The all-vanadium redox fl ow battery is a promising technology for large-scale
renewable and grid energy storage, but is limited by the low energy density
and poor stability of the vanadium electrolyte solutions. A new vanadium
redox fl ow battery with a signifi cant improvement over the current technology
is reported in this paper. This battery uses sulfate-chloride mixed electrolytes,
which are capable of dissolving 2.5 M vanadium, representing about a 70%
increase in energy capacity over the current sulfate system. More importantly,
the new electrolyte remains stable over a wide temperature range of − 5 to
50 ° C, potentially eliminating the need for electrolyte temperature control in
practical applications. This development would lead to a signifi cant reduction
in the cost of energy storage, thus accelerating its market penetration.