OXIS Energy to scale up production of Li-S batteries in 2014

OXIS Energy is planning on commercial production of their Lithium Sulfur batteries in 2014. The cells are expected to be around 200Wh/kg (low for Li-S but its still early) and achieve a little more than 1500 cycles to 80% capacity. They have been tested to be very safe (a nail puncture test resulted in a 1.4C rise in temperature and no expansion or pouch rupture).

These batteries are suited well for EVs and marginally for EREVs.

For EVs, the energy density is about double of what was in first generation EVs (Nissan Leaf). This means that replacing the pack with the new cells would provide almost double the range, from 75 miles to 130-150 miles. The cycle life of 1,500 cycles would provide for about 195,000-200,000 miles to 80% capacity (a nominal range of 104-120 miles). This would be a big boost for EVs.

For EREVs, the weight and size of the pack could be reduced by 1/2 over the 2010 baseline with the same electric range, or by 1/3 to achieve a 25-30% range increase. For something like the Volt, this would mean a return of the 5th seat and a boost in electric range from 38 miles to about 45 miles in a 19kWh pack using 13kWh of energy. Because cycle life is non-linear in Lithium batteries (well, it is for Li-Ion, I’m assuming that it is also that way for Li-S), by using only 70% of the battery we extend the cycle life by almost 60%, increasing the cycle life from 1500 to 2400 to 80%, which would be good for 108,000 electric miles – just barely exceeding the 8-year, 100,000 mile warranty supplied by auto manufacturers on EREVs and EVs (notwithstanding any gas-powered miles that also count under the warranty). This just-clearing-the-hurdle approach however doesn’t leave a lot of margin for environmental factors (heat, cold) and time-based degradation of the cells. Cycle life would need to be extended more (from 1500 to 2000 cycles), or cell energy density would need to be improved (more miles per battery cycle) to remedy this.

Ultimately, the biggest issue facing OXIS Energy isn’t the performance of the cell in 2014, rather what is promised by other companies for 2015 and 2016 – 300 and 400Wh/kg energy densities that will revolutionize EVs. If they can keep their Li-S chemistry competitive (and outrun Li-Ion in the mid- and long-term race), or if their competitors fail to deliver on their promises, they will be successful.

Leave a Reply

Your email address will not be published. Required fields are marked *