β-NaMnO₂: A High-Performance Cathode for Sodium-Ion Batteries

Abstract

There is much interest in Na-ion batteries for grid storage because of the lower projected cost compared with Li-ion. Identifying Earth-abundant, low-cost, and safe materials that can function as intercalation cathodes in Na-ion batteries is an important challenge facing the field. Here we investigate such a material, β-NaMnO2, with a different structure from that of NaMnO2 polymorphs and other compounds studied extensively in the past. It exhibits a high capacity (of ca. 190 mA h g(-1) at a rate of C/20), along with a good rate capability (142 mA h g(-1) at a rate of 2C) and a good capacity retention (100 mA h g(-1)after 100 Na extraction/insertion cycles at a rate of 2C). Powder XRD, HRTEM, and (23)Na NMR studies revealed that this compound exhibits a complex structure consisting of intergrown regions of α-NaMnO2 and β-NaMnO2 domains. The collapse of the long-range structure at low Na content is expected to compromise the reversibility of the Na extraction and insertion processes occurring upon charge and discharge of the cathode material, respectively. Yet stable, reproducible, and reversible Na intercalation is observed.

Review—Manganese-Based P2-Type Transition Metal Oxides as Sodium-Ion Battery Cathode Materials

“…On the other hand, an experimental study by Lei et al explored the Na x CoO 2 synthesis phase diagram. Na x MO 2 compounds are typically prepared via solid-state synthesis, 8,57 or a solution-state co-precipitation method, 9,12 with calcination temperatures ranging from 500 to 1000…”

“…126 The β-NaMnO 2 corrugated structure and an intergrowth model between α-and β-NaMnO 2 are presented in Figures 13a and 13b. 8 The broadening of the (011) peak in the powder XRD pattern of the pristine β-NaMnO 2 phase was successfully simulated using the DIFFaX simulation program with 25% of random stacking faults in the structure, corresponding to the insertion of a monoclinic α-NaMnO 2 cell in between two blocks of orthorhombic β-NaMnO 2 . The presence of structural defects was even more obvious in the 23 Na NMR, which exhibited three resonances at 237, 433, and 656 ppm (see Figure 14) instead of the unique Na crystallographic site expected for the ideal β structure.…”

Fabrication, Characterization, and Modulation of Functional Nanolayers

“…Unlike A x CoO 2 systems, the physical properties of A x MnO 2 have yet to be clarified, although Na x MnO 2 has recently been proposed as a new candidate for the cathode active material in Na-ion batteries [39][40][41] because Mn (Clarke number: 0.09) is more abundant than Co (Clarke number: 0.004). At least two crystallographic phases of NaMnO 2 are known; low-temperature α-NaMnO 2 [39,42] has an O3 layered structure with monoclinic symmetry and high-temperature β-NaMnO 2 [40] has a Pmnm structure with orthorhombic symmetry.…”

“…At least two crystallographic phases of NaMnO 2 are known; low-temperature α-NaMnO 2 [39,42] has an O3 layered structure with monoclinic symmetry and high-temperature β-NaMnO 2 [40] has a Pmnm structure with orthorhombic symmetry. It should be noted that the crystal symmetry of Na x MnO 2 strongly depends on x.…”

Observation on Sodium p-Toluenesulfonate Doped Polypyrrole Cathode for Sodium Ion Battery

“…[3][4][5] However, these inorganic intercalation materials usually possess a rigid structure and a small tunnel size, which may restrain ionic diffusion and transport to some degree. It is well known that organic solid polymers are more elastic and softer than inorganic compounds.…”