Lithos: Fueling Innovation through Sustainability
This project was created alongside Adheena Fatimah, Omar Alweheshy, and Fatma Al Arbawi.
There are so many things in our lives we take for granted. For most people, energy is likely one of those things. We take it for granted that we can push a button on our phone, and it will light up. It’s powered using stored energy.
But where did that energy come from? Well at the moment, likely fossil fuels. But now, we’re realizing the impacts that has, and we’re trying to switch to other sources of energy, such as renewables.
The reason your phone turns on, that your computer doesn’t have to be charged every day, that you can drive your electric car for 450 kilometers… it all comes down to the energy storage devices. The batteries.
All the devices I listed above use something called Lithium-ion batteries. These are the gold standard of batteries, and we depend heavily on them. However, lithium-ion batteries are unsustainable.
We created Lithos to tackle this problem. We wanted to focus on this problem because we recognize how big of an impact it’s going to have in the future. As we transition to intermittent energy sources, we will need more energy storage. And so we have to ensure that by trying to save the planet, we aren’t destroying it.
At Lithos, we envision a future of sustainable energy production. Switching away from fossil fuels doesn’t necessarily eliminate all our problems. If we can’t store the intermittent energy, then we won’t have the resources to power our lives. We need to make energy storage more sustainable.
Background
Lithium ion battery production increased 8 fold in 10 years. The lithium used in production has increased from 5160 metric tonnes in 2007 to 19780 metric tonnes in 2017. The market has expanded by 330%.
It is estimated that between 2021 and 2030, about 12.85 million tons of EV lithium ion batteries will go offline worldwide, and over 10 million tons of lithium, cobalt, nickel and manganese will be mined for new batteries.
We use lithium ion batteries in everything from our phones to our laptops to our ever-more-popular electric vehicles, so fueling this demand is essential.
Why do we even need batteries?
The entire concept behind batteries is storing the energy for later. And as we look to transition to renewables such as solar and wind, we need to keep the duck curve in mind.
The duck curve is essentially an imbalance between energy supply and demand. ☀️Solar produces the most energy in the middle of the day, when the sun is at it’s peak. But that’s when we don’t use very much energy at all.
If we rely on only intermittent energy sources, like solar, we won’t have energy all the time. And when the energy production is at it’s peak, if it went straight into the grid the energy surge would overwhelm it.
So, we have batteries! 🔋
The concept is the same with your phone. You charge it in the morning, and you (hopefully) don’t have to worry about it for the rest of the day. It just works.
Batteries have quite literally changed how we function as a society. We now don’t need to rely on always having an energy source at our disposal. We can store the energy for later.
Batteries are incredibly important for developing countries too. People may have less reliable access to power sources, but they obviously require energy to live. There are battery powered lamps, phones, and many other devices that people depend on in their daily lives.
Back to lithium ion batteries. Demand and production for batteries is skyrocketing right now, and lithium ion batteries are the clear favorites.
They have the highest energy densities of all secondary batteries, meaning they can fit into smaller spaces (like your phone). They are really efficient, and can survive many charge cycles, which is when the battery is charged and discharged. In addition, they only lose 5% of their charge while some other batteries lose 30%. So lithium ion batteries are the holy grail of batteries.
How do they work?
Basically, by moving lithium ions between a positive and negative electrode through an electrolyte. When the battery is charged, lithium ions are stored in the negative electrode, called the anode. When the battery is discharged, the lithium ions move through the electrolyte to the positive electrode, called the cathode.
The movement of the lithium ions creates a flow of electrons that can be used to power a device, such as a smartphone or electric vehicle. When the battery is recharged, the flow of electrons is reversed, and the lithium ions move back to the anode.
If the cathode and the anode touched, the battery would short circuit. Which would be bad. This is where the separator comes in: it prevents the anode and the cathode from touching, saving our battery from exploding. The separator is porous, meaning it has holes (pores) in it to allow the lithium ions to pass through. The final major component is called the electrolyte, which is the solution that the ions are in.
Demand for lithium ion batteries is going to continue to rise. If we want to transition away from gas powered cars, we will need batteries to power the electric ones. And guess what? Tesla, one of the major manufacturers of EVs (electric vehicles) uses lithium ion batteries. And the demand for phones and computers, which also use lithium ion batteries, is growing. 📈As we have more lithium ion batteries, the impacts increase.
