Batteries Charge To The Edge

Long-awaited advances in battery chemistry and materials science are beginning to roll out, opening the door for higher capacity, faster charging, and much lower likelihood of thermal runaway.

This is a high-stakes race, fueled by an insatiable demand for power everywhere from handheld devices to data centers. When Finland’s Donut Lab claimed earlier this year that it had developed a solid-state battery capable of storing 400 watt-hours per kilogram — roughly double the capacity of a lithium-ion battery, and with a charge time of less than 5 minutes — the company was besieged by a flood of doubters. China’s BYD met with similar disbelief when it said its new lithium-ion batteries can charge to 70% in 5 minutes and power a vehicle for 1,000 kilometers, with solid-state versions poised for commercialization.

Time will tell how accurate these particular claims are, but what’s clear is that the frequency of breakthroughs in battery technology is growing and the public appetite for them is huge. Increases in battery storage capacity have lagged well behind efficiency gains in silicon and software. Historically, capacity improvements have crept along at about 4% to 8% [1] a year, while demand for battery power has exploded. According to the Rocky Mountain Institute, battery sales are increasing roughly 40% per year. [2] This gap limits how far a vehicle can travel on a single charge, how many batteries are needed to back up a data center, or how much work can be done by robots before they need to return to their dock.

It’s not unusual to see production carmakers advertising 400 miles per charge, versus 200 to 300 miles several years ago. So far, this is largely a function of different electrolytes, which at the leading edge are typically highly volatile liquids. More storage capacity, and faster discharge for higher workloads, requires precise load balancing during use. Likewise, batteries must be kept cool while charging to prevent overheating. When things go wrong, such as a puncture of a separator between the anode and the cathode, a battery cell can heat to the point of combustion, setting off a chain reaction that can burn at up to 1,000° C, consuming a vehicle, a robot, a laptop computer, or anything combustible nearby.

This is why the whole battery industry is racing to develop a solid electrolyte, or at least one with sufficient viscosity to avoid thermal runaway.

“The majority of the market nowadays still relies on liquid electrolyte-based battery cells — what we call ternary systems — that use different chemistries on top of the lithium oxide material,” said Honsuk Lee, product engineer at Cadence. “There is lithium-ion phosphate, which includes high nickel content to improve the capacity of the battery. And there are a number of different chemistries that use liquid electrolytes. The downside to these is safety. If we use a liquid electrolyte, there are aggressive or exothermic reactions. It’s very difficult to design a product with that chemistry while maintaining safety, and that’s why people are looking into different and safer forms of batteries, including a solid electrolyte. A couple of OEMs are trying to fully utilize a solid electrolyte, but it’s not mainstream yet.”

The speed of change
So what’s taking so long? At least part of this is the normal testing process. In any safety-critical market, whether that is a car or an e-bike, a massive amount of research, simulation, and testing is required under widely varying conditions. This is compounded by the fact that batteries are being used today in ways that are very different than in the past, when they typically were considered disposable. They now need to last for years, often under harsh ambient conditions, and they need to keep a charge for extended periods of time. In addition, they need to charge quickly, because no one wants to sit around in a parking lot for 30 minutes.

“Increasing the speed of charging requires innovation and optimization on multiple levels,” said Puneet Sinha, senior director and global head of battery technology at Siemens EDA. “It starts with the cell design. Do the chemistries that companies are working with accept a fast charge? How thin does the electrode need to be? What will the cell design need to be to accept that charge. There’s a lot of design optimization and validation that needs to happen to accept a fast charge. We’re seeing a lot of digital twin solutions where you look at different materials, chemistry, design, and how fast they age. If you charge it many times, how does that affect aging? And when you dump that much energy, it creates a lot of heat. So how do you optimize the overall thermal management of the battery while it is being charged? These are variables that companies need to look at, going from the microstructure to cell design to overall battery pack thermal management.”

A lithium-ion battery generates electricity by moving ions from the cathode to the anode through an electrolyte during use, and in reverse during charging. But during rapid charging, the accelerated movement of electrons generates heat. This is why carmakers like Hyundai and Lucid are shifting from a 400V architecture to 800V, trading off charging current with voltage in order to reduce that heat. The downside is this requires a more complex battery management system, which increases the already high cost of an EV.

