Sheet-like Rechargeable Battery Developed Using New Principle (2)

Mar 1, 2014
Kouji Kariatsumari & Tsunenori Tomioka, Nikkei Technology Online

Continued from Sheet-like Rechargeable Battery Developed Using New Principle

Micronics Japan said that the "battenice" rechargeable battery has the following advantages.

(1) The battery consists only of solid materials, and, therefore, it does not leak. (2) The battery does not fire due to thermal runaway because it uses no inflammable material. (3) The battery does not use any rare metal/earth, eliminating the concern about material procurement. (4) The battery does not use environmentally harmful material. (5) The battery has a long cycle life, reducing waste. In an accelerated test, Micronics Japan confirmed a cycle life of 10,000 cycles or more, and it is aiming to achieve a cycle life of 100,000 cycles or more. (6) The output density of the battery is as high as that of a capacitor.

Then, will it replace a lithium (Li)-ion rechargeable battery? The answer is not necessarily yes at this point. The battenice is inferior to high-performance Li-ion rechargeable batteries in terms of energy density per electrode. And it is probably difficult to drastically improve its energy density without a technical breakthrough.

As for existing consumer Li-ion batteries, the "18650" cylindrical cell has an energy density of 650Wh/L or higher. On the other hand, Micronics aims to achieve an energy density of 500Wh/L with the new battery at the time of initial production.

Moreover, in the case of the new battery, up to only two thin charge layers can be formed on a substrate at this point (one on each side of the substrate). If the thickness of a charge layer is increased or if multiple charge layers are formed by using, for example, electrodes, it becomes difficult to keep the uniformity of charge layer, to which charge/discharge capability is added by applying ultraviolet light, in the thickness direction.

At this point, it is difficult to form a thick charge layer or stack multiple layers on a substrate. Therefore, it is necessary to form a charge layer on both sides of substrates (sheets) and stack the substrates to increase capacity and output voltage.

In fact, for the aforementioned prototype, a 1μm-thick battery layer was formed on a 10μm stainless-steel foil. Micronics Japan aims to realize an energy density of 500Wh/L by replacing the stainless-steel foil with a 10μm or thinner aluminum foil and forming battery layers on both side of the substrate. Though it might be possible to greatly improve energy density by drastically reducing the ratio of substrate thickness to the thickness of charge layer, there is a challenge in substrate handling, the company said.

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