The need for alternative anode materials for lithium-ion batteries (LIBs) is one of the decisive steps towards the electrification of our public and private transportation, since the state-of-the-art anode material graphite intrinsically limits the energy and power density of current LIBs.1,2 As a potential alternative, alloying metal-oxides such as ZnO and SnO2 have been widely studied, mostly due to their high theoretical specific capacities of 988 mAh g-1 and 1494 mAh g-1, respectively. Nevertheless, the pure oxides reveal poor electrochemical performance as a result of the eventually irreversible formation of the Li2O matrix and the pronounced volume variation, causing active material exfoliation.3–5 When doped with transition metals, however, the Li2O formation turns very reversible and the theoretically possible capacities can be achieved.6–9 As an example, Co-doped ZnO offers substantially higher specific capacities than pure ZnO (i.e., 966 mAh g-1 vs 330 mAh g-1). Recently, the class of TM-doped alloying metal oxides has been extended to Fe-doped GeO2, offering even higher specific capacities than transition metal doped SnO2 (theoretically 2152 mAh g-1).10 Within this study we enlighten the beneficial effects of iron doping on the structural evolution and electrochemical performance of GeO2. For this purpose, we combined a series of highly complementary in situ/operando techniques, including in situ high temperature XRD, operando dilatometry, and operando XRD. The results shed light on a commonly overlooked impact factor for the electrochemical performance of such materials and, in fact, metal oxides in general. 1. D. Bresser et al., J. Power Sources, 382, 176–178 (2018).2. Y. Yamada, Y. Iriyama, T. Abe, and Z. Ogumi, Langmuir, 25, 12766–12770 (2009).3. I. A. Courtney and J. R. Dahn, J. Electrochem. Soc., 144, 2045–2052 (1997).4. I. A. Courtney, W. R. Mckinnon, and J. R. Dahn, J. Electrochem. Soc., 146, 59–68 (1999).5. F. Mueller, D. Geiger, U. Kaiser, S. Passerini, and D. Bresser, ChemElectroChem, 3, 1311–1319 (2016).6. D. Bresser, S. Passerini, and B. Scrosati, Energy Environ. Sci., 9, 3348–3367 (2016).7. G. Giuli et al., Inorg. Chem., 54, 9393–9400 (2015).8. G. Giuli et al., Materials, 11, 49 (2017).9. Y. Ma et al., Sustain. Energy Fuels, 2, 2601–2608 (2018).10. J. Wu, N. Luo, S. Huang, W. Yang, and M. Wei, J. Mater. Chem. A, 7, 4574–4580 (2019).