Researchers are making critical advances in understanding and preventing one of the most significant dangers in modern energy storage: internal short circuits in lithium-ion batteries. These events, often caused by the growth of microscopic, needle-like metal structures known as dendrites, can degrade battery performance and, in the worst cases, lead to overheating and fire. While the industry has long pursued solid-state batteries as a safer alternative to conventional liquid-electrolyte designs, recent findings reveal new complexities in dendrite formation, while separate research demonstrates novel ways to suppress their growth entirely.
The core issue lies in the behavior of lithium metal during a battery’s charging cycle. Ideally, lithium ions would deposit onto the anode in a perfectly smooth, uniform layer. Under real-world conditions, however, especially during the fast charging consumers demand, the deposition can be uneven. This uneven plating allows tiny metallic filaments to sprout and grow across the electrolyte, the barrier that separates the anode and cathode. If these dendrites breach the separator and connect the two electrodes, they create a short circuit that can trigger a catastrophic failure known as thermal runaway.
The Persistent Problem of Dendrite Growth
Dendrites have been a primary obstacle slowing the development of next-generation lithium-metal batteries, which are theoretically capable of storing significantly more energy than current lithium-ion technologies. These microscopic, tree-like structures emerge on an anode’s surface due to factors like high current densities and imperfections on the electrode. As the battery cycles through charging and discharging, these filaments can lengthen and expand, much like a plant root growing through soil. The internal separator, often a thin polymer film, is the only physical barrier preventing them from reaching the cathode.
The consequences of a dendrite-induced short circuit are severe. At a minimum, it degrades the battery’s capacity and shortens its useful lifespan. In a more dangerous scenario, the uncontrolled flow of current generates intense heat. This can destabilize the flammable liquid electrolyte used in conventional batteries, creating a fire or explosion risk that has grounded flights and prompted massive product recalls. This fundamental safety challenge is a key driver behind the global research effort to develop batteries with solid, non-flammable electrolytes.
New Findings in Solid-State Systems
For years, researchers believed that solid electrolytes, particularly those made from polymer-based materials, could physically block dendrite growth due to their mechanical strength. However, a recent study from a team at the Technical University of Munich (TUM) has revealed that this is not always the case. Their work, published in Nature Communications, shows for the first time that dendrites can form directly inside the polymer electrolyte itself—the very material intended to prevent them.
An Unexpected Internal Threat
The TUM researchers discovered that lithium structures can grow within the bulk of the polymer, not just from the surface of the electrode. This finding is crucial for the future of solid-state battery design, as it complicates the assumption that a solid separator inherently guarantees safety. According to Fabian Apfelbeck, the study’s first author, this means that the electrolyte material itself can contribute to the very problem it was meant to solve. This work highlights that simply making the electrolyte solid is not enough; its chemical and mechanical properties must be carefully engineered to resist internal filament growth.
A Semisolid Electrode Solution
While some researchers uncover new challenges, others are demonstrating innovative ways to prevent dendrites from ever starting. A team led by researchers at MIT developed a novel approach using a semisolid electrode that creates a self-healing surface at the interface with the electrolyte. This method avoids the microscopic cracks and fissures present on brittle, solid metal anodes, which often act as the initial seeding points for dendrite formation.
Designing a Self-Healing Surface
The team created an electrode with a consistency more like a dental amalgam—a material that is mostly solid metal but can still flow and change shape. By using a sodium-potassium alloy that remains in a mixed solid-liquid phase at normal operating temperatures, the electrode surface can dynamically smooth itself out, eliminating the surface imperfections where dendrites take root. In a separate configuration, the team achieved a similar effect by placing a very thin layer of a liquid sodium-potassium alloy between a solid lithium electrode and the solid electrolyte.
Breakthroughs in Charging Speed
This semisolid approach yielded remarkable results for charging speed, a key metric for practical applications like electric vehicles. The researchers demonstrated that their system could operate at current densities 20 times greater than those using conventional solid lithium electrodes without any dendrite formation. Achieving high-current operation without dendrite growth is a critical step toward developing solid-state batteries that can be charged rapidly and safely. Professor Yet-Ming Chiang of MIT noted that this performance could unleash the potential of high-energy battery designs.
Implications for Battery Safety and Design
These parallel discoveries underscore the complexity of controlling lithium dendrite growth. The TUM findings serve as a critical warning for the solid-state battery industry, indicating that material selection for solid electrolytes must account for the possibility of internal dendrite formation. It is no longer sufficient to assume a solid barrier is an impenetrable one. At the same time, the MIT research provides a promising alternative pathway that could be adapted for many different types of solid-state battery architectures being developed worldwide. By focusing on the electrode interface, the semisolid design could complement and enhance the safety of various electrolyte materials.
The Path to Commercialization
The road to widespread adoption of lithium-metal and solid-state batteries remains challenging, but these research efforts mark significant progress. For the TUM team, the next steps involve further investigation into why dendrites form within polymers and how different material properties might stop this process. For the MIT researchers, the focus will be on demonstrating their semisolid system’s applicability across a range of battery designs and scaling up the technology. Ultimately, solving the dendrite problem is essential for creating batteries that are not only more powerful and longer-lasting but also fundamentally safer for use in everything from consumer electronics to electric vehicles.
