Layered P2-NaxMn3/4Ni1/4O2 Cathode Materials For Sodium-Ion Batteries: Synthesis, Electrochemistry and Influence of Ambient Storage

Abstract

Sodium-ion batteries promise efficient, affordable and sustainable electrical energy storage that avoids critical raw materials such as lithium, cobalt and copper. In this work, a manganese-based, cobalt-free, layered NaxMn3/4Ni1/4O2 cathode active material for sodium-ion batteries is developed. A synthesis phase diagram was developed by varying the sodium content x and the calcination temperature. The calcination process towards a phase pure P2-Na2/3Mn3/4Ni1/4O2 material was investigated in detail using in-situ XRD and TGA-DSC-MS. The resulting material was characterized with ICP-OES, XRD and SEM. A stacking fault model to account for anisotropic broadening of (10l) reflexes in XRD is presented and discussed with respect to the synthesis process. In electrochemical half-cells, P2-Na2/3Mn3/4Ni1/4O2 delivers an attractive initial specific discharge capacity beyond 200 mAh g−1, when cycled between 4.3 and 1.5 V. The structural transformation during cycling was studied using operando XRD to gain deeper insights into the reaction mechanism. The influence of storage under humid conditions on the crystal structure, particle surface and electrochemistry was investigated using model experiments. Due to the broad scope of this work, raw material questions, fundamental investigations and industrially relevant production processes are addressed.

Detailed Structural and Electrochemical Comparison between High Potential Layered P2-NaMnNi and Doped P2-NaMnNiMg Oxides

“…However, we already reported an additional O2-phase reflection apart from the (002) hkl plane . The (004) hkl plane at around ∼38° 2Θ (using a Cu X-ray tube) was identified, which is in close range to the observed reflection at 9.95° when using a radiation source of λ = 0.4132 Å.…”

“…However, we already reported an additional O2-phase reflection apart from the (002) hkl plane. 36 The (004) hkl plane at around ∼38°2Θ (using a Cu X-ray tube) was identified, which is in close range to the observed reflection at 9.95°when using a radiation source of λ = 0.4132 Å. At the end of the charge, at U = 4.300 V, P2 reflections are still present with a significant intensity, indicating that the P2 → O2 phase transition is not complete.…”

“…First, the Mn 0.75 Ni 0.25 (OH) 2 precursor was synthesized via coprecipitation in a continuous stirred tank reactor (CSTR, V = 1 L) by mixing Ni­(NO 3 ) 2 ·4H 2 O, Mn­(NO 3 ) 2 ·6H 2 O, NaOH, and NH 3 solution (Carl Roth) in appropriate ratios. The preparation procedure was described by Pfeiffer et al in more detail . Afterward, the precursor was dried and sieved to obtain homogenously sized particles.…”

“…The preparation procedure was described by Pfeiffer et al in more detail. 36 Afterward, the precursor was dried and sieved to obtain homogenously sized particles. In the second step (solid-state synthesis), the Mn 0.75 Ni 0.25 (OH) 2 precursor was mixed via wet impregnation with an aqueous NaOH solution (7 mol L −1 ) for the preparation of P2-MNO or with an aqueous solution containing appropriate ratios of NaOH (7 mol L −1 ) and 3.7 wt % MgCO 3 for P2-MNMO.…”

“…By having a closer look at the patterns of both P2-MNO and P2-MNMO, the 10l (102, 104, 106, and 108) reflections show reflection broadening, pointing out the possible presence of stacking faults as shown in our previous publication. 36 The determination of the successful incorporation of Mg into the crystal structure, and particularly in the TM sites, is quite challenging since Mg (0.72 Å) and Ni (0.69 Å) have very similar ionic radii. Based on Rietveld refinement results (Table S2), the observed slight increase in cell volume might indicate an enlargement of the lattice due to the slightly larger Mg 2+ ion.…”