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I published a video a while back about a solid state battery that’s available to purchase for yourself today, but very quickly, questions sprang up around its solid state bonafides. A few of you pointed me in the direction of a company that did a breakdown of Yoshino’s battery that showed it wasn’t “solid state.” Once I looked at this report, I found myself falling down the rabbit hole.

And during my descent, I’ve had multiple conversations with TechInsights, the company that did the breakdown, as well as my friend and fellow YouTuber, Ryan Inis Hughes from the channel Ziroth, who organized a breakdown in a university lab. I also had multiple conversations with battery researchers and experts in the field.

So, the burning question now becomes: “Is Yoshino’s battery actually solid state?” And if it’s not, why is the company calling it that in the first place? There’s a lot of solid information to unpack here…so let’s get into this charged discussion.

First off, I do need to apologize for the inaccuracy of my previous video, which is unlisted so the algorithm won’t promote it. And I want to thank all of you who gave me tips and observations about the TechInsights report that originally broke down the Yoshino battery cell. Those tips are what sent me down the path of this follow-up video.

Before publishing the original video, I did dig into one of Yoshino’s claims about its battery technology, which was originally stated to use an inorganic-polymer composite (IPC) as the solid electrolyte. That’s then paired with standard lithium ion battery components such as a graphite anode and nickel, cobalt, manganese (NCM) cathode. When I researched using polymers as a solid electrolyte, it looked promising. It is something that many companies are experimenting with. There’s plenty of research papers on it. I also verified Yoshino’s safety claims via thermal testing and nail penetration tests done by a third party. Again, based on the materials used, it seemed to check out. So, I moved forward.

However, what I didn’t do was break the cell open myself. If I had, I would have found what TechInsights found, which was that the anode and cathode were wet with some liquid electrolyte. Several other YouTubers have published videos showing themselves ripping into the cells and finding the same thing. A few also did some “penetration” tests that showed the cells suffering from thermal runaway and burning.

Just a note to everyone: That’s not proof of solid state status or lack thereof. Shooting batteries with arrows, using drills, or scraping away layers by hand is not how labs do nail penetration testing. It’s also not safe. Solid state batteries can still suffer thermal runaway and burn — because polymers or other reactive components can still burn. If you’re creating enough damage for the anode and cathode materials to touch and short circuit, you’re going to have a problem, solid state or not. I’ll get into more of that later though.

Regardless, the liquid inside looks pretty damning. The fact there’s a liquid electrolyte means that this isn’t an “all” solid state battery. That alone is what calls into question Yoshino’s “solid state” marketing claims because they give the impression that it’s all solid state to some people when it’s missing any kind of qualifier. BUT — and I know this isn’t going to go over well on the internet — it’s more nuanced than that, which is how I ended up exploring the disorienting twists and turns of battery Wonderland. I learned so much and found this absolutely fascinating, and I hope you do too.

What Actually is a Solid State Battery?

The beginning of the journey to figure out what’s going on with Yoshino’s battery requires a clear answer to the biggest question: what the heck is a solid state battery? Now, pause the video and drop your definition of a “solid state battery” into the comments. I have a feeling I know what most of you are going to write. Your understanding is probably about the same as mine, which is that a solid state battery has a solid state electrolyte … and maybe that there’s a lithium metal anode… but I bet a lot of people also wrote that it has no liquid electrolyte. Period.

Here’s the thing though. The only qualifier for a solid state battery is the use of a solid state electrolyte as part of the battery cell. One view of this is that underneath the general term “solid state” is “all solid state,” which is the ultimate goal: no liquid at all. However, and let me be clear on this, including some amount of liquid electrolyte in the cell doesn’t automatically disqualify the battery from being some form of a solid state battery. Instead, it puts it into a sub category. Think of it like a genus and species. The genus is solid state. The species can be all solid state, semi-solid state, quasi-solid state, and so on. In fact, the amount of liquid present in a solid state battery gives you a sense of what type of battery it is.

I spoke to Ali Khazaeli, the expert who broke down the battery for TechInsights, about this exact thing.

