Powering the next generation of electric vehicles with the highest capacity, lightest weight and lowest cost lithium-ion batteries.

Envia Systems’ mission is to bring about the mass-market commercialization revolution of xEVs. The main barriers to xEV adoption are cost, range and safety. Envia’s disruptive technologies in Lithium-ion battery materials remove these barriers by dramatically lowering battery costs, improving all-electric range and enhancing safety.

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Envia develops and manufactures innovative components that enable lighter, lower cost lithium-ion batteries. The company has developed a cathode material based on inexpensive metals (including manganese) that stores more energy per unit of weight than anything else in use today – twice the energy density of lithium cobalt oxide. Because of the material’s stability at higher voltages, it is able to access high capacities with long cycle life. The combination of high capacity and low cost metals helps to significantly lower the price per kilowatt-hour (kWh) of energy storage. By putting more energy in each battery, the number of batteries required decreases – by 50% in Envia’s case, dramatically reducing the overall cost of the application. Its proprietary nano-coating process and high voltage electrolyte and electrolyte additive technology enables high cycle life and long calendar life.

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.

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.

¹ H.Yang, S.Amiruddin, H.J.Bang, Y.K.Sun, J.Prakash, J. Ind. Eng. Chem.,Vol 12,No.1,(2006) 12-38
² S.H.Kang, K. Amine, J. Power Sources, Vol 146 (2005) 654-657