From kröhnkite- to alluaudite-type of structure: novel method of synthesis of sodium manganese sulfates with electrochemical properties in alkali-metal ion batteries

Abstract

The alluaudite-type of structure is of huge research interest as an open matrix ensuring fast alkali-metal ion mobility, a property that could contribute to the development of novel electrode materials for rechargeable alkali-metal ion batteries. In this contribution, we provide new data on the formation of well-crystallized sodium manganese sulfates Na 2+d Mn 2Àd/2 (SO 4 ) 3 with an alluaudite-type of structure by simple dehydratation of the corresponding dihydrate Na 2 Mn(SO 4 ) 3 $2H 2 O with a kröhnkite-type of structure. The structure of Na 2+d Mn 2Àd/2 (SO 4 ) 3 is determined on the basis of Rietveld refinement of powder XRD patterns, infrared (IR) and Raman spectroscopy and electron paramagnetic resonance at X-and Q-band frequencies (EPR). From a structural point of view, the release of two H 2 O molecule from the kröhnkite phase takes place by a transformation of the infinite [Mn(SO 4 ) 2 (H 2 O) 2 ] chains into Mn 2 O 10 dimers bounded by distorted Na(1)O-polyhedra. The anhydrous sulfates are able to participate in the electrochemical reaction delivering a reversible capacity of 135 mA h g À1 , when they are used as cathode materials in lithium ion cells. The stability of the alluaudite phase Na 2+d Mn 2Àd/2 (SO 4 ) 3 in the lithium electrolyte solution and the mechanism of the electrochemical reaction are discussed on the basis of ex situ EPR, IR and Raman spectroscopy. This is a first report on electrochemical activity of manganese-based sulfate with an alluaudite-type of structure.

Preparation, structure and properties of Na2Mn3(SO4)4: a new potential candidate with high voltage for Na-ion batteries

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a Recently, several excellent SO4-based polyanion cathodes for Na-ion batteries (NIBs) were exploited, e.g. 29 To search for more excellent SO 4 -based insertion materials for NIBs, We studied the Na 2 SO 4 -MnSO 4 system and isolated another new compound Na 2 Mn 3 (SO 4 ) 4 . To search for more excellent SO4-based materials for NIBs, we studied the Na2SO4-MnSO4 system and isolated a new compound Na2Mn3(SO4)4, which crystallizes in orthorhombic space group Cmc21 with a=14.8307(18) Å, b=9.9107(18)Å, c = 8.6845(12)Å, and Z=4.

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Novel Methods for Sodium‐Ion Battery Materials

“…The observed small hyperfine interactions of 23 Na ions can serve as direct evidence for the unpaired spin observed by pulsed EPR on the terephthalic molecule . In addition, Marinova et al prepared well‐crystallized alluaudite‐type Na 2+δ Mn 2−δ/2 (SO 4 ) 3 by simple dehydration of the kröhnkite‐type Na 2 Mn(SO 4 ) 3 ·2H 2 O, and the thermal dehydration process was interpreted from manganese coordination by in situ EPR spectroscopy from 290 to 380 K . The EPR spectrum undergoes a strong change at a temperature of 380 K (107 °C), which is a convolution of two overlapping signals with Lorentzian shape shown in Figure c–e.…”

“…Although the second signal can also be associated with Mn 2+ ions, they have completely different coordination relative to Mn 2+ in the kröhnkite phase. With the increase of temperature above 450 K, a further change of the EPR spectrum occurs with a water molecule being released, leading to a structural transformation into Na 2 Mn(SO 4 ) 2 , which has been further determined by the XRD patterns …”

“…e) Temperature variation of the g ‐factors, EPR linewidths. c–e) Reproduced with permission . Copyright 2015, The Royal Society of Chemistry.…”

Structural and thermal properties of Na2Mn(SO4)2·4H2O and Na2Ni(SO4)2·10H2O

“…Furthermore, the thermal treatment of the kröhnkite-phase at 227 C, led to the formation of an alluaudite-phase with the composition Na 2+g -Mn 1Àg/2 (SO 4 ) 3 . 20 A similar phase could also be prepared via a solid state synthesis route when a mixture of Na 2 SO 4 and MnSO 4 was Although, the ve phases were prepared from the same precursors, their crystal structures are different (Fig. 7).…”