“So the standard definition in the industry is that, if the amount of the electrolytes is more than 25% of the active part, the weight percent of the active part of the battery. So it’s going to be a lithium ion battery. If it’s less than 10%, it’s going to be a semi-solid state battery. If it’s less than 5%, then it’s going to be a quasi-solid state battery. In this situation, we get some advantage from the solid state technology, but it’s not “all-solid state” batteries. So it’s better to call this type of battery a semi-solid state battery. Or if they have a very small or tiny amount of the electrolyte, we call them a quasi-solid state battery.” -Ali Khazaeli

I like the clarity of how he’s defining the differences between semi and quasi solid state with the percentages. But something I found particularly interesting in my investigation is that the 5% difference between semi and quasi solid state liquid content really details the liquid’s role in the electrolyte’s function.

For instance, a solid ceramic electrolyte typically doesn’t flex or conform to a surface well, which might introduce additional resistance with the anode/cathode contacts. So, a small amount of liquid (like in a quasi-solid state battery) actually helps the ceramic make better interfacial contact with the anode/cathode by filling in those gaps. If the liquid content were increased, the ions might partially travel through the liquid and through the solid electrolytes to get the best of both worlds and still be safer than a mostly liquid electrolyte. Hopefully, this gives you a better picture as to why it can be advantageous to have some liquid in a solid state battery.

That said, different companies and research organizations will give you different frameworks for how they categorize solid state batteries. Some definitions focus on the percentage of liquid electrolyte. Others focus on the benefits you get out of the battery to determine semi, quasi, hybrid, or whatever qualifier you want to use. Even among experts in the field, there doesn’t appear to be a clear-cut definition or consensus on what is considered a “solid state” battery.

On that point, I had the chance to talk to the Chief Technology Officer and co-founder of Quantumscape, Tim Holme, recently. Here’s what he had to say about the definition of solid state.

“Could you kind of walk through at a high level? It’s not QuantumScape specifically, but like, what is a solid state battery? What makes it different from a traditional lithium ion?” -Matt Ferrell

“Yeah, well, I have a lot of empathy with people who are confused, because there isn’t a definition that everyone subscribes to of what is a solid state battery. And to make it worse, there are companies talking about quasi-solid state batteries, hybrid solid state batteries, condensed state batteries, throwing out a whole bunch of terms that are never even defined as to what they are, which just further muddies the picture.” -Tim Holme

“So to me, a solid state battery is a battery that at least one of the major components is a solid state. There’s an all-solid state battery where all of the electrolytes are solid. That is not liquid, not gas, not plasma, but solid. That’s an all-solid state battery. And then I think a solid state battery would be a battery where at least a major component is solid state. There are solid polymers that conduct lithium. So there are batteries that are made with all solid polymer conductors that would be solid state. There are also batteries that use sulfides, oxides, various different of more inorganic solid materials and those all could be called solid state batteries.” -Tim Holme

“There isn’t like, an IUPAC standard definition of what is a solid state battery. There are solid polymers, there are solid inorganic materials, and to me, a solid state battery would be any of those. I do think there’s a distinction between an all-solid state battery that has no liquids versus, if you say solid-state battery, that maybe isn’t an all-solid state battery.” -Tim Holme

This is a problem that is also discussed on the academic side. I came across research papers that were proposing a better way to classify these new battery technologies because of the confusion around how current definitions are used. The 2023 paper “Typology of Battery Cells – From Liquid to Solid Electrolytes,”1 goes as far to say:

“As research attention has recently expanded to diversifying the electrolyte chemistry, (all-)solid-state batteries and hybrid cells have become more prominent. However, there are several different types of electrolytes used in (all-) solid-state batteries and some electrolytes rely on the help of a liquid additive during cell operation. In line with this, the liberal use of descriptive terms for cases combining different types of electrolytes and materials, such as “hybrid”, [7] “composite”, [8] “quasi solid”, [9] “semisolid”, [10] or “almost solid”,[11] leave room for ambiguity about the electrolyte composition and ion conduction mechanism.”

Basically, these researchers are proposing defining a battery based on the main ion conduction mechanism of the electrolyte. This might help to better classify battery types and lessen the amount of disagreement on what is considered “solid state.” But the one thing that there’s no disagreement on — which is also probably what most of you wrote in the comments — is that an all solid state battery has no liquid electrolyte. Zero, zip, zilch, nada. However, as I just explained, that’s not the only type of solid state battery.

Also, it’s extremely important to remember that a solid state battery isn’t limited to a specific chemistry. What we’re focused on is the electrolyte material. So for a battery that has a standard graphite anode and an NMC cathode, it’s still lithium ions shuttling around … in other words, it’s still a lithium-ion battery, but with a solid state electrolyte as…well…the shuttle.

