How Can the Problem of Local Overheating During the Fast Charging of Solid-State Batteries Be Solved?

Author: Dr. James A. Whitmore | Last Updated: April 23, 2026 | Reading Time: ~10 minutes

Solid-state batteries are often called the “holy grail” for electric vehicles. They promise higher energy density, improved safety because they are non-flammable, and longer cycle life.

But when engineers try to push these batteries toward extreme fast charging—think 10 minutes to 80%—a hidden problem appears. The battery can develop uneven “hot spots.” Some internal areas can become 15 to 20 degrees Celsius hotter than the rest (source: Journal of Power Sources, Vol. 652, 2025 — thermal simulation of multilayer solid-state cells shows local temperature deviations of 15–20°C under fast charging).

This article looks at why this happens and how the industry is working to fix it.

Why Do Solid-State Batteries Get Hot Spots During Fast Charging?

The reason comes down to the materials inside the battery.

In a traditional liquid lithium-ion battery, the electrolyte is a flowing liquid. That liquid helps move heat around, keeping temperatures fairly even.

Solid-state batteries replace that liquid with a solid ceramic or polymer layer. The problem is that solids are not as good at conducting heat. Take a popular ceramic material called LLZTO. Its thermal conductivity is only about 1.59 watts per meter-kelvin (source: Journal of Power Sources, Vol. 652, 2025 — measured thermal conductivity of garnet-type LLZTO electrolyte). That is almost 250 times lower than copper.

When you pump high current into the battery during fast charging, the heat generated in one spot does not spread out quickly. It just builds up.

The interface between the solid electrolyte and the electrodes makes it worse. In a liquid battery, the liquid wets the solid surfaces perfectly. Contact is nearly 100%. In a solid-state battery, it is solid pressing against solid. At a microscopic level, there are tiny gaps and voids everywhere.

These gaps increase electrical resistance. Higher resistance means more heat is generated right at those spots. Worse, the current tends to crowd into the few areas that do have good contact. This crowding makes the local heating even more intense.

How serious is this problem? A set of public test results from February 2026 gives us a clear picture. The VTT Technical Research Centre of Finland tested a solid-state cell made by Donut Lab (source: VTT Technical Research Centre of Finland, Donut Lab Solid-State Battery Test Report, February 2026).

They charged it at an aggressive 11C rate. That translates to 286 amps of current, enough to go from 0 to 80% in just 4.5 minutes.

With only one passive aluminum heatsink, the cell surface temperature hit 90 degrees Celsius. That is the safety limit, and the test had to stop. When they switched to a dual-heatsink setup, the peak temperature dropped to 63 degrees Celsius.

The takeaway is simple: extreme charging speeds demand extreme cooling. The battery chemistry alone cannot handle the heat without help.

Approach One: Tackle the Source—Reduce Internal Resistance

Fast-charging heat comes from a principle called Joule heating. Current passing through resistance creates heat. So, if you want less heat, you need less resistance.

The Chinese battery giant CATL provides a good engineering example. They designed a standard 300mm cell and focused heavily on reducing impedance at the interfaces. The result was an internal resistance of just 0.25 milliohms for their lithium iron phosphate cells (source: CATL, Shenxing Battery launch presentation, August 2023, as reported by Reuters and CnEVPost). They claim this is a global record and about 50 percent lower than the industry average. Lower resistance means significantly less heat is generated to begin with.

Material science also offers a path forward. Some sulfide-based solid electrolytes now have ionic conductivity at room temperature that rivals liquid electrolytes (source: Kato et al., Nature Energy, 2016; ongoing industrial developments at Idemitsu Kosan and others). If these materials can be made chemically stable and mass-produced, they could greatly reduce the energy lost as heat during fast charging.

Approach Two: A Different Angle—Using a Temperature Gradient

In late 2025, a research team from Brown University published an interesting study in the journal Joule. They found a way to make solid electrolytes handle higher currents without failing.

