•Na0.093Li0.57Ni0.33Mn0.67O2 is synthesized by thermal treatment at 500 °C.•The initial discharge capacity is 261 mA h g−1.•The charge/discharge profiles show a novel high-potential plateau region at around 4.75 V.In this study, a new class of contenders for high-voltage and high-capacity positive electrode materials with the composition NaxLi0.7−xNi1−yMnyO2 (0.03 < x ≤ 0.25, 0.5 ≤ y ≤ 0.8) was synthesized by thermal treatment; these positive electrode materials synthesized by Na+/Li+ exchange using P3Na0.7Ni1−yMnyO2 (0.5 ≤ y ≤ 0.8) as the precursor exhibited a mixture of layered and spinel structures. The (dis)charge voltage-capacity curve of materials with these compositions significantly varied according to the residual Na and Mn content. Notably, HT-NaxLi0.7−xNi1−yMnyO2 (x = 0.093, y = 0.67) exhibited a maximum discharge capacity of 261 mA h g−1 at an average voltage of 3.36 V at 25 °C (between 2.0 and 4.8 V), which translates to an energy density of 943 W h kg−1. The obtained electrochemical performance is rationalized by the phase fractions of layered and spinel structures, which is triggered by the residual Na and Mn content in NaxLi0.7−xNi1−yMnyO2.

•O3-Li2/3Ni1/3Mn2/3O2 is synthesized by thermal treatment at 500 °C.•The initial discharge capacity of Li2/3Ni1/3Mn2/3O2 with thermal treatment at 500 °C is 257 mA h g−1.•The charge/discharge profiles show a novel high-potential plateau region at 4.8 V.A lithium nickel manganese oxide, O3-Li2/3Ni1/3Mn2/3O2, is synthesized from the precursor, P3-Na2/3Ni1/3Mn2/3O2, by a Na+/Li+ ion exchange reaction using molten salt. Post-heating at 300, 400, 500, 600, and 700 °C is carried out for 5 h in air. The products are characterized by powder XRD, inductively coupled plasma-atomic emission spectroscopy (ICP-AES), SEM, 6Li-magic-angle-spinning-NMR, and electrochemical measurements. The charge/discharge profiles of O3-Li2/3Ni1/3Mn2/3O2, thermally treated at 500 °C, show a high-potential plateau region at 4.8 V. Furthermore, sloping voltage profiles are observed at an average voltage of 3.21 V. An initial discharge capacity of 257 mA h g−1 is obtained between 2.0 and 4.8 V with a current density of 15 mA g−1 at 25 °C. This capacity corresponds to 0.90 electron transfers per formula unit. This study shows that Post-heating of O3-Li2/3Ni1/3Mn2/3O2 is effective to improve its electrochemical properties.

The new members of the Ag2–xNaxMn2Fe(VO4)3 (0 ≤ x ≤ 2) solid solution were synthesized by a solid-state reaction route, and their crystal structures were determined from single-crystal X-ray diffraction data. The physical properties were characterized by Mössbauer and electrochemical impedance spectroscopies, galvanostatic cycling, and cyclic voltammetry. These materials crystallize with a monoclinic symmetry (space group C2/c), and the structure is considered to be a new member of the AA′MM′2(XO4)3 alluaudite family. The A, A′, M, and X sites are fully occupied by Ag+/Na+, Ag+/Na+, Mn2+, and V5+, respectively, whereas a Mn2+/Fe3+ mixture is observed in the M′ site. The Mössbauer spectra confirm that iron is trivalent. The impedance measurements indicate that the silver phase is a better conductor than the sodium phase. Furthermore, these phases exhibit ionic conductivities 2 orders of magnitude higher than those of the homologous phosphates. The electrochemical tests prove that Na2Mn2Fe(VO4)3 is active as positive and negative electrodes in sodium-ion batteries.

