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. 2024 Mar 19;14(13):9228-9242.
doi: 10.1039/d4ra01454e. eCollection 2024 Mar 14.

Structural, morphological, electrical, and dielectric properties of Na2Cu5(Si2O7)2 for ASSIBs

Mohamed Ben Bechir  1 , Mehdi Akermi  2   3
Affiliations

Structural, morphological, electrical, and dielectric properties of Na2Cu5(Si2O7)2 for ASSIBs

Mohamed Ben Bechir et al. RSC Adv. .

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Expression of concern in

Abstract

Solid inorganic electrolyte materials are fundamental components for constructing all-solid-state sodium-ion batteries. These solid electrolytes offer considerable benefits related to safety, electrochemical performance, and mechanical stability in comparison to liquid organic electrolyte systems. This study investigates the sodium ion conduction mechanism and relaxation kinetics in the sorosilicate material Na2Cu5(Si2O7)2, a potential solid electrolyte, using impedance spectroscopy. Analysis of the DC conductivity data demonstrates that sodium ion mobility follows Arrhenius behavior with a thermal activation energy barrier of 1.21 eV. This work highlights the importance of carefully choosing an appropriate equivalent circuit model to extract DC conductivity parameters from impedance data, given the contributions from both grain and grain boundary effects. Analysis of the AC conductivity and dielectric constant as a function of frequency and temperature demonstrates that ionic conduction takes place in this material through a process in which charge carriers overcome correlated energy barriers, known as correlated barrier hopping. The neutron diffraction patterns were analyzed using soft bond valence sum (BVS) techniques to map the possible ionic conduction pathways within the unit cell. Examination of the data points to obstructions in the sodium ion diffusion routes along the a-axis and diagonal of the bc plane within the triclinic unit cell. These bottlenecks likely contribute to the high activation energy and correspondingly low ionic conductivity observed. Analysis of dielectric properties by modulus verified that the ionic conduction relaxation phenomena exhibit thermal activation and a distribution of relaxation times. In summary, this work elucidates the microscopic ionic conduction mechanism in Na2Cu5(Si2O7)2 through extensive analysis encompassing DC/AC conductivity, electric modulus, and dielectric constant measurements. The insights gained into the ionic conduction mechanism will aid in engineering optimized ionic conductor materials for battery technologies.

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Conflict of interest statement

There are no conflicts to declare.

Figures

Fig. 1
Fig. 1. At room temperature: patterns in X-ray and neutron diffractions of Na2Cu5(Si2O7)2.
Fig. 2
Fig. 2. (a) Constructed crystal structure of Na2Cu5(Si2O7)2. (b) Characterizing the sodium ion surroundings at the 2i site: a chemical analysis. (c) Expanding crystal structure analysis to emphasize inter-sodium ion distances. (d) Amplified perspectives on local crystal structure emphasizing conduction pathway constraints along (i) and (iv).
Fig. 3
Fig. 3. SEM images of Na2Cu5(Si2O7)2.
Fig. 4
Fig. 4. (a) Temperature-dependent fitting of Cole–Cole plots for Na2Cu5(Si2O7)2 with inset illustrating the equivalent circuit. (b) Illustrative depiction of Material's grain and grain boundary structure. (c) Inter-grain Na-ion migration via grain boundaries. Temperature-dependent variation of (d) Z′(f) and (e) Z′′(f). (f) Temperature dependence of Rg and Rgb. σdcvs. 1000/T plot of Na2Cu5(Si2O7)2.
Fig. 5
Fig. 5. (a) Variation of σ′(f) at different temperatures. (b) Variation of s with temperature. (c) The temperature dependency of the ln(σ′) at various frequencies. (d) Frequency dependence of Ea (eV).
Fig. 6
Fig. 6. Temperature-dependent changes in (a) M′(f) and (b) M′′(f) for Na2Cu5(Si2O7)2. (c) Variation of β with temperature. (d) Arrhenius plot of
Fig. 7
Fig. 7. Temperature-dependent of (a) ε′(f) and (c) ε′′(f) for Na2Cu5(Si2O7)2. (b) Frequency-dependent of ε′(T). (d) Variation of m with temperature.
Fig. 8
Fig. 8. Utilizing various equivalent circuit models for fitting experimental impedance Cole–Cole plot at 713 K.
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