Mechanistic insights into the lithiation and delithiation of iron-doped zinc oxide: The nucleation site model

The detailed mechanistic understanding of the electrochemical reactions occurring in lithium-ion battery electrodes is fundamental for their further improvement. Conversion/alloying materials (CAMs), such as Zn0.9Fe0.1O, one of the most recent alternatives for classic graphite anodes offer superior specific capacity and rate capability. However, despite fast kinetics, CAMs suffer from a large voltage hysteresis upon de-/lithiation and improvable coulombic efficiencies when cycled in a large voltage window. Here, we use isothermal microcalorimetry (IMC) together with operando XRD as well as ex situ 7Li NMR and 57Fe Mossbauer spectroscopy to investigate the asymmetric reaction mechanism of the lithiation and delithiation of Zn0.9Fe0.1O during electrochemical cycling. We demonstrate that the measured heat flow is correlated with compositional changes of the electrode material. This combination of highly complementary techniques allows us to propose a new nucleation site model for the initial lithiation of Zn...