•We have been able to grow CuMgVO4 and AgMgVO4 single crystals.•We solved their crystal structures using single crystal data.•We compared the crystal structures of CuMgVO4 and AgMgVO4.The new compounds CuMgVO4 and AgMgVO4 have been synthesized by a solid state reaction route. Their crystal structures were determined from single-crystal X-ray diffraction data. CuMgVO4 crystallizes with Na2CrO4-type structure with space group Cmcm, a = 5.6932 (10), b = 8.7055 (15), c = 6.2789 (10) Å, V = 311.20 (9) Å3, and Z = 4, whereas AgMgVO4 crystallizes in the maricite-type structure with space group Pnma, a = 9.4286 (14), b = 6.7465 (10), c = 5.3360 (8) Å, V = 339.42 (9) Å3, and Z = 4. Both structures of CuMgVO4, and AgMgVO4 contain MgO4 chains made up of edge-sharing MgO6 octahedra. In CuMgVO4 the MgO4 chains are interconnected through CuVO4 double chains made up of VO4 and CuO4 tetrahedra sharing corners and edges, however in AgMgVO4 the chains are interlinked by the VO4 and AgO4 tetrahedra sharing only corners.

The new compounds Li2Mg[PO4]F and Li9Mg3[PO4]4F3 have been synthesized by a solid state reaction route. The crystal structures were determined from single-crystal X-ray diffraction data. Li2Mg[PO4]F crystallizes with the orthorhombic Li2Ni[PO4]F structure, space group Pnma, a = 10.7874(3), b = 6.2196(5), c = 11.1780(4) Å, V = 721.13(10) Å3, and Z = 8, whereas Li9Mg3[PO4]4F3 crystallizes with hexagonal symmetry, space group P63, with a = 12.6159(6), c = 5.0082(4) Å, V = 690.32(7) Å3, and Z = 2. A merohedral twinning was taken into account for its structural refinement. The structure of Li2Mg[PO4]F contains MgO3F chains made up of edge-sharing MgO4F2 octahedra. These chains are interlinked by PO4 tetrahedra forming a 3D-Mg[PO4]F framework. The lithium atoms occupy mainly three distinct crystallographic sites. The structure of Li9Mg3[PO4]4F3 consists of corner-sharing MgO4F2 octahedra forming MgO4F chains running along the c axis. These chains are interlinked by PO4 tetrahedra forming a 3D-Mg3[PO4]4F3 framework with hexagonal and pentagonal tunnels, in which are located the Li atoms. This study reveals also a strong relationship between Li2Mg[PO4]F-, Mg1−xFexAl3[BO3][SiO4]O2- and P21/c-Li5V[PO4]2F2- structures; and between P63-Li9Mg3[PO4]4F3 and P21/c-Na2Mn[PO4]F. The ionic conductivities σ of the composite material Li6Mg4[PO4]3[SO4]F3 and Li9Mg3[PO4]4F3, estimated using electrochemical impedance spectroscopic analyses at 300 °C, are 3.9 × 10−5 and 10−4 S cm−1 with activation energies of 0.524 eV and 0.835 eV, respectively.

The title compounds were synthesized by a hydrothermal route from a 1:1 molar ratio of lithium fluoride and transition-metal acetate in an excess of water. The crystal structures were determined using a combination of powder and/or single-crystal X-ray and neutron powder diffraction (NPD) measurements. The magnetic structure and properties of Co(OH)F were characterized by magnetic susceptibility and low-temperature NPD measurements. M(OH)F (M = Fe and Co) crystallizes with structures related to diaspore-type α-AlOOH, with the Pnma space group, Z = 4, a = 10.471(3) Å, b = 3.2059(10) Å, and c = 4.6977(14) Å and a = 10.2753(3) Å, b = 3.11813(7) Å, and c = 4.68437(14) Å for the iron and cobalt phases, respectively. The structures consist of double chains of edge-sharing M(F,O)6 octahedra running along the b axis. These infinite chains share corners and give rise to channels. The protons are located in the channels and form O–H···F bent hydrogen bonds. The magnetic susceptibility indicates an antiferromagnetic ordering at ∼40 K, and the NPD measurements at 3 K show that the ferromagnetic rutile-type chains with spins parallel to the short b axis are antiferromagnetically coupled to each other, similarly to the magnetic structure of goethite α-FeOOH.

