Additives are also essential in improving battery safety, notably with the introduction of redox shuttles, the operation and limitations of which we have detailed, as well as cut-off additives.
We have described the specifications for the choice of these redox molecules to control the risks of battery overcharging and overdischarging. However, their use is limited to laptop batteries, and not to those of the electric vehicle, due to the temperature rise inherent in the shuttle's operating mechanism.
As for cut-off additives, they rely either on their decomposition at high potential, which leads to the formation of an insulating polymer - which thereby prevents thermal runaway -, or on the existence of a non-metal transition → metal at high potential, so that overcharging is prevented by the creation of an internal short-circuit. This process allows an overload current to pass harmlessly through the cell, offering the advantage of being reversible. Such additives can be added to the membrane, which acts as a toolbox.
However, the most robust approach remains the use of heterostructured separators with adjustable cut-off temperature, or even the development of ceramic-coated separators currently available in commercial cells.
