New batteries type page

2000/09/01 Azkune Mendia, Iñaki - Elhuyar Fundazioa Iturria: Elhuyar aldizkaria

• Elektronika

Conventional batteries that have been used so far have a positive electrode and a negative electrode, both are immersed in an ionic or electrolyte solution, which then supplies the external electrical circuit. When the electrical circuit is closed, the electron flows go from the negative electrode to the positive electrode by electric conductors, thus generating an electric current. To balance the system, inside the battery, positive ions go to the positive electrode along the electrolyte. When the battery is charging with an external power source, an inverse phenomenon occurs and the storage of electrons with negative electrode discharged (the battery is charged) is restored.

Batteries used in current electric cars include nickel and cadmium (Ni-Cd) or nickel and metal hydride (Ni-MH) electrodes immersed in liquid electrolytes. However, the prototype of the Massachusetts Institute of Technology or MIT does not contain liquid electrolyte. Negative electrode is lithium sheet and positive electrode metal oxide sheet. The electrolyte is a solid polymer (another sheet) and not liquid.

It is a reason to choose lithium, as it is the lightest metal of the periodic table. But it also generates elementary voltages higher than 3 volts, that is, twice as much as in the Ni-Cd and Ni-MH (1.23 volt) batteries. Consequently, with the same number of elemental electrical cells, twice as much energy is obtained.

Lithium batteries are not very new. Researchers have been working and preparing these works for about ten years. Right now, mobile phones and laptops run on lithium batteries. In addition, Nissan has announced that this year will market the electric car Altra EV in the United States.

The MIT prototype is also lithium, but very different. The above have liquid electrolyte. In a tank there are lithium salts where the two electrodes are immersed, one of lithium oxide and one of graphite. In the MIT prototype there is no liquid electrolyte (but polymer) and the physical energy is much greater.

The physical energy indicates how much W.h (or energy) can accumulate in every kilogram of battery. In lead and acid batteries the physical energy is 30 kWh, in 50 kWh Ni-Cd batteries, in 70 kWh Ni-HM batteries, in 100-140 kWh lithium ion and in 400 kWh lithium polymer according to MIT.

However, there is a technical barrier for the manufacture of this new battery, since the polymer acting as an electrolyte operates at a minimum temperature of 60ºC. Researchers try to reduce this barrier to lower temperatures. However, it has great advantages. Unlike others, this battery contains no fluid that can escape and can be a battery of any size and shape. In addition, according to MIT, the autonomy of the electric vehicle can reach 600 kilometers within five years.

Another field of application of polymeric lithium is that of mobile phones. Batteries weighing 19 grams and 3.5 millimeters thick will be used on mobile phones.