Electrochemical Study of Li[sub 3]Fe(MoO[sub 4])[sub 3] as Positive Electrode in Lithium Cells

Abstract

Li 3 Fe͑MoO 4 ͒ 3 undergoes a complex electrochemical reaction with lithium in which the reduction of Fe 3+ and Mo 6+ takes place along the first discharge of the cell at about 2.4 and 1.8 V, respectively. The intercalation process involved is fully reversible for low lithium contents, Li 3+x Fe͑MoO 4 ͒ 3 with 0 Ͻ x Ͻ 1, the inserted compound Li 3+1 Fe 2+ ͑MoO 4 ͒ 3 retaining the Li 3 Fe 3+ ͑MoO 4 ͒ 3 parent framework with only a slight increase of the cell volume ͑0.85%͒. In contrast, the electrochemical reaction of Li 3 Fe͑MoO 4 ͒ 3 with five lithium ions originates an irreversible decomposition of this material into a mixture of a FeO-type compound and an amorphous lithium-molybdate phase. This in situ formed blend is electrochemically active, being able to intercalate and deintercalate three lithium ions at an average voltage of 2 V ͑reversible specific capacity of 150 Ah/kg͒. The full discharge of the cells ͑down to the vicinity of 0 V͒ proceeds through the complete and irreversible reduction of Li 3 Fe͑MoO 4 ͒ 3 with 25 lithium ions, resulting in the breakdown of any existing crystalline framework.

The Adaptable Lyonsite Structure

“…High electrical conductivity was first observed for Li 2 Cu 2 A C H T U N G T R E N N U N G (MoO 4 ) 3 in 1981, [52] and a significant effort has since been made to investigate the conductivity of many of the molybdates. [19,[53][54][55][56][57][58] The lyonsite structure fits the criteria for NASICON ion conductors owing to the arrangement of the isolated (MO 4 ) nÀ polyanion tetrahedra. A review of various families of A x B y A C H T U N G T R E N N U N G (MoO 4 ) z molybdate families discusses the ionic conduction of lyonsite type molybdates.…”

Lithium Insertion into Li2MoO4: Reversible Formation of (Li3Mo)O4 with a Disordered Rock-Salt Structure

“…However, lattice parameters of the rhombohedral phase differed from these of pristine Li 2 MoO 4 , thus reflecting a change in the composition, see Table 1. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 10 seen at about 723 K. Mass-spectrometric analysis revealed solely H 2 and CH 3 The amorphization upon Li insertion is a common feature of molybdenum oxides. 27,28 compound up to at least 620 K, see Fig.…”

“…3,[6][7][8][9] For example, such a compound was found during Liinsertion into MnMoO 4 (Ref. 7) and ZnMoO 4 (Ref.…”

Phase formation features in the systems M2MoO4–Fe2(MoO4)3 (M=Rb, Cs) and crystal structures of new double polymolybdates M3FeMo4O15

“…Double molybdates MFe(MoO 4 ) 2 (M= Li-Cs), M 3 Fe(MoO 4 ) 3 (M =Li, K), M 5 Fe(MoO 4 ) 4 (M= K, Rb, Cs) [7][8][9][10][11][12][13][14][15][16][17][18][19] were described in literature; the crystal structures of MFe(MoO 4 ) 2 (M= Li, Na, K, Rb) [20][21][22][23][24][25], Li 3 Fe(MoO 4 ) 3 [26] and Rb 5 Fe(MoO 4 ) 4 [20] were determined. In the structures, the molybdenum atoms are tetrahedrally coordinated while the Fe 3 + cations usually have the octahedral coordination excluding the structure of the low-temperature Rb 5 Fe(MoO 4 ) 4 [20] where the iron atoms are located in square pyramids.…”

“…Double molybdates MFe(MoO 4 ) 2 (M=Na, K, Rb) exhibit interesting ferroelastic and antiferromagnetic properties [10][11][12][13][14], and Li 3 Fe(MoO 4 ) 3 is considered as a possible positive electrode in lithium cells [16,17]. However, despite detail characterization and attractive functional properties of some double iron(III) molybdates, none T-x diagrams have been constructed for the systems M 2 MoO 4 -Fe 2 (MoO 4 ) 3 (M=Li, Na, K, Rb, Cs) and only lithium and sodium containing systems were studied using X-ray diffraction [7].…”