Study of Electrolyte Decomposition in Batteries Using In Situ NMR Technique

Sammanfattning

Increasing the working voltage of lithium-ion batteries (LIBs) can enhance the energy density of LIBs as long the redox reactions of the electrodes can take place at higher potential. However, this will cause rapid capacity fading and performance degradation due to the electrolyte instability, which leads to decomposition. In this study, we studied the degradation process of LMNO-LTO-LP57 by utilizing an in situ cell. This cell allowed us to do NMR experiments without dissembling the cell, minimizing the risks of sample alteration. The experiments, including cycling at 0.5C with cut-off voltage at 1.50 and 3.50 V and aging experiments followed by 1D and 2D NMR experiments. The effect of an additive on the cell was also studied. The cycling profile of the in situ cell both with and without the additive was comparable to the coin cell. However, it was still difficult to get a consistent performance (capacity fading) of the in situ cell when compared to the coin cell. The NMR results suggest that the LP57 electrolyte was quite stable after 150 cycles, indicating that other factors play a more important role in the in situ cell performance degradation. The polymerization and degradation of the additive can also be observed in our NMR data after 150 cycles. The NMR data of the in situ cell from the aging experiment showed that after 25 days of aging, decomposition of the LP57 electrolyte was observed in the in situ cell without additive, while no decomposition products were detected in the in situ cell with additive. This study provides a baseline for further development on the in situ cell design.