At the "nano tech 2007" event held from February 21 to 23, 2007, NEC Corp. presented an organic secondary battery embedded with an IC card and some other devices. The company strongly appealed to the audience by showing that the battery can light a white LED (light emitting diode) even when it is curved, while demonstrating a high-speed charge and a contactless charge of the battery.
NEC displayed, among other items, a flexible cell and a card incorporating a thermo sensor and the aforesaid battery at its booth. Of the items on display, the thermo sensor card featuring a 6 mAh cell (an electrode measures 2.3 x 2.5 cm) can write measured temperature values every 2 seconds for 5 days (about 200,000 times), while the flexible cell with current capacity of 20 mAh is able to light the built-in 10 mA white LED for 2 hours, the company claims.
The organic radical secondary battery's key feature is its high-speed charge that finishes in only 30 seconds using radical reaction instead of ion exchange. It uses PTVE (poly [4-vinyloxy-2, 2, 6, 6-tetramethylpiperidine-N-oxyl]) organic radical material as the positive electrode activator, and its negative electrode seems to use metal lithium, which can make the thickness of an electrode thinner than the existing negative electrode material graphite. Dendrite may be viewed in metal lithium, which could lead to short-circuit between positive and negative electrodes, but very small capacity of a thin, micro cell, developed this time, appears to hardly cause a serious problem even if short-circuited.
An NEC spokesperson cited as a challenge that lies ahead the battery's self-discharge, which is even larger than that of other secondary batteries, and said, "We will strive to lower its self-discharge to Ni-hydrogen secondary battery level." NEC aims to apply the organic radical battery for power supply of RFID cards, electronic paper and sensor networks, among others, according to the spokesperson.
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