Overview
Recent reports indicate that the first-generation solid-state battery installed in the Zhiji L6 uses a "high ionic conductivity, high-temperature-resistant solid electrolyte" and a "dry-process, integrated solid electrolyte layer" manufacturing approach. To enhance lithium-ion conductivity in the solid electrolyte, Qingtao Energy added 10% wetting agent to the electrolyte. The newly developed solid electrolyte is only 10 μm thick and uses an inorganic coating to reduce the risk of cell short circuits.
Introduction to Solid-State Batteries
Solid-state batteries replace liquid electrolytes and separators with solid electrolytes. Compared with conventional liquid-based batteries, solid-state batteries offer higher energy density, improved safety, longer cycle life, and faster charging. These attributes make solid-state batteries a promising option for electric vehicles and other applications.
Main Solid Electrolyte Types
Sulfide Electrolytes
Sulfide solid electrolytes are mechanically soft and have high ionic conductivity, which supports high energy density and good electrochemical performance. However, they have drawbacks that limit their application. Sulfide electrolytes tend to be unstable in air and can react with oxygen and moisture, leading to electrolyte decomposition and reduced battery performance. They are also moisture-sensitive and can generate harmful gases. Despite these issues, sulfide electrolytes remain a major research focus.
Oxide Electrolytes
Oxide solid electrolytes are often introduced via separator coatings or electrode coatings. They can enhance battery stability and safety. Their main limitations are lower ionic conductivity, higher interfacial impedance, and compatibility challenges with electrode materials. These shortcomings constrain their wider application in solid-state batteries, although many organizations are pursuing related research and development.
Polymer Electrolytes
Polymer-based solid electrolytes form network structures that offer good mechanical stability. They can improve certain battery properties and enhance operational safety. Gel-state electrolytes, a form of polymer electrolyte, are already used in devices such as mobile phones and drones.
Impact on Polymer Materials
In conventional liquid lithium-ion batteries, components such as separators are typically made from polymer materials. As solid-state battery technology develops, the demand for some polymer materials may decline. For example, because a solid electrolyte can itself separate the electrodes, traditional polymer separators may no longer be required, which could reduce demand for separator materials and disrupt the separator industry.
Conversely, polymer materials will continue to play roles in some solid-state battery designs. Certain solid electrolytes are polymer-based; common polymers such as polyethylene oxide (PEO) and polyvinylidene fluoride (PVDF) have been used in solid-state battery research. Through doping and specialized processing, these polymers can achieve useful levels of conductivity, stability, and processability to meet some requirements of solid-state cells. Semi-solid or gel-state electrolytes, developed by major battery manufacturers, use polymer materials to form gel electrolytes that bring benefits such as reduced leakage risk, improved stability over long durations, and extended cycle life. Semi-solid designs are generally considered a transitional stage toward full solid-state production.
Beyond electrolytes, polymer materials are widely used across multiple battery manufacturing stages. Polymers provide encapsulation and protection against external damage, serve as adhesives to bond battery components and enhance structural stability, and offer insulation to mitigate internal short circuits. Their flexibility and ductility help batteries withstand different operating conditions. In summary, polymers remain essential for encapsulation, bonding, insulation, and other structural functions in battery assemblies.
Conclusion
As solid-state battery technology evolves, polymer material performance standards will also rise. Researchers and materials developers need to continue innovating to create polymers better suited to solid-state battery requirements. The shift to solid-state batteries presents challenges to the polymer materials industry but also creates opportunities. Polymer suppliers should closely follow solid-state battery development, pursue targeted innovation, and optimize products to meet changing market needs.