The new compound HP-Na2Co[PO4]F was synthesized by high pressure solid state reaction and its crystal structure was determined from single crystal X-ray diffraction data. The physical properties of HP-Na2Co[PO4]F were characterized by magnetic susceptibility, specific heat capacity, galvanometric cycling, and electrochemical impedance spectroscopy measurements. HP-Na2Co[PO4]F crystallizes with the space group P63/m, a = 10.5484(15), c = 6.5261(9) Å, V = 628.87(15) Å3 and Z = 6. The crystal structure consists of infinite chains of edge-sharing CoF2O4 octahedra. The latter are interconnected through the PO4 tetrahedra forming a 3D-Co[PO4]F-framework. The six coordinated sodium atoms are distributed over three crystallographic sites (2b, 6h, and 4f). The structure of HP-[Na11/3Na23/3Na32/3]Co[PO4]F is similar to [Na11/3Na23/3Sr1/3□1/3]Ge[GeO4]O. There is only one difference; Na3 occupies the 4f (1/3, 2/3, 0.0291) atomic position, whereas the Sr occupies the 2c (1/3, 2/3, 1/4) atomic position. The magnetic susceptibility follows a Curie–Weiss behavior above 50 K with Θ = −21 K indicating predominant antiferromagnetic interactions. The specific heat capacity and magnetization measurements show that HP-Na2Co[PO4]F undergoes a three-dimensional magnetic ordering at TN = 11.0(1) K. The ionic conductivity σ, estimated at 350 °C, is 1.5 × 10−7 S cm−1. The electrochemical cycling indicates that only one sodium ion could be extracted during the first charge in Na half-cell; however, the re-intercalation was impossible due to a strong distortion of the structure after the first charge to 5.0 V.

The new compound LiNaMg[PO4]F has been synthesized by a wet chemical reaction route. Its crystal structure was determined from single-crystal X-ray diffraction data. LiNaMg[PO4]F crystallizes with the monoclinic pseudomerohedrally twinned LiNaNi[PO4]F structure, space group P21/c, a = 6.772(4), b = 11.154(6), c = 5.021(3) Å, β = 90.00(1)° and Z = 4. The structure contains [MgO3F]n chains made up of zigzag edge-sharing MgO4F2 octahedra. These chains are interlinked by PO4 tetrahedra forming 2D-Mg[PO4]F layers. The alkali metal atoms are well ordered in between these layers over two atomic positions. The use of group–subgroup transformation schemes in the Bärnighausen formalism enabled us to determine precise phase transition mechanisms from LiNaNi[PO4]F- to Na2M[PO4]F-type structures (M = Mn–Ni, and Mg) (see video clip 1 and 2). The crystal and magnetic structure and properties of the parent LiNaNi[PO4]F phase were also studied by magnetometry and neutron powder diffraction. Despite the rather long interlayer distance, dmin(Ni+2–Ni+2) ∼ 6.8 Å, the material develops a long-range magnetic order below 5 K. The magnetic structure can be viewed as antiferromagnetically coupled ferromagnetic layers with moments parallel to the b-axis.

The basic structural chemistry of O3–LixCoO2 (0.25 ≤ x ≤ 1) oxides is reviewed. Crystal chemical details of selected compositions and group–subgroup schemes are discussed with respect to phase transitions upon electrochemical or chemical deintercalation of the lithium atoms. Furthermore, the theoretical crystal structures of LixCoO2 supercells (x = 0.75, 0.5, 0.33, and 0.25) are reported for the first time based on the combination of transmission electron microscopy (TEM) and X-ray (XRD) or neutron diffraction (ND) experiments. Li0.75CoO2 and Li0.25CoO2 supercells crystallize with the space group R3̅m, a4 = 5.6234 Å and 5.624 Å, and c4 = 14.2863 Å and 14.26 Å, respectively, whereas the Li0.5CoO2 supercell crystallizes with the space group P21/m, a7 = 4.865 Å, b7 = 2.809 Å, c7 = 9.728 Å, and β7 = 99.59°. The Li0.33CoO2 supercell may crystallize in different unit cells (hexagonal or orthorhombic or monoclinic). For Li0.75CoO2, the TEM superstructure reflections are due to only one type of lithium and vacancy ordering within the lithium layers; however, for x = 0.5, the superstructure reflections are due to an intergrowth of two Li0.5CoO2 monoclinic structures (P2/m, a5 = 4.865(3) Å, b5 = 2.809(3) Å, c5 = 5.063(3) Å, β5 = 108.68(5)°) with the lithium and vacancies alternating the 1g and 1f atomic positions, in two successive layers, along the c direction. For Li0.33CoO2, in most cases, the Li and vacancy ordering are similar to Li and Mn ordering in the Li2MnO3 structure. The phase transition mechanisms from O3–LiCoO2 to O3–Li0.25CoO2 and from O3–LiCoO2 to spinel–Li0.5CoO2 have been determined, and the structural relationship between O3–LiCoO2 and Li2MnO3 has been discussed in detail.Keywords: group−subgroup schemes; lithium battery; O3−LixCoO2 system; phase transition;