Impacts of Lithium Ion Batteries
Battery waste
95% of spent lithium ion batteries end up in landfills. Here, they can leach chemicals into the environment, pollute soil and water, and cause landfill fires.
Hydrofluoric acid (HF) is a hazardous gas that can leak from used-up lithium-ion batteries. HF is highly corrosive and can enter the human body through the skin or by inhaling. It readily penetrates the skin and settles in deeper layers where it releases its toxic components. This easily amounts to more than 80–800 times the US National Institute for Occupational Safety and Health Immediate Danger to Life or Health (IDLH). However, since HF is so reactive, unless there is a human present at the spill it’s likely not to affect them thankfully. But it’s still hazardous for the environment.
There are not many concrete stats on the impacts of lithium ion battery chemical leakages on the environment, however it has been addressed as a serious issue. 😭
Also, when lithium ion batteries are disposed in landfills, they can start fires. Lithium is an incredible flammable and reactive element, and lithium ion batteries already have a high potential for exploding.
In Britain, lithium ion battery landfill fires account for £158 million per year. [source] Not to mention the greenhouse gas emissions.
Also, when we simply throw these batteries in landfills, we are wasting the valuable materials. Lithium, cobalt, nickel, and more, which are all found in lithium ion batteries, are incredibly valuable materials. By not recycling, we are leaving 28 billion dollars on the table (in the US only). [source]
The Mining Process
Another part of the lithium ion battery life cycle that has a large impact on the environment is the mining. 40% of the CO2 emissions from lithium ion batteries come from the mining process. [source]
Producing one metric ton of lithium can result in 150–200kg of CO2 emissions and require 500,000 gallons of water. If we were able to completely eliminate these negative impacts, we could potentially reduce global CO2 emissions by up to 1.7% (based on the 2020 global CO2 emissions of 34 billion metric tons) and conserve millions of gallons of water annually.
Lithium is extracted in 2 ways: through brine or through ore.
Brine Production
87 percent of the world’s lithium comes from brine water. The lithium is extracted from brine pools that are found underground, and then put into pools above ground. This mixture is cycled through many different pools. The goal is to increase the concentration of lithium in the solution. Lithium is recovered in the form of lithium carbonate, which is the raw material used in lithium ion batteries.
The production process requires only evaporation by the sun, and leaves behind not only lithium but also magnesium, calcium, sodium, and potassium. For 1 tonne of lithium it takes 500000 gallons of brine. Brine mining can usually take 8 months to 3 years, but extracting lithium from brine is cheaper and easier than hard rock mining. Overall, it requires a lot of time, water, and is very harmful on the environment.
Hard rock mining
Mining from ore is the other option. This is more along the lines of your standard mining process. The other 13% of the world’s lithium is found in mines, and the lithium concentration in hard rock (pegmatites) are higher than those found in brine, but the mining process is more expensive both economically and environmentally. It is still a competitive method, at least in mines already operating.
Over 145 minerals contain lithium, but only 5 are used for lithium extraction: spodumene, lepidolite, amblygonite, and eucryptite. Spodumene is by far the most commonly used mineral for lithium extraction.
After spodumene is mined, it is heated to 1100 degrees Celsius then cooled to 65 degrees, then ground up, mixed, and roasted with concentrated sulphuric acid. The sulphuric acid kicks off a reaction in which lithium sulphate replaces hydrogen. The resulting slurry is filtered and a number of components are added. The pH level is adjusted, and the mixture is concentrated through evaporation. Finally, soda ash is added to create lithium carbonate.👍
This process causes land degradation, produces large amounts of CO2 (it is responsible for the majority of CO2 emissions produced from lithium ion batteries), and water pollution.
This doesn’t even mention the mining for the other materials in lithium ion batteries, such as cobalt or nickel. Cobalt is usuallly mined in the Democratic Republican of the Congo, and the mines have a lot of human rights issues.
One example showing the negative effects of mining is from May 2016. Dead fish were found in the waters of the Liqi River. Cow and yak carcasses were also found floating downstream, dead from drinking contaminated water. It was the third incident in seven years due to a sharp increase in mining activity, including operations run by China’s BYD, one of the world’ biggest supplier of lithium-ion batteries. After the second incident in 2013, officials closed the mine, but fish started dying again when it reopened in April 2016. This indicates the toxicity of the chemicals used in lithium ion batteries.
