Currently the extensive use of portable electronic devices have given rise to the high demand for reliable high energy density storage in the form of batteries. Today, lithium-ion batteries (LIBs) are the leading technology as they offer high energy density and relatively long lifetimes.[1] However, safety issues and the rarity of lithium brings about the relatively high cost of these batteries.[2] To address this issue, sodium-ion batteries (SIBs) have been developed as a low cost alternative for LIBs.[2, 3] Sodium’s similar chemistry to lithium enables accessible parallel implementation of LIB technology into SIB and its natural abundance ensures that sodium can be acquired at a much cheaper price compared to lithium.[4, 5] Recent development of sustainable and clean energy sources such as solar and wind has also escalated the need for SIBs.[4, 6] The unstable supply of energy generated from these renewable energy sources makes an efficient and reliable energy storage system crucial to ensure a continuous flow of energy during times where the energy production is poor.[3, 6] Such large scale stationary energy storage systems will be unsuitable for LIBs due to its relatively high cost, however with SIBs this could be realized.[3]

Nonetheless, challenges still remain for the development of SIBs. Optimization of electrode materials capable of reversible insertion/extraction of sodium-ions in a safe and economic way under high current density are required in order to produce commercially viable SIBs.[2, 7] Present materials commonly investigated for SIB positive electrodes are metal oxides, phosphates, sulfates and metal-organic frameworks (MOF), while carbon based materials are still a favorable choice as negative electrodes due to its low potential against Na, natural abundance, renewability, and low cost.[3, 4] Despite the fact that the reversible intercalation of sodium-ion into/from graphite is not significant, research has shown that other carbon based materials can be used.[8-10].

Although these electrode materials in SIBs have been studied from an electrochemical perspective, further work is still needed to understand the insertion/extraction mechanism of sodium ions into these materials and more importantly how sodium moves inside these materials. As the structure and chemical environment of materials are closely related to their properties, it is very important to understand the mechanism to be able to design new materials with desired properties. In this study, we use a combination of in-situ X-ray diffraction (XRD), solid state nuclear magnetic resonance (SS-NMR) and quasi-elastic neutron scattering (QENS) to study the mechanism of sodium-ion insertion/extraction in some selected electrode materials. XRD will provide long range ordering of the structure of the material. SS-NMR will provide the local environment of the sodium, and QENS enables insight on the diffusion mechanism of the sodium ions inside the selected materials. The combination of these three techniques will provide a more complete picture of the mechanism of sodium-ion insertion/extraction and movement inside the electrode materials. If these mechanisms can be properly understood, it will be possible to design a safe and reliable SIB which could be an alternative to LIB realizing a cheaper energy storage system for the world.

This talk will focus on our first results based on carbon based materials such as carbon nanotubes and graphene. With characterization using XRD and SS-NMR we were able to compare the structure and the chemical environment of the sodium within these carbons after charge and discharge, giving interesting insight on how these materials will behave in a battery.

 

References

[1] J.M. Tarascon, M. Armand, Nature, 414 (2001) 359-367.

[2] V. Palomares, P. Serras, I. Villaluenga, K.B. Hueso, J. Carretero-Gonzalez, T. Rojo, Energ. Environ. Sci., 5 (2012) 5884-5901.

[3] M. Sawicki, L.L. Shaw, RSC Advances, 5 (2015) 53129-53154.

[4] H. Kang, Y. Liu, K. Cao, Y. Zhao, L. Jiao, Y. Wang, H. Yuan, Journal of Materials Chemistry A, 3 (2015) 17899-17913.

[5] M.D. Slater, D. Kim, E. Lee, C.S. Johnson, Adv. Funct. Mater., 23 (2013) 947-958.

[6] N.-S. Choi, Z. Chen, S.A. Freunberger, X. Ji, Y.-K. Sun, K. Amine, G. Yushin, L.F. Nazar, J. Cho, P.G. Bruce, Angew. Chem. Int. Ed., 51 (2012) 9994-10024.

[7] J.C. Pramudita, D. Pontiroli, G. Magnani, M. Gaboardi, M. Riccò, C. Milanese, H.E.A. Brand, N. Sharma, ChemElectroChem, 2 (2015) 600-610.

[8] A. Ponrouch, A.R. Goñi, M.R. Palacín, Electrochem. Commun., 27 (2013) 85-88.

[9] V.G. Pol, E. Lee, D. Zhou, F. Dogan, J.M. Calderon-Moreno, C.S. Johnson, Electrochim. Acta, 127 (2014) 61-67.

[10] P. Thomas, D. Billaud, Electrochim. Acta, 47 (2002) 3303-3307.