•Lithium insertion mechanism into hard carbon is discussed.•7Li NMR, X-ray photoelectron spectroscopy, and hard X-ray photoelectron spectroscopy are used in this study.•The existence of different Li insertion sites is proved by these spectra.Non-graphitizable carbon (hard carbon) as a negative electrode material for lithium-ion batteries is investigated by X-ray photoelectron spectroscopy, and hard X-ray photoelectron spectroscopy (HX-PES). HX-PES spectra have peaks of both the solid electrolyte interphase on the hard carbon surface and the hard carbon itself. The change in spectrum with state of charge is observed by HX-PES. Hard carbon has two types of lithium insertion site; between graphene sheets and into nano-scale voids. These spectroscopic results are consistent with the lithium insertion mechanism into hard carbon.

•Li2Fe[PO4]F was prepared from LiNaFe[PO4]F by ion exchange using LiBr in ethanol.•Li2Fe[PO4]F and LiNaFe[PO4]F crystallize with the Li2Ni[PO4]F-type structure.•It is different from the Tavorite Li1+xFe[PO4]F- and the layered Na2Fe[PO4]F-type.•57Fe Mӧssbauer were collected at different stages of the galvanometric cycling.•Up to 1 mol of alkali metal is extractable between 1.0 V and 5.1 V vs. Li+/Li.The new compound Li1.65Na0.35Fe[PO4]F with the Li2Ni[PO4]F structure has been prepared from the analogous LiNaFe[PO4]F phase by ion exchange using LiBr in ethanol at 90 °C. The sample was characterized by powder X-ray diffraction, 57Fe Mӧssbauer spectroscopy, and electrochemical measurements. Li1.65Na0.35Fe[PO4]F crystallizes with orthorhombic symmetry, space group Pnma, with a = 10.5093(5) Å, b = 6.4999(2) Å, c = 11.0483(5) Å, V = 754.70(7) Å3, and Z = 8. The 57Fe Mӧssbauer data collected at different stages of galvanometric cycling confirmed that only 1 mol of alkali metal is extractable between 1.0 V and 5.1 V vs. Li+/Li with a discharge capacity between 135 and 145 mA h g−1. Li/Na electrochemical ion exchange occurs during cycling and leads to a lithium rich phase.

The new compound MnF2−x(OH)x (x ∼ 0.8) was synthesized by a hydrothermal route from a 1:1 molar ratio of lithium fluoride and manganese acetate in an excess of water. The crystal structure was determined using the combination of single crystal X-ray and neutron powder diffraction measurements. The magnetic properties of the title compound were characterized by magnetic susceptibility and low-temperature neutron powder diffraction measurements. MnF2−x(OH)x (x ∼ 0.8) crystallizes with orthorhombic symmetry, space group Pnn2 (no. 34), a = 4.7127(18), b = 5.203(2), c = 3.2439(13) Å, V = 79.54(5) Å3 and Z = 2. The crystal structure is a distorted rutile-type with [Mn(F,O)4] infinite edge-sharing chains along the c-direction. The protons are located in the channels and form O–H⋯F bent hydrogen bonds. The magnetic susceptibility measurements indicate an antiferromagnetic ordering at ∼70 K and the neutron powder diffraction measurements at 3 K show that the ferromagnetic chains with spins parallel to the c-axis are antiferromagnetically coupled to each other, similarly to the magnetic structure of tetragonal rutile-type MnF2 with isoelectronic Mn2+. MnF2−x(OH)x (x ∼ 0.8) is expected to be of great interest as a positive electrode for Li cells if the protons could be exchanged for lithium.

