<p>Ideally, wearable electronic devices should be paired with high-capacity flexible batteries to improve user comfort and increase usage time per charge. In this report, membrane electrodes consisting of pliable polymers, antimony oxide (Sb₂O₃) nanobelts and carbon nanotubes (CNTs) were prepared using a scalable phase inversion method without post-pyrolysis treatment for high-capacity flexible lithium-ion battery (LIB) anode. The unique asymmetric porous structure can effectively accommodate the large volume expansion of Sb₂O₃ based alloy anodes during lithiation and de-lithiation, resulting in excellent structural and electrochemical stability. 80% capacity of 650 mAh g⁻¹ for the flexible membrane electrode can be retained after 50 cycles at 136&#xa0;mA&#xa0;g⁻¹ as compared to 80% capacity loss of 400 mAh g⁻¹ for the control, thin film electrode. The electrochemical properties of membrane electrodes are related to polymer concentrations and substrates. Furthermore, membrane electrodes can maintain structural integrity even after 5,000 cycles of fatigue testing.</p> Graphical abstract <p></p>