Synergistic Effect of Anionic-Tuning and Architecture Engineering in BiPO4@C Anode for Durable and Fast Potassium Storage

Bismuth-based materials that adhere to the alloy/dealloy reaction mechanism are regarded as highly promising anode materials for potassium-ion batteries due to their high volume-specific capacity and moderate reaction potentials. However, their commercial viability has been limited by the effects of structural collapse due to volume distortion and impeded electron conduction, resulting in rapid capacity decline. In this work, a carbon-coated nanosized BiPO₄ rod (BiPO₄@C) was designed and fabricated to overcome the aforementioned challenges through the architecture engineering and anionic-tuning strategy. In particular, the nanosized nanorods significantly reduce the volume expansion; the incorporation of the bulk and open-skeleton anion PO₄^3- serves to mitigate the considerable volume distortion and generates the high ionic conductivity product (K₃PO₄) to ameliorate the poor ionic transport due to the structural deformation. The elaborated BiPO₄ rods exhibit high specific capacity (310.3 mAh g^-1, at 500 mA g^-1), excellent cycling stability (over 700 cycles at 500 mA g^-1) and superior rate performance (137.8 mAh g^-1, at 1000 mA g^-1). Systematic ex-situ XRD and TEM, as well as kinetic tests, have revealed the "conversion-multistep alloying" reaction process and the "battery-capacitance dual-mode" potassium storage mechanism. Moreover, the thick electrodes showed excellent specific capacity and rate performance, demonstrating their significant application potential in the next generation of SIBs.