Lead-Carbon Energy Storage Device Overview
The full technical description of Axion's proprietary
technology is a "multi-celled asymmetrically supercapacitive lead-acid-carbon hybrid battery." Like a lead-acid battery, our battery consists of a series of cells. Within the individual cells, however, our construction is more complex. Where the negative electrodes in lead-acid batteries are simple sponge lead plates, our negative electrodes are five-layer assemblies that consist of a carbon electrode, a corrosion barrier, a current collector, a second corrosion barrier and a second carbon electrode. These electrode assemblies are then sandwiched together with conventional separators and positive electrodes to make our battery, which is filled with an acid electrolyte, sealed and connected in series to the other cells.
We have been testing laboratory prototypes of Axion's
batteries since April 2004. Our test protocol requires a complete charge-discharge cycle every 7 hours to a 90% depth of discharge. During testing, our laboratory prototypes have withstood more than 1,600 cycles before failure. In comparison, most lead-acid batteries designed for deep discharge applications can only survive 300 to 500 cycles under these operating conditions. Based on the work completed during the laboratory development stage, we believe our application specific prototypes will offer several key performance advantages over conventional lead-acid batteries, including:
- significantly faster recharge rates;
significantly longer cycle lives in deep discharge applications; and
minimal required maintenance.
Over five years have been devoted to research and development on various aspects of this technology. Our work has focused on developing our intellectual property, characterizing baseline performance, developing proprietary treatment processes for the activated carbon we use in our electrodes, developing proprietary designs and manufacturing techniques for electrode assemblies and fabricating a series of material and design evaluation prototypes that range from single cell to multi-cell batteries.
Technology and Performance & Economics
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:
- Overall Reaction
PbO2 + 2H2SO4 + PbD 2PbSO4 + 2H2O (+2.050 V)
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+)x D 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.
Is Axion a possible take over target?