(C) Daily Kos This story was originally published by Daily Kos and is unaltered. . . . . . . . . . . Practical lithium-air battery shows 3x the energy density of today's best electric-vehicle batteries [1] ['This Content Is Not Subject To Review Daily Kos Staff Prior To Publication.', 'Backgroundurl Avatar_Large', 'Nickname', 'Joined', 'Created_At', 'Story Count', 'N_Stories', 'Comment Count', 'N_Comments', 'Popular Tags'] Date: 2023-02-04 A lithium-air battery rigged up for research at the University of Illinois-Chicago Electric vehicles are great, but there’s a lot of room for improvement in the batteries they use. Same goes for energy storage associated with renewables like solar and wind. Electric cars currently use lithum-ion batteries, because they have the best energy density (energy storage per weight) of any practical battery type we’ve got. But there’s another type of battery on tap that threatens to upend this and change the whole landscape. It’s the lithium-air battery, which has been around in labs for a while, but it’s been beset with technical challenges . It’s worth the aggravation, though, because as you can see below, its attainable energy density would rival that of even a liquid fuel like gasoline: Lithium-ion batteries can store up to about 200 watt-hours per kilogram (Wh/kg), and that’s good enough to run a Tesla or a cellphone. But with coming advances, Tesla may be on its way to becoming the MySpace of electric car manufacturers. There’s a whole lot of investment out there chasing these advances. Now, thanks to researchers at the Illinois Institute of Technology (IIT), Uinversity of Illinois-Chicago (UIC), and Argonne National Labs, we have a practical demonstration of a lithium-air battery that achieves an amazing 685 Wh/kg at room temperature — and it should be inexpensive to produce. Besides performance, it’s also got the advantage of being safer than lithium-ion batteries because it’s all-solid, containing no liquids that can leak out. It’s described in the February 3 issue of Science. To understand the advance that’s been made here, we have to understand a little bit about how a lithium-air battery works. How does energy get stored by lithium and air? The simplest energy-storage device I can think of is lifting a bucket of water. You put in some energy to hold the bucket a few feet off the ground, and when you’re ready to reclaim that energy, you dump it out. The water, on its way back to Earth, can strike a wheel and make it turn. The same thing goes for chemicals. We can expend some energy to make an acid like vinegar and a base like baking soda. In doing so, we’ve stored some energy, because when we mix them back together, heat and gas are released, and we can use those to do work. Lithium metal and oxygen have that same kind of relationship. Lithium loves to give up an electron, and oxygen loves to receive it. Because of that, these two will react vigorously to release energy, so if we can expend some energy to separate them, we can release it later by recombining them. Lithium is one of those metals (the Group I alkali metals ) that’s highly reactive with water and oxygen and so is never found as a pure metal in nature. We have to expend energy to isolate it. And when we put into water, a lot of energy is released… And in that sense, lithium metal is an energy-storage material. If we could harness all that energy release without flames shooting out of it, we’d be in good shape! One other great thing about lithium for a battery is that it’s by far the lightest metal , with about half the density of water, at 0.53 grams per cubic centimeter. Second place goes to potassium, at 0.89. Not even close. We try to take advantage of all this with the lithium-air battery. When lithium and oxygen react, a common product is lithium peroxide, Li 2 O 2 . That’s a transfer of two electrons from lithium to oxygen: 2 Li+ + 2 e- + O 2 → Li 2 O 2 (2 e- per O 2 ) Up to now, that has been the basis of the lithium-air battery. When we charge the battery, we’re expending energy to separate Li 2 O 2 (sitting within a porous material at the cathode) back into lithium ions (Li+), oxygen (O 2 ), and electrons (e-). Back at the anode, the lithium ions and electrons (e-) combine again to form lithium metal (Li). Then, when we need some battery power, we connect lithium metal to a source of oxygen (some air within that same porous cathode material) with a wire and let lithium atoms each donate their free electron to oxygen. This is the “discharge” phase: “Charge” phase: expend energy to separate Li 2 O 2 into lithium metal and oxygen (O 2 ). “Discharge” phase: let lithium donate its free electron to oxygen, creating Li+ ions, which flow over to meet the net negative charge That electron discharge is just like the water falling to Earth from the bucket that