That leads me to a question: Ask yourself, why do we want a solid state electrolyte? It’s not because it’s what the cool kids are doing. It’s all about the benefits that we get from that solid state material. The big selling points we hear all the time are safety, longevity, and energy density. So even if a semi-solid state battery has some liquid in there, if it can deliver one or more of those benefits, that’s what’s important. Now, let’s get into the details on what’s inside Yoshino’s battery cells.

What Did the Breakdowns Find?

When I first heard about TechInsights’ Yoshino breakdown, I downloaded the free report you can get on TechInsights’ website. While the free report did include some photos of the cells and the wetness on the separator, it raised more questions than it answered for me. In my first conversation with TechInsights, it turned out that its team hadn’t fully tested some of the chemical makeup of the separator, because the examiners concluded it wasn’t solid state immediately after seeing the liquid electrolyte. That’s understandable, but many of my questions stemmed from what Yoshino was claiming with the company’s solid state electrolyte. TechInsights was very accommodating, and its team was willing to go back and run some further analysis on things like the separator to fill in these gaps.

The TechInsights team then provided me with some videos and photos of what they saw as they opened the battery pack. The first thing to point out is the battery identification stamp. You can actually find the safety data sheet that’s associated with this number with a simple Google search. I have personally confirmed that this is Yoshino’s battery. Some have pointed to this saying that “li-ion cell” is a damning piece of evidence. It’s not. As I mentioned earlier, solid state is not a specific chemistry, and Yoshino is using a standard graphite anode and NMC cathode. It’s lithium-ion, so that isn’t shocking. These safety data sheets also don’t share all the details of the battery chemistries, so you can’t rely on them to fully list out every single ingredient. They’re partial information at best.

The cracked-open cell should look familiar if you’ve seen some of the other YouTubers that ripped open their packs. You can see here that there’s clearly a liquid. Right off the bat, this challenges any assertion that this is an all-solid state battery, but it doesn’t mean it’s not some form of solid state battery. You can even see the electrolyte liquid evaporate as it’s exposed to the air.

Over at TechInsights, Ali performed tests like Scanning Electron Microscopy analysis (SEM) and Energy-Dispersive Spectroscopy (EDS). These give you a closer look at the microscale surface features of a material as well as its chemical composition. Fourier-transform infrared spectroscopy (FTIR) provided more details on the polymer, as well. With these processes, they’re able to fill in the blanks on what actually makes some of the Yoshino batteries tick. This is the stuff I was super eager to hear about.

“The cathode was NMC as they claim that it was the NMC material. The anode was the graphite. So no trace of any silicon or other particle. The separator is a polymer … the separator is a little bit different from the regular lithium-ion battery. Because they have some PVDF on the separator side, which actually helps them to pass the nail test. So this battery is safe, because the separator is safe. It has some safety functionality. But it’s not an all-solid state battery because there’s a lot of electrolyte in it. And semi-solid state battery even, it remains questionable if it’s really 10 percent of the volume.” -Ali Khazaeli

Let’s break this down a little bit. Ali did confirm that the chemistry of the anode is graphite, just like Yoshino claims. He also confirmed that the cathode is NMC, just like Yoshino claims. Also, the PVDF he mentioned is a type of binder that’s usually used to hold the materials in the anode and cathode together. It’s chemically stable, offers good adhesion, and looks like it may have been used to adhere the separator.

But it’s the separator where things get a little spicy (my words, not Ali’s). Here’s why I say that. As I mentioned earlier, Yoshino’s IPC solid state polymer approach is a valid path some companies are taking towards bringing some form of solid state to market. In fact, the research paper titled, “Tailoring inorganic–polymer composites for the mass production of solid-state batteries” hits on this precisely. I was told that one or more of the researchers of that paper are involved with the Yoshino’s battery development, so this is the perfect place to look to figure this out.

The paper hits on aluminum oxide (Al₂O₃) in inorganic–polymer composite electrolytes to enhance ionic conductivity. Specifically, Al₂O₃ nanoparticles are cited as an effective way to suppress the crystallization of polymers by lowering its glass transition temperature. Technical jargon aside, it basically helps to keep those lithium ions flowing and can have a significant boosting effect for polymer-based electrolytes. The paper also hints at the possible presence of liquid components to enhance ionic conductivity, even though these are considered compromises rather than pure solid-state solutions​. A lot of this points at what could be considered a “semi-solid state” battery.

