DOE OSTI2012
For lithium-Sulfur (Li-S) batteries to be practical, economic and safe for powering electric vehicles more than 300 miles between charges the energy and cycle life must be improved. Li- S’s theoretical specific energy and energy density are (2,550 Wh/kg, 2,860 Wh/l), compared to (~600 Wh/kg, 1,800 Wh/l) for Li-ion. At less than 25% of theoretical specific energy (~560 Wh/kg at the cell level), Li-S batteries could power a 1500 kg, 5 passenger vehicle, more than 300 miles between charges with a battery pack weighing less than 300 kg. For commercial viability these cells must be safe, low cost and exhibit more than 1,000 full depth of discharge cycles. By implementing unique new physical barrier technologies this work targets (500 Wh/kg, 500 cycles) at the cell level by late 2013. After this program, (600 Wh/kg, 1,000 cycles) cells are targeted in >40 kWh battery packs by 2018 at < $200/kWh. The present state-of-the-art Li-S cells developed at Sion Power, in current commercial format delivers (2.8 Ah, 5.8 Wh, 350 Wh/kg) and are limited to ~50 cycles. These cells deliver only 14% of theoretical specific energy. By retooling and optimizing cell design and packaging to rebalance materials, this chemistry can reach (350 Wh/kg, ~100 cycles) in commercial cells. Much more than 100 cycles, at >350 Wh/kg, is unlikely for the present chemistry-only Li-S cell paradigm. Cycle life is limited almost exclusively by reactions between the Li-metal anode and the solvents necessary to promote cathode function. To release the transformational energy of Li-S the anode must be decoupled from the cathode chemistry. Prospects to achieve this decoupling through chemistry alone are challenging, therefore this program is to accelerate efforts to decouple anode and cathode chemistries by separating the electrodes with ion selective, thin film multi-layer, physical barrier membranes stabilized by externally applied pressure. This report will focus on efforts of Battelle to develop an anode stabilization layer and method to measure the ionic conductivity of this thin vacuum deposited polymeric layer.