This transcript was generated automatically and lightly edited for readability.

Oliver Strimpel: This is Geology Bites with Oliver Strimpel. Electric batteries play a central role in our transition away from fossil fuels. First, we need shipping-container-sized, grid-scale batteries to even out the peaks and troughs of renewable energy sources such as solar and wind, and match the supply of electricity to demand even when the sun is not shining and the wind is not blowing. Second, we need batteries for electric vehicles, which we're now producing at a rate of about 15 million a year. The batteries that make all this possible are lithium-ion batteries, so called because they store energy by moving lithium ions between the battery's electrodes: during charge from the cathode to the anode, and during discharge from the anode back to the cathode. But in addition to lithium, four other metals are critical ingredients of modern lithium-ion batteries: copper, nickel, cobalt and manganese. Where do we find these metals, and what geological processes concentrate them into economically significant deposits?

Adam Simon studies the chemical and physical processes that affect the mobility of elements in geological systems and is especially interested in how mineral deposits form. He is a professor of economic geology at the University of Michigan. Adam Simon, welcome to Geology Bites.

Adam Simon: Thank you, Oliver.

Oliver Strimpel: Batteries have four main components: the anode, the cathode, the electrolyte in which they are immersed, and a separator to separate the anode from the cathode. I said that lithium is in the electrolyte, but where are the other four critical metals needed?

Adam Simon: It's the cathode that is important, and that's the focus of our discussion today, because there are different types of cathodes. Each is composed of different types of metal: lithium cobalt oxide cathodes, lithium manganese oxide cathodes. The metals that are used to make the cathodes play a role in how much energy the battery can store and how quickly the battery can give up that energy to our devices.

Oliver Strimpel: So the nickel, cobalt and manganese are ingredients of the cathode?

Adam Simon: Yes.

Oliver Strimpel: OK, let's start by talking about the role that lithium and the other four metals actually play during the battery's operation. Singly charged lithium, Li+, is the ion that travels back and forth between the electrodes during the charge-discharge cycle. Why do we use lithium ions?

Adam Simon: Lithium is the lightest solid metal in nature. It has three protons and three electrons. Two of these electrons are held very tightly to the nucleus, but lithium is happy to give up this third electron and become a positively charged ion. We refer to this tendency for lithium to give up its third electron by saying that it has a very high electrochemical potential. That, combined with its light weight, means that lithium can store a lot of energy in a very small mass, and that's what makes it ideal for batteries.

Oliver Strimpel: And the copper, is it playing the role of a good conductor on one of the electrodes?

Adam Simon: Absolutely. Copper is an excellent electrical conductor, second only to silver, and copper is also very resistant to oxidation. We refer to the copper foil in the battery as a current collector. It's fused to the graphite anode, and it provides a highly conductive pathway for electrons to travel from the graphite anode to the external circuit. This is the electricity that flows within the battery during discharging that powers our devices. And then, in reverse, it's the electricity that we add to the battery when we recharge it. There's a lot of copper in lithium-ion batteries. In the average electric vehicle, if we sum all of the copper in the battery, it's about 20 kilograms of copper. And that's just the copper in the battery, not the copper in the motor and the wiring systems, which of course is a lot more copper.

Oliver Strimpel: OK, let's talk about the other three metals: nickel, cobalt and manganese. What role do they play when the battery is being used?

Adam Simon: Nickel provides a very high energy density, and that has to do with the oxidation-reduction processes of nickel within the cathode. Within the cathode, nickel is bonded with oxygen, and when a battery is discharged and charged, electrons are moving into and out of the cathode. That is facilitated by nickel moving back and forth from one oxidation state to another. Nickel's ability to do that allows it to store a lot of energy in the form of that electron transfer.

Oliver Strimpel: What about cobalt?

Adam Simon: Cobalt also provides very high energy density, and cobalt's electronic structure, meaning its ability to give up and to receive electrons during discharging and charging, allows batteries to be charged very rapidly and to have very good thermal stability. Most batteries today, depending on the ratio of nickel to cobalt, have somewhere on the order of 8 kilograms of cobalt.

Oliver Strimpel: So does the cobalt function in conjunction with the nickel in the cathode, or are they involved in two separate processes that coexist?

Adam Simon: When cobalt is bonded with nickel and manganese in what we call an NMC, nickel-manganese-cobalt, battery, the cobalt atoms, as well as the nickel atoms and the manganese atoms, are gaining and losing electrons during discharge and charge. So with cobalt, similar to what we described for nickel, its ability to gain electrons and lose electrons allows the cathode that contains cobalt to store a lot of that energy.

