Designing a 3D framework NaVOPO4 as a high-power, low-strain and long-life positive electrode material for Na-ion batteries

S Shraer, A Dembitskiy, I Trussov, A Komayko, D Aksyonov, N Luchinin, A Morozov, S Pollastri, G Aquilanti, S Ryazantsev, V Nikitina, A Abakumov, E Antipov, S Fedotov
In this paper, we offer a new NaVOPO4 polymorph adopting a KTiOPO4-type framework as a promising high-rate, low-strain and long-life positive electrode material for sodium-ion batteries. A carbon-coated NaVOPO4 demonstrates a specific capacity of ∼110 mAh g–1 at a C/10 rate at an average potential of ∼3.93 V vs. Na+/Na. The material maintains over 74 % of the initial capacity after 1000 cycles at a C/2 rate and around 87% at a 2C charge/discharge rate. Diffusion coefficients of 10–11 cm2 s–1 and DFT-calculated energy barriers of ∼0.15–0.35 eV indicate fast Na+ ion diffusion. Moreover, the operando XRD analysis coupled with DFT elucidates several phase transitions with a low volume variation of 2.4% in total, highlighting the reversibility and structural stability during Na+ de/insertion. Overall, NaVOPO4 exhibits attractive electrochemical performance and stability, making it a potential candidate for sodium-ion battery cathode materials.