Raman-imaging With Keeping the State of Charge Under the Air

Laser wavelength:532nm, Objective:x100/NA 0.85

Raman-imaging comparison  before of anode

Raman-imaging comparison after charge of anode

▲Raman-imaging comparison between before(a) and after charge(b) of anode.
(red; crystalline-Si, yellow; amorphous-Si, blue; graphite, green; Kedjen black)
 

Silicon that absorbs more Li+ than graphite is the leading material for high capacity anode in Li-ion batteries(LIB), but Silicon crystal has the disadvantage that it is almost broken throughout charge-discharge because of its drastic change of volume. The effective ways to prevent the silicon crystal damage are miniaturization and finely dispersion of silicon crystal with other ingredients of anode. Using sodium polyacrylate binder achieve the finely dispersion and it could be confirmed with the raman-imaging. Especially, it can be observed that the silicon particles are dispersed less than 1μm.

The above two figures display raman-imaging comparison between before and after charge of graphite-Sipolyacrylate anode. The charged anode was taken out from the cell in a glovebox, and then set it into LIBcell (closed vessel). This makes it possible to measure raman-imaging keeping the state of charge under the air. It could be confirmed that almost crystalline-Si was changed to amorphous shape because of intercalation of Li+. On the other hand, the graphite-Si-PVdF anode, which was not well dispersed, was observed to have the major change of form in the raman spectrum at G-band of carbon compared to silicon. Raman-imaging also can confirm the difference of electrical characteristic caused by dispersion form of ingredients of anode.

 

raman-image of graphite-Si-PVdF anode (before charge),The change of raman spectra before and after charge

Compared to the anode with PANa, the graphite-Si-PVdF anode can be seen that there is bias in the dispersion of the graphite and Kedjen black (c). In the case of PVdF binder, the difference in the raman spectra before and after charge is seen major changes in the G-band of carbon, and it means the intercalation of Li+ to carbon. In other words, it is suggested the possibility that intercalation of Li+ does not to silicon efficiently.

Figure c); raman-image of graphite-Si-PVdF anode (before charge)
Figure d) and e) ; The change of raman spectra before and after charge.

 
*These samples were offered by KOMABA Laboratory of Tokyo University of Science.