Electron diffraction tomography for ab initio structure

determination of polyanion cathode materials for

Li-ion batteries

Electron diffraction tomography (EDT) makes it possible to determine the crystal structure of nano-sized (~200 nm) single crystals. By

obtaining 60-85% of reciprocal space in 3D mostly out-of-zone axis dynamical diffraction contribution is minimized, therefore ab-initio methods

for crystal structure determination can be applied. EDT can be used for charged Li-ion battery cathode materials, of which the structure

determination using bulk diffraction techniques is hindered by the fact that only a small amount of the powder

(<5 mg ) can be obtained from electrochemical cells, it is multiphased and the particles are nanoscale sized.

Published as O. A. Drozhzhin, V. D. Sumanov, O. M. Karakulina, A. M. Abakumov, J. Hadermann, A. N. Baranov, K. J. Stevenson, E. V. Antipov.

Electrochimica Acta, 2016, 191,149–157

References:

[1] Palatinus, L.: PETS - program for analysis of electron diffraction data. Prague: Institute of Physics of the AS CR, 2011.

[2] A. Yamada, Y. Takei, H. Koizumi, N. Sonoyama, R. Kanno, K. Itoh, M. Yonemura, T. Kamiyama, Chem. Mater., 2006, 18, 804–813.

[3] N.V. Kosova, E.T. Devyatkina, A.I. Ancharov, A.V. Markov, D.D. Karnaushenko, V.K. Makukha; Solid State Ionics, 2012, 564–569

O. Karakulina1, A. Abakumov1, V. Sumanov2, O. Drozhzhin3, J. Hadermann1 1 Electron Microscopy for Materials Research (EMAT), University of Antwerp, Antwerp, Belgium, 2 Department of Inorganic Chemistry,

Moscow State University, Moscow, Russia, 3 Department of Electrochemistry, Moscow State University, Moscow, Russia

Method

Introduction

An EDT experiment consists of the tilting of a

single crystal (<200nm) with 1 degree steps and

collecting the corresponding electron diffraction

patterns.

LiMn0.5Fe0.5PO4

Results

Space group: Pnma

Conclusions

PETS software was used for the reconstruction of

reciprocal space in 3D [1].

LiFePO4 is a commercially used cathode material

for Li-ion batteries. The partial substitution of Fe

by Mn results in an increase in energy density due

to the higher voltage of Mn3+/Mn2+ redox couple

(4.1 V) [2].

LiMnyFe1-yPO4 (y=0.5-0.6) undergoes two first-

order phase transformations under charge

(discharge) process [3].

0 V 3.7 V 4.3 V

a, Å 10.3903(4) 10.2146(8) 9.7293(7)

b, Å 6.0474(2) 5.9883(5) 5.8562(4)

c, Å 4.7225(2) 4.7742(5) 4.7823(3)

V, Å3 296.7316(8) 292.033(2) 272.479(1)

x (Li) 0.95(7) 0.50(7) 0.16(11)

Rf, % 23 14 22

LiMn0.5Fe0.5PO4 (0 V). EDT parameters:

• tilting angles: ± 77o

• interplanar spacing limit: d > 0.6 Å

• observed reflections ( I>3(I) ): 3851

• symmetry independent reflections: 804

1. Structure determination and Li occupancy refinement

2. Mn/Fe-O octahedron distortion

0 V XRD

0 V EDT

3.7 V EDT

4.2 V EDT

Mn/Fe - O1 2.253(4) 2.220(8) 2.13(2) 2.08(2) Mn/Fe – O2 2.083(5) 2.118(8) 2.14(2) 2.01(2) Mn/Fe – O3 (1) 2.258(3) 2.270(6) 2.234(9) 2.19(1) Mn/Fe – O3 (2) 2.121(3) 2.056(5) 2.113(8) 2.029(9)

The crystal structure, namely atomic coordinates, geometry and Li occupancy, was determined for

pristine and electrochemically delithiated LiMn0.5Fe0.5PO4 (3.7V, 4.2 V) by means of electron

diffraction tomography. The quality of structure refinement is comparable with that for powder XRD.

Bond lengths are presented in Å.

In-situ XRD patterns of LiMn0.5Fe0.5PO4 upon charge-discharge

(left) and the corresponding voltage profile (right).

LiMn0.5Fe0.5PO4 (0 V): the difference (positive) Fourier map. The Li atoms

was removed from calculation for the visualisation of Li positions.

The selected area electron diffraction patterns of pristine and charged LiMn0.5Fe0.5PO4.

LixMn0.5Fe0.5PO4