Oliver Strimpel: Is there a similar story, then, with the manganese that you have in a cathode?

Adam Simon: Exactly. Manganese is used because it improves a battery's resistance to overheating during charging and discharging. Your listeners may have heard about thermal runaway, or lithium-ion batteries that can catch fire. What happens during thermal runaway is that a short circuit occurs within the battery that can result in melting the battery and possibly causing it to catch fire. This is why batteries in a lot of technologies, for example in laptops, have fans that remove the heat generated during charging and discharging.

Oliver Strimpel: And is it the manganese, then, that is really the determinant of the maximum safe charging rate for a battery?

Adam Simon: The maximum safe charging rate will vary according to the metals that are used in the cathode. In a nickel-manganese-cobalt battery, manganese plays a role. But each battery, even cobalt-free batteries, has its own charge-discharge rate, and that's dictated by the metal composition of the cathode.

Oliver Strimpel: We should mention that graphite is also needed for a lithium-ion battery.

Adam Simon: Correct. Graphite is a crystalline form of carbon. It has a perfectly ordered, layered crystal structure, which means that all of the carbon atoms are very strongly bonded to each other within the sheets and weakly bonded between the sheets. This allows lithium ions to easily move into and between the sheets of graphite, in a process that's referred to as intercalation. When we charge our battery, lithium ions move in between these sheets of graphite, and they pull an electron from the circuit. So the electron flows from the circuit through the copper, through the graphite to the lithium ions, where the lithium ions are then reduced from Li+ to lithium metal. Graphite holds those lithium ions until we close the circuit to use the energy, and then graphite allows the lithium ions to move out of those sheets.

Oliver Strimpel: OK. Let's move on to the mineralogy and geological origin of the battery-critical metals, starting with lithium. Where does it come from, and what processes concentrate it and bring it to the surface?

Adam Simon: Lithium supply is dominated by production from two very different types of lithium deposits. One we refer to as lithium pegmatites and the second as lithium brines. I'll talk about lithium pegmatites first, where lithium occurs in a mineral called spodumene. Spodumene is a mineral that contains lithium, aluminum and silicon bonded to oxygen. Pegmatites are igneous rocks of generally granitic composition, and in some of the pegmatites that we mine, spodumene crystals can be on the order of a meter in length or greater. Pegmatites form at the margins of granitic magma intrusions, and they appear to be the very last stages of the magma to crystallize. There's one group of pegmatites that is really important for lithium, called the lithium-cesium-tantalum group pegmatites. They represent about 25% of all of the known lithium resources. Lithium-rich pegmatites form from highly fractionated, water-rich silicate melts, and it's thought that multiple stages of melting of Earth's crust are required to concentrate lithium to high enough concentrations for the mineral spodumene to crystallize during sort of the last gasp of the magma.

In these systems, economic pegmatites contain as much as 2% lithium, and we find them around the world: Australia, China, Zimbabwe, Portugal, Brazil, Canada, Russia, the United States and other countries. The largest deposits in the world are found in Australia. In fact, Australia has five of the ten largest producing lithium mines in the world, and all five of these are lithium pegmatites in the greenstone belts of Western Australia.

The second important type of lithium deposit is lithium brines, and you can think of lithium brine deposits as really large volumes of salty groundwater enriched in lithium. We find lithium brine deposits in dry inland lake beds known as playas or salars, and these formed by the evaporation of freshwater. When freshwater in salars and playas evaporates, it tends to add elements such as lithium to the groundwaters, which is the opposite of what we find in the oceans, where the evaporation of ocean water doesn't lead to the formation of lithium-rich brines. The most economically important lithium brines in the world form in arid regions, in what we call the Lithium Triangle, in Bolivia, Chile and Argentina. These lithium reserves are just enormous. They're about 10 times greater than all of the lithium pegmatites in Australia. There are other lithium brines around the world: in the Clayton Valley in Nevada in the western United States, the Salton Sea in California, and Zabuye Lake on the Tibetan Plateau in China.

And then there are some new lithium resources that are being developed. Among them are some clay-hosted lithium deposits in Nevada, where lithium is hosted in sediments in rhyolitic calderas. After these calderas erupt, all of the rhyolitic material inside the caldera gets weathered by rain that falls on and percolates down through these rocks, converting them into clay. There's also a lot of research being done now to try and extract lithium from geothermal waters and oilfield brines, and this is commonly talked about in the news as direct lithium extraction: pumping groundwater up, pulling out the lithium, and then pumping the groundwater back down. So there's effectively no impact on the local environment other than to remove the lithium.

Oliver Strimpel: In these lithium brines, what's the origin of the lithium in the first place? Is it leached out of deposits that contain spodumene?

