Structural, magnetic and electrochemical investigation of novel binary Na2−x(Fe1−yMny)P2O7 (0 ≤ y ≤ 1) pyrophosphate compounds for rechargeable sodium-ion batteries

Recent Progress in Electrode Materials for Sodium‐Ion Batteries

“…[ 201 ] Nonetheless, the solid-solution phases of Na 2-x (Fe 1-y Mn y )P 2 O 7 (0 ≤ y ≤ 1) introduced by Barpanda et al did not exhibit Mn 2+ /Mn 3+ redox activity in Na-ion cells. [ 204 ] Co-based orthorhombic Na 2 CoP 2 O 7 was also investigated as a [ 108 ] Copyright 2014, Nature Publishing Group. c) Galvanostatic charge/discharge profi les of Na 2 FeP 2 O 7 at C/20.…”

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

“…While the metal-polyanion framework is essentially equivalent for the two compositions, a major difference between the two compounds has been identified in the number and relative occupancy of the Na sites. In particular, in Na 2 FeP 2 O 7 six distinct Na sites are present, with five of them being partially occupied [14], while in Na 2 MnP 2 O 7 Na sites are characterized by full occupancy [12]. Such a structural difference may be among the causes at the basis of a different electrochemical activity for the two polymorphs.…”

“…Such materials are known to crystallize in different polymorphic forms and, depending on the metal ion and the synthetic conditions, triclinic, monoclinic, orthorhombic or tetragonal structures have been reported [8][9][10][11]. Na 2 FeP 2 O 7 and Na 2 MnP 2 O 7 can be considered isostructural, crystallizing in the P-1 space group at room temperature [12]. In particular, among the possible polymorphs reported in the literature, this structure seems to be the most likely for the Na 2 MnP 2 O 7 composition when prepared by solid-state reaction under reducing conditions [13].…”

Preparation, structure, surface and impedance analysis of Na2Zn0.5Mn0.5P2O7 ceramics

“…Sodium-based pyrophosphate compounds such as Na 2 MP 2 O 7 (M = Mn, Fe, Co, Zn) are presently under intensive investigation. The β-Na 2 MnP 2 O 7 polymorph [5,6] and NaFeP 2 O 7 [7][8][9][10] crystallize in the triclinic structure (space group P -1), Na 2 CoP 2 O 7 crystallizes in the orthorhombic space group Pna2 1 [11], and Na 2 ZnP 2 O 7 crystallizes in the tetragonal space group P4 2 /mmm [12]. Charge/discharge capacity and redox potential measurements of these compounds were performed [6,8,13,14].…”

“…The Na 2 FeP 2 O 7 cathode was found to be electrochemically active, delivering a reversible capacity of 82 mAh/g with the Fe 3+ /Fe 2+ redox potential around 3 V (vs Na/Na + ) [8]. Attempts to improve the electrochemical properties of materials involved various cationic substitutions in the pyrophosphates by synthesizing new compounds, namely Na 2 Fe 0.5 Mn 0.5 P 2 O 7 [4], Na 2-x (Fe 1-y Mn y )P 2 O 7 (0 ≤ y ≤ 1) [7], NaCsMnP 2 O 7 and NaCsMn 0.35 Cu 0.65 P 2 O 7 [5]. The charge/discharge measurements indicate that the substituted Na 2 Fe 0.5 Mn 0.5 P 2 O 7 is chemically active with a reversible capacity of ~80 mAh/g at the C/20 rate with an average redox potential of 3.2 V (vs Na/Na + ) [14].…”