A solid-state battery is essentially battery technology that uses a solid electrolyte instead of liquid electrolytes which are instead behind lithium-ion technology.
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To be able to talk clearly about solid-state batteries, it is therefore important to take a step back and understand how lithium-ion batteries work in detail and their main differences compared with this new technology.
Every lithium-ion cell has:
In a current lithium-ion battery, the separator does not have any other functions apart from insulation and is totally submerged in the liquid electrolyte which soaks everything inside the cell and becomes a real medium through which lithium ions move between the cathode and anode, where the anode is made from a graphite structure. The lithium ions therefore move through the electrolyte and intercalate in the crystal structures of the two anode and cathode electrodes (structures which have empty spaces inside, where the lithium ions fit as they are very small particles).
The grey central layer is the solid-state separator which, on its own, acts both as the separator between the anode and cathode and as the electrolyte. It therefore becomes the medium through which the ions move and also has electric insulating properties and as a mechanical separator between the anode and cathode. The fact that there is this solid, resistant support allows the removal of the graphite structure on the anode part and ensures that lithium metal accumulates directly on the anode (there are also semi-solid solutions where the electrolyte is a gel).
How does a solid-state battery work?
When the cell is charging, the lithium particles move from the cathode, through the structure of the atoms that form the separator, and then move in between the separator itself and the anode’s electrical contact, thus forming a solid layer of pure lithium. In this way, the anode will only be formed of lithium particles and will have a smaller volume than a lithium-ion technology anode, which contains the graphite structure.
On paper, solid-state batteries promise many improvements over the current batteries on sale; in fact, solid electrolytes seem to offer greater energy density, a longer life and greater safety, all in a smaller size.
But it is important to remember that this technology is still in the development phase and, to date, lithium-ion batteries remain the best performing technology on sale, with a variety of chemistries, each used for different purposes, readily available and mass produced.
However, let’s have a look at the advantages offered by solid-state batteries:
Solid-state batteries do not have a liquid electrolyte, which in lithium-ion batteries is one of the most challenging components in terms of safety, because it is volatile and therefore more flammable. Furthermore, this is replaced by a thicker separator layer formed of a material that is mechanically more resistant to high temperatures (because it has a ceramic composition with various additives); this makes the separation between the anode and cathode more reliable, so much so that it prevents short circuits, even in the event of misuse or deterioration, and therefore the intrinsic safety of the cells increases.
Of course, not all lithium-ion batteries have the same level of safety. We spoke about this subject in the article “Risks associated with lithium: Can you really trust a lithium battery?”
Another advantage in terms of safety is the greater resistance to dendrites, or the sharp, uneven build-up of lithium that forms during movement from the cathode to the anode. In fact, lithium does not move evenly and tends to group together and form points which, like real pins, grow and, in some extreme cases, can pierce the separator. However, thanks to its thickness, solid separators are more resistant to piercing from dendrites and therefore avoid possible short circuits and the gradual deterioration of the cell.
The greater intrinsic safety helps bring another major improvement: the use of a pure metal anode encourages a huge increase in energy density. This is essentially down to the removal of the graphite anode (which in lithium-ion batteries contains the ions when they migrate). In a solid-state battery, during the transfer, only the ions remain and a bulky, heavy compound part is removed which does not actively help generate energy.
According to the latest studies, solid-state batteries have an energy density 2-2.5 times higher than current lithium-ion technology and this huge advantage would result in a lighter and smaller battery. This is certainly a breakthrough for electric mobility, which would benefit from greater range and a lighter weight, but let’s remember that we will only be certain of this figure when this technology is officially ready.
The latest studies have shown that solid-state batteries are able to charge up to 6 times faster than the current technologies on sale. But this figure is also still uncertain and will depend on how this new technology is developed. There are already solid-state battery prototypes that charge very quickly, but to the detriment of other decisive factors for achieving good performance. We will need to weigh up this advantage with other essential characteristics that these batteries should have, only then can we assess the best alternative, including in terms of cost.
