Invesitgation of the Gas Generation in Lithium Titanate Anode Based Lithium Ion Batteries
Here we analyzed LTO cells following high temperature (80ºC) calendar life storage at 100% SOC. We explored the relationship between volume expansion and impedance increase following high temperature storage. The results in Figure 1 indicate that with increasing gas volume expansion, the performance of the cells degrades. The gas species and quantities resulting from the cell volume expansion were collected and analyzed post-mortem using quadrupole mass spectrometry (MS) and combined gas chromatography / mass spectrometry (GC/MS). With this method, we introduced varying levels of water content into the cathode and anode, as well as the electrolyte. To facilitate determination of the origin of gas generation, we utilized deuterated water (D2O) introduced into the electrodes and electrolyte as well as 5% deuterated dimethyl carbonate (DMC) and ethylene carbonate (EC) based electrolytes. Figure 2 illustrates a comparison of gas compositions obtained from cells with 1600ppm D2O added to the electrolyte and 5wt% deuterated DMC in the electrolyte. The preliminary results illustrate that deuterated DMC in the electrolyte shows negligible breakdown to yield D2 based gas when compared to samples that contain heavy water (D2O) added into the electrolyte. This indicates that the primary source of gas generation in LTO based cells originates from residual moisture in the electrodes and electrolyte. This result reinforces the importance of maintaining low-moisture processing conditions for LTO-based lithium ion batteries.
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