Stretchable Polymer Electrolyte Enables Safer and Flexible Solid-State Batteries

Researchers at Empa have developed a stretchable polymer electrolyte that could significantly improve the performance and safety of solid-state batteries. The material, based on modified silicone, introduces flexibility into battery design while addressing key technical challenges associated with solid-state energy storage. The innovation may open new possibilities for flexible electronics, wearable devices and advanced battery systems in sectors such as product and automotive design.

Rethinking the Electrolyte

In conventional lithium-ion batteries, the electrolyte — the component that allows ions to move between electrodes during charging and discharging — is typically a flammable liquid. Solid-state batteries replace this liquid with a solid electrolyte, making them inherently safer and potentially capable of achieving much higher energy densities.

Higher energy density means more energy can be stored within a smaller volume, a crucial factor for electric vehicles, portable electronics and compact design-driven products.

However, most existing solid electrolytes are rigid materials. This rigidity introduces mechanical problems inside the battery during charging cycles, limiting performance and long-term durability.

Elastic Silicone Polymer Conducts Ions

Empa researchers from the Laboratory for Functional Polymers have addressed this challenge by developing a flexible electrolyte based on polysiloxane, better known as silicone. Silicone is naturally elastic, but in its standard form it cannot conduct ions — a fundamental requirement for battery operation.

To overcome this limitation, the research team chemically modified the polymer by introducing functional groups along its molecular backbone. These additions enable the silicone material to dissolve and transport ions while maintaining its elastic properties.

The result is a soft, stretchable electrolyte that combines ionic conductivity with mechanical flexibility.

Addressing Dendrites and Structural Voids

One of the major obstacles in next-generation lithium-metal batteries is the formation of dendrites — tree-like lithium structures that grow during repeated charging cycles and can eventually cause short circuits.

Solid electrolytes help suppress dendrite growth, but another problem arises when lithium ions leave the anode: microscopic voids form at the interface between the electrode and electrolyte. These voids can disrupt contact between the components and reduce battery capacity.

The elasticity of the new silicone-based electrolyte helps solve both issues. The solid material acts as a physical barrier to dendrite formation while its flexibility allows it to fill emerging voids and accommodate volume changes inside the battery.

Enabling Flexible Batteries

Beyond improving battery stability, the polymer electrolyte may also enable entirely new battery formats. Because the material can be processed into thin films only a few micrometres thick, it could support the development of flexible batteries.

Such systems could be particularly valuable for wearable electronics and medical devices. Current batteries used in implants such as pacemakers are typically rigid and uncomfortable for patients. The new material could serve both as an electrolyte and as a binder within the battery’s cathode, enabling softer and more adaptable energy storage systems.

The material is also scalable and potentially less expensive to manufacture than many existing solid polymer electrolytes, which could support future industrial adoption.

Researchers are now working to further improve the ionic conductivity of the silicone electrolyte while seeking industrial partners to commercialise the technology.

Source & photo: Empa