Overview of Inorganic Electrolytes for All-Solid-State Sodium Batteries

Abstract

All-solid-state sodium batteries (AS³B) emerged as a strong contender in the global electrochemical energy storage market as a replacement for current lithium-ion batteries (LIB) owing to their high abundance, low cost, high safety, high energy density, and long calendar life. Inorganic electrolytes (IEs) are highly preferred over the conventional liquid and solid polymer electrolytes for sodium-ion batteries (SIBs) due to their high ionic conductivity (∼10^-2-10^-4 S cm^-1), wide potential window (∼5 V), and overall better battery performances. This review discusses the bird's eye view of the recent progress in inorganic electrolytes such as Na-β"-alumina, NASICON, sulfides, antipervoskites, borohydride-type electrolytes, etc. for AS³Bs. Current state-of-the-art inorganic electrolytes in correlation with their ionic conduction mechanism present challenges and interfacial characteristics that have been critically reviewed in this review. The current challenges associated with the present battery configuration are overlooked, and also the chemical and electrochemical stabilities are emphasized. The substantial solution based on ongoing electrolyte development and promising modification strategies are also suggested.

Figure 1

Interfacial challenges and strategies for inorganic electrolytes in AS³B.

Figure 2

Crystal structures of (a) Na-β/β′′-Al₂O₃. Panel a is reproduced from ref (45). Copyright 2016 Elsevier Ltd. (b) Rhombohedral and monoclinic polymorph of Na₃Zr₂Si₂PO₁₂ (NASICON). Panel b is reproduced with permission from ref (22). Copyright 2018 Wiley VCH Gmbh. (c) P-2-type layered electrolyte. Panel c is reproduced from ref (40). Copyright 2018 American Chemical Society. (d) Cubic and tetragonal phases of Na₃PnS₄. Panel d is reproduced with permission from ref (46). Copyright 2020 American Chemical Society. (e) Structure of Na₁₀SnP₂S₁₂. Panel e is reproduced from ref (47). Available under a CC-BY 4.0 license. Copyright 2016 Richards et al.

Figure 3

Hierarchical development of inorganic electrolytes for AS³B.

Figure 4

(a) Rhombohedral crystal structure of NASICON (Na₄M₂(AO₄)₃). (b) Local structure exhibiting characteristic cation sites in the NASICON framework. (c) Literature report regarding NASICONs having a specific element. (f) Experimentally determined ionic conductivity plot log scale of the y-axis vs x-axis Na content of NASICONs at ambient temperature and 300 °C reported based on the literature. (g) Distribution curve between theoretically (DFT) predicted Na-rich ground states/likely synthesized-NASICONs and experimentally synthesized Na-rich NASICONs (bottom panel). (h) XRD patterns of experimentally synthesized NASICONs with impurities (Hf/Zr)O₂) and SnO₂, respectively. Panels a–c and f–h are reproduced from ref (54). Available under a CC-BY 4.0 license. Copyright 2021 Ouyang, B., et al. (d) Energy barriers for single-ion migration of Na⁺ (blue color) following the Na_II-Na_IV-Na_I-Na_IV-Na_III trajectory. (e) Energy barriers for Li⁺ (purple color) having a Li_II-Li_IV-Li_I-Li_IV-Li_III trajectory path. Panels d and e are reproduced from ref (56). Available under a CC-BY 4.0 license. Copyright 2022 Zhu, L., et al.

Figure 5

(a) Various chalcogenide-based electrolytes reported for AS³B. Panel a is reproduced from ref (58). Copyright 2020 Editorial Board of Acta Physico-Chimica Sinica. (b) Reported ionic conductivities of existing IEs for AS³B. Panel b is reproduced from ref (59). Copyright 2018 Elsevier Ltd. Schematic illustrations of the (c) Na Wyckoff site cage size and (d) DFT-MD Na⁺ ion activation energy (E_a) with error bars vs d0 plot. (e) Pathway bottleneck extracted from DFT-optimized structures. (f) DFT-MD E_a with error bars vs d₁ plot. Panels c–f are reproduced from ref (60). Copyright 2020 American Chemical Society. (g) Rietveld refinement of X-ray powder diffraction data and (h) crystal structure of cubic Na_2.88Sb_0.88W_0.12S₄. Panels g and h are reproduced from ref (61). Available under a CC-BY 4.0 license. Copyright 2019 Hayashi et al.

