A wet battery with zinc and bromine was previously only a potential candidate on paper for storing renewable energy and only releasing it into the power grid when needed.

The theoretical potential difference is 1.83 volts. The water-based electrolyte ensures that the construction is non-flammable. In addition, the simple construction of the cells and the use of readily available materials enable low production costs.

The catch: the extremely low pH value at the zinc electrode makes the system vulnerable. Hydrogen can escape, which ultimately leads to the destruction of the separator. This is due to the formation of zinc hydroxide, which closes the pores.

This severely limits the shelf life of such an accumulator, as it discharges itself after a short time. Until now, it had not been possible to replace the porous graphite electrodes, which are extremely acid-resistant, with a suitable material.

This has now been achieved at the Gwangju Institute of Science and Technology, Korea. A nitrogen-charged, mesoporous and carbon-coated graphite felt (NMC/GF for short) has completely new properties.

Another new feature is the manufacturing process by heating and cooling under an argon atmosphere. The pore sizes are in the low nanometer range. This prevents exchange with the environment, which at the same time blocks the destructive chemical processes inside.

The result is a zinc-bromide cell whose performance has dropped to 96 percent after 10,000 cycles. The energy efficiency, i.e. the difference between charging and discharging energy, drops in parallel from 80 to a still solid 76 percent.

Assuming the typical use of such a battery of one cycle per day, this would result in a shelf life of around 27 years. Not a bad result for a previously unreliable battery type.