What Ali at TechInsights found on the separator was a ceramic coating that included aluminum oxide and some kind of carbon-based material, which could be polyvinylidene difluoride (PVDF).

During my time pulling this video together, Yoshino was also very forthcoming with me about what’s inside its battery cells. The company provided me with its own SEM analysis and descriptions of the different components in use. It was at this point I found out some of the specifics that Yoshino claimed to be using, which is an LATP (Li1+xAlxTi2-x(PO4)3) solid electrolyte bonded to the cathode. Their EDS data appears to show the presence of Ti and P on an elemental map. The presence of aluminum (Al), oxygen (O), and phosphorus (P) from TechInsights’ EDS data seems to help back that claim up. However, there appeared to be a lack of titanium (Ti) in the EDS spectrum, but more on that later. LATP is a ceramic-like material that allows lithium ions to move through it efficiently. This helps to improve the safety, stability, and performance of the battery cell.

This investigation was not without its speed bumps. I asked my friend Ryan, who is a PhD student at the University of Bath (and has a great YouTube channel called Ziroth), if he could break down a Yoshino battery cell for me. He ended up working with another PhD student and colleague at the University, Howard Richards, on the analysis. I wanted to have a second independent take on Yoshino, separate from TechInsights. The mailing process was kind of a nightmare because you have to have special certification to ship lithium ion batteries, so I wasn’t able to easily get a battery pack for him myself. I actually bought the same exact model I have and tried to ship it to him … it didn’t work. It got returned to me. Yoshino was really helpful and willing to send a B4000 battery pack over to the University of Bath for me. The fact Yoshino was willing to do this with no strings attached was a sign to me that they’re really standing behind their product … but … there’s a major wrinkle.

After Howard completed his full breakdown and analysis, he couldn’t find any traces of the titanium for LATP, just like TechInsights. Curiouser and curiouser.

“I’ve been doing some extra digging in the literature since Howard shared some of the results that he’s recently got from the tests. And the one thing that I keep stumbling across is that in some of the literature where they have done LATP-coated NCM batteries. It’s such a tiny trace amount, it may be, like, to the point it’s not detectable. So, you’re talking like 0. 5 percent by weight, which I’m not sure, Howard, if you would be expecting to find that within the tests that you’ve done, but there’s a chance that it’s so small, that if it is present, we, …If you’d scan the wrong bit, if you’re, you know, you’ll, you’ll literally get counts of a very small area you’ve, you’ve scanned. I’m always trying to make sure we’re fair because the scientific process is famously difficult sometimes to replicate certain, um, results, but the percentage I’ve seen in the literature that people are using are in the 0. 5 percent to 2 percent per, uh, by weight of LATP.” -Ryan Inis Hughes

“So I guess I’d say that, yeah, I agree with Ryan. There is definitely the chance that there is a trace element. I think that’s why when we redid the tests, so we did kind of multiple tests on a sample, we also then took another sample from the other side of the sheet. ‘Cause I was there like, Oh, you know, you know, it’s only a kind of 15 millimeter disc. I don’t want to say that that one spot just happened to be where there wasn’t any LATP. In the EDX, which is the one we kind of expected to show it, because it should just show, um, all of the elements you have there, essentially. It should just be like, right, you’ve got this one, you’ve got this one, you’ve got this one. I think you may have seen the results as well, Matt, you can get them in like a nice pretty map and you can see where they are exactly and you can be like, okay, great. There’s like this region around 4. 5 KV on the spectrums that there should be kind of a second titanium peak. And there is a massive blank spot on that spectrum from about … I think it’s three and a half from memory to like five. So right where there should be kind of a little titanium peak, if there were LATP in there. There is kind of almost, there’s nothing at all, nothing detectable.” -Howard Richards

These observations appear to conflict with some of the data provided by Yoshino. One important caveat is that for the EDS data that showed Ti and P, Yoshino only supplied the elemental map, but not the accompanying spectrum. This might not sound important, but the spectrum of peaks correspond to the elements present. For all we know, the maps are simply noise. Yoshino did also provide XPS (x-ray photoelectron spectroscopy) data on Ti, which appeared to detect the element on the surface, but it’s also hard to tell the quantity present.