Figure 6

(a) X-ray diffraction pattern of NaB₁₁H₁₄ and Na_x+2y(B₁₁H₁₄)_x(B₁₂H₁₂)_y. (b–d) Chemical structures of NaB₁₁H₁₄ and Na_x+2y(B₁₁H₁₄)_x(B₁₂H₁₂)_y. LSV curves of (e) the Na/Na₅(B₁₁H₁₄)(B₁₂H₁₂)₂/Al cell in the range of 1.3 to −0.1 V vs Na/Na⁺ and (f) the Na/Na₅(B₁₁H₁₄)(B₁₂H₁₂)₂/Na₅(B₁₁H₁₄)(B₁₂H₁₂)_2+C/Pt cell from 2.0 to 4.0 V vs Na/Na⁺ at a scan rate of 0.05 mV/s at 60 °C. (g) GCD characteristics of a symmetric Na/Na₅(B₁₁H₁₄)(B₁₂H₁₂)₂/Na cell at 60 °C with current densities of 25 μA cm^–2 for the initial 24 h and 50 μA/cm² for the rest of the measurements (1 h for each direction). Figure 6 is reproduced from ref (64). Copyright 2020 American Chemical Society.

Figure 7

(a) Crystal structure of Na_2–xZn_2–xGa_xTeO₆. (b) Charge/discharge characteristics of the cell with configuration NVP/NZTO-Gx/Na (x = 0, 0.1) with 0.2 C at 80 °C. Panels a and b are reproduced from ref (41). Copyright 2018 Wiley VCH Gmbh. (c) X-ray diffraction pattern of NZTO-Cx (x = 0–0.05) samples. (d) Enlarged view of the X-ray pattern. Panels c and d are reproduced from ref (42). Copyright 2018 Elsevier Ltd. (e) Crystal structures of P2-type and O′3-type Na₂Zn₂TeO₆ with corresponding ionic conductivity values. Panel e is reproduced from ref (39). Copyright 2020 American Chemical Society.

Figure 8

Ionic conductivity and electrochemical stability window of different IEs for AS³B. Figure 8 is reproduced from ref (29). Copyright 2023 Wiley VCH GmbH.

Figure 9

Recently reported electrode materials: (a) cathodes and (b) anodes for AS³B. Figure 9 is reproduced from ref (99). Copyright 2017 Royal Society of Chemistry.

Figure 10

(a) Schematic diagram of AS³B with device configuration Na₄C₆O₆/Na₃PS₄/Na₁₅Sn₄. (b) SEM image of catholyte cross-sectional interface and cathode surface with EDX mapping. (c) Charge–discharge characteristics of fabricated AS³B at various cycle numbers at 0.1 C at 60 °C. (d) Charge–discharge characteristics at different current rates. (e) Plot of capacity and Coulombic efficiency with respect to cycle number at 0.2 C at 60 °C. Panels a–e are reproduced from ref (111). Copyright 2018 Wiley-VCH GmbH. (f) Unfavorable interface between oxide cathode and Na₃PS₄. (g) Favorable electrode–electrolyte interface between the organic cathode and Na₃PS₄ electrolyte. Panels f and g are reproduced from ref (112). Copyright 2019 Elsevier Ltd. (h and i) Schematic diagram of interfaces (Na₃V₂(PO₄)₃/Na_3.3Zr_1.7La_0.3Si₂PO₁₂/Na and Na₃V₂(PO₄)₃/ionic liquid/Na_3.3Zr_1.7La_0.3Si₂PO₁₂/Na). (j and k) Cycling performance and Coulombic efficiency characteristics of cell Na₃V₂(PO₄)₃/Na_3.3Zr_1.7La_0.3Si₂PO₁₂/Na and Na₃V₂(PO₄)₃/ionic liquid/Na_3.3Zr_1.7La_0.3Si₂PO₁₂/Na at room temperature at 10 C for 10 000 cycles. Panels h–k are reproduced from ref (109). Copyright 2016 Wiley-VCH GmbH.

Figure 11

Schematic diagram showing the contact model of IE and the Na metal-based anode: (a) a poor wetting ability ceramic pellet and (b) a good wetting ability artificial interlayer during the plating of sodium. (c and d) Nyquist plots of the device with configuration Na/NASICON/Na and Na/H-NASICON/Na symmetric cell, respectively, at 65 °C. (e) Capacity versus voltage curve of a Na/H-NASICON/gold foil at a scanning rate of 0.5 mV s^–1 and (f) cycling stability test of the Na/H-NASICON/Na symmetric cells at 65 °C. Figure 11 is reproduced from ref (102). Copyright 2017 American Chemical Society.

Figure 12

(a) Creep evolution of the sodium–solid electrolyte and lithium–solid electrolyte contact areas with time subjected to a stack pressure of 1.0 MPa. (b) Contact stress maps of the Na surface. (c) Li surface at loading for 0, 0.1, and 2 h. (d) Schematic diagram for the interfacial creep process. (e) Rates of increase in contact fraction with time of the Na-SE and Li-SE interfaces. Figure 12 is reproduced from ref (121). Copyright 2021 American Chemical Society.