we held up. We can use it to do work — to run a motor, for example. As lithium keeps losing its negatively charged electrons, it starts turning into Li+ and developing an overall positive charge. But all those electrons that flowed to the oxygen have set up a negative charge over there, and so the Li+ is attracted to that and heads over as well. But for the Li+ ions to make it over, we need a material that they can flow through that also keeps the lithium metal and oxygen separated. Lithium-ion batteries use a liquid to achieve this, but here we’re going to use a lightweight solid. Weighs less, no chance of leaks. So we need a solid that is a very good conductor of Li+, so as not to slow the battery down because Li+ can’t get to the cathode fast enough. One of the main contributions by the authors is that they developed a lightweight polymer-ceramic composite that conducts Li+ ions about 15x better at room temperature than other solid materials that have been tried up to now. People have come up with very good Li+ conductors for lithium-air batteries, to be sure, but these have been made of molten salts (liquid and heavy) that has to be utilized at high temperatures, so not very safe or easy or cheap to use. But there’s another key achievement here. Notice in the figure above that the product of the reaction between Li+ and O 2 is Li 2 O 2 . It’s shown that way in the figure because that’s the way this has been done up to now. Making Li 2 O 2 transfers two electrons from lithium for every oxygen, as we saw before, and that leads to an OK energy density for the battery. But it is also possible for a much better net reaction to occur: 4 Li+ + 4 e- + O 2 → Li 2 O (4 e- per O 2 ) If we could transfer four electrons for every oxygen molecule instead of two, that would really crank up the energy density of our battery. Here’s the simplest way that could go: Sequence of reactions for transferring 4 electrons from lithium atoms to each oxygen molecule. A star means “bound to a site on the cathode catalyst surface” One key problem in reaching Li 2 O at room temperature is that Li 2 O 2 would rather donate its hard-earned electrons back to oxygen and screw this whole thing up. But how can we keep Li 2 O 2 from reacting with oxygen when we need to have oxygen around? The authors believe there are two main reasons this happens: First, the Li+ conductor is so good that it provides excess Li+ to speed along the last reaction. There’s no problem getting electrons from the wire, but in previous solid-state batteries the Li+ just hasn’t gotten across fast enough to keep up. Second, the products that form first, LiO 2 and Li 2 O 2 , seem to form a coating over the surface of the catalyst material that still conducts ions but won’t let oxygen through. So they create a little hideout in which Li 2 O 2 can be further converted to Li 2 O without hindrance by oxygen. We see LiO 2 and Li 2 O 2 form as products for about 15 minutes of battery discharge, and after that, it’s all Li 2 O until the battery runs out of juice. It’s not clear whether the catalyst they designed for the cathode is special in this way, but the great thing about it is that it’s made of Earth-abundant elements (molybdenum phosphide) and is already inexpensive, so there’s no need to monkey around with that part of it anyway. So the authors have scored a double whammy here, with not only a great solid-state Li+ conductor, but also an inexpensive catalyst that is good at promoting forward and backward reactions with oxygen (so the system is rechargeable). They ran this battery through 1,000 cycles and didn’t see much of a dropoff in performance. The authors don’t even completely understand how the surface chemistry works yet, which is actually good news because further study has the potential to make it work even better. Prof. Mohammad Asadi, the lead inventor, says it’s on to commercial production next. Asadi says he plans to work with industry partners as he now moves toward optimizing the battery design and engineering it for manufacturing. "The technology is a breakthrough, and it has opened up a big window of possibility for taking these technologies to the market," says Asadi. The upshot of all of this is that we may have the basis for super-efficient car batteries and for storage of renewable energy. All because of a nice material that lithium ions like to zoom through at room temperature. [END] --- [1] Url: https://www.dailykos.com/stories/2023/2/4/2150996/-Practical-lithium-air-battery-shows-3x-the-energy-density-of-today-s-best-electric-vehicle-batteries Published and (C) by Daily Kos Content appears here under this condition or license: Site content may be used for any purpose without permission unless otherwise specified. via Magical.Fish Gopher News Feeds: gopher://magical.fish/1/feeds/news/dailykos/