When I asked Yoshino about why two separate groups could not confirm the LATP composition, the company’s official response kind of fit into what both Ryan & Howard said to me, as well as what Ali reported from TechInsights.

“For the characterization of multi-component materials, EDS testing may not be sufficiently accurate, as it may fail to detect metal elements present in low concentrations. It is recommended to use elemental mapping or inductively coupled plasma (ICP) analysis for detecting metal elements with low content to ensure more precise measurements.” -Yoshino

So it looks like the EDS tests Ali, Howard, and Ryan ran weren’t sensitive enough to detect the LATP. But wait … this is where it gets weirder. Yoshino also said the reason why Ryan and Howard found zero traces of an LATP is because the B4000 battery Yoshino sent uses a different cell makeup than the one in the B330 that I have, which is also the same model that TechInsights tested.

A direct quote from an email I got from Yoshino:

“Because we didn’t inform the factory which unit we had sent to Ryan, and only mentioned to them the TechInsights article, they (rightly) assumed we were referring to our 16.2AH battery (used in 3 of our 4 models). That battery does in fact use the LATP electrolyte (which I’ll come back to). Our 54AH battery that Ryan tested from our B4000 uses an inorganic/organic composite polymer electrolyte (CPEs) composed PVDF and SiO2 – which is still classified as a solid electrolyte.” -Yoshino

Yeah … this really had me scratching my head. Yoshino did offer to send the B330 over to the University of Bath so that Ryan and Howard could do another breakdown that is truly an apples to apples comparison with Tech Insights. However, after all of the conversations I’ve had with both Ali, Ryan, Howard, and others, it was clear this wouldn’t change the fundamentals I was trying to dig into. There’s a plausible explanation for why TechInsights didn’t detect the LATP because of the types of tests Ali ran. And for the other battery Howard found a coating of SiO2 on the cathode that he tested, which fits with Yoshino’s claims of the 54AH battery cell. But at the end of the day, both cells had liquid electrolytes, a separator, and solid particle coatings which have difficult-to-determine compositions.

Was Yoshino’s marketing of just “solid state” accurate or not?

Yoshino’s “Solid State” Marketing

That brings me right back to “What even is a solid state battery?” Ryan and Howard also accompanied me on this visit through the solid-state looking glass. Here’s their thoughts on it:

“The idea of a solid state battery was to replace both that liquid and the separator with one kind of polymer itself. So one plastic. So essentially you’re taking the separator, make it of something slightly different, and then you could get rid of the liquid, and you’d just have that separated there. So it would kind of do two jobs in one. It’s very simple to think about. Instead of two components, you’ve then got one.” -Howard Richards

That’s important, because Yoshino doesn’t have a solid state electrolyte pulling double duty in its battery cell. Instead, the company’s batteries still have the standard separator, plus the liquid electrolyte, along with their “solid state” coating on the cathode.

“So, okay, here’s, here’s maybe where I land on it. I think we need to have all solid state or semi solid state. And I don’t think solid state is in the middle of that, does that, if that makes sense? So I think that it’s more useful to define all solid state batteries. Or semi solid state batteries or liquid electrolyte. I think where I’m having issues coming up with the definition is for solid state battery, which maybe is where it becomes difficult to define because how solid does it have to be to be called solid? So I think for me, it’s liquid, semi solid state, or solid state. I think those are my categories. And within semi solid state, that’s where you get the spectrum.” -Ryan Inis Hughes

So now we’ve reached the crux of this video: just what kind of battery is Yoshino selling? We can all agree that it’s not, “all-solid state.” There’s no debating that, but based on what I’ve seen from the TechInsights report and the research papers, this is more akin to a semi-solid state battery. Yoshino updated its website after this controversy exploded to try and provide some explanations. The company says that the liquid accounts for 5-10% of the battery’s volume and “remains as a result of the manufacturing process.” Now, I’m going to play a couple of bits from a conversation with Ryan and Howard. Please note that this is before we knew the cell they tested was not the LATP model we expected.

