|Envia has developed Li-ion cells with an energy density of 400 Wh/kg using its proprietary HCMR cathode and Silicon-Carbon Composite anode. Credit: Envia Systems. Click to enlarge.|
Envia Systems, the developer of high energy density Li-ion batteries using nano silicon-carbon composite anodes and high capacity layered-layered manganese composite cathodes (earlier post), will announce at the Advanced Research Projects Agency - Energy (ARPA-E) Energy Innovation Summit (EIS) this week that it has produced Li-ion cells offering an energy density of 400 Wh/kg.
Demonstrated in a 40 Ah pouch cell, the new system could lower Li-ion cell costs to $180/kWh, according to Sujeet Kumar, Co-founder, President & CTO, with further reductions to come. The cells feature active materials with high specific capacity: a 300 mAh/g cathode and nano Si-C composite anode with a capacity of 1600 mAh/g. Kumar said that the results have been verified by ARPA-E at an independent cell test facility.
|Cost roadmap. Source: Envia Systems. Click to enlarge.|
In 2010, Envia Systems was awarded a $4-million grant from ARPA-E and another $1 million from the California Energy Commission (CEC) to support development of the high energy density Li-ion storage technology, targeted at plug-in hybrid and electric vehicles. Earlier this month at the Advanced Automotive Battery Conference, Kumar presented some of the details around the development of its high energy density cells.
HCMR Cathode. Envia’s cathode—which they have labeled “high capacity Manganese rich” (HCMR)—is a lithium-rich layered-layered Li2MnO3·LiMO2 composite. The HCMR composite cathode materials offer twice the specific capacity and lower cost compared to more conventional cathode materials such as LiCoO2 , LiMn2O4, and LiFePO4.
Lithium-rich layered-layered composite cathode can suffer from high irreversible capacity loss (IRCL), which is very undesirable; oxygen loss, which can lead to gassing in pouch cells; high DC-resistance and onset of rise in DC-R at higher SOC; fade in average voltage upon cycling; and high Mn dissolution leading to poor cycle life and calendar life.
By engineering the cathode composition, structure, dopants, morphology and nano-coating, Envia is able to precisely control and tune the specific capacity, cycle life, calendar life, rate capability and physical properties of the material to match any application, overcoming those obstacles, Kumar said.
The HCMR cathode materials offer capacity of 220-295 mAh/g, and power of >1200 W/kg; cycle life @ 80% DOD is more than 1,000.
|Envia HCMR vs. other Li-rich chemistries|
|Cycle life @ 80% DOD||>1000||<200|
|Operating environment||-30 to 55 °C||RT to 45 °C|
|Process Scalability||100s kg||small|
Si-C Anode. While silicon can show very high specific capacities (~4000 mAh/g) as a anode material, it suffers from poor cycle life due to pulverization resulting from the large volume expansion during Li alloying/de-alloying.
Envia nano-engineered its Si-C anodes with a resulting high capacity (1530 mAh/g reversible capacity at C/3); good rate capability (95.5% capacity retention from C/20 to C/3); and good cycling performance (90% capacity retention after 50 cycles in a half cell).
HCMR/Silicon Composite Full Cells. Combining the cathode and anode in 2032 coin cells, Envia delivered high cathode capacity (250 mAh/g capacity at loading level> 25 mg/cm2) and high anode loading density (1530 mAh/g capacity at loading >5mg/cm2).
GCC will be speaking further with Sujeet Kumar at the ARPA-E EIS this week about the new Envia cell.