Adam Simon: That lithium is dissolved from all of the rock formations that host the salty groundwater. On geologic time scales, salty groundwater is really effective at dissolving minerals in the rocks through which it flows, and lithium is very soluble when there's chlorine in the water.

Oliver Strimpel: And then the concentration happens through evaporation on the surface?

Adam Simon: Correct. In the Lithium Triangle in South America, the lithium brines are pumped to the surface and then put into pools, and as the water evaporates under the intense sunlight in the Atacama Desert, that concentrates lithium, which will precipitate out of the brine as either a lithium hydroxide or a lithium carbonate mineral.

Oliver Strimpel: I remember when I flew up from Santiago to Calama in the north of Chile, I saw out of the window these huge green ponds. I suppose these must have been lithium evaporation ponds.

Adam Simon: Absolutely. Yeah, you see those. That's a great flight. One of the concerns about using evaporation to concentrate lithium in that area is the amount of groundwater that is then effectively lost to the atmosphere through evaporation. This has stimulated a lot of research and development in direct lithium extraction. If we imagine putting pipes down into this lithium-rich groundwater, piping that water to the surface and then just selectively pulling the lithium out, we can pump that water back down underground, and that reduces the impact on the environment.

Oliver Strimpel: OK, let's move on to copper. We've been mining copper for a very long time, so presumably the sources of copper are pretty well established.

Adam Simon: There are several important types of copper deposits. The most important are what we call porphyry copper deposits, which supply about 60% of the world's copper, followed by sediment-hosted copper deposits. And then there are three other types: magmatic sulfide deposits, iron oxide copper-gold deposits and volcanogenic massive sulfide deposits. But I'll start by describing porphyry deposits. The word porphyry refers to the porphyritic texture of the igneous rocks that host the copper minerals in these deposits. A porphyritic rock is a mixture of large crystals, which we call phenocrysts, and small crystals that we call groundmass.

Oliver Strimpel: Is the copper in the big crystals or within the matrix?

Adam Simon: In the matrix, in very thin veins within the matrix. The most important porphyry copper deposits are found at convergent tectonic margins above active subduction zones: places such as the Andes in South America, the very volcanically active areas of Indonesia and the Philippines, Alaska, and the western United States, places like Arizona and Utah. Porphyry deposits form from magmas in volcanic systems. Magmas are composed of a liquid, which is a silicate-rich melt, and the silicate-rich melt contains copper and every other metal and element in the periodic table, plus solid minerals inside the magma, and then gases, carbon dioxide and water, that are dissolved in the melt. As a magma is moving from deep within Earth's crust towards the surface, all of these gases are dissolved in the melt.

In subduction zones, so imagine the Andes of South America, where we've got the Pacific Ocean plate moving from west to east and the very large South American plate moving from east to west, that compression can cause the crust in South America to get really thick: 30, 40, 50, 60 kilometers thick. And in really thick crust in subduction zone environments, the magmas get progressively more silica-rich and more water-rich. We refer to these types of magmas as granitic, the same types of granites I mentioned earlier that evolved into lithium pegmatites. What's important about granitic magmas is that they have a very high silica content, which increases the viscosity of the magma. So think about these magmas as something like frozen peanut butter. It's really hard for them to move. But eventually, when these magmas get close to the surface of the Earth, the melt part of the magma can no longer keep water dissolved, and so that water exsolves from the melt to form bubbles.

You can picture these as the bubbles in a glass of champagne. These bubbles are dominantly water, but elements like copper and sulfur and chlorine also really prefer to be in these bubbles rather than the melt. So copper and sulfur will partition, or transfer, from the melt into the bubbles. In the magma, these bubbles that contain copper and sulfur are really buoyant, and they ascend towards the top of the magma. When they get there, unlike our glass of champagne, where the bubbles can just pop, in a magma the bubbles will pond. At the top of the magma chamber, we get this coalescence of trillions of bubbles that form a layer of very copper-rich, sulfur-rich liquid. Eventually those bubbles can exert a lot of pressure outward on the magma, and they can cause an eruption. This is the eruption that you see if you pop the cork on champagne: all of that gas in the liquid immediately wants to get out to the atmosphere.

The same thing happens to form porphyry deposits, where these copper- and sulfur-rich bubbles erupt from the magma. But they're erupting at a kilometer, 2 kilometers, 3 kilometers below the surface. As soon as they erupt, they wiggle their way towards the surface through all of the rock above the magma chamber. They're cooling off, they're decompressing, and they're also reacting with all of the rocks through which they flow. This results in the almost instantaneous precipitation of minerals that are enriched in copper. All of this happens in a really small volume of the Earth's crust and results in the formation of porphyry copper deposits.

