All you need to know about Solid State Batteries

Have you ever experienced the typical frustration that manifests when you are charging your phone before an important trip and watch your battery slowly crawl from 10% to 20%? And then, once on the road, have you ever waited half an hour for your electric car to recharge? Well, I have. Many times.

And every single time, each second reminded me of the limits of today's lithium-ion batteries. They've powered our devices for decades, but their design, liquid electrolytes sloshing between electrodes, has begun to show its age. Now, a team of researchers at the University of California, Riverside (UCR) has taken a deep dive into what may be the successor of this technology: solid-state lithium batteries.

In a 2025 review published in Nano Energy, Ruoxu Shang, Talyah Nelson, Thanh Vy Nguyen, Charlotte Nelson, Harsha Antony, Brian Abaoag, Mihrimah Ozkan, and Cengiz S. Ozkan explore how replacing liquids with solids could change everything, from how fast we charge our EVs to how safely we store renewable energy.

Lithium-ion batteries (LIBs) have served us well since the 1990s. They're the unsung heroes inside smartphones, laptops, and electric cars. But as devices grow more powerful and the world pushes toward electrification, traditional batteries are nearing their limits.

For one, liquid electrolytes, the medium that lets lithium ions move, are flammable. That means under stress, these batteries can overheat, swell, or even catch fire. They also degrade over time, losing their ability to hold charge after a few thousand cycles. And though engineers have squeezed more and more energy into the same volume, there's a ceiling: the chemistry itself can only do so much.

That's where solid-state batteries (SSBs) come in. But what's different about them? As the name suggests, they replace that liquid electrolyte with a solid material, something ceramic or glass-like. By doing so, suddenly, they remove the flammability risk and open the door to new designs that could hold much more energy in the same space.

In fact, in a solid-state battery, both the electrodes and the electrolyte are solid. This creates a tighter, more stable system that's not only safer but potentially more powerful. Solid-state batteries promise greater energy density, faster charging, and much longer lifetimes.

How much better could they be? Current liquid batteries max out around 260 watt-hours per kilogram, but solid-state prototypes are already hitting 400 Wh/kg, that's about a 50% boost: imagine an electric vehicle that drives 50% farther on the same charge.

Even better, they could meet the U.S. Advanced Battery Consortium's dream target: 80% charge in just 15 minutes. That would put electric cars on par with refueling a gas tank.

Unfortunately, making that dream real isn't easy. SSBs still face mechanical, chemical, and manufacturing hurdles.

For starters, the solid electrolytes that carry lithium ions don't conduct as easily as liquids. Ions can get stuck at grain boundaries, tiny imperfections in the crystal structure, or at interfaces between materials. And even though early studies suggested solid electrolytes would stop dangerous dendrites (spiky lithium deposits that can short-circuit a cell), researchers now know those can still form under the right conditions.

To tackle this, scientists are experimenting with new materials like lithium phosphorus sulfides and garnet oxides, tweaking their chemistry and structure to make lithium ions glide more freely. Others are improving manufacturing techniques, using methods like hot pressing and sintering to remove pores and strengthen the material.

The paper also explores the engineering details of making these solid-state systems work. In place of the spongy, porous electrodes in current batteries, SSBs use dense layers stacked tightly together. This increases efficiency and removes the need for the heavy cooling systems required by flammable liquid batteries.

Several companies, Toyota, Samsung, Solid Power, and QuantumScape, are already racing to commercialize this technology. Each has its own approach, but they share the same goal: create a compact, high-energy battery that can be mass-produced safely and affordably.

Cost is still a sticking point. While SSBs might eventually be cheaper (since they skip the liquid handling and complex formation steps of traditional batteries), the materials and manufacturing methods are still evolving. The reactivity to humidity and oxygen makes large-scale production challenging. These batteries need special, controlled environments and often high pressures or temperatures to assemble correctly.

Finally, the review also explores the emerging world of in-operando diagnostics, that is, real-time techniques to watch batteries while they charge, discharge, and degrade. Tools like X-ray diffraction, electron microscopy, and thermal wave sensing let scientists peek inside a working battery to see how ions move, interfaces change, and materials expand or crack. This live feedback is crucial to identifying where energy is lost and why failures occur. By combining these imaging and electrical techniques, researchers can build "maps" of how heat, stress, and chemistry evolve inside a cell. It's a bit like giving the battery an MRI scan while it's running.

Another major focus of the paper is thermal stability. The authors point out that solid-state batteries are far less likely to experience thermal runaway, the dreaded feedback loop that leads to fires or explosions in lithium-ion packs.

Because the solid electrolytes are non-flammable, even extreme tests (like nail penetration or heat exposure up to 120°C) show they don't ignite. Companies like Hitachi Zosen Corporation have demonstrated solid-state designs that remain stable from –40°C to 120°C, ideal for everything from space missions to medical devices. However, “solid” doesn't mean “invincible.” High heat can still cause cracking, phase changes, or the release of toxic gases in some sulfide-based materials. Researchers are developing doped and composite versions, mixing different elements or nanoparticles, to raise decomposition temperatures and improve durability.

Clearly, one of the biggest selling points of SSBs is the potential for ultrafast charging. But how do you move lithium ions quickly through a solid?

The answer lies in ionic conductivity, how easily ions flow through a material. A good electrolyte acts like a superhighway for ions. If it's too resistive, the battery charges slowly and loses efficiency. The review describes how scientists use computational modeling and impedance spectroscopy to measure and optimize this movement.

Hot-pressing techniques, microstructural tuning, and even clever composite materials, like polymers laced with ceramic fillers, are all helping to push conductivity toward the magic threshold of 10⁻³ to 10⁻² siemens per centimeter, roughly matching liquid electrolytes.

Once researchers hit that target reliably, solid-state batteries could finally charge as fast as, or faster than, today's lithium-ion cells.

Even with all the progress, mass-market SSBs are still a few years away, but the direction is clear: the same way lithium-ion cells transformed how we live and move, solid-state batteries could transform how we store and share energy. So, hopefully, our car will charge as quickly as it fills with gas, our phones will last for days, and battery fires will be a thing of the past.

If you want to learn more, read the original article titled "A comprehensive review of solid-state lithium batteries: Fast Charging characteristics and in-operando diagnostics" on Nano Energy at http://dx.doi.org/10.1016/j.nanoen.2025.111232.