Nano self-assembly of fluorophosphate cathode induced by surface energy evolution towards high-rate and stable sodium-ion batteries

In the field of materials science and engineering, controlling over shape and crystal orientation remains a tremendous challenge. Herein, we realize a nano self-assembly morphology adjustment of Na3V2(PO4)(2)F-3 (NVPF) material, based on surface energy evolution by partially replacing V3+ with aliovalent Mn2+. Crystal growth direction and surface energy evolution, main factors in inducing the nano self-assembly of NVPF with different shapes and sizes, are revealed by high-resolution transmission electron microscope combined with density functional theory. Furthermore, NVPF with a two-dimensional nanosheet structure (NVPF-NS) exhibits the best rate capability with 68 mAh-g(-1 )of specific capacity at an ultrahigh rate of 20 C and cycle stability with 80.7% of capacity retention over 1,000 cycles at 1 C. More significantly, when matched with Se@reduced graphene oxide (rGO) anode, NVPF-NS//Se@rGO sodium-ion full cells display a remarkable long-term stability with a high capacity retention of 93.8% after 500 cycles at 0.5 C and -25 degrees C. Consequently, experimental and theoretical calculation results manifest that NVPF-NS demonstrates such superior performances, which can be mainly due to its inherent crystal structure and preferential orientation growth of {001} facets. This work will promise insights into developing novel architectural design strategies for high-performance cathode materials in advanced sodium-ion batteries.

Automated summary

In this study, the challenge of controlling the shape and crystal orientation of materials is explored in the field of materials science and engineering. Through the partial replacement of metal ions, a nano self-assembly morphology adjustment is achieved. The experimental results demonstrate that the nanostructured material exhibits superior battery performance and stability, which is attributed to its inherent crystal structure and preferential orientation growth.