Electrochemical Study of Na2Fe1−xMnxP2O7 (x = 0, 0.25, 0.5, 0.75, 1) as Cathode Material for Rechargeable Na-Ion Batteries

Abstract

Sodium-ion batteries (SIBs) are considered a good choice for post-lithium devices. Transition metal sodium pyrophosphates are among the most interesting cathode materials for SIBs. Here we study the electrochemical properties of the system Na 2 Fe 1´x Mn x P 2 O 7 (x = 0, 0.25, 0.5, 0.75, 1). By means of cyclic voltammetry (CV) and galvanostatic experiments, we confirm that pure Fe and Fe-rich compounds are promising for application in sodium batteries, whereas Mn-rich samples are less satisfactory, at least in case of solid-state reaction recipes and standard slurry preparations. Proper carbon coating is likely needed to improve the electrochemical behavior of Mn-rich samples.

Unique crystallization behavior of sodium manganese pyrophosphate Na2MnP2O7 glass and its electrochemical properties

“…Barpanda et al reported electrochemical properties of ␤-Na 2 MnP 2 O 7 which is same as the structure of Na 2 FeP 2 O 7 , as 3.6 V (Mn 2+ /Mn 3+ vs sodium anode) for 80 mAh/g [22]. The other groups also reported electrochemical properties in ␤-Na 2 MnP 2 O 7 [24][25][26][27][28] . On the other hand, some literatures are suggesting that ␤-Na 2 MnP 2 O 7 is electrochemically inactive rather than Na 2 FeP 2 O 7 [24,26] [22] Triclinic (P1) Three dimensional Octahedra 3.6 80 Na2CoP2O7 [4] Orthorhombic (Pna21) Layered Melilite tetrahedra 3.0 80 ing reagent.…”

Polymorphism in Na2(Co/Zn)P2O7 and Na2(Co/Fe)P2O7 Pyrophosphates: A Combined Diffraction and 31P NMR Study

“…This 3D open network presents 1D channels along different directions ([100], [−100], and [01–1]), where the Na ions are allocated and where they can diffuse, as reported in Figure g,h. This phase was observed for the systems containing Co, Fe, and Mn. ,,, All the described structures present 1D, 2D, or 3D pathways for the diffusion of Na ions, so making the whole class of compounds highly favorable for application in batteries.…”

“…The powder samples of the series of mixed-metal compounds Na 2 MP 2 O 7 were prepared by the traditional solid-state route ,− starting from stoichiometric amounts of Fe­(C 2 O 4 )*2H 2 O (Aldrich, 99%), Co­(C 2 O 4 )*2H 2 O (Aldrich, 99%), ZnO (Aldrich, >99%), NaH 2 PO 4 (Aldrich, 98%). The reagents were accurately mixed in acetone and the obtained mixture was then heated at 300 °C for 2 h to eliminate the organic components.…”

“…Several polymorphs were found for different compositions, and more phases can be stabilized for a given composition by playing on the synthesis route and thermal treatments. ,− Since different structures can lead to different electrochemical responses, one of the main strategies to further improve the performance of the pyrophosphate family in the last years has been the introduction of mixed compositions of the general formula Na 2 M 1– x M’ x P 2 O 7 , which can combine the electrochemical properties related to particular M/M’ couples and the stabilization of different polymorphs. Some recent works presented the structural and electrochemical investigation of the solid solution Na 2 (Fe/Mn)­P 2 O 7 series. , Several compositions related to the general formula Na 2 MP 2 O 7 with a wide range of M ions were already described and different structures reported in the literature, including tetragonal, orthorhombic, and triclinic crystal systems. − ,,, …”

The influence of P/As substitution in the melilite-like Na2Co(P2–xAsx)O7(x= 0.40 and 0.93) solid solutions

“…The study of energy storage and the development of highperformance rechargeable alkali-ion batteries currently progress by the synthesis of new materials in the solid state by chemists and by combined experimental and theoretical studies of cation conduction in the crystal frameworks. In this context, diphosphates with the formula A 2 MP 2 O 7 (A + is an alkaline cation and M 2+ is a divalent cation) are a class of materials with interesting structural features and promising electrochemical performances (Erragh et al, 1991(Erragh et al, , 1998Sanz et al, 1999;Dridi et al, 2001;Shakoor et al, 2015;Tealdi et al, 2016).…”