“All of the batteries have liquid electrolytes, so if you try to charge things very fast, especially with graphite or carbon-based anodes, there are challenges with lithium plating,” Sinha said. “If you try to charge fast, it can lead to some bad things like internal shorts. One way to avoid that is to move away from carbon-based anodes, which is why many companies are looking at silicon-based anodes, or changing the electrolyte from a liquid to more of a solid-state electrolyte. One of the key promises of battery technology is that it can be charged very fast because the overall possibility of lithium plating, which leads to dendrite formation, is theoretically minimized. However, it has challenges in terms of viscosity with more polymer-based electrolytes, which have implications for the overall performance and how you manufacture it. Many companies are investing in solid-state batteries, and one of the promises is that you can charge it fast without worrying about the safety implications.”

The Goldilocks effect
With batteries, results may vary by day and by location. They are highly susceptible to ambient temperatures. Use them on a hot day or a cold day and they behave differently. The ideal is somewhere in the middle, not too hot or cold.

When batteries heat up, they need to be cooled. So while an EV doesn’t have a radiator, it still has a cooling system, often in the floor of the vehicle where it’s not visible.

“You still have to run coolant through the battery. You need to continuously monitor the health of the battery during charge and discharge, even when it’s parked in a parking lot,” said Jim Pawloski, director of applications engineering at Infineon Technologies. “You want to make sure the cell voltage doesn’t cross a certain threshold and temperature. You want to be able to monitor the temperature because if the battery gets too hot, the separator — a very thin piece of material that separates the anode and the cathode — can melt. One of the more recent chemistries to limit this is LFP (lithium iron and phosphorus), which is very common for home use in backup storage batteries. But you don’t have the energy density you get in cars, where energy density is very important. There, it’s all about having the most energy in a given space and a given weight.”

Unlike in the past, it’s extremely rare for carmakers to issue warnings these days not to charge a car in a garage. Other devices, such as e-bike chargers, are far less sophisticated when it comes to monitoring heat while charging. In 2024, there were 4,203 fires due to batteries, including 193 explosions, according to UL Solutions. [3]

Battery management systems are complex, and they add significantly to the cost of these devices. “The thermal hydraulics cooling loop is often the most challenging,” said Bryan Kelly, principal engineer at Synopsys. “This area of mechatronics typically falls outside the hands-on expertise of many hardware/software battery pack design engineers. Although CFD software tools can support preliminary ‘what if’ thermal analyses, ultimately a virtual prototype of the complete cooling system — cooling plate, piping, hoses, manifolds, and related components — is essential. Such a model enables verification across different coolant types or mixture ratios, environmental conditions, and operating scenarios, and allows results to be validated against measurement data. In addition, this end-to-end thermal story of the battery pack simulation model makes it possible to study required heating at extremely low temperatures, evaluate hardware/software control behavior across wide temperature ranges, and simulate fault conditions, such as reduced coolant flow during high load current demand, that are difficult or impractical to reproduce on a physical test bench.”

This is important, because while electrical components can operate at extreme temperatures, batteries cannot. “Electrical components can go down to -40° C, and the internal temperature of a semiconductor can go as high as 150° C, and we still know how it’s going to operate,” said Infineon’s Pawloski. “It’s not going to degrade the performance too much over its lifetime. But a lithium-ion battery has to operate in a much narrower temperature range. When lithium-ion battery technology first came out, you got rid of a cell phone because the battery died, not because the phone died. That’s because they were pushing batteries to their limits, taking them to full charge and to full discharge. They really didn’t care about the temperature they were operating in. And why would they? It was designed for obsolescence. But that wasn’t going to work with automotive, because you want a car that is going to last 10 years or 100,000 miles, at a minimum. And the way to achieve that with lithium-ion batteries was to minimize the operating parameters.”

So for a nickel-manganese-cobalt (NMC) battery — a type of lithium-ion battery — the best solution is to charge it to 80% of capacity, and recharge it when it reaches 30% capacity. And it will generally operate within an optimal temperature range, which could involve cooling or heating the battery.