The new compounds Mn2(OH)2SO3, Mn2F(OH)SO3, and Mn5(OH)4(H2O)2[SO3]2[SO4] were synthesized using a hydrothermal route and their crystal structures were determined using single crystal X-ray diffraction data. Mn2(OH)2SO3 and Mn2F(OH)SO3 crystallized with the space group Pnma, a = 7.3580(14), b = 10.3429(20), c = 5.7611(11) Å, Z = 4; and a = 7.413(4), b = 10.139(5), c = 5.717(3) Å, Z = 4, respectively, whereas Mn5(OH)4(H2O)2[SO3]2[SO4] crystallized with the space group P21/m, a = 7.6117(7), b = 8.5326(7), c = 10.9273(9) Å, β = 101.6005(13)°, Z = 2. Mn2(OH)2SO3 and Mn2F(OH)SO3 consist of a 3D-framework of manganese octahedra sharing corners and edges and giving rise to 1D-tunnels along the a axis in which are located the sulfur atoms, whereas Mn5(OH)4(H2O)2[SO3]2[SO4] consists of a 3D-framework of MnO5, MnO6, SO3, and SO4 polyhedra. Mn5(OH)4(H2O)2[SO3]2[SO4] is the first transition metal mixed sulfate–sulfite inorganic compound. Bent and symmetrically bifurcated hydrogen bonds were observed in these materials.

•We investigated the synthesis of LiNaFe1−xMnx[PO4]F by solid state reaction.•We demonstrated that a solid solution exist only for x ≤ 1/4.•We solved the crystal structure of LiNaFe3/4Mn1/4[PO4]F using single crystal data.•We studied the electrochemical performances of LiNaFe1−xMnx[PO4]F.•The Mn-doped phases have poor electrochemical performances comparing to LiNaFe[PO4]F.The new compounds LiNaFe1−xMnx[PO4]F (x ≤ 1/4) were synthesized by a solid state reaction route. The crystal structure of LiNaFe3/4Mn1/4[PO4]F was determined from single crystal X-ray diffraction data. LiNaFe3/4Mn1/4[PO4]F crystallizes with the Li2Ni[PO4]F-type structure, space group Pnma, a = 10.9719(13), b = 6.3528(7), c = 11.4532(13) Å, V = 798.31(16) Å3, and Z = 8. The structure consists of edge-sharing (Fe3/4Mn1/4)O4F2 octahedra forming (Fe3/4Mn1/4)FO3 chains running along the b-axis. These chains are interlinked by PO4 tetrahedra forming a three-dimensional framework with the tunnels and the cavities filled by the well-ordered sodium and lithium atoms, respectively. The manganese-doped phases show poor electrochemical behavior comparing to the iron pure phase LiNaFe[PO4]F.

The new compound LiNaFe[PO4]F was synthesized by a solid state reaction route, and its crystal structure was determined using neutron powder diffraction data. LiNaFe[PO4]F was characterized by 57Fe Mössbauer spectroscopy, magnetic susceptibility, specific heat capacity, and electrochemical measurements. LiNaFe[PO4]F crystallizes with orthorhombic symmetry, space group Pnma, with a = 10.9568(6) Å, b = 6.3959(3) Å, c = 11.4400(7) Å, V = 801.7(1) Å3 and Z = 8. The structure consists of edge-sharing FeO4F2 octahedra forming FeFO3 chains running along the b axis. These chains are interlinked by PO4 tetrahedra forming a three-dimensional framework with the tunnels and the cavities filled by the well-ordered sodium and lithium atoms, respectively. The specific heat and magnetization measurements show that LiNaFe[PO4]F undergoes a three-dimensional antiferromagnetic ordering at TN = 20 K. The neutron powder diffraction measurements at 3 K show that each FeFO3 chain along the b-direction is ferromagnetic (FM), while these FM chains are antiferromagnetically coupled along the a and c-directions with a non-collinear spin arrangement. The galvanometric cycling showed that without any optimization, one mole of alkali metal is extractable between 1.0 V and 5.0 V vs. Li+/Li with a discharge capacity between 135 and 145 mAh g−1.