To date, what is certain is that liquid electrolytes tend to suffer at high temperatures, while solid electrolytes, on the contrary, become more high-performance at high temperatures and this would support their performance during fast charging, an operating phase that typically produces much higher temperatures.
Some people argue that a solid-state electrolyte, as it is not liquid, can allow a quicker, easier production process, which uses less material and energy; but this theory, while understandable, also cannot yet be proven and only will be when this technology is truly mass produced.
However, we can certainly say that at the moment the filling of the cell with the electrolyte is a process that requires plenty of time: the cell must be assembled empty and it must have a hole so the electrolyte can be filled up later on, you will then have to wait for the electrolyte to be completely absorbed and, afterwards, you will need to refill it to bring it to the right level and seal it. It therefore is certainly an influential phase in the production process and, with solid-state technology, there could potentially be a real improvement, but in order to draw sound conclusions, we need to wait for actual production of this type of cells.
As we have seen, solid-state batteries of the near future will potentially be able to provide huge advantages that will increase the performance and efficiency of vehicles and will revolutionise the electrification sector of the automotive industry. But the arrival of solid-state technology onto the market already seemed imminent a few years ago and instead the breakthrough has still not happened. How come?
Just as there are many advantages, there are also certain limits due to how young this technology is, as it is still not ready and constantly evolving. This is why we can call these limits real challenges to be addressed and major new goals to be achieved. Let’s find out together.
During charging and discharging, it is though the solid-state cell is breathing. The thickness of the lithium-metal anode increases during charging and decreases during discharging, and just like all unstable elements, this will eventually cause deterioration.
The main problem comes from the difficulty of keeping the solid-state cells fixed and compressed at the same time.
A cell should be compressed so that the internal layers do not detach, but it is not enough to fasten it to a containing structure, because this will constantly need to “breathe”. You therefore need to create a complex mechanical structure: in “tabletop” solid-state battery prototypes, plates are installed with springs that keep everything compressed, but this is a complex and expensive system that cannot be mass produced.
Due to its composition, it is not possible to stop a solid-state cell from swelling; however, research can work on how to make it less demanding in terms of pressure (so that the cell remains stable on its own without needing all this pressure, but perhaps only with the use of a filler), or on the study of advanced materials that allow the cell to expand while keeping it firmly fixed and compressed.
Ions are matter, atoms, and it therefore makes sense that they move more easily in a liquid, while a solid (a ceramic separator) must have a special composition to be able to allow ions to move freely.
There are already high-performance separators in this sense, but only at high temperatures, because solid electrodes only become good conductors at temperatures above 50 degrees. This limit means that solid-state technology is still hardly used in real vehicles, because we cannot assume that the battery is always hot. When the solid-state battery is not hot, its performance currently falls considerably. Work will need to be done to ensure that the solid electrolyte performs well at increasingly lower temperatures.
The cost of a solid-state battery is currently very high because we are talking about an extremely innovative technology; so the costs of both the materials and the production processes need to be higher than for mass-produced batteries. It is not yet clear what the final cost of this technology could be, but we can certainly assume that, if major car manufacturers are investing in this direction, they have enough evidence to believe that the cost can also be adapted to mass production.
Even though solid-state batteries still have a few problems to be resolved, their arrival on the market is now certain and we can expect their widespread use in any sectors where, to date, energy density is a limiting factor, because the space is currently not enough to store all the energy that is needed. In fact, as they have twice the energy density, solid-state batteries will double the range and are now seen as the future of the automotive market and, more generally speaking, of all transportation.
The industrial machinery sector and the electric vehicle sector are also looking at this new technology with interest: this is the case for very energy-intensive machinery or heavy vehicles, which often require extensive range and where, to date, the volume is low compared with the amount of energy that could be used.
The introduction of solid-state battery technology could definitely be useful for further expanding the category of electrified vehicles. If, along with their large energy density, solid-state cells therefore became competitive on all fronts, they could undoubtedly be a valid path for the future of industrial electrification too.
