A water-based battery with the potential to provide a cheap way to store wind or solar energy was developed at Stanford University. The manganese-hydrogen battery could fill a missing piece in modern energy systems by storing wind and solar energy for when it is needed, and, in turn, reduce the need to burn carbon-emitting fossil Postdoctoral scholar Wei Chen holds a prototype of the battery. Source: Jinwei Xufuels.

The three-inch-tall prototype generates only 20 mWh of electricity, comparable to the energy levels of LED flashlights sported on key rings. The researchers intend to scale up the technology to an industrial-grade system that could charge and recharge up to 10,000 times, creating a grid-scale battery with a ten-year lifespan.

The technology is based on a reversible electron-exchange between water and manganese sulfate, an abundant industrial salt. The cost for storing enough electricity to power a 100 W lightbulb for 12 hours is estimated to be one cent, due to the battery’s extended service life.

As the researchers tested the battery by attaching it to a power source, the electrons flowing in reacted with the manganese sulfate dissolved in the water to leave particles of manganese dioxide clinging to the electrodes. Excess electrons bubbled off as hydrogen gas, thus storing that energy for future use. The prototype demonstrated a discharge voltage of ~1.3 V, a rate capability of 100 mA cm−2 (36 s of discharge) and a lifetime of more than 10,000 cycles without decay. A gravimetric energy density of ~139 Wh kg−1 (volumetric energy density of ~210 Wh l−1) was documented, with a theoretical gravimetric energy density of ~174 Wh kg−1 (volumetric energy density of ~263 Wh l−1).