J. Kim, D.H. Seo, H. Kim, I. Park, J.K. Yoo, S.K. Jung, Y.U. Park, W.A. Goddard III, K. Kang, Unexpected discovery of low-cost maricite NaFePO4 as a highperformance electrode for Na-ion batteries, Energy Environ. Sci., 8, 540 (2015); https://doi.org/10.1039/c4ee03215b.

S.M. Oh, S.T. Myung, J. Hassoun, B. Scrosati, Y.K. Sun, Reversible NaFePO4 electrode for sodium secondary batteries, Electrochem. Commun. 22, 149 (2012); https://doi.org/10.1016/j.elecom.2012.06.014.

W. Tang, X. Song, Y. Du, C. Peng, M. Lin, S. Xi, B. Tian, J. Zheng, Y. Wu, F. Pan, K. P. Loh, High-performance NaFePO4 formed by aqueous ion-exchange and its mechanism for advanced sodium ion batteries. J. Mater. Chem. A 4, 4882 (2016); https://doi.org/10.1039/C6TA01111J.

A. Gutierrez, S. Kim, T.T. Fister, C.S. Johnson, Microwave-Assisted Synthesis of NaCoPO4 Red-Phase and Initial Characterization as High Voltage Cathode for Sodium-Ion Batteries. ACS Appl. Mater. Interfaces 9, 4391 (2017); https://doi.org/10.1021/acsami.6b14341.

V. Priyanka, G. Savithiri, R. Subadevi, M. Sivakumar, An emerging electrochemically active maricite NaMnPO4 as cathode material at elevated temperature for sodium-ion batteries. Appl. Nanosci., 10, 3945 (2020); https://doi.org/10.1007/s13204-020-01506-8.

X. Zhang, X. Rui, D. Chen, H. Tan, D. Yang, S. Huang, Y. Yu, Na3V2(PO4)3: An advanced cathode for sodium-ion batteries. Nanoscale, 11, 2556 (2019); https://doi.org/10.1039/C8NR09391A.

S.K. Pal, R. Thirupathi, S. Chakrabarty, S. Omar, Improving the Electrochemical Performance of Na3V2(PO4)3 Cathode in Na-Ion Batteries by Si-Doping, ACS Appl. Energy Mater. 3, 12054 (2020); https://doi.org/10.1021/acsaem.0c02188.

Y. Niu, Y. Zhang, M. Xu, A review on pyrophosphate framework cathode materials for sodium-ion batteries, J. Mater. Chem. A, 7, 15006 (2019); https://doi.org/10.1039/C9TA04274A.

P. Barpanda, J. Lu, T. Ye, M. Kajiyama, S.-C. Chung, N. Yabuuchi, S. Komaba, A. Yamada, A layer-structured Na2CoP2O7 pyrophosphate cathode for sodium-ion batteries, RSC Adv., 3, 3857 (2013); https://doi.org/10.1039/C3RA23026K.

A. Gezović, M. J. Vujković, M. Milović, V. Grudić, R. Dominko, S. Mentus, Recent developments of Na4M3(PO4)2(P2O7) as the cathode material for alkaline-ion rechargeable batteries: challenges and outlook, Energy Storage Materials, 37, 243 (2021); https://doi.org/10.1016/j.ensm.2021.02.011.

M. Nose, H. Nakayama, K. Nobuhara, H. Yamaguchi, S. Nakanishi, H. Iba, Na4Co3(PO4)2P2O7: A novel storage material for sodium-ion batteries, J. Power Sour., 234, 175 (2013); https://doi.org/10.1016/j.jpowsour.2013.01.162.

M. Nose, K. Nobuhara, S. Shiotani, H. Nakayama, S. Nakanishia, H.Ibaa, Electrochemical Li+ insertion capabilities of Na4-xCo3(PO4)2P2O7 and its application to novel hybrid-ion batteries, RSC Adv., 4, 9044 (2014); https://doi.org/10.1039/C3RA45836A.

F. Yang, Q. Liu, W. Xie, P. Xie, J.Shang, X. Shu, High-Content Lithium Aluminum Titanium Phosphate-Based Composite Solid Electrolyte with Poly(ionic liquid) Binder, Polymers (Basel). 14(7), 1274 (2022); https://doi.org/10.3390/polym14071274.

L. Gao, R. Zhao, S. Han, S. Li, R. Zou, Y. Zhao, Antiperovskite Ionic Conductor Layer for Stabilizing the Interface of NASICON Solid Electrolyte Against Li Metal in All-Solid-State Batteries. Batter. Supercaps. 4, 1491(2021); https://doi.org/10.1002/batt.202100123.

H. Raj, T. Fabre, M. Lachal, A. Neveu, J. Jean, M. C. Steil, R.Bouchet, V. Pralong, Stabilizing the NASICON Solid Electrolyte in an Inert Atmosphere as a Function of Physical Properties and Sintering Condi- tions for Solid-State Battery Fabrication. ACS Applied Energy Materials, 6(3), 1197 (2023); https://doi.org/10.1021/acsaem.2c02464.

Y. Zheng, Y. Yao, J. Ou, M. Li, D. Luo, H. Dou, Z. Li, K. Amine, A. Yu, Z. Chen, A review of composite solid-state electrolytes for lithium batteries: fundamentals, key materials and advanced structures. Chem. Soc. Rev. 49, 8790 (2020); https://doi.org/10.1039/D0CS00305K.

