Substitutional disorder: structure and ion dynamics of the argyrodites Li₆PS₅Cl, Li₆PS₅Br and Li₆PS₅I

Abstract

For the development of safe and long-lasting lithium-ion batteries we need electrolytes with excellent ionic transport properties. Argyrodite-type Li 6 PS 5 X (X: Cl, Br, I) belongs to a family of such a class of materials offering ionic conductivities, at least if Li 6 PS 5 Br and Li 6 PS 5 Cl are considered, in the mS cm À1 range at room temperature. Although already tested as ceramic electrolytes in battery cells, a comprehensive picture about the ion dynamics is still missing. While Li 6 PS 5 Br and Li 6 PS 5 Cl show an exceptionally high Li ion conductivity, that of Li 6 PS 5 I with its polarizable I anions is by some orders of magnitude lower. This astonishing effect has not been satisfactorily understood so far. Studying the ion dynamics over a broad time and length scale is expected to help shed light on this aspect. Here, we used broadband impedance spectroscopy and 7 Li NMR relaxation measurements and show that very fast local Li ion exchange processes are taking place in all three compounds. Most importantly, the diffusion-induced NMR spinlattice relaxation in Li 6 PS 5 I is almost identical to that of its relatives. Considering the substitutional disorder effects in Li 6 PS 5 X (X = Br, Cl), we conclude that in structurally ordered Li 6 PS 5 I the important inter-cage jump processes are switched off, hindering the ions from taking part in long-range ion transport. † Electronic supplementary information (ESI) available: Rietveld refinements and structural data, further NMR data. See Li 6 PS 5 I are also included. The lower part of the graph shows s DC T(1/T); the values given represent activation energies. For the sake of clarity, data of Li 6 PS 5 Br 0.75 I 0.25 (solid line, grey) have been plotted using an offset of +1 on the log scale.Li 6 PS 5 Cl 0.11(1) 0.18(2) 0.17(4) Li 6 PS 5 Br 0.06(1) 0.09(1) 0.10(4) Li 6 PS 5 I 0.23(1) 0.38(2) 0.18 (5) Paper PCCP

Lithium ion dynamics in LiZr2(PO4)3 and Li1.4Ca0.2Zr1.8(PO4)3

“…To study how Li + ion transport is affected by x as well as to investigate whether the starting materials influence the dynamic parameters, we measured complex impedances over a large temperature and frequency range. 26,42 Exemplarily, in Fig. 4a conductivity isotherms of rhombohedral LiZr 2 (PO 4 ) 3 are shown.…”

“…This situation resembles that of Li + ion dynamics in argyrodite-type Li 6 PS 5 I, which has been studied recently by our group. 42 Here, we assume that rapid forward-backward exchange processes between the sites A1 and A2 might be responsible for the peaks seen in NMR spin-lattice relaxometry. A2 sites might be occupied in samples with x > 0.…”

Lithium-Ion Transport in Nanocrystalline Spinel-Type Li[InxLiy]Br4 as Seen by Conductivity Spectroscopy and NMR

“…To investigate ionic transport further by means of electric modulus formalism (Hanghofer et al, 2019), we recorded the quantity M ′′ /ν (see also Figure 2C) as a function of temperature and for constant frequency (ν = 100 Hz and ν = 10 kHz, 173 K ≤ T ≤ 373 K). It turned out that, beginning from very low T, the quantity M ′′ /ν obeys a weaker-than-activated temperature behavior, in agreement with NCL-type electrical relaxation processes.…”

“…Presently, a range of Li-bearing oxides (Murugan et al, 2007;Buschmann et al, 2011;Thangadurai et al, 2014;Stanje et al, 2017;Uitz et al, 2017), sulfides (Kamaya et al, 2011;Wang et al, 2015;Dietrich et al, 2017), hydrides (Maekawa et al, 2009;Matsuo and Orimo, 2011;Kim et al, 2019), and thiophosphates (Deiseroth et al, 2008;Hanghofer et al, 2019) are being investigated with respect to ionic conductivity, stability and interfacial properties. Besides these classes of materials, halides (Lutz et al, 1990;Marx and Mayer, 1996;Gupta et al, 1997) are also regarded as up-and-coming materials to be employed as solid electrolytes.…”

Changing the Static and Dynamic Lattice Effects for the Improvement of the Ionic Transport Properties Within the Argyrodite Li6PS5-xSexI

“…[12][13][14][15][16] , and the lithium thiophosphates such as Li10GeP2S12, [17][18][19][20][21] Li2S-P2S5 glasses, [22][23][24][25][26] the thio-LISICONS, [27][28][29][30][31] and the Li6PS5X argyrodites. [32][33][34][35][36][37][38][39][40][41][42] While the thiophosphates are sensitive to ambient atmosphere and may not have the largest potential window, they demonstrate high ionic conductivity and high ductility, improving the processability and resulting contact to the active materials. 17,43,44 Standing out within this family of materials, the halide-containing argyrodites Li6PS5X (X = Cl, Br, I) have been explored with increasing interest.…”