As I’m sure you can tell, the mining process is all around terrible, as many mining practices are.
Battery Recycling: The solution?
Now we’re in a dilemma. We need lithium ion batteries. But they are terrible for the environment.
So, how do we fix this? You might have already considered this amazing solution: recycling. ♻️ Recycling batteries can prevent them from ending up in landfills and recover valuable materials.
When we had the same sort of scenario with plastics, what did we do? We jumped on the recycling train. We need plastics to function as a society (at this point they are so integrated) but we know that they are super bad for the environment.
However, I think we’re all aware that plastic recycling isn’t all its cracked up to be.
Don’t get me wrong, recycling is amazing. But the processes aren’t always the most effective. For example, plastic collection. Not all the plastic gets to the recycling facilities. Also the cost: due to all the processing that needs to happen, recycled plastic is more expensive. Which is why it’s so hard for us to switch.
This is the same issue with recycling lithium ion batteries. It’s too expensive, and collecting the batteries is an issue.
Redwood Materials, a battery recycling company, has solved part of the collection issue by partnering with battery giants like Tesla, Volkswagen, and Panasonic. Another option would be to incentivize people to return their batteries, perhaps something like a deposit. However, this is not something that we are extensively focusing on.
The cost comes down to two factors:
1️⃣Recovery methods
Current recovery methods are not optimized. The standard method is pyrometallurgy, however more and more companies are switching to pyro-hydrometallurgy, which is a combination of the two. Pyrometallurgy is really good at filtering out large amounts of the materials at low costs, and hydrometallurgy is more targeted, but in large quantities requires massive facilities.
Pyrometallurgy🔥is when you heat up the cathode (after shredding) so it melts, and then the different metals will settle in layers according to their densities. This is the most commonly used one right now, but it can’t recover targeted materials. It also produces black mass, which is usually just thrown away, wasting precious materials. It emits CO2 while operating, but about the same amount as hydrometallurgical processes when considering their whole life cycle. The interesting thing about pyrometallurgy is that because the battery is so energy dense, there is enough energy to power the process and heat it up to the high temperatures required. So the energy requirements aren’t actually all that high.
Hydrometallurgy💧is where you dissolve the cathode to help leach the chemicals out. The by product of it is toxic wastewater. In this process, the battery is shredded first. Hydrometallurgy requires large facilities, and produces toxic wastewater as a byproduct. While making the chemicals, it also emits CO2, while it doesn’t emit CO2 during the hydrometallurgical process.
2️⃣Disassembly processes
To recycle the battery, you must first break it down to its separate components, as they each require a different type of recycling. Currently, batteries are shredded, which doesn’t allow for this separation and results in lower material recovery (wasting money). If batteries are shredded there is also a high likelihood for explosions or fires. The recovered materials are also less pure, limiting their future applications. Another option is to manually disassemble the batteries. This is quite costly, slow, and requires a lot of labour. Not to mention it’s dangerous, as lithium ion batteries, being reactive, require a stable environment of argon gas while being disassembled, which is dangerous to humans.
With current recycling methods, only around 30–40% of the materials in lithium ion batteries are being recovered.
We’ve established we don’t want shredding, and we don’t want manual disassembly. What could solve this issue? Another potential solution may be robotics. However, there are currently some limiting factors with that.
Robotics for Recycling: Limiting Factors
Only 5% of lithium ion batteries are recycled, and as the total number of batteries grows, we can’t sustain that due to the many types of pollution that occur through lithium ion battery waste.
However, the main limitation for scaling up battery recycling right now is the high cost and lack of efficiency. And that mostly comes down to the disassembly process, as I talked about before. So why aren’t we using robotics to automate the process?
The main reason we still use humans for the disassembly process is that there are many different types of batteries. Robots can’t really adapt to the different methods that would be required to properly disassemble many different types of batteries.
Another reason is the complicated steps required to take apart a battery. These all have to be performed with extreme precision.
- Separating the positive and negative electrodes: use specialized tools to carefully pry open the cell and remove the positive and negative electrodes.
- The electrolyte, which is a flammable and corrosive liquid, is drained from the cell. This step requires careful handling and disposal to avoid any environmental or safety hazards.
