Neutron studies of Na-ion battery materials

Abstract

The relative vast abundance and more equitable global distribution of terrestrial sodium makes sodium-ion batteries (NIBs) potentially cheaper and more sustainable alternatives to commercial lithium-ion batteries (LIBs). However, the practical capacities and cycle lives of NIBs at present do not match those of LIBs and have therefore hindered their progress to commercialisation. The present drawback of NIB technology stems largely from the electrode materials and their associated Na+ ion storage mechanisms. Increased understanding of the electrochemical storage mechanisms and kinetics is therefore vital for the development of current and novel materials to realise the commercial NIB. In contrast to x-ray techniques, the non-dependency of neutron scattering on the atomic number of elements (Z) can substantially increase the scattering contrast of small elements such as sodium and carbon, making neutron techniques powerful for the investigation of NIB electrode materials. Moreover, neutrons are far more penetrating which enables more complex sample environments including in situ and operando studies. Here, we introduce the theory of, and review the use of, neutron diffraction and quasi-elastic neutron scattering, to investigate the structural and dynamic properties of electrode and electrolyte materials for NIBs. To improve our understanding of the actual sodium storage mechanisms and identify intermediate stages during charge/discharge, ex situ, in situ, and operando neutron experiments are required. However, to date there are few studies where operando experiments are conducted during electrochemical cycling. This highlights an opportunity for research to elucidate the operating mechanisms within NIB materials that are under much debate at present.

Spray‐coated Hard Carbon Composite Anodes for Sodium‐Ion Insertion

“…For example, hazelnut shell derived HC in 1 M NaPF 6 in EC : PC (1 : 1) showed capacity fading after the 50 th cycle due to low reversibility of Na + ion storage for HC particles with highest impurities and highest amorphous carbon structure [73] . Half‐cell studies, which are common in LIBs research have been initially adapted for SIBs employing HC anodes and Na metal cathodes [61,74] . However, it has been reported that for HC with Na metal lower rate capabilities have been obtained compared to full‐cell studies [60,69] .…”

“…[73] Half-cell studies, which are common in LIBs research have been initially adapted for SIBs employing HC anodes and Na metal cathodes. [61,74] However, it has been reported that for HC with Na metal lower rate capabilities have been obtained compared to full-cell studies. [60,69] Hence, our half-cell studies data are in line with half-cell studies reported in the literature.…”

Understanding High-Voltage Behavior of Sodium-Ion Battery Cathode Materials Using Synchrotron X-ray and Neutron Techniques: A Review

“…These unique characteristics provide neutrons with distinct advantages for battery studies, offering complementary information to X-ray studies. Due to its high sensitivity to light elements, especially Li, Na, and O, the neutron technology is able to distinguish them from other heavy elements, such as Ni, Mn, and Fe, which are common elements in SIB cathode materials [46].…”

“…These unique characteristics provide neutrons with distinct advantages for battery studies, offering complementary information to X-ray studies. Due to its high sensitivity to light elements, especially Li, Na, and O, the neutron technology is able to distinguish them from other heavy elements, such as Ni, Mn, and Fe, which are common elements in SIB cathode materials [46]. Some typical neutron scattering technologies are suitable for battery research including neutron diffraction (ND), small-angle neutron scattering (SANS), neutron total scattering combined with pair distribution function (PDF), inelastic neutron scattering (INS), quasielastic neutron scattering (QENS), and neutron imaging [46][47][48][49].…”

Applications of In Situ Neutron-Based Techniques in Solid-State Lithium Batteries

“…The QENS method is a direct method for studying ion dynamics using neutrons [88,89]. As represented in Figure 14, an incident neutron with an initial wavevector of k i interacts with the sample's atomic nucleus and scatters at a 2θ, resulting in a wavevector k f .…”