use x-ray absorption
spectroscopy to look at the chemistry and with all three of these structures
all three of these techniques we can really get a complete picture of what's going on
and we're going to use x-rays because x-rays are very good at seeing inside things
you can see bones inside your hand if you go to the doctor's office you can see inside suitcases when you
put your luggage through the x-ray scanners at the airport so we want to do a similar
thing but look at very very small parts of the battery
and to do that we're going to have to go to a synchrotron so this work was done at stanford synchrotron radiation light
source and the great thing about a synchrotron is it produces extremely bright x-rays so it's your
doctor's office machine times a million
this is a night view of the synchrotron which makes it look pretty
this is a more realistic view of the synchrotron um from the top and there's a booster ring where the electrons are
sped up and a storage ring we take the electrons from the storage ring and they produce x-rays i'm not going to go into
how that happens but we get really bright x-rays from it
and i said we're going to look through a battery and we're going to look through a battery while it's operating and so we
need an x-ray transparent battery i'm going to pass around two examples of
batteries now they're not really batteries because i've taken out
the flammable lithium metal and the toxic electrolyte
just in case someone decides to take them home but they're an example of what our
batteries look like and there's a picture of it here in case you're too anxious to get
it passed to you and here's a schematic of it we can pass x-rays through it
and all of the components are here we have a current collector which is going to
provide that electrical contact between the two electrodes and that's shown here
we have lithium metal which is right here in the picture we also have the electrolyte soaked in
the separator and the separator is this plastic piece right here
the separator prevents the two electrodes from touching and causing a short circuit
which is very important we want the electrons to go through the current collector not directly from one
electrode to the other and then we have the counter electrode the other electrode that's not lithium metal which you can't see in this picture it's on
the other side and then finally this polymer polyester film and it's just a bag it's very
similar to the bags you get electronics in except that it's not aluminized
now i said we wanted to image batteries while they operate the easiest way to image things or
investigate things is when they're dead and cut apart but that doesn't really tell you really
much about the object so the next best thing is to study your
frog inside an aquarium so you can see it living breathing eating but it's not
really in its natural environment so we really want to study batteries in a natural environment we want to study
them while they're cycling extremely realistically and that's our end goal we
want to make a documentary on batteries
so the first technique we're going to use is x-ray imaging it's a microscope so we're going to be able to look at
microscopic material inside our battery we're going to be able to look at these germanium particles
that are on the micron scale
so here is a picture of the microscope this is the ssrl director he sometimes visits the microscope
it doesn't really look like a visible light microscope that you'd have in science class but it works very
similarly except that it uses x-rays simona mistra did some of the work on
the the early rock on this battery um but he's now working at basf in germany
um and then here is a close-up shot of the microscope and this is our battery right here and you can see there's two
electrodes that are connected i said that we were going to be imaging
things on the micron scale and so here is a picture of germanium the bright particles are
germanium and this is a scale bar that says 5 microns now the human hair is 40 to 80
microns and a red blood cell is about 6 to 8 microns so that gives you an idea
of how small this is so as we put lithium ions in these
particles are going to start to fracture they're going to start to crack and then as we add more lithium ions
they're actually going to start to expand and the cracks are actually going to fill in because you're expanding
and then when we take out lithium ions the particles are going to shrink and as we completely remove all of the
lithium ions that we can we're going to end up with not a material that looks like this but it's going to be spongy
it's going to be porous so i'll show you the movie now and there's going to be a dot that's going across that can tell you where you
are on the cv curve so you can see not much happens at the
very beginning but once you reach this plateau here see the particles are expanding they're starting to crack
the cracks actually fill in and then as we remove the lithium ions
the particles contract and you end up with something very porous looking it doesn't look like what
it originally looked like here so i'll play it again just so you can watch it so this is germanium particles inside a
working battery
that was the first cycle we can also look at the second cycle and in the second cycle what we see
and i will show you in a second is that only this large particle is going to expand and contract
all of the small particles up here and the particles down here are no longer expanding and contracting
and that's really quick so i'll play it again
so only that large center particle is expanding and contracting and
that's really important because all of the small particles are no longer having lithium ions inserted into them and
taken out so they're no longer participating in the battery's capacity so we're
losing capacity and we looked at a lot of different locations in the same battery and what
we found is this is particle size this area over here most of the small particles are green
