Introduction of lithium ion batteries, capacitors and lithium ion capacitors

Japan's Fujitsu Corporation established the capacitor business promotion room, and its director, Suzuki, wrote an article before the birthday, and popularized the knowledge of lithium-ion capacitors, and compared it with the characteristics of lithium-ion batteries and electric double-layer capacitors.

Lithium-ion capacitors developed by Fujitsu are characterized by high output power and excellent charge-discharge cycle characteristics, mainly for automotive vehicles requiring high power such as hybrid vehicles.

1. Comparison of voltage, capacity and self-discharge

The difference in the composition of lithium ion capacitors and lithium ion batteries is mainly reflected in the positive electrode. The positive electrode of a lithium ion capacitor is activated carbon, which is different from the lithium oxide of a lithium battery. The negative electrode of the lithium ion capacitor is made of a carbon material, the electrolyte is made of a lithium ion organic substance, the positive electrode is stored by an electric double layer, and the negative electrode is stored by a redox reaction of lithium ions.

The energy density of lithium ion capacitors is lower than that of lithium ion batteries, but the output density is high; the energy density of monomer volume is 10~15Wh/L, which is much larger than the capacity of 2~8Wh/L of electric double layer capacitors. Double.

In terms of voltage, the maximum voltage of a lithium-ion capacitor can reach 4V, which is similar to a lithium-ion battery, and much higher than an electric double-layer capacitor, and is smaller than self-discharge.

2. Safety: Lithium battery replaces nickel-hydrogen battery and lead-acid battery is a big advancement in battery technology, but lithium battery safety accidents have also occurred frequently. As mentioned above, this is also caused by the difference in its positive electrode structure. . The positive electrode of a lithium battery uses lithium oxide, which not only contains a large amount of lithium, but also forms lithium dendrites to pierce the separator, and also contains oxygen as an important ignition element. Once the battery is short-circuited, it can develop into thermal decomposition as a whole, and reaction with the electrolyte can cause combustion.

The positive electrode of the lithium ion capacitor is activated carbon, and even if the internal short circuit reacts with the negative electrode, it does not react with the electrolyte. In theory, this is much safer than the lithium battery.

3. Long-life characteristics: In order to achieve long life, lithium batteries have a certain range of limits on the charging and discharging depth of lithium batteries, thus reducing the capacity that can be utilized substantially. The charging and discharging principle of electric double layer capacitors is simply adsorption. It is difficult to extend the actual life by simply removing the ions in the electrolyte and having a long life. However, even if the lithium ion capacitor lowers the positive electrode potential, the voltage of the cell itself is not greatly lowered, so that the capacity can be secured.

4. High temperature resistance: the weakness of the storage components is the temperature rise during operation. During repeated charge and discharge, the internal resistance will promote the temperature rise, thus affecting the life. This is because, under high temperature conditions, the electrolyte and the positive electrode are prone to oxidative decomposition. For this reason, it may be necessary to lower the potential of the positive electrode under high temperature conditions. However, when the potential is lowered, the overall voltage of the electric double layer capacitor is lowered, and the capacity cannot be ensured. Lithium batteries cannot be depressurized and are prone to safety problems. Only the lithium ion capacitor can be used at a position where the positive electrode potential is away from the oxidative decomposition region, and thus the high temperature performance is excellent.

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