Electrochemical tailoring MXene terminal to elevate operation voltage of Mo₂CT_x-protected current collector over 5 V

Elevating operation voltage of lithium ion battery (LIB) is inevitably restricted by the corrosion of cathode aluminum (Al) current collector. In this report, MXene (Mo₂CT_x) is proposed as an artificial passivation layer on Al surface. To broaden the electrochemical stability of Mo₂CT_x, a mild tactic of potentiostatic polarization is applied to tailor Mo₂CT_x terminal at around 5.3 V vs. Li/Li⁺ for 60 s. After electrochemical tailoring, the -F terminal ratio is significantly increased. The obtained Mo₂CF_x exhibits uniform electrical conductivity similar to bare Al and outstanding antioxidation over 5 V vs. Li/Li⁺. As a consequence, when Mo₂CF_x is requisitioned to protect Al current collector, a high-voltage LIB equipped with LiCo_1/3Ni_1/3Mn_1/3O₂ (NMC333) in LiPF₆ electrolyte manifests an overall enhanced electrochemical performance under a high cut-off voltage of 4.6 V. The discharge capacity retention is increased from 7.0 % to 62.3 % after 500 cycles at 0.5C. And the rate performance at 3C is also improved by about 300 %. This work contributes to the surface engineering and application of MXene nanosheets, as well as provides an effective strategy for developing stable high-voltage LIBs.