Preparation and electrical conductivity of (Cu0.5Ag0.5)7SiS5I-based superionic ceramics

doi:10.21203/rs.3.rs-34102/v1

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Preparation and electrical conductivity of (Cu0.5Ag0.5)7SiS5I-based superionic ceramics

https://doi.org/10.21203/rs.3.rs-34102/v1

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The ceramics based on (Cu0.5Ag0.5)7SiS5I solid solution of superionic conductor with argyrodite structure were prepared by using the powders with different particles size. The structural studies of powders were performed by XRD technique, while the ceramic samples with different average size of the crystallites were investigated by microstructural analysis. The total electrical conductivity of ceramic samples was measured by impedance spectroscopy in the frequency range from 10 Hz to 2×106 Hz and temperature interval from 292 K to 383 K. The contributions of ionic and electronic components into the total electrical conductivity were separated as well as their temperature behavior was studied. The dependences of ionic and electronic conductivity and their activation energies on average size of the crystallites in (Cu0.5Ag0.5)7SiS5I-based ceramic samples were investigated.

Materials Engineering

argyrodite

superionic conductor

ceramic

ionic conductivity

activation energy

Among ceramic materials, electrochemical ceramics have recently been widely studied in order to develop the latest technologies of electrochemical energy storage, which is caused by the rapid development of alternative energy sources, electric vehicles and portable electronic devices [1–5]. Electrochemical capacitors (supercapacitors), batteries and fuel cells are usually used as electrochemical energy storage devices [2]. The most promising materials in this regard are solid electrolytes used in all-solid-state batteries. It should be noted that the use of solid electrolyte instead of liquid one not only increases the safety of batteries, but also simplifies the design of the battery itself [5–8].

Since the efficiency of batteries directly depends on the properties of the working material, so the search for and improvement of new materials is relevant. Sulfur-containing solid electrolytes attract considerable attention due to the high ionic conductivity, which is provided by the peculiarities of their crystal structure [5, 6, 9–12], among which it is worth noting complex phosphorus sulfides with Li⁺ and Na⁺. Usually sulfur-containing superionic compounds with ionic conductivity of Li⁺ and Na⁺ are difficult to obtain in the crystalline state [11], so they are obtained in glass-ceramic form [10, 11, 13, 14].

It should be noted that promising superionic materials in this regard are presented by compounds with the structure of argyrodite [15–18], which have high values of ionic conductivity. They are characterized by a similar crystalline structure (tetrahedral dense packaging) and high variability of compositions [19, 20], which favors the formation of solid solutions. In addition, in recent years they have been obtained in the forms of composites, ceramics and thin films [21–24]. Сopper-containing argyrodites in ceramic form were studied in Ref. [23]. In this paper, we will focus on investigating new ceramic material (Cu_0.5Ag_0.5)₇SiS₅I based on argyrodites, in which half of the copper atoms are replaced by silver atoms. As far as we know nowadays, such studies have not been conducted. The electrical properties of (Cu_0.5Ag_0.5)₇SiS₅I mixed crystals were studied by impedance spectroscopy in Ref. [25].

Thus, the aim of this paper is to prepare ceramic samples based on (Cu_0.5Ag_0.5)₇SiS₅I solid solution, study their structural and electrical properties, separate the contributions of ionic and electronic conductivity components, and compare the electrical parameters of the obtained ceramic samples with the parameters of crystals. It should be noted that the production and study of argyrodites in the form of ceramic samples is relevant because they can successfully replace crystalline materials.

(Cu_0.5Ag_0.5)₇SiS₅I solid solution was synthesised from pre-synthesized Cu₇SiS₅I and Ag₇SiS₅I compounds in vacuumized quartz ampoules. The process of (Cu_0.5Ag_0.5)₇SiS₅I synthesis included step heating up to 1023 K at a rate of 100 K/h and ageing during 48 hours, further increase of temperature to 1470 K at a rate of 50 K/h and ageing at this temperature for 72 hours. The annealing temperature was 873 K, ageing at this temperature for 120 hours. Cooling to room temperature was performed in the oven off mode.

