Oxygen-Deficient α-MnO 2 Nanotube/Graphene/N, P Codoped Porous Carbon Composite Cathode To Achieve High-Performing Zinc-Ion Batteries.

A major drawback of α-MnO 2 -based zinc-ion batteries (ZIBs) is the poor rate performance and short cycle life. Herein, an oxygen-deficient α-MnO 2 nanotube (V O -α-MnO 2 )-integrated graphene (G) and N, P codoped cross-linked porous carbon nanosheet (CNPK) composite (V O -α-MnO 2 /CNPK/G) has been prepared for advanced ZIBs. The introduction of V O in MnO 2 can decrease the value of the Gibbs free energy of Zn 2+ adsorption near V O (ca. -0.73 eV) to the thermal neutral value. The thermal neutral value demonstrates that the Zn 2+ adsorption/desorption process on V O -α-MnO 2 is more reversible than that on α-MnO 2 . The as-made Zn/V O -α-MnO 2 battery is able to deliver a large capacity of 305.0 mAh g -1 and high energy density up to 408.5 Wh kg -1 . The good energy storage properties can be attributed to V O . Additionally, the V O -α-MnO 2 /CNPK/G composite possesses the structure of nanotube arrays, which results from the vertical growth of α-MnO 2 nanotubes on CNPK. This unique array structure helps to realize fast ion/electron transfer and stable microstructure. The electrochemical performance of V O -α-MnO 2 has been comprehensively improved by compositing with G and CNPK. The V O -α-MnO 2 /CNPK/G can achieve capacity up to 405.2 mAh g -1 , energy density of 542.2 Wh kg -1 , and long cycle life (80% capacity retention after 2000 cycles).