Ion-Defective High-Entropy NASICON Cathode Enabled by Multicomponent Substitution for Long-Life and Wide-Temperature Workability

An ion-defective high-entropy NASICON Na_3.15V_1.525(CrMgAlCuCo)_0.095(PO₄)₃ (HE-CMACC) cathode is ingeniously fabricated by introducing an appropriate amount of Na vacancies and various metal ions. Rate capability and sluggish diffusion kinetics are stimulated by ion defects and high-entropy doping. The HE-CMACC cathode material harvests sustainable long-term cycling durability. The HE-CMACC cathode retains a satisfactory capacity retention of 93.36% after 5000 cycles at 20 C, and it demonstrates excellent high-rate performance within the voltage window of 2-4.2 V (78 mAh g^-1 at 40 C). It also exhibits outstanding performance under extreme temperatures (85.76% after 1000 cycles at -20 °C and 87.01% after 850 cycles at 60 °C). Furthermore, in-situ relaxation time distribution (DRT) analysis proved that the high-entropy effect and Na vacancies can enhance electronic conductivity and promote ion diffusion. And in-situ X-ray Diffraction (XRD) results reveal that the fast sodium storage mechanism of HE-CMACC is dominated by solid solution reaction and a small volume strain (∼4.2%) during the process of electrochemical reaction. The full-cell HE-CMACC//HC assembled with hard carbon exhibits a discharge specific capacity of 87.18 mAh g^-1 at 20 C and a capacity retention rate of 93.25% after 400 cycles (at 5 C). The strategy of combining high-entropy effects with defect engineering provides important insights into the development of NASICON cathodes.