Data di pubblicazione08-05-2018
Data di priorità09-04-2018
TitolarePolitecnico di Milano
DipartimentoDepartment of Energy
AutoriAndrea Casalegno, Matteo Zago
A flow battery is an electrochemical cell in which the charging and discharging processes take place through oxidation-reduction reactions.
It consists of two half-cells, one positive and one negative, each containing an electrode and an electrolyte.
The electrolyte contains two types of ions: the oxidation-reduction ones, which are involved in the reaction, and the so-called exchange ions that are responsible for charge transport from one half-cell to another.
Generally, a problem found in these types of cells is the fact that the membrane that separates the half-cells is not selective to the passage of redox ions (cross-over phenomenon), thus reducing the useful capacity of the battery. A typical solution for this problem is the use of thicker membrane or additional membrane with smaller pore size. However, these solutions also partially block transport ions, causing ohmic losses. They also modify homogeneously the selectivity over the entire membrane surface, the ion concentration is variable from area to zone instead.
The novelty of this invention consist in coupling the central membrane with two layers (on the two membrane sides) of a porous barrier material with inhomogeneous ion selectivity. In particular, the barrier material blocks the ions more in those areas where their concentration is greater and less where the concentration of the ions is lower. In this manner the exchange ions are blocked less avoiding ohmic losses.
The parameters that modify the selectivity of the barrier material are: the size of the pores, the tortuosity of the path that the ions have to perform through the pores, the thickness of the material and its chemical composition. One of the simplest methods that can be used to create inhomogeneous selectivity is depositing the material by spraying, in this way it is very easy to vary locally the thickness of the material.