they were inactive in the second cycle they were not participating in the second cycle but the large particles are still
participating in the second cycle they're still expanding and contracting in the second cycle
luckily ninety percent of the volume is in the two largest particles so that
really only means that we've only lost about a quarter of the capacity after the first cycle
but that's not what we want to do we want to maintain capacity as we cycle it multiple times and this is one of the
reasons why we're not getting 2000 cycles in these batteries because we're not able um we're losing all of
the capacity of the small particles
so what we think is the reason why the small particles are not active in the second cycle
but the large particles are are because the large particles have a larger surface area and it's just probability
so it's a higher probability that they'll stay electronically connected so something i didn't really tell you yet
is that these germanium particles aren't sitting directly on the current collector on this metal that conducts
electrons they're actually inside a conductive matrix and the lift the
electrons have to move through the conductive matrix to reach the particles
so as you add lithium ions the particles expand and the conducting matrix also gets
pushed out but as you remove lithium ions the matrix doesn't necessarily contract with
the particles and so you get these voids around the particles but you're more likely to have some
connection with the conducting matrix if you have a large particle versus a small particle where these
electrons can't reach the small particle because it's no longer connected
so that's what we hypothesize is happening inside the battery
to fix this what we want to do in the future is use a self-healing polymer
essentially that's a glue that's going to keep our small particles together so there's a group at stanford that's
developed this polymer where you can pull it apart you can break it and you can put it back together and it
stretches just as if you hadn't broken it so we want to try to use this glue so where we have large particles that
expand but the glue which is in pink heals all the particles and sticks them
together after they've contracted after the lithium ions have been taken apart
so another thing that we can do with our microscope is to take cat scans so we
can take 3d images of materials and the cat scans
exactly like you get in the hospital where a patient sits on this table and
there's an x-ray source and an x-ray detector that go around in a circle
here and you can collect 2d images at many different angles and there's computer algorithms that put
those and put those images together into one 3d image
now we can't rotate our synchrotron so we rotate our sample but in the hospital
you really don't want to rotate patients so they don't so we rotate our sample and collect an image at different angles
and you can see that at different angles these 2d images look very different but if you put them into a computer algorithm you can get a
3d object out and so we can do that with our battery and so we did
so we looked not as we were cycling but before we cycled after we put lithium
atoms in lithium ions in and after we removed those lithium ions and this is the same two particles in time and they're 3d so
we can rotate them and because we have a 3d volume we can
actually calculate how much expansion we have we have about a 320 expansion
which is really close to the theoretical and you can also see that
when you when you've added lithium ions it seems like there's some cracks here and actually if you remove the lithium
ions you can actually see that those cracks have fractured the particle into three independent pieces and so we now
have evidence that these big particles are fracturing into small particles and
these small particles are no longer connected to each
other now i have to fight so moving on to our next technique we
learned about a lot about what the particles look like how they fracture how they expand contract but now we want
to know what chemistry is what alloys are we forming with this germanium and lithium metal together and so the first
technique we're going to look at for the looking at the chemistry is x-ray diffraction and that specializes in
looking at crystalline material so this is what the x-ray diffraction
setup looks like x-rays come from here this is our battery again right there and the data looks like this and it's
sitting i've actually projected it onto the imaging plate so it doesn't really look like that in real life
but on the computer it looks like that and nyan liu is helping with making the batteries he's a
stanford graduate now he's just graduated
so a quick theory about what x-ray diffraction is if you take x-rays and you shine them
onto a material that's very crystalline and crystalline means that the atoms are regularly oriented so they
are evenly spaced in a very structured environment
you get a scattered a scattering pattern with bright spots everywhere and this diffraction pattern
is unique to the crystal structure it tells you where the atoms sit if you instead of a single crystal you
have lots of little crystals randomly oriented instead of bright spots you get bright
rings on your diffraction pattern but they also tell you something about where the
atoms are situated so we can tell what sort of crystal structure we have and what sort of
chemistry we have inside of our battery so to take that data which are rings
concentric rings you want to analyze it and make it into a 1d plot or 2d plot
so you notice that all of the rings are centered and you can just look at a specific radius
and the intensity is the same everywhere around it so if you take a specific band and just
add up all of the intensities you can get a plot in q space which is basically
similar to the r the radius going outward so these are small circles these are large
circles and all of these different peaks you can identify and will tell you
something about your material
