The eighth characteristic of the present invention lies in that: in the activation device 11, the vanadium ions are activated by means of ultraviolet, wherein the dissolution and activation time is 30-300 minutes, the dissolution and activation temperature is 20-45° C., and the power density is 10-300 W/m³.

The electrolyte produced by the present invention is of high purity, high activity and simple assembly. The present invention has the following outstanding advantages:

(1) High purity: vanadium oxytrichloride which is easy to be highly purified is used as a raw material, and it is easy to obtain high-purity vanadium oxytrichloride with a purity of 2N-6N. Taking 5N vanadium oxytrichloride for example, a low-valence vanadium oxide with a purity of 4N5 (i.e., a purity of 99.995%) can be prepared by the present invention, and therefore a high-purity vanadium electrolyte can be formulated. In addition to the effective components, the total impurity content is lower than 5 ppm.

(2) Liquid phase hydrolysis: the operation is simple, which is convenient for industrial application.

(3) Realizing the heat utilization of the high-temperature tail gas and high-temperature reduction product in the fluidized bed: the high-temperature tail gas in the reduction fluidized bed is combusted for preheating of the vanadium powder material, so as to recover the sensible heat and latent heat of the high-temperature tail gas, and the sensible heat of the reduction product is recovered through the heat exchange between the reduction product and the fluidized nitrogen gas.

(4) Precise control of reduction: a rectangular multi-bin fluidized bed is used to achieve precise control over reduction of the valence state.