New insights into carbon-based and MXene anodes for Na and K-ion storage: A review

Na-ion batteries and K-ion batteries are promising alternatives to vastly used lithium-ion batteries mainly due to the larger natural abundance of sodium and potassium resources. Carbon-based and MXene materials have received increasing attention due to their unique layered structure to accommodate the larger sodium and potassium ions. It’s proposed that ionic size disparity (K+: 1.38 Å; Na+: 0.97 Å; Li+: 0.76 Å) leads to sluggish intercalation and extraction kinetics in larger alkali metal ions (AMIs). Nevertheless, the electrochemical inactivity of sodium intercalation in graphite suggests that different chemical properties of AMs and their interactions with carbon host and electrolytes is crucial for interfacial instability and irreversible capacity loss. Structural modifications by expanding interlayer spacing and defect engineering enable reduced diffusion barriers and enhanced insertion of sodium or potassium, but it blurs the electrochemical performance between battery and capacitor. This review provides insight into 2D carbon materials and their architectures for Na and K-ion batteries through an in-depth analysis of structure–property interdependence and different electrochemical mechanisms supported by both experimental and theoretical data to discuss the promises and challenges of post-lithium batteries. Finally, the perspectives and potential directions regarding material design concepts for 2D carbon-based nanomaterials and MXene phases for metal-ion storage are proposed.