Lithium-Ion Rechargeable Batteries

Lithium-Ion Rechargeable Batteries

Lithium-ion rechargeable batteries are also called swing, shuttle or ion-transfer batteries. These names reflect the basic principle of this type of accumulator quite well: the charge and discharge processes only essentially cause a transfer of lithium ions between the two electrodes. Lithium cobalt oxide (LiCoO2) is used as the cathode; in a discharged state the cobalt is trivalent, in a charged state it is quadrivalent. The anode is formed by a very fine carbon matrix (expanded graphite or carbon powder) in which lithium ions can be deposited.

There are other systems of lithium-ion secondary cells that work with other electrode materials, but the basic principle – the ‘ion swing’ and the deposition of lithium ions in the matrix – is the same.

Because of the instability of lithium in water, no aqueous electrolytes may be used for lithium batteries. Organic electrolytes with a high chemical resistance and good solubility for lithium salts, for example alcohol carbonate with lithium hexafluorophosphate (LiPF6) or lithium imide (LiN(SO2CF3)2) are used.

Typical performance data and uses (lithium cobalt oxide)

Cell terminal voltage: 3.6 volts (other systems: 3 – 4.3 volts)
Service life in charge cycles: 1,000 to over 1,000
For use in ambient temperatures: -20?C to +60?C
Typical energy density: 100 – 120 Wh/kg (theoretically > 450 Wh/kg)
Typical volumetric energy density: 200 – 300 Wh/l
Typical power density: 100 – 200 W/kg
Typical spontaneous discharge: approx. 5 – 10 % per month

One disadvantage is the relatively high price of the lithium-ion accumulator, which is why its use is currently restricted to applications where the cost of the high energy density is accepted by the customers, for example in mobile phone or notebook batteries.

The low specific weight of lithium results in a very high energy density for this type of accumulator, which also makes Li-Ion very interesting for drive purposes. A lot of effort is being put into research in this field.