Altair Nanotechnologies Inc., a leading provider of advanced nanomaterials and alternative energy solutions, detailed why its NanoSafe rechargeable, nano titanate battery technology provides fundamental improvements, including high power versus other rechargeable batteries.
In anticipation of Altairnano's delivery of its first NanoSafe battery pack for use in an electric vehicle in September, this is the final of four planned news releases identifying features of Altairnano NanoSafe batteries that may prove advantageous in the power rechargeable battery market. In the three previous releases, Altairnano detailed why its nano titanate battery technology delivers high battery safety, rapid recharge and long battery life. The combination of these features has the potential to make Altairnano's NanoSafe batteries ideal for power applications such as electric vehicles and hybrid electric vehicles.
How Does a Rechargeable Battery Work?
A battery consists of a positive electrode, a negative electrode, a porous separator that keeps the electrodes from touching, and an ionic electrolyte, which is the conducting medium for ions (charged particles) between the positive and the negative electrodes. When the battery is being charged, ions transfer from the positive to the negative electrodes via the electrolyte. On discharge these ions return to the positive electrode releasing energy in the process.
Existing Lithium Ion Batteries
Rechargeable lithium ion batteries currently use graphite for the negative electrode and typically lithium cobalt oxide for the positive electrode. The electrolyte is a lithium salt dissolved in an organic solvent which is flammable.
An important attribute of large format batteries is their ability to deliver power quickly. During charge, lithium ions deposit inside the graphite particles. However, the rate at which lithium ions can be removed during discharge - the useful power-producing cycle of a battery - is limited by the electro-chemical properties of the graphite and the size of the graphite particles. The electrochemical properties relate to the existence of a high resistance crust (call the Solid Electrolyte Interface or SEI) that impedes the removal of lithium - the first step in power production. Also, graphite's large particle size means that lithium atoms inside the particle must travel a long distance to escape. This further increases the impedance and reduces power.
So power is restricted by the ion removal capability in lithium ion batteries, resulting in power levels of the order of 1000 watts per kilogram (W/Kg). Also, power can be affected by external factors such as temperature. At low temperatures, the lithium ion removal rate is significantly less than at room temperature resulting in power delivery at these temperatures that is greatly reduced.
Given that power delivery is governed by fundamental properties of the materials the only option is to change the materials and chemistry of the battery.
The Altairnano NanoSafe Battery
Altairnano solved this problem by using an innovative approach to rechargeable battery chemistry by replacing graphite with a patented nano-titanate material as the negative electrode in its NanoSafe batteries. The outcome is that Altairnano's NanoSafe batteries deliver power per unit weight and unit volume several times that of conventional lithium ion batteries. Altairnano laboratory measurements indicate power density as high as 4000 W/Kg and over 5000W/litre. By using nano-titanate materials as the negative electrode material, the formation of an SEI is eliminated. In addition, the nano-titanate particles are up to 100 times smaller than a typical graphite particle thereby greatly reducing the distance a lithium atom must travel to be released from the particle. These properties also mean that even at very cold temperatures, a nano-titanate battery will produce high power.
The same technology also dramatically increases battery charge and discharge rates; rapid charge is important for next generation electric vehicles so they could be charged in a few minutes rather than hours as with current lithium ion technology. As has been indicated in previous releases the NanoSafe cell has demonstrated that surges of power can be delivered without risking thermal runaway or performance damage to the battery.
Altairnano will be demonstrating its NanoSafe battery technology at the California Air Resources Board Zero Emission Vehicles meeting in Sacramento, September 25th through 27th, 2006.