so this is the actual germanium battery and i've only taken a small
section of the diffraction peaks because there's lots of them it's a little hard to tell maybe between the purple and the
blue spots but these two purple peaks are from the plastic pouch so an
annoying thing about having a real battery is you have crystalline material from things that you don't actually care about so
you just have to deal with them and then we have a little tiny germanium peak which is the peak we actually care about
so we're going to look at how this germanium peak evolves as we add lithium ions and then
remove them and we're also going to see are there other peaks that are forming other places
so this is an extremely busy plot but the plot that i just showed you is the first one down here
and as you go up the plot we are in black adding lithium ions and then the red
ones are removing lithium ions and i've identified different peaks either germanium peaks in blue or
lithium 15 germanium four which is a lithium germanium alloy in green
so the first thing you see starting from the bottom as we add lithium ions the germanium peak starts
to slowly disappear so we're gradually losing crystalline germanium which is what we expect we're
putting in lithium ions we should be forming some sort of alloy and eventually but there's this big
space here these lithium-15 germanium four peaks appear in green
and that happens near the end of our cycle of adding lithium ions
when we start removing lithium ions those three peaks start to gradually disappear
and interestingly enough this germanium peak doesn't reappear so we aren't reforming crystalline
germanium so we already know we're doing something to this battery that's not reversible
and we want a rechargeable battery when we want everything to be completely reversible so we already know this is a bad sign
but there's a lot of blank spots in here that we don't know what's going on so we know at the beginning we have
crystalline germanium we don't know what's going on around here but then we get lithium 15 germanium 4
which is really nice that's a lot of lithium ions for a few germanium atoms
and then we don't know what's going on as we remove lithium ions because we see no extra peaks
but remember x-ray diffraction only shows us what's crystalline it's only going to show us crystalline material
regularly ordered material all of the other materials that were forming in these blank spots
must be amorphous so they're not they don't have regularly ordered atoms so we need another
technique if we want to really understand the chemistry everywhere else
so that's where we're going to the last technique and this is x-ray absorption spectroscopy and that's going to tell us
more about the amorphous material the non-crystalline material
so this work was done by linda lim she's also a stanford graduate student
there are two detectors of x-rays and then you put your sample in between so your battery's
sitting here and very similar to how the other setups were the batteries look very much the
same you've got your two electrodes connected and you can cycle your battery
so what information do we get from x-ray absorption spectroscopy first of all what is x-ray
absorption spectroscopy so it relies on the fact that every element in the periodic table absorbs
x-rays very well at a specific energy
so materials absorb x-rays at any energy but at specific x-ray energies
they absorb them very well so there's a very big jump in their absorption and that's very specific to the actual
element around this large jump in absorption
there's all these wiggles all of that information can tell us about the chemistry and the
structure of the material and so we're going to use all of those wiggles to tell us what's going on in the
battery how do those wiggles actually form
so if we have our specific atom that we're interested in we're
tuned we've we've changed our x-ray energy so that this atom absorbs very very well
and then there's surrounding atoms here if you hit that
specific atom with an x-ray that absorbs very well
electrons scatter off it and we can think of them as waves
and so it's a circular wave going out which will hit other atoms that are surrounding it and they will bounce the
wave back and that information if we can collect it will tell us about
these atoms that are surrounding the atom that we actually hit and it's very similar to dropping rocks in a
puddle you've got circular waves going out and they can interact with each other and they produce
little waves in our absorption pattern
so this information can tell us about the neighboring atoms how many atoms are
there it can also tell us what type of atom they are what elements they are
how close they are what's the distance between the atom we hit and the neighboring atoms
and the best thing is it works on amorphous materials so it can work on glass it can work on liquid it can work
on our germanium lithium alloy that we don't know what it is
so this is the actual data that's analyzed and i just want to show you very quickly
that there's pretty much three big bumps this hump here this hump here and this hump here and
this again is during cycling so the black is when we're adding
lithium ions and the first one is over here and as we go
towards you we're adding lithium ions and then the red is when we're removing lithium ions you can see that this large
peak at the beginning drops down and then sort of becomes nothing
wiggles more noise and then it kind of starts to reappeal pier at the very end
these little peaks here pretty much disappear after we start cycling the battery
so it's pretty noisy data but we think we can get some information about it this first peak tells you about the
nearest germanium atoms to the germanium atom we hit so it tells you the nearest germanium
germanium distances the second peak tells you about the second nearest ones
and the third peak tells you about the third nearest ones the shapes and the size of these peaks
are going to tell us about these atoms i'm not going to go through the nitty-gritty details of the analysis i'm
