Battery electrode materials need to do a lot of things well. They need to be conductors to get charges to and from the ions that shuttle between the electrodes. They also need to have an open structure that allows the ions to move around before they reach a site where they can be stored. The storage of lots of ions also causes materials to expand, creating mechanical stresses that can cause the structure of the electrode material to gradually decay.
Because it’s hard to get all of these properties from a single material, many electrodes are composite materials, with one chemical used to allow ions into and out of the electrode, another to store them, and possibly a third that provides high conductivity. Unfortunately, this can create new problems, with breakdowns at the interfaces between materials slowly degrading the battery’s capacity.
Now, a team of researchers is proposing a material that seemingly does it all. It’s reasonably conductive, it allows lithium ions to move around and find storage sites, and it’s made of cheap and common elements. Perhaps best of all, it undergoes self-healing, smoothing out damage across charge/discharge cycles.
High capacity
The research team, primarily based in China, set out to limit the complexity of cathodes. “Conventional composite cathode designs, which typically incorporate a cathode active material, catholyte, and electronic conducting additive, are often limited by the substantial volume fraction of electrochemically inactive components,” the researchers wrote. The solution, they reasoned, was to create an all-in-one material that gets rid of most of these materials.
A number of papers had reported good luck with chlorine-based chemicals, which allowed ions to move readily through the material but didn’t conduct electricity very well. So the researchers experimented with pre-loading one of these materials with lithium. And they focused on iron chloride since it’s a very cheap material.
