Lithium Copper(I) Orthophosphates Li 3– x Cu x PO 4 : Synthesis, Crystal Structures, and Electrochemical Properties

• Published in: Zeitschrift für anorganische und allgemeine Chemie (1950) 2014-04, Vol.640 (5), p.944-951
• Main Authors: Snyder, Katharina, Raguž, Branimir, Hoffbauer, Wilfried, Glaum, Robert, Ehrenberg, Hartmut, Herklotz, Markus
• Format: Article
• Language: English
• ISSN: 0044-2313; 1521-3749
• DOI: 10.1002/zaac.201300606

Along the quasi‐binary section Li 3 PO 4 ‐ Cu I 3 PO 4 three different phases Li 3– x Cu I x PO 4 each with extended homogeneity range occur under equilibrium conditions (650 ≤ ; ≤ 700 °C). According to single‐crystal X‐ray structure analyses Phase 1 (0 < x ≤ 0.7) adopts the HT‐ or β‐Li 3 PO 4 structure type [Li 2.6 Cu I 0.4 PO 4 , Pnma (no. 62), Z = 4, a = 10.4612(2) Å, b = 6.1690(3) Å, c = 4.9854(2) Å, R 1 = 0.023, wR 2 = 0.062, Goof = 1.12] and Phase 2 (0.9 ≤ x ≤ 1.8) is isotypic to LT‐ or α‐Li 3 PO 4 [Li 2.05 Cu I 0.95 PO 4 , Pnm 2 1 (no. 31), Z = 2, a = 6.2113(8) Å, b = 5.2597(7) Å, c = 4.9904(5) Å, R 1 = 0.040, wR 2 = 0.108, Goof = 0.98]. A preliminary structure model for the copper‐rich Phase 3 (2.1 ≤ x ≤ 2.8) [“Li 0.6 Cu I 2.4 PO 4 ”, P $\bar{3}$ (no. 147), a = 6.223(1) Å, c = 5.3629(5) Å] could be refined to R 1 = 0.07. Sharp 31 P‐MAS‐NMR resonances observed in the spectra of Li 2.6 Cu I 0.4 PO 4 ( δ iso = 10.4 ppm), Li 2.05 Cu I 0.95 PO 4 ( δ iso = 12.4 ppm), and Li 0.84 Cu I 2.16 PO 4 ( δ iso = 10.9 ppm) provide evidence for the absence of paramagnetic Cu 2+ ions. Pure copper(I) orthophosphate Cu I 3 (PO 4 ) exists as a homogeneous melt ( ≥ 800 °C) and can be obtained as thermodynamically metastable solid by quenching. It is isotypic to Phase 3 [ a = 6.284(3) Å, c = 5.408(5) Å]. Electrochemical delithiation of Li 2.05 Cu I 0.95 PO 4 (C/10, C/30) indicates two partially reversible oxidation processes between 3.75 V and 4.80 V (vs. Li 0 /Li + ).