The new compounds Li2−xNaxNi[PO4]F (x = 0.7, 1, and 2) have been synthesized by a solid state reaction route. Their crystal structures were determined from single-crystal X-ray diffraction data. Li1.3Na0.7Ni[PO4]F crystallizes with the orthorhombic Li2Ni[PO4]F structure, space group Pnma, a = 10.7874(3), b = 6.2196(5), c = 11.1780(4) Å and Z = 8, LiNaNi[PO4]F crystallizes with a monoclinic pseudomerohedrally twinned structure, space group P21/c, a = 6.772(4), b = 11.154(6), c = 5.021(3) Å, β = 90° and Z = 4, and Na2Ni[PO4]F crystallizes with a monoclinic twinned structure, space group P21/c, a = 13.4581(8), b = 5.1991(3), c = 13.6978(16) Å, β = 120.58(1)° and Z = 8. For x = 0.7 and 1, the structures contain NiFO3 chains made up of edge-sharing NiO4F2 octahedra, whereas for x = 2 the chains are formed of dimer units (face-sharing octahedra) sharing corners. These chains are interlinked by PO4 tetrahedra forming a 3D framework for x = 0.7 and different Ni[PO4]F layers for x = 1 and 2. A sodium/lithium disorder over three atomic positions is observed in Li1.3Na0.7Ni[PO4]F structure, whereas the alkali metal atoms are well ordered in between the layers in the LiNaNi[PO4]F and Na2Ni[PO4]F structures, which makes both compounds of great interest as potential positive electrodes for sodium cells.

18650-type cylindrical cells using LiNi1/3Mn1/3Co1/3O2 (NMC) and hard carbon as positive and negative electrode material, respectively, were fabricated and degraded by cycle tests. The capacity of the cells remained more than 95% and 85% after cycle tests at 25 and 50 °C, respectively. After the cycle tests, Li-deficient cubic phase was observed on the surface of NMC. This phenomenon should be related to the degradation mechanism of this type of cell.

X-ray photoemission spectroscopic and high-resolution hard X-ray photoemission spectroscopic studies of positive electrodes in LiNi0.73Co0.17Al0.10O2 and hard carbon based batteries were carried out to elucidate the mechanism of battery degradation. Li2CO3, hydrocarbons, ROCO2Li, polycarbonate-type compounds and LiF were observed on positive electrode surfaces and the amount of carbonates was found to have increased after cycle testing. Above 60 °C, signs of electrolyte decomposition were indicated. Near the surface of the positive electrodes, a Li-deficient cubic phase is present and grows with degradation. Capacity and power fade could be related to the amount of species on the surface and the thickness of the Li-deficient cubic phase near the surface.

The new compound LiNaMg[PO4]F has been synthesized by a wet chemical reaction route. Its crystal structure was determined from single-crystal X-ray diffraction data. LiNaMg[PO4]F crystallizes with the monoclinic pseudomerohedrally twinned LiNaNi[PO4]F structure, space group P21/c, a = 6.772(4), b = 11.154(6), c = 5.021(3) Å, β = 90.00(1)° and Z = 4. The structure contains [MgO3F]n chains made up of zigzag edge-sharing MgO4F2 octahedra. These chains are interlinked by PO4 tetrahedra forming 2D-Mg[PO4]F layers. The alkali metal atoms are well ordered in between these layers over two atomic positions. The use of group–subgroup transformation schemes in the Bärnighausen formalism enabled us to determine precise phase transition mechanisms from LiNaNi[PO4]F- to Na2M[PO4]F-type structures (M = Mn–Ni, and Mg) (see video clip 1 and 2). The crystal and magnetic structure and properties of the parent LiNaNi[PO4]F phase were also studied by magnetometry and neutron powder diffraction. Despite the rather long interlayer distance, dmin(Ni+2–Ni+2) ∼ 6.8 Å, the material develops a long-range magnetic order below 5 K. The magnetic structure can be viewed as antiferromagnetically coupled ferromagnetic layers with moments parallel to the b-axis.

The new compound LiNaFe[PO4]F was synthesized by a solid state reaction route, and its crystal structure was determined using neutron powder diffraction data. LiNaFe[PO4]F was characterized by 57Fe Mössbauer spectroscopy, magnetic susceptibility, specific heat capacity, and electrochemical measurements. LiNaFe[PO4]F crystallizes with orthorhombic symmetry, space group Pnma, with a = 10.9568(6) Å, b = 6.3959(3) Å, c = 11.4400(7) Å, V = 801.7(1) Å3 and Z = 8. The structure consists of edge-sharing FeO4F2 octahedra forming FeFO3 chains running along the b axis. These chains are interlinked by PO4 tetrahedra forming a three-dimensional framework with the tunnels and the cavities filled by the well-ordered sodium and lithium atoms, respectively. The specific heat and magnetization measurements show that LiNaFe[PO4]F undergoes a three-dimensional antiferromagnetic ordering at TN = 20 K. The neutron powder diffraction measurements at 3 K show that each FeFO3 chain along the b-direction is ferromagnetic (FM), while these FM chains are antiferromagnetically coupled along the a and c-directions with a non-collinear spin arrangement. The galvanometric cycling showed that without any optimization, one mole of alkali metal is extractable between 1.0 V and 5.0 V vs. Li+/Li with a discharge capacity between 135 and 145 mAh g−1.