Solid-state batteries are not science fiction, on the contrary! They are already reality in small applications, such as certain consumer batteries or some vehicles like buses, suitable for intensive use and where the battery is used non-stop for the whole day and even though it stays hot, it works without too many problems.
Solid-state technology is therefore already used with low volumes in:
One real life example are the 50 E70 vehicles with semi-solid-state batteries recently launched on the market by the Chinese Dongfeng Motor Corporation: it is a sort of technological first, where it seems that semi-solid-state batteries have shown excellent electrochemical properties through a series of simulation tests.
How will they behave in the long-term? The eyes of the entire automotive world are certainly on this Chinese car manufacturer, so we will see how it goes. It could also just be a great marketing opportunity to promote their brand and associate it with this new technology before the others, but there is no guarantee that they will reach mass production.
What is certain is that real solid-state batteries for automotive use are still in an experimental stage, with major challenges that are still ongoing and, to date, are limiting their mass production. However, many car manufacturers are interested in this promising technology, such as Mercedes, Volkswagen, Toyota and many others, which are investing huge resources into studying and developing it. They will be the ones to have the first definitive technology, already announced for between and , provided the limits are resolved.
Lithium Cobalt Oxide. Lithium Manganese Oxide. Lithium Nickel Cobalt Aluminum Oxide.
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These are just some of the various types of batteries that fall into the lithium ion family. They are generally named after the chemicals used in the cathode, which is what lithium ions flow towards when the battery is being used.
Different EV battery compositions optimize different things, such as the life span, maximum charge speed, or how much energy a cell can hold. The specific chemistry that is used depends heavily on how it is being used.
For instance, batteries with manganese have very low internal resistance and can be charged pretty fast. However, these batteries tend to have shorter lifetimes.
For EV use, the most popular batteries are NMC (lithium nickel manganese cobalt oxide) and NCA (lithium nickel cobalt aluminum oxides), which combine metals with nickel and cobalt to make them last longer and hold the most energy. However, LFP batteries, also known as lithium iron phosphate, or LiFePO4 (Li = lithium, Fe = iron, PO4 = phosphate) are the new kid on the block.
Nerdy Aside: Why do LFP batteries promise to be more resistant against heat-related aging and degradation? Simply put, the Fe-PO bond in LFP compositions is stronger than the Co-O bond in cobalt-based batteries, so that if abused (short-circuited, overheated, etc.) the oxygen atoms are much harder to remove. This means that under stress, a LFP battery is more likely to resist rapid rises in temperature, which can result in permanent battery damage or in dire cases - start a fire.
While we’re excited about the adoption of more LFP technology, we are scientists, and we do want to mention the compromises that come with using LFP packs.
Tesla announced a switch to the lithium iron packs in their standard range models in . The change started in China-made Standard Range vehicles and reached the US in .
On their heels came news from Ford in that they plan to switch to LFP packs in European Mustang Mach-Es and in select F-150 markets in . These new LFP packs are already on the road in Standard Range Mach-Es in the US, but in limited numbers. Recurrent only has a handful in our fleet so far. Fisker Ocean is also using LFP packs in their base configuration, the Sport.
Rivian announced a switch to LFP batteries and new cell configurations, allowing for faster production. They will start using LFPs in their Electric Delivery Vans for Amazon, and then switch over in their Standard Range trucks.
GM announced that its revamped Chevrolet Bolt EV would use LFP packs to help cut costs.
BMW also announced it will start using LFP batteries in .
Tesla announced in October that it was switching to LFP batteries for its standard range models in both Model 3 and Model Y.
But why did it keep cobalt batteries for the Long Range trims?
Since the LFP packs have lower energy density, you need a larger LFP battery for long range or mind-boggling acceleration. The larger battery adds weight and can reduce efficiency. Because of this, most automakers are only looking to use them in Standard Range and non-performance trims.
However, we will see how Ford fares with using LFP packs in their much larger, much heavier F-150s.