- Extracting the cathode and anode materials. Once the cathode and anode materials are extracted, they can be further processed using pyro-hydrometallurgical methods to recover the valuable metals and other materials.
If we can bridge these gaps, we will be able to create an exciting future with automated battery recycling.
Case Study
This project comes the closest so far to bridging the gap. Oak Ridge National Laboratory managed to make an AI- based robotics system that can disassembly EV batteries. It can disassemble 100 batteries in the same time it would take a human to disassemble 12. You can check it out here.
There is a literal 10X improvement in speed of disassembly. The thing is though, it can only disassemble EV batteries. And these aren’t everywhere. In fact, they’re practically nowhere.
Introducing Lithos
We leverage the power of machine learning and robotics to automate the complex process of battery recycling. Lithos makes disassembly more efficient and economical by seamlessly adapting to the different types of batteries. Our goal is to create a more sustainable future with closed-loop battery recycling.
There are 3 components to our process: machine learning, robotic arms, and pyro-hydrometallurgy processing. Let’s break down each one. But first, here is an overview of our solution.
- The robotics system, which includes cameras and sensors, captures real-time visual and positional data of the battery packs.
- AI algorithms analyze the captured data to identify the size, structure, and design characteristics of each battery pack.
- Based on the analysis, AI determines the appropriate disassembly process for each battery pack, taking into account factors such as size, shape, and safety risks.
- The robotics system, controlled by the AI system, adjusts its movements and tooling based on the AI instructions to perform efficient and safe disassembly.
- The robot employed in the system is the UR5 industrial robot, equipped with a six-degree-of-freedom arm. It utilizes different end-effectors tailored for specific functions during the disassembly process.
- The robot, guided by the AI system, carefully removes components such as connectors, screws, and fasteners using specialized tools attached to its end-effector.
- After disassembly, the robot ensures that the disassembled parts are sorted and separated appropriately for hydrometallurgy.
Machine Learning
The importance of having this component in our solution is that there are many different types of batteries. We need a system that can classify the battery accordingly and preform the appropriate action.
For this, we plan to use CNNs (convolutional neural networks), specifically YOLO. The way CNNs work is to identify images. If you’re interested in learning more, I’d recommend checking out the videos below, which explain the basics behind it.
The gist of it is that we would use computer vision (a camera) and machine learning (it picks up on patterns) along with CNNs to identify different components of the batteries.
How does a CNN work?
Have you ever played finding Waldo in a picture? The game is all about recognizing patterns — the pattern being Waldo’s red and white striped shirt, hat, and glasses.
A convolutional neural network is kind of like a really good Waldo-finder. It’s a computer program that’s designed to look at pictures and find patterns in them. Just like you, a neural network has eyes (a camera) that take in pictures. But instead of a brain like you, a neural network has lots and lots of tiny computer programs that work together to find patterns in the pictures. These tiny computer programs are called “neurons”.
The neural network looks at the picture one small piece at a time, and each neuron looks at a tiny part of the picture and tries to figure out what pattern it sees there. Then, all the neurons work together to look at the whole picture and decide what’s in it.
Just like you can find Waldo in a picture, a convolutional neural network can find all sorts of things in pictures. In this case, we want them to identify cathodes, separators, anodes, screws, ect.
Would highly recommend the second video. It explains YOLO, which stands for “you only look once”. The premise behind it is to speed up the process at which algorithms can recognize objects.
Robotic Arm
The machine learning algorithm can’t do everything itself. It needs a contact with the physical world to manipulate the battery and actually disassemble it. As the battery is being disassembled, there are different stages: pack to cell and cell to material.
Cell to Material
Cell to material is going from the individual battery cell, to the raw materials, which would be lithium and cobalt for example. This stage uses mainly pyrometallurgy.
There are different components in a battery, so in order to recycle them, you have to separate them. This is because the way that you would recycle each component is very different.
Alternatively, and this is what’s currently done, the battery is shredded and then the resulting mass undergoes either pyrometallurgy or hydrometallurgy, as it skips the disassembly step.
Pack to Cell
Pack to cell disassembly is going from a battery pack, like an EV battery, down to the individual cells. This is the part that is currently done manually, or simply shredded.
