Low-Pressure Argon/Hydrogen/Oxygen Plasma Treatment on LiMn₂O₄ Li-Ion Hybrid Supercapacitors

LiCl + Mn(NO 3 ) 2 ·4H 2 O pastes are screen-printed on a carbon cloth substrate and then calcined at 400 °C for 6 h in a tube furnace to convert them into LiMn 2 O 4 . Ar, Ar+5%H 2 , or Ar+5%O 2 low-pressure plasma is then used to treat the LiMn 2 O 4 /carbon cloth. The treated LiMn 2 O 4 /carbon cloth is then used as the electrode for a Li-ion hybrid supercapacitors (Li-HSCs) with a three-electrode configuration in 1-M Li 2 SO 4 liquid electrolyte. Ag/AgCl and Pt electrodes were used as reference and counter electrodes, respectively. Li-HSCs are characterized by galvanostatic charging/discharging, cyclic voltammetry, and electrochemical impedance spectroscopy. The results indicate that plasma treatment improves the Li-HSCs performance. In particular, Ar+5%O 2 plasma treatment increases the areal capacity by ∼24% to 23.12 μ A h cm −2 . It also improves the coulomb efficiency and capacity retention rate of LiMn 2 O 4 Li-HSCs.