Figure 4: Morphology and deposition mechanism.
(a) Field emission scanning electron microscopic (FESEM) images of the discharged SP cathode when the discharge capacity is limited to 3,000 mAh g−1. White scale bars, 1 μm. Green scale bars, 400 nm. (b) The FESEM images of the discharged HSC deposited onto CP cathode. White scale bars, 1 μm. Green scale bars, 400 nm. (c) The images of the discharged P-HSC deposited onto CP cathode. White scale bars, 1 μm. Green scale bars, 400 nm. The insets in a–c are the corresponding enlarged FESEM images. (d) Corresponding PXRD patterns of the three kinds of discharged cathode. It is found that the PXRD peaks can be assigned to Li2O2, although the morphology of the discharge product is different. (e) A mechanism for the electrochemical production of Li2O2 nanosheet-like aggregates on P-HSC deposited onto CP cathode. (f) A mechanism for the electrochemical production of Li2O2 toroidal aggregates on SP and HSC deposited onto CP cathodes. The panels i in e and f illustrate the nucleation processes of Li2O2. The panels ii in e and f illustrate that the small elongated hexagonal nanocrystallites come into being after the nucleation of Li2O2. The Li2O2 preferentially nucleates and grows on the prismatic crystal faces. The panels iii in e and f illustrate the formation of the observed toroidal and nanosheet-like aggregates.
