Mechanisms and Performances of Na_1.5Fe_0.5Ti_1.5(PO₄)₃/C Composite as Electrode Material for Na-Ion Batteries

Abstract

The properties, insertion mechanisms, and electrochemical performances of the Na1.5Fe0.5Ti1.5(PO4)3/C composite as electrode material for Na-ion batteries are reported. The composite was obtained by solid-state reaction and consists of porous secondary particles of submicron-sized particles coated by carbon. Detailed characterizations were performed by combining theoretical and experimental tools. This includes the determination of the crystal structure of Na1.5Fe0.5Ti1.5(PO4)3 from both first-principles calculations and X-ray diffraction providing Na distribution over M1 and M2 interstitial sites, which is of importance for ionic conductivity. Na1.5Fe0.5Ti1.5(PO4)3/C was used as an electrode material at 2.2 V versus Na+/Na0, exhibiting good Na-storage ability with a specific capacity of 125 mAh g–1, close to the theoretical value, for the first discharge at C/10, good capacity retention, and Coulombic efficiency of 95% and 99.5% at the 60th cycle, respectively, and high power rate with a decrease of the specific capacity of only 14% from C/10 to 2C. These good performances have been related to the morphology of the composite and the substitution of Fe for Ti, leading to an insertion mechanism that differs from that of NaTi2(PO4)3. This mechanism was quantitatively analyzed from operando 57Fe Mössbauer spectroscopy used for the first time in both galvanostatic and GITT modes.

An Aqueous Symmetric Sodium‐Ion Battery with NASICON‐Structured Na3MnTi(PO4)3

“…Recently, a number of transition metal oxides, Prussian blue analogues, and polyanionic frameworks have demonstrated stable sodium storage performance in aqueous electrolytes . Particular interests have also been focused on sodium storage in NASICON (Na Super Ionic Conductors)‐type compounds because of their structural stability, their large ionic channels, and the abundance of sodium‐insertion sites . The NASICON‐structured materials with the formula unit of A x M y (XO 4 ) 3 , where A, M and X are alkali metal, transition metal and nonmetal atoms, respectively, can be described as three‐dimensional polyanionic frameworks of corner sharing MO 6 octahedra and XO 4 tetrahedra with interconnected channels for the diffusion of alkali ions .…”

F-Doped NaTi2(PO4)3/C Nanocomposite as a High-Performance Anode for Sodium-Ion Batteries

“…There have been attempts to enhance the electrochemical properties of NTP by reducing particle size and combining it with the conductive network, but it is rare to improve the properties of NTP by doping. − It is well-known that doping effectively improves the intrinsic properties of electrochemical-active materials. − Lippens et al. reported Na 1.5 Fe 0.5 Ti 1.5 (PO 4 ) 3 /C composite with a steady specific capacity of 120 mA h g –1 at a current density of C/10, and the reversible capacity at 5 C is 91 mA h g –1 . In addition, anion doping is a flexible choice to improve kinetics and structural stability.…”

An Aqueous Symmetric Sodium‐Ion Battery with NASICON‐Structured Na3MnTi(PO4)3

“…[20][21][22][23][24] Particular interests have also been focused on sodium storage in NASICON (Na Super Ionic Conductors)-type compounds because of their structural stability, their large ionic channels,a nd the abundance of sodiuminsertion sites. [25][26][27] TheN ASICON-structured materials with the formula unit of A x M y (XO 4 ) 3 ,where A, Mand Xare alkali metal, transition metal and nonmetal atoms,respectively,can be described as three-dimensional polyanionic frameworks of corner sharing MO 6 octahedra and XO 4 tetrahedra with interconnected channels for the diffusion of alkali ions. [28,29] Ther edox potentials of NASICON-structured materials can be tuned by changing the elemental composition and/or the valence states of the transition metal ions.…”