Nanostructured LiMn₂O₄ composite as high-rate cathode for high performance aqueous Li-ion hybrid supercapacitors

Nanostructured spinel LiMn₂O₄ and super P composite with much enhanced electrochemical performance especially ultrahigh rate capability as the cathode for aqueous hybrid supercapacitors is synthesized by ball milling commercial LiMn₂O₄ particles together with super P. The as-prepared composite delivers a high capacitance of 306 F g⁻¹ at the current density of 1 A g⁻¹ and superb rate ability of 228.6 F g⁻¹ at 40 A g⁻¹ in 1 M Li₂SO₄ aqueous electrolyte. The capacitance of the nanostructured composite is 3.5 times higher than that of pristine LiMn₂O₄ even being charged and discharged 80 times faster. The excellent performances are ascribed to the nanosized LiMn₂O₄ well dispersed into the conductive carbon matrix. LiMn₂O₄ and super P composite//active carbon hybrid supercapacitor is assembled and the energy density can reach up to 21.58 Wh kg⁻¹ at 293.16 W kg⁻¹ and 13 Wh kg⁻¹ at 5200 W kg⁻¹. The hybrid device also shows an excellent cycling performance, which retains 85% of the initial capacitance after 4500 cycles. This work provides an effectively facile way to produce high performance LiMn₂O₄-based cathodes for hybrid suercapacitors in practical applications.