They did this by creating a temperature difference across the electrolyte. They heated one side with a ceramic ring while cooling the other side with a copper plate. The result? The critical current density of the LLZTO electrolyte tripled (source: Yu, Z., Sheldon, B. W., et al., Joule, December 2025. DOI: 10.1016/j.joule.2025.102232).

The mechanism is intuitive. The hot side wants to expand, but the cold side restricts it. This creates a compressive stress right inside the electrolyte layer. That pressure helps suppress the growth of lithium dendrites. Dendrites are tiny, needle-like structures that can pierce the battery and cause a short circuit. They are a major barrier to fast charging.

Zikang Yu from Brown noted that just a 20-degree Celsius temperature gradient can boost the charging performance of the battery by a factor of three (source: Yu et al., 2025; Brown University press release via EurekAlert!, December 2025).

This finding suggests a new strategy for engineers. Maybe the thermal management system does not need to make everything ice cold. Instead, it could actively create a temperature gradient to use mechanical stress as a safety feature while charging faster.

Approach Three: From Interfaces to Systems—Moving the Heat Out

Even with better materials, the heat has to go somewhere. This is where the cooling system design becomes critical.

Donut Lab’s test data shows the threshold clearly. A single heatsink led to a 90-degree Celsius shutdown. Two heatsinks kept things manageable at 63 degrees (source: VTT report, February 2026). For high-power fast charging, the cooling capacity of the pack is non-negotiable.

CATL has also shared details on a specific cooling design they call “shoulder cooling.” This targets the tab area of the cell. The tabs are where current concentrates, so they heat up the most. By placing cooling channels precisely at that spot, CATL claims they can improve cooling efficiency by another 20 percent (source: CATL technical presentation at the 2025 China EV100 Forum, as reported by Pandaily).

Another Chinese automaker, GAC, has demonstrated its “Phoenix Battery.” It uses a three-dimensional thermal management system. The company states it can handle a 6-minute charge to 80 percent even when the ambient temperature is a scorching 50 degrees Celsius (source: GAC Group, Phoenix Battery technology launch event, June 2023, reported by CarNewsChina).

Another promising technology is the vapor chamber. A vapor chamber uses a liquid-to-vapor phase change to spread heat incredibly fast. Placing one against the cell can pull heat away from hot spots and spread it across a larger surface area. From there, a traditional liquid cooling plate can carry the heat out of the pack. This “spread first, then remove” strategy is becoming a standard approach for fast-charging solid-state designs.

Approach Four: Faster Innovation with 3D Printing

Solid-state battery design is still in a phase of rapid evolution. Engineers need to test many different cooling channel shapes and layouts. The traditional way of doing this is slow. You design a part, have a metal mold made, and then test it. If it doesn’t work, you pay for a new mold and wait weeks. That timeline is too slow for a technology moving this fast.

3D printing changes that equation. Engineers can now print complex cooling structures directly. If a design needs a change, they can modify the file and print a new part within days. They can test parts made of high-conductivity resins, metal powders, or composites. This rapid iteration capability allows teams to see physical results of their cooling ideas in just 72 hours instead of months (source: 3D Systems, case study on battery cooling plate prototyping, 2025; industry benchmarks shared by Stratasys at Formnext 2025).

It is a tool that drastically compresses the development cycle.

What Could the Future Hold?

Thermal management for solid-state batteries is still evolving. One trend to watch is intelligent control. Machine learning models can be trained to predict where a hot spot will form before it actually happens. The cooling system could then proactively increase flow to that specific area. This shifts the system from being reactive to being predictive.

Another trend is integration. CATL already uses a pulse self-heating technology for cold weather. It warms the battery from the inside using the current itself, without needing an external heater (source: CATL, “Sodium-ion Battery and Integrated Intelligent Thermal Management” press release, 2022, reported by BloombergNEF). In the future, we might see a single control unit that handles both self-heating in winter and targeted cooling during fast charging.

The ultimate goal is not to make the battery as cold as possible. That wastes energy. The goal is balance. A good thermal management system is one that does exactly what is needed—no more, no less—to keep the battery safe, efficient, and affordable.

FAQ

Q1: If solid-state batteries are “inherently safe,” why do they overheat?