The new compound MnF2−x(OH)x (x ∼ 0.8) was synthesized by a hydrothermal route from a 1:1 molar ratio of lithium fluoride and manganese acetate in an excess of water. The crystal structure was determined using the combination of single crystal X-ray and neutron powder diffraction measurements. The magnetic properties of the title compound were characterized by magnetic susceptibility and low-temperature neutron powder diffraction measurements. MnF2−x(OH)x (x ∼ 0.8) crystallizes with orthorhombic symmetry, space group Pnn2 (no. 34), a = 4.7127(18), b = 5.203(2), c = 3.2439(13) Å, V = 79.54(5) Å3 and Z = 2. The crystal structure is a distorted rutile-type with [Mn(F,O)4] infinite edge-sharing chains along the c-direction. The protons are located in the channels and form O–H⋯F bent hydrogen bonds. The magnetic susceptibility measurements indicate an antiferromagnetic ordering at ∼70 K and the neutron powder diffraction measurements at 3 K show that the ferromagnetic chains with spins parallel to the c-axis are antiferromagnetically coupled to each other, similarly to the magnetic structure of tetragonal rutile-type MnF2 with isoelectronic Mn2+. MnF2−x(OH)x (x ∼ 0.8) is expected to be of great interest as a positive electrode for Li cells if the protons could be exchanged for lithium.

The new compounds Li2Mg[PO4]F and Li9Mg3[PO4]4F3 have been synthesized by a solid state reaction route. The crystal structures were determined from single-crystal X-ray diffraction data. Li2Mg[PO4]F crystallizes with the orthorhombic Li2Ni[PO4]F structure, space group Pnma, a = 10.7874(3), b = 6.2196(5), c = 11.1780(4) Å, V = 721.13(10) Å3, and Z = 8, whereas Li9Mg3[PO4]4F3 crystallizes with hexagonal symmetry, space group P63, with a = 12.6159(6), c = 5.0082(4) Å, V = 690.32(7) Å3, and Z = 2. A merohedral twinning was taken into account for its structural refinement. The structure of Li2Mg[PO4]F contains MgO3F chains made up of edge-sharing MgO4F2 octahedra. These chains are interlinked by PO4 tetrahedra forming a 3D-Mg[PO4]F framework. The lithium atoms occupy mainly three distinct crystallographic sites. The structure of Li9Mg3[PO4]4F3 consists of corner-sharing MgO4F2 octahedra forming MgO4F chains running along the c axis. These chains are interlinked by PO4 tetrahedra forming a 3D-Mg3[PO4]4F3 framework with hexagonal and pentagonal tunnels, in which are located the Li atoms. This study reveals also a strong relationship between Li2Mg[PO4]F-, Mg1−xFexAl3[BO3][SiO4]O2- and P21/c-Li5V[PO4]2F2- structures; and between P63-Li9Mg3[PO4]4F3 and P21/c-Na2Mn[PO4]F. The ionic conductivities σ of the composite material Li6Mg4[PO4]3[SO4]F3 and Li9Mg3[PO4]4F3, estimated using electrochemical impedance spectroscopic analyses at 300 °C, are 3.9 × 10−5 and 10−4 S cm−1 with activation energies of 0.524 eV and 0.835 eV, respectively.