“If I had to put my house deposit to bet on what it is, I think it would be, as Howard mentioned, it’s got this polymer electrolyte in there, and I think that’s part of what’s improving the safety, because we saw on puncture tests that it was performing well. Slightly better than other comparable NMC batteries. So I think that they had some safety benefits there. I think if I had to bet, I do think there could be like 0. 5 percent by weight LATP in there, which I’ve seen in the literature can improve the cycle life and is small enough that it could have been missed by the tests we did. That conclusion means that it is so far, to be 0.5 percent of something, that can be used as a solid electrolyte is so far down the spectrum I would have to put it as. Maybe not even. I wouldn’t even call it a semi solid state, I don’t think. I would call it an enhanced NMC and I can’t, hand on my heart, and say that they don’t use LATP because from what I’ve read in the literature it can be really, really, really hard to spot when you’ve got such tiny, tiny amounts of stuff in there.” -Ryan Inis Hughes

That kind of links into my conversation with Tim Holme, the CTO of Quantumscape, when he said, “a solid state battery is a battery that at least one of the major components is a solid state.” Is it a major component or not in Yoshino’s cells? That’s where I think the debate is happening, but Howard had a great — and pretty funny — analogy.

“I think if you were a vegetarian and someone gave you a beef burger and went, ‘Yeah, but it’s got lettuce in it,’ and called it a veggie burger, you’d be quite annoyed. So just ‘cause it contains something from a solid state battery, I don’t think necessarily makes a solid state battery. Having said that, I might go and jump on the fence even more than Ryan did, and essentially say that, I don’t want to discount that there is LATP in there. Or they’ve found a way for it to be really beneficial. And part of the reason I believe that is because we are essentially still really, really bad at making batteries. Like, we genuinely suck at it. I saw a presentation recently that said that a large battery manufacturer, who must remain nameless, was setting up a new gigafactory. In the first year of production … the first year … 96 percent of the cells had to be recycled. They weren’t good enough to go out. I think another good analogy I’ve seen as well is that — I think if you make a car I think you can have like 70 or 80 quality assurance points. I’ve seen referenced in a couple of places that CATL, when they make batteries, have 3,600 quality assurance points.” -Howard Richards

“The point to be made, I guess, on the Yoshino part of things is that for all we know, and this is why I don’t want to rule out them using LATP, is they might have found a very specific way that it works really, really well. And the thing I can’t dismiss is that the claims of cycle life that their cells have look really, really good for an NMC battery. And yes, it’s fantastic, and yes, it could be the very, very, looks like close to negligible amounts of LATP, it could be those trace amounts, they could be doing wonderful things.” -Howard Richards

“But on the other hand, it could just be them being really good at making sales. And I think that’s almost, I guess, I want to say that the shame almost about the marketing is that had it not been written as like a solid state battery. If those 4,000 cycles are reached for 80 percent of that battery, it’s done. Excellent. That is fantastic … it’s the calling it solid state though. As I said, if you’ve got a bit of lettuce in the burger, I don’t think it makes it a veggie burger.” -Howard Richards

Here’s where I’m going to challenge everyone. Does any of this actually matter? Are we debating semantics here? Personally, I say that at the end of the day, it’s what the battery can actually do that matters. BUT… companies have a responsibility to be transparent about what they’re selling, and consumers deserve to know exactly what they’re buying. This requires a level of care in marketing, and that means precise language.

So what did Yoshino have to say about all this? Here’s some of the statement that marketing vice president Vince Caito provided me with via email, which was my final communication with the company after months of discussions:

“We have always subscribed to the universally accepted definition of what constitutes a solid-state battery; and that is a solid-state battery is one that contains a solid-state electrolyte. Our batteries absolutely meet this definition by utilizing a solid-state electrolyte in place of liquid or gel electrolyte found in traditional lithium batteries…Yoshino’s power stations all use Lithium-NCM batteries with an Inorganic Polymer Composite electrolyte that is recognized by the scientific community as ‘solid-state.’”

There’s a couple of problems here that you might have noticed right away. But before I address those, I should note that the statements above are almost word-for-word copy that is already existing on Yoshino’s website at the time of writing. We’ll set that aside.

First off…”universally accepted”? The whole reason I’m making this video is because the definition of solid state is so contentious. Secondly, we now know for a fact that Yoshino batteries contain liquid electrolyte. So it is not true that solid-state electrolyte is used “in place of” liquid or gel … at least in whole.

