Ion aggregation will occur during operation of the thin film cell, while the aggregation involves two basic chemical processes of mezzanine and conversion. In the mezzanine, the metal ion (lithium, sodium or calcium) will fall into a gap in the atomic structure of the electrode, and when a plurality of lithium ions occupy the same space at the atomic framework of electrodes, the competition among each ion occurs due to the limited number of oxygen atoms in the vicinity. Mutual dragging of lithium, sodium or calcium ion inserted to the oxygen has slightly changed the adjacent bond, even though they will then leave, it has distorted the material and eventually led to its collapse failure. The role of mezzanine played in the structure of atomic vacancy formation swing is reversible, and this process will increases conductivity of the material, thus to benefit batteries and other equipments.

 

People have been very interested in the interaction between the mezzanine and conversion for a long time, and recently, US Pacific Northwest National Laboratory has finally displayed the collapse reason of tungsten trioxide (WO₃) electrode material directly through the images. The researchers used molecular beam epitaxy synthesis of tungsten trioxide thin film electrode material, and designed the thin film electrochemical device, situ studied by electron microscopy of high-resolution transmission, insight into the movement of electrons and ions in the energy material and directly heat the collapse reason of electrode material.

1. M represents to Li, Na or Ca in figure a;

2. Figure b displays WO₆ octahedral model of monoclinic tungsten trioxide and transportation of lithium, sodium or calcium ion along the channel to the vacancy center;

3. Figure c is the continuous TEM bright-field image, which displays structure evolution of WO₃ during the insertion of lithium, and the illustration shows the original electron diffraction pattern and fully lithiated phase; the white dotted line marking the front of surface position of the reaction, and highlight the volume expansion projection. Scale, 100nm;

4. Figure d is the high-resolution transmission electron microscope image of the local region of reaction (dotted line), illustration on the left is a boxed area atomic resolution annular dark-field image, scale, 1nm;

5. Figure e is the atomic resolution HAADF-STEM image of WO₃ after Ca inserted, scale of 2nm.