Multi-layered MXene V4C3T as new low-voltage insertion anode for Na-ion battery applications

We report an MXene V4C3Tx new low-voltage insertion anode and a comparison of the electrochemical performance with ester and ether-based electrolytes in half– and full–cell configuration with Na3V2(PO4)3@C (NVPC). Though MXene has been explored for Na-ion batteries (SIB), Mn+1XnTx with n = 3 has been hardly explored. Moreover, the ether-based electrolyte has not been used with any MXenes for electrochemical energy storage, especially in the SIB perspective. The initial irreversibility in the carbonate-based half–cell (V4C3Tx–C) is 128 mAh g−1 more than the tetraglyme–based half–cell (V4C3Tx–T). After 100 cycles, V4C3Tx–T maintains 84 mAh g−1, while V4C3Tx–C shows only 60 mAh g−1, which shows the better retention ability in the ether-based system. As for the rate performance, though V4C3Tx–T has a higher capacity in low currents, at higher currents, V4C3Tx–C shows higher values. This showed that the carbonate-based system has diffusion and capacitive-based Na–ion storage, which enabled it to have a high–rate performance. An extensive in–situ impedance study revealed significant formation of the passivation layer in V4C3Tx–C by irreversibly consuming Na–ions, which causes an increased initial Coulombic inefficiency, whereas no such significant SEI layer formation is evident for V4C3Tx–T. Full–cells were assembled with NVPC cathode in tetraglyme and carbonate-based electrolytes. The full–cell with ether electrolyte exhibited enhanced capacity, capacity retention, and rate performance compared to ester-based electrolytes. The full-cell displayed an energy density of ∼66 and ∼74 Wh kg−1 for tetraglyme and ester-based electrolytes, respectively.