Multi-acid design
This is the mixed acid design which adds hydrochloric to the usual sulfuric acid which has been used in VRFBs for a while. Adding the hydrochloric allows for roughly doubling the energy density of the electrolyte. Of course you still need twice the dissolved vanadium so the primary advantage is being able to make the battery system smaller. However, this comes at a cost in two ways. One, HCL is significantly more corrosive to seals than just H2SO4 so it is actually quite an engineering challenge to make a system which doesn't leak for a decent amount of time. Remember that what leaks is extremely hazardous so any battery must have secondary containment to be able to hold at least 110% of the volume of contained electrolyte. The second problem is that adding HCL adds chlorine to the system so under certain circumstances the battery can emit chlorine gas which is highly toxic. You better be darn sure of the design of such a battery put in your house. Are you absolutely SURE the vent (and these all need to be vented for expansion and contraction) is outside and the wind won't blow the gas into your house? I was in this industry and engineered a commercial system which made it to market. I *may* be convinced to place a sulfuric acid based system (they all contain small amounts of phosphoric acid) in my house but would never place one with HCL near my family. So sure we "gave" the technology to China or wherever but I would say, let them have it so long as they don't go installing it in the USA.
Biting the hand that feeds IT
