*2.5. Electrochemical Measurements*

The as-prepared FexOy/MnO2/HCS nanomaterials were used as electrode materials for LIBs. To prepare the working electrode, active materials, acetylene black (C-NERGY™ SUPER C65, Timcal, Congleton, UK) and PVDF (Solvay Plastics, Warszawa, Poland) were mixed in a weight ratio of 85:10:5. Subsequently, N-methyl-pyrrolidone (NMP, CHEMPUR, Piekary Slaskie, Poland) was added to the powder to form a slurry. The working electrodes were fabricated by coating the slurry onto copper foam (Sigma-Aldrich, Beijing, China) and dried in a vacuum at 80 ◦C overnight. The testing coin cells were assembled with the working electrode, metallic lithium foil (Sigma-Aldrich, Beijing, China) as a counter electrode, NKK TK4350 film as a separator (Sigma-Aldrich, Beijing, China) and 200 μL LiPF6 in 1:1 ethylene carbonate (EC)/dimethyl carbonate (DMC) as the electrolyte (Sigma-Aldrich, Beijing, China). The assembly of the cells was carried out in an argon-filled glovebox (M. Braun Co., Garching, Germany). Electrochemical studies by means of cyclic voltammetry (CV) and galvanostatic cycling with potential limitation (GCPL) were performed. The measurements were executed on a VMP3 multichannel potentiostat (BioLogic, Seyssient-Pariset, France) at room temperature.
