High-Capacity NASICON-Type Na₃V_1.8Cr_0.2(PO₄)₃ Cathode for High-Performance Sodium-Ion Batteries

Na₃V₂(PO₄)₃ (NVP) has been deemed a promising cathode material for sodium-ion batteries (SIBs). However, the low sodium-ion diffusion kinetics and inferior electronic conductivity of NVP are two major bottlenecks facing its practical application. Realizing multielectron redox reactions in NVP by a doping strategy is very efficient to enhance electronic conductivity and specific capacity, as well as ensuring structural stability of NVP. In this work, Cr-doped NVP, Na₃V_2-xCr_x(PO₄)₃ (0 ≤ x ≤ 0.6), is prepared by a sol-gel method, and its electrochemical performance is fully investigated. The optimized Cr-doping content is x = 0.2, and the V⁴⁺/V⁵⁺ redox couple is activated under higher voltage by Cr doping, which results in the Na₃V_1.8Cr_0.2(PO₄)₃ (NVCP-2) cathode delivering a high reversible capacity of 221.6 mAh g^-1 at 0.1 C and high-rate capability with a reversible capacity of 120.0 mAh g^-1 at 20 C in 1.0-4.3 V. Moreover, the NVCP-2 also shows an improved discharge capacity of 103.6 mAh g^-1 at 0.1 C and cycling stability compared with bare NVP in 2.4-4.3 V. Furthermore, the NVCP-2 cathode also exhibits excellent electrochemical performance in a NVCP-2||Na₃Zr₂Si₂PO₁₂||Na solid-state battery. This work demonstrates that the NVCP-2 cathode has substantial potential for application in high-performance SIBs.