Philips Rivets Li-ion Batteries

Advanced Battery Technology, Sep 2005

Philips is developing pre-shaped lithium-ion batteries to enable more design freedom in handheld electronic products. The cells are based on conventional lithium-ion technology, but are 'riveted' together using a polymer.

The batteries are built by stacking double-sided electrodes made from standard LiCoO^sup 2^ material between a single-sided cathode and a single-sided anode. Each electrode is pre-punched with a pattern of small holes around Imm in diameter.

A sheet of lithylene polymer is placed on the top and bottom of the stack, and separator layers are placed between the electrodes. To create channels through the stack these layers are melted using heated needles.

When the whole stack is annealed at 120°C, the lithylene melts through the holes, and on cooling the stack is mechanically stable. The battery adopts the shape of any preform it is cooled over. The final steps are packaging in a polymer-coated aluminum foil, introduction of the electrolyte, evacuation and sealing.

Initial storage capacity of the pre-shaped battery is around 800mAh. This falls to 85% after 400 cycles. The researchers found that the discharge capacity of the batteries when discharged at a high C rate is relatively poor, but said that alternative materials could improve matters.

Despite the innovation, team leader Professor Peter Notten said reducing the power consumption of devices is still key.