Polysulphide bromide accumulator

The polysulfide bromide battery is an electrical, rechargeable battery which is designed as a so-called redox flow battery and consists of two liquid electrolytes . As with all redox flow batteries, the two electrolytes are separated by a partially permeable membrane, which in this case only lets the positive sodium ions through. The salts sodium bromide (NaBr) or sodium tribromide (NaBr ₃ ) are used in the electrolyte on the negative electrode . Salts from the group of sodium polysulphides (Na ₂ S _x ) are used in the electrolyte on the positive electrode . The proportion of salts in the two electrolytes changes depending on the state of charge of the accumulator.

At the beginning of the 2000s, motivated by the comparatively inexpensive structure, an attempt was made to use this accumulator design in large-scale systems to compensate for load fluctuations in the power grid in battery storage systems . Examples of this are the battery storage in the Little Barford power station , which, due to technical difficulties, did not get beyond the trial operation.

Chemical processes

When charged, the electrolyte on the positive electrode consists primarily of sodium disulfide (Na ₂ S ₂ ) and the electrolyte on the negative electrode consists of sodium tribromide (NaBr ₃ ). The two electrolytes are in larger tanks and are pumped into the reaction chamber with a membrane between the electrolytes. During the discharge, the sodium disulphide is converted into sodium polysulphide (Na ₂ S ₄ ), the sodium tribromide is converted into sodium bromide (NaBr).

At the negative electrode the reaction equation for discharge reads:

${\displaystyle 2{\textrm {Na}}_{2}{\textrm {S}}_{2}\to {\textrm {Na}}_{2}{\textrm {S}}_{4}+2{\textrm {Na}}^{+}+2{\textrm {e}}^{-}}$

And on the positive electrode:

${\displaystyle {\textrm {NaBr}}_{3}+2{\textrm {Na}}^{+}+2{\textrm {e}}^{-}\to 3{\textrm {NaBr}}}$

When discharging, the processes run in the opposite direction.

Individual evidence

1. ^ H. Zhang: Advances in Batteries for Medium and Large-Scale Energy Storage . Woodhead Publishing Series in Energy, 2015, Chapter 9 - Polysulfide-bromine flow batteries (PBBs) for medium- and large-scale energy storage, p. 317 - 327 , doi : 10.1016 / B978-1-78242-013-2.00009-1 .
2. ↑ Adithi Amarnath, et al .: Bromine-polysulfide Redox-flow Battery Design: Cost Analysis . Ed .: Department of Chemical and Biomolecular Engineering - University of Tennessee. 2014 ( Online [PDF]).
3. ^ Review of Electrical Energy Storage Technologies and Systems and of their Potential for the UK. Retrieved August 20, 2019 .