Pushing Theoretical Potassium Storage Limits of MXenes through Introducing New Carbon Active Sites

Surface-driven capacitive storage enhances rate performance and cyclability, thereby improving the efficacy of high-power electrode materials and fast-charging batteries. Conventional defect engineering, widely-employed capacitive storage optimization strategy, primarily focuses on the influence of defects themselves on capacitive behaviors. However, the role of local environment surrounding defects, which significantly affects surface properties, remains largely unexplored for lack of suitable material platform and has long been neglected. As proof-of-concept, typical Ti₃C₂T_x MXenes are chosen as model materials owing to metallic conductivity and tunable surface properties, satisfying the requirements for capacitive-type electrodes. Using density functional theory (DFT) calculations, the potential of MXenes with modulated local atomic environment is anticipated and introducing new carbon sites found near pores can activate electrochemically inert surface, attaining record theoretical potassium storage capacities of MXenes (291 mAh g^-1). This supposition is realized through atomic tailoring via chemical scissor within sublayers, exposing new sp³-hybridized carbon active sites. The resulting MXenes demonstrate unprecedented rate performance and cycling stability. Notably, MXenes with higher carbon exposure exhibit a record-breaking capacity over 200 mAh g^-1 and sustain a capacity retention higher than 80% after 20 months. These findings underscore the effectiveness of regulating defects' neighboring environment and illuminate future high-performance electrode design.