In-situ Raman Spectroscopy Study Of Solid Electrolyte Interface On The Anode Material For Lithium Ion Batteries

With the development of our society, further requirements such as higher electrochemical capacity and better reversibility are advanced to lithium ion battery, which is a kind of reversible energy. In the first cycle of lithium ion battery, solvent decomposition reaction on the surface of electrode will lead to the formation of a passivating layer, commonly named solid electrolyte interface film (SEI film). It has great impact on the electrochemical capacity, security, reversibility, self-discharge and has become a focus in the study of lithium ion battery. Transition metal compound has been the focus as anode material in lithium ion battery since it has high lithium storage capacity and new energy storage mechanism. Thereinto, Cr₂O₃ is more fitting for its high electrochemical activity and low average working voltage. In-situ study can get real and accurate result through detecting the reacting system with detector directly without changing the real state and that makes great sense for SEI film since it is extraordinary thin and very sensitive to the environment. The in-situ Raman spectroscopy of SEI film on the anode material of Cr₂O₃ was studied in this paper: 1. To meet the needs of in-situ study of SEI film, the lithium ion simulate battery with optical quartz window was designed and made. The charge-discharge apparatus accurately control the state of battery when measuring, and we can realize the measurement and token of SEI film in an arbitrary state through co-employment with the co-focus micro-Raman spectroscopy. By this method we can obtain the information of the evolvement process . 2. It is believed that many kinds of ROLi and ROCO₂Li exist in the SEI film besides Li₂CO₃, LiOH·H₂O and LiF, while the lithium salts are difficult to be affirmed directly from the experiment for its complexity and instability. In this paper, a series of possibly existing species were calculated, and the Raman vibrational spectra were obtained. Through the comparison of the theoretical results and those from experiments, the components of the SEI film can be tentatively affirmed. 3. In order to gain active substrate of Surface Enhanced Raman Scattering(SERS), we deposited Ag grain on the surface of Cr₂O₃ particles. The ex-situ Raman spectra of SEI film were studied both before Ag deposited and after that. The tendencies of normal Raman spectra and SERS were similar, the Raman peaks at low voltages were richer than those at high voltages, which accorded with the HRTEM results. It also demonstrated the dynamic transformation of SEI film in the first cycle. In the ex-situ SERS study, the SEI signals were richer and stronger, and more components were enhanced and be detected, which also indicated the great enhancement effect of the substrate. Took the theoretical results as references, we analyzed 9 lithium salts with SERS and 5 lithium salts with normal Raman, without considering Li₂CO₃ and LiOH·H2O reported before. 4. The in-situ Raman spectra of SEI film were studied both before Ag deposited and after that. The in-situ spectra of normal Raman and SERS were obviously different: the former can't give any clear signal from SEI component and all Raman peaks measured can be assigned to electrode and anode material itself; the latter displayed great enhancement effect and the SERS signals of SEI film varied with the voltageslow voltages were richer than those at high voltages, which accorded with the HRTEM results. In the in-situ SERS study, the SEI signals were richer and stronger, and more components were enhanced and be detected. Took the theoretical results as references, we analyzed 16 lithium salts with SERS, without considering Li2CO3 , LiOH·H₂O reported before. 5. The comparison between the ex-situ and in-situ Raman study was also advanced. 9 components were detected in ex-situ SERS study in the first cycle with 16 components in the counterpart. The differences derived from the dissolution of some certain components into solvent in the sample preparation process. Our work at the same time demonstrated...