The company claims its battery is solid-state, but despite the presence of liquid electrolyte, Yoshino is not clarifying that its products aren’t all solid state. In fact, its official position is explicitly in favor of opting for less precision when describing this type of tech. As written in the company’s statement to me:

”Along with many experts in this field, Yoshino agrees there should only be two classifications of solid-state batteries: “All Solid-State” and “Solid-State”. If consumers are misled to believe there are other qualifiers, the market will be awash with manufacturers claiming “hybrid” or “semi” solid-state.”

But wouldn’t you agree that lettuce on a beef burger doesn’t make it a veggie burger?

I’d argue that by having no qualifier and just calling it “solid state” makes matters worse. Sticking to a broad definition would lump an incredible number of battery types together, each with wildly varying solid state benefits. That binary framework doesn’t help the consumer understand what they’re getting inside.

I’m going to step away from the metaphorical grill, here, and use a computer analogy instead of a burger one. An “all”-or-“solid” categorization system would be like computer companies advertising multi-core CPUs inside their machines, but not saying how many cores or clarifying the operating speed. If it’s more than one core, it’s multicore, sure. But is it 12 core…or 2 core? And what speed do they operate at?

Yoshino also said in the email that it asks “all potential customers to focus on the tangible benefits our advanced batteries provide.” On that I agree, so let’s go over those. Is Yoshino’s battery safer? Yes, it is. I know those Youtube videos of it catching on fire looks bad, but here’s the news flash … solid state batteries can catch on fire. They’re just a lot less likely to, and it also depends on the exact type of electrolyte used and damage done. Ceramic isn’t going to burn, but polymer can. Regardless of the electrolyte though, if you bring the anode and cathode in contact with each other … it’s game over no matter what.

Some of those Youtube videos were very destructive — and a serious health risk. As Howard put it to me:

“Part of what makes the liquid electrolyte batteries dangerous is not necessarily the lithium itself, so much as the solvents it’s dissolved into. Those solvents it’s dissolved into are generally carcinogenic, and so…when we’re dealing with an elab, it stays in an argon glove box. We don’t touch it.” -Howard Richards

Bottom line: If the experts aren’t going at these components bare-handed, neither should you. I saw one person scraping away through the layers with a utility knife … don’t do that! Another shot arrows with some gnarly looking arrowheads that clearly caused a lot of tearing on the way through. It still took two arrows before it caught fire, anyway. Another used a drill. That’s going to mix things together as it drills through the layers, which doesn’t conclusively prove anything.

If you are going to do penetration testing like that, you need to do it in a way that can be precisely repeated again and again. It’s the only way to get true apples to apples comparisons between different battery cells. For instance, what about comparing how an LFP cell reacts to a nail penetration vs. a standard NMC lithium cell vs. an NCM solid state battery? Yoshino’s third party testing report passed the nail penetration test with flying colors. It also did exceedingly well at the thermal testing and survived very high temperatures. So even if Yoshino’s products are solid state only in name, when it comes to the safety benefits, the company seems to be ticking that box.

What about longevity? For this, we’d have to take Yoshino’s word on their estimates. I know that’s going to be a tough pill to swallow for some — especially considering the confusing statements that we’ve gone over — but if its estimates are accurate, it’s very good. The company claims they’ll last for over 4,000 cycles compared to most of the LFP cells that range with a 3,000-3,500 cycle life. Again, another box potentially ticked in the solid state benefit column. Side note though, LFP’s 3,000-3,500 is incredible … that battery cell will most likely outlast most of the other components inside the product. LFP is fantastic and very safe.

So what about energy density? This is where the Yoshino doesn’t ace the test if you compare their NCM semi-solid state setup to a pure liquid NMC setup. It’s not really all that different. However, what they’ve done is create an NCM battery pack that’s as safe or safer than an LFP … which also means a higher energy density for the final product. On this one, I give them partial credit.

Based on all of that, we’re seeing some of the benefits of solid state in the final product that a consumer can have in hand today. Yoshino may have made a better and safer NCM battery because of the solid state electrolyte setup they’re using. But that’s all muted by the fact that Yoshino is misleading in its description of its battery pack’s composition, intentionally or otherwise.

For instance, when Ali and I talked, he mentioned they had assumed it may be a lithium metal battery anode because of the claimed higher energy density in their marketing materials. At that time on one of the pages, it talked about their “solid-state lithium battery” — not lithium-ion, which gives the impression that it might be lithium metal.

