Fluoride ion batteries work essentially in the opposite direction of lithium-ion cells and attract electrons instead of shedding them. Flouride (the ionized version of fluorine) is an interesting battery material because it has a low atomic weight and a very high capacity to store electrons. However, to achieve this, you must dissolve the fluoride ions in an electrolyte, and researchers have found that this only works with solid electrolytes that are heated to high temperatures.
To get around this, the Honda / NASA / Caltech team created a solution called Liquid Electrolyte called BTFE, which allows the dissolution of fluoride at room temperature. With two positively charged regions he uses the principle "opposites attract" and reacts strongly to negatively charged fluoride.
Scientists used the electrolyte with copper, lanthanum, and paired fluorine to create a prototype battery that can perform reversible chemical reactions at room temperature. All in all, the batteries have the potential for ten times the energy density of lithium-ion batteries and have, according to Honda, a "more favorable ecological footprint".
However, we have often heard these kinds of things before so the usual caution and reservations apply. For example, the team still has to figure out how to stabilize the anodes and cathodes, which tend to dissolve completely in the electrolyte. However, they are making progress and more tests are in progress ̵