Hi All.
Wow, interesting article. I am also working on a static ZBr2 battery which will be used in a UPS at home as we have plenty of planned power outages in SA
Still waiting for my KBr order before starting putting my theoretical knowlege into practical experiments.
In my online "research" I came across some interesting ideas that might help improve the DIY ZnBr2 cells.
1) According to a Chinese paper, adding a magnet to the anode side helps reduce dendrites as the zinc dendrites would have to counter the magnetic field. OK, crude method to help reduce dendrites... but might be helpfull to someone with lots of magnets .
2) In flow batteries a high velocity of electrolyte circulating around the anode helps reduce dendrites. As I see the use of a separator in this post, it might be of interest on a larger battery where one could circulate the electrolyte around the anode without disturbing the bromide from settling.
3) A 3:1 surface ratio between anode:cathode helps reduce dendrites. This came from a paper investigating anode/cathode ratio for flow batteries with same material anode and cathode. The confrimed theory is that the larger surface helps spread the zinc deposition on the anode across a larger surface making each spike less effective to grow. A 4:1 ratio did not have added benefits, thus 3:1 was considered an optimal ratio.
=> My battery design will thus include a split cathode in 3 independent "sectors" and only use 1 sector during charging whereas all 3 cathode sectors are used during discharge. In addition, should a dendrite reach that cathode sector the charging can be switched to the next cathode sector. In addition, (see 4) a targeted negative charge pulse can be used to break up the dendrites that reach the cathode.
4) Coming from the electronics side, the charge logic has been a main focus of my interest. Robert Murray mentioned an important keyword for charging the ZnBr2 batteries: electroplating. Dendrites & rough surfaces are a big issue in electroplating as well. To combat the rough surface during electroplating, the quality electroplating controllers use pulses instead of uninterrupted current supply and every x pulses (10th?) are negative. Simplified, the positive pulses accelerate the ions towards the Zn anode and during the pulse break the ions can float around & spread evenly at the anode surface instead of concentrate towards the closest dendrite spike. The negative pulse targets the dendrite itself as that is the path with the lease resistance between anode/cathode.
=> I think the effect of the charge controller for ZnBr2 batteries regarding dendrites are underestimated. My presumption is that following the electroplating charge logic will help reduce dendrites more than additives in the solution. That doesn't exclude combining charge controll and additives to even enhance the dendrite reduction.
Anyway, though I'd share this.
Mike