In order to disassemble this cells, we’d need the robot to remove wiring from the pack, and then removing the casing of the battery (which can have screws, clips, or glue). And then once that casing is removed, we’d need to separate the individual cells from each together, which would mean removing things like foam or plastic that holds the cell in place. Finally, the cell would have to be tested to make sure its voltage is safe. Once the cells are separated, they can be recycled or reused in other applications.
Pyro- Hydrometallurgy
Ok so the first thing you should know is that the anode and cathode won’t ever be able to be separated economically. They are 40–80 microns thick, so it doesn’t make sense. However, in some batteries, they are in continuous winding, so they can be unwound in a single piece. So, the cathode and the anode stay together, and they’re the ones undergoing the pyro-hydrometallurgy.
As I’ve mentioned before, pyrometallurgy is the most commonly used method for battery disassembly. Using pyrometallurgy alone is not ideal, and more and more companies are switching to pyro-hydrometallurgy, because they recognize the opportunity to drastically improve yield.
Here’s what the process would look like:
By combining pyrometallurgy and hydrometallurgy, we get the best of both. Pyrometallurgy is really good at filtering out large amounts of materials, about 90% are filtered out right away. This is great because it’s cheap and effective, and can narrow down to the most valuable parts pretty quickly.
Hydrometallurgy is much harder to create, as it involves dissolving the alloy multiple times in various solutions. There are many different basins that it must pass through, as you can see in the next video.
So in order to make this as economical and efficient as possible, we want to start with a smaller quantity of materials that need to undergo hydrometallurgy. Also, hydrometallurgy has toxic wastewater, so by reducing the amount that needs to be processed is a good thing.
The benefit of hydrometallurgy is that you can target specific materials. Because you’re only getting rid of a small portion each reaction, you can be more accurate, which helps to recover the most materials possible.
For example, when you get to a point where you have only nickel and cobalt left. These elements are right beside each other on the periodic table, and have incredibly similar properties, meaning that trying to separate them isn’t really going to work that well.
When you get to this point, you can make use of an organic compound. You make a compound that wants to bond with nickel, and you mix the waterface (which contains the nickel and cobalt) together really well. Then, you let the solution settle in the tank, and it will have separated into nickel and cobalt, because the the compound will have pulled out all the nickel ions out. This leaves the cobalt in the waterface. And when you take the top layer off, you are are left with pure nickel and pure cobalt. These solvents are also reused.
By combining pyro and hydrometallurgy, we reduce CO2 emissions and maximize material recovery and efficiency.
Here’s a look at the new supply chain.
When recycling graphite, you’d either grind it up, thermally purify it, or leach it chemically.
The porous separator typically gets thrown away because as the battery is going through the charging cycles, dendrites form on it. This is what causes the battery to die. But this isn’t really a big issue because the materials used aren’t particularly valuable.
The electrolyte is not easily recycled currently, but the majority of companies use the same composition. A promising method for recycling it is extracting the lithium salts.
The cathode, which is one of the most expensive parts of the battery, and the one with the rare elements. And it would work well for it to undergo hydrometallurgy, as that is literally the process for alloy dissolving. One common solvent used is sulphuric acid. Zhang et al. (1998) reported a recovery rate of over 99% for Co and Li, and Nan et al. (2005) reported a recovery rate of over 98% for Cu, using hydrometallurgy. [source]
By using pyrometallurgy first though, we make the hydrometallurgical process more effective and efficient.
We plan to partner with a company that already has an efficient cell to material process. To achieve maximum material recovery, typically you combine different types and various solvents. Namely, Redwood Materials, or Umicore. Redwood Materials has a material recovery rate of over 95%, and Umicore is a leading expert in the field.
It is important to note here that although Redwood Materials and Umicore have a very effective recycling process, they have not solved the issue of battery disassembly. This is where Lithos comes in.
In short, we combine CNNs, robotic arms, and pyro-hydrometallurgy to automate the process of lithium ion battery recycling. This will increase efficiency by an estimated 10X, and recover millions of dollars worth of materials, drastically reducing the need for mining, and keeping batteries out of landfills.
Implementation
Alpha
(2023- 2025)
We plan to look more in-depth at the regulations that exist with lithium ion battery recycling, such as the wastewater disposal from hydrometallurgy. In order to implement this solution effectively, we need to ensure that our solution meets all the legal and regulation requirements.