The ceramic samples were prepared from powders of different dispersion: 1) powders obtained by grinding in an agate mortar with an average particle size of ~ 10—50 µm; 2) powders obtained by grinding in a planetary ball mill PQ-N04 for 30 min and 60 min with a speed of 200 rpm. Then the powders were pressed at ~ 400 MPa and were annealed at 973 K during 36 hours. In such a way the polycrystalline ceramic samples were fabricated in the form of disks with a diameter of 8 mm and a thickness of 3–4 mm.

The structural properties of (Cu_0.5Ag_0.5)₇SiS₅I powders and ceramic samples were studied by XRD technique and microstructural analysis. The XRD measurements were performed be the diffractometer DRON 4–07 with CuKα radiation, angle scanning speed 2θ was 0.02 degree, exposure was 1 s. The ceramic samples were investigated by microstructural analysis using metallographic microscope METAM - R1.

Electrical conductivity measurements were carried out by impedance spectroscopy [26] in frequency range from 10 Hz to 2 × 10⁶ Hz and temperature interval from 292 to 383 K ranges with combination of high-precision LCR meters: Keysight E4980A and AT-2818. The amplitude of the alternating current constituted 10 mV. Measurement was carried out by a two-electrode method, on blocking (electronic) gold contacts. Gold contacts for measurements were applied by chemical precipitation from solutions [25].

Figure 1 shows the XRD patterns for (Cu_0.5Ag_0.5)₇SiS₅I powders with different average particle size. It is shown that XRD patterns for (Cu_0.5Ag_0.5)₇SiS₅I powders are similar to diffractogram for (Cu_0.5Ag_0.5)₇SiS₅I solid solution crystal [25]. Comparison of diffractograms indicates that the lines broadening occurs with particle size decrease (Fig. 1). The results of microstructural analysis for prepared (Cu_0.5Ag_0.5)₇SiS₅I-based ceramics are presented in Fig. 2. From histograms of crystallites size distribution for different ceramic samples, obtained from powders which grinding in agate mortar and planetary ball mill for 30 min and 60 min, the size of crystallites after annealing was determined (Fig. 2).

It is shown that the ceramic samples prepared by sintering powders obtained by grinding in a planetary ball mill are characterized by a more homogeneous microstructure, characterized by the distribution of particles in a narrower range, in contrast to the samples obtained by sintering a microcrystalline powder with a particle size of 10–50 µm (Fig. 2). As a result of recrystallization process, the average size of crystallites for samples obtained from powders grinding in an agate mortar is ~ 12 µm, while for samples obtained from powders grinding in a planetary ball mill for 30 min and 60 min is ~ 5 µm and ~ 3 µm, respectively.

Figure 3 presents the frequency dependences of total electrical conductivity for (Cu_0.5Ag_0.5)₇SiS₅I-based ceramics. With frequency increase the electrical conductivity grows which is typical for materials with ionic conductivity in solid state [27]. The insert to Fig. 3 shows the dependence of the total electrical conductivity on the size of crystallites. It is revealed that at decrease of size of crystallites from 12 µm to 3 µm the decrease of total electrical conductivity for (Cu_0.5Ag_0.5)₇SiS₅I-based ceramic samples is observed.

For separation of the total electrical conductivity into ionic and electronic components, a standard approach using electrode equivalent circuits (EEC) [27, 28] and their analysis on Nyquist plots was used. The parasitic inductance of the cell (~ 2 × 10^− 8 H) is taken into account during the analysis of all ceramic samples. It is shown that ceramic samples prepared on the basis of (Cu_0.5Ag_0.5)₇SiS₅I, are characterized by equal values of electronic and ionic components of electrical conductivity (σ_ion ~ σ_el). At Z'-Z" dependences for (Cu_0.5Ag_0.5)₇SiS₅I-based ceramics with average crystallites size of 12 µm, 5 µm, and 3 µm two semicircles are observed.

