Abstract text (incl. figure legends and references)

LiCoPO₄ is a promising cathode material for the high voltage lithium-ion batteries. However, the moderate cycling stability of the material limits its practical applications. One of the major reasons of the capacity fade of LiCoPO4 is related to its structural degradation: Li and Co site exchange leads to the blocking of the Li+ transport channels^[1]. The stabilization of the atomic structure of the material directly depends on the capability to gain knowledge on the degradation mechanisms though advanced characterization.

Cathode materials are obstinate candidates for TEM investigations due to their poor stability under the electron beam. To deal with radiolysis while imaging LiCoPO₄ reduced electron dose should be applied. Here, we exploit simultaneous ADF-STEM and iDPC-STEM^[2,3] imaging to investigate the LiCoPO₄ cathode material down to atomic scale, as iDPC-STEM allows for extremely low dose imaging of beam sensitive materials^[4,5]. By combining the experimental and simulation results a superstructure at the surface of the LiCoPO₄ nanoparticle is revealed, where every second Li site is partially occupied by Co atoms (Figure 1).

Figure 1. Simultaneously recorded, using HAADF and Panther detectors, high resolution ADF- and iDPC-STEM images (from left to right) of the superstructure at the surface of the LiCoPO₄ nanoparticle, viewed along the [001] zone axis, together with the corresponding simulations and proposed surface structure. The probe corrected beam conditions: HT 300kV, Convergence semi-angle 30 mrad, Beam current 15 pA.

[1] X. Wu, M. Meledina, J. Barthel, et. al., Energy storage materials 22 (2019) 138

[2] I. Lazić, E.G.T. Bosch and Sorin Lazar, Ultramicroscopy 160 (2016) 265

[3] I. Lazić and E.G.T. Bosch, Advances in Imaging and Electron Physics 199 (2017) 75

[4] B. Shen, H. Wang, H. Xiong, et al., Nature 607 (2022) 703

[5] I. Lazić, M. Wirix, M. L. Leidl et. al., Nature Methods 19, (2022) 1126