German conglomerate Freudenberg Sealing Technologies has introduced new nonwoven cell stack envelopes and cell caps for prismatic battery cells. Battery cell envelopes consist of nonwoven materials that wrap the cell stack and protect it during the assembly and provide the necessary electrical insulation, while custom-designed cell caps, developed in collaboration with cell manufacturers ensures optimum performance under a wide range of operating conditions.
Nonwoven cell envelopes advance new cell designs
Battery cell envelopes from Freudenberg Sealing Technologies consist of innovative nonwoven materials that wrap the cell stack and – just like conventional films – protect it during the assembly and provide the necessary electrical insulation. In addition, the nonwoven materials offer significant technical advantages over standard films used in this application today.
Nonwoven envelopes consist of fiber network forming an ultra-homogeneous pore structure. The fibers are surface treated for permanent electrolyte wettability. This results in a lower risk of entrapping gas bubbles as the cell is filled and helps to keep the cell stack wetted over the lifetime.
Compared to conventional foils, nonwoven materials filled with electrolyte also lead to an improved heat management within the cell – due to the resulting higher thermal conductivity. Similar to a sponge, the absorbed electrolyte in the nonwoven creates an additional electrolyte reservoir in the cell. The electrolyte is released when the nonwoven is compressed, which happens during the aging of the cell when the stack swells – just exactly when additional electrolyte is needed.
When acting as an in-cell compression element, thicker layers of nonwoven envelopes can absorb a large portion of the cell stack growth within the cell, allowing thinner compression elements between single cells. In addition, absorbing cell stack growth inside the cell results in a more even load distribution on the cell stack itself– therefore reducing the risk of dendrite formation and Lithium-plating.
Cell caps ensure long battery life
To boost the safety and performance of electric vehicles, Freudenberg Sealing Technologies offers custom-designed cell caps, developed in collaboration with cell manufacturers. All necessary functions are integrated, including rupture disks that dissipate escaping gases in case of a thermal runaway of the cell. These are manufactured on site for the local market with the lowest possible carbon footprint and in accordance with automotive standards such as IATF 16949.
Cell caps that are welded to the inner electrodes effectively seal and insulate the battery cells. Freudenberg Sealing Technologies’ cell caps are tested to be absolutely gas-tight and maintain this capacity throughout the cycle life of the battery. This ensures optimum performance under a wide range of operating conditions, minimizes the risk of gas leakage and increases safety. In addition, the cell caps have exceptional mechanical resistance to peak loads and fatigue. Their compatibility with various electrolytes, any coolants from outside and gases enables seamless integration into different electric vehicle systems. All materials used have been electrochemically tested.
“In these customer projects, we combine state-of-the-art materials with intelligent design and merge our expertise in sealing technology and engineering plastics with our knowledge of stamping technology. This allows us to set new standards to ensure perfect sealing and a long cycle life for the cell caps.”
Giulia Richard, Global Marketing Director at Freudenberg Sealing Technologies