The ЕЕС, which described the Nyquist plots, can be divided in two parts: one of them relates to ionic processes, another one to electronic processes. Low-frequency semicircles on the Nyquist plots correspond to the diffusion relaxation processes at the electrode/crystal boundary which is described by the capacity of the double diffusion layer C_dl and Warburg element of W_d, responsible for diffusion within the latter (Fig. 4). Serial to them were included the elements with R_gb/C_gb parameters which related to resistance and capacity of the grain boundaries of ceramic samples (the end of low-frequency semicircles) (Fig. 4). High-frequency semicircles correspond to the conductivity processes determined by the resistance of intra-grain boundaries, which is marked by R_db on the EEC (Fig. 4). Thus, the ionic conductivity of (Cu_0.5Ag_0.5)₇SiS₅I-based ceramic samples is determined by the sum of the resistance of grain boundaries R_gb and the resistance limiting the ion diffusion W_R. It should be noted that on EEC parallelly to the elements responsible for ion processes the electronic resistance R_e is included and determined electronic conductivity of the samples (Fig. 4). With crystallites size decrease (12 µm →5 µm→ 3 µm) the low-frequency shift of low-frequency semicircle on EEC is observed. It may be related to the increasing of influence of diffusion ionic processes as well as increasing of ionic relaxation time due to the electronic conductivity decreasing.

Temperature studies have shown that with increasing temperature, the increase of electronic conductivity gradually eliminates the influence of diffusion ionic processes at the boundaries of ceramics crystallites, as evidenced by the decrease of the high-frequency semicircle at 323 K (Fig. 4, curve 2). With further increase of temperature up to 373 K (Fig. 4, curve 3) there is a further reduction of the influence of diffusion ionic processes, which, together with the decrease in the thickness of the double diffusion layer, and the complete disappearance of the high-frequency semicircle.

Figure 5a shows the dependences of the ionic and electronic components of electrical conductivity on the size of crystallites in (Cu_0.5Ag_0.5)₇SiS₅I-based ceramic samples. It is revealed that the decrease in the size of crystallites leads to monotonous decrease of ionic and electronic components of electrical conductivity, while their ratio remains unchanged (σ_ion ~ σ_el).

The temperature dependences of the ionic and electronic components of electrical conductivity in the Arrhenius coordinates presents on Fig. 6. The linear behavior of above mentioned dependences was confirmed the thermoactivating character of electrical conductivity. From the presented temperature dependences of the ionic and electronic conductivity the activation energies were determined (Fig. 5b). It is shown that the activation energies of both components of electrical conductivity for (Cu_0.5Ag_0.5)₇SiS₅I-based ceramic samples nonlinearly depend on the size of crystallites (рис.5b). Thus, at the transition of the size of crystallites from 12 µm to 5 µm the slight increase of the activation energies of both components of electrical conductivity is observed, whereas at the transition of the size of crystallites from 5 µm to 3 µm the tendency to decrease of the activation energies of both components of electrical conductivity is revealed.

It should be noted that (Cu_0.5Ag_0.5)₇SiS₅I-based ceramics are characterized by disordered structure, which is associated with different reasons: (i) structural disordering, caused by the different size of crystallites; (ii) structural disordering, caused by the recrystallization process during annealing; (iii) compositional disordering, caused by the Cu⁺↔Ag⁺ cationic substitution. The combination of the above features in the final case leads to a change of the Nyquist plots for samples with different size of crystallites (Fig. 4) and causes the corresponding behavior of the total electrical conductivity (Fig. 3), its ionic and electronic components (Fig. 5), and its thermoactivation behavior (Figs. 6 and 7) for (Cu_0.5Ag_0.5)₇SiS₅I-based ceramics.