After some very public investigation this year, the world learned that the displayed dashboard range for most Teslas is higher than the actual, achievable range that the same cars actually get. Recurrent came up with a proprietary value, Real Range, to show the typical, achievable range we observe for an average Tesla. The chart below shows how much of the EPA range Teslas usually get, and the temperature dependence of this value.
What we see, at least for Tesla Model 3s, is two-fold:
Both of these results are exciting, although preliminary. They show differences in the ideal operating temperature for LFP batteries, which seem to get the highest range at around 70 degrees, compared to around 60 degrees for NCA packs.
They also show that the EPA range advertised for the Standard Range Model 3s is slightly closer to the truth than it is for the Long Range and Performance models. It’s important for Tesla drivers to know what their actual, achievable range is in the real world, in order to understand the limits and possibilities of their car. Of course, as we like to say with all things range, Your Mileage May Vary - and we’d love to hear your experience with your LFP battery!
Several studies show that LFP batteries have a cycle life of 2 to 4 times longer than NMC batteries. The higher cycle life is also part of the reason that Tesla recommends charging to 100%: you may not even notice any additional battery degradation on an LFP.
LFP batteries have a much higher threshold for heat, which is what causes thermal runaway, or battery fires. For LFP batteries, thermal runaway temperature is at 270 degrees C, as compared to 210 C for NMC and 150 C for NCA.
Although it's worth reiterating that the risk of any lithium battery catching on fire is very, very rare.
The recommendation to charge LFP batteries to 100% has nothing to do with the battery, and everything to do with the battery management system (BMS). Recurrent still suggests charging all lithium ion batteries to 80-85% for optimal life.
What we see in our data: Tesla drivers with LFP batteries in their cars charge beyond 90% far more than Tesla drivers with non-LFP batteries. Most non-LFP models are kept between 50% and 90% state of charge, while most LFP vehicles are charged between 90% and 100%.
Why this matters: LFP batteries hold up better to high states of charge, meaning that regularly charging them to 100% may not cause as much degradation as it would with a different battery chemistry.
Yes, LFP batteries can certainly charge in cold conditions, but it maybe slower to charge because the car needs to spend more time warming the battery. While preconditioning does resolve these issues, drivers who can’t always anticipate their cold weather trips might suffer.
In a video from November, , Bjorn Nyland shows that performance doesn’t suffer, but charging speed definitely does if you don't have time to precondition. He posits that BMS updates to the SR+ Model 3 might have improved range and thermal management in the vehicle’s second winter on the road.
We expect LFP batteries to hold up better to the heat and heat-related degradation, but the true test will be time. We will continue to analyze the range of EVs across the country with and without LFP batteries.
What we see in our data: There is fairly even distribution across the US of LFP and non-LFP battery packs. Since the LFP packs come in the Standard Range models, which are more affordable, they are gaining popularity in a lot of metro areas.
Why this matters: While no lithium ion batteries love being stored in hot conditions, LFP batteries may hold up better to heat. If you live in a hot climate and know your car will have to be out in the sun, this may be a good consideration when you decide between trim levels.
Nerdy Aside: Why do LFP batteries promise to be more resistant against heat-related aging and degradation?
Simply put, the Fe-PO bond in LFP compositions is stronger than the Co-O bond in cobalt-based batteries, so that if abused (short-circuited, overheated, etc.) the oxygen atoms are much harder to remove. This means that under stress, a LFP battery is more likely to resist rapid rises in temperature, which can result in permanent battery damage or in dire cases - start a fire.
In short, yes! Switching to LFPs would reduce or eliminate the need to rely on nickel and cobalt, which are often sourced from mining operations and countries with questionable track records. A move to LFP batteries also makes it easier for American companies to participate in a domestic supply chain secure from foreign influence.
Read more about how LFP batteries help address criticism about EVs.
LFP batteries have a lower operating voltage per cell than other common lithium ion batteries, which means that you might need more of them if you need a specific voltage (e.g. you want to hit a certain 0-60 time).
This means that LFP technology is not a one-size-fits-all solution. For heavy transport needs, LFP may not be as useful as cobalt-based batteries, since a higher workload may be needed.
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