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.

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