Abstract
Rechargeable sodium-ion batteries have recently attracted renewed interest as an alternative to Li-ion batteries for electric energy storage applications, because of the low cost and wide availability of sodium resources. Thus, the electrochemical energy storage community has been devoting increased attention to designing new cathode materials for sodium-ion batteries. Here we investigate P2- Na0.78Co1/2Mn1/3Ni1/6O2 as a cathode material for sodium ion batteries. The main focus is to understand the mechanism of the electrochemical performance of this material, especially differences observed in redox reactions at high potentials. Between 4.2 V and 4.5 V, the material delivers a reversible capacity which is studied in detail using advanced analytical techniques. In situ X-ray diffraction reveals the reversibility of the P2-type structure of the material. Combined soft X-ray absorption spectroscopy and resonant inelastic X-ray scattering demonstrates that Na deintercalation at high voltages is charge compensated by formation of localized electron holes on oxygen atoms.
Highlights
Rechargeable sodium-ion batteries have recently attracted renewed interest as an alternative to Li-ion batteries for electric energy storage applications, because of the low cost and wide availability of sodium resources
Among the alternatives to lithium-based battery chemistries, the sodium-ion battery (SIB) technology has remained in the research focus due to its potential to decrease the cost[1,2]
We investigate the redox mechanisms upon the charge/ discharge process of a Na//Na0.78Co1/2Mn1/3Ni1/6O2 electrochemical cell by using several advanced analytical tools such as in situ X-Ray diffraction (XRD), X-ray absorption spectroscopy (XAS), and resonant inelastic X-ray scattering (RIXS), which elucidate the participation of the anions redox reactions to compensate the sodium deintercalation at high voltages
Summary
Rechargeable sodium-ion batteries have recently attracted renewed interest as an alternative to Li-ion batteries for electric energy storage applications, because of the low cost and wide availability of sodium resources. Among the alternatives to lithium-based battery chemistries, the sodium-ion battery (SIB) technology has remained in the research focus due to its potential to decrease the cost[1,2] Sodium and lithium both belong to the alkali metal group in the periodic table and thereby share common characteristics such as having the same valence state and they can be inserted or intercalated in layered oxides[3,4]. Sodium layered oxides (NaxMO2, (M = TM = transition metal)) have attracted significant attention thanks to their ease of synthesis, high capacity and good rate capability Cathode materials such as NaxCoyMn1–yO26,7, NaxCoyTi1–yO28,9, and Na[FexMnyNiz]O210,11 have been extensively studied in literatures. Use of sacrificial salt to compensate the sodium deficiency has been demonstrated to compensate for this shortcoming[14,15]
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