The adoption of electric vehicles (EVs) remains highly fragmented due to two key constraints: charging and range. Even though there are already a good number of EVs with a compelling range and fast-enough charging, customers only seem to start taking them seriously when their range and charging speeds match those of an equivalent internal combustion engine (ICE) car.
All-solid-state batteries (ASSBs) are supposedly the cure-all for the concerns of owners coming from ICE cars. This is why automakers are in a race to be the first to bring to market an EV with ASSBs, as they see that this is going to be the turning point for widespread EV adoption—especially for single-car households. Thankfully, there is one battery company that says they are on track to mass-produce ASSBs as soon as 2029, a year ahead of their projected schedule.
To give you the most up-to-date and accurate information possible, the data used to compile this article was sourced from various manufacturers and other authoritative sources, including SK On, IT Home, EE Power and MG.
South Korea-Based SK On’s Solid Agenda
The battery company that’s on track to bring SSBs into mass production as soon as 2029 is South Korea-based SK On. The pilot plant with an area of 50,000 square feet was completed on September 15 at the SK On Institute of Future Technology in Daejeon, 93 miles from Seoul. Recent developments in the company have enabled SK On to discover a production breakthrough that brings it one step closer to mass-producing ASSBs.
A Noteworthy Production Breakthrough
SK On’s breakthrough comes from their Warm Isostatic Press-free (WIP) technology for ASSB manufacturing—a first in South Korea. According to SK On, WIP technology is a next-generation pressing process that applies uniform pressure to electrodes at elevated temperatures (77–212 °F) to improve density and performance. Though this solution minimizes battery heat generation and extends lifespan, it requires a cell-sealing process and is difficult to implement in a continuous automated production line, which results in lower productivity.
To retain the advantages of the WIP process while addressing its shortcomings for better productivity, SK On leveraged its unique cell design and normal pressing methods. Their improvements have reduced internal resistance within the electrodes. Finally, SK On improved the bonding between electrodes and solid electrolytes as well as optimized pressing conditions, this time for reduced interfacial resistance. This enables smoother ion transport, more stable charging and discharging, and a longer cycle life.
An All-Solid-State Battery With Twice The Energy Density
SK On aims to initially commercialize ASSBs with an energy density of 800 Wh/L, which is twice the 400–500 Wh/L that lithium-ion nickel-manganese-cobalt (NMC) batteries offer. As a long-term goal, however, SK On aims to achieve an energy density of 1,000 Wh/L. A higher energy density means having the ability to store more energy at any given size or volume. This means that ASSBs can be more compact than an NMC battery whilst offering the same or even more range, thus addressing the packaging and weight constraints of today’s EVs that use large batteries to achieve a long range.
But apart from SK On’s internal developments, the company teamed up with Solid Power last year to speed up the development of ASSBs. For reference, Solid Power already has investments and prospects from various automakers like BMW. SK On has also been pushing other next-generation battery technologies through South Korea’s Hanyang University. In May 2025, this partnership resulted in a threefold increase in the life cycle of sulfide-based ASSBs by applying a protective-film technology to lithium-metal anodes. SK On says that patents for this technology have already been applied for in South Korea and internationally.
ASSB’s Opportunities And Hurdles
For the most part, ASSBs have remained science fiction and promised principles, but ever since hearing about the technology from various automakers for the past few years, what have we learned so far about this battery technology?
High-Density, Long-Range Opportunities
The reason why ASSBs are the so-called “holy grail” of EV technology is that this battery will (hopefully) solve range anxiety and speed up charging times. With SK On’s goal of creating ASSBs with an 800 Wh/L of energy density, there is one company that is relatively close to that level—the Chinese battery company Farasis Energy. Mercedes-Benz bought a stake in Farasis Energy to provide batteries for its EVs. At the moment, its second-generation sulfide-based ASSBs have an energy density of 500 Wh/kg (not Wh/L), one of the outright highest for any battery today. For reference, in that same unit of measurement, an NMC battery is usually around 150–220 Wh/kg.
Though we still have not witnessed any numerical data backing up these claims, ASSBs also promise to be the holy grail of fast charging technology, safety, and durability. Safety, in particular, is one of its biggest selling points, since the lack of a flammable liquid from a liquid electrolyte makes ASSBs extremely safe—at least in theory. Durability is also a promised highlight, since the lack of liquid components means a more robust battery structure.
ASSB Development’s Pesky Dendrite Hurdles
Apart from mass production challenges, ASSBs continue to face a few hurdles, mostly centered around dendrite formation. According to EE Power, “dendrite formation happens during charging when the lithium metal electrochemically grows irregularly on negative electrodes”, which leads to the build-up of dendrites. The dendrites then react with the electrolyte and decompose it, slowly reducing the battery’s life span and capacity to hold energy. To combat this, automakers including Honda have experimented with adding a layer of polymer-based fiber between the electrodes at either end of the battery and the electrolyte in the middle. This promises to completely prevent dendrite formation (or at least substantially reduce it).
ASSBs Take To The Road For Real-World Testing
At this point, you’re probably curious if automakers, even in the prototype stages, have already put an EV with ASSBs on the road. Well, thankfully, this article couldn’t come at a more opportune time, because we even know a prototype that traveled far enough to even outperform some ICE cars.
What To Do With A Whopping 750-Mile Range
Here at TopSpeed, we’ve written about numerous ICE and hybrid vehicles that offer bladder-bursting ranges somewhere between 600 and 700 miles. On September 9, however, a Mercedes-Benz EQS with prototype ASSBs from Factorial that they revealed earlier this year completed a record-breaking EV drive, completing a whopping 1,205-kilometer (750-mile) journey on a single charge. The journey took the development team from Stuttgart in Germany to Malmö in Sweden, thus making it the longest drive ever conducted by an EV. The 750-mile drive they achieved exceeded even the company’s expectations. For one, Mercedes and Factorial were only hoping to achieve 620 miles. Yet, even after traveling for 750 miles, the EQS still had 85 miles of range left.
A Humble Hatch With A Semi-Solid-State Battery
But before we go into ASSBs, there is a battery technology that’s kind of a half step towards this technology. Say hello to semi-solid-state batteries, and Chinese EV automakers are at the forefront of this race. The first mass-produced EV with a semi-solid-state battery is the new MG 4, whose rounded design replaces the angular three-year-old first-generation model. Yeah, that’s how quickly the Chinese do model changes.
Anyway, with a semi-solid-state design, QingTao Energy is the provider of the battery, and they say that only five percent of the battery’s electrolyte is liquid. This results in an energy density of 180 Wh/kg, which merely matches an advanced NMC battery’s energy density. One of its claims as well is its 13.8 percent better range retention at 19 °F versus the lithium-iron-phosphate (LFP) batteries that Chinese automakers love. At its most efficient, the MG 4 has a CLTC-rated range of 334 miles out of a 70-kWh battery.