Аннотация:Co-containing fluoride-phosphates are of interest in sense of delivering high electrode potentials and attractive specific energy values as positive electrode materials for rechargeable batteries. In this paper we report on a new Co-based fluoride-phosphate, LiNaCoPO4F, with a layered structure (2D), which was Rietveld-refined based on X-ray powder diffraction data [P21/c, a = 6.83881(4) Å, b = 11.23323(5) Å, c = 5.07654(2) Å, = 90.3517(5) °, V = 389.982(3) Å3] and validated by electron diffraction and high-resolution scanning transmission electron microscopy. The differential scanning calorimetry measurements revealed that 2D-LiNaCoPO4F forms in a narrow temperature range of 520–530 °C and irreversibly converts to the known 3D-LiNaCoPO4F modification (Pnma) above 530 °C. The noncarbon-coated 2D-LiNaCoPO4F shows reversible electrochemical activity in Li-ion cell in the potential range of 3.0–4.9 V vs. Li/Li+ with an average potential of ≈ 4.5 V and in Na-ion cell in the range of 3.0–4.5 V vs. Na/Na+ exhibiting a plateau profile centered around 4.2 V, in agreement with the calculated potentials by density functional theory. The energy barriers for both Li+ and Na+ migration in 2D-LiNaCoPO4F amount to 0.15 eV along the [001] direction rendering 2D-LiNaCoPO4F as a viable electrode material for high-power Li- and Na-ion rechargeable batteries. The discovery and stabilization of the 2D-LiNaCoPO4F polymorph indicates that temperature influence on the synthesis of A2MPO4F fluoride-phosphates needs more careful examination with perspective to unveil new structures.
