Towards improved P2-type Na0.67Ni0.5 Mn0.5O2 with fast Na ion diffusion via a metal organic framework coating for sodium ion batteries

P 2- Na 0.67 Ni 0.5 Mn 0.5 O 2 (NNM), as a cathode material for sodium-ion batteries (SIBs), has a high specific capacity and electrochemical performance. However, it suffers from crystal structure changes and large polarization of Mn3+/Mn4+ after many cycles. Two-dimensional copper-benzoquinone (Cu-THQ) organometallic framework cathode material is synthesized for the first time by using low-cost tetrahydroxybenzoquinone disodium salt. Due to the Cu-THQ, Cu-THQ@NNM exhibits a specific capacity of 118.4 mAh g- 1 after 100 cycles at 1C with a high retention of 96.9 %. In addition, the Cu-THQ@NNM demonstrates excellent rate performance up to 64 mAh g- 1 at 10C with a high retention of 81 % after 200 cycles, which is higher than that of the NNM cathode (52.9 %). Molecular dynamics simulations were performed to calculate the Mean square displacements (MSDs) of Na ion in bulk NNM and Cu-THQ@NNM heterojunction and demonstrate that the Cu-THQ can effectively enhance the sodium ion transport capacity on the surface of NNM, thereby facilitating the enhancement of sodium ion diffusion kinetics. Additionally, in-situ X-ray powder diffraction revealed that the Cu-THQ layer effectively mitigated lattice stress during cycling and inhibited undesirable side effects and structural phase transitions. This work offers an effective method for preparing high-performance cathode materials for SIBs by coating highly active organometallic framework materials.