Lithium cobalt(II) pyrophosphate, Li1.86CoP2O7, from synchrotron X-ray powder data

Hui Zhou; Shailesh Upreti; Natasha A Chernova; M Stanley Whittingham

doi:10.1107/S1600536811038451

. 2011 Sep 30;67(Pt 10):i58–i59. doi: 10.1107/S1600536811038451

Lithium cobalt(II) pyrophosphate, Li_1.86CoP₂O₇, from synchrotron X-ray powder data

Hui Zhou ^a, Shailesh Upreti ^a, Natasha A Chernova ^a, M Stanley Whittingham ^a,^*

PMCID: PMC3201481 PMID: 22065824

Abstract

Structure refinement of high-resolution X-ray powder diffraction data of the title compound gave the composition Li_1.865CoP₂O₇, which is also verified by the ICP measurement. Two Co sites exist in the structure: one is a CoO₅ square pyramid and the other is a CoO₆ octahedron. They share edges and are further interconnected through P₂O₇ groups, forming a three-dimensional framework, which exhibits different kinds of intersecting tunnels containing Li cations and could be of great interest in Li ion battery chemistry. The structure also exhibits cation disorder with 13.5% Co residing at the lithium (Li1) site. Co seems to have an average oxidation state of 2.135, as obtained from the strutural stochiometry that closely supports the magnetic susceptibility findings.

Related literature

For related structures, see: Adam et al. (2008 ▶); Nishimura et al. (2010 ▶); Zhou et al. (2011 ▶). For related materials with Na⁺ and K⁺ cations, see: Erragh et al. (1991 ▶); Sanz et al. (1999 ▶); Beaury et al. (2004 ▶); Gopalakrishna et al. (2005 ▶); Bih et al. (2006 ▶); Guesmi et al. (2007 ▶). For related structural frameworks, see: Beaury et al. (2004 ▶); Fagginani & Calvo (1976) ▶; Sandström et al. (2003 ▶); Etheredge & Hwu (1995 ▶); El Maadi et al. (1995 ▶); Huang & Hwa (1998 ▶); Sanz et al. (1999 ▶); Erragh et al. (1998 ▶). Pseudovoigt profile coefficients as parameterized in Thompson et al. (1987 ▶) and Finger et al. (1994 ▶).

Experimental

Crystal data

CoLi_1.865O₇P₂
M _r = 245.82
Monoclinic,
a = 9.76453 (4) Å
b = 9.69622 (4) Å
c = 10.95952 (4) Å
β = 101.7664 (2)°
V = 1015.83 (1) Å³
Z = 8
Synchrotron radiation, λ = 0.413988 Å
μ = 0.89 mm⁻¹
T = 297 K
irregular shape, 15 × 13 mm

Data collection

Advanced Photon Source diffractometer
Specimen mounting: kapton capillary
Data collection mode: transmission
Scan method: continuous

Refinement

R _p = 0.057
R _wp = 0.080
R _exp = 0.049
R(F ²) = 0.04534
χ² = 2.624
24500 data points
269 parameters

Data collection: Advance Photon Source Argonne National Laboratory; cell refinement: GSAS (Larson & Von Dreele, 2000 ▶); data reduction: Powder4 (Dragoe, 2001 ▶); program(s) used to solve structure: GSAS; program(s) used to refine structure: GSAS; molecular graphics: CrystalMaker (Palmer, 2005 ▶); software used to prepare material for publication: publCIF (Westrip, 2010 ▶).

