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 charge rates measured in minutes versus hours required for other rechargeable batteries.
In anticipation of Altairnano's delivery of its first NanoSafe battery pack in September, this is the second of four planned news releases identifying features of Altairnano NanoSafe batteries that may prove advantageous in the power rechargeable battery market. The remaining two releases will discuss battery life and power capacity. On August 24, 2006 Altairnano detailed why its nano titanate battery technology delivers high battery safety. 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.
During charge, lithium ions deposit inside the graphite particles. However the rate at which lithium ions can deposit is limited by the electro-chemical properties of the graphite, and if they can not enter the graphite particles they, instead, may collect (plate) on the negative electrode's surface as lithium metal. This can occur if the ions are deposited too rapidly on the graphite electrode as might be the case if the battery is charged too quickly. If this plating occurs, the battery will severely degrade in performance and in extreme cases, will short, causing overheating and thermal runaway - a major fire hazard.
So the time to charge (charge rate) is restricted by the ion incorporation rate capability in lithium ion batteries, resulting in charge times measured in hours. Also, charge rate can be affected by external factors such as temperature. At low temperatures, the lithium ion incorporation rate is significantly less than at room temperature so charging at these temperatures may be much longer or impossible.
Given that the charge rate 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. By using nano-titanate materials as the negative electrode material, lithium metal plating does not occur because the electro-chemical properties of the nano-titanate allow the deposition of lithium in the particles at high rates. These electrical properties mean that even at very cold temperatures there is no risk of plating. No undesirable interaction takes place with the electrolyte in the Altairnano batteries, which permits the battery to be charged very rapidly, without the risk of shorting or thermal runaway. In fact, in recent laboratory testing, Altairnano has demonstrated that a NanoSafe cell can be charged to over 80% charge capacity in about one minute. Actual charge rates achieved in specific applications will vary due to the application environment.
The same technology also increases battery discharge rates which could be important to applications that require bursts of power, for example, a freeway electric vehicle accelerating rapidly. The NanoSafe cell has demonstrated that surges of power can be delivered without risking thermal runaway or performance damage to the battery.
By using patented nano-titanate materials in the battery construction, Altairnano NanoSafe cells have displayed very fast charge and discharge rates and appear to offer a safer solution than conventional lithium ion batteries.
Altairnano is delivering its first NanoSafe battery pack in September to Phoenix Motorcars for incorporation into an electric vehicle. Phoenix Motorcars, based in Ojai, California, is an early leader in the effort to mass produce full function, freeway ready electric automobiles.
NanoSafe is a trademark of Altair Nanotechnologies Inc.
