High-performance and low-cost manganese oxide/multiwalled carbon nanotubes composite as cathode material for aqueous magnesium ion battery

• The λ-MnO 2 /MWCNTs composite was synthesized with feasible solution method and applied as cathode in aqueous magnesium ion battery for the first time. • The λ-MnO 2 particles are distributed in MWCNTs network structure, which increased the specific surface area and conductivity of electrode material. • The λ-MnO 2 /MWCNTs composite showed good electrochemical performances in three electrode and MnO 2 /MWCNTs//AC full cell systems. • The mechanism of magnesium ion insertion/deinsertion in λ-MnO 2 /MWCNTs electrode was investigated in this paper. The aqueous magnesium ion batteries (AMIBs) with the advantages of low cost, intrinsical safety and environmentally friendly have received worldwide attention as promising candidates for green energy storage system. Herein, we report a composite material engineered from λ-MnO 2 particles and multiwalled carbon nanotubes (MWCNTs) as cathode for AMIB. The λ-MnO 2 possesses a spinel-type crystalline structure, which is beneficial for the insertion/deinsertion of Mg 2+ ions. The MWCNTs network shorts ionic diffusion distance and increases the interface of electrode material/electrolyte. Hence, the λ-MnO 2 /MWCNTs composite demonstrates a large capacity of 251 mAh g −1 at 50 mA g −1 in 0.5 M MgCl 2 solution, and high capacity retention of 86.2 % after 1000 cycles at 1000 mA g −1 in MgSO 4 solution. Furthermore, the λ-MnO 2 /MWCNTs//AC system is firstly assembled as full AMIB, which delivers a specific capacity of 84.8 mAh g −1 at 100 mA g −1 . The rate capability test is performed at 300 mA g −1 . This system displays a gradually rise tendency in the specific capacity at initial 100 cycles on account of the activation process. After 1000 cycles, the specific capacity is 56.9 mAh g −1 . This work develops an easily prepared, low-cost and good performance electrode material for AMIB system.