Friday, June 22, 2012

Lithium Batteries: Envia Systems - 400 Wh/kg is here! - Electric Cars with 300 Miles Range.

    If we can marry Tesla's abilities and ambitions with new Lithium batteries for Electric Cars from Envia Systems we can have the US based mass market production base for the Electric Cars.

Lithium Catalyst: Inside Tesla - They Are Coming - Tesla Model S

"Tesla Model S will bring Electric Cars into the headlines again. Responsible Luxury, High-End  performance and Electric Car - it is all represented by Tesla Model S now. The next step will be the real Electric Cars for the mass market. Volume will bring down the cost of the lithium batteries, battery leasing schemes will reduce the entry cost of Electric Car ownership and then we can never look back on the 19th century technology of controlled explosions under the hood burning Oil."

Lowest cost

Highest Range

Range 300 miles with Envia

One of the main barriers to mass EV adoption is range anxiety. Most electric vehicles have an 80-100 mile range. The key factor in determining the vehicle’s electric range is the energy density of the battery. Current technologies max out at 180 Wh/kg. Envia’s technology enables a 2-3X improvement in vehicle range compared to other Lithium cell chemistries.

Enhanced Safety

Another barrier to EV adoption is the perceived safety risk of lithium batteries resulting from recent post-crash fires of some electric vehicles. Thermal runaway in a lithium battery occurs when the cell exceeds the critical temperature above which an increase of the cell temperature is irreversible due to the exothermic heat associated with structural changes of the anode, cathode and the electrolyte. Although the thermal reactions are associated with solid electrolyte interface (SEI) decomposition at the anode¹, progressive reactions, which cause the cells to catch fire, are associated with the cathode.
Differential scanning calorimetry (DSC) is one of the techniques used to evaluate the heat associated with various components of the Li-ion battery. DSC is used to analyze the onset of the reaction, which is shown by an increase in an exotherm.
Layered cathode chemistries such as NCA have high specific capacities (although not quite as high as that of Envia’s HCMR cathode). As we shall see in the following discussion, the thermal stability of NCA is not as good as Envia’s cathode either.
The chart to the right shows the results of a DSC study² comparing NCA and a manganese-rich layered-layered cathode very similar to Envia’s cathode. Please note that the NCA material was only charged to 4.2V whereas the manganese-rich cathode was charged to 4.6V (for higher specific capacities).

In the DSC study, NCA shows one major exothermic peak around 275ºC followed by smaller complex exothermic peaks. However the major exothermic peak starts around 200ºC and

reaches its maximum at 275ºC. This is associated with structural changes in association with the oxygen loss. The following multiple peaks are associated with progressive decomposition of the cathode. However in case of the cathode material similar to Envia’s, only one major peak is observed around 275ºC with an onset temperature around 260ºC.
The higher onset temperature implies a higher thermal stability of the Envia-like cathode compared to NCA. The sharper peak in the manganese-rich cathode also implies the lack of a continuous reaction thereby reducing the amount of heat produced during any event and lessening the likelihood of a thermal runaway.
Envia conducted its own nail penetration testing using 20Ah and 40Ah cells per USABC test protocols to validate its material. Cells made with Envia’s HCMR™ cathode passed the nail penetration test while cells with other layered chemistries did not perform well.

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