X-rays Reveal Secret Life of Batteries

Public lecture presented by Johanna Nelson Weker

Lecture Date: Tuesday May 27th, 2014. Making the transition from fossil fuels to cleaner, renewable energy sources for the world's automobile fleet will require dramatic improvements in rechargeable batteries: They will need to be lighter, less expensive, run 300-plus miles on a single charge and last the lifetime of the vehicle. While lithium-ion batteries promise to fulfill all these requirements, progress has been frustratingly slow and incremental. To speed things up, researchers are using powerful synchrotron-based X-rays to peer inside lithium-ion batteries while they operate. These studies of batteries in action are revealing the detailed physical and chemical changes that take place as a battery charges and discharges. Understanding how batteries function -- and what causes them to eventually fail -- will help scientists design the next generation of battery technologies.



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


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

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