Communication—O3-Type Layered Oxide with a Quaternary Transition Metal Composition for Na-Ion Battery Cathodes: NaTi_0.25Fe_0.25Co_0.25Ni_0.25O₂

Abstract

NaTi 0.25 Fe 0.25 Co 0.25 Ni 0.25 O 2 is explored as a cathode material for Na-ion batteries. Synthesized by a solid-state reaction, the compound is phase-pure with the O3-type layered structure and consists of Ti 4+ , Fe 3+ , Co 3+ , and Ni 2+ according to X-ray absorption spectroscopy. The cathode delivers 163 mAh/g and 504 Wh/kg at C/20 in the first discharge with 89% capacity retention after 20 cycles and demonstrates superior rate capability with micron sized particles, in which discharge capacity at 30 C is 80 mAh/g. Our results indicate that the Ti-containing quaternary material can be a potential cathode composition for Na-ion batteries. Rechargeable batteries that reversibly cycle Na ions are a costeffective alternative to the Li-based technology to meet increasing demand and need for grid-level energy storage.1 Unlike Li cathode chemistries that heavily rely on Co and Ni, Na-intercalating oxides tend to form energy-dense layered structures with almost all transition metals including Cu, 2-4 allowing a broad selection and combination of redox centers to tune electrochemical properties and air-stability. In particular, Fe is an attractive metal due to its high redox potential and natural abundance.5 However, the performance of layered NaFeO 2 as a cathode is impractical; Fe 4+ migration upon desodiation destabilizes the structure, leading to poor Na ion mobility and irreversibility. 6 The charged state stability of the layered structure, and thereby their electrochemical properties, 7 can be enhanced by partially substituting Fe into redox-inactive elements and/or other transition metals.8-11 Li et al. proposed an optimal Fe content (< ∼33%) that promotes Na diffusion at the high state of charge.12,13 Here, we use Ti 4+ as a structural stabilizer and report an O3-type 14 Na transition metal oxide (O3-NaMO 2 ) composition, NaTi 0.25 Fe 0.25 Co 0.25 Ni 0.25 O 2 (TFCN), for the optimized Fe redox activity. Our results demonstrate a substantial amount of reversible Na intercalation and high rate capability of TFCN, implying that the material may be successfully used as a Na-ion battery cathode. MethodsA stoichiometric amount of transition metal precursors (TiO 2 , Fe 2 O 3 , Co 3 O 4 , and NiCO 3 , all from Sigma-Aldrich) were mixed with 20% excess Na 2 O (Sigma-Aldrich) by planetary ballmilling at 500 rpm for 4 hours. The resulting mixture was fired at 900• C for 12 hours under flowing O 2 , quenched to room temperature, and transferred to an Ar-filled glove box to prevent air-exposure. The crystal structure and particle morphology of as-prepared TFCN were analyzed by X-ray diffraction (XRD, PANalytical X'Pert Pro) with Rietveld refinement and scanning electron microscopy (SEM, Zeiss Merlin), respectively. Transition metal oxidation states were probed by X-ray absorption spectroscopy (XAS) obtained at Advanced Photon Source (13ID-E) in Argonne National Laboratory. For half-cell tests, cathodes were prepared by mixing the active material, Super P (Timcal) carbon, and polytetrafluoroethylene (Dupont) binder i...

Direct Observation of Alternating Octahedral and Prismatic Sodium Layers in O3‐Type Transition Metal Oxides

“…We provide a comprehensive perspective on the phase transitions in O3-NaTi0.25Fe0.25Co0.25Ni0.25O2, a compound which shows high energy density and good cycle life. [16,17] By combining in situ XRD, high resolution-scanning transmission electron microscopy (HR-STEM), X-ray absorption spectroscopy (XAS), and first-principles modeling, we visualize and rationalize the structural change in this O3-type transition metal oxide at high voltage. Our finding is that the strong Jahn-Teller distortion effect in Fe 4+ creates a Na-O-Fe 4+ interaction which can be better accommodated in a structure in which octahedral and prismatic Na stackings alternate, stabilizing an OP2-type (ABCAABCA stacking) structure.…”

“…each transition metal were previously determined as Ti 4+ , Fe 3+ , Co 3+ , and Ni 2+ . [16,17] In Figure 4a . Its contribution to the overall capacity is small as the edge shifts only slightly to higher energy.…”

Rational Design of Environmental Benign Organic–Inorganic Hybrid as a Prospective Cathode for Stable High-Voltage Sodium Ion Batteries

“…To the best of our knowledge, the capacity values and stability achieved from the NNMF-PANI3 electrode at elevated cycling conditions is the best reported value among O3-layered materials. ,,,− The capacity and stability comparison of various O3-layered materials with the NNMF-PANI3 electrode is summarized in Table , which further demonstrates the enhanced performance of this hybrid electrode. For instance, Yabuuchi et al obtained a capacity retention of 61% after only 30 cycles from an O3–Na­[Fe 0.5 Mn 0.5 ]­O 2 electrode between 1.5 and 4.3 V at 12 mA g –1 . , Because the long-term cyclability is a key factor in implementing any rechargeable energy storage systems in practical applications, the NNMF-PANI3/Na + cell is cycled for 750 cycles at a 2 A g –1 current density between 2 and 4.5 V with the result presented in Figure d.…”

Readiness Level of Sodium‐Ion Battery Technology: A Materials Review

“…[35] Despite these multiple steps involved, the material ensures a good reversibility, symptom of the high tolerance to phase transition of a layered structure in which covalent bonds are not involved in vertical ordering. 25 Ni 0.25 O 2 , [224] showed how titanium doping is a wise approach in stabilizing such heterogeneous layered structures. A benefit of Ni-rich layered phases resides also in the great difference in the ionic radii of Na + (1.02 Å) and Ni 2+ (0.69 Å), which likely avoids ion exchange between Na + and Ni 2+ in the layers, extending stability and the high-capacity delivery.…”

“…Further improvements are thus required to make them not sensitive toward air for their mass production, effort recently put in developing a water-proof cathode material O3-Na 0.9 [Cu 0.22 Fe 0.30 Mn 0.48 ] O 2 are heading in the right direction. [222] Quaternary O3 structures, namely Na[Ni 0.4 Fe 0.2 Mn 0.4-x Ti x ]O 2 , [223] NaTi 0.25 Fe 0.25 Co 0.25 Ni 0.25 O 2 , [224] showed how titanium doping is a wise approach in stabilizing such heterogeneous layered structures. A structure stabilization effect has been called upon Ti positive effect.…”