The term “inherently safe” refers to the fact that the solid electrolyte is not flammable and does not leak like liquid. This greatly reduces the risk of fire. However, the battery still generates heat due to electrical resistance, just like any other battery. Thermal management is still essential to keep it operating within safe limits.

Q2: Where are the hot spots located in a solid-state battery?

The most common trouble spots are the tab region and the interface between the electrolyte and the electrodes. The tab region handles the highest concentration of current. The interface has higher resistance due to imperfect solid-to-solid contact. Both are prime locations for heat buildup.

Q3: Do solid-state batteries need a stronger cooling system than liquid batteries?

Not necessarily “stronger,” but definitely “smarter.” Because solid electrolytes do not spread heat well, the cooling system needs to be precise. It is more about targeting specific hot spots rather than just flooding the entire pack with coolant.

Q4: When will consumers be able to buy an EV with a solid-state battery?

Based on public timelines, Toyota is targeting 2027 for its first production vehicle with a solid-state battery (source: Toyota Motor Corporation investor briefing, October 2023). CATL has started production in Hefei and plans to supply cells to Li Auto around 2027 (source: CATL production base announcement via CnEVPost, March 2025). Early models will likely be in the premium segment, with wider adoption taking a few more years.

Q5: Are any solid-state batteries on the market today?

Yes, on a limited scale. Donut Lab’s solid-state battery was used in the Verge TS Pro electric motorcycle starting in early 2026 (source: Verge Motorcycles press release, January 2026). This is one of the earliest commercial applications. In September 2025, QuantumScape also demonstrated a Ducati V21L racing prototype equipped with its QSE-5 solid-state cells at the IAA Mobility show in Munich (source: QuantumScape Corporation press release, September 2025).

References

[1] VTT Technical Research Centre of Finland. Donut Lab Solid-State Battery Test Report, February 2026.
[2] Yu, Z., Sheldon, B. W., et al. “Dendrite suppression in garnet electrolytes via thermally induced compressive stress.” Joule, December 2025. DOI: 10.1016/j.joule.2025.102232.
[3] Journal of Power Sources. “Study on electrochemical-thermal coupling model and thermal characteristics of multilayer structure of solid-state batteries.” Volume 652, October 2025. DOI: 10.1016/j.jpowsour.2025.237582.
[4] QuantumScape Corporation. QSE-5 Solid-State Battery Demonstration at IAA Mobility 2025, September 2025.
[5] Brown University. “Putting the squeeze on dendrites: New strategy addresses persistent problem in next-generation solid-state batteries.” EurekAlert!, December 2025.
[6] CATL. Shenxing Battery launch presentation, August 2023 (reported by Reuters and CnEVPost).
[7] GAC Group. Phoenix Battery technology launch event, June 2023 (reported by CarNewsChina).
[8] CATL. Technical presentation at the 2025 China EV100 Forum (reported by Pandaily).
[9] CATL. Integrated intelligent thermal management press release, 2022 (reported by BloombergNEF).
[10] Verge Motorcycles. Press release on Donut Lab battery integration into Verge TS Pro, January 2026.
[11] Toyota Motor Corporation. Solid-state battery investment update, investor briefing, October 2023.
[12] CATL. Hefei production base announcement, March 2025 (reported by CnEVPost).
[13] 3D Systems / Stratasys. Battery cooling plate prototyping benchmarks, shared at Formnext 2025.

About the Author:

Dr. James A. Whitmore,Senior analyst specializing in EV powertrain systems. He previously spent nine years with a Detroit-based automotive engineering firm, where he led thermal management evaluations for next-generation battery technologies, including solid-state designs for major European and North American automakers.

Disclaimer

The information in this article is based on publicly available data as of April 23, 2026. It is provided for educational and industry discussion purposes only. The data, test results, and technical specifications cited come from publicly released sources, and the author does not guarantee their absolute accuracy. Solid-state battery technology is evolving rapidly. Timelines for specific products may shift due to development progress, supply chain issues, or market conditions. Readers should refer to official manufacturer announcements for the latest information. This article does not represent the official position of any company or institution.

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