This disclosure relates to a methane-assisted metal ion battery. The methane-assisted metal ion battery includes an electrolyte including a salt of a metal in aqueous state. The metal is selected from an alkali metal, an alkali earth metal, a transition metal, or a combination thereof. The methane-assisted metal ion battery further includes a positive electrode including a compound of the metal. The positive electrode is in contact with the electrolyte. The methane-assisted metal ion battery further includes a negative electrode electrically coupled to the positive electrode. The negative electrode includes an electrocatalyst and is configured to reduce atmospheric methane to generate carbon nanoparticles and hydrogen molecules (H2) when the battery is charging and to oxidize hydrogen molecules (H2) to generate hydrogen ions (H+) and free electrons when the battery is discharging. The methane-assisted metal ion battery further includes a separator including a permeable membrane.