Oliver Strimpel: OK, let's move on and talk about nickel. What's its geological origin and the context in which we find it?

Adam Simon: We get nickel from two main types of deposits: laterites and sulfide deposits. Laterites today supply about half of the world's nickel, and they're forecast to supply about 80% of nickel within the next decade. Most of our nickel from laterites comes from Indonesia, New Caledonia and the Philippines. These are areas that contain huge amounts of ultramafic rocks, like peridotite and dunite, that are really rich in magnesium in the mineral olivine. These ultramafic rocks can contain as much as several thousand parts per million nickel in olivine, where nickel substitutes for magnesium. Olivine in these rocks on the surface of the Earth is really thermodynamically unhappy. As warm rainwater percolates down through the ultramafic rock, it reacts with and breaks down olivine, and this releases the magnesium, the nickel and the iron in the olivine to the groundwater.

As soon as this happens, if the groundwater contains dissolved oxygen, iron immediately precipitates as an iron oxide that adsorbs nickel from the water, and that results in the concentration of nickel in very thin zones within these ultramafic rocks. If the groundwater is reduced, then nickel can remain dissolved in the groundwater, and it will percolate down to the bottom of the weathered zone, where it can precipitate as minerals like garnierite, which is a really complex nickel silicate mineral. Again, it precipitates in a very thin layer from which we can mine the nickel.

Oliver Strimpel: OK. We hear a lot about cobalt because it mainly comes from the Democratic Republic of Congo, which is problematic because of child labor and other issues. What is the geological origin of the cobalt?

Adam Simon: In the Democratic Republic of Congo and other areas, cobalt is associated with copper, and these deposits are referred to as sediment-hosted copper-cobalt deposits. They contain copper and cobalt in the form of copper oxides and cobalt oxides and copper and cobalt sulfide minerals, and they're found concentrated in layers in sedimentary rocks. We find them in the African Copperbelt, which extends from Angola across the Democratic Republic of the Congo into Zambia, and also in the Kupferschiefer in Germany and Poland. In fact, the word Kupferschiefer means copper shale, and people have been mining copper in this area for at least 1,000 years.

Oliver Strimpel: Do we know what the geological origin of that very large African Copperbelt is and how it came to be enriched in copper and other metals?

Adam Simon: That area in the geologic past contained really expansive, shallow continental and marine sedimentary basins; think of the Gulf of Mexico or the Mediterranean Sea as a modern analog. So we've got the deposition of muds and silts and sands to form really thick sequences of mudstones and sandstones and siltstones. And it's within those sandstones that the salty groundwater is first born, probably from the dissolution of evaporites, after all of the water has evaporated and precipitated salts at the bottom of these basins.

The general model for how these deposits form in the African Copperbelt involves the movement of oxidized, copper-bearing, salty hydrothermal fluids. So think salty groundwater, similar to what we talked about for lithium, but in this case the salty groundwater is able to dissolve high concentrations of copper and cobalt. As long as the groundwater is percolating through rocks that are oxidized, so think oxidized sandstones or red beds, the copper and cobalt are perfectly happy to be dissolved in that salty groundwater. But if that salty groundwater encounters rocks that are very reduced, rocks such as shales, mudstones or siltstones that contain high concentrations of carbon and sulfur, then the sulfur in these reduced rocks will reduce the cobalt and copper in the groundwater flowing through the oxidized rocks. At the interface between the reduced and oxidized rocks, the sulfur in the reduced rocks will react with copper and cobalt in the oxidized groundwater to precipitate sulfides that are enriched in copper and cobalt. This happens in relatively localized volumes, in sheet-like or lens-like ore bodies, which form very high concentrations of copper and cobalt in small volumes of rock.

In the African Copperbelt, over geologic time, in the upper few tens of meters to maybe 100 meters of these deposits, rainwater has percolated from the surface down through these rocks and oxidized the cobalt sulfide minerals to cobalt oxide minerals. That makes the cobalt much more attractive economically to mine, because it's easier to process and produce cobalt from an oxide mineral than from a sulfide mineral. The second place we get cobalt is from the nickel-rich laterites that we talked about. These nickel-rich laterites also contain relatively high concentrations of cobalt, on the order of a few hundred to a few thousand parts per million, and cobalt is produced as a byproduct of nickel mining in these regions.

Oliver Strimpel: The last critical metal is manganese. Can you tell us about the origin of the manganese deposits?

