Conventional lead acid batteries are comprised of two electrodes: a positive electrode made of lead dioxide (PbO2) and a negative electrode made of sponge lead (Pb). Both the lead dioxide and sponge lead materials are pasted onto lead grids that act as the current collector. Two half reactions occur on the electrodes during charge and discharge that are described by the well known double sulphate theory for lead acid batteries:
The PbC® battery is a hybrid device that uses the standard lead acid battery positive electrode and a supercapacitor negative electrode that is made of activated carbon. The specific type of activated carbon we use has an extremely high surface area (1500 m2/g) and has been specifically formulated by Axion for use in electrochemical applications. During charge and discharge, the positive electrode undergoes the same chemical reaction that occurs in a conventional lead acid battery, i.e. lead dioxide reacts with acid and sulphate ions to form lead sulphate and water. The main difference in the PbC® battery is the replacement of the lead negative electrode with an activated carbon electrode that does not undergo a chemical reaction at all. Instead, the very high surface area activated carbon electrode stores the protons (H+) from the acid in a layer on the surface of the electrode. This new negative half reaction can be written as the following:
Negative Electrode in the PbC® battery technology nC6x-(H+)xD nC6(x-2)-.(H+)x-2 + 2H+ + 2e- (discharged)
In conventional lead acid batteries the concentration of acid changes from being very concentrated in the charged state to somewhat dilute in the discharged state as the acid is converted to water. In contrast, the PbC® battery stores H+ in the negative electrode in the fully charges state which move to the positive electrode during discharge where they are neutralized to form water. The result is reduced acid concentration swings from the charged to discharged state which reduces grid corrosion on the positive electrode and leads to longer life of the positive electrode.