At the time I wrote this script, Yoshino was displaying a quote from the Washington Post on its official website that talks about the benefits of solid state batteries. It reads: “Solid-state batteries, which do not contain liquid electrolytes and can charge quicker, last longer and be less prone to catching fire than the lithium-ion batteries currently in use.” The part that jumps out at me is, “which do not contain liquid electrolytes…” But Yoshino’s does, and by having that quote on the website, the company is setting false expectations. Perhaps their definition of liquid electrolytes might be “all-liquid” electrolytes. Again, semantics are a pain when defining the materials for a solid state battery, but the ambiguity seems helpful from a marketing standpoint.

Not to mention, it’s a little odd to use an out-of-context quote from a news article that’s specifically about car batteries to describe your own product that’s intended for a different use case. It’s not like this quote in isolation offers consumers with an expert’s review. It’s formatted like a testimonial…but it’s definitely not one. Take that as you will.

Is Yoshino lying about the benefits of its battery? When it comes to safety, lifespan, and so on, it looks like it does what it claims. However, the high level term “solid state” leaves the door open to interpretation as to what kind of solid state. It would be understandable for a consumer to immediately jump to “all solid state,” which sets themselves up for disappointment when the battery is cracked open to reveal a liquid. But that doesn’t mean it’s not solid state … it’s just not an all solid state battery.

Other battery companies that make similar products, however, make this distinction and call them semi-solid state. For instance, one competitor, Zendure, markets their battery as a semi-solid state NMC battery. Even though what that means will still vary based on who you ask, that alone helps to better set consumer expectations (in other words, this is not “all-solid state”).

Based on what we’ve talked about today, I’ll let you come to your own conclusions about Yoshino. But from a technical standpoint, here’s what we can at least conclude about its battery. One of my science advisory board members put together a great report for me on all of this. Here’s his summary breakdown:

“Based on the gathered information from TechInsights, our academic collaborators, and Yoshino itself, it appears that this Yoshino battery cell, at best, likely consists of a semi-solid state or hybrid battery architecture. It is certainly not an “all solid” state battery.”

“The anode is graphite and the cathode is based on an NCM chemistry (which can still be flammable). The electrolyte separator consists of a polymer (likely PVDF) coated with a ceramic material (alumina or silica particles depending on the cell tested). LATP may or may not be present as some of the elements are shown but still lacking a detectable amount of titanium. The liquid present is likely lithium hexafluorophosphate (LiPF6) in a solvent, which is seen in the SDS, and works in tandem with the solid components to achieve energy densities that are close to or exceeding that of traditional Li-ion batteries.”

“It is difficult to determine the specific type of battery since we do not know what conduction mechanisms the battery follows and the quantities of materials used for the electrolyte. As a potential IPC electrolyte with liquid content, it could have a gel-like structure or more broadly consisting of a hybrid material composition that could still be under the solid-state umbrella.”

At the end of the day, this was a fantastic learning experience that I was happy to have. I didn’t realize how muddy the definitions were for solid state batteries. And it was also fascinating to learn how labs break down battery cells to draw far more conclusive evidence than we ever could do at home … even with our arrows, drills, and utility knives.

Do I think Yoshino built a better battery cell? Yes. Am I happy with the Yoshino B330 battery pack I bought for myself? Yes. Do I think Yoshino is playing fast and loose with the term “solid state”? Yes, I do. Do I think Yoshino should rethink how it’s marketing its battery to remove any ambiguity? Yes, absolutely. Am I getting a little freaked out about asking myself so many questions? Yes.

Seriously though, I was a communication and information design major when I was an undergrad. I took courses in semiotics, history of language, and how languages evolve over time. Even if Yoshino is technically (and by “technically” I mean linguistically, not technologically) accurate about its usage of the term “solid state” in its marketing, there’s a massive disconnect with not just the average person off the street, but battery experts, too.

How the mass population uses and understands a term can change and shift. If there’s a difference between the technical definition of a word and public understanding and use of that word, that’s a type of semantic shift or drift. Heck, the term “paradigm shift” in itself is a shift from its original meaning. So as much as Yoshino is sticking to its guns on how it’s using the “solid state” term, I’d say the company is losing that argument with everyone else’s semantic understanding of it.

You can’t expect a large population to shift their thinking to align with your own. You need to go with the flow, so to speak, and lean into that public understanding and come up with a way to remove that ambiguity … whether through education or by changing how you talk about it.

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