just going to tell you the results so we already knew that we started out
with crystalline germanium what we found out now
is that the next thing we have is amorphous lithium-7 germanium two
we add more lithium ions and we get lithium-9 germanium four and
these are both amorphous and then we get our crystalline
lithium-15 germanium four which we knew from diffraction
and then we don't know because there were a bunch of wiggles that were pretty much noise
but then at the very end that peak reappeared and that is from amorphous germanium
so we didn't get crystalline germanium back but we got amorphous germanium back which is almost just as good
but we still have a big question mark here so there's a lot of work left to do but let's apply what we've learned so
far so we use the three different techniques imaging
and the diffraction and spectroscopy to learn about the morphology changes what is happening
to these particles visually and also their chemical changes
we know that the smaller particles become inactive in the second cycle they're not expanding and contracting
and so that's contributing to a capacity loss which we want to prevent
we also know the largest particles break up and they completely fracture into smaller particles which we also want to
prevent and from the chemistry we can see
what alloys lithium-germanium alloys we're creating and we also know that we start out with
crystalline germanium but we end up with amorphous germanium and so we don't end up with what we started with so we're
losing capacity there as well
so what do we want to do how do we want to make our battery better going forward well first we want to use small
particles we want to use small particles because they don't fracture they don't crack
but they don't stay connected so we also want to use the self-healing polymer this glue that's going to keep our small
particles together and well connected and so hopefully with those two things
we can design a high-capacity battery a battery that's going to get us 300 miles to a charge 400 miles to a
charge and is going to last the lifetime of our car and those are the two things we want
so we're going to improve the range but not destroy the cycle life the lifetime of
the battery now of course we still have to work on the price and the charge time
but that's a whole nother talk so we've made some improvements
and so bringing it all back why do we want a battery that's going to last longer
it's going to have a higher capacity well we want to use be able to use clean energy for our large section 28
of our energy is consumed by transportation so we want to be able to convert all of that energy into clean
energy and so we need to really improve these this battery technology that's going to
go into our cars and then finally science is not done alone i did not do
all of this um i have lots of help nyan liu as i said before he made a lot
of these batteries he's just graduated from stanford his um
principal investigator was ishway his advisor linda lim she did the diffraction and
also the spectroscopy and she's a stanford graduate student as well and then
staff scientists at slack joy andrews michael tony and eugene liu
also helped and i want to thank you guys for your attention
there we go thank you very much joanna
i'm not following my own advice let's see if we can make this
yeah okay now i'll follow my own advice my advice is if you'd like to ask a
question raise your hand attract the attention of these people out here with the microphones
we're recording this session so please wait for the microphone before you ask your question
so who's curious about this
well just in the last uh what two weeks or so there was an announcement by from ibm research i think about self-healing
polymers does that apply to you or their examples had
nothing to do with batteries but does that work apply to you um naively i would say yes i don't know the specific
work you're talking about but the self-healing polymers that the stanford group bow group is working
on was recently published i don't know where their funding came from but yeah any of these these
polymers that's going to keep everything together especially if they're good conductors of electrons that would
be even ideal what's the next one
okay you mentioned at the beginning at the beginning that they had fast recharge for batteries like 15-30
minutes but this wasn't good for the battery does
x-ray analysis help you towards faster charging of
batteries there is a whole thing a matter of heat dissipation in which case you need to get a a cooling system in
the battery or what what is the issue mostly the issue is how quickly can you
put lithium ions on into a material so for germanium for example
oftentimes you only can put in about a third of the elec of the lithium ions
and then the battery stops charging so when you set when it says that it's completely charged you're really not
completely charged so it's more than a heat dissipation problem more than heat yes um it also depends on the material there
are some materials that can charge more quickly than other materials but they often don't have as high a capacity
a couple of questions a couple of questions first you say the small particles become
disconnected so they're no longer active what makes you think they won't cr crack if they are
connected ah so i didn't really highlight in the in the movie but the smallest particles the
ones that were about had diameters about three microns or or smaller didn't show
any cracks at all as they expanded and contracted
so they can actually expand contract indefinitely assuming they stay
connected electronically and the second question is are you trying different electrolytes to
get the small particles back into contact um we think it's mostly the
polymer matrix that's the issue and not the electrolyte we haven't done too many experiments on
different electrolytes
you mentioned earlier um you chose germanium because it imaged better in the light um but carbon actually would make a