Other advances
Another potential breakthrough technology here involves heating batteries when they are too cold to operate efficiently, and automatically clamping down on heat when it approaches the danger zone.

“For electric vehicles, you need to be able to tolerate a very wide range of temperatures in a harsh environment that can be very cold and very hot,” said Chao-Yang Wang, professor in Penn State’s Materials Science and Engineering Department and co-founder and chairman of FastLion Energy. “In the future, we want to have management-free lithium-ion battery technology, where the cell can adjust itself to tolerate cold like -30° C and very hot, like 60° C in the desert. The future is a concept called all-climate battery technology. The cell will adjust the temperature by itself and be able to tolerate a wide range of harsh environments without external management, because that costs money and reduces energy density of the pack.”

Enabling that requires a high-viscosity electrolyte with a high boiling point. “We also can use bigger particles — single crystals — with a lower surface area that will enhance the thermal stability. But those materials will deteriorate your low-temperature performance, so at low temperatures today we may have difficulty at -30° C or -20° C, but if you make improvements with high temperature tolerance, you may have difficulty at 0° C. That can easily be solved by internal heating, or self-heating. Lithium-ion cells still contain energy. It’s just that you have a difficult time extracting it or producing power. But if you self-heat the cell a little bit, using its own energy, you can quickly enhance the ability to produce power. It only takes seconds to self-heat from -30° C to 0° C or the freedom point.”

Wang foresees multiple different electrolytes coming to market, from solid state to gelatinous materials to what’s called condensed matter. “But even with solid state batteries, you need self-heating at the low-temperature end because, by itself, it’s going to have even more trouble starting than the current liquid electrolyte batteries,” he said. “We definitely have to go to a more heat-tolerant level. We’re very close. We have been working on this since about 2016. It will probably take a couple more years to commercialize. In the lab, we’re already demonstrating it’s successful. The key challenge is how to commercialize it.”

Alongside of this, there are more mechanical solutions being developed to reduce the chances of thermal runaway. These include solid state transformers to convert AC to DC more safely, as well as solid-state circuit breakers, which are much faster than traditional circuit interrupts.

“Typically you need to connect high-energy consumers, like Nvidia data centers, to the medium-voltage grid,” said Peter Wawer, division president for green industrial power at Infineon. “Medium voltage grid, in terms of electricity transmission lines, means 35 kV. Today, you need a transformer to transform high-voltage AC to low-voltage AC, and then to the AC-DC conversion. As we speak, a lot of startups, and also bigger companies, have started to work with us on solid-state transformers.”

Cutting the circuits more quickly using semiconductor-based circuit breakers is another improvement. Wawer said this can increase the speed of protection by orders of magnitude. “Everybody has in his private environment a circuit breaker, which is simply a fuse. Typically it’s down in the basement, and if something happens, you go there, switch it on. It’s very cheap, very reliable. But the requirements are increasing, and the fascinating thing about this topic is that so far it has been in a market totally owned by electronic switchgear makers, which has nothing to do with semiconductors. And due to the requirements now popping up with respect to speed of reaction for protecting the switch gear, very slowly, and hopefully a bit faster, it’s turning out to be market for semiconductors. To give you an idea about the whole market, it’s about a €10 billion market.”

Conclusion
Batteries are everywhere. They power smartphones, notebook computers, and smart watches for a day or more, and they can propel electric vehicles as far as 500 miles on a single charge. The challenges now include making them safer, increasing their capacity and useful lifespan, and enabling them to operate across a wide temperature range. But they also need to be cheaper.

Each of these requirements is complex, and collectively the challenges are daunting. Still, the entire electronic ecosystem is working to solve these issues, which will be needed as more intelligence moves from the cloud to the edge. Batteries are key enablers for an untethered and less structured future filled with all sorts of smart devices, and the market for this technology is expected to boom over the next few years as some of the thorniest problems are solved and the necessary infrastructure is built.

References

1. Average range cited by numerous industry sources and discussion boards.
2. Rocky Mountain Institute, “The Rise Of Batteries In Six Charts And Not Too Many Numbers.”
3. UL Solutions, Lithium-ion Battery Incident Reporting.

Brian McHugh contributed to this report.