LiFeMnPO-on-MXene heterostructures as highly reversible cathode materials for Lithium-ion batteries.

Two-dimensional (2D) heterostructure materials, incorporating the collective strengths and synergetic properties of individual building blocks, have attracted great interest as a novel paradigm in electrode materials science. The family of 2D transition metal carbides and nitrides (e.g., MXenes) has become an appealing platform for fabricating functional materials with strong application performance. Herein, a 2D LiFeMnPO (LFMP)-on-MXene heterostructure composite is prepared through an electrostatic self-assembly procedure. The functional groups on the surface of MXenes possess highly electronegative properties that facilitate the incorporation of LFMPs into MXenes to construct heterostructure composites. The special heterostructure of nanosized-LiFeMnPO and MXene provides rapid Li and electron transport in the cathodes. This LiFeMnPO-3.0 wt% MXene composite can exhibit an excellent rate capability of 98.3 mAh g at 50C and a very stable cycling performance with a capacity retention of 94.3 % at 5C after 1000 cycles. Furthermore, NaFeMnPO-3.0 wt% MXene with stable cyclability can be obtained by an electrochemical conversion method with LiFeMnPO-3.0 wt% MXene. Ex-situ XRD suggests that LiFeMnPO-on-MXene achieves a highly reversible structural evolution with a solid solution phase transformation (LFMP→LiFeMnPO (LFMP), LFMP→LFMP) and a two-phase reaction (LFMP←→FeMnPO (FMP)). This work provides a new direction for the use of MXenes to fabricate 2D heterostructures for lithium-ion batteries.