A sulfuric leap for batteries

MIT Technology Review : A new battery created by Yi Cui of Stanford University and his colleagues may be able to reach the US Department of Energy’s goal of a $100 per kWh. Their hybrid battery blends the design of flow batteries with that of lithium-sulfur batteries. Flow batteries use a pair of liquid electrolytes and an expensive ion-transfer membrane with minimal extra electronics to extract the energy. Lithium-sulfur batteries use solid electrodes with a high storage potential but a limited number of recharges because of the buildup of lithium polysulfides, which reduces the amount of lithium and sulfur available for reactions. Cui and his team realized that the dissolved polysulfides stored more energy than the electrolytes used in flow batteries. They created a battery that uses a single metallic lithium electrode and an electrolyte in which lithium polysulfide could dissolve. An inexpensive coating on the lithium electrode replaced the ion-transfer membrane. The team was able to recharge the battery 2000 times before storage capacity was significantly reduced. To make a commercial product they will have to achieve 5000 recharges. To reach that goal, they may have to increase the amount of lithium to the point where the battery exceeds the $100/kWh price point. Even so, a commercialized version of the battery would be a significant step forward in technology.