F. Sanz, C. Parada, J.M. Rojo, C. Ruíz-Valero, Synthesis, structural characterization, magnetic properties, and ionic conductivity of Na4MII3(PO4)2 (P2O7) (MII = Mn, Co, Ni), Chem. Mater., 13 1334 (2001); https://doi.org/10.1021/cm001210d.

F. Sanz, C. Parada, U. Amador, M.A. Monge, C. Ruíz-Valero, Na4Co3(PO4)2P2O7, a new sodium cobalt phosphate containing a three-dimensional system of large intersecting tunnels, J. Solid State Chem., 123, 129 (1996); https://doi.org/10.1006/jssc.1996.0161.

S.M. Wood, C. Eames, E. Kendrick, M.S. Islam, Sodium Ion Diffusion and Voltage Trends in Phosphates Na4MII3(PO4)2 (P2O7) (M = Fe, Mn, Co, Ni) for Possible High-Rate Cathodes, J. Phys. Chem. C., 119, 15935 (2015); https://doi.org/10.1021/acs.jpcc.5b04648.

H. Moriwake, A. Kuwabara, C.A.J. Fisher, M. Nose, H. Nakayama, S. Nakanishi, H. Iba, Y. Ikuhara, Crystal and electronic structure changes during the charge- discharge process of Na4Co3(PO4)2P2O7, J. Power Sources., 326, 220 (2016); https://doi.org/10.1016/j.jpowsour.2016.07.006.

H. Zhang, I. Hasa, D. Buchholz, B. Qin, D. Geiger, S. Jeong, U. Kaiser, S. Passerini, Exploring the Ni redox activity in polyanionic compounds as conceivable high po- tential cathodes for Na rechargeable batteries, NPG Asia Mater., 9, e370 (2017); https://doi.org/10.1038/am.2017.41.

H. Kim, G. Yoon, I. Park, K.Y. Park, B. Lee, J. Kim, Y.U. Park, S.K. Jung, H.D. Lim, D. Ahn, S. Lee, K. Kang, Anomalous Jahn-Teller behavior in a manganese-based mixed-phosphate cathode for sodium ion batteries, Energy Environ. Sci. 8, 3325 (2015); https://doi.org/10.1039/c5ee01876e.

X. Ma, X. Wu, P. Shen, Rational Design of Na4Fe3(PO4)2(P2O7) Nanoparticles Embedded in Graphene: Toward Fast Sodium Storage Through the Pseudoca- pacitive Effect, ACS Appl. Energy Mater., 1, 6268 (2018); https://doi.org/10.1021/ac- saem.8b01275.

H. Kim, I. Park, D.H. Seo, S. Lee, S.W. Kim, W.J. Kwon, Y.U. Park, C.S. Kim, S. Jeon, K. Kang, New Iron-Based Mixed-Polyanion Cathodes for Lithium and Sodium Rechargeable Batteries: Combined First Principles Calculations and Experimental Study, J. Am. Chem. Soc. 134, 10369 (2012); https://doi.org/10.1021/ja3038646.

H. Kim, I. Park, S. Lee, H. Kim, K.Y. Park, Y.U. Park, H. Kim, J. Kim, H.D. Lim, W.S. Yoon, K. Kang, Understanding the electrochemical mechanism of the new iron- based mixed-phosphate Na4Fe3(PO4)2(P2O7) in a Na rechargeable battery, Chem. Mater., 25, 3614 (2013); https://doi.org/10.1021/cm4013816.

J.Y. Jang, H. Kim, Y. Lee, K.T. Lee, K. Kang, N.S. Choi, Cyclic carbonate based- electrolytes enhancing the electrochemical performance of Na4Fe3(PO4)2(P2O7) cathodes for sodium-ion batteries, Electrochem. Commun., 44, 74 (2014); https://doi.org/10.1016/j.elecom.2014.05.003.

N.V Kosova, A.A. Shindrov, Effect of Mixed Li+/Na+-ion Electrolyte on electro- chemical perforamce of Na4Fe3(PO4)2(P2O7) in hybrid batteries, Batteries, 5, 39 (2019); https://doi.org/10.3390/batteries5020039.

A.J. Fernández-Ropero, M. Zarrabeitia, M. Reynaud, T. Rojo, M. Casas-Cabanas, Toward Safe and Sustainable Batteries: Na4Fe3(PO4)2(P2O7) as a Low-Cost Cathode for Rechargeable Aqueous Na-Ion Batteries, J. Phys. Chem. C., 122, 133 (2018); https://doi.org/10.1021/acs.jpcc.7b09803.

M.H. Lee, S.J. Kim, D. Chang, J. Kim, S. Moon, K. Oh, K.Y. Park, W.M. Seong, H. Park, G. Kwon, B. Lee, K. Kang, Toward a low-cost high- voltage sodium aqueous rechargeable battery, Mater. Today. 29, 26 (2019); https://doi.org/10.1016/j.mattod.2019.02.004.

A.R. West, Solid State Chemistry and Its Applications (Wiley, Hoboken, 1984).

D.C. Sinclair, A.R.West, Electrical properties of a LiTaO3 single crystal, Phys.Rev. B Condens. Matter. 39(18), 13486 (1986); https://doi.org/10.1103/PhysRevB.39.13486.

E. Barsoukov, J.R. Macdonald, Impedance Spectroscopy Theory, Experiment, and Applications (Wiley, Hoboken, New Jersey, 2005).