Amorphous FePy (0.1 < y < 0.7) thin film anode for rechargeable lithium battery

•Amorphous FePy films with different P contents (0.1 < y < 0.7) were prepared.•This is the first time to report the lithium-reactive iron richer FePy films.•FePy films have higher capacity and cycling stability with larger P content.

Lithium reactive amorphous iron phosphide thin films are successfully prepared using electrochemical deposition. A series of reactions involving hypophosphite ions and phosphine gas lead to the formation of FePy films with y < 0.5. The introduction of ammonium ions to the plating bath elevates the y value up to 0.7 by activating a phosphine gas-free Fe-P co-deposition reaction. The larger P content in the film results in higher capacity and cycling stability, with positive implications for its use as the anode for a rechargeable lithium battery.