Construction of a bi-continuous charge transport network towards high-performance vanadium-based phosphate cathode materials for potassium ion batteries

As one class of most promising cathode materials for potassium ion batteries (KIBs), polyanionic compounds still suffer from unsatisfactory effective capacity and rate performance due to their poor intrinsic electronic conductivity. In this paper, nanoscale K3V3(PO4)4 (KVP) particles with a bi-continuous charge transport network (denote as KVP-S) are designed and prepared. Carbon nanotubes (CNTs) play a crucial role in this design, not only effectively inhibiting the aggregation and growth of particles, but also providing a three-dimensional (3D) electron conductive network. Benefiting from the advantages of nanoscale particle size and bi-continuous charge transport network, the KVP-S electrode exhibits a high capacity (118mAh g-1 at 20 mA g-1), outstanding rate performance (102 mAh g-1 at 0.5 C; 66 mAh g-1 at 5 C) and excellent cycling stability (94% retention after 50 cycles at 1 C). Even at a higher rate of 5 C, it still maintains a high capacity retention of 92% after 300 cycles. More importantly, the capacity can maintain 80 mAh g-1 at 1 C when the mass loading is extended to 4 mg cm-2, In addition, in situ X-ray diffraction (XRD) and ex situ (X-ray photoelectron spectroscopy) XPS analyses reveal that the potassium storage mechanism of KVP-S is two single-phase solid solution reactions, involving V2+/V3+/V4+ three-electron redox conversions with a total volume change of 5.5%. This study provides a new way to rationally design nanoscale particle electrodes with highly conductive charge transport networks.