One of the challenges in the development of batteries consists of investigating new electrode materials and comprehending the mechanism of lithium uptake. Herein, we report on the first operando measurements of electron magnetism in a battery during cycling. We have succeeded in designing a non-magnetic cell and have investigated the lithiation mechanism of FeSb2, a high energy density anode material. The stepwise increase of the magnetic moment reveals an increase of amorphous Fe nanoparticle size, while Sb undergoes reversible alloying with Li.
