One-step multiple structure modulations on sodium vanadyl phosphate@carbon towards ultra-stable high rate sodium storage

Abstract

• A template-assisted sol–gel strategy is proposed for multi-structure engineering of NVP@C cathode material. • Simultaneous realizations of pore constructing, nanosizing and carbon compositing can be achieved in one step. • Pore structure of NVP@C can be tuned by adjusting the diameter of PS nanospheres. • A novel mesoporous-macroporous structure can be realized due to the demulsification of PS emulsion. • The mesoporous-macroporous NVP@C exhibits extraordinary rate capability and cycling stability at high rate. Na 3 V 2 (PO 4 ) 3 (NVP) is recognized as a promising sodium ion battery (SIB) cathode material due to its high working potential and robust three-dimensional framework. However, the poor intrinsic electronic conductivity and huge volume change during sodium ion insertion/desertion process hinder its further applications, which makes its structure modulations highly desirable. Herein, a facile template-assisted sol–gel strategy is developed to realize multiple structure modulations of NVP@C in one-step. With citric acid as chelating agent and polystyrene (PS) nanospheres as template, the realization of nanosizing NVP particles, hybridizing NVP particle with carbon material and constructing pore structure on NVP@C can be facially achieved. More importantly, the pore structure can be tuned by the diameter of used PS nanospheres. When the diameter of PS nanospheres is down to 70 nm, the corresponding 70-PS NVP possesses a hierarchically mesoporous-macroporous structure due to the demulsification effect, which can shorten the ion diffusion pathway, increase the contact surface area between the electrolyte and active material, improve the diffusion kinetics and buffer the volume change. Benefiting from the above superiority, the sample exhibits an extraordinary rate capability and a prominent cycling stability at high rate (104 mAh g −1 after 5000 cycles at 50C), which surpass most of the recently reported SIB cathode materials. This work opens a facile revenue for boosting the electrochemical performance of electrode materials through characteristic pore construction, nanosizing and integration with carbonaceous materials.