The new compounds Li2−xNaxNi[PO4]F (x = 0.7, 1, and 2) have been synthesized by a solid state reaction route. Their crystal structures were determined from single-crystal X-ray diffraction data. Li1.3Na0.7Ni[PO4]F crystallizes with the orthorhombic Li2Ni[PO4]F structure, space group Pnma, a = 10.7874(3), b = 6.2196(5), c = 11.1780(4) Å and Z = 8, LiNaNi[PO4]F crystallizes with a monoclinic pseudomerohedrally twinned structure, space group P21/c, a = 6.772(4), b = 11.154(6), c = 5.021(3) Å, β = 90° and Z = 4, and Na2Ni[PO4]F crystallizes with a monoclinic twinned structure, space group P21/c, a = 13.4581(8), b = 5.1991(3), c = 13.6978(16) Å, β = 120.58(1)° and Z = 8. For x = 0.7 and 1, the structures contain NiFO3 chains made up of edge-sharing NiO4F2 octahedra, whereas for x = 2 the chains are formed of dimer units (face-sharing octahedra) sharing corners. These chains are interlinked by PO4 tetrahedra forming a 3D framework for x = 0.7 and different Ni[PO4]F layers for x = 1 and 2. A sodium/lithium disorder over three atomic positions is observed in Li1.3Na0.7Ni[PO4]F structure, whereas the alkali metal atoms are well ordered in between the layers in the LiNaNi[PO4]F and Na2Ni[PO4]F structures, which makes both compounds of great interest as potential positive electrodes for sodium cells.

The new compound HP-Na2Co[PO4]F was synthesized by high pressure solid state reaction and its crystal structure was determined from single crystal X-ray diffraction data. The physical properties of HP-Na2Co[PO4]F were characterized by magnetic susceptibility, specific heat capacity, galvanometric cycling, and electrochemical impedance spectroscopy measurements. HP-Na2Co[PO4]F crystallizes with the space group P63/m, a = 10.5484(15), c = 6.5261(9) Å, V = 628.87(15) Å3 and Z = 6. The crystal structure consists of infinite chains of edge-sharing CoF2O4 octahedra. The latter are interconnected through the PO4 tetrahedra forming a 3D-Co[PO4]F-framework. The six coordinated sodium atoms are distributed over three crystallographic sites (2b, 6h, and 4f). The structure of HP-[Na11/3Na23/3Na32/3]Co[PO4]F is similar to [Na11/3Na23/3Sr1/3□1/3]Ge[GeO4]O. There is only one difference; Na3 occupies the 4f (1/3, 2/3, 0.0291) atomic position, whereas the Sr occupies the 2c (1/3, 2/3, 1/4) atomic position. The magnetic susceptibility follows a Curie–Weiss behavior above 50 K with Θ = −21 K indicating predominant antiferromagnetic interactions. The specific heat capacity and magnetization measurements show that HP-Na2Co[PO4]F undergoes a three-dimensional magnetic ordering at TN = 11.0(1) K. The ionic conductivity σ, estimated at 350 °C, is 1.5 × 10−7 S cm−1. The electrochemical cycling indicates that only one sodium ion could be extracted during the first charge in Na half-cell; however, the re-intercalation was impossible due to a strong distortion of the structure after the first charge to 5.0 V.

The new compounds Mn2(OH)2SO3, Mn2F(OH)SO3, and Mn5(OH)4(H2O)2[SO3]2[SO4] were synthesized using a hydrothermal route and their crystal structures were determined using single crystal X-ray diffraction data. Mn2(OH)2SO3 and Mn2F(OH)SO3 crystallized with the space group Pnma, a = 7.3580(14), b = 10.3429(20), c = 5.7611(11) Å, Z = 4; and a = 7.413(4), b = 10.139(5), c = 5.717(3) Å, Z = 4, respectively, whereas Mn5(OH)4(H2O)2[SO3]2[SO4] crystallized with the space group P21/m, a = 7.6117(7), b = 8.5326(7), c = 10.9273(9) Å, β = 101.6005(13)°, Z = 2. Mn2(OH)2SO3 and Mn2F(OH)SO3 consist of a 3D-framework of manganese octahedra sharing corners and edges and giving rise to 1D-tunnels along the a axis in which are located the sulfur atoms, whereas Mn5(OH)4(H2O)2[SO3]2[SO4] consists of a 3D-framework of MnO5, MnO6, SO3, and SO4 polyhedra. Mn5(OH)4(H2O)2[SO3]2[SO4] is the first transition metal mixed sulfate–sulfite inorganic compound. Bent and symmetrically bifurcated hydrogen bonds were observed in these materials.