Adam Simon: Most of our manganese comes from sedimentary deposits that precipitated from seawater during seawater evaporation. So again, thinking about modern-day basins like the Mediterranean Sea, if we imagine the Mediterranean Sea evaporating on geologic time scales, under the right conditions within the water, manganese will precipitate out of that water to form manganese minerals. These sedimentary manganese deposits supply most of the world's production, and they consist of layers of manganese carbonates and oxides that were precipitated as chemical sediments.

We find manganese deposits on Earth that formed both before and after the Great Oxidation Event, about 2.5 billion years ago, when the Earth's atmosphere went from having a very low concentration of oxygen to, gradually, the much higher concentration of oxygen we have today. Manganese deposits that formed before the Great Oxidation Event are dominated by manganese 2+ minerals, so manganese-bearing carbonates, and manganese deposits that formed after the Great Oxidation Event tend to be dominated by manganese 3+ and 4+ in oxides and hydroxides. We very commonly find these oxidized manganese deposits associated with banded iron formations, where iron in the world's oceans precipitated as iron 2+ and 3+ in minerals like hematite and magnetite.

Oliver Strimpel: So it sounds like, when you think about it globally, we have a pretty abundant supply of all these critical metals, albeit some of them beset by geopolitical problems, but it doesn't sound like we'll be running out of any of them soon.

Adam Simon: No, we have more than enough of each of these metals to build the batteries that the energy transition requires. It's the batteries for the energy transition from combustion engines to battery electric vehicles. It's also the energy transition for a majority of people around the world, from very low energy to what we think of as normal amounts of energy consumption in the European Union, the United States and other countries. So we know we have enough of these metals around the world. The challenge is the rate at which mining companies can extract them to make them available for manufacturing the batteries and other technologies.

Oliver Strimpel: Are all the five metals we've talked about likely to remain critical for batteries, or do you think new technologies will reduce our need for them or create a demand for other elements?

Adam Simon: I think the general consensus is that these metals will be the most important for electrification and energy storage for at least the next few decades. Research and development now is focused on increasing energy density, which is really important for battery electric vehicles; increasing power density, so how much energy a battery can provide per instant of time; and increasing the charging rate, so allowing batteries to be recharged much faster than they are today. There's lots of research and development on increasing battery lifespan and the cycle life of a battery. When we buy a phone today, it's designed for us to charge and discharge it somewhere on the order of 500 or 600 times. Well, why can't we have phones where we can discharge and recharge the battery 1,000 or 5,000 times? There's also work to continue to reduce battery costs. Battery costs have dropped 99% in the last 30 years, but can we continue to make batteries cheaper while also making them better and safer?

There's a lot of research being done on solid-state batteries: instead of having a liquid electrolyte, having a solid electrolyte, which could be a ceramic, and also replacing the graphite anode with other anodes, graphite combined with silicon, possibly silicon anodes, and even using lithium metal as an anode. So I think over the next few decades, the metals that we've talked about here will continue to dominate batteries, but we'll see the composition of the cathodes change, and we'll see all of the positive factors of batteries just continue to get better.

Oliver Strimpel: So what are you working on at the moment in your research?

Adam Simon: Among all the metals in the periodic table, my favorite has always been copper. Copper is the metal that is most fundamental to all technologies. We can play around with the ratio of nickel to cobalt in batteries. We can reduce just a bit the amount of copper that we need, but we need copper to generate electricity, to move electricity, to store electricity. And the amount of copper that society will need over the next few decades for the energy transition is more than the amount of copper we have mined since the end of the Stone Age. So where is all this copper going to come from? Mining companies are discovering less and less new copper. So I focus on trying to understand how we search for and discover new copper deposits.

Oliver Strimpel: And how do you do that?

Adam Simon: With a couple of partners, we looked at waters that move through natural copper deposits, groundwater and surface water, and we started analyzing the composition of waters from around the areas of known copper deposits all over the world. When we analyze water samples, we measure everything from lithium to uranium, so every metal in the periodic table, and we measure all of the metal abundances, plus the isotopic abundances. Then we use those data to figure out what metal isotopic signature in groundwater and surface water is a fingerprint for that water having interacted with copper minerals in the subsurface. And we figured out what that fingerprint is. So we're applying our technology to help mining companies screen areas around the world for the presence or absence of copper minerals. All we need is a few hundred milliliters of water, and that water can come from any natural source: a spring, a seep, a small lake or pond. We've even sampled water from the Zambezi River, and we can tell you whether or not it fingerprints the presence of copper minerals.

Oliver Strimpel: Adam Simon, thank you very much.

Adam Simon: Well, thank you, Oliver. I really appreciated this opportunity to chat with you about batteries and the metals that we need to make them.

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