Multi-layered MXene V4C3Tx as new low-voltage insertion anode for Na-ion battery applications

We report an MXene V 4 C 3 T x 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 Na 3 V 2 (PO 4 ) 3 @C (NVPC). Though MXene has been explored for Na-ion batteries (SIB), M n +1 X n T x 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 (V 4 C 3 T x –C) is 128 mAh g −1 more than the tetraglyme–based half–cell (V 4 C 3 T x –T). After 100 cycles, V 4 C 3 T x –T maintains 84 mAh g −1 , while V 4 C 3 T x –C shows only 60 mAh g −1 , which shows the better retention ability in the ether-based system. As for the rate performance, though V 4 C 3 T x –T has a higher capacity in low currents, at higher currents, V 4 C 3 T x –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 V 4 C 3 T x –C by irreversibly consuming Na–ions, which causes an increased initial Coulombic inefficiency, whereas no such significant SEI layer formation is evident for V 4 C 3 T x –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.