Supplementary Material

Crystal structure: contains datablock(s) I. DOI: 10.1107/S1600536811038451/br2175sup1.cif

e-67-00i58-sup1.cif^{(13.5KB, cif)}

Rietveld powder data: contains datablock(s) I. DOI: 10.1107/S1600536811038451/br2175Isup2.rtv

e-67-00i58-Isup2.rtv^{(2.2MB, rtv)}

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Acknowledgments

Use of the Advanced Photon Source at the Argonne National Laboratory was supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE–AC02-06CH11357. The research at Binghamton was supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies of the US Department of Energy under Contract No. DE–AC02-05CH11231, under the Batteries for Advanced Transportation Technologies (BATT) Program subcontract # 6807148.

supplementary crystallographic information

Comment

A₂MP₂O₇ is a large family, in which various frameworks are encountered consisting of MO₆ octahedra (Fagginani et al., 1976; Sandström et.al., 2003) and MO₄ polyhedra (Etheredge et al., 1995; Erragh et al., 1998; Sanz et al., 1999) interconnected through P₂O₇ groups (Fig. 1). Dimeric M₂O₁₀ units, built up of two edge-sharing MO₆ octahedra, are only observed for some A₂MP₂O₇ pyrophosphates (El Maadi et al. 1995; Huang et al. 1998) and dimeric M₂O₁₁ units(corner-shared MO₆) seem to be much more rare, just observed for Na₂CoP₂O₇ (Erragh et al. 1991). Two forms of structures were found for Na₂CoP₂O₇ by Erragh et al. 1991: one is triclinic and another one is orthorhombic. The tetragonal structure of Na₂CoP₂O₇ was reported by Sanz et al. 1999 and they found that the tetragonal form could be a derivative of the orthorhombic form, with a higher point symmetry for the former. In addition, the tetragonal structured Na₂CoP₂O₇ was described by Guesmi et al. 2007. To our knowledge, the A₂CoP₂O₇ with Li as cation has never been reported.

Here, we report a new Li containing solid with a three-dimensional framework (Fig. 2) crystallizing in the monoclinic space group P2₁/a. Its structure is similar to the recently reported Li₂MnP₂O₇ (Adam et al. 2008), a new member of the A₂MP₂O₇ family: original M₂O₉ units, built up of one MO₅ trigonal bipyramid sharing one edge with one MO₆ octahedron, sharing corners with P₂O₇ pyrophosphate groups to form undulating (M₄P₈O₃₂)_∞ layers. A 3-D framework results from the interconnection between metal oxide and pyrophosphate groups, and the lithium cations are located in the tunnels thus formed (Fig 2). The structure of the related Fe-compound has been studied by us (Zhou et al. 2011) and Nishimura et al. (2010), as well as the electrochemical properties, which showed that it is a good candidate for the cathode material of lithium-ion batteries. The title compound also has the potential to work as the cathode material for lithium-ion batteries. We present here its crystal structure, as determined and refined from synchrotron powder X-ray diffraction data (Fig. 3).

Experimental

The powder sample was synthesized through a "wet" method based on mixing stoichiometric aqueous solutions of the precursors followed by thermal treatments. The general procedure involves the mixing of soluble precursors in distilled water followed by a slow evaporation through continuous stirring to dryness before annealing the resultant solids. The precursors for the synthesis were Li(CH₃COO),Co(CH₃COO)₂. 4H₂O,and NH₄H₂PO₄, which were dissolved in 100 ml distilled water in a molar ratio of 2:1:2 (1.32 g, 2.49 g and 2.3 g respectively) to give a 0.02 molar lithium solution. The self-adjusted pH of all the solutions were found to be around 4.5. The solution was stirred and evaporated on a hot-plate in the hood followed by vacuum oven drying overnight at 363 K. The resulting solid was preheated in a H2/He (8.5°/91.5° by volume) atmosphere at 673 K for 4h to decompose the precursors followed by reheating under the same atmosphere up to 873 K for 16h with intermittent grinding to obtain the pink colored powder as final product. The sample was also analyzed with a Perkin-Elmer ICP-OES Optima 7000 DV for the elemental content. The average result of 3 analyses showed that the ratio of Li: Co: P is 1.85: 0.996:2. In addition, the SQUID magnetic study on the sample using a Quantum Design MPMS XL SQUID magnetometer showed that the effective magnetic moment of it is 5.23m_Bwhich is typical divalent Co.