better battery so is this work if i understood correctly silicon silicon would make a better battery
i'm going the wrong direction okay um would this work be applicable to those
other materials in the same column of the periodic chart um some things are and some things aren't um so silicon does
actually fracture more easily than germanium and so now that we've shown it to work we're
actually going to move to silicon and do the same type of experiments with silicon as well
but we believe that what you can see is that um
even a hundred nanometer particles in silicon will fracture when germaniums it's it's
ten times that
okay i had some questions about the cv curves uh i noticed during the
charging or discharging phase there was a really large change like an order of magnitude and the cell
potential and it almost looks like a phase change going on
and that also has a lot in i'm i do electrical engineering and a lot and
and and that kind of voltage variation it's not impossible to deal with but it
does complicate the the power controllers for the motor and the charger yeah
so do you expect that kind of curve with silicon yes silicon actually um has a lower
curve there's the plateau is down here because there's kind of a perverse reversion that the highest current
will have to be drawn near the lowest part of the capacity
and uh that actually means more heating and things from resistive losses and
things yeah do you have any more anyway
so i will mention that this is an anode material and so most cathode materials have plateaus much higher
and we do want to to have the anode have a plateau really low so that we can
have a large voltage window oh okay i see the the cathode would i
always yeah i remember my redox tables there's always a pair yeah i i actually avoided
cathode and anode just to simplify things in general yeah i know they're they're even reversed in cells versus
electroplastic
uh you you mentioned that uh to make a a better battery you would need two things
one to make sure the particles stay smaller and the second one that there's a glue
that keeps them together but from what you explain it looks like you may also make have to make sure that
you preserve the crystal or is that not necessary
it's not necessary although one could conceive of starting instead of starting with crystalline germanium starting with
amorphous germanium and then you wouldn't have that capacity loss but the capacity lost from going
from crystalline germanium to amorphous is not that large not compared to losing those particles
so you could start with amorphous germanium you would like
you could start with amorphous silicon amorphous silicon actually doesn't fracture as much yeah
after this after optimizing putting every possible
optimization to this process where do we get in that curve leading to the field in that graph
and what's next after that so to really go
go really far in that curve and i'll show it
to really go far in that curve we have to go beyond lithium-ion batteries and that's really the answer
i will get back to the curve
um so lithium ions really going to keep us in this circle um
maybe go closer to lithium metal but if we really want to get close to the fossil fuel
we need to think of something completely different so germanium would solve the problem in
five years if we want to solve the problem in 20 to 50 years
most people are looking at lithium air batteries which is uh using lithium metal
but we need we need something creative to fill that gap
you just answered okay what i was gonna ask a question over there
um can you i've seen a number of other talks of different nano structures and things that people are working on and
i've seen lots of slides of my cross picky my cross microscopy
but can you tell us what is different about the synchrotron that other people haven't been able to do
with other techniques to look at the ions expanding um
so in terms of microscopy so just imaging with a microscope there's three main
microscopes that you think of visible light microscope which you could not get the resolution
you couldn't see these small particles the small the cracks in the small particles if you used a visible light
microscope you also can't see through metal so our n um our germanium particles are
sitting on nickel foil so you couldn't see through that the other end if you want really high
resolution images you would go to an electron microscope but electron microscopes can only go through a couple
hundred nanometers worth of material so you can design very specialized batteries that would work in an electron
microscope but they're not really realistic so they're more like the frog in the in the aquarium rather than the
frog in the forest
i'm just curious how much longer does do you have for your funding um
what i really what i really need to ask is is you have money i wish i did
um sorry how how much of the sort of plan you outlined in
terms of going forward you actually expect to be able to accomplish um in your current so um
we have linda lim the graduate student who's worked on some of this is continuing her phd work on this and part
of it is extending this beyond and we have another graduate student also just now starting and he's going to
be focused mostly using the self-healing polymer and also looking at silicon
so we're definitely moving forward with it after publishing a few
papers on looking at real batteries with x-rays we've actually had a number
of companies in the area come and say we want to use your synchrotron we want your expertise
so it's it's being noticed
okay so let's thank joanna very much
now as as as usual here not only will joanna stay around but also the people who are holding the
microphones or people from her lab and so they can also answer your questions so if you'd like to just walk around the
room and ask more questions we're happy to oblige you and the next one of these will be at the end of July
uh speaker to be announced i'm sorry but uh hopefully we'll see you then thank you very much