Understanding the Effect of Interplanar Space and Preintercalated Cations of Vanadate Cathode Materials on Potassium-Ion Battery Performance.

Nonaqueous potassium-ion batteries (KIBs) have been regarded as a promising alternative energy system to lithium-ion batteries, due to the abundance of the K resource and unique electrochemical properties. However, exploring suitable KIB cathode materials remains a great challenge, owing to the much larger size of the K ion than that of the Li ion. Here, a series of layered vanadates have been developed as cathodes for KIBs to elucidate the key factors that determine the electrochemical performance of KIBs, including the interlayer distance between adjacent (100) planes ( d ₁₀₀ ) and preintercalated cations. Compared to NH ₄ V ₃ O ₈ nanowires with a d ₁₀₀ of 7.80 Å, (NH ₄ ) _0.5 V ₂ O ₅ nanowires with a wider d ₁₀₀ of 9.52 Å show a faster K ⁺ diffusion and much higher reversible capacity. The preintercalation of potassium ions into V-O slabs is also crucial to the stability of the structure of vanadates, which leads to better electrochemical cycling stability in K _0.5 V ₂ O ₅ than that in (NH ₄ ) _0.5 V ₂ O ₅ and NH ₄ V ₃ O ₈ nanowires. These findings reveal the great potential of the vanadate cathode in future KIBs and provide a new direction to rationally design a stable layered intercalation compound for practical KIBs.