Visualizing lithium ions in the crystal structure of Li3PO4 by in situ neutron diffraction

Li3PO4 is known to demonstrate Li+ ionic conductivity, making it a good candidate for solid electrolytes in all-solid batteries. Understanding the crystal structure and its connection to Li+ diffusion is essential for further rational doping to improve the ionic transport mechanism. The purpose of this study is to investigate this mechanism using anisotropic displacement parameters (ADPs), nuclear density distribution and bond valence mapping. In situ neutron powder diffraction experiments have been performed using the high-resolution powder diffractometer ECHIDNA at the OPAL reactor, Australian Centre for Neutron Scattering, Australian Nuclear Science and Technology Organisation, NSW, Australia. The ADPs and nuclear density distribution were determined from the analysis of neutron diffraction data using the Rietveld method, whereas the bond valence map was calculated from the refined structure. The crystal structure remained unchanged as the temperature was increased (3, 100, 300 and 400 K). However, the ADPs show a greater increase in anisotropy in the a and b axes compared with the c axis, indicating the tendency of the ionic movement. By combining nuclear density distribution and bond valence mapping, the most likely lithium-ion diffusion in the crystal structure can be visualized.

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Time-resolved in situ neutron diffraction studies of Li-ion battery materials

Acta Crystallographica Section A Foundations and Advances ◽

10.1107/s2053273314096466 ◽

2014 ◽

Vol 70 (a1) ◽

pp. C353-C353 ◽

Cited By ~ 1

Author(s):

Neeraj Sharma

Keyword(s):

Crystal Structure ◽

Neutron Diffraction ◽

Lithium Ion Batteries ◽

Lithium Ion ◽

Electrochemical Process ◽

Atomic Scale ◽

Structure Evolution ◽

Time Resolved ◽

In Situ Neutron Diffraction

Lithium-ion batteries are ubiquitous in society, used in everything from children's toys to mobile electronic devices, providing portable power solutions. There is a continuous drive for the improvement of these batteries to meet the demands of higher power devices and uses. A large proportion of the function of lithium-ion batteries arises from the electrodes, and these are in turn mediated by the atomic-scale perturbations or changes in the crystal structure during an electrochemical process (e.g. battery use). Therefore, a method to both understand battery function and propose ideas to improve their performance is to probe the electrode crystal structure evolution in situ while an electrochemical process is occurring inside a battery. Our work has utilized the benefits of in situ neutron diffraction (e.g. sensitivity towards lithium) to literally track the time-resolved evolution of lithium in electrode materials used in lithium-ion batteries (see Figure 1). With this knowledge we have been able to directly relate electrochemical properties such as capacity and differences in charge/discharge behaviour of a battery to the content and distribution of lithium in the electrode crystal structure. This talk will showcase some of our in situ investigations of materials in lithium-ion batteries, such as LiCoO2, LiFePO4, Li1+yMn2O4, LiNi0.5Mn1.5O4 and Li4Ti5O12/TiO2 electrodes. In addition, selected examples of our work using time-resolved in situ X-ray diffraction to probe other batteries types, such as primary lithium and secondary (rechargeable) sodium-ion batteries will be presented. Using time-resolved diffraction data, a comprehensive atomic-scale picture of battery functionality can be modelled and permutations can be made to the electrodes and electrochemical conditions to optimize battery performance. Therefore, crystallography and electrochemistry can mesh together to solve our energy needs.

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