Comparison of the values of ionic and electronic conductivities, as well as their ratio for crystal and ceramic samples of (Cu_0.5Ag_0.5)₇SiS₅I solid solution have shown that the ionic conductivity and the ratio σ_ion/σ_el of ceramic sample with an average crystallite size of 12 µm is slightly greater than that of crystal ones (σ_ion = 2.2 × 10^− 3 S/cm and σ_ion/σ_el = 0.9 for crystal) [25]. Thus, studies show that (Cu_0.5Ag_0.5)₇SiS₅I-based ceramics is characterized by high electrical parameters, comparable or even higher than in the corresponding crystals. This, in turn, makes their use in solid ionic devices more promising due to their greater manufacturability and ease of production compared to crystals.

The compound of (Cu_0.5Ag_0.5)₇SiS₅I solid solution with the same content of copper and silver atoms was synthesized and three types of ceramic samples were made on its basis by pressing and sintering. Powders of different dispersion were obtained by grinding in an agate mortar as well as in a planetary ball mill. X-ray diffraction spectra showed that during grinding the structure of the argyrodite type is preserved, however, as the particle size decreases, the diffraction bands expand. The obtained ceramic samples were investigated by microstructural analysis, which resulted in the dependences of size distribution and average crystallites size for (Cu_0.5Ag_0.5)₇SiS₅I ceramic samples.

Impedance studies of the total electrical conductivity for (Cu_0.5Ag_0.5)₇SiS₅I ceramic samples were performed in the frequency range from 10 Hz to 2 × 10⁶ Hz and temperature interval from 292 K to 383 K. With increasing frequency, an increase of the total electrical conductivity and its decrease with decreasing crystallite size were observed. Using Nyquist plots the electrical conductivity of (Cu_0.5Ag_0.5)₇SiS₅I-based ceramics was separated into ionic and electronic components. It is revealed that in the studied ceramic samples the values of ionic and electronic components are almost equal (σ_ion ~ σ_el), with decreasing crystallites size they decrease, аnd their ratio σ_ion/σ_el remains unchanged. Temperature studies have shown that the temperature dependences of ionic and electronic components are described by the Arrhenius law, which confirms the thermoactivating character of conductivity. Revealed high values of electrical parameters for ceramic samples of (Cu_0.5Ag_0.5)₇SiS₅I solid solution, which are comparable to the values for crystals, make them promising to develop on their basis electrochemical devices.