We also plan to further develop our robotics system to achieve the maximum efficiency and effectiveness. Currently, a gap that we have is the design of the robot for disassembling the battery. Battery designs are quite literally made not to be disassembled.
We’ll so this through training in tandem with the AI training. While exposing our robot to more and more sample data, we expect that it will be able to recognize battery types and perform the appropriate procedures.
Beta
(2025–2027)
In this phase, we plan make Redwood Materials one of our beachhead customers. Redwood Materials is a company focusing on lithium ion battery recycling. It was founded by the co-founder of Tesla.
You can check out their website here. https://www.redwoodmaterials.com/
We feel that their mission aligns with ours, as they want to create a closed-loop system for lithium ion batteries. They have achieved 95% material recovery from the batteries due to their combination of pyrometallurgy and hydrometallurgy. However, the one area that they have not solved is battery disassembly.
We also plan to get user feedback. We will scale to 5 recycling facilities near our base and test them out there, monitoring the results against the expected impact. Based on their feedback, we will continuously improve the process, to ensure that it is as effective, economical, and efficient as possible.
To incentivize the facilities to adopt our technology by showing them the impact it will have. This is discussed more in the next section.
Version 1
(2028–2030)
In this phase, we will launch our product, based on user feedback from Beta phase. We plan to scale to 100 recycling facilities, and disassemble 70% of batteries. We will continue iterating upon our solution to achieve 100% disassembly. In order to do this we need to make our process more economical, which we expect to happen as the adaptation becomes greater.
Impact
By using robotics, Lithos expects to increase battery recycling efficiency 10X, from 12 to 100 batteries in the same time frame. Lithos makes recycling 73.7% cheaper and 10X faster. We reduce the need for environmentally damaging mining by 90%, recovering a rough estimate of millions to tens of millions of dollars in materials. We do not shred the batteries, eliminating the avoiding 65% of recycling facility fires that are caused by shredding and reduce the injury rate to zero
Conclusion
Lithium ion battery disposal is something that is going to become of increasing importance as EV production continues to increase. We can’t keep dumping 95% of batteries in landfills. We need to make recycling cheaper and more effective, to create an economic incentive for recycling batteries. Here at Lithos, we make battery recycling 73.7% cheaper, and battery disassembly 10X faster. We drastically reduce the need for mining, and by keeping batteries out of landfills, we also prevent environmental damage.
By combining machine learning, robotics, and pyro-hydrometallurgy, Lithos fuels innovation and sustainability. If you’re as passionate about sustainability as we are, join us! We’d love to have you. Check out our website here: lithosbattery.com
Citations
A final shoutout to my team, Adheena Fatimah, Omar Alweheshy, and Fatma Al Arbawi. Was awesome working with you guys 💖
We would like to give a special thanks to Kurt Vandeputte, Jennah Dohms, Ahmed Hassan, Graeme Epp, Unmol Sharma, Reja Sabet, Eric Rountree, Anne-Sophie Verhaeghe, Faysal Munshi, Tobias Grether-Murray, and Theodore Grether-Murray.
A review of physical processes used in the safe recycling of lithium ion batteries (warwick.ac.uk)
suschem-02–00011-v2 (1).pdf
Socio-environmental impacts of lithium mineral extraction: towards a research agenda — IOPscience
Comprehensive review on recycling of spent lithium-ion batteries — ScienceDirect
https://pubs.acs.org/doi/10.1021/acs.chemrev.9b00535
Lithium mining: What you should know about the contentious issue (volkswagenag.com)
The Six Major Types of Lithium-ion Batteries: A Visual Comparison (visualcapitalist.com)
Ranked: Top 25 Nations Producing Battery Metals for the EV Supply Chain (visualcapitalist.com)
How Does Lithium Mining Actually Work and Will We Have Enough? (grabcad.com)
How your phone battery creates striking alien landscapes — BBC Future
How lithium gets from the earth into your electric car — The Washington Post
Lithium-ion cell and battery production processes | SpringerLink
Lithium-Ion Cell Production Processes | SpringerLink
Lithium ion battery production — ScienceDirect
From laboratory innovations to materials manufacturing for lithium-based batteries | Nature Energy
U.S. set to loan Redwood Materials $2 bln for EV materials plant | Reuters
WO2022140294A1.pdf (storage.googleapis.com)
https://www.sciencedirect.com/science/article/abs/pii/S0378775306022452
