Invesitgation of the Gas Generation in Lithium Titanate Anode Based Lithium Ion Batteries

Lithium ion batteries containing lithium titanate (LTO), Li₄Ti₅O₁₂ are promising energy storage systems for their high rate capabilities, safety, and long cycle-life. However, gas generation and associated swelling, which can be observed under high-temperature operation, present a challenge to the large-scale application of lithium ion batteries made from LTO anodes. Research has suggested various causes for gas generation,  including residual moisture in the electrodes and electrolyte [1] and catalysis involving the Ti³⁺/Ti⁴⁺ redox couple combined with water electrolysis.[2,3]  It is important to understand the source of gas generation so as to avoid it with proper manufacturing conditions, such as tight control over moisture levels.  However, at this time the mechanism of gas evolution from LTO anode based lithium ion battery systems is not well established.

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.

(1) Belharouak, I.; Koenig, G. M.; Tan, T.; Yumoto, H.; Ota, N.; Amine, K. Journal of the Electrochemical Society 2012, 159, A1165.

(2) He, Y.-B.; Li, B.; Liu, M.; Zhang, C.; Lv, W.; Yang, C.; Li, J.; Du, H.; Zhang, B.; Yang, Q.-H.; Kim, J.-K.; Kang, F. Sci. Rep. 2012, 2.

(3) Bernhard, R.; Meini, S.; Gasteiger, H. A. Journal of the Electrochemical Society 2014, 161, A497.