Gogotsi Y, Simon P. P. True performance metrics in electrochemical energy storage. Science. 2011;334:917–8.
Fernao Pires V, Romero-Cadaval E, Vinnikov D. D, et al. Power converter interfaces for electrochemical energy storage systems – A review. Energy Convers Manag. 2014;86:453–75.
Li H, Zhang X, Zhao Z, et al. Flexible Sodium-Ion Based Energy Storage Devices: Recent Progress and Challenges. Energy Storage Materials. 2020;26:83–104.
Nykvist B, Nilsson M. Rapidly falling costs of battery packs for electric vehicles. Nature Climate Change. 2015;5:329–32.
Wu Z, Xie Z, Yoshida A, et al. Utmost limits of various solid electrolytes in all-solid-state lithium batteries: A critical review. Renew Sustain Energy Rev. 2019;109:367–85.
Fergus LW. Ceramic and polymeric solid electrolytes for lithium-ion batteries. J Power Sources. 2010;195:4554–69.
Zhang Z, Zhang Q, Ren C, et al. A ceramic/polymer composite solid electrolyte for sodium batteries. J Mater Chem A. 2016;4:15823–8.
Wang Y, Richards W, Ong S, et al. Design principles for solid-state lithium superionic conductors. Nature Mater. 2015;14:1026–31.
Lian P-J, Zhao B-S, Zhang L-Q, et al. The inorganic sulfide solid electrolytes for all-solid-state lithium secondary batteries. J Mater Chem A. 2019;7:20540–57.
Park KH, Kim DH, Kwak H, et al. Solution-Derived Glass-Ceramic NaI × Na₃SbS₄ Superionic Conductors for All-Solid-State Na-Ion Batteries. J Mater Chem A. 2018;6:17192–200.
Tatsumisago M, Hayashi A. Sulfide Glass-Ceramic Electrolytes for All-Solid-State Lithium and Sodium Batteries. J Appl Glass Sci. 2014;5:226–35.
Ma Q, Tsai C-L, Wei X-K, et al. Room temperature demonstration of a sodium superionic conductor with grain conductivity in excess of 0.01 S cm^-1 and its primary applications in symmetric battery cells. J Mater Chem A. 2019;7:7766–76.
Hayashi A, Noi K, Sakuda A, et al. Superionic glass-ceramic electrolytes for room-temperature rechargeable sodium batteries. Nat Commun. 2012;3:856.
Xu RC, Xia XH, Yao ZJ, et al. Preparation of Li₇P₃S₁₁ glass-ceramic electrolyte by dissolution-evaporation method for all-solid-state lithium ion batteries. Electrochim Acta. 2016;219:235–40.
Jung WD, Kim J-S, Choi S, et al. Superionic Halogen-Rich Li-Argyrodites Using In Situ Nanocrystal Nucleation and Rapid Crystal Growth. Nano Lett. 2020;20:2303–9.
Zhou L, Assoud A, Zhang Q, et al. New Family of Argyrodite Thioantimonate Lithium Superionic Conductors. J Am Chem Soc. 2019;141:19002–13.
Wang H, Yu C, Ganapathy S, et al. A lithium argyrodite Li₆PS₅Cl_0.5Br_0.5 electrolyte with improved bulk and interfacial conductivity. J Power Sources. 2019;412:29–36.
Deiseroth H-J, Kong S-T, Eckert H, et al. Li₆PS₅X: a class of crystalline Li-rich solids with an unusually high Li + mobility. Angew Chem Int Ed. 2008;47:755–8.
Kuhs WF, Nitsche R, Scheunemann K. The argyrodites – a new family of the tetrahedrally close-packed structures. Mater Res Bull. 1979;14:241–8.
Nilges T, Pfitzner A. A structural differentiation of quaternary copper argyrodites: Structure – property relations of high temperature ion conductors. Z Kristallogr. 2005;220:281–94.
Orliukas AF, Kazakevicius E, Kezionis A, et al. Preparation, electric conductivity and dielectrical properties of Cu₆PS₅I-based superionic composites. Solid State Ionics. 2009;180:183–6.
Studenyak IP, Izai VY, Studenyak VI, et al. Influence of Cu₆PS₅І superionic nanoparticles on the dielectric properties of 6СВ liquid crystal. Liq Cryst. 2017;44:897–903.
Šalkus T, Kazakevičius E, Banys J, et al. Influence of grain size effect on electrical properties of Cu₆PS₅I superionic ceramics. Solid State Ionics. 2014;262:597–600.
Studenyak IP, Kranjčec M, Izai VY, et al. Structural and temperature-related disordering studies of Cu₆PS₅I amorphous thin films. Thin Solid Films. 2012;520:1729–33.
Studenyak IP, Pogodin AI, Studenyak VI, et al. Electrical properties of copper- and silver-containing superionic (Cu_{1 – x}Ag_x)₇SiS₅I mixed crystals with argyrodite structure. Solid State Ionics. 2020;345:115183(6).
Orazem ME, Tribollet B. Electrochemical Impedance Spectroscopy. New Jersey (USA): John Wiley & Sons; 2008.
Ivanov-Schitz AK, Murin IV. Solid State Ionics, vol. 1. S.-Petersburg (Russian Federation): Univ. Press, 2000 (in Russian).
Huggins RA. Simple method to determine electronic and ionic components of the conductivity in mixed conductors: a review. Ionics. 2002;8:300–13.

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Preparation and electrical conductivity of (Cu0.5Ag0.5)7SiS5I-based superionic ceramics

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Journal Publication

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Abstract

Figures

1 Introduction

2 Materials And Methods

3 Results And Discussion

4 Conclusions

References

Status:

Journal Publication

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